Bio9 lab - skeletal muscle

Motor unit

A motor neuron and all of the muscle fibers it innervates

One motor neuron's action potential causes

all the muscle fibers it connects to contract

NMJ is made of

axon terminal, synaptic cleft, and motor endplate of the muscle fiber.

At regular points along the muscle fiber, the sarcolemma extends deep into the center of the fiber to form structures called

t tubules

Local depolarization of the motor endplate initiates a ? that travels along the ? and down t-tubules

Ap, sarcolemma

Sarcomeres are joined together by

z lines

what happens at the Z lines

actin/myosin are joined

actin =

myosin =

thin

thick

The process of progressive activation of motor units is called

recruitment

the number of action potentials delivered to a muscle within a set period of time

frequency

tetanus

sustained maximal muscle contraction

twitch

a quick cycle of contract/relax

Summation

accumulation of contraction

isometric

same length, joint doesn't move, develops tension (gravity)

isotonic

muscle shortens,tension stays same, concentric,ecentric

Eccentric

muscle lengthens

concentric

muscle shortens

proportion of fibers in the muscle contracting

- threshold

few

proportion of fibers in the muscle contracting

- maximal stimulus

100%/all

proportion of fibers in the muscle contracting

- above max status

100%/all

1

tetanus

2

Incomplete tetanus

3

Action potential/ap

4

Summation

5

Twitch

Why do toxins like those from Clostridium tetani harm your muscles?

They stop nerves from letting muscles relax, causing painful spasms and stiffness

If breathing muscles are affected, it can be deadly.

How does latency differ between ulnar nerve stimulation at the wrist vs. the elbow

shorter at the wrist and longer at the elbow.

Why is latency longer when the ulnar nerve is stimulated at the elbow?

signal has to travel a longer distance to reach the muscle, so it takes more time.

Conduction velocity (signal)

50 meters/per second

In skeletal muscle, what is a minimum unit of contraction caused by a single action potential called?

twitch

myofibril, endomysium, muscle, muscle fiber, epimysium, sarcomere, fascicle, perimysium

order them small to big

Sarcomere, myofibril, muscle fiber, endomysium, fascicle, perimysium, muscle, epimysium

functions of skeletal muscle

locomotion, posture, heat, joint support

Motor units that control larger groups of muscles (like posture) are generally much ? in size

larger

to prevent constant muscle stimulation, how is ACh cleared quickly from the synaptic cleft?

broken down by enzyme and recycled back into vesicles

The removal of which ion causes the muscle to relax after contraction?

Ca2+

Excitation contraction coupling

converts electrical stim to motor stim