Lecture 7 special sense

Principles of Human Anatomy and Physiology, 11e 1

Chapter 17

The Special Senses

Lecture OutlineSmell, taste, vision, hearing and equilibrium


Chemical Senses

• Interaction of molecules with receptor cells

• Olfaction (smell) and gustation (taste)

• Both project to cerebral cortex & limbic system

– evokes strong emotional reactions


Olfactory Epithelium

• The receptors for olfaction, which are bipolar neurons, are in the nasal epithelium in the superior portion of the nasal cavity.

• They are first-order neurons of the olfactory pathway.

• Supporting cells are epithelial cells of the mucous membrane lining the nose.

• Basal stem cells produce new olfactory receptors.


Cells of the Olfactory Membrane• Olfactory receptors

– bipolar neurons with cilia or olfactory hairs

• Supporting cells

– columnar epithelium

• Basal cells = stem cells

– replace receptors monthly

• Olfactory glands

– produce mucus


Gustatory Sensation: Taste

• Taste is a chemical sense.

– To be detected, molecules must be dissolved.

– Taste stimuli classes include sour, sweet, bitter, and salty.

• 10,000 taste buds found on tongue, soft palate & larynx

• 3 cell types: supporting, receptor & basal cells


Physiology of Taste

• Receptor potentials developed in gustatory hairs cause the release of neurotransmitter that gives rise to nerve impulses.

• Mechanism

– dissolved substance contacts gustatory hairs

– receptor potential results in neurotransmitter release


VISION Accessory Structures of Eye - Overview

• More than half the sensory receptors in the human body are located in the eyes.

• A large part of the cerebral cortex is devoted to processing visual information.

• Eyelids or palpebrae

– protect & lubricate

– epidermis, dermis, CT, orbicularis oculi m., tarsal plate, tarsal glands & conjunctiva

• Tarsal glands

– oily secretions

• Conjunctiva

– palpebral & bulbar

– stops at corneal edge


Extraocular Muscles

• Six muscles that insert on the exterior surface of the eyeball


Tunics (Layers) of Eyeball

• The eye is constructed of three layers.

– Fibrous Tunic(outer layer)

– Vascular Tunic (middle layer)

– Nervous Tunic(inner layer)


Vascular Tunic -- Muscles of the Iris

• Constrictor pupillae (circular) are innervated by parasympathetic fibers while Dilator pupillae (radial) are innervated by sympathetic fibers.

• Response varies with different levels of light


Photoreceptors

• shapes of their outer segments differ

• Rods

– specialized for black-and-white vision in dim light

– allow us to discriminate between different shades of dark and light

– permit us to see shapes and movement.

• Cones

– specialized for color vision and sharpness of vision (high visual acuity) in bright light

– most densely concentrated in the central fovea, a small depression in the center of the macula lutea.


Photoreceptors

• The macula lutea is in the exact center of the posterior portion of the retina, corresponding to the visual axis of the eye.

– The fovea is the area of sharpest vision because of the high concentration of cones.

– Rods are absent from the fovea and macula and increase in density toward the periphery of the retina.


Layers of Retina

• Pigmented epithelium

– nonvisual portion

– absorbs stray light & helps keep image clear

• 3 layers of neurons (outgrowth of brain)

– photoreceptor layer

– bipolar neuron layer

– ganglion neuron layer

• 2 other cell types (modify the signal)

– horizontal cells

– amacrine cells


Rods & Cones--Photoreceptors• Rods----rod shaped

– shades of gray in dim light

– 120 million rod cells

– shapes & movements

– distributed along periphery

• Cones----cone shaped

– sharp, color vision

– 6 million

– fovea of macula lutea

• densely packed region

• at exact visual axis of eye

• 2nd cells do not cover cones

• sharpest resolution (acuity)


Pathway of Nerve Signal in Retina

• Light penetrates retina

• Rods & cones transduce light into action potentials

• Rods & cones excite bipolar cells

• Bipolars excite ganglion cells

• Axons of ganglion cells form optic nerve leaving the eyeball (blind spot)

• To thalamus & then the primary visual cortex


Photoreceptors

• Named for shape of outer segment

• Receptors transduce light energy into a receptor potential in outer segment

• Photopigment is integral membrane protein of outer segment membrane

– photopigment membrane is folded into “discs” & replaced at a very rapid rate


process of image formation on the retina.

