Reflexes 1 Flashcards by Anna Dunlop

what are the different fibre types, based on conduction velocity?

\+ Aα
\+ Aβ	
\+ Aγ
\+ Aδ
\+ B
\+ C

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what is the conduction velocity, diameter and function of Aα fibres?

+ 70-120 m/s
+ 12-20 μm
+ proprioception, somatic motor

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what is the conduction velocity, diameter and function of Aβ fibres?

+ 30-70 m/s
+ 5-12 μm
+ touch, pressure

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what is the conduction velocity, diameter and function of Aγ fibres?

+ 15-30 m/s
+ 3-6 μm
+ motor to muscle spindles

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what is the conduction velocity, diameter and function of Aδ fibres?

+ 12-30 m/s
+ 2-5 μm
+ pain, temperature

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what is the conduction velocity, diameter and function of B fibres?

+ 3-15 m/s
+ 1-3 μm
+ preganglionic autonomic

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what is the conduction velocity, diameter and function of C fibres?

+ 0.5-2 m/s
+ 0.1-2 μm
+ postganglionic sympathetic, pain and possibly heat, cold and pressure

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what are the different fibre types, based on sensory function?

\+ IA
\+ IB
\+ II
\+ III
\+ IV

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what is the origin and equivalent fibre (based on conduction velocity) of IA?

+ muscle spindles

+ Aα

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what is the origin and equivalent fibre (based on conduction velocity) of IB?

+ golgi tendon organs

+ Aα

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what is the origin and equivalent fibre (based on conduction velocity) of II?

+ muscle spindles; touch and pressure receptors

+ Aβ and Aγ

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what is the origin and equivalent fibre (based on conduction velocity) of III?

+ pain and temperature receptors

+ Aδ

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what is the origin and equivalent fibre (based on conduction velocity) of IV?

+ pain and other receptors

+ C

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where is each muscle controlled by a pool of motor neurons?

+ anterior part of spinal cord (anterior horn)

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alpha motor neurons are also known as what?

lower motor neurons

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what does a motor unit consist of?

motor neuron and muscle fibres it innervates

the spectrum of motor unit sizes within a muscle depends on what?

precision of control (small units = highly precise)

2. force of contraction required/a low precision (large units = postural or calf muscles)

what increases muscle tension?

increasing the number of motor units recruited in the muscle

what type of muscle fibres do small neurons innervate?

+ slow oxidative muscle fibres (small motor units)

+ can give low power but sustained effort

what type of muscle fibres do large neurons innervate?

+ fast glycolytic muscle fibres (large motor units)

+ can give high power but fatigue quickly

what are key features of lower motor neurons?

innervate skeletal muscle
arranged topographically in spinal cord
all release neurotransmitter ACh
all have excitatory effect on the muscle fibres with which they synapse

chain fibres

innervated by both IA and II sensory nerve fibres
IA give rate of change
II give total length
most common fibre type in spindle
so called because the fibres nuclei are arranged in a chain in the central portion

bag fibres

only innervated by type IA fibres so only give rate of change in length info
only 1 or 2 per spindle
so called because of the swelling in the equatorial region which houses the nuclei

muscle spindles

stretch receptors embedded in muscles
monitor length and rate of change in length
are peripheral nerve endings of afferent fibres wrapped around modified muscle fibres (i.e. intrafusal fibres)
several together wrapped by connective tissue
rate of firing determined by magnitude of stretch and speed of stretch

what types of muscle spindle fibres monitor length?

nuclear chain fibre + nuclear bag fibre

what types of muscle spindle fibres monitor rate of change in length?

nuclear bag fibre

muscle spindles and stretch reflex

- reflexes are mediated by the muscle spindles which are found in the muscle, not in the tendon - tapping the tendon is just an easy way to stretch the muscle and thus elicit the response

mechanism of reciprocal innervation

1. influence of spindle sensory nerve fibres from one (homonymous) muscle on motor neurones projecting to antagonist muscles 2. the effect is opposite to that on their own muscle 3. relaxes antagonist muscles and facilitates shortening of homonymous muscle 4. requires involvement of a local inhibitory neuron in the reflex onto the antagonist muscles

golgi tendon organs

- afferent nerve fibres wrapped around collagen bundles - monitor the tension in the muscle (are in series with the muscle fibres) - compliment the info from the muscle spindles in the CNS - mechanosensitive type IB sensory fibre afferent - as the tendon is put under increasing tension, the more the collagen fibres lock onto it and stretch the type IB sensory fibres - this increases the receptor/generator potential and speeds signal frequency

how golgi tendon organs function

1. stretch or extrafusal fibre contraction 2. tension is exerted on tendon 3. collagen bundles straightened 4. tendon stretch is typically greater with active contraction than passive stretch 5. AP result

GTO in a reflex arc

- provide reflex inhibition to motor neurons in the tendon they are located (i.e. their homonymous MNs) via disynaptic reflex - the more alpha MNs are activated by the CNS, the more the muscles contract and the more tension develops - as tension develops the GTOs increase their rate of firing and so increase the inhibition to the alpha MNs - this consequently reduces tension in the muscle

role of GTOs

during normal use GTOs are thought to regulate the amount of tension that develops in a muscle and in extreme conditions, to

skeletal muscle is a combination of...

1. alpha MN mediated contraction (under control of CNS) 2. gamma MN mediated spindle fibre contraction enabling accurate feedback 3. GTO mediated inhibitory feedback to the alpha MNs

reflexes involving special senses

- rotatory nystagmus - post rotatory nystagmus - interpretation of movement within images on the retina - used to make postural adjustments to preserve balance

rotatory nystagmus

eye movements driven by moving visual images

post rotatory nystagmus

eye movements driven by the movement of fluid in the semi-circular canals of the inner ear

baroreceptor reflex

- occurs via the medullary cardiovascular centre | - arterial baroreceptors respond to changes in pressure: increasing firing rate in response to inc. pressure