The skeletal system

<<Overview<<

  • Bone- a rigid but living organ made up of all 4 types of tissues
    • Connective tissue- the majority is bone (osseous) tissue but cartilage and dense connective tissue cover the bone’s external surface
    • Nervous tissue- in the bone, has nerves
    • Epithelial tissue- in the bone blood vessels, provides nourishment
    • Muscle tissue- skeletal muscle tissue, attached to the bone

}}Function}}

  • Support
    • the skeleton is a framework holding up the entire body
  • Protection
    • the skeleton guards the body’s most vital organs,
    • ex. the skull protecting the brain
    • ex. rib cage protecting the heart
  • Movement
    • skeletal muscles are connected to bones via tendons and use bone as levers at joints to produce movements
  • Storage
    • stores minerals like calcium and phosphate, which can be released into the blood when needed
    • stores energy in the form of fat in yellow bone marrow
  • Hematopoiesis- blood cell formation
    • occurs in the red bone marrow of certain bones
  • Hormone production
    • critical for helping to maintain homeostasis
    • ex. produces osteocalcin which regulates insulin secretion, glucose regulation, and energy usage

{{Classification{{

  • bones are classified by their location (in the axial vs. the appendicular skeleton) and shape
  • the function of a bone depends on its function
  • 4 types of bones:
    • long bones
    • short bones
    • flat bones
    • irregular bones
  • Long bones- longer than they are wide
    • tend to have a long shaft with either end being a bit wider
    • Examples:
    • arm: humerus, radius, and ulna
    • hand bones: metacarpals and phalanges
    • leg bones: femur, tibia, and fibula
    • footbones: metatarsals and phalanges
  • Short bones- more cube-shaped
    • tend to be as wide as they are long
    • provide support and stability with little movement
    • Examples:
    • wrists: carpals
    • ankles: tarsals
    • sesamoid bone- patella, a special type of short bone, means to be shaped like a sesame seed, embedded within tendons
  • Flat bones- thin and flat, often with a little curve
    • have a large surface area for attaching to muscles
    • Examples:
    • sternum
    • shoulder blades (scapula)
    • ribs
    • cranial bones of the skull
  • Irregular bones- everything else, have a highly specialized shape and structure
    • Examples:
    • coxal (hip): ilium, ischium, pubic
    • vertebrae

]]Bone structure]]

  • bone is a dense and smooth layer of compact (cortical) bone tissue on the outside surrounding the more porous spongy bone tissue on the inside
  • the external surface of a bone is rarely smooth, and often has distinct bone markings that correspond to how the bone and its attached muscles and ligaments work together
Compact bone
  • made up of osteons- the basic structural unit; long cylinders that act as tiny weight-bearing pillars in the bone
    • lamella- hollow tubes grouped together to make compact bone
    • filled with tiny salts and collagen fibers that allow the bone to resist torsion and stress
      • the salt is hard
      • the collagen is rubbery and durable
    • Haversian canal- runs through the middle of each osteon and contains small blood vessels for nourishment and nerve fibers for signaling
Spongy bone
  • less organized than compact bone
  • no osteons
  • have trabeculae- tiny bone struts that are key for helping the bone to resist stress: also where bone marrow is
Bone markings
  • Projections- where muscles and ligaments attach
  • Surfaces- form joints
  • Depressions and openings- for blood vessels and nerves to run through

[[Bone cells[[

  • Osteocytes- maintain healthy bone structure
    • housed in the lacunae- gaps between the lamellae
    • monitor and maintain quality in response to stimuli
  • Osteoblasts- build and construct bones by calcifying bone as it forms
  • Osteoclasts- critical in the regeneration of the bone through bone remodeling by absorbing bone tissue wherever it is not needed or is degenerating

^^Bone formation^^

  • Ossification (osteogenesis)- the process of bone tissue formation
    • key to forming your skeleton as an embryo
    • essential for bone growth from childhood up to early adulthood
    • used for bone remodeling and repair later in life
  • Articular cartilage and epiphyseal plates don’t go through ossification
  • Intramembranous ossification- a type of ossification, the bone that develops from a fibrous membrane and creates a membranous bone, Ex: the clavicle and skull
  • Endochondral ossification- bone develops by replacing cartilage and creates endochondral bone Ex: all other bones
    • glassy dense collagen hyaline cartilage and chondrocyte cells become dense collagen and calcium osseous tissue and osteocyte cells

Bone remodeling

  • bone is constantly remodeled
    • bones would become brittle and fracture
  • The process:
  1. osteocytes release chemical signals to tell osteoclasts to go to the damage
  2. osteoclasts release enzymes there that allow them to digest the calcium phosphate, putting the calcium and phosphate back into the blood (restoration)
  3. macrophages promote bone tissue remodeling
  4. osteoblasts come in and build new bone before thru undergo apoptosis

