Module 3 Somatic System Flashcards
what are the four somatic senses
touch, pain, temp, body position
where are somatic receptors located
all over the body
what are the types of somatic sensation receptors
mechanoreceptors, nociceptors, thermoceptors (also nociceptive thermoreceptors), proprioceptors
where do somatosensory afferents send information
skin surface –> central circuits
what is the structure of a pseudounipolar neuron
one axon split into two branches; one sends info to PNS, the other to spinal cord (dorsal root ganglion cells)
both touch and pain/temp take the same pathway
dorsal horn (ipsilateral) –> 2nd order neurons (decussate) –> contralateral ascent
what are the different types of receptors
free nerve endings (nociceptors, thermoreceptors) and encapsulated (most cutaneous receptors
capsule function
sensitive to mechanical deformation/activated by temp and chemicals
how do capsules work
- stimuli applied to skin deform or change receptor
- alters the ionic permeability of the receptor creating generator (receptor) potentials
- triggers action potentials
what does Merkel’s disks specialize in
light touch and tactile discrimination
what does Meissner’s corpuscle specialize in
low frequency vibration in glaborous skin (30-50 Hz)
what do Pacinian corpuscles specialize in
vibration at 250 - 350 Hz
what do Ruffini’s corpuscles specialize in
detecting something slipping through your hands
- skin stretch, sustained pressure
which corpuscles have a small receptive field
Merkel and Meissner
which corpuscles have a large receptive field
Pacinian and Ruffini
where are Merkel disks located
tip of epidermal sweat ridges
Merkel sensory function
form and texture perception
Merkel effective stimuli
edges, point, corners, curvature
Merkel receptive field area
9 mm^2
Merkel innervation density
100/cm^2
Merkel spatial acuity
0.5mm
Meissner location
dermal papillae (close to skin surface)
Meissner sensory function
motion detection; grip control
Meissner effective stimuli
skin motion
Meissner receptive field area
22 mm^2
Meissner innervation density
150/cm^2
Meissner spatial acuity
3 mm
Pacinian location
dermis and deeper tissues
Pacinian sensory function
perception of distant events through transmitted vibrations; tool use
Pacinian effective stimuli
vibration
Pacinian receptive field area
entire finger or hand
Pacinian innervation density
20/cm^2
Pacinian spatial acuity
10+ mm
Ruffini location
dermis
Ruffini sensory function
tangential force; hand shape; motion direction
Ruffini effective stimuli
skin stretch
Ruffini receptive field area
60 mm^2
Ruffini innervation density
10/cm^2
Ruffini spatial acuity
7+ mm
which corpuscles does reading Braille require
Merkel & Meissner
which corpuscle is the most noisy
Pacinian
what sensory functions do muscle spindles have
proprioception
what sensory functions do Merkel, Meissners, Pacinian, and Ruffini corpuscles have
touch
what sensory functions do free myelinated nerve endings have
pain, temperature
what sensory functions do free unmyelinated nerve endings have?
pain, temperature, itch
how is somatosensory information organized
into 4 dermatomes (each innervates a certain portion), and into 30 spinal segments
how is spinal cord gray matter divided
into dorsal horn, intermediate zone, ventral horn
what is the function of dorsal columns
touch info ascends via dorsal columns
shingles cause
virus affects 1 spinal segment
where do the axons from mechanosensory tract project
dorsal horn –> ipsilateral ascent –> 2nd order neurons (medulla); upper body –> cuneate nucleus, lower body –> gracile nucleus; decussation –> contralateral ascent –> VPL thalamus –> primary sensory cortex
- dorsal column medial lemniscal pathway
where does the trigeminal pathway enter the brain
through the pons
what is the trigeminal pathway
trigeminal nerve –> pons –> 2nd order neurons –> axons decussate –> ascend contralaterally –> VPM thalamus –> primary sensory cortex
where does the primary somatosensory cortex receive input from
VP nucleus of thalamus
which area receives the most dense connections
area 3b
where does the ventral posterior complex of thalamus project to
primary somatosensory cortex
where does area 3a of primary somatosensory cortex project to
secondary somatosensory cortex, and area 2
where does area 3b of the primary somatosensory cortex project to
secondary somatosensory cortex, area 1 (texture), and area 2 (size and shape)
where does area 1 of primary somatosensory cortex project to
secondary somatosensory cortex
where does area 2 of primary somatosensory cortex project to
parietal areas 5, 7, and secondary somatosensory cortex
where does the secondary somatosensory cortex project to
amygdala and hippocampus
where do parietal areas 5, 7 project to
premotor and motor cortices
what kind of information does the primary somatosensory cortex receiveq
simple segregated streams of sensory information
where does integration occur
in posterior parietal cortex
what is the posterior parietal cortex involved in
somatic sensation, visual stimuli, and movement planning
what does damage to the posterior parietal cortex cause
inability to recognize objects (agnosia/neglect syndrome)
characteristics of cortical somatotopy
not continuous, not to scale, relative size of cortex devoted to each body part depends on the density of sensory input
how are neurons in primary somatosensory cortex organized
in functionally distinct columns
- neurons in each column respond to the same kinds of stimuli
what does life without pain cause
progressive degeneration of joints, spinal vertebrae, skeletal deformation, infection
nociceptor characteristics
- transduction of pain
- free, unmyelinated nerve endings
- signal that body tissue is being damaged
what are the types of damage detected by nociceptors
mechanical (strong pressure, sharp objects), thermal (activates when tissues start to be destroyed), chemical (environmental agents/ those from tissues itself (pH, histamine, etc)
types of nociceptors
polymodal, mechanical, thermal, chemical
hyperalgesia
part of damaged skin becomes very sensitive, causes neurotransmitters (CGRP - calcitonin vasodilator) and inflammatory factors (IL -1beta, NGF, TNF - alpha), and histamine to be released
- they bind nociceptors and activate them
primary hyperalgesia
affects direct site
secondary hyperalgesia
affects area around direct site
bradykinin function
- Product of enzymatic breakdown of kininogen
- Binds and depolarizes nociceptors
prostaglandins function
- Generated by enzymatic breakdown of lipid membrane
- Increase the sensitivity of nociceptors to other stimuli
substance P function
Can be secreted by axons branches in adjacent cells; cause the release of histamine
A delta fibers characteristics
fully myelinated and responsible for initial pain
Cfiber characteristic
long-lasting, less severe pain
type I A delta fibers
low threshold for mechanical and chemical stimulation but high threshold for temperature
type II A delta fibers
high threshold for mechanical and chemical stimulation but low threshold for temperature
what do C fibers respond to
all stimuli with subtypes with preference for heat/chemical stimuli
referred pain
pain we feel in different parts of the body with different source (angina, appendicitis)
what is the anterolateral pathway
nociceptive afferents –> dorsal horn –> second order neurons in dorsal horn –> decussation and contralateral ascent via anterolateral tract
rexed lamina pathway in anterolateral pathway
C fibers –> dorsal horn –> second order neurons layer 1 –> contralateral transmission to brain
A delta fibers pathway
layer 1 –> layer 5 –> contralateral transmission –> brain
why does cross-talk occur (referred pain)
layer 5 of the rexed lamina receives cutaneous info as well as visceral nociception info
