Nervous system Flashcards
List the parts of a neurone
- Cell body
- Dendrites
- Axon
- Myelin sheath
- Nodes of Ranvier
- Axon terminal
Describe the cell body
Contains the organelles. Proteins + neurotransmitter chemicals are made here.
Describe the dendrites
Branch out from the cell body. Carry action potential to surrounding cells
Describe the axon
A long conductive fibre that runs all the way through the cell. Carries nervous impulses along neuron.
Describe Schwann cells
Wrap around the the axon to form the myelin sheath which is a lipid = acts as an insulator therefore charge can only pass through the gaps = Nodes of Ranvier
What is the resting potential and it’s charge?
- When a neuron isn’t conducting impulses = a difference between the charge inside/outside.
- There are more positive K+/Na+ outside than inside therefore inside more negative
- The charge is -70 mV
How is resting potential established and maintained?
- Through the Na+/K+ pump the resting potential is maintained
- 2 K+ in and 3 Na+ out are actively transported through the pump
- This creates a electrochemical gradient which allows facilitated diffusion of K+ out from higher to lower and Na+ to diffuse in from higher to lower
- But membrane is more permeable to K+ = more move out = -70mV charge
- There are more K+ protein channels than Na+ and some of the Na+ channels close while all of K+ are open
What is the action potential and it’s charge?
- When the neurons voltage increases beyond a set point from the resting potential = nervous impulse
- This is called depolarization
- Due to the membrane being more permeable to Na+ = positive charge produced
- The charge is +40mV
How is the action potential generated?
- A stimulus is introduced to the
-70mV = enough energy to open the voltage gated Na+ channels = Na+ going in at the same time as K+ out = voltage increase - If voltage increases more than -55 mV = more energy to open voltage gated Na+ channels = sharp increase in voltage to +40 mV = DEPOLARIZATION
- Voltage reaches +40 mV = action potential achieved but cannot go over +40 mV as this causes voltage gated Na+ channels close / 2 K+ channels to open so double K+ diffused out = voltage drop = REPOLARIZATION
- Voltage drop overshoots beyond charge for resting potential = HYPERPOLARIZATION
Explain the all or nothing principle
NOTHING:
If depolarization does not go over -55 mV = action potential not reached = no impulse produced
ALL:
- If depolarization goes over - 55 mV = action potential produced and will peak at the same maximum voltage of +40 mV
- A bigger stimuli will increase frequency of action potential peaks
Why is the refractory period important?
In this period the axon cannot be stimulated and the Na+ channels are recovering
1) Discrete impulses produces: action potentials are separate from each other so each impulse can be processed separately
2) Action potential travels in 1 direction: prevents spread of action potential in 2 directions = prevent response to stimulus
3) Limits number of impulses that can be produced: limit number of action potentials produced = prevent over reaction to stimulus and overwhelming senses that would hinder your survival instincts
What factors affect the speed of conducting an impulse?
1) Myelination
2) Axon diameter
3) Temperature
How does myelination affect the speed of conductance?
- Schwann cells which are lipids form myelin sheath = insulations so don’t let ions/impulses pass through them so they pass through the gaps = Nodes of Ranvier
- Action potential jump from node to node = SALTATORY CONDUCTION
- Action potential travels faster as it doesn’t need to be produced along the whole length just nodes
How does axon diameter affect the speed of conductance?
- Wider diameter = speed increases
- Wider = less ion leakage = action potential travels faster
How does temperature affect the speed of conductance?
- Higher temperature = faster
- Increases rate of diffusion of ions
- Respiration enzymes work faster = more ATP for active transport of Na+/K+ pump
