Chapter 16: Special sense

sensory receptor

a structure speciazed to detect a stimulus

Sensation

-physical process or a subjective awareness of the stimulus (intensity)

Perception

the process of sensory infomation to make sense of its significance

Transduction

the conversion of one form of energy to another

Aboslute Threshold

the minimum stimulus that causes a change in signal transduction

Receptor potential

small local eletrical change on a receptor brought by a stimulus

Weber’s Law

"just noticeable difference” for a stimulus is proportional to the magnitude of the stimulus, and this proportion is constant over most of the range of possible stimuli.

Modality

type of stimulus or sensation it produces

labeled line code

all action potential are identical

Receptive field

area within, where a sensory neuron detects stimuli

location

endcoded by which nerve fibers are firing

Intensity

endcode in three ways

Duration

how long the stimulus lasts

Sensory adaptation

If a stimulus is prolonged, firing of the neuron gets slower over time

Phasic receptors

adapt rapidly: generate burst of action potentials when first stimulated, then quickly reduce or stop signaling even though the stimulus continues

Tonic receptors

adapt slowly: generate nerve singals more steadily throughout presence of stimulus

Propioceptors

-body postion, muscle tension, and joint motion

unencapsulated nerve endings

lack connective tissues wrappings

Free nerve endings

• for pain and temperature

• Skin and mucous membrane

Tactile (Merkerl) discs

• For light touch and texture- found in epidermis basal layer

Hair receptors

• Coil around a hair follicle

• Monitior movement of hair

• Adapt qucikly

Taste two mechanisms of action

• Activate second-messenger systems

• Depolarize cells direclty

Hearing

a response to virbrating air molecules

Equilibrium

the sense of motion, body orientation, and balance

Taste hairs are

epithelial cells

Sound

any audible vibration of molecules

Pitch

our sense of whether a sound is “high” or “low”

Loudness

the perception of sound energy, intesity, or amplitude of the vibration

Conductive deafness (often reversible)

• conditions interfere with transmission to inner ear (damaged tympanic membrane, otitis media, blockage of audtiory canal, and ostosclerosis).

Sensorineural (nerve) deafness

• death of hair cells or any nervous system elements concenred wit hearing (No surgery)

Encapsulated nerve endings

are wrappped by glial cells or connective tissue

Tactile (Messinner) corpuscles

• light touch and texture

• dermal papillae or hairless skin (fingertips, eyelids, palms)

Krause end bulbs

• tactile; in mucous membranes in lips and tongue

Lamellar (pacinian) corpuscles

• deep pressure, stretch, tickle, and vibration

• Periosteum of bone, and deep dermis of skin

Bulbous (Ruffini) corpuscles

• Heavy touch, pressure, joint movements

Pain

discomfort caused by tissue injury or toxic stimulation, and typically leading to evasive action- important since it helps protect us.

Nociceptors

• two types providing different pain sensations (slow and fast pain)

Somatic pain

from skin, muscles, and joints

Visceral pain

• from the viscera

• stretch, chemical irritants, or ischemia of viscera (poorly localized)

Referred pain

pain in viscera often mistankenly thought to come from the skin or other superfical site

Basal cells

• stem cells that replace taste cells every 7 to 10 days

Supporting cells

• Resemble taste cells without taste hairs, synaptic vesicles, or sensory role

5 primary sensations

1. Salty

2. Sweet

3. Sour

4. Bitter

5. Umami

Taste

• to be tasted, molecules must dissolve in saliva and flood the taste pore

Mouthfeel

• detected by branches of lingual nerve in papilae

Taste is influence by..

food texture, aroma, temperature, and appearance

Gustation (taste)

• sesnation that begins with actions of chemical stimulatns (tastants on

Facial nerve (CN VLL)

• Collects sensory information from taste buds over anterior two-thirds of tongue from papilae.

Glossopharynegal nerve (CN IX)

• from posterior one-third of tongue

Vagus nerve (CN X)

• from taste buds of palate, pharynx, and epliglottis

Activate second-messenger systems

• carbohydrates, amino acids, glutamate, sugar bind to receptors which activates G proteins and second-messenger within the cell

Depolarize cells directly

• Sodium and acids penetrate cells and depolarize them direclty.

Regardless of the two mechanisms of action

• results in release of neurotransmitters that stimulate dendries at base of taste cells.

Olfaction

• sense of smell response to odorants (chemicals)

Olfactory mucosa

• olfactory cells (neuorns), epithelial supporting cells, and basal stem cells.

Olfactory cells

are nonmotile