S2 Neuro Exam 4: Somatosensory System

Front 1

Obj.
Define
receptor potential

Back 1

stimulus energy on receptor (axon terminal) creates a receptor potential which leads to an AP

(AP further conveys info to CNS via sensory ganglion cell axons)

Front 2

Define
stimulus transduction

Back 2

process of transforming stimulus energy into an electrical signal

Front 3

(indirect/direct) pathways have 3 neurons, are somatotopically organized, & serve a sensory discriminative function, & project to the contralateral primary somatosensory cortex

Back 3

DIRECT


(indirect project more diffusely & serve a more general affective-arousal function, project to limbic)

Front 4

Obj
Define
receptor specificity

Back 4

receptors are specialized to be more responsive to one kind of stimulation

Front 5

What is an adequate stimulus?

Back 5

the specific type of stimulus to which each type of receptor responds w/ the greatest sensitivity

(Ex. mechanical stimulus- mechanoreceptors)

Front 6

Obj
Define
receptor adaptation

Back 6

a decrease in response of a sensory nerve fiber to a steady stimulus

Front 7

_________ respond to stimuli that damage or threaten to damage tissue, stimuli may be mechanical, thermal, or chemical.

___________ terminals are free nerve endings

Back 7

Nociceptors



Nociceptive terminals

Front 8

Obj.
describe the process of frequency coding

Back 8

the magnitude/intensity of a stimulus is coded by the frequency of AP generated by the receptive neuron (number of receptors activated)

Front 9

Obj.
describe the process of population coding

Back 9

the CNS interprets stimulus modality (touch, pain, temp, etc) by the types of receptors that are activated

Front 10

The ________ is the level of stimulus at which a receptor will respond & a ___________ is the range of intensity after the threshold in which the receptor will continue to react

Back 10

threshold

dynamic range

*(successive recruitment of receptors w/ diff threshold & overlapping ranges necessary)

Front 11

Obj.
Compare & Contrast the physiological functions of rapidly adapting receptors & slowly adapting receptors

Back 11

rapidly adapting receptors-
detect changes in stimuli strength (phasic receptors)
code velocity & acceleration
(mechanoreceptors)

slowly adapting receptors-
detect stimuli of constant strength (tonic receptors)
code intensity & duration
(mechanoreceptors & thermoreceptors)

Front 12

What type of receptor is non-adapting?

Back 12

nociceptors

Front 13

Obj.
Describe the morphology, innervation, function and distribution of muscle spindles

Back 13

morphology-
nuclear bag fibers w/ central nuclei
nuclear chain fibers w/ nuclei in a row along length
innervation-
annulospiral afferents (Ia) innervate nuclear bag & nuclear chain fibers &
flower spray endings (II) innervate nuclear chain fibers
function-
annulospiral respond to brief or sustained stretch and vibration
flower spray endings respond to sustained stretch
distribution-
intrafusal muscle fibers surrounded by CT capsule, in parallel w/ extrafusal muscle fibers

Front 14

.Obj.
Describe the morphology, innervation, function and distribution of golgi tendon organs

Back 14

morphology-
high threshold receptor in series w/ extrafusal muscle fibers
innervation-
Ib afferents
function-
limit muscle contraction in response to stretch
distribution-
located at junction of muscle & tendon

Front 15

Obj.
Define
receptive field

Back 15

the area (size varies) in which stimuli can activate a neuron through its receptive endings

* each sensory neurons has a receptive field that conveys spatial info to CNS

Front 16

Obj.
Explain the relationship btwn peripheral innervation density & receptive field size

Back 16

The size of the receptive fields & receptor density per unit area determine the discriminative ability of the area (localization)
--> smaller field & more receptors per area= better localization

Front 17

Obj.
Compare & Contrast between small & large diameter afferents

Back 17

small diameter:
-slower
-more control of nociception (noxious stimuli)
-more sensitive to local anesthetics

large diameter:
-faster
-more control of epicritic touch, vibratory, & postural sensations (non-noxious stimuli)
-more sensitive to nerve pressure block, anoxia

Front 18

Differentiate btwn the medial & lateral division of the Dorsal Root Entry Zone (DREZ)

Back 18

medial division:
large diameter afferent
non-noxious input from somatic structures

lateral division:
small diameter afferent
pain & temp sensations

Front 19

Describe the pathway of large diameter afferents in the medial division

Back 19

ascend w/i direct dorsal column pathway--> synapse w/i dorsal column nuclei
--> synapse in dorsal horn giving off second order projections--> ascend in postsynaptic dorsal column pathway (dorsal column)
--> synapse in dorsal horn= segmental pain modulation
--> synapse in intermediate zone--> ascend w/i anterior spinocerebellar tract
--> synapse in ventral horn= myotatic reflex

Front 20

Describe the pathway of small diameter afferents in the lateral division

Back 20

bifurcated upon entry--> send collaterals up & down Lissauer's tract--> enter dorsal horn
--> synapse in dorsal horn projection neurons--> ascend in contralateral anterolateral tract
--> synapse on dorsal horn interneurons= segmental modulation of pain
activate somatic & preganglionic motor neuron--> initiate segmental somatic & visceral reflexes

Front 21

Obj.
Describe the functional classification of dorsal horn neurons

Back 21

nociceptive specific-
receive input from small diameter afferent
convey pain related info

wide dynamic range-
receive large & small diameter afferents
convey pain, temp, touch, & visceral sensation

low-threshold mechanoreceptive-
recieve large diameter afferents
convey touch & propropception info

thermoreceptive-
receive small diameter afferents
convey temp info

Front 22

Which type of dorsal horn neuron most likely mediates referred pain?

