Anatomy and Physiology I, Final Exam, Part 2, UWEC

Hearing

a response to vibrating air molecules

Equilibrium

the sense of motion, body orientation, and balance/coordination, balance, and orientation in three-dimensional space

Senses within the ear

Both senses reside in the inner ear, a maze of fluid-filled passages and sensory cells

Fluid is set in motion and the sensory cells convert this motion into an informative pattern of action potentials

Sound

Any audible vibration of molecules

–A vibrating object (e.g., tuning fork) __**pushes**__ on air molecules

–These, in turn, push on other air molecules

Air molecules hitting eardrum cause it to vibrate

Pitch

**Our sense of whether a sound is “high” or “low”**

–Determined by vibration frequency: hertz (Hz) or cycles/second

–Human hearing range is 20 to 20,000 Hz

•Infrasonic frequencies below 20 Hz, Ultrasonic frequencies above 20,000 Hz

–Speech is 1,500 to 5,000 Hz, where hearing is most sensitive

–Most hearing loss with age is in range of 250 to 2,050 Hz

Loudness

The perception of sound energy, intensity, or amplitude of the vibration

–Expressed in __**decibels**__ (dB)

Prolonged exposure to sounds > 90 dB can cause damage

Auricle (pinna)

Directs sound down the auditory canal

Shaped and supported by elastic cartilage

Outer Ear

A funnel for conducting vibrations to the tympanic membrane (eardrum)

Middle Ear

•located in the air-filled tympanic cavity in temporal bone

–__**Tympanic membrane**__ (eardrum)

Tympanic cavity that contains auditory ossicles

Auditory canal (external acoustic meatus)

passage leading through temporal bone to tympanic membrane Guard hairs protect outer end of canal

Cerumen

Earwax, mixture of secretions of ceruminous and sebaceous glands and dead skin cells

Pharyngotympanic tube

tube that connects middle-ear to nasopharynx Equalizes air pressure on both sides of tympanic membrane

Normally closed, but swallowing or yawning open it

Allows throat infections to spread to middle ear.

Auditory ossicles

HAs the Malleus, incus, and stapes

Malleus

has long handle attached to inner surface of tympanic membrane

Incus

articulates with malleus and stapes

Stapes

shaped like a stirrup; footplate rests on oval window—where inner ear begins

Otis media

middle-ear infection, is common in children

Auditory tube is short and horizontal Infections easily spread from throat to tympanic cavity and mastoid air cells

Fluid accumulates in tympanic cavity producing pressure, pain, and impaired hearing, Can spread, leading to meningitis, Can cause fusion of ear ossicles and hearing loss

Bony labyrinth

Passageways in temporal bone

Membranous labyrinth—fleshy tubes lining bony labyrinth

–Filled with __**endolymph**__: similar to intracellular fluid

–Floating in __**perilymph**__: similar to cerebrospinal fluid

Cochlea

**Organ of Hearing**

Winds 2.5 coils around a screw-like axis of spongy bone, the modiolus

Threads of the screw form a spiral platform that supports the fleshy tube of the cochlea

Scala vestibuli

Within the cochlea, superior chamber Filled with perilymph Begins at oval window and spirals to apex

Scala tympani

Within the cochlea, inferior chamber Filled with perilymph Begins at apex and ends at round window Secondary tympanic membrane: covers round window

Scala media

(cochlear duct): middle chamber Filled with endolymph

Contains spiral organ—organ of Corti: acoustic organ that converts vibrations into nerve impulses

Spiral organ

organ of Corti: acoustic organ that converts vibrations into nerve impulses

• has epithelium composed of hair cells and supporting cells

• Hair cells have long, stiff microvilli called stereocilia on apical surface

  • Gelatinous tectorial membrane rests on top of stereocilia

Inner hair cells

single row of about 3,500 cells Provides for hearing, volume, decibel, pitch, etc, and whether or not there is a noise.

