5.1.3 Neuronal Communication

Question 1

What is a neurone?

Answer 1

a specialised nerve cell that transmits electrical impulses rapidly around the body

Question 2

What is the function of a sensory neurone?

Answer 2

to transmit electrical impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain

Question 3

What is the structure of a sensory neurone?

Answer 3

• one dendron (transmits impulse to cell body)
• cell body
• one axon (transmits impulse from cell body)
• dendron and axon have a myelin sheath

Question 4

What is the function of a relay neurone?

Answer 4

to transmit electrical impulses between neurones

Question 5

What is the structure of a relay neurone?

Answer 5

• cell body
• have many short dendrons and axons
• non-myelinated

Question 6

What is the function of a motor neurone?

Answer 6

to transmit electrical impulses from a sensory or relay neurone to an effector (aka muscle or gland)

Question 7

What is the structure of a motor neurone?

Answer 7

• cell body
• lots of short dendrons (transmit impulses to cell body)
• one long myelinated axon (transmits impulses from cell body)

Question 8

What is a cell body of a neurone?

Answer 8

• made up of nucleus, endoplasmic reticulum and mitochondria in cytoplasm
• produces neurotransmitters

Question 9

What is an axon?

Answer 9

• a singular, elongated nerve fibre

- transmits impulse away from cell body

Question 10

What are dendrons?

Answer 10

• short extensions that come out of the cell body
• split into smaller dendrites
• transmit impulses towards cell body

Question 11

What is a myelin sheath?

Answer 11

layers of plasma membrane around the axon

• produced by Schwann cells growing around the axon
• act as an insulating layer so that impulse can be transmitted quicker

Question 12

What are nodes of Ranvier?

Answer 12

small gaps between each Schwann cell where the impulse jumps from one node to the next

Question 13

What cells produce the myelin sheath?

Answer 13

Schwann cells

Question 14

Why are impulses transmitted quicker in myelinated neurones?

Answer 14

at every node of Ranvier, the impulse jumps from one node to the next, which means it is transmitted quicker

Question 15

What are sensory receptors?

Answer 15

groups of specialised cells which detect a change and convert this detected stimulus into a nerve impulse
-are usually located in sense organs

Question 16

What are the main types of sensory receptors?

Answer 16

• photoreceptor
• thermoreceptor
• chemoreceptor
• mechanoreceptor

Question 17

What is the stimulus of a thermoreceptor?

Answer 17

heat

Question 18

What is the stimulus of a photoreceptor?

Answer 18

light

Question 19

What is the stimulus of a chemoreceptor?

Answer 19

chemicals

Question 20

What is the stimulus of a mechanoreceptor?

Answer 20

pressure and movement

Question 21

Name an example of a thermoreceptor

Answer 21

end-bulbs of Krause

-located in the tongue

Question 22

Name an example of a photoreceptor

Answer 22

cone cell

-located in eye

Question 23

Name an example of a chemoreceptor

Answer 23

olfactory receptor

-located in nose

Question 24

Name an example of a mechanoreceptor

Answer 24

Pacinian corpuscle
-located in skin

Baroreceptor
-located in blood vessels near heart

Question 25

How does the Pacinian corpuscle convert its stimulus into an impulse?

Answer 25

- in resting state, stretch-mediated Na+ channels are too narrow for Na+ to pass through (resting potential) - when pressure is applied, the corpuscle changes shape so the axon stretches so its membrane is deformed, causing the Na+ channels to widen - Na+ diffuse in - this makes the membrane potential becomes +ve (is depolarised) which is known as a generator potential - this generator potential creates an action potential so the impulse passes along the neurone

Question 26

What is resting potential?

Answer 26

potential difference across membrane when it's not transmitting an impulse (aka it is at rest) - membrane is polarised - potential difference is about -70mV

Question 27

How is resting potential established?

Answer 27

- sodium/potassium pump actively transports 3Na+ out for every 2K+ it transports in - Na+ channels are closed so Na+ can't move back into the axon but K+ channels are open so K+ can diffuse out of the axon - this means there are more +ve ions outside the axon so the axon is more -ve so reaches a resting potential of -70mV

Question 28

What is the potential difference at resting potential?

