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BIO 2310 - Exam 3 (Muscles) > Muscle Activity > Flashcards

Flashcards in Muscle Activity Deck (12):

irritibility vs contractility

I - ability to receive and respond to stimulud

C - ability to shorten by force when an adequete stimulus is received


what is needed for mm to contract

nerve stimulus and action potential 

- sk mm stimulated by nerve impulse to contract

- one motor neuron (aka nerve cell) may stimulate fre or hundred mm cells, the one neuron and all the mm cells stimulated are called a motor unit


motor unit

consists of neuron and all the muscle fibers it activates


axon terminal, and synaptic cleft

nn fiber/axon extends from neuron to mm and branches into number of axon terminals

-each terminal forms junctions with sarcolemma of different mm cell and create a NMJ

- connection points - synaptic cleft

- never touch


Steps of NMJ

1. nerve impulse reaches axon teminal, NT released (acetylcholine or ACh)

2. diffuses accross synaptic cleft, attaches to receptors (membrane proteins) that are part of sarcolemma

3. sarcolemma becomes more permeable ot Na+, it rushes into mm cell, while 2 K+ rush out (more Na enters than K+ leaves)

4. cells inside have excess of +ions, results in change in electrical surrenct and action potential is generated

5. Once AP started, cant be stopped. travels over entire surface of sarcolemma, 

6. contraction of mm



acetylcholine NT sent in AP

after AP, Ach is broken down to acetic acid and choline by enzyme acetylcholinesterase

- only one nerve impulse will make only one contraction

- this way the mm will not continue ot contract over and over in the absence of nerve impulse

- the mm cell relaxes until next stimulation


action potential visualization


"all or none" 

contraction of sk mm

mm cell will contract to its fullest when stimulated adequetly, no partial contractions


are skeletal mm organs?


thousand of mm cells that recat to a stimuli with a graded response


graded response

being able to vary the response of a mm contraction, allows for proper control of mm system

occurs in 2 ways:

1. changing frequency of stimulation

2. changing the strength of the stimulus (or by changing the # of cells being stimulated)

this allows us to pick up a pen vs picking up a 30 lbs weight


is impoulse does not slow down and continues to be delivered to mm...

mm will not relax completely, impulses builds until contraction of mm gets stronger and smoother

- this mm is now considered complete tetanus/tetanic contraction

- until this point is reached, mm is said to be incomplete tetanus


tetanus of lockjaw

caused by bacterium and causes mm to go into controllable spasm

can cause respiratory arrest

tetanos = convulsive, tension