Brain

I. EMBRYONIC DEVELOPMENT OF THE BRAIN

  • Neural Plate Formation

    • A 3-week embryo begins forming a neural plate along the ectoderm midline.

  • Neural Tube Development

    • By the 4th week, the neural plate folds back within itself to form the neural tube.

  • Brain and Spinal Cord Formation

    • The brain forms anteriorly while the spinal cord develops posteriorly.

  • Development of Ventricles

    • The ventricles of the brain arise from expansions of the neural tube.

II. REGIONS & ORGANIZATION OF THE BRAIN

  • Regions

    • Cerebral Hemispheres (Cerebrum)

    • Diencephalon (Middle)

    • Brain Stem: Includes Pons, Midbrain, Medulla Oblongata

    • Cerebellum (Back of Brain)

  • Ventricles

    • Hollow chambers filled with cerebrospinal fluid lined with ependymal cells.

    • The largest are the paired lateral ventricles, which are C-shaped and separated by the septum pellucidum (transparent walls).

    • The third ventricle is located in the diencephalon.

    • The cerebral aqueduct connects the third ventricle to the fourth ventricle, dorsal to the pons and superior to the medulla oblongata.

    • The choroid plexus, a knot of capillaries within each ventricle, forms cerebrospinal fluid (CSF).

  • Appearance of Brain

    • Approximately 2 fistfuls of quivering pinkish-gray tissue, wrinkled like a walnut, with the consistency of oatmeal.

    • Average adult brain weighs about 3.5 pounds.

  • Markings on Cerebral Cortex (Neocortex)

    • Cerebral Hemispheres: Most superior part of the brain; 83% of brain mass.

    • Gyri: Elevated ridges on the surface also known as twisty parts.

    • Sulci: Grooves that separate the gyri.

    • Fissures: Deeper grooves that separate the brain into large regions.

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  • Specific Fissures

    • Longitudinal fissure: Separates the brain into right and left hemispheres.

    • Transverse fissure: Separates the cerebellum from the cerebrum.

  • Five Lobes of the Brain

    • Frontal: Anterior lobe.

    • Parietal: Superior lobe, back/top of the brain.

    • Temporal: Lateral lobe; lateral sulcus separates it from frontal lobe.

    • Occipital: Posterior lobe; separated from parietal lobes by the parieto-occipital sulcus.

    • Insula: Buried deep within the lateral sulcus.

  • Central Sulcus

    • Separates frontal and parietal lobes.

    • Precentral gyrus (on frontal lobe) & Postcentral gyrus (on parietal lobe) border either side of the central sulcus.

  • Regions of Cerebral Hemispheres

    • Outer Cortex: Gray matter composed of cell bodies of neurons; highly ridged and convoluted.

    • Internal White Matter: Composed of nerve fiber tracts carrying impulses to and from the cortex.

    • Basal Nuclei: Islands of gray matter regulating voluntary motor activities to the skeletal system.

  • Hemispheric Lateralization

    • Left Hemisphere: Controls verbal language, math calculations, logic, and word recognition.

    • Right Hemisphere: Handles spatial abilities, face recognition, visual imagery, and music.

    • Each hemisphere is responsible for sensory and motor functions of the opposite side of the body.

  • Corpus Callosum

    • A bundle of axons linking the centers of the right and left hemispheres.

  • Major Regions of Cerebral Cortex (Neocortex)

    • Motor Areas: Control voluntary movements.

      • Primary motor cortex located on the precentral gyrus of the frontal lobe, controlling skilled voluntary movements.

      • Premotor cortex controls learned motor skills that are patterned by nature.

      • Broca's area is involved in speech production and located in the left hemisphere.

      • The frontal eye field controls voluntary eye movement.

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  • Sensory Areas of the Cerebral Cortex

    • Provide conscious awareness of sensations from sensory organs.

      • Primary somatosensory cortex (postcentral gyrus of parietal lobes) responsible for receiving information from the entire body via skin receptors and proprioceptors.

      • The sensory cortex varies its dedication based on the number of receptors rather than size.

      • Areas such as the face, lips, and fingertips are the most sensitive.

  • Somatosensory Association Cortex

    • Located posterior to the primary somatosensory cortex; integrates sensory inputs and evaluates sensations.

