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- Each eyeball is positioned in a bony depression in the skull called orbit
- Only the anterior one-sixth of the eye’s surface can normally be seen
- The accessory structure of the eye includes extrinsic eye muscles, eyelids, conjunctiva, and lacrimal apparatus
EYELIDS
o Anteriorly the eyes are protected by the eyelids, which meet at the medial and lateral corners of the eye, the Medial and Lateral Commissure (canthus) respectively o Space between the eyelids is called the Palpebral fissure o Projecting from the border of each eyelid are the eyelashes
o Meibomian glands
- Also called as Tarsal glands and they modified sebaceous glands associated with the eyelid edges and produce an oily secretion that lubricates the eyes o Ciliary glands = Are modified sweat glands that lie between the eyelashes
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CONJUCTIVA
o A delicate membrane that lines the eyelids and covers part of the outer surface of the eyeball o It ends at the edge of the transparent cornea by fussing with the corneal epithelium o Conjunctiva secretes mucus that helps to lubricate eyeball at keep it moist LACRIMAL APPARATUS
o Consist of lacrimal glands and several ducts that drains the lacrimal secretion into the nasal cavity
o Lacrimal glands
- Are located above the lateral end of each eye. They continually release a dilute salt solution (tears) onto the anterior surface of the eye through several ducts o All the tears will be flush across the eyeball into the lacrimal canaliculi medially, then into the lacrimal sac , and finally into the nasolacrimal duct.
EXTRINSIC EYE MUSCLE
o Six extrinsic eye muscles (external eye muscle) are attached to the outer surface of each eye. o These muscles produce gross eye movements and make it possible for the eyes to move
Name Action Cranial Nerve Lateral Rectus
Moves laterally VI. Abducens
Medial Rectus
Moves medially III. Oculomotor Superior Rectus
Elevates and turns it medially
III.
Oculomotor Inferior Rectus
Depresses and turns laterally
III.
Oculomotor Superior Oblique
Elevates and turns it laterally
III.
Oculomotor Inferior Oblique
Depresses and turns it laterally
IV. Trochlear
OUTLINE
I. The Eye and Vision a. Anatomy of the Human Eye b. Physiology of Vision II. The Ear: Hearing and Balance a. Anatomy of the Ear b. Equilibrium c. Hearing III. Chemical Sense: Smell and Taste a. Olfactory Receptors and sense of Smell b. Taste buds and the sense of Taste
HUMAN ANATOMY AND PHYSIOLOGY WITH
PATHOPHYSIOLOGY
SPECIAL SENSES
LECTURED BY: JUSTO GILVERT DE JESUS
Transcribed by: T.J.A
I. The Eye and Vision
A. ANATOMY OF THE HUMAN EYE
EXTERNAL AND ACCESSORY STRUCTURE
- The eye itself is called the eyeball and it is a hollow sphere.
- The wall of the eye is composed of three tunics (layers) and its interior is filled with fluids called humors that help to maintain its shape
FIBROUS COAT
o The outermost layer of the eyeball is called the fibrous coat/layer o Sclera
- White thick connective tissue and it is seen anteriorly as the “white of the eye”
- Gives attachment to the extrinsic muscles of the eye o Cornea
- Located at the central anterior portion of fibrous layer that is transparent in color. This “window” is the cornea through which light enters the eye.
- The only tissue in the body that can be transplanted from one person to another without the worry of rejection because it has no blood vessels thus it is beyond the reach of the immune system
VASCULAR COAT
o This is also referred to as the Uvea. It is the middle layer of the eyeball and has three distinguishable regions o Choroid
- Most posterior region and it is a blood- rich nutritive tunic that contains a dark pigment.
- The pigment prevents light from scattering inside the eye. o Ciliary Body
- Moving anteriorly, the choroid is modified to form two smooth muscle structures, which is the Ciliary Body
- When ciliary muscle contracts, the lens become more convex
- With ciliary processes producing aqueous humor
o Iris
- The pigmented iris has a rounded opening, the pupil, through which light passes.
