The muscular system is one of the major systems of the human body, responsible for movement, posture, stability, and even vital functions like circulation and digestion. This anatomy study guide on the muscular system help to provide an understanding of the structure and function of this system for students of anatomy and physiology, healthcare professionals, and anyone interested in how the body moves and operates. In this study guide, we will explore the function, structure, and the anatomy and physiology of the muscular system.

THE MUSCULAR SYSTEM CAN BE BROKEN DOWN INTO THE FOLLOWING TOPICS:

• Functions of the Muscular System
• Structure of Muscular System
• Anatomy of the Muscular System
• Physiology of the Muscular System
• Common Disorders of the Muscular System

Function of the Muscular System

The muscular system consists of over 600 muscles that perform various functions in the human body. Here are the key functions of the muscular system:

Movement

Muscles are the primary drivers of all voluntary and involuntary movements in the body. Skeletal muscles attach to bones and contract to produce movement, allowing us to walk, run, lift objects, and perform everyday tasks.

Posture and Stability

The muscular system helps to maintain posture and stabilize joints, ensuring that the body remains in a balanced and upright position. Postural muscles, such as those in the back and abdomen, work continuously to support the spine and keep the body aligned.

Heat Production

Muscles generate heat as a byproduct of contraction. This heat helps maintain body temperature, making the muscular system essential for thermoregulation.

Circulation and Respiration

Certain muscles, such as the heart (cardiac muscle) and the diaphragm (skeletal muscle), are vital for circulation and respiration. The heart pumps blood throughout the body, while the diaphragm aids in breathing.

Digestive and Excretory Function

Smooth muscles in the walls of the digestive tract contract to move food through the digestive system via a process called peristalsis. Additionally, smooth muscles control the elimination of waste from the bladder and intestines.

Structure of the Muscular System

The muscular system is divided into three types of muscles, each with distinct structures and functions:

Skeletal Muscle

• Voluntary Muscle: Skeletal muscles are under conscious control, meaning we can control their movement.
• Striated Appearance: Microscopically, skeletal muscles have a striped or striated appearance due to the organized arrangement of actin and myosin filaments.
• Muscle Fibers: Each skeletal muscle is composed of bundles of long, cylindrical cells called muscle fibers, which contract in response to nerve signals.
• Attachment to Bones: Skeletal muscles are attached to bones by tendons, enabling movement at joints.

Cardiac Muscle

• Involuntary Muscle: Found only in the heart, cardiac muscle works without conscious control.
• Striated but Different: Like skeletal muscle, cardiac muscle is striated, but its cells are shorter, branched, and interconnected through intercalated discs, which allow for synchronized contractions.
• Heart Function: Cardiac muscle contractions pump blood throughout the body, ensuring that oxygen and nutrients are delivered to tissues.

Smooth Muscle

• Involuntary Muscle: Smooth muscles are controlled unconsciously by the autonomic nervous system.
• Non-striated Appearance: Unlike skeletal and cardiac muscles, smooth muscles lack striations and have a smooth, uniform appearance.
• Location and Function: Smooth muscle is found in the walls of hollow organs like the stomach, intestines, blood vessels, and bladder. It helps move substances through the body, such as food through the digestive tract or blood through arteries.

Anatomy of the Muscular System

In this section we attempt to cover at length many of the most important muscles of the Muscular System. We attempt to do this to aid students and professionals in the physical therapy field with their study and work to help others with rehabilitation and recovery. 

*If there are any mistakes in this section please feel free to contact us so that we can make the necessary corrections.

The anatomy of the muscular system consists of over 600 muscles that work together to enable movement, maintain posture, and support vital functions such as circulation and digestion. Muscles are classified into three types: skeletal muscles, which are voluntary and responsible for body movement; cardiac muscle, which controls heart contractions; and smooth muscle, found in organs and responsible for involuntary functions like digestion. Skeletal muscles are attached to bones by tendons and are made up of fibers containing myofibrils, which consist of sarcomeres—the fundamental units of muscle contraction. This system is essential for both voluntary movements, like walking, and involuntary processes, such as breathing.

