The nervous system

The nervous system Definition -- It is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body

nervous system

Structural Classification of the Nervous System -- In most animals the nervous system consists of two parts, central and peripheral. -- The central nervous system of vertebrates (such as humans) contains the brain and spinal cord. -- The peripheral nervous system consists of sensory neurons, clusters of neurons called ganglia, and nerves connecting them to each other and to the central nervous system.

Functions of the Nervous System 1. Sensory input – gathering information To monitor changes occurring inside and outside the body (changes = stimuli) 2. Integration to process and interpret sensory input and decide if action is needed. 3. Motor output A response to integrated stimuli The response activates muscles or glands

Nervous Tissue: Type of cells The nervous system contains two main categories or types of cells: neurons and glial cells. 1. Neurons -- Cells specialized to transmit messages (electrically excitable cell that transmits information by electrical and chemical signaling). -- A typical neuron possesses a cell body (often called the soma), dendrites, and an axon. Dendrites and axon are thin structures that arise from the cell body, often extending for hundreds of micrometers and branching multiple times, giving rise to a complex "dendritic tree". -- The cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates.

Neuron Anatomy Dendrites Cell body Axon Nucleus -- Dendrites conduct impulses toward the cell body, while axons conduct impulses away from the cell body. Dendrites Cell body Nucleus Axon

Functional Classification of Neurons (A) Sensory (afferent) neurons Carry impulses from the sensory receptors (B) Motor (efferent) neurons Carry impulses from the central nervous system (C) Interneurons (association or relay neurons) Found in neural pathways in the central nervous system as they connect sensory and motor neurons.

3 main types of nerve cells sensory neurone relay neurone motor neurone

Sensory neurons Carries impulses from receptors e.g pain receptors in skin to the CNS( brain or spinal cord)

Carries impulses from sensory nerves to motor nerves. Relay neuron Carries impulses from sensory nerves to motor nerves.

Motor neuron Carries impulses from CNS to effector e.g. muscle to bring about movement or gland to bring about secretion of hormone e.g ADH

2. Glial cells -- They are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system. -- A very important type of glial cell (oligodendrocytes that produce myelin sheath around nerve fibers in the central nervous system, and Schwann cells in the peripheral nervous system) generates layers of a fatty substance called myelin that wraps around axons and provides electrical insulation which allows them to transmit action potentials much more rapidly and efficiently .

Neuroglia vs. Neurons Neuroglia divide. Neurons do not. Most brain tumors are “gliomas.” Most brain tumors involve the neuroglia cells, not the neurons. Consider the role of cell division in cancer!