Central Processing of Sensory Signals Flashcards
descending inhibition
activity from higher areas in the brain can “screen out” certain sensory information
2 types of descending inhibition
- presynaptic inhibition
2. postsynaptic inhibition
what does presynaptic inhibition inhibit
specific sensations
what does postsynaptic inhibition inhibit
all synaptic inputs
how long does presynaptic inhibition last? postsynaptic?
presynaptic = several milliseconds postsynaptic = less than 1 millisecond
presynaptic inhibition
reduces transmitter release at synapse between 1st and 2nd order sensory neurons
postsynaptic inhibition
hyperpolarises membrane of 2nd order sensory neurons
convergence
multiple afferent neurons synapse with each interneuron
divergence
each afferent neuron synapses with multiple interneurons
how are pain receptors activated
damaged tissue releases prostaglandins and histamine
what does pain fiber activity cause
release of substance P in spinal cord
what is caused by the release of substance P
signals in projection neurons ascend to brain pain centers
aspirin function
inhibits prostaglandin synthesis and release from damaged tissues
opioid function
opioid receptors block substance P release
analgesia
suppression of pain
endogenous opiates
opiates created by the brain during the fight or flight response
endogenous opiate production pathway
- periaqueductal grey matter
- reticular formation
- opiates produced
what else can inhibit projection neurons
the firing of large sensory afferents
example of large sensory afferents
- rapid movement
- acupuncture
- transcutaneous electrical stimulation
4, rubbing the skin
gabapentin function
blocks conduction in C-fibre axons (inhibits pain)
referred pain
feeling somatic pain due to visceral pain
what causes referred pain
convergence of visceral and somatic afferents on ascending projection neurons in the spinal cord
how do pain and temperature afferents form tracts in the spinal cord
synapse 2nd order interneurons that cross within 2 segments and ascend in spinothalamic tracts
spinothalamic tracts
anterolateral tracts
how do mechanoreceptive afferents form tracts in the spinal cord
afferents ascend in dorsal columns and THEN synapse 2nd order interneurons and cross in the brainstem
where do all ascending pathways synapse (except smell)
in the thalamus
how are motor commands transmitted from higher brain areas
through the brainstem to the spinal cord
how do sensory afferents contribute to motor control
- mediate spinal reflexes
2. ascend to brainstem, cerebellum, and cerebral cortex to provide feedback
what other area does motor feedback come from
visual and balance centers
desired state
a motor command issued to neuronal networks in the spinal cord
what creates a desired state
brain, cerebellum, brainstem
what type of motoneurons send signals to muscles
alpha motoneurons
actual state
sensory receptors communicate this back to the CNS to compare to the desired state
error signal
signal outputted to the muscles to reduce difference between actual state and desired state
where are Ia and II sensory axons located
in parallel with muscle fibers
what do Ia and II sensory axons respond to
changes in muscle length
where are Ib sensory endings located
in tendons
what to Ib sensory endings respond to
muscle force
what else do muscle spindle endings respond to
vibration
