Chapter 13 Part 1

Chapter 13 - The Anatomy of the Nervous System

Overview of the Nervous System

Human Nervous System Diagram (Figure 13.1)

  • The human nervous system enables complex functions such as balance, integrating sensory information regarding balance, body position, and touch, primarily through the interactions of the central nervous system (CNS) and peripheral nervous system (PNS).

  • The CNS includes both the brain and spinal cord, while the PNS includes all other neural elements.

13.1 The Embryologic Perspective: Embryonic Development of the Nervous System

  • Note: This section is skipped.

13.2 The Central Nervous System

Structure

  • Components:

    • Brain: Divided into four regions:

    • Cerebrum

    • Diencephalon

    • Brainstem

    • Cerebellum

    • Spinal cord: considered a single structure.

Functions of the CNS

  1. Cerebrum:

    • Largest part of the brain.

    • Controls all conscious thoughts and intellectual functions.

    • Responsible for processing somatic sensory and motor information.

    • Divided into two hemispheres by the longitudinal fissure.

  2. Cerebral Anatomy:

    • Gray Matter:

      • Found in the cerebral cortex and basal nuclei.

    • White Matter:

      • Located deep to the cerebral cortex.

      • Surrounds basal nuclei.

Cerebral Cortex Features

  • Has a folded surface structure called the cerebral cortex, which increases the surface area available for cortical functions.

  • Features include:

    • Gyri: Rounded elevations increasing surface area.

    • Sulci: Shallow depressions between gyri.

    • Fissures: Deep grooves separating major regions of the brain.

Specific Structures of the Cerebrum

  • Central Sulcus: Separates the anterior frontal lobe from the posterior parietal lobe.

    • Precentral Gyrus: Forms the anterior border of the central sulcus (associated with motor function).

    • Postcentral Gyrus: Forms the posterior border of the central sulcus (associated with sensory perception).

  • Lateral Sulcus: Separates the frontal lobe from the temporal lobe.

  • Insula: Known as the medial lobe; lies medial to the lateral sulcus.

  • Parieto-occipital Sulcus: Separates the parietal lobe from the occipital lobe.

Lobes of the Cerebral Cortex

  1. Frontal Lobe: Involved in motor function and reasoning.

  2. Parietal Lobe: Processes somatosensory information (sensations from the body).

  3. Occipital Lobe: Responsible for vision.

  4. Temporal Lobe: Associated with hearing, balance, and smell.

  5. Insula (Medial Lobe): Involved in taste and olfactory functions.

White Matter of the Cerebrum

  • Composition: Contains various types of fibers responsible for interconnecting different parts of the brain.

  1. Association fibers:

    • Connect areas within the same hemisphere.

      • Arcuate fibers: Short fibers connecting one gyrus to another.

      • Longitudinal fasciculi: Longer bundles connecting the frontal lobe with other lobes in the same hemisphere.

  2. Commissural fibers:

    • Connect two hemispheres. Example: Corpus callosum, anterior commissure.

  3. Projection fibers:

    • Link the cerebral cortex to lower brain structures, including the diencephalon, brainstem, cerebellum, and spinal cord.

      • Pass through the internal capsule: Contains all ascending and descending projection fibers.

Basal Nuclei

  • Comprises masses of gray matter within the white matter of the cerebrum.

  • Functions:

    • Direct subconscious activities.

    • Prevent unnecessary motor movements.

    • Assist in planning desired movements, particularly those that are repetitive or learned.

  • Components include:

    1. Caudate Nucleus: Large with a head and slender tail.

    2. Lentiform Nucleus: Composed of putamen and globus pallidus.

    3. Claustrum: Thin layer of gray matter adjacent to the putamen.

  • Role in Disorders: Abnormalities can lead to conditions such as Parkinson’s disease due to increased activity (failure to suppress movements).

Limbic System

  • A functional grouping that:

    • Establishes emotional states.

    • Links functions of the cerebral cortex with autonomic functions of the brainstem.

    • Facilitates memory storage and retrieval.

Components of Limbic System

  1. Limbic Lobe:

    • Comprising the cingulate gyrus, dentate gyrus, parahippocampal gyrus, and hippocampus.

  2. Amygdaloid Body: Acts as an interface between various sensory systems and the limbic system.

  3. Fornix: A tract of white matter connecting the hippocampus to hypothalamus.

  4. Anterior Nuclei of Thalamus: Relays information from the mammillary body to the cingulate gyrus.

Function of the Cerebrum

  • The cortex of each hemisphere interprets somatosensory information and issues motor commands to the opposite side of the body, with pathways crossing (decussation) at the medulla.

  • The relationship between specific functions and specific cortical areas is generally imprecise.

  • Sensory and Motor Areas:

    • The primary motor cortex (frontal lobe) sends motor commands to skeletal muscles.

    • The primary somatosensory cortex (parietal lobe) receives sensory input from the body.

Special Sensory Primary Cortices

  • Primary Visual Cortex (in occipital lobe): Receives visual information.

  • Primary Auditory Cortex (in temporal lobe): Receives auditory information.

  • Primary Olfactory Cortex (in temporal/insula lobes): Deals with smell information.

  • Primary Gustatory Cortex (in insula lobe): Processes taste information.

Integrative Areas

  • Found in both hemispheres, receive and process information from various sensory modalities.

