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Unit 2—Principles of Support & Movement
Dr. Achilly
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Part 1: Bone tissue
“Concepts” chapter 8
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Functions
Bone tissue serves many functions: Support—framework for
body & attachment point for muscles.
Protection—for soft internal organs
Assists movement—muscles need to be attached to stable structures in order to produce movement.
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Functions Mineral reserve—stores calcium &
phosphorus to help maintain homeostasis in their blood levels.
Blood cell production—some bones have red marrow which produces red & white blood cells & platelets.
Triglyceride storage—yellow bone marrow stores these for energy reserve.
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Structure
Bone is made up of several tissues: Osseous Cartilage (fibrous connective tissue) Connective (for binding and support) Epithelium (covering) Adipose (fat) Nervous
Each bone is considered an organ & each is continually remodeling.
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Macroscopic Structure
In a typical long bone (femur, humerus) you’ll find: Diaphysis—shaft or long main part of bone. Epiphyses(pl)—distal and proximal ends Metaphyses(pl)—regions where diaphysis joins
each epiphysis (sing). When still growing this region contains an epiphyseal plate —an area of cartilage that allows for elongation. This plate is replaced by an epiphyseal line when the bone stops growing.
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Macroscopic Structure
Articular cartilage—thin layer that covers the epiphysis when the bone articulates (forms a joint) with another. This hyaline cartilage is slippery and absorbs shock.
Periosteum—sheath that surrounds the bone. These cells are bone-forming & add to thickness of bone. They also protect, nourish, repair & serve as attachment for tendons & ligaments. Perforating Sharpey’s fibers act like thumbtacks to hold the periosteum to the bone.
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Macroscopic Structure
Medullary cavity—aka marrow. Space within the diaphysis.
Endosteum—thin membrane that lines the medullary cavity.
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Microscopic Structure
Not solid. Bone calcifies when crystals of hydroxyapatite (calcium, magnesium, potassium…) form around a framework of collagen.
Bone is hard & flexible. Composed of 4 types of cells:
Osteogenic— divide & develop into osteoblasts.
Osteoblasts—bone building. Secrete extracellular matrix & initiate calcification. Become osteocytes.
Osteocytes—mature bone cells.
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Microscopic Structure
Osteoclasts—concentrated in endosteum. Face bone surface. Release enzymes that break down bone matrix. Called resorption.
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Microscopic Structure
Bone has spaces that act as storage areas, canals for blood/nerve supply.
Classified based on size/amount of spaces.
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Microscopic Structure
Compact bone Few spaces, very strong. Found beneath
periosteum and makes up most of the diaphysis.
Blood/lymphatic vessels & nerves penetrate bone thru perforating canals (Volkmann’s). Connect to central canals called haversian canals.
Orientation of these structural units (osteons) can change with age, stress, injury.
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Microscopic Structure
Spongy bone No regular osteons. Irregular lattice of
trabeculae instead. Lighter Makes up more areas of flat bones and
the epiphyses of long bones. Orient along lines of stress. Helps
bones transfer stress w/o breaking. Red marrow located here.
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Microscopic structure
Bones are well supplied with arteries, veins & nerves.
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Bone formation
Intramembranous ossification Flat bones in embryo form this way. Osteogenic cells cluster where bone will
form. Extracellular matrix is secreted to begin calcification.
Trabeculae and periosteum develop.
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Bone formation
Endochondral ossification Bone replaces a cartilage “scaffold.” Seen in long bones. Starts as primary ossification center
develops in diaphysis. Ossification spreads inward. Medulla (marrow) eventually forms.
Secondary ossification center develops at birth in the epiphyses. Ossification spreads outward.
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Infant’s hand showing only partial ossification of bones.
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Bone growth
Increase length Diaphysis lengthens b/c of activity at
epiphyseal plate. New chondrocytes (cartilage forming cells) form on epiphyseal side while old chondrocytes on diaphyseal side are replaced by bone.
Damage to epiphyseal plate can cause bone to not reach its normal length.
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Salter-Harris IV Fracture . White arrow points to metaphyseal fracture and yellow arrow to a fracture of the distal tibial epiphysis in this Salter-Harris IV fracture of the ankle.
