Cerebral Hemispheres and Diencephalon

Introduction

  • Human Anatomy and Physiology Eleventh Edition Chapter 12 Part B: The Central Nervous System

  • Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College

  • Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved

12.2 Cerebral Hemispheres: Cerebral White Matter

  • Cerebral White Matter: Second of the three basic regions of cerebral hemispheres.

    • Function: Responsible for communication between cerebral areas, and between the cortex and lower CNS.

    • Composition: Consists of myelinated fibers bundled into large tracts.

    • Classification: According to direction they run:

      • Association Fibers: Horizontal running fibers that connect different parts of the same hemisphere.

      • Commissural Fibers: Horizontal fibers that connect gray matter of two hemispheres.

      • Projection Fibers: Vertical fibers that connect hemispheres with lower brain or spinal cord.

        • Internal Capsule: A compact band of projection fibers on each side of the brain stem that passes between the thalamus and some of the basal nuclei.

        • Corona Radiata: Projection fibers that radiate through cerebral white matter to cortex.

12.3 Basal Nuclei (Ganglia)

  • Basal Nuclei: Third of the three basic regions of the cerebrum.

    • Components of Each Hemisphere's Basal Nuclei:

      • Caudate Nucleus

      • Putamen

      • Globus Pallidus

      • Caudate nucleus + putamen = striatum

    • Associations: Closely associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain).

    • Functions:

      • Influence muscle movements.

      • Play a role in cognition and emotion.

      • Regulate intensity of slow or stereotyped movements.

      • Filter out incorrect/inappropriate responses.

      • Inhibit antagonistic/unnecessary movements.

    • Disorders: Examples include Parkinson's disease and Huntington's disease.

12.4 The Diencephalon

  • Components: Consists of three paired gray-matter structures that enclose the third ventricle:

    • Thalamus

    • Hypothalamus

    • Epithalamus

Thalamus

  • Structure: Bilateral egg-shaped nuclei that form superolateral walls of third ventricle.

    • Comprises 80% of diencephalon.

    • Connections: Bilateral nuclei connected by interthalamic adhesion (intermediate mass) and contain several nuclei, named for their location.

    • Main Function: Acts as relay station for information coming into cortex.

      • Sorts, edits, and relays ascending input such as:

        • Impulses from hypothalamus for regulating emotion and visceral function.

        • Impulses from cerebellum and basal nuclei to help direct motor cortices.

        • Impulses for memory or sensory integration.

      • Overall, mediates sensation, motor activities, cortical arousal, learning, and memory.

Hypothalamus

  • Location: Located below thalamus, forms cap over brain stem and forms inferolateral walls of third ventricle.

    • Important Nuclei:

      • Mammillary Bodies: Paired anterior nuclei acting as olfactory relay stations.

      • Infundibulum: Stalk connecting to the pituitary gland.

    • Role: Main visceral control and regulating center vital to homeostasis.

      • Chief homeostasis controls include:

        • Autonomic Nervous System Control:

          • Regulates blood pressure, rate and force of heartbeat, digestive tract motility, and pupil size.

        • Physical Responses to Emotions: Involvement in limbic system perceiving pleasure, fear, rage, biological rhythms, and drives (e.g., sex drive).

    • Additional Functions:

      • Regulates body temperature (via sweating or shivering).

      • Regulates hunger and satiety in response to nutrient blood levels or hormones.

      • Regulates water balance and thirst.

      • Regulates sleep-wake cycles via suprachiasmatic nucleus of thalamus, which sets our biological clock.

      • Controls endocrine system functions such as secretions of anterior pituitary gland and production of posterior pituitary hormones.

    • Clinical Note: Hypothalamic disturbances can lead to various disorders, such as severe body wasting, obesity, sleep disturbances, dehydration, and emotional imbalances. These can result from tumors, radiation, surgery, or trauma.

Epithalamus

  • Location: Most dorsal portion of the diencephalon, forms roof of the third ventricle.

    • Components: Contains the pineal gland (body) which extends from the posterior border and secretes melatonin, helping to regulate the sleep-wake cycle.

12.5 Brain Stem

  • Composition: Consists of three regions: midbrain, pons, medulla oblongata.

    • Similar in structure to spinal cord but contains nuclei embedded in white matter.

    • Functions: Controls automatic behaviors necessary for survival, contains fiber tracts connecting higher and lower neural centers, and nuclei associated with 10 of the 12 pairs of cranial nerves.

Midbrain

  • Location: Positioned between diencephalon and pons.

