Nervous system- module 5

Question 1

What dos the sensory neurone do

Answer 1

Transmit nerve impulses from receptors to CNS

Question 2

what does the Relay neurone do

Answer 2

Transmits nerve impulses between sensory and motor neurones

Question 3

role of motor neurone

Answer 3

Transmit nerve impulses from CNS to receptors

Question 4

flow diagram of stimulus to response in nervous system

Answer 4

Stimulus -> receptor - sensory neurone - relay - motor - effector - response

Question 5

what are Pacinian corpuscles

Answer 5

Mechanoreceptors. they detect mechanical stimuli, such as pressure and movement.
Found deep in the skin are abundant in fingers and soles of the feet

Question 6

How do Pacinian corpuscles convert pressure into a nervous impulse? process

Answer 6

1) pressure applied to Pacinian corpuscle
2)Lamellae become deformed and press on sensory nerve ending
3)Stretch mediated sodium channels change shape (widen) in the sensory neurone cell
4)sodium ion channels open
5) sodium ions diffuse into cell
6)creates generator potential (if threshold met)
7) Leads to action potential (nerve impulse) down sensory neurone

Question 7

structure of sensory neurone

Answer 7

Short dendrites & long dendron to carry impulses from receptor cells to cell body.
One short axon that carries impulses from cell body to CNS

Question 8

structure of motor neurone

Answer 8

Short dendrites that carry nerve impulses from CNS to cell body (located in CNS).
One long axon that carries impulses from cell body to effectors.

Question 9

structure of cell body of neurone

Answer 9

Cell body- contains nucleus and other organelles. Has large amounts of ER & mitochondria to make neurotransmitters.

Question 10

where do dendrites and axons carry electrical impulses

Answer 10

Dendrites and dendrons carry electrical impulses towards cell body.
Axons- carry nerve impulses away from cell body.

Question 11

How is resting potential maintained

Answer 11

1)when a neurone is transmitting an impulse, the potential difference across its membrane is called a resting potential
2)the potential difference across the membrane at rest is around -70mV
3)This resting potential is due to sodium-potassium pumps and potassium ion channels
4)The pumps use active transport to pump 3 sodium ions(Na^+) out of the neurone for every 2 potassium ions(K^+). This requires ATP
5) The membrane isn’t permeable to sodium ions, so they can’t move back into the neurone. This creates a sodium ion electrochemical gradient
6) Potassium ion channels are open when the neurone is at rest, so the membrane is permeable to potassium ions
7)Some potassium ions move by facillitated diffusion back outr of tge neurone down the concentration gradient
8)In total, more positive ion move out of the neurone rather than in, making the outside of the neurone more positively charged than the inside. The membrane is said to be polarised

Question 12

What happens after a stimulus to a neurone

Answer 12

energy of stimulus triggers some sodium ion channels to open, making the membrane more permeable to Na+

Na+ ions diffuse into axon down electrochemical gradient. Makes inside of neurone less negative

Question 13

what happens during depolarisation

Answer 13

potential difference reaches the threshold (around -55mV) which opens voltage-gated sodium ion channels -> more Na+ diffuse into neurone - this is positive feedback

Question 14

what happens at a potential difference of +40mV

Answer 14

voltage-gated sodium ion channels close and voltage-gated potassium ion channels open.
Sodium ions can no longer enter the axon

Potassium ions diffuse out of the axon, causing the inside of the axon to become more negative than the outside

Question 15

what happens during hyperpolarisation

Answer 15

as the voltage-gated potassium ion pumps are slow to close, too many potassium ions diffuse out of the neurone.
This causes the potential difference to become more negative than the the resting potential (less than -70mV)

Question 16

What happens during repolarisation

Answer 16

the sodium potassium pumps returns the membrane to resting potential by pumping sodium ions out and potassium ions in

Question 17

refractory period

what is it

what does it ensure

Answer 17

After an action potential, the neurone can’t be excited straight away
the ion channels need to recover and can’t be made to open.

This acts as a time delay and ensures that action potentials don’t overlap and pass as separate impulses.
It also ensures impulses are unidirectional -only travel in one direction

Question 18

Wave of depolarisation

Answer 18

-when an action potential happens, some sodium ions diffuse sideways, opening channels in the next part of the neurone.

-they always move away from areas in the refractory period as the channels can’t open there- these are called localised currents

-This triggers the action potential in the next segment

this means a wave of depolarisation moves along the neurone - the electrical impulse is said to ‘propagate’ down the axon

Question 18

Wave of depolarisation

Answer 18

-when an action potential happens, some sodium ions diffuse sideways, opening channels in the next part of the neurone.

