Reflex Movement Flashcards
what are the types of movement
involuntary actions (reflexes), semi-automatic actions and voluntary actions
what are involuntary actions centred on?
spinal cord and brainstem
what type of circuit is an involuntary action?
monosynaptic (only 2 neurons)
how many neurons are involved in voluntary movement?
2
where do the cell bodies of the motor neurons sit in the spinal cord?
in the ventral horn of the grey matter
what is the common final pathway of involuntary and voluntary movement?
motor neurons as they both result in muscle contraction
what are motor neurons activated by?
various brain regions (cortex) and various peripheral receptors (reflex)
what are the 3 horns of a spinal cord segment?
dorsal, intermediate, ventral
how do sensory fibres recruit motor neurons?
they do it directly resulting in a motor response
what happens as a result of am intervening interneuron in a reflex pathway?
it recruits the motor neuron instead of the sensory neuron making the response slower
what are the 7 steps of the reflex pathway?
1 - stimulus activates receptor, 2 - receptor, 3 - afferent neuron has an action potential along axon, 4 - synapse (transmission released here), 5 - efferent motor neuron has an action potential along axon, 6 - effector muscle/gland, 7 - response
what receptors and nerves are involved in the tendon-jerk reflex?
proprioreceptor endings, group 1a muscle afferents, homonymous motor neurons
what receptors are involved in the cutaneous reflexes?
mechanoreceptor endings and nociceptor endings
what is the stretch reflex?
important postural reflex, alters tension in muscle to help maintain constant length
what are group 1a muscle afferents?
A alpha axons
what does it mean if a reflex pathway contains group 1a muscle afferents
the reflex is a really quick one
what axon is used for the monosynaptic reflex arc and what does this mean?
the A alpha axon meaning that the response given is the quickest you can get
what are the steps of the ankle jerk reflex?
hammer tap to achilles tendon - stretches spindles within gastrocnemius - action potentials conducted along group 1a muscle afferents to spinal cord - monosynaptic activation of motor neurons of gastrocnemius muscle - axon potentials travel along A alpha motor axon - gastrocnemius muscle contracts - foot extends
what are the steps of the jaw jerk reflex?
hammer tap to chin - stretches spindles of jaw elevator muscles - action potentials conducted along group 1a muscle afferents to brainstem - monosynaptic activation of motor neurons of jaw elevator muscle - axon potentials travel along A alpha motor axon - jaw elevator muscles contract - jaw jerks upwards and mouth closes
what are the protection mechanisms of the somatic reflexes?
escape mechanism, prevention of muscle overloading, prevention of inadvertent foreign body ingestion, digestive aid
what is the stimulus for the flexion withdrawal reflex?
a noxious stimulus e.g. burning fingers but can’t drop what you’re holding so you can control your response a bit
what is the interneuron like for the flexion withdrawal reflex?
it is disynaptic with one end influencing the response to the situation
what is the receptor for muscle loading activated by?
stretch and contraction
what do afferent signals in muscle loading do?
inhibit motor neuron activation
what does the muscle loading reflex do?
prevents overloading of muscle
what is the bite force in the jaw controlled by?
increasing loading of periodontal ligament
what does anaesthesia of molars do to maximum bite force?
increases it
what innervates somatic muscle loading?
golgi tendon organs
what do golgi tendon organs give rise to?
group 1 afferents
what is the pharyngeal reflex (gag reflex) activated by?
mechanoreceptor afferent from the posterior part of the tongue/soft palate
what happens in the pharyngeal (gag) reflex
stimulation of sensory fibres from the glossopharyngeal and/or trigeminal nerve - afferents terminate in the brainstem (spino trigemino-thalamus) - interneurons project from spino-trigemino-thalamus to nucleus ambiguous - vagus afferents terminate innervated muscles
what does the pharyngeal reflex result in?
mass contraction of both sides of the posterior oral and pharyngeal musculature
how does bilateral contraction occur in the oral cavity?
neurons bifurcate to innervate the nucleus ambiguous on both sides
what is the outcome of the salivary reflex?
increased salivary flow
what are the stimuli of the salivary reflex?
gustatory, visual, olfactory, chewing forces
