Difference between revisions of "2011 Group 6 Project"

From CellBiology
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|Botulism
 
|Botulism
|A disease caused by the excrement of the bacteria  ''Clostridium Botulinum.'' This excrement, known as Botulinum toxin, is an extremely lethal neurotoxin. It works by blocking the release of acetylcholine at neuromuscular junctions, resulting paralysis and ultimately respiratory failure. The bacteria may enter the body through wounds, or improperly canned or preserved food. Infant botulism occurs when living bacteria or its spores are eaten and grow within the baby's gastrointestinal tract. However, recently developed medical techniques use the toxin beneficially (botox).
+
|A disease caused by the excrement of the bacteria  ''Clostridium Botulinum.'' This excrement, known as Botulinum toxin, is an extremely lethal neurotoxin. It works by blocking the release of acetylcholine at neuromuscular junctions, resulting paralysis and ultimately respiratory failure. The bacteria may enter the body through wounds, or improperly canned or preserved food. <ref>Agarwal AK, Goel A, Kohli A, Rohtagi A, Kumar R. Food-borne botulism. J Assoc
 +
Physicians India. 2004 Aug;52:677-8. PubMed PMID: 15847370.</ref>
 +
Infant botulism occurs when living bacteria or its spores are eaten and grow within the baby's gastrointestinal tract. However, recently developed medical techniques use the toxin beneficially (botox).
 
|Clinical manifestation of muscle weakness without fever is characteristic of botulism. It starts with facial muscles weakness, which then spreads to the arms and legs. Symptoms include diplopia or ptosis, dysphagia and dyspnoea. In addition, patients may experience dry mouth and GI related symptoms e.g. vomiting and constipation especially in infants.
 
|Clinical manifestation of muscle weakness without fever is characteristic of botulism. It starts with facial muscles weakness, which then spreads to the arms and legs. Symptoms include diplopia or ptosis, dysphagia and dyspnoea. In addition, patients may experience dry mouth and GI related symptoms e.g. vomiting and constipation especially in infants.
 
|For infants, Botulism Immune Globulin Intravenous-Human (BIG-IV) also known as BabyBIG. Antitoxins (Trivalent, Heptavalent)  
 
|For infants, Botulism Immune Globulin Intravenous-Human (BIG-IV) also known as BabyBIG. Antitoxins (Trivalent, Heptavalent)  

Revision as of 13:28, 9 May 2011

NMJunction.jpg

The Neuromuscular Junction

Introduction

A Neuromuscular junction (NMJ) is a connection between an axon of a motor neuron and the motor end plates on a muscle fibre. The NMJ can be found in both smooth and skeletal muscle fibres, with different purpose and mechanisms which may involve different receptors. Starting with historic researches, this group project establishes detailed information on how this junction works, which may lead to a skeletal muscle contraction, followed by a description for each of its engines involved during this process. Additionally, the NMJ is the site of some well-known diseases which will be briefly described in a table of NMJ’s disorders. Currently, the NMJ is a research topic in many areas such as pharmacology, pathology, physiology and medicine.


History

Thomas Willis

Historic researchers in NMJ:

In 1672, Myasthenia gravis (MG) was first described by Thomas Willis. It is an acquired autoimmune disease with antibodies against the nicotinic acetylcholine receptor (AChR) at the NMJ. [1]

In 1842, Claude Bernard concluded that the arrow poison 'curare' acts at the NMJ to interrupt the stimulation of muscle by nerve impulses. [2]

In 1850, Claude Bernard demonstrated that paralysis was mediated via the NMJ, although the precise mechanism remained unknown. [3]

In 1914, Sir Henry Dale, (in 1936, he was warded the Nobel Prize for Medicine and Physiology), investigating the pharmacological properties of ACh, distinguished two actions that were reproduced by the alkaloids, muscarine and nicotine. As the effects of muscarine mimicked the parasympathetic nervous system, he termed the receptors muscarinic, whereas those in autonomic ganglia and at the skeletal NMJ were termed nicotinic. [4]

In 1949, At the Paris conference Jack C. Eccles was convinced of the part played by acetylcholine at the neuromuscular junction but still thought of electric currents as being responsible for excitation and inhibition in the central nervous system. [5]

In 1952 - 1954, the name end-plate potential is used since Fatt&Katz (1952) and Del Castillo & Katz (1954) studied the endplate potential (epp) at NMJ. They concluded that the ACh molecules were released in packets containing several thousand ACh molecules revealing the quantal nature of synaptic transmission.[6] [7]

In 1986, M. John Anderson experiments with Xenopus laevis embryos and observes that proteolytic enzyme systems used in tissue remodeling may also contribute to nerve and muscle cell interaction during synaptogenesis. [6]

In 2000, Discovery of the Rabies virus entry at the neuromuscular junction in nerve-muscle cocultures. [8]

Mechanism of action

The mechanism of action of NMJ involves many steps and engines which harmonically follow each other in which the ability of a muscle to contract or relax depend on. These steps are:

  • Nerve impulse reaches the motor nerve terminal[9]
  • Specialized proteins forming ion channels in its cell membrane open quickly[10]
  • Calcium enters into the axon terminal[11]
  • Synaptic vesicles are filled with ACh[12]
  • Ca causes some of the vesicle membranes to fuse with the nerve terminal membrane[13]
  • ACh content is released into synaptic cleft[14]
  • ACh diffuses rapidly across the gap and binds to the ACh receptors (AChRs)[15]
  • When this binding occur, small positively charged sodium (Na) ions enter the muscle[16]
  • This lead to the depolarization across membrane[17]
  • End-plate potential in turn opens the voltage-sensitive Na channels at the synaptic fold[18]
  • An “all or nothing” action potential starts which propagates along the muscle fibre in each direction[19]
  • Initiation of a muscle contraction occur[20]
  • Then, the AChR pore closes[21]
  • ACh unbinds and broken down [22]

For a visual representation of these steps, see this video

Summary:

A nerve impulse reaches the motor nerve terminal and triggers the opening of specialized ion protein channels. Calcium ions rush through the opening into the axon terminal, prompting the formation and release of acetylcholine synaptic vessicles. The vessicle membranes fuse with the nerve terminal membrane and release acetylcholine into the neuromuscular junction gap. Acetylcholine then binds with receptors. This chemical binding induces the release of sodium ions which enter the muscle and depolarize across the membrane. End-plate potential then opens voltage-sensitive sodium channels at the synaptic fold, initiating an action potential that propagates along the muscle fibre in each direction and causes the muscle to contract. Acetylcholine receptor pores then close. Acetylcholine is broken down and recycled.


Motor neuron

Motor Neuron

Motor neurons are efferent neurons that originate in the ventral horn of the spinal cord. They synapse with muscle fibres and carry information from the central nervous system to muscles, facilitating muscle contraction.

