Unit 6 - Nervous System - 6.1.1-6.1.5

Unit 6: Nervous System

6.1 Overview and Objectives

• Central & Peripheral Nervous Systems

  • Understand the distinction between CNS and PNS.

  • Identify and label a neuron.

  • Recognize various types of nervous cells.

  • Describe the generation and propagation of action potential.

  • Comprehend the mechanisms of nerve signaling.

  • Identify types of neurotransmitters.

6.2 Functions of the Nervous System

• Sensory Input

  • Involves sensory receptors gathering information about the internal and external environments.

  • Produces information known as sensory input.

• Integration

  • Process of interpreting sensory input to make decisions regarding movements or responses.

• Motor Output

  • Activation of effectors (muscles or glands) to elicit responses based on integration outcomes.

6.3 Central Nervous System (CNS)

• Components

  • Made up of the brain and spinal cord.

  • Acts as the command center of the body.

• Functions

  • Receives, interprets, and dictates responses to impulses.

6.4 Peripheral Nervous System (PNS)

• Components

  • Includes cranial and spinal nerves.

  • Connects the CNS to the rest of the body.

• Divisions

  • Sensory (Afferent) Division: Transmits impulses from sensory receptors to the CNS.

  • Motor (Efferent) Division: Carries impulses from the CNS to muscles and glands.

    • Somatic Nervous System: Voluntary control of skeletal muscles.

    • Autonomic Nervous System (ANS): Involuntary control over cardiac and smooth muscles, and glands.

      • Sympathetic Division: Mobilizes body systems during activity (fight or flight).

      • Parasympathetic Division: Conserves energy and promotes housekeeping functions during rest.

6.5 Neurons

• General Structure

  • Cell Body: Contains organelles; crucial for processing information.

  • Dendrites: Branching extensions that receive signals and transmit them towards the cell body.

  • Axon: Long projection that transmits impulses away from the cell body.

  • Axon Hillock: Conical part of the cell body where the axon begins.

  • Myelin Sheath: Insulates axons for faster impulse conduction.

  • Nodes of Ranvier: Gaps in myelin sheath that facilitate rapid impulse transmission.

• Classification of Neurons

  • Unipolar: Single process; mainly sensory.

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

  • Multipolar: Multiple processes; major type in the CNS, including motor neurons.

6.6 Neuroglia (Glial Cells)

• Types in CNS

  • Astrocytes: Star-shaped; regulate neurotransmitter levels and blood flow.

  • Microglial Cells: Small phagocytic cells that clean up debris.

  • Ependymal Cells: Line cavities and help circulate cerebrospinal fluid (CSF).

  • Oligodendrocytes: Form myelin sheaths around axons.

• Types in PNS

  • Schwann Cells: Myelinate axons in the PNS.

  • Satellite Cells: Support and protect neuron cell bodies in ganglia.

6.7 Action Potential Generation

• Membrane Potential

  • The charge difference across the neuron's membrane.

  • Inside cell negatively charged due to fixed anions.

  • Sodium (Na+) outside and potassium (K+) inside influence action potentials.

• Process of Action Potential

  1. Resting Membrane Potential: Na+ and K+ channels are primarily closed.

  2. Depolarization: Na+ channels open; influx causes inner membrane to become positive.

  3. Repolarization: Na+ channels close, K+ channels open; K+ exits the cell to restore negative internal environment.

6.8 Nerve Signaling

• Propagation of the Impulse

  • Action potentials jump from one node of Ranvier to the next in myelinated axons, speeding up transmission.

  • Local currents carry the electrical signal along the axon, rapidly triggering next action potentials at successive nodes.