Neurons: Flashcards
Basic structure, electrical and chemical processes, Neurotransmitters
Basic Structure of Neurons:
Neuron’s have long, thin fibres that extend out from the cell body. Two types of Fibres extend form the cell body, Axons and Dendrites.
Axons are fibres that carry signals AWAY from the cell body where communication occurs, each neuron typically has one axon, that axon has many branches. These can be short or long (There is a axon that reaches from your spinal cord to your big toe which is several feet long)
Dendrites are the fibres that RECEIVE signals from the axons of other neuron’s, a neurone can have many dendrites and dendrites also have many branches.
Action Potential:
The neurons call membrane is a semipermeable barrier meaning it lets some chemical ions pass but block others. The ions are atoms that carry negative and positive electrical charge.
Polarisation:
The cell pumps positively charged ions through its membrane which makes the inside of the call slightly more negative than the outside
Positively charged Ions are attracted to those with a negative charge, this creates a force called electrochemical potential. The cell membrane lets some of the positive charged ions through openings called channels the channels are along the axon and dendrites actings as gates.
Depolarisation:
Changes in the environment cause these ‘gates’ to open and positively charged ions rush into the channel cause the next gate to open further along the axon and depolarise.
Depolarisation and Polarisation process:
The speed of an axon potential depends on the diameter of the axon (larger the faster) and whether a fatty substance called MYELIN is present. Myelin improves conduction and wraps around an axon like electrical tape.
There are gapes in the Myelin called nodes of Ranvier which allow the transfer of ions needed for the germination of an action potential. The nodes of Ranvier are where action potentials are initially propagated. The actions potential then jumps to the next node where is is regenerated.
Neurons can fire over and over because the gates open briefly then close, between firing there is a very short rest called a refractory period and the call returns to a polarised state when depolarisation is complete the neuron fires again.
Excitatory and Inhibitory Potential:
Is a change in the membrane potential of the postsynaptic cell is called postsynaptic potential.
Excitatory Potential (FIRE):
If a positively charged ions such as sodium or calcium flow into the neuron it becomes slightly less polarised, as this depolarisation can cause a neutron to fire an action potential, a depolarising postsynaptic potential is called an excitatory postsynaptic potential.
Inhibitory Potential (DO NOT FIRE):
If positively charged ions such as potassium flow out of the neurons of if negatively charged ions flow in the neuron become slightly more polarised, this hyper polarisation makes it less likely to fire an action potential. This is called a inhibitory postsynaptic potential.
Neurotransmitter Release and Reception:
Neurotransmitters are chemical messengers that assist in the transfer of signals from one neuron to another. These chemicals are stored in little bags called vesicles at the tips of axons. When an action potential reaches the end of an axon a neurotransmitter is released into the synapse where it spreads to reach the next or postsynaptic cell. When they reach the membrane of the postsynaptic cell neurotransmitters bind to proteins called neural receptors, only binding to receptors that fit properly like a puzzle. the receptors only allow certain neurotransmitter where the neurotransmitters can bind to several receptor types.
when the neurotransmitter binds to the receptor, it triggers channels in the postsynaptic membrane to open allowing chemical ions to flow in or out which produces a change in the membrane potential, The chemical signal that crosses the synapse creates an electrochemical signal in the postsynaptic cell.
Main Neurotransmitters that effect the brain:
Acetylcholine - This is used by neurons in the parasympathetic nervous system to slow heart rate, activate digestive system, and also used by the neurons to make muscles contract. They are in large numbers in the midbrain and striatum where they occur in circuits that are important for movement. Neurons that use Acetyclocholine (Cholinergic neurons) make major pathways in the limbic system such as hippocampus and areas in forebrain that are involved in memory.
Serotonin:
Used by cells in parts of the brain that are invvled in regulation of sleep, mood and eating. Most of the cells that use it as a neurotransmitter occur in an area along midline of the hindbrain. axons that use seretonin send branches throughout the forebrain such as hypothalamus, cerebral cortex and hippocampus.
Norepinephrine:
Invovled in arousal as well as learning and mood regulation, it is one of the neurotransmitter used in the sympathetic nervous system to activate and paper for action. norepinephrine covers a lot of area in the brain including half being in cells of locus coeruleus near the recticular formation in the hindbrain. Because these neurotransmitters are in such varsity they affect serveral categories of behviour, in wakefulness, sleep, learning and mood regulation.
Dopmine:
Used in parts of the brain involved in regulating movement and experiencing pleasure. Used in parts of the brain such as substantia nigra and striatum which are important for movement.
Gamma-amino butyric acid (GABA):
Neurotransmitter that inhibits the firing of neurons. Neurons that use GABA play a role when you fall asleep. It is a major inhibitory neurotransmitter in the Central Nervous System.
