THE SPECIAL SENSESVictoria Frawert

Anatomy

THE SENSES

There are five general senses: Touch, sight, taste, smell, and hearing. Equilibrium is considered a special sense as well, found in the ear. Chemical Senses (Taste & Smell)

Chemoreceptors – Receptors for taste & smell that only respond to chemicals.

Excited by chemicals dissolved in saliva & airborn chemicals dissolved in nasal membranes.

Taste buds: located in oral cavity; 10,000; most in tongue papillae; each taste bud has 40-100 epithelial cells made of 3 major types.

Supporting Cells: separate and insulate Receptor Cells: deal with taste Basal cells: like stem cells, they give rise to new cells

Taste Sensations Sweet at tip of tongue Salty & sour on the sides Bitter in the back

Physiology of Taste Activation

To be tasted, first must be dissolved in saliva, diffuse into the pore and make contact with gustatory hairs which trigger neurotransmitters to elicit action potentials in these fibers.

Adapt rapidly 3-5 seconds & completely in 1-5 minutes

Taste Transduction Process in which stimulus energy is converted into a nerve

impulse due to influx of different ions

Gustatory Pathway Taste is carried in two cranial nervers

Facial: anterior 2/3rds of tongue Glossopharyngeal: posterior 1/3rd

Taste triggers reflexes in digestion such as increasing saliva & gastric juice

Influence of other sensations on taste Taste is 80% smell, when olfactory receptors are blocked food

becomes bland Thermoreceptors, mechanoreceptors, nociceptors, temperature

and texture can enhance or detract

Olfactory & Sense of Smell Structure

Detects chemicals in solution Olfactory Epithelium:

Located on roof of nasal cavity Contain olfactory receptor cells with columnar

supporting cells Covered by mucous to trap airborn molecules

Physiology In order to smell the substance must be in a gaseous state Must be water soluble to dissolve in olfactory epithelium Bind to protein receptors which open ion channels that

send action potentials to olfactory bulb Pathway

Send impulses from bulb down tract Thalmus Frontal Lobe or Hypothalmus to interpret and

elicit emotional responses to odor Imablances include anosmias (without smells) from

head injuries; unicinate fits (olfactory hallucinations)

EYE & VISION

Accessory Structures Eyebrows

Shade the eyes Prevent perspiration into eye

Eyelids Palpabrae protects eye Levator palpebrae superioris raises eyelid Eyelashes trigger blinking

Conjunctiva Mucous membrane over eyelids and anterior surface

of eyeball (white part) Vascular, when irritated eyes are blood shot

Lacrimal Apparatus Consist of gland and ducts that drain

excess secretions into nasal cavity Secretes saline solution (tears) Contains mucous, antibodies, and

lysosomes to clean eye & destroy bacteria Eye muscles

Movement is controlled by 6 muscles Four Rectus muscles: Superior, Inferior,

Lateral, Medial Two Oblique muscles: Superior, Inferior Nerve Innervation: abducens, trochlear,

oculomotor

Lens : Divides eye into anterior and posterior segments Transparent, flexible structure that can

change shape to allow focus of light on retina Avascular Becomes less elastic through life causing

focus impairment Cataract – cloudy lens due to thickening of

lens or diabetes

Structure of the Eyeball Divided into 3 tunics

Fibrous – dense avascular tissue Sclera: white part that protects, shapes, and

provides attachment for eye muscles Cornea: buldges anteriorly and allows light into eye

Vascular Choroid – highly vascular & provides nutrition Ciliary Body – encircles lense and keeps it in place Iris – contains pupil and changes in shape due to

light Sensory – contains the retina, which are

photoreceptors of rods & cones Optic Disc (blind spot) – Where optic nerve exits eye Rods – dim light Cones – bright light and color

Filled with humors to maintain shape Vitreous humor – in posterior Aqueous humor – in anterior (if undrained causes

glaucoma)

Physiology Wavelength & Color

Eyes respond to visible light spectrum Progresses from red to violet

Refraction & lenses Light travels in straight lines and blocked by

nontrasnparent objects Light reflects or bounces off a surface Reflection accounts for most of light reaching our eyes;

as light changes mediums it can bend or refract. Focus

Your lens refracts the light to your focal point which projects on your retina

Images are upside down & reversed Myopia – nearsighted Hyperopia – farsighted Astigmatism – unequal curvature of lens leading to

blur

Photoreception Photoreceptors are modified neurons

Outer segment connected to inner, inner connects to cell body which has synaptic endings.

Rods Sensitive to low light, best at night

Cones Require high light, provides color

EAR: HEARING & BALANCE Structure – three areas: Outer, middle, &

inner ear Outer Ear

Auricle or Pinna: ear composed of elastic cartilage & skin to direct sound waves to external auditory canal

External auditory meatus: Short curved tube from auricle to eardrum Lined with skin, sebaceous glands, & ceruminous

glands (secrete earwax) Tympanic membrane ( ear drum ) boundary between

outer & middle ear

Middle Ear (tympanic cavity) Small air filled mucus lined cavity Between eardrum & bony wall with two openings oval (vestibular) & round (cochlear)

window Contains pharyngotympanic (auditory tube) running from middle ear to nasopharynx

& helps equalize pressure Otitis Media – middle ear inflammation

Inner Ear Behind eye socket & contains receptor information 2 Major divisions

Bony (osseous ) labyrinth Vestibule – contains saccule and utricle which have equilibrium receptors that respond to

gravity & changes of head position Cochlea – contains the organ of corti which is the sensory organ for hearing Semicircular Canals – respond to movement of head

Membranous Labyrinth Series of sacs and ducts containing endolymph fluid to help conduct sound vibrations.

Sound & Mechanisms of Hearing Sound – a disturbance of pressure Frequency – measurement of offurrences of a

repeated event per unit of time Distance between two crests is a wavelength Frequency is expressed in hertz Range for humans is 20-20,000 Hz Amplitude or height of wave is related to intensity Loudness is measured in decibles

We can hear from .1 dB to over 120 dB Threshold for pain is 130 dB Hearing loss occurs with exposure to 90 dB Noisy restaurant is 70 dB, normal talking is 50 dB A rock concert is 120 dB. You do the math.

Transmission Sound waves move through the air, membranes, bones,

fluids to reach receptor cells in the organ of corti. Vibrations excite hair cells which send messages to

cochlear nerve and brings the impulses to the brain for processing

Imbalances of Hearing Deafness – any hearing loss

Conduction deafness When something hampers sound conduction to

fluids of inner ear Ruptures, perforated eardrum can cause problems

Sensorinerual Damage to neural structures of cochlear hair cells Can be partial or complete & generally there is

gradual loss of hearing throughout life Cells can be damaged to extremely loud noises or

prolonged exposure Can be fixed with cochlear implants

Tinnitus Ringing of ear Symptom of pathology and not disease 1st symptom of cochlear nerve degeneration Can be from inflammation or medication or trauma

Meniere’s Syndrom Affects semicircular & cochlear canals Causes vertigo, nausea, vomitting Standing erect is near impossible Caused by excess fluid, rupture or infection Mild cases can be cleared with anti motion drugs,

sometimes surgery

Equilibrium & Orientation Responds to head movement without awareness Receptors of inner ear are divided into two parts

Static Sensory receptors for static are the maculae Found in saccules and utricle Monitor position of head in space, control posture

Dynamic Receptor for dynamic are the crista ampullaris Excited by head movement but major stimuli are

rotatory These areas are at work when twirling or feeling ill on a

boat