NERVOUS

SYSTEM 2

Functionally, the nervous system includes 2 main components:

Nervous System

Somatic nervous Somatic nervous systemsystem

Autonomic nervous Autonomic nervous systemsystem

Receives visceral sensation from the viscera and controls the activities of organs, glands

and various involuntary muscles

Receives different somatic sensation from the body and controls different voluntary

activities

Structurally, the nervous system is divided into:

Nervous SystemNervous System

Central nervous system

Peripheral nervous system

Brain Spinal Cord

Spinal nerves

Cranial nerves

Autonomic nerves Autonomic nerves

and gangliaand ganglia

CENTRAL NERVOUS SYSTEM It is the part of the nervous system, which is present in midline

of the body and protected within bony cages. It is covered by 3 meninges:

Dura mater Arachnoid mater Pia mater

It is bathed in a layer of fluid called cerebrospinal fluid, which is present in the “subarachenoid space”.

It is responsible to : Integrate and coordinate incoming and outgoing neural signals. Carry out higher mental functions such as thinking and learning.

The central nervous system is formed of: Brain: lies in the skull Spinal cord: lies within the vertebral column

Overview of the central nervous system

THE BRAIN

Is the part of the central nervous system, which occupies the vertebral canal.

Begins at the foramen magnum as continuation of medulla oblongata.

It ends opposite the lower border of 1st lumbar vertebra.

THE SPINAL CORDTHE SPINAL CORD It shows enlargements in

the regions giving rise to large nerves of the limbs. These enlargements are: Cervical enlargement: Is

found opposite the brachial plexus.

Lumbar enlargement: Is found opposite the lumbar plexus.

THE SPINAL CORD It has:

Anterior median sulcus (fissure): anteriorlyPosterior median septum: posteriorly2 posterolateral sulci (one on each side)2 anterolateral sulci (one on each side)

Cross section of the spinal cord shows the following features:

The spinal segments: the part of the spinal cord giving attachment to a pair of spinal

nerves is called the “spinal segment”. There are 31 such segments, which give

attachment to the spinal nerves.

PERIPHERAL NERVOUS SYSTEM

Peripheral NS

Spinal nerves Cranial nerves

Spinal nerves

Spinal nerves

RegionRegion No. of vertebraeNo. of vertebrae No. of spinal nervesNo. of spinal nerves

CervicalCervical 7 8

ThoracicThoracic 12 12

LumbarLumbar 5 5

SacralSacral 55 5 5

CoccygealCoccygeal 2-42-4 1 1

Spinal nerve Each nerve divides immediately into

anterior (ventral) and posterior (dorsal) primary rami going to the front and back of the body respectively.

The spinal nerve emerge from the spinal column through an opening (intervertebral foramen) between the adjacent vertebrae. This is true for all spinal nerves except for the first spinal nerve (pair) which emerges between the occipital bone and the atlas.

Cranial Nerves

Cranial nerve Type Major function

I Olfactory Sensory Smell

II Optic Sensory Vision

III Oculomotor Motor Movement of the eyeball

IV Trochlear Motor Movement of the eyeball

V Trigeminal Mixed Sensory from head and neckMotor to muscles of mastication

VI Abducent Motor Movement of the eyeball

VII Facial Mixed Motor to facial musclesSecrtomotor to the salivary, lacrimal glands

Taste sensation from the tongue

VIII Vestibule-cochlear Sensory HearingSense of equilibrium

IX Glossopharyngeal Mixed Motor to some muscles of pharynxSecrtomotor to the parotid glandTaste sensation from the tongue

X Vagus Mixed Motor to muscles of the larynxParasympathetic supply to the heart, smooth muscles of

digestive and respiratory tractsTaste sensation from palate and epiglottis

XI Accessory Motor Motor to muscles of the palate and pharynx

XII Hypoglossal Motor Motor to muscles of the tongue

Cranial Nerves