Skeletal System and Bone Types
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Questions and Answers

How many bones are in the adult human skeleton?

  • 80
  • 206 (correct)
  • 300
  • 126

    • The appendicular skeleton consists of 80 bones.

    False

    What type of bone is mostly composed of spongy bone tissue surrounded by a thin layer of compact bone?

    short bones

    The skeleton is part of the _________ system, which combines both muscular and skeletal systems.

    <p>musculoskeletal</p> Signup and view all the answers

    Match the following types of bone with their descriptions:

    <p>Long bones = Longer than they are wide and curved to absorb shock Flat bones = Thin plates of compact bone with spongy interiors Sesamoid bones = Develop in areas of high mechanical stress Irregular bones = Variable shapes and distributions</p> Signup and view all the answers

    What unique property do cervical vertebrae have compared to other vertebrae?

    <p>They have bifid spinous processes.</p> Signup and view all the answers

    The hyoid bone is the same as the Adam's apple in males.

    <p>False</p> Signup and view all the answers

    What type of cartilage makes up the costal cartilages?

    <p>hyaline cartilage</p> Signup and view all the answers

    The ____ of the vertebral column protects the spinal cord.

    <p>vertebral column</p> Signup and view all the answers

    Match the vertebral sections with their corresponding properties:

    <p>Cervical = C1 is called atlas Thoracic = Articulates with the ribs Lumbar = Short and thick spinous processes Sacrum = Five fused vertebrae</p> Signup and view all the answers

    Which bone is considered the 'keystone' of the cranial floor?

    <p>Sphenoid bone</p> Signup and view all the answers

    The maxilla forms the upper jaw of the skull.

    <p>True</p> Signup and view all the answers

    What is the function of fontanels in infants?

    <p>Allow for brain growth and facilitate passage through the birth canal</p> Signup and view all the answers

    The ____ (smallest) bone of the facial bones lies near the tear ducts.

    <p>lacrimal</p> Signup and view all the answers

    Match the following cranial bones with their functions:

    <p>Occipital bone = Forms the posterior and inferior portion of the skull Temporal bone = Accommodates bones of the inner ear Frontal bone = Forms the forehead Ethmoid bone = Forms parts of the nasal cavity and orbits</p> Signup and view all the answers

    What is the primary function of the pectoral girdle?

    <p>Connecting the limbs to the axial skeleton</p> Signup and view all the answers

    The scapula is an anterior bone of the pectoral girdle.

    <p>False</p> Signup and view all the answers

    What is the name of the joint where the clavicle joins the sternum?

    <p>sternoclavicular joint</p> Signup and view all the answers

    The radius is the ______ bone of the forearm, while the ulna is the ______ bone.

    <p>lateral, medial</p> Signup and view all the answers

    Match the following bones with their characteristics:

    <p>Clavicle = Collarbone that connects to the sternum Scapula = Shoulder blade with acromion Humerus = Proximal upper limb bone Ulna = Medial and longest forearm bone</p> Signup and view all the answers

    Which part of the pelvic girdle forms the anterior and inferior portion?

    <p>Pubis</p> Signup and view all the answers

    The femur is the longest bone in the body.

    <p>True</p> Signup and view all the answers

    What is the unique anatomical name for the thumb?

    <p>pollex</p> Signup and view all the answers

    The ________is the only broken bone in the majority of wrist fractures.

    <p>scaphoid</p> Signup and view all the answers

    Match the following parts of the pelvic girdle with their functions:

    <p>Ilium = Accommodates the femoral head Ischium = Forms the buttocks Pubis = Forms the anterior portion Sacrum = Joins the pelvic girdle to the spine</p> Signup and view all the answers

    Which of the following joints join the tibia and fibula?

    <p>Tibiofibular joints</p> Signup and view all the answers

    The obturator foramen is the smallest foramen in the body.

    <p>False</p> Signup and view all the answers

    What type of connective tissue joins the diaphysis of the bones in the forearm?

    <p>interosseous membrane</p> Signup and view all the answers

    The prominent heads of the metacarpals are known as the __________.

    <p>knuckles</p> Signup and view all the answers

    What is the function of the patella?

    <p>Protects the knee joint</p> Signup and view all the answers

    What type of joint is characterized by bones joined by dense irregular connective tissue and lacks an articular cavity?

    <p>Fibrous joints</p> Signup and view all the answers

    Synchondroses are joints that allow for considerable movement between the bones.

    <p>False</p> Signup and view all the answers

    What type of connective tissue is primarily found in syndesmoses?

    <p>Dense irregular connective tissue</p> Signup and view all the answers

    A ______ is a cone-shaped joint between teeth and the mandible or maxilla.

    <p>gomphosis</p> Signup and view all the answers

    Match the following types of joints with their characteristics:

    <p>Sutures = Connect cranial bones with dense irregular CT Syndesmoses = Involves interosseous membranes Synchondroses = Connect bones with hyaline cartilage Gomphosis = Joint between teeth and jaw</p> Signup and view all the answers

    Which type of joint permits only uniaxial movement?

    <p>Hinge joints</p> Signup and view all the answers

    Bursae help reduce friction between bones and soft tissues.

    <p>True</p> Signup and view all the answers

    What is the term for the movement of a bone away from the midline?

    <p>abduction</p> Signup and view all the answers

    The joint between the metacarpal of the thumb and the trapezium is an example of a _____ joint.

    <p>saddle</p> Signup and view all the answers

    Match the following types of synovial joints with their movements:

    <p>Plane joints = Gliding movement Hinge joints = Flexion/extension movement Pivot joints = Rotation movement Condyloid joints = Biaxial movement</p> Signup and view all the answers

    Which component of the synovial joint secretes synovial fluid?

    <p>Synovial membrane</p> Signup and view all the answers

    The term 'double-jointed' refers to having extra joints in the body.

    <p>False</p> Signup and view all the answers

    What is the primary function of synovial fluid?

    <p>Nourishes chondrocytes and reduces friction</p> Signup and view all the answers

    The _________ layer of the articular capsule is made of dense irregular connective tissue.

    <p>fibrous</p> Signup and view all the answers

    What type of joint allows for the greatest range of motion?

    <p>Ball-and-socket joint</p> Signup and view all the answers

    Which type of muscular tissue is responsible for moving blood through the heart?

    <p>Cardiac muscle</p> Signup and view all the answers

    Muscular tissue can be stretched without tearing, which is known as contractility.

    <p>False</p> Signup and view all the answers

    What is the scientific study of muscular tissue called?

    <p>myology</p> Signup and view all the answers

    The connective tissue that wraps around individual fascicles of muscle fibers is called __________.

    <p>perimysium</p> Signup and view all the answers

    Match the type of muscular tissue with its function.

    <p>Skeletal muscle = Contracts to move bones and stabilize positions Cardiac muscle = Contracts to pump blood Smooth muscle = Regulates passage of substances Myocytes = Muscle fibers</p> Signup and view all the answers

    Which protein is primarily responsible for the contraction of muscle fibers?

    <p>Myosin</p> Signup and view all the answers

    Skeletal muscle fibers can divide to increase muscle mass.

    <p>False</p> Signup and view all the answers

    What is the name of the membrane that surrounds a muscle fiber?

    <p>sarcolemma</p> Signup and view all the answers

    The two types of protein filaments in a sarcomere are _____ and _____ filaments.

    <p>thick, thin</p> Signup and view all the answers

    Match the muscle structure with its function:

    <p>Sarcoplasm = Cytoplasm of muscle cells T-tubules = Conduct electrical impulses Myofibrils = Contractile units Sarcoplasmic reticulum = Stores calcium ions</p> Signup and view all the answers

    What role does dystrophin play in muscle cells?

    <p>It connects actin filaments to the dystrophin-glycoprotein complex.</p> Signup and view all the answers

    Muscle contraction requires both ATP and calcium ions (Ca2+).

    <p>True</p> Signup and view all the answers

    What happens to the Z-discs during muscle contraction?

    <p>They come together.</p> Signup and view all the answers

    The protein that blocks the myosin-binding sites on thin filaments until calcium binds is called _________.

    <p>tropomyosin</p> Signup and view all the answers

    Match the following components with their roles in muscle contraction:

    <p>Calcium ions = Bind to troponin to expose myosin-binding sites Myosin = Form cross-bridges with actin ATP = Provide energy for the power stroke Dystrophin = Anchor muscle fibers to the extracellular matrix</p> Signup and view all the answers

    What describes the role of the muscle belly?

    <p>The thickened portion between tendons.</p> Signup and view all the answers

    Third-class levers always produce a mechanical advantage.

