what is a reflex ?
it is the simplest motor operation possible.
- they are rapid and automatic.
reflexes are highly stereotypical, what does that mean?
- they are consistent, always the same process
what are the types of spinal cord reflexes
- myotatic
- flexor
- cross extensor
what is the myotatic reflex for
it is the STRETCH reflex, and maintains muscle tone
what is the FLEXOR withdrawal reflex for
to remove limbs from harm
what is the cross extensor reflex for
to maintain postural balance
general pathway of a reflex arc
sensory receptors detect stimulus - synapse onto alpha motor neurons in ventral horn - innervate the muscle to cause movement
where are the sensory receptors for the myotatic reflex found
the muscle spindles in the intrafusal muscle fibres
what type of afferent neurons does information from the intrafusal muscle fibres in the myotatic reflex project to the spinal cord in
type 1A and 2 neurons.
type 1A = encode static information about how much the muscle has stretched
type 2 = signals dynamic info about changes in the muscle length.
why is the myotatic reflex classed as the simplest type of reflex ?
it is monosynaptic
(singular synapse in the ventral horn of the SC)
what is the polysynaptic reflex
- it is an additional step to the myotatic stretch reflex
- when an agonist (quads) contract, the antagonist will relax
- this is due to interneurons in the grey matter of the SC inhibiting the alpha motor neurons of the hamstring muscle in the grey matter of the spinal cord.
where are receptors that are part of the golgi tension reflex found?
in the collagen of the tendons.
- the tendons are in series with the extrafusal muscle fibres, so receive direct information regarding the muscle tension
how many synapses involved in the golgi tension reflex?
it is di-synaptic, so 2
what is the point of the golgi tension reflex
it prevents the overstretching or tearing of muscles and tendons - due to much contraction
which reflex opposes the myotatic stretch reflex
the golgi tension reflex
what are the afferent neurons in the golgi tension reflex ?
the type 1B afferent neurons
what is the pain withdrawal reflex called
the flexor response
what type of receptor are painful stimuli detected by
nociceptive receptors. they are cutaneous (in the skin)
what is ‘special’ about the flexor withdrawal reflex compared to the polysynaptic or myotatic reflexes
the interneurons will ascend/ descend multiple levels of the spinal cord.
- they will then excite motor neurons at various levels, resulting in the movement of more than one muscle/ muscle groups
- allows for the movement of an entire limb - known as synergistic activation
what is the idea of reciprocal innervation
whilst the alpha motor neurons of the flexor muscles are activated to contract, there are inhibitory interneurons that inhibit the alpha motor neurons of the other muscles in the pair.
- causes them to relax.
- this is a co-ordinated response, known as reciprocal innervation
what is the cross-extensor reflex
it basically opposes the flexor withdrawal response, in order to maintain balance and posture.
- the interneurons in the SC will decussate, and excite the opposite muscles on the CONTRALATERAL side of the body.
what side of the body does the flexor-withdrawal response work on
the ipsilateral side
what do gamma motor neurons do
they innervate the muscle spindles (intrafusal) to maintain sensitivity, even when the muscles are contracting.
why is the knee-tap used to test for damage to the reflex pathway:
it can establish whether it is damage to upper or lower motor neurons.
- if it is lower motor N damage: no response
- if it is upper motor N damage: hyperreflexia - will overextend the reflex due to loss of descending output control.
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wk 1 - Dan - OVERVIEW16
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wk 1 - dan - overview of brain anatomy15
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week 1 - Dan - the meninges16
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week 1 - Dan- bones and sutures of the skull12
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week 2 - dan - neurons and glial cells22
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week 2 - Paul - synapses33
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week 3 - dan - spinal cord37
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week 3 - dan - cerebral blood flow32
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week 3 - dan - CSF26
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week 4 - Bashir - PNS27
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week 4 - bashir - principles of sensory pathways25
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week 7 - reflex pathways30
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week 11 - neuroscience futures15
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week 11 - clinical neuroscience (dan)26
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week 10 - development of the cortex26
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week 10 - axon targeting and growth23
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week 10 - developmental plasticity16
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week 10 - computational neuroscience17
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week 8 - the thalamus46
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week 8 - vision and the visual pathways22
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week 8 - the auditory system19
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week 8 - the vestibular system13
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organisation of the motor system32