  • Efferent neurons
  • Originate in the ventral horn of the spinal cord[23]
  • Synapse with muscle fibres[24]
  • Carry information from the central nervous system to muscles[25]
  • Facilitate muscle contraction
  • Somatic once are directly involved in the contraction of skeletal muscles[26]
  • Excitatory
  • Influenced by input descending from the brain[27]
  • Affected by a class of diseases known as motor neuron diseases[28]
  • Amyotrophic lateral sclerosis is characterized by loss of lower neurons in spinal cord and brain stem and upper motor neurons that project in corticospinal tracts. Skeletal muscles innervated by the degenerated lower motor neurons show neurogenic atrophy.[29]

Acetylcholine (ACh)

Acetylcholine is one of the principle neurotransmitters of the peripheral nervous system. It plays a large role in skeletal muscle movement and the regulation of smooth muscle. Acetylcholine is first released by a motor neuron at the neuromuscular junction, and proceeds to bind and activate a receptor protein. It is an effective deliverer of sodium ions, which stimulate muscle contractions and excite nerves. The enzyme acetylcholinesterase (AChE) hydrolyzes acetylcholine into acetic acid and choline. Choline is recycled into acetylcholine again, repeating the process. AChE inhibitors delay the degradation of acetylcholine, so that there is a higher concentration of it. These inhibitors are commonly used to reverse muscle relaxants and sometimes to treat Alzheimer’s disease.

  • Cholinergic neurons[30]
  • Skeletal muscle movement
  • Regulation of smooth muscle
  • One of the principle neurotransmitters of the peripheral nervous system
  • Released by a motor neuron at the NMJ[31]
  • Bind and activate a receptor protein[32]
  • A very effective deliverer of sodium ions, which stimulate muscle contractions and excites nerves[33]
Acetylcholine Nicotine.jpg
  • The enzyme acetycholinesterase (AChE) hydrolyzes acetylcholine into acetic acid and choline[34]
  • Choline travels back to be recycled into acetylcholine and start the process over again[35]
  • Concentration of ACh remains higher if the AChE is inhibited[36]
  • AChE inhibitors delay the degradation of acetylcholine[37]
  • This inhibitors are used to reverse muscle relaxants and sometimes to treat Alzheimer's disease[38]

Acetylcholine Receptors (AChR's)

There are two main types of AChRs. Nicotinic AChRs, or nAChRs, are ionotropic receptors located between neurons and also in the neuromuscule synapse. Thay control skeletal muscle contraction. Muscarinic AChRs, or mAChRs, are metabotropic receptors located at the synapses of nerves with smooth or cardiac muscle. They control smooth muscle contraction by triggering signal transduction.

Nicotinic and Muscarinic receptors are receptors for acetylcholine. The important difference between the two is their mode of action

  • Nicotinic receptors (nAChRs)

-Controls skeletal muscle contraction [39]

-Ionotrophic receptors

-located at synapses between two neurons and at synapses between neurons and skeletal muscle cells

  • Muscarinic receptors (mAChRs)

-Controls smooth muscle contraction[40]

-Metabotropic receptors (G-protein coupled receptors)

-located at the synapses of nerves with smooth or cardiac muscle

-Trigger a chain of chemical events referred to as signal transduction

-Excitation and inhibition response

-Response of mAChRs is slower

For more information on nAChRs and mAChRs see: Nicotinic and Muscarinic Acetylcholine Receptors

Motor End Plate

The motor endplate (also known as the myoneural junction) is a specialized region of the sarcolemma. It is highly folded for increased surface area and contains a high concentration of AChRs. It receives neurotransmiters in order to propagate action potentials. It is responsible for the terminal tree like branching muscle fibre motor axons, and maintains muscle tone through the stretch reflex.

  • Specialised region of the sarcolemma
  • Highly folded
  • Holds a high concentration of AChRs [41]
  • Also called Myoneural Junction [42]
  • Receive neurotransmitters in order to propagate an Action Potential [43]
  • Responsible for the terminal tree like branching of a motor axon on a muscle fibre [44]
  • Maintains muscle tone through stretch reflex [45]

Important Structural Components

Table of components

Important structural components of the NMJ
Component Location Description Picture
Presynaptic membrane The presynaptic membrane is the membrane of the neuron that faces the membrane of the muscle. In between these two membranes is the synaptic cleft In a NMJ, the presynaptic membrane is the axon terminal. This is where the nerve axon terminates. The axon terminal contains many ion channels for the intake of Ca+ and also is responsible for exocytosis of acetylcholine vesicles into the synaptic cleft Presynaptic membrane.jpg
Synaptic cleft The space between the presynaptic membrane (axon terminal) and the postsynaptic membrane (motor end plate) Separates the presynaptic from the post synaptic cells, the electrical signal cannot cross this space from the neuron, but activates a chain of reactions that causes the muscle to contract. [46] Synaptic cleft.jpg
Synaptic vesicles Found within the axon terminals of the neuron The synaptic vesicles are membranous organelles that contain the neurotransmitter Acetylcholine (Ach). They are released from the presynaptic membrane through exocytosis. Ach is released when it fuses with the postsynaptic membrane.[47]
Synaptic vesicles.jpg
Ion gated channels and receptors Ion gated channels and receptors are located on the presynaptic membrane (axon terminal) and on the postsynaptic membrane (motor end plate) The depolarisation/repolarisation of the NMJ membrane is controlled by sodium, potassium, calcium, and chlorine ion channels. These channels are either opened or closed in response to certain chemical or voltage changes. The release of ions into the presynaptic membrane, synaptic cleft and postsynaptic membrane controls the depolarisation of the membrane and thus an action potential occurring. Ion channels.jpg
Postsynaptic membrane Separated from presynaptic membrane by synaptic cleft In the NMJ, the postsynaptic membrane is the motor end plate. Myonuclei are located underneath this membrane where they locally synthesise AChRs and other postsynaptic proteins. MuSK provides a structural scaffold necessary to initiate aggregates of postsynaptic molecules. Characterised by the accumulation of nAChRs and voltage-gated sodium channels. [48] Postsynaptic membrane.jpg
Schwann Cell
Mitochondria 562px-Animal mitochondrion diagram en (edit).svg.png
Basal lamina (BL) Surrounds the Schwann cells of the axon and muscle fibre, Projects into folds that enclose the postsynaptic membrane Layer of extracellular matrix, Synaptic cleft is filled with dense BL, Contain ACh-esterase, Lamina densa comprising the intermediate part of BL, procollagen type 4 is the most important component [7]

