Muscular System

Characteristics of Muscle Tissue excitability  ability to receive and respond to stimuli contractility  ability of a muscle to shorten and thicken elasticity  ability of a muscle to return to its original shape extensibility  ability of a muscle to be stretched

Function of Muscle Tissue motion  movement of whole body  localized movements maintenance of posture  helps hold body upright in stationary positions (standing and sitting) heat production  occurs when muscles contract  helps maintain normal body temperature

Function of Muscle Tissue support of soft tissue  abdominal wall and muscles of pelvic floor support the weight of visceral organs and protect internal tissues guards entrances and exits  sphincter muscles encircle opening of digestive and urinary tracts  control swallowing, defecation, and urination

Types of Muscle Tissue Skeletal  location=attached to bones  function=moves parts of skeleton  nervous control=conscious control Smooth  location=walls of hollow internal structure like blood vessels and alimentary canal  function=processes related to maintaining internal environment of body  nervous control=involuntary control Cardiac  location=heart wall  function=pump blood throughout the entire body  nervous control=involuntary control

Skeletal Muscle

Smooth Muscle

Cardiac Muscle

The Principal Skeletal Muscles The Facial Muscles  orbicularis oculi  frontalis -zygomaticus major -zygomaticus minor  masseter - nasalis  orbicularis oris -mentalis -platysma The Muscles of the Neck and Shoulders  sternocleidomastoid  trapezius  deltoid

The Principal Skeletal Muscles The Muscles of the Back  Trapezius  Latissimus dorsi  Infraspinatus  Teres major  Teres minor  External oblique The Muscles of the Chest and Abdomen  Pectoralis major  External oblique  Rectus abdominis  Internal oblique

The Principal Skeletal Muscles The Upper Arm Muscles Serratus anterior Biceps brachii Triceps brachii The Lower Arm Muscles Brachioradialis Extensor carpi radialis longus Pronator teres Extensor digitorum communis Extensor carpi ulnaris

The Principal Skeletal Muscles The Muscles of the Buttocks  Gluteus medius  Gluteus maximus  Biceps femoris

The Principal Skeletal Muscles The Upper Leg Muscles Adductor longus Sartorius Gracilis Rectus femoris Vastus lateralis Vastus medialis The Lower Leg Muscles Gastrocnemius Soleus Flexor digitorum longus Tibialis posterior Tibialis anterior Extensor digitorum longus

Gross Anatomy of Muscle Connective tissue  endomysium surrounds each individual muscle fiber ties into adjacent muscle fibers stem cells are scattered throughout to help damaged muscle repair itself

Gross Anatomy of Muscle Connective tissue  perimysium surrounds bundles of muscle fibers made of collagen & elastic fibers contains blood vessels and nerves

Gross Anatomy of Muscle Connective tissue  epimysium surrounds the entire muscle made of collagen fibers seperate the muscle from surrounding tissues and organs

Gross Anatomy of Muscle Connective tissue  tendon found at the end of each muscles formed by the collagen fibers of all three layers it is called this when muscle is joined to bone fibers are interwoven into the periosteum of the bone contraction of muscle exerts a pull on tendon and attached bone causing movement

Gross Anatomy of Muscle Connective tissue  aponeurosis made of the same tissue as tendons joins muscle to muscle

Gross Anatomy of Muscle Muscle tissue  actin and myosin two main proteins that make up the myofibril  myofibrils thousands of these structures make up a muscle cell  muscle cell also known as a muscle fiber  fascicles bundles of muscle fibers  muscle bundles of fascicles

Gross Anatomy of Muscle Blood Vessels  found in the epimysium and perimysium  bring the oxygen, nutrients needed for muscle contraction  carry away the waste products produced in muscle contraction Nerves  found in the epimysium and perimysium  muscles will only move with nervous stimulation  nerve fibers are found in epimysium, perimysium, and endomysium

Microanatomy of Muscle muscle cells are “typical” cells they are much bigger 100 micrometers in diameter, 24 inches in length multinucleated (hundreds of nuclei on one cell)