Microscopic Anatomy of Skeletal Muscle

Skeletal muscle cells possess unique features that contribute to their function in movement and contraction. Here’s a closer look at their microscopic structure:

• Multinucleate Cells: Skeletal muscle fibers contain multiple nuclei, which are essential for managing the large volume of cytoplasm within each cell.
• Sarcolemma: The plasma membrane of muscle cells, known as the sarcolemma, houses several oval nuclei just beneath its surface, helping control cellular activities.
• Myofibrils: These long, ribbon-like organelles nearly fill the cytoplasm of the muscle cell. Myofibrils push the nuclei aside and are responsible for the muscle’s ability to contract.
• Light and Dark Bands: Alternating bands of light and dark along the myofibrils give the muscle its characteristic striped or striated appearance. This arrangement is key to muscle contraction.
• Sarcomeres: Each myofibril is made up of contractile units called sarcomeres, aligned end-to-end like boxcars in a train. Sarcomeres are the fundamental units of muscle contraction.
• Myofilaments:
  • Thick Filaments: Composed primarily of the protein myosin, these filaments also contain ATPase enzymes, which split ATP to fuel muscle contractions.
  • Thin Filaments: Composed of actin and regulatory proteins, these filaments control the binding of myosin and are anchored to the Z disc, marking the boundaries of each sarcomere.

• Cross Bridges: These are projections on the thick filaments, called myosin heads, which form connections with the thin filaments during contraction, driving the shortening of the muscle.

• Sarcoplasmic Reticulum (SR): This specialized smooth endoplasmic reticulum surrounds each myofibril like a sleeve. Its key function is to store and release calcium, which is crucial for triggering muscle contractions.

Muscle Movements, Types, and Names

Skeletal muscles are attached to bones or other connective tissue structures at two points, which allows for various types of body movements. Here's a breakdown of key movements:

• Origin: This is the point where the muscle is attached to the immovable or less movable bone.

• Insertion: The point where the muscle attaches to the movable bone. When the muscle contracts, the insertion moves toward the origin.

• Flexion: Movement that decreases the angle between two bones, bringing them closer together. This is common in hinge joints like the elbow but also occurs in ball-and-socket joints such as the shoulder.

• Extension: The opposite of flexion, extension increases the angle between two bones, moving them farther apart. It commonly occurs in the limbs when straightening.

• Rotation: This involves movement of a bone around its longitudinal axis, such as turning the head from side to side or rotating the arm.

• Abduction: Movement of a limb away from the midline of the body, like raising the arm or leg to the side.

• Adduction: The opposite of abduction, it brings a limb back toward the midline, such as lowering the arm to the side of the body.

• Circumduction: A combination of flexion, extension, abduction, and adduction, resulting in a circular movement. This is typical in ball-and-socket joints, where the proximal end stays stationary, and the distal end moves in a circle.

These various body movements allow for the wide range of motion necessary for daily activities and complex tasks.Understanding these components gives insight into how skeletal muscles contract and generate movement at the microscopic level.The anatomy of the muscular system can be divided into specific muscle groups, which work together to perform various functions.

Special Movements

Some body movements do not fit into the standard categories and occur at only a few specific joints. These special movements include:

• Dorsiflexion and Plantar Flexion:
  • Dorsiflexion: Lifting the foot so that the top of the foot moves toward the shin.
  • Plantar Flexion: Depressing the foot so the toes point downward, as in standing on tiptoes.

• Inversion and Eversion:
  • Inversion: Turning the sole of the foot inward, so it faces medially.
  • Eversion: Turning the sole of the foot outward, so it faces laterally.

• Supination and Pronation:
  • Supination: Rotating the forearm laterally, so the palm faces upward or anteriorly, and the radius and ulna are parallel.
  • Pronation: Rotating the forearm medially, so the palm faces downward or posteriorly, crossing the radius over the ulna.

• Opposition: In the hand, opposition involves the movement of the thumb toward the tips of the fingers, enabled by the saddle joint between the first metacarpal and the carpals, allowing grasping motions.

These specialized movements enable more precise and functional movements in activities such as walking, gripping, and fine motor control.

Interactions of the Skeletal Muscles in the Body

Muscle of the Upper Limb

The muscles of the upper limb can be divided into three distinct groups, each responsible for different types of movement. 