Light microscopy and electron microscopy pictures of the Neuromuscular Junction

Light Micrograph of a NMJ

This is a light microscopy image of a neuromuscular junction. You can see the striated muscle fiber on the left hand side with the neuron that innervates this muscle fiber on the right. Light microscopy was invented around the 1600's and was the first type of microscope used by scientists. [49] The image from an optical microscope can be captured by a normal camera to generate a micrograph. Digital microscopes are available which just use a CCD camera to examine a sample, and the image is shown directly on a computer screen without the need for eyepieces. The main limitations with light microscopy is that the maximum normal magnification only reach around 1000x normal. [50]

Benefits of light microscopy:

  • Cheap
  • Simple to use
  • Gives good detail to very small objects
  • Can view living specimens (as opposed to the electron microscope where specimens need to be fixed)
  • Can view specimens in colour (as opposed to the electron microscope where specimens are in black and white)
Scanning Electron Micrograph of a NMJ

This is a scanning electron micrograph of a neuromuscular junction. This type of microscope was invented in the 1930's. The scanning electron microscope uses electrons to scan a sample which can be magnified from about 10 times to more than 500,000 times, which is about 250 times the highest magnification of light microscopes. [51] In the following two pictures you can see the highly folded region of the post synaptic membrane (motor end plate) where the neuron synapses with the muscle fiber. These folds increase the surface area of the junction and thus the number of available acetylcholine receptors. The increased number of AchR's allows the membrane to depolarise more quickly so the muscle fiber is activated to contract in a smaller period of time. More AChR's are also needed for the membrane potential to reach threshold so an action potential can propagate. [52]

Advantages of Electron microscopy:

  • Higher resolution and magnification
  • Capability to observe inside of samples
  • Greater depth of field, creating more of a 3D image
  • Finer magnification control, to be able to view a wider range of magnifications instead of a set 100x to 400x

[53]

Transmission Electron Micrograph

Differences between scanning EM and transmission EM:

-Scans a beam of electrons across the object (does not penetrate the object)

-Measures energy from the electrons to create a three-dimensional picture of the surface of an object

-Able to produce images of larger objects (eg an ant)

-The SEM can magnify up to 200,000x

-Passes a beam of electrons THROUGH a specimen

-Can view inside objects

-The TEM can magnify up to 1,000,000x

Cellular organization of skeletal muscle:

The NMJ innervates muscle to contract, the following points outline the components of skeletal muscle:

  • Epimysium, an external sheath of dense connective tissue surrounds the entire skeletal muscle
  • Muscle fibers are arranged in regular bundles
  • The connective tissue, perimysium surrounds each bundle
  • Each fiber is surround by a delicate connective tissue called endomysium which is mainly composed of basal lamina and reticular fibers

The sliding filament theory of muscle contraction video. Click here

Muscle fibers:

Skeletalmuscle.jpg

Muscle fibers are characterized by the presence of multiple nuclei located below the sarcolemma. The fibers contain sarcoplasm, a semifluid cytoplasm filled with mitochondria and myofibrils. Filaments lie parallel to the long axis of the myofibrils. Each myofibril is surrounded by the sarcoplasmic reticulum. The sarcoplasmic reticulum is a saclike membranous network associated with transverse tubules which are connected with the sarcolemma. Transverse tubules, or T-tubules, help to transmit signals from the sarcolemma to the myofibrils.

  • Characterized by the presence of several nuclei
  • These nuclei are located below the sarcolema
  • Contain a semifluid cytoplasm called sarcoplasm
  • Sarcoplasm is filled with mitochondria and myofibrils
  • Filaments (thin and thick) lie parallel to the long axis of the myofibrils
  • Sarcoplasmic reticulum ( SR- a saclike membranous network) surrounds each of the myofibrils
  • SR is associated with transverse tubules ( T tubules) which are connected with the sarcolema
  • T tubules help to transmit signals from the sarcolemma to the myofibrils

Proteins of muscle filaments:

  • Actin

Found in all eukaryotic cells. Consists of two strands of globular monomers of 5.6nm diameter that twist around each other in a double helical formation. Each monomer contains a binding site for myosin. The two major subcategories are microfilaments and thin filaments. Actin interacts with the cellular membrane to mediate processes such as cytoskeletal formation and maintenance, cell signalling, and muscle contraction.

- long filamentous polymers

- consists of two strands of globular monumers

- diameter 5.6nm

- twisted around each other

- double helical formation

- each monomer contain a binding site for myosin


  • Myosin

Dissociates into two idental heavy chains and two pairs of light chains. Heavy chains are thin, rod-like molecules that twist together. The heads of heavy chains contain ATP-binding sites, enabling ATPase activity and actin binding. Plays a vital role in muscle contraction and cell motility.

- large complex

- dissociated into two identical heavy chains and two pairs of light chain

- heavy chains are thin, rod-like molecules which are twisted together

- the heads of heavy chains have ATP-binding sites, ATPase activity and the ability to bind to actin

- the light chains are associated with the head

  • Troponin (Tn)
Tropomyosin.jpg

Tn binds to the surface of tropomyosin (Tm). The Tn complex consists of three subunits:

1. TnT: attaches to tropomyosin

2. TnC: binds Ca ions

3. TnI: inhibits the actin-myosin interaction

  • Tropomyosin (Tm)

Tm is a long thin molecule consisting of two polypeptide chains. Tm molecules are bound head to tail forming a polymer that runs over the actin subunits, binding to actin and acting as a molecular barrier. This molecular barrier acts by blocking myosin-binding sites on actin in relaxed muscle, preventing crossbridge cycling. In the presence of calcium ions, Tm changes formation and exposes myosin-binding sites. Multiple Tm isoforms exist.

- long thin molecule

- contains two polypeptide chains

- Tm molecules are bound head to tail

- forming a polymer that run over the actin subunits

- binds to actin and acts as a molecular barrier

- blocks myosin-binding sites in relaxed muscle

- thus, prevents the crossbridge cycle from occurring

- myosin-binding sites are exposed when Ca ions are released

- several Tm’s isoforms

Actin/Myosin Movie 1 [8]

Actin/Myosin Movie 2 [9]

Development of the neuromuscular junction

Formation of the neuromuscular junction during embryonic period is only partially understood. It is a multistep process requiring coordinated interactions between nerve terminals and muscle.

- During week 9, i.e. beginning of the fetal period, the first neuromuscular junctions appear on the newly created myotubes (muscle fibers formed from the fusion of myoblasts into multi-nucleated fibers).

- The growing end of motor neuron axons secret a protein called agrin.

- MuSK is a receptor tyrosine kinase on muscle cell. Once activated by a signal protein (agrin in this case), the kinase domain of MuSK transfers a phosphate group from ATP to selected tyrosine side chains on itself. This process is called autophosphorylation.

- Upon activation by agrin, MuSK signals via proteins (CK 2, Dok-7 and rapsyn) to induce clustering of acetocholine receptors (AChR).