Microanatomy of Muscle sarcolemma  the cell membrane of the muscle cell  conducts electrical impulses that cause muscle to contract sacroplasm  the cytoplasm of the muscle cell  electrical impulses from t-tubules end up here

Microanatomy of Muscle transverse tubules  a network of narrow tubules  reached through a number of openings on the surface of the sacrolemma  filled with extracellular fluid  these help coordinate the contraction of muscle fiber  these circle the myofibrils in conjunction with the sacroplasmic reticulum that make a terminal cisternae  form a triad

Microanatomy of Muscle myofibrils  structure that is 1 to 2 microns in diameter and as long as the entire muscle cell  each muscle fiber is made of 100 to 1000s of these structures  these are encircled by t-tubules

Microanatomy of Muscle myofibrils  made of bundles of thick and thin myofilaments  these are made of the proteins actin and myosin  responsible for contraction of the muscle fiber  attached to the sacrolemma at the end of each cell  their contraction shortens the entire cell  mitochondria & granules of glycogen are found throughout the entire cell

Microanatomy of Muscle sarcoplasmic reticulum (SR)  a specialized form of the smooth endoplasmic reticulum  forms a tubular network around every myofibril  on each side of a T tubule, the SR expands to make terminal cisternae  terminal cisternae along with t-tubule form a triad  in these structures are high conc of Ca+2 ions  these ions are pumped across the cell membrane into the excellular fluid  muscle contraction begins when Ca+2 ions are released from the terminal cisternae into the sarcoplasm

Microanatomy of Muscle sacromere  Thick and thin filaments are organized into these  every myofibril is made of ~10,000 sarcomeres  the arrangement of the thick and thin filaments produces a banded appearances

Microanatomy of Muscle sacromere  Zone of Overlap  Z lines boundary of one sacromere  M line made of proteins that connect the central portion of each thick filament to its neighbors  A band a very dark band of thick filaments  I band a very light band of thin filaments

Microanatomy of Muscle Thick Filaments  this is made of the protein myosin which has a tail and a globular head  myosin is oriented away from the center of the sarcomere  heads are facing outward  when the active sites on actin are exposed, the myosin heads bind with the active sites

Microanatomy of Muscle Thin Filaments  made of the protein actin wrapped in the protein tropomyosin  actin has a binding site that will interact with the myosin cross bridges  tropomyosin covers those active sites and is held in place by a chemical called troponin  the muscle will contract only when the binding sites are exposed  when the sites are covered, the muscle is relaxed

Microanatomy of Muscle How muscle is moved  Calcium ions unlock the active site by making troponin change positions  This makes the tropomyosin move and exposes the active sites on the actin  myosin/actin binding occurs  contraction begins

Microanatomy of Muscle Sliding Filaments  this is a theory that was developed to explain how muscles moved  here is what scientists saw when the sacromere contracts the I band gets smaller the Z lines move closer together the zones of overlap got larger the width of the A band doesn't change  best explanation for data one filament was staying still one filament was moving

Microanatomy of Muscle Cross Bridges  the myosin cross bridges are responsible for the movement of the muscle fiber  a cross bridge binds to the actin active site  the cross bridge pivots toward the center of the sacromere  it pulls the actin with it  it detaches and binds again  this continues until the two microfilaments are touching each other  cycle is known as attach, pivot, detach, and return

Sliding Filament Theory

Sliding Filaments and Cross-Bridges

Sliding Filaments and Cross Bridges

Relaxed and Contracted Sacromere

The Neuromuscular Junction Arrival of an action potential at the synaptic terminal Release of acetylcholine (ACh) Ach binding at the end of motor end plate Appearance of an action potential in the sacrolemma

The Contraction Cycle Active Site exposed when Ca ions bind to troponin Myosin cross-bridge forms and attaches to the exposed active site on actin With the help of ATP, myosin head pivots toward the center of the sarcomere ADP and inorganic group are released Myosin cross bridges detach when myosin head binds to another ATP Detached myosin head is reactivated as ATP splits and cycle is repeated beginning with step 2