The first group ( muscles that move the shoulder) consists of muscles that originate from the shoulder girdle and cross the shoulder joint to insert into the humerus, such as the deltoid and pectoralis major, which are responsible for movements like arm flexion, extension, abduction, and rotation. 

The second group ( muscles that move the elbow) includes muscles that control movement at the elbow joint, such as the biceps brachii and triceps brachii, which are essential for flexing and extending the elbow. 

Lastly, the third group ( muscles of the forearm) comprises the muscles of the forearm, which primarily manage wrist and finger movements. These muscles, like the flexor carpi radialis and extensor digitorum, are involved in fine motor skills and grip strength, allowing for intricate hand movements and daily tasks. Together, these muscle groups provide a wide range of motion and functionality in the upper limb.

Muscles that Move the Shoulder

• Deltoid:
  • A large, triangular muscle that covers the shoulder joint. It is responsible for arm abduction (lifting the arm away from the body), as well as assisting with flexion, extension, and rotation of the arm.

• Pectoralis Major:
  • A large, fan-shaped muscle located on the chest. It functions to flex the arm, adduct it toward the body, and medially rotate the humerus, helping with movements like pushing or lifting.

• Latissimus Dorsi:
  • A broad, flat muscle of the lower back. It extends to the humerus and is involved in arm extension, adduction, and medial rotation, playing a role in pulling motions like rowing or chin-ups.

• Teres Major:
  • A small, round muscle located on the back of the shoulder. It helps with medial rotation and adduction of the arm and assists in stabilizing the shoulder joint.

• Rotator Cuff Muscles:
  • Supraspinatus: Located in the upper part of the shoulder, it assists in abduction of the arm and stabilizes the shoulder joint.
  • Infraspinatus: A muscle on the posterior aspect of the shoulder, responsible for lateral rotation of the arm and stabilizing the shoulder.
  • Teres Minor: Positioned just below the infraspinatus, it also helps with lateral rotation of the arm and shoulder stabilization.
  • Subscapularis: Located on the anterior surface of the scapula, it is responsible for medial rotation of the arm and stabilizing the shoulder joint.

• Trapezius:
  • A large, diamond-shaped muscle extending from the neck and upper back to the shoulder. It helps with scapular elevation, retraction, and rotation, allowing shoulder shrugging and arm movements.

• Levator Scapulae:
  • A muscle that runs along the side of the neck to the scapula. It elevates the scapula, assisting in movements like shrugging.

• Rhomboid Major and Minor:
  • These muscles are located between the scapula and the spine. They work to retract and elevate the scapula, playing a role in shoulder and arm stabilization.

Each of these muscles plays a critical role in shoulder movement, allowing for a wide range of actions such as lifting, rotating, and stabilizing the arm and shoulder joint.

Muscles that Move the Elbow

• Biceps Brachii:
  • A two-headed muscle located on the front of the upper arm. It is primarily responsible for elbow flexion(bending the elbow) and supination of the forearm (turning the palm upward).

• Brachialis:
  • A deep muscle located underneath the biceps brachii. It assists with flexion of the elbow, playing a major role in bending the arm.

• Brachioradialis:
  • A muscle of the forearm that assists in elbow flexion, particularly when the forearm is in a neutral position (thumb facing upward). It is most active during quick movements and stabilizes the elbow.

• Triceps Brachii:
  • A three-headed muscle located on the back of the upper arm. It is the primary muscle responsible for elbow extension (straightening the arm).

• Anconeus:
  • A small, triangular muscle located near the elbow that assists the triceps brachii in elbow extension and helps stabilize the elbow joint.

• Pronator Teres:
  • A muscle located on the forearm that assists with forearm pronation (turning the palm downward) and also aids in flexion of the elbow.

• Supinator:
  • A deep muscle of the forearm that works to supinate the forearm, turning the palm upward. It works in conjunction with the biceps brachii for this movement.

These muscles work together to allow flexion, extension, pronation, and supination of the elbow joint, making it possible to perform a wide variety of arm movements, from bending the elbow to rotating the forearm.

Muscles of the Forearm

• Flexor Carpi Radialis:
  • A muscle on the anterior side of the forearm that aids in flexing the wrist and abducting the hand (moving it toward the thumb side).

