Neuroscience Overview: The Brain Structure

The Brain - Overview

• The brain is comprised of the forebrain, hindbrain, and midbrain.
• The forebrain is the largest part of the brain and contains telencephalon (Cerebrum), Diencephalon (thalamus, hypothalamus, epithalamus), and the Limbic System.
• The hindbrain includes the Cerebellum, Brainstem, and Reticular Formation.
• The midbrain connects the hindbrain and forebrain.
• The forebrain, hindbrain, and midbrain are enlargements of the neural tube.

The Cerebral Peduncles

• The cerebral peduncles are located ventrally in the midbrain.
• The peduncles contain descending motor pyramidal tracts.
• The corticospinal tract is a motor pathway that descends from the cerebral cortex to the spinal cord.

The Tectum

• The Tectum is located on the dorsal side of the midbrain.
• The Latin word for roof is tectum referring to its location above the cerebral aqueduct.
• The Tectum consists of the Corpora Quadrigemina, four bumps that include two superior colliculi (visual reflex center) and two inferior colliculi (auditory reflex centers).

The Tegmentum

• The Tegmentum is located in the midbrain.
• The tegmentum contains the red nucleus and the substantia nigra.
• The red nucleus, a subcortical motor center, is involved in motor coordination.
• The substantia nigra is a cluster of pigmented neurons that produces dopamine and plays a role in motor control.
• The tegmentum extends through the brainstem, anterior to the ventricular space.

The Crus Cerebri

• The Crus Cerebri is located on each side of the midbrain.
• The crus cerebri contains the corticospinal (motor) tract.
• The crus cerebri carries motor messages from the cerebral cortex to the spinal cord.

The Medulla Oblongata

• The Medulla Oblongata is located in the hindbrain.
• All ascending (sensory) and descending (motor) fibers connecting the brain and spinal cord pass through the medulla.
• The medulla oblongata contains visceral nuclei responsible for regulating vital functions including:
  • Respiratory rate
  • Heart rate
  • Blood pressure
  • Coughing
  • Vomiting

The Pyramids

• The Pyramids are located on the ventral side of the medulla.
• The Pyramids contain fibers from the corticospinal tract.
• The fibers from the corticospinal tract cross over in the pyramids before entering the spinal cord.

The Reticular Formation

• The Reticular Formation is a web-like structure found in the brainstem.
• The formation is a network of interconnected neurons and nuclei.
• The functions of the reticular formation include:
  • Relaying sensory information
  • Regulating skeletal and visceral muscle activity
  • Filtering out repetitive stimuli (habituation)
  • Playing a role in the sleep-wake cycle
  • Maintaining consciousness

The Reticular Activating System (RAS)

• The Reticular Activating System (RAS) is a component of the Reticular Formation.
• The RAS is responsible for arousal and wakefulness.
• The RAS coordinates the sleep-wake cycle and wakefulness.

The Cerebellum

• The Cerebellum is located in the hindbrain.
• The Cerebellum consists of two hemispheres (right and left) connected by the vermis.
• The cerebellum consists of a cortex of gray matter with folds called folia and white matter in the interior known as the arbor vitae.
• The Cerebellum receives sensory information related to body position and movement from the spinocerebellar tract.
• The Cerebellum regulates motor output, ensuring coordination and balance.