Neurons and Electrical Impulses in the Nervous System

Question 1

what are neurons

Answer 1

nerve cells present in the nervous system that are specialised for communication. they connect with each other and with other excitable cells like muscles and glands. there are various types and their structure is related to their function

Question 2

what are the different elements to the classical neuron

Answer 2

dendrites, axons and axon terminals

Question 3

where are inputs received on neurons

Answer 3

the dendrites

Question 4

where are the outputs produced on neurons

Answer 4

axon terminals

Question 5

what are the different types of neuron

Answer 5

• purkinje cell
• spinal interneuron
• sensory neuron
• pyramidal neuron
• motor neuron
• bipolar cell

Question 6

where are purkinje cell neurons found

Answer 6

the cerebellum

Question 7

where are spinal interneurons found

Answer 7

the spine

Question 8

where are pyramidal cells found

Answer 8

cerebral cortex

Question 9

where are motor neurons found

Answer 9

spinal cord

Question 10

where are bipolar cells found

Answer 10

retina

Question 11

what is the membrane potential

Answer 11

potential difference that exists across the membrane of all cells

Question 12

what does resting membrane potential arise from

Answer 12

the separation of charges on either side of the membrane

Question 13

what is resting membrane potential determined by

Answer 13

diffusion of potassium ions from the cell interior through the potassium channels. the sodium potassium pump also contributes by moving unequal amounts of sodium and potassium

Question 14

how can membrane potential be altered

Answer 14

by applying an electric current to the cell ie a stimulus. the hyperpolarising current moves the membrane potential further from 0, and a depolarising current moves the membrane potential closer to 0. the membrane potential then returns to the original resting level, and these responses are graded. the amplitude will depend on the size of the stimulus

Question 15

what value does the membrane potential have to reach in order to have depolarisation

Answer 15

-55mV

Question 16

what is action potential amplitude independent of

Answer 16

stimulus intensity

Question 17

what is action potential

Answer 17

a large change in membrane potential, where the membrane potential overshoots zero and reverses polarisation

Question 18

describe the process of generating action potential

Answer 18

• stimulus applied
• depolarisation
• membrane potential moves toward 0 mV
• membrane potential reaches threshold (-55mV) for opening of voltage gated sodium ion channels
• membrane potential moves rapidly toward 0 mV
• start of the action potential
• upstroke of the action potential is due to entry of sodium ions
• sodium ions diffuse inward through voltage gated channels
• when the membrane potential reaches about +35mV the sodium channels shut and the potassium channels open
• potassium channels are also voltage gated
• potassium leave the cell and this makes membrane potential more negative
• after overshoot, the membrane potential returns to original resting level

Question 19

give a summary of action potential

Answer 19

• all or none
• independent of stimulus
• at the threshold, the voltage gated sodium channels open and sodium diffuse in which leads to depolarisation
• at the peak the sodium channels close and the voltage gated potassium channels open. potassium ions diffuse out and there is repolarisation
• resting membrane potential

Question 20

how do local anaesthetics work

Answer 20

they stop nerve conduction by blocking the sodium channels

Question 21

what is the refractory period

Answer 21

after action potential is intiated, the neuron cannot generate another action potential until the first one has ended. this period of inexcitability is known as the refractory period, and happens due to the inactivation of voltage gated sodium channels. the action potentials cannot add together, so they are all or none events

Question 22

how is action potential propagated across the neuron

Answer 22

action potential in one section of axon depolarises adjacent resting parts of the axon, so the action potential is regenerated further along the axon, and the action potentials travel along the axon as waves of depolarisation

Question 23

what does the speed of action potential propagation increase with

Answer 23

the axon diameter

Question 24

do large axons conduct impulses faster or slower than smaller ones

Answer 24

faster

Question 25

in what size of axon is rapid conduction achieved

Answer 25

very large

Question 26

why did vertebrates evolve a means of increasing action potential conduction speed

Answer 26

their speed of action potential propagation is too slow to enable the fast postural reflexes present in vertebrates

Question 27

what is myelination

Answer 27

wrapping a layer of myelin round an axon

Question 28

what does myelination do

Answer 28

it increases the action potential conduction speed

Question 29

what is myelination of axons

Answer 29

myelin is a fatty layer formed by wrapping the membranes of glial cells round the axon, which insulates the axon and improves conduction

Question 30

what are nodes of ranvier

Answer 30

the intervals that interrupt the sheaths of myelin around axons in myelination

Question 31

what is saltatory conduction

Answer 31

the action potential jumps along the axon from node to node

Question 32

what do chemical synapses occur between

Answer 32

- neurons and neurons - neurons and muscle cells - neurons and gland cells

Question 33

what do cells communicate via

Answer 33

synaptic vesicles

Question 34

what are the events at a chemical synapse

Answer 34

- action potential depolarises presynaptic ending - an influx of calcium into the presynaptic ending - vesicles migrate toward the plasma membrane - release of transmitter into the cleft - transmitter binds to receptors on post synaptic cells - leads to changes in post synaptic cells - inactivation of the transmitter

