ANAPHY SPECIAL LENSES

THE SPECIAL SENSES

FIVE SENSES

  • Vision (Sight)

  • Smell (olfaction)

  • Taste

  • Touch

  • Hearing

    • Equilibrium is also considered a special sense, found in the ear

Taste Buds

  • Taste buds are found in papillae of the tongue mucosa

  • Papillae - three types: filiform, fungiform, and circumvallate

  • Fungiform and circumvallate papillae contain taste buds

  • Approximately 10,000 taste buds - 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 Sensation

  • There are five basic taste sensations

    • Sweet - sugars, saccharin, alcohol, and some amino acids

    • Salt - metal ions

    • Sour - hydrogen ions

    • Bitter - alkaloids such as quinine and nicotine

    • Umami - elicited by the amino acid glutamate

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 by two cranial nerves

  • Facial anterior 2/3rds of tongue

  • Glossopharyngeal: posterior 1/3^rd

  • 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

Sense of Smell (Olfaction)

  • The organ of smell is the olfactory epithelium, which covers the superior nasal concha

  • Olfactory receptor cells are bipolar neurons with radiating olfactory cilia

  • Olfactory receptors are surrounded and cushioned by supporting cells
    Basal cells lie at the base of the epithelium

Olfaction

  • Olfactory epithelium

  • Detects chemicals in solution

  • Covered by mucous to trap airborne molecules

  • Physiology

  • 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

  • Imbalances include anosmia (without smells) from head injuries; unicinate fits (olfactory hallucinations)

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

Iris

  • The colored part of the eye

  • Pupil - central opening of the iris

    • Regulates the amount of light entering the eye during:

  • Close vision and bright light - pupils constrict

  • Distant vision and dim light - pupils dilate

  • Changes in emotional state - pupils dilate when the subiect matter is appealing or requires problem-solving skills

Sensory Tunic: Retina

  • A delicate two-layered membrane

  • Pigmented layer - the outer layer that absorbs light and prevents its scattering

  • Neural layer, which contains:

    • Photoreceptors that transduce light energy

    • Bipolar cells and ganglion cells

    • Amacrine and horizontal cells

  • Extraocular 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

Lacrimal Apparatus

  • Consists of the lacrimal gland and associated ducts

  • Lacrimal glands secrete tears

  • Tears

    • Contain mucus, antibodies, and lysozyme

    • Enter the eye via superolateral excretory ducts

    • Exit the eye medially via the lacrimal punctum

    • Drain into the nasolacrimal duct

Fibrous Tunic

  • Forms the outermost coat of the eye and is composed of:

    • Opaque sclera (posteriorly)

    • Clear cornea (anteriorly)

  • The sclera protects the eye and anchors extrinsic muscles

  • The cornea lets light enter the eye

Vascular Tunic (Uvea)

  • Has three regions: choroid, ciliary body, and iris

  • Choroid region

    • A dark brown membrane that forms the posterior portion of the uvea

    • Supplies blood to all eye tunics

Vascular Tunic

Ciliary Body

  • A thickened ring of tissue surrounding the lens

  • Composed of smooth muscle bundles (ciliary muscles)

  • Anchors the suspensory ligament that holds the lens in place

The Retina: Ganglion Cells and the Optic Disc

  • Ganglion cell axons:

    • Run along the inner surface of the retina

    • Leave the eye as the optic nerve

  • The optic disc:

    • Is the site where the optic nerve leaves the eye

    • Lacks photoreceptors (the blind spot)

Retinal Photoreceptors

  • Rods:

    • Respond to dim light

    • Are used for peripheral vision

  • Cones:

    • Respond to bright light

    • Have high-acuity color vision

    • Are found in the macula lutea

    • Are concentrated in the fovea centralis

Blood Supply to the Retina

  • The neural retina receives its blood supply from two sources

    • The outer third receives its blood from the choroid

    • The inner two-thirds is by the central artery and vein

Photoreception:

Functional Anatomy of Photoreceptors

  • Photoreception - process by which the eye detects light energy

  • Rods and cones contain visual pigments (photopigments)

    • Arranged in a stack of disk-like infoldings of the plasma membrane that change shape as they absorb light

Rods

  • Functional characteristics

    • Sensitive to dim light and best suited for night vision

    • Absorb all wavelengths of visible light

    • Perceived input is in gray tones only

    • Sum of visual input from many rods feeds into a single ganglion cell

    • Results in fuzzy and indistinct images

Inner Chambers and Fluids

  • The lens separates the internal eye into anterior and posterior segments

  • The posterior segment is filled with a clear gel called vitreous humor that:

    • Transmits light

    • Supports the posterior surface of the lens

    • Holds the neural retina firmly against the pigmented layer

    • Contributes to intraocular pressure

Anterior Segment

  • Composed of two chambers

    • Anterior - between the cornea and the iris

    • Posterior - between the iris and the lens

  • Aqueous humor

    • A plasma like fluid that fills the anterior segment

    • Drains via the canal of Schlemm

  • Supports, nourishes, and removes wastes

Refraction and Lenses

  • When light passes from one transparent medium to another its speed changes and it refracts (bends)

  • Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal point

  • When a convex lens forms an image, the image is upside down and reversed right to left

Cones

  • Functional characteristics.

    • Need bright light for activation (have low sensitivity)

    • Have pigments that furnish a vividly colored
      View

    • Each cone synapses with a single ganglion cell

    • Vision is detailed and has high resolution

The Ear: Hearing and Balance

  • The three parts of the ear are the inner, outer, and middle ear

  • The outer and middle ear are involved with hearing

  • The inner ear functions in both hearing and equilibrium

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)

  • A small, air-filled, mucosa-lined cavity

    • Flanked laterally by the eardrum

    • Flanked medially by the oval and round windows

  • Epitympanic recess - superior portion of the middle ear

  • Pharyngotympanic tube - connects the middle ear to the nasopharynx

    • Equalizes pressure in the middle ear cavity with the extemal air pressure

Ear Ossicles

  • The tympanic cavity contains three small bones: the malleus, incus, and stapes

    • Transmit vibratory motion of the eardrum to the oval window

    • Dampened by the tensor tympani and stapedius muscles

Inner Ear

  • Bony labyrinth

    • Tortuous channels worming their way through the temporal bone

    • Contains the vestibule, the cochlea, and the semicircular canals

    • Filled with perilymph

  • Membranous labyrinth

    • Series of membranous sacs within the bony labyrinth

    • Filled with a potassium-rich fluid