Week 6 Flashcards
What is tactile acuity?
ability to distinguish between two points
______ receptive fields permit high resolution of spatial detail
small
What is the two-point discrimination test?
prong distances provide two-point threshold (score) or minimum separation needed between two point to perceive them as two units
What cutaneous receptors would be most likely responsible for tactile acuity?
merkel
Tactile acuity thresholds are determined by…
Merkel receptors (SA1) - superficial mechanoreceptors
What is the grating acuity test?
placing a grooved stimulus on the skin and asking the participant to indicate the orientation of the grating
What 3 factors determine tactile acuity?
- receptive fields
- density of receptors
- representation within somatosensory cortex
Is the density of the 4 receptor types the same across different skin regions?
No, it varies
Describe the density of the 4 cutaneous receptors on the hand
the tip of the fingers has high concentrations of SAI and FAIs, while SAII and FAIIs are more equally distributed
What are the tactile acuity mechanisms?
- high density of merkel cells (SA1 afferents) in the fingertips
- merkel receptors are densely packed on the fingertips
body surfaces that have a _____ density of receptors with smaller receptive fields have _____ 2-point discrimination threshold
higher; lower
Why is 2-point discrimination low on the fingers
accurate grasping movements
Why is 2-point discrimination lower on the face?
protective
receptive field sizes correlate with….
spatial acuity
When does sensation occur?
when the peripheral receptors are stimulated
When does perception occur?
when the brain interprets the sensory stimulation
What does the thalamus do?
relay information from the sensory receptors to areas of the cortex
Peripheral nerve fibers travel in…
bundles to the spinal cord
What are the two major pathways of th somatosensory?
medial lemniscal and spinothalamic
What is the medial lemniscal pathway?
pathway consists of large fibers that carry proprioceptive and touch information
What is the spinothalamic pathway?
pathway consists of smaller fibers that carry temperature and pain information
- cross over to the opposite side of the body and synapse in thalamus, and then one to somatosensory cortex (S1)
Somatosensory information ascends in ________ tracts in _____________
afferent; spinal cord
Somatosensory information projects to which parts of the brain?
primary somatosensory (S1) and parietal cortex
Where is the primary somatosensory cortex?
located in a ridge of cortex (postcentral gyrus) which is found in the parietal lobe
A body map (homunculus) on cortex shows…
more cortical space allocated to parts of the body that are responsible for detail
What does the somatosensory homunculus visualize?
the proportional sensory perception mapping of the body surfaces in the brain
- amount of cortical tissue devoted to each body surface proportional to sensitivity of that part
Which parts of the body are considered to be most sensitive?
lips, tounge, hands, feet and genitals
Homunculi reflect sensitivity & function. How does the homunculus change across species?
the somatosensory cortex map of the body reflects the density of peripheral receptors, representation within the somatosensory cortex & had clear functional relevance
How does tactile acuity change across the fingers? What about density of merkel receptors?
tactile acuity decreases (threshold increases) from index to pinky, but the density of merkel receptors is the same across the fingers