Answer 28

-70mV

Question 29

What is an action potential?

Answer 29

when an electrical impulse is created by the depolarisation in the membrane of a neurone

Question 30

How is an action potential generated?

Answer 30

- neurone is at resting potential (-70mV) where some K+ channels are open and Na+ channels are closed - energy of the stimulus causes voltage-gated Na+ channels to open so Na+ diffuse out of the axon, making it less -ve - by positive feedback, more voltage-gated Na+ channels open so more Na+ leave and the inside of the axon becomes more +ve (it is depolarised) - when pd reaches +40mV, voltage-gated Na+ channels close and voltage-gated K+ channels open - K+ diffuse out of axon, making the inside of the axon more -ve (it is repolarised) - as lots of K+ diffuse out, axon becomes more -ve than at normal rest (it is hyperpolarised) - voltage-gated K+ channels close and sodium/potassium pump actively transports Na+ in and K+ out, bringing the axon back to resting potential (-70mV)

Question 31

What is the potential difference of the axon once it is depolarised?

Answer 31

+40mV

Question 32

What is a synapse?

Answer 32

the gap between two neurones or a neurone and an effector

Question 33

How is an impulse transmitted across a synapse?

Answer 33

- action potential (Na+) reaches the end of the pre-synaptic neurone - the depolarisation of the pre-synaptic neurone causes Ca2+ channels to open - Ca2+ diffuse in - this causes vesicles containing neurotransmitters t move across the pre-synaptic knob and to fuse with the pre-synaptic membrane so that the neurotransmitters are released into the synapse by exocytosis - the neurotransmitters diffuse across the synapse and bind to receptors on Na+ channels on the post-synaptic membrane, causing these channels to open - Na+ diffuses into post-synaptic knob and along the neurone, causing an action potential (aka impulse) to be generated

Question 34

What neurotransmitter do cholinergic synapses use?

Answer 34

acetylcholine

Question 35

What is acetylcholine broken down into after an impulse is transmitted across a cholinergic synapse?

Answer 35

acetyl and choline | -by acetylcholinesterase

Question 36

How do synapses ensure impulses are only transmitted in one direction?

Answer 36

receptors for neurotransmitters are only on the post-synaptic membranes

Question 37

What is an inhibitory synapse?

Answer 37

a synapse where when neurotransmitters bind to receptors on the post-synaptic membrane, the membrane is hyperpolarised (pd becomes more -ve) which prevents an action potential from being fired

Question 38

What is an excitatory synapse?

Answer 38

a synapse where when neurotransmitters bind to receptors on the post-synaptic membrane, the membrane is depolarised (pd becomes less -ve) which causes an action potential to be fired if the threshold is reached

Question 39

What is synaptic divergence?

Answer 39

when one neurone connects to several neurones so the information can be dispersed to different parts of the body

Question 40

What is synaptic convergence?

Answer 40

when multiple neurones connect to one neurone so information can be amplified

Question 41

What is summation?

Answer 41

the process where whether a new action potential is generated after the synapse is controlled based on the conc of neurotransmitter released by the pre-synaptic neurone -an action potential is only generated when the neurotransmitters reach a threshold

Question 42

What is spatial summation?

Answer 42

when neurones converge and multiple pre-synaptic neurones release neurotransmitters which diffuse across the synapse to the post-synaptic neurone -if only one of the pre-synaptic neurones receives the signal (and releases neurotransmitters) no action potential would be generated on the post-synaptic knob

Question 43

What is temporal summation?

Answer 43

occurs when there is only one pre and post-synaptic neurone and higher frequencies of action potentials in the pre-synaptic neurone cause higher concs of neurotransmitters to be released so lots bind to the receptors on the post-synaptic neurone and cause an action potential/impulse to be triggered -if there is only one action potential/impulse received, only low concs of neurotransmitters could be released so not enough bind to the post-synaptic neurone to trigger an action potential

Question 44

What is the threshold when an action potential is being created?

Answer 44

-50mV