Lecture 3: Structure and Function of cells of the NS Flashcards
Dendrites
-Branch out from cell body, increase the surface area
Axon terminals
- communicate with dendrites of other neurons
- when nerve impulses reach terminal boutons they release neurotransmitters
Soma
-Nucleus (DNA), mitochondria (energy) and endoplasmic reticulum (protein synthesis)
Axon (inside myelin sheath)
- carries info (action potential) from the cell body to the terminal boutons:
- afferent carry info into a region
- efferent carry info away from a region
What percentage of cells in the brain are glial?
80%
Glial cells: Astrocytes
provide physical support, nutrients and involved in phagocytosis (helps prevent infection and fight against disease in the brain)
Glial cells: Microglia
Phagocytosis and prevention against infection
Glial cells: Oligodendrocytes
support axons and produces myelin sheath in CNS
Glial cells: Schwann cells
supports axons and produces myelin sheath in PNS
Myelin sheath
- 80 % lipid; 20% protein
- Consists in segments with small portions of uncoated axon between segments (Nodes of Ranvier)
- The function of the myelin sheath is to increase the speed at which the axon propagates an electrical signal
What is electrical transmission?
=within the neutron, along the axon
What is chemical transmission
=between the neuron
- involves the release of neurotransmitters from the terminal to the post synaptic cell
- Impulse at terminal causes release of neurotransmitter into synapse which interact with specialized receptors on adjacent neurons
The cell membrane
- Known as bilayer
- Protein channels: allow certain ions to move in and out of the cell
- Membrane is selectively permeable: allows certain ions to cross it at certain times
- Sodium, potassium, chlorine, and calcium cross through channels that are sometimes closed
Neuron at rest overview
know in more detail
At rest, you have the sodium potassium pump that maintains your resting potential of -70 by pumping out sodium ions and replacing them with potassium ions
Chloride ions
- Concentration and electrical gradient balance
- want to go from high concentration to a low concentration, want to stay on outside of the cell as its more positive and they are negatively charged. So concentration and electrical gradients balance each other out
The resting potential, why bother?
- Allows brain cells to respond very quickly to external stimuli
- When brain cell is stimulated sodium is going to rush into the cell so maintaining this resting state in which the cell is more negative, mean that once you get this stimulation, the sodium ions are going to rush into the cell and create an action potential
- So by maintaining this negative resting potential it enables neurons to respond quickly to external stimuli
What happens when brain cell is activated?
**
Rues regarding action potentials
- Action potential only travels in one direction: from cell body to axon terminals because of hyperpolarization
- Myelination speeds up propagation of action potential: *saltatory conduction. Because action potential jump between the gaps in myelin sheath
- Refractory period**go over
- All or nothing law: neuron will only fire if threshold of excitation reached
- Rate law intensity represented by rate
First 4 stages of Communication between neurons: synapse
- Action potential reaches the terminal bouton in the pre-synaptic neuron
- Depolarisation of the terminal bouton
- Synaptic vesicles migrate and fuse with the presynaptic membrane
- Vesicles release chemical neurotransmitter into the synaptic cleft
Last 4 sarges of Communication between neurons: synapse
- Neurotransmitter attaches to binding sites of receptors on the postsynaptic membrane.
- Degeneration: neurotransmitters are broken down and deactivated by enzymes
- Re-uptake: neurotransmitters taken back up by the pre-synaptic terminal
- Auto-receptors on the presynaptic membrane become activated by the neurotransmitter in the synapse and this causes a decrease in synthesis or release of neurotransmitter
Excitatory postsynaptic potentials
*depolarising
- Na+ channel (sodium) opens: excitatory post-synaptic potential (EPSP)
- Partial depolarisation (decrease in the negative state i.e. more positive)
- Increases the likelihood that the postsynaptic neuron will fire
Inhibitory postsynaptic potentials
*hyperpolarising
- K+ channel opens (potassium): inhibitory post-synaptic potential (IPSP)
- Hyperpolarisation (increase in the negative i.e. it becomes more negative)
- Decreases the likelihood that the postsynaptic neuron will fire
Integration of post-synaptic potentials
- Each postsynaptic neuron will have synapses with many presynaptic neurons
- Neural integration: interaction of excitatory and inhibitory synapses on a particular neuron
- The rate at which a neuron fires is dependent upon the relative activity of the excitatory and inhibitory synapses on the postsynaptic dendrites and soma
