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Year 2: Neurobiology II > Lecture 2: Somatosensory system > Flashcards

Lecture 2: Somatosensory system Flashcards

1
Q

what are receptors and the 2 subgroups

A

things that detect stimuli

can be a cell or a nerve ending

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2
Q

difference between microscopic and macroscopic receptors

A

macro = a STRUCTURE that detects a stimuli (like a hair cell or ORN)

micro = a MOLECULE that interacts with the stimulus

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3
Q

cells that acts as receptors

A

can be a neuron (i.e. olfactory receptor neuron)

or can be other cell type (hair cell, rods, cones, etc)

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4
Q

how does a free nerve ending act as a receptors

A

specialized capsules

can function as a mechanoreceptor, chemoreceptor, thermoreceptor, or nociceptor

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5
Q

what is a mechanoreceptor

A

detects touch, vibration, stretch

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6
Q

what is a chemoreceptor

A

detects taste, smell, pH, O2, etc

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7
Q

what is a thermoreceptor

A

detects hot/cold and FLAVOR OF FOOD

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8
Q

what is a nociceptor

A

detects pain and noxious stimuli

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9
Q

what are special sensory receptors

A

special receptors that pick up various types of signals

i.e. like rods and cones that pick up electromagnetic waves

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10
Q

what organelle are receptors rich in

A

mitochondria

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11
Q

what are the special sensations

A

taste
smell
vision
hearing
vestibular

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12
Q

describe the localization of sensations; unconsious vs conscious and where these signals project to in brain

A

conscious maintains somatotopy and signals project to S1

unconscious project to subcortical structures like the RF or cerebellum

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13
Q

describe how a receptor graded potential works

A

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)

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14
Q

describe how an action potential works

A

frequency of a stimulus determines the intensity of the AP

AP changes with the receptor graded potential

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15
Q

explain how stimuli act on receptors similarly to how neurotransmitters act on postsynaptic membrane

A

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)

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16
Q

what are slow adapting receptors

A

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

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17
Q

what are rapid adapting receptors

A

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

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18
Q

5 types of cutaneous mechanoreceptors

A

meissner corpuscles

merkel cells

hair follicles

ruffini endings

pacinian corpuscles

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19
Q

what are meissner corpuscles

A

found on hairless skin (i.e. palms, lips)

detect flutter/vibration

rapid adapting

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20
Q

what are merkel cells

A

detect complex/fine touch

allow us to perceive object edges

slow adapting

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21
Q

what are hair follicles

A

on hairy skin only

detect fine touch and movement

can be rapid or slow adapting

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22
Q

what are ruffini endings

A

somatic

detect stretch in skin

slow adapting

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23
Q

what are pacinian corpuscles

A

in the whole body; have various functions

detect vibration in skin

rapid adapting

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24
Q

where are cutaneous mechanoreceptors most abundantly found

A

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

25
Q

what are intrafusal vs extrafusal muscle fibers

A

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

26
Q

nuclear chain vs bag cells

A

intrafusal fiber types

chain = nuclei are in a line

bag = nuclei are clustered in a “bag”

27
Q

where do you find GTOs and what is their innervation

A

at muscle tendon junction

type Ib sensory fibers innervate

ruffini like sensory endings

28
Q

what fibers innervate the joint capsules

A

type Ib sensory fibers

ruffini like endings

pacinian type endings

29
Q

cutaneous mechanoreceptors have what type of neuronal axon

A

A beta (aka type II)

myelinated, large diameter, fast conduction

30
Q

A alpha senseory neurons types

A

type Ia = for muscle spindles

type Ib = for GTO

detect stretch

31
Q

A beta sensory neurons are also called what type/what is their function

A

type II

secondary receptors for mm spindles and contribute to cutaneous mechanoreceptors

32
Q

clinical test for vibration should be conducted at what frequency and why

A

128Hz

only frequency picked up by pacinian type endings

33
Q

fasciculus gracilis processes what type of information

A

sensory info below T6

34
Q

fasciculus cuneatus processes what type of information

A

sensory info above T6

35
Q

fasciculus interfascicularis and the septomarginal fasciculus contain what type of pathways

A

visceral and some somatic pain pathways

36
Q

describe the DCML pathway

A

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

37
Q

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

A

shell = information about proprioception

core = information about vibration and fine touch

38
Q

the trigeminothalamic pathway interprets information about what areas of the body

A

face and anterior scalp

39
Q

describe the path of the trigeminothalamic pathway

A

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

40
Q

in the trigeminothalamic pathway, what information is given from the trigeminal ganglion vs the mesencephalic nucleus

A

trigeminal ganglion = fine touch, vibration, and limited proprioception

mesencephalic nucleus = proprioception of mm/joints/periodontal ligaments

41
Q

which CNs follow the spinal trigeminal nucleus pathway with limited info

A

CNs VII/IX/X

(7, 9, 10)

42
Q

what is the blood supply to the DCML before the decussation as well as the somatotopy of the tract at this time

A

before decussation = dorsal column

blood supply = posterior spinal artery

Somatotopy of Neck to LE = LATERAL TO MEDIAL

43
Q

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

A

blood supply = anterior spinal artery

somatotopy from neck to LE = POSTERIOR TO ANTERIOR

44
Q

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

A

blood supply = basilar branches/PICA/AICA

somatotopy from neck to LE = MEDIAL TO LATERAL + INVERTED

45
Q

somatotopy of S1

A

From medial to lateral +interior (makes a C shape) = lower limb to face

46
Q

the thalamogeniculate aa branch from

A

posterior cerebral artery (PCA)

47
Q

the anterior cerebral artery supplies what

A

medial and superior portions of both the frontal and parietal lobes

48
Q

the middle cerebral artery supplies what

A

the lateral portions of the frontal and parietal lobes
+
superior temporal lobes

49
Q

what is the somatotopy of the medial lemniscus tract (after decussation) toward the thalamus

A

anterior to posterior = neck to LE

Head = deep to medial

50
Q

what info is encoded at the different sections of Brodmanns areas that correspond to S1 ( 3ab, 1, 2)

A

Proprioception information:
3a = info from mm spindles and GTO
2 = joint capsule info

conscious sensations:
3b + 1 = fine touch, crude touch, sharp P!, temp

51
Q

posterior spinocerebellar tracts relay what type of information

A

unconscious proprioception

52
Q

describe the path of the posterior spinocerebellar tract/cuneocerebellar tract for unconscious proprioception

A
  1. proprioceptive axons synapse at clarke’s nucleus
  2. post synaptic axons ascend ipsilaterally
    - posterior spinocerebellar tract = info about LE and body
    - cuneocerebellar tract (only from C2-T4) = neck info
  3. travel through ipsilateral inferior cerebellar peduncle to the spinocerebellum
53
Q

anterior spinocerebellum relays what type of info

A

motor info

54
Q

describe the path of the anterior spinocerebellum

A
  1. proprioceptive axons synapse at clarkes nucleus
  2. post synaptic axons decussate at the anterior funiculus
  3. 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
55
Q

describe the trigeminocerebellar pathway

A

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

56
Q

Tabes dorsalis: what is it, what causes it, and what are the S&S

A

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

57
Q

differential dx for tabes dorsalis

A

peripheral neuropathy with proprioceptive loss

guillan barre syndrome

58
Q
A

Year 2: Neurobiology II (10 decks)

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