Nervous System Overview

Overview of the Nervous System

• Master Control System: The nervous system is responsible for controlling and communicating throughout the body via rapid electrical and chemical signals.
• Immediate Responses: Signals are specific and lead to almost immediate responses.

Functions of the Nervous System

• Sensory Input:

  • Gathers information about internal and external changes.
  • Relies on sensory receptors to collect data.

• Integration:

  • Processes and interprets the collected sensory information.

• Motor Output:

  • Activates effector organs (muscles and glands) to produce a response.

Divisions of the Nervous System

• Central Nervous System (CNS):

  • Comprises the brain and spinal cord.
  • Acts as the integration and control center of the body.

• Peripheral Nervous System (PNS):

  • Consists of nerves outside the CNS (extending from the brain and spinal cord).
  • Includes spinal nerves and cranial nerves.

Peripheral Nervous System (PNS) Divisions

• Functional divisions:
  • Sensory (Afferent) Division:
  • Somatic Sensory Fibers: Convey impulses from skin and muscles to CNS.
  • Visceral Sensory Fibers: Convey impulses from internal organs to CNS.
  • Motor (Efferent) Division:
  • Transmits impulses from CNS to effector organs.
  • Divided into Somatic and Autonomic Nervous Systems.
    • Somatic Nervous System: Controls voluntary muscles.
    • Autonomic Nervous System: Regulates involuntary functions (smooth muscle, cardiac muscle, glands).

Nervous Tissue Histology

• Neuroglia: Supporting cells that surround and protect neurons.
• Neurons: Excitable cells transmitting electrical signals.

Types of Neuroglia

• Astrocytes: Support and brace neurons, control chemical environment.
• Microglial Cells: Monitor neurons, migrate toward injured areas to remove debris.
• Ependymal Cells: Line cavities in CNS and circulate cerebrospinal fluid (CSF).
• Oligodendrocytes: Form myelin sheaths in CNS to insulate axons.
• Satellite Cells: Similar function to astrocytes but in PNS.
• Schwann Cells: Form myelin sheaths in PNS; vital for nerve regeneration.

Neuron Structure

• Cell Body: Contains the nucleus; supports the neuron's metabolic needs.
• Processes:
  • Dendrites: Receptive regions that receive signals.
  • Axon: Conducts impulses away from the cell body; contains axon terminals that release neurotransmitters.

Myelination

• Myelin Sheath: Composed of myelin, protects and insulates axons to increase transmission speed.
• In PNS: Formed by Schwann cells; segments wrapped around the axon.
• In CNS: Formed by oligodendrocytes; can wrap around multiple axons.

Structural Classification of Neurons

• Multipolar: Most common; multiple processes (1 axon, multiple dendrites).
• Bipolar: Rare; 1 axon and 1 dendrite.
• Unipolar: One process that divides into two axonal branches (one to sensory receptors, one to CNS).

Functional Classification of Neurons

• Sensory Neurons: Carry impulses toward the CNS; mostly unipolar.
• Motor Neurons: Carry impulses from the CNS to effectors; mostly multipolar.
• Interneurons: Connect sensory and motor neurons; mostly located within the CNS.

The Central Nervous System (CNS)

• Regions:

  • Cerebral Hemispheres
  • Diencephalon
  • Brain Stem (midbrain, pons, medulla)
  • Cerebellum

• Cerebral Cortex: Thin layer of gray matter; responsible for consciousness, sensory perception, and voluntary motor function.

• Cerebral White Matter: Myelinated fibers linking different parts of the CNS.

Protection of the CNS

• Bone (skull): Physically protects the brain.
• Meninges: Three protective membranes (dura mater, arachnoid mater, pia mater).
• Cerebrospinal Fluid (CSF): Cushions the brain and maintains buoyancy.
• Blood-Brain Barrier: Protects the brain by restricting bloodborne substances from entering the CNS.

Brain Structures

• Ventricles: Fluid-filled cavities producing and containing CSF.
• Lateralization of Cortical Function: Specialization of each hemisphere for certain functions; e.g. language processing predominantly in the left hemisphere.

Regions of the Brain

• Cerebral Hemispheres: Contain five lobes (frontal, parietal, temporal, occipital, insula).
• Thalamus, Hypothalamus, and Epithalamus: Components of the diencephalon.
• Brain Stem: Various nuclei and functionally crucial for life processes.
• Cerebellum: Integrates motor control and cognitive functions.

Summary of Functions

• Understanding the nervous system's architecture and functions helps in recognizing how it controls every aspect of human behavior, reactions, and bodily functions. Insight into neurons, glial cells, and CNS structures is paramount in the study of neuroanatomy and physiology.