Nervous system: The senses

Question 1

What are the layers surrounding the eye?

Answer 1

Outer sclera
Choroid
Retina

Question 2

What structure makes up the blind spot?

Answer 2

The optic disc - contains only blood vessels and nerves so no photoreceptors

Question 3

What structure makes up the most precise vision?

Answer 3

The fovea - has the highest concentration of cones

Question 4

What is the role of the photoreceptor cells?

Answer 4

The rods pick up low levels of light in black and white image
The cones are responsible for high acuity coloured vision

Question 5

What is the role of the horizontal cells?

Answer 5

They are responsible for inhibiting impulses in order to manage the vision

Question 6

What is the structure and function of the pigmented layer?

Answer 6

Forms part of the retina and contains melanin.
Acts an anchor for photoreceptor cells and absorbs bright light to protect the eye - therefore albinos have to wear sunglasses.

Question 7

What is papilloedema?

Answer 7

Swelling of the optic disc due to raised intracranial pressure.
Can lead to blindness (alongside the risks from raised intracranial pressure itself) if not treated promptly.

Question 8

Why do lesions in the visual cortex cause macular sparring?

Answer 8

Lesions in the visual cortex are due to blockage of its blood supply - the posterior cerebral artery. The macular however has a dual blood supply (also the middle cerebral artery) so its vision is unaffected.

Question 9

What ion causes depolarisation of hair cells?

How does this occur?

Answer 9

K+ ions - bending of the stereocilia by vibrations causes the K+ channels to open. There is high K+ outside the cell so entry depolarises

Question 10

What types of hair cells are there in the ear?

Answer 10

1 row of inner hair cells which sense sound

3 rows of outer hair cells which amplify the sound

Question 11

How is the sound information transmitted to the brain?

Answer 11

The inner hair cells are the primary sense organ
Transmitter release triggers action potentials
APs propagate into the brain via CN8
CN8 innervated the cochlear nucleus and auditory brainstem

Question 12

How do we localise sound?

Answer 12

Sense location by the delay in time and difference in volume between the 2 ears

Question 13

What are some general causes of hearing impairment?

Answer 13

• loud noise
• congenital defects
• infections eg glue ear
• aminoglycosides degenerate hair cells
• trauma to the temporal bone
• age

Question 14

What are some treatments for hearing impairment?

Answer 14

• hearing aids
• cochlear implants which direct the electrical stimulation of spiral implants
• cochlear nucleus implants (bypass the ear)