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Neurobiology and Physiology Notes

CASE STUDY: BETTY JACKSON

  • Patient Profile: 29-year-old graphic designer.

  • Symptoms: Difficulty reading, clumsiness, excessive fatigue since summer 2019.

  • Diagnosis: Multiple Sclerosis (MS) confirmed by MRI showing demyelination plaques.

  • Treatment: Referred to physiotherapy for rehabilitation.

ACTION POTENTIAL PROPAGATION

  • Mechanism: Action potentials propagate by setting off new potentials in adjacent unactivated sections of the axon.

  • Directionality: Propagation occurs away from recent activity due to refractory nature of previous sections.

NEURON FUNCTIONALITY

  • Functional Classification: Action potentials initiated near cell ends for skeletal muscles, propagated along axons.

  • Recovery Patterns: Different nerve fibers recover at differing rates determined by diameter and myelination.

    • Motor fibers: ~80–120 m/s

    • Touch/pressure: ~35–90 m/s

    • Sharp pain: ~5–40 m/s

    • Dull pain/temperature: ~0.5–2 m/s

MYELIN SHEATH

  • Composition and Function: Lipid-rich layer that insulates axons, facilitating faster signal propagation at nodes of Ranvier.

  • Saltatory Conduction: Action potentials jump between nodes, enhancing speed.

GRADED POTENTIALS VS ACTION POTENTIALS

  • Graded Potentials: Local changes in membrane potential due to stimuli; not capable of long-distance propagation.

  • Action Potentials: All-or-nothing response, propagate over length of the axon, depend on threshold level.

GLIAL CELLS

  • Roles: Support neurons, regulate environment, and involved in response to injury/disease.

  • Types:

    • Oligodendrocytes: Myelinate CNS axons

    • Astrocytes: Support and maintain BBB; neurotransmitter regulation

    • Microglia: Immune defense in CNS

    • Ependymal cells: Line brain cavities; produce cerebrospinal fluid

    • Schwann cells: Myelinate PNS axons

    • Satellite cells: Support ganglia in PNS

BLOOD-BRAIN BARRIER

  • Function: Protects CNS by regulating substance entry; astrocytes play a significant role.

  • Challenges: Drug delivery can be complicated by the barrier's selective permeability.