Exam 2 - Lecture 25 (Neuromuscular Junction) Flashcards
What do somatic motor neurons innervate?
skeletal muscle
Why are multipolar neurons named so?
They have many dendrites that shoot out of the cell body
What is a motor unit?
Functional unit of somatic motor system, made of a single motor neuron and all the muscle it innervates
The _____ the # of motor units involved, the more forceful the contraction is.
greater
What is present at the terminal end of a motor axon?
Motor end plate with many nerve endings
What are the components of a neuromuscular junction?
Motor end plate + junctional fold of sarcolemma
What NTM is present in NMJs?
ACh
What is the postsyn. receptor in NMJs?
AChR
What is found at the periphery of the nerve ending at the NMJ?
Schwann cell
What are the 5 steps of neuromuscular transmission?
- AP opens VG Ca2+ channels
- Synaptic vesicles release ACh by exocytosis
- ACh binds to AChR; opens ligand-gated channels for Na+
- Na+ influx and membrane depolarization occur
- VG Na+ and K+ channels open when membrane voltage > threshold voltage of muscle cell
- APs of sarcolemma
What is the postsyn. site in a NMJ?
Sarcolemma
What are 2 deficits of the NMJ?
- Tic paralysis
2. Myasthenia gravis
What type of NMJ deficit is tick paralysis?
presynaptic deficit
What type of NMK deficit is Myasthenia gravis?
Postsyn. deficit
What happens in tick paralysis?
NTX secreted by feeding female wood tick interferes with release of ACh
What are the symptoms of tick paralysis?
Generalized muscle weakness
When do clinical signs of tick paralysis show?
7-9 days after attachment of ticks
When does recovery from tick paralysis occur?
1-3 days after removal of ticks
What is the pain sensation of the body during tick paralysis and why?
Normal because disease acts on motor neuron, not sensory (pain is still present).
What happens in myasthenia gravis?
Autoimmune disease where Ab’s block, alter, or destroy AChR, decreasing the number of available receptors
What are the consequences of myasthenia gravis?
Progressive loss of muscle strength, exercise-induced motor weakness that improves following rest
What drug is used to treat myasthenia gravis and how does it work?
Anti-ACh-esterase; prevents ACh esterase from degrading AChR so that more of them are available for attachment of ACh.
