Physiology Flashcards
What do motor units contain?
a single aplha neuron and all of the muscle fibres it innervates
What initiates skeletal muscle contraction?
neurogenic
What links excitation and contraction in skeletal muscle?
Ca from sarcoplasmic reticulum
Is a neuromuscular junction present in skeletal muscle or cardiac muscle?
Skeletal
What initiates cardiac muscle contraction?
myogenic - pacemaker potential
Are gap junctions present in cardiac or skeletal muscle?
cardiac
What links excitation in cardiac muscle?
Ca from the ECF and sarcoplasmic reticulum
What is the transmitter at neuromuscular junctions?
acetylcholine
what are myofibrils?
alternating sections of myosin and actin, arranged into sacromeres
What is the functional unit of muscle?
sarcomeres
What are the zones of sacromeres?
A band, H zone, M line, I band
Where is a sacromere found/where does it span?
between two z lines
What is the A band?
thick filaments with thin portions that overlap at the end
What is the H zone?
light area in the middle of the A band
What is the M line?
extends vertically down the H zone and the A band
What is the I band?
remaining portion of filament that does not project into the A band
What happens when a surface action potential is reached?
Ca is released from the lateral sacs of the SR, when the action potential spreads down the transverse T tubules
this causes cross bridge formation - actin and myosin
What does skeletal muscle contraction depend on?
number of muscle fibres contracting
tension developed by each muscle fibre
What is twitch summation?
muscle stimulated once = twitch
stimulated again before it can relax = greater tension twitch
What is a muscles optimal length?
point where maximal tension is achieved - its resting length
i.e. point of optimal overlap of thick filament and thin filament cross bridge
Describe isoTonic contraction?
FIXED POSTION
Tension constant, length changes
Describe isometric contraction?
MOVEMENT
Tension changes, length constant
Describe slow oxidative type 1 muscle fibres?
RED
used for prolonged, low work aerobic activities - walking
Describe fast oxidative type 2a muscle fibres?
WHITE
use aerobic and anaerobic metabolism and are useful in prolonged moderate work - jogging
Describe fast oxidative type 2b muscle fibres?
WHITE
use anaerobic metabolism and are useful in short term, high intensity activities
What is the stretch reflex?
A negative feedback mechanism that resists passive change in muscle length to maintain the optimal length of muscle
What is the receptor for the stretch reflex?
muscle spindle
What is the effector for the stretch reflex?
increased firing in afferent neurones
What are extrafusal fibres?
ordinary muscle fibres
What are intrafusal fibrers?
muscle spindles - specialised muscle fibres
What are muscle spindles supplied by?
gamma motor neurones
What is the action of muscle spindles when muscle is stretched?
increased discharge from sensory endings
What is the role of gamma motor neurones?
ajust the level of tension in muscle spindles to maintain their sensitivity when the muscles shorten during contraction
What does electromyography measure?
detects the presence of muscular activity, frequencey and amplitude of muscle fibres
