Lecture 2: Somatosensory system Flashcards
what are receptors and the 2 subgroups
things that detect stimuli
can be a cell or a nerve ending
difference between microscopic and macroscopic receptors
macro = a STRUCTURE that detects a stimuli (like a hair cell or ORN)
micro = a MOLECULE that interacts with the stimulus
cells that acts as receptors
can be a neuron (i.e. olfactory receptor neuron)
or can be other cell type (hair cell, rods, cones, etc)
how does a free nerve ending act as a receptors
specialized capsules
can function as a mechanoreceptor, chemoreceptor, thermoreceptor, or nociceptor
what is a mechanoreceptor
detects touch, vibration, stretch
what is a chemoreceptor
detects taste, smell, pH, O2, etc
what is a thermoreceptor
detects hot/cold and FLAVOR OF FOOD
what is a nociceptor
detects pain and noxious stimuli
what are special sensory receptors
special receptors that pick up various types of signals
i.e. like rods and cones that pick up electromagnetic waves
what organelle are receptors rich in
mitochondria
what are the special sensations
taste
smell
vision
hearing
vestibular
describe the localization of sensations; unconsious vs conscious and where these signals project to in brain
conscious maintains somatotopy and signals project to S1
unconscious project to subcortical structures like the RF or cerebellum
describe how a receptor graded potential works
potential stops when the stimuli stops
can have a lag effect like with vision (persistence of vision = you continue to see an image for a split second even after the object is no longer in line of sight)
intensity depends on AMPLITUDE (stronger/longer stimuli produce greater graded potential)
describe how an action potential works
frequency of a stimulus determines the intensity of the AP
AP changes with the receptor graded potential
explain how stimuli act on receptors similarly to how neurotransmitters act on postsynaptic membrane
when the stimuli act on the receptive area it has the same effect as a neurotransmitter binding to the post synaptic membrane
ionotropic receptors = ligand/modality gated ion channels
metabotropic receptors = G protein coupled receptor
when stimuli interact with receptor, it is either excitatory (depolarization) or inhibitory (hyperpolarization)
what are slow adapting receptors
good for static stimuli/telling static position
respond constantly to stimuli; continues to fire AP as long as it is stimulated
i.e. a mm spindle; signals are continually sent saying that the muscle is being stretched until it is no longer occurring
what are rapid adapting receptors
good for dynamic stimuli; good indicator of movement or change in stimulus
adapt greatly and quickly
some only signal at the beginning and end of stimulus, whereas some signal throughout just at a very diminished level
i.e. like when a hair is pulled; you get the signal quick but as soon as it happens you do not feel it anymore
5 types of cutaneous mechanoreceptors
meissner corpuscles
merkel cells
hair follicles
ruffini endings
pacinian corpuscles
what are meissner corpuscles
found on hairless skin (i.e. palms, lips)
detect flutter/vibration
rapid adapting
what are merkel cells
detect complex/fine touch
allow us to perceive object edges
slow adapting
what are hair follicles
on hairy skin only
detect fine touch and movement
can be rapid or slow adapting
what are ruffini endings
somatic
detect stretch in skin
slow adapting
what are pacinian corpuscles
in the whole body; have various functions
detect vibration in skin
rapid adapting
where are cutaneous mechanoreceptors most abundantly found
in fingertips and on lips
they have small receptive fields which allows for great details/signals to be sent back to the brain about what is being felt = allow for fine/discriminative touch
sparse in the trunk where there is an increased size of the receptive field
what are intrafusal vs extrafusal muscle fibers
extrafusals = main movers/contractors
- alpha motor neuron
-generate most of the tension/cause contractions
- make up bulk of skeletal muscle
intrafusals = found in mm spindle; detect proprioception and motor info
- gamma motor neurons (not as much force)
- type Ia and II sensory fibers innervate to detect proprioception and motor info
-nuclear chain and bag cells are 2 structural types
nuclear chain vs bag cells
intrafusal fiber types
chain = nuclei are in a line
bag = nuclei are clustered in a “bag”
where do you find GTOs and what is their innervation
at muscle tendon junction
type Ib sensory fibers innervate
ruffini like sensory endings
what fibers innervate the joint capsules
type Ib sensory fibers
ruffini like endings
pacinian type endings
cutaneous mechanoreceptors have what type of neuronal axon
A beta (aka type II)
myelinated, large diameter, fast conduction
A alpha senseory neurons types
type Ia = for muscle spindles
type Ib = for GTO
detect stretch
A beta sensory neurons are also called what type/what is their function
type II
secondary receptors for mm spindles and contribute to cutaneous mechanoreceptors
