Muscle Physiology- Pt 2 Quiz

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Questions and Answers

Where is the cell body of a motor neuron typically located?

Muscle fibers

Neuromuscular junction

Peripheral nerves

Spinal cord and brain stem (CNS) (correct)

What is unique about the relationship between a motor neuron and muscle fibers?

Each motor neuron can only attach to one type of muscle fiber

Each muscle fiber can only have one motor neuron attached (correct)

Each motor neuron is attached to only one muscle fiber

Each muscle fiber is attached to multiple motor neurons

What is the term for the group of muscle fibers stimulated by a single motor neuron?

Synaptic complex

Muscle fiber bundle

Neuromuscular junction

Motor unit (correct)

What is the direction of electrical impulses across the neuromuscular junction?

Unidirectional, from motor neuron to muscle fiber Signup and view all the answers

What is the pre-synaptic side of the neuromuscular junction also referred to as?

Presynaptic terminal Signup and view all the answers

What is the function of the synaptic cleft in the neuromuscular junction?

A small gap between the pre- and post-synaptic sides Signup and view all the answers

After the influx of calcium into the presynaptic terminal (due to the opening of the voltage gated calcium channels), what immediately happens next?

Synaptotagmin enzymes are activated Signup and view all the answers

What happens to small amounts of acetylcholine in the synaptic cleft?

They diffuse out of the cleft and are no longer available for use Signup and view all the answers

What is the result of organophosphate toxicosis on acetylcholinesterase?

irreversible inactivation Signup and view all the answers

What is the effect of irreversible inactivation of acetylcholinesterase?

Excess acetylcholine and overstimulation of nicotinic receptors Signup and view all the answers

What is the purpose of acetylcholinesterase in the synaptic cleft?

To break down acetylcholine into acetyl acid and choline Signup and view all the answers

What is the result of prolonged overstimulation of nicotinic receptors within chronic cases of Organophosphate Toxicosis?

Flaccid paralysis Signup and view all the answers

What is the effect of botulinum toxin on SNARE proteins?

Cleavage of SNARE proteins Signup and view all the answers

Which of the following has these 7 toxin types: A, B, C, D, E, F, G?

Botulism Signup and view all the answers

What is the primary cause of animal poisoning?

Organophosphate toxicosis Signup and view all the answers

How can botulism be contracted?

Through ingestion of contaminated uncooked or undercooked food Signup and view all the answers

What is the result of overstimulation of the central receptors in Organophosphate Toxicosis?

Nervousness and ataxia Signup and view all the answers

What is the primary symptom of botulism?

Progressive motor paralysis Signup and view all the answers

What is the result of overstimulation of the muscarinic receptors in Organophosphate Toxicosis?

Dyspnea and hypersalivation Signup and view all the answers

What is the underlying cause of Myasthenia Gravis?

Abnormal reduction of acetylcholine receptors Signup and view all the answers

Which type of Myasthenia Gravis is present from birth?

Congenital form Signup and view all the answers

What is the typical age at which symptoms of congenital Myasthenia Gravis become apparent?

6-9 weeks of age Signup and view all the answers

What is the difference between Carbamate toxicosis and Organophosphate Toxicosis?

Carbamate toxicosis is reversible, while Organophosphate Toxicosis is not Signup and view all the answers

When is the anti-toxin most effective in treating botulism?

During the first hours after ingestion of contaminated food Signup and view all the answers

Where are the acetylcholine receptors located in the postsynaptic membrane?

At the mouth of the junctional folds Signup and view all the answers

What is the purpose of the subneural clefts in the synaptic cleft?

To increase the surface area of the muscle membrane Signup and view all the answers

What is the result of giving anti-toxin to a patient after the botulism toxin has already been activated?

State of anaphylaxis Signup and view all the answers

What is the primary function of mitochondria in the pre-synaptic terminal?

Production of ATP and acetyl-CoA for acetylcholine production and release Signup and view all the answers

Which of the following causes exercise -induced weakness?

Myasthenia Gravis Signup and view all the answers

Which species are fairly resistant to all types of botulism toxins?

Dogs and cats Signup and view all the answers

Which of the following statements is correct?

Small motor units control finer muscle movement. Large motor units control more powerful movements. Signup and view all the answers

What is the function of the active zone in the presynaptic terminal?

To hold vesicles in the right place for release Signup and view all the answers

How many motor endplates can a muscle fiber have?

1 Signup and view all the answers

What is the maximum number of motor units that a motor neuron axon terminal can have?

50 Signup and view all the answers

Which of the following is an autoimmune disorder where IgG is against the acetylcholine receptors?

Acquired form of Myasthenia Gravis Signup and view all the answers

What is an extraocular muscle an example of?

Small motor unit Signup and view all the answers

Study Notes

Motor Neurons

Located in the CNS (spinal cord and brain stem)
Axon travels through peripheral nerves and synapses with effector organs (muscle fibers)
Each muscle fiber can only have one motor neuron attached
Each motor neuron can be attached to multiple muscle fibers
Demonstrates an "all or nothing" response associated with motor units

Neuromuscular Junction (NMJ)

Specialized synapse between a motor neuron and a muscle fiber
Each muscle fiber can only have one neuromuscular junction
Electrical impulses (action potentials) only travel unidirectionally across the NMJ
Composed of:
- Pre-synaptic side (AKA pre-synaptic terminal)
- Post-synaptic side/membrane (AKA terminal plate)
- Synaptic cleft

Pre-synaptic Terminal

Terminal portion of the motor neuron with a button-like shape (synaptic button)
Contains enzyme acetylcholinesterase that destroys acetylcholine by breaking it down into acetyl acid and choline
Choline is recycled and transported back to the pre-synaptic terminal

Organophosphate Toxicosis

Caused by insecticide, pesticide, and antiparasitic exposure at a toxic level
Irreversible inactivation of acetylcholinesterase, leading to excess acetylcholine and overstimulation of acetylcholine receptors
Symptoms:
- Muscle spasm and twitching (fasciculations)
- Dyspnea (bronchoconstriction and increased bronchial secretions)
- Diarrhea, vomiting, frequent urination, hypersalivation, colic, miosis
- Nervousness, ataxia, seizures, hyperreactivity
- Prolonged overstimulation can lead to desensitization of receptors and flaccid paralysis

Botulism

Caused by ingestion of Botulinum Toxin (neurotoxin) produced by Clostridium botulinum
Targets and destroys SNARE proteins via cleavage, preventing acetylcholine release
Common in birds and chickens, but can occur in fish, horses, cattle, dogs, and cats
Symptoms:
- Progressive motor paralysis
- Vomiting/regurgitation, dilated pupils, inability to blink, difficulty chewing or swallowing
- Atonic bladder, constipation/reduced peristalsis
Anti-toxin treatment available if given shortly after ingestion of contaminated food

Myasthenia Gravis

Abnormal reduction of acetylcholine receptors on the neuromuscular endplate
Causes exercise-induced weakness
Can be congenital or acquired
Congenital form:
- Present from birth
- Recurrent and progressive muscle fatigue apparent at 6-9 weeks of age

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