Anaphy - Senses

Sense

Sense

the ability to perceive stimuli

Sensation

the process initiated by stimulating sensory receptors; conscious awareness of stimuli received by sensory neurons

Sensory receptors

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

General senses

• have receptors distributed over a large part of the body
• include the senses of touch, pressure, pain, temperature, vibration, itch, and proprioception which is the sense of movement and position of the body and limbs

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

• senses of smell (olfaction), taste, sight, hearing, and balance

Mechanoreceptors

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

Chemoreceptors

respond to chemicals, such as odor molecules.

Photoreceptors

respond to light

Thermoreceptors

respond to temperature changes.

Nociceptors

respond to stimuli that result in the sensation of pain.

Merkel disks

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

Hair follicle receptors

associated with hairs; also involved in detecting light touch

Meissner corpuscles

receptors for fine, discriminative touch; located just deep to the epidermis; very specific in localizing tactile sensations

Ruffini corpuscles

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

Pacinian corpuscles

the deepest receptors; associated with tendons and joints; relay information concerning deep pressure, vibration, and position (proprioception).

Pain

characterized by a group of unpleasant perceptual and emotional experiences

Local anesthesia

• a treatment where chemical anesthetics are injected near a sensory receptor or nerve, resulting in reduced pain sensation.
• action potentials from pain receptors in local areas of the body can be suppressed

General anesthesia

• produces loss of consciousness
• a treatment where chemical anesthetics that affect the reticular formation are administered.

Referred Pain

- perceived to originate in a region of the body that is not the source of the pain stimulus
- felt when deeper structures, such as internal organs, are damaged or inflamed
- occurs because sensory neurons from the superficial area to which the pain is referred and the neurons from the deeper, visceral area where the pain stimulation originates converge onto the same ascending neurons in the spinal cord

Olfaction

▪ sense of smell
▪ occurs in response to airborne molecules, called odorants
▪ receptors are located in nasal cavity and hard palate
▪ there are at least 400 functional olfactory receptors in humans
▪ multiple combinations of odorants & receptors detect 10,000 different smells
▪ olfactory range and sensitivity is even greater in some animals than in humans, due to a larger number and more types of olfactory receptors.

Taste buds

• sensory structures that detect taste stimuli
• oval structures located on the papillae of the tongue, throughout other areas of the mouth & pharynx, such as on the palate, the root of the tongue, & the epiglottis

40 taste cells

Inside each taste bud

taste hairs that extend into taste pores.

Each taste cell contains hairlike processes

Vision

The visual system includes the eyes, the accessory structures, and sensory neurons.

orbits.

The eyes are housed within bony cavities

Eyebrows

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

Eyelids

• protect the eyes from foreign objects
• protect the eye by closing and then opening quite rapidly (blink reflex).
• Blinking, which normally occurs about 20 times per minute, also helps keep the eyes lubricated by spreading tears over the surface.

Conjunctiva

• a thin, transparent mucous membrane covering the inner surface of the eyelids and the anterior surface of the eye
• secretions of the conjunctiva help lubricate the surface of the eye.

Conjunctivitis

the inflammation of the conjunctiva

Gonococcal Ophthalmia Neonatorum

the most severe form of conjunctivitis

Lacrimal Apparatus

• Consists of the lacrimal gland and a system of ducts

Lacrimal gland

- Lie superior and lateral to each eye - Exocrine tear gland producing lacrimal fluid (tears) → lacrimal canaliculi → lacrimal sac → nasolacrimal duct

Lacrimal canaliculi

• small ducts that collect excess tears in the medial angle of the eyes

Lacrimal sac

• an enlargement of the nasolacrimal duct, which opens into the nasal cavity

Tarsal Gland/ Meibomian gland

• sebaceous gland embedded in the tarsal plate of each eyelid; makes a lubricant called sebum which is discharged through tiny openings in the edges of the lids

Sty/Stye/Hordeolum

• an inflamed swelling on the edge of an eyelid, caused by bacterial infection of the gland at the base of an eyelash.
• develops from an eyelash follicle or an eyelid oil gland that becomes clogged from excess oil, debris or bacteria.
• infection of the tarsal gland

Chalazion

infection or retention cyst of a meibomian gland, showing as a beady nodule on the eyelid

Sclera

- firm, white outer connective tissue layer of the posterior five-sixths of the fibrous tunic - helps maintain eye shape, protects internal structures, & provides attachment sites for the extrinsic eye muscles
- its small portion can be seen as the "white of the eye

• Cornea

- transparent anterior sixth of the eye; structure that covers iris and pupil - permits light to enter; bends or refracts the entering light

Vascular Tunic

Middle layer

Fibrous Tunic

outermost protective layer composed of dense connective tissue

Choroid

- posterior portion of the vascular tunic, associated with the sclera
- 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 O2 and nutrients to retina

Ciliary body

- contains ciliary muscles that changes the diameter of the lens both near and distant vision

• Lens

- a flexible, biconvex, transparent disc that refract or bend light
- held in place by the suspensory ligaments, which are attached to the smooth muscles of the ciliary body.

Iris

- the colored part of the eye
- contractile structure consisting mainly of smooth muscle surrounding an opening called the pupil
- regulates the diameter of the pupil

Pupil

- central part of the iris
- controls the amount of light entering the eye through its diameter

Retina

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

Pigmented retina

keeps light from reflecting back into the eye

Sensory retina

contains photoreceptor cells, called rods and cones, which respond to light; also contains numerous interneurons

Cones

• require much more light
• responsible for color vision
• There are three types of cones, each sensitive to a different color: blue, green, or red.

