Muscle Tissue and the Muscular System: Study Guide (Chapters 10 & 11)

Muscle Tissue

General Functions of Skeletal Muscle

Skeletal muscle performs several essential functions in the human body:

• Body Movement: Muscles contract to produce movement of the skeleton.

• Maintenance of Posture: Continuous contractions stabilize joints and maintain posture.

• Protection and Support: Muscles protect internal organs and support their position.

• Regulation of Elimination: Sphincter muscles control the passage of materials through openings.

• Heat Production: Muscle contractions generate heat, helping maintain body temperature.

Characteristics of Skeletal Muscle

• Excitability: Ability to respond to stimuli by generating electrical changes.

• Conductivity: Ability to propagate electrical signals along the membrane.

• Contractility: Ability to shorten forcibly when stimulated.

• Extensibility: Ability to be stretched without damage.

• Elasticity: Ability to return to original length after stretching.

Connective Tissue Layers of Skeletal Muscle

• Epimysium: Dense irregular connective tissue surrounding the entire muscle.

• Perimysium: Surrounds bundles of muscle fibers (fascicles); contains blood vessels and nerves.

• Endomysium: Surrounds individual muscle fibers; provides electrical insulation and capillary support.

Tendons and Aponeuroses

• Tendon: Cordlike structure attaching muscle to bone, composed of dense regular connective tissue.

• Aponeurosis: Thin, flattened sheet of dense regular connective tissue; serves as a broad attachment for muscles.

Blood Vessels and Nerves in Muscle

• Muscles are highly vascularized to supply oxygen and nutrients and remove waste.

• Each muscle fiber is innervated by a motor neuron, allowing voluntary control.

Multinucleation of Skeletal Muscle Fibers

• Skeletal muscle fibers are multinucleated due to the fusion of myoblasts during development.

Microscopic Anatomy of Muscle Fibers

• Sarcolemma: Plasma membrane of a muscle fiber.

• T-tubules: Invaginations of the sarcolemma that transmit action potentials into the cell.

• Sarcoplasmic Reticulum (SR): Specialized endoplasmic reticulum that stores calcium ions.

• Triad: Structure formed by a T-tubule and two terminal cisternae of the SR.

Thick and Thin Filaments

• Thick Filaments: Composed of myosin molecules.

• Thin Filaments: Composed of actin, troponin, and tropomyosin.

Organization of Myofibrils, Myofilaments, and Sarcomeres

• Myofibrils: Long, cylindrical structures within muscle fibers, made of myofilaments.

• Myofilaments: Protein filaments (thick and thin) responsible for contraction.

• Sarcomere: Functional contractile unit of muscle, defined by Z-discs.

Energy Production in Muscle Fibers

• Mitochondria: Site of aerobic respiration.

• Glycogen Granules: Storage form of glucose.

• Myoglobin: Oxygen-binding protein.

• Creatine Phosphate: Provides rapid ATP regeneration.

Motor Units

• Motor Unit: A single motor neuron and all the muscle fibers it innervates.

• Size varies depending on the degree of control required (fine vs. gross movements).

Neuromuscular Junction

• Synaptic Knob: End of the motor neuron axon.

• Synaptic Cleft: Gap between neuron and muscle fiber.

• Motor End Plate: Specialized region of the sarcolemma with ACh receptors.

Muscle Fiber at Rest

• Resting membrane potential is maintained.

• Calcium ions are stored in the SR.

• Myosin binding sites on actin are blocked by tropomyosin.

Excitation-Contraction Coupling

• Action potential triggers ACh release.

• ACh binds to receptors, leading to depolarization of the sarcolemma.

• Calcium is released from the SR, initiating contraction.

Sarcomere Changes During Contraction

• Sarcomere shortens as Z-discs move closer together.

• I-band and H-zone decrease in width; A-band remains constant.

Muscle Relaxation

• ACh is broken down by acetylcholinesterase.

• Action potential ceases; calcium is pumped back into the SR.

• Troponin-tropomyosin complex covers myosin binding sites.

ATP Production in Muscle

• Myosin Kinase & Creatine Kinase: Catalyze rapid ATP regeneration.

• Glycolysis: Anaerobic breakdown of glucose.

• Aerobic Respiration: Complete oxidation of glucose in mitochondria.

ATP Supply and Exercise

• Short, intense activity relies on phosphagen system.

• Moderate activity uses glycolysis and aerobic respiration.

Oxygen Debt

• Extra oxygen required after exercise to restore metabolic conditions.

Muscle Fiber Types

• Criteria: Speed of contraction and primary ATP source.

• Types: Slow oxidative (Type I), fast oxidative (Type IIa), fast glycolytic (Type IIb).

Muscle Twitch and Recruitment

• Twitch: Single contraction-relaxation cycle.

• Recruitment: Increasing number of active motor units increases force.

Summation and Tetany

• Wave Summation: Increased force with rapid stimuli.

• Incomplete Tetany: Partial relaxation between stimuli.

• Tetany: Sustained contraction with no relaxation.

Muscle Tone and Contractions

• Muscle Tone: Resting tension in muscles.

• Isometric: Tension without length change (e.g., holding a weight steady).

• Isotonic: Tension with length change (e.g., lifting a weight).

Length-Tension Relationship

• Optimal sarcomere length produces maximal tension.

Muscle Fatigue

• Reduced ability to produce force; caused by ion imbalances, ATP depletion, etc.

Exercise and Muscle Adaptation

• Endurance Training: Increases mitochondria and capillaries.

