Cells of the Nervous System

Cells of the Nervous System

• Neurons are signal-transmitting cells composed of dendrites (input), cell bodies, and axons (output).

• Dendrites and cell bodies are visible with Nissl staining (stains RER), while axons do not have RER.

• Neurofilament protein and synaptophysin are neuronal markers.

• Astrocytes provide physical support, repair, remove excess neurotransmitters.

• They also form a part of the blood-brain barrier and buffer glycogen.

• GFAP proteins identify astrocytes

• Myelinate CNS axons (including cranial nerves II)

• Oligodendrocytes myelinate multiple axons in the CNS (around 30 axons are myelinated by a single oligodendrocyte).

• They are identified histologically as "fried eggs."

• Oligodendrocytes are prevalent in white matter

• They are damaged in multiple sclerosis, leukodystrophies, and progressive multifocal leukoencephalopathy.

• Ependymal cells line the ventricles and central canal of the spinal cord.

• Ciliated and microvilli are used to circulate CSF and absorb it.

• Specialized ependymal cells in the choroid plexus produce cerebrospinal fluid (CSF).

• Microglia are phagocytic cells in the CNS, acting as scavengers.

• Activated microglia release inflammatory mediators (e.g., nitric oxide, glutamate).

• They are involved in HIV-associated dementia.

• Satellite cells surround neuron cell bodies in ganglia.

• Schwann cells myelinate axons in the PNS (cranial nerves III-XII).

• Schwann cells myelinate single axons.

• They are damaged in Guillain-Barré Syndrome

CNS Glial Cells

• CNS glial cells originate mostly from the neuroectoderm, except microglia, which come from the mesoderm.
• PNS glial cells originate from the neural crest ectoderm.
• Myelin is a multilayered sheath, electrically insulating axons.
• Increased insulation leads to faster conduction velocity ("saltatory conduction") at nodes of Ranvier.

Neuron Action Potential

• Resting potential: the membrane is more permeable to K+ than Na+.
• Depolarization: Na+ channels open, Na+ flows inward.
• Repolarization: Na+ channels close, and K+ channels open, K+ flows outward.
• Hyperpolarization: K+ channels close slowly, leading to slightly more negative potential than resting.
• Na+/K+ pump restores ion concentrations to original levels.

Sensory Receptors

• Free nerve endings: pain and temperature receptors found in all body tissues except cartilage and the eye lens.
• Meissner corpuscles: located in hairless skin, adapt quickly to light touch, low-frequency vibration, skin indentation.
• Pacinian corpuscles: located in deeper skin layers, ligaments, and joints; adapt quickly to deep pressure.
• Merkel discs: adapt slowly to pressure (deep static touch), shape, and edge.
• Ruffini corpuscles: adapt slowly; detect skin stretching, joint angle change.

This quiz explores the various types of cells within the nervous system, including neurons, astrocytes, oligodendrocytes, and ependymal cells. Learn about their structural features, functions, and roles in neurological health and disease. Test your understanding of neuronal markers and cell characteristics in the central nervous system.