• Flexor Carpi Ulnaris:
  • Located on the medial side of the forearm, it is responsible for flexing the wrist and adducting the hand (moving it toward the pinky side).

• Flexor Digitorum Superficialis:
  • A deeper muscle that flexes the fingers at the proximal interphalangeal joints and also assists in wrist flexion.

• Flexor Digitorum Profundus:
  • Situated beneath the flexor digitorum superficialis, it flexes the distal interphalangeal joints (the tips of the fingers) and helps with wrist flexion.

• Flexor Pollicis Longus:
  • A long muscle that flexes the thumb and also aids in flexion of the wrist.

• Extensor Carpi Radialis Longus:
  • A muscle on the posterior side of the forearm that extends the wrist and aids in abduction of the hand.

• Extensor Carpi Radialis Brevis:
  • Similar to the extensor carpi radialis longus but shorter, it also helps in wrist extension and abduction of the hand.

• Extensor Carpi Ulnaris:
  • Located on the posterior side of the forearm, this muscle works to extend and adduct the wrist.

• Extensor Digitorum:
  • A muscle that extends the fingers and also assists in wrist extension. It helps spread the fingers and extend them simultaneously.

• Extensor Pollicis Longus:
  • A muscle that extends the thumb at the thumb joint and assists in thumb abduction.

• Extensor Pollicis Brevis:
  • Shorter than the extensor pollicis longus, it helps extend the thumb and contributes to thumb movement.

• Pronator Teres:
  • A muscle located on the anterior forearm that assists in pronation (turning the palm downward) of the forearm and also aids in elbow flexion.

• Supinator:
  • A deep muscle in the posterior forearm that supinates the forearm (turning the palm upward), working with the biceps brachii to achieve this motion.

• Palmaris Longus:
  • A small muscle that helps with wrist flexion. Not everyone has this muscle, and its absence does not significantly impact function.

These muscles enable a variety of movements in the wrist, fingers, and forearm, including flexion, extension, pronation, and supination, allowing for fine motor control and strength needed for tasks like gripping, writing, and manipulating objects.

Professor Long 2401 Lab Muscles of the Arm

*For students, professionals, and researchers here is a guide to manual muscle testing of the upper limb:

A Guide to Mastering Upper Extremity Manual Muscle Testing with a Handheld Dynamometer

Muscles of the Lower Limb

The muscles of the lower limb can be divided into three main groups based on the joints they move. 

First, the muscles causing movement at the hip joint include powerful muscles like the gluteus maximus, iliopsoas, and the adductor group, which are responsible for hip flexion, extension, abduction, and adduction, allowing for movements like walking, climbing, and squatting. 

Second, the muscles causing movement at the knee joint are primarily the quadriceps femoris, which extends the knee, and the hamstrings, which flex the knee, both crucial for activities like running, jumping, and sitting. 

Finally, the muscles causing movement at the ankle and foot include the gastrocnemiusand soleus, which allow for plantar flexion (pointing the toes), as well as the tibialis anterior, which enables dorsiflexion (raising the foot). These muscles play a key role in balance, walking, and posture maintenance.

Muscles that move the Hip Joint

• Gluteus Maximus:
  • The largest muscle in the buttocks, responsible for hip extension, lateral rotation, and abduction. It is crucial for movements like climbing stairs, standing up from a sitting position, and running.

• Gluteus Medius:
  • Located on the outer surface of the pelvis, it aids in hip abduction and medial rotation. It helps stabilize the pelvis during walking.

• Gluteus Minimus:
  • The smallest of the gluteal muscles, located beneath the gluteus medius. It also contributes to hip abduction and medial rotation, stabilizing the pelvis.

• Iliopsoas:
  • Comprising the iliacus and psoas major, this muscle group is the primary hip flexor, allowing for movements such as walking, running, and lifting the knee.

• Tensor Fasciae Latae (TFL):
  • A small muscle on the lateral side of the thigh, it assists with hip abduction, medial rotation, and stabilizes the knee via the iliotibial (IT) band.

• Adductor Longus:
  • Part of the adductor muscle group, it is responsible for hip adduction (bringing the leg toward the body) and assists in medial rotation.

• Adductor Magnus:
  • The largest of the adductor muscles, it contributes to hip adduction, extension, and medial rotation.