- Formation of clusters of AChR occur and are concentrated in the central regions of the myofibers.

- ACh released by branching nerve endings causes AChR-induced postsynaptic potentials that appear to determine endplate localization. Thus ACh regulates and refines the localization and stabilization of developing synaptic contacts.

- The active ACh/AChR contact sites may prevent AChRs clustering in non-contacted regions.

- Motor axons branch onto specific regions (endplates) of individual muscle fibers.

The precise mechanisms that control AChR aggregation, guide ingrowing axons and xontribute to correct synaptic patterning are unknown. A study proposed that the muscle AChR is central to this process.

Novel Mouse Model Reveals Distinct Activity-Dependent and –Independent Contributions to Synapse Development

During early embryonic period, AChRs are composed of α2βγδ subunits (AChRγ) and are replaced by adult AChRs composed of α2βεδ subunits (AChRε) during later embryonic stages and early postnatal development.

Genetic mutation of genes coding for subunits of the AChR can greatly affect its activity. The mutation of ε subunit can reduce AChR’s affinity for ACh. This mutation was used to generate γ/ε-fc mice, in which a mutated ε subunit cDNA fragment is fused into the γ subunit gene by homologous recombination to replace AChRγ with functionally “silent” receptors (AChRγ/ε-fc) during embryonic development. Mice diaphragms were dissected and prepared for the study.

The study findings show that AChRγ/ε-fc is expressed, clustered in endplate-like structures, and developmentally regulated like AChRγ in wild type (WT) mice. However, the lack of AChR-mediated activity leads to a series of synaptic abnormalities during embryonic development.

The γ/ε-fc mice exhibit abnormal endplate distribution, axonal growth, muscle innervation, NMJ formation and distribution, as well as endplate morphology. Thus, the γ/ε-fc mouse line demonstrates the contribution of activity-dependent and -independent AChR-mediated processes to the formation of NMJs.


- Endplates distribution

Journal.pone.0016469.g004.png

The endplates in γ/ε-fc diaphragms are spread out (B), not as centrally located as in WT diaphragms (A). Endplate band of γ/ε-fc diaphragm is more dispersed (C). The percentage of diaphragm witdth (%DW) occupied by endplate band in embryonic week 18 (E18) is reduced comparing to that in E16 in WT (p=0.022) (D). This is due to the lateral growth of myotubes without affecting endplate distribution. In γ/ε-fc diaphragm, there is no significant change (p>0.6) in %DW between E18 and E16. This implies that new endplates are continuously being formed in myotubes.

Method: Endplates were imaged using a Zeiss Axioplan2 microscope, visualized with Alexa-488-labeled α-bungarotoxin.


- Innervation of individual endplates

The innervations pattern of γ/ε-fc diaphragms is disorganised where aberrantly located endplates attract nerves otherwise spreading directionless.

Journal.pone.0016469.g005 conew1.png

In WT diaphragms (A), nerve branches (green) terminate on endplates (red). In γ/ε-fc diaphragms (B), longer branches are formed to contact the wider spread out endplates and they continue to grow beyond the endplate, contacting additional endplates. Close-up of a single γ/ε-fc endplate (C) shows additional nerve sprouting after endplate innervations.

Method: Images of endplates were taken using a Leica TCS NT confocal microscope. Neurofilament and endplates are GFP- and r-bgt-labeled.


- Presence of Multiple Endplates

Presumably, the effect of ACh prevents formation of additional NMJs on the same myofiber through unknown, possibly activity-regulated retrograde signals. If lack of activity impairs retrograde signalling, formation of multiple synapses on the same myofiber could be expected, i.e. the fiber could present several fully innervated endplates. Slow muscle fibers were used to test this hypothesis as they are present in smaller numbers than fast fibers in the developing diaphragm.

Journal.pone.0016469.g007 conew1.png Journal.pone.0016469.g007 conew2.png

(A) and (B) are confocal images showing muscle fibers (blue) and endplates (green) in WT and γ/ε-fc mice respectively. Asterisks mark location of endplates on individual muscle fibers. The γ/ε-fc diaphragm presents multiple endplates on single muscle fibers (B). (C) illustrates a higher percentage of muscle fibers of γ/ε-fc embryo display more than one endplates per fiber when compared to WT embryo during different embryonic stage. (D) shows that average number of endplates per muscle fiber in E18 WT (1,12±0,03, white) and γ/ε-fc (1,95±0,07, gray) embryos (p<0,001).

Method: Muscle fibers are stained with anti-slow myosin antibody and endplates by Alexa488-labeled α-bungarotoxin. Confocal pictures were taken using a Leica TCS NT (Leica Microsystems) confocal microscope.

Common neuromuscular junction disorders

Neuromuscular junction disorders are due to impaired transmission of impulses at the neuromuscular junction. This may result from disorders that affect receptor function, pre- or postsynaptic membrane function, or acetylcholinesterase activity. The majority of diseases in this category are associated with autoimmune, toxic, or inherited conditions.


Neuromuscular junction disorders
Disorder Description Clinical Manifestation Treatment Picture
Myasthenia gravis Autoimmune neuromuscular disorder caused when antibodies block post-synaptic acetylcholine receptors in neuromuscular junctions. When the passage acetylcholine across the synapse is inhibited, muscles are unable to function normally and as a result they are quick to fatigue. [54] There are two forms of clinical manifestations of myasthenia gravis: ocular and generalized.In about 10-40% cases, weakness is restricted to the ocular muscles. The rest experience a fluctuating degree and variable combination of weakness in ocular, bulbar, limb, and respiratory muscles. Common symptoms include breathing difficulty, chewing or swallowing difficulty, fatigue, facial paralysis, double vision and eyelid drooping. [55] There is no cure, but long-term remission is possible. Some medications, such as neostigmine, improve the communication between the nerve and the muscle. Immunosuppressants may be used if symptoms are severe and other medications don't work well enough [56] Myasthenia.jpg
Lambert–Eaton Myasthenic Syndrome (LEMS) Autoimmune, presynaptic disorder which involves impaired release of acetylcholine. [57] Symptoms include impaired proximal muscle function, eg hip and shoulder movement. Caused by antibody blockage voltage-gated calcium channels (VGCCs) in the presynaptic cell, resulting in decreased release of acetylcholine at the neuromuscular junction. Most occurrences follow cancer although LEMS may be diagnosed first. [58] Symptoms resemble those of Myasthenia gravis, most notably muscle weakness in limbs Azathioprene, steroids, and/or immunoglobin as immune system suppressants. Pyridostigmine, dyaminopyridine to enhance acetylcholine release. [59]
X-ray of a small cell lung cancer (SCLC) that often precedes LEMS
Botulism A disease caused by the excrement of the bacteria Clostridium Botulinum. This excrement, known as Botulinum toxin, is an extremely lethal neurotoxin. It works by blocking the release of acetylcholine at neuromuscular junctions, resulting paralysis and ultimately respiratory failure. The bacteria may enter the body through wounds, or improperly canned or preserved food. [60]

Infant botulism occurs when living bacteria or its spores are eaten and grow within the baby's gastrointestinal tract. However, recently developed medical techniques use the toxin beneficially (botox).

