reflexes

Question 1

what are the different types of movement which can be initiated?

Answer 1

• involuntary actions- reflexes
• semi-automatic actions
• voluntary actions

Question 2

what are reflexes?

Answer 2

• unconscious, involuntary responses
• centred on the spinal cord (spinal nerves) or the brainstem (cranial nerves)
• stereotyped responses
• rapid reflexes, short latency and minimal delay

Question 3

what is the common final motor pathway?

Answer 3

recruitement of motor neurones and subsequent engagement with muscles

Question 4

where can motor neuron cell bodies be found?

Answer 4

ventral horn of spinal cord for somatic muscles
OR
brainstem in cranial nerve nuclei

Question 5

what are motor neurons activated by?

Answer 5

various brain regions (cortex)
OR
various peripheral receptors (reflex)

Question 6

what makes up a muscle spindle?

Answer 6

intrafusal fibres
wrapped around by sensory endings (mecanoreceptors)
these fuse together to give rise to a group 1a afferent fibre

Question 7

where does the afferent peripheral nerve of a stretch reflex go?

Answer 7

all the way through the dorsal to the ventral horn

Question 8

describe the order of events in initiating a stretch reflex

Answer 8

• stimulus
• activation of mechanoreceptor
• stimulus transduction- AP conduction along sensory axon
• synaptic transmission
• motor neuron recruitment- AP conduction along motor axon
• synaptic transmission- effector recruitment
• response

Question 9

what can you see in an EMG electromyogram of a reflex?

Answer 9

• stimulus artefact
• lag period (latency)
• bidirectional response (amplitude)

Question 10

what do both the sensory afferent and motor efferent stretch reflex pathways have in common?

Answer 10

A alpha axon

Question 11

what is the difference in latency between ankle jerk and jaw jerk reflex?

Answer 11

latency for jaw jerk is less than ankle jerk
- because it is a much shorter distance

Question 12

what is the different in amplitude between ankle jerk and jaw jerk reflex?

Answer 12

amplitude for jaw jerk is less than ankle jerk
- because masseter muscle is smaller than gastrocnemius

Question 13

what are examples of tendon-jerk reflexes which maintain posture and muscle tone?

Answer 13

• propioceceptor endings
• group 1a muscle efferents
• homonymous motor neurons

Question 14

what are examples of cutaneous reflexes?

Answer 14

• mechanoreceptor endings
• nociceptor endings

Question 15

what are the importance of protection mechanisms?

Answer 15

• escape mechanisms
• prevention of muscle overloading
• prevention of inadvertent ingestion of a foreign body
• digestive aid

Question 16

what is a flexion withdrawal reflex?

Answer 16

withdrawal reflex in response to a nocious stimulus

Question 17

describe the pathway of a flexion withdrawal reflex?

Answer 17

• spinal filamic pathway
• interneuron recruitement in dorsal horn to move away from source of pain (axon spilts in two)

Question 18

what do the nerve endings in the tendon of the muscle do and what are they called?

Answer 18

prevent the muscle from being overloaded
- golgi tendon organs, group 1b muscle afferents which inhibit the motor neuron activation- inverse myotactic reflex

Question 19

how it bite force controlled in the jaw muscles (no golgi tendon organs)?

Answer 19

• increased loading of periodontal ligament
• afferents inhibit jaw elevator muscle motor neurons
• anaesthesia of the molars risks increasing patients bite force

Question 20

describe the gag reflex (pharyngeal reflex)

Answer 20

• activation by mecanoreceptor afferents from posterior part of tongue
• stimulates sensory fibres from the glossopharyngeal nerve and or trigeminal nerve
• afferents terminate in the brainstem
• interneurons project from brainstem to nucleus ambiguus (vagus nerve motor nucleus)
• vagus nerve afferents terminate innervate muscles
• mass contraction of both sides of posterior oral and pharygeal

Question 21

describe the salivary reflex

Answer 21

• involve glands as effector organ
• stimuli can be gustatory, visual, olfactory or mechanical
• outcome is increased salivary flow

Question 22

What is a monosynaptic circuit and an example?

Answer 22

• no interneuron present
• eg muscle stretch reflex