Back 22

wide dynamic range neurons

Front 23

Obj.
Pathway & function of Spinocervicothalamic tract

Back 23

pathway:
ipsilateral projection of dorsal horn in lateral funiculus to end in the lateral cervical nucleus (C1-3)
--> axons join medial lemniscus & project to thalamus & cerebral cortex

function:
return of pain sensation after anterolateral tract lesions

Front 24

Obj,
Pathway & function of Dorsal column-medial lemniscal system

Back 24

pathway:
-recieves inputs from contralateral somatosensory cortex & reticular formation
-dorsal column nuclei from medial lemniscus after axons cross midline
-ascends to the somatosensory nuclei of the thalamus (VPL)

function:
tactile discrimination & proprioception

Front 25

In addition to the somatotopically organized arrangement seen throughout the dorsal Column-Medial Lemniscal pathway, the VPL also is arranged how?

Back 25

according to modality

Front 26

The postsynaptic posterior column pathway conveys ____________________ to the dorsal column nuclei

Back 26

non-discriminitave touch
(as well as noxious input from thoracic & pelvic viscera)

Front 27

The spinocervical tract conveys ______________ via large diameter afferents that ascend in the dorsal column before synapsing in the dorsal horn.

Back 27

vibration info

Front 28

Obj.
Pathway & function of dorsal spinocerebellar tract

Back 28

pathway:
projects from lower extremity to Nucleus of Z, rostral to dorsal column nuclei

function:
conveys conscious proprioception from lower extremity

Front 29

The primary somatosensory (S1) cortex is arranged in columns that respond to ____________

Back 29

one submodality & have similar peripheral receptive fields

Front 30

S1 also has 4 distinct areas, to diff submodalities:
Area 1 responds to _______________
Area 2 responds to ________________
Area 3a responds to _______________
Area 3b responds to _______________

Back 30

1- texture (detected by multiple fingers)
2- golgi tendon organ & joint afferents
3a- muscle spindle proprioceptive inputs
3b- size, texture, of object from cutaneous receptors

Front 31

Diff types of proprioceptive input travel in diff columns. What are the 3 types of proprioceptive columns?

Back 31

single joint or muscle group responder

final position signaler

several joint & muscle group responder & signaler

Front 32

SI has extensive cross innervation btwn areas of receptive fields. What does this allow?

Back 32

plasticity- adjacent digits can expand receptive fields to take over areas formerly occupied by the amputated digits

Front 33

Neurons in the secondary somatosensory cortex (SII) located inside the lateral fissure, connect w/ the _________ & _________.

What are these connection involved in?

Back 33

insular cortex & limbic system



memory of tactile stimuli (a task learned by one hand can be performed by another)

Front 34

The parietal association cortex (areas 5 & 7) recieve inputs associated with _________________ & produces conscious _________ & __________

Back 34

sensory-motor interrelationships

conscious perception & interpretation

Front 35

Areas 5 & 7 also have primary projections to premotor cortex for _______________

Back 35

motor planning

Front 36

Obj.
Describe the mechanism for sensory discrimination in the dorsal column-medial lemniscal system

Back 36

DIRECT pathway
-first order processing of info from overlapping receptive fields occurs at the dorsal column nuclei by feed forward & feedback inhibition
-lateral inhibition provides contrast sharpening (via relay nuclei)
-descending inputs influence incoming sensory info & provides means for attention to be focused on central input

Front 37

Obj.
Describe the main types of somatic nociceptive & thermoreceptive units

Back 37

cutaneous nociceptors:
C-polmodal nociceptors- responds to multiple stimuli, mechanical tissue damage, noxious thermal stimuli, algesic compounds
High threshold mechanoreceptor- respond to rough stimuli w/o damage (pinch, rub, stretch)

cutaneous thermoreceptors:
warm & cool thermoreceptors- responds to innocuous warm & cold stimuli

Front 38

Obj.
Describe features of nociceptor sensitization

Back 38

with tissue damage or repeated stimulation of free nerve endings, receptors lower threshold & increase firing rate to set levels of noxious stimuli

* partially due to local increase in tissue damage products--> primary hyperalgesia

-flare response may be seen outside of area as a result of axon reflex

Front 39

What is axon reflex?

Back 39

the activation of adjacent branches of a neuron's receptive field as part of the discharge of the injured area-->
causes release of chemical intermediaries (substance P, histamine, etc)-->
leading to neurogenic inflammation

Front 40

What is neurogenic inflammation

Back 40

a tissue reaction (redness, heat, pain, & swelling) that occurs beyond the immediate area of injury

Front 41

Obj.
Describe features of central sensitization

Back 41

response properties of dorsal horn projection neurons change in response to tissue damage/high freq input--> altered synaptic efficacy & neuronal transcription:
-threshold for activation decreases
-responsiveness increases
-receptive field expands to encompass areas outside tissue damage--> secondary hyperalgesia

Front 42

Obj.
Differentiate btwn primary & secondary hyperalgesia

Back 42

primary hyperalgesia- increased pain response, occurs w/ increased sensitivity of free nerve endings in area of tissue damage

secondary hyperalgesia-
increased perception of pain in response to noxious input AWAY from site of tissue damage

Front 43

Describe allodynia

Back 43

normally innocuous stimuli evokes pain

Front 44

Which tract supplies sensory info regarding location, magnitude, duration, quality?

Back 44

DIRECT anterolateral system

Front 45

What does the INDIRECT anterolateral system convey?

Where does it project?

Back 45

info regarding the arousal of pain (unpleasantness)


contains projections from WDR neurons in the deep dorsal horn & intermediate zone

Front 46

The indirect anterolateral pathway has poor somatotopy & _____________ receptive fields

Back 46

large bilateral