Central Nervous System: Major Brain Regions and Functions

Central Nervous System (CNS)

• The CNS consists of the brain and spinal cord.

Brain: Major Regions

• The brain has four major regions: Diencephalon, Brainstem, Cerebrum, and Cerebellum.

Diencephalon

• The Diencephalon is divided into three parts: Thalamus, Epithalamus, and Hypothalamus.
• Thalamus:
• Largest part of the Diencephalon.
• Influences mood and registers pain.
• Epithalamus:
• Small area superior and posterior to the Thalamus.
• Involved in emotional and visceral response to odors.
• Pineal body is located in the Epithalamus and plays a role in the onset of puberty.
• Hypothalamus:
• Most inferior part of the Diencephalon.
• Important in maintaining homeostasis.
• Regulates body temperature, hunger, and thirst.
• Plays a central role in controlling hormone secretion from the pituitary gland.

Brainstem

• The Brainstem connects the spinal cord to the rest of the brain.
• The Brainstem is divided into three parts: Medulla Oblongata, Pons, and Midbrain.

Medulla Oblongata

• Inferior part of the Brainstem.
• Continuous with the spinal cord.
• Extends from the foramen magnum to the pons.
• Contains cranial nerves (CN) 9, 10, 11, and 12.
• Regulates heart rate, blood vessel diameter, breathing, swallowing, vomiting, coughing, sneezing, and balance.

Pons

• Immediately superior to the Medulla Oblongata.
• Means "bridge" in Latin.
• Contains cranial nerves (CN) 5, 6, 7, and 8.
• Lower part of the Pons controls breathing, swallowing, and balance.
• Other nuclei in the Pons control functions such as chewing and salivation.

Midbrain

• Superior to the Pons.
• Smallest region of the Brainstem.
• Contains cranial nerves (CN) 3 and 4.
• Found superior and inferior colliculi.
• Superior colliculi: involved in visual reflexes and turning the head.
• Inferior colliculi: major relay centers for auditory nerve pathways in the CNS.
• General functions: coordination of eye movements and control of pupil diameter and lens shape.
• Contains a nuclear black mass called Substantia Nigra, which is associated with Parkinson's Disease and Levodopa treatment.

Cerebrum

• Largest part of the brain.
• Divided into left and right hemispheres by a longitudinal fissure.
• The surface of each hemisphere is wrinkled by presence of eminences called Gyri and furrows called Sulci or Fissures.
• The Cerebrum is divided into four lobes: Frontal, Parietal, Occipital, and Temporal.

Frontal Lobe

• Principal motor area (4).
• Important in the control of voluntary motor functions, motivation, aggression, mood, and olfactory (smell) reception.
• Brocas area (44, 45) is associated with Brocas aphasia (executive, motor, nonfluent, anterior).

Parietal Lobe

• Principal center for the reception and conscious perception of most sensory information, such as touch, pain, temperature, balance, and taste.
• Principal sensory area (3, 1, 2).

Occipital Lobe

• Functions in the reception and perception of visual input.
• Principal visual cortex (17).

Temporal Lobe

• Involved in olfactory (smell) and auditory sensations and plays an important role in memory.
• Associated with abstract thought and judgment.
• Primary auditory cortex (41, 42).
• Wernicke's area (22) is associated with Wernicke's aphasia (receptive, sensory, fluent, posterior).

Cerebellum

• Composed of gray matter.
• Posterior and inferior to the Cerebrum.
• Involved in balance, maintenance of muscle tone, and coordination of fine motor movements.
• Major function of the Cerebellum is that of a comparator.
• Also involved in learning motor skills (e.g., riding a bicycle, playing a piano).

Spinal Cord

• Extends from the foramen magnum to L2 (before the 2nd lumbar vertebra).
• Has a central gray part organized into horns and a peripheral white part forming nerve tracts.
• Roots of the spinal nerve extend out of the cord.

Vertebral Column

• Surrounds and protects the spinal cord.
• Divided into five regions: Cervical (7), Thoracic (12), Lumbar (5), Sacral (5), and Coccyx (4 fused vertebra).