Lecture Notes: Neuromuscular Junction and Transmission

Overview

• Topic: Neuromuscular Junction and Transmission
• Previous Video: Skeletal Muscle Structure, Sarcomere
• Current Focus: Neuromuscular junction, neuromuscular transmission

Anatomy of the Spinal Cord

• Spinal Cord Cross Section:
  • Posterior Side: Back part
  • Anterior Side: Front part with neuron clump
  • Anterior/Ventral Gray Horn:
    • Contains somatic motor neuron cell bodies
    • Gray due to lack of myelination

Somatic Nervous System

• Characteristics:
  • Voluntary control
  • Supplies skeletal muscles

Muscle Excitability and Stimulation

• Muscles: Excitable and require a stimulus
• Stimulus Pathway:
  • Cerebral cortex sends impulses
  • Impulses travel via spinal cord to skeletal muscle
  • Alpha Motor Neuron: Connects to muscle

Action Potentials

• Action Potential:
  • Generated by stimulation of somatic motor neuron cell bodies
  • Voltage-Gated Sodium Channels: Sodium inflow causes depolarization
  • Depolarization: Positive charges move along axon

Synaptic Bulb and Neurotransmitter Release

• Axon Terminal/Synaptic Bulb: Site of neurotransmitter release
• Voltage-Gated Calcium Channels:
  • Open at ~+30 mV
  • Calcium influx due to voltage threshold

Acetylcholine (ACH) Synthesis and Transport

• Components:
  • Choline: Essential nutrient from diet
  • Acetate: From acetyl-CoA in mitochondria
  • Enzyme: Choline acetyltransferase(acetyl plus choline with release of coA) and acetylcholinesterase (AChE)breaks it in post syn mem
  • ACH synthesized in synaptic bulb

Vesicle Transport and Release Mechanism

• Vesicle Transport:
  • Protons pumped into vesicle using ATP
  • Secondary active transport moves ACH into vesicle

Snare Proteins

• Types:
  • V-Snares:, Synaptobrevin
  • T-Snares: SNAP25, Syntaxin
• Role of Calcium:
  • Acts as a cross-link between snares
  • Facilitates vesicle fusion and neurotransmitter release

Summary of Neuromuscular Transmission Steps

1. Stimulation: Somatic motor neuron cell bodies
2. Propagation: Action potential down alpha motor neuron
3. Depolarization: Sodium channel activation
4. Calcium Influx: Opens channels at synaptic bulb
5. ACH Synthesis: Choline and acetate reaction
6. ACH Transport: Into vesicle
7. Vesicle Fusion: Calcium-induced snare interaction
8. Exocytosis: Release of acetylcholine

Repolarization

• Potassium Channels: Open, allowing potassium out
• Result: Cell becomes negative; resting state

Upcoming Topics

• Next Video: Effect of acetylcholine on muscle cells at the junction