Reflexes 1 Flashcards
what are the different fibre types, based on conduction velocity?
\+ Aα \+ Aβ \+ Aγ \+ Aδ \+ B \+ C
what is the conduction velocity, diameter and function of Aα fibres?
+ 70-120 m/s
+ 12-20 μm
+ proprioception, somatic motor
what is the conduction velocity, diameter and function of Aβ fibres?
+ 30-70 m/s
+ 5-12 μm
+ touch, pressure
what is the conduction velocity, diameter and function of Aγ fibres?
+ 15-30 m/s
+ 3-6 μm
+ motor to muscle spindles
what is the conduction velocity, diameter and function of Aδ fibres?
+ 12-30 m/s
+ 2-5 μm
+ pain, temperature
what is the conduction velocity, diameter and function of B fibres?
+ 3-15 m/s
+ 1-3 μm
+ preganglionic autonomic
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
what are the different fibre types, based on sensory function?
\+ IA \+ IB \+ II \+ III \+ IV
what is the origin and equivalent fibre (based on conduction velocity) of IA?
+ muscle spindles
+ Aα
what is the origin and equivalent fibre (based on conduction velocity) of IB?
+ golgi tendon organs
+ Aα
what is the origin and equivalent fibre (based on conduction velocity) of II?
+ muscle spindles; touch and pressure receptors
+ Aβ and Aγ
what is the origin and equivalent fibre (based on conduction velocity) of III?
+ pain and temperature receptors
+ Aδ
what is the origin and equivalent fibre (based on conduction velocity) of IV?
+ pain and other receptors
+ C
where is each muscle controlled by a pool of motor neurons?
+ anterior part of spinal cord (anterior horn)
alpha motor neurons are also known as what?
lower motor neurons
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
- influence of spindle sensory nerve fibres from one (homonymous) muscle on motor neurones projecting to antagonist muscles
- the effect is opposite to that on their own muscle
- relaxes antagonist muscles and facilitates shortening of homonymous muscle
- 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
- stretch or extrafusal fibre contraction
- tension is exerted on tendon
- collagen bundles straightened
- tendon stretch is typically greater with active contraction than passive stretch
- 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…
- alpha MN mediated contraction (under control of CNS)
- gamma MN mediated spindle fibre contraction enabling accurate feedback
- 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
