Chapter 13

Chapter 13 Lecture Notes: Anatomy & Physiology - An Integrative Approach

13.1 Overview of Brain Anatomy

  • Four Major Brain Regions:

    • Cerebrum

    • Two hemispheres

    • Five lobes per hemisphere

    • Diencephalon

    • Brainstem

    • Cerebellum

  • Outer Surface Structure:

    • Gyri: Ridges on the brain's surface.

    • Sulci: Depressions between gyri.

    • Fissures: Deep sulci.

  • Orientation Terms:

    • Anterior = rostral

    • Posterior = caudal

13.1a Brain Anatomy Views

  • Left Lateral View of Human Brain: Identifies various lobes and structures (Figure 13.1a).

  • Inferior View of Human Brain: Further identification of structures (Figure 13.1b).

  • Midsagittal View of Human Brain: Key features displayed (Figure 13.1c).

13.1b Development of Brain Divisions

1. Neurulation

  • Formation of Nervous Tissue: Starts in the 3rd week of embryonic development.

  • Structure Formation:

    • Part of the embryo’s ectoderm layer develops into a thick neural plate.

    • The notochord underneath induces the neural plate to form the neural tube, which will develop into the Central Nervous System (CNS).

2. Neural Tube Formation Steps:

  1. Neural plate develops a neural groove: Lateral margins proliferate into neural folds; tips form neural crest cells (Figure 13.2, part 1).

  2. Neural groove deepens: Folds rise and approach each other (Figure 13.2, parts 2, 3).

  3. Neural tube formation: Folds meet, forming the tube which contains the neural canal.

    • Fusion begins in the middle, progresses outward.

    • Openings at cranial and caudal ends close (neuropores) by the end of the 4th week (Figure 13.2, part 4).

3. Neural Tube Defects

  • Openings at both ends of the neural tube:

    • If they do not close, defects occur:

    • Anencephaly: Substantial or complete absence of a brain; fatal soon after birth.

    • Spina bifida: Failure to close the caudal portion.

      • Spina bifida cystica: Severe; large cyst in the back, potential paralysis.

      • Spina bifida occulta: Less severe; partial bony arch defect, more common.

  • Risk of neural tube defects reduced by adequate intake of Vitamin B12 and folate during pregnancy.

4. Formation of Primary Brain Vesicles

  • By late 4th week:

    • Forebrain (prosencephalon)

    • Midbrain (mesencephalon)

    • Hindbrain (rhombencephalon) (Figure 13.3a).

5. Secondary Brain Vesicles Formation

  • By the 5th week:

    • Telencephalon: becomes the cerebrum.

    • Diencephalon: becomes thalamus, hypothalamus, and epithalamus.

    • Mesencephalon: becomes midbrain.

    • Metencephalon: becomes pons and cerebellum.

    • Myelencephalon: becomes medulla oblongata (Figure 13.3b).

6. Brain Development from 13-26 Weeks

  • Continuation of brain development during this period.

  • Telencephalon envelops the diencephalon and develops surface folds (Figure 13.3c,d).

7. Brain at Birth

  • Most gyri and sulci are present at birth (Figure 13.3e).

13.1c Gray Matter and White Matter Distribution in Brain

  • Brain and spinal cord consist of gray and white tissue:

    • Gray Matter: Composed of neuron cell bodies, dendrites, and unmyelinated axons.

    • Cortex: Superficial layer of gray matter.

    • Nuclei: Regions of gray matter located deep within the brain or near its surface.

    • White Matter: Composed of myelinated axons, organized in bundles termed tracts.

13.2 Protection and Support of the Brain

  • Protection provided by:

    • Bone of the skull

    • Meninges:

    • Three connective tissue layers protecting brainsoft tissue, enclosing blood vessels, nurturing circulation of cerebrospinal fluid.

      • Layers (deep to superficial):

      • Pia Mater: Thin layer, adheres to brain's surface, composed of areolar connective tissue.

      • Arachnoid Mater: Lies external to pia mater; contains a web of collagen and elastic fibers.

      • Dura Mater: Tough outer layer of connective tissue (in two layers).

        • Meningeal Layer (deeper) and Periosteal Layer (superficially fused with cranial bones).

13.2a Clinical Views on Meninges

  • Epidural Hematoma:

    • Pool of blood in the epidural space, often results from head trauma, leads to severe neurological injury if untreated.

  • Subdural Hematoma:

    • Hemorrhage in subdural space typically from ruptured veins; compresses brain tissue.

  • Meningitis:

    • Inflammation of meninges caused by infections; untreated may lead to brain damage.

  • Encephalitis:

    • Inflammation of brain, often viral; may lead to severe symptoms.

13.2b Brain Ventricles

  • Functionality of Ventricles:

    • Cavities lined with ependymal cells containing cerebrospinal fluid (CSF).

    • Connect with other brain ventricles and the central canal of the spinal cord.

  • Structure includes:

    • Two Lateral Ventricles: Separated by septum pellucidum.