    <p>False</p> Signup and view all the answers

    What is the term used for the end of a muscle attached to a moving bone?

    <p>insertion</p> Signup and view all the answers

    In a second-class lever, the load is located between the __________ and the fulcrum.

    <p>effort</p> Signup and view all the answers

    Match the types of levers with their examples:

    <p>First-class lever = Scissors Second-class lever = Wheelbarrow Third-class lever = Forceps Fourth-class lever = Not applicable in human anatomy</p> Signup and view all the answers

    Which muscle acts as the agonist during flexion at the elbow joint?

    <p>Biceps brachii</p> Signup and view all the answers

    The triceps brachii must contract to allow movement at the elbow joint during flexion.

    <p>False</p> Signup and view all the answers

    What is the term for muscles that stabilize intermediate joints to allow movement at another joint?

    <p>synergists</p> Signup and view all the answers

    To permit movement at the Y joint, muscle X must _____ the joint.

    <p>contract</p> Signup and view all the answers

    Match the following muscles with their respective actions:

    <p>Platysma = Pulls the corners of the mouth laterally and inferiorly Masseter = Elevates the mandible Biceps brachii = Flexes the elbow joint Orbicularis oris = Closes and purses the lips</p> Signup and view all the answers

    What is the primary function of the skeletal system related to mineral homeostasis?

    <p>Provides a source of calcium and phosphorus</p> Signup and view all the answers

    The diaphysis of a long bone is located at the ends of the bone.

    <p>False</p> Signup and view all the answers

    What is the term for the process by which mineral salts deposit on collagen fibers to harden bone tissue?

    <p>calcification</p> Signup and view all the answers

    The cells that are known as the stem cells of bone are called __________.

    <p>osteoprogenitor cells</p> Signup and view all the answers

    Match the following components of long bones with their descriptions:

    <p>Diaphysis = Bone shaft Epiphysis = Knobby ends of bones Metaphysis = Connects diaphysis and epiphyses Periosteum = Outer covering of bones</p> Signup and view all the answers

    What type of ossification forms most bones, including long bones?

    <p>Endochondral ossification</p> Signup and view all the answers

    The zone of calcified cartilage contains living chondrocytes.

    <p>False</p> Signup and view all the answers

    What is the primary role of osteoblasts in bone formation?

    <p>To secrete the extracellular matrix (ECM) of bone tissue</p> Signup and view all the answers

    Bone growth occurs at the ______ plate of long bones.

    <p>epiphyseal</p> Signup and view all the answers

    Match the following zones of the epiphyseal plate with their descriptions:

    <p>Zone of resting cartilage = Anchors epiphyseal plate to bone Zone of proliferating cartilage = Contains actively dividing chondrocytes Zone of hypertrophic cartilage = Contains large cells arranged in columns Zone of calcified cartilage = Contains layers of dead chondrocytes</p> Signup and view all the answers

    What type of bone tissue is primarily found at the ends of long bones, known for being lighter and capable of handling stress along multiple axes?

    <p>Spongy bone tissue</p> Signup and view all the answers

    Osteocytes secrete collagen and other components of bone ECM.

    <p>False</p> Signup and view all the answers

    What is the name of the process by which bone forms?

    <p>ossification</p> Signup and view all the answers

    The structural unit of compact bone is called the ________.

    <p>osteon</p> Signup and view all the answers

    Match the following types of bone cells with their descriptions:

    <p>Osteoblasts = Secrete bone matrix and form new bone Osteocytes = Mature bone cells that maintain bone tissue Osteoclasts = Break down bone tissue and resorb minerals Chondrocytes = Cells that create cartilage</p> Signup and view all the answers

    Study Notes

    Skeletal System Divisions

    • The human skeleton is made up of 206 bones.
    • The skeleton is divided into two main groups: the axial skeleton and the appendicular skeleton.
    • The axial skeleton consists of 80 bones and includes the bones of the head, neck, and trunk.
    • The appendicular skeleton consists of 126 bones and includes the bones of the limbs, including the pectoral and pelvic girdles.
    • The skeleton works together with the muscular system to form the musculoskeletal system.
    • The musculoskeletal system facilitates movement.

    Bone Types

    • There are five main types of bones: long, short, flat, sesamoid, and irregular.
    • Long bones are longer than they are wide and are curved to absorb shock. They contain spongy bone tissue in the epiphyses (ends of the bone) and compact bone tissue in the diaphysis (shaft of the bone).
    • Short bones are nearly as long as they are wide and consist mostly of spongy bone tissue surrounded by a thin layer of compact bone.
    • Flat bones are thin plates of compact bone with spongy bone interiors.
    • Sesamoid bones are thin, small bones that develop in areas of high mechanical stress and protect tendons by modulating tension applied during movement.
    • Irregular bones can be oddly shaped or distributed in the body.

    Bone Surface Markings

    • Bone surface markings have physiological functions.
    • Depressions and openings provide passage for blood vessels and nerves. These include foramina, fossae, and meati.
    • Processes, projections, or outgrowths are attachment points for ligaments and tendons. These include condyles, facets, heads, crests, and processes.

    Skull: Cranial and Facial Bones

    • The skull protects the brain.
    • The skull is the point of attachment for the facial muscles.
    • It forms portions of the orbits, nasal, and oral cavities.
    • The skull includes the auditory ossicles, which are responsible for hearing.

    Cranial Bones

    • The skull contains 22 bones; some are paired.
    • The frontal bone forms the forehead and the supraorbital foramen provides passage for the supraorbital artery and nerve.
    • The ethmoid bone forms the medial portion of the orbits and anterior portion of the cranial floor.
      • The crista galli is a triangular process where the membrane that separates the two halves of the brain attaches.
      • The cribriform plate contains the olfactory foramina, which provide passage for sensory structures required for smell.
      • The perpendicular plate forms the superior part of the nasal septum.
    • The sphenoid bone is the "keystone" of the cranial floor and contains the optic foramen which allows passage of the ophthalmic artery and optic nerve.
    • The temporal bones form the lateral and inferior portions of the cranium.
      • The zygomatic arch forms the lateral part of the "cheekbone".
      • The mandibular fossa forms a cavity that accommodates the mandibular condyle and forms the temporomandibular joint.
      • The styloid process is the point of attachment for neck and tongue muscles.
      • The mastoid process is the point of attachment for neck muscles.
      • The external auditory meatus forms the ear canal and directs sound waves towards the auditory ossicles.
    • The auditory ossicles transmit sound waves.
      • The malleus (hammer), incus (anvil), and stapes (stirrup) are impacted by soundwaves hitting the tympanic membrane, vibrating them and ultimately sending vibrations to the auditory sensory structures.
    • The occipital bone forms the posterior and inferior portion of the skull.
      • The occipital condyles form joints with the first cervical vertebra (atlas) forming the atlantooccipital joint.
      • The foramen magnum provides passage for the spinal cord to connect with the brain.
    • The parietal bones form the superior and lateral portions of the skull.

    Facial Bones

    • 14 facial bones form the anterior portion of the skull.

    • The mandible is the only movable bone of the skull and forms the lower jaw.

      • The condylar process articulates with the mandibular fossa of the temporal bone.

    • The maxillae form the upper jaw.

      • The palatine process forms most of the hard palate, which separates the oral cavity from the nasal cavity.
      • The remaining portion of the hard palate is formed by the palatine bones.

    • The palatine bones are L-shaped bones that complete the posterior portion of the hard palate.

    • The zygomatic bones form the anterior portion of the "cheekbones" and the inferior and lateral walls of the orbits.

    • The vomer is Latin for "ploughshare" and forms the inferior portion of the nasal septum.

    • The inferior nasal conchae are pretty, curled bones that form the lateral walls of the nasal cavity.

      • They swirl air and trap airborne invaders.

    • The nasal bones form the bridge of the nose.

    • The lacrimal bones, the smallest of the facial bones, are located near the tear ducts (lacrimal ducts).

    Special Features of the Skull

    • The orbits contain the eyes and are made of seven bones: frontal, lacrimal, ethmoid, zygomatic, sphenoid, maxilla, palatine.

    • Sutures are found in the skull, which are where bones grow together.

      • At birth, the skeleton isn’t completely ossified (formed).
      • These "soft spots" are known as fontanels.
      • Mesenchymal tissue persists before becoming dense connective tissue.
      • Fontanels allow for the growth of the brain to fit within the cranium.
      • They also facilitate passage of the newborn's head through the birth canal during labor.

    • The coronal suture connects the frontal and parietal bones.

    • The sagittal suture connects the parietal bones superiorly.

    • The lambdoid suture connects the parietal bones to the occipital bone.

    • The squamous suture connects the parietal bone to the temporal bone.

