Nervous System and Neuroglia Notes

Ossification Types
- Intramembranous Ossification
  - Direct conversion of mesenchymal tissue into bone.
  - Primarily forms flat bones (e.g., skull, clavicles).
  - Involves the creation of bone matrices surrounded by blood vessels.
- Endochondral Ossification
  - Bone develops by replacing hyaline cartilage.
  - Common in long bones (e.g., femur, humerus).
  - Involves the formation of a cartilage model that is gradually replaced by bone.
Long Bone Growth at Epiphyseal Plates
- Growth plates allow the long bones to grow in length.
- Composed of cartilage that is converted to bone through ossification.
- Zone of proliferation allows for active mitosis, adding new cartilage cells.
- Zone of hypertrophy where older cells enlarge and calcify.
- Eventually, the plate thins and fuses during skeletal maturation, halting growth.
Bone Fracture Repair Steps
1. Hematoma Formation: A blood clot forms at the fracture site.
2. Fibrocartilaginous Callus Formation: Formation of a soft callus connects broken ends.
3. Bony Callus Formation: Replacement of the soft callus with a hard bony callus.
4. Bone Remodeling: The bony callus reshapes and strengthens over time.

General Functions
- The nervous system: a control and communication system.
- Rapid and specific transmission through electrical and chemical signals.
- Major functions:
  - Gathering: Input from sensory receptors.
  - Processing: Interpretation to generate appropriate responses.
  - Motor Output: Activation of muscles and glands to produce a response.

Central Nervous System (CNS)
- Comprises the brain and spinal cord.
- Acts as the integration center for sensory input and motor output.
Peripheral Nervous System (PNS)
- Includes all nervous tissue outside the CNS.
- Composed of spinal nerves and cranial nerves.
Divisions of the PNS
- Afferent (Sensory) Division: Carries impulses to the CNS via sensory receptors.
  - Somatic: From skin, skeletal muscles, and joints.
  - Visceral: From organs in the ventral body cavity.
- Efferent (Motor) Division: Transmits impulses to effectors.
  - Somatic Nervous System: Voluntary control of skeletal muscles.
  - Autonomic Nervous System (ANS): Involuntary control of smooth and cardiac muscles.
    - Divisions: Sympathetic and Parasympathetic.

Nervous Tissue Types
- Neurons: Excitable cells transmitting electrical signals.
- Neuroglia (Glial Cells): Support and protect neurons.
  - Four types in CNS:
    - Astrocytes: Maintain chemical environment and support neurons.
    - Microglial Cells: Perform immune functions and remove debris.
    - Oligodendrocytes: Form myelin sheaths around CNS axons.
    - Ependymal Cells: Line brain cavities and circulate cerebrospinal fluid (CSF).

Astrocytes
- Support neurons and participate in information processing.
Microglial Cells
- Act as the immune defense in the CNS; perform phagocytosis of pathogens.
Oligodendrocytes
- Insulate axons with myelin, increasing signal transmission speed.
Ependymal Cells
- Line the central cavities and aid in circulating CSF.
Satellite and Schwann Cells
- Satellite Cells: Surround neuron cell bodies in ganglia, similar to astrocytes.
- Schwann Cells: Myelinate PNS axons and assist in nerve regeneration.

Formed by Oligodendrocytes in the CNS and Schwann Cells in the PNS.
Myelin is a lipid-rich layer that insulates axons.
Increases speed of nerve impulse transmission.
Presence of gaps, nodes of Ranvier, allows for efficient signal propagation.