The Peripheral Nervous System · 2020-03-24 · Middle Ear Tympanic cavity–an air-filled cavity...
Transcript of The Peripheral Nervous System · 2020-03-24 · Middle Ear Tympanic cavity–an air-filled cavity...
THE SENSES
The Peripheral Nervous System:
Types of Sensory Receptors:
Chemoreceptors
Nocireceptors
Thermoreceptors
Mechanoreceptors
Photoreceptors
Sensation
Feeling that occurs when sensory messages
have been interpreted by the brain.
Projection
Phenomenon allowing us to know the source
of sensation
Occurs when the cerebral cortex has
interpreted sensory input
Sensory adaptation
Occurs when a receptor becomes “used to” a stimulus
and no longer notices the stimulus.
Example:
A person entering a room with a horrible odor smells
the odor at first, but the longer they are in the room,
the less noticeable the odor becomes.
The chemoreceptors of their nose (olfaction/smell)
have adapted.
The Senses
Touch and pressure
Temperature
Pain
Special senses
Smell
Taste
Hearing
Equilibrium
Sight
Touch and Pressure Senses
Controlled by sensory nerve fibers in the epithelium
Uses:
Meissner’s corpuscles in the hairless skin for light
touch
Pacinian corpuscles in deeper subcutaneous skin
layers for deep touch and heavy pressures
Temperature Senses
Adapt quickly
Two types:
Heat receptors
Detect temperatures between 77◦F (25
◦C) and 113
◦F (45
◦C)
Cold receptors
Detect temperatures between 50◦F (10
◦C) and 68
◦F (20
◦C)
Temperatures above 113◦F and below 50
◦F are not detectable by
these receptors and are considered pain because they would cause tissue damage.
Pain Sense
Serves as a protective function
Is stimulated by chemicals released from damaged tissues
Awareness occurs when the hypothalamus gets the impulse, the cerebral cortex judges intensity, locates source, and causes the emotional or motor response.
Referred pain is the transfer of pain from a visceral organ to some other body part through nerve pathways that conduct impulses from both parts.
Heart attacks are felt in the left arm and shoulder, the chin, etc. as well as the left chest where the heart is actually located because all of those locations share a common sensory nerve.
Pain Fibers
Two main types:
Acute pain fibers
• Myelinated neurons
• Conduct quickly
• Stop when stimulus discontinues
Chronic pain fibers
• Unmyelinated neurons
• Conduct slowly
• Responsible for dull aching pains that are hard to pinpoint the exact
location.
Special Senses
Smell picked up by the olfactory nerve
a chemoreceptor
called olfaction.
Taste picked up by the tastebuds, chemoreceptors located on the tongue
Primary tastes are sour, sweet, salty, bitter, and umami
Minor tastes: alkaline and metallic.
Hearing picked up by the vestibulocochlear nerve; a mechanoreceptor
Equilibrium picked up by the vestibulocochlear nerve.
Sight controlled by the photoreceptors of the eye and the optic nerve.
The Ear
Has three divisions:
1. Outer Ear
2. Middle Ear
3. Inner Ear
Outer Ear
Channels sound to the middle ear
Two structures
Auricle/pinna—outer flap; catches
sound waves
External auditory meatus– (ear
canal)
Middle Ear
Tympanic cavity– an air-filled cavity
Tympanic membrane—eardrum; vibrated sound
waves that enter the ear
Ossicles—tiny bones that transmit sound from the
eardrum to the oval window
Malleus—hammer
Incus—anvil
Stapes--stirrups
Eustacian tube—connects the middle ear to the throat
to equalize air pressure on both sides of the eardrum
Inner Ear
Semicircular canals—3 fluid-filled hoops at right
angles to each other; contain hair cells that aid in
equilibrium
Cochlea—snail-shell shaped, bony organ that
contains the oval window, round window, and the
organ of corti.