Dark line indicates epiphyseal plate
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Bone growth
Increase in thickness Bone grows outward from periosteum. Cells here
become osteoblasts and build new osteons. Bones are always being remodeled. Bones
subjected to heavy loads will grow thicker. Remodeling is dependent upon intake of nutrients
and presence of hormones. Minerals: calcium, phosphorus, iron, manganese,
fluoride, magnesium Vitamins: C, K, B12, A Hormones: growth factors, androgens
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Bone and homeostasis
Bone is a major calcium reservoir.
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Cartilage
In order to bring 2 bones together in a joint, cartilage is needed. Made of collagen fibers for strength &
chondroitin sulfate for resilience. Three types:
Hyaline—found at ends of bones, most abundant, but weakest. Reduces friction and absorbs shock.
Fibrocartilage—found in intervertebral discs, menisci. Strongest. Reduces friction.
Elastic—Found in larynx, ear. Gives support and maintains shape.
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Part 2: Axial skeleton
“Concepts” chapter 9
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Divisions of the skeletal system
Axial Bones that lie on
the longitudinal axis of the body.
Skull Hyoid Auditory ossicles Vertebral column Thorax (sternum
& ribs)
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Divisions of the skeletal system
Appendicular Pectoral (shoulder) girdle = clavicle &
scapula Upper limb = humerus, ulna, radius,
carpals, metacarpals, phalanges Pelvic girdle = coxal/innominate bones Lower limb = femur, patella, fibula,
tibia, tarsals, metatarsals, phalanges
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206 bones total
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Bone types
Long Greater length than width (femur)
Short Nearly equal in length and width (carpals)
Flat Flat & thin (cranial, sternum)
Irregular Complex shapes (vertebrae, calcaneus)
Sesamoid bones Shaped like sesame seeds (patella)
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Which bone types are seen in these images?
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Surface markings
In general there are 2 major surface markings on bones of the body: Depressions (aka foramen, fossa,
sulcus)—allow nerves, vessels or tendons to pass thru bones.
Processes (aka condyle, facet, crest, trochanter, tuberosity)—help to form joints or points for ligament attachment.
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View of the base of the cranium
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Skull
Made of 22 bones grouped into two categories: Cranial Facial
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Skull
Cranial bones (8) encase brain Frontal bone 2 parietal bones 2 temporal bones Occipital bone Sphenoid bone Ethmoid bone
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Floor of cranium
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Skull
Facial bones 2 nasal bones 2 maxillae 2 zygomatic bones Mandible 2 lacrimal bones 2 palatine bones 2 inferior nasal conchae vomer
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Skull practical practice
Nice link: http://www.gwc.maricopa.edu/class/bio
201/skull/antskul.htm
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Skull
Bones of the skull continue to grow until about age 14.
There is space between the sutures to allow for growth.
Babies have fontanels (soft spots) where ossification of the bone has not occurred.
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Hyoid bone
Unique because it doesn’t articulate with any other bone.
Suspended from styloid processes of temporal bones by ligament & muscles.
Helps support & anchor tongue & its muscles.
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Vertebral column
a.k.a. spine Consists of bone, connective tissue Surrounds & protects the spinal cord. Adult spine consists of 26 vertebrae
7 cervical 12 thoracic 5 lumbar 1 sacrum 1 coccyx
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Vertebral column
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Vertebral column
Four normal curves in adult spine: Cervical lordosis Thoracic kyphosis Lumbar lordosis Sacral kyphosis
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Vertebral column
Between each vertebrae is an intervertebral disc. Outer fibrocartilage
ring Inner spongy, soft
tissue Help to form
strong joints & absorb shock.
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Vertebral column
Vertebrae will look different depending upon the area of the spine.
They all have 3 common parts: Body Vertebral arch Processes
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Vertebral column
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Vertebral column
The first 2 cervical vertebrae are unique.
Atlas (C1) has no body, articulates with cranium, has large transverse processes(TP’s).
Axis (C2) has no body, but has peg-like structure called the dens.
Allows for rotation & nodding motion of cranium.
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Vertebral column
Mid sagittal section thru C1 & C2
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Vertebral column
Thoracic vertebrae: Larger & stronger than cervical Longer TP’s Articulate with ribs
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Vertebral column
Lumbar vertebrae Largest & strongest vertebrae Support the most body weight
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Vertebral column
Sacrum forms when 5 sacral vertebrae fuse. Forms strong base
for vertebral column.
