Compare and contrast skeletal, cardiac, and smooth muscle .

Assignment Question

1. Compare and contrast skeletal, cardiac, and smooth muscle 2. List the special characteristics of all muscle 3. Describe the function of muscular tissue 4. Draw and explain the gross anatomical features of skeletal muscles (include epimysium, perimysium, and endomysium) 5. Define myofibrils, sarcomeres, thick and think filaments, sacrolemma, sarcoplasm, sarcoplasmic reticulum, sarcomere, & t tubule 6. Draw a picture and explain the steps in the sliding filament model Please complete Ch 10 HW first. It will help you with lab. Feel free to print out the unlabeled drawings and write the muscle names/ function on it (instead of drawing). 1. Compare and contrast the various actions and interactions of muscles 2. Define prime mover, antagonist, and synergist 3. Describe the various ways muscles are named 4. Describe each principal muscle movement 5. Identify/ locate each muscle of the head, neck, thorax, abdomen, shoulder, and extremities 6. List the location and major actions of the muscles

Assignment Answer

Muscular Tissue: Structure, Function, and Interactions

Introduction

Muscular tissue is a critical component of the human body, responsible for generating movement, maintaining posture, and supporting vital functions such as respiration, circulation, and digestion. The human muscular system is composed of three main types of muscle tissues: skeletal, cardiac, and smooth muscle. Each type of muscle has unique structural and functional characteristics, and they work together in a coordinated manner to facilitate a wide range of movements and physiological processes. This essay will delve into the comparative analysis of skeletal, cardiac, and smooth muscle tissues, discussing their special characteristics, functions, anatomical features, and the sliding filament model of muscle contraction. Additionally, we will explore the actions and interactions of muscles, the definitions of prime mover, antagonist, and synergist, the nomenclature of muscles, and the identification of major muscles throughout the body.

1. Comparison and Contrast of Skeletal, Cardiac, and Smooth Muscle

Skeletal Muscle: Skeletal muscles are the most common and widely recognized type of muscle tissue. They are attached to the skeleton and are under voluntary control. Skeletal muscles are striated, meaning they have a striped appearance under a microscope due to the regular arrangement of actin and myosin filaments. The contraction of skeletal muscles is responsible for body movements such as walking, running, and lifting objects. These muscles are multinucleated, with each muscle fiber containing multiple nuclei located at the periphery of the cell. Skeletal muscle fibers can be quite long, extending the entire length of the muscle.

Cardiac Muscle: Cardiac muscle is found exclusively in the walls of the heart. It is responsible for pumping blood throughout the circulatory system, and its contractions are involuntary, meaning they occur without conscious control. Cardiac muscle cells are striated, like skeletal muscle, but they differ in structure. Cardiac muscle cells are typically branched and interconnected by specialized junctions called intercalated discs. These intercalated discs allow for coordinated contractions across the heart muscle, ensuring efficient pumping of blood. Unlike skeletal muscle, cardiac muscle cells each contain a single nucleus.

Smooth Muscle: Smooth muscle, as the name suggests, lacks the striated appearance seen in skeletal and cardiac muscle tissues. Smooth muscle is found in various internal organs, including the digestive tract, blood vessels, and respiratory passages. Its contractions are involuntary and slow, allowing for sustained contractions that regulate functions such as peristalsis in the digestive system and the regulation of blood flow. Smooth muscle cells are spindle-shaped with a single, centrally located nucleus. They are not multinucleated like skeletal muscle cells.

2. Special Characteristics of Muscle Tissues

Muscle tissues, regardless of type, share some special characteristics that distinguish them from other tissues in the body:

a. Excitability (Irritability): All muscle tissues can respond to electrical or chemical signals, initiating contractions in response to specific stimuli.

b. Contractility: Muscles have the unique ability to shorten and generate tension, enabling them to produce movement.

c. Extensibility: Muscles can be stretched without being damaged, allowing for a wide range of motion.

d. Elasticity: After being stretched or contracted, muscles can return to their original length and shape.

