senses

senses

• are the means by which the brain receives information about the environment and the body

• are ability to perceive stimuli

sensation

is the process initiated by stimulating sensory receptors

perception

is the conscious awareness of those stimuli

sensory receptors

are sensory nerve endings or specialized cells capable of responding to stimuli by generating action potentials that are propagated to the spinal cord and brain.

1. general senses

2. special senses

we recognize many more senses and divide them into two basic groups:

general senses

receptors over large part of body that sense touch, pressure, pain, temperature, and itch

1. somatic senses

2. visceral senses

2 groups of general senses

somatic senses

provide sensory information about the body and the environment

visceral senses

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

special senses

are more specialized in structure and are localized to specific parts of the body. (senses)

1. smell

2. taste

3. vision

4. hearing

5. balance

special senses are:

1. mechanoreceptors

2. chemoreceptors

3. photoreceptors

4. thermoreceptors

5. nociceptors

types of receptors

mechanoreceptors

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

• detect movement

• ex. touch, pressure, vibration

chemoreceptors

• respond to chemicals.

• For example, odor molecules bind to —, allowing us to perceive smells.

photoreceptors

respond to light

thermoreceptors

respond to temperature changes.

nociceptors

respond to stimuli that result in the sensation of pain

proprioception

, which is the sense of movement and position of the body and limbs

free nerve endings

• Structurally, the simplest and most common types of sensory receptors are —

• These are relatively unspecialized neuronal branches similar to dendrites.

• some — respond to painful stimuli, some to temperature, some to itch, and some to movement

touch receptors

• are structurally more complex than free nerve endings.

• Many—- are enclosed by capsules.

1. merkel disks

2. hair follicle receptors

3. meissner corpuscles

4. ruffini corpuscle

5. pacinian corpuscle

types of touch receptors

merkel disks

detect light touch and pressure

hair follicle receptors

• associated with hairs, are also involved in detecting light touch.

• Light touch receptors are very sensitive but not very discriminative, meaning that the point being touched cannot be precisely located.

meissner corpuscle

• are receptors for fine, discriminative touch and are located just deep to the epidermis.

• These receptors are very specific in localizing tactile sensation

ruffini corpuscle

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

pacinian corpuscle

• are the deepest receptors and are associated with tendons and joints.

• These receptors relay information concerning deep pressure, vibration, and body position (proprioception).

righting reflex

that enables us to maintain an upright position, even if our body is on “uneven ground.”

pain

• is characterized by a group of unpleasant perceptual and emotional experiences

• can be localized or diffuse

localized

type of pain sensation that is sharp, pricking, or cutting pain resulting from rapidly conducted action potentials

diffuse

type of pain sensation that is , burning, or aching pain resulting from action potentials that are propagated more slowly

local anesthesia

suppresses action potentials from pain receptors in local areas of the body through the injection of chemical near a sensory receptor or nerve.

general anesthesia

• Pain sensations can also be suppressed if loss of consciousness is produced. T

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

referred pain

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

• we sense — when deeper structures, such as internal organs, are damaged or inflamed

olfaction

sense of smell is called

odorants

olfaction occurs in response to airborne molecules called—

mucus

keeps the nasal epithelium moist, traps and dissolves airborne molecules, and facilitates the removal of molecules and particles from the nasal epithelium.

400

There are at least— functional olfactory receptors in humans.

10,000

These multiple combinations of odorants and receptors allow us to detect an estimated —- different smells.

taste buds

• sensory structures that detect taste stimuli

• are oval structures located on papillae on tongue, hard palate, throat

40 taste cells

Specialized epithelial cells form the exterior supporting capsule of each taste bud, and the interior consists of about —

taste hairs

Each taste cell contains hairlike processes, called —-, that extend into taste pores

1. sweet

2. sour

3. salty

4. bitter

5. umami

Taste sensations are divided into five basic types:

visual system

• includes the eyes, the accessory structures, and sensory neurons.