Outer hair cells

three rows of about 20,000 notch/trangle-shaped cells

Adjusts response of cochlea to different frequencies Increases precision

Tympanic membrane

–Has 18 times area of oval window

–Ossicles concentrate the energy of the vibrating membrane on an area 1/18 that size

–Ossicles create a greater force per unit area at the oval window and overcome the inertia of the perilymph

–Ossicles and their muscles have a protective function

•Lessen the transfer of energy to the inner ear

Tectorial membrane

Sterocilia of outer hair cells are bathed in high K+ fluid, the endolymph

Create electrochemical gradient, outside of cell is +80mV inside around -40mV

Tip is embedded in _______ ___________

Tip link

Stretchy protein filament that connects ion channel of one stereocilium to the sidewall of the next

Stimulation of Chochlear hair cells

Stretchy protein filament (tip link) connects ion channel of one stereocilium to the sidewall of the next

Tallest stereocilium is bent when basilar membrane rises up toward tectorial membrane

Pulls on tip links and opens ion channels

K+ flows in —depolarization causes release of neurotransmitter

Stimulates sensory dendrites and generates action potential in the cochlear nerve

Sensory coding

•Variations in loudness (amplitude) cause variations in the intensity of cochlear vibrations

–Soft sound produces relatively slight up-and-down motion of the basilar membrane

–Louder sounds make the basilar membrane vibrate more vigorously

•Triggers higher frequency of action potentials, Brain interprets this as louder sound

Pitch depends on

•which part of __**BASILAR MEMBRANES**__ vibrates

–At basal end, membrane attached, narrow and stiff

Brain interprets signals as high-pitched

–At distal end, 5 times wider and more flexible

Brain interprets signals as low-pitched

Deafness

hearing loss

Conductive deafness

conditions interfere with transmission of vibrations to inner ear

Damaged tympanic membrane, otitis media, blockage of auditory canal, and otosclerosis

Otosclerosis

fusion of auditory ossicles that prevents their free vibration

Sensorineural (nerve) Deafness

death of hair cells or any nervous system elements concerned with hearing Factory workers, musicians, construction workers

Vestibular apparatus

• constitutes receptors for equilibrium​

• Three semicircular ducts​

  • Detect only angular acceleration (dynamic equilibrium)​

• Two chambers​, Anterior saccule and posterior utricle​

  • Responsible for static equilibrium and linear acceleration​

Static equilibrium

the perception of the orientation of the head when the body is stationary

Dynamic equilibrium

perception of motion or acceleration ​

Linear acceleration—change in velocity in a straight line (elevator)​

Angular acceleration—change in rate of rotation (car turns a corner)​

Macula

2 by 3 mm patch of hair cells and supporting cells in the saccule and utricle​

Otoliths

calcium carbonate–protein granules that add to the weight and inertia and enhance the sense of gravity and motion​

Kinocilium

Each hair cell has 40 to 70 stereocilia and one true cilium, embedded in a gelatinous otolithic membrane​

Macula sacculi

is nearly vertical on the wall of saccule, responds to vertical acceleration and deceleration

Semicircular ducts

3 ducts that detect rotary movement and are perpendicular to eachother, and are filled with endolymph and opens up as a dilated sac (ampulla) next to the utricle​

Crista ampullaris

Mound that consists of hair cells with stereocilia and a kinocilium buried​ in a mound of gelatinous membrane called the cupula​ (one in each duct), whin an ampulla.

Light

• visible electromagnetic radiation​

• Human vision: limited to wavelengths of light from **400 (blue) to 700nm (red)**​

• Light must cause a photochemical reaction to produce a nerve signal​

Vision (sight)

perception of objects in the environment by means of light they emit or reflect​

Ultraviolet radiation

< 400 nm; has too much energy and destroys macromolecules​

Infrared radiation

> 700 nm; too little energy to cause photochemical reaction, but does warm the tissues​

Optical components

transparent elements that admit light, refract light rays, and focus images on retina: cornea, aqueous humor, lens, vitreous body​

