Section 3 Somatosensory Flashcards
4 features of the stimulus encoded by somatosensory receps:
nature, intensity, duration, location
Deeper receps sense:
movement of large portions of tissues, pulling it from bone
These are low-threshold mechanoreceptors:
free nerve endings
Myleinated S afferent receptors:
Low threshold mechanoreceptors (MR), Nocioceptors, cool receptors
Unmyelinated S afferent receps:
nocioceptors, warm and cool receptors, itch receps, low-threshold MRs (CT)
Low-threshold MRs that are myelinated transmit?
discriminative touch
Low-threshold MRs that are unmyelinated transmit?
Emotional Touch
What wraps around the base of a hair?
Straight or spiral endings
Generator Potential:
Will generate an AP if large enough
T or F? Generator Potentials always lead to APs.
F. only if large enough
T or F? Mechanoreceptor channels propogate APs.
F. Voltage-sensitive Na channels do
What allows ions to pass through the membrane to initiate a GP?
Conformational change of MR channels
Are generator potentials graded or all-or-nothing?
graded
T or F? A graded potential can lead to an all-or-nothing AP.
T
The larger the hair movements:
the more channels open, and more AP generation
Input is pooled here in the hopes of generating an AP:
the trigger zone
What does the # of APs generated depend upon?
Stimulus strength and type of MR.
T or F? A weak stimulus activates fewer endings than a strong or larger stimulus.
T
Most mechanoreceptors are associated with:
special strucutures that allow them to respond to a particular kind of stimulus
Do mechanoreceps respond better to steady stimuli or changing stimuli.
Depends on the type of recep
What causes GPs in Meissner corpuscles?
Axons trapped in layers gets squished, pressure compresses the nerve ending
Meisnner Corpuscle is involved in what and located where:
fine, tactile discrimination, near skin surface
Where do the axon endings of Meissner’s corpuscles lie?
w in a stack of epi cell inside a thin capsule
What type of sensory input do Meissner’s corpuscles transmit?
fine tactile discrimination
Rapid adaptation (aka fast adaption):
receps that only respond to changing stimuli
Rapid adaptation is good for:
rapid changes in intensity or location of a stimulus
When do rapid adapting receps send no signal?
when the pressure remains constant
When do rapid adapting receps send signals?
lots when P is inc, few when P is dec
Merkel endings:
disc-shaped nerve terminals that contact Merkel cells in basal epidermis
T or F?
Both Merkel cells and the nerve endings respond to touch. T
Are Merkel endings slow or rapid adapting?
slow
How do Miessner’s Corpuscle’s and Merkel cells differ in the beginning of stimulus?
(inc pressure) same kind of response
Keep pressure on: the Merkel cells don’t adapt and keep reporting back about the stimulus
Are Meissner’s corpuscles slow or rapid adapting?
rapid
This type of receptor will continue to send APs with maintained pressure while this type will not.
Merkel cells, Meissner’s Corpuscles
Pacinian Corpuscles:
subcuatneous, all over body (nerve in middle of onion), very sensitive, fast adapting, respond best to vibration
This receptor is a fluid-filled capsule:
Pacinian corpuscle
What do Pacinian corpuscles respond best to?
vibration
This type of recep responds well to rapid indentations of the skin, essentially no response to a steady state stimulus:
Pacinian corpuscle
Name the rapid adapting receps:
Pacinian and Meissner’s Corpuscles
How to test for the first signs of peripheral neuropothy:
Hit tuning fork against heel
What receptor type is used to test for peripheral neuropathy?
Pacinian corpuscles
Ruffini endings:
subcutaneous, common in the mouth, finger-like projections located bw longitudinal non-elastic collagen strands, compress these and get a GP, slow adaptors
What receptor type is most common in the CT of the mouth?
Ruffini endings
What are the slow-adapting receps?
Merkel Cells and Ruffini endings
These receptors are good for sensing details of shapes:
Merkel cells
These receps are good for sensing skin stretch:
Ruffini endings
What are the 2 surface receps?