• Adductor Brevis:
  • A smaller adductor muscle that aids in hip adduction and medial rotation.

• Pectineus:
  • Located in the upper thigh, it aids in hip flexion, adduction, and medial rotation, supporting the adductors in leg movement.

• Sartorius:
  • The longest muscle in the body, it runs across the front of the thigh, allowing for hip flexion, abduction, and lateral rotation. It also assists in knee flexion.

• Piriformis:
  • A small muscle located deep in the buttock, it aids in lateral rotation and abduction of the hip, particularly when the hip is flexed.

• Quadratus Femoris:
  • A flat, square-shaped muscle located on the posterior side of the hip, responsible for lateral rotation of the hip.

These muscles collectively enable a wide range of movements at the hip joint, including flexion, extension, abduction, adduction, and rotation, allowing for functional tasks such as walking, running, and maintaining balance.

Muscles that move the Knee Joint

• Quadriceps Femoris:
  • A group of four muscles located on the front of the thigh, primarily responsible for knee extension. The group includes:
    • Rectus Femoris: The only quadriceps muscle that also crosses the hip joint, it assists in hip flexionin addition to knee extension.
    • Vastus Lateralis: Located on the outer side of the thigh, it plays a major role in knee extension.
    • Vastus Medialis: Found on the inner side of the thigh, it contributes to knee extension and helps stabilize the patella.
    • Vastus Intermedius: Positioned underneath the rectus femoris, this muscle also assists in knee extension.

• Hamstrings:
  • A group of three muscles on the back of the thigh responsible for knee flexion and hip extension. The hamstring muscles include:
    • Biceps Femoris: This muscle extends the hip and flexes the knee, and also assists in lateral rotation of the leg when the knee is flexed.
    • Semitendinosus: This muscle helps with knee flexion, hip extension, and medial rotation of the leg.
    • Semimembranosus: Similar to the semitendinosus, it aids in knee flexion, hip extension, and medial rotation.

• Sartorius:
  • The longest muscle in the body, it crosses both the hip and knee joints. It aids in knee flexion, hip flexion, abduction, and lateral rotation of the thigh.

• Gastrocnemius:
  • This calf muscle crosses the knee joint and assists in knee flexion while also playing a major role in plantar flexion of the foot at the ankle.

• Popliteus:
  • A small muscle located behind the knee, it helps "unlock" the knee by initiating knee flexion and assists with medial rotation of the tibia when the knee is flexed.

• Gracilis:
  • This slender muscle runs along the inner thigh and helps with knee flexion and hip adduction. It is important in stabilizing the knee joint.

• Tensor Fasciae Latae (TFL):
  • Though primarily involved in hip abduction and medial rotation, it also indirectly contributes to knee stabilization via the iliotibial (IT) band.

These muscles work together to facilitate knee flexion, extension, and stabilization, enabling critical movements like walking, running, jumping, and maintaining balance.

Muscles Causing Movement at the Ankle and Foot

• Gastrocnemius:
  • A large, two-headed calf muscle that is involved in plantar flexion of the foot (pointing the toes downward). It also assists in knee flexion.

• Soleus:
  • A flat muscle located beneath the gastrocnemius, it works in tandem with the gastrocnemius to achieve plantar flexion of the foot, particularly during walking or standing.

• Tibialis Anterior:
  • Located on the front of the shin, this muscle is responsible for dorsiflexion (lifting the foot upward) and inversion of the foot (turning the sole inward).

• Tibialis Posterior:
  • A deep muscle located behind the tibia, it plays a crucial role in plantar flexion and inversion of the foot. It also supports the arch of the foot.

• Fibularis (Peroneus) Longus:
  • Located on the lateral side of the leg, it assists in plantar flexion and eversion of the foot (turning the sole outward), helping stabilize the foot when standing or walking.

• Fibularis (Peroneus) Brevis:
  • A shorter muscle that also helps with plantar flexion and eversion of the foot. It works alongside the fibularis longus to maintain balance.

• Extensor Digitorum Longus:
  • Found on the front of the leg, it extends the toes (except the big toe) and aids in dorsiflexion of the foot.

• Extensor Hallucis Longus:
  • A smaller muscle that extends the big toe and assists in dorsiflexion of the foot.

