Chapter 19 B: Senses: Vision, Equilibrium and Hearing

What helps form visual images of the enviroment?

• eyes uses photoreceptors

Extrinsic Muscles

• outside of the eye muscles that move that eye

Eyelids

• open and close the eye

medial canthus

• where eyelids meet (inner corner)

lateral canthus

• where the eyelids meets (outer corner)

Lacrimal caruncle

• pinky flesh structure on medial corner of eye

Conjuctivia

• is the lining of the eyelids and over the anterior surface of the eye

  • does not cover cornea

Lacrimal Apparatus

• produces, collects and drains lacrimal fluid (tears) from the eye

What do tears do?

• tears lubricate the anterior surface of the eye

what do lacrimal glands do?

• secrete tears

what do lacrimal canaliculi do?

• canals that drain the excess tears off of surface of eye

what does the lacrimal sac do?

• holds tears —> drains into nasolacrimal duct

Nasolacrimal duct

• where fluid enters nasal cavity

where is the anterior cavity located and what is contained within in?

• anterior cavity is the front of the lens

• contains circulating aqueous humor

what is aqueous humor?

• watery fluid that cycles old and new fluid

where is the posterior cavity located and what is contained within in?

• posterior cavity is behind the lens

• contains vitreous humor

What is vitreous humor?

• jelly-like substance; thicker; helps maintain shape (perminant)

what are the eye wall layers?

• fibrous tunic

• vascular tunic

• retina

“tunic”" = layer

What is Glaucoma?

• increased pressure within eye due to too much aqueous humor

What two regions is the fibrous tunic composed of?

• 1. Cornea

• 2. Sclera

Cornea

• clear; anterior portion of the eye

Sclera

• the white of the eye

what are the thee regions of the vascular tunic? (posterior to anterior)

1. Choroid

2. Ciliary body

3. Iris

Choroid

• contains vast network of capillaries supplying nutrients and oxygen to the retina

Ciliary body

• changes lens shape

  • changes shape due to tension in ciliary body

Iris

• pigmented part of the anterior eye; defines pupil

• set of two muscles that regulate the size

pupil

• controls amount of light entering eye

• hole where light enters

Within the iris, what are the two pupillae and what do they do?

• Sphincter pupillae: circular ; contracts in bright light (decreases in size)

• Dillator pupillae: radial ; increases size of pupiil, letting more light in ; low light

What layer is the retina in?

• internal layer of the eye

Neural layer

• houses photoreceptors and associated neurons

  • receives light; converts energy into nerve impulses

What three distinct layers form the neural layer?

1. photoreceptors cells (outermost layer)

2. Bipolar cells

3. ganglion cells (innermost layer)

What is are photoreceptor cells composed of?

• rods and cones

what is the difference between rods and cones?

• rods: important in dim light

  • 120 million/retina

  • more numerous in the periphery

  • night vision

  • low acuity (ability to distinguish detail)

  • vision in shades of grey

• cones: important for precise vision and color

  • 6 million/retina

  • concentrated in the fovea

  • day vision

  • high aquity

  • color vision

what do Bipolar cells synapse with?

• synapse with photoreceptors and ganglion cells

  • inner middle layer

where do the axons of ganglion cells leave through and what do they form?

• ganglion cells (innermost layer of retina)

• axons of these cells leave the retina and form the optic nerve (CN II)

What is the optic disc and where is it lcoated?

• is a “blind spot” on the retina lacking photoreceptors

• located where ganglion cell axons exit retina to form optic nerve and blood vessels enter and exit the retina

What is the fovea centralis and where is it located?

• is a depression in the retina containing the highest proportion of cones and almost no rods

  • area of sharpest vision

• located within the macula lutea (lateral to optic disk)

What is “Accommodation” in the lens?

• ability of the lens to change shape to focus on image

  • far away image —> lens thin

  • close image —> lens thicker

what do retinal photoreceptors convert?

• convert light to neural signals

what is the optic chiasm?

• where axons from the retina cross to the other side

optic tracts

• extend laterally, posteriorly from chiasm

Optic radiation

• extends from thalamus to occipital lobe

  • continuation of impulse

What is visual acuity?

• the ability to distinguish fine detail

what does 20/20 vision mean?

• 20 feet away/average = 20

  • NORMAL

what does 20/<20 vision mean (ex: 20/15, 20/10)?

• 15 —> most people would need to walk to 15 ft.

  • VISION IS BETTER THAN NORMAL

What does 20/>20 vision mean?

• WORSE THAN NORMAL

Nearsightedness (myopia)

• inability to focus on things far away because eye is elongated

  • treatment: contacts or glasses (thinner in middle; thicker outside)

Farsightedness (hyperopia)

• inability to focus on objects close because eyeball is too short (focal point behind eye)

  • treatment: glasses —> thinner outside ; thicker inside

What is presbyopia?

• age related farsigntedness ; lens loosing ability to accomodate

Astigmatism

• irregularity on cornea or lens

Conjunctivitis

• inflammation of conjunctiva “pink eye”

• virus and bacteria

• young children

• highly contageous

Cataracts

• clouding of the lens due to age

  • treatment: surgery (replace with new lens)

Glaucoma

• increased pressure within the eye

  • too much aqueous humor

    • pressure translated to optic nerve —> vision lost over time

  • treatment: medicinal marijuana

Diabetic Retinopathy

• small, unstable blood vessels develop inside the eye

  • unstable = prone to rupture —> blood leaks in —> leads to blind spot

  • treatment: some laser —> but comes back

Stabismus

• misalignment of eyes due to one set of extrinsic muscles being stronger than the other

  • treatment: patches/ or surgery

The ear contains organ of ____ and _____?

• equilibrium and hearing

What are the 3 distinct anatomic regions of the ear?

1. External ear

2. middle ear (oscicalles)

3. Inner ear

what is the pathway in the external ear?

• auricle (directs sound waves in)

• external acoustic meatus (tunnel)

• tympanic membrane (eardrum)

  • vibration (amplify’s sound waves)

Deep within the external auditory meatus, glands produce what?

• produce a waxlike secretion called cerumen

What are the two main sections/areas of middle ear?

• Auditory tube: connects middle ear to nasopharynx

• Auditory ossicles (small bones ): transmit sound waves to inner ear

What are the three auditory ossicles?

1. Malleus

2. Incus

3. Stapes

Where is the inner ear located?

• within petrous portion of temporal bone

What within the inner ear assists with equilibrium?

• utricle, saccule, semicircular canals

What within the inner ear assists with hearing?

• cochlea

What is equilibrium?

• refers to awareness of head position

what does the vestibular apparatus consist of?

• sensory receptors in utricle, saccule, and semicircular ducts

What do the utricle and saccule detect?

• detect:

  • static equilibrium (head position when head is stationary)

  • linear acceleration

What do the semicircular ducts detect?

• detect angular acceleration (rotational movements)