Lecture 16: The Special Senses Flashcards Preview

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Flashcards in Lecture 16: The Special Senses Deck (32):

Describe the structure and function of accessory eye structures, eye layers, the lens, and humours of the eye



Accessory structures of the eye to protect the eye and aid eye function. Name them

-eyelids (palpebrae)
-lacrimal apparatus
-extrinsic eye muscles


Be able to label the eye.

Do it!


Give the structure and function of the following:
Eyelids (upper and lower)
Eyelashes (nerve endings of follicles initiate blinking
Lubricating glands associated with the eyelids

Eyebrow: shading the eye and preventing perspiration from reaching the eye
Eyelids: protect the eye. Levator palpebrae-give the upper eyelid mobility
Eyelashes: nerve endings if follicles initiate reflex blinking
Lubricating glands associated with the eyelids:
-tarsal glands
-sebaceous gland associated with follicles



Transparent membrane
-palpebral conjunctiva- lines the eyelids
-bulbar conjunctiva-covers the white of the eyes
-produces a lubricating mucous secretion
Refer to slide 8 for picture


Lacrimal apparatus

Lacrimal gland and ducts that connect to nasal cavity
Lacrimal secretion (tears)
-dilute saline solution containing mucus, antibodies, and lysozyme
-blinking spreads the tears towards the medial commissure
-tears entered paired lacrimal canaliculi via the lacrimal puncta
-drain into the nasolacrimal duct
Slide 10 for picture


Extrinsic eye muscles

6 strap like extrinsic eye muscles
-originate from the bony orbit
-enable the eye to follow moving objects

Four rectus muscles: names indicate the movement they promote
Two oblique: muscles move the eye in the vertical plane and rotate the eyeball


Label the diagram of the eye muscles on side 15 and 16

Do it


Summary of muscle actions on eye and innervating cranial nerves

Lateral rectus muscle-moves eye laterally (abducens)
Medial rectus muscle- moves eye medially (3- oculomotor)
Superior rectus muscle- elevates eye (3)
Inferior rectus muscle - depresses eye (3)
Inferior oblique- elevates eye and turns it laterally (3)
Superior oblique- depresses eye and turns it laterally (trochlear) 4


Structure of the eyeball
Wall of eyeball contains 3 layers, what are they?

Fibrous (outer)
Vascular (middle)
Sensory (inner)
Internal cavity is filled with fluids called humors
The lens separates the internal cavity into anterior and posterior segments


Label diagram on slide 16

Do it


Describe the fibrous layer and what it consists of

Outermost dense avascular connective tissue
Two regions: sclera and cornea
Sclera: opaque (white)
-protects and shapes the eyeball
-anchors extrinsic eye muscles
Cornea: transparent
-numerous pain receptors here contribute the blinking and tearing reflexes


Describe the vascular layer and what it consists of

Middle pigmented layer (uvea)
3 regions: choroid, ciliary body and iris
1. Choroid: posterior portion of the uvea
-supplied blood to all layers of the eyeballs
-brown pigment absorbs light to prevent visual confusion
2. Ciliary body
-ring of tissue surrounding the lens
-smooth muscle bundles (ciliary muscles) controls lense shape
-ciliary zonule (Suspensory ligament) holds lens in position
3. Iris
-the coloured part of the eye
Pupil- central opening that regulates the amount of light entering the eye
-bright light-sphincter papillae (circular muscle) contracts; pupils constrict


Sensory layer: retina

Delicate 2 layered membrane
1. Pigmented layer
-outer layer
-absorbs light
-stores vitamin A
2. Neural layer

Ganglion cell axons
-run along the inner surface of the retina

Optic disc (blind spot)
-site where the optic nerve leaves the eye
-lacks photoreceptors

Two sources of blood supply
-choroid supplies the outer third (photoreceptors)
-central artery and vein of the retina supply the inner 2 thirds


What are the 2 kinds and their properties

Rods- more of them at peripheral region of retina, away from the macula lutes
-operate in dim light
-provide indistinct , fuzzy, non coloured peripheral vision
-found in the macula lutea: concentrated in the fovea centralis
-operate in bright light
-provide high acuity coloured vision


What are the internal chambers and fluids of the eye?

