Central Nervous System: Structure and Function (Chapter 12 Study Guide)

Central Nervous System (CNS)

Overview

The Central Nervous System (CNS) comprises the brain and spinal cord, serving as the primary control center for the body. It processes sensory information, coordinates motor output, and is responsible for higher cognitive functions.

• Brain: Responsible for processing and integrating information, memory, and consciousness.

• Spinal Cord: Conducts signals to and from the brain and mediates reflexes.

Brain Development

Embryological Formation

During embryonic development, the brain and spinal cord originate from the neural tube. The anterior end of the neural tube expands and forms three primary brain vesicles, which further differentiate into five secondary vesicles.

• Primary vesicles: Forebrain, Midbrain, Hindbrain

• Secondary vesicles: Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon

• Posterior end: Develops into the spinal cord

Additional info: The flexures (midbrain and cervical) cause the telencephalon and diencephalon to angle toward the brain stem, shaping the adult brain structure.

Brain Regions at Birth

By birth, the brain is organized into four major regions:

• Cerebral Hemispheres

• Diencephalon (includes thalamus, hypothalamus, epithalamus)

• Brain Stem (midbrain, pons, medulla oblongata)

• Cerebellum

Gray Matter and White Matter in the CNS

Basic Pattern

The CNS exhibits a distinct pattern of gray and white matter distribution:

• Gray matter: Contains neuron cell bodies and short, nonmyelinated neurons.

• White matter: Composed of myelinated axons (with some nonmyelinated axons).

• Spinal cord: Central cavity surrounded by gray matter, with white matter external to gray matter.

Distribution in Brain Regions

Ascent into the brain stem and higher regions introduces additional complexity:

• Brain stem: Additional gray matter nuclei scattered within white matter.

• Cerebrum and cerebellum: Outer layer of gray matter (cortex) and scattered gray matter nuclei within white matter.

• Nuclei- clusters of neuron cell bodies which are hubs for processing and relaying information

• Tracts - Are bundles of axons from neuron**

Ventricles of the Brain

Structure and Function

The brain contains fluid-filled chambers called ventricles, which are continuous with each other and the central canal of the spinal cord. They are filled with cerebrospinal fluid (CSF) and lined by ependymal cells.

• Lateral ventricles: Paired, C-shaped chambers in each hemisphere, separated by the septum pellucidum.

• Third ventricle: Located in the diencephalon, connected to lateral ventricles via interventricular foramen.

• Fourth ventricle: Located in the hindbrain, connected to the third ventricle via the cerebral aqueduct; continuous with the central canal of the spinal cord.

• Openings: Three openings connect the fourth ventricle to the subarachnoid space (paired lateral apertures and median aperture).

Cerebral Hemispheres

Surface Markings and Lobes

The cerebral hemispheres form the superior part of the brain and account for approximately 80% of its mass. Surface features include gyri (ridges), sulci (shallow grooves), and fissures (deep grooves).

• Longitudinal fissure: Separates the two hemispheres.

• Transverse cerebral fissure: Separates cerebrum from cerebellum.

• Lobes: Frontal, Parietal, Temporal, Occipital, Insula (buried under other lobes).

Regions of the Cerebral Hemispheres

Each hemisphere consists of three basic regions:

• Cerebral cortex: Superficial layer of gray matter; site of conscious mind, sensory perception, voluntary motor initiation, communication, memory, and understanding.

• White matter: Deep to the cortex; responsible for communication between regions.

• Basal nuclei: Deep gray matter within white matter; involved in motor control and cognition.

Additional info: The cortex is only 2–4 mm thick but constitutes 40% of the brain's mass.

Cerebral Cortex Functional Areas

Motor Areas

Motor areas are located in the frontal lobe and control voluntary movement.

• Primary motor cortex: Located in the precentral gyrus; controls precise, skilled skeletal muscle movements via pyramidal cells.

• Premotor cortex: Plans movements, coordinates learned and patterned motor skills.

• Broca’s area: Motor speech area, usually in the left hemisphere; directs muscles of speech production.

• Frontal eye field: Controls voluntary eye movements.

• Questions on midterm is the definition

Sensory Areas

Sensory areas are distributed across the parietal, insular, temporal, and occipital lobes, providing conscious awareness of sensation.

• Primary somatosensory cortex: Located in postcentral gyri; receives sensory information from skin and proprioceptors.

• Somatosensory association cortex: Integrates sensory input for object recognition.

• Visual areas: Primary visual cortex (occipital lobe); visual association area interprets visual stimuli.

• Auditory areas: Primary auditory cortex (temporal lobe); auditory association area stores sound memories.

• Vestibular cortex: Responsible for balance awareness.

• Olfactory cortex: Perception of odors.

• Gustatory cortex: Perception of taste.

• Visceral sensory area: Perception of visceral sensations (e.g., upset stomach).

Multimodal Association Areas

These areas receive inputs from multiple sensory areas and are involved in higher cognitive functions.

• Anterior association area (prefrontal cortex): Intellect, cognition, recall, personality, judgment, reasoning, planning.

• Posterior association area: Pattern and face recognition, spatial localization, language comprehension (Wernicke’s area).

• Limbic association area: Emotional impact, memory formation.

Lateralization and Cerebral Dominance

Lateralization refers to the division of labor between hemispheres. The left hemisphere is dominant for language, math, and logic, while the right hemisphere specializes in visual-spatial skills, intuition, emotion, and artistic abilities.

• Cerebral dominance: 90% of humans have left-sided dominance (usually right-handed).

• Communication: Hemispheres communicate via the corpus callosum and other fiber tracts.

Cerebral White Matter

Fiber Types

Cerebral white matter consists of myelinated fibers organized into tracts, classified by their direction:

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

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

• Projection fibers: Connect hemispheres with lower brain or spinal cord.

• Final exam question on how the brain correlates with the muscles

Basal Nuclei (Ganglia)

Structure and Function

Basal nuclei are deep gray matter structures within the cerebrum, closely associated with the diencephalon and midbrain.

• Functions: Influence muscle movements, regulate movement intensity, play roles in cognition and emotion, filter inappropriate responses, inhibit unnecessary movements.

• This can also be apart of Parkinson's disease

The Diencephalon

Components

The diencephalon consists of three paired gray-matter structures surrounding the third ventricle: thalamus, hypothalamus, and epithalamus.

• Thalamus: Relay station for information entering the cerebral cortex; sorts, edits, and relays sensory and motor signals.

• Hypothalamus: Main visceral control center; regulates autonomic functions, emotions, body temperature, hunger, thirst, sleep-wake cycles, and endocrine system.

• Epithalamus: Contains the pineal gland, which secretes melatonin to regulate sleep-wake cycles.

Clinical Relevance

Homeostatic Imbalances

Damage to specific functional areas of the cerebral cortex can result in loss of function, such as stroke or cerebral hemorrhage. Understanding the anatomical location and function of these areas is crucial for clinical diagnosis.

• Example: Loss of speech production may indicate damage to Broca’s area.

• Example: Loss of sensation in a specific body region may indicate damage to the primary somatosensory cortex.

Additional info: Homeostatic imbalances are often referenced as clinical cases (e.g., Homeostatic Imbalance 12.1, 12.2, 12.3).