3.8 - The nervous system

Question 1

What is a stimulus?

Answer 1

A detectable change in the internal or external environment.

Question 2

What is the pathway from stimuli to effector?

Answer 2

The stimuli is detected by the nervous system and specialised receptor cells convert the energy into electrical energy to be carried along neuron’s before reaching an effector to produce a response.

Question 3

What are the two types of effectors?

Answer 3

• Muscles
  -Glands

Question 4

What are the two main parts to the nervous system?

Answer 4

• Central Nervous System
• Peripheral Nervous System

Question 5

What is with the CNS and what does it do?

Answer 5

-The brain and the spinal cord which processes information provided by the stimulus and co-ordinates the response.

Question 6

What are the two branches of the peripheral nervous system?

Answer 6

• The autonomic nervous system
  The somatic nervous system

Question 7

What does the somatic nervous system do?

Answer 7

It is made of nerves that carry impulses from the receptor cells to the CNS and from the CNS to the effectors.

Question 8

What does the autonomic nervous system do?

Answer 8

Provides unconscious control of the internal organs e.g., heartbeat

Question 9

What is a neurone and what are the three types?

Answer 9

Highly specialises cell that carry nerve impulses in one direction.
- Sensory
- Relay
- Motor

Question 10

What is a sensory neurone?

Answer 10

Carries nerve impulses from the receptor cells in the sense organ to the CNS.

Question 11

What is a relay neuron?

Answer 11

Found in CNS, connects sensory and motor neurones

Question 12

What is a motor neurone?

Answer 12

Transports the nerve impulse from the CNS to the effectors

Question 13

What is the function of the spinal cord?

Answer 13

Acts as a communication pathway between the brain and the rest of the body.

Question 14

What is the grey matter in the spinal cord?

Answer 14

Central region that contains cell bodies and synapses.

Question 15

What is the white matter in the spinal cord?

Answer 15

The area surrounding the grey matter that contains axons surrounded by fatty myelin which gives it its colour.

Question 16

What enters the spinal cord through the dorsal root?

Answer 16

The sensory neurone carrying information into the CNS.

Question 17

What exits the spinal cord through the ventral root?

Answer 17

The motor neurone carrying information to the effectors.

Question 18

What is located in the dorsal root ganglion?

Answer 18

Cell bodies of sensory neurones.

Question 19

What is a nerve net?

Answer 19

A nerve net is a set of interconnected neurones that form a ganglion but not a brain.

Question 20

What type of animals contain nerve nets?

Answer 20

Invertebrates such as hydra.

Question 21

What direction do nerve impulses travel in a nerve net?

Answer 21

Any direction.

Question 22

Are nerve impulses slower or faster in nerve nets? Why?

Answer 22

Slower as they are not covered by a myelin sheath.

Question 23

What are the dendrites and what are their function?

Answer 23

Thin fibre that carries impulses towards the cell body, they may have several.

Question 24

What is an axon and what is its function?

Answer 24

The fibre carrying impulses away from cell body. Only one per cell body.

Question 25

What are the Schwann cells and what are their function?

Answer 25

Cells that surround and support the axon to create the myelin sheath allowing for efficient impulse transmission.

Question 26

What are the nodes of Ranvier and what are their function?

Answer 26

Small gaps in-between the myelin sheath where the membrane is exposed allowing for rapid transmission.

Question 27

What is the axon terminal and what is its function?

Answer 27

The end terminal of the axon which shoots neurotransmitter so the impulse can transmit to next neurone.

Question 28

What is meant by a neurone being an 'excitable' cell?

Answer 28

It can change its resting potential to change the potential difference across the cell membrane.

Question 29

What is the average resting potential across a cell membrane? What is the term used to describe the cell at this state?

Answer 29

- 70mV. The cell is polarised.

Question 30

When a cell is polarised is the inside more positive or negative?

Answer 30

Negative

Question 31

How is the negative inside created and maintained in a polarised cell, by diffusion?

Answer 31

There are channels within the cell, both potassium and sodium. The inside of the polarised cell has a high concentration of potassium and a low concentration of sodium. Therefore, naturally the potassium wants to diffuse out and sodium wants to diffuse in. But the channels for sodium are closed at this state but the channels for potassium are open meaning that potassium can diffuse out but sodium can't diffuse in, creating the more positively charged outside.