• Resistance Training: Increases muscle fiber size (hypertrophy).

• Inactivity: Leads to atrophy.

Aging and Muscle

• Decreased muscle mass, strength, and flexibility.

Comparison of Muscle Types

• Skeletal: Striated, voluntary, multinucleated.

• Cardiac: Striated, involuntary, intercalated discs.

• Smooth: Non-striated, involuntary, single nucleus.

Smooth Muscle

• Located in walls of hollow organs (e.g., intestines, blood vessels).

• Contracts via sliding filament mechanism; regulated by autonomic nervous system.

• Multiunit: Individual fibers contract independently.

• Single-unit: Fibers contract as a group via gap junctions.

Muscular System: Axial and Appendicular Muscles

Muscle Attachments

• Superior/Proximal Attachment: Usually less movable (origin).

• Inferior/Distal Attachment: Usually more movable (insertion).

Muscle Fascicle Organization

• Circular: Concentric rings (e.g., orbicularis oris).

• Parallel: Fibers run parallel to long axis (e.g., sartorius).

• Convergent: Broad origin, narrow insertion (e.g., pectoralis major).

• Pennate: Feather-like arrangement (unipennate, bipennate, multipennate).

Muscle Roles

• Agonist: Prime mover of a movement.

• Antagonist: Opposes the agonist.

• Synergist: Assists the agonist.

Muscle Naming Criteria

• Action, body region, attachments, fiber orientation, shape, size, number of heads.

Examples of Muscle Names

• Action: Flexor digitorum (flexes fingers)

• Region: Brachialis (arm)

• Attachments: Sternocleidomastoid (sternum, clavicle, mastoid process)

• Orientation: Rectus abdominis (straight)

• Shape: Deltoid (triangle)

• Size: Gluteus maximus (large)

• Heads: Biceps brachii (two heads)

Muscles of Facial Expression

• Include orbicularis oculi, orbicularis oris, zygomaticus major, etc.

Extrinsic Eye Muscles

• Six muscles: superior, inferior, medial, lateral rectus; superior, inferior oblique.

• Innervated by cranial nerves III (oculomotor), IV (trochlear), VI (abducens).

Muscles of Mastication

• Masseter, temporalis, medial and lateral pterygoids.

• Move the mandible for chewing.

Tongue Muscles

• Intrinsic: Change shape of tongue.

• Extrinsic: Move tongue (genioglossus, hyoglossus, styloglossus, palatoglossus).

Pharyngeal Muscles

• Superior, middle, and inferior pharyngeal constrictors; aid in swallowing.

Suprahyoid and Infrahyoid Muscles

• Suprahyoid: Above hyoid; elevate hyoid (e.g., digastric, mylohyoid).

• Infrahyoid: Below hyoid; depress hyoid (e.g., sternohyoid, omohyoid).

Neck Muscles

• Anterolateral: Sternocleidomastoid, scalenes.

• Posterior: Splenius capitis, semispinalis capitis.

Deep Back Muscles

• Erector spinae group (iliocostalis, longissimus, spinalis) extends vertebral column.

Muscles of Respiration

• Diaphragm, external and internal intercostals.

Abdominal Wall Muscles

• External oblique, internal oblique, transversus abdominis, rectus abdominis.

Pelvic Floor Muscles

• Support pelvic organs; include levator ani, coccygeus.

Perineum Boundaries

• Diamond-shaped region between pubic symphysis, ischial tuberosities, and coccyx.

Thoracic Muscles and Pectoral Girdle

• Anterior: Pectoralis minor, serratus anterior.

• Posterior: Trapezius, rhomboids.

Muscles Moving the Arm

• Flexion: Pectoralis major, anterior deltoid.

• Extension: Latissimus dorsi, posterior deltoid.

• Abduction: Deltoid, supraspinatus.

• Adduction: Pectoralis major, latissimus dorsi.

Rotator Cuff Muscles

• Supraspinatus, infraspinatus, teres minor, subscapularis.

Arm Compartments

• Anterior: Flexors (biceps brachii, brachialis).

• Posterior: Extensors (triceps brachii).

Forearm Muscles

• Anterior: Flex wrist, hand, fingers.

• Posterior: Extend wrist, hand, fingers.

Intrinsic Hand Muscles

• Thenar, hypothenar, and midpalmar groups.

Thigh Muscles

• Anterior: Flex hip (iliopsoas, rectus femoris).

• Medial: Adduct thigh (adductors).

• Posterior: Extend hip (gluteus maximus, hamstrings).

Gluteal Region Muscles

• Gluteus maximus, medius, minimus; abduct and extend thigh.

Knee Joint Muscles

• Quadriceps (anterior) extend knee; hamstrings (posterior) flex knee.

Leg Compartments

• Anterior: Dorsiflex foot (tibialis anterior).

• Lateral: Evert foot (fibularis muscles).

• Posterior: Plantarflex foot (gastrocnemius, soleus).

Muscle Group Actions

• Each group acts together to produce coordinated movement.

Muscle Type	Striations	Control	Nuclei	Location
Skeletal	Yes	Voluntary	Multinucleated	Attached to bones
Cardiac	Yes	Involuntary	1-2 per cell	Heart
Smooth	No	Involuntary	Single	Walls of hollow organs

Additional info: This study guide is based on the learning objectives for Chapters 10 and 11, covering muscle tissue structure, function, contraction mechanisms, muscle types, and the organization and actions of major muscle groups in the human body.