    • The zygomatic arch is a prominent bony portion that runs laterally and posteriorly from the zygomatic bone and is formed by the zygomatic bone and temporal bone.

    • Sinuses consist of cavities lined with mucous membranes within facial bones. They trap invaders and lighten the skull.

    The Hyoid Bone

    • The hyoid bone is a unique bone that does not articulate with any other bone.
    • Muscles of the tongue attach to the hyoid bone.
    • This bone does not form the Adam’s apple in males; the Adam's apple is made of thyroid cartilage.

    Vertebral Column

    • The vertebral column supports and moves the skull, protects the spinal cord, provides attachment points for back and abdominal muscles, contains intervertebral discs to cushion vertebrae from shock, and protects many nerves.

    Properties of the Vertebral Column

    • The vertebral column is divided into subregions.
    • It is curved to improve shock absorption.
    • The normal curves of the spine include four curves acquired over time.
      • The cervical vertebrae curve is acquired after holding up one's head.
      • The lumbar vertebrae curve is acquired after learning to walk.

    Intervertebral Discs

    • Intervertebral discs are made of fibrocartilage and lie between vertebrae, compressing throughout the day due to dehydration.
    • This is why we are tallest in the morning, as the force of gravity is lessened on the vertebrae while lying down.

    Vertebral Anatomy

    • The body of the vertebrae bears weight and contains nutrient foramina.
    • The vertebral foramen provides passage for the spinal cord.
    • Superior articular processes articulate with the inferior articular processes of the vertebrae above them, and are surfaces where bones connect to one another.

    Cervical Vertebrae

    • Cervical vertebrae are the most superior vertebrae.
    • They form the neck and are numbered C1-C7.
    • Cervical vertebrae contain special features:
      • C1 (atlas) has no body, no spinous process, a distinct anterior arch, and a large vertebral foramen that accommodates the C2 dens.
      • C2 (axis) contains a large superior and anterior projection known as the dens, which passes through the vertebral foramen of the atlas. The atlanto-axial joint permits turning of the head left and right.
    • C3-C7 have spinous processes that are bifid (two-headed), and their transverse processes contain the transverse foramen which provides passage for the vertebral arteries.

    Thoracic Vertebrae

    • Thoracic vertebrae are numbered T1-T12.
    • They contain large transverse processes for articulations with the ribs.
      • Demifacets are unique to the thoracic vertebrae and are surfaces where the head of one rib connects with two vertebrae.

    Rib Anatomy

    • The head of a rib articulates with demifacets on two vertebral bodies.
    • The neck is the narrowed region adjacent to the head.
    • The tubercle is a posterior and lateral projection that articulates with facets on the transverse processes of thoracic vertebrae.

    Lumbar Vertebrae

    • Lumbar vertebrae (L1-L5) are short and thick with spinous processes. They are points of attachment for back muscles.

    • The sacrum is five fused vertebrae that articulates with the pelvic girdle at the sacroiliac joints. The vertebral canal becomes the sacral canal at the sacral vertebrae and ends at the sacral hiatus (inferior opening).

    • The coccyx is the tailbone made up of four fused coccygeal vertebrae (Co1-Co4).

    The Thoracic Cage

    • The thoracic cage forms the ribcage and breastbone.
    • The sternum is the breastbone and is the medial bone to which the ribs attach.
      • The manubrium is the most superior part of the sternum.
      • The body is the long intermediate portion of the sternum.
      • The xiphoid process is the tiny inferior bone of the sternum.
      • The suprasternal notch is a medial depression between the clavicular notches.
      • The clavicular notches are the sites of articulation between the sternum and the clavicles.

    Ribs

    • True ribs are the first seven ribs, articulating with the thoracic vertebrae and the sternum.
    • False ribs articulate with the thoracic vertebrae but not the sternum.
      • Ribs 8-10 articulate with the costal cartilage of the 7th rib.
      • Costal cartilages are made of hyaline cartilage.
    • Floating ribs (11-12) do not articulate with any bones anteriorly.

    Disorders of the Axial Skeleton

    • Scoliosis is a lateral bending of the vertebral column.

      • It is an abnormal curve of the vertebral column, usually at the thoracic vertebrae.
      • Scoliosis can be inherited or compensatory (in response to unequal leg length).
      • Signs of scoliosis include uneven shoulders and/or waist and difficulty breathing in severe cases.
      • Symptoms include chronic back pain and arthritis.
      • Treatment options include bracing, physical therapy, or surgery.

    • Spina bifida is incomplete closing of the vertebral column during fetal development.

      • It is often characterized by a protrusion of the spinal cord (meningocele).
      • Folic acid supplementation during pregnancy decreases the risk of spina bifida.
      • Treatment options include physical therapy and surgery.

    Summary

    • The axial skeleton includes the bones of the cranium, face, vertebral column, and thoracic cage.
    • The axial skeleton is a source of red bone marrow.
    • It protects internal organs, including the brain, spinal cord, and viscera of the thoracic cavity.

    Appendicular Skeleton Functions

    • Anchors the limbs to the axial skeleton
    • Attaches to skeletal muscle

    Pectoral Girdle

    • Two lateral sides, each composed of a clavicle and a scapula
    • Clavicle is the collarbone (anterior)
    • Scapula is the shoulder blade (posterior)
    • Provides structural support to the shoulder region

    Clavicle

    • S-shaped bone forming the anterior portion of the pectoral girdle
    • Joins the sternum at the sternoclavicular joint
    • Only direct connection between the pectoral girdle and axial skeleton

    Scapula

    • Triangular flat bone forming the posterior portion of the pectoral girdle
    • Acromion is the "high point" of the shoulder, articulating with the clavicle at the acromioclavicular joint
    • Spine is a thick ridge extending inferiorly and medially from the acromion
    • Coracoid process is a lateral and superior projection, serving as an attachment point for muscles and ligaments of the arms and chest
    • Glenoid cavity is a depression accommodating the humeral head

    Upper Limbs

    • Composed of 30 bones divided into three regions: humerus (proximal upper limb), radius and ulna (forearm), and carpals + metacarpals + phalanges (wrist and hand)

    Humerus

    • Humeral head is a large, rounded epiphysis articulating with the glenoid cavity of the scapula, forming the glenohumeral joint

    Ulna

    • Medial and longest forearm bone
    • Head of the ulna is at the distal portion, joined to the wrist by fibrocartilage
    • Olecranon is a projection at the proximal end, forming the bony part of the elbow

    Radius

    • Lateral bone of the forearm, shorter than the ulna
    • Head of the radius is located at the proximal end, articulating with the humerus and ulna
    • Distal end articulates with the ulna and carpals

    Radius and Ulna Connection

    • Joined by joints at the epiphyses (two proximal joints at the elbow and one distal joint at the wrist)
    • Interosseous membrane joins the diaphysis, composed of fibrous connective tissue

    Carpals

    • The carpus or wrist is formed by the distal radioulnar joint and radiocarpal joints
    • Scaphoid is the most commonly fractured bone in wrist fractures

    Metacarpals

    • Intermediate between carpals and phalanges
    • Prominent heads of metacarpals form the "knuckles"
    • Numbered 1-5, thumb to little finger

    Phalanges

    • Bones of the digits, most distal bones of the upper limb
    • Thumb is called the pollex
    • Numbered as digits 1-5, thumb to little finger

    Pelvic Girdle

    • Joins the lower limbs to the axial skeleton
    • Stabilizes the position of the axial skeleton during lower limb movement
    • Protects organs of the reproductive, digestive, and excretory systems

    Coxal (Hip) Bones

    • Two hip or coxal bones fan out laterally from the sacrum
    • Each coxal bone is divided into three regions: ilium, ischium, and pubis

    Ilium

    • Acetabulum is a depression accommodating the femoral head
    • Iliac crest is the superior and lateral border of the coxal bones
    • Sciatic notch houses the sciatic nerve
    • Sacroiliac joint is the portion of the ilium that joins the sacrum

    Ischium

    • Forms the inferior and posterior portion of the pelvic girdle, contributing to the acetabulum
    • Known as the "butt bones"

    Pubis

    • Forms the anterior and inferior portion of the pelvic girdle
    • Pubic symphysis is the anterior joining of the two coxal bones held together by fibrocartilage
    • Pubic arch lies inferior to the pubic symphysis, formed by the inferior joining of the coxal bones
    • Obturator foramen is the largest foramen in the body, allowing passage for blood vessels and nerves, enabling rotation and abduction

    True and False Pelves

    • The pelvis can be divided into a superior and inferior portion by the pelvic brim
    • False pelvis is the portion superior to the pelvic brim
    • True pelvis is the portion inferior to the pelvic brim

    Pelvic Axis

    • Pelvic inlet is the superior opening defined by the pelvic brim
    • Pelvic outlet is defined by the inferior opening of the true pelvis
    • Pelvic axis is an imaginary line connecting the center of the inlet to the center of the outlet

    Male and Female Pelves

    • The male and female pelves have distinct features.
    • The female pelvis has a wider pelvic brim and false pelvis, a larger pubic arch exceeding 90 degrees.
    • The male pelvis has a smaller false pelvis, narrower pelvic brim, and a smaller pubic arch.

