– Neurons are nerve cells that transmit info throughout the body and are the foundation of the nervous system.
– In general, neurons have a cell body (soma), a dendrite, and an axon.
– Different neurons will have different perks to their structure (longer dendrites/axons, myelin sheath etc.)
– The dendrite is where information is received from the synapse
– The axon is where that signal is sent to another neuron.
– Neurons can have thousands of synapses with other neurons.
– When an axon wants to send info away from the cell body an action potential occurs.
– When a neuron is at rest, or not sending a signal, it is at resting potential.
– Resting potential is approximately -70 mV
– All action potentials are the same size.
– Resting potential is occurring because of the sodium potassium pump.
– The sodium ions are moving to the outside and it is positive, while some potassium ions move to the inside. Because there are a greater number of sodium ions outside than potassium, the electric potential occurs
– When a stimulus causes a neuron to come out of rest, the sodium gates of the membrane open, allowing the sodium on the outside to rush into the cell
– In order to get an action potential, the depolarization must reach a certain threshold level in order to fire the message. If not, it will not occur (“All or none” principle)
– Now the inside of the cell is positive and the outside is negative.
– Once the action potential reaches it’s peak, the sodium gates close, and the potassium gates open.
– The potassium goes out of the cell while the sodium stays inside. This is called repolarization.
– Once the potassium gates close, because there is more potassium on the outside than there is sodium on the inside, the potential drops lower than the resting potential for a moment.
– The sodium gates will open once again, letting the sodium go back inside, going back to the original resting potential.
– Although the messages being sent from neuron to neuron are chemical, the procedure sending these messages from dendrite to axon are electrical.
– Within each axon terminal, there are vesicles that contain neurotransmitters
– Each neurotransmitter sends a different kind of message to the connecting dendrite.
– When a signal comes through the presynaptic ending, the vesicles within the axon terminal go towards the presynaptic membrane, and release the neurotransmitters that were wanted.
– There is also mitochondria in the axon terminal, the powerhouse of the cell.
– These neurotransmitter diffuse through the synaptic cleft and into a receptor site
– This is the postsynaptic ending.
– Each receptor site is like a lock, and neurotransmitters are like the keys to those specific receptor sites.
– These chemical messages may either be excitatory or inhibitory.
– Excitatory means that it wants the message to be passed on
– Inhibitory means that it doesn’t want the message to be passed on and will prevent it from doing so.
– After use, these neurotransmitters are either destroyed or recycled back into the axon terminal.