Chapter 13

Central Nervous System Overview

• Central Nervous System (CNS): Consists of the brain and spinal cord.

• Directional Terms Unique to the CNS:

  • Rostral: Toward the nose.

  • Caudal: Toward the tail.

Functions of the Brain (1 of 2)

• Controls important bodily functions:

  • Heart rate

  • Respiratory rate

  • Blood pressure

• Involvement in:

  • Autonomic nervous system regulation

  • Endocrine system coordination

  • Innervation of the head via cranial nerves.

  • Responsible for complex neural functions:

    • Intelligence

    • Consciousness

    • Memory

    • Sensory-motor integration

    • Emotion

    • Behavior

    • Socialization

Embryonic Development of the Brain (1 of 5)

• Development starts from the rostral part of the neural tube.

• Formation of three primary brain vesicles in a 4-week-old embryo:

  • Prosencephalon: Forebrain

  • Mesencephalon: Midbrain

  • Rhombencephalon: Hindbrain.

  • Secondary Brain Vesicles:

    • Prosencephalon: Divides into telencephalon and diencephalon.

    • Mesencephalon: Remains undivided.

    • Rhombencephalon: Divides into metencephalon and myelencephalon.

  • Structures of the adult brain derive from secondary brain vesicles:

    • Telencephalon: Forms the cerebral hemispheres.

    • Diencephalon: Contains thalamus, hypothalamus, and epithalamus.

    • Metencephalon: Develops into pons and cerebellum.

    • Myelencephalon: Forms the medulla oblongata.

Basic Parts and Organization of the Brain

• Classified into four main regions:

  • Brain Stem: Midbrain, pons, medulla.

    Cerebellum

  • Diencephalon

  • Cerebrum: Made of two hemispheres with four lobes.

Ventricles of the Brain (1 of 3)

• Expansions of the central cavity filled with cerebrospinal fluid (CSF).

• Lined with ependymal cells, they are continuous with each other and the central canal of the spinal cord.

• Lateral Ventricles: Located in the cerebral hemispheres; horseshoe-shaped.

• Third Ventricle: Located in the diencephalon; connected to lateral ventricles via interventricular foramen.

• Cerebral Aqueduct: Connects third and fourth ventricles.

• Fourth Ventricle: Located in the hindbrain; connects to the central canal of the spinal cord.

Distribution of Gray and White Matter

• Organization:

  • Centrally located gray matter (neuron cell bodies)

  • Externally located white matter (axons).

  • Cortex: Additional layer of gray matter in the cerebrum and cerebellum.

Brain Stem Overview

• Comprises:

  • Midbrain

  • Pons

  • Medulla Oblongata

Brain Stem Functions

• General functions include:

  • It acts as a passageway for fiber tracts between the cerebrum and spinal cord.

  • Heavily involved in innervating the face and head.

  • Produces automatic behaviors necessary for survival.

  • Integrates auditory and visual reflexes.

Medulla Oblongata Functions

• Most caudal parts of the brain stem continuously with the spinal cord.

• Four pairs of cranial nerves attach here (CN 8, 9, 10, 11).

• Core contains the reticular formation influencing autonomic functions:

  • Cardiac center

  • Vasomotor center

  • Medullary respiratory center

  • Centers for hiccupping, sneezing, swallowing, and coughing.

Medulla Oblongata Anatomy (2 of 4)

• Major structures include:

  • Pyramids of the medulla: Ventral surface landmarks.

  • Decussation of the pyramids: Site where motor tracts cross over.

  • Inferior cerebellar peduncles: Connect the medulla to the cerebellum.

  • Olive: Contains inferior olivary nucleus.

Brain Stem: The Pons

• It acts as a bridge between the midbrain and medulla oblongata.

• Contains nuclei of cranial nerves (V, VI, VII).

• Includes motor tracts from the cerebral cortex and pontine nuclei connecting cortex and cerebellum.

Midbrain Overview (1 of 4)

• Situated between the diencephalon and pons.