Oval window—struck by the stapes; vibrates fluid
inside the inner ear and stimulates hearing receptors
Organ of Corti—hearing receptors
Vestibule—contains the utricle and saccule; used in
static equilibrium
Hearing and Equilibrium
Equilibrium Dynamic equilibrium
Determined by fluid movement in the semi-circular canals
Deals with orientation in regards to a horizontal plane
Static equilibrium
Determined by hairs in the vestibule of the inner ear
Deals with orientation in relation to the ground
Sound Travels as waves (compressions and rarefactions)
Speed is 346 m/sec or 775 mi/hr
Characteristics:
Loudness—amplitude, decibels
Pitch –waves/sec; hertz (Hz)
Quality—smoothness of a wave
The Eye
Accessory structures
Eyelid
Conjunctiva
Lacrimal apparatus
Lacrimal gland
Lacrimal duct
Tears--lysozyme
Eyebrows
Eyelashes
The Eye -- continued
Structures of the eye
Cornea
Sclera
Optic Nerve
Lens
Pupil
Iris
Retina
Rods
Cones
Vision
Occurs due to the physical properties of light
Light travels at a speed of 300,000 km/sec
Refraction
Bending of light as it passes through a more
dense medium
Depends on the curvature of the medium
Concave Lenses—diverge the light
Convex Lenses—converge light
OTHER IMPORTANT
TERMS AND CONCEPTS
RELATED TO VISION AND
SIGHT
Convergence Movement of the eyes inward to adjust focus on the retina
Crossed eyes if objects are brought too close to the eyes
Accomodation Ability of the lens to achieve sharp focus
Field of Vision What you can see without moving the eyes
Peripheral Vision Wide view
Monocular Vision Vision with one eye
Binocular vision Ability to focus what is seen with two eyes
Depth perception Stereoscopic vision
Seeing in 3 dimensions—lateral, vertical, and horizontal
Dark and Light Adaptation
Dark Adaptation
The ability to distinguish objects when moving from light to dark
Conversion speed equals the speed at which rhodopsin is reformed from opsin
and retinene after being struck by light
Purkinje Shift—
Shift from cone reception to rod reception at dusk
Night Blindness
Slow return to dark adaptation due to lack of vitamin A
Light Adaptation
Adaption moving from dark to light
Rod reception changes to cone reception
Color Vision
Determined by the cones in your eyes
What we can see as the visible spectrum of light (ROY G. BIV)
Longer wavelengths than visible are infrared (heat); shorter ones are ultraviolet
or UV
Afterimage
Afterimage is the carryover of a visual impression
Two types:
Positive
Seen the same as the original stimulus
Negative
Seen in a complimentary color of the orginal
stimulus
Due to cone fatigue
Visual Acuity
Visual acuity is the sharpness or degree of detail
Cones are responsible
Influence by brightness, size, color, and retinal area
stimulated
Measured with the Snellen Eye Chart (“E” chart)
20/20 vision—means the eye can see from 20 feet what a normal eye
can see from 20 feet
20/10—means the eye can see from 20 feet what the normal eye
should see from 10 feet
20/100-means the eye can see from 20 feet what a normal eye can
see from 100 feet.
Ear disorders and clinical terms
Deafness
Can be complete or partial
Sensory—disturbed inner ear circulation or fluid pressure and aging are
causes; rarely leads to total deafness
Conductive
Due to blockage, perforated eardrum, middle ear infection, or ossicle
disease
Usually can be corrected by cleaning the ear , surgical reconstruction,
or hearing aids
Otosclerosis
hereditary cause of partial deafness;
progressive; ossicles lose ability to move
treated with prosthetic stapes replacement
Tympanoplasty
Surgical reconstruction of the middle ear bones
Tinnitus
Head noise or ringing in the ears
Vertigo
Dizziness due to changes in inner ear circulation
Meniere’s disease
Dizziness due to increased inner ear pressure
Otitis media
Middle ear inflammation
Eye Disorders
Myopia
Nearsightedness
Can’t see distant objects clearly
Cornea refracts too much light or eyeball is too long
Corrected by a concave lens
Hypermyopia
Farsightedness
Distant objects seen more clearly
Light rays focus behind retina
Presbyopia
Farsightedness due to age
Lens loses elasticity
Corrected by a convex lens
Astigmatism
A cornea or lens with an imperfect curvature
Symptoms include eyestrain and headache
Corrected by glasses or contacts
Cataract
Clouding of the lens
Usually in elderly
Treated by lens removal , contacts/glasses, or prosthetic
lens implants
Glaucoma
Depression of the optic disc due to an increase in anterior chamber fluid
Causes a restricted field of vision or blindness
Treated by drugs or surgery that cause aqueous humor to drain
Conjuctivitis
Inflamed or irritated conjunctiva membrane of the eye
Also called Pink Eye
If bacterial or viral it is highly contagious
Noncontagious forms can be caused by pollen, smoke, dust, wind, air pollution
Treated by antibiotics and eyedrops
Iritis
Inflammation of the iris
Uveitis
Inflammation of the uvea
Retinoblastoma
Tumor of the retina
Keratitis
Inflammation of the cornea
Color Blindness
Hereditary inablility to distinguish colors
Carried on the X chromosome
Two Kinds:
Dichromatic
Red/green –common form
Blue/yellow--rare
Monochromatic
Extremely rare
Black and white vision
Colorblindness Color Wheel
The outer ring of colors
is the normal color
wheel.
The inner rings show
how colorblind
individuals of various
degrees see the same
colors.
Ishihara’s Color Plates used to diagnose
types and degrees of colorblindness
How a stoplight is perceived if you
have red-green colorblindness
Spherical Aberrations
Results in a series of focal points
Causes a fuzzy perimeter image
Eye corrects by decreasing pupil size
Chromatic Aberrations
Causes a “halo” effect of rainbow colors surrounding an
object