    Lower Limb

    • Composed of 30 bones divided into four regions: femur (thigh), patella (kneecap), tibia and fibula (lower leg), and tarsals, metatarsals, and phalanges of the foot (tarsus or ankles and feet)

    Femur

    • Longest, strongest, and heaviest bone in the body
    • Joins the pelvic girdle at the acetabulum
    • Femoral head is the large, round proximal epiphysis
    • Femoral neck is the constricted portion just distal to the head, susceptible to hip fractures
    • Medial and lateral condyles are distal knobby projections, articulating with the tibia and patella

    Patella

    • Sesamoid bone articulating with the femur and tibia
    • Protects the knee joint
    • Stabilizes tendon position when the knee is bent
    • Increases leverage of the quadriceps femoris muscle

    Tibia

    • Longer bone of the lower leg
    • Tibial tuberosity is a large anterior and proximal projection, serving as an attachment point for the patellar ligament
    • At the distal end of the tibia, the medial malleolus articulates with the talus (a tarsal), forming the medial bony "ankle bone"

    Fibula

    • Smaller bone of the lower leg (lateral)
    • Only articulates with the tibia and the talus (a tarsal)
    • Fibulotalar joint forms the large lateral “ankle bone”, known as the lateral malleolus

    Tibia and Fibula Connection

    • Joined by joints at the epiphyses (proximal and distal tibiofibular joints)
    • Interosseous membrane joins the diaphysis

    Tarsus

    • Composed of seven tarsals
    • Metatarsals are numbered 1-5, medial to lateral
    • Phalanges are numbered 1-5 by digit (like the hand)
    • Big toe is called the hallux

    Tarsals

    • Located in the posterior portion of the foot
    • Talus articulates with the fibula to form the lateral malleolus
    • Calcaneus is the largest and strongest tarsal, forming the heel bone

    Summary

    • The upper limbs are attached to the axial skeleton via the pectoral girdle, while the lower limbs are attached via the pelvic girdle.
    • The limbs move around articulations or joints, formed at bone-bone contacts.
    • The appendicular skeleton stabilizes the axial skeleton, enabling muscles to move the limbs.

    Introduction to joints

    • Joints are also known as articulations or arthroses
    • Scientific study of joints = arthrology

    Classification of joints

    • Joints are classified by their structure
    • Two key structural features:
      • Presence of an articular cavity between bones
      • Type of connective tissue connecting bones

    Fibrous joints

    • Bones connected by dense irregular connective tissue (CT)
    • No articular cavity
    • Generally immobile
    • Three types:
      • Sutures: Connect cranial bones with a thin strip of dense irregular CT (synostoses in adults)
      • Syndesmoses: Thicker and longer strip of dense irregular connective tissue (interosseous ligament or membrane)
      • Gomphoses: Cone-shaped joint between teeth and the mandible or maxilla

    Cartilaginous joints

    • Bones joined by cartilage; no articular cavity
    • Little or no movement
    • Two subtypes:
      • Synchondroses: Connect bones with hyaline or fibrocartilage cartilage
      • Symphyses: Connect bones with fibrocartilage, still covered in hyaline cartilage at articular surfaces

    Synovial joints

    • Distinguished by presence of articular cavity between bones
    • Bounded by articular capsule which secretes lubricating fluid
    • Bones covered in articular cartilages (hyaline cartilage)
    • Freely moveable

    Components of synovial joints

    • The articular capsule has two layers:
      • Fibrous layer: Outer layer of dense irregular CT, attaches to periosteum and forms ligaments at some joints
      • Synovial membrane: Inner layer of areolar CT, secretes synovial fluid

    Synovial fluid functions

    • Nourishes chondrocytes of articular cartilage
    • Contains oxygen and nutrients
    • Contains immune cells
    • Reduces friction between bones at joints
    • Absorbs shock

    Other synovial joint components

    • Accessory ligaments: Provide extra reinforcement
    • Articular discs or menisci: Fibrocartilage padding that absorbs shock and distributes weight evenly
    • Bursae: Reduce friction between moving structures, found between bones and soft tissue (tendons, ligaments)
    • Tendon sheaths: Tube-shaped bursae that wrap around tendons to reduce friction

    Movements

    • Synovial joints are the only freely movable joints
    • Four main categories of movement:
      • Gliding: Nearly flat bones slide back-and-forth and side-to-side
      • Angular movements: Increase or decrease angles between articulating bones
        • Flexion: Decreases angle
        • Extension: Increases angle
        • Lateral flexion: Decreases angle in the coronal plane
        • Abduction: Movement of a bone away from the midline
        • Adduction: Movement of a bone toward the midline
        • Circumduction: Movement around a joint to move the distal part of a limb in a circle
      • Rotation: Turning of a bone along its longitudinal axis (medial or lateral)
      • Special movements: Movements unique to specific joints

    Special movements

    • Mandible:
      • Elevation: Moved upward
      • Depression: Moved downward
      • Protraction: Moved forward
      • Retraction: Moved backward
    • Hands and feet:
      • Dorsiflexion: Bending the foot toward the shin
      • Plantar flexion: Bending the foot toward the sole
      • Inversion: Turning sole to face midline
      • Eversion: Turning sole to face away from the midline
    • Supination: Turning the palm to face the sky
    • Pronation: Turning the palm to face the floor
    • Opposition: Movement of the pollex (thumb) at the carpometacarpal joints to touch the other fingers

    Types of synovial joints

    • Six types:
      • Plane joints
      • Hinge joints
      • Pivot joints
      • Condyloid joints
      • Saddle joints
      • Ball-and-socket joints

    Plane joints

    • Permit gliding movements
    • Movements are biaxial
    • Examples:
      • Intercarpal or tarsal joints
      • Sternoclavicular joints
      • Vertebrocostal joints

    Hinge joints

    • Movement is uniaxial (flexion/extension)
    • Usually one bone is fixed, the other moves
    • Examples:
      • Knee joints
      • Elbow joints
      • Ankle joints
      • Interphalangeal joints

    Pivot joints

    • Rounded surface of bone fitted to a ring made by a ligament + other bone
    • Permits uniaxial movement
    • Examples:
      • Atlanto-axial joint (shake your head no)
      • Radioulnar joints (supination/pronation)

    Condyloid joints

    • Also known as ellipsoidal joints
    • Oval-shaped protrusion fits an oval-shaped depression
    • Permits biaxial movement (flexion/extension, abduction/adduction, circumduction)
    • Example: radiocarpal joints (wrist)

    Saddle joints

    • One bone looks like a saddle and the other looks like a rider
    • Permits biaxial movement (flexion/extension, abduction/adduction, circumduction)
    • Example: Carpometacarpal joint between proximal metacarpal of the thumb and trapezium

    Ball-and-socket joints

    • Ball-shaped projection fits into a cup-shaped depression
    • Permits triaxial movement (flexion/extension, abduction/adduction, circumduction, rotation)
    • Examples: Shoulder and hip joints

    Special examples of joints

    • The temporomandibular joint (TMJ)
      • Only freely moveable joint in the skull
      • Combination of hinge and plane joints
      • Articulation between the condylar process of the mandible and mandibular fossa of the temporal bone
      • Articular components:
        • Articular capsule
        • Multiple ligaments
        • Meniscus subdivides synovial cavity into:
          • Superior: Permits slight rotation, lateral displacement, protraction/retraction
          • Inferior: Permits depression/elevation
      • Movements permitted:
        • Depression/elevation
        • Protraction and retraction
        • Lateral displacement
        • Some rotation

    The glenohumeral joint (shoulder)

    - Ball-and-socket joint
- Thin, loose articular capsule (important for range of motion) 
- Articular components: 
    - Many ligaments reinforce the joint
    - Glenoid labrum: Fibrocartilage lip or rim of the glenoid cavity
    - Bursae: Four pads to absorb shock and reduce friction
- Movements: 
    - Flexion, extension, hyperextension
    - Abduction, adduction
    - Medial and lateral rotation 
    - Circumduction
    - Great range of motion but less stable than the coxal joint

