Chapter 12: The Central Nervous System – Structure and Function

Overview of the Nervous System

Main Divisions: CNS and PNS

The nervous system is divided into the Central Nervous System (CNS) and Peripheral Nervous System (PNS). The CNS consists of the brain and spinal cord, while the PNS includes all neural tissue outside the CNS.

• CNS: Integrates and processes information; includes the brain (cerebrum, diencephalon, cerebellum, brainstem) and spinal cord.

• PNS: Transmits sensory and motor signals between the CNS and the rest of the body.

Example: Sensory input from the skin travels via the PNS to the CNS for processing.

Development of the Brain

Embryonic Brain Vesicles

The brain develops from primary and secondary vesicles during embryogenesis, which differentiate into major adult brain structures.

• Primary vesicles: Prosencephalon, Mesencephalon, Rhombencephalon

• Secondary vesicles: Telencephalon, Diencephalon, Metencephalon, Myelencephalon

• Adult structures: Cerebrum, diencephalon, midbrain, pons, medulla oblongata, cerebellum

Additional info: The neural tube forms the basis for the entire CNS.

Organization of the CNS

Major Components

• Cerebrum: Higher mental functions

• Diencephalon: Thalamus, hypothalamus, epithalamus, subthalamus

• Cerebellum: Coordination of movement

• Brainstem: Midbrain, pons, medulla oblongata

• Spinal Cord: Conduction of signals to/from the brain

The Cerebrum

Structure and Function

The cerebrum is responsible for higher order mental functions such as reasoning, planning, and voluntary movement.

• Gray matter: Cerebral cortex and deep nuclei (basal nuclei, limbic system)

• White matter: Myelinated axon tracts connecting different brain regions

• Gyri: Ridges on the surface

• Sulci: Grooves between gyri

• Fissures: Deep grooves dividing major regions

Anatomy of the Cerebral Hemispheres

• Longitudinal fissure: Divides left and right hemispheres

• Lobes: Frontal, parietal, occipital, temporal, insula

Cerebral Cortex

The cerebral cortex is the most complex region, involved in conscious processes and higher functions.

• Thin sheet of gray matter (1.5–4.5 mm thick)

• Mostly neocortex: neurons organized into six layers

• Contralateral control: each hemisphere controls the opposite side of the body

• Lateralization: functions are not symmetrical between hemispheres

Cerebral White Matter

• Commissural tracts: Connect left and right hemispheres (e.g., corpus callosum)

• Association tracts: Connect areas within the same hemisphere

• Projection tracts: Connect cerebrum with lower brain regions and spinal cord (e.g., internal capsule)

Functional Organization of the Cerebral Cortex

Early Studies and Modern Methods

• Brodmann areas: 52 functional regions based on cytoarchitecture

• PET scan: Measures blood flow changes with radioactive tracers

• fMRI: Measures blood oxygenation changes

• EEG: Records electrical activity; used in epilepsy diagnosis

• Awake brain surgery: Used to map functional areas during surgery

Motor Areas

• Primary motor cortex: Located in precentral gyrus of frontal lobe; controls voluntary movement

• Motor homunculus: Map of body regions controlled by specific cortical areas

• Inputs: Premotor cortex, supplementary motor area, thalamus, cerebellum

• Outputs: Lower motor neurons, spinal cord, basal nuclei, cerebellum

Sensory Areas

• Somatosensory: Parietal lobe

• Visual: Occipital lobe

• Auditory: Temporal lobe

• Olfactory: Medial temporal lobe

• Gustatory: Insula and parietal lobe

• Vestibular: Parietal and temporal lobes

Somatic Sensation: Parietal Lobe

• Primary somatosensory cortex: Receives information from skin and muscles; spatial discrimination

• Somatosensory association cortex: Integrates sensory information for comprehensive understanding

Visual Areas: Occipital Lobe

• Primary visual cortex: Receives input from retinas

• Visual association cortex: Object recognition and location

Auditory Areas: Temporal Lobe

• Primary auditory cortex: Pitch, rhythm, loudness

• Auditory association area: Recognition of sounds, memory of sounds

Multimodal Association Areas & Higher Order Functions

• Anterior association area (Prefrontal cortex): Intellect, cognition, personality, planning, judgment

• Posterior association area: Integration of sensory stimuli, pattern and face recognition, spatial awareness, language comprehension

Cerebral Lateralization

• Emotional functions: Left frontal cortex (positive emotions), right frontal cortex (negative emotions)

• Attention: Right parietal cortex

• Facial recognition: Right temporal cortex

• Language: Left temporal cortex

Language Association Areas

• Broca's area: Speech production, grammar, syntax (frontal lobe)

• Wernicke's area: Language comprehension (temporal and parietal lobes)

Examples of aphasia: Broca's aphasia (impaired speech production), Wernicke's aphasia (impaired comprehension)

Basal Nuclei

Structure and Function

• Located deep within cerebral hemispheres

• Includes caudate nucleus, putamen, globus pallidus

• Initiate voluntary movement, inhibit involuntary movement

• Connected with substantia nigra (midbrain)

Functional Brain System: The Limbic System

Role in Emotion and Memory

• Includes hippocampus, amygdala, cingulate gyrus

• Regulates emotions (pleasure, fear, anger, aggression)

• Involved in learning and memory

Organization of the CNS: Diencephalon

Components

• Thalamus: Relay station for sensory and motor signals; gateway to cerebral cortex

• Hypothalamus: Homeostasis, autonomic control, endocrine regulation

• Epithalamus: Pineal gland (melatonin secretion, sleep/wake cycle)

• Subthalamus: Movement control (connected to basal nuclei)

Functions of Thalamic Nuclei

• Relay sensory and motor signals to cortex

• Integrate and process information

• Regulate cortical activity and consciousness

The Hypothalamus

• Major center for integration

• Regulates homeostasis, motivational state, endocrine functions

• Controls circadian rhythms and sleep-wake cycles

The Cerebellum

Structure and Function

• Posterior/inferior portion of brain

• Coordinates movement, reduces motor error

• Divided into hemispheres and lobes

• Connected to brainstem via cerebellar peduncles

The Brainstem

Structure and Function

• Evolutionarily ancient; controls basic survival functions

• Subdivisions: midbrain, pons, medulla oblongata

• Contains cranial nerve nuclei, reticular formation

• Regulates breathing, heart rate, reflexes, movement, alertness

Summary Table: Major Brain Structures and Functions

Structure	Main Functions
Cerebrum	Higher mental functions, voluntary movement, sensory perception
Diencephalon	Relay sensory/motor signals, homeostasis, endocrine regulation
Cerebellum	Coordination of movement, motor learning
Brainstem	Basic survival functions, cranial nerve nuclei, alertness
Basal Nuclei	Initiate/inhibit movement, behavior, cognition
Limbic System	Emotion, memory, motivation

Additional info: This guide covers the foundational anatomy and physiology of the central nervous system, focusing on structure, function, and integration of major brain regions.