Nervous system

Question 1

What is the role of the nervous system?

Answer 1

Is to collect, process and respond to information in the environment and to co-ordinate the workings of organs and cells in the body.

Question 2

What are the 2 main sections that split the nervous system?

Answer 2

central nervous system (CNS) and the peripheral nervous system (PNS)

Question 3

What does the CNS do?
List 2

Answer 3

1) this consists of the brain and spinal cord
2) it processes information sent to it.

Question 4

What does the PNS do?
List 2

Answer 4

1) It consists of all the nerves in the body.
2) it transports communications between the CNS and other anatomical structures.

Question 5

Where are neurones found?

Answer 5

The majority of the PNS is made up of nerve cells.

Question 6

What are the 3 main types of neurones that the body contains?

Answer 6

Sensory, relay and motor neurone

Question 7

What does the sensory neurone do?

Answer 7

Carry impulses from receptors to the CNS.

Question 8

What does the relay neurone do?

Answer 8

Connect sensory neurones to motor neurones.

Question 9

What does the motor neurone do?

Answer 9

Carry impulses from CNS to effectors.

Question 10

What does the dendrites do and where are they found?

Answer 10

Receive signals from other neurones. They are found on the post synaptic end of a synapse.

Question 11

What does the axon do?

Answer 11

conducts or transmits the impulses or action potential down the neurone.

Question 12

What does the axon terminal do?

Answer 12

transmit signals to other neurones or cells across a synapse - the pre-synaptic end of the synapse.

Question 13

What does the cell body do?

Answer 13

contains cytoplasm and nucleus.

Question 14

What does the Schwann cells do?

Answer 14

wrap themselves along the axon - make a myelin sheath.

Question 15

What does the myelin sheath do?

Answer 15

insulates the axon - it speeds up the transport of action potentials by allowing saltatory conduction.

Question 16

What do the nodes of ranvier do?

Answer 16

small uninsulated gaps between Schwann cells - allow saltatory conduction to occur.

Question 17

what are the 4 main stages of transmitting an impulse along an axon?

Answer 17

1) resting state
2) depolarisation
3) repolarisation
4) refactory period

Question 18

what is a nerve impulse?

Answer 18

it is a wave of electrochemical changes that occur across the axon.

Question 19

what is resting state?

Answer 19

1) this is the state when no impulse is being conducted - sodium and potassium ion channels in the nerve membrane are closed.
2) the axon area has a relative potential of 70 mV compared to outside the cell.

Question 20

what is depolarisation?

Answer 20

During this period, sodium ion channels in the axon membrane open, and sodium ions diffuse into the cell down the concentration gradient, making the axon charge more positive, up to +40 mV. During the depolarisation stages, some Na+ ions diffuse along the axon, triggering depolarization in the next area.

Question 21

what is repolarisation?

Answer 21

during this period sodium ion channels close and potassium ion channels open - potassium ions diffuse out of the cell - this makes the axon charge more negative, down to 90 mV.

Question 22

what is the refactory period?

Answer 22

all ion channel proteins are closed - a sodium-potassium pump actively transports sodium ions out of the axon and potassium ions into the axon - this gets the potential difference to 70 mV.

Question 23

what happens when a response to a signal occurs?
list 3 steps

Answer 23

1) the dendrite end of the axon becomes depolarised.
2) the depolarisation spreads down the axon, the first section repolarises.
3) the action potential continues to travel down the axon.

Question 24

what is saltatory conduction?

Answer 24

in myelinated neurones the speed at which the action potential travels is increased.

Question 25

how does saltatory conduction occur? list 4

Answer 25

1) area at repolarisation -----> Na+ channels closed and K+ channels open. - action potentials can only occur at nodes of Ranvier. - so local circuits of current are set up to trigger depolarisation at the next node of Ranvier. 2) area at action potential ------> all Na+ channels open and K+ channels closed. 3) node starting to become depolarised --------> Na+ channels starting to open and K+ channels closed. 4) node at resting potential ------> all ion channels closed. - in this way, the action potential jumps from one node of Ranvier to the next. - this speeds up action potential transmission.

Question 26

what do synapses do?

Answer 26

they allow action potentials to be transmitted from one neurone to another. They also ensure action potentials only experience a one way flow.

Question 27

what happens at the synapse? list 9

Answer 27

1) action potential arrives and depolarises the pre-synaptic membrane. 2) calcium ion channels open and calcium ions diffuse into the pre-synaptic knob. 3) synaptic vesicles move to and fuse with the presynaptic membrane by exocytosis. 4) neurotransmitters are released into the synaptic cleft. 5) neurotransmitters diffuse across the synaptic cleft. 6) NT binds to the receptor proteins. 7) the receptor proteins open allowing sodium ions to diffuse into the post-synaptic knob. 8) the post-synaptic membrane is depolarised. 9) a new action potential is formed.