  • Visual Cortex

    • Located in the occipital lobe, processes visual information from the retina.

  • Auditory Areas

    • Primary auditory cortex found on the temporal lobe interprets sounds including speech.

  • Olfactory and Gustatory Cortex

    • Awareness of smells occurs in the frontal lobe near the eyes and in the temporal lobes.

    • Gustatory cortex is located in the insula for taste awareness.

  • Prefrontal Cortex

    • Most anterior portion of the frontal lobe; integrates information for various actions and involved in cognitive functions such as intelligence and emotions.

  • Wernicke's Area

    • Found in the left hemisphere's temporal lobe, involved in understanding language and sounding out unfamiliar words.

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III. DIENCEPHALON

  • Thalamus

    • Egg-shaped structure serving as a relay station for sensory inputs to the sensory cortex and is the gateway to the cerebral cortex.

  • Hypothalamus

    • Located below the thalamus; crucial for maintaining body homeostasis by regulating the autonomic nervous system and bodily functions such as temperature and hunger.

    • Involves emotional responses and the control of endocrine systems.

  • Pituitary Gland

    • Size of a pea, hangs from the hypothalamus; it releases various hormones that regulate multiple bodily functions.

  • Mammillary Bodies

    • Paired structures involved in memory relay.

  • Epithalamus

    • Most dorsal portion of the diencephalon including the pineal gland, which secretes melatonin to regulate sleep-wake cycles.

IV. BRAIN STEM

  • Structure

    • Approximately 3 inches long, consisting of the midbrain, pons, and medulla oblongata; provides pathways for nerve tracts.

  • Midbrain

    • Involved in pain suppression and links emotional responses to the autonomic nervous system.

    • Contains cranial nerve nuclei including the substantia nigra, associated with dopamine release.

  • Pons

    • Relays conversations between the motor cortex and cerebellum and hosts cranial nerves involved in facial sensations and movements.

  • Medulla Oblongata

    • Regulates vital activities, including cardiovascular and respiratory centers.

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V. CEREBELLUM

  • Appearance

    • Large cauliflower-like structure composed of two hemispheres; 11% of brain mass.

    • Outer cortex is gray matter, while the inner is white matter known as the arbor vitae.

  • Function

    • Coordinates muscle contractions and maintains equilibrium by processing sensory information.

VI. FUNCTIONAL BRAIN SYSTEMS

  • Limbic System

    • Involves emotional responses and connects with memory formation.

  • Reticular Formation

    • Maintains awareness of stimuli and regulates sleep-wake cycles.

VII. PROTECTION OF CNS

  • Physical Protection

    • The cranium and vertebrae encase the brain and spinal cord.

  • Cerebrospinal Fluid (CSF)

    • Acts as a liquid cushion for the brain, circulating continuously through the ventricles and protecting against blows.

  • Meninges

    • Three protective membranes: Dura mater (outer), arachnoid mater (middle), and pia mater (inner).

  • Blood-Brain Barrier

    • Composed of impermeable capillaries that maintain stable brain environment while preventing harmful substances from entering.

VIII. BRAIN DISFUNCTIONS

  • Traumatic Brain Injuries (TBI)

    • Include concussions, cerebral edema, and chronic traumatic encephalopathy (CTE).

  • Cerebrovascular Accident (CVA)

    • Also known as a stroke, can be ischemic from clots or hemorrhagic from bleeding.

  • Transient Ischemic Attacks (TIA)

    • Temporary episodes akin to strokes; symptoms brief but serious.

  • Alzheimer's Disease

    • Progressive degeneration leading to dementia.

  • Cerebral Palsy

    • Neuromuscular disability due to motor cortex damage.

  • Spina Bifida

    • Neural tube defect where spinal cord membranes close incompletely.

IX. SPINAL CORD

  • Protection

    • The spinal cord is safeguarded by vertebrae, meninges, and cerebrospinal fluid.

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  • Gray and White Matter

    • Gray matter is butterfly-shaped; dorsal horns contain sensory neurons, while ventral horns hold motor neurons.

  • Disorders of the Spinal Cord

    • Include spastic paralysis, paraplegia, and multiple conditions affecting motor function.

  • Amyotrophic Lateral Sclerosis (ALS)

    • A progressive neuromuscular disease affecting motor neurons, leading to loss of function.