Question 35

what are some general methods of inactivation of transmitter

Answer 35

- reuptake into the presynaptic cell - enzyme destruction

Question 36

what are some neurotransmitter examples

Answer 36

amino acid derivatives - acetylcholine, dopamine, glutamate, glycine, noradrenaline, serotonin and GABA. peptides - substance P, VIP, enkephalins, endorphins

Question 37

what is VIP

Answer 37

vasoactive intestinal polypeptide

Question 38

what is GABA

Answer 38

gamma amino butyric acid

Question 39

what do the effects of transmitters on cells depend on

Answer 39

the type of receptor and second messengers in the post synaptic cell

Question 40

what happens to the activity of a cell if it is depolarised

Answer 40

increased activity known as excitory

Question 41

what happens to the activity of a cell if it is hyperpolarised

Answer 41

decreased activity known as inhibitory

Question 42

what occurs at an excitatory synapse

Answer 42

transmitter causes depolarisation, there is excitatory post synaptic potential which brings the membrane potential nearer to the firing threshold

Question 43

what occurs at an inhibitory synapse

Answer 43

transmitter causes hyperpolarisation. there is inhibitory post synaptic potential which takes the membrane potential further from the firing threshold

Question 44

what can neurons receive inputs from

Answer 44

many other neurons

Question 45

can single post synaptic potentials have an effect on the membrane potential of the post synaptic cell

Answer 45

no they are too small

Question 46

why is it necessary for excitatory post synaptic potentials to add together or summate

Answer 46

the post synaptic potentials are very small and have little effect on the membrane potential of the post synaptic cell

Question 47

when will a post synaptic cell fire

Answer 47

if it receives sufficient excitation to drive the membrane potential beyond threshold. this occurs when it receives many excitatory inputs and few inhibitory inputs within a short time period

Question 48

what is convergence

Answer 48

when each neuron receives many inputs from other cells

Question 49

what is divergence

Answer 49

when each neuron synapses many other cells

Question 50

is the neuron more likely to fire if the excitatory inputs predominate

Answer 50

yes

Question 51

what is a neuromuscular junction

Answer 51

a synapse between a motor nerve and a muscle fibre. it is also referred to as a motor end plate, and the area of contact is greater than in a nerve nerve synapse. one action potential in the nerve leads to muscle contraction.

Question 52

what is the transmitter at a neuromuscular junction

Answer 52

acetylcholine

Question 53

what is acetylcholine broken down by

Answer 53

the enzyme acetyl cholinesterase

Question 54

what are the events at neuromuscular junctions

Answer 54

- the action potential depolarises the motor nerve ending - an influx of calcium ions into the nerve ending - vesicles migrate toward the plasma membrane - release of acetylcholine into the cleft, which then diffuses into the cleft and binds to receptors on post synaptic cells. - choline and acetate are taken up by the neuron

Question 55

can drugs affect synaptic activity

Answer 55

yes

Question 56

how can drugs affect synaptic activity

Answer 56

- synthesis or storage of transmitter - release of transmitter - action of transmitter on receptor - second messenger system - inactivation of transmitter

Question 57

how does botox paralyse facial muscles

Answer 57

prevents the release of neurotransmitter from motor nerves

Question 58

how does the drug beta blocker affect synaptic activity

Answer 58

it blocks beta adrenergic receptors and therefore blocks the release of adrenaline

Question 59

how does black widow spider venom affect synaptic activity

Answer 59

causes neurons to release excessive signalling molecules

Question 60

what does the drug curare do

Answer 60

paralyse muscles

Question 61

how does nicotine affect synaptic activity

Answer 61

increases communication between reward related neurons

Question 62

how does physostigmine affect synaptic activity

Answer 62

interferes with the metabolism of the neurotransmitter acetylcholine

Question 63

what is the axon hillock

Answer 63

the start of the axon

Question 64

what do ligand gated channels respond to

Answer 64

ligands, such as neurotransmitters

Question 65

what does an influx of positive charge into the cell cause

Answer 65

an excitatory post synaptic potential, which leads to depolarisation

Question 66

what does an influx of negative charge into the cell cause

Answer 66

inhibitory post synaptic potential, which leads to repolarisation

Question 67

what can multiple excitatory post synaptic potentials lead to

Answer 67

pushing the membrane potential to a particar threshold value, and this value will depend on the tissue type

Question 68

what is resting membrane potential charge

Answer 68

negative

Question 69

why is myelinated axons a faster way for signals to cross

Answer 69

due to saltitory conduction

Question 70

what is the soma

Answer 70

the cell body

Question 71

why is there a refractory period

Answer 71

to stop action potentials occuring too closely to each other, or going in the opposite direction back down the axon