Special Senses

Question 1

What are the three classifications of sensory systems?

Answer 1

1. Visceral: information that is not part of the somatic nervous system
2. General: in the integument that mediate touch, pain, temp, proprioceptors from joints and skeletal muscles
3. Special: other sensory abilities: hearing seeing smelling tasting and balance

Question 2

What system is sight mediated by?

Answer 2

Only the CNS

Question 3

Where does the retina develop from?

Answer 3

Parts of the CNS— they grow outwards from the rest of the diencephalon during embryonic development

Question 4

Where is the anterior cavity? Where is the posterior cavity?

Answer 4

• the aqueous humour containing area between the cornea and the lens
• the vitreous humour containing area between the retina and the lens

Question 5

What structures provide protection for the eye?

Answer 5

Eye lids, eye lashes, conjunctiva, lacrimal apparatus

Question 6

What is the iris made out of? What are the two layers?

Answer 6

• connective tissue plus two smooth muscle layers
  1) dilator layer contracts in darkness, dilating the pupil to allow more light through
  2) sphincter layer contracts in bright light, contracting the pupil to reduce light entering

Question 7

What controls the shape of the lens? Why does it change shape?

Answer 7

Muscles in the ciliary body; to keep the focal point constant (accommodation)

Question 8

What does the retina do? What is it made of?

Answer 8

Thin sheet of neuronal tissue that supports cells on the inner surface of the vitreous chamber

Question 9

What is the macula? What is the optic disc?

Answer 9

• the structure that contains the fovea centralis, point where the visual image is the sharpest and there are the most photoreceptors
• where the axons of the optic nerve leave the eye to travel to the rest of the brain

Question 10

Where are the photoreceptors found?

Answer 10

In the deepest neural layer of the retina, in close proximity to the pigmented choroid layer at the very back of the eye

Question 11

What are the two types of photoreceptors? What are they made out of?

Answer 11

Rods and cones; light sensitive opsin proteins

Question 12

Where is light transduced on the photoreceptors? How does transduction happen?

Answer 12

The outer segments (rods and cones); photopigments in the outer segments combine an opsin protein with a photosensitive retinal molecule

Question 13

When do photoreceptors release NT, when are they hyperpolarized?

Answer 13

• released constantly in darkness (constant influx of Na+ through internal ligand gated channels)
• hyperpolarized when opsins absorb photons (photon absorption by photopigments activates an enzyme that destroys the internal ligand, closing the channels)

Question 14

Where are rods more commonly found and where are cones more commonly found?

Answer 14

Rods: periphery of the retina
Cones: in the centre (macula/fovea)

Question 15

What are the characteristics of rods?

Answer 15

• sensitive to light (in high intensity light the opsins absorb photons very fast and can’t respond to future photons)
• high convergence onto bipolar neurons
• use rhodopsin protein which gives high sensitivity to blue-green

Question 16

What are the characteristics of cones?

Answer 16

• less sensitive to light (but can keep signalling in bright light)
• less convergence
• three kinds of cones: red, blue and green

Question 17

Why is rod-only vision associated with no colour vision? Why is it associated with poor visual acuity?

Answer 17

• colour vision happens with cones and there is not enough light to activate cones
• rods are more convergence onto bipolar neurons, so there is less fine visual actuity

Question 18

Where is visual information relayed to?

Answer 18

The primary visual cortex (diencephalon) , via the retinal ganglion cells

Question 19

What two senses is the inner ear responsible for? How are these two structures different?

Answer 19

• hearing and balance

- hearing senses external stimuli, balance is an interoreceptor that detects the position of your head

Question 20

What are the hair cells in the ear called? Is it part of the CNS?

Answer 20

• Stereocilia

- no, but it can release NTs and trigger AP’s in sensory neurons

Question 21

How does the inner ear detect sound waves?

Answer 21

Pressure waves enter the ear canal and make the tympanum vibrate, moving the ossicles which send pressure waves into the perilymph , which distorts the membranes separating the chambers

Question 22

Where are the sensory cells for hearing found? Where are the auditory hair cells found?

Answer 22

• the labyrinth (bony shell, internal membranous system that separates endolymph and perilymph)
• in the spiral organ which is in the cochlear duct, sandwiched between the tectorial membrane and the basilar membrane

Question 23

What kind of channels does the movement of hair cells open?

Answer 23

Mechanically gated ion channels open, allowing positive charges to enter the hair cell, which depolarizes it
- then voltage gated calcium channels open, which causes NT release onto the sensory nerve dendrite

Question 24

How is the basilar membrane tuned?

Answer 24

• the base is thick and tuned for high frequencies
• the apex is floppy and tuned for low frequencies
• in order to reach all the way to the apex, the sound waves must be large, and the larger the movements, the more depolarization of the hair cells in that location

Question 25

Why are high frequency hair cells more likely to be damaged?

Answer 25

• high frequency cells are closer to the oval/round windows so they get the front of the pressure
• high frequency=more movement=more metabolic stress

Question 26

Where do sensory neurons send auditory information?

Answer 26

• the hindbrain

Question 27

What is tonotopy?

Answer 27

• organization according to pitch

Question 28

How is the location of the sound stimuli computed by interneuron circuits?

Answer 28

The hindbrain detects the differences in the time or intensity of sounds caused by the different locations of the sounds relative to the two ears

Question 29

When do you need a cochlear implant?

Answer 29

If you don’t have hair cells