Fundamentals of Brain Anatomy & Physiology – Lecture Overview

Overview: Neurons & Core Biochemistry

• Neurons
  • Fundamental cells of the nervous system; myriad shapes & functions.
  • Core activity = regulated movement of ions (Na\^+, K\^+, Ca\^{2+}) across a selectively-permeable membrane.
  • Remarkable takeaway: Complex cognition narrowly depends on simple ion gradients and membrane proteins.

Sensory Perception & Optical Illusions

• Ambiguity in visual input can mislead cortical interpretation.
  • “The Dress” internet debate
  • Colors perceived as either black/blue or white/gold.
  • Key variable: where the brain infers the light source.
  • Checkerboard shadow illusion
  • Squares A and B are identical grayscale values.
  • Brain compensates for implied shadow cast by a green cylinder, lightening or darkening squares accordingly.
• Principle: Brain reconciles incomplete data using best (but sometimes wrong) assumptions.

Brain Organization: Macroscopic Components

• Two global parts
  • Brainstem (continuous with spinal cord).
  • Higher cortex (cerebrum).

Brainstem (inferior → superior)

• Medulla oblongata: Autonomic centers—heart rate, respiration.
• Pons
  • Distinct “ground-beef” texture (illustration) shared with cerebellum.
  • Bridges cerebellum ↔ cerebrum; assists in breathing rhythm.
• Midbrain (Tectum)
  • Visual & auditory reflexes, startle response.
• Thalamus (relay switchboard)
  • Filters & directs almost all ascending/descending info.
• Hypothalamus (under thalamus)
  • Homeostatic control; interface with endocrine system.

Cerebellum

• Posterior/inferior “mini-brain”; motor coordination, proprioception, learned motor patterns.

Cerebrum: Lobes & Landmarks

• Central Sulcus = key landmark dividing frontal & parietal lobes.
  • Precentral gyrus (anterior) → primary motor cortex.
  • Postcentral gyrus (posterior) → primary somatosensory cortex.
• Lobes (color-code reference)
  • Frontal (motor planning, decision, personality).
  • Parietal (somatic sensory integration).
  • Temporal (audition, memory, language).
  • Occipital (vision).
  • Insula (deep; taste, visceral sensation, self-awareness—mentioned briefly).
• Additional fissures/sulci
  • Lateral Sulcus (separates temporal from frontal/parietal; deep fissure—temporal lobe “droops”).
  • Longitudinal Fissure (divides left/right hemispheres).

Surface Vocabulary

• Sulcus (plural sulci): valley.
• Gyrus (plural gyri): ridge.

Blood–Brain Barrier (BBB)

• Formed by tight junctions + astrocyte “perivascular feet”.
• Forces substances to cross capillary endothelial cells (transcellular, not paracellular).
• Freely permeable: \text{O}2, \text{CO}2, ethanol, some lipophilic drugs.
• Requires carriers: glucose (insulin-independent transporters), amino acids.
• Enzymatic detox inside endothelium; barrier “tightness” is adjustable.
• Select regions lack tight BBB for endocrine monitoring (circumventricular organs)
  • Hypothalamus, posterior pituitary, pineal gland.

Clinical Tie-ins & Examples

• Rabies Virus
  • Neurotropic; enters CNS → encephalopathy.
  • Symptoms: anxiety, hydrophobia, hypersalivation, paralysis, hallucinations.
  • Behavioral manipulation hypothesis links historical vampire/Dracula lore to rabies outbreaks in Eastern Europe.
• Meningitis
  • Inflammation of meninges (dura, arachnoid, pia).
  • Signs: fever, stiff neck, severe headache, vomiting; may follow ear/sinus infections.
  • Severe cases → cerebral edema & hemorrhage → death.
• Brain Freeze (Sphenopalatine Ganglioneuralgia)
  • Rapid cooling of palate → vascular & neural response → sharp cranial pain.

Meninges (Protective Coverings)

• Dura mater – tough, leathery outer sheath.
• Arachnoid mater – web-like middle layer; sub-arachnoid space houses cerebrospinal fluid (CSF).
• Pia mater – delicate inner layer; follows gyri/sulci; carries surface vessels.

Cerebrospinal Fluid (CSF)

• Produced by choroid plexus; circulates ventricles → sub-arachnoid space.
• Functions
  • Buoyancy: suspends brain, preventing contact with jagged cranial floor.
  • Protection: shock absorber for impacts (concussion, shaken baby syndrome).
  • Chemical stability: maintains optimal ionic/enzymatic environment.

Cranial Nerves (CN I–XII)

• Arranged anterior → posterior; emerge from cerebrum (I–II) & brainstem (III–XII).
• Sensory fibers illustrated in blue; motor in red.
• Highlights
  • CN I (Olfactory) & II (Optic): pure sensory.
  • CN III (Oculomotor), IV (Trochlear), VI (Abducens): eye muscle control (motor).
  • CN V (Trigeminal): mixed—facial sensation + mastication muscles.
  • CN VII (Facial): mixed—taste (sensory) & facial expression (motor).
  • Remaining nerves follow similar mixed/pure patterns (details to be emphasized in later lectures & labs).
• Practical scope: Know nerves specifically referenced in text/lectures—exam targets will be sign-posted.

Neural Development Snapshot

• Post-fertilization: rapid mitosis forms hollow blastula → elongates.
• Neural crest cells rise like bilateral waves → fuse to enclose neural tube.
• Tube differentiates rostro-caudally:
  • Forebrain, midbrain, hindbrain vesicles.
  • Spinal cord derived from caudal tube.
• Detailed embryonic names (prosencephalon, mesencephalon, etc.) not required.

Brain Blood Supply & Metabolic Priority

• Brain receives ~15\% of cardiac output and ~20\% of body’s \text{O}_2/glucose.
• Active transport of glucose ensures continuous fuel—even during systemic hypoglycemia.

Key Numbers & Equations (Quick Reference)

• Normal core body temp \approx 98.6^\circ\text{F} (hypothermia = below this; hypothalamus monitors).
• Cardiac output portion to brain \approx 0.15 \times Q_{tot}.

Ethico-Philosophical Notes

• Illusions remind us perception ≠ reality; underscores need for scientific methodology when interpreting sensory data.
• BBB exemplifies evolutionary trade-offs: protection vs. pharmacological access—relevant to drug design & neuro-ethics.

Real-World Connections & Next Steps

• Sports medicine: concussion protocols leverage CSF protective concepts.
• Pharmacology: designing agents capable (or incapable) of BBB traversal.
• Upcoming Lecture (Brain II): deeper functional maps, autonomic regulation, and special senses.