clinical test for vibration should be conducted at what frequency and why
128Hz
only frequency picked up by pacinian type endings
fasciculus gracilis processes what type of information
sensory info below T6
fasciculus cuneatus processes what type of information
sensory info above T6
fasciculus interfascicularis and the septomarginal fasciculus contain what type of pathways
visceral and some somatic pain pathways
describe the DCML pathway
1st order neuron in dorsal root ganglion
2nd order neuron = both the gracile nucleus and the cuneate nucleus (both located in the caudal medulla)
the post synaptic axons form the internal arcuate fibers and cross at the caudal medulla
fibers continue on to the contralateral VPL nucleus of the thalamus
in the DCML path, once signals reach the ventral posterior lateral nucleus of the thalamus, what information is relayed at the shell vs core portion
shell = information about proprioception
core = information about vibration and fine touch
the trigeminothalamic pathway interprets information about what areas of the body
face and anterior scalp
describe the path of the trigeminothalamic pathway
1st order neuronal cell bodies:
- trigeminal ganglion
-mesencephalic nucleus
2nd order = these axons mentioned above project to the motor nucleus (for myotatic reflex) or the main sensory nucleus
axons decussate at caudal pons
3rd order = synapse at ventral posterior medial nucleus of thalamus
VPM projects to S1; somatotopy maintained
in the trigeminothalamic pathway, what information is given from the trigeminal ganglion vs the mesencephalic nucleus
trigeminal ganglion = fine touch, vibration, and limited proprioception
mesencephalic nucleus = proprioception of mm/joints/periodontal ligaments
which CNs follow the spinal trigeminal nucleus pathway with limited info
CNs VII/IX/X
(7, 9, 10)
what is the blood supply to the DCML before the decussation as well as the somatotopy of the tract at this time
before decussation = dorsal column
blood supply = posterior spinal artery
Somatotopy of Neck to LE = LATERAL TO MEDIAL
what is the blood supply to the DCML after the decussation in the medial lemniscus, rostral medulla as well as the somatotopy of the tract at this time
blood supply = anterior spinal artery
somatotopy from neck to LE = POSTERIOR TO ANTERIOR
what is the blood supply to the DCML after the decussation in the medial lemniscus, pons as well as the somatotopy of the tract at this time
blood supply = basilar branches/PICA/AICA
somatotopy from neck to LE = MEDIAL TO LATERAL + INVERTED
somatotopy of S1
From medial to lateral +interior (makes a C shape) = lower limb to face
the thalamogeniculate aa branch from
posterior cerebral artery (PCA)
the anterior cerebral artery supplies what
medial and superior portions of both the frontal and parietal lobes
the middle cerebral artery supplies what
the lateral portions of the frontal and parietal lobes
+
superior temporal lobes
what is the somatotopy of the medial lemniscus tract (after decussation) toward the thalamus
anterior to posterior = neck to LE
Head = deep to medial
what info is encoded at the different sections of Brodmanns areas that correspond to S1 ( 3ab, 1, 2)
Proprioception information:
3a = info from mm spindles and GTO
2 = joint capsule info
conscious sensations:
3b + 1 = fine touch, crude touch, sharp P!, temp
posterior spinocerebellar tracts relay what type of information
unconscious proprioception
describe the path of the posterior spinocerebellar tract/cuneocerebellar tract for unconscious proprioception
- proprioceptive axons synapse at clarke’s nucleus
- post synaptic axons ascend ipsilaterally
- posterior spinocerebellar tract = info about LE and body
- cuneocerebellar tract (only from C2-T4) = neck info - travel through ipsilateral inferior cerebellar peduncle to the spinocerebellum
anterior spinocerebellum relays what type of info
motor info
describe the path of the anterior spinocerebellum
- proprioceptive axons synapse at clarkes nucleus
- post synaptic axons decussate at the anterior funiculus
- axons then ascend contralaterally to the spinocerebellum
- anterior spinocerebellum tract enters cerebellum through bilateral superior cerebellar peduncles
- rostral spinocerebellar tract (C2-T4 only) enter through superior/inferior cerebellar peduncles
describe the trigeminocerebellar pathway
proprioceptive info for face
Mesencephalic nucleus travels through superior cerebellar peduncle to ipsilateral cerebellum
other info from trigeminal nuclei (mainly) and main sensory nucleus (minorly) travels through inferior cerebellar peduncle to the ipsilateral cerebellum
Tabes dorsalis: what is it, what causes it, and what are the S&S
what = progressive locomotor/sensory ataxia; degeneration of DCML causes functional loss
why = infection via treponema pallidum or STD that causes neurosyphilis
S&S = wide stance/feet grasping for floor/steppage gait
differential dx for tabes dorsalis
peripheral neuropathy with proprioceptive loss
guillan barre syndrome
