Lecture 28- Neuromuscular Junction Flashcards
What is the definition of a motor unit?
The lower motor neuron and the group of muscle fibers it innervates
What is required when using more strength (such as picking up a large weight compared to a phone)
Recruiting more motor units
What distinguishes a neuromuscular synapse and a neuromuscular junction?
Synapse- a junction between a Neuron and the next cell
NM Junction- type of synapse specifically between motor neurons and muscle cells
What is the first step in the neuromuscular junction?
Arrival of an action potential at the synaptic terminal of the motor neuron
What is the second step in the neuromuscular junction?
Release of Acetylcholine into synaptic cleft
What is the third step in the neuromuscular junction?
Diffusion of Acetylcholine across the synaptic cleft
What is the fourth step in the neuromuscular junction?
Activation of Acetylcholine receptors on motor end plate (part of sarcolemma that has ACh receptors)
What is the fifth step in the neuromuscular junction?
Production of muscle fiber action potential
What is the final step in the neuromuscular junction?
Termination of Acetylcholine activity by the enzyme acetylcholinesterase (AChE)
What is acetylcholinesterase?
Enzyme that prevents overstimulation of a muscle fiber
What is Acetylcholine?
A neurotransmitter that functions as a chemical messenger between the motor neuron and the muscle fiber.
What is the output region of the neuromuscular synapse?
Lower motor neuron (secretes acetycholine)
What is the input region of the neuromuscular synapse?
The muscle fiber
What is the role of nicotine acetylcholine receptors?
Transduce a chemical signal into an electrical signal with maximum efficiency and speed
What are nicotine acetylcholine receptors?
Ligand-gated ion channels/muscle receptors found at the skeletal neuromuscular junction where they mediate neuromuscular transmission
Are muscles multinucleate?
Yes
What is the sarcolemma?
The plasma membrane of a muscle cell
What is the role of transverse tubules?
Allow transmission of the action potential, with its attendant ion shifts, to all parts of the cell, which allows rapid activation of the entire cell
Where are transverse tubules located?
Invaginations (dips) within the sarcolemma (plasma membrane of a muscle cell)
What is the sarcoplasmic reticulum?
Specialized form of the endoplasmic reticulum of muscle cells, dedicated to calcium ion (Ca2+) handling
Necessary for muscle contraction and relaxation
What does each muscle fiber receive innervation from?
ONE motor neuron
How many motor neurons can innervate a muscle fiber?
Multiple
How many motor fibers can be found in a muscle?
Many (100s-1000s)
What does acetylcholinesterase do to prevent over stimulation of a muscle?
Cleaves Acetylcholine into a molecule of acetate and a molecule of choline
What is excitation-contraction coupling (EC-Coupling)?
The link between the generation of a action potential (nerve impulse) in the sarcolemma and the start of a muscle contraction