Question 32

How is the negative inside created and maintained in a polarised cell, by active transport?

Answer 32

There are sodium/potassium pumps within a cell, they pump potassium out and sodium in. However, for every 3 potassium ions pumped out only 2 sodium ions are pumped in and therefore the outside is more positively charged.

Question 33

What can be used to pick up voltage change across a neurone?

Answer 33

A pair of electrodes that feed into an oscilloscope.

Question 34

Explain the process of depolarisation of a membrane

Answer 34

When the membrane is exposed to a stimulus then the voltage gated sodium channels open, this means sodium ions can diffuse through and the inside becomes more positive to reach +40mV which is considered depolarisation.

Question 35

Explain the process of depolarisation of a membrane

Answer 35

When depolarisation reaches its peak then the sodium channels shut and the potassium ones open causing potassium to flood back in and cause the inside to return to a negative state,

Question 36

Explain the process of hyper-polarisation of a membrane

Answer 36

Following depolarisation after a stimulus too many potassium ions diffuse into the axon causing it to reach -80mV which is considered hyper polarised. It returns back to polarisation when sodium pumps reopen.

Question 37

What happens when a stimulus is not intense enough?

Answer 37

Not enough sodium channels open and therefore does not reach full depolarisation.

Question 38

What is meant by the absolute refractory period?

Answer 38

Occurs during depolarisation and depolarisation, no stimulation can occur so no new signals can travel across membrane.

Question 39

What is meant by the relative refractory period?

Answer 39

Occurs during hyper-polarisation, a very intense new signal would have to be fired in order to stimulate the membrane.

Question 40

What is meant by the 'all or nothing' rule?

Answer 40

The intensity of a stimulus must be above a certain threshold to initiate action potential, if it exceeds this then a full action potential is generated and this is maintained through out the axon. No energy is lost along the way. No matter the intensity of the stimulus the action potential will always remain the same size.

Question 41

What happens if the stimulus intensity is very high?

Answer 41

This does not affect the size of the action potential it just means the frequency of the action potential increases (more depolarisation on a graph)

Question 42

What is meant by the nerve impulse is a filter? What is the benefit?

Answer 42

It means that the stimuli must be of a certain intensity to stimulate the brain meaning that our brains do not have to be overloaded with information from minor stimulus.

Question 43

How does temperature affect impulse transmission?

Answer 43

Ions move faster at higher temperatures as they have more kinetic energy therefore warm blooded animals such as birds would have higher transmission rates.

Question 44

How does diameter of axon affect impulse transmission?

Answer 44

If axons are thicker in diameter this means they have a higher volume and therefore it's easier for ions to move through meaning impulses can travel faster.

Question 45

How does Myelination affect impulse transmission?

Answer 45

If the nerve is myelinated it is protected by a fatty sheath in-between these cells are gaps called nodes of ranvier. Depolarisation can only occur in non insulated areas therefore the impulse can jump from node to node instead of travelling across the whole cell creating faster transmission known as saltary conduction.

Question 46

What are the two types of synapses?

Answer 46

- Electrical synapse - Chemical synapse

Question 47

What is an electrical synapse?

Answer 47

When the gap junction is small enough so that the electrical impulse can be directly transferred to the adjacent neurone.

Question 48

What is a chemical synapse?

Answer 48

The gap is too big for the nerve impulse to directly travel through and therefore is transmitted by a neurotransmitter that diffuses across from the pre-synaptic membrane to the post synaptic membrane.

Question 49

What happens when an action potential reaches the pre-synaptic membrane?

Answer 49

Calcium channels open so calcium ions enter the presynaptic knob.

Question 50

What do the calcium ions do in the presynaptic knob?

Answer 50

They cause the synaptic vesicles to move towards to edge and release their neurotransmitters through exocytosis.

Question 51

What happens to neurotransmitters in the synaptic cleft?

Answer 51

They diffuse across to reach receptors on the post synaptic membrane.

Question 52

What happens when the neurotransmitters bind with the receptors on the post synaptic membrane?

Answer 52

The sodium channels open and an action potential is reached/

Question 53

How do sedative drugs work?

Answer 53

They create fewer action potentials in the post synaptic neurone.