Nervous Coordination and Muscles

Question 1

what is the nervous system?

Answer 1

• uses nerve cells to pass electrical impulses along their length
• they stimulate their target cells by secreting neurotransmitters

Question 2

what is the hormonal system?

Answer 2

• produces hormones that are transported in the blood plasma to their target cells
• the target cells have specific receptors that are stimulated by the change in concentration of the hormones
• responses are long-lasting and widespread

Question 3

what are some differences between the hormonal and the nervous system?

Answer 3

• communication via hormones vs nerve impulses
• transmission by the blood system vs neurones
• transmission is relatively slow vs very rapid
• hormones travel to all parts of the body but only target cells respond vs nerve impulses travel to specific parts of the body
• response is widespread vs localised
• response is slow vs rapid
• response is often long lasting vs short lived
• effect may be permanent and irreversible vs temporary and reversible

Question 4

what is a motor neurone made up of?

Answer 4

• cell body: including large amounts of rough ER for production of proteins and neurotransmitters
• dendrons: extensions of the cell body extend into branched fibres called dendrites, that carry nerve impulses towards the body
• axon: long fibre carries nerve impulses away from the cell body
• Schwann cells: surround the axon, giving electrical insulation. they wrap around the axon many times so that layers of membranes build up
• myelin sheath: covers the axon, formed of layers of Schwann cells. these membranes are rich in a lipid called myelin
• nodes of Ranvier: constrictions between adjacent Schwann cells where there is no myelin sheath

Question 5

what are the different types of neurones?

Answer 5

• sensory neurones: transmit nerve impulses from a receptor to an intermediate or motor neurone. they have one dendron that is often very long
• motor neurones: transmit nerve impulses from an intermediate or relay neurone to an effector, such as a gland or muscle. have a long axon and many short dendrites
• relay neurone: transmits impulses between neurones.

Question 6

what is a nerve impulse?

Answer 6

• a wave of electrical activity that travels along the axon membrane. it is a temporary reversal of the electrical potential difference across the axon membrane.

Question 7

what is the resting potential?

Answer 7

• the inside of an axon is negatively charged to the outside
• usually -65mV in humans
• the axon is said to be polarised

Question 8

how is the resting potential generated?

Answer 8

• sodium ions are actively transported out of the axon by sodium-potassium pumps
• potassium ions are actively transported into the axon by sodium-potassium pumps
• active transport of sodium ions is greater than potassium ions and 3 sodium ions move out for every 2 potassium ions that move in
• (there is a relative positive charge outside the axon)
• sodium ions diffuse back into the axon and potassium ions diffuse out, but most potassium gates are open but most sodium gates are closed

Question 9

what is an action potential?

Answer 9

• when a stimulus is detected by the nervous system, there is a temporary reversal of the charges either side of the axon membrane
• the -65mV charge becomes a +40mV

Question 10

what is depolarisation?

Answer 10

• when the charges are reversed either side of the axon membrane, this part of the membrane is depolarised
• this occurs because the voltage gated channels in the axon membrane change shape and open or close

Question 11

describe the generation of an action potential

Answer 11

• at resting potential, potassium voltage gated channels are open, but sodium voltage gated channels are closed
• energy of the stimulus causes some sodium voltage gated channels to open and sodium ions diffuse in the axon. due to their positive charge, there is a reversal of potential difference across the membrane
• more sodium channels open and there is a greater influx of sodium by diffusion
• once action potential of +40mV has been established, sodium voltage gated channel close and potassium voltage gated channels open
• potassium ions diffuse out of the axon, and repolarisation begins
• this causes a temporary hyperpolarisation (the inside of the axon is more negative relative to the outside). the potassium ions channels close and the sodium-potassium pumps cause sodium ions to be pumped out and potassium in. the axon is depolarised and the resting potential of -65mV is reestablished.