Coccyx forms when ~4 coccygeal vertebrae fuse.
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Thoracic cage
Consists of sternum, ribs & thoracic vertebrae.
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Thoracic cage
Sternum has 3 parts: Manubrium
(articulates with clavicle)
Body (articulates with ribs)
Xiphoid process
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Thoracic cage
Ribs Support the thoracic cavity 12 pairs Pairs 1-7 articulate with sternum Pairs 8-10 are “false ribs” because they
don’t articulate with sternum. They attached via cartilage to each other & to rib pair #7
Pair 11-12 are floating ribs. They only attach posteriorly to T11 & 12
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Part 3: Appendicular skeleton
“Concepts” chapter 10
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While the axial skeleton’s main function was protection of internal organs, the appendicular skeleton’s role is more important for movement.
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Pectoral (shoulder) girdle
Attaches upper limb to axial skeleton.
Consists of clavicle & scapula
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Pectoral (shoulder) girdle
Clavicle S-shaped Articulates with manubrium & acromion
of scapula Frequently fractured
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Pectoral (shoulder) girdle
Scapula Triangular flat bone The many spines, projections & fossae
serve as attachment points for muscles & ligaments of the shoulder.
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Upper limb
Consists of 30 bones: Humerus Ulna (forearm) Radius (forearm) 8 carpals (wrist) 5 metacarpals (palm) 14 phalanges (fingers)
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Upper limb
Humerus Proximal end articulates with glenoid
cavity of scapula Distal end articulates with radius & ulna
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Upper limb
Ulna On finger side of forearm
Radius On thumb side of forearm
Both articulate with humerus. Radius also articulates with ulna in 3
places.
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Ouch!
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Upper limb
Carpals 8 small bones
joined to each other by ligaments lined up in two rows.
Names are based on their shapes.
Anterior view of carpals
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Upper limb
Metacarpals & phalanges Form palm & fingers
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Pelvic (hip) girdle
Consists of 2 hip (coxal) bones These join anteriorly at pubic
symphysis & posteriorly with the sacrum.
This complete ring is called “bony pelvis.”
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Bones of pelvis
Pelvis is a bony ring formed by 2 innominate bones, sacrum & coccyx.
Innominate bone = ilium, ischium, & pubis. These 3 bones fuse early in life.
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Bones of pelvis
Sacrum is made of 5 fused vertebrae.
Coccyx is made up of 3-5 rudimentary vertebrae.
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Articulations
Sacroiliac joint Sacrum is joined to ilium by ligaments. Small amount of motion is present at SI joint.
Hip joint Where femur articulates with innominate. Head of femur fits into deep acetabulum which
has a fibrocartilage lip called a labrum. Ball & socket joint. Capsule encloses joint. Ligaments & bones
make it one of the strongest articulations.
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Lower limb
Consists of 30 bones: Femur Patella Tibia Fibula 7 tarsals 5 metatarsals 14 phalanges
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Lower limb
Femur Longest, strongest
bone in body Articulates with
acetabulum, tibia & patella
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Lower limb
Patella Sesamoid bone Increases leverage of thigh
musculature (quadriceps femoris) Protects knee joint
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Lower limb
Many ligaments stabilize the knee. Articular capsule—not a complete capsule,
but more like a sheath of ligaments and tendons from the surrounding musculature.
Medial & lateral patellar retinacula—tendons of quadriceps myo insertion.
Patellar ligament—from the tendon of the quadriceps insertion that extends from patella to tibial tuberosity.
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Lower limb
Tibial (medial) collateral ligament—medial side of joint. Runs from medial condyle of femur to medial condyle of tibia. Firmly attached to medial meniscus, so tearing the ligament often damages the meniscus.
Fibular (lateral) collateral ligament—lateral side of joint. Runs from lateral condyle of femur to lateral side of fibular head.
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Knee
Post. view of left knee
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Lower limb
Intracapsular ligaments—within capsule. Connect tibia and femur. Named based on attachment to tibia.
Anterior cruciate (ACL): extends posteriorly & laterally from anterior side of intercondylar area of tibia to femur. Limits hyperextension and ant. sliding of tibia on the femur.