• We obtain much of our information about the world through the —

accessory structures

protect, lubricate, and move the eye

1. eyebrows

2. eyelids

3. conjunctiva

4. lacrimal apparatus

5. extrinsic eye muscles

accessory structures include:

eyebrows

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

• They also help shade the eyes from direct sunlight

eyelids

• protect the eyes from foreign objects

• If an object suddenly approaches the eye, the —- protect the eye by closing and then opening quite rapidly

• Blinking also helps keep the eyes lubricated by spreading tears over the surface

conjunctiva

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

• secretions of the — help lubricate the surface of the eye.

lacrimal apparatus

produce tears

extrinsic eye muscles

are skeletal muscles and are responsible for the movement of each eyeball

eyeball

is a hollow, fluid-filled sphere

tunics

The wall of the eyeball is composed of three tissue layers, or —

1. fibrous tunic

2. vascular tunic

3. nervous tunic

3 tunics:

fibrous tunic

the outermost tunic which consists of the sclera and cornea

sclera

• is the firm, white, outer connective tissue layer

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

cornea

• is the transparent anterior sixth of the eye, which permits light to enter

• As part of the focusing system of the eye, the — also bends, or refracts, the entering light.

vascular tunic

The middle tunic of the eye is called the — because it contains most of the blood vessels of the eye.

choroid

• This very thin structure consists of a vascular network and many melanin-containing pigment cells, causing it to appear black

• The black color absorbs light, so that it is not reflected inside the eye

• delivers 02 and nutrients to retina

ciliary body

• is continuous with the anterior margin of the choroid

• helps hold lens in place

ciliary muscles

• ciliary body contains smooth muscles called —

• controls shape of lens

suspensory ligaments

• ciliary muscles which attach to the perimeter of the lens by —

• helps holds lens in place

lens

• is a flexible, biconvex, transparent disc

• focuses light onto retina

iris

• is the colored part of the eye

• surrounds and regulates pupil

pupil

• which controls the amount of light entering the eye.

• lots of light = constricted

• little light = dilated

nervous tunic

is the innermost tunic and consists of the retina.

retina

covers the posterior five-sixths of the eye and is composed of two layers

pigmented retina

outer layer, with the choroid, keeps light from reflecting back into the eye

sensory retina

contains photoreceptor cells as well as numerous interneurons

rods and cones

photoreceptor cells which include —, respond to light

rods

• are 20 times more common

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

• do not provide color vision.

cones

• require much more light

• hey do provide color vision.

• There are three types each sensitive to a different color: blue , green, or red

1. macula

2. fovea centralis

When the posterior region of the retina is examined with an ophthalmoscope, two major features can be observed:

macula

is a small spot near the center of the posterior retina

fovea centralis

• center of macula

• is the part of the retina where light is most focused when the eye is looking directly at an object.

• contains only one cone cells, and is the region with the greatest ability to discriminate fine images, which explains why objects are best seen straight ahead

optic disk

• white spot medial to macula

• blood vessels enter eye and spread over retina

• axons exit as optic nerve
  • no photoreceptors

• called blind spot

1. anterior chamber

2. posterior chamber

3. vitreous chamber

The interior of the eyeball is divided into three areas, or chambers:

anterior chamber

• located between cornea and lens

• filled with aqueous humor

aqueous humor

helps maintain pressure, refracts light, and provide nutrients to inner surface of eye

posterior chamber

• located behind anterior chamber

• contains aqueous humor

glaucoma

If aqueous humor flow from the eye through the venous ring is blocked, the pressure in the eye increases, resulting in a condition called

vitreous chamber

• located in retina region

• filled with vitreous humor: jelly-like substance

vitreous humor

• jelly-like substance

• r helps maintain pressure within the eye and holds the lens and the retina in place, refracts light

light refraction

bending of light

focal point

• As the light rays converge, they finally reach a point at which they cross. The crossing point is called the —

• occurs just anterior to the retina

• the tiny image that is focused on the retina is inverted compared to the actual object.

accommodation

• Changes in shape of the lens so image can be focused on retina

• enables eye to focus on images closer than 20 feet

rhodopsin

photosensitive pigment in rod cells

opsin

colorless protein in rhodopsin

retinal

• yellow pigment in rhodopsin

• requires vitamin A

color blindness

• is the absence of perception of one or more of perception of one or more color

• loss may involve perception of all three colors or of one or two colors.

• Most forms of — occur more frequently in males and are X-linked genetic traits

night blindness

A person with a vitamin A deficiency may have a condition called — characterized by difficulty seeing in dim light

retinal detachment

Night blindness can also result from —- which is the separation of the sensory retina from the pigmented retina.

optic nerve

leaves the eye and exists orbit through optic foramen to enter the cranial cavity

optic chiasm

where 2 optic nerves connect

optic tracts

route of ganglion axons

visual field

the image seen by each eye is the — of that eye

ears

The organs of hearing and balance are located in the —

1. external ear

2. middle ear

3. inner ear

Each ear is divided into three areas:

external ear

is the part extending from the outside of the head to the tympanic membrane, commonly called the eardrum

middle ear

air filled chamber with ossicles

inner ear

is a set of fluid-filled chambers medial to the middle ear