Neuron
- Recieves and transmits information to the other cells
- They do not divide (fully developed)
- Basic structural unit of the nervous system
- It transmits and processes information through electrical and chemical changes
3 Different type of Neurons
- Sensory (Afferent) Neuron
- Interneuron
- Motor (Efferent) Neuron
3 General Basic Functions of Neurons
- Recieves signals (information)
- Integrate incoming signals
- Communicate signals to target cell
Sensory (Afferent) Neuron
Perceives information from outside and inside the body
Brings information to the CNS so it can be processed
Afferent pathways
Interneuron
Also known as Relay neurons
Only found in the CNS (connects one neuron to another)
Receives information from other neurons (sensory or another interneuron)
Transmit information to other neurons (Motor or another interneuron)
The “in between” neurons
Motor (Efferent) Neuron
Receives information from other neurons
Conveys information to muscles, glands and organs
Efferent pathways
Soma (cell body)
Contains organelles ( nucleus, mitochondria, etc)
- Also responsible for the metabolic work of the neuron
Dendrites
Carries nerve impulses towards the soma/ cell body
- Dendritic spines = increase surface area and point of communication
Axon
Carries nerve impulses away from the soma/ cell body to other
neurons, organs or muscles.
Axon Hillock
An expansion of the cell body
Axon Collaterals
Branches of the axon
Myelin Sheath
Insulating layer covering the axon
It allows electrical impulse to transmit quickly and efficiently
Nodes of Ranvier
Gaps between the sheaths
This serves to allow facilitate rapid conduction of nerve impulses
Chemical Transmission (Synaptic Transmission)
🔹 1. The Synapse
Neurons don’t touch each other
The small gap between neurons = synaptic cleft
🔹 2. Action Potential Arrives
The electrical signal (action potential) travels down the axon to the axon terminal (end of the neuron)
🔹 3. Neurotransmitter Release
The action potential opens calcium (Ca²⁺) channels Calcium rushes in → causes vesicles to release neurotransmitters into the synaptic cleft
Neurotransmitters = chemical messengers
🔹 4. Neurotransmitters Bind
Neurotransmitters cross the synaptic cleft and bind to receptors on the next neuron
This changes the voltage of the next neuron:
Excitatory → may trigger an action potential
Inhibitory → makes firing less likely
🔹 5. Signal Continues
If excitatory → the next neuron fires its own action potential
If inhibitory → the signal is stopped
🔹 6. Neurotransmitter Removed
Neurotransmitters are quickly:
Broken down by enzymes
Reabsorbed by the first neuron (reuptake)
Diffuse away
This ensures the synapse is ready for the next signal.
Electrical
A neuron at rest maintains a resting potential of -70 mV due to unequal ion distribution and the sodium–potassium pump. When a stimulus is received and the membrane potential reaches the threshold of -55 mV, voltage-gated sodium channels open, allowing Na⁺ ions to rush into the cell. This causes depolarization, where the membrane potential rapidly rises to approximately +30 mV through a positive feedback mechanism. At the peak of the action potential, sodium channels close and voltage-gated potassium channels open, allowing K⁺ ions to diffuse out of the neuron. This causes repolarization, returning the membrane potential toward -70 mV. Excess potassium efflux leads to hyperpolarization, where the membrane potential briefly falls below resting potential. Finally, the sodium–potassium pump restores normal ion distribution and the neuron returns to its resting state, ready for the next impulse.