Aqueous humor

Serous fluid secreted by ciliary body into posterior chamber—posterior to cornea, anterior to lens​ Reabsorbed by scleral venous sinus at same rate it is secreted​

Cornea

transparent anterior cover​ of the eye

Lens

Lens fibers—flattened, tightly compressed, transparent cells that form lens​

Suspended by suspensory ligaments from ciliary body​

Changes shape to help focus light

Rounded with no tension or flattened with pull of suspensory ligaments

Vitreous body (humor)

• fills vitreous chamber (posterior segment)​

• Jelly fills space between lens and retina

Fovea centralis

pit in center of macula lutea​, higher concentration of cones

Macula lutea

patch of cells on visual axis of eye, yellow patch, contains lots of cones/photoreceptors

Retina

Attached to eye only at optic disc (posterior exit of optic nerve) and ora serrata (anterior edge of retina)​

Pressed against rear of eyeball by vitreous humor​

If detached, causes blurry areas of vision and can lead to blindness

Optic Disc

Blind spot, Optic nerve exits retina and there are **no receptors** there 

Visual Filling

Brain fills in green bar across blind spot area​

Brain ignores unavailable information until saccades (fast eye movements) redirect gaze​

Pupillary constrictor

• smooth muscle encircling pupil​

• Parasympathetic stimulation narrows pupil​

Pupillary dilator

• spoke-like myoepithelial cells​

• Sympathetic stimulation widens pupil​

Pupillary constriction and dilation occurs:

When light intensity changes​ When gaze shifts between distant and nearby objects​

Photopupillary reflex

• pupillary constriction in response to light​

• Mediated by autonomic reflex arc​

• Brighter light signaled to pretectal region of midbrain​

• Excites parasympathetic fibers in oculomotor nerve that travels to ciliary ganglion in orbit​

• Postganglionic parasympathetic fibers stimulate pupillary constrictor​

Refraction

• the bending of light rays​

• Speed of light is 300,000 km/s in a vacuum, but slower in air, water, glass, or other media​

Refractive index

• a measure of how much it retards light rays relative to air​

• Angle of incidence at 90° light slows but does not change course​

• Any other angle, light rays change direction (are refracted)​

• The greater the refractive index and the greater the angle of incidence, the more refraction​

Cornea refracts light ___ than lens does

• More

• Lens merely fine-tunes image​

• Lens becomes rounder to increase refraction for near vision

Emmetropia

• Default state in which eye is relaxed and focused on an object more than 6 m (20 ft) away​

• Light rays coming from that object are essentially parallel​

• Rays focused on retina without effort​

• Light rays coming from a closer object are too divergent to be focused without effort​

Convergence of eyes

Eyes orient their visual axis toward object

Constriction of pupil

Blocks peripheral light rays and reduces spherical aberration (blurry edges)​

Accomodation of lens

change in the curvature of the lens that enables you to focus on nearby objects​

Ciliary muscle contracts, suspensory ligaments slacken, and lens takes more convex (thicker) shape​

Light refracted more strongly and focused onto retina​

Near point of vision

closest an object can be and still come into focus (lengthens with age)​

Pigment epithelium

• most posterior part of retina​

• Absorbs stray light so visual image is not degraded​

Light absorbing cells

* Rods and cones derive from same stem cells as ependymal cells of brain​

Rod cells

• (night, or scotopic, vision or monochromatic vision)​

• Uses visual pigment rhodopsin ​

Cone cells

• (color, photopic, or day vision)​

• Outer segment tapers to a point​, contain photopsin (iodopsin)​ Contains different amino acid sequences that determine wavelengths of light absorbed​

Histology of retina

• Pigment epithelium​

• Rod and cone cells​

• Bipolar cells​

  • Rods and cones synapse on bipolar cells

  • Bipolar cells synapse on ganglion cells​

Ganglion cells

• Single layer of large neurons near vitreous​, initiate action potentials, Axons form optic nerve​

• Some absorb light with pigment melanopsin and transmit signals to brainstem​

• Detect light intensity/UV radiation for pupil control and circadian rhythms; do not contribute to visual image​

• the only retinal cells that produce action potentials​

Light changes in rhodopsin

In dark, retinal is bent (cis-retinal) and retinal and opsin are together​

In light, retinal molecule straightens (trans-retinal), and retinal dissociates from opsin (bleaching)​

Generating an optic nerve signal

When rhodopsin has a molecule called retinal, and when is ready to receive light it is bent, and when it gets the light it straightens out, and this begins an action potential that allows us to see light. Cones function similar, but regenerate potopsin in 90 seconds.