Posterior cruciate (PCL): extends anteriorly & medially from posterior side of tibia to femur. Prevents posterior sliding of tibia when knee is flexed.
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Lower limb
Knee joint also has several bursae or sacs filled w/ synovial fluid that decrease friction. Prepattellar bursa:
btwn patella and skin Infrapatella bursa:
btwn superior end of tibia & patellar ligament.
Suprapatellar bursa: btwn inferior part of femur quadriceps myo.
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Lower limb
Tibia (shin bone) Articulates with femur & fibula
on proximal end Articulates with fibula & talus on
distal end Fibula
Lateral side of leg Distal end forms lateral
malleolus
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Lower limb
Tarsals Form ankle
joint & part of foot
Metatarsals & phalanges make up the forefoot
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Arches
Bones and ligaments of foot form 4 arches. Help support body weight, absorb
shock
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Arches
Anterior metatarsal arch Formed by distal heads of metatarsals.
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Arches
Transverse arch Runs across tarsal bones (cuboid &
cuneiforms)
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Arches
Medial longitudinal arch Medial border of calcaneus to distal
head of 1st metatarsal. Supported by plantar calcaneonavicular
ligament. Lateral longitudinal arch
Outer aspect of foot. Calcaneus to 5th metatarsal.
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Part 3—Joints & homeostasis
“Concepts” chapter 11
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Types of joints
Can be classified based on function or structure.
Functionally a joint can be: Synarthrosis—
immovable Amphiarthrosis—
slightly moveable Diarthrosis—freely
moveable
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Types of joints
Structurally a joint can be: Synovial—freely movable.
Ends of bones covered in hyaline cartilage (articular cartilage).
Enclosed in a sac like capsule (synovial membrane) that is filled with fluid and forms a synovial cavity.
Allows movement and strength, plus prevents dislocation.
Synovial fluid nourishes the avascular cartilage, absorbs shock and lubricates.
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Synovial joint
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Types of joints
Fibrous—not much movement if any.
No synovial cavity Bones held
together by fibrous connective tissue
Cartilaginous—little or no movement
No synovial cavity Bones connect by
cartilage
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Types of synovial joints
Gliding (planar) Joint surfaces are flat or slightly curved. E.g. intercarpal, acromioclavicular
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Types of synovial joints
Hinge Allows motion in a
single plane Convex side of
bone fits into concave side of another
Usually one bone stays fixed during movement
E.g. knee, elbow
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Types of synovial joints
Pivot Allows rotation Rounded surface of
one bone fits into a ring formed by another bone & a ligament.
E.g. atlanto-axial joint, radioulnar joint
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Types of synovial joints
Ellipsoid (condyloid) Joint surfaces are oval
shaped depression/projection.
Allows movement around 2 axes.
E.g. radiocarpal, tempromandibular
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Types of synovial joints
Saddle Modified condyloid
—in shape of saddle and rider.
Allows freer biaxial movement.
E.g. base of thumb
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Types of synovial joints
Ball & socket Allows for motion in
3 planes (180o) Ball like surface of
one bone fits into cup like surface of another.
E.g. shoulder, hip
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Movements of synovial joints
Flexion—decrease in the angle between the articulating bones. Lateral flexion dorsiflexion
Extension—increase in that angle. Hyperextension Plantar flexion
extension
flexion
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Movements of synovial joints
Abduction—movement of bone away from midline. For fingers, middle finger is point of
reference Adduction—movement of bone
toward the midline. Circumduction—movement in a
circle. Combines flexion, abduction, extension & adduction.
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Abduction…not!
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Movements of synovial joints
Rotation—bone revolves around its longitudinal axis.
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Movements of synovial joints
Inversion—moving soles of feet (plantar surface) medially.
Eversion—movement of soles away from each other.
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Movements of synovial joints
Supination—turning palm anteriorly
Pronation—turning palm posteriorly
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Part 4—Muscle tissue & homeostasis
“Concepts” chapter 12
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Role of muscles
None of these movement of the skeletal system would be possible without muscles.
No single muscle acts alone to produce a movement. Many muscles must be coordinated.
Myo usually connects 2 bones and crosses a joint. A contracted myo shortens—i.e. pulls on one bone
while the other bone is stationary. Myo fxn can be determined by knowing its origin
and insertion. Most myo’s work in opposing pairs (e.g.
flexor/extensor).
