CENTRAL NERVOUS SYSTEM CNS

ORGANIZATION OF NERVOUS SYSTEMDR. ZAHOOR ALI SHAIKH LECTURE--- 11First We Will Discuss ORGANIZATION & CELLS OF NERVOUS SYSTEM then we will talk about Overview of Central nervous system [CNS]2ORGANIZATION OF NERVOUS SYSTEMThe Nervous system is organized into 1. Central Nervous System (CNS) -- BRAIN -- SPINAL CORD 2. Peripheral Nervous System -- Nerve fibers that carry information between CNS and other parts of body at periphery. 3Organization of nervous system 4

CNSCentral nervous system regulates body activities.

CENTRAL NERVOUS SYSTEM 1) BRAIN 2) SPINAL CORD

5PERIPHERAL NERVOUS SYSTEM PNS Peripheral Nervous System is sub divided into 1) Afferent Division (Sensory) which carry information to CNS 2) Efferent Division (Motor) which carry information from CNS to muscle and glands. 6PNS [cont]Efferent (Motor) division of PNS is further divide into --Somatic Nervous System it is under our voluntary control E.g. fibers of motor neuron that supply skeletal muscle. --Autonomic Nervous System it is not under our control ( involuntary) and supply smooth muscle and glands. 7PNS [cont]Autonomic Nervous System (ANS) ANS supplies cardiac muscle, smooth - muscle, glands. ANS is divided into 1) Sympathetic ANS 2) Parasympathetic ANS

Enteric ANS in the wall of digestive tract 8ORGANIZATION OF NERVOUS SYSTEM9

9PERIPHERAL NERVOUS SYSTEMNeurons in peripheral nervous system transmit signals between the central nervous system and receptors ,and Effectors in the body.In Peripheral Nervous System, there are 12 pairs of cranial nerves.There are 31 pairs of spinal nerve, from spinal cord. - 31 pair of Spinal nerve exit from cervical (8 pairs), thoracic (12 pairs), lumber (5 pairs), sacral (5 pairs), and coccygeal (1 pair).

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CRANIAL NERVES12

Cranial Nerves

12 pairs13

Spinal Nerves

31 pairs FUNCTIONAL CLASSES OF NEURONS14FUNCTIONAL CLASSES OF NEURONSThere are THREE functional types of Neurons 1) Afferent Neurons which carry information to CNS. 2) Efferent Neurons which carry information away from CNS (to the periphery). 3) Interneurons They form interactive net-work between neuron.15FUNCTIONAL CLASSES OF NEURON16

AFFERENT NEURONAfferent Neuron has sensory RECEPTOR , that generates action potential in response to a particular stimulus. Sensory impulse are taken by axon toward the spinal cord.

17EFFERENT NEURONEfferent Neuron lies in the peripheral nervous system. It has cell body in the CNS . Efferent axon leaves the cell body and goes to innervate muscle. 18INTERNEURONSInterneurons lie in the CNS. About 99% of all neurons are Interneurons. Human CNS has more than 100 billion Interneurons. 19 GLIAL CELLS OR NEUROGLIA20GLIAL CELLS or NEUROGLIAGlial cells are connective tissue of CNS. Glial cells support the interneurons physically, metabolically, and functionally. They do not conduct nerve impulses. Glial cells are of FOUR types. 21GLIAL CELLS or NEUROGLIA (cont)There are 4 type of Glial Cells 1. Astrocytes 2. Oligodendrocytes 3. Microglia 4. Ependymal Cells 22GLIAL CELLS23

Important Functions Of Glial Cells1. Astrocytes Functions i. Formation of blood brain barrier ii. Formation of neural scar tissue

2. OligodendrocytesFunctions i. Forms myelin sheath in the CNS. 24Important Functions Of Glial Cells3. MicrogliaFunctions i. Phagocytosis [defense cells of CNS] ii. Release nerve growth factor.

4. Ependymal CellsFunctions i. Formation of Cerebrospinal fluid [CSF]. ii. Work as Neural Stem Cell to form new neurons and glial cells. 25Protection Of The Brain26Protection Of Brain As CNS is very delicate, it is protected by skull bone [covers the brain] and Vertebral column [surrounds the spinal cord].Meninges cover brain and spinal cord. Meninges lie between bony covering [outside] and nervous tissue [inside]. Meninges are Durameter, Arachnoid and Piameter.CSF - Cerebro Spinal Fluid is present in subarachnoid space. CSF works as cushion. Blood - brain barrier it selectively allows the materials to pass to brain.