• Contains the Cerebral Aqueduct and Cerebral Peduncles, conveying pyramidal tracts.

Midbrain Functions (2 of 4)

• Periaqueductal gray matter: Involved in fight-or-flight reactions and mediating visceral pain responses.

Midbrain Structures (4 of 4)

• Contains two pigmented nuclei:

  • Substantia nigra: Neurons with melanin linked to basal nuclei.

  • Red nucleus: Largest nucleus of the reticular formation.

Cerebellum Overview (1 of 6)

• Located dorsal to pons and medulla, responsible for:

  • Smoothing and coordinating body movements.

  • Maintaining equilibrium.

• It is composed of two hemispheres: the anterior lobe and the posterior lobe; the surface features folia (ridges).

Cerebellum Anatomy (3 of 6)

• Major regions in the cerebellum include:

  • Cortex: Gray matter.

  • Arbor vitae: Internal white matter.

  • Deep cerebellar nuclei.

Coordinating Movement Steps

1. The cerebellum receives movement information from the motor cortex.

2. Compares intended movement with actual body position.

3. Sends instructions back to the motor cortex for fine-tuning.

Higher Cognitive Functions of the Cerebellum

• Involvement in:

  • Learning new motor skills.

  • Cognition (language, problem-solving).

Cerebellar Peduncles

• Thick tracts connecting the cerebellum to the brain stem include:

  • Superior

  • Middle

  • Inferior cerebellar peduncles.

• Fibers are ipsilateral (same side).

Diencephalon Overview

• Forms the central core of the forebrain, surrounded by cerebral hemispheres.

• Composed of:

  • Thalamus

  • Hypothalamus

  • Epithalamus

• Primarily consists of gray matter.

The Thalamus (1 of 2)

• Comprises 80% of the diencephalon; major relay station for sensory messages.

• Sends axons to cerebral cortex regions for processing sensory information.

• Converging afferent impulses synapse in thalamic nuclei.

• Acts as the “gateway” to the cerebral cortex, amplifying or toning down signals.

The Hypothalamus (1 of 2)

• Found between the optic chiasm and mammillary bodies.

• Controls visceral functions, regulating:

  • ANS

  • Emotional responses

  • Body temperature

  • Hunger and thirst signals

  • Sleep-wake cycles

  • Endocrine system function.

  • Involved in memory formation and behavior control.

Epithalamus Overview

• Forms part of the “roof” of the third ventricle.

• Contains the pineal gland (melatonin secretion, circadian rhythm control).

Cerebrum Overview (1 of 3)

• Accounts for 83% of brain mass, with fissures that separate regions:

  • Transverse fissure: Separates cerebrum from cerebellum.

  • Longitudinal fissure: Separates cerebral hemispheres.

Cerebrum Anatomy (2 of 3)

• Sulci: Grooves on the surface of the cerebral hemispheres.

• Gyri: Twisted ridges between sulci; notable gyri and sulci are consistent among individuals.

Lobes of the Cerebrum

• Divided into lobes named after skull bones:

  • Frontal lobe

  • Parietal lobe

  • Occipital lobe

  • Temporal lobe.

• Central Sulcus: Separates frontal and parietal lobes, bordered by precentral and postcentral gyri.

The Cerebral Cortex (1 of 3)

• Home of conscious mind enabling:

  • Awareness of self and sensations.

  • Control over voluntary movements.

  • Communication and memory functions.

• Composed primarily of gray matter.

Functional Regions of the Cerebral Cortex

• Functional Areas Include:

  • Sensory areas

  • Association areas

  • Motor areas.

• Each area handles distinct functions; memory and language are widely distributed across regions.

Sensory Areas

• Specific areas are responsible for conscious awareness of sensation:

  • Located in parietal, temporal, and occipital lobes.

Primary Somatosensory Cortex (1 of 2)

• Located along the postcentral gyrus; involved in general somatic senses and spatial discrimination.

