Somatosensory Systems

Question 1

Somatosensory

• defn/function
• types of sensations

Answer 1

sensory info from the skin and muscles

Skin - touch (pressure & vibration), pain & temp

Muscle - proprioception and pain

Question 2

Somatosensory Receptors (3)
- location

Answer 2

located @ distal end of the peripheral afferent neurons

3 main types:

1. mechanoreceptors: mechanical deformation by touch, pressure, stretch or vibration
   - -> muscle spindles, GTO
2. chemoreceptors - chemicals released by cells
3. thermoreceptors - respond to heat or cold

Question 3

Proprioceptive Afferent Neurons of the Somatosensory system (4 categories)

Answer 3

Ia = muscle spindles - muscle stretch (DTR)
Ib = GTO - tendon tension
II = muscle spindles - slow and steady muscle stretch
^^all CONSCIOUS proprioception

Paciniform & Ruffini receptors in joint capsule detect joint movement
^^ UNCONSCIOUS proprioception

Ia/Ib = large myelinated 
II = medium myelinated

Question 4

Touch & Pressure Afferent Neurons of the Somatosensory system (1 category - 5 types)

Answer 4

Alpha beta - touch, vibration, skin stretch & pressure

including Meissners, pacinian, ruffini, merkels and hair follicles

**Superficial fine touch primarily done by Meissner’s corpuscles & Merkel’s discs

**medium myelinated

Question 5

Pain & temp Afferent neurons of the Somatosensory system (2)

Answer 5

All are free nerve endings

1. Alpha gamma = faster pain, sharp, localized
2. C = dull, achy pain

Question 6

Muscle Spindle

Answer 6

detects quick stretch of the muscle (Ia afferents) or static stretch (II afferents)

Question 7

Golgi Tendon Organs

Answer 7

detects tension in tendons and transmits (Ib afferents)

Question 8

Paciniform corpuscles & Ruffini endings

Answer 8

located in cutaneous skin & in joint

detect unconscious proprioception (II afferents)

Question 9

Receptive field

• what is it
• distribution pattern

Answer 9

area of skin innervated by a single AFFERENT neuron

Smaller receptive fields DISTALLY and bigger fields PROXIMALLY
- allows for fine touch and motor control w/ the hands

Question 10

Overview of Somatosensory Pathways (4)

- associated receptors/afferents

Answer 10

1. Dorsal column/medial lemniscus - Alpha beta or I/II
2. Spinothalamic (lateral pain system) - Alpha omega
3. Medial pain system (divergent) including spinomesencephalic, spinoreticular & spinolimbic - C fibers
4. Spinocerebellar - unconscious relay of proprioception

Question 11

Primary Sensory Cortex

• area?
• function
• location

Answer 11

S1 - areas 3-1-2
located at postcentral gyrus, somatotopically organized (LE closer to midline)
–> occlusion of ACA affect LE
–> occlusion of MCA affects face & hands

Function: registers receptor activation - can discriminate shape, texture or size of objects

receives directly from the thalamus

Question 12

Secondary Sensory Cortex

• area
• function

Answer 12

S2 - areas 5 & 7

Function: process info from that sensory system ALONE

• sterognosia: use touch sensation to determine what the object is based on prior sensory info
• -> memory of tactile and spatial environment

Question 13

Sensory Association Cortex

• area
• function

Answer 13

Areas 39-40

Function: integrate related activity of different sensory systems to fully comprehend environment