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NERVOUS SYSTEM. By Dr. Ishtiaq Ali. INTRODUCTION:. DIVISIONS OF NERVOUS SYSTEM: Nervous system controls all the activities of the body. It is quicker than the other control system in the body namely, the endocrine system. Primarily the nervous system is divided into two parts.
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NERVOUS SYSTEM By Dr. Ishtiaq Ali
INTRODUCTION: • DIVISIONS OF NERVOUS SYSTEM: Nervous system controls all the activities of the body. It is quicker than the other control system in the body namely, the endocrine system. Primarily the nervous system is divided into two parts.
Central nervous system { CNS } • Peripheral nervous system { PNS }.
CENTRAL NERVOUS SYSTEM: The central nervous system includes brain and spinal cord. It is formed by neurons and the supporting cells called neuroglia. The structures of brain and spinal cord are arranged in two layers namely, the gray matter and white matter. The gray matter is formed by nerve cell bodies and the proximal parts nerve fibers arising from the nerve cell body. The white matter is formed by nerve fibers.
In brain the white matter is centrally placed and gray matter is in the outer part. In spinal cord white matter is in the outer part and gray matter is in the inner part. 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 the arachnoid mater and pia mater is known as subarachnoid space. This space is filled with a fluid actually suspended in the cerebrospinal fluid.
PARTS OF BRAIN: Brain consists of three major divisions: • Prosencephalon • Mesencephalon • Rhombencephalon.
1. Prosencephalon: It is otherwise known as fore brain. It is further divided into two parts: a. Telencephalon which includes cerebral hemispheres, basal ganglia, hippocampus and amygdaloid nucleus.
b. Diencephalon, consisting of thalamus, hypothalamus, metathalamus and subthalamus.
2. Mesencephalon • It is also known as midbrain.
3. Rhombencephalon: Rhombencephalon or hindbrain is subdivided into two portions: • Metencephalon formed by pons and cerebellum. • Myelencephalon or medulla oblongata. Midbrain, pons and medulla oblongata are together called the brainstem.
PERIPHERAL NERVOUS SYSTEM: The peripheral nervous system (PNS) is formed by the 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:
Somatic nervous system • Autonomic nervous system.
A. SOMATIC NERVOUS SYSTEM: The somatic nervous system is concerned with somatic function. It includes the nerves supplying the skeletal muscles. Somatic nervous system controls the movements of the body by acting on the skeletal muscles.
B. AUTONOMIC NERVOUS SYSTEM: The autonomic nervous system is concerned with regulation of visceral or vegetative functions. so, it is otherwise called vegetative or involuntary nervous system. The autonomic nervous system consists of two divisions, • Sympathetic division • Parasympathetic division.
NEURON: INRODUCTION: Neuron is defined as “ The structural and functional unit of the nervous system” it is otherwise called nerve cell. Neuron is like any other cell in the body having nucleus and all the organelles in the cytoplasm.
However, it is different from other cell by two ways: • Neuron has branches or processes called AXON and DENDRITES. • Neuron does not have centrosome; so it cannot undergo division.
CLASSIFICATION OF NEURON The neurons are classified by three different methods: • Depending upon the number of poles • Depending upon the function • Depending upon the length of the axon.
FUNCTION OF THE NERVOUS SYSTEM The nervous system is involved in some way in nearly every body function. Some major functions of the nervous system are:
Sensory input: Sensory receptors monitor numerous external and internal stimuli that may be interpreted as touch, temperature, taste, smell, sound, blood pressure, and body position. Action potentials from the sensory receptor travel along nerves to the spinal cord and brain, where they are interpreted.
2. Integration: The brain and spinal cord are the major organs for processing sensory input and initiating responses. The input may produce an immediate response, may be stored as memory, or may be ignored.
3. Homeostasis: The nervous system plays an important role in the maintenance of homeostasis. This function depends on the ability of the nervous system to detect, interpret, and respond to changes in internal and external conditions. In response, the nervous system can stimulate or inhibit the activities of other systems to help maintain a constant internal environment.
4.Mental activity : The brain is the center of mental activity, including consciousness, memory, and thinking.
5.Control of muscles and glands : Skeletal muscles normally contract only when stimulated by the nervous system. thus, through the control of skeletal muscle, the nervous system controls the major movements of the body. the nervous system also participates in controlling cardiac muscle, smooth muscle, and many gland