• 1) Refraction:

• bending of light as medium changes to focus light into central fovea

• 2) Accommodation of lens for near/distance vision:

• shape of lens changed by ciliary muscle to make light focus on retina

• 3) Constriction of pupil:

• ANS reflex to prevent scattering of light through edges of lens

• 4) Convergence of eyes:

• to focus both eyes on same object and provide binocular (3D) vision

• Images are focused on the retina upside‑down and mirror‑image, and the brain then translates this information.


Anatomy of the Ear Region


HEARING AND EQUILIBRIUM - Overview

• The external (outer) ear collects sound waves.

• The middle ear (tympanic cavity) is a small, air-filled cavity in the temporal bone that contains auditory ossicles (middle ear bones, the malleus, incus, and stapes), the oval window, and the round window.

• The internal (inner) ear is also called the labyrinth because of its complicated series of canals.


Anatomy of the Ear Region


External Ear• The external (outer) ear collects

sound waves and passes them

inwards

• Structures

– auricle or pinna

– external auditory canal

– tympanic membrane or eardrum


Middle Ear Cavity


Middle Ear Cavity

• Air filled cavity in the temporal bone

• Separated from external ear by eardrum and from internal ear by oval & round window

• 3 ear ossicles connected by synovial joints– malleus attached to eardrum, incus & stapes attached by foot

plate to membrane of oval window– stapedius and tensor tympani muscles attach to ossicles

• Auditory tube leads to nasopharynx– helps to equalize pressure on both sides of eardrum

• Connection to mastoid bone =mastoiditis


Inner Ear---Bony Labyrinth

• The bony labyrinth is a series of cavities in the petrous portion of the temporal bone.

• It can be divided into three areas named on the basis of shape: the semicircular canals and vestibule, both of which contain receptors for equilibrium, and the cochlea, which contains receptors for hearing.


Cranial nerves of the Ear Region


Overview of Physiology of Hearing


Physiology of Hearing - Overview

• Auricle collects sound waves

• Eardrum vibrates

– slow vibration in response to low-pitched sounds

– rapid vibration in response to high-pitched sounds

• Ossicles vibrate since malleus is attached to the eardrum

• Stapes pushes on oval window producing fluid pressure waves in scala vestibuli & tympani

• Pressure fluctuations inside cochlear duct move the hair cells against the tectorial membrane

• Microvilli are bent producing receptor potentials


Physiology of Hearing

• The auricle directs sound waves into the external auditory canal.

• Sound waves strike the tympanic membrane, causing it to vibrate back and forth.

• The vibration conducts from the tympanic membrane through the ossicles (through the malleus to the incus and then to the stapes).

• The stapes moves back and forth, pushing the membrane of the oval window in and out.


Physiology of Hearing - Review

• The movement of the oval window sets up fluid pressure waves in the perilymph of the cochlea (scala vestibuli).

• Pressure waves in the scala vestibuli are transmitted to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear.

• As the pressure waves deform the walls of the scala vestibuli and scala tympani, they push the vestibular membrane back and forth and increase and decrease the pressure of the endolymph inside the cochlear duct.


Physiology of Hearing - Review

• The pressure fluctuations of the endolymph move the basilar membrane slightly, moving the hair cells of the spiral organ against the tectorial membrane; the bending of the hairs produces receptor potentials that lead to the generation of nerve impulses in cochlear nerve fibers.

• Pressure changes in the scala tympani cause the round window to bulge outward into the middle ear.


Physiology of Equilibrium (Balance)

• Static equilibrium

– maintain the position of the body (head) relative to the force of gravity

– macula receptors within saccule & utricle

• Dynamic equilibrium

– maintain body position (head) during sudden movement of any type--rotation, deceleration or acceleration

– crista receptors within ampulla of semicircular ducts


Otolithic Organs: Saccule & Utricle

• The maculae of the utricle and saccule are the sense organs of static equilibrium.

• They also contribute to some aspects of dynamic equilibrium


Detection of Position of Head

• Movement of stereocilia or kinocilium results in the release of neurotransmitter onto the vestibular branches of the vestibulocochler nerve


Crista: Ampulla of Semicircular Ducts

• Small elevation within each of three semicircular ducts• Hair cells are covered with cupula (gelatinous material)

• When you move, fluid in canal tends to stay in place, thus bending the cupula and bending the hair cells - and altering the release of neurotransmitter


Detection of Rotational Movement

• Nerve signals to the brain are generated indicating which direction the head has been rotated

Health & Medicine

Lecture 7 special sense