CNS/Sensory VII

Question 1

Hair cells contain what kind of receptors?

Answer 1

Mechanoreceptors.

Question 2

How does the transduction process occur in hair cells?

Answer 2

It occurs with the movement of hair cells. The hair cells are connected by a stringlike-feature called a tip link, and when the stereocilia move in a given direction, it can mechanically pull open the ion channels in the stereocilia or close them again.

Question 3

Mechanotransduction at the […] activates […]

Answer 3

Tip link, afferent neurons

Question 4

Explain how the tip links activate afferent neurons.

Answer 4

When the ion channels open, K+ flows in, which depolarizes the cell. This allows voltage-gated Ca2+ channels to open, allowing the inflow of Ca2+. This allows for the release of neurotransmitters to afferent neurons, which can then fire an action potential.

Question 5

What direction of stereocillia movement opens the ion channels?

Answer 5

When they bend in the direction of the taller stereocillia.

Question 6

K+ causes [hyperpolarization/depolarization] of the membrane of hair cells, because […]

Answer 6

Depolarization, the cochlear fluid is rich in K+, so it flows into the cell instead of the normal out.

Question 7

What is tinnitus?

Answer 7

Ringing in the ears

Question 8

What are the two types of tinnitus? Explain the difference between them, including the cause.

Answer 8

Transient: lasts less than 24 hours, usually due to loud noises. It is caused by breaking tip links, but they eventually grow back.
Chronic: has many causes, but predominantly loud noise. Its origin can be the inner ear, nerve, or central pathways.

Question 9

Explain how auditory information travels from the afferents to its final destination.

Answer 9

It travels along the 8th cranial nerve to the medulla, where it splits off and travels up both sides of the brainstem to the midbrain and thalamus. It then goes from the thalamus to both sides of the primary auditory cortex.

Question 10

What is the purpose of the auditory pathways being bilateral?

Answer 10

This is the case because it helps us localize sound, as there is a time delay between the sound on both sides. There’s also a small difference in amplitude.

Question 11

Give 3 reasons why someone might need a cochlear implant?

Answer 11

Hair cell loss due to aging, loud sounds, or ototoxic drugs.

Question 12

Describe how cochlear implants work.

Answer 12

They are implanted through the round window. An electrode is placed scala tympani. The electrodes are spaced along the cochlear to stimulate groups of afferent fibers that respond to different frequencies.

Question 13

What are the major vestibular organs?

Answer 13

The semicircular canals, the utricle, and the saccule.

Question 14

What is the function of each of the vestibular organs?

Answer 14

Semicircular canals: angular acceleration
Utricle: linear acceleration - horizontal
Saccule: linear acceleration - vertical

Question 15

What is the vestibular ocular reflex?

Answer 15

It moves your eyes in response to your head movements. The eyes rotate in the opposite direction than the direction the head rotates in. The gaze does not change.

Question 16

How does transduction occur in the vestibular organs?

Answer 16

Like in the auditory system, it happens via hair cells being moved and the stereocilia tip links pulling ion channels open.

Question 17

Describe the organization of the semicircular canals.

Answer 17

These canals are fluid-filled. They have a bulge with hair cells (called the ampula). In this bulging area, they have the cupula, which blocks the fluid on both sides. The hair cells stick their stereocilia into the cupula.

Question 18

Describe how the semicircular canals respond to movement.

Answer 18

When you rotate your head, fluid will resist moving (inertia). This exerts a pressure on the cupula that causes it to bend. But the stereocilia are stuck in the cupula so they bend too. This bending will pull open mechanically gated ion channels.
When you stop, the fluid puts a force on the cupula. This triggers a feeling of dizziness.

Question 19

Describe the organization of the utricle and saccule.

Answer 19

The utricle and saccule operate similarly. There’s an area where their hair cells are attached to the bone in the inner ear. The hair bundles stick up into the otoliths that are floating in a jelly-like substance.

Question 20

Describe how the utricle and saccule adapt to motion.

Answer 20

When you move, the bones move but there’s a lag with the otoliths, since they are in fluid. The lagging of movement exerts a force on the stereocilia, causing transduction.

Question 21

Describe the major structures on the tongue that allow you to taste.

Answer 21

The food goes on the papillae, which detect the chemicals that dissolved in the saliva. These substances then get into the grooves around the papillae, which is where the taste buds are. The taste buds themselves are made up of taste cells surround a taste pore.

Question 22

How does information about flavour end up at the brain?

Answer 22

Once the dissolved chemicals end up in the taste pore, it sends a signal along the taste afferents to the brain.

Question 23

How many taste buds do we have?

Answer 23

Around 10,000

Question 24

What are the 5 basic tastes?

Answer 24

Salty, sour, bitter, sweet, umami

Question 25

When you taste salty food, what is going on chemically in the tongue?

Answer 25

Sodium ions are flowing into taste cells.

Question 26

When you taste sour food, what is going on chemically in the tongue?

Answer 26

You are taste high acid. The inflow of protons causes transduction by activating certain ion channels (like Na+) or blocking them (like K+)

Question 27

Why do we experience bitter taste?

Answer 27

It is a protection mechanism, as many harmful things in nature will taste bitter to warn us not to eat them

Question 28

When you taste bitter food, what is happening chemically in the tongue?

Answer 28

2 things: bitter substances can block K+ channels or bind to specialized receptors that trigger G-protein cascades.

Question 29

When you taste sweet food, what is happening chemically in the tongue?

Answer 29

The glucose and fructose bind to receptors that cause a G-protein cascade

Question 30

When you taste umami, what is happening chemically in the tongue?

Answer 30

They activate glutamate receptors that trigger G protein cascades.

Question 31

If you add sodium glutamate to food, what taste are you enhancing and why?

Answer 31

It will enhance umami, as the G protein cascade is triggered by glutamate.

Question 32

Describe the pathway that taste signals follow after leaving the tongue.

Answer 32

They travel along the cranial nerves to the medulla, then the thalamus, then the ipsilateral gustatory cortex. The whole process is ipsilateral.

Question 33

Where are the olfactory receptor cells located?

Answer 33

They are located in the olfactory epithelium, which lines the top of the nasal cavity.

Question 34

Describe how a smell reaches the brain.

Answer 34

The molecules get into the nose then dissolve in the mucus that lines the nasal cavity. It then reaches the olfactory epithelium, and its receptor cells transmit a signal to the olfactory bulb. The olfactory bulb processes the signal and then sends it to the CNS.

Question 35

Describe the 3 steps involved in olfactory signal transduction.

Answer 35

1. Oderant molecules bind to receptors
2. G protein activation is triggered
3. Ion channels are opened

Question 36

How many oderant receptor types do we have?

Answer 36

We have around 1000 different types of oderant recetors. Each cell has one type.

Question 37

How many different odours are we capable of discriminating? Why?

Answer 37

Over 10,000. Despite having 1000 oderant receptor types, a given type of odour molecule can bind to different receptors and produce a population of activated receptors.

Question 38

After transduction, describe the path of the olfactory signal.

Answer 38

The receptor cells send their axons across the skull bone at the top of the nasal cavity. It goes through the limbic system.

Question 39

Odours are said to be tied to […], because […]

Answer 39

Emotion/memory. This is because olfactory signals go through the limbic system, which is connected to emotional responses and memories.