    The elbow joint

    - A joint formed by: Humerus, Ulna, Radius 
- Articular components:
    - Articular capsule
    - Collateral ligaments: Strong connections between humerus and radius or ulna
    - Annular ligament: Holds radial head to radial notch of the ulna 
    - Bursa at the olecranon
- Movements: 
    - Flexion or extension (hinge joint)

    The coxal or hip joint

    - Ball-and-socket joint formed by the acetabulum of the coxal bone + head of the femur
- Very stable joint due to:
    - Number and arrangement of ligaments 
    - Specific fit of the femoral head in the acetabulum
- Articular components:
    - Thick articular capsule
    - Acetabular labrum: Fibrocartilage lip of the acetabulum that prevents displacement of the femoral head
    - Accessory ligaments: Numerous and strong
- Movements: 
    - Flexion/extension 
    - Abduction/adduction 
    - Lateral and medial rotation
    - Circumduction

    The knee joint

    - A modified hinge joint
- Three joints that share one synovial cavity:
    - Lateral joint between femur and tibia
    - Medial joint between femur and tibia 
    - Anterior patellofemoral joint (a plane joint)
- Articular components:
    - No single identifiable articular capsule (collection of muscle tendons serves a similar function)
    - Cruciate ligaments: Accessory ligaments that cross one another
    - Collateral ligaments: Reinforce connection between femur + tibia, femur + fibula
    - Menisci: One medial, one lateral 
- Movements: 
    - Flexion/extension 
    - Some rotation

    Joint diseases and disorders

    • Arthritis:
      • Osteoarthritis: Progressive loss of articular cartilage
    • Sprains and strains:
      • Sprains: Forceful stretching or tearing of ligaments (no bone dislocation)
      • Strains: Partially torn or stretched muscle or tendon (treat with PRICE)

    Summary

    • Joints are the sites of contact between bones, classified by structure or function
    • Synovial joints are the only freely moveable joints
    • Movements permitted around joints are a consequence of synovial joint structure
    • Joint diseases or disorders may be treated with PRICE

    Introduction to Muscular Tissue

    • There are three types of muscular tissue: skeletal, cardiac, and smooth.
    • Skeletal muscle tissue contracts to move bones and stabilize body positions.
    • Cardiac muscle tissue contracts to move blood through the heart.
    • Smooth muscle tissue contracts to regulate the passage of substances through the body, for example, in the GI tract and blood vessels.
    • All muscles generate heat during contraction.
    • The scientific study of muscular tissue is called myology.
    • Muscular tissue has four special properties: excitability, contractility, extensibility, and elasticity.
    • Muscular tissue is electrically excitable, producing electrical signals called muscle action potentials.
    • Nerve tissues are also excitable.
    • Muscular tissue is contractile, and muscle action potentials stimulate contraction.
    • Contractions generate tension on bones, resulting in movement.
    • Muscular tissue is extensible, meaning it can be stretched without tearing, like the smooth muscle around the stomach.
    • Muscular tissue is elastic, meaning it can return to its resting length after stretching.
    • Connective tissues called fascia physically group muscles with similar functions together and provide passage for nerves and vasculature.

    The Structure of Skeletal Muscle

    • The cells of skeletal muscle tissue are called muscle fibres.
    • They are elongated cells also known as myocytes.
    • Cells contain bunched protein filaments called myofibrils.
    • Muscle fibres + connective tissue + nerve and blood supply = muscle (an organ).
    • Muscles are surrounded by connective tissue layers called the fascia.
    • The fascia are composed of three layers: epimysium, perimysium, and endomysium.
    • Epimysium is the most superficial layer, composed of dense irregular CT that wraps muscles.
    • Perimysium is the intermediate layer, composed of dense irregular CT that wraps fascicles, which are bundles of muscle fibres (cells).
    • Endomysium is the deepest layer, composed mostly of reticular fibres that wrap individual muscle fibres.
    • The fascia form tendons, which connect muscles to bones as a thick rope-like structure.
    • Aponeuroses are a special type of tendon that forms broad sheets, like the epicranial aponeurosis which connects the two bellies of the occipitofrontalis muscle.
    • Muscular tissue requires oxygen-rich blood and is extensively vascularized.
    • Skeletal muscles are extensively innervated by somatic motor neurons, which regulate voluntary muscle contraction.
    • Axons branch from the spinal cord to muscles, usually with one branch per muscle fibre.

    Skeletal Muscle Fiber Structure

    • You are born with every muscle fibre you will ever have. They start as immature cells called myoblast in the womb, which fuse as they mature, resulting in large, multinucleate cells.
    • The plasma membrane of myocytes is called the sarcolemma.
    • Electrical signals run along the sarcolemma and fold inwards or invaginate forming T-tubules.
    • The cytoplasm of myocytes is called the sarcoplasm.
    • Sarcoplasm is densely packed with myofibrils and rich in glycogen (carbohydrate energy store).
    • Sarcoplasm also contains myoglobin.
    • Myoglobin is only found in muscle cells and binds oxygen at an iron-containing centre called heme.
    • Myocytes receive oxygen from both inside and outside the cell.
    • Myofibrils are long threads of contractile protein filaments (approximately 2 nm in diameter).
    • The regular pattern of overlapping filaments gives skeletal and cardiac muscle a striated appearance.
    • The sarcoplasmic reticulum stores and releases calcium.
    • The SR is the specialized smooth endoplasmic reticulum in muscle cells.
    • It is extensively folded around each myofibril, with membrane folds called cisternae.
    • The terminal cisternae specifically release Ca2+ to each T-tubule.
    • When two terminal cisternae meet a T-tubule, it forms a triad.
    • Muscle fibres do not divide, but they can enlarge (hypertrophy) by laying down new protein.
    • Muscular hypertrophy is an increase in sarcoplasmic volume, which increases the volume of cellular contents, especially myofibrils.
    • Hypertrophy is a response to increased mechanical stress, hormones (e.g. anabolic steroids), or disease (e.g. increased demand on a diseased heart).

    Sarcomere Structure

    • Myofibrils are bundles of thread-like structures called myofilaments.
    • Each myofilament is made of contractile units called sarcomeres, joined end-to-end.
    • Each sarcomere consists of overlapping thick and thin filaments.
    • The thick filaments extend from the midline (M-line) of the sarcomere and are made of myosin.
    • The thin filaments extend from the ends (Z-discs) of the sarcomere and are made of actin.
    • The sarcomere is divided into zones and bands:
      • The A band is where the thick and thin filaments overlap and everything in between.
      • The H zone is the region between the zones of overlap around the M-line and contains only thick filaments.
      • The I band is the region between zones of overlap around the Z-discs and contains only thin filaments.

    Muscle Contraction

    • Muscles generate force by contraction.
    • Muscle contraction involves three types of proteins: contractile proteins, regulatory proteins, and structural proteins.
    • Contractile proteins shorten the sarcomere.
    • Myosin is a motor protein that converts chemical potential energy in ATP to mechanical energy.
    • Each thick filament consists of approximately 300 myosin proteins.
    • Myosin heads extend radially from the ends of thick filaments, contact thin filaments, and pull thin filaments toward the M-line.
    • Each myosin head has an ATP-binding site and an actin-binding site.
    • Actin is a cytoskeletal protein that forms long threads twisted around one another to form helical thin filaments, containing myosin-binding sites.
    • Regulatory proteins associate with the thick and thin filaments to control contraction.
    • Troponin binds Ca2+ and moves tropomyosin.
    • Tropomyosin blocks myosin-binding sites on thin filaments.
    • Structural proteins stabilize and/or connect the sarcomere and surrounding structures.
    • Titin is a large elastic protein that spans the M-line to Z-discs and stabilizes the position of thick filaments.
    • Dystrophin connects thin filaments to integral membrane proteins in the sarcolemma.
    • Dystrophin reinforces sarcomere structure and transmits tension of sarcomeres to tendons.

    Muscle Contraction by the Sliding Filament Model

    • The sarcomere shortens as the thin filaments slide over the thick filaments.
    • This mechanism is called the sliding filament model.
    • The filaments themselves do not change in length.
    • The contraction cycle involves myosin binding the thin filaments, pulling them into the M-line, and then releasing them.
    • This iterative binding and release is called the contraction cycle.
    • The contraction cycle involves four steps:
      • Myosin binds and hydrolyzes ATP, energizing myosin and changing its conformation (cocked, like a gun).
      • Myosin binds thin filaments to form a cross-bridge.
      • Myosin pulls the thin filaments toward the M-line (power stroke).
      • Myosin detaches from thin filaments, requiring the binding of a new ATP molecule to myosin.
    • Myosin-binding sites on the thin filaments are obscured until troponin binds Ca2+.
    • Ca2+ changes troponin's conformation.
    • Troponin moves tropomyosin off the myosin-binding sites on actin.
    • Myosin can now form a cross-bridge.
    • Muscle contraction requires both ATP and Ca2+.
    • As myosin pulls on the thin filaments, the Z-discs come together, the sarcomere shortens, the H zone disappears, and the I band narrows.

