Anatomy & Physiology: Structure and Function of the Brain

Development and Structure of the Brain

Development of the Brain

The brain develops from the neural tube, which forms three primary vesicles that give rise to the major regions of the adult brain.

• Forebrain (prosencephalon): Develops into the cerebrum and diencephalon in adults.

• Midbrain (mesencephalon): Remains the midbrain in the adult brain stem.

• Hindbrain (rhombencephalon): Becomes the pons, medulla oblongata, and cerebellum.

If the neural tube does not close completely, it can result in neural tube defects such as spina bifida. Other abnormalities include microcephaly, hydrocephaly, and cerebral palsy.

Regions of the Brain

• Cerebral hemispheres

• Diencephalon

• Brain stem (midbrain, pons, medulla)

• Cerebellum

Brain Ventricles

Ventricular System

The brain contains four interconnected ventricles filled with cerebrospinal fluid (CSF):

• Lateral ventricles: One in each hemisphere, separated by the septum pellucidum.

• Third ventricle: Located in the diencephalon, communicates with lateral ventricles via the interventricular foramen and with the fourth ventricle via the cerebral aqueduct.

• Fourth ventricle: Located dorsal to the pons and superior to the medulla, connects to the central canal of the spinal cord and has three openings (apertures) to the subarachnoid space.

Structure of the Cerebrum

Cerebral Hemispheres

The cerebrum consists of two hemispheres that are mirror images of each other, separated by the longitudinal fissure and connected by the corpus callosum.

• Gyri: Elevated ridges (convolutions) on the surface.

• Sulci: Shallow grooves separating gyri.

• Fissures: Deeper grooves, such as the longitudinal fissure (separates hemispheres) and transverse cerebral fissure (separates cerebrum from cerebellum).

Lobes of the Cerebrum

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

• Insula: Lies deep within the lateral sulcus.

Cerebral Cortex

• Thin layer of gray matter covering the surface of the cerebrum.

• Contains approximately 40% of brain mass.

• Responsible for conscious thought, perception, and voluntary movement.

Functions of the Cerebral Cortex

General Functions

• Responsible for higher brain functions: sensory perception, voluntary movement, reasoning, memory, and language.

• Divided into three main functional areas: motor, sensory, and association areas.

• Each hemisphere controls the opposite side of the body (contralateral control).

• Hemispheres are specialized for different functions (lateralization).

Motor Areas

• Primary Motor Cortex: Located in the precentral gyrus of the frontal lobe; contains pyramidal cells that form the pyramidal (corticospinal) tracts for voluntary movement.

• Premotor Cortex: Anterior to primary motor cortex; involved in planning and coordinating learned motor skills.

• Broca's Area: Usually in the left hemisphere; controls muscles involved in speech production.

• Frontal Eye Field: Controls voluntary eye movements.

Sensory Areas

• Primary Somatosensory Cortex: Located in the postcentral gyrus of the parietal lobe; receives sensory input from skin and proprioceptors.

• Somatosensory Association Area: Posterior to primary somatosensory cortex; integrates and interprets sensory input.

• Visual Areas: Occipital lobe; includes primary visual cortex and visual association area.

• Auditory Areas: Temporal lobe; includes primary auditory cortex and auditory association area.

• Olfactory Cortex: Frontal lobe and medial aspect of temporal lobe; perception of smell.

• Gustatory Cortex: Insula; perception of taste.

• Vestibular (Equilibrium) Cortex: Insula; conscious awareness of balance.

Association Areas

• Prefrontal Cortex: Involved in intellect, complex learning, personality, and decision making.

• General Interpretation Area: Integrates information from multiple sensory association areas (usually in the left hemisphere).

• Language Areas: Includes Wernicke's area (language comprehension) and Broca's area (speech production).

• Visceral Association Area: Insula; conscious perception of visceral sensations.

Lateralization of Cortical Function

• Each hemisphere has unique functions; left is usually dominant for language, math, and logic; right is dominant for visual-spatial skills, emotion, and artistic abilities.

White Matter and Basal Nuclei

White Matter

• Consists of myelinated fibers connecting different brain regions.

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

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

• Projection fibers: Connect the cortex with lower brain regions and spinal cord.

Basal Nuclei

• Subcortical nuclei involved in motor control, cognition, and emotion.

• Include the caudate nucleus, putamen, and globus pallidus.

• Regulate initiation and termination of movements and inhibit unnecessary movements.

Diencephalon

Components of the Diencephalon

• Thalamus: Relay station for sensory information to the cerebral cortex.

• Hypothalamus: Main visceral control center; regulates homeostasis (body temperature, hunger, thirst, sleep-wake cycles, endocrine functions).

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

Brain Stem

Structure and Function

The brain stem connects the cerebrum to the spinal cord and consists of the midbrain, pons, and medulla oblongata. It contains nuclei for cranial nerves and controls vital functions such as heart rate, respiration, and blood pressure.

• Midbrain (mesencephalon): Contains cerebral peduncles, cerebral aqueduct, and corpora quadrigemina (superior and inferior colliculi).

• Pons: Contains nuclei that relay signals from the forebrain to the cerebellum and medulla.

• Medulla oblongata: Contains centers for cardiovascular, respiratory, and reflex functions.

Table: Major Brain Regions and Their Functions

Region	Main Functions
Cerebral Cortex	Conscious thought, voluntary movement, sensory perception, language, reasoning
Basal Nuclei	Motor control, cognition, emotion
Thalamus	Relay of sensory information to cortex
Hypothalamus	Homeostasis, endocrine regulation, autonomic control
Brain Stem	Vital functions (heart rate, breathing), cranial nerve nuclei
Cerebellum	Coordination of movement, balance, posture

Key Terms and Definitions

• Gyri: Elevated ridges on the cerebral cortex.

• Sulci: Shallow grooves separating gyri.

• Fissure: Deep groove separating large brain regions.

• Pyramidal cells: Large neurons in the primary motor cortex.

• Contralateral: Opposite side control (each hemisphere controls the opposite side of the body).

• Lateralization: Specialization of function in each hemisphere.

• Association area: Region of the cortex integrating information from multiple sources.

Additional info:

• Broca's area and Wernicke's area are critical for language production and comprehension, respectively.

• The corpus callosum is the largest commissural fiber tract connecting the two hemispheres.

• Damage to specific cortical areas can result in loss of function, such as aphasia (language impairment) or agnosia (inability to recognize objects).