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Fun (?) Facts
Myo’s make up 40-50% of adult body weight.
Responsible for transforming chemical energy into mechanical energy to: Move Stabilize Regulate organ volume Generate heat Propel & store fluids & solids thru several body
systems
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Types of Muscular Tissue
Skeletal Most of this type moves bones of
skeleton Appears striated or striped under a
microscope. Mostly under voluntary control of the
somatic division of the nervous system. Some subconscious control—e.g.
diaphragm, myo’s of posture
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Types of Muscular Tissue
Cardiac Only found in wall of heart. Involuntary. Because of the “pacemaker” in the
heart, this myo is autorhythmic. Can be adjusted by hormones &
neurotransmitters.
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Types of Muscular Tissue
Smooth Located in walls of vessels, airways,
organs, attached to hair follicles in skin. No striations. Regulated by the autonomic nervous
system (ANS), so they are involuntary.
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Properties
All myo tissue has: Electrical excitability (produces action
potentials). Contractility (myo shortens & pulls on
attachment points). Extensibility (stretches w/o being
damaged). Elasticity (can return to its original
length after stretch or contraction).
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Skeletal Myo Tissue
Each skeletal myo is an organ. Each is made of thousands of
muscle cells (aka myo fibers). A group of myo fibers is called a
fascicle. Many fascicles make up a myo.
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Skeletal Myo Tissue
Three layers of connective tissue protect & strengthen skeletal myo.
1. Epimysium2. Perimysium3. Endomysium
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Skeletal Myo Tissue
Epimysium Outermost layer Encircles entire
myo
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Skeletal Myo Tissue
Perimysium Surrounds fascicle These fascicles
give meat its “grain” appearance.
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Skeletal Myo Tissue
Endomysium Separates each
myo fiber (myo cell) from each other.
Often these 3 layers extend beyond the myo to form the tendon that attaches the myo to a bone.
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Skeletal Myo Tissue
Each myo is supplied with an artery & usually 2 veins.
Capillary beds w/in the myos supply nutrients & take away wastes.
The somatic nerve (collection of many neurons) may supply many myos.
Each axon branches many times to contact many myo fibers.
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Skeletal Myo Tissue
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Skeletal Myo Tissue--microscopic
A myo fiber has hundreds of nuclei. The plasma membrane that surround each cell is called a sarcolemma.
There are tiny in-foldings in the sarcolemma called transverse (T) tubules. They form tunnels that are open to the outside of the fiber & filled with interstitial fluid. Myo nerve impulses (action potentials) spread down the T tubules.
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Skeletal Myo Tissue--microscopic
Cytoplasm of a muscle fiber is called sarcoplasm. It contains lots of glycogen for ATP synthesis.
Myo cells have a special oxygen-carrying protein called myoglobin. Delivers O2 for ATP synthesis. Gives meat its red color.
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Skeletal Myo Tissue--microscopic
Sarcoplasm is filled with small fibers called myofibrils. Give skeletal myo
its striated appearance.
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Skeletal Myo Tissue--microscopic
Also within sarcoplasm is a system of membranous sacs called sarcoplasmic reticulum (SR)—very much like ER of other cells.
SR stores Ca 2+ which is needed for myo contraction.
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Skeletal Myo Tissue--microscopic
Growth of myo’s during exercise is a result of hypertrophy or the increase in the diameter of each muscle fiber (not an increase in the number of cells).
When myo’s aren’t used they atrophy—the muscle fibers’ diameter gets smaller.
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Skeletal Myo Tissue--microscopic
Myofibrils are made up of 3 kinds of proteins: Contractile
(generate force for contraction)
Regulatory (switch contraction on & off)
Structural (keep all the parts together & link myofibrils to sarcolemma)
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Skeletal Myo Tissue--microscopic
Each myofibril contains many smaller structures called filaments (sometimes called myofilaments). Actin is a thinner filament Myosin is thicker
The arrangement of these filaments makes up the functional unit of the muscle called a sarcomere.
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Skeletal Myo Tissue--microscopic
Z disc—plate region that separates each sarcomere
A band—extends the length of the thick filament with some thin filament overlap
I band—lighter, contains thin filament only H zone—in center of A band, thick
filament only M line—middle of sarcomere, contains
support proteins that stabilize thick filaments
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Skeletal Myo Tissue--microscopic
Actin & myosin are the contractile proteins.