    The Length-Tension Relationship

    • The amount of filament overlap matters.
    • If the thick and thin filaments completely overlap at rest, there is no room for thin filaments to slide, reducing tension.
    • If the thick and thin filaments barely overlap at rest, there are too few cross-bridges, reducing tension.
    • There's an optimal sarcomere length with sufficient filament overlap to generate maximal tension.

    Muscle Action Potentials

    • Muscles store Ca2+ in the sarcoplasmic reticulum and export it using membrane transporters.
    • Muscle fibres are electrically excitable, and signals from somatic motor neurons stimulate an action potential.
    • The neuromuscular junction (NMJ) is where neurons and muscles meet.
    • Somatic motor neurons release neurotransmitters, such as acetylcholine, which bind to protein receptors on muscle cells and induce an action potential in muscle cells.
    • The Na+-K+ pump keeps the inside of animal cells negative compared to the outside.
    • During an action potential, the membrane potential becomes rapidly positive, called depolarization.
    • The restoration of a negative membrane potential after depolarization is called repolarization.
    • Voltage-gated ion channels are integral for changes in membrane potential during action potentials.
    • Voltage-gated sodium (Na+) channels (VGNCs) open when a change in membrane potential occurs, allowing Na+ ions to enter the cell, causing depolarization.
    • Voltage-gated potassium (K+) channels (VGKCs) are slower to open and allow K+ ions to flow rapidly out of the cell during repolarization.
    • VGNCs close as membrane repolarizes.

    Excitation-Contraction Coupling

    • Action potential travels along sarcolemma to voltage-gated Ca2+ channels (VGCCs) at T-tubules.
    • VGCCs plug Ca2+ release channels in the SR membrane.
    • Action potentials open VGCCs at triads.
    • This releases and opens the Ca2+ release channels of the SR, spilling Ca2+ into the sarcoplasm and binding to troponin, initiating muscle contraction.
    • VGCCs in the sarcolemma close, SR Ca2+ release channels close and reassociate with the VGCCs, and Ca2+-ATPases actively pump Ca2+ back into the SR and out of the cell during relaxation.
    • This process is called excitation-contraction coupling.

    Control of Muscle Tension

    • Usually, one action potential equals one contraction.
    • More frequent action potentials lead to more tension.
    • Each somatic motor neuron axon can form multiple NMJs with muscle fibers.
    • A motor unit is one somatic motor neuron plus all the skeletal muscle fibres it synapses with (averaging 150).
    • Large muscles have many motor units distributed throughout.
    • All muscle fibres in a motor unit contract and relax synchronously.
    • A twitch contraction is the contraction generated in all skeletal muscle fibres of one motor unit due to one action potential.
    • Twitch contractions have three phases:
      • Latent period (2 msec): delay between stimulus and muscle action, where action potential moves through sarcolemma and Ca2+ is released from SR.
      • Contraction period (10-100 msec): cross-bridges form and sarcomeres shorten, producing maximum tension.
      • Relaxation period (10-100 msec): Ca2+ is pumped back into the SR, myosin detaches from actin, and tension decreases.
    • A refractory period is the time when a muscle fibre is unresponsive to a new action potential during a contraction.

    Muscle Tone

    • Muscle tone is produced by small involuntary contractions of alternating motor units.
    • It helps stabilize positions and keeps movements smooth.
    • For large muscles, weak motor units work first, followed by stronger motor units (motor unit recruitment).
    • There are different types of muscle contractions:
      • Isotonic contractions occur when the muscle changes length while maintaining constant tension.
        • Concentric isotonic contractions shorten the muscle, reducing the angle around a joint.
        • Eccentric isotonic contractions lengthen the muscle while resisting a load.
      • Isometric contractions occur when the muscle generates tension without overcoming the resistance of the load, resulting in no movement.

    Muscle Metabolism

    • Muscles need ATP for the contraction cycle and active transport of Ca++ pumps in the SR.
    • Muscles generate ATP in three ways:
      • Consuming creatine phosphate:
        • Creatine is a small molecule synthesized in the liver, kidneys, and pancreas.
        • During rest, unused ATP is dephosphorylated into creatine phosphate.
        • During work, muscles rapidly dephosphorylate creatine phosphate to regenerate ATP.
        • Both phosphate transfers are catalyzed by creatine kinase.
      • Anaerobic cellular respiration:
        • Occurs when oxygen is limited (e.g. during intense exercise).
        • Glucose is converted into pyruvate and then lactate, producing ATP.
        • This pathway is less efficient than aerobic respiration.
      • Aerobic cellular respiration:
        • Occurs when oxygen is plentiful (e.g. during moderate exercise).
        • Glucose, fatty acids, and amino acids are used to produce ATP.
        • This pathway is more efficient than anaerobic respiration, producing more ATP.

    Aerobic Respiration

    • Muscles can use glucose from glycogen stores or blood
    • Glucose is broken into 2 pyruvate molecules in 10 chemical reactions
    • This process is called glycolysis
    • Pyruvate is transported to the mitochondria if sufficient oxygen is available
    • Reactions convert carbons in glucose to CO2 which is exhaled
    • Electrons from chemical bonds are transferred to the electron transport chain (ETC)
    • The flow of electrons down the ETC releases free energy that is used to synthesize ATP
    • Oxygen acts as the final electron acceptor, allowing the release of energy

    Anaerobic Glycolysis

    • If oxygen is restricted, muscles cannot respire the products of glycolysis
    • Pyruvate is fermented into lactic acid
    • Lactic acid fermentation converts pyruvate to lactic acid and regenerates NAD+, allowing glycolysis to continue making ATP in low-oxygen conditions

    Oxygen Debt

    • Muscles need oxygen after exercise to replenish myoglobin, convert lactic acid back to glucose in the liver, and replenish creatine phosphate

    Types of Muscle Fibers

    • There are three types of skeletal muscle fibers with different structures, functions, and appearances:
      • Slow oxidative fibers
      • Fast oxidative glycolytic fibers
      • Fast glycolytic fibers

    Slow Oxidative Fibers

    • Dark red (lots of myoglobin and capillaries)
    • "Slow" refers to the length of the contraction cycle (100–200 msec)
    • Also called "slow twitch"
    • Do not fatigue easily; function during endurance activities and in postural muscles
    • "Oxidative" refers to aerobic respiration as the primary metabolic mode

    Fast Oxidative-Glycolytic Fibers

    • Dark red (lots of myoglobin and capillaries)
    • "Fast" refers to the length of the contraction cycle (50–100 msec)
    • Also called "fast twitch"
    • Can use aerobic or anaerobic respiration
    • Largest fibers
    • Fatigue more quickly than slow oxidative fibers
    • Function in activities requiring a combination of strength and endurance (e.g., sprinting)

    Fast Glycolytic Fibers

    • White (low myoglobin and capillaries)
    • "Fast" refers to the length of the contraction cycle (50–100 msec)
    • Also called "fast twitch"
    • Fatigue quickly
    • Function in bursts of intense movement (e.g., weight lifting)
    • The primary metabolic mode is anaerobic glycolysis

    Muscular System Overview

    • All skeletal muscles are under voluntary control.
    • Functions of the muscular system include supporting body movement and generating heat.

    Muscle Anatomy

    • Origin: End of the muscle attached to a stabilized or stationary bone, usually proximal.
    • Insertion: End of the muscle attached to a moving bone, usually distal.
    • Muscle Belly: The thickened portion between tendons.
    • Actions: Movements possible when the muscle contracts.
    • Reverse Muscle Actions (RMAs): Occur when the origin and insertion are reversed. Some muscles are capable of both actions and RMAs. RMAs do not occur when the muscle relaxes.

    Levers

    • Muscles move bones by acting as levers.
    • Lever: A rigid structure that moves around a fixed point called a fulcrum.
    • Load: Resistance against effort.
    • Effort: Force required to move a load.
    • Bones are levers moved by muscle effort.

