Topic 10: Skeletal Muscle Physiology - Muscle Contraction Flashcards
Why are muscles excitable?
- respond to stimuli and produce action potentials
Why are muscles contractile?
- can shorten and thicken
Why are muscles extensible?
- stretch when pulled
Why are muscles elastic?
- return to original shape after contraction or extension
What are the functions of muscles? (4)
- movement
- posture, facial expression
- heat production (37C)
- protection of viscera - body wall
Each muscle fiber (cell) is innervated by how many neurons?
- 1 neuron
The axon of a motor neuron branches to where? (2)
- branches to innervate several muscle fibers
1 neuron = 150 fibers within same whole muscle
What is a motor unit?
- a SINGLE motor neuron and ALL of the muscle fibers it innervates
What is the structure of a neuromuscular junction? (3)
- presynaptic cell (neuron) with ACh (nt) vesicles
- postsynaptic cell (muscle) membrane (sarcolemma) which is specialized with ACh receptors in motor end plate
- two membranes separated by a synaptic cleft
What is the function of a neuromuscular junction? What are the steps? (6)
1) AP reaches axon terminal and synaptic end bulb of neuron
2) Calcium enters via voltage gates, causing exocytosis of ACh
3) ACh binds to ACh receptors on motor end plate
4) Chemical Gates open and sodium enters causing EPP (depolarizing GP)
5) EPP causes opening of Na+ voltage gates on adjacent sarcolemma, causing AP
6) Propagates along sarcolemma
In a neuromuscular junction, what characteristics does the AP formed have?
- same properties/channels as on a neuron
What is the bigger picture in the whole neuromuscular junction steps?
WE WANT A CONTRACTION, thats why we propagate along the sarcolemma
1 neuron AP has how many EPP and AP?
-1 EPP and 1 AP
Why is the AP (neuron) always a critical stimulus? (3)
- lots of ACh released
- motor end plate as many receptors
- so to inhibit skeletal muscle, you must inhibit motor neuron
