Nervous Tissues� By Rasha Mohammed

• The nervous system is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body. It is essentially the body's electrical wiring.
•  nervous system is the major controlling, regulatory, and communicating system in the body. It is the center of all mental activity including thought, learning, and memory
• Like other systems in the body, the nervous system is composed of organs, principally the brain, spinal cord, nerves, and ganglia. Together these carry out the complex activities of the nervous system. 
• Structurally, the nervous system has two components:
• * the central nervous system(CNS)
• * the peripheral nervous system(PNS).

The central nervous system (CNS)

CNS is the part of the nervous system consisting of the brain and spinal cord. The central nervous system is so named because it integrates information it receives from, and coordinates and influences the activity of all parts of the bodies

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The peripheral nervous system (PNS)

• (PNS) is the part of the nervous system that consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the (CNS) to the limbs and organs, essentially serving as a communication relay going back and forth between the brain and the extremities

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Functions of the Nervous System

• 1. Gathers information from both inside and outside the body - Sensory Function
• 2. Transmits information to the processing areas of the brain and spine
• 3. Processes the information in the brain and spine – Integration Function
• 4. Sends information to the muscles, glands, and organs so they can respond appropriately – Motor Function

• �Basic Cells of the Nervous System�Nerves are cylindrical bundles of fibers that start at the brain and central cord and branch out to every other part of the body.� The nervous system comprises of two group of cells:-� 1)glialcells2)neurons. � Neurons are responsible for sensing change and communicating with other neurons. Glial cells work to support, nourish, insulate neurons and remove waste products.� Neurons send signals to other cells through thin fibers called axons, which cause chemicals known as neurotransmitters to be released at junctions called synapses

• 1) Neuron •
• The neuron is the basic unit in the nervous system. It is a specialized conductor cell that receives and transmits electrochemical nerve impulses. A typical neuron has a cell body and long arms that conduct impulses from one body part to another body part.

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Parts of a Neuron

• Cell Body with nucleus & most of cytoplasm •
• Cell body or Soma – contains the nucleus, the neuron’s intracellular organelles (such as the mitochondria and Golgi apparatus) and it is the location for cellular metabolism. It is also contains the Nissl Substance. These are granules containing rough endoplasmic reticulum and free ribosomes, making it the site of protein synthesis.

• •
• Dendrite
• The cell body has several highly branched, thick extensions that appear like cables and are called dendrites. The exception is a sensory neuron that has a single, long dendrite instead of many dendrites, The dendrite's function is to carry a nerve impulse into the cell body.
• Axon – fiber
• An axon is a long , thin process that carries impulses away from the cell body to another neuron or tissue. There is usually only one axon per neuron
• It arises from the soma from an area called the axon hillock, where action potentials are initiated. The action potentials are conducted through the axon to the axon terminal.

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• .
• Schwann Cells-
• The neurilemma is the layer of Schwann cells with a nucleus. Its function is to allow damaged nerves to regenerate. Nerves in the brain and spinal cord do not have a neurilemma and, therefore cannot recover when damaged.
• cells which produce myelin or fat layer in the Peripheral Nervous System •
• Myelin sheath
• The neuron is covered with the Myelin Sheath or Schwann Cells. These are white segmented covering around axons and dendrites of many peripheral neurons. The covering is continuous along the axons or dendrites except at the point of termination and at the nodes of Ranvier.
• Node of Ranvier
• gaps or nodes in the myelin sheath •
• Impulses travel from dendrite to cell body to axon

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• Glia, also called glial cells or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses
• They maintain homeostasis, form myelin, and provide support and protection for neurons.
• . They have four main functions:
• (1) to surround neurons and hold them in place
• (2) to supply nutrients and oxygen to neurons
• (3) to insulate one neuron from another
• (4) to destroy pathogens and remove dead
• neurons.

2- Neuroglial

* SPINAL CORD :-- In cross section spinal cord is oval in shape , from dorsal side is divided into two halves, left and right half by dorsal median septum From the anterior ( ventral ) side there is fissure called the median fissure �The spinal cord surround by the connective tissue layers of the MENINGES :-� 1- the thick and fibrous outer DURA MATER.� 2- the thinner and middle ARACHNOID� 3- the delicate inner PIA MATER , which they closely� adheres to the surface of the spinal cord .�The PIA MATER occur directly around the� white mater and the gray mater.

Spinal cord

• The spinal cord in cross-section has a central region of darker gray matter which look like a butterfly or H- shape and the rest is lighter white matter. The gray matter is made up of neuroglia cells and neuron cell bodies. The white matter is made up of neuron axons, mostly but not all myelinated

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the CNS is devoid of neurons and consist primarily of myelinated axons .the myeline sheath around the axons imparts a white color to this region, while the lack of myelin imparts a gray and the color to the gray mater of the CNS