lecture 9 Flashcards
sensory transduction
conversion of stimulus energy to electrical signal in sensory receptor cell
mechanoreceptor
touch, hearing, balance Somatosensory neurons Proprioceptors Auditory hair cells Vestibular hair cells
chemoreceptor
taste and smell
photoreceptor
vision
receptor potentials
Graded in amplitude according to the strength of the stimulus
Amplitude is then converted into action potential frequency
Intensity is represented by the frequency of action potentials
Sensory coding for stimulus intensity and duration
1) generation potentail strength and duration vary upon the stimulus
2) generation potential is integrated at the trigger zone
3) frequency of the action potential is proportional to stimulus intensity. duration of a series of action potentials is proportional to stimulus duration
4) neurotransmitter release varies with the pattern of action potentials arriving at the axon terminal
where is most sensory information processed
thalamus
Sensory pathways cross the body’s midline
1) pain, temperature, and coarse touch cross the midline in the spinal cord
2) fine touch, vibration, and proprioception pathways cross the midline in the medulla
3) sensory pathways synapse in the thalamus
4) sensations are perceived in the primary somatic sensory cortex
The Somatosensory System:The Sense of Touch
2 Components:
Detection of mechanical stimuli
Detection of painful stimuli and temperature
Why is it so important?
Identify objects
Monitor internal and external forces
Detect harmful circumstances
bi-directional communication
somatosensory cortex
Neural representation of the body surface
Topographically faithful map
Size reflects disproportional sensitivity
the amount of space on the sensory cortex devoted to each party of the body part is proportional to the sensitivity of that part
Homunculus = “little human”
-Neural representation of the body surface
-Topographically faithful map
-Size reflects disproportional sensitivity
Mechanosensory receptors
-pressure -vibration -stretch
pacinian corpuscle
ruffini’s corpuscle
merkel’s disk
nociceptors
no nerve endings
merkel receptors
Mechanosensory endings in the skin
surface receptors
fires to continuous pressures
perception: fine detail
meisnner corpuscle
Mechanosensory endings in the skin
surface receptors
fires to “on” and “off”
perception: handgrip control
ruffiini cylinder
Mechanosensory endings in the skin
deep receptors
fires to continous pressures
perception: stretching
Mechanosensory endings in the skin
deep receptors
fires to “on” and “off”
perception: vibration and fine texture by moving fingers
sensory transduction
conversion of stimulus energy to electrical signal in sensory receptor cell
Possible mechanism for mechanoreceptor opening:
Response to pressure by having the channel pore anchored to the extracellular and intracellular matrix
pain perception pathways
impulse (pain message) -> peripheral branches of nociceptors-> dorsal route ganglia-> cell body of the nociceptor->Nociceptors synapse onto dorsal horn neurons in the spinal cord-> projects to the brain
“bottom up” representation of pain
pain-> nociceptors-> dorsal horn neurons in the spinal cord ->thalamus ->somatosensory cortex
how the pain is sent to the brain
sensory pathway
“top down” representation of pain
hypothalamus amygdala prefrontal cortex anterior cingulate cortex (ACC integrates sensory input with emotional and cognitive state) emotional pathway placebos affect this pathway
volume control for pain
Prefrontal cortex, amygdala, ACC and hypothalamus (emotional pathway) project to PAG in midbrain which projects to RVM in medulla
normally this pathway decreases pain perception (analgesic effect) but when mood is depressed, this can increase pain perception. Or in fearful situations, this can decrease pain perception.
gate theory
Regions of the spinal cord that receive messages from pain receptors also receive input from other skin receptors and from axons descending from the brain.
These other areas can provide input which can close the “gates” and decrease pain perception.
which neurotransmitter is responsible for pain
and the process
Substance P]The pain afferent neuron releases Substance P as its neurotransmitter.Substance P results in increased intensity of pain
what causes the release of substance p
A calcium spike in the primary nociceptor
Painful stimuli induces an action potential in the sensory neuron
