Muscle Structure and Function Quiz

Muscle Structure and Function

• Two adjacent sarcomeres display banding patterns critical for muscle function.
• Sarcomeres consist of actin and myosin myofilaments responsible for muscle contraction via the sliding filament model.
• During contraction, actin and myosin slide past each other, shortening the muscle without reducing filament lengths.

Excitability and Action Potentials

• Resting cells have sodium (Na+) and potassium (K+) channels closed.
• Action potentials occur as Na+ channels open and close, altering charge differences across the plasma membrane.
• Motor neurons transmit action potentials to muscle fibers at the neuromuscular junction.

Neuromuscular Junction Components

• Motor neuron communicates with a muscle fiber through the neuromuscular junction (synapse).
• Key structures include the presynaptic terminal, postsynaptic membrane, synaptic cleft, synaptic vesicles, and neurotransmitters (e.g., acetylcholine).
• Motor units consist of muscle fibers stimulated by a single motor neuron.

Muscle Contraction Mechanism

• Muscle contraction begins when an action potential travels down the motor neuron.
• Calcium ions (Ca2+) trigger the release of acetylcholine, leading to sodium influx into the muscle fiber.
• Ca2+ binding to troponin exposes myosin-binding sites on actin.
• Myosin heads pull actin filaments toward the center of the sarcomere, causing contraction.

ATP and Muscle Contraction

• ATP is essential for muscle contractions, facilitating cross-bridge formation between myosin and actin.
• Energy is released when ATP is converted to ADP and inorganic phosphate (P).
• Rigor mortis occurs post-mortem when ATP is depleted, locking muscle fibers in contraction.

Muscle Fiber Types

• Slow Twitch Fibers:

  • Contract slowly, resist fatigue, and are utilized in endurance activities (e.g., long-distance running).
  • Primarily use aerobic respiration and derive energy from fat; rich in myoglobin.

• Fast Twitch Fibers:

  • Contract quickly and fatigue rapidly; suited for vigorous, short bursts of activity (e.g., sprinting).
  • Rely on anaerobic respiration for energy from glycogen; less myoglobin leads to paler muscle color.

Muscle Terminology and Nomenclature

• Origin: Non-movable attachment of a muscle.
• Insertion: Movable attachment of a muscle.
• Belly: Central part of the muscle.
• Muscles are named based on location, origin/insertion, size, shape, or function.

Muscles of Head and Neck

• Facial Expression:

  • Occipitofrontalis: Elevates eyebrows.
  • Orbicularis oculi: Facilitates blinking.
  • Zygomaticus: Responsible for smiling.

• Mastication:

  • Masseter: Primary muscle for chewing.

Tongue and Swallowing Muscles

• Intrinsic Muscles: Change tongue shape, located within the tongue.
• Extrinsic Muscles: Move the tongue, originating from surrounding bones.
• Suprahyoid and Infrahyoid Muscles: Stabilize or elevate/depress the hyoid bone, crucial for swallowing.

Thoracic and Abdominal Wall Muscles

• Thoracic Muscles:

  • External intercostals: Elevate ribs for inhalation.
  • Internal intercostals: Depress ribs during forced exhalation.
  • Diaphragm: Main muscle for quiet breathing.

• Abdominal Wall Muscles:

  • Rectus abdominis: Compresses the abdomen.
  • External and internal abdominal obliques, transverse abdominis: Assist in abdominal compression.

Test your knowledge on muscle structure, function, and the physiology of the neuromuscular junction. This quiz covers critical topics such as the sliding filament model and the mechanisms of action potentials. Understand how muscle fibers communicate with motor neurons to facilitate movement.