Nervous System: Fundamentals

Nervous System OverviewNervous system is made up of the brain, spinal cord, cranial nerves and spinal nerves.

Nervous system is responsible for the communication between cells, tissues, organs and organ system in an effort to control and integrate functions of and between cells, tissues, organs and organ systems.

What you think, feel, taste, desire, see, hear….everything is a reflection of the actions of this system.

Nervous System OverviewOne can break this system into three major functions, each dependent on the other. These functions are:

Sensory inputIntegration

Motor output

It is important you think of the physical parts of nervous system as the “hard wiring” of the body. When you push a key on your computers keyboard, the action (sensory input) is converted into an electrical signal. This signal is sent via wires into your computer where it is interpreted (integration) with the appropriate hardware to perform a function (motor output).

Neurons are the functional cellular unit of the Nervous System. They are the wires that carry signals through out the body.

Nervous System Organization We will study the nervous system from two broad perspectives -

cellular and tissues/organs There are two principle cell types: Neurons and Neuroglia Basic functional unit of the nervous system is the neuron. The majority of cells in the nervous system are Neuroglia or glia

cells. Nervous System is divided into two broad categories….

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

NOTE: Although Central and peripheral are used to indicate specific parts of the nervous system, these terms can be used to indicate the direction

5 types of Glia Cells

Astrocytes – Largest and most numerous. Attach to blood capillaries of the brain.

Microglia – stationary cells of CNS. Engulf and destroy microorganisms and cell debris

Ependymal – resemble epithelial cells. Line fluid filled cavities in brain and spinal cord

Oligodendrocytes – Few branches. Help hold nerve fibers together. Produce myelin sheath around nerve fibers in CNS

Schwann Cells – only in PNS. Produce myelin sheath in PNS.

Multipolar

BipolarUnipolar

Central Nervous System Overview

Consists of the brain and spinal cord. Cells only found within the brain and spinal cord are

considered part of the CNS. Cells which begin or end in the brain or spinal cord are not considered part of the CNS.

CNS includes neural tissue, blood vessels and other connective tissues

CNS functions as the integration and command center CNS interprets sensory input, evaluates the input and

dictates motor responses

Peripheral Nervous System (PNS) Overview Consists of nerve tissue found outside of the brain and spinal

cord (on the periphery). Cells that begin or end in the brain and spinal cord are

considered part of the PNS. Nerve cells that begin in the brain are called cranial nerves Nerve cells that begin in the spinal cord are called spinal

nerves Carries sensory information to the CNS and carries motor

information from the CNS. It is the link between the sensory input and parts that integrate

the signal as well as the link between the product of the integration and the motor output (the action).

Division of the Peripheral Nervous System The Peripheral Nervous System can be

divided into two broad divisions – the afferent division and the efferent division.

The Afferent Division

The afferent division is sensory input. The signal comes from the receptors and moves toward the CNS. These neurons can be called Sensory Afferent Neurons. If the signal originates from the skin, skeletal muscles, and joints, then the nerves which carry the signal are called somatic sensory nerve fibers. If the signal comes from the organs within the ventral body cavity then the nerves which carry the signal are called visceral sensory nerve fibers.

The Efferent Division

The efferent division is motor output so the signal moves from the CNS to an effector (muscle or gland). The efferent division has two main parts: Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS).

The Somatic Nervous System (SNS) conducts the signal from the CNS to Skeletal muscles. It consists of somatic motor nerves. This system is under conscious control, it is voluntary.

The Autonomic Nervous System (ANS) conducts the signal from the CNS to cardiac muscle, smooth muscle and glands. These are involuntary meaning they are not under conscious control. The ANS can be further divided into Sympathetic and Parasympathetic divisions. Sympathetic is the fight or flight response where as parasympathetic is the “rest, digest and repair”