The Brain: Structure and Function

The Brain

Four Main Parts

  • The brain consists of four main parts:
    1. Cerebrum
    2. Brain stem
    3. Cerebellum
    4. Diencephalon

Major Parts of the Brain

  • Cerebrum:
    • Includes the cerebral hemispheres.
    • Responsible for higher thinking.
    • Gyri: The folds on the surface of the cerebrum.
    • Sulci: The grooves on the surface of the cerebrum.
  • Brain Stem:
    • Includes the midbrain, pons, and medulla oblongata.
    • Controls vital functions.
  • Cerebellum:
    • Responsible for balance and equilibrium.
  • Diencephalon:
    • Located deep within the cerebrum.
    • Acts as a homeostasis center.

Lobes and Key Structures

  • Lobes:
    • Frontal Lobe
    • Parietal Lobe
    • Occipital Lobe
    • Temporal Lobe
  • Key Structures:
    • Lateral Sulcus
    • Central Sulcus
    • Pre-central Gyrus
    • Post-Central Gyrus
    • Cerebellum
    • Brain Stem
    • Corpus Callosum
    • Thalamus
    • Hypothalamus
    • Midbrain
    • Pons
    • Medulla

Brain Matter

  • Gray Matter (Cortex):
    • Composed of cell bodies of neurons.
  • White Matter (Tracts):
    • Composed of axons of neurons.
    • Located deep within the brain.

Areas of the Cerebrum and Their Functions

  • Frontal Lobe:
    • Voluntary motor functions
    • Judgment
    • Planning
    • Memory
  • Parietal Lobe:
    • Input from sensory neurons
    • Taste (Gustatory Cortex)
  • Occipital Lobe:
    • Visual center
  • Temporal Lobe:
    • Hearing
    • Smell
    • Learning
    • Memory
    • Visual recognition

Functional Areas of the Cortex

  • Motor Cortex:
    • Located in the precentral gyrus.
  • Sensory Cortex:
    • Located in the postcentral gyrus.
  • Broca's Area (Motor Speech):
    • Generates motor signals for the larynx, tongue, cheeks, and lips.
    • Transmits signals to the primary motor cortex for action.
    • Lesion (damage) results in slow speech.
  • Wernicke's Area (Sensory Interpretation):
    • Permits recognition of spoken and written language.
    • Creates plan of speech.
    • Lesion (damage) results in speech that doesn't make sense.
  • Visual Center:
    • Located in the occipital lobe.
  • Auditory Center:
    • Located in the temporal lobe.

Meninges

  • The meninges are protective membranes surrounding the brain and spinal cord.
  • Layers:
    • Dura Mater
    • Arachnoid Mater
    • Pia Mater

Dura Mater

  • Fibrous connective tissue.
  • Periosteal Layer: Fused to the skull (not seen in the spinal cord).
  • Meningeal Layer (Deep Layer): Extends down into the longitudinal fissure as the Falx Cerebri.

Arachnoid Mater

  • Closely adheres to the Dura Mater.
  • Subarachnoid Space: Located between the Arachnoid and Pia Mater; filled with Cerebrospinal Fluid (CSF).

Pia Mater

  • Closest to the brain.
  • Follows into the sulci of the brain.

Arachnoid Vili

  • Protrusions into Superior Sagittal sinuses.

Falx Cerebri

  • Dura mater in longitudinal fissure.

Hematoma

  • Epidural Hematoma:
    • Blood collects between the Dura Mater and the skull.
    • Caused by a blow to the head.
    • Increases pressure against the brain, leading to DAMAGE.
  • Subdural Hematoma:
    • Blood collects between the Dura Mater and the Arachnoid Mater.
    • Increases pressure against the brain, leading to DAMAGE.

Cerebrospinal Fluid (CSF)

  • Location: Ventricles of the brain and subarachnoid space.
  • Functions:
    1. Maintain proper environment for the brain.
    2. Nutrition/excretory function.
    3. Protection.
    4. Regulate intracranial pressure.
  • Composition:
    • 99% water.
    • Ions: Na^+, Cl^-, Mg^{++}.
    • Much less protein than blood.
    • Glucose (70% of blood).
    • Fewer cells.
  • Production:
    • Choroid plexus filters filtrate containing glucose, oxygen, vitamins, and ions (Na^+, Cl^-, Mg^{2+}, etc.).
  • Flow:
    • Choroid plexus in lateral ventricles → Third ventricle → Cerebral aqueduct → Fourth ventricle → Subarachnoid space (or down the central canal) → Arachnoid villi → Superior sagittal sinus

Ventricles

  • Lateral Ventricles
  • Intraventricular Foramen
  • Third Ventricle
  • Cerebral Aqueduct
  • Fourth Ventricle

Hydrocephalus

  • Occurs when more CSF is produced than is reabsorbed.

Terminology

  • Longitudinal Fissure: Separates the right and left hemispheres.
  • Gyrus (Gyri): The folds on the surface of the brain.
  • Sulcus (Sulci): The grooves on the surface of the brain.
  • Falx Cerebri: A dural fold located in the longitudinal fissure.
  • Lobes: Frontal, parietal, occipital, and temporal.

Cerebral Cortex

  • The cortex is made up of areas that control major functions, because this is where most of the NEURONS in the brain are located!
  • Right side of the brain controls the left side of the body.
  • Left side of the brain controls the right side of the body.

Functional Areas of the Cortex

  1. Motor: Precentral gyrus of the frontal lobe controls voluntary movements.
  2. Sensory: Postcentral gyrus of the parietal lobe receives sensory information.
  3. Broca: Motor speech area in the frontal lobe.
  4. Wernicke: Speech interpretation area in the parietal lobe.
  5. Visual Center: Occipital lobe.
  6. Auditory Center: Temporal lobe.

Motor and Sensory Cortex

  • Motor Cortex (Precentral Gyrus):
    • Controls motor movements on the opposite side of the body.
  • Somatic Sensory Cortex (Postcentral Gyrus):
    • Receives almost all sensory information.

Basal Nuclei

  • Masses of gray matter deep within the white matter.
  • Send and receive signals from the substantia nigra (midbrain) and the cerebral cortex.
  • Functions:
    • Control of