THE NERVOUS SYSTEM

FUNCTIONS collection of sensory input integration motor output The function of the nervous system is to detect changes in the: External or Internal environments External or Internal environments So, it bring about appropriate responses in Muscles, Organs and Glands.

ORGANIZATION STRUCTURAL CNS PNS FUNCTIONAL Sensory division (Afferent) Motor division (Efferent) – autonomic – somatic

Prof. Saeed Makarem It is the basic structural (anatomical), functional and embryological unit of the nervous system. The human nervous system is estimated to contain about Neurons What is neurone?

Prof. Saeed Makarem The functions of the neuron is to receive and integrate incoming information from sensory receptors or from other neurons and to transmit information to other neurons or effector organs.The functions of the neuron is to receive and integrate incoming information from sensory receptors or from other neurons and to transmit information to other neurons or effector organs.

Prof. Saeed Makarem Information is passed between neurons at specialized regions called synapses In the synapses the membranes of adjacent cells are in close apposition (contiguity not continuity).

Prof. Saeed Makarem There is wide diversity in the shape and size of neurons in different parts of the nervous system.There is wide diversity in the shape and size of neurons in different parts of the nervous system. But all share certain common characteristics.But all share certain common characteristics. There is a single cell body from which a variable number of branching processes emerge.There is a single cell body from which a variable number of branching processes emerge.

Prof. Saeed Makarem Most of these processes are receptive in function. They are known as Dendrites.

Prof. Saeed Makarem The dendrites possess: A variable number of shot processes. They form the receptive element of the neurone.

Prof. Saeed Makarem One of the processes leaving the cell body is called the axon which carries information away from the cell body.One of the processes leaving the cell body is called the axon which carries information away from the cell body. Axons are highly variable in length and may divide into several branches or collaterals through which information can be distributed to a number of different destinations simultaneously.Axons are highly variable in length and may divide into several branches or collaterals through which information can be distributed to a number of different destinations simultaneously. At the end of the axon, specializations called terminal buttons occur.At the end of the axon, specializations called terminal buttons occur. Here information is transferred to the dendrites of other neurones.Here information is transferred to the dendrites of other neurones.

Prof. Saeed Makarem Transmission of information between neurons almost always occurs by chemical rather than electrical means.Transmission of information between neurons almost always occurs by chemical rather than electrical means. Action potential causes release of specific chemical that are stored in synaptic vesicles in the presynaptic ending.Action potential causes release of specific chemical that are stored in synaptic vesicles in the presynaptic ending. These chemicals are known as neurotransmitters and diffuse across the narrow gap between pre- and postsynaptic membranes to bind to receptors on the postsynaptic cell.These chemicals are known as neurotransmitters and diffuse across the narrow gap between pre- and postsynaptic membranes to bind to receptors on the postsynaptic cell.

Neuroglia, or glia cells constitute the other major cellular component of the nervous system. It is a specialized connective tissue for the nervous system. Unlike neurones, neuroglia do not have a direct role in information processing but they are essential for the normal functioning of nerve cells. Neuroglia, or glia cells constitute the other major cellular component of the nervous system. It is a specialized connective tissue for the nervous system. Unlike neurones, neuroglia do not have a direct role in information processing but they are essential for the normal functioning of nerve cells. Prof. Saeed Makarem Neuroglia

Prof. Saeed Makarem Three main types of neuroglial cell are recognized: 1. 1.Oligodendrocytes (oligodendroglia) they form the myelin sheath that surrounds many neuronal axons, which increase the rate of conduction.

Prof. Saeed Makarem 2- Microglia have a phagocytic role in response to nervous system damage.

Prof. Saeed Makarem 3. 3.Astrocytes are thought to form a selectively permeable barrier between the circulatory system and the neurons of the brain and spinal cord. 'blood-brain barrier'This is known as the 'blood-brain barrier' and has a protective function.

Central & peripheral nervous systems

Prof. Saeed Makarem The nervous system is divided into: 1- Central nervous system (CNS).1- Central nervous system (CNS). 2- Peripheral nervous system (PNS).2- Peripheral nervous system (PNS).

Prof. Saeed Makarem The central nervous system consists of the brain and the spinal cord, lying within the protection of the cranium and vertebral column, respectively.The central nervous system consists of the brain and the spinal cord, lying within the protection of the cranium and vertebral column, respectively. This is the most complex part of the nervous system.This is the most complex part of the nervous system. It contains the majority of nerve cell bodies and synaptic connections.It contains the majority of nerve cell bodies and synaptic connections.