  • Engage in complex motor activities and analytical functions, including higher cognitive functions.

Broca’s and Wernicke’s Areas

  1. Broca’s Area: Located in the frontal lobe, responsible for speech production and associated with the left hemisphere.

    • Regulates patterns of breathing and vocalization in speech.

  2. Wernicke’s Area: Associated with language comprehension and coordinates access to memories regarding visual and auditory stimuli.

Prefrontal Cortex Functions

  • Involved in coordinating information from all cortical association areas and performing abstract intellectual functions.

  • Associated with predicting consequences of actions.

  • Historical note on prefrontal lobotomy used to attempt 'curing' mental illnesses in the mid-20th century.

13.3 Diencephalon

Structure

  • Located beneath the cerebrum and cerebellum, comprised of three regions:

    • Epithalamus

    • Thalamus

    • Hypothalamus

Thalamus

  • Filters and relays sensory information (except smell) from the spinal cord and cranial nerves to the cerebral cortex:

    • Determines priorities for processing sensory information for the cortex.

    • It is connected via interthalamic adhesion bridging both sides and separating the thalamus into left and right components.

Hypothalamus

  • Positioned below and anterior to the thalamus, integral for the regulation of:

    • Emotions

    • Autonomic functions

    • Hormone production

  • Functions include:

    1. Secreting ADH (antidiuretic hormone) and oxytocin.

    2. Regulating body temperature.

    3. Supervising autonomic functions.

    4. Coordinating voluntary and autonomic function.

    5. Linking the nervous and endocrine systems.

Hypothalamus Structures

  • Mammillary Bodies: Regulate reflex eating movements.

  • Infundibulum: A narrow stalk connecting the hypothalamus to the pituitary gland and involved in endocrine functions.

13.4 Brain Stem

Overview

  • Connects the spinal cord to the brain, facilitating information relay efficiently between the two.

  • Composed of three major regions:

    • Midbrain

    • Pons

    • Medulla Oblongata

Midbrain

  • Processes visual and auditory stimuli, responsible for maintaining consciousness.

  • Components include:

    • Tectum: Contains sensory nuclei known as the corpora quadrigemina, which includes superior (vision) and inferior (hearing) colliculi.

    • Tegmentum: Includes structures like the red nucleus and substantia nigra important for various functions and associated with movement.

Pons

  • Connects the cerebellum to the brainstem.

  • Contains tracts relaying sensory and motor information, along with nuclei involved in respiratory control and sensorimotor functions between cerebellum and other CNS parts.

Medulla Oblongata

  • The lowest part of the brainstem, connecting the brain to the spinal cord and coordinating complex autonomous reflexes.

  • Contains nuclei controlling vital autonomic functions such as heart rate and breathing.

Pyramids of Medulla Oblongata

  • Features many motor axons that decussate (cross over) at the anterior surface, structurally grouped into pyramids.

  • Specifically noted for resulting anatomical and functional implications in motor control.

Collected Functions of the Brain Stem

  • The midbrain, pons, and medulla serve varied functions, including processing sensory data, generating reflexes, maintaining consciousness, facilitating communication between different brain regions, and regulating autonomic processes vital for homeostasis.

13.5 Cerebellum

General Function

  • The second largest part of the brain, responsible for coordinating repetitive body movements, smoothing transitions between movements, adjusting postural muscles, and fine-tuning both conscious and subconscious movements.

Anatomical Features

  • Composed of two hemispheres, covered by a gray matter layer called the cerebellar cortex.

  • Key structural features:

    • Folia: Folds in the cerebellar cortex that increase surface area.

    • Vermis: Narrow band of cortex separating the left and right hemispheres.

    • Arbor Vitae: The intricate branching structure of internal white matter in the cerebellum, described as the “tree of life.”

Cerebellar Disorders

  • Ataxia: A disorder associated with disturbances in muscular coordination, can arise from trauma, stroke, or intoxication.

13.6 Spinal Cord

Structure

  • Housed within protective membranes (meninges) and vertebral column, serves as a conduit for sensory and motor information carried between the brain and body.

  • Comprised of four main regions: cervical, thoracic, lumbar, sacral, exhibiting bilateral symmetry with 31 segments that give rise to spinal nerves.

  • Regions are divided by grooves: anterior median fissure (deeper, anterior) and posterior median sulcus.

  • The central canal within the spinal cord contains cerebrospinal fluid (CSF).

Cross-Sectional Anatomy of the Spinal Cord

  • Shows how gray matter (cell bodies and unmyelinated axons) is organized into posterior horns (sensory nuclei), anterior horns (motor nuclei), and lateral horns (visceral motor nuclei in thoracic/lumbar segments) and is surrounded by white matter (myelinated axons).

Functional and Structural Organization of White Matter

  • Organized into distinct anatomical regions:

    • Posterior White Columns: Between the posterior horns and posterior median sulcus.

    • Anterior White Columns: Between the anterior horns and anterior median fissure.

    • Lateral White Columns: Found on each side of the spinal cord.

  • The anterior white commissure is where axons cross from one side of the spinal cord to the other.

Conclusion

  • The anatomy of the nervous system encompasses complex interactions between the brain, spinal cord, and periphery that are foundational for sensory perception, motor control, and cognitive function. Understanding this intricate structure supports further study of neurological health and disorders.