- it can increase or decrease the diameter of its aperture (the pupil) to admit more or less light
SENSORY/NERVOUS COAT
o The innermost sensory layer of the eye is the delicate two-layered retina, which extends anteriorly only to the ciliary body. o Retina
- It is the sensory/nervous coat that contains the photoreceptor cells, and they perceived colors
- The photoreceptors contain millions of receptor cells which is the rod and the cone Rods – stimulated for low intensity light that is used for night vision (scotopic vision) Cones – stimulated for high density light that is used for day vision (photopic vision)
THE LENS
- Light entering the eye is focused on the retina by the lens, a flexible biconvex crystal-like structure.
- The lens is dividing the eye into two segment or chambers: the anterior and posterior segments
- Anterior Segment
- contains aqueous humor
- It is like blood plasma and is continually secreted by a special area of the choroid.
- Maintains interocular pressure
- Posterior Segment
- contains vitreous humor
- Vitreous humor helps prevent the eyeball from collapsing inward by reinforcing it internally.
INTERNAL STRUCTURE: THE EYEBALL
- Auditory/Audition - the process of hearing, is accomplished by the organs of the ear.
- The ear is an engineering marvel because its sensory receptors can transduce sound vibrations with amplitudes
- Anatomically, the ear is divided into three major areas: the external (outer) ear, the middle ear, and the internal (inner) ear.
- The external and middle ear structures are involved with hearing only. The internal ear functions in both equilibrium and hearing.
o The external ear, or outer ear, is composed of the auricle and the external acoustic meatus. o Auricle or Pinna
- is what most people call the “ear”—the shell-shaped structure surrounding the auditory canal opening.
- Collects sound waves o External Acoustic Meatus
- the ear/auditory canal carved into the temporal bone of the skull.
- It guides the sound waves to the tympanic membrane
- In its skin- lined walls are the ceruminous glands, which secrete waxy yellow cerumen, or earwax, which provides a sticky trap for foreign bodies and repels insects. o Tympanic Membrane
- Sound waves entering the auditory canal eventually hit Tympanic Membrane
- also known as the ‘eardrum’
- A thin membrane separating outer from middle ear
o The middle ear cavity, or tympanic cavity, is a small, air-filled, mucosa-lined cavity within the temporal bone. o Uses a bony system to amplify sound vibration o Medial Boundary
- a bony wall with two openings, the oval window and the inferior, membrane covered round window. o Lateral Boundary
- Tympanic membrane with handle of the malleus attached o Anterior Boundary
- Eustachian tube (connects middle ear and nasopharynx) Connects middle ear to throat; equalizes pressure on eardrum o Posterior Boundary
- mastoid process is a smooth conical projection of bone located at the base of the mastoid area of the temporal bone. o Ossicles in the middle ear Malleus – hammer that is attached to tympanic membrane Incus – serves as the anvil Stapes – smallest bone of the human body. It presses on the oval window of the inner ear
INTERNAL (INNER) EAR
o generates action potentials to transmit sound and balance information to the brain o Contains bony chambers called osseous or bony labyrinth enclosing the membranous labyrinth and filled with plasma like fluid perilymph o The bony labyrinth consists of three subdivisions: Vestibule (equilibrium), Cochlea (hearing receptors) , and Semicircular Canal (detection of balance) o The organ of corti (organ of hearing) is found in the Cochlea o The bony labyrinth is filled with a plasma like fluid called perilymph o Suspended in the perilymph is a membranous labyrinth contains a thicker fluid called endolymph
II. The Ear: Hearing and Balance
A. ANATOMY OF THE EAR
EXTERNAL (OUTER) EAR
INTERNAL (INNER) EAR
MIDDLE EAR
- Consists of receptors located in the inner ear on both sides of the head 8th cranial nerve transmits the vestibular information (for equilibrium) from the receptors to the CNS
Functions:
