Senses (Chapter 9)

senses

brain receives information about the environment and the body

sensation

process initiated by stimulating sensory receptors

perception

conscious awareness of those stimuli

Five senses

smell, taste, vision, hearing, touch

general senses

have receptors distributed over a large part of the bode

2 groups of general senses

somatic and visceral

somatic senses

provide sensory information about the body and the environment

visceral senses

provide information about various internal organs, primarily involving pain and pressure

basis of classification of senses

location of sensory receptors and types of stimuli involved

special senses

more specialized in structure and are localized to specific parts of the body

5 special senses

smell, taste, vision, hearing, balance

sensory receptors

sensory nerve endings or specialized cells capable of responding to stimuli by developing action potentials

mechanoreceptors

respond to mechanical stimuli, such as the bending or stretching of receptors

chemoreceptors

respond to chemicals

photoreceptors

respond to light

thermoreceptors

respond to temperature changes

nociceptors

respond to stimuli that result in pain

7 general senses

touch, pressure, pain, temperature, vibration, itch, proprioception

proprioception

sense of movement and position of the body and limbs

free nerve endings

simplest and most common types of sensory receptors

receptors for temperature

cold receptor and warm receptor

cold receptors

respond to decreasing temperatures but stop responding at temperatures below 12°C

warm receptors

respond to increasing temperatures but stop responding at temperatures above 47°C

touch receptors

more complex than free nerve endings, enclosed by capsules

types of touch receptors

merkel disks, hair follicle receptors, meissner corpuscles, ruffini corpuscles, pacinian corpuscles

merkel disks

small, superficial nerve endings involved in detecting light touch and superficial pressure

hair follicle receptors

associated with hairs, involved in detecting light touch

meissner corpuscles

receptors for fine, discriminative touch and are located just deep to the epidermis, tactile sensation

ruffini corpuscles

deeper tactile receptors and play an important role in detecting continuous pressure in the skin

pacinian corpuscles

deepest receptors and are associated with tendons and joints, relay information about deep pressure, vibration, body position

importance of proprioception

maintain posture and ability to perform all various body movements

righting reflex

enables us to maintain an upright position

pain

a group of unpleasant perceptual and emotional experiences

types of pain sensation

1. localized, sharp, pricking, or cutting pain

2. diffuse, burning, or aching pain

Superficial pain sensations

highly localized as a result of the simultaneous stimulation of pain receptors and tactile receptors

Deep or visceral pain sensations

not highly localized because of the absence of tactile receptors in the deeper structures

local anesthesia

suppresses action potentials from pain receptors in local areas

general anesthesia

treatment where chemical anesthetics that affect the reticular activating system are administered

referred pain

perceived to originate in a region of the body that is not the source of the pain stimulus

sense of smell (olfaction)

occurs in response to airborne molecules, called odorants, that enter the nasal cavity

olfactory neurons

bipolar neurons within olfactory epithelium

initiation of action potential for olfaction

binding of the odorant to the receptor

neuronal pathways of olfaction

carry action potentials from the olfactory neurons to the areas of the cerebrum that allow for perception and interpretation of the stimuli

process of olfaction

1. axons from olfactory neurons form olfactory nerves

2. enters olfactory bulb

3. relay action potentials to brain through olfactory tracts

4. terminates olfactory cortex

5. perception of smell

taste buds

sensory structures that detect taste stimuli

papillae

enlargements on the surface of the tongue, contain taste buds

taste cell

contains taste hairs

taste hairs

extend through a tiny opening in the surrounding stratified epithelium, called a taste pore

basic types of taste sensations

1. sour

2. salty

3. bitter

4. sweet

5. umami

umami

savory

heat damage to tongue

death to epithelial cells, including taste cells in the taste buds.

cranial nerves that carry taste sensations

1. facial nerve

2. glossopharyngeal nerve

3. vagus nerve

facial nerve transmission of taste

from the anterior two-thirds of the tongue

glossopharyngeal nerve transmission of taste

carries taste sensations from the posterior one-third

vagus nerve transmission of taste

carries some taste sensations from the root of the tongue

taste area of the brain

insula

visual system

eyes, the accessory structures, and sensory neurons

orbits

bony cavities that houses the eyes

accessory structures of the eyes

eyebrows, eyelids, conjunctiva, lacrimal apparatus, extrinsic eye muscles

eyebrows

protect the eyes by preventing perspiration from running down the forehead and into the eyes, causing irritation

eyelids

protect the eyes from foreign objects

blink reflex

object suddenly approaches the eye, the eyelids protect the eye by closing and then opening quite rapidly

blinking

helps keep the eyes lubricated by spreading tears over the surface

conjunctiva

thin, transparent mucous membrane covering the inner surface of the eyelids and the anterior surface of the eye

conjunctivitis

inflammation of the conjunctiva

lacrimal apparatus

lacrimal gland situated in the superior lateral corner of the orbit and a nasolacrimal duct and associated structures in the inferior medial corner of the orbit

lacrimal gland

produces tears

lacrimal canaliculi

small ducts in the medial angle of the eyes that collects excess tears

lacrimal sac

enlargment of nasolacrimal duct, where canaliculi opens

nasolacrimal duct

where tears pass though to go to nasal cavity

number of extrinsic eye muscles in each eyeball

six

extrinsic eye muscles

responsible for the movement of each eyeball

rectus muscles

1. superior

2. inferior

3. medial

4. lateral

oblique muscles

1. superior

2. inferior

eyeball

hollow, fluid-filled sphere

tunics of the eyeball

1. fibrous

2. vascular

3. nervous

fibrous tunic

consists of the sclera and cornea

vascular tunic

consists of the choroid, ciliary body, and iris

nervous tunic

consists of the retina

sclera

firm, white, outer connective tissue layer of the posterior five-sixths of the fibrous tunic

function of sclera

helps maintain the shape of the eye, protects the internal structures, and provides attachment sites for the extrinsic eye muscles

“white of the eye”

small portion of the sclera

cornea

transparent anterior sixth of the eye, which permits light to enter, bends or refracts light

choroid

posterior portion of the vascular tunic, associated with the sclera

black color of the choroid

absorbs light

ciliary body

contains smooth muscles called ciliary muscles

ciliary muscles

attaches to the perimeter of the lens by suspensory ligaments

lens of the eyes

flexible, biconvex, transparent disc

iris

colored part of the eye, controls the amount of light entering the eye

pupil

where light passes through

As light intensity increases, the pupil

constricts

as light intensity decreases, the pupil

dilates

retina

covers the posterior five-sixths of the eye

layers of retina

1. pigmented

2. sensory

pigmented retina

keeps light from reflecting back into the eye

sensory retina

contains photoreceptor cells as well as numerous interneurons

rods

function in dim light because they are very sensitive, meaning they require lower levels of light to be stimulated

cones

require much more light, and they do provide color vision

types of cones each sensitive to a different color

1. red

2. green

3. blue

(RGB)

interneurons of the sensory retina

regulate and relay changes in photoreceptor activity along the visual pathway