Nervous System Physiology By Dr. SHAHAB SHAIKH PhD MD MBBS Lecture – 1: Introduction to nervous system •••••••••••••••••••••••••••••••••• Faculty of Medicine Al Maarefa Colleges of Science & Technology

NERVOUS SYSTEM It is the chief control and coordinating system of the body It adjust the body to its surrounding and regulates all body activities both Voluntary and Involuntary The basic structural and functional unit of the nervous system is nerve cell which is also called Neuron Information processing in the nervous systems takes place through exchange of nerve impulses (Action Potentials) Maintains Homeostasis by three main functions Sensory function Integrative function Motor function

ORGANIZATION OF NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM - CNS Integrates and correlates incoming sensory information Source of thoughts, emotions and memories Most motor signals originate in CNS Consists of … Brain Spinal Cord

PERIPHERAL NERVOUS SYSTEM - PNS Nerve fibers that carry information between CNS and other parts of body at periphery. Afferent Division (Sensory) –carry information to CNS Efferent Division (Motor) – which carry information from CNS to muscle and glands.

PERIPHERAL NERVOUS SYSTEM - PNS Efferent (Motor) division of PNS further divide into Somatic Nervous System it is under our voluntary control E.g. Nerve fibers of motor neuron that supply skeletal muscle. Autonomic Nervous System it is not under our control (involuntary) and supplies smooth muscle and glands. Enteric Nervous System Local network of nerves in the GIT controlling the secretory and motor activities of GIT and under influence of ANS

PERIPHERAL NERVOUS SYSTEM - PNS Autonomic Nervous System (ANS) ANS supplies cardiac muscle, smooth muscle, glands. ANS is divided into Sympathetic Parasympathetic

PERIPHERAL NERVOUS SYSTEM - PNS Neurons in peripheral nervous system transmit signals between the Receptors & CNS or CNS and Effectors in the body. In Peripheral Nervous System, there are … 12 pairs of Cranial Nerves. 31 pairs of Spinal Nerve. Origins of the 31 pair of Spinal nerve … Cervical (8 pairs) Thoracic (12 pairs) Lumbar (5 pairs) Sacral (5 pairs) and Coccygeal (1 pair)

SPINAL NERVES

PERIPHERAL NERVOUS SYSTEM - PNS

CRANIAL NERVES

NEURON Structural and functional unit of the nervous system The human nervous system contain about 1012 neurons Most neurons consists of following part Cell body or Soma Axon or nerve fiber Dendrite

FUNCTIONAL CLASSES OF NEURONS There are THREE functional types of Neurons Afferent Neurons Carry information to CNS. Efferent Neurons Carry information away from CNS (to the periphery). Interneurons They form interactive network between neuron.

AFFERENT NEURONS Afferent Neuron has sensory RECEPTORS , that generates action potential in response to a particular stimulus. The generated Sensory impulse is conducted by axon toward the spinal cord or brain. Also called as sensory neurons

EFFERENT NEURONS They conduct impulses from the brain and spinal cord to effectors like Muscles and Glands. Also called as Motor neurons

INTERNEURONS Interneurons lie in between the afferent and efferent neurons in the CNS. About 99% of all neurons are Interneurons. Important in integrating responses to peripheral information. Interconnections between interneurons are responsible for various phenomena associated with the concept of ‘Mind’ such as Thoughts, Emotions, Creativity, Intellect, Memory and Motivation

NEUROGLIAL CELLS Glial cells are connective tissue of CNS. Glial cells are of FOUR types. Astrocytes Oligodendrocytes Microglia Ependymal Cells Glial cells support the interneurons physically, metabolically, and functionally. They do not conduct nerve impulses.

FUNCTIONS OF GLIAL CELLS Astrocytes Functions Physical support to neurons Help transfer nutrients to neurons Take up and degrade released neurotransmitter Enhance synapse formation & ↑ Synaptic transmission Maintain normal Brain ECF ion concentration Formation of blood – brain – barrier Repair of brain injuries & formation of neural scar tissue Oligodendrocytes Forms myelin sheath in the CNS.

FUNCTIONS OF GLIAL CELLS Microglia Functions Phagocytosis [defense cells of CNS] Release nerve growth factor Ependymal Cells Line internal cavities of brain and spinal cord Formation of Cerebrospinal fluid [CSF]. Work as Neural Stem Cell – to form new neurons and glial cells

Protection of Brain

Protection Of Brain As CNS is very delicate, it is protected by – Skull bone and Vertebral column 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.

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. Clinical Note: Hydrocephalus [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.

Brain Metabolism Brain constitutes only 2% of Body weight but receives 15% of blood pumped by the heart. Under normal resting conditions the brain uses 20% of the O2 and 50% of the Glucose consumed in the body. Brain function depends on continuous supply of Oxygen & Glucose as brain cannot resort to anaerobic metabolism like other tissues and it uses only glucose for energy production but can not store it. Brain damage results if there is - No O2 supply for 4 to 5 mins or - No glucose supply for 10 to 15 mins.

OVER VIEW OF CENTRAL NERVOUS SYSTEM (CNS) Dr Shahab Shaikh

Central Nervous System CNS has an estimated 1012 neurons which are assembled into complex network Functions: Subconsciously regulate internal environment Perception of own body and surrounding environment Reflex responses to external environment changes & stimuli Voluntarily control movements Experience Emotions Higher Cognitive processes like thought and memory

Central Nervous System .

CEREBRUM Cerebrum constitutes 80% of total brain weight. Outer layer, i.e. cerebral cortex of cerebrum is highly convoluted. It has gyri [ridges] and sulci [depression]. GRAY Matter is the Cerebral cortex , which consists of cell bodies of neuron and their dendrites, as well as connective tissue glial cells. WHITE Matter is the myelinated nerve fibers (Axons) . Its white appearance is due to Myelin sheath.

CEREBRUM

Basal Nuclei These are masses of gray matter located deep within the cerebral white matter Functions: Co-ordination of movements Muscle tone regulation Posture maintenance

Diencephalon Diencephalon is present in the interior of cerebrum. It has 2 components: - Thalamus - Hypothalamus Thalamus All sensory information passes. Crude awareness of sensation. Hypothalamus Regulates body temperature, has thirst and food intake center, regulates autonomic nervous system.

Brain Stem Brain 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.

Cerebellum Cerebellum 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.

CEREBRUM Cerebrum is the largest portion human brain. It is divided into TWO halves, Right and Left cerebral hemispheres. The two hemispheres are connected by CORPUS CALLOSUM which consists of about 300 million axons. Cerebral cortex– It is the outer shell of Gray matter covering the inner white matter. Each cerebral hemisphere is divided into FOUR LOBES. Frontal lobe Parietal lobe Temporal lobe Occipital lobe

CEREBRAL HEMISPHERE

LOBES OF BRAIN Central 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.

LOBES OF BRAIN Parietal lobe It is located posterior to the central sulcus. It has sensory cortex at post central gyrus. Temporal Lobe Located laterally [on the sides of head]. It has auditory cortex.

LOBES OF BRAIN Occipital Lobe Located posteriorly [back of head]. It has visual cortex ( center).

FUNCTIONAL AREAS OF BRAIN Functional areas of Cerebral cortex

Functional areas of Cerebral cortex

References Human physiology by Lauralee Sherwood, 8th edition Text Book Of Physiology by Guyton & Hall, 11th edition

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