• Flexor Digitorum Longus:
  • Located on the back of the lower leg, this muscle flexes the toes (except the big toe) and helps with plantar flexion of the foot.

• Flexor Hallucis Longus:
  • A deep muscle that flexes the big toe and assists in plantar flexion of the foot. It is important for maintaining balance while walking.

• Plantaris:
  • A small muscle running alongside the gastrocnemius, it assists with plantar flexion and knee flexion, although its role is relatively minor.

• Extensor Digitorum Brevis:
  • Located on the top of the foot, it helps extend the toes, aiding in toe extension and contributing to foot balance.

These muscles work together to enable plantar flexion, dorsiflexion, inversion, eversion, and toe movements, all of which are crucial for activities like walking, running, jumping, and maintaining balance.

*For students, professionals, and researchers here is a guide to manual muscle testing of the lower limb:

A Guide to Mastering Lower Extremity Manual Muscle Testing with Handheld Dynamometers

Physiology of the Muscular System

The physiology of the muscular system involves the processes by which muscles contract, generate force, and produce movement in the body. This system is composed of three types of muscle tissue—skeletal, cardiac, and smooth muscle—each with distinct functions. Skeletal muscles, which are under voluntary control, contract when stimulated by nerve impulses. These impulses trigger the release of calcium ions, leading to the interaction of actin and myosin filaments within the muscle fibers, a process known as the sliding filament theory. This interaction causes the muscle to shorten and produce movement. Cardiac muscle is responsible for the contraction of the heart and operates involuntarily, while smooth muscle controls involuntary movements in organs like the digestive tract and blood vessels. Energy for these contractions comes from ATP, and muscle metabolism can shift between aerobic and anaerobic processes depending on the demand. The muscular system works in coordination with the nervous system to maintain posture, generate movement, and regulate vital functions like breathing and circulation.

Skeletal Muscle Activity

Skeletal muscle activity begins when muscle cells are stimulated by a nerve impulse. The process starts at the neuromuscular junction, where a nerve impulse triggers the release of the neurotransmitter acetylcholine (ACh). ACh causes the muscle cell membrane, or sarcolemma, to temporarily become permeable, allowing sodium ions to rush in and potassium ions to exit. This exchange generates an action potential, an electrical current that spreads across the sarcolemma and initiates muscle contraction. The sliding filament theory explains how this works: calcium ions released from storage bind to regulatory proteins on the actin filaments, exposing binding sites for myosin. Myosin heads attach to actin, pulling the thin filaments toward the center of the sarcomere, which results in muscle contraction. Once the contraction is complete, acetylcholine is broken down by enzymes, allowing the muscle to relax until the next nerve impulse arrives. This process enables muscles to contract and relax in a coordinated manner, facilitating movement.

Nerve Stimulus and the Action Potential in Skeletal Muscle Activity

For skeletal muscle activity to occur, muscle cells must be stimulated by a nerve impulse, which triggers the entire process of contraction. Here's how this process unfolds:

• Neurotransmitter Release:
  • When a nerve impulse reaches the axon terminals of a motor neuron, it triggers the release of a chemical called a neurotransmitter. The specific neurotransmitter that stimulates skeletal muscle cells is acetylcholine (ACh).

• Temporary Permeability of the Sarcolemma:
  • Once enough acetylcholine binds to receptors on the muscle cell’s sarcolemma (the muscle cell membrane), the membrane becomes temporarily more permeable. Sodium ions rush into the muscle cell, while potassium ions diffuse out. This exchange of ions creates the conditions for electrical activity in the cell.

• Generation of Action Potential:
  • More channels open in the sarcolemma, allowing additional sodium ions to enter. This generates an action potential, an electrical current that spreads across the muscle cell. Once started, the action potential is unstoppable and propagates across the entire surface of the sarcolemma, triggering the contraction of the muscle cell.

• Breakdown of Acetylcholine:
  • After the contraction is initiated, acetylcholine is quickly broken down into acetic acid and choline by enzymes on the sarcolemma. This breakdown ensures that each nerve impulse results in only one muscle contraction, allowing the muscle to relax until it receives another signal.

This entire process ensures precise control of muscle contractions, enabling coordinated movements in the body.

