L14 - Somatic sensation Flashcards by Max Kam

Define the 4 modalities of somatic senses.

Touch (Mechanoception)
Body position & movement (Proprioception)
Temperature (Thermoception)
Pain (Nociception)

How well did you know this?

Not at all

Perfectly

3 types of sensations?

special sense, visceral sense and somatic sense

How well did you know this?

Not at all

Perfectly

Location of soma and 5 types of mechanoreceptors?

Located in dorsal root ganglion or trigeminal ganglia

a) Encapsulated:
 Meissner’s corpuscles
 Pacinian corpuscles
 Ruffini corpuscles

b) Unencapsulated:
 Merkel disc
( Hair follicle receptor)

How well did you know this?

Not at all

Perfectly

List the submodalities of mechanoreception?

1.Touch 2.Pressure 3.Vibration and flutter

How well did you know this?

Not at all

Perfectly

Define receptive field of mechanoreceptors?

area of the skin in which a stimulus activates a particular mechanoreceptor

How well did you know this?

Not at all

Perfectly

Submodality, location, receptive field size and rate of adaptation of Meissner’s corpuscles?

Touch, flutter, movement
Superficial
Small, discrete hot spots of receptive field (more sensitive)
Moderately rapid adapting

How well did you know this?

Not at all

Perfectly

Submodality, location, receptive field size and rate of adaptation of Pacinian corpuscles?

Vibration/ acceleration + rapid repetitive displacement of skin
Deeper layer
No hotspots of receptive field, big area
Rapidly adapting

How well did you know this?

Not at all

Perfectly

Submodality, location, receptive field size and rate of adaptation of Ruffini corpuscles ?

Skin stretch, depth of skin indentation, intensity and texture
Deep layer
No hotspot of receptive field, big area
Slowly adapting

How well did you know this?

Not at all

Perfectly

Submodality, location, receptive field size and rate of adaptation of Merkel disc?

Touch, pressure, form, depth of skin indentation
Superficial layer
Small hotspots (more sensitive)
Slowly adapting

How well did you know this?

Not at all

Perfectly

Define rate of adaptation in mechanoreceptors?

decline in firing rate of afferent fibers with prolonged stimulus

Slow = continue to respond through duration of applied stimulus

Rapid = Respond to constantly applied stimulus only at the first instance

How well did you know this?

Not at all

Perfectly

Define the 3 rates of adaptation and give examples of mechanoreceptors.

Slowly adapting: Merkel disk, Ruffini’s corpuscle
Moderately Rapid adapting: Meissner’s corpuscle, hair follicle receptor
Rapidly adapting: Pacinian corpuscle (in glabrous and hairy skin)

How well did you know this?

Not at all

Perfectly

Compare what submodalities of stimuli are measured in mechanoreceptors of different rate of adaptation?

Slowly: Measures depth of skin indentation + Intensity detector + perceives form & texture

Moderately rapid = Velocity detector + Perceives flutter & motion

Rapidly = Acceleration, vibration +rapid repetitive displacement of skin

How well did you know this?

Not at all

Perfectly

3 qualities of proprioception? Definition?

Sense of body position and sense of movement (kinesthesia)

Position(static limb position & trunk orientation)
Movement(dynamic movement; velocity & direction of joint movement)
Forces generated by muscle contractions

How well did you know this?

Not at all

Perfectly

Perception of head / body position in space is derived from integrative inputs of?

 Proprioceptors
 Labyrinth receptors of the inner ear
 Visual input

How well did you know this?

Not at all

Perfectly

Test for proprioception?

Romberg test:

 Requires patient to maintain balance while standing with feet together, eyes closed

 Tests whether the isolated proprioceptive components are working properly when visual cues are missing

How well did you know this?

Not at all

Perfectly

3 types of proprioceptors? Respective function?

Muscle spindle = Sense muscle length or stretch (static) & velocity of stretch during body movement (dynamic)
Golgi tendon organ = muscle tension
Joint receptor = dynamic response, finger position
(4. cutaneous mechanoreceptors)

How well did you know this?

Not at all

Perfectly

Compare the nerve endings between muscle spindle and joint receptors?

Muscle spindle = intrafusal muscle fibers = Annulospiral and flower-spray endings (sensitivity controlled by activity of γ motor neuron)

Joint receptor = Free nerve ending & corpuscular receptors @ connective tissues, capsule and ligaments of joints

Muscle spindle sensitivity is controlled by which type of neuron?

Activity of γ motor neuron

Types of thermoreceptors and mechanism?

 Cold, warm receptors

 Express temperature-gated ion channels (identified by mints, capsaicin)

Different mechanisms of mechanoreceptors? (3)

Activated by mechanical stimulus (force changes conformation of ion channel) = action potential:

1) Direct activation through lipid tension
2) Direct activation through structural proteins
3) Indirect action through membrane structural proteins

Describe how temeprature detection changes in: constant temp, changing temp, extreme temp?

