Muscular System: Types and Function

Muscular System: Types and Function

• The muscular system comprises approximately 40-50% of total body weight and is composed of highly specialized cells.
• Bone cannot move on its own; all movement results from muscle contraction and relaxation.
• Muscles are responsible for producing body movement, maintaining posture, storing and moving substances within the body, and producing heat.

Learning Objectives

• Identify the key characteristic of skeletal muscle.
• Explain the function of muscle tissue.
• List the three types of muscle tissue: cardiac, smooth, and skeletal.
• Differentiate among smooth, cardiac, and skeletal muscle.
• Explain the terminology used to name skeletal muscle.
• Articulate the functions of smooth, cardiac, and skeletal muscles.

Muscle Tissue

• The human body has approximately 650 muscles and 187 joints.

The Muscular System (anatomical overview)

• Various muscles, including facial muscles, muscles of the back, abdomen muscles, muscles of the leg, muscles of the forearm, muscles of the hand, and muscles of the foot, are essential for movement and posture.

Facial Muscles

• Facial muscles are responsible for facial expressions.
• The facial muscles control functions like closing the eyes, raising the eyebrows, smiling, and frowning.
• These muscles are critical for communicating emotions and interacting socially.

Muscles of the Back

• These muscles are crucial in supporting the trunk and back.
• The muscles of the back are responsible for posture and movements, like flexing and extending the back.

Abdomen Muscles

• These muscles keep the abdomen stable.
• The muscles of the abdomen are vital for protecting internal organs and facilitating movement.

Muscles of the Leg

• These muscles are essential for leg movement, posture, and balance.
• The leg muscles are critical for activities such as walking, running, and jumping.

Muscles of the Forearm

• These muscles are necessary for forearm movements and hand functions.

Muscles of the Hand

• These muscles are responsible for the fine motor skills of the hands.

Muscles of the Foot

• These muscles are responsible for foot movement, balance, and posture.

Functions of Muscular Tissue

• Muscles produce body movement.
  • Includes all types of movements, whether visible or not, like lifting objects, peristalsis, heart beating, and bladder contractions.
• Maintain body posture by contracting continuously.
• Store and move substances within the body by sustaining contraction and relaxation of smooth muscles.
• Produce heat, which is needed for maintaining body temperature.

Type of Muscle Tissues

• Muscle cells are also known as fibers.
• There are three types of muscle tissues:
  • Cardiac muscle
  • Smooth muscle
  • Skeletal muscle
• Each type of muscle cell has different structures, locations, and functions.

1. Cardiac Muscle

• Cardiac muscle is involuntary and is exclusively found in the heart
• The cells are cylindrical, striated, and branched.
• The cells are interconnected, forming a complex network.
• The site where the cells connect is called an intercalated disc.
• Cardiac muscle cells contain only one nucleus.

2. Smooth Muscle

• Smooth muscles function involuntarily.
• The cells are non-striated and have a single nucleus.
• Smooth muscle lines the walls of hollow organs.
• Smooth muscle cells are tubular in structure, propelling substances through tracts.
• Contraction occurs in a wave-like pattern.

3. Skeletal Muscle

• Skeletal muscle is also known as voluntary muscle.
• The skeletal muscle cells are striated and have numerous nuclei.
• Skeletal muscles are attached to bones by tendons and act to move the skeleton.
• Skeletal muscles are necessary for movement and posture in the body.

Skeletal Muscle Comparison of Types

• The comparison outlines the differences in location, function, control mode, shape, and characteristics of skeletal, cardiac, and smooth muscles.

Skeletal Muscle Structure (gross anatomy)

• The organization of skeletal muscle fibers into fascicles, epimysium, perimysium, and endomysium is explained. The parts of the fascicle include fascicle (part of the muscle), muscle fiber (cell), perimysium, sacrolemma, endomysium, and myofibril.

Skeletal Muscle Structure (microscopic anatomy)

• Discusses the following structure of skeletal muscle fiber: sarcolemma, myofibrils, sarcoplasmic reticulum, and numerous mitochondria.

