Nervous System By Dr. Maher T. AL-Hadidi And Dr. Amjad Al- Shatart University of Jordan

Divisions Central NS (CNS): Peripheral NS (PNS): Somatic NS (SNS): Divided structurally into: Central NS (CNS): Brain spinal cord. Peripheral NS (PNS): Cranial nerves & their ganglia :12 pairs, exit skull via specific foramina. Spinal nerves & their ganglia: 31 pairs, exit vertebral column via IV Foramen. Plexuses: Network of Nerves. Ganglia (= Swelling): masses of nervous tissue contains plenty of neurons. Divided functionally into: Somatic NS (SNS): The Part supplies Voluntary structures Body wall and limbs. Autonomic NS (ANS): Part supplies involuntary structures, e.g.. Cardiac muscle Smooth muscles Glands

Spinal Cord An elongated cylindrical cable extending from foramen magnum ending as conus medullaris between L1/L2 vertebrae. About 45cm in males, 42cm in females and about 1cm diameter. Has 2 enlargements: Cervical (C5-T1) Lumbar (L1-S3) Organized into 31 spinal segments, each gives 2 spinal nerves, that leave through IVF of the same level of its spinal segment. Inferiorly, the Lumbosacral roots do not leave the (IVF) at the same level of their spinal segments. The roots of these nerves gathered inferiorly as group of fibers called Cauda equina (horse tail).

Spinal segment Each divided into right and left sides by anterior median fissure and posterior median sulcus. Consists of central gray matter and peripheral white matter. Gray matter Butterfly- or H-shaped area. Consists cell bodies + their processes + interneurons + neuroglia + blood vessels. Central canal located in the center of the crossbar of the H, called gray commissure (a band joining symmetrical fibers). Nuclei: Masses of cell bodies, form functional groups in gray matter. Sensory nuclei: receive input from receptors via sensory neurons. Motor nuclei: provide output to effectors using motor neurons

Spinal segment Gray matter Subdivided into: Ventral horn: Found at all levels of SC. Contain cell bodies of somatic motor neurons and motor nuclei, which provide nerve impulses for contraction of skeletal muscles. Dorsal horn: Found at all levels of SC. Receives and processes sensory input. Contain somatic and autonomic sensory nuclei. Lateral horn: Extends from T1-L3. Receives viscerosensory input. Contain cell bodies of autonomic motor neurons (preganglionic sympathetic) that regulate activity of smooth muscle, cardiac muscle and glands.

Spinal segment-- White matter Contain bundles of myelinated fibers. Organized by sulci into 3 columns. Anterior column. Posterior column. Lateral column. Each column contains specific bundles of axons having common origin or end and carrying similar information. Tracts: bundles that travel long distance up or down the spinal cord, are either Ascending tracts: Conducts impulses towards the brain. Descending tracts: Conducts impulses down the spinal cord. Sensory and motor tracts inside spinal cord are continuous with similar ones in the brain.

Spinal nerves 31 pair

A 3 layered-tubular sheath surround the spinal cord. Spinal Cord Meninges A 3 layered-tubular sheath surround the spinal cord. Consist of 3 layers: 1-Dura matter (outer layer). Dense layer of fibrous tissue. 2-Arachnoid (middle layer): Delicate CT membrane. 3-Pia matter (inner layer): Transparent fibrous membrane that stick on the spinal cord.

Spinal Cord Meninges Read only Meningeal spaces located between the 3 meninges and the vertebral canal. Include 3 spaces: Extradural space Filled with fat, CT and blood vessels. (danger) Subdural space Contains serous fluid. Subarachnoid space A wide space that Contains cerebrospinal fluid (CSF) (danger). Extends to lower border of S2.

Nervous System Brain

The Brain Lies within cranial cavity. Weighs ~1500gm in adult. Covered by 3 meninges. Bathed by CSF. Consist of: Cerebrum (2 hemispheres) Diencephalon (within brain) Thalamus Hypothalamus Brainstem Midbrain, Pons, Medulla Cerebellum (little brain). Each have a cavity for CSF either a ventricle or a duct.

Limbic lobe (= border lobe) (internal Each hemisphere divided externally into 4 lobes by: A-Central sulcus B-Lateral sulcus Lobes Frontal lobe Parietal lobe Occipital lobe Temporal lobe Limbic lobe (= border lobe) (internal

Brain-- (Medial view) Read only

Cerebrospinal Fluid . Produced by choroid plexuses within ventricles at a rate of 500ml/day. Total volume 140ml. Absorbed by arachnoid villi which drain it into SSS and venous circulation.

Cerebrospinal Fluid Functions Protective cushion against force injury. Lower brain weight about 30 times by its floating mechanism. Plays an active part in the nourishment of the nervous tissue. Remove waste products of neuronal metabolism through absorption by arachnoid villi. Read only

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