Reflexes and touch

Question 1

What is the difference between reflexes and responses?

Answer 1

1. Responses are conscious decisions whereas reflexes are ways in which the body can sense what is happening in the environment and change how the effector responds.
2. No conscious thinking is required.

Question 2

Give an example of a reflex pathway.

Answer 2

The knee jerk reflex - a monosynaptic reflex.

Question 3

What are the two neurotransmitters involved in excitation and inhibitation of muscles?

Answer 3

Glutamate is involved in the excitatory circuit and the inhibitory circuit involves GABA.

Question 4

What does the word oculomotor relate to?

Answer 4

Motion of the eye.

Question 5

Where must reflected light be focused in the eye?

Answer 5

The retina.

Question 6

Describe the steps in the pupil reflex.

Answer 6

1. Eye reflexes are at optic nerve (sensory afferent- receives light input and projects to visual cortex)
2. Light enters eye and activates specialised receptors, information goes to visual cortex
3. Size of pupil is determined by iris
4. Ciliary muscle determines shape of lens
5. Optic tract also innervates the brain stem, an area called the pretectal nucleus
6. This in turn innervates the oculomotor nerve, The action potentials go back down the oculomotor nerve
7. Reflex change in pupil size in response to light
8. Pupil constriction- pupil constricts to prevent diverging light rays hitting the periphery of the retina resulting in a blurred image

Question 7

What are Pacinian corpuscles?

Answer 7

1. Mechanoreceptors that are found on the end of axons that respond to pressure.

Question 8

What are Meissner’s corpuscles?

Answer 8

1. Mechanoreceptors that have a much smaller receptive field - more precise than Pacinian.

Question 9

How do touch receptors show adaptation?

Answer 9

1. Action potentials are only created during change rather than the degree of pressure - you are not able to constantly feel clothes on your skin.
2. Ones called corpuscle- adapt. Fire action potentials as you are being touched and stop even though you are still being touched, but starts again when touch stops
3. Ones that aren’t called corpuscle don’t adapt – constantly firing action potentials

Question 10

What are the 5 types of taste?

Answer 10

Salty, bitter, sour, sweet and umami (savoury e.g. parmesan, seaweed).

Question 11

How is the sensation of taste created?

Answer 11

1. Ligand gated ion channels are opened by agonists (the chemicals in food) which creates action potentials.
2. There is sensory input into the gustatory cortex which creates the sensation of taste.

Question 12

How is the sensation of smell created?

Answer 12

1. Odours are inhaled through the nose and go through the nasal cavity.
2. These odorants are dissolved in the mucus lining and interact Olfactory cells – depolarise neurones which fire action potential which got to olfactory cortex
3. The agonist for the response is the airborne chemicals.

Question 13

How is such a wide variety of taste created, despite there only being 5 different types?

Answer 13

A lot of the sensation of taste is created through the different smell receptors.

Question 14

how do skeletal muscles work

Answer 14

1. only have 2 states: contracting and not contracting

2. there is no input when they are relaxed

Question 15

How does GABA work

Answer 15

1. causes hyperpolarisation

2. so depolarisation is less likely

Question 16

do reflexes have to involve the spinal cord

Answer 16

no

Question 17

With distant objects, the lens…

Answer 17

1. flattens

2. less refraction of light required

Question 18

How do Meissner’s touch receptors show adaption

Answer 18

1. APs fire when they start touching, then after a while stops, then start firing again when stops touching

Question 19

Describe what happens with antagonist muscles

Answer 19

1. More than one synapse is involved.
2. Muscle spindle is activated as it senses the stretch
3. The monosynapse goes back to the same muscle spindle but another synapse also occurs at the inhibitory interneuron,
4. GABA is released (inhibitory neurotransmitter), causes agonist muscle to contract so muscle spindles can relax

Question 20

Give an example of an extensor/flexor reflex

Answer 20

1. E.g. standing on drawing pin
2. Different neurones- differ by diameter and myelination, thick heavily myelination ones are for touch
3. Pain neurones are thin and not heavily myelinated, so action potential is slow
4. Therefore, reflex is very fast but pain signal takes a few seconds to reach the brain
5. Lots of different muscles must contract/relax at same time in order for this reflex to occur so lots of synapses- but still a reflex as conscious brain is not involved

Question 21

What are touch receptors

Answer 21

1. Mechanoceptors- have special ion channels which open up in response to movement
2. Differ in terms of receptive field or how they adapt to sensation
3. Receptive field- touch receptor is touched and activated, action potentials generated and go to spinal cord and then to somatosensory cortex
4. Small receptive fields allow an accurate sense of touch (meissner’s corpsucles have small receptive fields so there are lots in our hands)

Question 22

How do corpuscles adapt

Answer 22

1. Corpuscles have capsules
2. Squashes capsule down which squashes neurones
3. Capsule forms around thing it touches taking pressure of neurone so no longer activated
4. When touch is removed capsule deforms again and causes neurone to be activated