Sarcomeres

• The basic functional units of skeletal muscle are sarcomeres.
• The sarcomere has a banded appearance.
• The interaction between thick and thin filaments in sarcomeres results in muscle contraction.

Myofilaments: Actin and Myosin

• Thick filaments are predominantly composed of the protein myosin, while thin filaments consist mainly of actin.
• The organization of myofilaments within a sarcomere is detailed, highlighting their role in contraction.
• Specific features of myosin, including its globular heads (cross bridges) and rod-like tails, are highlighted, as well as the active sites found on the actin filament.

Arrangement of Filaments in a Sarcomere

• Thick and thin filaments overlap in a pattern forming striations and bands.
• Thin filaments are only found in the I band, while both thin and thick filaments are found in the A band.
• Z lines separate adjacent sarcomeres.

Filaments and the Sarcomere

• Thick and thin filaments overlap, causing striations (light I bands and dark A bands).
• Sarcomeres are compartments with Z lines separating them.
• Six thin filaments encompass each thick filament in the overlap region.

Main Outline Structure of Sarcomere

• Thick filaments (myosin) are within the A band, and the I band only contains thin filaments (actin).
• Z lines demarcate the boundaries of sarcomeres, and the region between two Z lines is a single sarcomere.
• The H zone is the central part of the A band where thin filaments don’t reach.

Microscopic Structure of Striped Muscle

• The structure of a striated muscle at a microscopic level is described and the components are labeled.
• The main components and their functions are explained.

Muscle Contraction: Sliding Filament Theory

• The sliding filament theory describes how sarcomeres shorten during muscle contraction.
• Muscle contraction causes actin filaments to slide over myosin, shortening the sarcomere, with the lengths of the filaments (actin and myosin) remaining constant.

Energy for Muscle Contraction

• Muscle contractions require energy (ATP).
• Blood vessels deliver oxygen and nutrients for ATP production.
• Muscle contractions are stimulated by the central nervous system (CNS).

Chemical Energy Sources

• ATP is the direct source of energy for muscle contraction.
• The break down of ATP releases considerable energy.
• Anaerobic glycolysis converts glucose into energy (ATP) using lactic acid as a by-product.
• Aerobic glycolysis in the Krebs cycle converts glucose into 38 ATPs.
• Creatine Phosphate (CP) or phosphogen acts as a reservoir of high energy phosphate in muscles.

Nerve and Blood Supply

• Muscle fibers need nerve impulses to contract.
• Blood vessels deliver nutrients and oxygen for energy production.
• Blood vessels also remove waste products.

Contracture Deformity

• Contractures restrict normal movement due to stiffness or constriction in muscles, joints, tendons, ligaments, or skin.
• They occur when normally pliable connective tissues become stiff, limiting range of motion.

Muscular Dystrophy

• Muscular dystrophies affect muscle function due to a lack of dystrophin.
• Conditions are inherited, meaning passed down through families.
• Occur in childhood or adulthood.
• Various types exist, including Becker muscular dystrophy, a less severe form.

Neuro Muscular Junction

• The neuromuscular junction (synapse) in the neuron-muscle interaction.
• Acetylcholine (ACh) neurotransmitter is essential.
• The neurotransmitter ACh diffuses across the synaptic cleft and binds to receptors on the sarcolemma. This initiates nerve impulses at neuromuscular joints resulting in muscle contractions.

Excitation-Contraction Coupling

• The process of converting a nerve impulse into a muscle contraction is called excitation-contraction coupling.
• ACh release from the motor neuron triggers a cascade of events leading to muscle contraction.
• Release and reuptake of calcium ions leads to muscle contraction and relaxation.

This quiz explores the muscular system, including its types and functions. You'll identify various muscle tissues, their characteristics, and their roles in the human body. Test your knowledge on skeletal, smooth, and cardiac muscles along with their anatomical details.