Clinical manifestation of muscle weakness without fever is characteristic of botulism. It starts with facial muscles weakness, which then spreads to the arms and legs. Symptoms include diplopia or ptosis, dysphagia and dyspnoea. In addition, patients may experience dry mouth and GI related symptoms e.g. vomiting and constipation especially in infants. For infants, Botulism Immune Globulin Intravenous-Human (BIG-IV) also known as BabyBIG. Antitoxins (Trivalent, Heptavalent)
This 14 year old boy was fully conscious at the time of this photograph
Congenital myasthenic syndrome (CMS) Inherited disorder where not enough acetylcholine crosses the neuromuscular synapse with onset at or shortly after birth or in early childhood. [61] CMS can be pre-synaptic, where not enough acetycholine is produced or released in the first place, or post-synaptic, where acetylcholine receptors malfunction and do not stay open long enough. Symptoms are similar to those expressed through Myasthenia gravis. [62] Treatments vary depending on the type of CMS. Cholinesterase inhibitors, quinine, and fluoxetine are some effective clinical treatments. [63] Ptosis.jpg
Black widow spider venom The black widow spider produces a protein venom that causes a complete depletion of acetylcholine. [64] Local pain from the spider bite may be followed by severe muscle cramps, abdominal pain, weakness and tremors. In worse cases symptoms include nausea, vomiting, fainting, dizziness, chest pain, and respiratory difficulties [65] Alpha-latrotoxin causes the opening of cation channels in the presynaptic membrane. This channel opening causes increased release of neurotransmitters which over-stimulates motor endplates, causing pain, muscle cramps, tremors etc. [66] Most bites can be treated with opioid analgesics. Antivenom is usually only used in severe cases as it has a high incidence of allergic reactions. [67] Redbackspider.jpg
Cobratoxins Cobratoxins bind specifically to the acetylcholine receptor. [68] Cobratoxin causes paralysis by preventing the binding of acetylcholine to the nicotinic receptor (nicotinic acetylcholine receptor antagonist). Acetylcholine causes muscles to contract when activated, so when these receptors are blocked by cobratoxin, it results in muscle paralysis. [69] There seems to be no current cure for cobratoxin, but cobratoxin is controversially used as an analgesic due to its ability to block the connection between muscle and neuron. [70] Indiancobra.jpg
Aminoglycosides and excess Magnesium These interfere with calcium-mediated release of quanta. Symptoms include nausea and vomiting, impaired breathing, hypotension, hypocalcemia, arrhythmia and asystole [71] Increased magnesium decreases impulse transmission across the neuromuscular junction. This results in loss of deep tendon reflexes, and muscle paralysis. Since this also affects smooth muscle function, excess magnesium can cause decreased or stopped respiration [72] Usually treatment is to simply stop the cause of the overdose. If severe symptoms are present, sometimes dialysis and an IV drip are required [73] Magnesium.jpg

Current associated research

  • Analysis of neuromuscular development and function in C. elegans. Nicotine addiction occurs as a result of nicotinic neurotransmission, which plays a critical role in the vertebrate nervous system. Current studies work to identify the genes required for neurotransmission, such as acr-16 and cam-1. [74]

Neurexin in Embryonic Drosophila Neuromuscular Junctions (2010): In this study, Chen et al unfolded the role of the neurexin in Drosophila glutamate receptor abundance. Their results suggested that neurexin in embryos is present both pre and postsynaptically. Presynaptic neurexin promotes presynaptic active zone formation and neurotransmitter release, but along with postsynaptic neurexin, also suppresses formation of ectopic glutamate receptor clusters. During the research several methods were used. Starting with the hybridization where embryos were manually staged and dissected to examine neurexin expression. Dissections were performed as for confocal imaging and electrophysiology. For electron microscopy, genotyped Drosophila eggs were dechorionated with bleach. [10]

Muscle Mitochondrial Uncoupling Dismantles Neuromuscular Junction and Triggers Distal Degeneration of Motor Neurons (2009): Dupuis et al looked at abnormalities of the mitochondrial energy metabolism. Their findings proved that this defect is sufficient to generate motor neuron degeneration and suggest that therapeutic strategies targeted at muscle metabolism might prove useful for motor neuron diseases. Furthermore they suggested that muscle selective alterations in mitochondrial function might initiate NMJ pathology and participate in triggering motor neuron degeneration in ALS. Biochemical measurements were carried out followed by electromyography recordings and PCR analysis. [11]

Future research

  • Botulinum neurotoxin works at the neuromuscular junction, but many questions remain about the way it works. What proteins are involved in the transport the neurotoxin into the cholinergic nerve terminal? What factors control how long the toxin acts? New biotechnology has made further research feasible. Answers to these questions would restrict the toxin’s appeal as a tool for bioterrorists and increase its effectiveness as a therapeautic agent for disorders of the neuromuscular junction. [12]
  • Analysis of neuromuscular development and function in C. elegans. Future studies involving organisms such as C. elegans will identify the molecular machinery that is required for the development and function of the neuromuscular junction [75]
  • Synaptic vesicle dynamics within neuromuscular junctions of synapto-phluorin expressing mice.Relationships between synaptic structure and function at the mammalian neuromuscular junction. Current experiments involving the expression of various genes such as synapto-pHlaurin (spH) in transgenic lines of mice reveal reasons for changes in synaptic strength and structure. These experiments lay the groundwork for future studies that will look into the processes underlying the plasticity of the nervous system. [76]




  • Potential Application of Induced Pluripotent Stem Cells in Cell Replacement Therapy for Parkinson's Disease.

