Nervous system 3- Electrical Events Flashcards
Describe the somatic nervous system
Motor neurones to skeletal muscle. Voluntary control
Why two systems make up the peripheral system
The somatic nervous system and autonomic nervous system
Describe the autonomic nervous system
Neruones to visceral organs, no voluntary control. Made up of sympathetic and parasympathetic
Why are communication pathways rapid
Peripheral nerves transmit information rapidly. Nerve impulses travel to and from the central nervous system.
What are the main components of a neurone
Synapse, nucleus, soma, axon, Schwann cell, terminus
What is the approximate concentration of Na+ inside and outside the cell membrane
Inside = 15 mM Outside = 150 nM
What is the approximate concentration of K+ inside and outside the cell membrane
Inside = 150 mM Outside = 5 mM
What is the approximate concentration of Cl- inside and outside the cell membrane
Inside = 10 mM Outside = 100 mM
Why are there unequal concentrations of ions either side of the cell membrane
- 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
What does what can get through the cell membrane depend on
Size, electrical charge, molecular shape, solubility
Why do membranes differ in permeabilities
It depends on lipids and proteins present and their arrangement
Describe cell membranes in their resting state
- Fairly permebale to K+ and Cl-. 2. Poorly permeable to Na+. 3. Impermeable to various large organic anions formed in the cells
What happens at a concentration gradient
Substances move down the concentration gradient from high concentration to low concentration
What happens at an electrical gradient
Ions move down the electrical gradient from positive side to negative side
Describe a cell in steady state
- 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
Why does a cell in it’s resting state have a potential difference
The outside of the cell is positive compared to the inside of the cell
How can the potential difference of a cell be measured
By using a microelectrode
What is the resting membrane potential of a typical neurone
-70mV
What are the 3 stages that happen during an action potential
- Depolarisation 2. Repolarisation 3. Hyperpolarisation
What happens during depolarisation
- 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.
What happens immediately after an action potential peaks
Repolarisation
What happens during repolarisation
- 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
What is hyperpolarisation
- The depolarisation continues past the resting -70mV. 2.This causes the K+ voltage-gated channels to close. 3. The cell returns to resting potential
Why can’t an new action potential occur directly after an action potential
Due to the refractory period
What is absolute refractory
When an action potential is at it’s peak and there is no way another action potential can occur
What is relative refractory period
Occurs immediately after the absolute refractory period. Another action potential could potentially occur but must be much stronger than initial stimulus.
Where does the propagation of action potentials occur
In unmyelinated neurones
What is the propagation of action potentials
There is an inactive area at resting potential -> Active area which is being depolarised (a graded potential) -> an inactive area at resting potential.
Which directions can action potentials travel in
Only one direction. From the cell body to the end of the axon
What does myelinated cells result in
Faster transmission
Where and how do action potentials travel down myelinated cells
They occur at the nodes of Ranvier. Local circuit currents cause depolarisation of adjacent node of Ranvier so a new AP is initiated here
How often do the nodes of Ranvier occur
Every 0.2-2mm
What happens to the propagation of action potentials at cooler temperatures
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
