WEEK 5

Question 1

What is a neural reflex?

Answer 1

A stereotyped, involuntary reaction of the CNS to specific sensory input

Question 2

What are the three general functions of reflexes?

Answer 2

Protective-limb withdrawal, cough reflex
Postural control-walking
Homeostasis-BP

Question 3

Describe the characteristic chain of components of a reflex arc

Answer 3

sensory receptor-afferent neurone-(integration centre)-efferent neurone-effector

Question 4

What is the role of sensory receptors in the reflex arc?

Answer 4

Where information comes into reflex arc, detect sensory stimuli-can be part of sensory neurone/can be afferent neurone

Question 5

What is the role of afferent/sensory neurones in the reflex arc?

Answer 5

Convey AP from sensory receptor site towards CNS

Question 6

What is the role of the integration centre in the reflex arc?

Answer 6

It contains interneurones (not relay neurones) in CNS/enteric NS which cause modulation, allowing adjustment of reflex arc activity via brain involvement

Question 7

What is the role of efferent/motor neurones in the reflex arc?

Answer 7

Convery AP from CNS to effector

Question 8

What is the role of the effector in the reflex arc?

Answer 8

causes reflex action-muscle/gland

Question 9

What is the role of simple stretch reflexes?

Answer 9

Posture control, adjusting degree of skeletal muscle contraction to allow postural change

Question 10

What sensory receptors are responsible for simple stretch reflexes?

Answer 10

Proprioceptors

Question 11

Give two examples of proprioceptors

Answer 11

Muscle spindles

Golgi tendon organs (GTO)

Question 12

What are muscle spindles?

Answer 12

Proprioceptors consistent of intrafusal muscle fibres enclosed in a sheath (spindle), providing information on muscle length/stretch and the rate of stretch (myotatic reflex)

Question 13

Process of muscle spindle action in knee jerk reflex

Answer 13

Spindles stretched when quadricep muscles lengthen, depolarisation causing AP, sensory neurone carries AP into spinal cord via dorsal root and synapses directly to motor neurone (MONOSYNAPTIC)/inhibitory interneurone, motor neurone carries/doesn’t carry AP to quadricep/hamstring muscles, quadricep muscles contract/hamstring muscles relax, leg extension

Question 14

What are golgi tendon organs (GTO)?

Answer 14

Sensory nerve endings found within tendons that are activated when muscle contracts due to collagen fibre stretching in tendons

Question 15

Process of GTO action

Answer 15

muscle contraction, depolarisation of GTO nerve endings, AP transmitted to interneurone via sensory neurone, synapse with excitatory interneurone (POLYSYNAPTIC), synapses with inhibitory interneurone, synapses with motor neurone, motor neurone lacks AP, less muscle contraction (reverse myotatic reflex)

Question 16

What is a monosynapse?

Answer 16

When there is only one synapse between afferent and efferent neurones (no interneurone involvement)

Question 17

What is a polysynapse?

Answer 17

When there is more than one synapse between afferent and efferent neurones (interneurone involvement)

Question 18

Describe the cross extensor reflex

Answer 18

nociceptors receive pain in right foot, depolarisation causes AP, sensory neurone carries AP to spinal cord via right dorsal root, synapse with ascending pathways to brain for pain and postural adjustment, synapse with interneurones which cause inhibition of AP in quadriceps/activation of AP in hamstring in right side of spinal cord (right leg), synapse with interneurones which cause activation of AP in quadriceps/inhibition of AP in hamstring in left side of spinal cord (left leg), causes inhibition of extension in right leg and inhibition of flexion in left leg

Question 19

What are the structural features that may be affected by neuronal injury?

Answer 19

Epi/Peri/Endoneurium, Axon and Myelin sheath

Question 20

What are the three Sedon classification of nerve injuries?

Answer 20

Neuropraxia, Axonotmesis, Neurotmesis (->increasing in severity)

Question 21

What is Neuropraxia?

Answer 21

disturbance (compression) to neuronal connective tissue and myelin sheath

Question 22

What is Axonotmesis?

Answer 22

damage to the axon and its myelin sheath

Question 23

What is Neurotmesis?

Answer 23

complete transection of nerve

Question 24

What is the cause and result of Neuropraxia?

Answer 24

temporary loss of neuronal function, most likely due to disturbance of myelination, complete restoration of function upon recovery

Question 25

What is the cause and result of Axonotmesis?

Answer 25

usually result of stretch of a nerve/its severe crush, very good chance of function recovery due to connective tissue remaining intact-guides nerve sprouts

Question 26

What is the cause and result of Neurotmesis?

Answer 26

entire nerve fibre severed, damaging axon and connective tissue, complete recovery doesn't occur

Question 27

How does the local environment change in response to neuronal damage?

Answer 27

Based on behaviour of 3 classes of glial cells: Oligodendrocytes/Schwann Cells (myelination) Astrocytes (provide neurones with nutrients) Microglia (provide immune response of NS)

Question 28

Signs of neuronal reaction minutes after inury

Answer 28

no AP conduction beyond site of injury two ends of axon exposed and start leaking intracellular fluid cut ends soon pull apart, sealing themselves and swelling

Question 29

Signs of neuronal reaction an hour or so after injury

Answer 29

synaptic terminal degenerates | astroglia surround terminal-pulling apart Pre- and Post-S neurones

Question 30

Signs of neuronal reaction days/weeks after injury

Answer 30

fate of proximal segment-cell body undergoes chromatolysis, injured nerve seals wounded stump forming neuroma, nerve segment doesn't die fate of distal segment-Wallerian degeneration, soon dies due to loss of nutritional support from cell body, digestion by phagocytosis (myelin sheath and connective tissue preserved for regrowth of proximal end)

Question 31

What is chromatolysis?

Answer 31

Dissolution of Nissl bodies, occurring at proximal segment. Cell body becomes very active producing lots of proteins for cell repair, volume of cell body increases and it becomes bloated displacing nucleus to peripheral margins of soma

Question 32

Acute phase of denervated muscle that isn't reinnervated

Answer 32

Muscle immediately paralysed, becomes areflexic, fasciculations start but subside if muscle not reinnervated

Question 33

Chronic phase of denervated muscle that isn't reinnervated

Answer 33

bulk loss due to denervation/lack of use (denervation/disuse atrophy), muscle death, muscle replaced by connective tissue incl. fat (fibrosis)

Question 34

Process of neuronal axon regeneration in PNS

Answer 34

1) macrophages clean up debris 2) macrophages release mitogens inducing Schwann cell division 3) repopulation of nerve sheaths with myelin 4) Schwann cells produce laminin 5) macrophages make interlukin, inducing Schwann cells to make Nerve Growth Factor 6) axons sprout, and some enter new Schwann cell tubes

Question 35

What is Crush Syndrome?

Answer 35

a severe, often fatal condition following a severe crushing injury characterised by fluid and blood loss, shock, haematuria and renal failure->traumatic rhabdomyolysis

Question 36

What occurs to neurones adjacent to damaged neurone?

Answer 36

Transneuronal degeneration (retrograde->Pre-S neurone, anterograde->Post-S neurone)