    • Cerebral Peduncles: Two ventral bulges containing pyramidal motor tracts that form pillars holding up the cerebrum.

    • Cerebral Aqueduct: Channel running through midbrain that connects third and fourth ventricles.

    • Periaqueductal Gray Matter: Nuclei that play a role in pain suppression and the fight-or-flight response, includes nuclei that control cranial nerves III (oculomotor) and IV (trochlear).

    • Midbrain Nuclei: Include:

      • Corpora Quadrigemina: Paired dorsal protrusions consisting of:

        • Superior Colliculi: Visual reflex centers.

        • Inferior Colliculi: Auditory relay centers.

      • Substantia Nigra: Functionally linked to basal nuclei; degeneration in this area causes Parkinson’s disease.

      • Red Nucleus: Relay nuclei for some descending limb flexion motor pathways, part of the reticular formation.

Pons

  • Location: Situated between midbrain and medulla oblongata.

    • Fourth Ventricle: Separates pons from cerebellum.

    • Composition: Composed of conduction tracts.

      • Longitudinal Fibers: Connect higher brain centers and spinal cord.

      • Transversal/Dorsal Fibers: Relay impulses between motor cortex and cerebellum.

    • Cranial Nerve Origins: Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial).

    • Functions: Some nuclei play a role in the reticular formation, while others assist in maintaining normal breathing rhythm.

Medulla Oblongata

  • Overview: Also known as the medulla; blends into spinal cord at foramen magnum.

    • Fourth Ventricle: Contains the continuation of the central canal of the spinal cord; the medulla and pons form the ventral wall.

    • Choroid Plexus: Capillary-rich membrane that forms cerebrospinal fluid.

  • Key Structures:

    • Pyramids: Two ventral longitudinal ridges formed by pyramidal tracts from the motor cortex.

    • Decussation of the Pyramids: The point where pyramidal tracts cross over to the opposite side of the body.

    • Olives: Swellings caused by underlying inferior olivary nuclei that relay stretch information from muscles and joints to the cerebellum.

    • Cranial Nerves: Include cranial nerves VIII (vestibulocochlear), IX (glossopharyngeal), X (vagus), and XII (hypoglossal).

    • Vestibular and Cochlear Nuclei: Mediate equilibrium responses.

    • Nucleus Cuneatus and Nucleus Gracilis: Relay ascending sensory information from the spinal cord.

  • Functions:

    • Medulla is an autonomic reflex center, functioning similarly to the hypothalamus.

    • Functional Groups:

      • Cardiovascular Center: Adjusts heart contraction force and rate.

      • Vasomotor Center: Adjusts blood vessel diameter for blood pressure regulation.

      • Respiratory Centers: Generate respiratory rhythm; control rate and depth of breathing (in collaboration with pontine centers).

      • Regulates:

        • Vomiting

        • Hiccupping

        • Swallowing

        • Coughing

        • Sneezing

12.5 Cerebellum

  • Overview:

    • Comprises 11% of brain mass and is located dorsal to the pons and medulla.

    • Functions to process input from the cortex, brain stem, and sensory receptors to provide precise, coordinated movements of skeletal muscles.

    • Also plays a significant role in balance.

Cerebellar Anatomy

  • Connective Structure: Cerebellar hemispheres connected by wormlike vermis.

    • Folia: Transversely oriented gyri present in the cerebellum.

    • Lobes: Each hemisphere has three lobes: anterior, posterior, and flocculonodular.

    • Gray Matter Composition: Thin cortex with a distinctive treelike pattern of white matter called arbor vitae.

    • Purkinje Fibers: Originate in cortex and synapse with the cerebellum.

    • Cerebellar Homunculi: Show sensory maps of the entire body.

Cerebellar Processing

  • Functionality: Fine-tunes motor activity in the following manner:

    • Receives impulses from cerebral cortex indicating intent to initiate voluntary muscle contraction.

    • Receives incoming signals from proprioceptors throughout the body, as well as from visual and equilibrium pathways.

      • These pathways continuously inform the cerebellum of the body’s position and momentum.

    • Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction.

    • Sends a “blueprint” of coordinated movement to the cerebral motor cortex and brain stem nuclei.

Cognitive Functions of the Cerebellum

  • Neuroimaging Insights: Suggests that the cerebellum plays roles in cognitive functions such as thinking, language, and emotion.

    • Similar to motor processes, it may compare actual output of higher functions with expected output and adjusts accordingly.