Nerves

Question 1

Define nerve nets

Answer 1

The simplest type of nervous system and consists of a nerve cell with short extensions that join into ganglia and branch in serveral connections. Two cell types. Limited number of stimuli so small number of effectors

Question 2

Describe Hydra

Answer 2

Cnidaira, nerve net, radial symmetry, simple pattern, easy to manipulate, regenerates tentacles rapidly.
Can detect light, pressure, and chemical (not direction)

Question 3

Describe the function of the myelin sheath

Answer 3

1) provides electrical insulation, increasing transmission speed
2) prevents exchange of ions
3) protects axon

Question 4

Define resting potential

Answer 4

The potential difference across the membrane of a cell when no nervous impulse is being conducted. For a neurone it’s -70mV and is said to be polarised

Question 5

Define an oscilloscope trace

Answer 5

A graph showing the voltage change across the membrane with time. Used to measure the magnitude and speed of transmission of an impulse

Question 6

Describe how resting potential is maintained

Answer 6

Large negatively charged ions, organic acids, lots of phosphate ions, the membrane is morepermeable to potassium ions, sodium potassium pump

Question 7

Describe depolarisation

Answer 7

1) some Na+ VGC are open
2) some Na+ diffuses in
3) threshold potential (-55mV) is reached
4) more Na+ VGC open
5) Na+ rapidly diffuses in
6) inside of axon is positively charged compared to outside
7) action potential (+44mV) is generated and an impulse is transmitted

Question 8

Describe repolarisation

Answer 8

1) Na+ VGCs close (less Na+ diffuses in)
2) K+ VGCs open
3) K+ rapidly diffuses out of axon
4) inside of axon is negatively charged compared to outside

Question 9

Describe hyperpolarisation

Answer 9

Potential difference across the membrane is lower than resting potential
1) K+ VGCs close
2) Na+ K+ pump restored resting potential

Question 10

Describe how impulses are kept discreet

Answer 10

Hyperpolarisation: as potential difference is lower than resting potential it’s harder to generate an action potential as more Na+ needs to diffuse in to reach threshold potential

Question 11

Define refractory period

Answer 11

Period in which no new action potentials can be initiated

Question 12

Define saltatory conduction

Answer 12

Transmission of a nervous impulse along a mylienated neurone in which the action potential jumps from one node of Ranvier to the adjacent node