Nervous Impulse

Question 1

How is the resting potential established in axons?

Answer 1

Sodium potassium pump 
Using ATP 
3 sodium out, for every 2 in 
Membrane permeable to potassium but not to sodium so potassium ions diffuse down electrochemical gradient via potassium ion channels (facilitated diffusion)  
Outside is more positive than inside

Question 2

How is a generator potential generated?

Answer 2

When stimulus is detected the membrane becomes excited increasing it’s permeability. This allows more ions to diffuse in and our changing the membrane potential.

Question 3

When is an action potential formed?

Answer 3

When the generator potential is greater or equal to the threshold level

Question 4

Describe the process of waves of depolarisation

Answer 4

Action potential occurs
Sodium ions that enter diffuse sideways clasp using new sodium ion channels to open and to diffuse in
This spreads and causes the wave of depolarisation to travel along the neurone

Question 5

Describe an action potential.

Answer 5

Stimulus excites membrane,
Sodium channels open
Sodium diffuse in down electrochemical gradient, membrane becomes more positive
When threshold level is met, more sodium channels open and diffuse in causing depolarisation
Sodium ion channels close, potassium ion channels open and potassium ions diffuse out membrane becomes more negative again
Potassium ion channels slow to close so too many k+ diffuse out of the neurone (too negative)
Ion channels reset and the SP pump returns the membrane to the resting potential

Question 6

What happens when a big stimulus occurs compared to a small one?

Answer 6

The frequency of the action potentials increases (they are the same size regardless)

Question 7

How does myelinated affect the speed of conduction along a neurone?

Answer 7

In myelinated neurones, depolarisation only occurs at the nodes of ranvier and the myelin sheaths cytoplasm conducts enough electrical charge to depolarise the next node so the impulse jumps from node to node, this increases the speed of the conduction as it does not travel along the entire neurone

Question 8

How does an increase in temperature affect the speed of conduction along the neurone?

Answer 8

Increase in speed
As the rate of diffusion of sodium ions into the neurone is quicker (only till 40oC as after this temperature proteins denature)

Question 9

How does axon diameter affect the speed of conduction along a neurone?

Answer 9

Increase the speed of conduction as with a wider axon diameter, there is less resistance to the flow of ions

Question 10

Describe the process of synaptic transmission

Answer 10

Action potential arrives at presynaptic neurone
Causes calcium job channels to open and calcium ions to diffuse into the presynaptic neurones knob
Calcium ions cause vesicles containing neurotransmitter (acetyl choline) to diffuse and bind to the membrane of the knob
Exocytosis occurs and the neurotransmitter diffuses down concentration gradient in the synaptic cleft and binds to receptors on the post synaptic neurone
Causes sodium ion channels to open and diffuse in
If excitatory post-synaptic potential is greater than threshold action potential is generated.
In the synaptic cleft, Ach is removed so the response does not keep occurring
It is broken down by acetylcholinesterase into ethanoic acid and choline which are reabsorbed by the presynaptic neurone.
ATP is used to reform acetylcholine

Question 11

What is spatial summation?

Answer 11

Where two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone. The small amounts of neurotransmitter combined is enough to reach the threshold and reach the action potential

Question 12

What is temporal summation?

Answer 12

This is where two or more nerve impulses arrive in quick succession from the same presynaptic neurone. This makes an action potential more likely as more neurotransmitter is released into the synaptic cleft

Question 13

What is a receptor?

Answer 13

A cell or protein that causes a response to a particular stimulus. Converting the energy of the stimulus into electrical energy

Question 14

What are the 3 types of neurones and what are there functions?

Answer 14

Sensory neurone - transmit electrical impulses from receptors to the central nervous system (CNS)
Motor neurone - transmits electrical impulses from CNS to effectors
Relay neurone - transmits electrical impulses between sensory and motor neurones

Question 15

What is a simple reflex?

Answer 15

Rapid, involuntary response to a stimulus
Communication pathway goes through the spinal chord but not through conscious areas of the brain, so the response occurs automatically
These are protective responses
Reduce risk of damage to Organism

Question 16

What is a tactic response?

Answer 16

Directional movement in response to a stimulus. Direction of stimulus affects response

Question 17

What is a kinetic response?

Answer 17

Non- directional or random movement in response to a stimulus. Intensity of stimulus affects response

Question 18

How do hormonal and nervous systems differ?

Answer 18

Hormones diffuse into the blood, not released directly onto target cells. They diffuse out of the blood all over the body but only bind to specific receptors on target cells
Chemical communication is therefore slower
They aren’t broken down as easily as neurotransmitters and so affects of hormones last longer
Hormones transported all over the body, so the response is more widespread providing the target cells are there

Question 19

What are chemical mediators?

Answer 19

Chemical messengers that act locally
They are secreted from cells all over the body (not just glands)
They travel short distances to their target cells so produce quick responses
They bind to specific receptors on target cells to cause a response

Question 20

What is histamine?

Answer 20

A chemical mediator that is stored in mast cells and basophils (types of cells in the immune system).
Released in response to infection or injury
Increases permeability of capillaries nearby to allow more immune system cells to move to the infected area

Question 21

What is prostaglandins?

Answer 21

Group of chemical mediators produced by most body cells. They’re involved with loads of things like inflammation, fever, blood pressure etc.

Question 22

What are pacinian corpuscles?

Answer 22

Mechanoreceptors detecting mechanical stimuli (pressure and vibrations). Found in skin
Contain sensory nerve ending surrounding by lamellae (connective tissue)
When stimulated the lamellae deform and press on the nerve ending causing the deformation of stretch mediated sodium channels in the neurones membrane. These open and cause sodium ions to diffuse in creating a generator potential

Question 23

What are photoreceptors?

Answer 23

Receptors in your eye that detect light. Light enters through the pupil, controlled by iris muscles. Rays focused by the lens onto the retina. The retina contains photoreceptors cells these produce a response to the stimuli of light.

Question 24

What is the fovea?

Answer 24

An area of the retina that contains lots of photoreceptors.
Impulses from these are carried to the brain by the optic nerve - the brain interprets these impulses and produces images we see.

Question 25

What is the blind spot?

Answer 25

Where the optic nerve leaves the eye is called the blind spot there aren’t many photoreceptors here and so it is not sensitive to light.

Question 26

Describe what occurs when light enters the eye

Answer 26

Light hits photoreceptors and is absorbed by light sensitive pigments (rhodopsin). Light bleaches the pigment, causing a chemical change and altering the membrane permeability to sodium.
This causes a generator potential which if it reaches the threshold will trigger an action potential which is sent along a bipolar neurone. These connects photoreceptors to the optic nerve that carries the impulses to the brain

Question 27

Give the features of rods?

Answer 27

Found in peripheral parts of the retina
Give information in black and white 
Very sensitive to light
Low visual acuity. 
Many rods connect to one neurone

Question 28

Give the features of cones

Answer 28

Packed in the fovea 
Give in formation in colour 
3 types - red, green and blue sensitive 
Stimulated by different proportions which is why we see colour 
Low light sensitivity 
High visual acuity 
One cone joins to one neurone