Muscle Spindle, GTO, Muscle fibres Flashcards
Name the 2 types of muscle fibres
Slow twitch/ Type I
Fast twitch/ type II
How do slow twitch fibres obtain their energy
Oxidative metabolism (hence rich in enzymes)
How do fast twitch fibres obtain their energy
Faster glycolytic process
Which type of fibres are ore resistant to fatigue
Slow twitch are have increased resistance to fatigue
What type of activities are slow twitch fibres well suited for
Activities related to physical effort requiring strength and endurance that depend for energy metabolism on oxidative processes
What type of activities are fast twitch fibres well suited for
Suited to rapid alternating effort
Why is there a difference in the types of activities each fibre is suited for
Glycogen stores are more rapidly depleted than oxygen supplies, hence why type 2/fast twitch fibres are less suited for continuous types of activity
Which fibres are more prone to anatomic changes to altered energy demands
Type II/fast twitch are more prone, as they can increase in number in adults that increase their strenous exercise
What does a motor unit consist of
single alpha motor neuron and the muscle fibres it innervates–> this includes motor end plate
How many muscle fibres are there are fine movements compared to larger musculature
Muscles for fine movement will have only a few muscle fibres
In large musculature, a single motor unit may innervate many hundreds of muscle fibres
What is the neuromuscular junction
Where an alpha motor neuron enters the skeletal muscle and branches, terminating at the motor end plate (where muscle fibre synapses with skeletal muscle)
Give an example of and explain a pathology that targets the NMJ
Myasthenia Gravis:
Muscle weakness
Autoimmune disease
Antibodies against acetylcholine receptor hence the neurotransmitter is not able to be received by post synaptic neuron
Example muscle tone during resting periods
Muscle is always in a partial state of contraction
There is no intermediate stage (all or none response) hence a few muscle fibres within the muscle must be contracted at all times to maintain tone
How do muscle fibres maintain tone without getting fatigued
Asynchronous firing
Different groups of motor units are bought into action at different times through asynchronous firing of nervous impulses in the motor neurons in VH (alpha motor neuron)
Name some poprioceptive receptors/mechanisms
Muscle spindle–> detect change in length
GTO–> detect change in muscle tension
Inner ear–> gives information about position of head and hence balance
Eye are also proprioceptive
What makes up a muscle spindle?
Intrafusal muscle fibres–> nuclear chain and bag fibres
Where are muscle spindles found
In skeletal (striated) muscle, and lie in the long axis of extrafusal muscle They lie in the same plane and direction as the muscle action in order to detect the change in length
Where are muscle spindles most numerous
at tendinous attachment of muscle, here can detect change in length best
Especially numerous in muscles that perform highly skilled movement (e.g. hand)
What nerve is extrafusal muscle mass innervated by
Alpha motor neuron
What nerve innervates intrafusal muscle fibres
Gamma motor neuron
What is the role of the nerve that innervates intrafusal muscle fibres
Gamma motor neuron keeps intrafusal fibres tuat so that they are able to pick up changes in length and the rate of change
What are nuclear bag fibres
Numerous nuclei present in the centre
Expanded fibres (larger in diameter- ‘belly’)
Extend beyond CT capsule at each end to attach to extrafusal fibres
What are nuclear chain fibres
Nuclei ‘line up’ to form a ‘chain-like’ structure
Small in diameter and more narrow fibre (tube like shape)
Do not extend beyond the CT capsule
How many intrafusal muscle fibres are there within each spindle
2-14 intrafusal muscle fibres per spindle
Must have an even number of intrafusal muscle fibres because you have a nuclear bag and chain fibre to each muscle spindle
Name the 2 types on sensory innervation in muscle spindle
Annuospiral ending (Type Ia afferent) Flower-spray endings (Type II afferent)
What are annulospiral endings
Type Ia afferent Primary nerve endings Closer to the centre of the spindle Detect both change in length and rate of change More highly myelinated, hence faster
What are flower spray endings
Type II afferent
Secondary nerve endings
Closer to the ends of the spindle
Only detect change in length
Function of GTO
Detect changes in muscle tension (typically when muscle is concentrically/eccentrically contracted)
Where are golgi tendon organs located
Present in tendons, located near musculotendinous junciton
How is a GTO formed
Consists of a fibrous capsule surrounding a small bundle of loosely arranged collagenous fibres
Composed of skeletal muscle cells (extrafusal muscle fibres) which enter a funner-like capsule that is filled with collagen fibre bundles
Nerve fibres are entwined throughout these collagen fibres and are triggered when tension in the muscle is transferred to the collagen fires of the GTO
How do GTO respond to increased muscle tension/contraction exerted on a tendon
By inhibiting further muscle tension
What is the effect of GTO on agonnist and antaogonist
GTO action is inhibitory on agonist and excites the antagonist
this decreases tension and hence is protective (prevents muscle tears)
How do muscle spindles and GTO respond to isoetric contraction
Muscle spindle–> decrease in firing rate of nerve impulse as there is no change in length in muscle spindle
GTO–> increase in firing rate of nerve impulses as there is an increase in tension
How to muscle spindle and GTO respond to passive stretching
Muscle spindle and GTO both discharge/increase firing rate, however firing rate of GTO is much less than muscle spindle as there is not as much increase in tension as there is in length
How do muscle spindle and GTO respond to active contraction
Muscle spindle increases nerve impulses during the initial stage of contraction, however as contraction continues it decreases as the change in length inst as significant
GTO firing increases as build up/increase in tension
