8A - Nervous System

Question 1

Why is unmyelinated neurone slow

Answer 1

Because depolarization must occur along the whole membrane of the axon

Question 2

Myelinated myelin axon

Answer 2

Increase the speed at which action potential can travel along the neurone
—> section of the axon that surrounded by myelin sheath depolarization cannot occur myelin sheath stops the diffusion of sodium and potassium ions

The action potential therefore appear to jump from one node to the next
—: saltatory conduction

Question 3

Factor affecting the speed of conduction

Answer 3

BIGGER DIAMETER - action potential are conducted quicker along axon
-less resistance to the flow of ions than in the cytoplasm of a smaller axon
—> less resistance means depolarization reaches other part the neurone quicker

Question 4

Resting potential

Answer 4

There are more positive ions, Na+ and K+ outside compared to inside therefore the inside of the neurone is comparatively more negative at -70mV

Question 5

Resting potential process

Answer 5

1) sodium - potassium pumps moves 3Na+ ions out and 2K+ ions and active transport - ATP - this creates sodium ion electrochemical gradient -> more Na+ ions outside the cell than inside

2) the sodium-potassium pumps also move potassium ions in t the neurone but the membrane is permeable to potassium ions so they through potassium ion channel

Question 6

Process of action potential

Answer 6

1) STIMULUS
excites the membrane which causes sodium ion channels to open —> membrane becomes more permeable to sodium ions diffuses into the neurone down the sodium ion electrochemical gradient - inside less negative

2) depolarization
If the potential difference reaches the threshold (-55mV)
- more sodium ion channel open - more sodium ions diffuse neurones
- when +40mV reaches the Na+ channel closes and the K+ channel opens

3) REPOLARISATION
The membrane is now permeable to K+ ions diffuses out of the neurone down conc.gradient -starts to get back resting potential

4) hyperpolarisation
Potassium ions channel are slow to close so there is a slight overshoot where too many potassium ions diffuse out of the neurone - the potential becomes more negative than resting potential

Question 7

All or nothing principle

Question 8

Synapses

Answer 8

1) arrival of an action potential at the sympatic knob opens calcium ion channels in the pre-synaptic membrane. Calcium ion channel in the presynaptic membrane. Calcium ions flow from the synaptic cleft

2) calcium ion causes vesicles of transmitter substances to fuse with the pre-synaptic membrane and they release a transmitter substance into the synaptic cleft . The transmitter substances diffuse across the synaptic cleft

3)the transmitter substances binds with a receptor protein on the post synaptic

4) Na+ channels opens, as the sodium ions rushes into the cytoplasm of the post-synaptic neurone , depolarization of the postsynaptic membrane occurs

Question 9

Nicotine

Answer 9

Mimics the effect of acetylcholine and binds to specific acetylcholine receptor in postsynaptic membrane known as nicotine receptor

Trigger action potential in post synaptic neurone but later can be unresponsive to more stimulation for sometime

Trigger the release dopamine —> pleasure sensation

Question 10

Lidocaine

Answer 10

Lidocaine molecules block voltage- gated Na+ channels

This prevent the action potential in postsynaptic neurone

Prevent feeling pain

Question 11

Cobra venom

Answer 11

Reversibly bind to acetylcholine receptor in postsynaptic membrane and neuromuscular junction

It prevent the transmission of impulse = no action potential

Muscle is not stimulated to contract and becomes paralyzed

Inability to breathe
—> death

Question 12

How to increase the response on the nervous system

Answer 12

Increase the amount of neurotransmitters

Increase the release of neurotransmitters from the vesicles at the presynaptic membrane

Bind to post-synaptic receptor and activate them or increase the effect of the normal neurotransmitters

Prevent the deg ration of neurotransmitters by enzyme or prevent reputable into presynaptic knob

Question 13

What effects decreasing the response

Answer 13

Blocks the synthesis of neurotransmitters

Causes neurotransmitters to leak from vesicles and be destroyed by enzyme

Prevent the release of neurotransmitters from vesicles

Blocks the receptors and prevent neurotransmitters binding

Question 14

What do the rods detect

Answer 14

Detect light (black and white)

Question 15

How are the rods detributed and sensitive to

Answer 15

Sensitive to Low light level

Spread evenly across retina

Question 16

What do cones detect

Answer 16

Detect colour

Question 17

How does rhodopsin in the light affect

Answer 17

Light present

• light is detected by rod cell as photoreceptors

-then the light is absorbed by rhodopsin (contain cis -retinal)

• the cis-retinal is converted to trans-retinal which make rhodopsin unstable and split into trans-retinal and opsin

-which create generator potential. HYPERPOLARISATION IS NEEDED SO, NA+ CHANNEL CLOSED.
—> fewer sodium ions enter rod cell
—> sodium pump continues to work at the same rate, pumping the sodium ions out of the rod cell so the interior becomes more negative than usual.

