Nerves And Neurotransmission Flashcards
Nerves
Bundle of fibres that transmit impulses between areas of the body and within the brain
Peripheral nervous system
Afferent (sensory)
Efferent (motor)
Efferent (motor) has what two systems
Somatic - voluntary
Autonomic - involuntary and reflex
The autonomic system can be subdivided into what
Sympathetic
Parasympathetic
What is nervous system made up of
Glial cells (structure and support)
Schwann cells
Neurons ( generate and send impulses)
Structure of neuron
Cell body / soma
Axon
Axon hillock is that connects cellbody to axon
Dendrites
Neurons generate impulses called what
Action potentials
Action potential impulses transmission
Presynaptic neurone:
Generated in axon hillock
Travel down axon to axon terminals
Axon terminals forms a junction with another cell = synapse
Release of chemicals= neurotransmitters
Post synaptic neurone:
Neurotransmitter diffuses across synapse to target cell
Binds to receptors
Drug receptor complex
Generation of signals in receiving cell
Sodium Ion concentration outside the cell compared to inside
Outside= high conc of sodium ions
Intercellular= relatively low conc of sodium ions
Potassium ion conc inside and outside of the cell
Intercellular= high potassium conc
Outside the cell= low potassium con
How is the ion concentrations maintained
Various ion channels and ion pumps
Sodium potassium ATPase
Transports Na+ from inside cell to outside and K+ from outside to inside
Resting conformation has 3 binding sites for sodium ions
Pump can also bind to atp
When atp becomes dephosphorylated, the pump becomes phosphorylated
Conformation of the pump changes so is now exposed to extra cellular side and sodium ions is released into extra cellular fluid
Binding sites for potassium open
Pump becomes dephosphorylysed and phosphorus is released
Potassium ions released back into cell
Repeat
Equilibrium potential of an ion equation
(Not needed)
RT/ZF ln [ion out/ ion in]
Equilibrium potential of potassium
-90mV
No movement of potassium ions
Typical membrane potential of cell is -70
Voltage gated ion channel states
Change in voltage across cell membrane
Voltage gated ion channels are activated
Voltage channel open state
Ions cross channel
Time dependent
Ion channel conformation changes
Ball and chain closes the end part of the ion channel (inactive state)
Membrane potential changes to near rest, ion channel returns to closed state
Types of receptors in dendrites
Glutamate, acetylcholine = neurotransmitters in brain
NMDA receptors= Sodium and calcium, more positive ions goes into the cell, excitatory post synaptic potential (EPSP)
Ampa receptor = sodium ions causes an excitatory response
Inhibitory post synaptic potential
Inhibitory ensures neurones don’t become overactive
Hyper polarisation
Action potentials initiated at axon initial segment
High conc of sodium channels/ potassium
Epsp reach soma/ cell body
Membrane potential becomes more positive (depolarisation)
Reaches threshold potential
Sodium channels open up, fast depolarisation
Membrane potential decreases= repolarisation
Potential becomes less than resting potential (hyperpolaristaion)/ refractory state
Reaches resting potential
Resting membrane of cell
-70mV
‘Leak’ K+ channels
Depolarisation
Na+ channels begin to open
Membrane depolarised
Regenerative
Peak of action potentials
Na+ channels begin to inactivate
Prevents their activation a second time
Blocks initiation of another action potentials within a short period of time= Absolute refractory period
Voltage gated K+ channels open more slowly than Na+
Repolarisation
Voltage gated K+ channels are open
Hyperpolarisation/ relative refractory period
More k+ channels are open than at rest
Membrane potential approaches Ek
Allows Na+ channels to recover from inactivation
Resting potential
Voltage gated K+ channels close
Membrane returns to rest
Ready for another action potentials
