Coverings of the CNS• 1) Bone – Cranium, Vertebrae• 2) Meninges – Three connective tissue membranes

covering the brain and spinal cord• a) Dura Mater – outermost , composed of tough

fibrous connective tissue. Vascular. Attached to cranium but not to the vertebrae. Epidural Space exists between the vertebra and Dura Mater. Composed of fat.

• b) Arachnoid Mater – middle layer. Thin, web-like layer

• c) Pia Mater – innermost layer. Very thin, vascular. Clings to the surface of the brain. Aids in nourishing underlying brain cells

• Subarachnoid Space – exists between the Arachnoid and Pia Mater. Filled with cerebrospinal fluid.

The Brain• Composed of 100 Billion Neurons – Divided

into 4 major regions

• 1) Cerebrum – largest region. Surface has elevated ridges called Gyri, separated by shallow grooves called Sulci and less numerous but deeper grooves called Fissures.

• Sulci and fissures divide the cerebrum into lobes named for the cranial bones above them.

• Divided into hemispheres by the Longitudinal Cerebral Fissure.

• Hemispheres connected by a bridge of nerve fibers called the Corpus Callosum

• Impulses cross over to the other side of the body in the brainstem. Impulses from the right side of the brain control muscles on the left side of the body.

• Hemisphere Dominance – both hemispheres participate in basic functions. In most people one side acts as a dominate hemisphere for other functions. 90% of people are left hemisphere dominant

• Within cerebral hemispheres and brainstem are interconnected cavities called Ventricles

• The ventricles are continuous with the central canal of the spinal cord and are filled with Cerebrospinal Fluid

• Cerebrospinal fluid (CSF) completely surrounds the brain and functions to:

• 1) support and protect

• 2) Maintain ion concentration of the CNS

• 3) Remove wastes

Functions of the Cerebrum

• 1) Interpret sensory impulses

• 2) Initiate voluntary muscle movement

• 3) Store Information

• 4) Reasoning

• 5) Personality, Intelligence

• 2) Diencephalon – Sits atop the brainstem and consists of 3 regions

• Thalamus – relay station for sensory impulses

• Hypothalamus – Plays a role in the regulation of body temperature, water balance and metabolism. Also thirst, appetite, pain and pleasure centers are in the hypothalamus.

• Epithalamus – tissues lining the epithalamus form cerebrospinal fluid

• 3) Brain Stem – Bundle of nerve tissue that connects the cerebrum to the spinal cord. It also has many areas of gray matter that controls vital activities. 3 Main Regions

• a) Midbrain – Center for auditory and visual reflexes

• b) Pons – Relay impulses from the medulla to the cerebrum

• c) Medulla Oblongata – Regulates blood pressure, heart rate, breathing and certain reflexes

• 4) Cerebellum – Acts as a control center in the coordination of skeletal muscle movements

Cranial Nerves• 12 pairs of nerves arise from the underside

of the brain that mostly serve the head and neck

• Numbered in order, front to back• Most are mixed nerves, but three are

sensory only• Olfactory – Sense of smell• Optic – Sense of Vision• Vestibulocochlear – Hearing and balance• Vagus – Sensations and movements of

Visceral organs.

Spinal Cord

• Extends from the foramen magnum to the disk between the 1st and 2nd Lumbar vertebrae

• It is surrounded and protected by the meninges

• The meninges extends below the end of the cord and provide for safe sampling of CSF below L3 (spinal tap)

• Spinal cord gives rise to 31 pairs of spinal nerves that exit the vertebrae and serve the body close by.

• Nerves exiting below the end of the cord travel through the vertebral canal and form the Cauda Equina (horse’s tail)

• Cross section of the cord reveals a core of gray matter surrounded by white matter. Pattern of gray matter resembles a butterfly

• Neurons of the gray matter are interneurons. Neurons in the white matter are nerve tracts

• Central canal filled with Cerebrospinal Fluid

• Divided into right and left halves much like the brain

Spinal Cord Functions

• 1) Reflex Center (gray matter)

• 2) Conduct impulses to and from the brain (white matter)

Peripheral Nervous System

• Nerves that branch out of the CNS to different parts of the body

• 2 Divisions – Somatic and Autonomic• Somatic Nerves – Nerves that lead to the

skin and skeletal muscles involved in conscious activities

• Autonomic Nerves – Nerves that lead to the visceral organs involved in unconcious activities

Autonomic Nervous System

• Further subdivided into the Sympathetic and Parasympathetic divisions

• Impulses from one set of nerves activate an organ. Impulses from the other nerves inhibit the organ

• Sympathetic division is concerned with preparing the body for energy expending, stressful or emergency situations

• 31 pairs of spinal nerves originate from the spinal cord

• All are mixed nerves. Not named but numbered

• 8 pairs of Cervical nerves

• 12 pairs of Thoracic nerves

• 5 pairs of Lumbar nerves

• 5 pairs of Sacral nerves

• 1 pair of Coccygeal nerves

• Each spinal nerve emerges from the spinal cord as two short branches or “roots”

• The dorsal root is composed of sensory fibers and the ventral root is composed of motor fibers

• The dorsal and ventral root unite to form a spinal nerve which passes outward from the vertebral canal through the intervertebral foramen

• After emerging from the vertebral canal, main portions of the spinal nerves combine to form complex networks called plexuses

Plexuses

• 1) Cervical Plexus – C1-C4 – muscles of the neck, diaphragm

• 2) Brachial Plexus – C5-T1 – arm, forearm, hand

• 3) Lumbosacral Plexus – T12-S5 – Lower abdomen, legs