There are two major branches of the nervous system, the central nervous system and the peripheral nervous system. The CNS includes the brain and the spinal cord.

<aside> 💡

The retina and the optic nerve are parts of the CNS that are often overlooked. They have the same developmental origin as the rest of the CNS, therefore similar histologically and functionally.

</aside>

The CNS can be broken up into 7 main parts:

1. spinal cord
2. medulla oblongata
3. pons
4. cerebellum
5. midbrain
6. diencephalon
7. cerebrum

<aside> 💡

cells found in the CNS include astrocytes, oligodendrocytes, neurons, microglia and ependymal cells.

</aside>

The PNS is made up of all the nerves that branch out from the spinal cord (cranial and spinal nerves). Basically the CNS is the central processing unit while the PNS is the system that collects information and executes actions that’re decided by the CNS.

The PNS is made up of the autonomic (sympathetic and parasympathetic) and somatic nervous systems(sensory and motor).

There are also two main cell types in the nervous system, neurons (make up only 10% of the cells in the nervous system) and glial cells.

The development of the nervous system:

The section it the level of the arrow is shown the the picture on the right.

The CNS and PNS have different developmental origins.

The neural tube will give rise to all the central nervous system tissues whilst the neural crest will give rise to the peripheral nervous system. The neural canal will give rise to the ventricles of the brain.

Neurons:

Characteristics of neurons:

• have a high metabolic rate
• require continuous and abundant supply of glucose and oxygen
• have extreme longevity (most are formed during fetal development and remain functional even in old age
• they are typically non-mitotic (mitotic activity is lost during fetal development)

The modal structure of a neuron