 Static temperature detection: detect constant skin temperature

 Dynamic temperature detection / sensation: detect transient changes in skin temperature

 Below 10oC / above 45oC (extreme temperatures) = stimulate nociceptors

Different modalities of somatosensation are transmitted by the same type of fibers. True or false?

False

Different modalities of somatosensation have different:

 Thickness of afferent axons
 Myelination
 Speed of conduction of action potential

Describe the segregation of sensory afferent fibers with different modalities when they enter the spinal cord?

Segregate into different laminae of the grey matter in dorsal horn of spinal cord

Pain, temperature (Aδ, C fibers) = I, II, V laminae (enters laterally into dorsal horn)

Mechanoreceptors of skin(Aβ fibers) + Proprioceptor (Aα fibers) = IV (enters medially into dorsal horn)

Compare the ascending pathways taken by different sensory afferents?

Proprioception, Mechanoception = DCML

Thermo, Nociception = spinothalamic

List the sensations relayed by DCML?

Mechanoception, proprioception For discriminative touch (recognition of shape, size & texture), pressure, vibration, proprioception

List the sensations relayed by Spinothalamic tract?

Thermoception, Nociception Crude touch, temperature and pain, tickle, itch

List the sensations relayed by Spinocerebellar tract?

mechanoception and proprioception

Divide the somatosensory cortex into 3 groups.

* Primary somatosensory cortex (S-I; areas 3, 2, 1) * Secondary somatosensory cortex (S-II; area 43) * Posterior parietal cortex (areas 5, 7, 39, 40)

Function of the somatosensory cortex?

1) DECODE the localization and types/qualities of the sensory information from contralteral side of body 2) INTEGRATE multiple input sensory information from different locations and of different types/qualities >> Higher order processing

Explain how the somatosensory cortex can decode sensory info.

Highly organized according to the location of the sensory receptors Unique group/patterns of neurons activated by stimuli of specific modality/submodality from a particular location

Relate the areas of thalamus corresponding to Brodmann areas of primary somatosensory cortex after sensory activation.

1) Proprioceptive stimuli: •VPS (ventral posterior superior nucleus) >> 3a, 2 2) Tactile (mechanoceptive) stimuli: •VPL (ventral posterior lateral nucleus) >> 3b, 1, 2 •VPM (ventral posterior medial nucleus) >> 3b, 1, 2 3) Pain and temp: •VPI >> S2 (secondary somatosensory cortex) Most inputs from the thalamus go to areas 3a and 3b, which then project to areas 1 and 2

What sensory info can Brodman area 2 of Primary somatosensory cortex process?

Area 2 process both tactile and proprioceptive information

Describe the organization of primary somatosensory cortex (S-1)

* 6 layers of neurons (molecular, external granular, external pyramidal...etc); arranged into functional columns (1,2,3a,3b,4,5) * Each column is very narrow and all neurons within the column receive inputs from the same body area with a specific sensory submodality

Receptive field of neuron in SI is much larger than that of the mechanoreceptor on the skin. True or False?

True SI neuron receives inputs from multiple receptor neurons

Define what brodmann area 1, 2, 3a and 3b in primary somatosensory cortex process?

 1: texture of objects (rapidly adapting receptors on skin)  2: size, shape of objects (pressure, joint position in deep tissue)  3a: muscle stretch receptors in deep tissue  3b: slowly, rapidly adapting receptors in skin

Describe preliminary higher order processing of the somatosensory cortex?

neurons in S1 stimulated by specific combination of stimuli, e.g. respond to specific motion >> Processing to deduce Direction and Orientation

Location of Primary somatosensory cortex S-I?

Postcentral gyrus & in depth of central sulcus Brodmann area 1, 2, 3a, 3b

Function of secondary somatosensory cortex?

* Receives inputs from S-I * Recognize objects * Input to amygdala and hippocampus (for emotion and memory)

Function of posterior somatosensory cortex?

* Receives inputs from S-I and S-II * Integrates different sensory modalities (e.g. tactile and visual stimuli for eye-hand coordination) * Output to motor areas; for guidance of movement

Clinical presentation of lesion of S-I?

Impaired mechanoreceptive, proprioceptive senses: - Difficulty with simple tactile tests - contralateral loss of discriminative touch (difficulty to discriminate size and form of objects) - Impaired positional sense

Clinical presentation of lesion of Posterior parietal cortex?

* Only mild difficulty with simple tactile tests * Tactile apraxia (disturbed hand movement with an object) * Deficit in the ability to relate to extrapersonal space; e.g. constructional apraxia, neglect syndrome