-if the threshold is reached the action potential is created and the impulse is sent to the optic nerve and then the brain.

Question 18

How does rhodopsin affect the dark

Answer 18

Rhodopsin is resynthesised (ATP is required to convert the trans-retinal back to cis-retinal)

Join with opsin and becomes rhodopsin

Question 19

Process of habituation

Answer 19

1) repeated exposure to a stimulus decrease the amount of calcium ion that enter the presynaptic neurone

2) this decrease in the influx of calcium ion means that less neurotransmitters is released from vesicles into the synaptic cleft so fewer neurotransmitters can bind to receptor in the postsynaptic membrane

3) fewer sodium ions channel on the postsynaptic membrane open - reduced chance of the threshold for can action potential being reached on the postsynaptic membrane

4)as a result fewer signals are sent to the effector to carry out the response

Question 20

Why is myelin sheath important/role

Answer 20

Protects the nerves from damage

Speeds up the transmission of the nerve impulse

Question 21

Cones and colour vision what pigments and how it works

Answer 21

Iodopsin needs to be hit with more light energy than rhodopsin in order to breakdown and so it is not sensitive to low light intensity

3 type iodopsin - red yellow blue

The cones provide colour vision because the brain interpret the number of different types of cones stimulated as different colours

Question 22

After changing the pigment take time to become functional again

Answer 22

As the rhodopsin reforms in your rods

Retinal and opsin reforms into rhodopsin requiring ATP

Question 23

Process of spinal reflexes

Answer 23

1) stimulus is received by a sensory receptor
2) an impulse travel up the sensory neurone through the dorsal root ganglion into the grey matter of the spinal cord. It synapses with a relay neurone which then synapse with a motor neuron within the grey matter
3)there impulse passes along the motor neuron leaving the spinal cord through the ventral root. It then travels to an effector organ
4)the motor end plate in the muscle transfer the stimulus to the muscle which then contract moving the body part away from danger.

Question 24

Cranial reflexes process

Answer 24

1)light may enter one or both eyes at the same time and effect on the pupils is the same

2)light falling on the sensory cells of the retina cause impulse to travel along neurons in the optic nerve to the brain. The brighter the light, the bigger the frequency of action potential

3)the impulse is detected in a control centre in the midbrain

4) the impulse then travels along two neurones to further control Centre

5)in the control centre the nerve impulse synapse with branches of the parasympathetic cranial nerve which transmit impulse to the iris

6) these stimulate the effectors

7) the circular muscle contract and the radial muscle relax so the pupil contract

Question 25

Sympathetic system ganglionic length

Answer 25

Preganglionic fibre - are short

Postganglionic fibre - long

Question 26

Parasympathetic system ganglionic length

Answer 26

Preganglionic fibre - very long

Postganglionic fibre - very short

Question 27

What does sympathetic nervous system neurotransmitters

Answer 27

Noradrenaline

Rapid response in the target organ system

Fight or flight
Eg- active or under physical or psychological strength

Question 28

Parasympathetic nervous system neurotransmitters

Answer 28

Acetylcholine
REST AND DIGEST

Maintain a normal functioning of the body and restore calm after stressful situation

Question 29

Where is the sympathetic system close to

Answer 29

CNS system

Question 30

What is the parasympathetic close to

Answer 30

The ganglia is near to the effector or the organs

Question 31

Additional role of synapses
Unidirectionality of impulse transmission

Answer 31

-synapse ensure the one way transmission of impulse
-impulse can only pass in one direction at synapse because neurotransmitters is released on one side and it’s receptor are on the other

Question 32

Amplification of nerve signals by summation

Answer 32

Insufficient to generate an action potential in the post-synaptic neurone
- only a small amount of acetylcholine May release into the synaptic cleft
-a small number of sodium ion channels are opened on the postsynaptic axon membrane
-insufficient number of sodium ion pass through the membrane
The threshold potential is not reached