CNS Anatomy and Spinal Cord Overview

CNS Anatomy

• Central Nervous System (CNS): Composed of brain and spinal cord.
• Gray Matter: Contains unmyelinated cell bodies, dendrites, and axons.
• White Matter: Primarily composed of myelinated axons.

Spinal Cord

• Spinal Cord: Major pathway for information flow between the brain and the body (skin, muscles, joints).
• Regions: Divided into cervical, thoracic, lumbar, sacral, and coccygeal segments.
• Spinal Nerves: Each segment gives rise to a pair of spinal nerves, which split into roots:
  • Dorsal Roots: Carry sensory information into the spinal cord (afferent).
  • Ventral Roots: Carry motor information out of the spinal cord (efferent).
• Nuclei: Clusters of neuronal cell bodies within the CNS.
• Ganglia: Clusters of neuronal cell bodies within the peripheral nervous system (PNS).

Spinal Reflexes

• Spinal Reflexes: The spinal cord can initiate a response to a stimulus without input from the brain.
• Importance: Crucial for body movement, enabling rapid responses to stimuli.

Brain

• Brain: The organ responsible for complex cognitive functions and human attributes.
• Structure: Weighs around 1.4 kg, contains 85 billion neurons with thousands of synapses.
• Major Divisions:
  • Cerebrum
  • Cerebellum
  • Diencephalon
  • Medulla
  • Midbrain
  • Pons

Brainstem

• Brainstem: The oldest and most primitive region of the brain, consisting of:
  • Medulla
  • Pons
  • Midbrain
• Function:
  • Relays ascending and descending tracts.
  • Contains 11 out of 12 cranial nerves, responsible for head & neck sensory and motor information.
  • Contains nuclei involved in basic bodily functions, including sleep-wake cycles, muscle tone, breathing, blood pressure, and pain modulation.

Medulla

• Structure: Contains ascending (sensory) and descending (motor) tracts.
• Function:
  • 90% of corticospinal tracts decussate (cross over) at the pyramids.
  • Control of involuntary functions, including cardiovascular and respiratory centers.
  • Contains centers for vomiting, swallowing, coughing, sneezing, and hiccupping.

Pons and Midbrain

• Pons:
  • Contains nuclei and tracts responsible for relaying information between the cerebellum and cerebrum.
  • Assists the medulla in regulating breathing.
• Midbrain:
  • Connects the lower brainstem to the diencephalon.
  • Primary control center for eye movement.
  • Relays auditory and visual reflexes.
  • Contains the substantia nigra.

Reticular Formation

• Reticular Formation:
  • Network of neuronal cell bodies distributed throughout the brainstem.
  • Involved in:
    • Consciousness, arousal, attention
    • Sensory information filtering
    • Muscle tone regulation
    • Vital function control

Cerebellum

• Cerebellum: Second largest brain structure consisting of two hemispheres.
• Function:
  • Processes sensory information and coordinates movement execution.
  • Sends feedback signals to the cerebral cortex to correct movements and ensure smoothness.
  • Regulates posture and balance.

Diencephalon

• Diencephalon: Region located between the brainstem and cerebrum.
• Structures:
  • Thalamus: Relay center for sensory and motor information to the cerebrum.
  • Hypothalamus: Homeostasis control center, influencing autonomic and endocrine functions.
• Endocrine Structures:
  • Pineal gland: Produces melatonin, involved in sleep-wake cycles.
  • Pituitary gland: Anterior and posterior lobes contribute to endocrine function.

Pituitary

• Pituitary Gland: A key player in the endocrine system, receiving control from the hypothalamus.
• Posterior Pituitary: Neural tissue storing and releasing hormones produced by the hypothalamus.
• Anterior Pituitary: Endocrine tissue that releases hormones under hypothalamic control.

Cerebrum

• Cerebrum: Largest and most distinctive part of the brain.
• Gray Matter: Contains:
  • Cerebral cortex: Responsible for higher-level processing
  • Basal ganglia: Regulate movement initiation and termination
  • Limbic system: Involved in emotions and motivation
• Hemispheres: Two hemispheres connected by the corpus callosum.
• Lobes: Each hemisphere divided into four lobes: frontal, parietal, temporal, occipital.

Basal Ganglia

• Basal Ganglia: Group of nuclei (globus pallidus, putamen, caudate nucleus) responsible for movement regulation.
• Function:
  • Receives input from the cerebral cortex
  • Provides output to motor areas of the cortex.

Limbic System

• Limbic System: Often referred to as the "emotional brain."
• Function:
  • Controls a wide range of emotions including pain, pleasure, docility, affection, and anger.