Central Nervous System (CNS)

Spinal Cord Structure and Function

The spinal cord is a major component of the CNS, responsible for transmitting neural signals between the brain and the rest of the body. It consists of gray and white matter, and is organized into various horns and tracts.

• Posterior Gray Horns: Contain sensory neurons. Damage: May result in loss of sensory function below the level of injury.

• Anterior Gray Horns: Contain motor neurons. Damage: May result in motor deficits such as paralysis.

• White Matter: Composed of myelinated axons forming ascending (sensory) and descending (motor) tracts.

• Decussation: Many tracts cross over (decussate) in the spinal cord or brainstem, leading to contralateral control.

• Fasciculus Cuneatus: Sensory tract; synapse occurs in the medulla oblongata.

• Ascending Tracts: Carry sensory information to the brain.

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

Example: Damage to the posterior gray horns can cause loss of sensation, while damage to the anterior gray horns can cause motor deficits.

Spinal Nerves and Plexuses

Spinal nerves emerge from the spinal cord and form complex networks called plexuses, which innervate various body regions.

• Brachial Plexus: Supplies the upper limb.

• Lumbar Puncture: A procedure to collect cerebrospinal fluid (CSF) from the lumbar region, typically between L3-L4 or L4-L5.

• Spinal Tap: Another term for lumbar puncture.

Brain Structure and Function

Major Brain Regions

The brain is divided into several regions, each with specialized functions.

• Cerebrum: Responsible for higher mental functions, including reasoning, memory, and voluntary movement.

• Cerebellum: Coordinates movement and balance.

• Brainstem: Includes the midbrain, pons, and medulla oblongata; controls vital functions such as breathing and heart rate.

• Hypothalamus: Regulates homeostasis, hormone release, and autonomic functions.

• Broca's Area: Involved in speech production.

• Auditory Cortex: Processes sound information; located in the temporal lobe.

• Parietal Lobe: Processes sensory information and spatial orientation.

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

• Commissural, Projection, and Association Fibers: Connect different regions within the brain.

Example: The right corticospinal tract usually carries more motor information from the left cerebral cortex.

Cerebrospinal Fluid (CSF)

CSF is a clear fluid that surrounds the brain and spinal cord, providing protection and nourishment.

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

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

• Functions: Cushions the CNS, removes waste, and maintains chemical stability.

Neural Pathways and Synapses

Sensory and Motor Pathways

Neural pathways transmit sensory and motor signals throughout the body.

• Sensory Pathways: First, second, and third order neurons relay information from receptors to the brain.

• Motor Pathways: Upper and lower motor neurons transmit signals from the brain to muscles.

• Decussation: Many pathways cross over to the opposite side of the CNS.

Example: The site of synapse between the second and third order neurons of the fasciculus cuneatus is in the thalamus.

Functional Areas and Special Structures

Specialized Brain Areas

Specific regions of the brain are responsible for distinct functions.

• Broca's Area: Speech production.

• Auditory Cortex: Hearing.

• Superior and Inferior Colliculi: Visual and auditory reflexes.

• Limbic System: Involved in emotion, behavior, and memory.

• Precentral Gyrus: Primary motor cortex; controls voluntary movements.

• Postcentral Gyrus: Primary somatosensory cortex; processes sensory input.

Functions of Cranial Nerves

Cranial nerves have motor, sensory, or both functions, and are essential for head and neck innervation.

• Motor Only: Oculomotor, trochlear, abducens, accessory, hypoglossal.

• Sensory Only: Olfactory, optic, vestibulocochlear.

• Both: Trigeminal, facial, glossopharyngeal, vagus.

Tables

Comparison of Brain Regions and Their Functions

Order of Sensory Neurons

Key Terms and Definitions

• Decussation: Crossing over of nerve fibers from one side of the CNS to the other.

• Fasciculus Cuneatus: Ascending sensory tract for touch and proprioception from the upper body.

• Commissural Fibers: Connect corresponding regions of the two hemispheres.

• Projection Fibers: Connect the cortex with lower brain or spinal cord centers.

• Association Fibers: Connect different parts of the same hemisphere.

Formulas and Equations

• CSF Formation Rate:

• Nerve Conduction Velocity: where is velocity, is distance, and is time.

Additional info:

• Some questions referenced specific tracts and nuclei; details were expanded for clarity.

• Tables were inferred from the context of the questions and standard anatomy & physiology knowledge.