chp 7 muscles Flashcards
different types of muscle tissue
Skeletal Muscle: Voluntary, striated, attached to bones, responsible for movement.
Cardiac Muscle: Involuntary, striated, found in the heart, responsible for pumping blood.
Smooth Muscle: Involuntary, non-striated, found in walls of organs (e.g., intestines, blood vessels), controls movement of substances.
hierarchy of muscle structure, biggest to smallest
muscle, muscle fascicles, muscle fibers, myofibrils, myofilaments
Describe the structure of a skeletal muscle.
Composed of muscle fibers grouped into fascicles, which are surrounded by connective tissue layers:
Endomysium (around individual muscle fibers).
Perimysium (around fascicles).
Epimysium (around the entire muscle).
Myofibrils inside muscle fibers contain myofilaments (actin & myosin), which produce striations.
Explain how a skeletal muscle is attached to a bone or other tissues
Tendons: Tough, cord-like structures that connect muscles to bones.
Aponeuroses: Flat, sheet-like connective tissues that attach muscles to other muscles or tissues.
Describe the structure of a muscle fiber.
Sarcolemma (muscle fiber membrane).
Sarcoplasm (cytoplasm, containing mitochondria and glycogen).
Myofibrils (contractile elements made of sarcomeres).
Sarcomeres (functional unit of contraction, bounded by Z lines).
Sarcoplasmic Reticulum (SR) (stores calcium).
Describe a motor unit.
A motor unit consists of:
One somatic motor neuron.
All the muscle fibers it innervates.
Small motor units = precise movements (e.g., eyes).
Large motor units = powerful contractions (e.g., legs).
Describe the structure and function of a neuromuscular junction.
Structure:
Terminal bouton (end of motor neuron).
Synaptic cleft (gap between neuron and muscle).
Motor end plate (muscle fiber’s specialized membrane).
Function:
Releases acetylcholine (ACh).
ACh binds to receptors, triggering muscle contraction.
Acetylcholinesterase (AChE) breaks down ACh to prevent constant contraction.
Describe the physiology of contraction.
Sliding filament
Excitation: ACh triggers an action potential in the muscle fiber.
Calcium Release: Action potential causes the sarcoplasmic reticulum to release Ca²⁺.
Cross-Bridge Formation: Ca²⁺ binds to troponin, shifting tropomyosin, allowing myosin to bind to actin.
Power Stroke: Myosin pulls actin toward the center of the sarcomere.
ATP Role: ATP detaches myosin and re-energizes it for the next cycle.
Relaxation: AChE breaks down ACh, Ca²⁺ is pumped back into SR, contraction stops.
Explain the all-or-none contraction of muscle fibers.
A muscle fiber contracts completely or not at all when stimulated by a threshold stimulus.
Strength of contraction does not vary at the fiber level.
Discuss how graded contractions of whole muscles produce a variety of contraction strengths
Motor unit recruitment: More motor units activated = stronger contraction.
Wave summation: Repeated stimuli before relaxation increases contraction force.
Tetany: Continuous contraction due to high-frequency stimulation.
Explain the relationship between a muscle’s attachments and its action
Origin: Fixed attachment (less movement).
Insertion: Movable attachment (more movement).
Action: Muscle contracts to pull insertion toward origin.
Explain how agonists and antagonists function in the production of body movements
Agonist (Prime Mover): Muscle that performs the main movement (e.g., biceps brachii in elbow flexion).
Antagonist: Opposes the movement (e.g., triceps brachii in elbow flexion).
Synergists: Assist prime movers.
List the criteria used for naming muscles. (7)
Function (e.g., flexor, extensor).
Shape (e.g., deltoid = triangular).
Relative Position (e.g., anterior, posterior).
Location (e.g., tibialis anterior).
Site of Attachment (e.g., sternocleidomastoid = sternum + clavicle + mastoid).
Size (e.g., maximus, minimus).
Fiber Orientation (e.g., rectus = straight, oblique = angled).
Identify the major muscles on a diagram
Describe the major disorders of the muscular system.
Cramps: Sudden involuntary contractions due to dehydration or electrolyte imbalance.
Fibrosis: Excess connective tissue replaces muscle, reducing function.
Fibromyalgia: Chronic pain and fatigue disorder.
Muscular Dystrophy: Genetic disorder causing progressive muscle weakening.
Strains: Overstretching or tearing of muscle fibers.
Neurological Disorders Affecting Muscles:
Botulism: Toxin blocks ACh release, causing paralysis.
Myasthenia Gravis: Autoimmune disease reducing ACh receptors, leading to weakness.
Poliomyelitis: Viral infection destroying motor neurons.
Spasms: Involuntary muscle contractions.
Tetanus: Bacterial infection causing sustained contractions.
Describe the location and action of the major muscles of the body
Facial Expression: Occipitofrontalis, orbicularis oculi, orbicularis oris, zygomaticus.
Mastication: Masseter, temporalis.
Neck Muscles: Sternocleidomastoid (head rotation).
Abdominal Wall: Rectus abdominis, external oblique.
Breathing Muscles: Diaphragm, intercostals.
Pectoral Girdle: Trapezius, rhomboids.
Arm Movement: Pectoralis major, deltoid, rotator cuff muscles.
Forearm Movement: Biceps brachii (flexion), triceps brachii (extension).
Hand Movement: Flexor and extensor muscles.
Thigh Movement: Gluteus maximus, adductors.
Leg Movement: Quadriceps (extension), hamstrings (flexion).
Foot Movement: Tibialis anterior, gastrocnemius.
