The Nervous System PDF

Dr. Abdussalam lahresh The Nervous System  DIVISIONS OF NERVOUS SYSTEM Nervous system controls all the activities of the body. Primarily, nervous system is divided into two parts: 1. Central nervous system 2. Peripheral nervous system. CENTRAL NERVOUS SYSTEM Central nervous system (CNS) in...

Dr. Abdussalam lahresh The Nervous System  DIVISIONS OF NERVOUS SYSTEM Nervous system controls all the activities of the body. Primarily, nervous system is divided into two parts: 1. Central nervous system 2. Peripheral nervous system. CENTRAL NERVOUS SYSTEM Central nervous system (CNS) includes brain and spinal cord. It is formed by neurons and supporting cells called neuroglia. Structures of brain and spinal cord are arranged in two layers, namely gray matter and white matter. abdussalam lahresh  DIVISIONS OF NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM Gray matter is formed by nerve cell bodies and the proximal parts of nerve fibers, arising from nerve cell body. White matter is formed by remaining parts of nerve fibers. In brain, white matter is placed in the inner part and gray matter is placed in the outer part. In spinal cord, white matter is in the outer part and gray matter is in the inner part abdussalam lahresh  DIVISIONS OF NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM Brain is situated in the skull. It is continued as spinal cord in the vertebral canal through the foramen magnum of the skull bone. Brain and spinal cord are surrounded by three layers of meninges called the outer dura mater, middle arachnoid mater and inner pia mater. The space between arachnoid mater and pia mater is known as subarachnoid space. This space is filled with a fluid called cerebrospinal fluid. Brain and spinal cord are actually suspended in the cerebrospinal fluid. abdussalam lahresh DIVISIONS OF NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM abdussalam lahresh  DIVISIONS OF NERVOUS SYSTEM Parts of Brain Brain consists of three major divisions: 1. Prosencephalon 2. Mesencephalon 3. Rhombencephalon Prosencephalon is otherwise known as forebrain. It is further divided into two parts: i. Telencephalon: which includes cerebral hemispheres, basal ganglia, hippocampus and amygdaloid nucleus ii. Diencephalon: consisting of thalamus, hypo thalamus, metathalamus and subthalamus. abdussalam lahresh  DIVISIONS OF NERVOUS SYSTEM Parts of Brain Mesencephalon is also known as midbrain. Rhombencephalon or hindbrain is subdivided into two portions: i. Metencephalon, formed by pons and cerebellum ii. Myelencephalon or medulla oblongata brainstem abdussalam lahresh DIVISIONS OF NERVOUS SYSTEM Parts of Brain abdussalam lahresh  DIVISIONS OF NERVOUS SYSTEM „PERIPHERAL NERVOUS SYSTEM Peripheral nervous system (PNS) is formed by neurons and their processes present in all regions of the body. It consists of cranial nerves, arising from brain and spinal nerves, arising from the spinal cord. It is again divided into two subdivisions: 1. Somatic nervous system. 2. Autonomic nervous system. 3. abdussalam lahresh  DIVISIONS OF NERVOUS SYSTEM „PERIPHERAL NERVOUS SYSTEM Somatic nervous system is concerned with somatic functions. It includes the nerves supplying the skeletal muscles. Somatic nervous system is responsible for muscular activities and movements of the body. Autonomic nervous system is concerned with regulation of visceral or vegetative functions. So, it is otherwise called vegetative or involuntary nervous system. Autonomic nervous system consists of two divisions, sympathetic division and parasympathetic division. abdussalam lahresh DIVISIONS OF NERVOUS SYSTEM abdussalam lahresh  NERVOUS SYSTEM Neuron Neuron or nerve cell is defined as the structural and functional unit of nervous system. Neuron is similar to any other cell in the body, having nucleus and all the organelles in cytoplasm. However, it is different from other cells by two ways: 1. Neuron has branches or processes called axon and dendrites 2. Neuron does not have centrosome. So, it cannot undergo division. abdussalam lahresh  NERVOUS SYSTEM Neuron Neurons are classified by three different methods. A. Depending upon the number of poles B. Depending upon the function C. Depending upon the length of axon. Based on the number of poles from which the nerve Fibers arise, neurons are divided into three types: 1. Unipolar neurons 2. Bipolar neurons 3. Multipolar neurons abdussalam lahresh NERVOUS SYSTEM Neuron Depending upon the number of poles abdussalam lahresh  NERVOUS SYSTEM Neuron On the basis of