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THE NERVOUS SYSTEM By Prof. Khaled Na3im THE NERVOUS SYSTEM REGULATES ALL THE BODY FUNCTION . The (N.S) is formed of 3 system s: The central nervous system , ( CNS ). The peripheral nervous system , (PNS ). The autonomic nervous system , (ANS ). The ( C . N . S ) : includes the brain + spinal cord .The brain = . Cerebrum . Cerebellum . Brain stem ( midbrain, pons and medulla oblongata ) The ( p . N . S ) : The PNS is made up of the cranial nerves and the spinal nerves . .The cranial nerves are 12 pairs. . The spinal nerves are 31 pairs : . 8 Cervical .12 Thoracic . 5 Lumbar . 5 Sacral . One Coccygeal THE NERVE CELL ( THE NEURON ) The neuron ( nerve cell ) is the functional and anatomical unit of the nervous system Neurons Humans have about 100 billion neurons in their brain alone! While variable in size and shape The neuron is formed of three parts. 1.Dendrites receive information from another cell and transmit the message to the cell body. 2.The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells except the centrioles. 3.The axon conducts messages away from the cell body out . The neuron The neuron Mylinated nerve = Mylinated axon The neuron Synapses The synapse is a junctional space between a nerve cell and another cell or effector is called a synapse. Messages travel within the neuron as an electrical action potential. The space between two cells is known as the synaptic cleft. To cross the synaptic cleft requires the actions of neurotransmitters. Neurotransmitters are stored in small synaptic vessicles clustered at the tip of the axon . Types of Neurons Three types of neurons occur. Sensory neurons typically have a long dendrite and short axon, and carry messages from sensory receptors to the central nervous system. Motor neurons have a long axon and short dendrites and transmit messages from the central nervous system to the muscles (or to glands). Interneurons are found only in the central nervous system where they connect neuron to neuron. The brain the brain made up : Is 3 anatomical parts : 1) cerebrum . 2) cerebellum . 3) brain stem . The cerebrum The cerebrum is formed of 2 cerebral hemispheres , right and left . The 2 cerebral hemispheres form the largest part of the brain, occupying the anterior and middle and posterior cranial fossae in the skull and extending backwards over the tentorium cerebelli. They are made up of the cerebral cortex, the basal ganglia, tracts of synaptic connections, and the ventricles containing CSF . THE CEREBRUM IS CONSISTED OF: 2 cerebral hemispheres : right and left . Lobes of the hemispere Each hemisphere is divided into 4 lobes : 1) frontal lobe . 2) Parietal lobe . 3) Occipital lobe . 4) Temporal lobe . Lies anterior contains most of the motor areas ( it controls movements , recent memory and personality ) THE FRONTAL LOBE : Lies superior contains most of the sensory areas . THE PARIETAL LOBE : Lies posterior and contains the centers of visions . THE OCCIPITAL LOBE : Lies inferior and contains the centers of hearing . THE TEMPORAL LOBE : The cerebellum The Cerebellum It is formed of 2 cerebllar hemispheres . Controls : 1) Equilibrium 2) Coordination . Thr cerebellum The cerebellum is a large structure at the back of the brain, immediately behind the brainstem and below the occipital cortex. The cerebellum receives direct inputs from the sensory fibers in the spinal cord as well as indirect inputs from the motor cortex, possibly as a copy of the commands being sent downward to the spinal cord. Histology of the brain The Brain stem Is formed of 3 parts : 1) Midbrain . 2) Pons . 3) Medulle . The midbrain The midbrain (mesencephalon) occupies only a small region in humans (it is relatively much larger in "lower" vertebrates). We shall look at only three features The reticular Formation the reticular formation: collects input from higher brain centers and passes it on to motor neurons . The Substantia Nigra the substantia nigra: helps "smooth" out body movements; damage to the substantia nigra causes Parkinson's disease VTA the ventral tegmental area (VTA): packed with dopamine-releasing neurons The pons The pons seems to serve as a relay station carrying signals from various parts of the cerebral cortex to the cerebellum . The medulla The medulla looks like a swollen tip to the spinal cord. Nerve impulses arising here . Medulla rhythmically stimulate the intercostal muscles and diaphragm — making breathing possible The Blood Supply of the Brain Food and oxygen are carried to the brain by many blood vessels. These vessels are found on the surface of the brain and deep within the brain. The blood vessels (and nerves) enter the brain through holes in the skull called foramina . Blood Supply Of The Brain Although the brain is only about 2% of the total body weight in humans, it receives 15-20% of the body's blood supply. Because brain cells will die if the supply of blood which carries oxygen is stopped, the brain has top priority for the blood. Even if other organs need blood, the body attempts to supply the brain with a constant flow of blood