3. Function of Muscular Tissue

The primary function of muscular tissue is to produce movement. However, this overarching function can be further broken down into several important roles:

a. Skeletal Muscle Functions:

• Producing body movements such as walking, running, and jumping.
• Maintaining posture and body position against gravity.
• Generating heat through muscle contractions (thermogenesis).

b. Cardiac Muscle Function:

• Pumping blood throughout the circulatory system to deliver oxygen and nutrients to tissues and organs.
• Maintaining the continuous rhythmic beating of the heart.

c. Smooth Muscle Function:

• Regulating the diameter of blood vessels (vasoconstriction and vasodilation) to control blood flow and blood pressure.
• Facilitating peristalsis in the digestive tract to move food and waste through the system.
• Controlling the diameter of airways in the respiratory system.

4. Gross Anatomical Features of Skeletal Muscles

Skeletal muscles have a complex hierarchical structure that includes three layers of connective tissue:

a. Epimysium: The epimysium is the outermost layer of connective tissue that surrounds the entire muscle. It provides protection and helps transmit the force generated by the muscle to the bones or other structures.

b. Perimysium: Beneath the epimysium, the perimysium divides the muscle into fascicles, which are bundles of muscle fibers. It contains blood vessels and nerves that supply the muscle fibers within each fascicle.

c. Endomysium: The endomysium is the innermost layer of connective tissue and surrounds individual muscle fibers (muscle cells). It contains capillaries and nerve fibers that supply the muscle fibers with oxygen and nutrients.

Inside the muscle fiber itself, there are various organelles and structures that play essential roles in muscle contraction:

• Myofibrils: Myofibrils are long, cylindrical structures within muscle fibers that contain the contractile proteins actin and myosin. These proteins are organized into repeating units called sarcomeres.
• Sarcomeres: Sarcomeres are the basic functional units of a myofibril. They are responsible for muscle contraction and give skeletal muscle its striated appearance. Sarcomeres contain thin (actin) and thick (myosin) filaments arranged in a precise pattern.
• Sarcolemma: The sarcolemma is the plasma membrane of a muscle fiber. It surrounds the muscle cell and controls the movement of ions, allowing for the transmission of electrical signals necessary for muscle contraction.
• Sarcoplasm: Sarcoplasm is the cytoplasm of a muscle fiber. It contains the usual cellular organelles, such as mitochondria for energy production, and myoglobin, a protein that stores oxygen.
• Sarcoplasmic Reticulum: The sarcoplasmic reticulum is a specialized endoplasmic reticulum found in muscle cells. It stores and releases calcium ions (Ca2+), which play a crucial role in muscle contraction.

5. Definitions of Key Muscle Structures

a. Myofibrils: Myofibrils are cylindrical organelles found within muscle fibers that contain the contractile proteins actin and myosin. These proteins are organized into sarcomeres and are responsible for muscle contraction.

b. Sarcomeres: Sarcomeres are the repeating units within myofibrils that consist of thin actin filaments and thick myosin filaments. Sarcomeres are the functional units of muscle contraction.

c. Thick and Thin Filaments: Thick filaments are composed of myosin protein, while thin filaments are composed of actin, troponin, and tropomyosin proteins. The interaction between these filaments during muscle contraction is essential for generating force.

d. Sarcolemma: The sarcolemma is the plasma membrane of a muscle fiber. It controls the flow of ions and electrical signals, facilitating muscle contraction.

e. Sarcoplasm: Sarcoplasm is the cytoplasm of a muscle fiber, containing organelles like mitochondria and myoglobin, which store oxygen.

f. Sarcoplasmic Reticulum: The sarcoplasmic reticulum is an endoplasmic reticulum specialized for muscle cells. It stores and releases calcium ions (Ca2+), which are critical for muscle contraction.

