General Sensory

Carroll University Path-A Program 2026

Mechanoreceptors detect:

deformation, touch and pressure

Thermoreceptors detect:

temperature

Nociceptors detect:

tissue damage, pain

Photoreceptors detect:

photons of light

Chemoreceptors detect:

chemicals, taste and smell

Proprioceptors detect:

position

How is sensation perceived?

Determined by the characteristics of the receptor and the central connections of the axon connected to the receptor

Mechanical deformation causes:

the plasma membrane will stretch to open ion channels

The application of the chemicals cause:

opening of ion channels

A change in temperature alters:

the permeability of the membrane

Electromagnetic radiation causes:

damages/alters the plasma membrane

What is receptor potential?

Membrane potential (Vm) of the receptor

The receptor potential rises above the threshold, which generates what?

An action potential

The greater the intensity of the stimulus causes a greater receptor potential, which causes:

a greater rate of action potential generation (how fast you can generate the action potential)

What occurs when a continuous stimulus is applied?

Receptors respond rapidly at first, but the response declines until all receptors stop firing

The rate of adaption varies with:

the type of receptor

Receptors respond when a ____ is taking place.

change

What is a slow adapting (tonic) receptor?

Receptor that continues to fire action potentials as long as the stimulus is present.

What is the function of slowly adapting (tonic) receptors?

Keep the brain informed of the stimulus

What are some examples of slowly adapting (tonic) receptors?

Muscle spindles

Golgi tendon organs

Chemoreceptors

Baroreceptors

Will slowly adapting receptors adapt to extinction?

Yes

As long as the stimulus is present, but it may take hours or days

What is a rapidly adapting (phasic) receptor?

Respond only to change

Fires intensely when a stimulus is first applied but quickly decreases or stops its firing, even if the stimulus continues

The rapidly adapting (phasic) receptors are important for predicting what?

Future position or condition of the body (movement, balance)

What are some examples of rapidly adapting (phasic) receptors?

Pacinian corpuscle (deep pressure)

Semicircular canals

The larger the nerve fiber diameter, does this cause the rate of transmission to be faster or slower

FASTER

What are the two types of nerve fiber classifications?

Type A

Type C

What are Type A nerve fibers?

Myelinated fibers or varying sizes

FAST TRANSMISSION SPEED

subdivided into alpha, beta, delta, gamma

What are Type C nerve fibers?

Unmyelinated fibers

Small with slow transmission speed

Gradations of signal intensity can be achieved by:

Increasing the number of fibers stimulated (spatial summation)

Increasing the rate of firing in a limited number of fibers (temporal summation)

Why is signal intensity important?

Signal intensity is critical for interpretation of the signal by the brain, like pain.

What is sensory modulation?

Filtering real signals enter CNS at regular intervals, noise arrive randomly

What is an example of sensory modulation

At a party, the TV is on, but you are focused on studying, so you may not remember what was on the TV usually

What is lateral inhibition?

Receptor gets influenced by input by other receptor cells

Makes sure that the sensation is felt, not distributed by to many receptors, other nearby receptors are INHIBITED

What is the Weber-Fechner relationship?

Smallest change in stimulus intensity we can perceive (humans can detect 2.5%)

Tactile is a type of a somatic sensation, what are some examples?

touch

pressure

vibration

tickle and itch

Position or proprioceptive is a type of somatic sensation, what are some examples?

static positon

rate of change

thermoreceptive is a type of somatic sensation, what is an example?

detect heat and cold

Nociceptive is a type of somatic sensation, what is an example?

detect pain and are activated by any factor that damages tissue

What are some type of tactile receptors?

Free nerve endings

Meissner’s corpusles

Merkel’s discs

Hair end organ

Ruffini end organ

Pacinian corpuscle

What do free nerve endings detect and where are they found?

Detect touch and pressure

Found everywhere in the body

What is the function of Meissner corpuscles and where are they located?

Rapidly adapting (within a fraction of a second) and detect light touch

Found on non-hairy skin, lips, finger tips

What is the function of Merkel discs?

Rapidly respond at first, then slowly adapt, detect the “steady state”

Where are Merkel discs located?

Both found in hairy and non-hairy skin

What is the function of the hair end organ?

Adapts rapidly and detects movement over the body (hair on arm)

What is the function of Ruffini’s end organ?

Slowly adapting and respond to continued deformation of skin and joint movements

What is the function of the Pacinian corpuscle?

Very rapidly adapting and is stimulated by only rapid movement and deep pressure, detects pressure and vibration

Meissner’s corpuscles, hair receptors, Pacinian corpuscles and Ruffini end organs transmits signals in what nerve fibers?

type Ab nerve fibers

70 m/s, FAST

Free nerve endings transmit signals in what nerve fibers?

