Hearing, Chemical senses and touch

Question 1

What is another name for smell?

Answer 1

Olfaction

Question 2

In what way is smell similar across species?

Answer 2

• Olfactory sensory neurons project endings through glomeruli
• Projections through mitral cells (mammals)/ Projection neurons (insects) to
• Higher order brain systems (cortex in mammals)

Question 3

How does smell work in the human system?

Answer 3

• Olfactory epithelium is in the top of nasal cavity
• Odours come up into the nose to the olfactory bulb regions
• We find the endings of olfactory receptor neurons in olfactory bulb regions
• Our cilia project out onto air space in which the olfactory receptor neurons have their receptors, which are activated by different odorants.
• reception of odours causes change to action potential activity in the O RN (c-olfactory receptor) neurons
• neurons will then project into glomeruli within the olfactory bulb and each glomerulus has input from similar types of neurons. So there is convergence of information in glomeruli.

Question 4

What type of receptors are human olfactory receptors?

Answer 4

GPCRs

Question 5

What does odorant binding lead to?

Answer 5

opening of a cyclic nucleotide-gated channel and depolarisation of olfactory receptor neurons.

Question 6

Which pathway does odorant binding activate?

Answer 6

cAMP pathway

Question 7

How does the odorant binding lead to depolarisation?

Answer 7

• Odorant receptor causes activation of a g-protein, GTP is turned into GDP this causes activation of adenylate cyclase that causes ATP to be broken down to cAMP and cyclic GMP opens sodium channels causing depolarisation.
• When cyclic nucleotide gated channels open they allow is calcium ions. This influx of calcium in turn activates calcium activated chloride channels. Chloride ions then leave the cell leading to increased depolarisation

Question 8

What does it mean that smell has combinatorial coding?

Answer 8

• Odorants have diverse chemical structure, and we cannot really predict how something smells based on the structure of the molecule
• Each odorant binds to various receptors and activates many neurons, and in turn each neuron is activated by many odorants – combinatorial code

Question 9

In which direction is information flow in both olfaction and vision?

Answer 9

From top to bottom

Question 10

What additional olfactory organ do most vertebrates have and what is it’s function?

Answer 10

In addition to their nose, most vertebrates have an additional olfactory organ – the vomeronasal organ located in the nasal cavity, just above the roof of the mouth, and its function appears to be to respond to non-volatile chemical cues in the environment.

Question 11

What type of signals does the vomeronasal organ respond to?

Answer 11

responds to a wide range of signals. Some will provide information about prey, but others will give the animal information about the status of members of the same species

Question 12

What are intraspecies signals called?

Answer 12

pheromones

Question 13

Why do pheromones have the potential to produce profound changes in the behaviour of an animal?

Answer 13

• the signalling pathway that the VNO uses, sends signals to the hypothalamus, which is a major neuroendocrine centre
• The hypothalamus influences the reproductive system and the production of adrenal steroids

Question 14

What do we detect sound as?

Answer 14

Variations in air pressure

Question 15

What are normal hearing ranges for humans?

Answer 15

20 Hz to 20, 000 Hz

Question 16

What does it mean if a sound has lower frequency and lower intensity waves?

Answer 16

• Lower frequency waves = lower pitch

* lower intensity = quieter

Question 17

What is the auditory system made up of?

Answer 17

1. External ear
2. Middle ear (bones: malleus, incus, stapes)
3. Inner ear (cochlea)

Question 18

What is the vestibular system made up of?

Answer 18

1. Semi-circular canals (posterior, horizontal, anterior)

2. Otolith organs (utricle, saccule)

Question 19

What is the cochlea and how is it involved with hearing?

Answer 19

• Spiral structure full of fluid
• Sound waves set up through movement of basement membrane: tensor tympani (muscle)
• Movement of Hair cells transduce sound into electrical signals. Outer hair cells provide active amplification, inner hair cells send signal to brain

Question 20

What are the bones of the middle ear?

Answer 20

• Incus
• Malleus
• Stapes

Question 21

How do the hair cells of the ear work?

Answer 21

• Have cilia on the hair cells which are permeable to potassium, mechanosensitive (when they are moved they are subject to stress and this opens channels) potassium channel
• Potassium enters cells and causes depolarisation

Question 22

What is the tonotopy of the cochlea?

Answer 22

• Frequency of response of hair cells arranged in ordered manner
• High frequency sounds being perceived closer to the base of tonotopy
• Alike inputs come together
• Spiral ganglion

Question 23

What is sound localisation in space?

Answer 23

Position of sound source is detected by comparing the time of the sound arrival to both ears (interaural time difference)

Question 24

What is the vestibular system?

Answer 24

The balance system

Question 25

What is the vestibular system made up of?

Answer 25

• Two organs:
   otolith organs Saccule and Utricle which are involved with acceleration
   Semi-circular canals detect head rotation and balance

Question 26

What do we have inside the organs of the vestibular system?

Answer 26

hair cells which are held between the cell bodies

Question 27

What do Otolith organs do?

Answer 27

• Otolith organs use calcium carbonate (CaCO3) crystals to detect force of gravity and acceleration
• As fluid moves in semi-circular canals the crystals move, this bends hair cells, potassium channels open

Question 28

What contains mechanosensation cells?

Answer 28

The dermis and epidermis

Question 29

What are different types of mechanosensation cells?

Answer 29

• Merkel cells
• Ruffini ending
• Meissner corpuscle
• Pacinian corpuscle
• Free nerve endings

Question 30

When do all the mechanosensation cells respond and what do the endings allow you to dictate?

Answer 30

• They all respond at different times of stimulus

- The endings allow you to dictate strong, sharp, dull sustained types of pressure on your skin

Question 31

What do you do to measure Piezo in Merkel cells (touch)

Answer 31

• Record intracellularly using a patch electrode
• Have a stimulus probe which you cause to deform membrane of cell
• See a whole cell inward current as sodium comes into cell due to mechanosensitive excitation of channels

Question 32

Using physiology and genetics what can we identify with mechanosensation cells?

Answer 32

What sort of channels are present in what type of cells

Question 33

What does the somatosensory cortex make sense of?

Answer 33

all the different inputs from the sensory areas