Nervous System Overview

Introduction

• Nervous system controls all organs, physiological and psychological reactions.
• Works through electrical and chemical signals to/from nerve cells.
• Composed of several levels of organization: central and peripheral systems.

Functions of Nervous System

Sensory Input

• Sensory receptors detect stimuli (e.g., spider on skin).

Integration

• Processing and deciding responses (e.g., remove spider or stay calm).

Motor Output

• Responses activated by nervous system (e.g., moving hand to remove spider).

Central and Peripheral Nervous Systems

Central Nervous System (CNS)

• Comprised of brain and spinal cord.
• Main control center.

Peripheral Nervous System (PNS)

• Nerves that branch off from brain/spine to rest of the body.
• Communication in both directions.

Divisions of PNS

Sensory (Afferent) Division

• Picks up sensory stimuli and sends information to brain.

Motor (Efferent) Division

• Sends directions from brain to muscles and glands.

Somatic Nervous System (Voluntary)

• Controls skeletal muscle movement.

Autonomic Nervous System (Involuntary)

• Controls heart, lungs, stomach, etc.

Sympathetic Division

• Mobilizes body into action.
• "Fight or flight" response.

Parasympathetic Division

• Relaxes the body.
• "Rest and digest" response.

Nervous Tissue

• Densely packed with cells (less than 20% extracellular space).

Neurons (Nerve Cells)

• Respond to stimuli and transmit signals.
• Long-lived, irreplaceable, high metabolic rate.
• Structure: soma, dendrites (listeners), axon (talker).

Types of Neurons

• Multipolar Neurons: Three or more processes (common).
• Bipolar Neurons: Two processes (rare, found in sensory organs like retina).
• Unipolar Neurons: One process (sensory receptors).

Functional Classification

• Sensory (Afferent) Neurons: Transmit impulses to CNS.
• Motor (Efferent) Neurons: Transmit impulses from CNS to muscles/glands.
• Interneurons: Transmit impulses within CNS.

Glial Cells (Neuroglia)

• Support and protect neurons.
• Outnumber neurons 10 to 1.

Types of Glial Cells in CNS

• Astrocytes: Anchor neurons to blood supply, exchange materials.
• Microglial Cells: Immune defense in brain/spinal cord.
• Ependymal Cells: Create, secrete, circulate cerebrospinal fluid.
• Oligodendrocytes: Produce myelin sheath.

Types of Glial Cells in PNS

• Satellite Cells: Support neuron cell bodies.
• Schwann Cells: Produce myelin sheath.

Summary

• Nervous system is crucial for sensory input, integration, motor output.
• CNS and PNS are main components.
• Neurons and glial cells play specific roles in function and protection of the nervous system.
• Next lesson: How nerve cells use chemistry and electricity to communicate.

Credits

• Episode by Kathleen Yale, edited by Blake de Pastino.
• Consultant: Dr. Brandon Jackson.
• Directed by Nicholas Jenkins and Michael Aranda.
• Graphics: Thought Café.