In-Depth Notes on the Nervous System

General System Functions

• The nervous system is primarily responsible for maintaining body homeostasis.
• Chief functions include:
  • Monitoring information from the environment.
  • Integrating that information.
  • Responding appropriately.

Organization of the Nervous System

Anatomical Divisions

1. Central Nervous System (CNS):

   • Composed of the brain and spinal cord.

2. Peripheral Nervous System (PNS):

   • Composed of cranial and spinal nerves.

Functional Divisions of the Nervous System

1. Sensory (Afferent) Division:

   • Conveys impulses to the CNS from sensory receptors.

2. Motor (Efferent) Division:

   • Conveys impulses away from the CNS to effectors (muscles and glands).

Further Subdivisions of the Motor Division

• Somatic Motor:
  • Innervates skeletal muscle (voluntary control).
• Autonomic Motor:
  • Innervates cardiac and smooth muscle, and glands (involuntary control).

Central Nervous System

• Brain and Spinal Cord: The two main components of the CNS.

The Brain

Functions:

• Manages voluntary movements, sensation interpretation, consciousness, and cognitive functions.

Organizational Structure:

• The brain is divided into four major parts:
  1. Cerebrum
  2. Diencephalon
  3. Brain Stem
  4. Cerebellum

Cerebral Structure

Cerebral Ventricles:

• 4 Ventricles filled with cerebrospinal fluid (CSF):
  • 2 lateral ventricles (in the cerebral hemispheres).
  • Third ventricle (in the diencephalon).
  • Fourth ventricle (in the brain stem).

Hemispheres and Lobes

• The cerebrum consists of two hemispheres, with critical distinctions:
• Left Hemisphere:
  • Specialized for language and mathematical skills.
• Right Hemisphere:
  • Better at visual-spatial skills and artistic abilities.

Lobes of the Cerebral Hemispheres:

1. Frontal Lobe:

   • Controls voluntary motor functions, mood, aggression, and olfaction.
   • Responsible for higher intellectual functions and verbal communication.

2. Parietal Lobe:

   • Evaluates sensory information (touch, pain, balance, taste, temperature).

3. Temporal Lobe:

   • Involves processing auditory stimuli and memory.
   • Important for abstract thought and judgment.

4. Occipital Lobe:

   • Responsible for visual processing.

5. Insular Lobe:

   • Involved in memory and integration of cerebral functions.

Cerebral Cortex

• The outermost layer of the brain where conscious thought occurs, primarily composed of gray matter.

Motor and Sensory Areas of the Cerebral Cortex

Motor Areas:

• Primary Motor Area: Initiates voluntary movements.
• Premotor Area: Coordinates learned motor skills.
• Prefrontal Area: Involved in complex behaviors and decision-making.

Sensory Areas:

• Primary Sensory Areas: Perception of sensory inputs such as:
  • Visual Information (Visual Cortex).
  • Auditory Information (Auditory Cortex).
  • Smell (Olfactory Cortex).
  • Taste (Gustatory Cortex).

Cerebral Medulla

• The inner layer of the brain made up of white matter fibers:
  • Association Fibers: Connect different parts within the same hemisphere.
  • Commissural Fibers: Connect corresponding regions of the two hemispheres.
  • Projection Fibers: Connect the cerebral cortex to lower brain structures.

Diencephalon

• Encloses the third ventricle and includes:
  • Thalamus: The relay station for sensory and motor signals.
  • Hypothalamus: Regulates autonomic functions like thirst, hunger, temperature, etc.
  • Epithalamus:
  • Includes the habenula (emotion response) and the pineal gland (secretes melatonin).

Brainstem

• Comprises:

1. Midbrain: Contains major relay and reflex centers.
2. Pons: A conduction area affecting respiration and cranial nerves.
3. Medulla Oblongata: Regulates vital functions like respiration and heart rate.

Cerebellum

• Known as the “little brain,” it consists of two hemispheres and coordinates smooth, well-timed movements.

Protection of the Brain

• Bone, Meninges, and Cerebrospinal Fluid protect the brain and spinal cord.

Meninges Layers (Superficial to Deep):

1. Dura Mater
2. Arachnoid Mater
3. Pia Mater

Cerebrospinal Fluid (CSF):

• Formed by choroid plexuses; circulates through the ventricles and subarachnoid space, providing support and nourishment.

Blood-Brain Barrier (BBB):

• Protects the brain by allowing selective permeability; enables essential substances to enter while restricting harmful ones.

Spinal Cord

Anatomy and Protection:

• Functions as a 2-way conduction pathway for impulses and serves as a reflex center.
• It is protected by the vertebral column and meninges, extending from the foramen magnum to the first lumbar vertebra.
• Contains 31 pairs of spinal nerves.

Cross-sectional Anatomy:

1. Gray Matter: Contains neuron cell bodies located in an H-shaped structure with ventral (motor), lateral (visceral), and dorsal (sensory) horns.
2. White Matter: Composed of myelinated axons, divided into three columns (funiculi) for ascending and descending pathways.