ch 12.Central Nervous System: Structure and Function

Central Nervous System (CNS): Structure and Function

Nervous System Organization

The nervous system is divided into the central and peripheral components, each with distinct roles in processing and transmitting information throughout the body.

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

• PNS (Peripheral Nervous System): Includes cranial nerves and spinal nerves.

• Sensory (afferent) division: Carries information toward the CNS.

• Motor (efferent) division: Carries information away from the CNS to effectors.

CNS Overview

The CNS acts as the body's main integrative and control center, responsible for processing sensory data and directing responses.

• Main structures: Brain and spinal cord

• Functions: Integration, coordination, and control of bodily activities

Embryonic Development of the CNS

The CNS develops from the embryonic neural tube, which differentiates into primary brain vesicles.

• Neural tube: Embryonic structure giving rise to the CNS

• Primary brain vesicles:

  • Prosencephalon: Forebrain

  • Mesencephalon: Midbrain

  • Rhombencephalon: Hindbrain

Adult Brain Regions

The adult brain is organized into four main regions, each with specialized functions.

• Cerebral hemispheres

• Diencephalon

• Brain stem (composed of midbrain, pons, medulla oblongata)

• Cerebellum

Gray Matter vs. White Matter

Brain and spinal cord tissue is classified based on the presence of neuron cell bodies or myelinated axons.

• Gray matter: Contains neuron cell bodies, dendrites, and glial cells.

• White matter: Composed of myelinated axons (fiber tracts).

• Brain: Gray matter is outer (cortex), white matter is inner.

• Spinal cord: Gray matter is inner (center), white matter is outer.

Ventricles and Cerebrospinal Fluid (CSF)

The brain contains interconnected cavities called ventricles, filled with cerebrospinal fluid (CSF) produced by the choroid plexus.

• CSF functions: Cushions, protects, and provides buoyancy to the brain.

• Choroid plexus: Specialized capillaries that produce CSF.

Cerebral Hemispheres

The cerebral hemispheres constitute the largest portion of the brain, responsible for higher cognitive functions.

• Account for approximately 83% of brain mass.

• Separated by the longitudinal fissure.

• Gyri: Elevated ridges

• Sulci: Shallow grooves

Lobes of the Brain

The cerebral cortex is divided into distinct lobes, each associated with specific functions.

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

• Insula

• Central sulcus: Separates frontal and parietal lobes

Cerebral Cortex Functions

The cerebral cortex is the site of conscious mind, enabling sensation, communication, memory, and voluntary movement.

• Controls the contralateral (opposite) side of the body.

• Responsible for higher-order functions.

Functional Areas of the Cortex

The cortex is organized into motor, sensory, and association areas, each with specialized roles.

• Motor areas: Control voluntary movement

• Sensory areas: Receive sensory input

• Association areas: Integrate and interpret information

Motor Areas

Motor areas are primarily located in the precentral gyrus and are responsible for voluntary movement.

• Precentral gyrus: Primary motor cortex

• Broca’s area: Controls speech production

Sensory Areas

Sensory areas receive and process information from the body and environment.

• Postcentral gyrus: Primary somatosensory cortex

• Visual cortex: Located in the occipital lobe

• Auditory cortex: Located in the temporal lobe

Association Areas

Association areas integrate sensory and motor information, contributing to complex functions such as judgment and planning.

• Prefrontal cortex: Involved in judgment, planning, and personality

Lateralization of Cortical Function

Each cerebral hemisphere specializes in certain functions, a phenomenon known as lateralization.

• Left hemisphere: Language, logic, mathematics

• Right hemisphere: Spatial ability, creativity, emotion

Cerebral White Matter

White matter in the cerebrum consists of myelinated fibers that connect different brain regions.

• Corpus callosum: Major fiber tract connecting left and right hemispheres

Basal Nuclei

Basal nuclei are deep gray matter structures involved in motor control and regulation of movement.

• Located deep within cerebral white matter

• Help initiate and regulate voluntary movements

Diencephalon

The diencephalon is a central brain region containing several important structures.

• Thalamus: Relay station for sensory information

• Hypothalamus: Controls homeostasis (temperature, hunger, hormones, autonomic functions)

• Epithalamus: Includes the pineal gland (regulates sleep-wake cycles)

Brain Stem

The brain stem controls vital automatic functions and serves as a conduit for information between the brain and spinal cord.

• Midbrain: Visual and auditory reflexes

• Pons: Bridge/relay between brain regions

• Medulla oblongata: Regulates heart rate and breathing

Cerebellum

The cerebellum coordinates movement and balance, ensuring smooth and precise motor activity.

• Fine-tunes voluntary movements

• Maintains posture and equilibrium

Limbic System

The limbic system is involved in emotion and memory formation.

• Amygdala: Processes emotions

• Hippocampus: Essential for memory formation

Reticular Formation

The reticular formation maintains alertness and consciousness, with the reticular activating system (RAS) keeping the brain awake and responsive.

Brain Waves

Brain activity can be measured by an electroencephalogram (EEG), which records different types of brain waves.

• Alpha waves: Relaxed, awake state

• Beta waves: Alert, active thinking

• Delta/Theta waves: Associated with sleep

Protection of the Brain

The brain is protected by multiple layers and structures.

• Bone: Skull

• Meninges: Three connective tissue membranes

  • Dura mater

  • Arachnoid mater

  • Pia mater

• Cerebrospinal fluid (CSF): Provides cushioning and buoyancy

Spinal Cord Overview

The spinal cord serves as a two-way communication pathway between the brain and body and is the center for reflexes.

• Extends from the foramen magnum to the level of L1/L2 vertebrae

• Conducts sensory and motor information

Spinal Cord Anatomy

The spinal cord is organized into regions of gray and white matter, each with specific functions.

• Gray matter: Central region, contains neuron cell bodies

• White matter: Outer region, contains myelinated axons

• Dorsal horns: Receive sensory input

• Ventral horns: Send motor output

Spinal Cord Pathways

Information travels through the spinal cord via ascending and descending pathways, often crossing to the opposite side (decussation).

• Ascending tracts: Carry sensory information to the brain

• Descending tracts: Carry motor commands from the brain

• Decussation: Crossing over of nerve fibers to the contralateral side

Summary Table: Major CNS Structures and Functions

Structure	Main Function
Cerebral Cortex	Conscious processing, sensation, voluntary movement
Thalamus	Relay station for sensory information
Hypothalamus	Homeostasis regulation (temperature, hunger, hormones)
Cerebellum	Coordination of movement and balance
Spinal Cord	Communication between brain and body, reflexes

Key Terms and Definitions

• Contralateral: Refers to the opposite side of the body

• Gyri: Elevated ridges on the cerebral cortex

• Sulci: Shallow grooves on the cerebral cortex

• Decussation: Crossing over of nerve fibers in the CNS

• Choroid plexus: Network of capillaries producing CSF

Additional info:

• The pineal gland (part of the epithalamus) secretes melatonin, which regulates circadian rhythms.

• Reflexes are rapid, automatic responses to stimuli, mediated by the spinal cord without direct involvement of the brain.