Study Guide: The Muscular System (Anatomy & Physiology)

The Muscular System

Overview

The muscular system is responsible for movement, posture, and heat production in the human body. Muscles work in coordination to produce voluntary and involuntary movements, and are classified based on their structure, function, and location.

Muscle Roles and Types

Prime Mover (Agonist)

• Definition: The muscle that produces the most force during a particular movement.

• Example: Brachialis is the prime mover in elbow flexion.

• Application: Lifting a heavy object primarily uses the prime mover for that action.

Antagonist

• Definition: A muscle that opposes the action of the prime mover.

• Example: Triceps brachii is the antagonist to the brachialis during elbow flexion.

• Application: Antagonists help control and refine movement, preventing injury.

Synergist

• Definition: A muscle that assists the prime mover in performing its action.

• Example: Biceps brachii acts as a synergist during elbow flexion.

• Application: Synergists stabilize joints and add extra force to movement.

Fixator

• Definition: A muscle that stabilizes the origin of the prime mover so that it can act more efficiently.

• Example: Muscles that fix the scapula during arm movements.

• Application: Fixators prevent unwanted movement at a joint.

Muscle Classification Criteria

• Location: e.g., Temporalis (overlies the temporal bone)

• Shape: e.g., Deltoid (triangular)

• Size: e.g., Gluteus maximus (largest), Gluteus minimus (smallest)

• Direction of fibers: e.g., Rectus abdominis (fibers run straight), External oblique (fibers run diagonally)

• Number of origins: e.g., Biceps brachii (two heads), Triceps brachii (three heads), Quadriceps femoris (four heads)

• Action: e.g., flexor, extensor, adductor

Facial Muscles and Their Functions

• Puckering the lips: Orbicularis oris

• Blinking the eyes: Orbicularis oculi

• Smiling: Zygomaticus major

Key Muscle Groups

Intercostal Muscles

• Location: Between the ribs

• Function: Aid in breathing by expanding and contracting the chest cavity

Pelvic Floor Muscles

• Function: Support pelvic organs, maintain bowel and bladder control, and improve sexual function

• Clinical Note: Strengthening these muscles can prevent prolapse and improve overall health

Muscles of the Hand

• White Structures: Tendons (flexor and extensor tendons)

Quadriceps Femoris (Anterior Thigh)

• Muscles: Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius

• Function: Extension of the knee

Hamstrings (Posterior Thigh)

• Muscles: Biceps femoris (long & short head), Semitendinosus, Semimembranosus

• Function: Flexion of the knee

Tendons and Aponeuroses

Tendon

• Definition: A fibrous connective tissue that connects muscle to bone

• Examples: Achilles tendon (heel), tendons of biceps femoris and semitendinosus (posterior thigh)

Aponeurosis

• Definition: A broad, flat sheet-like connective tissue that connects muscles to the parts they move

• Difference from Tendon: Tendons are cord-like, aponeuroses are flat and sheet-like

Vocabulary Table: Muscle System Terms

Vocab Term	Use in a Sentence	Synonym	Reminds me of...
Sphincter	The pyloric sphincter controls the flow of food from the stomach to the small intestine.	Circular muscle rings	Rubber band
Tendon	There is a white tendon connecting my biceps to my humerus.	Muscle to bone connecting band	Time I suffered from hip tendonitis
Prime mover	The brachialis is the prime mover in elbow flexion.	Main muscle	Lifting heavy weights at gym
Synergist	The biceps brachii acts as a synergist during elbow flexion.	Helper muscle	Teamwork
Antagonist	The triceps brachii is the antagonist when flexing the elbow.	Opposing muscle	Stretching arm out after lifting
Quadriceps	The quadriceps help extend the knee when you stand up.	Anterior thigh	Sore thigh after leg day
Hamstrings	The hamstrings are active when bending the knee during running.	Back thigh	Pain after running, pulled hamstring

Additional Information

• Muscle Naming: Muscles are often named based on their location, shape, size, direction of fibers, number of origins, and action.

• Muscle Actions: Muscles can act as flexors, extensors, adductors, or abductors depending on the movement they produce.

• Clinical Relevance: Understanding muscle anatomy is essential for diagnosing and treating musculoskeletal injuries.