PMID: 21495962

Current research has shown that the use of embryonic stem cells to replace damaged tissue can be beneficial in various neurodegenerative diseases. These stem cells integrate and form connections with host cells. The problem with some stem cell treatments is the capability of these cells to form long axons from the spinal cord to the muscle cell and forming a junction with the muscle. Further research into the signaling mechanisms of the NMJ may find additional mechanisms by which transplanted cells may be of therapeutic benefit. [77]

External links

Glossary

  • acetylcholine (ACh): A chemical neurotransmitter in the brain and peripheral nervous system; the dominant neurotransmitter in the peripheral nervous system, released at neuromuscular junctions and synapses of the parasympathetic division.
  • acetylcholinesterase (AChE): An enzyme found in the synaptic cleft, bound to the postsynaptic membrane, and in tissue fluids; breaks down and inactivates acetylcholine molecules.
  • actin: The protein component of microfilaments that forms thin filaments in skeletal muscles and produces contractions of all muscles through interaction with thick (myosin) filaments
  • action potential: A conducted change in the transmembrane potential of excitable cells, initiated by a change in the membrane permeability to sodium ions; see also nerve impulse.
  • axon: The elongate extension of a neuron that conducts an action potential.
  • axon hillock: In a multipolar neuron, the portion of the cell body adjacent to the initial segment.
  • choline: A breakdown product or precursor of acetylcholine.
  • cholinergic synapse: A synapse where the presynaptic membrane releases acetylcholine on stimulation.
  • cholinesterase: The enzyme that breaks down and inactivates acetylcholine.
  • depolarization: A change in the transmembrane potential from a negative value toward 0 mV.
  • electrical coupling: A connection between adjacent cells that permits the movement of ions and the transfer of graded or conducted changes in the transmembrane potential from cell to cell.
  • gap junctions: Connections between cells that permit electrical coupling.
  • innervation: The distribution of sensory and motor nerves to a specific region or organ.
  • ion: An atom or molecule bearing a positive or negative charge due to the donation or acceptance, respectively, of an electron.
  • ionotrophic receptors in the NMJ are receptors that allow ions to pass through them when they bind to acetylcholine
  • muscarinic receptors: Membrane receptors sensitive to acetylcholine and to muscarine, a toxin produced by certain mushrooms; located at all parasympathetic neuromuscular and neuroglandular junctions and at a few sympathetic neuromuscular and neuroglandular junctions.
  • myasthenia gravis: A muscular weakness due to a reduction in the number of acetylcholine receptor sites on the sarcolemmal surface; suspected to be an autoimmune disorder.
  • nerve impulse: An action potential in a neuron cell membrane.
  • neurofilaments: Microfilaments in the cytoplasm of a neuron.
  • neuromuscular junction: A synapse between a neuron and a muscle cell.
  • nicotinic receptors: Acetylcholine receptors on the surfaces of sympathetic and parasympathetic ganglion cells; respond to the compound nicotine.
  • peripheral nervous system (PNS): All neural tissue outside the central nervous system.
  • repolarization: The movement of the transmembrane potential away from a positive value and toward the resting potential.
  • resting potential: The transmembrane potential of a normal cell under homeostatic conditions.
  • sarcolemma: The cell membrane of a muscle cell.
  • sarcomere: The smallest contractile unit of a striated muscle cell.
  • sarcoplasm: The cytoplasm of a muscle cell.
  • signal Transduction is the process by which an extracellular signaling molecule activates a membrane receptor that in turn alters intracellular molecules creating a response
  • sliding filament theory: The concept that a sarcomere shortens as the thick and thin filaments slide past one another.
  • synapse: The site of communication between a nerve cell and some other cell; if the other cell is not a neuron, the term neuromuscular or neuroglandular junction is often used.
  • thick filament: A cytoskeletal filament in a skeletal or cardiac muscle cell; composed of myosin, with a core of titin.
  • thin filament: A cytoskeletal filament in a skeletal or cardiac muscle cell; consists of actin, troponin, and tropomyosin.
  • threshold: The transmembrane potential at which an action potential begins.
  • tropomyosin: A protein on thin filaments that covers the active sites in the absence of free calcium ions.
  • troponin: A protein on thin filaments that binds to tropomyosin and to G actin.