    • Third Ventricle: Narrow space in diencephalon connecting to lateral ventricles via interventricular foramen.

    • Fourth Ventricle: Between pons and cerebellum, connects to third ventricle via cerebral aqueduct.

13.2c Cerebrospinal Fluid (CSF)

  • Characteristics:

    • Clear, colorless liquid, provides buoyancy, protection, and stability of environment (nutrient transport, waste protection).

  • Formation: Produced by the choroid plexuses in the ventricles, modified from blood plasma through ependymal cells.

  • CSF Circulation Process:

    • CSF flows into the subarachnoid space; excess CSF leaves through arachnoid villi into dural venous sinuses.

13.2d Blood-Brain Barrier (BBB)

  • Functions:

    • Regulates allowed substances, protects neurons from potentially harmful substances in blood.

    • Composed of specialized endothelial cells with tight junctions; communication maintained through astrocyte perivascular feet.

    • Reduced in certain areas for functional purposes (e.g., choroid plexus).

13.3 Cerebrum

  • Cerebrum Function: Origin of complex intellectual functions including sensory perception, memory, and voluntary muscle control.

  • Cerebral Hemispheres: Left and right hemispheres divided by the longitudinal fissure, connected by white matter tracts (e.g., corpus callosum).

  • Lateralization: Some functions more dominated by one hemisphere (e.g., language in left hemisphere).

13.3a Lobes of the Cerebrum

  • Five Lobes: Frontal, parietal, temporal, occipital, and insula.

    • Frontal Lobe: Controls voluntary movement, concentration, verbal communication, decision-making.

    • Parietal Lobe: Evaluates sensory input regarding shape and texture of objects.

    • Temporal Lobe: Functions in hearing and smell.

    • Occipital Lobe: Responsible for vision.

    • Insula: Involved in memory and taste perception.

13.3b Functional Areas of the Cerebrum

  • Motor Areas:

    • Primary Motor Cortex: Controls skeletal muscle on opposite side of the body.

    • Broca's Area: Controls speech production.

    • Premotor Cortex: Coordinates learned, skilled movements.

  • Sensory Areas:

    • Primary Somatosensory Cortex: Receives input from various sensory receptors.

    • Visual Cortex: Processes visual information.

    • Auditory Cortex: Processes auditory information.

13.3f Cerebral Nuclei

  • Role: Regulate motor output; connected to motor control, mood and emotional responses.

    • Caudate Nucleus: Affects walking rhythm.

    • Lentiform Nucleus: Composed of putamen and globus pallidus.

    • Amygdaloid Body: Involved in emotions.

Clinical View: Common Disorders

  • Cerebral Palsy: Group of neuromuscular disorders resulting from brain damage during developmental stages.

  • Huntington's Disease: Affects basal nuclei causing rapid jerky movements leading to severe influence on cognition.

  • Parkinson’s Disease: Affects movement due to dopamine loss in substantia nigra.

13.4 Diencephalon Components

  • Epithalamus: Contains the pineal gland (melatonin secretion).

  • Thalamus: Relay station for sensory information.

    • Filters and directs signals to appropriate parts of the cortex.

  • Hypothalamus: Important for regulating the autonomic nervous system and hormonal control.

    • Controls temperature, hunger, thirst, sleep-wake cycles, and emotional behavior.

13.5 Brainstem

  • Connects cerebrum with the spinal cord and contains centers for autonomic and reflex functions.

  • Components: Midbrain, pons, medulla oblongata.

13.6 Cerebellum

  • Coordinates and fine-tunes movements, maintains posture and equilibrium.

  • Cerebellar Peduncles: Connect cerebellum to brainstem regions.

13.7 Limbic System

  • System involved in processing emotions and memories; contains structures such as the hippocampus and amygdala.

13.8 Higher-Order Brain Functions

  • Involving learning, memory, reasoning; analysis through electroencephalograms (EEGs) for various conditions (seizures, sleep studies).

13.9 Cranial Nerves

  • 12 Pairs of Cranial Nerves: Originate in the brain and categorized by sensory or motor functions

    • CN I (Olfactory): Sense of smell.

    • CN II (Optic): Visual processing.

    • CN III (Oculomotor): Eye movement.

    • CN IV (Trochlear): Controls superior oblique muscle.

    • CN V (Trigeminal): Sensation in the face; motor functions in mastication.

    • CN VI (Abducens): Controls lateral rectus muscle.

    • CN VII (Facial): Muscles of facial expression and taste.

    • CN VIII (Vestibulocochlear): Balance and hearing.

    • CN IX (Glossopharyngeal): Taste and voluntary control of swallowing.

    • CN X (Vagus): Regulation of cardiac and digestive functions.

    • CN XI (Accessory): Shoulder elevation and head turning.

    • CN XII (Hypoglossal): Tongue movements.

Conclusion

  • The complexity of brain structure and function highlights the importance of understanding neurological processes and their implications on behavior and health. This chapter provides key insights into the anatomical structures and functional systems within the nervous system, paving the way for further exploration and understanding in the field of anatomy and physiology.