LECTURE3.GROSS ANATOMY OF CNS_19304d65992e61effc7d87a893f7a6db

LECTURE 3: DIVISIONS OF THE CENTRAL NERVOUS SYSTEM & CORTICAL REGIONS

GROSS ANATOMY REGIONS AND ORGANIZATION

  • Cerebral Hemisphere: Comprising the left and right hemispheres, associated with higher brain functions such as reasoning, creativity, and emotions.

  • Diencephalon: Acts as a relay and processing center for sensory information, playing a crucial role in the regulation of homeostasis and controls various functions including hunger, thirst, and the sleep-wake cycle.

  • Cerebellum: Responsible for fine motor control, balance, and coordination, ensuring smooth execution of voluntary movements through feedback from sensory systems.

  • Brain Stem: Connects the brain to the spinal cord, regulating vital life functions like heart rate, breathing, and consciousness.

    • Midbrain: Involved in vision, hearing, and motor control.

    • Pons: Serves as a pathway for signals between the cerebellum and the rest of the brain and is important for sleep regulation.

    • Medulla oblongata: Responsible for autonomic functions, such as voluntary movement control and involuntary actions (e.g., breathing).

SPINAL CORD

  • Central cavity surrounded by gray matter that contains neuron cell bodies.

  • External white matter composed of myelinated fiber tracts that facilitate communication between different regions of the nervous system.

BRAIN STRUCTURE

  • Similar pattern to spinal cord with additional areas of gray matter in the brain, essential for processing and responding to stimuli.

  • Cerebral Hemispheres and Cerebellum: External gray matter known as cortex, which is essential for higher-order brain functions.

    • The cortex in the brainstem diminishes as one moves down the brain.

    • Scattered gray matter nuclei amid white matter contribute to various brain functions.

VENTRICLES OF THE BRAIN

  • Filled with cerebrospinal fluid (CSF) that cushions the brain and removes waste.

  • Lined by ependymal cells, which produce and circulate CSF.

  • Connected to one another and to the central canal of the spinal cord:

    • Lateral ventricles to third ventricle via interventricular foramen.

    • Third ventricle to fourth ventricle via cerebral aqueduct.

    • Structures include: Septum pellucidum, Inferior horn, Anterior horn, Median aperture, and more.

LATERAL VENTRICLES

  • Paired, C-shaped structures located in the cerebral hemispheres, separated by the septum pellucidum.

  • The third ventricle is centrally located in the diencephalon, while the fourth ventricle is found in the hindbrain with openings for CSF flow.

CEREBRAL HEMISPHERES FIVE LOBES

  • Frontal lobe: Involved in executive functions, decision-making, planning, and voluntary movement.

  • Parietal lobe: Integrates sensory perception and management of bodily sensations.

  • Temporal lobe: Important for processing auditory information and is also involved in memory and emotion.

  • Occipital lobe: Primarily responsible for visual processing.

  • Insula: Plays a role in consciousness and emotional regulation.

  • Key features include:

    • Central sulcus separates the precentral gyrus (frontal) and postcentral gyrus (parietal).

    • Parieto-occipital sulcus delineates the occipital and parietal lobes.

    • Lateral sulcus outlines temporal lobes.

BASIC REGIONS OF CEREBRAL HEMISPHERES

  • Composed of two main regions:

    • Cerebral cortex: Superficial layer of gray matter; serves as the site for cognitive processes.

    • White matter: Internal structures containing myelinated axons.

    • Basal nuclei: Deeply located structures that influence movement regulation and cognitive functions.

CEREBRAL CORTEX

  • A thin (2-4 mm) superficial layer that comprises roughly 40% of brain mass.

  • Functions encompass consciousness, awareness, sensory perception, motor initiation, and complex cognitive tasks such as communication, memory storage, and understanding.

FOUR GENERAL CONSIDERATIONS

  • Functional areas divided into three types:

    • Motor areas: Control voluntary movements.

    • Sensory areas: Responsible for sensory perception.

