7 - Cerebrum

Organization and Function of the Cerebrum

Course Information

  • Course Name: Human Anatomy & Physiology

  • Year: 2025-2026

  • Course Code: HTHSCI 1H06 A/B

  • Institutions: McMaster University and Mohawk College

Lecture Outline

  • Topics for Discussion:

    • Organization of the Central Nervous System (CNS)

    • Grey & White Matter

    • Cerebral Cortex

    • Surface Features of the Brain

    • Functional Areas of the Brain

    • Types of White Matter Tracts

    • Structure & Function of Deep Nuclei

    • Structure & Function of the Basal Nuclei (Motor Control)

    • Structure & Function of the Limbic System (Emotion & Memory)

Brain Vasculature

  • Venous Drainage:

    • Straight and Inferior Sagittal Sinus

    • Sigmoid Sinus

    • Superior Sagittal Sinus

    • Great Cerebral Vein (of Galen)

    • Cortical Veins

    • Transverse Sinus

    • Internal Jugular Veins (to Superior Vena Cava & Heart)

Overview of the Central Nervous System Structures & Functions

  • Primary Functions:

    • Thinking

    • Memory

    • Voluntary Motor Movements

    • Sensory Perception

  • Major Structures and Functions:

    1. Cerebral Cortex: Functions as a sensory/motor relay center & regulates autonomic functions.

    2. Diencephalon: Manages autonomic functions and cranial nerve activities.

    3. Brainstem: Coordinates movement and balance.

    4. Cerebellum: Integrates motor output, sensory input, reflexes, and interfaces with the peripheral nervous system (PNS).

    5. Spinal Cord: A vital conduit for transmitting information.

Organization of the CNS

  • Tissue Types:

    • White Matter: Composed of myelinated axons responsible for communication.

    • Grey Matter: Comprised of neuron cell bodies (somas).

  • Cerebral Cortex Composition:

    • Outer Grey Matter: Neuron somas.

    • Inner White Matter: Axons of neurons.

  • Deep Grey Matter Includes:

    • Basal Nuclei (Ganglia)

    • Limbic System

  • Spinal Cord Structure:

    • Grey Matter on the inside.

    • White Matter on the outside.

Organization of the Cerebrum

  • Where:

    • Superficial Grey Matter: Comprising neurons.

    • White Matter Tracts: Comprising axons.

    • Deep Nuclei: Neurons formed around the ventricles, lateral to the thalamus.

  • Diencephalon: Integrative structure for autonomic functions.

Cerebral Cortex Characteristics

  • Surface Area:

    • Each cerebral hemisphere has a total surface area of about 1.3 square feet (0.12 m²).

  • **Major Lobes: **

    • Frontal Lobe

    • Parietal Lobe

    • Temporal Lobe

    • Occipital Lobe

    • Limbic Lobe

  • Naming:

    • Lobes named after the associated bones of the skull.

Surface Features of the Cerebral Cortex

  • **Features: **

    • Fissures: Deep grooves (e.g., Longitudinal Fissure, Central Sulcus, Lateral Fissure) that separate the hemispheres and lobes.

    • Sulci: Shallow grooves.

    • Gyri: Hills or ridges on the brain.

Functional Areas of the Cerebral Cortex

  • Homunculus Model: Shows the distribution of sensory and motor neuron density across the body.

    • More sensory and motor cortical neurons are dedicated to the head and upper limbs than to the trunk and lower limbs.

  • Cerebral Blood Supply:

    • Anterior cerebral artery

    • Middle cerebral artery

  • Functional Areas by Lobe:

    • Frontal Lobe:

    • Primary Motor Cortex

    • Premotor Cortex

    • Intellect

    • Frontal Eye Field

    • Parietal Lobe:

    • Somatosensory Cortex

    • Association Cortex

    • Common Integrative Area

    • Temporal Lobe:

    • Auditory Cortex

    • Association Cortex

    • Limbic System

    • Occipital Lobe:

    • Visual Cortex

    • Association Cortex

  • Broca’s & Wernicke’s Areas:

    • Broca's Area: motor functions related to speech.

    • Wernicke's Area: sensory language comprehension.

Hemispheric Lateralization

  • Left Hemisphere Functions:

    • Analytical, logical, scientific, mathematical thinking.

    • Language processing (spoken and written).

    • Controls movements/sensations on the right side of the body.

    • Aphasia types: receptive, expressive, and global.

  • Right Hemisphere Functions:

    • Holistic, intuitive, creative, artistic, musical cognition.

    • Controls movements/sensations on the left side of the body.

  • Lateralization Variance:

    • Variability in lateralization of specialized functions among individuals.

  • Gender Difference:

    • Lateralization is less pronounced in females compared to males (anterior commissure more developed in females).

