Basic Buliding Blocks And Axonal Neurotransmission Flashcards
What is a neuron?
Basic cellular unit of the nervous system
Different range with different functions
Basic components
Dendrites
Cell body/soma
Axon
Presynaptic terminals
Connections between neurones
Axonal transmission
Synaptic transmission
Axonal transmission
Transmission of information from location A to B
Synaptic transmission
Integration/processing of information and transmission between neurones
The neurones resting potential
The inside of the neurone has a negative electrical charge because of the ions within the neurone
-70mV
Reached using Na+/K+ ATP pump
Neuronal cell membrane semi permeable
Some substances which are electrically charged (+ve or –ve) cross readily – potassium (K+) and chloride (Cl-)
Some cross with difficulty – sodium (Na+)
Some not at all – large organic proteins (-ve charge)
What are the forces determining distribution of charged ions?
Diffusion
Electrostatic attraction/repulsion
Sodium potassium pump
Slide 11
The action potential
Neurone fires- a sudden pulse where the -ve resting potential is temporarily reversed
All or nothing process to transmit information
What events occur in the action potential?
Depolarization and threshold- voltage gated sodium ion channels open, allowing Na+ into the axon cytoplasm
Reversal of membrane potential
Repolarization of resting potential- voltage gated K+ ions open, allowing more K+ to diffuse out than Na+ in
Refractory period- Limits the no. of AP an excitable membrane can produce in a given time - so APs can be separated
-Absolute refractory period = during repolarisation - neuron cannot generate new AP
-Relative refractory period = hyperpolarisation - neuron can generate new AP if stimulus = larger than one previously
Membrane permeability changes
The membrane potential remains in this resting ‘stable’ state until something disturbs the balance
Neurotransmitter initiate such changes at the dendrites of neurones
Neurotransmitters activate receptors on dendrites / soma
Receptors open ion channels
Ions cross plasma membrane, changing the membrane potential
The potential changes spread through the cell
If the potential changes felt at the axon hillock are positive (+mV), and large enough, an action potential is triggered
Depolarisation/Hyperpolarisation
Depolarise -more +ve V
Polarised at -70mV= RMP
Hyperpolarise -more -ve V
Excitably neurotransmitters depolarise the cell membrane causing them to push towards the membrane
This increases probability of an action potential being evoked
This causes an excitably post synaptic potential
Inhibitory neurotransmitters hyperpolarise the cell membrane decreasing the probability of an action potential being evoked
This causes an inhibitory post synaptic potential (ISPS)
An action potential will be evoked if the membrane potential is depolarised beyond the threshold of excitation
Postsynaptic potentials
Voltage changes spread away (decrementally) from point of origin (Passive Conduction)
Whether AP is generated depends on what reaches the axon hillock
Excitatory post synaptic potential (EPSP).