The Nervous System, Part 1: Crash Course Anatomy & Physiology

Introduction

• Description of a typical morning routine, including waking, dressing, eating, and letting the dog out.

• Actions are examples of how the nervous system operates through electrical and chemical signals.

• Importance of the nervous system to all organisms, illustrating that it controls organs and physiological responses.

Overview of the Nervous System

• Announcement of an exploration of the nervous system in upcoming episodes.

• The nervous system is essential for thoughts, actions, and emotions, classified into three main functions:

  • Sensory input

  • Integration

  • Motor output

Example of Sensory Input and Response

• Spider Example:

  • Sensory receptors on the skin detect the spider (sensory input).

  • Integration decides the reaction: remain calm or react (integration).

  • Reaction is the hand removing the spider (motor output).

Organization of the Nervous System

• Divided into two main parts:

  • Central Nervous System (CNS): Brain and spinal cord; main control center.

  • Peripheral Nervous System (PNS): Nerves branching from the CNS to the body.

Functions of the Peripheral Nervous System

• Afferent Division: Conducts sensory information to the brain.

• Efferent Division: Sends commands from the brain to muscles and glands.

  • Somatic Nervous System: Controls voluntary movements.

  • Autonomic Nervous System: Manages involuntary actions, such as heartbeat and digestion.

    • Sympathetic Division: Activates fight or flight response.

    • Parasympathetic Division: Calms the body after activation.

Nervous Tissue Composition

• Nervous tissue is primarily composed of cells with minimal extracellular space (less than 20%).

• Neurons: Main signaling cells.

• Neuroglia (Glial Cells): Support and protect neurons; approximately half the brain's mass.

Types of Glial Cells in the CNS

• Astrocytes: Anchor neurons to blood supply and regulate exchange of materials.

• Microglial Cells: Immune defense against pathogens in the CNS.

• Ependymal Cells: Line brain cavities and produce cerebrospinal fluid.

• Oligodendrocytes: Insulate neurons with myelin sheath.

Types of Glial Cells in the PNS

• Satellite Cells: Surround and support neuron cell bodies.

• Schwann Cells: Insulate axons in the peripheral nervous system.

Neuronal Characteristics

• Neurons are long-lived, amitotic, and require high metabolic support (supply of glucose and oxygen).

• Basic structure of neurons includes:

  • Soma (Cell Body): Contains organelles and supports cell life.

  • Dendrites: Specialized to receive signals from other cells.

  • Axon: Transmits impulses away from the cell body.

Types of Neurons

• Neurons classified by process structure extending from cell body:

  • Multipolar Neurons: Most common; multiple processes (multiple dendrites and one axon).

  • Bipolar Neurons: Two processes; rare, found in special sensory organs.

  • Unipolar Neurons: One process; primarily in sensory receptors.

Neuronal Function Classification

• Based on impulse travel direction:

  • Sensory (Afferent) Neurons: Carry impulses to the CNS (usually unipolar).

  • Motor (Efferent) Neurons: Transmit impulses away from the CNS to muscles (mostly multipolar).

  • Interneurons (Association Neurons): Located in CNS, connect sensory and motor neurons (most abundant, multipolar).

Application: The Spider Example Revisited

1. Sensory Neuron Activation: Unipolar sensory neurons sense the spider.

2. Signal Processing: Signal travels to the spinal cord through multipolar interneurons.

3. Motor Response: Signals sent to leg muscles resulting in a reflex action (kicking).

4. Cognition: Brain processes the information to categorize the stimulus (as a spider) and choose an appropriate response.

Conclusion

• Recap of sensory input, integration, and motor output within the nervous system.

• Overview of organization and function of different nervous system components.

• Preparation for the next discussion on how nerve cells communicate chemically and electrically.