6. The Sliding Filament Model of Muscle Contraction

The sliding filament model is a fundamental concept in muscle physiology that explains how muscles contract at the molecular level. This model describes the interaction between thin and thick filaments within sarcomeres, resulting in muscle shortening and force generation.

a. Initial State:

• In a relaxed muscle, actin and myosin filaments partially overlap within the sarcomere but are not in direct contact.
• The binding sites on actin are covered by tropomyosin molecules, preventing myosin from attaching to actin.

b. Excitation-Contraction Coupling:

• Muscle contraction begins with an electrical signal, called an action potential, that travels along the sarcolemma.
• The action potential reaches the sarcoplasmic reticulum, triggering the release of stored calcium ions (Ca2+).
• Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the actin binding sites.

c. Cross-Bridge Formation:

• With tropomyosin out of the way, myosin heads can bind to exposed binding sites on actin, forming cross-bridges.
• ATP is hydrolyzed to provide energy for the myosin heads to change shape and generate force.

d. Sliding Filaments:

• Myosin heads undergo a power stroke, pulling the thin actin filaments toward the center of the sarcomere.
• As a result, the sarcomere shortens, and the muscle contracts.
• ATP is required to detach myosin heads from actin, allowing them to reset and form new cross-bridges.

e. Muscle Contraction:

• This cycle of cross-bridge formation, power stroke, and detachment continues as long as calcium ions are present and ATP is available.
• When the nervous signal ceases, calcium ions are actively transported back into the sarcoplasmic reticulum, and the muscle relaxes.

7. Actions and Interactions of Muscles

Muscles do not work in isolation; they often act together to produce coordinated movements. Understanding the actions and interactions of muscles is crucial for comprehending how various body movements occur.

a. Prime Mover (Agonist):

• The prime mover is the muscle primarily responsible for producing a specific movement.
• For example, during a bicep curl, the biceps brachii is the prime mover responsible for flexing the elbow.

b. Antagonist:

• The antagonist is a muscle that opposes the action of the prime mover.
• In the same bicep curl example, the triceps brachii acts as the antagonist, extending the elbow to counter the biceps’ flexion.

c. Synergist:

• Synergist muscles assist the prime mover in performing a movement.
• They may stabilize joints or provide additional force to enhance the action of the prime mover.
• In the bicep curl, muscles like the brachialis and brachioradialis can act as synergists.

d. Fixator:

• Fixator muscles stabilize the origin of the prime mover, preventing unwanted movement at the joint.
• They ensure that the prime mover’s force is directed toward the desired action.
• In the bicep curl, muscles around the shoulder joint may act as fixators to stabilize the shoulder girdle.

8. Muscle Naming Conventions

Muscles are named based on various criteria, including their location, size, shape, action, and the number of origins or heads. Common naming conventions include:

• Location: Muscles may be named based on their location in the body. For example, the brachialis muscle is located in the arm.
• Size: Some muscles are named according to their size. The gluteus maximus, for instance, is the largest muscle of the buttocks.
• Shape: Muscles with distinctive shapes may have names reflecting their appearance. The deltoid muscle has a triangular shape.
• Action: Many muscles are named based on their primary action. The extensor digitorum muscle extends the fingers.
• Number of Origins/Heads: Muscles with multiple origins or heads may have names that reflect this feature. The biceps brachii has two heads.

