Topic 6 - Nervous Coordination

Question 1

What are neurons?

Answer 1

Specialised cells that transmit electrical impulses throughout the body enabling communication with the nervous system.

Question 2

What are the six structures in a neuron?

Answer 2

1. Dendrites.
2. Axon.
3. Axon terminal.
4. Cell body.
5. Schwann cells
6. Notes of Ranvier.

Question 3

What is the cell body?

Answer 3

Contains the nucleus and cytoplasm with organelles such as mitochondria and ribosomes to produce proteins and energy required for impulse transmission. The site of metabolic activity within the neurone.

Question 4

What are dendrites?

Answer 4

• branched extensions from the cell body
• Conduct nerve impulses towards the cell body.

Question 5

What are axons?

Answer 5

• A long single extension that transmits impulses away from the cell body to the next neuron or effector.
• Enclosed in a myelin sheath neurons to increase the speed of impulse transmission

Question 6

What the axon terminal?

Answer 6

• End of the axon that forms synapses with other neurons or factors such as muscles or glands.

Question 7

What are Schwann cells?

Answer 7

• surround the axon in myelinated neurones producing the myelin sheath which acts as an electrical insulator.

Question 8

What are notes of ranvier?

Answer 8

• gaps in the myelin sheath
• Enable a faster transmission.

Question 9

What is a sensory neuron?

Answer 9

Carries impulses from receptors to the central nervous system.

Question 10

What is a motor neuron?

Answer 10

Transmits impulses from the CNS to factors such as muscles or glands.

Question 11

What is a relay neuron?

Answer 11

Found in the CNS and connect sensory neurons to motor neurones.

Question 12

What is meant by a neurons resting potential?

Answer 12

The state of a neuron when it is not transmitting an impulse at this state the neurons membrane is polarised due to a different in electrical charge between inside and outside of the membrane.

Question 13

The resting potential is maintained at approximately 70 my by what three different ways?

Answer 13

Sodium potassium pumps
Potassium channels
Neuron is negatively charged inside

Question 14

Explain how a sodium potassium pump maintains a neurons resting potential.

Answer 14

Actively transport three sodium ions out and two potassium irons in creating an electro chemical gradient.

Question 15

Explain how potassium channels maintain arresting potential in a neuron

Answer 15

Allow potassium to diffuse out further contributing to the positive charge outside.

Question 16

Explain how the inside of the neuron being negatively charged maintains a resting potential.

Answer 16

The inside of the neuron is negatively charged compared to the outside due to the presence of large negatively charged proteins and fewer positive ions.

Question 17

What is an action potential?

Answer 17

Rapid temporary reversal of a neuron membrane potential triggered when the cells reach a threshold, allowing an electrical signal to travel along the neuron.

Question 18

When stimulated how does the membrane of a neuron become depolarised?

Answer 18

• Sodium channels open allowing sodium ions to flood into the cell making the inside more positive.
• If the stimulus is strong enough it reaches the threshold potential and triggers a full action potential
• The action potential propagate along the neuron transmit the signal

Question 20

What are the two key features of resting potential?

Answer 20

1. Voltage difference.
2. Ion distribution.

Question 21

Explain voltage different in resting potential

Answer 21

• The inside of the neuron has a negative charge relative to the outside with a typical resting potential of 70 my.
• This is caused by an imbalance of ions across the membrane.

Question 22

Explain ion distribution during resting potentials

Answer 22

There is a higher concentration of sodium ions outside the axon and a higher concentration of potassium ions inside the axon

Question 23

What is the role of the sodium potassium pump?

Answer 23

The sodium potassium pump actively transport ions:
- three sodium irons are pumped out of the neuron
- Potassium irons are pumped into the neuron
Create an electro chemical gradient with more positive ions outside the neurone.

Question 24

How does membrane permeability affect ion diffusion?

Answer 24

• The membrane is in permeable sodium ions so sodium cannot diffuse back into the axon.
• The membrane is partially permeable to potassium ions allowing some potassium to diffuse out the potassium ion channels contributing to the positive charge outside.

Question 25

How does the sodium potassium pump work?

Answer 25

It uses ATP for active transport maintaining the resting potential.

Question 26

What are nerve impulses?

Answer 26

Electrical signals transmitted along neurons, enabling communication within the nervous system. They occur due to changes in the voltage across the neuron membrane, caused by the movement of ions.

Question 27

What is an action potential?

Answer 27

- a nerve impulse is initiated when the neuron membrane becomes depolarised creating an action potential. - An action potential occurs if the stimulus exceeds the threshold.

Question 28

What are the four phases of an action potential?