Meissner’s Corpuscles and Merkel cells
What are the 2 deep receps?
Pacinian corpuslces and Ruffini endings
C-tactile afferents:
slowly conducting, unmy, in hairy skin, very low indentation forces and stroking, best at neutral temp, large, vaguely-defined receptive fields, correlated with pleasant sensations, connected to sections of the brain involved with emotional processing
T or F? C-Tactile Afferents are good for localization and discrimination.
F
What are C-tactile afferents good for?
affective, emotional processing
Receptive fields:
location where a change in the stimulus leads to a change in the firing of the cell
Receptive fields give you info about:
the size of the field
Smaller recep field, (more/less) discriminative ability, fibers innervate (smaller/larger) regions (like fingertips
more, smaller
Size is a function of:
how widely the nerve endings of the receptive field branches
Do the fingers and lips have many or few receptive fields?
many
The greater the representation in the homonculus:
the more axons innervate the tissues
Which receps have small receptive field sizes and which have large recep field sizes?
small: Meissner’s corpuscles and Merkel cells, large: Pacinian corpuscle and Rufffini endings
T or F? Deep receptors have relatively large receptive fields.
T
T or F? Surface receptors have relatively large receptive fields.
F. Relatively small
T or F? Some receptor field in the dorsal (posterior) column nuclei collect input from multiple secondary afferents.
F. multiple PRIMARY afferents (convergence)
Where are the second-order neurons of receptive fields located?
medulla (nuc gracilus and cuneatus, right?)
Some receptive fields in the dorsal (posterior) column nuclei are large bc:
they collect input from multiple primary afferents
Some receptive fields in the dorsal (posterior) column nuclei are small bc:
of inhibitory circuits
T or F? The receptive fields of a cell in the medulla is the same size as any one of its inputs.
F. larger
What will receptive fields in the dorsal (posterior) column nuclei respond best to?
large stimulus bc they all add their excitation onto the target cell (convergence)
Explain why some receptive fields are small.
Touch only surrounding areas: no response, each connected to interneurons that inhibit target cell, surrounding cells inhibit the cell
Where does the stimulus have to be to respond well with a small receptive field?
touch sensor only, inhibited if you also touch, or only touch, surrounding area, tells brain small stimulus in an isolated area of touch
Center-surround organization is typical in:
thalamus, cortex, visual, and auditory systems
What does CSO tell us?
where things are and where they are not
How are neurons arranged in the somatosensory cortex?
columns, cells in each column respond to a specific type of input from a specific part of the body (vibration, touch, etc.)
How is information in the SS cortex processed?
in columns, goes all the way through the cortex
Off-center, on-surround:
inhibited if center is touched, activated if periphery is touched
Explain how orientation and direction is sensed in the finger.
Push finger, must be in the right receptor field location and orientation, turn 90’ and you get no response, selectivity for edge orientation and direction
Areas where somatosensory info comes together with visual, chemosensory, and other types of info:
polysensory
Why are polysensory areas important?
Determining how palatable food is
T or F? Attention can modify activity of cortical somatosensory neurons.
T
Role of attention:
Modifying activity of S cortex AND SS axons. Focus on R foot, you can turn this sense up and your SS cortex will inc in action depending on level of (?) attention
What area of the brain filters response?
thalamus
How many different types of nerve fibers are there in the oral cavity?
6: a-beta, A-delta-fast, A-delta-slow, and 3 kinds of C fibers
What structures receive and transmit information from the PL?
free nerve endings (pain probably) and Ruffini mechanoreceps
Fxn of Periodontal Ruffini endings:
provide info about tooth loading and direction the teeth are being pushed
Ruffini endings fire the most when the teeth are pushed in these directions (top 4)
Distal, Facial, Up, then Mesial
T or F?The perio ligament will remain after a dental implant.
F. Disappears
Why don’t you get nervous info about a tooth after an implant has been placed?
No perio ligament, no info about tooth loading for regulation of oral motor function either
What type of receptors are free nerve endings?
Low-threshold mechanoreceptors
