Topic 11 - Nervous System 2 Flashcards
Learning Objectives
- Explain the relationship between body fluids, cell membranes and function in the nervous system
- Explain how the cell membrane potential develops
- Explain how an action potential is generated
- Describe the factors affecting the speed of transmition in a neuron
- Explain the process of nuerotransmission
- Descibe the structure of synapse
- Explain the role of neurotransmitters
- Define excitory and inhibitory postsynaptic potentials and explain how they are generated
- Explain the role of receptors and ezymes in synaptic function
The Nuerone
Basic structural unit of the NS (nerve cell)
- Communicate at the synapse
- Information for communication is coded in forms of an action potential
- Dendrite receives signal from another neuron and sends another through its axon terminals
Neurone anatomy
- Dendrite
- Cell Body
- Nucleus
- Axon
- Myelin Sheath
- Node of Ranvier
- Schwann Cell
- Axon terminal
Cell membrane
- Phospholipid bilayer (Heads and tial)
- Protein molecules imbedded
- Seperates intra/extracellular fluid
Neurone at rest
An electrical potential exists across the membrane (Outside is more positively charged)
- Membrane potential is -65 to -70mV
Membranse is most permiable to K+ ions as they can flow along concentration gradient through K+ channels at rest.
Membrane is NOT permiable to Na+ at all
Action potential process
- To initiate an action potential, membrane potential must raise from a negative to a positive value.
- The neurone receives a stimulus from a synaptic input of another neurone onto its dendrites
- The threshold potential then raises from around -90mV to -50mV
- This causes volage gated Na+ ion channels to open
- Na+ ion then flood into the cell, raising the membrane potential further, depolarising it to +40mV.
- The Voltage gated Na+ ion channels then close
- Voltage gated K+ ion channels open, allowing K+ to rush out of the cell, repolarising it
- The membrane potential then drops from +40mV to -80mV, leading to hyperpolarisation
- Voltage gated K+ ion channels then close, equilibrium then slowly occurs through the work of Na-K pumps and diffusion of K+ ions.
- Membrane potential raises to -70mV at the resting potential with a refractory period preventing another action potential for a while.
Propogation of the action potential
Depolarisation phase spreads across the axon, allowing it to move from the cell body along the axon towards the axon terminals.
Only moves away from the cell body and cannot travel backwards due to the refractory period
All action potentials are the same, A stronger stimuli uses an increase in frequency of action potentials.
Myelination (Myelin)
- Insulation around the axon stops the need of the whole axon to undergo depolarisation/ repolarisation
- Are present in CNS and PNS
- Produced by Schann Cells in PNS
- Produced by Oligandocytes in CNS
- Approx. 80% lipid (dissalowing spead of molecules across it)
- Contains nodes of ranvier to speed up the process of depolarisation (Creating Saltatory conduction.)
Synapse
- Where the action potential of an axon communicates with the dendrite of another cell
- Relies on neurotransmitters which are synthesised in the cell body of a neuron (Transported along axon and stored bundled vessicles in presynaptic terminal)
Synapse transmitting information process
- An action potential reaches the axon terminal
- Voltage gated Ca2+ channels open, allowing calcium ions into the cell
- This triggers vessicles to release neurotransmitters into the synaptic cleft
- Neurotransmitters then diffuse across the synaptic cleft and bind to specific receptors on the post synaptic cleft
- Receptors are activated and open ligand ion channels with the corresponding neurotransmitters
- This raises the resting membrane potential of the following neurone to -50mV from -70mV
- Neurotransmitters are then broken down by enzymes or taken up by presynaptic terminal to be used again
- Drugs can target neurotransmitters such as serotonin and prevent the neurotransmitters from being broken down or taken up
Neurotransmitters
Glutamate
GABA
Acetylcholine
Glutamate
Major excitatory neurotransmitter
Opens Na+ channels, causing excitatory post synaptic potentials (EPSP)
GABA
Major Inhibitory neurotransmitter
Opens Cl- channels, causing inhibitory post synaptic potentals (IPSP)
Acetylcholine
Can be excitatory or inhibitory in the brain
Only excitatory in muscle
Summination
Allows for an action potential to be produced as 1 EPSP isn’t enough
Creates a bigger stimulus
Temporal OR Spatial
