Senses - Touch and Proprioception

Somatosensory - Senses (7)

1. touch

2. pressure

3. vibration

4. proprioception

5. temperature

6. itch

7. pain

Sensor - Locations (3)

1. skin

2. muscles

3. joints 

Receptors - Types (4)

1. thermoreceptor

2. meissner’s corpuscle

3. nociceptor

4. pacinian corpuscle

Thermoreceptor

senses temperature

Meissner’s Corpuscle 

senses light touch

Meissner’s Corpuscle - Location

• palm

• soles of feet

• eyelids

• genitals

• nipples

Nociceptor

senses pain

sensitive to stimuli that damage or threaten to harm tissue

Pacinian Corpuscle

senses deep touch or pressure or vibration

Pacinian Corpuscles - Location

• dermis

• deep tissue

Peripheral Nervous System (PNS)

• 12 cranial nerves

• 31 pairs of spinal nerves 

Dermatome

sensory area on the body innervated by a specific spinal cord 

Sensory Impulse Direction

northbound

Motor Impulse Direction

southbound

Somatosensory Afferent

conveys information from the skin surface to the central circuits

Peripheral Somatosensory Receptors (3) 

1. mechanoreceptors

2. chemoreceptors

3. thermoreceptors

Mechanoreceptors

responds to mechanical deformation of the body by…

• touch

• pressure

• stretch

• vibration

Chemoreceptors

responds to substances released by the cells

including damaged cells following injury, or infection

Thermoreceptors

respinds to heat or cooling

Receptive Field

area of skin innervated by a single afferent neuron

• distal parts have higher density of receptors than proximal parts 

• fields are smaller distally, and larger proximally 

Proprioception Receptors - Location

muscle and joints to sense body position

sensory information sent by musculoskeletal system

Cutaneous Receptors - Responses

• pain

• temp

• touch

• vibration

• discriminative touch

Cutaneous Receptors - Location

superficial and deep skin

Cutaneous Receptors - Types (6)

1. free nerve endings

2. merkel’s disc

3. meissner’s corpuscles 

4. root hair plexus

5. ruffini corpuscles

6. pacinian 

Free Nerve Endings

superficial skin touches

Merkel’s Disc

deep skin receptor

Root Hair Plexus

hair movement

Ruffini Corpuscles

intense pressure

C2 Dermatome

back of head

C3 Dermatome

back of neck

C6 Dermatome

outer arm

C7 Dermatome

middle finger

C8 Dermatome

inner arm

T1

armpits

T5

nipple

T10

umbilicus

L3 Dermatome

inner thigh/knee

L4 Dermatome

inner shank

L5 Dermatome

outer shank

S1 Dermatome

outer foot

S2 Dermatome

up posterior

lower extremity

S3,4,5 Dermatome

concentric circles around anus

Sensory Pathways (3)

1. conscious relay pathway

2. divergent pathway

3. nonconscious pathway

Conscious Relay Pathway

brings discriminative info about location to conscious awareness in cerebral cortex

light touch, proprioception, nociceptive, temperature

corresponds to somatotopic areas of brain

Divergent Pathway

bring info to brainstem and a cerebrum

does not correspond to somatotopic areas of brain

Nonconscious Pathway

brings movement related info to cerebellum

Tract, Column, lemniscus, Fascicle

bundle of axons in the CNS with the same origin and end point

Somatosensory Pathways

named for the origin and termination of the tract

contains 2nd neuron in series

Projection Neurons

neurons with long axons that connect distant regions of the nervous system

Sensory Pathways - Parts (3)

1. first order neuron

2. second order neuron

3. third order neuron

1st Order Neuron - Dorsal Column

sensory receptor → medulla (CNS)

located outside spinal cord in dorsal root ganglia

connects to 2nd order in the gray matter of spinal cord

2nd Order Neuron - Dorsal Column

medulla (CNS) → somatosensory thalamus

located in brainstem

can decussate from one side of the CNS to the other

3rd Order Neuron - Dorsal Column

thalamus → cerebral cortex (primary somatosensory cortex)

located in post central gyrus

Dorsal Column/Medial Lemniscus Pathway

carries sensation of

• touch

• conscious proprioception (1/3 head and rest of body)

• visceral pain

in the grey matter of the spinal cord

Dorsal Column/Medial Lemniscus Pathway - Cunate Tract

upper limb

trunk

neck

Dorsal Column/Medial Lemniscus Pathway - Gracile Tract

lower limbs

Anterolateral Columns/Spinal Thalamic Pathway

carries sensation of

• pain

• temp

• crude touch (discriminative)

in the white matter of the spinal cord

Crude Touch

nociception & temperature

Nociception

fast, discriminative, lateral or spinothalamic

have c-fibers (unmyelinated) and fibers (myelinated)

1st Order Neuron - Anterior Column

sensory receptor → dorsal anterior horn

located in white matter of spinal cord

2nd Order Neuron - Anterior Column

decussates at midline

dorsal anterior gray horn → thalamus

3rd Order Neuron - Anterior Column

thalamus → cerebral cortex

Proprioception

sense that brings awareness to our body’s position in space

Kinesthesia

awareness of body’s movement in space

Muscle Spindle

collection of muscle fibers, sensory endings, and motor endings

Sensory Endings

respond to stretch (muscle length)

Afferents - Type 1 A

monitors quick and tonic stretch of a muscle spindle 

monitors velocity of change in muscle length

Afferents - Type 1 B

monitors stretch and tension in tendons

Afferents - Type 2

monitors tonic stretch of muscle 

Golgi Tendon Organ (GTO)

provides information about tension in tendons

affected by tension with passive stretch and active contraction

Joint Receptors

responds to mechanical deformation of the capsule and ligaments 

Joint Receptors - Types

• Ruffini’s Endings (Type 2)

• Pacinian Corpuscles (Type 2)

• Ligament Receptors (Type 1b)

• Free Nerve Endings 

Joint Receptor - Ruffini’s Corpuscles

Type 2

signals extreme joint range movement

respond more to passive than active movement 

Joint Receptor - Pacinian Corpuscles

Type 2

respond to movement but not when joint position is constant

Joint Receptor - Free Nerve Endings

respond to inflammation

Proprioceptive Pathways (2)

1. unconscious pathway

2. conscious pathway

Proprioceptive Pathway - Unconscious 

uses spinocerebellar tracts

ends up in cerebellum

'“righting reactions”

Proprioceptive Pathway - Conscious Pathway

uses dorsal column pathway to thalamus

ends up in parietal cortex 

ends up in brain making specific decisions to acts 

Diabetes

dysfunction in proprioceptive neurons (especially in ankle)

leads to ataxia

Sense of Touch Disorders

• diabetes

• alcoholism

• autoimmune diseases

• exposure to toxic chemicals

• vitamin deficiency

• heart and blood medications 

• traumatic brain injury

• spinal cord injury

• brain and spine cancers

• ischemia of the spine and brain