    Types of Levers

    • First-class levers: Fulcrum is between effort and load.
      • Examples: Seesaw, scissors.
      • Rare in the human body.
      • E.g. Looking up at the ceiling (Effort: posterior neck muscles, Fulcrum: atlanto-occipital joint, Load: anterior portion of skull)
    • Second-class levers: Load is between effort and fulcrum.
      • Examples: Wheelbarrow.
      • Produce a mechanical advantage, allowing for little effort to move a load a short distance.
      • E.g. Standing on your toes (Effort: gastrocnemius muscles, Load: body weight, Fulcrum: metatarsophalangeal joints)
    • Third-class levers: Effort is between the fulcrum and the load.
      • Examples: Forceps.
      • Most common levers in the body.
      • Always produce a mechanical disadvantage, requiring a lot of effort to move small loads a short distance.
      • E.g. Bending your elbow (Fulcrum: elbow joint, Effort: biceps brachii, Load: weight of distal upper limb)

    Muscle Actions

    • Muscles work in groups, typically opposing pairs.
    • Agonist: Muscle that exerts effort to move a lever (bone).
    • Antagonist: Muscle that opposes the agonist, relaxing to allow agonist movement.
    • Synergist: Muscle that stabilizes intermediate joints during contraction, allowing movement at a specific joint.
    • Fixator: Muscle that stabilizes one end of a bone to allow movement at the other end.

    Muscle Naming

    • Muscles are named based on factors including:
      • Direction: E.g. Transversus abdominis muscles run perpendicular to the midline.
      • Size: E.g. Latissimus dorsi muscles are the widest of the back.
      • Shape: E.g. Serratus anterior muscles have a saw-shape.
      • Action: E.g. External anal sphincter decreases the diameter of the anus.
      • Number of Origins: E.g. Biceps brachii has two origins.
      • Location: E.g. Occipitofrontalis has a frontal and occipital belly.
      • Origin and Insertion: E.g. Sternocleidomastoid originates on the sternum and inserts on the mastoid process.

    Muscles of the Face

    • Facial muscles permit facial expressions including:
      • Expression of emotions.
      • Speech and vocalization.
      • Chewing (mastication).

    Muscles of the Eye and Mouth

    • Orbicularis oculi: Closes the eyelid.
    • Orbicularis oris: Closes the lips and purses the lips.
    • Occipitofrontalis: Has two bellies connected by the epicranial aponeurosis.
      • Frontal belly: Raises eyebrows and wrinkles forehead.
      • Occipital belly: Raises hair and pulls scalp posteriorly.

    Muscles that Move the Mandible

    • Platysma: Pulls corners of the mouth laterally and inferiorly, permitting frowning and depressing the mandible.
    • Masseter and temporalis: Elevate the mandible; masseter closes the jaw.

    Muscles of the Neck

    • Sternocleidomastoid: Located one on each side of the neck.
      • Originates anteriorly (manubrium) and inserts posteriorly (temporal bone).
      • Functions include:
        • Rotating the head.
        • Extending the head at the atlanto-occipital joint.
        • Capable of RMA (elevation of the sternum).
      • Unilateral contraction results in head tilting towards the contracted side and rotating to the opposite side.

    Muscles of the Abdomen

    • Functions include:

      • Protecting abdominal viscera.
      • Moving the vertebral column.

    • Muscles arranged in layers:

      • External obliques: Most superficial.
      • Internal obliques: Intermediate.
      • Transversus abdominis: Deepest.

    • Fascicle arrangement provides a mesh network for additional protection to the abdominopelvic cavity viscera.

    • Rectus abdominis: Runs longitudinally along the anterior of the abdominal cavity, divided by tendinous intersections, creating the "6-8 pack."

    Diaphragm

    • Bounds the thoracic cavity inferiorly.
    • Circular muscle with origins on many bones and tissues, inserting on the central tendon.
    • Contraction of the diaphragm moves it downwards, expanding the lungs for inhalation.

    Muscles that Move the Pectoral Girdle

    • Functions include:

      • Moving the clavicle and scapula.
      • Stabilizing the scapula during humerus movement.

    • Serratus anterior: Fan-shaped muscle.

      • Originates on ribs, inserts on scapula.
      • Abducts the scapula (RMA: elevation of ribs).
      • Assists in pushing and punching.

    • Trapezius: Originates on the occipital bone, inserts on the scapula.

      • Functions include:
        • Rotation.
        • Adduction.
        • Depression.
        • Stabilization of the scapula.

    Muscles that Move the Upper Limb

    • Function: Move the humerus.

    • Pectoralis major:

      • Functions include:
        • Adduction.
        • Medial rotation.
        • Flexion of the arm.

    • Deltoid:

      • Wraps the shoulder posteriorly, laterally, and anteriorly.
      • Functions include:
        • Abduction.
        • Medial/lateral rotation.
        • Flexion/extension of the arm.

    • Latissimus dorsi:

      • Triangular muscle located posterior and lateral.
      • "Swimmer's muscle."
      • Functions include:
        • Extension.
        • Adduction.
        • Medial rotation of the arm.
      • RMA: Elevation of the vertebral column and torso.

    Muscles that Move the Forearm

    • Function: Move the radius and ulna.

    • Biceps brachii:

      • Has two heads (originate on the scapula, insert on the radius).
      • Functions include:
        • Flexion of the arm at the elbow joint.
        • Supination of the hand.

    • Triceps brachii:

      • Originates on the scapula and humerus.
      • Inserts at the olecranon of the ulna.
      • Function: Extension of the forearm at the elbow joint.

    • Brachioradialis:

      • Flexes the arm at the elbow joint, controlling speed of movement.
      • Supinates and pronates the hand.

    Muscles that Move the Lower Limb

    Gluteal Muscles

    • Function: Move the femur.

    • Gluteus maximus:
      -One of the largest muscles in the body.

      • Originates on the pelvis, inserts on the fascia of thigh muscles.
      • Functions include:
        • Extension of the leg at the hip joint.
        • Lateral rotation of the femur at the hip joint.
      • RMA: Extension of the torso.

    • Gluteus medius:

      • Deep to the gluteus maximus.
      • Originates on the ilium, inserts on the femur.
      • Functions include:
        • Abduction.
        • Medial rotation of the femur.

    Flexor Compartment of the Thigh

    • Includes the "hamstrings."
      • Three muscles:
        • Flex the distal lower limb at the knee joint.
        • Extend the leg at the hip joint.
    • Biceps femoris: Has two heads (long and short).
      • Originate on the ischium and femur, insert on the tibia and fibula.
      • Lateral "hamstring."
    • Semitendinosus:
      • Originates on the ischium, inserts on the tibia.
      • Intermediate "hamstring."
    • Semimembranosus:
      • Originates on the ischium, inserts on the tibia.
      • Most medial"hamstring."

    Extensor Compartment of the Thigh

    • The "quads."
    • Anterior to the flexor compartment of the thigh.
    • Functions include:
      • Extension of the distal lower limb at the knee joint.
      • Flexion of the leg at the hip joint (rectus femoris).
    • Vastus lateralis, vastus medialis, and vastus intermedius: Originate on the femur.
    • Rectus femoris: Originates on the ilia.
    • All insert on the patellar tendon.

    Medial Compartment of the Thigh

    • Gracilis:
      • Originates on the pubis, inserts on the tibia.
      • Functions include:
        • Adduction of the thigh at the hip.
        • Medial rotation of the thigh.
        • Flexion of the leg around the knee joint.

    Muscles that Move the Foot

    • Soleus and gastrocnemius:

      • Located in the superficial posterior compartment of the leg.

    • Soleus:

      • Originates on the fibula and tibia, inserts onto the calcaneal (Achilles) tendon.
      • Function: Plantar flexion of the foot at the ankle joint.

    • Gastrocnemius:

      • Originates on the femur, inserts at the calcaneal tendon.
      • Functions include:
        • Plantar flexion of the foot at the ankle joint.
        • Flexion of the lower limb at the knee joint.

    • Tibialis anterior:

      • Originates on the tibia, inserts on the metatarsals and tarsals.
      • Functions include:
        • Dorsiflexion of the foot at the ankle joint.
        • Supination (inversion) of the foot at intertarsal joints.

    Homeostatic Imbalances of the Muscular System

    • Muscle injuries are often activity-related.
      • Regular, moderate-intensity exercise provides protection against injury.
      • Stretching, good nutrition, and sleep are also important.

    Minor Injuries

    • Spasms: Involuntary contraction of a muscle or muscle group.
      • Painful spasms are called cramps.
      • Most common cause: Dehydration.
      • Other causes: Injury, overuse, prolonged periods in one position, and inadequate blood flow.
    • Muscle soreness: Often due to microscopic muscle damage, e.g. torn sarcolemmas, Z-discs.
      • May be accompanied by swelling or inflammation.
      • Delay onset muscle soreness (DOMS): Occurs 24-48 hours after high-intensity exercise.

    Treatment of Minor Injuries

    • PRICE: Protection, Rest, Ice, Compression, Elevation.

