Nervous System Structures and Terminology

Overview

Lecture covers nervous system structures, neuron basics, and cell nucleus functions.
Emphasis on terminology differences between central and peripheral nervous system structures.
Discusses neuron types, components, and cell repair capacity differences.

Gray matter: clusters of nerve cell bodies in the central nervous system.
Cortex: outer layer (Latin for "bark"); cerebral cortex is a relatively thin outer sheet.
Nucleus (brain): mass of neurons deep in the brain; plural "nuclei".
Substantia: group of related neurons deep in brain or spinal cord (e.g., substantia gelatinosa for pain transmission).
Locus: small, well-defined group of cells.
Ganglion / Ganglia: clusters of neurons in the peripheral nervous system (Greek origin); exception: basal ganglia (subcortical brain structures).
Nerve: bundle of axons in the peripheral nervous system; typically does not include cell bodies.

White matter: collections of axons (CNS); visible in spinal cord cross-sections.
Tract: CNS axons bundled with common origin and destination and shared function.
- Example: Corticospinal tract — origin in primary motor cortex (M1), terminates in the spinal cord (final common pathway).
Bundle: collection of axons that may not share a common origin or destination; organizational grouping.
Capsule: collection of axons, often from cerebrum to brainstem.
- Example: Internal capsule — connects cerebral cortex to brainstem.
Commissure: axons crossing from one brain side to the other.
Lemniscus: ribbon-shaped tract; example medial lemniscus transmits touch information from brainstem to primary somatosensory cortex (S1).

Neuron: basic functional unit of the nervous system.
Estimated ~10^11 neurons in the human brain with many types.
Example neuron types and roles:
- Alpha motor neuron: final common pathway for muscle contraction; drives actions like breathing and movement.
- Gamma motor neuron: motor neuron whose activity primarily contributes to sensory function (modulates sensory apparatus).
Three main neuronal components:
- Soma (cell body): metabolic center; site of major biochemical activity.
- Nucleus (cell): contains DNA; houses genetic information needed for protein synthesis.
- Axons/dendrites implied as parts of neuron for transmission and input.

Cell nucleus contains DNA — likened to a "big book of life" with chapters (human cells typically have 23 chromosome pairs).
Most body cells have two copies of the genome (diploid).
Cells repair by making new proteins, guided by DNA instructions in the nucleus.
Differences in repair and protein synthesis capacity:
- Neurons: single nucleus, limited ability to self-repair after major damage.
- Muscle cells: multinucleated, high capacity for protein synthesis and growth.
- Red blood cells: anucleate (no nucleus), cannot synthesize new proteins; damaged RBCs cannot repair and are replaced. Typical RBC lifespan ~120 days.

Gray Matter: clusters of neuronal cell bodies (CNS).
White Matter: collections of axons (CNS).
Cortex: outer layer of an organ (e.g., cerebral cortex).
Nucleus / Nuclei: deep brain clusters of neurons; also cell nucleus (genetic control center).
Substantia: group of neurons; used in brain and spinal cord contexts.
Ganglion / Ganglia: PNS neuron clusters.
Nerve: PNS axon bundle (transmits signals between locations).
Tract: CNS axon bundle with shared origin/destination/function.
Bundle: grouped axons without necessarily shared origin/destination.
Capsule: axonal collection connecting cerebrum and brainstem (e.g., internal capsule).
Commissure: axons connecting brain hemispheres.
Lemniscus: ribbon-shaped tract (e.g., medial lemniscus for touch).

Instructor will provide a short video to cover remaining slides by the end of the week.
New material will start on Thursday following the video release.