9. Principal Muscle Movements

Muscles produce a wide range of movements at joints throughout the body. Understanding these principal muscle movements is essential for grasping how muscles contribute to everyday activities and sports.

a. Flexion:

• Flexion involves decreasing the angle between two bones at a joint, typically in the sagittal plane.
• Examples include bending the elbow or bringing the knee toward the chest.

b. Extension:

• Extension is the opposite of flexion and involves increasing the angle between two bones at a joint.
• Examples include straightening the elbow or knee.

c. Abduction:

• Abduction refers to moving a body part away from the midline of the body.
• Raising the arm to the side, away from the body, is an example of abduction.

d. Adduction:

• Adduction is the opposite of abduction, involving moving a body part toward the midline.
• Lowering the raised arm back to the side of the body is an example of adduction.

e. Rotation:

• Rotation is the movement of a bone around its longitudinal axis.
• Turning the head from side to side or twisting the trunk are examples of rotational movements.

f. Circumduction:

• Circumduction is a circular movement that combines flexion, extension, abduction, and adduction.
• It creates a conical or circular path, such as swinging the arm in a circle.

g. Pronation:

• Pronation involves the rotation of the forearm, turning the palm downward or backward.
• It is the position the hand takes when holding a bowl of soup.

h. Supination:

• Supination is the opposite of pronation, rotating the forearm to turn the palm upward or forward.
• Holding a tray or pouring from a pitcher is an example of supination.

i. Dorsiflexion:

• Dorsiflexion involves flexing the foot at the ankle joint, bringing the toes closer to the shin.
• Lifting the toes off the ground when walking is dorsiflexion.

j. Plantarflexion:

• Plantarflexion is the opposite of dorsiflexion, pointing the foot downward, as in standing on tiptoes.

k. Eversion:

• Eversion is the outward tilting of the sole of the foot.
• It occurs when the outer edge of the foot is raised.

l. Inversion:

• Inversion is the opposite of eversion, tilting the sole of the foot inward.
• It occurs when the inner edge of the foot is raised.

10. Location and Major Actions of Muscles

The human body contains numerous muscles, each with specific actions and locations. While it’s beyond the scope of this essay to list every muscle, we can provide examples of muscles in various regions of the body and their primary actions.

Head and Neck Muscles:

• Sternocleidomastoid: Flexes the neck and rotates the head.
• Frontalis: Elevates the eyebrows and wrinkles the forehead.
• Masseter: Closes the jaw during chewing.

Thorax and Abdominal Muscles:

• Pectoralis Major: Adducts and flexes the arm at the shoulder joint.
• Rectus Abdominis: Flexes the trunk and compresses the abdomen.
• Diaphragm: Contracts to aid in inhalation and creates a pressure gradient for breathing.

Shoulder and Upper Limb Muscles:

• Deltoid: Abducts and flexes the arm at the shoulder joint.
• Biceps Brachii: Flexes the forearm at the elbow joint.
• Triceps Brachii: Extends the forearm at the elbow joint.

Back Muscles:

• Latissimus Dorsi: Adducts and extends the arm at the shoulder joint.
• Erector Spinae: Extends the vertebral column and maintains posture.
• Trapezius: Elevates and depresses the scapula, as well as retracts and rotates it.

Pelvic and Lower Limb Muscles:

• Gluteus Maximus: Extends and laterally rotates the hip.
• Quadriceps Femoris (Rectus Femoris, Vastus Lateralis, Vastus Medialis, Vastus Intermedius): Extends the leg at the knee joint.
• Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus): Flexes the leg at the knee joint and extends the thigh at the hip joint.
• Gastrocnemius: Plantarflexes the foot at the ankle joint and flexes the leg at the knee joint.
• Tibialis Anterior: Dorsiflexes the foot at the ankle joint.

Conclusion

Muscular tissue is a diverse and vital component of the human body, encompassing skeletal, cardiac, and smooth muscle types. Each type has distinct structural and functional characteristics, enabling them to perform specific roles in maintaining bodily functions and facilitating movement. The sliding filament model explains the mechanism of muscle contraction, detailing the interaction between actin and myosin filaments. Understanding the actions and interactions of muscles, along with muscle naming conventions, is crucial for comprehending how muscles contribute to various movements and functions throughout the body. Muscles play a central role in the biomechanics of the human body, and a comprehensive understanding of their anatomy and physiology is essential for healthcare professionals and anyone interested in the functioning of the human body.