Propagation of Action Potentials Quiz

• New action potentials are not generated at every point in membranes due to a limited number of voltage-gated sodium channels.

• Graded potentials do not result in action potentials at every point.

• Saltatory conduction is the jumping of action potentials between nodes of Ranvier in myelinated nerve fibers.

• Myelin is formed by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system.

• Myelin sheath covers the nodes of Ranvier in myelinated axons.

• An active node at the peak of an action potential causes local current flow, which depolarizes the adjacent inactive node, bringing it to threshold.

• Factors affecting the speed of impulse conduction include myelination and the diameter of the fiber.

• Nerve fibers are classified based on axon diameter and presence of myelination.

• Examples of demyelination diseases include Guillain-Barré syndrome, multiple sclerosis, and dementias.

• Guillain-Barré syndrome is caused by the immune system damaging the peripheral nervous system, resulting in muscle weakness and loss of reflexes.

• Multiple sclerosis is an immune-mediated inflammatory demyelinating disease of the central nervous system, characterized by multiple lesions and neurological symptoms.

• Dementia is a degenerative disease affecting memory, language, and other cognitive abilities.

• Alzheimer's disease is the most common cause of dementia.

• Self-assessment: A 27-year-old nurse named Nadia experienced tingling and numbness in her hands and feet, followed by muscle weakness and fatigue. She fell during a ward round, and electrophysiological studies revealed decreased motor nerve conduction velocity. A diagnosis of multiple sclerosis was made based on history and investigations.

• Decreased impulse conduction speed can be attributed to demyelination or axonal damage.

• Nadia's symptoms of muscle weakness and fatigue can be correlated with the decreased speed of impulse conduction.

• Factors affecting impulse conduction speed include myelination, axon diameter, and temperature.

• Other causes of demyelination include viral infections, toxins, and trauma.

• EE (Enteric Nervous System) and ANS (Autonomic Nervous System) are two different parts of the nervous system

• The Somatic Motor System is controlled by a single nerve, while the ANS has two nerves: the preganglionic and postganglionic nerves

• The ANS has two divisions: the Sympathetic Division (Fight or Flight Response) and the Parasympathetic Division (Rest and Digest Response)

• The Sympathetic Division increases heart rate and blood pressure, depresses digestive function, and increases sweating

• The Parasympathetic Division slows heart rate, falls in pressure, increases digestive functions, and stops sweating

• The Sympathetic Division has its ganglia located in the Thoracolumbar outflow, while the Parasympathetic Division has its ganglia in the Craniosacral outflow

• Autonomic ganglia are located outside the CNS in the PNS, providing a location for synapse and are of two types: Sympathetic and Parasympathetic

• Sympathetic ganglia are located along the sympathetic trunk and there are about 24 ganglia in each sympathetic trunk

• Parasympathetic ganglia are smaller and located more peripherally than sympathetic ganglia, typically situated adjacent to the viscera they supply

• The Sympathetic Nervous System has a wide distribution targeting peripheral effectors and internal organs in the head, neck, thorax, abdomen, and pelvis

• Sympathetic preganglionic fibers exit the spinal cord at T1-L2 segments and join the sympathetic chain as white rami communicans

• Parasympathetic ganglia include the Ciliary, Pterygopalatine, Otic, and Submandibular ganglia, among others, and are located adjacent to the viscera they supply

• The Sympathetic Nervous System has a wide distribution targeting peripheral effectors as skin glands, erector pili muscles, and blood vessels, as well as internal organs in the head, neck, thorax, abdomen, and pelvis.

Test your knowledge on the propagation of action potentials in nerve cells, including the differences between graded and action potentials, as well as saltatory conduction in myelinated nerve fibers.