The senses Flashcards
What are the 3 tunics (Layers) of the eyeball from outer most layer to inner most?
- Fibrous tunic (outer layer)
- Vascular tunic
- Retina (inner layer)
Describe the fibrous tunic?
Divided into 2 parts
-Cornea: Transparent layer covers the iris and the curved shape helps to focus light onto the retina (Refraction)
-Sclera: white part of the eye, provides shape and support to the eyeball. Posteriorly pierced by optic nerve and site of attachment for extrinsic muscles
Describe the vascular tunic?
It is composed of three parts: the choroid, the ciliary body, and the iris.
Describe the Retina?
The retina is a layer of photoreceptors cells (Rods & Cones) and glial cells within the eye that captures incoming photons and transmits them along neuronal pathways as both electrical and chemical signals for the brain to perceive a visual picture.
Function of Rods
Rods are responsible for vision at low light levels (scotopic vision). They do not mediate color vision, and have a low spatial acuity. They are distributed in the periphery of the retina.
Function of Cones
Cones are active at higher light levels (photopic vision), are capable of color vision and are responsible for high spatial acuity.
More rods or cones in the eye?
There are more Rods (120mil) compared to Cones (6mil)
What are the cavities & chambers in the interior of the eyeball?
Anterior cavity (to the Lens) has 2 chambers
- Anterior chamber between the cornea & iris
- Posterior chamber between iris and Lens
Posterior Cavity (lies between the lens & retina. Contains jelly like substance that maintains the shape of the eye
What/where are tears produced?
Lacrimal apparatus produces tears
Function of eyelids for the eye?
Shield & protect eyeball from mechanical injury & drying out
Function of eyelashes for the eye?
Protects the eyes from airborne dirt, dust or debris (irritants) entering the eye
Function of eyebrows for the eye?
Protect the eye from moisture & maintain sight
Function of Lacrimal apparatus?
Produces tears to protect eyeball & cornea through moisture & antibodies against infection.
Contains lysosomes to kill pathogens
Function of Lacrimal apparatus?
Produces tears to protect eyeball & cornea through moisture & antibodies against infection.
Contains lysosomes to kill pathogens
Function of the extrinsic eye muscles?
Controls movement of eyeball & superior palpabra
Name the 3 cranial nerves involved in the movement of extrinsic eye muscle?
Oculomotor nerve III
Abducens nerve VI
Trochlear nerve IV
How much tears are produced each day (in volume)?
About 1ml of tears are produced per day.
Function of tears?
Tears protect, clean, lubricate & moisten eyes.
Tears spread medially over the eye by blinking & moisten eyeballs
Tears contain lysosomes a protective enzyme
What are some age related changes to vision & eyes?
- Decreased tear production (dry eyes)
- Lens loss of its elasticity & transparency results in cataracts
- Sclera thickens & changes colour
- Iris fades/develops irregular pigments, slower adaption to darken areas (creates increase fall risk)
- Sharpness of vision decreases
- Colour & depth perception decreases
What are the 4 major progresses of image formation?
- Refraction
- Accommodation
- Pupil constriction/dilation
- Convergence
What is Refraction?
Refraction is done by the cornea & lens it involves bending light rays to focus an image on the central fovea
What is accommodation in the process of image formation?
Accomodation is the of the shape of the lens to allow sharp focusing of light onto the retina.
What is pupil dilation/constriction?
It is the smooth muscle of the iris that controls the amount of light entering the eye & helps to prevent scattered of light.
What is convergence of the eyes?
Medial movement of the eyes to keep both eyes focusing on an object
What is the neuronal pathway from the retina to in the eye to the primary visual area of the cerebral cortex?
The Visual Pathway
1. Cortex of occipital lobes
2. Nucleus of abducent nerve
3. Nucleus of trochlear nerve
4. Nucleus of oculomotor nerve
5. Medial geniculate body
6. Superior colliculus
7. Lateral geniculate body
8. Pulvinar
9. Commissure of Gudden
10. Optic tract
11. Optic chiasma
12. Crossed fibers
13. Uncrossed fibers
14. Optic nerve
15. Retina
What is the role of the midbrain in the visual pathway?
the superior colliculus of the midbrain - for control of eye movements; the pretectum of the midbrain - for control of the pupillary light reflex
What is the role of the hypothalamus in the visual pathway?
Establishes sleep patterns based upon the circadian rhythms of light & dark
control of diurnal rhythms and hormonal changes.
What are the 3 main anatomical regions of the ear?
External ear: Auricle/Pinna (outer ear), auditory canal & tympanic membrane
Middle ear: Small air filled cavity, ossicles, eustachian tube
Inner ear: divided into 3 areas vestibule, cochlea, semicircular canal
Where is perilymph found?
In the bony labyrinth in the inner ear
Where is endolymph found?
Found in the membranous labyrinth within the bony labyrinth
What is the function of the auricle/pinna of the ear?
Directs sound waves towards the tympanic membrane
What is the function of the external auditory canal?
Cereiminous glands produce cerumen (ear wax) to lubricate & protect the external canal
What is the function of the tympanic membrane?
Sounds waves vibrate the tympanic membrane & transfers that energy to the ossicles
What cranial nerve is involved in hearing & equilibrium?
Cranial nerve: vestibulocochlear (VIII)
Identify the branches of the vestibulocochlear (VIII) nerve?
2 branches: Vestibular & cochlear
Carries impulse from the vestibular & organ of corti
The action potential travels to the primary auditory area via the cochlear branch of this nerve
Describe the passage of a sound wave generated in the air moving through the structures of the ear?
- Sound waves vibrate the Tympanic membrane
- Vibrate of the ossicles transfers & amplifies the vibration motion to the oval window
- Pressure waves are created in the perilymph of the cochlea
- Pressure waves travel through the perilymph, pass through the vestibular membrane & into the endolymph
- Pressure waves in the endolymph cause the basilar membrane to vibrate which moves the hair cells & creates action potential (if threshold is met)
Describe equilibrium
Equilibrium is the state of being BALANCED & refers to the position of the head in relation to the body
Describe the path of a nerve impulse starting from the cochlea.
- Cochlea receptors (hair cells) generate the nerve impulse
- Impulse carried to the medulla where axons cross over
- Impulse ascends to the midbrain
- Ascends to the thalamus
- Ascends to the primary auditory area in the temporal lobe
What is the difference between static & dynamic equilibrium?
Static helps maintain the position of the head relative to the force of gravity
Dynamic maintains position of the head during sudden movements
Where are the receptors for static equilibrium located>
Vestibule
Where are the receptors for dynamic equilibrium located>
Semicircular canals
Identify 2 causes of hearing loss?
- Exposure to loud noises
- Aging break down of the inner ear
Genetics, meds, infections, head trauma
What is presbycusis?
Age associated progressive loss of hearing in BOTH ears
What causes presbycusis?
Related to the damage & loss of hair cells & degeneration of the nerve pathway for hearing
Caused by prolong exposure to loud noise
What are the structures found in the Inner ear?
Inner ear is divided into 3 areas
- The vestibule
- Cochlea
- Semicircular canals which have 2 main divisions (Bony & membranous labyrinths)
What structure can be found in the middle ear?
Ossicles
1. Malleus (attached to the tympanic membrane)
2. Incus
3. Stapes (attached to the oval window)
Auditory/Eustachian tube
