37. Sense Organs

Question 1

How do sensory receptor types vary?

Answer 1

By modality (what they react to), by distribution, and by origin of stimuli (internal/external)

Question 2

Where are special sense receptors located?

Where are general sense receptors located?

Answer 2

In the head

Widely distributed, may be clustered in areas

Question 3

How do sensory receptors transduce stimuli into potentials?

Answer 3

Through the opening of ion-gated channels

Question 4

What is the concept of graded potentials?

Answer 4

The magnitude of the receptor potential varies with the strength of the stimulus

Question 5

How is stimulus intensity encoded?

How is stimulus duration encoded?

Answer 5

Number of receptors activated and rate of APs

Duration of APs in sensory neurons

Question 6

How do special sense receptors differ structurally from general sense receptors?

Answer 6

Synapse on ganglion cells, have high specificity

Question 7

Which sensory systems axons do not decussate?

Answer 7

Olfactory and gustative systems

Question 8

What is the purpose of the thalamus in the role of special senses?

Answer 8

Serves as a sensory relay, sends to different parts of cortex for processing

Question 9

What areas of the body experience sensory magnification?

Answer 9

Mouth, tongue, tip of index finger

Fovea of eye

Question 10

What are olfactory receptors?

Answer 10

Bipolar neurons

Question 11

What is the organisation of olfactory receptor cells?

Answer 11

Randomly distributed in nasal mucosa, multiple cells synapse only the same glomeruli in the olfactory bulb

Question 12

How do odorant molecules stimulate the olfactory sense?

Answer 12

Bind to G protein on cilia, depolarises cell and sends AP to olfactory bulb

Question 13

What is the purpose of mitral cells in the olfactory bulb?

Answer 13

Forward the signal from olfactory receptor cells to the primary olfactory cortex

Question 14

What is cranial nerve I?

Answer 14

Olfactory nerve

Question 15

Which structures make up the primary olfactory cortex?

Answer 15

Piriform, enthorinal cortex, amygdala

Question 16

What is the purpose of the orbitofrontal cortex?

Answer 16

Associate olfactory info with gustatory info

Question 17

How many receptor cells make up a taste bud?

Answer 17

50-150, plus support cells

Question 18

How are different tastes sensed?

Answer 18

Each has its own receptors based on shape and ion charges

Question 19

Where is flavour integrated?

Where is this information sent?

Answer 19

Secondary gustatory cortex

Hypothalamus and amygdala

Question 20

Where do the taste receptors send signals to?

Answer 20

The gustatory nucleus in the brain stem, onto the thalamus

Question 21

Which photopigments are contained in rods?

Which photopigments are contained in cones?

Answer 21

Rhodopsin

Opsin

Question 22

What type of vision are rods responsible for?

Where are they located?

Answer 22

Low light/night vision and grey shades

Located peripherally in the retina

Question 23

Why are photoreceptors hyperpolarised by light?

Answer 23

Reduces noise in the final image

Question 24

How are neurons arranged in the retina?

Answer 24

Photoreceptors - bipolar cells - retinal ganglion cells

Question 25

Which cells send APs along the optic nerve?

Answer 25

Retinal ganglion cells only

Question 26

Which structures receive visual information?

Answer 26

Primary visual cortex - through the LGN
Superior colliuculus - control of eye movements, coordination with auditory info
Suprachiasmatic nucleus - control of body clock and circadian rhythms

Question 27

Which optical fibres decussate?

Answer 27

Half of the fibres coming from one eye decussate at the optic chiasm, and project in the contralateral LGN. The other half remain ipsilateral

Question 28

Which type of receptors detect auditory stimuli?

Answer 28

Mechanoreceptors (hair cells)

Question 29

How are sound waves transduced in the ear?

Answer 29

Distortion of the basilar membrane causes stereocilia of the hair cells to bend and discharge APs

Question 30

How are different frequencies of sound differentiated?

Answer 30

Different regions of the basilar membrane vibrate for different frequencies

Question 31

How are APs transmitted from the cochlea to the brain?

Answer 31

Vestibulocochlear nerve (CN-VIII) sends to cochlear nucleus, send to inferior colliculus then thalamus, then auditory cortex

Question 32

What region of the cochlea do low frequency sounds vibrate?

Answer 32

The inner spiral

Question 33

Where are high frequency sounds processed in the auditory cortex?

Answer 33

Deeper into the brain, further from the skull

Question 34

How is head position sensed?

How is head motion sensed?

Answer 34

Utricle and saccule

Semi-circular canals

Question 35

What type of motion do saccule and utricle respond to?

Answer 35

Acceleration in a straight line, ie gravity

Question 36

What are contained within the saccule and utricle?

Answer 36

Otoliths which displace the gelatine and bend stereocilia

Question 37

What is contained within the semi-circular canals?

Answer 37

Hair cells in a gelatinous cup which shifts due to angular acceleration or deceleration

Question 38

How are different directions of head rotation transduced?

Answer 38

One direction causes excitation of nerve, many APs, and the other direction causes inhibition, firing less APs

Question 39

Where are vestibular info projected to?

Answer 39

The vestibular nucleus in the brainstem, into spinal cord, cerebellum, superior colliculus, and primary somatosensory cortex