Lecture 3 Flashcards
Histology
Staining of the nerve tissue
Membrane proteins
- Channel: diffusion, permeability depends on number of channels
- Gate: conformation, change depends on voltage or chemical stimulus
- Pump: active transport, requires energy (ATP)
Neuronal metabolism
- Glucose as fuel (through blood-brain barrier)
- Brain consumes a lot of oxygen due to glucose consumption
- Glucose can be synthesized by the liver
- Vitamin B1 enables glucose use
Types of glial cells
- Schwann cell (myelin sheath)
- Astrocyte
- Oligodendrocyte
- Microglia (Phagocytotic)
- Ependymal cells
Types of neurons
- Primary sensory neurons
- Motor neurons
- Interneurons
Astrocyte
Type of glial cell.
Regulate the chemical content of extracellular space.
Actively remove neurotransmitters from synaptic cleft.
Influence neurite growth.
Structural integrity.
Maintain blood brain barrier
Oligodendrocyte and Schwann cells
Oligodendrocytes are found in the CNS and Schwann cells in the PNS
Both provide myelin sheaths to the axons of neurons
Microglia
Remove debris left by dead or degenerating neurons or glia.
Involved in remodeling synaptic connections by gobbling them up
Blood-brain barrier
Selectively permeable. Passive: small molecules (O2, CO2), Active: glucose, amino acids
Function: maintains composition of brain fluid by preventing toxic substances from entering the brain
Astrocytes maintain tight junctions
Sodium-potassium pump
Pushes sodium outside and potassium inside
3:2 sodium:potassium
Electrochemical potential
Ions encounter 2 forces: electrical and chemical gradient
Sum determines whether the ion will diffuse in or out
Concentration gradient
Pushes potassium out of the cell
Pushes sodium and chloride into the cell
Electrical gradient
Pushes chloride out of the cell
Pushed potassium and sodium into the cell
Excitatory post-synaptic potentials (EPSP)
- Chemical stimulus in synapse -> Sodium channels open
- Positive charge ions (sodium) flow into cells and diffuse along membrane
- Cell membrane depolarises locally
Inhibitory post-synaptic potential (IPSP)
- Chloride channels open
- Negative charge flows in
- Membrane hyperpolarizes locally
Conduction of graded potentials
The current fades aways over a distance due to diffusion of charge over an increasingly large surface area.
Also due to outward leakage of potassium ions (+) through constitutively open potassium channels.
Molecular basis of action potential
- Voltage dependent sodium channels in axon hillock
- When threshold is reached these sodium channels open
- Massive influx of sodium so the membrane potential shoots up and then action potential.
Termination of action potential
- Opening of voltage dependent potassium channels, with a delay
- Slow inactivation of voltage dependent sodium channels
Active propagation of action potential
Repeating depolarization at neighbouring parts of the axon (Nodes of Ranvier).
Events at the electrochemical synapse
- Action potential reaches presynaptic terminal
- Depolarization causes opening of Ca2 (+) channels and calcium moves in
- Calcium causes vesicles to fuse with presynaptic membrane
- Transmitter is released into cleft by exocytosis
- Transmitter binds to receptor in postsynaptic membrane which opens or closes channels
- Opening/closing of channels causes excitatory or inhibitory potential
Types of CNS synapses by function
- Type 1: assymmetrical, excitatory, influx Na and Ca
- Type 2: symmetrical, inhibitory, influx Cl
Types of CNS synapses by connection
- Axodendritic
- Axosomatic
- Axoaxonic
