Chapter 15: The Special Senses

Dr. Runyan Unit 5 Exam

Touch

General Sense; Wide-Spread Receptors

Vision, Taste, Smell, Hearing, Equilibrium

Special Sense; Localized Receptors

Special Sensory Receptors

70% in the eye

Half of the cerebral cortex is involved in visual processing

Conjunctiva

Transparent mucous membrane that produces a lubricating mucous secretion

Lines inside of the eyelid and the white of the eyes

Lacrimal Apparatus

Lacrimal gland and ducts that drain into nasal cavity

Blinking spreads tears towards the medial commissure

Lacrimal Gland

Located in orbit above lateral end of eye

Produces tears

Lacrimal Secretion

Dilute saline solution containing mucus, antibodies, and antibacterial lysozyme

Strabismus (Cross-Eye)

Weakness of external eye muscles

Eye rotates medially or laterally

Eye may alternate focusing on objects, or only controllable eye

Sty

Inflammation of any of the smaller sebaceous glands of the eye

Pinkeye

Conjunctival infection caused by bacteria or viruses; highly contagious

Ciliary Body

Smooth muscle bundles

Ciliary Muscles: Control shape of lens

Ciliary Processes

Formation/secretion of aqueous humor

Iris

Between cornea and lens, continuous with ciliary body

Makes up the pupil

Pupil

Central opening that regulates amount of light entering eye

Close vision and bright light; pupil constricts; parasympathetic control

Distant vision and dim light; pupil dilates; sympathetic control

Retina

Photoreceptors —> Bipolar Cells —> Ganglion Cells

Ganglion cell axons exit the eye as optic nerve

Optic Disc

Site where optic nerve leaves eye

Lacks photoreceptors; referred to as blind spot

Rods

Dim light

No color vision or sharp images

Cones

Bright light

High-resolution, color vision

Macula Lutea

Area of retina that contains mostly cones; central vision

Fovea Centralis

Area in center of macula lutea containing only cone photoreceptors

High resolution, central, color vision

Region with best visual acuity

Lens

Changes shape to focus light on retina

Dividing line for anterior and posterior segment

Posterior Segment

Contains vitreous humor

Vitreous Humor

Transmits light

Supports posterior surface of lens

Contributes to intraocular pressure

Anterior Segment

Contains aqueous humor

Aqueous Humor

Plasma fluid continuously formed

Glaucoma

Drainage of aqueous humor is blocked

Increase in pressure within eye compressing retina and optic nerve

Leads to blindness

Cataract

Clouding of the lens

Macular Degeneration

Degeneration of macula

Loss of central vision

Uvetis

Inflammation of the uvea

The vascular layer

Cornea

Produces majority of the refractory power

Distant Vision

Ciliary muscles relaxed

Ligaments pulled tight

Lens is flat

Near Vision

Ciliary muscle contracted

Ligaments are relaxed

Lens is round

Rods

High sensitivity

Converging pathways, causing fuzzy, indistinct images

Contains a single pigment; perceived in gray tones only

Cones

Low sensitivity; require bright light for activation

Nonconverging pathways

High resolution vision

Retinal

Light-absorbing molecule that combines with opsins to form visual pigments

Functions in the visual pathway

Synthesized from vitamin A

Dark

Photo receptors constantly releasing inhibitory neurotransmitter

Bipolar cells and ganglion cells are inhibited

No neurotransmitter released

Light

Photoreceptors stop releasing neurotransmitter

Bipolar cells and ganglion cells are activated

Neurotransmitter released

Smell (olfaction), Taste (gustation)

Chemoreceptors

Responds to dissolved chemicals

Olfactory Neurons

Contains stem cells give rise to new neurons every 30-60 days

Internal Ear

Hearing and equilibrium

Responds to mechanical stimuli

Pharyngotympanic Tube

Connects middle ear to nasopharynx

Equalizes pressure in middle ear cavity with external air pressure

Endolymph

An extracellular fluid that is high in potassium

Vestibule

Saccule & Utricle

Head position relative to gravity; linear acceleration

Macula

Saccule

Continuous with cochlear duct

Utricle

Continuous with semicircular canals

Semicircular Canals

Semicircular ducts

Rotational angular acceleration

Crista ampullaris

Inner ear, vestibular apparatus, semicircular canals, vestiubule

Location of equilibrium receptors

Cochlea

Cochlear duct

Hearing

Spiral organ

Ampulla

Enlarged area of ducts housing equilibrium receptor region called crista ampullaris

Pitch

Perception of different frequencies

Higher the frequency, the higher the _____

Inner Hair Cells

Relays signals for hearing of the brain

Bending Upwards

Bending of stereocilia toward tallest ones pull on tip links; opening ion channels

Potassium & calcium flow into cell

Causes receptor potential leading to release of glutamate

Bending Downwards

Bending of stereocilia toward shorter ones causes tip links to relax

Ion channels close, leading to repolarization; possibly hyperpolarization

Outer Hair Cells

Does not relay signals for hearing of brain

Increase fine-tuning responsiveness of inner hair cells

Amplifies motion of basilar membrane

Protects inner hair cells from loud noises

Perception of Pitch

Impulses from hair cells in different positions

Interpreted by brain as specific pitches

Detection of Loudness

Determined by brain as increase in number of action potentials

Hair cells will experience larger deflections

Maculae

Sensory receptor organs that monitor static equilibrium

One is located on each saccule wall and utricle wall

Responds to linear acceleration forces

Cristae Ampullaris

Receptor for rotational acceleration

Rotational angular movements

Conduction Deafness

Blocked sound conduction to fluids of internal ear

Impacted earwax, perforated eardrum, otitis media, otosclerosis of ossicles

Causes of deafness

Sensorineural Deafness

Damage to neural structures at any point from cochlear hair cells to auditory cortical cells

Cause: Gradual hair cell loss

Mechanically-Gated Ion Channels

Channel responsible for initial changes in the membrane potential of the hair cells of the inner hear