somesthesis Flashcards
what are the 2 major groups of tactile receptors?
slowly adapting mechanoeceptors and rapidly adapting mechanoreceptors ( pg. 541)
what do slowly adapting mechanoreceptors respond to?
an enduring stimulus
when do rapidly adapting mechanoreceptors respond?
only at the onset and sometimes the termination of a long stimulus.
name two rapidly adapting mechanoreceptors
meissner’s corpuscle and pacinian corpuscle
name two slowly adapting mechanoreceptors
merkel receptors and ruffini’s corpuscle
every hair on the body is a __________
mechanoreceptor
what areas of the body have the smallest receptor field sizes?
sensitive areas with lots of receptors e.g. lips and finger tips
which areas of the body have the greatest capacity for fine spatial discrimination?
the highly sensitive areas like lips and finger tips
what are 2 major ascending systems that carry somatosensory information to the cerebral cortex?
the dorsal column-lemniscal system and the anterolateral system
what does the dorsal column-lemniscal system mediate?
tactile sensations including vibration and proprioception ( the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement)
what does the anterolateral system mediate?
it carries mainly information about pain and temperature
what are the peripheral mechanoreceptors innervated by and where do their cell bodies lie?
the sensory ( afferent) axons whose cell bodies lie in the dorsal root ganglia.
where does crossing of the sensory fibers occur?
in the caudal medulla oblongata
where do the sensory fibers synapse?
in the cuneate and gracile nuclei= the dorsal column nuclei
what happens at the level of the dorsal column nuclei receptor?
neurons coverage onto single 2nd order neurons:
their receptive fields enlarge due to convergence of input from many 1˚ neurons
and they become more complex b/c 2nd order neurons have BOTH excitatory and inhibitory regions while 1st order only have excitatory receptive fields
what does lateral inhibition w/ a punctate stimulus show ( point source deformation of the skin for e.g. )?
this demonstrates how the primary units of a point source ( like a pin for example) stimulates or influences it’s own 2˚ units and the neighboring 2˚ units. ( pg. 553)
what is two point discrimination and what s the basis for it?
the ability to discern that two nearby objects touching the skin are truly two distinct points, not one.
this occurs because the two 1˚ units that share a neighbor in the middle will have a negative effect on the common neighbor at the 2˚ unit while each of the 2˚ units of the point sources will be stimulated.
what is the medial lemniscus?
the fiber bundle in which the the sensory fibers travel to the brain once the decussate at the dorsal column nuclei.
the right side of the brain receives sensory input from _________ side of the body?
the left
where do the medial lemniscus fibers synapse?
on the ventral posterior nucleus of the thalamus
what is on the lateral division of the ventral posterior nucleus?
trunk and limbs terminating cells
what is on the medial division of the ventral posterior nucleus?
the input from the face
what is the part of the cortex that receives somatosensory input from the ventral posterior nucleus?
the post central gyrus
how are projections from the medial division of the ventral posterior nucleus directed in the post central gyrus?
the medial division ( face) of the ventral posterior nucleus projects to the lateral portion of the post central gyrus. (see pgs 563-564)
how are projections from the lateral division of the ventral posterior nucleus directed in the post central gyrus?
the lateral division ( trunk and limbs) of the ventral posterior nucleus projects to the medial and superior portion of the post central gyrus. ( the foot is most medial in the post central gyrus) ( see pgs 563-564)
what are the broadman areas of sensory information?
3a, 3b, 1, and 2
what does broadman area 3a respond to?
deep tissue input
what does broadman area 3b respond to?
activation of rapidly or slowly adapting cutaneous receptors
what does broadman area 1 respond to?
activation of rapidly adapting cutaneous receptors
what does broadman area 2 respond to?
deep pressure
where are the cells that respond only to a stimulus when it moves across the skin in a particular direction located?
in the most posterior portion of the sensory information section mostly in area 2 but also in 1 but not in areas 3a and 3b.
what occurs in broadman areas 5 and 7 (located posteriorly in the posterior parietal complex)?
processing of sensory information becomes even more complex
how did the hand rotation experiment with the monkeys demonstrate that plasticity can occur in adulthood?
since the monkeys were encouraged to use their three fingers and not use the pinky or thumb to get a reward, more cortex became devoted to the middle fingers was increased so that after the experiment was done they still used those 3 fingers more.
