Flashcards in Physiology Deck (153)
What is a motor unit?
a single alpha motor neuron and all the skeletal muscle fibres it innervates
What does the number of muscle fibres per motor unit depend on?
the functions served by the muscle- eg. fine or gross movements
What is the difference between the initation of contraction in cardiac and skeletal muscle?
in cardiac it is myogenic (pacemaker potentional) whereas in SK it is neurogenic
What are the factors that determine the gradation of contraction in SK muscles compared to cardiac muscle
in SK muscle it is by motor unti recruitment and the summation of contractions whereas in cardiac muscle it depends on the extent of the heart filling with blood
What is excitiation contraction coupling?
the process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre
What stimulates the calcium release from the sarcoplasmic reticulum?
when the surface AP spreads down the transverse tubules
What are T-tubules?
extensions of hte surface membrane that dip into the muscle fibre
What is the predominant structure of SK muslce fibres?
What protein gives the lighter appeanace in myofibrisl?
What protein causes the darker appearance in the fibres?
What is the functional unit of muscle?
What is the defintion of a sarcomere?
the length of a myofibril between 2 Z-lines
What are the Z-lines?
they connect the thin filmanets of 2 adjoining sarcomeres
What is the A-band?
made up of thick filaments along with portionso f thin filaments that overlap in both ends of thick filaments
What is the H-zone?
lighter area within the middle of the A-band where thin filaments dont reach
What is the M-line?
extends vertically down middle of A-band within the centre of H-zone
What is the I-band?
consists of remaining portion of thin filaments that do not project in A-band (light area)
How is muscle tension produced?
sliding of actin filaments on myocin filaments, this is an ATP-dependent interaction
Why is ATP required for both contraction and relaxation?
ATP is used to take back calcium into the SR as well power and release the cross bridges (binds to actin to prepare for myosin binding, binds to myosin to unbind it from actin)
How does calcium switch on cross bridge formation?
calcium binds to troponin which results in the repositioning of troponin-tropomyocin complex to uncover the cross bridge binding site on actin
What does gradation of SK muscle tension depend on?
number of muscle fibres contracting within the muscle and tension developed by each contracting muscle fibre
What is motor unit recruitment?
stimulation of more motor units to achieve a stronger contraction
How can motor unit recruitment be done in a way to prevent muscle fatigue?
What does the tension developed by each contracting muscle fibre depend on?
frequency of stimulation and summation of contrations as well as the lenght of muscle fibre at the onset of contraction
Why is it possible to summate twitches in SK muscle?
the duration of AP is much shorter tahn the duration of the resulting twitch
What is twitch summation?
when a muscle fibre is restimulated before it has completely relaxed and the second twitch is added onto the first twitch (increasing contraction)
What is tetanus?
maximal sustained contraction
When does tetanus occur?
if a muscle fibre is stimulated so rapidly that it does not ahve an opportunity to relac at al between stimuli
Why can cardiac muscle not be tetanise?
the AP takes as almost as long as the muscle contraction adn there is a long refractory period