    Severe Injuries

    • May require rehabilitation and/or medication.
      • Non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids.

    Bone Structure

    • Bone is a complex organ composed of bone tissue, cartilage, connective tissue, epithelial tissue, adipose tissue, and nervous tissue.
    • The study of bone structure is called osteology.
    • Bones provide support, protection, aid in movement, regulate mineral homeostasis, are the site of red blood cell production, and store triglycerides.

    Long Bone Structure

    • Long bones are longer than they are wide.
    • Consist of a diaphysis (bone shaft), epiphyses (knobby ends), metaphyses (connecting diaphysis and epiphyses), articular cartilage, periosteum (outer covering), medullary cavity (hollow diaphysis), and endosteum (lining of medullary cavity).

    Bone Tissue

    • Bone tissue is a connective tissue with cells sparsely distributed in a hard extracellular matrix (ECM).
    • ECM of bone is composed of water, collagen fibers, and mineral salts.
    • Mineral salts deposit on collagen fibers, hardening the ECM.
    • Mineral salts provide hardness, and collagen fibers provide tensile strength.
    • This process is called calcification.

    Minerals of Bone

    • The mineral salts of bone ECM include hydroxyapatite, calcium phosphate, calcium hydroxide, and a smaller proportion of calcium carbonate.

    Bone Cells

    • Cells make up only 2% of bone tissue.
    • Four types of bone cells:
      • Osteoprogenitor cells: stem cells found deep in the periosteum.
      • Osteoblasts: secrete collagen and other ECM components, do not divide, and become osteocytes.
      • Osteocytes: mature bone cells, do not divide or secrete, and acquire nutrients and eliminate wastes.
      • Osteoclasts: catabolize bone, formed by fusion of monocytes, secrete lysosomal enzymes and acids for bone resorption.

    Types of Bone Tissue

    • Two types of bone tissue: spongy and compact.
    • Spongy bone is lighter than compact bone, fills bones for easier movement, supports and protects red bone marrow, and handles stress along multiple axes better than compact bone.
    • Compact bone is the strongest type of bone tissue, resistant to mechanical stress, and has a densely packed ECM.

    Compact Bone Structure

    • Structural unit of compact bone is the osteon.
    • Osteons are arranged along lines of stress and can change with lifestyle and bone remodeling.
    • Osteonic canals contain blood vessels for nutrient and hormone delivery.
    • Concentric lamellae are rings of ECM surrounding the osteonic canal.
    • Interstitial lamellae are remnants of old concentric lamellae.
    • Circumferential lamellae surround the long bone and connect to the periosteum.
    • Osteocytes reside in lacunae, connected by canaliculi filled with extracellular fluid.
    • Interosteonic canals provide passage for blood vessels and nerves.
    • Bone tissue heals quickly due to extensive vascularization.

    Spongy Bone Structure

    • Spongy bone tissue is not composed of osteons.
    • Structural unit of spongy bone is the trabeculae, plates or projections of bone tissue also arranged along areas of stress.
    • Trabeculae are surrounded by red bone marrow and blood vessels.
    • Red bone marrow contains blood stem cells.

    Nerve and Blood Supply of Bone

    • Bone is well-vascularized.
    • Periosteal arteries nourish the periosteum.
    • Nutrient arteries penetrate the diaphysis and branch into bone marrow entering via nutrient foramen.
    • Epiphyseal and metaphyseal arteries nourish the internal tissues of the epiphyses.
    • Veins exit through the same entrance as arteries.
    • Nerves run similar paths to blood vessels through bones.

    Functions of Blood and Nerve Supply

    • Blood supply: nutrient delivery, waste removal, support for bone remodeling, hormone transport, immune function.
    • Nerve supply: pain perception, regulation of bone metabolism, response to mechanical stimuli, vascular regulation, communication with other systems.

    Ossification

    • Ossification is the process of bone formation.
    • Four phases of life requiring bone formation: development of the embryonic skeleton, development during childhood and adolescence, during bone remodeling, and during fracture repair.
    • Two patterns of ossification: intramembranous and endochondral.

    Intramembranous Ossification

    • Bone develops directly from mesenchymal tissue.
    • Occurs in four steps:
      1. Formation of ossification center: mesenchymal cells differentiate into osteoprogenitor cells and then osteoblasts.
      2. Calcification: osteoblasts secrete mineral salts.
      3. Formation of trabeculae: connective tissue becomes red bone marrow.
      4. Formation of periosteum: mesenchymal tissue compacts and hardens.

    Endochondral Ossification

    • Bone develops from hyaline cartilage.
    • Occurs in six steps:
      1. Mesenchymal cells differentiate into chondroblasts and form hyaline cartilage.
      2. Chondroblasts secrete ECM, leading to interstitial and appositional growth.
      3. Penetration of nutrient artery stimulates differentiation of osteoprogenitor cells into osteoblasts, forming trabeculae.
      4. Primary ossification extends toward the ends of bones.
      5. Secondary ossification center forms at birth.
      6. Hyaline cartilage at joints becomes articular cartilage and cartilage remaining at the metaphysis ossifies eventually.

    Bone Growth

    • Bones grow interstitially (lengthwise) and appositionally (circumferentially).

    Interstitial Growth

    • Occurs at the epiphyseal plate of long bones.

    • Four zones:

      1. Zone of resting cartilage: anchors the epiphyseal plate to bone.
      2. Zone of proliferating cartilage: actively dividing chondrocytes.
      3. Zone of hypertrophic cartilage: mature chondrocytes arranged in columns.
      4. Zone of calcified cartilage: layers of dead chondrocytes.

    • At maturity, the epiphyseal plate closes, chondrocytes cease to divide, and becomes the epiphyseal line.

    Appositional Growth

    • Occurs when periosteal cells become osteoblasts, forming ridges of ECM around periosteal vessels.
    • Ridges fuse, the former periosteum becomes the endosteum, and new concentric lamellae are formed.
    • New concentric lamellae increase the diameter of the bone.
    • Osteoclasts in the endosteum catabolize bone, leading to medullary cavity growth.

    Factors Affecting Bone Growth

    • Nutrition: dietary calcium and vitamin D are essential for ossification.
    • Hormones: growth factors, thyroid hormones, estrogen, and testosterone influence bone growth.
    • Exercise: weight-bearing exercise stimulates bone remodeling and increases bone density.

    Bone Remodeling

    • A lifelong process that involves bone resorption (destruction of ECM) and deposition (building new ECM).

    • Occurs during growth, after injury, and with changes in exercise and diet.

    • Osteoclasts resorb bone, releasing minerals into the blood.

    • Osteoblasts deposit bone along lines of mechanical stress.

    Bone Remodeling and Exercise

    • Weight-bearing exercise stimulates bone remodeling.
    • A sedentary lifestyle or injury leads to bone loss.

    Bone Remodeling and Calcium Homeostasis

    • Bone stores 99% of the body's calcium.
    • Calcium has roles in nerve and muscle cell function, blood clotting, and enzyme catalysis.
    • Plasma calcium levels are carefully regulated (9-11 mg/100 mL).
    • Low calcium levels can lead to heart and respiratory dysfunction.

    Fractures and Bone Repair

    • Fractures are breaks in bones.
    • Can be microscopic (stress fracture) or large (compound fracture).
    • Causes: trauma, repeated stressful activities, disease.

    Fracture Treatment

    • Reduction: realignment of broken bone ends.
    • Closed reduction: without surgery.
    • Open reduction: with surgical intervention.
    • Splints, casts, and other immobilization techniques aid in healing.

    Bone Repair Phases

    • Reactive phase: fracture hematoma formation, inflammation.
    • Reparative phase: fibrocartilaginous callus formation, bony callus formation.
    • Bone remodeling phase: osteoclasts remove dead bone, and compact bone replaces spongy bone.

    Bone Disorders

    • Osteoporosis: loss of bone density, increased bone resorption, increased risk of fracture, disproportionately affects elderly women.
    • Rickets and osteomalacia: vitamin D deficiency, lead to inefficient calcium absorption and bone softening and deformation.

    Summary

    • Bone is a complex organ with two types of tissue: spongy and compact.
    • Ossification is the process of bone formation, with two patterns: intramembranous and endochondral.
    • Bone growth is influenced by nutrition, hormones, and exercise.
    • Bone remodeling is a lifelong process essential for calcium homeostasis.

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    Explore the divisions of the skeletal system, including the axial and appendicular skeletons, as well as the various types of bones. This quiz covers the fundamental aspects of the human skeleton, its function, and the relation to the muscular system. Test your knowledge on how these components work together to allow for movement.

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