reflexes Flashcards
what are the different types of movement which can be initiated?
- involuntary actions- reflexes
- semi-automatic actions
- voluntary actions
what are reflexes?
- unconscious, involuntary responses
- centred on the spinal cord (spinal nerves) or the brainstem (cranial nerves)
- stereotyped responses
- rapid reflexes, short latency and minimal delay
what is the common final motor pathway?
recruitement of motor neurones and subsequent engagement with muscles
where can motor neuron cell bodies be found?
ventral horn of spinal cord for somatic muscles
OR
brainstem in cranial nerve nuclei
what are motor neurons activated by?
various brain regions (cortex)
OR
various peripheral receptors (reflex)
what makes up a muscle spindle?
intrafusal fibres
wrapped around by sensory endings (mecanoreceptors)
these fuse together to give rise to a group 1a afferent fibre
where does the afferent peripheral nerve of a stretch reflex go?
all the way through the dorsal to the ventral horn
describe the order of events in initiating a stretch reflex
- 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
what can you see in an EMG electromyogram of a reflex?
- stimulus artefact
- lag period (latency)
- bidirectional response (amplitude)
what do both the sensory afferent and motor efferent stretch reflex pathways have in common?
A alpha axon
what is the difference in latency between ankle jerk and jaw jerk reflex?
latency for jaw jerk is less than ankle jerk
- because it is a much shorter distance
what is the different in amplitude between ankle jerk and jaw jerk reflex?
amplitude for jaw jerk is less than ankle jerk
- because masseter muscle is smaller than gastrocnemius
what are examples of tendon-jerk reflexes which maintain posture and muscle tone?
- propioceceptor endings
- group 1a muscle efferents
- homonymous motor neurons
what are examples of cutaneous reflexes?
- mechanoreceptor endings
- nociceptor endings
what are the importance of protection mechanisms?
- escape mechanisms
- prevention of muscle overloading
- prevention of inadvertent ingestion of a foreign body
- digestive aid
what is a flexion withdrawal reflex?
withdrawal reflex in response to a nocious stimulus
describe the pathway of a flexion withdrawal reflex?
- spinal filamic pathway
- interneuron recruitement in dorsal horn to move away from source of pain (axon spilts in two)
what do the nerve endings in the tendon of the muscle do and what are they called?
prevent the muscle from being overloaded
- golgi tendon organs, group 1b muscle afferents which inhibit the motor neuron activation- inverse myotactic reflex
how it bite force controlled in the jaw muscles (no golgi tendon organs)?
- increased loading of periodontal ligament
- afferents inhibit jaw elevator muscle motor neurons
- anaesthesia of the molars risks increasing patients bite force
describe the gag reflex (pharyngeal reflex)
- 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
describe the salivary reflex
- involve glands as effector organ
- stimuli can be gustatory, visual, olfactory or mechanical
- outcome is increased salivary flow
What is a monosynaptic circuit and an example?
- no interneuron present
- eg muscle stretch reflex
