Reflexes Flashcards
what are the three types of movement
involuntary actions
semi automatic actions
voluntary actions
what is involved in involuntary actions
these are reflexes that are centred in the spinal cord and brain stem that have no conscious element
what is the reflex action centred on
spinal cord for the spinal nerves and cranial nerves are in the brainstem
what type of pathway is involved in reflexes
monosynaptic circuit
what is the speed of reflexes
they are rapid, and have short latency
what is latency
the time between the stimulus and the response
what is the common final pathway of a reflex
motor neurons
where are somatic motor neuron bodies found
the spinal cord
where are cranial nerve cell bodies found
brainstem
what activates motor neurons in a reflex
various brain regions and various peripheral receptors
what is stimulated in the knee jerk response
group 1a muscle fibres that link the dorsal and ventral roots at spinal level
what initiates the reflex response
activation of mechanoreceptors that are muscle spindles in the belly of the muscle that respond to the stretch of the muscle itself
what is the muscle afferent in reflexes
1a
are mechanoreceptors in the muscle always active
yes - there is always a steady rate of activity from mechanoreceptors to give an indication of the tone of the muscle itself. when they are stretched further than what is normal, there is generation of action potential
what spinal afferents alwyas active when muscle is contracting
no
describe the knee jerk reflex
- mechanical stimulus applied to the patella tendon in the knee
- tendon pulls on the quadriceps to activate muscle spindles
- generation of action potential that is conducted along the a alpha axon
- into the ventral horn of the spinal cord
- synaptic transmission between the central terminals and the motor neurons they are innervating
- action potential conducted along motor axon as it exist via the ventral roots
why are reflex actions so short
the 1a alpha axon is large and has strongly myelination.
only involves one synapse
list the components of the stretch reflex pathway in order
- stimulus
- receptor activation
- stimulus transduction
- action potential conduction along sensory axon
- synaptic transmission
- motor neuron recruitment, action potential conduction along motor axon
- synaptic transmission for effector recruitment
- response
what is the muscle efferent axon in reflexes
a alpha, same as the sensory afferent
describe the reflex pathway for 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 elevatory muscles
- axon potentials travel along the motor axon
- jaw elevatory muscles contract
- jaw jerk upward, mouth closes
what are the jaw elevator muscles
masseter
temporalis
medial pterygoid
describe the reflex pathway of the ankle jerk reflex
- hammer tip to achilles tendon
- stretches spindles within gastrocnemius
- action potentials are conducted along group 1a muscle afferents to the spinal cord
- monosynaptic activation of motor neurons of the gastrocnemius muscle
- axon potentials travel along the motor axon
- gastrocnemius muscle contracts
- foot extends
what is plantar extension
the extension of the foot
what is the measure of electrical activity within skeletal muscle
bidirection of the electromyogram
what are the key features on the myogram to look for when looking at reflexes
latency and amplitude of response
why is the latency for the jaw jerk reflex less than that for the ankle jerk reflex
the neural pathway for the jaw jerk reflex is shorter than that for the ankle jerk
what is the amplitude of a reflex
the measure of electrical activity in skeletal muscle
why is the amplitude for the jaw jerk reflex smaller than in the ankle jerk
the masseter is a small muscle and there are less muscle fibrils that have to be recruited.
what is the muscle activated in the ankle jerk reflex
the gastrocnemius
which neurons are involved in maintenance of posture and muscle tone
proprioceceptor endings
group 1a muscle afferents
homonymous motor neurons
which receptors are involved in cutaneous reflexes
mechanoreceptor endings and nociceptor endings
what are the protection mechanisms of somatic reflexes
- escape mechanism
- prevention of muscle overloading
- prevention of inadvertent ingestion of a foreign body
- digestive aid
what kind of pathway is the flexion withdrawal reflex
disynaptic
describe the flexion withdrawal reflex
- interneuron is recruited
- interneuron axon splits and sends a branch to the higher centres for the perception of pain to reinforce that input via the spinothalamic pathway
- input projects directly to the motor neurons to initiate the withdrawal reflex
what are golgi tendon organs
a population of nerve endings in the tendon that prevent muscle overloading, that give rise to group 1b muscle afferents
how are golgi tendon organs activated
stretching and contraction of the muscle itself, they act to prevent overwork of the muscle by recruiting 1b afferents to inhibit the motor neurons that innervate the muscle group
what is the inverse stretch reflex
this is when the golgi tendon organ inhibit the contraction of muscle to prevent it overloading
what is another name for the inverse stretch reflex
the inverse myotactic reflex
describe how muscle overloading occurs in the rest of the body
there are no golgi tendons in the jaw muscles
bit force is instead controlled through the loading of mechanoreceptors in the periodontal ligament
the afferents inhibit jaw elevator muscle motor neurons
why is it important to consider periodontal ligament when anaesthetising a patient
anaesthetising the sensory afferents in the periodontal ligament can increase the bite force of the patient which can damage their jaw as they are unaware of how hard they are biting down
what activates the pharyngeal refledx
mechanoreceptor afferents from the posterior part of the tongue and soft palate
there is stimulation of sensory fibres from the glossopharyngeal nerve and trigeminal nerve which terminate in the brain stem
where do the IX and V sensory afferents terminate
the brain stem is the SpVn
what happens once IX and V terminate in the SpVn
interneurons will project from here to go to the nucleus ambiguus to the vagus nucleus
the vagus afferents will terminate and innervate muscles
what contracts in the gag reflex
there is mass contraction of both sides of the posterior oral and pharygneal musculature
what does SpVn mean
the spinal trigeminal nucleus in the brain stem
why is there bilateral contraction in the gag reflex even if stimulus is on one side
to increase the chance of expelling the foreign particle
what is the stimulus of the salivary reflex
- gustatory stimuli
- visual
- olfactory
- chewing forces
what is the outcome of the salivary reflex
increased salivary flow