• Contralateral Projection: Opposite sides of the body send sensory inputs to cerebral hemispheres.

• Sensory Homunculus: Represents the body map of the sensory cortex.

Visual Areas (1 of 2)

• Primary Visual Cortex: Located deep on medial occipital lobe; largest sensory area.

• Receives visual input from the retina, exhibiting contralateral function.

• Visual Association Area: Surrounds primary visual cortex, processing color, form, and movement.

Auditory Areas (1 of 2)

• Primary Auditory Cortex: Located on the superior edge of the temporal lobe; conscious awareness of sound.

• Auditory association area evaluates different sounds.

Vestibular and Gustatory Cortices

• Vestibular Cortex: Involved in balance awareness, located in the insula.

• Gustatory Cortex: Manages conscious taste awareness, also located in the insula.

Olfactory Cortex (1 of 2)

• Located medially in the cerebrum, receives signals from olfactory nerves for smell awareness.

Visceral Sensory Areas

• Located within the lateral sulcus (insula), processing sensations like pain and hunger.

Motor Areas Overview

• Located in the posterior frontal lobe, these areas control motor functions:

  • Premotor cortex

  • Primary motor cortex

  • Frontal eye field

  • Broca’s area.

Primary Motor Cortex (1 of 3)

• Located in precentral gyrus, managing voluntary body movements via pyramidal neurons.

• Supplementary Motor Area (SMA): Involved in planning and coordinating complex movements

• Contralateral Control: Pyramidal axons cross to the opposite side, influencing movements.

Frontal Eye Field and Broca's Area

• Frontal Eye Field: Controls voluntary eye movements to follow targets.

• Broca’s Area: Manages speech production, linking comprehension and emotional tones in speech.

Multimodal Association Areas (1 of 2)

• Large cortical regions integrating sensory inputs from various modalities:

  • Three Main Areas:

    • Posterior association area

    • Anterior association area

    • Limbic association area.

• Located at the interface of sensory regions, it integrates sensory information into coherent perception.

• Dorsal Stream: Responsible for spatial relationships; identifies object location.

• Ventral Stream: Responsible for recognizing objects, words, and faces.

Auditory Pathways

• Auditory stimuli processed in two streams to evaluate location and sound identification.

Posterior Association Areas (1 of 2)

• Language-related areas are primarily located in the left cerebral cortex, coordinating auditory and visual aspects of speech.

• Located in the frontal lobe designed for complex functions:

  • Thinking, reasoning, memory,

  • Planning movements, and integrating experiences.

• Also carries out

  • Impulse control, mental flexibility,

  • Social skills and emotional intelligence.

• Damage can lead to mental and personality disorders, affecting judgment and attention.

Limbic Association Area

• Focused on memory and emotions, integrating sensory and motor behaviors, crucial for memory formation.

Lateralization of Cortical Functioning (1 of 2)

• Hemispheres control opposite sides of the body; specialized cognitive functions:

  • Left Hemisphere: Controls language, math, logic.

  • Right Hemisphere: Involves visual-spatial skills and emotional understanding.

Cerebral White Matter (1 of 3)

• Fibers for communication between brain regions, categorized into:

  • Commissural Fibers: Connect hemispheres (e.g., corpus callosum).

  • Association Fibers: Connect parts of the same hemisphere.

Cerebral White Matter (2 of 3)

• Projection Fibers: Vertical pathways connecting the cortex to lower brain regions.

Deep Gray Matter of the Cerebrum

• Comprises basal nuclei (ganglia) for motor control, memory-related nuclei, and the amygdaloid body (limbic system).

Basal Ganglia Functions

• Cooperate with the cerebral cortex for:

  • Motor function control, movement intensity regulation, and muscle selection.

  • Involved in time estimation during tasks.

Functional Brain Systems Overview

• Brain networks include the limbic system (emotional processing) and the reticular formation (alertness and arousal).

Limbic System Components (1 of 2)

• Spans the medial region of the cerebrum, influencing emotions and memory with components like septal nuclei and hippocampal formation.