Type Ad nerve fibers (5-30 m/s)

SOME are Type C unmyelinated fibers (0.5-2 m/s)

If the information is more critical, is the transmission rate slower or faster?

FASTER

What are the two pathways for sensory information?

Dorsal column-medial leminiscal system

Anterolateral system

Almost all sensory information enters the spinal cord through:

the DORSAL root of spinal nerves

The dorsal column system contains large what for fast transmission?

Large myelinated nerve fibers

What information is carried by the dorsal column system?

touch

Vibration

position

fine pressure

The anterolateral system has smaller what for slow transmission?

Smaller myelinated and unmyelinated fibers

The anterolateral system has a low degree of spatial orientation, which means:

Cannot point to exact spot

What information is carried by the anterolateral system?

pain

temperature

crude touch, pressure

tickle and itch

sexual sensation

Where is the somatic sensory cortex located?

Postcentral gyrus

Each side of the somatic sensory cortex receives information from where?

The opposite side of the body (contralateral)

There is unequal representation of the body, meaning:

the brain does not map the body based on physical size, but rather the density of sensory receptors and the level of functional importance of each body part

What areas of the body have the greatest area of representation?

Lips, then face and the thumb

What areas of the body have the least amount of area of representation?

Trunk, followed by the lower body

How is the cortex organized?

There are six separate layers of neurons

Layer 1 of the cellular organization of the cortex is located where?

Near the surface of the cortex

Layer IV of the cellular organization of the cortex is located where?

Deep in the cortex

Where do incoming signals enter the cortex (layer)?

Layer IV (4)

Layers 1 and 2 of the cortex receive signals from where?

Diffuse input from lower brain centers

Layers 2 and 3 of the cortex neurons send axons to:

Closely related areas of the cortex

Layer V (brain and spinal cord) and VI (thalamus) send axons to:

Distant location

Within the layers of neurons in the cortex, they are also arranged in:

columns

stretch, p, p, touch, stretch, INTERMINGLED

Destruction of the Somatic area 1 results in:

1. loss of discrete localization

2. inability to judge degree of pressure

3. inability to determine the weight of an object

4. asterognosia (inability to determine shape or form of an object)

5. inability to judge texture

Where are somatic association areas located?

BEHIND THE SOMATIC SENSORY CORTEX, PARIETAL LOBE OF CORTEX

What is the function of the somatic association areas?

Help decipher meaning

Loss of the somatic association areas results in what?

The ability to recognize complex objects and changes in personality

What is the function of pain?

Protection

What are the two types of pain?

Fast pain

Slow pain

What is fast pain?

felt within a 0.1 second

sharp, localized

What is the slow pain?

Felt within >0.1 second

Dull, aching, throbbing pain, not localized

All pain receptors are:

Free nerve endings

How can pain receptors become stimulated?

Mechanical (stretch)

Thermal

Chemicals

What are some examples of substances that are related to pain?

Bradykinin

Serotonin

Histamine

Prostaglandins

Substance P

What is the connection between pain and adaption?

Pain receptors do NOT adapt to stimulus, they adapt to extinction

Rate of tissue damage is the cause of pain at what temperature?

45 C

What is bradykinin responsible for?

Most responsible agent for causing tissue damage (pain)

If extracts from damaged tissue is injected into the skin of another person:

will cause pain in the other person

How is fast pain transmitted?

by Type A Delta fibers

How is fast pain transmitted (what tract)?

Neospinothalamic tract

How fast is fast pain transmitted?

6-30 m/sec

How is slow pain transmitted?

type C fibers (unmyelinated)

How is slow pain transmitted (what tract)?

Paleospinothalamic tract

How fast is slow pain transmitted?

0.5-2 m/sec

Within the neospinothalamic tract, the pain fibers may travel up or down 1-3 segments and terminate on neurons in the:

dorsal horn

the 2nd neuron in the neospinothalamic tract, what occurs?

the tract crosses contralaterally

Some neurons terminate in the _____ but most go all the way to the ______.

reticular substance

ventrobasal complex of the thalamus

All 3rd order neurons in the neospinothalamic tract go back to:

cortex

Most pain fibers terminate diffusively in the medulla and pons in what tract?

Paleospinothalamic tract

Does removal of the somatic sensory areas of the cortex destroy the ability to perceive pain?

NO, pain impulses to lower areas can cause conscious perception of pain

In regard to pain, the cortex is important for:

Determining the quality/appreciate the pain

Is the brain capable of surpressing pain fibers?

Yes

Periaqueductal gray area neurons send axons to where?

Nucleus raphemagnus

nucleus paragigantocellularis

Raphemagnus and paragigantocellularis neurons send axons to:

dorsal horns of the spinal cord