Exam #4

Monday, December 8th, 2025

What does cutaneous mean?

anything related to the skin - involved in the somatosensory system

What are the three parts of the somatosensory system?

1. cutaneous senses - perception of touch and pain from stimulation from skin

2. proprioception - ability to sense the position of the body and limbs

3. kinesethsis - ability to sense the movement of the body and limbs

What is the skin?

the heaviest and lagest organ of the body 

What types of functions does the skin serve?

• warns us of danger from touch

• protects us from the bacteria or chemical agents penetrating into the body

• helps us keep our organs and fluids inside the body

What are the structures of the skin?

epidermis - outer layer of the skin (visible to us) made up of dead skin cells

dermis - below the epidermis, contains mechanoreceptors

What are mechanoreceptors?

sensory receptors that respond to pressure, stretching, and vibration

when they receive touch information neurons from the skin area fire in two different ways

What are two ways the neurons fire in the skin?

slowly adapting receptors (SA) and rapidly adapting (RA) receptors

How do slowly adapting (SA) receptors fire?

continuous firing from pressure

How do rapidly adapting (RA) receptors fire?

firing only occurs at the beginning and end of pressure; no firing occurs in the middle

What two mechanoreceptors are located near the epidermis?

merkel receptors (SA1) and missner corpuscles (RA1)

What size are the cutaneous receptive fields for SA1 and RA1?

small

What two mechanoreceptors are located deeper in teh dermis?

Ruffini cyclindes (SA2) and Pacinian corpuscles (RA2 or PC)

What size are the cutaneous receptive fields for SA2 and RA2?

large

What are Merkley receptors (SA1)?

slowly adapting receptor

perceiving specific details of touch

What are Meissner corpuscles (RA1)?

rapidly adapting receptor

perceiving handgrip control

What are Ruffini cylinder (SA2)?

slowly adapting receptors

perceiving the stretching of skin

What are Pacinian corpuscles (RA2 or PC)?

rapidly adapting receptors

perceiving vibration and fine texture through movement and touch

What is the neural pathway from the skin to the brain?

nerve fibers (axons) fire from the peripheral nervous system (skin areas) to the central nervous system (spinal cord and brain)

What are the two major pathways into the spinal cord?

medial lemniscal pathway and spinithalamic pathway

What information does the medial lemniscal pathway carry?

large fibers, carry proprioceptive (position of the bdoy) and touch info (mechanoreceptors)

What information does the spinothalamic pathway carry?

small fibers, carry temperature and pain information 

Where do the neurons fire after going from the two pathways into the spinal cord?

both pathways go from the spinal cord and reach the ventrolateral nucleus of the thalamus then fire to the somatosensory cortex.

Where do the signals get sent in the somatosensory cortex?

the somatosensory receiving area (S1) and the secondary somatosensory cortex (S2) both areas are located within the parietal lobe

What is the somatosensory cortex?

contains an organized map of various parts of our body 

What is the monunculus?

Latin for “little man,” another name to refer to the body map

How are the parts of our bodies represented in the homunculus?

some parts of the body are disproportionately represented or magnified

Why is there magnification in certain parts of the body and not others in the homunculus? 

the magnification is due to us using that area of the body more, allowing us to perceive greater details of that body part

What is experience-dependent plasticity?

our brains can change and adapt to experience, and train for touch and other senses

How does experience-dependent plasticity change one’s cortical representation?

it becomes larger if that function is used often, representations of our brain areas are not totally fixed