Rods

• very sensitive to light • can function in dim light, but do not provide color vision • responsible for vision in low illumination (night vision)

Rhodopsin

• photosensitive pigment in rod cells • Composed of a protein opsin and a yellow pigment retinal that requires Vitamin A

Night Blindness (Nyctalopia)

characterized by difficulty seeing in dim light

retinal detachment,

separation of the sensory retina from the pigmented retina.

Macula lutea

•small yellow spot near center of the posterior retina
• contains a small central pit (fovea centralis)

Fovea centralis

• contains only cone cells
• the region with the greatest ability to discriminate fine images
• the area of sharpest vision

Optic disc / Blind spot

• white spot medial to macula
• the area where the optic nerve exits the eye and blood vessels enter.
• contains no photoreceptor cells and does not respond to light

\ Anterior chamber

• located between cornea and lens

aqueous humor

(watery fluid)

Aqueous humor

- helps maintain pressure within the eye, refracts light, and provides nutrients to the inner surface of the eye
- its presence keeps the eye inflated
- If its flow from the eye through the venous ring is blocked, the pressure in the eye increases, resulting in a condition called glaucoma

Glaucoma

- Excessive pressure build-up in aqueous humor; may destroy retina or optic nerve, resulting in blindness

Posterior chamber

• located behind anterior chamber
• also filled with aqueous humor

Vitreous chamber

filled with vitreous humor, a transparent, jellylike substance

Vitreous humor

- helps maintain pressure within the eye, holds the lens & retina in place, and refracts light
- does not circulate

Light Refraction

• Bending of light
• Light passing through a len's concave surface diverges (light rays are bent).
• Light passing through a len's convex surface converges.

Focal point

the crossing point where light rays converge
- occurs anterior to retina
- the tiny image that is focused on the retina is inverted compared to the actual object - Converging light rays cross at the focal point and are said to be focused

Accommodation

- The ability to adjust the focusing apparatus to account for changes in distance from the viewed object
- In accommodation for near vision, the ciliary muscle contracts, causing increased rounding of the lens, the pupil contracts, and the optic axes converge. These three actions constitute the accommodation reflex.
- The ability of the eye to accommodate decreases with age

Myopia

• Nearsightedness—ability to see close but not distant objects; caused when refractive power of cornea and lens is too great relative to length of eye

Hyperopia

Farsightedness—ability to see distant but not close objects; caused when cornea is too flat or lens has too little refractive power relative to length of eye

Presbyopia

• decrease in near vision, due to reduced flexibility of lens and reduction in accommodation • a normal part of aging • lens becomes less elastic • reading glasses required

Astigmatism

• irregular curvature of lens, so image is not sharply focused • glasses or contacts required to correct

Colorblindness

ya recessive x-linked disorder in which an individual cannot distinguish between certain colors

Strabismus

• one or both eyes are misdirected
• can result from weak eye muscles

Diplopia

• double vision

Glaucoma

- increased pressure in eye
- can lead to blindnes

External (Outer) Ear

• Extends from outside of head to eardrum

Auricle (Pinna)

- the fleshy part of the external ear on the outside of the head; acts as a radiator in thermoregulationexternal portion of the ear

• Tympanic membrane (Eardrum)

a thin membrane that separates the external ear from the middle ear; covers the end of the external auditory meatus to form a boundary with the middle ear; vibrates when struck by airborne sound waves, carrying the sound energy into the middle ear

Middle Ear

• Contains three auditory ossicles: malleus, incus & stapes

• Malleus (hammer)

a tiny, club-shaped bone attached to the eardrum, vibrates when soundwaves pass to it from the eardrum

Incus (anvil)

bone that connects malleus to stapes; vibrates when it receives energy from the malleus

Stapes (stirrup)

ossicle joined to the incus, from which it receives vibrations.

Auditory tube/Eustachian tube

collapsible tube running between the middle ear and the pharynx; enables air pressure to be equalized between the outside air and the middle ear cavity

Oval window

an oval opening at the head of the cochlea, connecting the middle and inner ear, through which sound vibrations of the stapes are transmitted

Round window

an opening on the medial wall of the middle ear that leads into the cochlea and is covered by the secondary tympanic membrane; also called fenestra of cochlea

Bony labyrinth (osseous labyrinth)

that contains the membranous labyrinth of the inner ear; divided into 3 regions: the cochlea, the vestibule, and the semicircular canals

cochlea

involved in hearing

vestibule & semicircular canals

involved primarily in balance

Membranous labyrinth -

- filled with endolymph and surrounded by perilymph; includes the cochlear duct, utricle, saccule, and semicircular ducts

Endolymph

clear fluid in the membranous labyrinth

Perilymph

- the fluid between the membranous and bony labyrinths

Cochlea

• a long passage/canal shaped like a snail's shell
• divided into three compartments by the vestibular & basilar membranes

Scala vestibuli

• extends from the oval window to the apex of the cochlea • filled with perilymph

Scala tympani

• extends in parallel with the scala vestibuli from the apex back to the round window
• filled with perilymph

Cochlear duct

--formed by the space between the vestibular membrane (wall of the membranous labyrinth that lines the scala vestibuli) and the basilar membrane (wall of the membranous labyrinth that lines the scala tympani) • filled with endolymph

Spiral organ/organ of Corti

• a specialized structure inside the cochlear duct
• contains specialized sensory cells called hair cells, which have hairlike microvilli, often referred to as stereocilia

Tectorial membrane

• acellular gelatinous shelf, in which hair tips are embedded
• vibrates against hair cells

Hair cells

• attached to sensory neurons that when bent produce an action potential