36 Questions
Where is the cell body of a motor neuron typically located?
Spinal cord and brain stem (CNS)
What is unique about the relationship between a motor neuron and muscle fibers?
Each muscle fiber can only have one motor neuron attached
What is the term for the group of muscle fibers stimulated by a single motor neuron?
Motor unit
What is the direction of electrical impulses across the neuromuscular junction?
Unidirectional, from motor neuron to muscle fiber
What is the pre-synaptic side of the neuromuscular junction also referred to as?
Presynaptic terminal
What is the function of the synaptic cleft in the neuromuscular junction?
A small gap between the pre- and post-synaptic sides
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
What happens to small amounts of acetylcholine in the synaptic cleft?
They diffuse out of the cleft and are no longer available for use
What is the result of organophosphate toxicosis on acetylcholinesterase?
irreversible inactivation
What is the effect of irreversible inactivation of acetylcholinesterase?
Excess acetylcholine and overstimulation of nicotinic receptors
What is the purpose of acetylcholinesterase in the synaptic cleft?
To break down acetylcholine into acetyl acid and choline
What is the result of prolonged overstimulation of nicotinic receptors within chronic cases of Organophosphate Toxicosis?
Flaccid paralysis
What is the effect of botulinum toxin on SNARE proteins?
Cleavage of SNARE proteins
Which of the following has these 7 toxin types: A, B, C, D, E, F, G?
Botulism
What is the primary cause of animal poisoning?
Organophosphate toxicosis
How can botulism be contracted?
Through ingestion of contaminated uncooked or undercooked food
What is the result of overstimulation of the central receptors in Organophosphate Toxicosis?
Nervousness and ataxia
What is the primary symptom of botulism?
Progressive motor paralysis
What is the result of overstimulation of the muscarinic receptors in Organophosphate Toxicosis?
Dyspnea and hypersalivation
What is the underlying cause of Myasthenia Gravis?
Abnormal reduction of acetylcholine receptors
Which type of Myasthenia Gravis is present from birth?
Congenital form
What is the typical age at which symptoms of congenital Myasthenia Gravis become apparent?
6-9 weeks of age
What is the difference between Carbamate toxicosis and Organophosphate Toxicosis?
Carbamate toxicosis is reversible, while Organophosphate Toxicosis is not
When is the anti-toxin most effective in treating botulism?
During the first hours after ingestion of contaminated food
Where are the acetylcholine receptors located in the postsynaptic membrane?
At the mouth of the junctional folds
What is the purpose of the subneural clefts in the synaptic cleft?
To increase the surface area of the muscle membrane
What is the result of giving anti-toxin to a patient after the botulism toxin has already been activated?
State of anaphylaxis
What is the primary function of mitochondria in the pre-synaptic terminal?
Production of ATP and acetyl-CoA for acetylcholine production and release
Which of the following causes exercise -induced weakness?
Myasthenia Gravis
Which species are fairly resistant to all types of botulism toxins?
Dogs and cats
Which of the following statements is correct?
Small motor units control finer muscle movement. Large motor units control more powerful movements.
What is the function of the active zone in the presynaptic terminal?
To hold vesicles in the right place for release
How many motor endplates can a muscle fiber have?
1
What is the maximum number of motor units that a motor neuron axon terminal can have?
50
Which of the following is an autoimmune disorder where IgG is against the acetylcholine receptors?
Acquired form of Myasthenia Gravis
What is an extraocular muscle an example of?
Small motor unit
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
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
