Central Nervous System (CNS)

Overview of the CNS

The central nervous system consists of the brain and spinal cord, serving as the main control center for the body. It processes sensory information, coordinates voluntary and involuntary responses, and is essential for cognition, emotion, and homeostasis.

• Brain: The primary organ for processing information, thought, memory, and emotion.

• Spinal Cord: Transmits signals between the brain and the rest of the body; involved in reflexes.

Spinal Cord

Anatomy and Structure

• Gray Matter: Contains neuron cell bodies; organized into horns (anterior, posterior, lateral).

• White Matter: Composed of myelinated axons; organized into columns (funiculi).

• Central Canal: A small channel in the center of the spinal cord containing cerebrospinal fluid (CSF).

Functions and Pathways

• Posterior Gray Horns: Contain sensory neurons. Damage leads to loss of sensory function.

• Anterior Gray Horns: Contain motor neurons. Damage leads to motor deficits or paralysis.

• Ascending Tracts: Carry sensory information to the brain.

• Descending Tracts: Carry motor commands from the brain to the body.

Decussation and Commissures

• Decussation: The crossing of nerve fibers from one side of the CNS to the other, often in the medulla oblongata or spinal cord.

• Commissures: Bundles of nerve fibers that connect the two sides of the CNS (e.g., anterior white commissure).

Spinal Nerves and Plexuses

• Brachial Plexus: Network of nerves supplying the upper limb.

• Lumbar Plexus: Supplies the lower limb.

• Cranial Nerves: Twelve pairs, some sensory, some motor, some both.

Reflexes

• Reflex Arc: The neural pathway involved in a reflex action, typically including a sensory neuron, interneuron, and motor neuron.

Brain Anatomy and Functions

Major Brain Regions

• Cerebrum: Responsible for higher brain functions, including thought, memory, and voluntary movement.

• Cerebellum: Coordinates movement and balance.

• Brainstem: Includes the midbrain, pons, and medulla oblongata; controls vital functions.

• Diencephalon: Includes the thalamus and hypothalamus.

Functional Areas

• Primary Visual Cortex: Located in the occipital lobe; processes visual information.

• Auditory Cortex: Located in the temporal lobe; processes auditory information.

• Broca's Area: Involved in speech production; typically in the left frontal lobe.

• Wernicke's Area: Involved in language comprehension.

• Prefrontal Cortex: Involved in complex mental functions, behavior, conscience, and personality.

• Parietal Lobe: Processes sensory information from the body.

• Occipital Lobe: Processes visual information.

• Temporal Lobe: Processes auditory information and is involved in memory and emotion.

Specialized Structures

• Corpus Callosum: Connects the left and right cerebral hemispheres.

• Thalamus: Relay station for sensory information.

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

• Superior and Inferior Colliculi: Located in the midbrain; involved in visual and auditory reflexes, respectively.

Cerebrospinal Fluid (CSF)

• Formation: Produced by the choroid plexus in the ventricles.

• Functions: Cushions the brain and spinal cord, removes waste, and circulates nutrients.

• Absorption: Reabsorbed into the venous system via arachnoid granulations.

Neural Pathways and Sensory Systems

Sensory Pathways

• First-Order Neurons: Transmit sensory information from receptors to the spinal cord or brainstem.

• Second-Order Neurons: Relay information from the spinal cord or brainstem to the thalamus; often decussate (cross over).

• Third-Order Neurons: Transmit information from the thalamus to the cerebral cortex.

Motor Pathways

• Upper Motor Neurons: Originate in the cerebral cortex or brainstem and synapse on lower motor neurons.

• Lower Motor Neurons: Originate in the spinal cord and innervate skeletal muscles.

Decussation of Tracts

• Pyramidal Tracts: Most fibers decussate at the medullary pyramids.

• Lateral Corticospinal Tract: Decussates in the medulla; controls limb movements.

• Anterior Corticospinal Tract: Decussates at the spinal cord level; controls trunk muscles.

Tables

Comparison of White Matter and Gray Matter in the Spinal Cord

Major Sensory and Motor Pathways

Key Terms and Definitions

• Decussation: The crossing of nerve fibers from one side of the CNS to the other.

• Commissure: A bundle of nerve fibers connecting the two sides of the CNS.

• Fasciculus Cuneatus: A tract in the dorsal column carrying sensory information from the upper body.

• Fasciculus Gracilis: A tract in the dorsal column carrying sensory information from the lower body.

• Broca's Area: Region in the frontal lobe involved in speech production.

• Wernicke's Area: Region in the temporal lobe involved in language comprehension.

Sample Equations and Diagrams

• Nernst Equation (for membrane potential):

• Ohm's Law (for neural conduction):

Additional info:

• Some questions referenced specific cranial nerves, tracts, and nuclei. For a full understanding, students should review the cranial nerve table and the organization of the brainstem.

• Emotion is primarily associated with the limbic system, especially the amygdala.