Bone damage

  • Fracture- break
  • Treatment- reduction (realignment of the broken bone ends) and immobilization (keeping bone stable so it has time to heal itself
Repair
  1. hematoma- forms due to hemorrhaged blood clots (from where blood vessels in the bone were torn during the break)
  2. fibrocartilage callus- forms that span the break and connects the broken ends
  3. osteoblasts begin forming spongy bone and replacing the cartilaginous callus
  4. bone remodeling then occurs

}}Joints}}

  • Joints (articulations)- the meeting places between 2 or more bones, classified by structure or function
    • give the skeleton mobility and hold it together
  • body movement happens when muscles contract across joints, moving one bone toward another
  • Connective tissue
    • Ligaments- attach bones to bones
    • Tendons- attach muscles to bones

Functional classification

  • classified based on what they do and how much they can move
  • the less movable a joint is the more stable it is

3 Types

  1. Synarthroses- non-moving joints

   

  1. the part of the skull that protects the brain, the cranium
    1. Amphiarthroses- slightly-moving joint

   

  1. where pubic bones meet in the pelvis
    1. Diarthroses- freely moving joints

   

  1. knee and elbow joints, in our limbs

Structural classification of joints

  • based on what binds the bones together in the joint and if a cavity is present
  • Fibrous joints- connect bones with the collagen fibers of dense connective tissue, mostly immovable
    • Sutures- fibrous joints, that hold skull bones together
    • Syndesmosis- hold longer bones together by ligaments
    • Gomphoses- hold teeth in their sockets
  • Cartilaginous joints- connect bones with cartilage, can be rigid but also slightly movable
    • Synchondrosis- an immovable joint, made of a bar or plate of hyaline cartilage
    • Symphysis- a slightly movable joint, made of fibrocartilage
  • Synovial joint- connect bones with dense connective tissue and fluid-filled joint cavity
    • allows them to be freely movable (all are diarthrosis)

Synovial joint

Synovial joints make up

  • Articular cartilage- covers the opposing bone surfaces
  • Joint (articular) cavity
  • Joint (articular) capsule- fibrous, encloses the joint cavity
  • Synovial fluid- in the cavity, acts as a lubricant
  • Sensory nerve fibers and blood vessels- in joint capsules and synovial membrane

Configurations

  • gliding
  • hinge
  • pivot
  • condylar
  • saddle
  • ball and socket
Gliding
  • also known as a “plane” joint
  • allow gliding movement
    • when one flat bone surface glides or slips over another
  • wrists and ankles
Hinge
  • moves in one direction
  • allows angular movements like flexion and extension
    • Flexion- bending in a way that decreases the angle of the joint so the articulating bones get closer
    • Extension- the reverse of flexion
    • hyperextension- going beyond the anatomical position
  • the elbow and interphalangeal joints
Pivot
  • allow rotation as well as twisting movements back and forth
    • Supination- turn/ twist forward
    • Pronation- turn/ twist backward
  • where the humerus meets the radius and the ulna at the elbow
Condylar
  • like a pedestal with a joint on top
  • allows movement like flexion/ extension, as well as abduction and adduction
    • Abduction- “moving away”, moving a limb away from the median plane, along the frontal plane
    • Adduction- “moving forward”, opposite of abduction
    • in the wrist
Saddle
  • allows opposition movements as well as flexion and abduction
    • thumb joints
Ball and socket
  • lots of maneuverability
  • alow rotational movement, abduction/ adduction, flexion/ extension
    • rotation- turning of the bone around its own long axis
    • shoulder and hip joints

Other types of movements at different joints

  • Circumduction- moving limb in a circle
    • arm ircles
  • Elevation and depression- lifting and lowering a body part superiorly
  • Protraction and retraction- sticking your jaw out and back in
  • Dorsiflexion and plantar flexion- lifting foot up and back down at the ankle
  • Inversion and eversion- turning the foot inward and outward

Muscle Contractions

  • bones can’t move without the joints that connect them and the muscles that stretch over those joints
  • movement occurs when muscles contract
    • pull and never push
  • Insertion- the movable bone during a muscle contaction
  • Origin- the bone that moves less or not at all
    • scapula in a bicep curl
Contraction types
  • Isotonic- causes a change in the length of the muscles
    • pushups
  • Isometric- no change in length
    • doing a plank

Muscular system

Overview

  • the main function of the muscular system is movement

  • muscles contract in order to produce a movement

    • pull and never push

  • Insertion- the muscle is attached to a movable bone

  • Origin- where muscle is attached to an immovable bone

  • muscles do and undo each other

  • other functions- maintain posture, stabilize joints, generate heat

Classification

  • muscles can be classified into 3 groups:
  • Prime movers (agonists)-muscles most responsible for producing a certain movement
  • Antagonists- muscles that oppose or do the reverse of a movement
    • usually stretched or relaxed when a prime mover is active
    • can regulate prime movers by adding resistance
    • located on the opposite side of a joint from the prime mover
  • Synergists- muscles that helo the prime mover, such as stabilizing across a joint of adding some (oomph)
    • fixator- synergists muscles that specifically immobilize the muscle’s origin bone to increase the prime mover’s effectiveness
    • help maintain an upright posture