    • Association areas: Integrate information from different modalities.

  • Each hemisphere has cross-body control for movement and sensation (contralateral control).

  • There is lateralization of cortical functions, with certain cognitive processes localized to specific hemispheres.

MOTOR AREAS OF THE CEREBRAL CORTEX

  • Primary motor cortex: Composed of large pyramidal cells located in the precentral gyrus; controls precise, skilled voluntary movements.

  • Motor homunculi: Represent the map of contralateral motor innervation of the body in the primary motor cortex.

  • Premotor cortex: Responsible for planning movements and coordinating learned motor skills.

  • Broca's area: Typically located in the left hemisphere; directs muscles associated with speech production.

SENSORY AREAS OF CEREBRAL CORTEX

  • Primary somatosensory cortex: Located in the postcentral gyrus of parietal lobe; interprets sensory information and spatial discrimination.

  • Visual areas: Primary visual cortex located at the posterior tip of the occipital lobe; visual association area interprets stimuli based on experiences.

  • Auditory areas: Primary auditory cortex processes sound information.

MULTIMODAL ASSOCIATION AREAS

  • Integrate inputs from various sensory areas and send outputs further:

    • Anterior association area (prefrontal cortex): Involved in high-level functions like planning and decision making.

    • Posterior association area: Integrates sensory information for complex perceptual tasks.

    • Limbic association area: Connects emotional experience with memory and decision-making processes.

LIMBIC SYSTEM

  • Known as the emotional brain, consists of structures such as the amygdaloid body and cingulate gyrus.

  • Influences emotional responses and memory formation.

LATERALIZATION OF CORTICAL FUNCTION

  • Both hemispheres are structurally similar but perform different functions:

    • Left hemisphere: Dominant for language processing, mathematical calculations, and logical reasoning.

    • Right hemisphere: Associated with visual-spatial skills, emotional intelligence, and intuition.

  • Interhemispheric communication occurs rapidly through fiber tracts.

CEREBRAL WHITE MATTER

  • Composed of myelinated fibers crucial for communication:

    • Association fibers: Connect different areas within the same hemisphere.

    • Commissural fibers: Connect gray matter of both hemispheres (e.g., corpus callosum).

    • Projection fibers: Connect the cerebral hemispheres with lower brain centers and the spinal cord.

BASAL NUCLEI (GANGLIA)

  • Comprised of subcortical nuclei: Caudate nucleus, Putamen, Globus pallidus, essential for coordinating movement.

  • Involved in emotional regulation and cognitive processes.

DIENCEPHALON

  • Contains three paired structures:

    • Thalamus: Makes up about 80% of the diencephalon and acts as a gateway for most sensory information.

    • Hypothalamus: Regulates autonomic nervous system functions and endocrine activity.

    • Epithalamus: Includes the pineal gland, contributing to the regulation of sleep-wake cycles.

BRAIN STEM REGIONS

  • Composed of:

    • Midbrain: Controls involuntary eye movements, hearing, and reflexes related to vision and audition.

    • Pons: Functions as a relay center between the brain and cerebellum, important for regulating sleep.

    • Medulla oblongata: Responsible for vital processes like heart rate, respiratory rhythm, and blood pressure regulation.

CEREBELLUM

  • Represents 11% of brain mass, crucial for ensuring smooth and coordinated movements.

  • Receives signals regarding body position and motion from various sensory systems, contributing to balance and motor learning.

PROTECTION OF THE BRAIN

  • Bone (Skull): Provides a hard protective covering for the brain.

  • Meninges: Three protective layers covering and protecting the CNS: Dura mater, Arachnoid mater, and Pia mater.

  • Cerebrospinal Fluid (CSF): Offers buoyancy to CNS structures, absorbs impacts, and provides nutrients while removing waste from the brain.

BLOOD BRAIN BARRIER

  • A selective barrier that protects the brain by controlling the movement of substances in the bloodstream, allowing essential nutrients to pass while blocking harmful substances.