The Nervous System

Question 1

What does the CNS comprise of?

Answer 1

Brain and spinal chord

Question 2

What are the tough protective membranes on the brain and spinal chord collectively called?

Answer 2

Meninges

Question 3

Brain structure

Answer 3

grey matter on outside, white matter in centre

Question 4

What is grey matter?

Answer 4

Tissue in the brain and spinal chord.
- less myelin than white matter
- largely nerve fibres of relay neurones and the cell bodies of relay and motor neurones
- high concentration of axon terminals (endings) and dendrites

Question 5

What is white matter?

Answer 5

Nerve fibres surrounded by myelin which is fatty so looks white
- large network of nerve fibers (axons) in your brain that allows the exchange of infomation and communication between different areas of your brain

Question 6

ADD MORE CARDS ON CNS GENERAL

Question 7

What is resting potential?

Answer 7

The potential difference across the membrane of a cell when no nervous impulse is being conducted.

Question 8

Why is a neurone described as polarised?

Answer 8

There is a potential difference across the cell membrane. The membrane is more negative on the inside

Question 9

What causes the resting potential of axons?

Answer 9

negative ions of large proteins, of organic acids such as pyruvate and of phosphates e.g. ATP4- in the cytoplasm.

The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement. In neurons, potassium ions are maintained at high concentrations within the cell while sodium ions are maintained at high concentrations outside of the cell. This means some potassium channels are open allowing it to diffuse out, while channels that allow Na+ to diffuse in are closed. Sodium-Potassium exchange pumps pump K+ ions back in and Na+ ions back out. The Na+ ions are pumped out faster than the K+ ions are brought in. The overall result is the inside of the membrane is more negative compared to the outside

Question 10

What is the somatic nervous system?

Answer 10

pairs of nerves that originate in the brain or spinal chord and their branches. It is part of the peripheral nervous system. These nerves contain fibres of sensory neurones which carry impulses to receptors in the CNS and motor neurones which carry impulses away from the CNS

Question 11

What are the two types of cell in a nerve net?

Answer 11

1. ganglion cells to provide connections in several directions
2. sensory cells to detect stimuli e.g. temerature and light

Question 12

Why do you use a hydra for studying nerve nets?

Answer 12

• simple pattern
• easy to manipulate in experiments
• regenerates rapidly

Question 13

What are Schwann cells?

Answer 13

Glial cells that surround and support nerve fibres. They wrap themselves around the developing axon and withdraw their cytoplasm, leaving a multi-layered phospholipid myelin sheath.

Question 14

What is the synaptic knob?

Answer 14

Swelling at end of axon, in which neurotransmitter is synthesised

Question 15

What is resting potential?

Answer 15

The potential difference across the membrane of a cell when no nervous impulse is being conducted

Question 16

What is it called when a conduction jumps between the nodes of ranvier?

Answer 16

Saltatory conduction

Question 17

What are Nissl granules?

Answer 17

cytoplasmic granules containing ribosomes grouped on the RER

Question 18

What is a neurotrasmitter?

Answer 18

A chemical secreted in response to an action potential which carries a chemical signal across a synapse from one neurone to the next where a new action potential is initiated.

Question 19

How does the diameter of the axon effect speed of conduction?

Answer 19

The greater the diameter of the axon, the greater its volume in relation to the area of the membrane. More sodium ions can flow through axon so impulses travel faster

Question 20

What is temporal summation?

Answer 20

Depolarisation builds up over time to reach the threshold at which an action potential is initiated

Question 21

What is Spatial summation?

Answer 21

several pre-synaptic neurones synapse with the same post-synaptic neurone all contribute to the growing depolarisation which generates an action potential when it is large enough

Question 22

What are the 5 properties of a synapse?

Answer 22

• transmit infomation between neurones
• pass impulses in one direction
• act as junctions
• protect the response system from overstimulation (the impulse is always the same size whatever the stimulus)
• filter out low-level stimuli (action potential only initiated when threshold value is reached)

Question 23

What is meant by all or nothing?

Answer 23

a threshold value must be reached for a signal to be initiated otherwise there is no action potential

Question 24

What happens when acetylcholine binds at the post synaptic membrane?

Answer 24

Receptor protein changes shape, opening a channel which allows sodium ions to diffuse in (down their concentration gradient). This depolarises the post-synaptic neurone and if a threshold potential difference is reached an action potential is initiated. If insufficient acetylcholine is bound, the post-synaptic membrane will not be depolarised enough to exceed to the threshold value so an action potential will not be produced

Question 25

Why does acetylcholine need to be removed from the synaptic cleft?

Answer 25

it would constantly initiate new impulses otherwise

Question 26

How is acetylcholine removed from the synaptic cleft?

Answer 26

1. direct up-take into the pre-synaptic neurone
2. active transport of calcium ions out of the synaptic end bulb so no more exocytosis of acetylcholine occurs
3. Hydrolysis of acetylcholine. The enzyme acetylcholinesterase breaks it down to choline and ethanoic acid, they diffuse back across the synaptic cleft into the pre-synaptic neurone to re-form acetylcholine

Question 27

Why is there lots of mitochondria in the end bulbs of neurones?

Answer 27

energy in the form of ATP is needed to re-form the neurotransmitters and for their exocitosis

Question 28

Why do neurotransmitters only transmit impulses in one direction?

Answer 28

1. hyperpolarisation happens behind an action potential so depolarisation could not happen at that point
2. synaptic vesicles only occur at the end bulb of the pre-synaptic neurone
3. neurotransmitter receptors only occur on the post-synaptic membrane

Question 29

What are the effects of sedatives and stimulants?

Answer 29

Sedatives- inhibits nervous system, creating fewer action potentials in post-synaptic neurones
stimulants- stimulate nervous system by allowing more action potentials in the post-synaptic neurone

Question 30

How do drugs work?

Answer 30

1. Mimic the action of neurotransmitters by having a similar shape and binding to the post-synaptic neurone- increasing the frequency of action potentials as often the drug (e.g. nicotine) is not removed so it continues to intiate action potentials.
2. Durgs may prevent the break down of neurotransmitters so remains in the cleft causing repeated firing of the post-synaptic neurone. e.g. inhibiting the action of acetylcholinesterase

Question 31

Where do Psychoactive drugs act?

Answer 31

act on the central nervous system by affecting different neurotransmitters or their receptors which affects the firing of neurones

Question 32

What are the two types of synapse?

Answer 32

• electricle (gap junction small enough that impulse can jump directly from one neurone to the next)
• chemical - too big for impulse to jump. Neurotransmitter diffuses across synaptic celft to continue the impulse in the post-synaptic neurone

Question 33

What effects conduction speed of nervous impulses?

Answer 33

• temperature
• diameter of the axon
• Myelination

Question 34

What is the absolute refractory period?

Answer 34

Period during which no new action potential may be intitated

Question 35

What is depolarisation?

Answer 35

Temporary reversal of potential across the membrane of a neurone such that the inside becomes less negative and the outside as an action potential is transmitted.