MOD3 contractions p2

explain excitable membranes:

found in skeletal muscle fibres and neurons

how are action potentials produced in excitable membranes:

depolarisation and repolarisation events

why do skeletal muscle fibres contract:

due to stimulation by motor neurons

what is the neuromuscular junction:

synapse between a neuron and skeletal muscle fibre

name 4 steps of muscle contraction:

excitation

excitation-contraction coupling

contraction cycle

relaxation

what occurs in excitation:

in neuromuscular junction

axon terminal of motor neuron releases the neurotransmitter acetylcholine

what does acetylcholine do:

binds to chemically gated sodium channel and sodium enters the cell, causing depolarisation

generates an action potential

explain excitation-contraction coupling:

action potential travels down transverse tubules to triads

calcium ions are released from terminal cisternae

calcium binds to troponin changing troponin shape

explain function of troponin-tropomyosin complex:

exposes active sites on thin filaments

initiates contraction cycle

explain the contraction cycle:

active site is exposed

myosin binds to actin (cross bridge forms)

myosin head pivots, causing power stroke

myosin and actin seperate

myosin reactivates

how is muscle tension generated:

when muscles contract, they produce tension (pull)

to produce movement, tension must overcome resistance

why does an entire muscle shorten at the same rate:

all sarcomeres contract together

speed of shortening depends on contraction cycle rate

duration of contraction cycle depends on:

duration of neural stimulus

presence of free calcium ions

availability of ATP

how does the excitation-contraction coupling end: (relaxation)

calcium ion detaches from troponin

troponin returns to go position

active sites are recovered by tropomyosin and the contraction ends

what do muscle fibres do:

either producing tension or relaxed

amount of tension produced depends on:

number of strokes performed

frequency of stimulation

length of sarcomeres

what is a cross bridge:

when myosin binds to actin

how is maximum tension produced:

when maximum number of cross bridges form

when zone overlap is large

explain frequency of a twitch:

lasts 7-10 milliseconds

explain frequency of sustained muscular contractions:

require many repeated stimuli

define myogram:

graph that shows tension development in muscle fibres

what are the 3 phases of a single twitch:

latent period

contraction phase

relaxation phase

explain latent period:

action potentional moves across sarcolemma

sarcoplasmic reticulum releases calcium ions

explain contraction phase:

calcium ions bind to troponin and cross bridges form

tension builds

explain relaxation phase:

calcium ion levels fall

cross bridges detach and tension increases

explain ATP usage of contracting muscles:

use a lot of ATP

more ATP must be produced to sustain contraction

what occurs when excess ATP is produced:

transfers energy to creatine

creates creatine phosphate

explain function of enzyme creatine kinase:

converts ADP to ATP

what are the 2 ways ATP is generated by:

glycolysis

aerobic metabolism

explain glycolysis:

breaks down glucose

produces 2 ATP per molecule

explain aerobic metabolism:

breaks down fatty acids