Neurons - Anatomy Overview

Going to be covering nerves and synapses this week so here’s a recap!

  • Soma (cell body) contains the nucleus which produces RNA to support cell functions, + organelles surrounding the nucleus which are mostly made of up endoplasmic reticulum. Supports and maintains the functioning of the neuron.
  • Dendrites - cellular extensions with many branches ‘dendritic tree’. majority of input occurs via the dendritic spine. The sum of all excitatory (neuron fires) or inhibitory (prevents firing) signals determines whether the neuron fires or not. If firing the action potential is transmitted down the axon.
  • Axon - fine, cable-like projection that can extend thousands of times the diameter of the soma in length. The axon carries nerve signals away from the soma (and also carries some types of information back to it). Can undergo branching - communication with target cells. 
  • Axon hillock - where the axon emerges from the soma. the part of the neuron that has the greatest density of voltage-dependent sodium channels - therefore the most easily excited part of the neuron and the spike initiation zone for the axon - most negative action potential threshold. Can also receive input from other neurons.
  • Axon terminal where neurotransmitters are released into the synaptic cleft to signal the next neuron

Myelin sheath

Myelin is a fatty material that wraps around axons and increases the speed of electrical transmission between neurons. It is broken up by nodes of Ranvier, between which electrical impulses jump. Myelin is produced by schwann cells in the PNS and oligodendrocytes in the CNS.

Classes of neurons

Sensory neurons bring information into the CNS so it can be processed.

Motor neurons get information from other neurons and convey commands to  muscles, organs and glands.

Interneurons,found only in the CNS, connect one neuron to another. 

Types of neuron

Multipolar neurons have one axon and many dendritic branches. These carry signals from the central nervous system to other parts of the body eg muscles and glands.

Unipolar neurons are also known as sensory neurons. They have one axon and one dendrite with branches. Pass signals from the outside of the body, such as touch, along to the central nervous system.

Bipolar neurons have one axon and one dendrite branch. They pass signals from one neuron to the next inside the central nervous system.

Pyramidal neurons have one axon and two main dendrite branches. These cells pass signals inside the brain and tell the muscles to move.

Purkinje neurons are found in the cerebellum, controlling balance, coordination, and timing of actions. They have one axon and a dense and complicated dendrite arrangement.