Touch (II) Flashcards
labeled lines
the brain recognizes the senses as distinct because their action potentials travel along separate nerve tracts
sensory transduction
Conversion of energy from stimulus into a change in membrane potential in a receptor cell
receptor (generator) potential
- local change in membrane
- analogous to EPSPs
free nerve endigs
pain and temperature
merkel’s disc
- somatosensory cell
- touch
meissner’s corpuscle
- somatosensory cell
- touch
hair follicle receptor
- somatosensory cell
- touch
pacinian corpuscle
- somatosensory cell
- vibration and pressure
ruffini corpuscle
- somatosensory cell
- stretch
proprioceptors
- mechanoreceptors found in tendons
- provide information about changes in muscle tension
- force and position
- “self receptors”
sensory events are encoded as _____
streams of action potentials
the intensity of a stimulus can be represented by…
the number and thresholds of activated cells
stimuli stretching cell membranes opens….
sodium channels which creates a graded generator potential. if this exceeds the firing threshold, an action potential is generated
somatosensory system
- determines whether body sensations arise from outside or within the body
- not just in your skin
- surrounds visceral organs
how is a stimulus’ location determined?
based on an orderly map like (somatotopically) representation of the position of the activated receptors
receptive field
the area within which the presence of a stimulus will alter a sensory neuron’s firing rate.
divisions of the spinal cord
cervical
thoracic
lumbar
sacral
cervical
neck, arms, shoulders
thoracic
trunk
lumbar
lower back
front of legs
feet
sacral
back of legs/feet
dermatome
- region of skin innervated by a particular spinal nerve
- organized by structure
what travels in the dorsal column of the spinal cord?
touch and proprioception
pain
how does motor information leave the spinal cord?
ventral root
dorsal root ganglion
- unipolar neuron cell bodies are outside of the spinal cord
- afferent
afferent nerve fibers
carries sensory information into spinal cord
dorsal column system/pathway
- delivers touch and proprioception information to brain (soft, rough, vibrating)
- doesn’t tell you about temperature or pain
primary somatosensory cortex
- S1
- in post central gyrus (in parietal lobe)
primary somatosensory cortex
- S1
- in postcentral gyrus (in parietal lobe)
- receives touch information from the opposite side of the body
- S1 cells arranged as sensory homunculus
secondary sensory cortex
- S2
- receives direct projections from S1
where do the S1 axons extend to?
- motor cortex
- sensory association cortices
what is the S2 implicated in
tactile learning and memory
polymodal neurons
neurons processing information from multiple sensory modalities
nociceptors
- peripheral receptors on free nerve endings
- respond to painful stimuli
first (Early) pain
- sharp, stinging initial pain feeling
- ex: stubbed your toe
how is the first/early pain relayed?
by myelinated A delta axon fibers
second (later) pain
- dull, throbbing, lingering pain
- dull pain until the tissue is repaired
how is the second/later pain relayed?
by unmyelinated C fibers
how are the affective and motivational aspects of second pain mediated?
- by a complex pathway that reaches integrative centers in limbic areas
insular cortex (insula)
important pain region
periaquaductal gray (PAG)
- important pain region
- pain off center
- receives info from S1 and S2
prefrontal cortex
- long term emotional implications
- judgement and decision making
- pain
anterior cingulate & insulate cortex
- long term emotional consequences
- unpleasantness
- social rejection
- pain
primary & secondary somatosensory cortex
- location
- intensity
- qualities of pain
how can pain be modified
- competing tactile sensation, emotion, and cognition
what does PAG activation release (via connections with medulla)
endogenous opioids in spinal cord to shut down pain
when is the PAG activated?
in threatening situations (momentary reduction in pain increases survival)
gate control theory
pain asserts that non-painful input closes the nerve “gates” to painful input, which prevents pain sensation from traveling to the central nervous syst
small nerve fibers
- pain axons
- C and A delta fibers
large nerve fibers
- touch axons
- directly related to brain
- shut down ability for pain signals to reach brain
placebo response
- expectation of relief from prefrontal cortex
- induces release of endogenous opioids in some individuals
- increased activity in PAG & prefrontal cortex
