Ch. 12 The Central Nervous System(4)

Chapter 12: Central Nervous System

Lobes and Sulci of the Cerebrum

  • Frontal Lobe

    • Precentral gyrus: Primary motor area.

    • Central sulcus: Divides frontal and parietal lobes.

    • Postcentral gyrus: Primary sensory area.

  • Parietal Lobe

    • Parieto-occipital sulcus: Separates parietal lobe from occipital lobe.

    • Lateral sulcus: Separates temporal lobe from frontal and parietal.

  • Occipital Lobe: Responsible for visual processing.

  • Temporal Lobe: Involved in auditory processing.

  • Cerebellum: Coordinates voluntary movements.

  • Terms:

    • Gyrus: Ridge of cortex.

    • Sulcus: Groove of cortex.

    • Fissure: Deep sulcus.

    • Cortex: Outer layer of gray matter.

    • White matter: Inner layer made of myelinated axons.

Gray and White Matter

  • Spinal Cord Structure:

    • Central cavity (spinal canal) surrounded by gray matter.

    • Outer white matter composed of myelinated axons.

  • The cerebrum and cerebellum have areas of gray matter (nuclei) within white matter.

  • Gray Matter includes:

    • Neuron cell bodies and short nonmyelinated neurons.

  • White Matter composed of:

    • Primarily myelinated axons with some nonmyelinated.

Central Nervous System (CNS)

  • Composed of the brain and spinal cord.

  • Cephalization: Increased neuron concentration in the head, reaching highest in humans.

Basic Pattern of the CNS

  • Brain:

    • Composed of pinkish-gray tissue with distinct surface anatomy (cerebral hemispheres, cerebellum, brain stem).

    • Cerebellum contains gray matter in nuclei.

    • Cerebrum has nuclei and gray matter in the cortex.

  • Spinal Cord:

    • Central canal surrounded by gray matter, with an external region of white matter (myelinated fibers).

Cerebral Cortex

  • Superficial gray matter; accounts for 40% of brain mass.

  • Functions: Enables sensation, communication, memory, understanding, voluntary movements.

  • Each hemisphere acts contralaterally, meaning the right hemisphere controls the left body side and vice versa.

  • Hemispheres have unequal functions; whole cortex involved in conscious behavior.

Functional Areas of the Cerebral Cortex

  • Three types:

    • Motor Areas: Control voluntary movement.

    • Sensory Areas: Conscious awareness of sensation.

    • Association Areas: Integrate diverse information.

Motor Areas in Frontal Lobe

  • Primary Motor Cortex: Located in precentral gyrus, controls skilled voluntary movements.

  • Premotor Cortex: Plans movements, sequences motor tasks.

  • Frontal Eye Field: Controls voluntary eye movements.

  • Broca’s Area: Language production and speech preparation.

Sensory Areas in Parietal Lobe

  • Primary Somatosensory Cortex: Located in postcentral gyrus; processes information from skin and proprioceptors.

    • Exhibits spatial discrimination: Identifies stimulated body regions.

  • Somatosensory Association Cortex: Integrates sensory information for a comprehensive understanding of stimuli.

Homunculus Representation

  • Functionally maps the body in the motor (precentral gyrus) and sensory (postcentral gyrus) cortices.

  • Motor Map: Represents different body parts with varying sizes relative to their motor control.

  • Sensory Map: Similar representation for sensory reception by body area.

Visual Areas in Occipital Lobe

  • Primary Visual Cortex: Located at the posterior tip; receives visual information from retinas.

  • Visual Association Area: Processes visual information (color, form).

Auditory Areas in Temporal Lobe

  • Primary Auditory Cortex: Processes sounds related to pitch and loudness.

  • Auditory Association Area: Stores auditory memories, interprets sounds.

Anterior Association Area (Prefrontal Cortex)

  • Located in the frontal lobe; involved in intellect, complex learning, personality.

  • Responsible for working memory associated with judgment and planning.

  • Develops slowly in children, influenced by social feedback.

Posterior Association Area

  • Covers parts of temporal, parietal, and occipital lobes.

  • Involved in pattern recognition and spatial localization.

Language Areas

  • Located around the left lateral sulcus:

    • Wernicke’s Area: Language comprehension.

    • Broca’s Area: Speech production.

    • Other areas involved in auditory-visual coordination for language processing.

Visceral Association Area

  • Located in insula's cortex; involved in conscious perception of visceral sensations.

Lateralization of Cortical Function

  • Lateralization: Each hemisphere has distinct functions.

    • Left hemisphere: Language, math, logic.

    • Right hemisphere: Visual-spatial tasks, emotion, artistic skills.

Cerebral White Matter

  • Composed of myelinated fibers responsible for inter-hemispheric and hemispheric communication.

  • Types of fibers:

    • Commissures: Connect gray areas of both hemispheres.

    • Association Fibers: Connect different parts of the same hemisphere.

    • Projection Fibers: Connect the cerebral cortex to lower brain centers.

Diencephalon

  • Central core of the forebrain; includes thalamus, hypothalamus, and epithalamus.

  • Encloses the third ventricle.

Thalamic Function

  • Key role in mediating senses, motor activities, and memory.

Hypothalamus Functions

  • Controls visceral activities like heartbeat and digestion, thermal regulation, sleep cycles, and emotional perception.

Epithalamus

  • Dorsal part of diencephalon; includes pineal gland for melatonin secretion and choroid plexus producing cerebrospinal fluid (CSF).

Brain Stem

  • Consists of midbrain, pons, and medulla oblongata.

  • Controls vital functions and serves as a pathway for communication between higher brain and lower centers.

Medulla Oblongata

  • Autonomic control; manages cardiovascular and respiratory centers.

  • Involved in reflex actions (vomiting, hiccupping).

Cerebellum

  • Coordinates muscular activity for smooth movement; processes information subconsciously.

    • Contains arbor vitae for white matter distribution.

Functional Brain Systems

  • Limbic System: Emotion processing (fear, danger recognition).

  • Reticular Formation: Manages consciousness, filters sensory stimuli to prevent overload.

Protection of the Brain

  • Protected by bone, meninges, and cerebrospinal fluid; the blood-brain barrier shields harmful substances.

Meninges Structure

  • Consists of dura mater, arachnoid mater, and pia mater, which cover and protect the CNS.

Dura Mater

  • Strongest outer layer; forms sinuses separating layers to contain venous blood.

Arachnoid Mater

  • Middle layer with subarachnoid space filled with CSF, includes villi for CSF absorption.

Pia Mater

  • Delicate tissue layer adhering closely to the brain.

Cerebrospinal Fluid (CSF)

  • Nourishes and protects the brain, creating a cushioning effect.

Choroid Plexuses

  • Produce CSF through blood filtration and maintain ion concentration.

Blood-Brain Barrier Functions

  • Selective barrier allowing nutrient passage, shielding brain from harmful substances; absent in specific areas for monitoring blood chemical composition.

Spinal Cord Protection

  • Enclosed within vertebral column; plays critical communication role and protected by bone, meninges, and CSF.

White Matter in the Spinal Cord

  • Divided into three funiculi with ascending, descending, and transverse fibers.

Developmental Aspects of the CNS

  • Vulnerable to environmental factors (e.g., drugs, radiation) during development. Visual cortex matures after birth.

Aging and the CNS

  • Cognitive declines common but not typically significant until into the 80s; factors like alcohol abuse can accelerate decline.