Myosin functions as the motor protein in all types of myo tissue. It pushes or pulls on cellular structures to create movement.
It transform chemical energy (ATP) into mechanical energy.
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Skeletal Myo Tissue--microscopic
Each myosin molecule is shaped like 2 golf clubs twisted together.
About 300 of them make up one thick filament.
Myosin heads point away from M line.
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Skeletal Myo Tissue--microscopic
Actin thin filaments are attached to Z disc.
Each actin molecule is twisted with others to form a helix.
Actin molecules have myosin-binding sites where the heads attach.
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Skeletal Myo Tissue--microscopic
Small amounts of regulatory proteins are part of the thin filament: Tropomyosin Troponin
They cover the myosin-binding sites in a relaxed myo.
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Skeletal Myo Tissue--microscopic
Structural proteins are needed to stabilize & add elasticity to myo’s. Titin—very large protein, anchors thick
filaments to the Z disc & M line. Can stretch to 4X its length & springs back, helps sarcomere return to resting length, may also prevent overstretching.
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Skeletal Myo Tissue--microscopic
Myomesin—forms M line, binds titin Nebulin—nonelastic, wraps around thin
filaments & anchors it to Z line Dystrophin—protein that links thin
filaments to integral proteins of the sarcolemma, reinforces & transmits tension generated by sarcomere to the myo tendon.
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What happens when muscles contract?
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Sliding Filament Mechanism
Myo contraction results from a sliding of the actin & myosin filaments across each other. They do not change their length, but the sliding allows the sarcomere to shorten.
When enough sarcomeres shorten, the overall myo length decreasesmovement
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Sliding Filament Mechanism
When a myo is relaxed, Ca2+ conc. in cytosol is very low.
As myo action potential (AP) propagates along the sarcolemma & thru the T-tubules, lots of Ca2+ is released from the SR.
Ca2+ combines with troponin, causing it to change shape.
The troponin-tropomyosin complex falls away from the actin filament, exposing the myosin head binding sights.
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Sliding Filament Mechanism
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Sliding Filament Mechanism
Once the myosin-binding sites are open, the contraction cycle begins.
Myosin head contains an ATPase (an enzyme that hydrolyzes ATP into ADP).
The hydrolysis of ATP leaves the ADP still attached to the myosin head & puts it into a high energy configuration.
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Sliding Filament Mechanism
Myosin head attaches to the binding site on the actin filament forming a crossbridge.
The power stroke occurs next. Myosin head rotates, sliding the thin filament past the thick filament toward the M line.
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Sliding Filament Mechanism
At end of power stroke, myosin head remains attached until another molecule of ATP binds. Once this happens, the head detaches from actin.
Contraction cycle continues as long as there is Ca2+ & ATP.
Each of the 600 myosin heads form crossbridges 5X/sec.
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Sliding Filament Mechanism
With each contraction cycle sarcomere shortens neighboring sarcomeres shorten muscle fiber shortens connective tissue around myo becomes taut tendons become taut pull on bone movement
Animation
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Neuromuscular Junction
You know that somatic motor neurons are the ones that cause myo contraction.
Myo fiber contracts in response to one or more AP’s propagating along the sarcolemma.
Myo AP’s start at neuromuscular junction (NMJ).
End of motor neuron synapses with muscle fiber.
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Neuromuscular Junction
Skeletal motor neurons contain vesicles full of ACh (acetylcholine neurotransmitter).
Region on sarcolemma opposite of the neuron end bulb is called a motor end plate. There are ACh receptors here.
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Neuromuscular Junction
Arrival of AP at end bulb ACh release into synapse.
ACh binds to receptors on motor end plate.
Na+ gates in myo fiber open & AP is triggered.
Myo AP causes Ca2+ release. ACh in synaptic cleft is immediately
broken down.
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Myo Metabolism
Unlike most cells in your body, myo’s must switch quickly between a low level of activity to high.
They need huge amounts of ATP for contraction & Ca2+ pumping.
Three ways to produce ATP:1. From creatine phosphate2. Anaerobic respiration3. Aerobic respiration
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Myo Metabolism
Creatine phosphate Excess ATP
produced while myo’s are relaxing is converted to creatine phosphate by taking one –P from ATP & transferring it to a molecule of creatine.
