Nervous system 3- Electrical Events

Question 1

Describe the somatic nervous system

Answer 1

Motor neurones to skeletal muscle. Voluntary control

Question 2

Why two systems make up the peripheral system

Answer 2

The somatic nervous system and autonomic nervous system

Question 3

Describe the autonomic nervous system

Answer 3

Neruones to visceral organs, no voluntary control. Made up of sympathetic and parasympathetic

Question 4

Why are communication pathways rapid

Answer 4

Peripheral nerves transmit information rapidly. Nerve impulses travel to and from the central nervous system.

Question 5

What are the main components of a neurone

Answer 5

Synapse, nucleus, soma, axon, Schwann cell, terminus

Question 6

What is the approximate concentration of Na+ inside and outside the cell membrane

Answer 6

Inside = 15 mM Outside = 150 nM

Question 7

What is the approximate concentration of K+ inside and outside the cell membrane

Answer 7

Inside = 150 mM Outside = 5 mM

Question 8

What is the approximate concentration of Cl- inside and outside the cell membrane

Answer 8

Inside = 10 mM Outside = 100 mM

Question 9

Why are there unequal concentrations of ions either side of the cell membrane

Answer 9

1. Large organic anions are produced by the cell and cannot cross the membrane 2. Active transport (Na+/K+ pump) actively transports Na+ out of the cell and K+ into the cell

Question 10

What does what can get through the cell membrane depend on

Answer 10

Size, electrical charge, molecular shape, solubility

Question 11

Why do membranes differ in permeabilities

Answer 11

It depends on lipids and proteins present and their arrangement

Question 12

Describe cell membranes in their resting state

Answer 12

1. Fairly permebale to K+ and Cl-. 2. Poorly permeable to Na+. 3. Impermeable to various large organic anions formed in the cells

Question 13

What happens at a concentration gradient

Answer 13

Substances move down the concentration gradient from high concentration to low concentration

Question 14

What happens at an electrical gradient

Answer 14

Ions move down the electrical gradient from positive side to negative side

Question 15

Describe a cell in steady state

Answer 15

1. Net passive efflux of K+. 2. Net passive influx of Na+. 3. Cell is not loosing Na+, K+, Cl- or A-. 4. Outside of cell is positive compared to inside of cell

Question 16

Why does a cell in it’s resting state have a potential difference

Answer 16

The outside of the cell is positive compared to the inside of the cell

Question 17

How can the potential difference of a cell be measured

Answer 17

By using a microelectrode

Question 18

What is the resting membrane potential of a typical neurone

Answer 18

-70mV

Question 19

What are the 3 stages that happen during an action potential

Answer 19

1. Depolarisation 2. Repolarisation 3. Hyperpolarisation

Question 20

What happens during depolarisation

Answer 20

1. After a stimulus the membrane depolarises due to a change in potential difference. 2. Na+ voltage-gated channels open. 3. There is a rapid influx of Na+ into the cell. 4. Causes more Na+ voltage-gated channels to open via a positive feedback loop.

Question 21

What happens immediately after an action potential peaks

Answer 21

Repolarisation

Question 22

What happens during repolarisation

Answer 22

1. Na+ voltage-gated channels close. 2. Decreases the permeability of Na+ into the axon. Strong electrochemical gradient established. 3. K+ voltage-gated channels open. 4. K+ leaves the cell. 4. The potential of the cell is decreased

Question 23

What is hyperpolarisation

Answer 23

1. The depolarisation continues past the resting -70mV. 2.This causes the K+ voltage-gated channels to close. 3. The cell returns to resting potential

Question 24

Why can’t an new action potential occur directly after an action potential

Answer 24

Due to the refractory period

Question 25

What is absolute refractory

Answer 25

When an action potential is at it's peak and there is no way another action potential can occur

Question 26

What is relative refractory period

Answer 26

Occurs immediately after the absolute refractory period. Another action potential could potentially occur but must be much stronger than initial stimulus.

Question 27

Where does the propagation of action potentials occur

Answer 27

In unmyelinated neurones

Question 28

What is the propagation of action potentials

Answer 28

There is an inactive area at resting potential -\> Active area which is being depolarised (a graded potential) -\> an inactive area at resting potential.

Question 29

Which directions can action potentials travel in

Answer 29

Only one direction. From the cell body to the end of the axon

Question 30

What does myelinated cells result in

Answer 30

Faster transmission

Question 31

Where and how do action potentials travel down myelinated cells

Answer 31

They occur at the nodes of Ranvier. Local circuit currents cause depolarisation of adjacent node of Ranvier so a new AP is initiated here

Question 32

How often do the nodes of Ranvier occur

Answer 32

Every 0.2-2mm

Question 33

What happens to the propagation of action potentials at cooler temperatures

Answer 33

It is slower due to decreased a decrease in speed of metabolic activity. Results in the period of inactivation at sodium voltage-gated channels being longer. So signals are not sent because gates have not yet closed from previous action potential