Muscle Contractions and Movement Quiz

Introduction to Human Anatomy 7101101

• Course name: Introduction to Human Anatomy
• Course code: 7101101

Lectures 10 and 11: Muscular System (4 hours)

• Topic: Muscular System
• Duration: 4 hours

Muscle Types

• Three types are described based on characteristics:
  • Voluntary or involuntary control
  • Appearance under microscope (striated or smooth)
  • Location (body wall, limbs, or hollow organs/blood vessels)
• Types of muscles:
  • Skeletal striated muscle
  • Cardiac striated muscle
  • Smooth muscle

Cardiac Striated Muscle

• Involuntary visceral muscle
• Forms most of the heart walls
• Adjacent parts of great vessels (e.g., aorta)
• Pumps blood
• Cells branch and anastomose
• Transverse striations
• Intercalated discs
• Single, central nucleus
• Strong, quick, and continuous rhythmic contraction
• Involuntary, intrinsically (myogenically) stimulated and propagated
• Modified by autonomic nervous system

Smooth Muscle

• Involuntary visceral muscle
• Forms walls of most vessels and hollow organs
• Moves substances by coordinated sequential contractions (pulsations or peristaltic contractions)
• Cells are single and spindle-shaped
• Lack striations
• Single, central nucleus
• Weak, slow, rhythmic, or sustained tonic contractions
• Involuntary, autonomic nervous system

Skeletal Muscles

• Voluntary somatic muscle
• Forms most of the named muscles
• Composed of skeletal striated muscle
• Organs of locomotion
• Provide static support
• Help give form to the body
• Produces heat through shivering

Skeletal Muscle Structure

• Have fleshy, reddish, contractile portions (one or more heads or bellies)
• Some have white non-contractile portions (tendons) composed of collagen bundles
• Provide attachment
• Tendons are included when measuring muscle length

Myofibril Structure

• Rod-like units
• Composed of actin, myosin, and other proteins
• Organized into thick (myosin) and thin (actin) filaments
• Filaments repeat along the lengths of the myofibril
• Contract by sliding filaments

Muscle Fiber Structure

• Cylindrical, multinucleate
• Comprised of numerous myofibrils
• Enclosed by endomysium
• Muscle fascicles are bundles of muscle fibers
• Surrounded by perimysium
• Muscle is a group of fascicles
• Enclosed by epimysium (deep fascia)

Muscle Attachment

• Most skeletal muscles are attached directly or indirectly to bones, cartilages, ligaments, or fascias.
• Some muscles attach to organs (like eyeballs), skin, or mucous membranes (like the tongue).
• Tendons of some muscles can appear as flat sheets (aponeuroses)
• Tendons attach muscles to a ridge and/or series of spinous processes; deep fascia.
• They may also attach to another muscle's aponeurosis.

Muscle Names

• Most muscles are named on the basis of their function or the bones to which they're attached.
• Examples include abductor digiti minimi, sternocleidomastoid.

Muscle Functional Types

• Prime mover (agonist): The main muscle responsible for a specific movement.
• Antagonist: A muscle that opposes the action of another muscle.
• Fixator: Stabilizes the origin of the agonist and/or the joint to aid the agonist movement.
• Synergist: Assists the prime mover, often providing a weaker or less mechanically advantaged component of the movement

Muscle Contraction

• Isometric Contraction: Muscle length stays the same, but tension increases. Important for maintaining posture or resisting gravity
• Isotonic Contraction: Muscle length changes during movement.
  • Concentric: Muscle shortens.
  • Eccentric: Muscle lengthens.

Reflexive Contraction

• Skeletal muscles are also reflexive.
• The myotatic reflex (stretch reflex) produces movement after tapping a tendon.
• The respiratory movements are often reflexively controlled by carbon dioxide and oxygen levels in blood.

Tonic Contraction

• Even when relaxed, muscles of a conscious individual are slightly contracted (muscle tone).
• Muscle tone helps maintain posture and joint stability
• Usually absent in unconscious individuals (e.g., during deep sleep, or under general anesthesia), or after nerve damage

Motor Unit

• Functional unit of a muscle
• Consists of a motor neuron and its associated muscle fibers
• When stimulated, all the muscle fibers contract simultaneously.
• Fiber number varies according to muscle size and function

Muscle Growth & Regeneration

• Skeletal muscle fibers cannot divide but can be replaced by newer fibers
• Derived from satellite cells.
• New fibers are insufficient for major muscle regeneration after degeneration/trauma
• New fiber growth/repair takes place with fibrous scar tissue
• Hypertrophy is increase in size of existing fibers.

Cardiac Muscle

• Forms parts of the myocardium, aorta walls, pulmonary veins, and superior vena cava
• Involuntary contractions
• Heart rate intrinsically regulated by pacemaker
• Impulse-conducting system and autonomic nervous system (ANS)
• Striated appearance under microscopy
• Rapid and strong contractions

Smooth Muscle Growth & Hypertrophy

• Smooth muscle cells respond to increased demands by undergoing compensatory hypertrophy
• Smooth muscle cells may also increase in number (hyperplasia) in pregnancy, in the uterine wall for example.
• New smooth muscle cells develop from pericytes along small blood vessels.

Test your knowledge on the types of muscle contractions, their roles, and muscle tone. This quiz covers important concepts related to movement mechanics and the functions of various muscle groups. Perfect for students looking to deepen their understanding of anatomy and physiology.