References

  1. Farrugia M.E. 2002, "Myasthenia Gravis", JR Coll Physicians Edinb, vol 34, pp. 14-18.
  2. Leake, C. D. An Historical Account of Pharmacology to the Twentieth Century; Charles C. Thomas: Springfield, IL, 1975.
  3. Sneader, W. Drug Discovery: The Evolution of Modern Medicines; Wiley: New York, 1985
  4. Feldberg WS. Henry Hallett Dale, 1875-1968. Biogr Mem Fellows R Soc. 1970;16:77–174.
  5. Hodgkin, Alan. Chance & design: reminiscences of science in peace and war (p.324)
  6. Fatt P & Katz B (1951). An analysis of the end-plate potential recorded with an intra-cellular electrode. J Physiol 115, 320–370
  7. del Castillo J & Katz B (1954). Quantal components of the end-plate potential. J Physiol 124, 560–573
  8. Lewis, P., et al. Muscle & Nerve. Published in May 2000.
  9. Thesleff S. Transmitter release in botulinum-poisoned muscles. J Physiol (Paris). 1984;79(4):192-5. Review. PubMed PMID: 6152289.
  10. Kurshan PT, Oztan A, Schwarz TL. Presynaptic alpha2delta-3 is required for synaptic morphogenesis independent of its Ca2+-channel functions. Nat Neurosci. 2009 Nov;12(11):1415-23. Epub 2009 Oct 11. PubMed PMID: 19820706; PubMed Central PMCID: PMC2996863.
  11. Katz B, Miledi R. The role of calcium in neuromuscular facilitation. J Physiol. 1968 Mar;195(2):481-92. PubMed PMID: 4296699; PubMed Central PMCID: PMC1351674.
  12. Hirose S, Vieth WR. Transport of acetylcholine in a membrane. Laminate model of the neuromuscular junction. Appl Biochem Biotechnol. 1984 Feb;9(1):81-93. PubMed PMID: 6476821.
  13. Birks RI, Burstyn PG, Firth DR. The form of sodium-calcium competition at the frog myoneural junction. J Gen Physiol. 1968 Dec;52(6):887-907. PubMed PMID: 4301843; PubMed Central PMCID: PMC2225848.
  14. Hirose S, Vieth WR. Transport of acetylcholine in a membrane. Laminate model of the neuromuscular junction. Appl Biochem Biotechnol. 1984 Feb;9(1):81-93. PubMed PMID: 6476821.
  15. Hirose S, Vieth WR. Transport of acetylcholine in a membrane. Laminate model of the neuromuscular junction. Appl Biochem Biotechnol. 1984 Feb;9(1):81-93. PubMed PMID: 6476821.
  16. Birks RI, Burstyn PG, Firth DR. The form of sodium-calcium competition at the frog myoneural junction. J Gen Physiol. 1968 Dec;52(6):887-907. PubMed PMID: 4301843; PubMed Central PMCID: PMC2225848.
  17. Walke W, Staple J, Adams L, Gnegy M, Chahine K, Goldman D. Calcium-dependent regulation of rat and chick muscle nicotinic acetylcholine receptor (nAChR) gene expression. J Biol Chem. 1994 Jul 29;269(30):19447-56. PubMed PMID: 8034713.
  18. 1: Birks RI, Burstyn PG, Firth DR. The form of sodium-calcium competition at the frog myoneural junction. J Gen Physiol. 1968 Dec;52(6):887-907. PubMed PMID: 4301843; PubMed Central PMCID: PMC2225848.
  19. Walke W, Staple J, Adams L, Gnegy M, Chahine K, Goldman D. Calcium-dependent regulation of rat and chick muscle nicotinic acetylcholine receptor (nAChR) gene expression. J Biol Chem. 1994 Jul 29;269(30):19447-56. PubMed PMID: 8034713.
  20. Walke W, Staple J, Adams L, Gnegy M, Chahine K, Goldman D. Calcium-dependent regulation of rat and chick muscle nicotinic acetylcholine receptor (nAChR) gene expression. J Biol Chem. 1994 Jul 29;269(30):19447-56. PubMed PMID: 8034713.
  21. Hirose S, Vieth WR. Transport of acetylcholine in a membrane. Laminate model of the neuromuscular junction. Appl Biochem Biotechnol. 1984 Feb;9(1):81-93. PubMed PMID: 6476821.
  22. Birks RI, Burstyn PG, Firth DR. The form of sodium-calcium competition at the frog myoneural junction. J Gen Physiol. 1968 Dec;52(6):887-907. PubMed PMID: 4301843; PubMed Central PMCID: PMC2225848.
  23. Walke W, Staple J, Adams L, Gnegy M, Chahine K, Goldman D. Calcium-dependent regulation of rat and chick muscle nicotinic acetylcholine receptor (nAChR) gene expression. J Biol Chem. 1994 Jul 29;269(30):19447-56. PubMed PMID: 8034713.
  24. Wu H, Xiong WC, Mei L. To build a synapse: signaling pathways in neuromuscular junction assembly. Development. 2010 Apr;137(7):1017-33. Review. PubMed PMID: 20215342; PubMed Central PMCID: PMC2835321.
  25. Pappas GD, Peterson ER, Masurovsky EB, Crain SM. Electron microscopy of the in vitro development of mammalian motor end plates. Ann N Y Acad Sci. 1971 Sep 15;183:33-45. PubMed PMID: 4107829.
  26. Walke W, Staple J, Adams L, Gnegy M, Chahine K, Goldman D. Calcium-dependent regulation of rat and chick muscle nicotinic acetylcholine receptor (nAChR) gene expression. J Biol Chem. 1994 Jul 29;269(30):19447-56. PubMed PMID: 8034713.
  27. Pappas GD, Peterson ER, Masurovsky EB, Crain SM. Electron microscopy of the in vitro development of mammalian motor end plates. Ann N Y Acad Sci. 1971 Sep 15;183:33-45. PubMed PMID: 4107829.
  28. [1]
  29. [2]
  30. Imeri L, Opp MR. How (and why) the immune system makes us sleep. Nat Rev Neurosci. 2009 Mar;10(3):199-210. Epub 2009 Feb 11. Review. PubMed PMID: 19209176; PubMed Central PMCID: PMC2839418.
  31. Elmqvist D, Feldman DS. Influence of ionic environment on acetylcholine release from the motor nerve terminals. Acta Physiol Scand. 1966 May;67(1):34-42. PubMed PMID: 5963300.
  32. Morisot P. [Physiology of the motor plate]. Anesth Analg (Paris). 1966 Apr-Jun;23(2):459-70. Review. French. PubMed PMID: 5327039.
  33. Levine L. An electrophysiological study of chelonian skeletal muscle. J Physiol. 1966 Apr;183(3):683-713. PubMed PMID: 5919565; PubMed Central PMCID: PMC1357516.
  34. Elmqvist D, Feldman DS. Influence of ionic environment on acetylcholine release from the motor nerve terminals. Acta Physiol Scand. 1966 May;67(1):34-42. PubMed PMID: 5963300.
  35. Morisot P. [Physiology of the motor plate]. Anesth Analg (Paris). 1966 Apr-Jun;23(2):459-70. Review. French. PubMed PMID: 5327039.
  36. Imeri L, Opp MR. How (and why) the immune system makes us sleep. Nat Rev Neurosci. 2009 Mar;10(3):199-210. Epub 2009 Feb 11. Review. PubMed PMID: 19209176; PubMed Central PMCID: PMC2839418.
  37. Levine L. An electrophysiological study of chelonian skeletal muscle. J Physiol. 1966 Apr;183(3):683-713. PubMed PMID: 5919565; PubMed Central PMCID: PMC1357516.
  38. Lindstrom J. Nicotinic acetylcholine receptors in health and disease. Mol Neurobiol. 1997 Oct;15(2):193-222. Review. PubMed PMID: 9396010.
  39. Guyton AC, Hall JE: Textbook of Medical Physiology (2006) Elsevier Saunders, Philadelphia. P.87
  40. Guyton AC, Hall JE: Textbook of Medical Physiology (2006) Elsevier Saunders, Philadelphia. P.87
  41. Kelly AM, Zacks SI. The fine structure of motor endplate morphogenesis. J Cell Biol. 1969 Jul;42(1):154-69. PubMed PMID: 5786980; PubMed Central PMCID: PMC2107582.
  42. Junqueira C.L. & Caraneiro J., 2005. Basic Histology, text & atlas, 11th edition. McGraw-Hill Companies.
  43. Ogata T, Murata F. Fine structure of motor endplate in red, white and intermediate fibers of mammalian fast muscle. Tohoku J Exp Med. 1969 Jun;98(2):107-15. PubMed PMID: 5811099.