Prof. Saeed Makarem The peripheral nervous system constitutes the link between the CNS & structures in the periphery of the body.The peripheral nervous system constitutes the link between the CNS & structures in the periphery of the body. It receives sensory information from the body.It receives sensory information from the body. It sends controlling impulses in response to these information.It sends controlling impulses in response to these information. The peripheral nervous system consists:The peripheral nervous system consists: 1- Cranial nerves1- Cranial nerves 2- Spinal nerves.2- Spinal nerves.

Prof. Saeed Makarem Spinal nerves supplying the upper or lower limbs form the brachial or lumbar plexus.Spinal nerves supplying the upper or lower limbs form the brachial or lumbar plexus. Nerve cell bodies that are aggregated within the CNS are called GANGLIA Nerve cell bodies that are aggregated within the CNS are called GANGLIA

Prof. Saeed Makarem Neurones that detect changes and control the activity of, the viscera are collectively referred to as the autonomic nervous system.Neurones that detect changes and control the activity of, the viscera are collectively referred to as the autonomic nervous system. Its components are present in both the central and peripheral nervous systems.Its components are present in both the central and peripheral nervous systems. Autonomic Nervous System

SYMPATHETIC & PARASYMPATHETIC SYSTEMS The autonomic nervous system is divided into two anatomically and functionally distinct parts: Sympathetic: Or Thoracolumbar outflow Parasympathetic: Or Craniosacral outflow.

Prof. Saeed Makarem Sympathetic and parasympathetic divisions are generally have antagonistic effects on the structures that they innervate.Sympathetic and parasympathetic divisions are generally have antagonistic effects on the structures that they innervate.

Prof. Saeed Makarem The autonomic nervous system innervates:The autonomic nervous system innervates: Smooth muscle, Smooth muscle, Cardiac muscle,Cardiac muscle, Secretory glands.Secretory glands. It is an important part of the homeostatic mechanisms that control the internal environment of the body.It is an important part of the homeostatic mechanisms that control the internal environment of the body.

Afferent, Efferent & Interneuron Nerve cells that carry information from peripheral receptors to the CNS are referred to as afferent neuronesNerve cells that carry information from peripheral receptors to the CNS are referred to as afferent neurones neurones carry impulses away from the CNS Efferent neurones carry impulses away from the CNS If they innervate skeletal muscle to cause movement they are also referred to as motor neurons.If they innervate skeletal muscle to cause movement they are also referred to as motor neurons. The vast majority of neurones, however, lies entirely within the CNS and are usually called interneuron The vast majority of neurones, however, lies entirely within the CNS and are usually called interneuron

PARTS OF THE BRAIN Cerebral hemispheres Diencephalon Cerebellum Brain stem

CEREBRAL HEMISPHERES The largest part of the brain They have elevations, called gyri Gyri are separated by depressions called sulci Each hemisphere is divided into 4 lobes Lobes are separated by deeper grooves called fissures or sulci. FRONTAL PARIETAL TEMPORAL OCCIPITAL

TISSUE OF THE CEREBRAL HEMISPHERES The outer layer is the gray matter or cortex Deeper is located the white matter, composed of bundles of nerve fibers, carrying impulses to and from the cortex Basal nuclei are made from gray matter and are located deep within the white matter They help the motor cortex in the regulation of voluntary motor activities Basal nuclei

DIENCEPHALON The diencephalon is located between the 2 hemispheres and is linked to them and to the brainstem. The major structures of the diencephalon are the thalamus, hypothalamus and Epithalamus.

BRAIN STEM The brainstem has three parts: midbrain, Pons and medulla oblongata.

CEREBELLUM Cerebellum has 2 cerebellar hemispheres and a convoluted surface. It has an outer cortex of gray matter and an inner region of white matter. It provides precise coordination for body movements and helps maintain equilibrium. Cerebellum has 2 cerebellar hemispheres and a convoluted surface. It has an outer cortex of gray matter and an inner region of white matter. It provides precise coordination for body movements and helps maintain equilibrium.

BRAIN VENTRICLES Brain is bathed by the cerebrospinal fluid (CSF) Inside the brain, there are spaces (ventricles) filled with CSF There are 4 ventricles  2 lateral ventricles: are in the hemispheres  3 rd ventricle: in the diencephalon  4 th ventricle: between the Pons & the cerebellum  Cerebral aqueduct: connects the 3 rd to the 4 th ventricle

CEREBROSPINAL FLUID CSF is constantly produced by the choroid plexuses inside each ventricle. Inside the brain, CSF flows from the lateral ventricles to the 3 rd and 4 th ventricles. From the 4 th ventricle, part of the CSF flows down in the central canal of the spinal cord. Most of the CSF drains from the 4 th ventricle in the subarachnoid space around the brain and returns to the dural sinuses through the arachnoids villi.