Nerves And Receptors

Question 1

3 main types of neuron

Answer 1

Sensory, intermediate and motor
Most have a cell body, dendrites, axon, Schwann cells, myelin sheath and nodes of Ranvier.
Electrical impulse moves from dendrite to axon.

Question 2

Reflex arc

Answer 2

Stimulus - receptor - sensory neuron - intermediate neuron - motor neuron - effector (muscle)

Allows rapid reaction - prevent damage to body tissues, don’t need to be learnt. Only 3 neurons.

Question 3

Resting potential is maintained

Answer 3

Sodium ions pumped out of axon by sodium-potassium pump using active transport (ATP needed)
3 sodium ions pumped out of axon for every 2 potassium ions in
Membrane is more permeable to potassium

Question 4

Stages of an action potential

Answer 4

1) Some potassium ion channels always open with K+ leaving from axon out of the cell by diffusion
2) Voltage-gated sodium ion channels open
3) Sodium ions enter axon by diffusion
4) Axon becomes depolarised (have a +40mV charge). More Na+ channels open (positive feedback)
5) Sodium ion channels close
6) More potassium channels open
7) Potassium ions leave axon by diffusion
8) Axon becomes hyper-polarised (-85mV)
9) Some potassium ion channels close
10) Sodium-potassium pump restores resting potential (-65mV)

Question 5

Myelinated axons

Saltatory conduction

Answer 5

Myelin insulates axon
Ions can only pass through plasma membrane of axon at nodes of Ranvier so action potential are only generated here
Impulse jumps from node to node
Much quicker

Question 6

Unmyelinated axon

Answer 6

Whole length of the membrane must be depolarised

Question 7

Refractory period

Answer 7

Time during which a new action potential cannot be generated as the cell is in hyperpolarisation.
Sodium ion channels are closed, so cannot enter.
Helps action potentials pass in one direction and form discrete impulses.

Question 8

All or nothing principle

Answer 8

If enough sodium ions enter the cell it reaches its threshold, so it will cause more sodium ion voltage gates channels to open and cause depolarisation.
If not then there is no impulse.
All action potentials are the same size of +40mV.

Question 9

Pacinian corpuscle

Answer 9

A receptor in the skin and joints that detect pressure
When the membrane layers surrounding the end of the neurone are distorted it causes the stretch-mediated sodium ion channels to open.
Sodium ions move into the neurone, if enough enter for the charge to reach the generator potential then an action potential will be transmitted along the sensory neurone.

Question 10

Rod cells

Answer 10

Allow us to see black and white

Low visual acuity due to several rod cells being attached to each bipolar cell

Question 11

Cone cells

Answer 11

Detect colour
High visual acuity due to lots of them being near the fovea. Also each connects to a single bipolar neurone so the brain receives info from each cone cell individually.

Question 12

If neurone transmits series of impulses

Answer 12

Oxygen consumption increases
More respiration
More ATP supplied for active transport in sodium-potassium pump