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 1 st and 2 nd 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 L 3 (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