o maintains body balance o coordinates eye, head, and body movements o permits the eyes to remain fixed on a point in space as the head moves
- The equilibrium receptors of the inner ear, collectively called the vestibular apparatus, can be divided into two branches: Static and Dynamic equilibrium
STATIC EQUILIBRIUM
o Within the membrane sacs of the vestibule are receptors called maculae that are essential to our sense of static equilibrium o The maculae report on changes in the position of the head in space with respect to the pull of gravity when the body is not moving o Important to control posture o When the body is in a state of rest
DYNAMIC EQUILIBRIUM
o found in the semicircular canals, respond to angular or rotational movements of the head rather than to straight-line movements. o Mediated largely by the semicircular canals and can detect motion of head in space o When the body is moving at a constant velocity
Mechanism of Hearing
- Sound waves are produced
- Sound waves are collected by the Auricle
- Received by the External Auditory Meatus ang guides the waves towards the eardrum
- Waves cause Tympanic Membrane to vibrate
- Ossicles (malleus, incus, and stapes) amplify vibrations, which enter inner ear
- Movement of hairs lining cochlea trigger nerve impulses
- Impulses are transmitted by auditory nerve to the brain for interpretation
Within the membranes of the Cochlea
- Within the membranes of the cochlea is the organ of corti containing the hearing receptors or hair cells
- Sound waves that reach the cochlea through the vibrations of the eardrum ossicles and oval window set the cochlea fluids into motion
- Receptor cells resting on the basilar membrane, the organ of corti are stimulated when these hairs are bent or tweaked by the movement of the gel-like tectorial membrane that lies over them.
- Once stimulated, the hair cells transmit impulses along the cochlear nerve to the auditory cortex in the temporal lobe the primary auditory area (Brodmann’s Area 41)
HOMEOSTATIC IMBALANCE
- Deafness – defined as hearing loss of any degree from a slight of loss to a total inability to hear sounds Two types of Deafness :
- Conduction Deafness - Temporary or permanent Results when something interferes with conduction of sound vibrations to the fluids of the inner ear. Interruption in transmission to the inner ear
Causes:
- Obstruction of ear canal
- rupture eardrum
- impacted cerumen (earwax)
- otosclerosis
- otitis media
- Sensorineural Deafness - Results from degeneration or damage to receptor cells to cochlear nerve, or to neurons of auditory cortex. In other words, sound waves are not perceived by the brain as sounds Causes:
- Old age (presbycusis)
- Heredity
- Exposure to loud noises/viral infections
- Side effects of medication
HEARING AND DIAGNOSTIC TEST
Weber’s Test - The base of the vibrating tuning fork is applied in the midline
Rinne’s Test - The base of the tuning fork is placed over the mastoid process of the skull When it can no longer be heard, it is removed and then is held in front of the ear
B. EQUILIBRIUM
C. HEARING
VESTIBULAR SENSE
- A single, long microvillus, called a gustatory hair, projects from each receptor cell to the surface through the taste pore
- The gustatory hair protrudes through the taste pore and when they are stimulated, they depolarize, and impulses are transmitted to the brain.
- Three cranial nerves contain axons of the first- order gustatory neurons that innervate the taste buds Facial Nerves (CN VII.) - serves taste buds in the anterior 2/3 of the tongue Glossopharyngeal (CN IX.) - serves taste buds in the posterior 1/3 of the tongue Vague (CN X.) - serves taste buds in the throat and epiglottis
THE FOUR BASIC TASTE SENSATION
Sweet Receptors - respond to substances such as sugars, saccharine, some amino acids, and some lead salts
Sour Receptors - respond to hydrogen ions (H+), or the acidity of the solution
Bitter Receptors – respond to alkaloid
Salty Receptors – responds to metal ions
- Umami - a taste discovered by the Japanese, is elicited by the amino acid glutamate, which appears to be responsible for the “beef taste” of steak and the flavor of monosodium glutamate, a food additive.
