9: Special Senses

Question 1

sensory receptors

Answer 1

sensory receptors = specialised cells that monitor conditions inside or outside the body
simplest receptors = dendrites of sensory neurons
branching tips of dendrites are free nerve endings
all sensory information arrives at CNS in form of action potentials in a sensory (afferent) fibre
arriving information = sensation
conscious awareness of sensation = perception
1% information reaches conscious awareness

Question 2

general senses

Answer 2

temperature
pain
touch
pressure
vibration
proprioception

Question 3

special senses

Answer 3

smell (olfaction)
taste (gustation)
vision
balance (equilibrium)
hearing

Question 4

smell

Answer 4

paired olfactory organs
organs located in nasal cavity , either side of septum
each organ has an olfactory epithelium containing olfactory receptor cells
exposed dendritic bulb from each receptor has up to 20 cilia-shaped dendrites that extend into mucus
mucus = prevents build up of stimuli

Question 5

process of smelling

Answer 5

1. air swirls in nasal cavity
2. at olfactory organs, lipids and other chemicals diffuse into mucus before stimulating olfactory receptors
3. dissolved chemicals interact with receptors (odorant binding proteins)
4. binding of odorants changes permeability of receptor membrane = action potential
5. information relayed to CNS

Question 6

olfactory pathways

Answer 6

olfactory cranial nerves (I)
olfactory epithelium > olfactory nerves > olfactory bulb > olfactory tract > CNS
reaches cerebral cortex directly

Question 7

taste

Answer 7

receptors located over surface of tongue and adjacent to pharynx/larynx
taste buds = taste receptors and specialised epithelial cells
lie along epithelial projected called papillae
each taste bud
gustatory epithelial cells extend microvilli into surrounding fluids through a narrow opening (a taste pore)
primary taste sensations: sweet, salty, sour, bitter

Question 8

process of tasting

Answer 8

dissolved chemicals contacting the taste hairs stimulate a change in the membrane potential of the gustatory epithelial cells = action potential

Question 9

taste pathways

Answer 9

facial (VII), glossopharyngeal (IX), and vagus (X) cranial nerves
synapse within nucleus in the medulla oblongata
gustatory cortex

Question 10

vision

Answer 10

light enters eye and is refracted at the cornea and lens
light absorbed at retina by photoreceptors (rods and cones)
cones = approx. 5 million = central vision = colour
rods = approx. 100 million = peripheral vision = light presence

Question 11

process of seeing

Answer 11

light interacts with light sensitive molecules (photopigments) in the photoreceptors
photopigments consists of rhodopsin - made of opsin and retinal
in presence of light, rhodopsin splits altering the flow of electrical current

Question 12

visual pathways

Answer 12

two optic nerves (II) reach the diencephalon at the optic chiasm
half nerve fibres from each eye cross over to reach the thalamus on opposite side of brain
nuclei in thalamus relays visual information to reflex centres in brain stem as well as visual cortex of cerebrum

Question 13

hearing

Answer 13

inner ear has receptor complex located in temporal bone of skull
hair cells = mechanoreceptors

Question 14

middle ear

Answer 14

air filled cavity
separated from the outer ear by tympanic membrane (ear drum)
3 auditory ossicles (bones) : malleus, incus, stapes

Question 15

inner ear

Answer 15

receptors lie in the membranous labyrinth - contains two fluids called endolymph and perilymph
bony cochlea contains cochlear duct
cochlear duct sandwiched between a pair of perilymph-filled chambers
bony labyrinth walls are dense bone everywhere except round window and oval window

Question 16

organ of corti

Answer 16

hair cells of cochlear duct located in Organ of corti
sits above basilar membrane
stereocilia of hair cells in contact with tectorial membrane

Question 17

process of hearing

Answer 17

1. sounds waves arrive at tympanic membrane
2. movement of tympanic membrane causes displacement of auditory ossicles
3. movement of stapes at opal window causes pressure waves in the perilymph of vestibular duct
4. pressure waves distort the basilar membrane on their way round to the round window
5. vibration of the basilar membrane causes vibration of the hair cells against the tectorial membrane
6. info relayed to CNS over the cochlear branch of the cranial nerve VIII

Question 18

auditory pathways

Answer 18

axons of cranial nerve VIII enter medulla oblongata and synapse at cochlear nucleus
synapse in thalamus
auditory cortex of temporal lobe

Question 19

equilibrium

Answer 19

all sensations provided by hair cells of the vestibular apparatus - semi circle canals and otoliths
receptors in semi-circular canals respond to rotational movement
hair cells located in ampulla
raised structure in ampulla called crista
stereocilia embedded in cupula
in otoliths, utricle detect horizontal liner accelerations and saccule detect vertical linear acceleration (gravity)