Chapter 9 The Muscular System

Introduction Skeletal muscles: movement in environment Smooth muscles: intestines, ureters, veins and arteries Cardiac muscle: pumps blood through heart and blood vessels 40% - 50% of body weight

The Types of Muscle

The Types of Muscle (cont’d.) Skeletal: voluntary, striated, multinucleated Smooth: involuntary, nonstriated and uninucleated Cardiac: involuntary, striated and uninucleated

The Anatomy of Skeletal or Striated Muscle

The Anatomy of Skeletal or Striated Muscle (cont’d.) Skeletal muscle cell surrounded by sarcolemma Fasciculi: bundles of fascicles Fascicles: individual bundles of muscle fibers

The Anatomy of Skeletal or Striated Muscle (cont’d.) Perimysium: surrounds each fascicle Epimysium: covers the perimysium Fascia: covers the epimysium Myosin: A bands Actin: I bands Z lines H zone

The Anatomy of Skeletal or Striated Muscle (cont’d.) Sarcomere: between two adjacent Z lines Actual contraction process occurs here Sarcotubular system T system and sarcoplasmic reticulum

The Physiology of Muscle Contraction

Introduction Motor unit: all muscle cells innervated by one motor neuron Muscle cell properties Excitability Conductivity Contractility Elasticity

Neuroelectrical Factors Na+ higher concentration outside muscle cell K+ higher concentration inside muscle cell Resting potential: charge outside positive and inside negative Electrical potential: rush of Na+ inside cell K+ moves outside cell attempting to balance

Neuroelectrical Factors (cont’d.) Action potential Calcium released Troponin and tropomyosin action inhibited Activated myosin links to actin filaments

Chemical Interactions Myosin heads contain ATP ATP releases energy upon myosin/action link Energy released used to pull action Sodium: potassium pump pumps out sodium Resting potential restored

Energy Sources ATP: energy source for muscle contraction ATP production Glycolysis Krebs citric acid cycle Electron transport Alternate sources: fatty acids and phosphocreatine

The Muscle Twitch

The Muscle Twitch (cont’d.) Stimulus > latent period > contraction > relaxation Contraction strength depends on Strength, speed and duration of stimulus Weight of load Temperature All-or-none law

Muscle Tone

Muscle Tone (cont’d.) State of partial contraction throughout whole muscle Maintains pressure on abdominal contents Helps maintain blood pressure Aids digestion Types Isotonic, isometric

The Anatomy of Smooth Muscle

The Anatomy of Smooth Muscle (cont’d.) Found in hollow structures Involuntary, uninucleated, nonstriated Arrangement (two layers) Longitudinal (outer) Circular (inner)

The Anatomy of Cardiac Muscle

The Anatomy of Cardiac Muscle (cont’d.) Autonomic nervous system control Involuntary, uninucleated, striated Intercalated disks: coordinate contraction Cardiac muscles: contract, relax and contract 75 times/minute

The Naming and Actions of Skeletal Muscles

The Naming and Actions of Skeletal Muscles (cont’d.) Shape Origin and insertion Location Direction of fibers

The Naming and Actions of Skeletal Muscles (cont’d.) Origin: more fixed attachment of muscle Insertion: movable attachment of muscle Tendons: attach muscle to bone Aponeurosis: wide flat tendon

The Naming and Actions of Skeletal Muscles (cont’d.) Flexors: bend limb at a joint Extensor: straighten limb at a joint Abductors: move limb away from midline Adductors: bring limb toward midline Rotators: revolve limb around axis

The Naming and Actions of Skeletal Muscles (cont’d.) Dorsiflexors: raise the foot Plantar flexors: lower the foot Supinators: turn palm upward Pronators: turn palm downward

The Naming and Actions of Skeletal Muscles (cont’d.) Levators: raise a part of the body Depressors: lower a part of the body Prime movers or agonists: bring about an action Antagonists: oppose agonists Synergists: assist prime movers

The Function and Location of Selected Skeletal Muscles

Superficial Muscles Superficial muscles of the body, anterior view

Superficial Muscles (cont’d.) Superficial muscles of the body, posterior view

Muscles of Facial Expression Occipitalis Frontalis Zygomaticus Levator labii superioris Orbicularis oris and buccinator

Muscles of Facial Expression (cont’d.) Muscles of the head and neck, anterior view

Muscles of Facial Expression (cont’d.) Muscles of the head and neck, lateral view

Muscles of Mastication Masseter Temporalis Pterygoid

Muscles of the Eye Superior rectus Inferior rectus Medial rectus Lateral rectus Superior and inferior oblique

Muscles Moving the Head Sternocleidomastoid Contraction of both causes flexion of neck Contraction of one causes rotation to left or right

Muscles Moving the Shoulder Girdle Levator scapulae Rhomboids Pectoralis minor Trapezius Serratus anterior

Muscles Moving the Humerus Pectoralis major Latissimus dorsi Teres minor Deltoid Supraspinatus Infraspinatus

Muscles Moving the Elbow Brachialis Biceps brachii Brachioradialis Triceps brachii Anconeus

Muscles Moving the Wrist Flexor carpi Extensor carpi

Muscles Moving the Hand Supinator Pronator teres Pronator quadratus

Muscles Moving the Thumb Flexor pollicis Extensor pollicis Adductor pollicis Abductor pollicis Opponens pollicis

Muscles Moving the Fingers Flexor digitorum Extensor digitorum Interossei

Muscles of the Abdominal Wall External oblique Internal oblique Transversus abdominis Rectus abdominis

Muscles of the Abdominal Wall (cont’d.)

Muscles of Respiration or Breathing Diaphragm Main muscle External and internal intercostals Expand the ribs

Muscles Moving the Femur Psoas Iliacus Gluteus maximus Gluteus medius Gluteus minimus Tensor fascia lata

Muscles Moving the Knee Joint Biceps femoris Semitendinosus Semimembranosus Popliteus Gracilis Sartorius Quadriceps femoris

Muscles Moving the Foot Gastrocnemius Tibialis posterior Soleus Peroneus longus Plantaris Tibialis anterior Peroneus tertius

Muscles Moving the Toes Flexor hallucis Extensor hallucis Flexor digitorum Extensor digitorum Abductor hallucis Abductor digiti minimi

Animation – Accessory Muscle Use The following animation illustrates how the accessory muscles assist with the breathing process [Insert accessorymuscle.swf]

Summary Described the gross and microscopic anatomy of skeletal muscle Contrasted skeletal, smooth and cardiac muscle anatomy Described muscle contraction and the role of neuroelectrical and chemical factors and energy sources Named major muscles of the body