Nervous System Overview

Basic Functions of the Nervous System

• Sensation: Involves collecting sensory input from the environment through receptors that monitor internal and external stimuli.
• Integration: Processing and interpreting sensory information to determine appropriate responses.
• Reaction: Motor output activation of muscles and glands via neurotransmitters.

Structural Organization of the Nervous System

• Central Nervous System (CNS): Comprises the brain and spinal cord.
• Peripheral Nervous System (PNS): Includes 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Nervous Tissue Composition

• Grey Matter: Contains neuronal cell bodies, short processes, neuroglia, and blood vessels.
• White Matter: Composed of long processes (axons) of neurons.
• Ganglion: A collection of neuron cell bodies located outside the CNS.
• Nucleus: A collection of neuron cell bodies located inside the CNS.
• Plexus: A network formed by a collection of nerve fibers.

Human Brain Structure

• Located in the cranial cavity and divided into four major regions:
  • Cerebrum: Consists of two cerebral hemispheres.
  • Diencephalon: Includes the thalamus, hypothalamus, subthalamus, and epithalamus.
  • Cerebellum: Responsible for coordination and balance.
  • Brainstem: Comprises the midbrain and pons.

Spinal Cord Details

• Length: Measures approximately 42-45 cm.
• Location: Situated within the vertebral canal.
• Starts at: Medulla oblongata.
• Ends at: Conus medullaris, terminating at the L2 vertebra.
• Spinal Nerves: Gives rise to 31 pairs.

Protection of the CNS

• Bones: Skull and vertebral column provide primary protection.
• Meninges: Three protective layers surrounding the CNS.
• Cerebrospinal Fluid (CSF): Provides cushioning and nourishment.

Meningeal Coverings

• Dura Mater: The outermost layer.
• Arachnoid Mater: The middle layer.
• Pia Mater: The innermost layer closely adhering to the brain and spinal cord.

Peripheral Nerves

• Composed of sensory, motor, or mixed fibers.
• Cranial Nerves: 12 pairs attached to the brain.
• Spinal Nerves: 31 pairs connected to the spinal cord, categorized as:
  • 8 Cervical
  • 12 Thoracic
  • 5 Lumbar
  • 5 Sacral
  • 1 Coccygeal

Spinal Nerves and Nerve Plexuses

• Each spinal nerve has two roots:
  • Dorsal Root: Contains sensory fibers and sensory ganglion (DRG).
  • Ventral Root: Contains motor fibers.
• Plexuses formed primarily from ventral rami, excluding the thoracic region.

Cranial Nerves List

• 1st: Olfactory
• 2nd: Optic
• 3rd: Oculomotor
• 4th: Trochlear
• 5th: Trigeminal
• 6th: Abducent
• 7th: Facial
• 8th: Vestibulocochlear
• 9th: Glossopharyngeal
• 10th: Vagus
• 11th: Accessory
• 12th: Hypoglossal

Dermatomes

• Defined as the skin segment supplied by a segmental spinal nerve.

Autonomic Nervous System (ANS)

• A subdivision of the peripheral nervous system regulating involuntary body activities.
• Innervates cardiac muscle, smooth muscle, and internal organs.

Axonal Structure in ANS

• The first (preganglionic) neuron's axon leaves the CNS to synapse with the second (ganglionic) neuron.
• The second (postganglionic) neuron extends to the target organ.

Divisions of the Autonomic Nervous System

• Sympathetic Division: Involves T1-L2 segments, mobilizing body resources during stress ("fight or flight").
• Parasympathetic Division: Involves cranial outflow and S2-S4 spinal segments, conserving energy and facilitating routine maintenance ("rest and digest").