Mechanism of Muscle Contraction: The Sliding Filament Theory

The Sliding Filament Theory explains the process of muscle contraction at the molecular level, describing how actinand myosin filaments interact to produce movement in skeletal muscles. Here's how the process works:

• Activation by the Nervous System:
  • When muscle fibers are activated by a nerve impulse, the myosin heads attach to binding sites on the actinfilaments, and the sliding action begins.

• Relaxed Muscle Cell:
  • In a relaxed muscle cell, regulatory proteins on the actin filaments prevent the binding of myosin. However, when an action potential travels along the sarcolemma and excites the muscle, calcium ions are released from intracellular storage areas, specifically from the sarcoplasmic reticulum.

• Contraction Trigger:
  • The release of calcium serves as the final trigger for contraction. Calcium binds to the regulatory proteins on the actin filaments, causing a change in their shape and position, which exposes the binding sites on the actin for the myosin heads to attach.

• Attachment and Sliding:
  • Once myosin attaches to actin, it "springs the trap" by pulling the actin filaments toward the center of the sarcomere. This movement, driven by the myosin heads snapping toward the center, results in the shortening of the muscle fiber, which is the basis of muscle contraction.

This sliding filament mechanism allows muscles to contract and relax repeatedly, enabling movement and force generation as needed for various activities like walking, lifting, and posture maintenance.

Age-Related Physiological Changes in the Musculoskeletal System

As we age, the speed and power of muscle contractions gradually decline. While regular exercise can help maintain muscle strength, there is an inevitable decrease in the number of muscle fibers by the time individuals reach their 50s, a condition known as sarcopenia. Along with muscle loss, there is a reduction in overall height and stature, often due to changes in the spine. Conditions such as kyphosis (a forward curvature of the spine), osteoporosis (loss of bone density), and increased susceptibility to pathologic fractures become more common.

Additionally, reaction time tends to slow with age, partly due to reduced muscle tone, which can further hinder quick responses. This decline in muscle tone is often linked to decreased physical activity, which not only weakens muscles but also contributes to the loss of balance and coordination. These physiological changes highlight the importance of maintaining regular physical activity to mitigate the effects of aging on the musculoskeletal system.

Common Disorders of the Muscular System

Muscle Strains and Tears

A strain occurs when a muscle or tendon is overstretched or torn. Common in sports injuries, muscle strains often affect the hamstrings, quadriceps, or back muscles.

Muscular Dystrophy

A group of inherited disorders characterized by progressive muscle weakness and degeneration. Duchenne muscular dystrophy is one of the most common types, primarily affecting boys.

Myasthenia Gravis

An autoimmune disorder that affects the communication between nerves and muscles, leading to muscle weakness and fatigue.

Tendonitis

Inflammation of the tendons, often caused by repetitive strain or overuse. It commonly affects areas such as the elbow (tennis elbow), shoulder, and Achilles tendon.

Related video on the Muscular System:

*Source: Mometrix Academy

Conclusion

The muscular system plays an integral role in virtually every movement and function of the body. From generating force for movement to maintaining posture and assisting in circulation, muscles are essential for overall health and vitality. Understanding the structure and physiology of muscles is crucial for anyone studying anatomy, working in healthcare, or simply interested in improving physical performance.

For those looking to assess muscle strength and function, manual muscle testing using tools like handheld dynamometers offers a precise way to measure muscular performance. You can learn more about muscle strength testing in the blog post How Understanding the Muscular System Enhances Manual Muscle Testing with Handheld Dynamometers. 

For additional review and insight on the Muscular System go to the following website:  Nurseslabs - Muscular System Anatomy and Physiology

Rehab Therapy Supplies offers the following products that relates to the Muscular System:

• Anatomical Chart - Musculature, Laminated
• Anatomical Chart - Knee Joint, Laminated
• Anatomical Chart - Hand and Wrist, Laminated
• Anatomical Chart - Foot and Ankle, Laminated
• Anatomical Chart - Acupuncture Body, Laminated
• Anatomical Arm Models
• Anatomical Leg Models
• Anatomical Muscle Models

*Source: the website nurseslabs.com was used as a source for this blog post.

**If there are any mistakes in this anatomy study guide we would love for you to contact us so we can correct them.