The lens and ciliary zonule separate the anterior and posterior segments
Posterior segments contains vitreous humor that:
-transmits light
-supports posterior surface of the lens
-holds the neural retina firmly against the pigmented layer
-contributes to the intra ocular pressure

Anterior segments is composed of 2 chambers
-anterior chamber- between the cornea and the iris
-posterior chamber- between the iris and the lens


Internal chambers and fluids

Anterior segments contain aqueous humor
-plasma like fluid
-drains via the scleral venous sinus (canal of schlemm) at the sclera- cornea junction
-supplies nutrient and oxygen mainly to the lens and cornea but also the retina, and removes wastes



Biconvex, transparent, flexible, elastic and avascular
-allows precise focusing of light on the retina
-lens becomes denser, more convex, and less elastic with age


Focusing light on the retina

Pathway of light entering the eye: cornea- aqueous humor- lens- vitreous humor- neural layer of retina- photoreceptors
Light is refracted
-at the cornea
-entering the lens
-leaving the lens
Change in lens curvature allows for fine focusing of an image


Focusing for close vision

Close vision requires:
Accommodation- changing the lens shape by ciliary muscles to increase refractory power
-near point of vision is determined by the maximum bulge the lens can achieve

Constriction- the accommodation of the pupillary reflex constricts the pupils to prevents the most divergent light rays from entering eye

Controlled by oculomotor, parasympathetic fibres


Visual pathway to the brain

-Axons of retinal ganglion cells form the optic nerve
-medial fibres of the optic nerve decussate at the optic chiasm
-most fibres of the optic tracts continue to the superior colliculi
-the optic radiation fibres connect to the primary visual cortex in the occipital lobes


Sense of smell

Taste and smell (olfaction)
-their chemoreceptors respond to chemicals in aqueous solution
-olfactory epithelium in the roof of the nasal cavity
-bundles of axons of olfactory receptor cells form the filaments of the olfactory nerve (CN 1)


Sense of taste

Receptor organs are taste buds
-found on the tongue: CN 7 and 9
-found on the epiglottis: CN 10
Taste is 80% smell
-thermoreceptors, mechanoreceptors and nociceptors in the mouth also influence taste
-Cranial nerves 7, 9 and 10 carry impulses from the taste buds to the gustory cortex in the insula


What are the 5 taste sensations

1. Sweet
2. Bitter
3. Umami
4. Sour
5. Salty


The ear: hearing and balance
What are the 3 parts of the ear?

1. External
2. Middle
3. Internal

External ear and middle ear are involved with hearing
Internal ear (labyrinth) functions in both hearing and equilibrium
Receptors for hearing and balance: CN 8


Label diagram on slide 34

Do it


List the parts of the external ear

The auricle (pinna)
External acoustic meats (auditory canal)
Tympanic membrane
-boundary between external ear and middle ears
-connective tissue membrane that vibrates in response to sound
-transfers sound energy to bones of the middle ear


List the parts of the middle ear

A small cavity in the temporal bone
Pharyngotympanic (auditory tube) -connects the middle ear to the nasopharynx
-equalizes pressure in the middle ear cavity with the external air pressure
Ear ossicles: 3 small bones in tympanic cavity: the malleus, incus and stapes
-suspended by ligaments and are synovial joints
-transmit vibratory motion of the eardrum to the oval window


List the parts of the internal ear

Bony labyrinth
-three parts: vestibule, semicircular canals, and cochlea
-central egg-shaped cavity of the bony labyrinth
-contains 2 membranous sacs
Semicircular canals:
-3 canals (anterior, lateral, and posterior) that each define 2/3 of a circle
-a spiral, conical, bonds chamber
-the cochlear branch of nerve 8 runs from the spiral organs of corti to the brain


Transmission of sound to the internal ear

Sound waves vibrate the tympanic membrane
Ossicles vibrate and amplify the pressure at the oval window
-pressure waves move through the perilymph


Equilibrium and orientation

Vestibular apparatus consists of the equilibrium receptors in the semicircular canals and vestibule


How are the receptors activated?

What is the equilibrium pathway to the brain?

Bending in the opposite direction
-hyperpolarizes vestibular nerve fibres
-reduces the rate if impulse generation
Thus the brain is informed of the changing position of the head

Equilibrium pathway to the brain
-impulses travel to the vestibular nuclei in the brain stem or the cerebellum, both if which receive input
-3 modes of input for balance and orientation
-vestibular receptors
-visual receptors
-somatic receptors