Chapter 16 Skin Touch Movement Flashcards
somatosensory receptors
receptors that are responsive to touch and poking; presumably based on some sort of mechanically-gated ion channels, perhaps similar to the channels on inner ear hair cells that open as the hairs bend
dorsal-root ganglion
clusters of cells near the spinal cord where cell bodies for the dendrite nerve fibers are located; DRG nerve fibers innervating the skin are contiguous with the axons that send signals into the central nervous system; DRG dendrite functions just like an axon, except that action potentials propagate toward the cell body instead of away from it
Wilder Penfield (1891-1976)
Canadian neurosurgeon who electrically stimulated various regions of the cerebral cortex in patients on whom he was performing brain surgery; by stimulating various parts of the brain and listening to how patients described their associated experiences, he characterized the location of somatosensory cortex in the parietal lobe; he was the first to describe the somatosensory map of the body
somatosensory body map
map of which part of the cortex is associated with which part of the body
primary somatosensory cortex S1
region of the parietal lobe that receives neurons from densely packed somatosensory dendrites connected to many separate neurons each having small receptive fields; from here, information is sent to other more posterior regions of the parietal lobe (S2, S3, …); a lesion in S1 produces a simple loss of sensation in a particular region of the body
Two point discrimination test
measures somatosensory acuity; touch a U shaped wire on the subjects skin such that the two ends of the U touch the skin at the same time -
when the U is touching the fingertips or the lips, the ends of the U can be very close together and the subject will still be able to experience two separate points of touch (higher degree of somatosensory acuity is a result of the densely packed somatosensory dendrites)
when the U is touching the subject’s back, the ends must be moved farther apart in order for the subject to experience two separate points of touch
Posterior somatosensory cortex (S2, S3, etc…)
secondary somatosensory cortex; contain maps of the body, but the things represented in these maps are far less clear than is the case for S1; lesions are associated with various kinds of somatosensory weirdness - somatosensory agnosias
neglect syndrome
touch sensation is intact but is usually ignored or not recognized unless one’s attention is specifically drawn to it; caused by lesions in secondary somatosensory cortex
phantom limb
the feeling of a presence of an amputated limb (i.e. in a person with an amputated arm, the region of parietal lobe that normally receives signals from the arm is no longer getting that input, so these neurons do not sit idle but form connections with the neurons in the adjacent regions of the body map, so any somatosensory input that activates neurons in these adjacent areas would also spill over and activate neurons in the arm area)
primary motor cortex (M1)
immediately anterior to the central sulcus into the frontal lobe; a body map of neurons in the movements of our body; contralateral connection between M1 and the body
when neurons in M1 fire, signals propagate via the spinal cord and eventually arrive at synapses with muscles of the body, the neuromuscular junctions, releasing acetylcholine and triggering contraction of muscle fibers
partial paralysis
lesions in M1 produce an inability to move muscles associated with the corresponding part of the body map
supplementary motor/premotor areas
anterior to M1 in the frontal lobes that are also intimately involved in the control of body movement; neurons in these areas are active before the generation of signals in M1 and are involved in planning and sequencing muscle movements; lesions do not result in paralysis but give rise to disorganizations of movement
apraxia
disorders in the organization of movement
mirror neurons
neurons that fire when seeing other people move their arms in a similar way; implications of this kind of extensive cortical interconnectivity are the subject of active investigation and theorizing
cerebellum
part of the brain that wraps around the brainstem and is very densely packed with neurons and neural connections; centrally involved in the regulation of movement (timing [primary role] and coordination); number of nerve cells in the cerebellum are 50 billion (more neurons in the cerebellum alone than there are in all the rest of the brain); sustained damage causes jerky movements (unable to smoothly execute movements)