Glutamate

Rods release _______ when in the dark, an inhibitory transmittor, lowering the threshold of an action potential.

Bipolar cells

are sensitive to these on and off pulses of glutamate secretion​

Some are inhibited by glutamate and excited when secretion stops​

These cells excited by rising light intensities​

Duplicity thpoery of vision

• explains why we have both rods and cones​

• A single type of receptor cannot produce both high sensitivity and high resolution​

• It takes one type of cell and neural circuit for sensitive night vision​

  • It takes a different cell type and neuronal circuit for high-resolution daytime vision

Extensive neuronal convergence

600 rods converge on bipolar cell

many bipolar cells converge on each ganlion cell

Results in high degree of spatial summation, but produces a coarse image/low resolution

Fovea centralis

• contains only 4,000 tiny cone cells (no rods)​

• No neuronal convergence​, each cone has a ganglion

• Each foveal cone cell has “private line to brain”​

• Can’t look directly at things in low-light

• High resolution color vision

mixture

• Color perception based on ____________ of nerve signals representing cones of different absorption peaks​

• Example: old tvs that only had red green or blue pixels.

Stereoscopic vision

• depth perception —ability to judge distance to objects​

• Requires two eyes with overlapping visual fields which allows each eye to look at the same object from different angles​

Fixation point

• point in space on which the eyes are focused​

• Looking at object within 100 feet, each eye views from slightly different angle​

• Provides brain with information used to judge position of objects relative to fixation point​

Senescence of Vision

• Loss of flexibility of lenses (presbyopia)​

• Cataracts (cloudiness of lenses) becomes common​

• Night vision is impaired due to fewer receptors, vitreous body less transparent, pupil dilators atrophy, and enzymatic reactions become slower​

• Glaucoma risks increase

Senescence of Hearing

• Tympanic membrane and ossicle joints stiffen​

• Hair cells and auditory nerve fibers die​

• Death of vestibular neurons results in dizziness​

Gap junctions

Pores in cell membrane allow signaling molecules, nutrients, and electrolytes to move from cell to cell

Neruotransmitters

Released from neurons to travel across synaptic cleft to second cell

Hormones

Chemical messengers that travel in the bloodstream to other tissues and organs

Paracrines

Secreted into tissue fluids to affect nearby cells​ (Helpful for infections, not in other parts of the body)

Endocrine system

glands, tissues, and cells that secrete hormones

Endocrinology

the study of this system and the diagnosis and treatment of its disorders

Endocrine glands

organs that are traditional sources of hormones

• No ducts ​

• Contain dense, fenestrated capillary networks which allow easy uptake of hormones into bloodstream​

• “Internal secretions”​

• Intracellular effects such as altering target cell metabolism​

Exocrine glands

• Have ducts; carry secretion to an epithelial surface or the mucosa of the digestive tract: “external secretions”​

• Extracellular effects (food digestion)​

Liver

The cells of this organ defy rigid classification- releases hormones, releases bile into ducts, releases albumin and blood-clotting factors into blood (not hormones)​

Chemicals that function as hormones and neurotransmitters

Norepinephrine, dopamine, and antidiuretic hormone​

Norepinephrine and glucagon

Neuroendocrine cells that both cause **glycogen hydrolysis** in liver​.

Target organs/cells

* Those organs or cells that have receptors for a hormone and can respond to it​
* Some target cells possess enzymes that convert a circulating hormone to its more active form​