Neuronal Communication

Question 1

In a sensory neurone where is the cell body located?

Answer 1

in the middle of two extensions

Question 2

Which extension in a sensory neurone carries impulses from the sensory receptors towards the cell body?

Answer 2

the dendron

Question 3

Electrical impulses are carried away from the cell body in a sensory neurone by which extension?

Answer 3

the axon

Question 4

What type of cells form the myelin sheath?

Answer 4

Schwann cells

Question 5

What are the gaps in between the Schwann cells called?

Answer 5

the nodes of Ranvier

Question 6

What does myelin sheath act as?

Answer 6

an electrical insulator

Question 7

Where are dendrites located on a motor neurone?

Answer 7

around the cell body

Question 8

Where is the cell body located on a motor neurone?

Answer 8

at one end

Question 9

Does a motor neurone have a dendron?

Answer 9

No only an axon

Question 10

What direction does an electrical impulse travel along an axon of a motor neurone?

Answer 10

from the cell body to the axon terminal

Question 11

Do relay neurones have axons or dendrites?

Answer 11

relay neurones can have multiple short dendrons and short axons

Question 12

What direction does an electrical impulse travel along a relay neurone?

Answer 12

from dendrites to axons

Question 13

What is the state called when there is no electrical impulse travelling along a neurone?

Answer 13

resting state

Question 14

In a resting neurone, what is the charge inside of the membrane compared to the outside? What do scientists call the membrane?

Answer 14

negative and they say that the membrane is polarised

Question 15

What is the resting potential of a neurone?

Answer 15

-70 mV

Question 16

In an axon membrane, the sodium-potassium pump does what?

Answer 16

actively transports sodium ions out of the axon and, at the same time, it actively transports potassium ions into the axon

Question 16

In every pump of the sodium-potassium pump, how many sodium ions are pumped out of the axon?

Answer 16

3

Question 16

In every pump of the sodium-potassium pump, how many potassium ions are pumped into the axon?

Answer 16

2

Question 16

In a resting state, are the ion channels in the axon membrane mainly open or closed?

Answer 16

• sodium ion channels are mainly closed so there is a low rate of diffusion of sodium ions into the axon
• the potassium ion channels are mainly open so there is a high rate of diffusion of potassium ions out of the axon

Question 17

What are the two factors that contribute to the resting potential of an axon membrane?

Answer 17

• the sodium-potassium pump transfers three sodium ions out of the axon for every two potassium ions transferred in
• the outward movement of potassium ions via facilitated diffusion through ion channels

Question 18

What does the Pacinian corpuscle detect?

Answer 18

pressure

Question 19

Where are Pacinian corpuscles located?

Answer 19

in the deep layers of the skin

Question 20

Where on the body are high numbers of Pacinian corpuscles located and where else are Pacinian corpuscles located?

Answer 20

the fingertips and soles of the feet and they are also in joints

Question 21

Why are Pacinian corpuscles also found in joints?

Answer 21

they detect when the joints are changing direction

Question 22

What does a Pacinian corpuscle produce in response to pressure? And what do scientists call this?

Answer 22

a nervous impulse (a generator potential)

Question 23

Why do scientists say that the Pacinian corpuscle acts as a transducer?

Answer 23

the Pacinian corpuscle converts mechanical energy (pressure) into the energy of a nervous impulse

Question 24

What is located in the centre of a Pacinian corpuscle?

Answer 24

the end of the sensory neurone

Question 25

In a Pacinian corpuscle, what is the end of the sensory neurone surrounded by?

Answer 25

many layers of connective tissue

Question 26

In a Pacinian corpuscle, what is between each layer of connective tissue?

Answer 26

a layer of gel

Question 27

In the membrane of the end of the sensory neurone in a Pacinian corpuscle, what are the sodium ion channels called?

Answer 27

stretch-mediated sodium channels

Question 28

What happens when pressure is applied to a Pacinian corpuscle?

Answer 28

Pressure causes the shape of the Pacinian corpuscle to change. This shape change causes the membrane of the neurone to stretch which causes the stretch-mediated sodium channels to widen so now sodium ions diffuse through the channels into the neurone. This causes the interior of the neurone to become positively charged (the neurone has depolarised). A generator potential has been created.

Question 29

What does the generator potential (in a Pacinian corpuscle) cause? What do scientists call this?

Answer 29

a wave of depolarisation to pass down the sensory neurone to the CNS and scientists call this wave of depolarisation an action potential

Question 30

As well as ion channels and sodium-potassium pumps, what other protein structures are in an axon membrane?

Answer 30

voltage-gated ion channels

Question 31

When do voltage-gated ion channels open?

Answer 31

when the membrane potential reaches a certain value

Question 32

What does a stimulus trigger first on the axon membrane?

Answer 32

the energy of the stimulus triggers voltage-gated sodium ion channels to open and sodium ions now rapidly diffuse into the axon

Question 33

After a stimulus is detected, what does the initial rapid diffusion of sodium ions into the axon cause?

Answer 33

this causes the inside of the axon to become less negative and this now triggers more voltage-gated sodium ion channels to open, allowing more sodium ions to diffuse into the axon (scientists call this positive feedback)

Question 34

After a stimulus is detected, what is the influx of sodium ions into the axon called?

Answer 34

depolarisation

Question 35

After the depolarisation of the membrane, the inside of the membrane reaches a potential of what?

Answer 35

+40mV

Question 36

During an action potential, what happens when the membrane potential reaches around +40mV?

Answer 36

this triggers the voltage-gated sodium ion channels to close and the voltage-gated potassium ion channels to open - sodium ions stop diffusing into the axon and potassium ions now diffuse out of the axon down their electrochemical gradient

Question 37

Steps of sliding filament model

Answer 37

1, Tropomyosin (held in place by troponin) prevents myosin head from attaching to binding site on actin. 2, Calcium ions (from sarcoplasmic reticulum) bind to troponin which moves/pulls tropomyosin. 3, Myosin head (ADP attached) can now attach to binding site on actin. 4, Myosin head bends which moves actin filament. ADP released. (power stroke) 5, ATP attaches to the myosin head. Causes myosin head to detach from actin. 6, Hydrolysis of ATP to ADP - provides energy for myosin head to resume its normal position. 7, Myosin head attaches to another binding site + repeats.

Question 38

A muscle fibre only contains enough ATP to allow for how many seconds of contraction?

Answer 38

1 - 2 seconds

Question 39

Why is creatine phosphate important in a muscle cell?

Answer 39

creatine phosphate maintains a supply of ATP in a muscle cell by rapidly transferring an inorganic phosphate to ADP, reforming ATP