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 cellsThe 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

Cell body

Nucleus

Dendrites

Axon

--Dendrites conduct impulses toward the cell body, while axons conduct impulses away from the cell body.

Functional Classification of Neurons

(A )Sensory (afferent) neuronsCarry 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)

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!