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Cerebro Spinal Fluid [CSF]It surrounds brain and spinal cord.It is present in subarachnoid space.It is formed by choroid plexuses [capillaries in the piameter] of ventricles in the brain.Volume of CSF is about 125 150 ml.

29CSF [cont]Clinical NoteHydrocephalus [water in the brain].Occurs if CSF accumulates more, due to the block in its circulation or reabsorption.If hydrocephalus is untreated, increased CSF pressure can lead to brain damage and mental retardation. Treatment surgically shunting the excess CSF to veins elsewhere in the body.

30Important InformationBrain function depends on 1. Oxygen 2. GlucoseBrain needs continuous supply of O2 and Glucose.Brain damage results if - brain gets no O2 supply for 4 to 5mins or - no glucose supply for 10 to 15mins.31OVER VIEW OF CENTRAL NERVOUS SYSTEM (CNS)32OVER VIEW OF CNSParts of Brain (from top to bottom) 1. Forebrain a) Cerebrum i) Cerebral cortex ii) Basal nuclei b) Diencephalon i) Thalamus ii) Hypothalamus

33OVERVIEW OF CNS (cont)Parts of Brain (cont) 2. Brain stem - Mid brain - Pons - Medulla 3. Cerebellum34

MAJOR COMPONENTS OF THE BRAIN35.CEREBRUMCerebrum constitutes 80% of total brain weight.Outer layer, i.e. cerebral cortex of cerebrum is highly convoluted. It has gyri [ridges] and sulci [depression].3637

Basal NucleiBasal Nuclei are present deep in the cerebrum.Functions: - Co-ordination of movements - Muscle tone regulation 38Diencephalon Diencephalon is present in the interior of cerebrum.It has 2 components: - Thalamus - HypothalamusThalamusAll sensory information passes.Crude awareness of sensation.HypothalamusRegulates body temperature, has thirst and food intake center, regulates autonomic nervous system.

39Brain StemBrain Stem [mid brain, Pons, Medulla].Brain Stem is continuous below with spinal cord.Functions:Majority of cranial nerves originate from brain stem.Control Center for cardiovascular, respiratory system.Regulation of postural reflexes.Role in sleep wake cycle.40CerebellumCerebellum is attached at the back portion of brain stem.Functions:Balance of body.Muscle tone.Co-ordination and planning of skilled movements e.g. dance.4142

CEREBRUMCerebrum is the largest portion human brain. It is divided into TWO halves, Right and Left cerebral hemispheres. They are connected by CORPUS CALLOSUM which consists of about 300 million axons connecting two cerebral hemispheres. Cerebral cortex It is the outer shell of Gray matter covering the inner white matter.43CEREBRUM (cont)QWhat is the GRAY Matter ? A It is the Cerebral cortex , which consists of cell bodies and their dendrites, as well as connective tissue glial cells. Q What is the WHITE Matter ? A It is the myelinated nerve fibers (Axons) . Its white appearance is due to Myelin sheath (lipid layer). 44CEREBRAL CORTEX NOTE Gray matter of cerebral cortex is like computers of CNS. White matter is like wires that connect the computers to each other. 45CEREBRAL HEMISPHEREEach cerebral hemisphere is divided into FOUR LOBES. 1) Frontal lobe 2) Parietal lobe 3) Temporal lobe 4) Occipital lobe 4647

Cortical LobesLOBES OF BRAINCentral Sulcus separates the Frontal and Parietal lobe . Frontal Lobe It is located at the front and at the top. It has MOTOR CORTEX area in the PRE -CENTRAL GYRUS- which controls the motor activity.Motor speech area. Elaboration of Thought.48LOBES OF BRAINParietal lobe It is located posterior to the central sulcus.It has sensory cortex at post central gyrus.

Temporal LobeLocated laterally [on the sides of head].It has auditory cortex.49LOBES OF BRAINOccipital Lobe Located posteriorly [back of head].It has visual cortex ( center).

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Functional areas of Cerebral cortexThank you52