Reflexes 1

Question 1

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

Answer 1

\+ Aα
\+ Aβ	
\+ Aγ
\+ Aδ
\+ B
\+ C

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

+ muscle spindles

+ Aα

Question 10

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

Answer 10

+ golgi tendon organs

+ Aα

Question 11

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

Answer 11

+ muscle spindles; touch and pressure receptors

+ Aβ and Aγ

Question 12

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

Answer 12

+ pain and temperature receptors

+ Aδ

Question 13

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

Answer 13

+ pain and other receptors

+ C

Question 14

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

Answer 14

+ anterior part of spinal cord (anterior horn)

Question 15

alpha motor neurons are also known as what?

Answer 15

lower motor neurons

Question 16

what does a motor unit consist of?

Answer 16

motor neuron and muscle fibres it innervates

Question 17

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

Answer 17

1. precision of control (small units = highly precise)

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

Question 18

what increases muscle tension?

Answer 18

increasing the number of motor units recruited in the muscle

Question 19

what type of muscle fibres do small neurons innervate?

Answer 19

+ slow oxidative muscle fibres (small motor units)

+ can give low power but sustained effort

Question 20

what type of muscle fibres do large neurons innervate?

Answer 20

+ fast glycolytic muscle fibres (large motor units)

+ can give high power but fatigue quickly

Question 21

what are key features of lower motor neurons?

Answer 21

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

Question 22

chain fibres

Answer 22

• 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

Question 23

bag fibres

Answer 23

• 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

Question 24

muscle spindles

Answer 24

• 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

Question 25

what types of muscle spindle fibres monitor length?

Answer 25

nuclear chain fibre + nuclear bag fibre

Question 26

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

Answer 26

nuclear bag fibre

Question 27

muscle spindles and stretch reflex

Answer 27

- 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

Question 28

mechanism of reciprocal innervation

Answer 28

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

Question 29

golgi tendon organs

Answer 29

- 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

Question 30

how golgi tendon organs function

Answer 30

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

Question 31

GTO in a reflex arc

Answer 31

- 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

Question 32

role of GTOs

Answer 32

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

Question 33

skeletal muscle is a combination of...

Answer 33

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

Question 34

reflexes involving special senses

Answer 34

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

Question 35

rotatory nystagmus

Answer 35

eye movements driven by moving visual images

Question 36

post rotatory nystagmus

Answer 36

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

Question 37

baroreceptor reflex

Answer 37

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