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Myo Metabolism
When the ATP is needed, the –P is transferred back to ADP to make ATP.
This mechanism only produces enough energy for short bursts of activity.
Your liver, kidneys & pancreas make creatine (it’s derived from some proteins in your diet).
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Myo Metabolism
Anaerobic cellular respiration Doesn’t require oxygen. The pyruvic acid made at the end of
glycolysis in converted to lactic acid. 2 ATP result. This, combined with creatine-P, allow
for slightly longer bursts of activity.
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Myo Metabolism
Aerobic cellular respiration For activity that lasts longer than 30
sec. Requires oxygen for the full breakdown
of glucose yielding 36 ATP. Oxygen diffuses into myo cells & it is
also released from myoglobin w/in the cells.
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Control of Myo Tension
A single nerve impulse creates one myo AP.
AP’s always have same size, but myo contractions can vary in force.
The rate of impulses to a myo determines tension.
↑ frequency of stimulation ↑ force
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Control of Myo Tension
Each myo fiber has one NMJ, but the somatic nerve may branch to many fibers.
Motor unit—a somatic motor neuron & all the myo fibers it stimulates.
Myo’s for precise movement have small motor units.
The more motor units recruited, the stronger & longer the contraction.
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Control of Myo Tension
It takes time for myo AP to cause a contraction (latent period 2 msec)
Also myo’s have a refractory period where Ca2+ is being transported back into the SR.
Myo can’t contract again until after refractory period is over.
Different types of myo fibers vary in their refractory period lengths.
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Myo Fiber Types
Not all myo fibers are the same. Some have more myoglobin,
mitochondria & capillaries (appear redder).
Some vary in the speed of their contraction cycle.
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Myo Fiber Types
Slow oxidative fibers (aka Type I) More myoglobin, capillaries & mito The more mitomore oxidation Slow contraction cycle Fatigue-resistant For sustained contractions Examples?
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Myo Fiber Types
Fast oxidative-glycolytic fibers (aka Type IIa) Contain lots of myoglobin & mito like
Type I Moderate resistance to fatigue Contraction cycle is faster than Type I More abundant in lower limb fibers Active in walking/sprinting
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Myo Fiber Types
Fast glycolytic fibers (aka Type IIb) Contain most myofibrils, so can
generate most power. Low myoglobin, mito & cap., so white in
color. Have lots of glycogen that’s broken
down anaerobically. Good for intense, short duration
activities (e.g. weight lifting). Fatigue quickly
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Type I(slow oxidative)
Type IIa(fast oxidative)
Type IIx (IIb)(fast glycolytic
Myo Fiber Types Most skeletal myo’s are a mixture of all
3 types, but proportions vary.
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Myo Fiber Types
The ratio of different myo types in each skeletal myo is genetically determined.
As a result some people will be naturally suited for sprinting vs. long distance running.
By doing various exercises, you can induce some changes in the fibers, e.g. FG to FOG with endurance exercise.
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Cardiac Myo Tissue
Has same arrangement of actin & myosin.
Cardiac myo remains contracted 10-15X longer than skeletal due to prolonged delivery of Ca2+ into sarcoplasm.
More & larger mito. Requires constant supply of oxygen.
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Smooth Myo Tissue
Involuntary Found in organs & vessels Contractions are slower (b/c there
are no T-tubules) & last longer (b/c Ca2+stays in the cytosol for longer).
Smooth muscle tone—a state of continued partial contraction. Important in GI tract where walls must maintain steady pressure on the contents.
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Role of muscles
Origin—the muscle attachment on the fixed bone. Usually proximal.
Insertion—muscle attachment on the moving bone. Usually distal.
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Role of muscles
Agonist (prime mover)—main myo causing the movement.
Antagonist—stretches/yields to agonist.
Synergist—prevents unwanted movement/stabilizes an intermediate joint.
Fixator—stabilizes the origin of the prime mover.
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Role of muscles
While you will not be asked to memorize muscle origins & insertions, you should be able to figure out the movement if given this information.
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Role of muscles
For example, the vastus lateralis O: greater trochanter of
femur I: tibial tuberosity
Because a muscle shortens when it contracts, its action will be to extend the lower leg.
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The End