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

What is tactile acuity?

our ability to detect details on the skin

What are the two different ways of perceiving tactile acuity?

two-point threshild and grating acuity

What is the two-point threshold?

minimum separation needed between two points to perceive them as two points

What is grating acuity?

placing a grooved stimulus on the skin and asking people to indicate the orientation (direction) of the grating

What does it mean by higher density in the Merkel receptors?

a higher density of Merkle receptors in fingertips is shown in two-point threshold and grating acuity studies 

What does it mean by high tactile acuity - what does it represent in terms of the size of the cutaneous receptive fields in the skin?

body areas with high tactile acuity have larger areas in somatosensory cortex and have smaller cutanous receptive fields in the skin

What does the Pacinian corpuscle help us perceive?

vibrations

What are corpuscles and how do the receptors fire during vibration?

onion-like structures that transmit electrical signals (neural firing) to the nerve fibers (axons) when rapidly applied pressure (vibrations) occurs, but not when there is continuous pressure 

What is surface texture?

being able to sense or touch based on bumps and grooves of a surface

What is the duplex theory of texture perception?

we perceive texture based on spatial cues and tempral cues

What are spatial cues?

detect texture based on the size, shape, and distribution of surface elements

What are temporal cues?

detect detailed (fine) texture based on the rate (time) of vibration as skin is moved across the surface

What is active touch?

person explores objects by touching them

What is passive touch?

object is applied to the skin (person is not doing the touching)

What is haptic perception?

our ability to perceive three-dimensional objects by actively exploring the objects with our hands and fingers 

How long does it take for people to identify objects accurately?

1 to 2 seconds

What three distinct systems are used to identify objects in haptic perception?

sensory system

motor system

cognitive system

What is the sensory system?

detecting cutaneous sensations (eg, touch, temperature, texture)

What is the motor system?

moving fingers and hands

What is the cognitive system?

thinking about the info provided by sensory and motor systems 

What is social touch?

focuses on the effects of a person touching another person, also called interpersonal touch

What part of the skin contains CT afferents?

the hairy part of our skin

What do CT afferents do?

detect touch through slowly stroking the hair and causes the neurons to fire slowly

(CT= C-tactile, afferent = nerves sending into the brain and spinal cord)

What is the social touch hypothesis?

touch may be involved in two functions discriminative and affective functions of touch 

What is the discriminative function of touch?

sensing details, texture, vibrations, and objects from the skin

activated in the somatosensory cortex 

What is the affective functions of touch?

sensing pleasure and positive emotions associated with social touch and activated in the insula (based on slow stroking)

What is pain and what is its function?

an unpleasant sensory and emotional experience associated with acutal or potential tissue damage, it functions to warn us about dangerous situations

(ex: burning yourself)

What is inflammatory pain?

caused by damage to tissues and joints or by tumor cells

What is neuropathic pain?

caused by damage to the central nervous system (brain or spinal cord)

What is nociceptive pain?

caused by specialized skin receptors known as nociceptors signaling impending (soon to happen) damage to the skin. types of nociceptors respond to heat, chemicals, severe pressure, and cold

What is the direct pathway model of pain?

an early model in the 1950s and 1960s suggested that pain is caused when nociceptors are activated and sent to the brain

What are some problems with the direct pathway model of pain?

pain can be effected by a person’s mental state

pain can occur without stimulation of the skin (pain in the phantom limb)

pain can be affected by attention 

What is the gate control model?

there are different pathways by which pain is signaled to the spinal cord via a gate control system of circuit, which is sent to the brain; these gates are located in the dorsal horn of the spinal cord which neurons fire and cause the gates to open or close

How does the gate control model work?

when gates open or close, the neural info is sent to transmission cells (neurons that send pain info to the brain)

closed gate = pain is reduced

open gate = pain increases 

What are the three pathways for activiting the gate control system?

nociceptors, mechanoreceptors, and central control

What are nociceptors?

neurons excite (fire) to open the gate and transmission cells, and pain increases

What are mechanorecptors?

neurons from skin inhibit (reduce firing) by closing the gate and transmission cells, and pain is inhibited 

What is the central control?

cognitive functions (eg. attention, expectation, distraction) send neurons to fire from the cortex to the gate control system to open or close the gate

What are the four cognitive ways of influencing pain?

expectation

shifting attention

content of emotional distraction

hypnotic suggestion

How do expectations influence pain?

when surgical patients are told what to expect, they request less pain medication and leave the hospital earlier 

How does shifting attention influence pain?

virtual reality technology has been used to keep patients’ attention on stimuli other than the pain-inducing stimulation

How does the content of emotional distraction influence pain?

participants could keep their hands in cold water longer when shown positive pictures

How does hypnotic suggestion influence pain?

fMRI study showed that hypnosis can produce pain and activate brain areas related to pain

What is the multimodal natura of pain?

people describe pain based on sensory components of pain and on affective (emotional) component of pain

What is the sensory component of pain?

describing pain based on what they physically feel

What is the affective (emotional) component of pain?

describing pain based on emotional association

What are opiods?

drugs used to reduce pain and increase euphoria (a good happy feeling)

types of opiods include opium and heroin

How do chemicals in the brain affect pain perception?

the brain contains opiate receptors to process chemicals involved in pain.

What are endorphins?

nautral painkillers, which reduce pain in our bodies

What does naloxone do?

a drug that blocks heroin from getting into the opiate receptor sites in the brain and prevents the release of endorphins from entering the opiate receptors which causes people to feel increased pain 

What is empathy?

the ability to share anc vicariously experience someone else’s feeling

What part of the brain is associated with people feeling a sense of pain when watching someone else experiencing pain?

the anterior cingulate cortex (ACC) and the anterior insula

What is gustation?

taste

What is olfaction?

smell

How are gustation and olfaction “gatekeepers” of the body?

they help identify things to survive/reject and create good and bad emotional responses

How long do taste receprots live and die?

1-2 weeks

How long do olfacory receptors live and die?

5-7 weeks

What are the five basic taste sensations?

salty, sour, sweet, birtter, umami

What is salty?

sodium chloride

What is sour?

hydrochloric acid

What is sweet?

sucrose

What is bitter?

quinine

What is umami?

monosodium glutatmate (MSG)

What is the function of the taste system?

determine which substances to consume and avoid

What is the function of sweetness?

offers nutrient value

What is the function of bitterness?

determine what is potentially harmful

What is the function of saltyness?

presence of sodium; craving if the body is depleted of sodium from sweating

Is there always a perfect connection between taste and effect of substance?

no

What are papillae?

ridges and valleys the tongue consists of

What is filiform papillae?

shaped like cones, found in the entire tongue surface

What is fungiform papillae?

shaped like mushrooms, found in tip and sides of the tongue