NERVOUS SYSTEM 2

Functionally, the nervous system includes 2 main components: Nervous System Somatic nervous system Receives different somatic sensation from the body and controls different voluntary activities Autonomic nervous system Receives visceral sensation from the viscera and controls the activities of organs, glands and various involuntary muscles

Structurally, the nervous system is divided into: Nervous System Central nervous system BrainSpinal Cord Peripheral nervous system Spinal nerves Cranial nerves Autonomic nerves and 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 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): anteriorly Posterior median septum: posteriorly 2 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

Region No. of vertebrae No. of spinal nerves Cervical Cervical 7 8 Thoracic Thoracic Lumbar Lumbar 5 5 Sacral 5 5 Coccygeal 2-4 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 nerveTypeMajor function I OlfactorySensory Smell II OpticSensory Vision III OculomotorMotor Movement of the eyeball IV TrochlearMotor Movement of the eyeball V TrigeminalMixed Sensory from head and neck Motor to muscles of mastication VI AbducentMotor Movement of the eyeball VII FacialMixed Motor to facial muscles Secrtomotor to the salivary, lacrimal glands Taste sensation from the tongue VIII Vestibule-cochlearSensory Hearing Sense of equilibrium IX GlossopharyngealMixed Motor to some muscles of pharynx Secrtomotor to the parotid gland Taste sensation from the tongue X VagusMixed Motor to muscles of the larynx Parasympathetic supply to the heart, smooth muscles of digestive and respiratory tracts Taste sensation from palate and epiglottis XI AccessoryMotor Motor to muscles of the palate and pharynx XII HypoglossalMotor Motor to muscles of the tongue

Cranial Nerves