-they always move away from areas in the refractory period as the channels can’t open there- these are called localised currents

-This triggers the action potential in the next segment

this means a wave of depolarisation moves along the neurone - the electrical impulse is said to ‘propagate’ down the axon

Question 19

what effects the speed of conduction of action potentials

Answer 19

Myelination

Axon diameter

Temperature

Question 20

how does axon diameter affect the speed of conduction of action potentials

Answer 20

The bigger the axon diameter, the faster the impulse is transmitted.
There is less resistance to the flow of ions in the cytoplasm, compared with that in a smaller axon

Question 21

how does temperature affect the speed of conduction of action potentials

Answer 21

the higher the temperature, the faster the nerve impulse. Because ions diffuse faster at higher temperatures. Generally only occours up to 40oC because denature

Question 22

Myelination

Answer 22

-myelin sheath = electrical insulator
it is made of schwann cell wrapped around the axon or dendron
-The bare parts between schwann cells are called the nodes of Ranvier
-Sodium ion channels are concentrrated at these nodes
-Myelinated axons transfer electrical impulses much faster than non-myelimnated axons (due to saltatory conduction)

Question 23

Saltatory Conduction

Answer 23

-depolarisation can only occour at nodes of Ranvier where no myelin is present -> sodium ions can only pass through channels here
-Longer localized circuits arise between the adjacent nodes -> action potential ‘jumps’ from one node to another

-Quicker as less channels to open, so less ions to move
-energy efficient -> less ATP needed for repolarisation in Na+K+ pump
-Myelin not permeable to sodium or potassium ions
-sodium ions diffuse into axon during depolarisation, diffuse along axon, sets up local current - causes sodium to diffuse to next node
-Sodium moves towards more negative region

Question 24

what neurotransmitter is used in a cholinergic synapse

Answer 24

acetylcholine ACh

Question 25

what is a synapse

Answer 25

a junction between two neurones or a neurone and effector cell
-Ensures impulses are unidirectional
-Impulses are transmitted in synapses using neurotransmitters

Question 26

Process of synaptic transmission

Answer 26

1)Action potential reach end of synaptic neurone
2) depolarisation causes voltage-gated Ca^2+ cahnnels to open
3)Ca^2+ diffuse into presynaptic knob
4)Vesicles containing ACh fuse with presynaptic membrane
5)ACh released into synaptic cleft by exocytosis
6)ACh diffuses across synaptic cleft and binds to cholinergic receptors on sodium ion channels
7)Sodium ion channels open and sodium ions diffuse into postsynaptic neurone
8)Action potential triggered if threshold is met
9)ACh molecules at receptors broken down by acetylcholinesterase

Question 27

SYNAPTIC DIVERGENCE

Answer 27

when one neurone connects to many neurones.

information can be dispersed to many different parts of the body

Question 28

synaptic convergence

Answer 28

When many neurones connect to one neurone

information can be amplified (make stronger)
higher in frequency

Question 29

Summation

Answer 29

where the effect of neurotransmitters released is added together (the sum)

(If a stimulus is weak, only a small amount of neurotransmitter will be released which might not be enough to excite the post synaptic membrane to threshold level)

Question 30

Spatial summation

Answer 30

where two or more presynaptic neurones converge and release their neurotransmitters at the same time -> this can be enough altogether to reach the threshold and trigger an action potential

It allows signals from multiple stimuli to be coordinated in a single response

Question 31

Temporal summation

Answer 31

where two or more impulses arrive in quick succession from the same presynaptic neurone.
-Action potential is more likely as more Neurotransmitter is released into the synaptic cleft

Follow each other extremely quickly so they don’t get broken down

Question 32

how can chemicals affect transmission of nerve impulses

Answer 32

-mimic shape of neurotransmitter
-Block receptors
-Inhibit release of neurotransmitters
-Inhibit enzyme that breaks down neurotransmitters

Question 33

how can a chemical mimic shape of neurotransmitter affect transmission of nerve impulses

Answer 33

chemicals mimic NTs action at receptors e.g: nicotine mimics ACh so binds to same cholinergic receptors in the brain

Question 34

how can a chemical that Blocks receptors affect transmission of nerve impulses

e.g:

Answer 34

block receptors so they can’t be activated by NTs -> results in muscles being paralysed

(e.g curare blocks the ACh so muscle cells can’t be stimulated)

Question 35

how can a chemical Inhibiting the release of neurotransmitters affect transmission of nerve impulses

e.g:

Answer 35

can inhibit release of NTs from the presynaptic neurone, so fewer receptors are activated. E.g: opioids block calcium ion channels so fewer vesicles fuse with the presynaptic membrane and less NT is released

Question 36

how can a chemical -Inhibit enzyme that breaks down neurotransmitters to affect transmission of nerve impulses

Answer 36

Some inhibit the enzyme that breaks down NTs -> more NTs in the synaptic cleft to bind to receptors and are therefore longer
e.g: nerve gas stops ACh from being broken down - can lead to loss of muscle control

Question 37

what two types of nuerotransmitter are there

Answer 37

excitatory

inhibitory

Question 38

what is a excitatory neurotransmitter

Answer 38

a neurotransmitter that results in the depolarisation of the post synaptic neurone. If the threshold is reached in the post synaptic membrane, an action potential is triggered

e.g: acetylcholine

Question 39

what is an inhibitory neurotransmitter

Answer 39

a neurotransmitter which results in the hyperpolarisation of the post synaptic membrane. This prevents an action potential from being triggered.

e.g: GABA in the brain

Question 40

why is the enzyme in the synaptic clefts necessary

Answer 40

-so that neurotransmitters are broken down and

releases them from the receptors

can be recycled

stimulus is not maintained, so another stimulus can arrive and affect the synapse