What type of lower motor neurones innervate the muscle bulk
alpha motor neurones
What type of lower motor neurone innervate a muscle spindle
gamma motor neurones
where do the axons of lower motor neurons exit the spinal cord
the ventral roots
How are motor neurone distrinuted in the spinal cord
they are not distriuted equally - there are higher numbers in the cervical enlargement and lumbar enlargement
What is a motor unit
the alpha motor neurone and all of the skeletal muscle fibres it innervates - ies the smallest functional component of the motor system
what is the motor neurone pool
the collection of alpha motor neurones that innervates a single muscle
How is the force of muscle contraction graded
frequency of action potentials
recruitment of additional synergistic motor units
How are lower motor neurones cell bodies distributed in the ventral horn
those innervating axial muscles are more medial, distal muscle are more lateral
those innervating flexors are dorsal, extensors are ventral
What ate type one muscle fibres
slow oxidative - slow contraction and relaxation
resist fatigue
red fibres
what are type two a fibres
fast contraction an relaxation fatigue resistant
red fibres
what are type 2 b fibres
fast contraction but easily fatigued
white fibres
poorly vascularised
which skeletal muscle fibres types have high myoglobin and which have low
types 1 and 2a - high
type 2b - low
which type of motor unit is most numerous
slow
which type of muscle fibres are associated with fast fatiguing motor units
type 2b
What type of muscle fibres are associated with fatigue resistant muscle fibres
Type 2a
what type of muscle fibre is associated with slow motor units
type 1
what type of motor neurone is required for standing
slow - with type 1 muscle fibres - resisting fatigue
What type of motor unit is required for walking/jogging
fast fatigue resistant - type 2a muscle fibres
What type of motor unit is require for movements such as jumping
fast fatigable - type 2b
what does it mean to have a small motor unit
each alpha fibre is only supplying a few muscle fibres - needed for fine movements eg extraocular eye movement
what does it mean to have a large motor unit
each alpha motor neurone supplies a large number of muscle fibres
What is the myotatic reflex
when a skeletal muscle is stretched in contracts
what organ within the muscle senses the change in length
muscle spindle
what motor neurons are the efferents for the muscle spindle
gamma motor neurones
What neurotransmitter mediates the myotatic reflex
glutamate
what is different about mytatic reflexes
it is a monosynaptic reflec arc - synapse occurs in the spinal cord
What sensory neurones innervate the spindle fibres and act as the the afferent limb of the reflex arc
Ia sensory neurones
How can the intrafusal fibres be subdivided in the muscle spindle
Bag 1 - sensitive to rate of change of muscle length - innervated by dynamic gamma motor neurones
bag 2- sensitive to changes in absolute length of muscle fibre - innervated by static gmn
chain fibres - sensitive to absolute length - static gamma fibres
which afferent fibre is more sensitive to rate of change of muscle lenght
1a
Which afferent fibres is more sensitive to changes in absolute length
II
Where are Golgi tendons located
at the junction of muscle and tendon
what do Golgi tendons do
monitor changes in mucles tension in series with extrafusal fibres
they therefore act to regulate muscle tension to protect muscle form overload
What sensory afferents innervate Golgi tendons
group Ib
what is the inverse myotatic reflex
group Ib afferents form Golgi tendons synpats on inhibitory interneurons which synsaps on alpha motor neurons to relax the muscle
polysynaptic (unlike myotatic reflex which is monsynaptic)
where are proprioceptive axons present
in connective tissue of joints eg joint capsules and ligaments
where does proprioception arise from
muscle spindles
Golgi tendon organs
joint receptors
what is reciprocal inhibition
when the extensor contracts - flexor must relax and vice versa
what mediated the recipricol inhibition
inhibitory interneurons
what do excitatory interneurons mediate
the flexor reflex
the crossed extensor reflex
what is the flexor refelx
contraction of flexors occurs due to noxius stimulus eg pain
what is crossed extensor reflex
noxius stimuli causes limb to extend - enhances postural support during withdrawal of foot from pain you do not fall over
