Overview of the Nervous System

Study Notes

The nervous system is divided structurally into the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS consists of the brain and spinal cord.
The PNS consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves, along with their associated ganglia.

Students will be able to describe the structural and functional divisions of the nervous system.
Students will be able to describe the different types of cells forming nervous tissue.
Students will be able to name the parts of the nervous system and discuss their functions.

Functionally, the nervous system is divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS).
The somatic nervous system is voluntary and conveys messages from sense organs to the CNS and from the CNS to target organs.
The autonomic nervous system is involuntary and controls functions of the body not under conscious control, including the heart, intestines, and other organs. It has two divisions; sympathetic and parasympathetic.

Preganglionic nerves are located in the gray matter of the thoracolumbar spinal cord.
Preganglionic sympathetic nerve fibers terminate in sympathetic ganglia.
Postganglionic sympathetic neurons arise from sympathetic ganglia (paravertebral ganglia) and extend to the target organ.
Sympathetic responses prepare the body for arousal, including increased breathing and heart rate, and decreased digestive activity.

Preganglionic nerves extend from neurons in the gray matter of the brainstem and sacral segments of the spinal cord to parasympathetic ganglia close to each internal organ.
Postganglionic nerves are short and extend from parasympathetic ganglia located in or on the structure being innervated.
Parasympathetic activity facilitates non-emergency responses, such as increased motility of the gastrointestinal tract (GIT).

The brain is about one-fiftieth of the body weight, located within the cranial cavity.
The brain is composed of cerebrum, diencephalon, and cerebellum.
The brainstem is divided into midbrain, pons, and medulla oblongata. These structures are interconnected.
The brainstem is connected to the spinal cord.

The largest part of the brain, divided by the longitudinal cerebral fissure into right and left hemispheres.
Contains gyri (elevated areas) and sulci (depressions), which increase the surface area.
The superficial layer (peripheral part) is composed of nerve cell bodies (grey matter) forming the cerebral cortex, and deeper layers consist of nerve fibers (white matter).
Divided into lobes (frontal, parietal, temporal, and occipital).

Mental activity (memory, intelligence, moral sense, learning).
Sensory perception (pain, temperature, touch, sight, hearing, taste, and smell).
Initiation and control of skeletal muscle contraction.

The midbrain is located between the cerebrum and pons, and is involved in connecting the cerebrum with lower brain parts. It acts as a relay station.
The pons is situated in front of the cerebellum, and above the medulla oblongata. It acts as a bridge between the hemispheres of the cerebellum and connects higher brain levels to the spinal cord.
The medulla oblongata extends from the pons above to the spinal cord below. It contains vital centers for vital signs (cardiac, respiratory, and vasomotor centers) and reflex centers (vomiting, coughing, sneezing, and swallowing).

Elongated, cylindrical part of the central nervous system.
Lies within the vertebral canal, surrounded by meninges and cerebrospinal fluid.
Extends from the medulla oblongata to the lower border of the first lumbar vertebra.
The distal end (conus medullaris) is cone-shaped. The spinal nerves continue below the end of the cord.