  44. Pye RJ, Greaves MW. Benign rheumatoid nodules of the skin. Br J Dermatol. 1979 Jul;101 Suppl 17:58-9. PubMed PMID: 465342.
  45. Buckley GA. The structure and development of the motor end-plate. Physiotherapy. 1972 Aug;58(8):274-6. PubMed PMID: 4669373.
  46. 1: Rusakov DA, Savtchenko LP, Zheng K, Henley JM. Shaping the synaptic signal: molecular mobility inside and outside the cleft. Trends Neurosci. 2011 Apr 4. [Epub ahead of print] PubMed PMID: 21470699.
  47. 1: Rees RP. The morphology of interneuronal synaptogenesis: a review. Fed Proc. 1978 May 15;37(7):2000-9. Review. PubMed PMID: 205437.
  48. 1: Vrbová G, Wareham AC. Effects of nerve activity on the postsynaptic membrane of skeletal muscle. Brain Res. 1976 Dec 24;118(3):371-82. PubMed PMID: 1009425.
  49. Stephen G. Lipson, Ariel Lipson, Henry Lipson, Optical Physics 4th Edition, Cambridge University Press, ISBN 9780521493451
  50. O1 Optical Microscopy By Katarina Logg. Chalmers Dept. Applied Physics. 2006-01-20
  51. Erni R, Rossell MD, Kisielowski C, Dahmen U. Atomic-resolution imaging with a sub-50-pm electron probe. Phys Rev Lett. 2009 Mar 6;102(9):096101. Epub 2009 Mar 2. PubMed PMID: 19392535.
  52. Saint DA, McLarnon JG, Quastel DM. Anion permeability of motor nerve terminals. Pflugers Arch. 1987 Jul;409(3):258-64. PubMed PMID: 3627946.
  53. Drummy LF, Yang J, Martin DC. Low-voltage electron microscopy of polymer and organic molecular thin films. Ultramicroscopy. 2004 Jun;99(4):247-56. PubMed PMID: 15149719.
  54. McGrogan A, Sneddon S, de Vries CS. The incidence of myasthenia gravis: a systematic literature review. Neuroepidemiology. 2010;34(3):171-83. Epub 2010 Feb 2. Review. PubMed PMID: 20130418.
  55. Losen M, Stassen MH, Martínez-Martínez P, Machiels BM, Duimel H, Frederik P, Veldman H, Wokke JH, Spaans F, Vincent A, De Baets MH. Increased expression of rapsyn in muscles prevents acetylcholine receptor loss in experimental autoimmune myasthenia gravis. Brain. 2005 Oct;128(Pt 10):2327-37. Epub 2005 Sep 8. PubMed PMID: 16150851.
  56. Losen M, Martínez-Martínez P, Phernambucq M, Schuurman J, Parren PW, De Baets MH. Treatment of myasthenia gravis by preventing acetylcholine receptor modulation. Ann N Y Acad Sci. 2008;1132:174-9. PubMed PMID: 18567867.
  57. Mareska M, Gutmann L. Lambert-Eaton myasthenic syndrome. Semin Neurol. 2004 Jun;24(2):149-53. Review. PubMed PMID: 15257511.
  58. Verschuuren JJ, Wirtz PW, Titulaer MJ, Willems LN, van Gerven J. Available treatment options for the management of Lambert-Eaton myasthenic syndrome. Expert Opin Pharmacother. 2006 Jul;7(10):1323-36. Review. PubMed PMID: 16805718.
  59. Rees JH. Paraneoplastic syndromes: when to suspect, how to confirm, and how to manage. J Neurol Neurosurg Psychiatry. 2004 Jun;75 Suppl 2:ii43-50. PubMed PMID: 15146039; PubMed Central PMCID: PMC1765657.
  60. Agarwal AK, Goel A, Kohli A, Rohtagi A, Kumar R. Food-borne botulism. J Assoc Physicians India. 2004 Aug;52:677-8. PubMed PMID: 15847370.
  61. Hantaï D, Richard P, Koenig J, Eymard B. Congenital myasthenic syndromes. Curr Opin Neurol. 2004 Oct;17(5):539-51. Review. PubMed PMID: 15367858.
  62. Eymard B, Ioos C, Barois A, Estournet B, Mayer M, Fournier E, Yasaki E, Prioleau C, Bauché S, Gaudon K, Leroy JP, Koenig J, Richard P, Hantaï D. [Congenital myasthenic syndromes due to mutations in the rapsyn gene]. Rev Neurol (Paris). 2004 May;160(5 Pt 2):S78-84. Review. French. PubMed PMID: 15269664.
  63. Farrugia ME. Myasthenic syndromes. J R Coll Physicians Edinb. 2011 Mar;41(1):43-7; quiz 48. PubMed PMID: 21365067.
  64. Martin, Louise (1988). Black Widow Spiders. Rourke Enterprises, Inc.. pp. 18–20.
  65. Preston-Malfham, Ken (1998). Spiders. Edison, New Jersey: Chartwell Books. p. 40.
  66. Insects and Spiders. New York: St. Remy Media Inc. / Discovery Books. 2000. p. 35.
  67. Martin, Louise (1988). Black Widow Spiders. Rourke Enterprises, Inc.. pp. 18–20.
  68. YANG CC. CRYSTALLIZATION AND PROPERTIES OF COBROTOXIN FROM FORMOSAN COBRA VENOM. J Biol Chem. 1965 Apr;240:1616-8. PubMed PMID: 14285499.
  69. Konstantakaki M, Changeux JP, Taly A. Docking of alpha-cobratoxin suggests a basal conformation of the nicotinic receptor. Biochem Biophys Res Commun. 2007 Aug 3;359(3):413-8. Epub 2007 Jun 4. PubMed PMID: 17555709.
  70. Hue B, Buckingham SD, Buckingham D, Sattelle DB. Actions of snake neurotoxins on an insect nicotinic cholinergic synapse. Invert Neurosci. 2007 Sep;7(3):173-8. Epub 2007 Aug 21. PubMed PMID: 17710455.
  71. Pritchard JA. The use of the magnesium ion in the management of eclamptogenic toxemias. Surg Gynecol Obstet. 1955; 100:131–140
  72. Lu JF,Nightingale CH. Magnesium sulfate in eclampsia and pre-eclampsia. Clin Pharmacokinet. 2000; 38:305–314
  73. Pritchard JA. The use of the magnesium ion in the management of eclamptogenic toxemias. Surg Gynecol Obstet. 1955; 100:131–140
  74. Analysis of neuromuscular development and function in C. elegans [3] Accessed 8 May 2011.
  75. Analysis of neuromuscular development and function in C. elegans [4] Accessed 8 May 2011.
  76. Synaptic vesicle dynamics within neuromuscular junctions of synapto-phluorin expressing mice. [5] Accessed 8 May 2011
  77. Stem cell-derived neurotrophic support for the neuromuscular junction in spinal muscular atrophy PMID20955113

Coordinator Comment to all Groups

I will add a general comment that will be the same to all groups under this heading.

Referencing Extension Problem

--Mark Hill 13:16, 3 May 2011 (EST) As mentioned in the lecture, I am aware of the referencing extension problem on your project pages. I have the following temporary solution, of removing the extension, so that groups can continue to add content to their project pages. I am also giving everyone a 1 week extension before the peer assessment.

This should only be done if your project page is not allowing you to save changes!

A. The Easy Way....

The following 4 steps can be done on the webpage or select all content in edit mode, copy and paste into a text editor. All steps must be completed before you attempt to save.

  1. In page edit mode, find all <pubmed> reference tags.
  2. Replace this tag with [http://www.ncbi.nlm.nih.gov/pubmed/ Note, there should be no spaces between the internet address and the pmid number.
  3. Now find all </pubmed> reference tags.
  4. Replace this second tag with ]

This will generate a numbered reference list that we can later fix up.


B. The Better Looking Result....

Whatever is between the <ref> </ref></pubmed> tags is what will appear in your reference list, so you can format the reference and link to appear in your reference list.

2011 Projects: Synaptic Junctions | Gap Junctions | Tight Junctions | Desmosomes | Adherens Junctions | Neuromuscular Junction