Limbic System Functions (2 of 2)

• Key for emotional regulation, memory strengthening, and behavioral response catalysis (e.g., fear).

Reticular Formation Functions (1 of 2)

• Found in the brain stem, with widespread neuron projections essential for arousal and maintaining consciousness.

Reticular Formation Functions (2 of 2)

• Reticular Activating System (RAS): Regulates alertness, consciousness, and sleep cycles.

Protection of the Brain

• Protected by the skull, meninges, cerebrospinal fluid (CSF), and blood-brain barrier.

Meninges Functions

• Cover and protect the CNS, contain blood vessels, and support CSF circulation.

  • Dura Mater: Strongest, with two layers, covering the brain and enclosing dural sinuses.

Arachnoid and Pia Mater

• Arachnoid Mater: Beneath the dura, allows CSF movement into sinuses.

• Pia Mater: Delicate layer adhering tightly to brain surfaces, following convolutions.

Cerebrospinal Fluid (CSF) Overview (1 of 2)

• Serves as a cushion, nutrient delivery, waste removal, and chemical signaling medium.

• Produced in choroid plexuses within the brain's ventricles.

Circulation of CSF

• Flows through ventricles into the subarachnoid space and is absorbed into the dural venous sinuses via arachnoid granulations.

Blood-Brain Barrier

• Prevents most toxins in the blood from entering the brain, allowing only essential nutrients and some substances like alcohol and nicotine to pass.

Spinal Cord Functions (1 of 4)

• Attaches spinal nerves, facilitates two-way conduction pathways, and functions as a major reflex center.

  • Extends from foramen magnum to L1 or L2 vertebra.

Anatomy of the Spinal Cord (2 of 4)

• Conus Medullaris: Inferior end of the spinal cord.

• Filum Terminale: Connective tissue filament anchoring to the coccyx.

• Cervical and Lumbar Enlargements: Sites where nerves for limbs arise.

• Cauda Equina: Collection of spinal nerve roots at the end.

Spinal Cord Segmentation

• Spinal segments correlate with spinal nerves, indicated by the nerve that emerges from it (e.g., T1 region for the first thoracic nerve).

White Matter of the Spinal Cord

• Outer region containing myelinated/non-myelinated axons enabling communication.

  • Types of fibers include ascending, descending, and commissural fibers.

Gray Matter of the Spinal Cord (1 of 2)

• Shaped like an 'H', containing cell bodies of neurons:

  • Dorsal Horns: Interneurons.

  • Ventral/Horns: Motor neuron cell bodies.

Protection of the Spinal Cord

• Shielded by vertebrae, meninges, and CSF; meninges include a single dura layer encasing the cord, along with arachnoid and pia mater.

Clinical Application: Lumbar Puncture

• Procedure for obtaining CSF, involves needle insertion into subarachnoid space.

Sensory and Motor Pathways in the CNS

• Connect brain and peripheral body systems through multineuron pathways, with tracts classified into:

  • Ascending Pathways: Carry sensory information to rostral CNS areas.

  • Descending Pathways: Relay motor instructions to caudal regions.

Ascending Pathways

• Conduct general sensory impulses using chains of first, second, and third-order neurons:

  • Main Ascending Pathways: Dorsal column pathway, spinothalamic pathway, spinocerebellar pathway.

Disorders of the Central Nervous System (1 of 3)

• Spinal Cord Damage:

  • Paralysis: Loss of motor function;

  • Parasthesia: Loss of sensation.

  • Paraplegia: Lower limb paralysis from T1-L3 injury.

  • Quadriplegia: Cervical region paralysis affecting all limbs.

Disorders of the Central Nervous System (2 of 3)

• Brain Dysfunction:

  • Degenerative Diseases: e.g., stroke, Alzheimer’s.

Disorders of the Central Nervous System (3 of 3)

• Congenital Malformations: Neural tube defects, cerebral palsy, characterized by impaired voluntary muscle control.