The Nervous System

Question 1

What are neurones

Answer 1

Specialised cells for the rapid transmission of nerve impulses

Question 2

What are nerves

Answer 2

Bundles of nerve fibres called axons or dendrons which are long extensions of a single neurone

Question 3

Differences between sensory and motor neurones: dendron

Answer 3

Sensory neuron has a long dendron and motor no one has no dendron

Question 4

Differences between sensory and motor neurones: axon

Answer 4

Sensory have a short axons and motor has a long axon

Question 5

Differences between sensory and motor neurones: cell body

Answer 5

Sensory cell body attached to dendron motor cell body at end of neurone

Question 6

Differences between sensory and motor neurones: dendrites

Answer 6

Motor dendrites connect to cell body

Question 7

Cell body

Answer 7

Contains nucleus and other organelles surrounded by granular cytoplasm

Question 8

Dendrites

Answer 8

Highly branched fibres that receive stimuli from receptors or adjacent neurones they connect impulses towards the cell body

Question 9

Axon

Answer 9

Extension of the neurone carries nerve impulses away from the cell body transmits nerve impulses to other neurons or receptors

Question 10

Myelin sheath

Answer 10

Thick insulating layer around axon that has high electrical resistance from Schwann cells helps transmit neurons faster

Question 11

Node of ranvier

Answer 11

Gaps along the myelin sheath where axon is exposed which aids the transmission of the nerve action potential along the axon

Question 12

What is the resting potential

Answer 12

-70mv

Question 13

Describe resting potential

Answer 13

The sodium potassium pump creates a concentration gradient across the membrane

K+ diffuses out down the concentration gradient so the outside is positive and the inside is negative

The electrical gradient will put potassium back into the cell

At -70mv potential difference the two gradients counteract eachother- no movement of k

Question 14

What is resting potential maintained by

Answer 14

Sodium pump, relative permeability of membrane, and movement of potassium ions

Question 15

What is action potential?

Answer 15

Change in permeability if cell membrane to sodium ions which causes a temporary reversal of charge

Question 16

Describe an action potential

Answer 16

Few sodium ions diffuse in from Axon

Sodium gates open and sodium floods in down the concentration of electrochemical gradient

Axon positive on the inside and negative on the outside for 1 ms

Depolarisation= +40mv

At the end of this brief depolarisation sodium channels close again and Excess sodium rapidly pumped out actively in preparation for the next impulse

Question 17

Describe the 4 stages of ionic changes during axon excitation

Answer 17

1) Voltage dependent sodium channels open so they flow into the axon depolarising the membrane

2) Voltages dependent sodium channels close and the volted potassium channels open- potassium leaves axon depolarising membrane
Sodium is pumped out

3) Hyperpolarisation slight overshoot of the membrane potential to more negative than resting potential
4) Voltage dependent potassium channels close potassium diffuses back into the axon to recreate resting potential

Question 18

Salatory conduction

Answer 18

In myelinated neurones ions can only pass in and out of the axons freely at the nodes of Ranvier- action potentials only occur at the nodes. Action potential jumps from one to the next which speeds up transmission as ionic movements associated with action potential occur less frequently and less time

Question 19

How does the action potential move across the synapse

Answer 19

Calcium channels open in the presynaptic neuron

Calcium ions flood in due to reversal of charges

Vesicles on the pre-synaptic neurone fuse with the membrane

Neurotransmitter ACh is released into the synaptic cleft by exocytosis

It diffuses across the synaptic cleft and binds to receptors on sodium ion channels on post synaptic neurone

Channels open and sodium ions flood in down the concentration gradient setting an action potential

Postsynaptic membrane depolarises if the threshold value is reached an action potential is generated

ACh is broken Down into acetyl and co-line in the synaptic left which defuses back into the presynaptic neuron ATP is used to re-combine them

Question 20

Role of synapses: convergence

Answer 20

Many pre-synaptic neurone is converge on any single postsynaptic neuron
Many stimuli warning us about one danger

Question 21

Role of synapses: divergence

Answer 21

Axons of most pre-synaptic neurons divided into many branches that diverge to many postsynaptic neurones

Question 22

Role of synapses: acclimatisation

Answer 22

After repeated stimulation a synapse run out of vesicles so no response

Question 23

Neurotransmitters: cholinergic nerves

Answer 23

Nerves using acetylcholine in voluntary response

Question 24

Neurotransmitters: Adrenergic nerves

Answer 24

Use noradrenaline in the autonomic system

Question 25

Autonomic system: sympathetic

Answer 25

Secretes noradrenaline

Increased heart rate, pupil dilation and ventilation

Question 26

Autonomic system: parasympathetic

Answer 26

Secretes acetylcholine

Decreased heart rate, pupil construction, decreased ventilation

Question 27

The reflex arc

Answer 27

Nerves are sent to the spinal-cord not the brain for a faster reaction

Question 28

Structure of the spinal-cord

Answer 28

Tube made up of core grey matter surrounded by white matter

Question 29

Grey matter

Answer 29

Consists of the cell bodies of neurons in the CNS

Question 30

White matter

Answer 30

Nerve fibres of neurons in the CNS