Answer 28

Depolarisation Repolarisation Hyperpolarisation Resting potential reestablished

Question 29

What is the polarisation in action potential?

Answer 29

- when stimulated voltage gated sodium ion channels open allowing sodium ions to diffuse into the neuron - The inside becomes less negative and can reach a value of approximately 40 mV

Question 30

What is the repolarisation phase of an action potential potential?

Answer 30

- sodium ion channels close and voltage gated potassium ion channels open allowing potassium ions to diffuse out - This restores the inside of the neuron to a negative charge

Question 31

What is the hyperpolarisation phase of an action potential?

Answer 31

Potassium ion channels remain open longer than necessary causing the potential to drop below the resting potential.

Question 32

What is the resting potential reestablished phase of an action potential?

Answer 32

The sodium potassium pump restores the resting potential by actively transporting three sodium iron out and two potassium ions in.

Question 33

What is the refractory period?

Answer 33

- After an action potential there is a short period where the neuron cannot generate another impulse. - This ensures impulses are unidirectional and prevent overlap.

Question 34

What is propagation of nerve impulses?

Answer 34

- The action potential causes localised changes in the membrane potential triggering adjacent sections of the membrane to depolarise. - this result in the impulse moving along the neuron.

Question 36

What is meant by saltatory conduction?

Answer 36

- In myelinated neurons, the action potential jumps between the notes of ranvier significantly increasing the speed of transmission. - in non-myelinated neurons, the impulse travels continuously along the membrane which is slower.

Question 37

What is the significance of nerve impulses?

Answer 37

- They enable rapid communication between sensory receptors the central nervous system and effectors - They are central responses to stimuli such as reflex actions and voluntary movement.

Question 38

What is the absolute refractory period phase of the refractory period?

Answer 38

- During this phase, no action potential can be generated regardless of the strength of the stimulus. - This occurs because the sodium ion channels remain closed preventing depolarisation

Question 39

What is the relative refractory period phase of the refractory period?

Answer 39

- during this phase and new action potential can be generated but only if the stimulus is stronger than usual. - This is because the membrane is hyper polarised

Question 40

What are the three functions of the refractory period?

Answer 40

- Ensures that action potentials travel in One Direction only by preventing the propagation of a backwards impulse. - Produces discrete impulses by ensuring that each action potential is separate from the next - Limits the frequency of nerve impulses ensuring the neuron has time to recover

Question 41

What is the all or nothing principle?

Answer 41

- an action potential is only generated if the stimulus reaches a threshold value. - If the threshold is not reached, no action potential is produced - All action potential generated have the same magnitude regardless of stimulus strength

Question 42

What is a myelin sheath?

Answer 42

Axon surrounded by myelin sheet conduct impulses much faster than non-myelinated axons.

Question 43

How can temperature affect action potentials?

Answer 43

Higher temperatures increase the kinetic energy of ions which accelerates their diffusion across the axon membrane during action potentials.

Question 44

How can temperature influence the ATP yield?

Answer 44

Temperature can also influence the rate of respiration which produces the ATP required for the sodium potassium pump to restore resting potentials.

Question 45

What is the formula for maximum frequency of impulses?

Answer 45

Maximum impulse frequency (Hz) = 1/refractory period (s)

Question 46

What are cholinergic synapses?

Answer 46

Junctions between two neurons or between a neuron and an effect that use the neurotransmitter acetylcholine to transmit nerve impulses.

Question 47

What are the four key features of the cholinergic synapse?

Answer 47

1. Pre-synaptic neuron. 2. Synaptic left. 3. Post synaptic neuron. 4. Enzyme action.

Question 48

Explain the pre-optic neuron in the cholonergic synapse?

Answer 48

- Contains vesicles filled with acetylcholine - when an action potential arrives at the synaptic knob voltage gated calcium ions channel allowing calcium ions to diffuse into the knob

Question 49

Explain the synaptic cleft during cholinergic synapse

Answer 49

- A gap between the presynaptic and post-synaptic membranes. - acetylcholine it released into this cleft by excytosis and diffuses across the to the post membrane.

Question 50

Explain the post an Arctic neuron in the choloergic synapse.

Answer 50

- The post synaptic membrane contains specific receptors that bind acetylcholine - finding open ligand-gated sodium ion channels causing sodium ions to enter and polarised the membrane

Question 51

Explain enzyme action during the cholonergic synapse

Answer 51

- acetylcholine is broken down by the enzyme acetylcholinesterase into choline and ethanoic acid. - These products are reabsorbed by the presynaptic neuron to re-synthesise acetylcholine using ATP.