Brain and Cranial Nerves Notes

The Brain & Cranial Nerves

• The brain is responsible for dreams, passion, plans, and memories.
• It is more versatile than the spinal cord but has slower response times.

Brain Organization

• Composition: 98% neural tissue, approximately 3 lbs (1200 cc).
• No direct correlation between brain size and intelligence, with males typically having 10% larger brains.
• Major divisions include:
  • Cerebrum
  • Cerebellum
  • Diencephalon
  • Mesencephalon (Midbrain)
  • Pons
  • Medulla Oblongata

Protection and Support

• Structures protecting the brain include:
  1. Bones of the Cranium
  2. Cranial Meninges
  • Dura mater
  • Arachnoid mater
  • Pia mater
  1. Cerebrospinal Fluid (CSF)

Cranial Meninges Extensions

• Dural folds act as "seat belts" to keep the brain stable.
• CSF acts as a shock absorber to protect the brain.

Traumatic Brain Injuries (TBI)

• Annual statistics reveal:
  • 17 million TBIs per year
  • 1.3 million ER visits
  • 275,000 hospitalizations
  • 52,000 deaths

Chronic Traumatic Encephalopathy (CTE)

• A progressive degenerative disease related to repeated head trauma, initially known as dementia pugilistica.
• Commonly found in athletes from contact sports, like football and boxing.
• Key Scientist: Dr. Bennet Omalu's work on football player Mike Webster.

Dural Folds

• Falx Cerebri: Between the two cerebral hemispheres.
• Tentorium Cerebelli: Separates cerebrum from cerebellum.
• Falx Cerebelli: Separates cerebellar hemispheres.

Brain's Ventricular System

• Lateral Ventricles (1 & 2): Located within each cerebrum.
• Third Ventricle: Located in the diencephalon; connected to laterals via the Interventricular Foramen.
• Fourth Ventricle: Situated between the pons and cerebellum, connected to the third via the Cerebral Aqueduct.

CSF Production and Function

• Produced by the choroid plexus through specialized ependymal cells, roughly 500ml/day but totaling only 150ml in the body (replaced every 8 hours).
• Functions:
  • Cushions the brain
  • Supports the brain structure
  • Transports nutrients, chemicals, and waste.

Blood Supply to the Brain

• Arterial Supply: Main sources are the Internal Carotid and Vertebral Arteries.
• Venous Drainage: Through Internal Jugular Veins and Vertebral Veins.
• Cerebrovascular Accidents (CVAs): Known as strokes, occur when blood supply is disrupted, leading to brain death in minutes.

Blood-Brain Barrier

• Formed by endothelial cells in CNS capillaries with tight junctions, permitting only lipid-soluble substances to pass freely (e.g., CO2, O2).
• Astrocytes influence permeability.

The Cerebrum

• Largest brain portion, responsible for conscious thought, intellect, and sensory processing.
• Composed of gray and white matter, with two hemispheres.

Cerebral Anatomy

• Gyri: Elevated portions increasing surface area (~2.5 ft²).
• Sulci: Shallow grooves.
• Fissures: Deeper grooves separating regions.

Hemispheric Functions

• Each hemisphere processes sensory information and sends motor responses to the opposite side of the body.
• Distinct functional localizations:
  • Frontal Lobes: Motor functions, memory, emotional control.
  • Occipital Lobes: Vision processing.
  • Parietal Lobes: Sensory information for touch, pressure, pain.
  • Temporal Lobes: Auditory processing, long-term memory storage, language recognition.
  • Insula: Taste sensation and interoceptive awareness.

Central Sulcus

• Divides the frontal and parietal lobes.

White Matter of the Brain

• Types of Fibers:
  • Association Fibers: Connect regions within a hemisphere.
  • Commissural Fibers: Connect left and right hemispheres (e.g., Corpus Callosum).
  • Projection Fibers: Connect to diencephalon, brainstem, cerebellum, and spinal cord.

Basal Nuclei

• Groups of gray matter involved in muscle tone control and coordinated movement.
• Includes:
  • Caudate Nucleus
  • Lentiform Nucleus (Globus Pallidus and Putamen)

Cortex & Association Areas

• Primary Areas: Precentral (motor) and Postcentral (sensory) gyri.
• Association Areas: Interpret sensory data, maintaining memory and coordination of learned movements.

Integration Centers

• Wernicke's Area: Interpretive centers in the left hemisphere for understanding spoken and visual inputs.
• Broca’s Area: Controls speech and language production.
• Prefrontal Cortex: Involved in predicting outcomes and emotional regulation.

Hemispheric Lateralization

• Left Hemisphere: Dominates language skills, analytical tasks, and precise finger movements.
• Right Hemisphere: Handles sensory analyses, emotional context, and facial recognition.

Limbic System

• Integrates emotional states and memory, linking thought with instinctual drives.
  • Amygdaloid Body: Involved in emotional responses (fight or flight).
  • Hippocampus: Essential for long-term memory formation.

The Diencephalon

• Integrates conscious and unconscious sensory and motor signals.
• Components:
  • Epithalamus: Contains the choroid plexus and pineal gland (melatonin production).
  • Thalamus: Relay station for sensory information to primary sensory areas.
  • Hypothalamus: Regulates autonomic functions, emotions, and hormonal balance.

Midbrain (Mesencephalon)

• Contains structures for vision (superior colliculi) and hearing (inferior colliculi).
• Contains the substantia nigra which releases dopamine (impaired in Parkinson's disease).

Medulla Oblongata

• Contains autonomic nuclei regulating cardiac, respiratory functions, and links to spinal cord.

Epilepsy and Seizures

• Neurological disorders caused by abnormal brain activity, manifesting as seizures.
• Treatment may involve medication or surgery.

Cranial Nerves

• 12 pairs that can be sensory, motor, or mixed.
• Important to know their names, numbers, functions, and types (sensory/motor).

Mnemonics for Cranial Nerves

• Names and Functions:
  • CNI: Smell
  • CNII: Vision
  • CNIII: Eye muscle control
  • etc.
• Mnemonic Examples:
  • On, Old, Olympics… (for names)
  • Some Say Marry Money… (for sensory/motor)