function, nerve cells are classified into two types: 1. Motor or efferent neurons 2. Sensory or afferent neurons. Depending upon the length of axon, neurons are divided into two types: 1. Golgi type I neurons 2. Golgi type II neurons. abdussalam lahresh  NERVOUS SYSTEM STRUCTURE OF NEURON Neuron is made up of three parts: 1. Nerve cell body 2. Dendrite 3. Axon. Dendrite and axon form the processes of neuron. Dendrites are short processes and the axons are long processes. Dendrites and axons are usually called nerve fibers. abdussalam lahresh  NERVOUS SYSTEM STRUCTURE OF NEURON abdussalam lahresh  NERVOUS SYSTEM NERVE CELL BODY Nerve cell body is also known as soma or perikaryon. It is irregular in shape. Like any other cell, it is constituted by a mass of cytoplasm called neuroplasm, which is covered by a cell membrane. The cytoplasm contains a large nucleus, Nissl bodies, neurofibrils, mitochondria and Golgi apparatus. Nissl bodies and neurofibrils are found only in nerve cell and not in other cells. Nissl bodies or Nissl granules are small basophilic granules found in cytoplasm of neurons and are named after the discoverer. These bodies are present in soma and dendrite but not in axon and axon hillock abdussalam lahresh  NERVOUS SYSTEM Neuron Dendrite is the branched process of neuron and it is branched repeatedly. Dendrite may be present or absent. If present, it may be one or many in number. Dendrite has Nissl granules and neurofibrils. Dendrite transmits impulses towards the nerve cell body. Usually, the dendrite is shorter than axon. Axon is the longer process of nerve cell. Each neuron has only one axon. Axon arises from axon hillock of the nerve cell body and it is devoid of Nissl granules. Axon extends for a long distance away from the nerve cell body. Length of longest axon is about 1 meter. Axon transmits impulses away from the nerve cell body. abdussalam lahresh  NERVOUS SYSTEM Neuron Dendrite is the branched process of neuron and it is branched repeatedly. Dendrite may be present or absent. If present, it may be one or many in number. Dendrite has Nissl granules and neurofibrils. Dendrite transmits impulses towards the nerve cell body. Usually, the dendrite is shorter than axon. Axon is the longer process of nerve cell. Each neuron has only one axon. Axon arises from axon hillock of the nerve cell body and it is devoid of Nissl granules. Axon extends for a long distance away from the nerve cell body. Length of longest axon is about 1 meter. Axon transmits impulses away from the nerve cell body. abdussalam lahresh  NERVOUS SYSTEM Neuron Each nerve is formed by many bundles or groups of nerve fibers. Each bundle of nerve fibers is called a fasciculus. The whole nerve is covered by tubular sheath, which is formed by a areolar membrane. This sheath is called epineurium. Each fasciculus is covered by perineurium and each nerve fiber (axon) is covered by endoneurium abdussalam lahresh  NERVOUS SYSTEM Neuron Axon has a long central core of cytoplasm called axoplasm. Axoplasm is covered by the tubular sheathlike membrane called axolemma. Axolemma is the continuation of the cell membrane of nerve cell body. Axoplasm along with axolemma is called the axis cylinder of the nerve fiber. Axis cylinder of the nerve fiber is covered by a membrane called neurilemma abdussalam lahresh  NERVOUS SYSTEM Neuron Nerve fiber which is insulated by myelin sheath is called Myelinated nerve fibers. Myelin sheath is a thick lipoprotein sheath that insulates the myelinated nerve fiber. Myelin sheath is not a continuous sheath. It is absent at regular intervals. The area where myelin sheath is absent is called node of Ranvier. abdussalam lahresh  NERVOUS SYSTEM Neuron Functions of Myelin Sheath: 1. Myelin sheath is responsible for faster conduction of impulse through the nerve fibers. 2. Myelin sheath has a high insulating capacity. Because of this quality, myelin sheath restricts the nerve impulse within single nerve fiber and prevents the stimulation of neighboring nerve fibers. Neurilemma is a thin membrane, which surrounds the axis cylinder. It is also called neurilemmal sheath or sheath of Schwann. It contains Schwann cells, which have flattened and elongated nuclei abdussalam lahresh  NERVOUS SYSTEM Classification of Nerve Fibers abdussalam lahresh  NERVOUS SYSTEM Classification of Nerve Fibers Based on structure, nerve fibers are classified into two types: i. Myelinated Nerve Fibers Myelinated nerve fibers are the nerve fibers that are covered by myelin sheath. ii. Non-myelinated Nerve Fibers