Chapter 7 – Part 1

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

Functions of the Nervous System
3.
Motor output

A response to integrated stimuli

The response activates muscles or glands

Structural Classification of the
Nervous System
1.
Central nervous system (CNS)

Consist of the brain and spinal cord

Act as the integrating and command center

Interpret incoming sensory information and issue instructions

Structural Classification of the
Nervous System
2.
Peripheral Nervous
System (PNS)

Nerves outside the brain and spinal cord

These nerves serve as communication lines.

They link all parts of the body by carrying impulses from the sensory receptors to the
CNS and from the CNS to the appropriate glands or muscles.

Functional Classification of the
Peripheral Nervous System

Sensory (Afferent) Division

Nerve fibers that carry information to the central nervous system

Keeps the CNS constantly informed of events going on both inside and outside the body.

Functional Classification of the
Peripheral Nervous System

Motor (Efferent) Division

Nerve fibers that carry impulses away from the central nervous system

These impulses activate muscles and glands; that is, they effect (bring about) a motor response.

Functional Classification of the
Peripheral Nervous System

Motor (Efferent) Division

Two subdivisions
1.
Somatic Nervous System = Voluntary

Allows us to consciously control our skeletal muscles.
2.
Autonomic Nervous System = Involuntary

Regulates the activity of the smooth and cardiac muscles and glands.

The ANC has two parts: The sympathetic and parasympathetic (Each typically brings about opposite effects)

Organization of the Nervous System

Nervous Tissue

Made up of two principal types of cells:
1.
Supporting cells

Functions: Support, insulate, and protect

Not able to transmit nerve impulses

Never lose their ability to divide, whereas most neurons do.

Most brain tumors are formed by neuroglia cells.
2.
Neurons
• Are able to transmit nerve impulses

Supporting Cells (Also Called
Neuroglia )

Supporting cells of the CNS:
1.
Astrocytes
2.
Microglia
3.
Ependymal
4.
Oligodendrocytes

Supporting cells of the PNS:
1.
Schwann cells
2.
Satellite cells

Nervous Tissue: Support Cells of the CNS (Neuroglia)

Astrocytes

Abundant, starshaped cells

Brace neurons

Form a living barrier between capillaries and neurons

Help protect the neurons from harmful substances that might be in the blood.

Control the chemical environment of the brain

Pick up excess ions and recapture released neurotransmitters

Nervous Tissue: Support Cells of the CNS

Microglia

Spider-like phagocytes

Dispose of debris (such as dead brain cells and bacteria)

Ependymal cells

Line cavities of the brain and spinal cord

Circulate cerebrospinal fluid

Nervous Tissue: Support Cells of the CNS

Oligodendrocytes

Wrap their flat extensions tightly around the nerve fibers.

Produce myelin sheath (fatty insulating coverings) around nerve fibers in the
CNS

Nervous Tissue: Support Cells of the PNS

Satellite cells

Protect and cushion neuron cell bodies

Schwann cells

Form myelin sheath around nerve fibers in the PNS

Nervous Tissue: Neurons

Neurons = Nerve Cells

Cells specialized to transmit messages

Major regions of neurons
1.
Cell body – Nucleus and metabolic center of the cell
2.
Processes – Fibers that extend from the cell body

Neuron Anatomy

Cell Body

Nissl substance –
Specialized rough
ER

Neurofibrils –
Intermediate cytoskeleton
(filaments) that maintains cell shape

Neuron Anatomy

Cell Body

Nucleus

Large nucleolus

Contains the usual organelles except for centrioles

Neuron Anatomy

Extensions -
Processes outside the cell body

Dendrites – Conduct impulses toward the cell body

Axons – Conduct impulses away from the cell body

Processes or Extensions

Processes vary in length -
From microscopic to 3-4 feet

The longest one in humans reach from the lumbar region of the spine to the big toe.

Neurons may have hundreds of the branching dendrites, depending on the neuron type.

Each neuron only has one axon.