Anatomy of the Brain and Spinal Cord: Key Structures and Functions

Brain Anatomy

Cerebrum

The cerebrum is the largest part of the brain, responsible for higher brain functions such as thought, memory, and voluntary movement. It is divided into four main lobes, each with distinct functions.

• Four Main Lobes: Frontal, Parietal, Temporal, and Occipital lobes.

• Gyri: Elevated ridges on the cerebral surface that increase surface area.

• Sulci: Shallow grooves separating gyri.

• Longitudinal Fissure: Deep groove dividing the cerebrum into left and right hemispheres.

• Transverse Fissure: Separates the cerebrum from the cerebellum.

• Lateral Sulcus: Separates the temporal lobe from the frontal and parietal lobes.

• Corpus Callosum: Large band of neural fibers connecting the two cerebral hemispheres.

• Fornix: Arching, fibrous band involved in memory.

• Lateral Ventricles: Paired cavities within the cerebrum containing cerebrospinal fluid (CSF).

• Septum Pellucidum: Thin membrane separating the lateral ventricles.

Diencephalon

The diencephalon is located beneath the cerebrum and contains several important structures involved in sensory processing and endocrine function.

• Epithalamus: Contains the pineal gland, which regulates circadian rhythms.

• Pineal Gland: Secretes melatonin.

• Choroid Plexus: Produces cerebrospinal fluid.

• Thalamus: Relay station for sensory information.

• Intermediate Mass: Connects the two thalamic nuclei.

• Hypothalamus: Regulates homeostasis, endocrine functions, and autonomic nervous system.

• Mammillary Bodies: Involved in memory.

• Pituitary: Master endocrine gland.

• Infundibulum: Stalk connecting hypothalamus to pituitary.

• Optic Chiasma: Site where optic nerves cross.

Brainstem

The brainstem connects the brain to the spinal cord and controls vital functions such as breathing and heart rate.

• Pons: Relays signals between cerebrum and cerebellum; involved in sleep and respiration.

• Medulla Oblongata: Controls autonomic functions like heart rate and breathing.

• Pyramids: Motor fibers crossing to opposite sides.

• Olives: Relay sensory information.

• 4th Ventricle: Contains CSF; located between pons and cerebellum.

Cerebellum

The cerebellum is responsible for coordination, balance, and fine motor control.

• Posterior and Anterior Lobes: Main divisions of the cerebellum.

• Vermis: Central region connecting the two hemispheres.

• Folium (Folium/Folia): Leaf-like folds increasing surface area.

• Sulci: Grooves between folia.

• Arbor Vitae: Tree-like arrangement of white matter.

Midbrain

The midbrain is involved in vision, hearing, motor control, sleep/wake, and arousal.

• Colliculi (Corpora Quadrigemina): Superior colliculi (visual reflexes) and inferior colliculi (auditory reflexes).

• Cerebral Aqueduct: Connects the third and fourth ventricles.

Spinal Cord Anatomy

External Features

The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.

• Posterior Median Sulcus: Shallow groove on the dorsal side.

• Anterior Median Fissure: Deep groove on the ventral side.

Internal Structure

• Columns (Funiculi): Bundles of nerve fibers; anterior, posterior, and lateral columns.

• Horns: Regions of gray matter; anterior (motor), posterior (sensory), and lateral (autonomic).

• Central Canal: Small channel containing CSF.

• Gray Commissure: Connects the two sides of gray matter.

Spinal Nerves and Roots

• Dorsal Root: Contains sensory (afferent) fibers.

• Dorsal Root Ganglion: Contains cell bodies of sensory neurons.

• Ventral Root: Contains motor (efferent) fibers.

• Spinal Nerve: Formed by the union of dorsal and ventral roots; mixed nerve carrying both sensory and motor information.

Example: Pathway of a Reflex Arc

• Sensory input enters via the dorsal root.

• Interneurons in the gray matter process the signal.

• Motor output exits via the ventral root.

Additional info: The structures listed are essential for understanding the organization and function of the central nervous system, as covered in ANP chapters on the nervous system and its anatomy.