structure and functions of cells of the nervous system

Question 1

contrast the locations of the central and peripheral nervous systems:

Answer 1

• Central nervous system= the brain and spinal cord.
• Peripheral nervous system= nerves and the rest of the body.
• Relies on the use of sensory neurons (detects changes in environment and sends info to the CNS) and motor neurons (contractions of muscles/ secretion of glands) and interneurons (located entirely within the CNS)

Question 2

what Is the cell body of a neuron?

Answer 2

(soma)= contains the nucleus of the neuron cell and can vary in shape.

Question 3

what are dendrites?

Answer 3

receive neural messages that are transmitted across the synapse from the terminal button to the cell membrane.

Question 4

describe the function of the axon:

Answer 4

the outer surface carries information from the cell body to the terminal buttons. Carries the action potential which requires a chemical and electrical impulse.
○ Action potential= a brief electrical and chemical event that that starts at the end of the axon (near the cell body) and travels towards the terminal buttons. (outside of an axon)

Question 5

what is axoplasmic transport and what are the different types?

Answer 5

Axoplasmic transport= propels substances that run along “tracks” inside of the axon.
- Anterograde axoplasmic transport= movement from cell body to terminal buttons.
- Retrograde axoplasmic transport= movement from terminal buttons to cell body.

Question 6

what is the function of the myelin sheath?

Answer 6

fatty substance that provides insulation for the electrical substance.

Question 7

what is the function of the terminal buttons?

Answer 7

the bud at the end of an axon branch which forms synapses with another neuron- sends information to that neuron.

Question 8

explain neural communication in withdrawal reflexes:

Answer 8

If an individual picks up a hot object that causes pain in their hands, the motor neuron will send an impulse through its axon from the terminal buttons. However, the individual is able to override the pain in order to place the hot object on a table. This is because ethe brain sends an impulse called the inhibitory neuron. This is when an axon from the brain reaches the spinal cord where its terminal buttons form synapses with an inhibitory interneuron, which releases and inhibitory neurotransmitter to decrease the motor neuron activity and prevent the individual rom dropping the hot object.

Question 9

what is the resting potential of a neuron?

Answer 9

when the neuron is at rest and not involved in communicating with other neurons, remains at approx. -70mV.

Question 10

what is hyperpolarisation?

Answer 10

when the inside of the axon is more negative in comparison to the outside.Makes it harder for the cell to send a message to the postsynaptic cell.

Question 11

what is depolarisation of a neuron?

Answer 11

when the inside of the axon is more positive in comparison to the outside. Makes it much more likely that the neuron will send its message to the postsynaptic cell.

Question 12

what is the action potential in a neuron?

Answer 12

a burst of rapid depolarisation followed by hyperpolarisation which begins to spread along the cell membrane starting at the point the cell body (soma) meets the axon and moves towards the terminal buttons, triggering them to release the neurotransmitter into the synapse.

Question 13

what is diffusion?

Answer 13

movement of molecules from a place of high concentration to low concertation.

Question 14

what is electrostatic force?

Answer 14

forces exerted by the attraction or repulsion of molecules.

Question 15

what is intracellular fluid?

Answer 15

(internal) organic anions, potassium, sodium and chloride ions.

Question 16

what is extracellular fluid?

Answer 16

(external) potassium, sodium, chloride ions.

Question 17

what happens to the organic anion of a neuron during diffusion and electrostatic force?

Answer 17

cannot pass through the cell membrane (not permeable).

Question 18

what happens to potassium during diffusion and as a result of electrostatic force?

Answer 18

diffusion pushes it out of a cell, electrostatic pressure forces it back in due to outside being more positively charged (k= +ve charge so is repelled), tends to stay where it is as the forces balance each other out.

Question 19

what happens to sodium as a result of diffusion and the electrostatic force?

Answer 19

greatest concentration outside the axon. Diffusion pushes it inwards, inside of axon is negatively charged so electrostatic pressure also pushes it inwards (Na= +ve charge so is attracted).

Question 20

what happens to chloride ions during diffusion and as a result of the electrostatic force in a neuron?

Answer 20

greatest concentration outside the axon. Diffusion pushes it inwards, inside of axon more negatively charged, the electrostatic pressure forces it back out (Cl= -ve charge so is repelled) and opposing forces balance each other out.

Question 21

what is the sodium-potassium pump and what is its function?

Answer 21

made up of protein molecules embedded in the membrane, driven by energy provided by molecules of ATP produced by the mitochondria.
continuously pushes sodium ions out of the axon, for every 3 sodium ions pushed out, 2 potassium ions are pushed in (increase the intracellular concentration of K+ within a cell)- known as sodium-potassium transporters.

Question 22

summarise the series of ion movements during the action potential:

Answer 22

1. The membrane potential must reach the threshold of excitation.
2. Sodium channels in the membrane open and Na+ rushes in (due to diffusion and electrostatic pressure)- known as voltage-dependent ion channels as they are only opened by changes in the membrane potential. (The interior of the cell starts to become more positive).
3. Voltage-dependent potassium channels begin to open (K+ leaves cell), open later than sodium channels as the require greater levels of depolarisation to open.
   i. At the same time, sodium channels become refractory= the channels become blocked and cant open again until the membrane reaches the resting potential.
4. The outflow of cations causes the membrane potential to return to its resting value, which causes the potassium channels to close again.
   i. Same time, sodium channels reset.
5. Membrane is more negatively charged and only returns to resting value once the potassium channels finally close.
6. Sodium-potassium transporters remove the Na+ that leaked into the cell and retreive the K+ that leaked out of the cell.

Question 23

describe the propagation of an action potential:

Answer 23

• The all or none law refers to the fact that when the threshold is reached, the action potential either occurs or it doesn’t. this refers to its rate of firing where the action potential either sends a rapid or a slow firing along the neuron as it always remains the same size.
• Rate laws refers to the principle that variations in the intensity of a stimulus or other information being transmitted in an axon are represented in variations in which the axon fires.

Question 24

what are myelinated axons?

Answer 24

Myelinated axons= myelin sheaths are joined by Nodes of Ranvier which regenerate the axon and allow for more effective conduction of information across a neuron cell. As the axon is passing each Node of Ranvier, the impulse gets smaller (but is retriggered) but remains large enough to transmit the neurotransmitter into the synapse- called decremental conduction.

Question 25

what are unmyelinated axons?

Answer 25

Unmyelinated axons= the impulse seemingly jumps from node to node, which is known as saltatory conduction.