White Matter Tracts

  • Types of White Matter Tracts:

    1. Commissural Fibers: Connect between the two hemispheres (e.g., Corpus Callosum, Anterior Commissure).

    2. Association Fibers: Connect within the same hemisphere, between lobes (e.g., Fornix).

    3. Projection Fibers: Connect distant CNS parts (e.g., Internal Capsule).

  • Imaging Techniques:

    • MRI diffusion tensor imaging utilized to visualize these tracts.

Basal Nuclei (Ganglia) Functions

  • Roles:

    • Initiates and terminates motor movements.

    • Eliminates unnecessary movements and controls subconscious actions (e.g., natural arm swinging).

    • Starts/stops cognitive processes, attention, memory, planning, emotional regulation.

  • Components:

    • Caudate Nucleus: head and tail portions.

    • Lentiform Nucleus: includes Putamen & Globus Pallidus.

  • Related Structures:

    • Substantia Nigra of Midbrain: involved in dopamine production.

  • Neglected Terms:

    • "Striatum" refers to the combination of Caudate and Putamen.

Disorders Related to Basal Nuclei

  • Common Motor Disorder Examples:

    • Huntington’s Chorea: Neurodegeneration in the striatum leading to increased motor activity.

    • Parkinson’s Disease: Lack of dopamine impacting striatum causes difficulty in initiating/stopping movements and may affect the nigrostriatal pathway.

Deep Grey Matter Composition

  • Visual Characteristics in Section:

    • Basal Nuclei Location: Around outer ventricles including caudate and lentiform nuclei, potentially involving the amygdala.

    • Limbic System Structures: Located around the inner ventricles, including amygdala, hippocampus, fornix, and mammillary bodies.

Limbic System Overview

  • Definition: Often referred to as the “emotional brain,” it also plays a significant role in memory and regulation of behaviors.

  • Key Structures:

    • Hippocampus

    • Fornix

    • Mammillary Bodies

    • Amygdala

    • Entorhinal Cortex

    • Cingulate Gyrus

    • Prefrontal Cortex

  • Structural Connections:

    • White Matter Tracts form arcs to connect the cited structures.

Limbic System Functions: Emotion & Memory

  • Hippocampus Functions:

    • Involved in encoding and consolidating memories (long-term memory formation).

    • Memory processing involves all somatic sensations and special senses.

  • Amygdala Functions:

    • Analyzes anger and fear expressions, assesses danger, and elicits fear responses.

    • Provides emotional context to memories, regulating autonomic function via hypothalamic output.

  • Fornix: Connects hippocampus to mammillary bodies for memory processing.

  • Mammillary Bodies: Act as an olfactory relay nucleus and contribute to emotional responses.

Amnesia: Clinical Connections

  • Definition: Memory loss of facts/experiences.

  • Types:

    • Anterograde Amnesia: Loss of ability to form new memories post-brain injury.

    • Retrograde Amnesia: Loss of long-term memories previously formed.

  • Case Study - Henry Molaison (H.M.):

    • Underwent bilateral medial temporal lobe excision for seizure control, resulting in severe anterograde amnesia.

    • No effect on perceptual/intellectual function and no retrograde amnesia; retained normal recall for pre-surgery events.

Types of Memory

  • Declarative Memory Breakdown:

    • Short-Term Memory:

    • Function: Acquisition and short-term storage of episodic (events) or semantic (facts) memories.

    • Location: Medial temporal lobe.

    • Long-Term Memory:

    • Function: Long-term storage of declarative memories (episodic and semantic).

    • Location: Neocortex.

  • Non-Declarative Memory (Procedural):

    • Function: Acquisition and long-term retention of non-declarative (procedural/muscle) memory.

    • Location: Cerebellum and basal ganglia.

Procedural Memory Overview

  • Procedural Pathways:

    • Procedural memory involves Premotor Cortex, THALAMUS, CEREBELLUM for motion recognition, vision, balance, position.

    • Early experiences influence procedural learning via Basal Nuclei, THALAMUS, and Premotor Cortex pathways.

Summary of Key Takeaways

  • The cerebral cortex is subdivided by lobes with specific functionalities influenced by distinct cortical regions.

  • White matter tracts facilitate connections across regions (association fibres), between hemispheres (commissural fibres), and throughout the CNS (projection fibres).

  • The Basal Nuclei, consisting of the caudate, putamen, and globus pallidus, are essential for both proper motor function and procedural memory regulation.

  • The Limbic System encompasses multiple regions responsible for emotion, memory, and homeostasis.

  • The hippocampus plays a crucial role in the encoding and consolidation of episodic and semantic memories for long-term storage across cortical areas.

  • Studies such as those involving H.M. illustrate that different brain regions manage various memory systems, highlighting distinctions between short-term and long-term memory, as well as between declarative and procedural memory.

Next Lecture

  • Topics to Discuss Next Time:

    • Diencephalon

    • Brainstem

    • Cerebellum