BIO 2311 - Skeletal Muscle and Neurophysiology

SKELETAL MUSCLE: Anatomy & Structure and Function

• Connective tissue layers: Epimysium -> Perimysium -> Endomysium -> Sarcoplasmic Reticulum.

• Structure hierarchy:

  • Z-line to Z-line (sarcomere)

  • Sarcomeres

  • Myofibrils

  • Muscle fibers

  • Fascicles

  • Skeletal muscle

• Muscle fibers:

  • Wrapped in sarcolemma (plasma membrane)

  • Contains sarcoplasm and myofibrils

• Sarcoplasmic reticulum: Stores calcium; terminal cisternae enlarge SR sacs.

• Triad: T-tubule + 2 terminal cisternae; crucial for calcium release during contraction.

• Sarcomere components:

  • Thin filaments: actin, troponin, tropomyosin

  • Thick filaments: myosin

  • Titin stabilizes thick filaments.

• Sliding filament theory: Filaments slide, A band constant, H- and I-bands shrink as muscle contracts.

• Tropomyosin: Blocks active sites; Ca² binds to troponin, moving tropomyosin to expose actin.

• Cross-bridge formation: Myosin binds to actin -> contraction begins.

• Excitation-contraction coupling: AP reaches neuromuscular junction -> ACh released -> triggers Ca² release.

• Twitch phases: Latent (lag), contraction, relaxation.

BIOELECTRICITY AND NEUROPHYSIOLOGY

• Nervous tissue: Neurons + neuroglia (glial cells outnumber neurons).

• Neuron structure: Dendrites, soma, axon, synaptic terminals.

• Myelination: Speeds up signal (saltatory for myelinated; continuous for unmyelinated).

• Transmembrane potential (TMP): Charge difference across membrane (RMP of neurons = -70 mV).

• Ion gradients: Na influx, K efflux drive membrane potential.

• Gated channels:

  • Closed (inactive)

  • Open (active)

  • Closed (can be activated)

  • Leak (passive), gated (active).

• Excitable cells: Only neurons & muscle cells can generate action potentials.

• Potentials: TMP, RMP, graded, action potential, depolarization, repolarization, hyperpolarization.

• Action potential: All-or-nothing event if threshold (~10-15 mV depolarization) is met.

• Facilitation: Bringing axon closer to threshold (~5 mV short).

ACTION POTENTIAL STAGES

1. Depolarize to threshold

2. Na in

3. Na close/K open

4. Repolarization

5. Refractory

SYNAPTIC COMMUNICATION

• Neurotransmission process:

  • Chain communication via synapses (functional junctions)

  • Neuromuscular: neuron to muscle; neuroglandular: neuron to gland.

• Types of synapses: Electrical (direct contact) & chemical (via neurotransmitters).

• Chemical synapse components: Pre-synaptic terminal, synaptic cleft, neurotransmitter vesicles.

• Neurotransmitter functions: Regulate membrane permeability by opening/closing ion channels.

• Neurotransmission events:

  1. AP reaches terminal

  2. Ca² influx

  3. Vesicle release

  4. NT binds receptor.

• Potentials: EPSP (depolarize) & IPSP (hyperpolarize).

• Summation types: Temporal (rapid fire, same neuron) & Spatial (multiple neurons together).

INTRODUCTION TO THE NERVOUS SYSTEM

• CNS components: Brain + Spinal cord

• PNS components: Nerves

• PNS divisions:

  • Afferent: Incoming info (Somatic: skin/muscles, Visceral: organs)

  • Efferent: Outgoing (Somatic: voluntary, Autonomic: involuntary, visceral).