Human Anatomy: The Muscular System

Differentiate the three main types of muscle tissue found in the human body.

Skeletal muscle (voluntary, striated, attached to bones), Cardiac muscle (involuntary, striated, found in the heart), and Smooth muscle (involuntary, non-striated, found in walls of internal organs).

List the primary functions of the muscular system.

The primary functions include producing movement, maintaining posture and body position, stabilizing joints, and generating heat.

What are the four main functional characteristics of muscle tissue?

The four main characteristics are excitability (responsiveness), contractility (ability to shorten), extensibility (ability to stretch), and elasticity (ability to recoil to original length).

Describe the hierarchical organization of skeletal muscle from largest to smallest.

Skeletal muscle is organized from the largest muscle organ, to fascicles, then muscle fibers (cells), myofibrils, sarcomeres, and finally myofilaments (actin and myosin).

What is a sarcomere and what is its significance?

A sarcomere is the basic contractile unit of skeletal muscle, extending from one Z-disc to the next. It contains the myofilaments responsible for muscle contraction.

Name the two primary types of myofilaments involved in muscle contraction.

The two primary myofilaments are actin (thin filaments) and myosin (thick filaments).

Briefly explain the 'sliding filament model' of muscle contraction.

Muscle contraction occurs as actin filaments slide past myosin filaments, causing the sarcomere to shorten. Myosin heads bind to actin, pivot, and pull the actin towards the center of the sarcomere.

What is the neuromuscular junction (NMJ)?

The neuromuscular junction (NMJ) is the specialized synapse where a motor neuron communicates with a skeletal muscle fiber, transmitting nerve impulses to initiate muscle contraction.

Which neurotransmitter is released at the neuromuscular junction to initiate muscle contraction?

Acetylcholine (ACh) is the neurotransmitter released at the neuromuscular junction that binds to receptors on the muscle fiber to initiate an action potential.

How does calcium (Ca2+) trigger muscle contraction?

Calcium ions bind to troponin, causing it to change shape. This movement then pulls tropomyosin away from the actin binding sites, allowing myosin heads to attach to actin and begin the cross-bridge cycle.

What is the primary role of ATP in muscle contraction and relaxation?

ATP provides the energy for the detachment of myosin heads from actin, the power stroke of the myosin head, and the active transport of calcium back into the sarcoplasmic reticulum during relaxation.

Differentiate between a muscle's origin and insertion.

The origin is the attachment point of a muscle that remains relatively immobile or fixed during contraction, while the insertion is the attachment point that moves when the muscle contracts.

Define agonist (prime mover) and antagonist muscles.

An agonist (prime mover) is the muscle primarily responsible for producing a specific movement, while an antagonist is a muscle that opposes or reverses that movement.

Explain the difference between isotonic and isometric muscle contractions.

Isotonic contractions result in muscle length changes and movement (e.g., lifting a weight), while isometric contractions generate tension without changing muscle length or producing movement (e.g., holding a plank).

List two common criteria used to name skeletal muscles.

Skeletal muscles are often named based on their location, shape, size, direction of muscle fibers, number of origins, location of attachments, or action they perform.