Anatomy of the Nervous System

Study Notes

The nervous system consists of two main interconnected divisions: the central nervous system (CNS) and the peripheral nervous system (PNS)
The CNS includes the brain and spinal cord
The PNS includes nerves, ganglia, enteric plexuses, and sensory receptors

The brain is enclosed and protected by the skull in the cranial cavity
It contains approximately 85 billion neurons
The brain consists of three main parts: forebrain, midbrain, and hindbrain
The forebrain consists of two cerebral hemispheres and diencephalons
The cerebral hemispheres have four lobes: frontal, parietal, temporal, and occipital
Each lobe has specific functions, such as motor control, sensory reception, and speech processing

The CNS has two types of cavities: ventricles and central canals
Ventricles are wide cavities that include the lateral ventricles, third ventricle, and fourth ventricle
Central canals are narrow cavities that include the central canal of the midbrain and the central canal of the spinal cord

The spinal cord is enclosed and protected by the bones of the vertebral column
It is approximately 45 cm in length and has 31 segments
Each segment gives origin to a pair of spinal nerves
The spinal cord is covered by three meninges: pia mater, arachnoid mater, and dura mater

The PNS includes cranial nerves and their branches, spinal nerves and their branches, and sensory receptors
Cranial nerves are 12 pairs of nerves that emerge from the brain and are distributed in the head and neck
Spinal nerves are 31 pairs of nerves that emerge from the spinal cord and are distributed in the rest of the body
Sensory receptors are structures that monitor changes in the internal and external environment

The autonomic nervous system (ANS) has sensory and motor components
The ANS is divided into two main subdivisions: the sympathetic nervous system and the parasympathetic nervous system
The sympathetic nervous system causes dilatation of the eye pupil, increase heart rate, dilatation of bronchi, and vasoconstriction of arteries
The parasympathetic nervous system causes constriction of the pupil, decrease heart rate, constriction of the bronchi, and does not supply the arteries
The enteric nervous system (ENS) is a third subdivision of the ANS that consists of neurons in the gastrointestinal tract that function independently of the ANS and CNS to some extent