Anatomy Of The Nervous System

The Nervous System

The nervous system plays a crucial role in maintaining homeostasis (balance) in the human body. It utilizes sensory receptors to gather information about changes in both internal and external environments. The nervous system is a complex network of interconnected systems composed of various subsystems, each with specific structures and functions.

Structure and Function of Neurons

Neurons (Nerve Cells)

• Basic Elements: Neurons are the fundamental units of the nervous system.
• Components:
  • Cell Body (Soma): The main processing center of the neuron.
  • Dendrites: Thin branching extensions that conduct nerve impulses toward the cell body.
  • Axon: A single branch that carries nerve impulses away from the cell body.
  • Myelin Sheath: A protective covering that insulates the axon and increases impulse transmission speed.
  • Terminal End Fibers: Located at the axon’s end, these fibers transmit impulses across a synapse to the next neuron.
  • Nucleus: Contains the cell's genetic material and regulates its functions.

Impulse Transmission

• Impulses travel along the axon and are transmitted to the next neuron via neurotransmitters across the synapse.

Properties of Neurons

• Excitability: The ability to respond to stimuli.
• Conductivity: The ability to transmit nerve impulses.

Types of Neurons

1. Efferent (Motor) Neurons:
   • Convey information from the Central Nervous System (CNS) to muscles and glands.
2. Afferent (Sensory) Neurons:
   • Carry information from sensory receptors to the CNS.
3. Interneurons:
   • Process and relay sensory information within the CNS.

Neuroglia (Supporting Cells)

• Function: Support, protect, connect, and remove debris from the nervous system.
• Types:
  • Astrocytes: Supportive roles and blood-brain barrier maintenance.
  • Oligodendroglia: Produce the myelin sheath in the CNS.
  • Microglia: Act as immune cells in the brain.

Major Components of the Nervous System

1. Central Nervous System (CNS)

• Components: Composed of the brain and spinal cord.
• Functions: Integrates and coordinates sensory and motor information, controls higher functions like memory, learning, and emotion.

2. Peripheral Nervous System (PNS)

• Components: All nerves that connect the CNS to the rest of the body.
• Function: Carries sensory and motor information between the CNS and organs/tissues.

Central Nervous System (CNS) Details

Brain

• Weight: Approximately 3 pounds in adults; 75% water.
• Oxygen Consumption: Uses 20% of the body's oxygen supply.
• Neurons: Contains over 100 billion neurons.
• Parts of the Brain:
  • Cerebrum: Responsible for higher cognitive functions.
  • Diencephalon: Contains the thalamus and hypothalamus, involved in sensory relay and homeostasis.
  • Brain Stem: Includes the midbrain, pons, and medulla oblongata; controls basic life functions.
  • Cerebellum: Coordinates movement and balance.

Brainstem

• Midbrain: Involved with visual reflexes.
• Pons: Controls certain respiratory functions; connects different parts of the brain.
• Medulla Oblongata: Regulates heart rate, breathing, and reflexes such as swallowing and coughing.

Cerebellum

• Location: Inferior to the occipital lobes of the cerebrum.
• Function: Coordinates musculoskeletal movements, maintains posture, balance, and muscle tone.

Cerebrum

• Structure: Divided into two hemispheres, connected by the corpus callosum.
• Lobes:
  • Frontal Lobe: Involved in decision-making, problem-solving, and emotional regulation.
  • Parietal Lobe: Processes sensory information related to touch, temperature, and pain.
  • Temporal Lobe: Involved in hearing, memory, and language.
  • Occipital Lobe: Responsible for visual processing.

Diencephalon

• Components: Thalamus, hypothalamus, epithalamus.
• Functions: Acts as a relay center for sensory information; regulates vital functions like heart rate, blood pressure, and temperature control.

Spinal Cord

• Structure: Extends from the medulla oblongata to the lumbar region of the spine.
• Function: Transmits signals between the brain and the body; protected by the vertebral column and meninges.
• Meninges Layers:
  • Dura Mater: Tough outer layer.
  • Arachnoid Mater: Middle web-like layer containing cerebrospinal fluid (CSF).
  • Pia Mater: Innermost layer containing blood vessels.

Peripheral Nervous System (PNS) Details

• Function: Connects the CNS to the limbs and organs; responsible for both sensory and motor functions.
• Divisions:
  • Sensory (Afferent) Division: Carries information to the CNS.
  • Motor (Efferent) Division: Carries information from the CNS to muscles and glands.
    • Somatic Nervous System: Controls voluntary movements.
    • Autonomic Nervous System: Regulates involuntary functions (divided into sympathetic and parasympathetic systems).

Cranial Nerves

• There are 12 pairs of cranial nerves, each with specific functions:
  1. Olfactory: Sense of smell.
  2. Optic: Sense of vision.
  3. Oculomotor: Eye movements.
  4. Trochlear: Aids eye muscle movements.
  5. Trigeminal: Sensation in the face and motor functions for chewing.
  6. Abducens: Controls eye movements.
  7. Facial: Taste, facial expressions, and glands.
  8. Vestibulocochlear: Hearing and balance.
  9. Glossopharyngeal: Taste, swallowing, and salivary glands.
  10. Vagus: Controls heart and digestive tract functions.
  11. Accessory: Controls muscles in the neck and shoulders.
  12. Hypoglossal: Controls tongue movements.