The Nervous System

The Nervous SystemDr Saw Ai YongThe nervous system is divided into 2 main parts,1.The central nervous system and2.The peripheral nervous systemThe Central Nervous System (C.N.S)CNS consists of brain and spinal cord enclosed in cranium and vertebral column.Both are surrounded and protected by layers of non-nervous tissue, collectively term meninges. These layers from without inward, are the dura, arachnoid and pia maters.The space between the arachnoid and pia mater, the subarachnoid space contains cerebrospinal fluid (CSF). CNS is composed of large amount of excitable nerve cells and their processes , which is supported by specialized tissue called neuroglia. The interior of the CNS is organized into gray and white mater. Gray mater- consists of bodies of nerve cells and proximal portion of their processes embedded in neuroglia, it has a gray colour White mater- consists of nerve fibers embedded in neuroglia, it has a white colour due to presence of lipid material in the myelin sheaths of many nerve fibers. The principal roles of the CNS are to integrate and coordinate incoming and outgoing neural signals for the higher mental functions such as thinking and learning.

Peripheral Nervous System (PNS)PNS is composed of cranial nerves, spinal nerves and their associated ganglion.The peripheral nerves consist of bundles of nerve fibers or axons. Although surrounded by fibrous sheath as they run to different parts of the body, they are relatively unprotected and are commonly damaged by trauma.PNS conveys neural impulses to the CNS from the sense organs (eg the eyes and ears) and from sensory receptors in various part of the body (eg in muscle) The PNS also conveys neural impulses from CNS to the muscles and glands.Major Divisions of the CNS and PNS

CNS PNSBrain Cranial nerves and their ganglia -12 Forebrain pairs that exit the skull through the Cerebrum foramina DiencephalonMidbrainHindbrain Pons Medulla oblongata Cerebellum

CNS PNSSpinal cord Spinal nerves and their ganglia- 31 pairs that exit the the vertebral column through the intervertebral foraminaCervical segment 8 cervical spinal nervesThoracic segment 12 thoracic spinal nervesLumbar segment 5 lumbar spinal nervesSacral segment 5 sacral spinal nervesCoccygeal segment 1 coccygeal spinal nerve Both CNS and PNS are composed of somatic and autonomic components.The somatic component is concerned with the innervation of straited muscles, tendons, joints and skin.The autonomic nervous system is concerned with the innervation of involuntary structures such as the heart, smooth muscles and glands.Although the nervous system is divided into somatic and autonomic components, the division is not clear cut in the CNS.The division is clear cut only in the PNS.However, in both divisions, the functional unit is a reflex arcconsisting of -Afferent or sensory component-An intercalated or interconnecting neurone and-Efferent or motor component

IIIIIIIIII Sensory neuron (afferent)II Connector neuronIII Motor neuron (efferent)IIIIII8Somatic Nervous System Autonomic Nervous System1.Motor neurons have cell Motor neurons are cells of thebodies in the anterior horn of autonomic ganglia situated outsideThe spinal cord. The CNS.

2.Motor endings are motor end Motor endings are not discrete likeplates of the striated muscles on the striated muscles, but they are a composite plexus between and around all the smooth muscle fibers and glands

3.The connector neurone is The connector neurone is the pre-wholly situated inside the CNS ganglionic neurone with its cell bodies is the lateral horn of the spinal cord or in the nuclei of III, VII, IX & X cranial nerves The Autonomic Nervous SystemANS is a system of nerves and ganglia concerned with the distribution of impulses to the heart, smooth muscles and glands.The ANS consists of 2 parts1.The Sympathetic system and2.The Parasympathetic systemIn basic morphologic plan, the sympathetic and parasympathetic systems are identical, for each possess preganglionic fibers, peripheral autonomic cells and postganglionic fibers.The sympathetic system stimulates activities that are performed during emergency and stress situations (eg., fight, fright and flight situations)The parasympathetic system stimulates activities that conserve and restore body resources (eg heart beats slow)

IIIVIIIXXT1 L2S 2,3,411

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Cervical ganglia 3Thoracic ganglia 11Stellate gangliaLumbar ganglia 4Sacral ganglia 4Ganglia impar14

Parasympathetic 15Differences between Sympathetic & Parasympathetic systemsSympathetic1.Thoraco-lumbar outflow. (T1 to L2)2.Preganglionic neurone lateral horn3. Preganglionic fiber short4. Ganglion near vertebral column5. Postganglionic fiber long

ParasympatheticCranio-sacral outflow (CN: 3,7,9 & 10 and S 2,3,4)Preganglionic neurone brainstem & sacral segment of spinal cordPreganglionic fiber longGanglion near target organPostganglionic fiber short

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186. Neurotransmitter at pre-ganglionic ending Acetylcholine (Ach)

7. Neurotransmitter at post-ganglionic ending norepinephrine( a few ending, Acetylcholine-sweat gland)8. Action Prepares body for emergency

9. Widespread due to many postganglionic fibers6. Acetylcholine

7. Acetylcholine at all endings

8. Conserves & restores energy

9. Discrete action with few postganglionic fibers

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Sympathetic activities (Fight, Flight & Fright) Parasympathetic activities (Conserve and store body resources)20Typical Spinal NerveA typical spinal nerve arises from the spinal cord by two roots. The ventral root contains motor or efferent fibers from motor neurone in the ventral horn of the spinal cord. The dorsal root carries sensory or afferent fibers from cells in the dorsal root ganglion.The dorsal and ventral roots unite to form a spinal nerve, which divides into two branches a dorsal ramus and a ventral ramus.The dorsal and ventral rami of spinal nerves contain1.The motor or efferent fibers from ventral horn cells of the spinal cord. 2.Sensory or afferent fibers of dorsal root ganglion cells and 3.Autonomic fiber.

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24NerveA bundle of nerve fibers or axons in the PNS is called a nerve.

Nerve plexusA network of nerve is called nerve plexus ( eg, the coeliac plexus in the superior part of abdomen

GanglionA collection of nerve cells or neurones is called a ganglia (eg the spinal ganglia)

Peripheral nerveA peripheral nerve conveys sensory input to the CNS and motor output to the muscle and glands Medical Application1.Spinal cord injuryies2.Spinal nerve injuries3.Head injuries4.Fractures of the skull5.Brain injuries6.Intracranial haemorrhage & cerebral haemorrhage7.Space occupying lesions within the skull8.Abnormal autonomic function9.Computed Tomography (CT)10.Magnetic Resonance Imaging (MRI)11.Positron Emission Tomography (PET)(9,10, 11- can detect the lesions of brain and spinal cord)Objectives of Nervous SystemTo classify the nervous systemTo compare CNS and PNSTo compare SNS and ANSTo compare the sympathetic and the parasympathetic nervous systemTo describe the spinal nerveTo know the medical application of nervous system

References1.Grays Anatomy ( The Anatomical Basis of Clinical Practice) (Fourtieth Edition) Churchill Livingstone Elsevier2.Textbook of Human Neuroanatomy Seventh Edition Inderbir Singh Jaypee Brothers Medical Publishers Ltd New Delhi