Nonmyelinated nerve fibers are the nerve fibers which are not covered by myelin sheath. Nerve fibers are classified into two types, on the basis of distribution: i. Somatic Nerve Fibers Somatic nerve fibers supply the skeletal muscles of the body. ii. Visceral or Autonomic Nerve Fibers Autonomic nerve fibers supply the various internal organs of the body. abdussalam lahresh  NERVOUS SYSTEM Classification of Nerve Fibers On the basis of origin, nerve fibers are divided into two types: i. Cranial Nerve Fibers Nerve fibers arising from brain are called cranial nerve fibers. ii. Spinal Nerve Fibers Nerve fibers arising from spinal cord are called spinal nerve fibers. Functionally, nerve fibers are classified into two types: i. Sensory Nerve Fibers Sensory nerve fibers carry sensory impulses from different parts of the body to the central nervous system. ii. Motor Nerve Fibers Motor nerve fibers carry motor impulses from central nervous system to different parts of the body. abdussalam lahresh  NERVOUS SYSTEM Classification of Nerve Fibers Depending upon the neurotransmitter substance secreted, nerve fibers are divided into two types: i. Adrenergic Nerve Fibers Adrenergic nerve fibers secrete noradrenaline. ii. Cholinergic Nerve Fibers Cholinergic nerve fibers secrete acetylcholine. abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers EXCITABILITY Excitability is defined as the physiochemical change that occurs in a tissue when stimulus is applied. Stimulus is defined as an external agent, which produces excitability in the tissues. Chronaxie is an important parameter to determine the condition of nerve fiber. Clinically, the damage of nerve fiber is determined by measuring the chronaxie. It is measured by chronaxie meter. abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers When a nerve fiber is stimulated, based on the strength of stimulus, two types of response develop: 1. Action potential or nerve impulse 2. Electrotonic potential or local potential abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers ACTION POTENTIAL OR NERVE IMPULSE Action potential in a nerve fiber is similar to that in a muscle, except for some minor differences abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers ELECTROTONIC POTENTIAL OR LOCAL POTENTIAL Electrotonic potential or local potential is a non- propagated local response that develops in the nerve fiber when a subliminal stimulus is applied. abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers CONDUCTIVITY Conductivity is the ability of nerve fibers to transmit the impulse from the area of stimulation to the other areas. Action potential is transmitted through the nerve fiber as nerve impulse. Normally in the body, the action potential is transmitted through the nerve fiber in only one direction. Depolarization occurs first at the site of stimulation in the nerve fiber. It causes depolarization of the neighboring areas. Like this, depolarization travels throughout the nerve fiber. Depolarization is followed by repolarization. abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers CONDUCTIVITY Saltatory conduction is the form of conduction of nerve impulse in which, the impulse jumps from one node to another. Conduction of impulse through a myelinated nerve fiber is about 50 times faster than through a nonmyelinated fiber. It is because the action potential jumps from one node to another node of Ranvier instead of travelling through the entire nerve fiber abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers REFRACTORY PERIOD Refractory period is the period at which the nerve does not give any response to a stimulus. 1.Absolute Refractory Period Absolute refractory period is the period during which the nerve does not show any response at all, whatever may be the strength of stimulus. 2. Relative Refractory Period It is the period, during which the nerve fiber shows response, if the strength of stimulus is increased to maximum. abdussalam lahresh  NERVOUS SYSTEM Properties of Nerve Fibers SUMMATION When one subliminal stimulus is applied, it does not produce any response in the nerve fiber because, the subliminal stimulus is very weak. However, if two or more subliminal stimuli are applied within a short interval of about 0.5 millisecond, the response is produced. ADAPTATION While stimulating a nerve fiber continuously, the excitability of the nerve fiber is greater in the beginning. Later the response decreases slowly and finally the nerve fiber does not show any response at all. abdussalam lahresh Thank you