Introduction to Anatomy - Nervous System

Introduction to Anatomy - Nervous System

• The nervous system controls all bodily functions
• It is composed of specialized nerve cells called neurons.
• Neurons receive stimuli and send impulses to effectors (muscles or glands).

Divisions of the Nervous System

• The nervous system is divided into three main parts:
  • Central Nervous System (CNS):
    • Brain
    • Spinal cord
  • Peripheral Nervous System (PNS):
    • Cranial nerves
    • Spinal nerves
  • Autonomic Nervous System (ANS):
    • Sympathetic nervous system (fight-or-flight response)
    • Parasympathetic nervous system (rest-and-digest response)

Protection of the CNS

• The brain and spinal cord are protected by:
  • Skull and vertebral column
  • Meninges (dura mater, arachnoid mater, pia mater)
  • Cerebrospinal fluid

The Brain

• Parts of the brain:

  • Cerebrum: Divided into two hemispheres connected by the corpus callosum. Each hemisphere has a lateral ventricle.
  • Cerebellum: Composed of two hemispheres connected by the vermis.
  • Brainstem: Contains the midbrain, pons, and medulla oblongata.

• Lobes of the cerebrum:

  • Frontal lobe
  • Parietal lobe
  • Temporal lobe
  • Occipital lobe

The Spinal Cord

• Begins as a continuation of the medulla oblongata at the base of the skull.
• Ends at:
  • In newborns: at the level of the third lumbar vertebra (L3).
  • In adults: at the lower border of L1.
• Location: Upper two-thirds of the vertebral canal.
• Length: 45 cm in males and 42 cm in females.
• Segments: 31 segments giving rise to 31 pairs of spinal nerves.
• Enlargements:
  • Cervical enlargement: Origin of brachial plexus.
  • Lumbosacral enlargement: Origin of lumbosacral plexus.

Cerebrospinal Fluid (CSF)

• Definition: Fluid filling the ventricles and subarachnoid space.
• Volume: ~130 ml
• Function:
  • Reduces brain weight
  • Drains waste products
  • Protects the central nervous system
  • Regulates intracranial pressure

Peripheral Nervous System

• Composed of:
  • Cranial nerves (12 pairs)
  • Spinal nerves (31 pairs)
  • Ganglia

Cranial Nerves

• 12 pairs connected to the brain.
• Classifications:
  • Sensory nerves
  • Special sensory nerves
  • Motor nerves
  • Mixed nerves

Spinal Nerves

• 31 pairs originating from the spinal cord.

Autonomic Nervous System

• Part of the nervous system controlling involuntary functions (heart, smooth muscles, glands).
• Distributed through central and peripheral nervous system.
• Two divisions:
  • Sympathetic system (thoracolumbar outflow):
    • Prepares the body for an emergency (fight or flight).
    • Increases heart rate, blood pressure, inhibits peristalsis, and closes sphincters.
  • Parasympathetic system (craniosacral outflow):
    • Responsible for restoring energy
    • Decreases heart rate, increases peristalsis, and opens sphincters.