Nervous Coordination

Question 1

name and describe the features of a myelinated motor neurone

Answer 1

• cell body - contains nucleus + most other organelles
• Axon - conducts nerve impulses which may myelinated or unmyelinated
• Myelin Sheath - made of up of Schwann cells and consists mainly of lipids providing electrical insulation
• Nodes of Ranvier - gaps in the myelin sheath ( only depolarised place on the axon)
• Synaptic Knobs - allow communication with other neurones or with effectors

Question 2

define resting potential

Answer 2

• the potential difference across a membrane of an axon when an impulse is not being transmitted

Question 3

describe how the resting potential is maintained

Answer 3

• more potassium channel proteins are open than sodium channel proteins so there is a net loss of positively charged ions from the axon
• the sodium potassium pump actively transports 3 sodium out and 2 potassium in which maintains an electrochemical gradient

Question 4

what would occur if neurones are treated with a respiratory inhibitor

Answer 4

• no respiration = no production of ATP = no release of energy = sodium/potassium pump cannot function therefore the concentration of the ions would eventually reach equilibrium, and the potential difference would be 0

Question 5

describe what happens when a receptor is stimulated(nerve impulse)

Answer 5

• there is an increase in the permeability of the axon membrane to sodium ions and so they diffuse in down a conc gradient
• this causes more sodium channels to open and so more sodium ions diffuse in causing the negative resting potential to be cancelled out and eventually become positively charged (axon becomes depolarised)
• when the membrane is fully depolarised the sodium channels close and potassium channels open leading to more positively charged potassium ions diffusing out of the axon making inside less positive
• this starts the process of repolarisation and the sodium/potassium pump restores the resting potential by actively removing sodium ions which have entered and returning potassium ions back into the axon

Question 6

how is an action potential transmitted along a neurone

Answer 6

• transmitted along a wave of depolarisation as the action potential jumps from one node to the next (saltatory conduction)

Question 7

what is the refractory period?

Answer 7

• the period after an action potential when a neurone cannot generate another action potential

Question 8

what does the refractory period allow

Answer 8

• allows for discrete (separate) impulses
• ensures that the impulse travels in one direction along an axon

Question 9

what is the ‘All or Nothing’ principle

Answer 9

• a stimulus must be above a certain threshold level for an impulse to be generated
• stronger stimuli result in greater frequency of impulses than a weaker stimuli however amplitude of impulse always remains the same

Question 10

what factors affect the speed of transmission along neurones

Answer 10

• temperature
• axon diameter
• myelination

Question 11

how does temp affect speed of transmission

Answer 11

• increase in temp increases speed of transmission due to the ions having a greater kinetic energy and therefore diffusing faster
• above a certain temp, channel proteins and enzymes (affecting respiration) would be denatured

Question 12

how does axon diameter affect speed of transmission

Answer 12

• greater the diameter the faster the transmission due to the reduced resistance

Question 13

how does myelination affect speed of transmission

Answer 13

• as myelination of axon increases , transmission speed increases as there are less gaps where depolarisation occur (node of Ranvier)
• depolarisation occurs along the whole membrane in non-myelinated neurones = slower speed of transmission