unit 2—principles of support & movement

Unit 2—Principles of Support & Movement

Dr. Achilly

Part 1: Bone tissue

“Concepts” chapter 8

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.

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.

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.

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.


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.


Medullary cavity—aka marrow. Space within the diaphysis.

Endosteum—thin membrane that lines the medullary cavity.

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.


Osteoclasts—concentrated in endosteum. Face bone surface. Release enzymes that break down bone matrix. Called resorption.


Bone has spaces that act as storage areas, canals for blood/nerve supply.

Classified based on size/amount of spaces.


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.


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.

Microscopic structure

Bones are well supplied with arteries, veins & nerves.

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.

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.

Infant’s hand showing only partial ossification of bones.

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.

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

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

Bone and homeostasis

Bone is a major calcium reservoir.

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.

Part 2: Axial skeleton


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)

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

206 bones total

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)

Which bone types are seen in these images?

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.

View of the base of the cranium

Skull

Made of 22 bones grouped into two categories: Cranial Facial

Skull

Cranial bones (8) encase brain Frontal bone 2 parietal bones 2 temporal bones Occipital bone Sphenoid bone Ethmoid bone

Floor of cranium

Skull

Facial bones 2 nasal bones 2 maxillae 2 zygomatic bones Mandible 2 lacrimal bones 2 palatine bones 2 inferior nasal conchae vomer

Skull practical practice

Nice link: http://www.gwc.maricopa.edu/class/bio

201/skull/antskul.htm

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.

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.

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

Vertebral column

Vertebral column

Four normal curves in adult spine: Cervical lordosis Thoracic kyphosis Lumbar lordosis Sacral kyphosis

Vertebral column

Between each vertebrae is an intervertebral disc. Outer fibrocartilage

ring Inner spongy, soft

tissue Help to form

strong joints & absorb shock.

Vertebral column

Vertebrae will look different depending upon the area of the spine.

They all have 3 common parts: Body Vertebral arch Processes

Vertebral column

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.

Vertebral column

Mid sagittal section thru C1 & C2

Vertebral column

Thoracic vertebrae: Larger & stronger than cervical Longer TP’s Articulate with ribs

Vertebral column

Lumbar vertebrae Largest & strongest vertebrae Support the most body weight

Vertebral column

Sacrum forms when 5 sacral vertebrae fuse. Forms strong base

for vertebral column.

Coccyx forms when ~4 coccygeal vertebrae fuse.

Thoracic cage

Consists of sternum, ribs & thoracic vertebrae.

Thoracic cage

Sternum has 3 parts: Manubrium

(articulates with clavicle)

Body (articulates with ribs)

Xiphoid process

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

Part 3: Appendicular skeleton


While the axial skeleton’s main function was protection of internal organs, the appendicular skeleton’s role is more important for movement.

Pectoral (shoulder) girdle

Attaches upper limb to axial skeleton.

Consists of clavicle & scapula


Clavicle S-shaped Articulates with manubrium & acromion

of scapula Frequently fractured


Scapula Triangular flat bone The many spines, projections & fossae

serve as attachment points for muscles & ligaments of the shoulder.

Upper limb

Consists of 30 bones: Humerus Ulna (forearm) Radius (forearm) 8 carpals (wrist) 5 metacarpals (palm) 14 phalanges (fingers)

Upper limb

Humerus Proximal end articulates with glenoid

cavity of scapula Distal end articulates with radius & ulna

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.

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

Upper limb

Metacarpals & phalanges Form palm & fingers

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.”

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.

Bones of pelvis

Sacrum is made of 5 fused vertebrae.

Coccyx is made up of 3-5 rudimentary vertebrae.

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.

Lower limb

Consists of 30 bones: Femur Patella Tibia Fibula 7 tarsals 5 metatarsals 14 phalanges

Lower limb

Femur Longest, strongest

bone in body Articulates with

acetabulum, tibia & patella

Lower limb

Patella Sesamoid bone Increases leverage of thigh

musculature (quadriceps femoris) Protects knee joint

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.

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.

Knee

Post. view of left knee

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.

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.

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

Lower limb

Tarsals Form ankle

joint & part of foot

Metatarsals & phalanges make up the forefoot

Arches

Bones and ligaments of foot form 4 arches. Help support body weight, absorb

shock

Arches

Anterior metatarsal arch Formed by distal heads of metatarsals.

Arches

Transverse arch Runs across tarsal bones (cuboid &

cuneiforms)

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.

Part 3—Joints & homeostasis


Types of joints

Can be classified based on function or structure.

Functionally a joint can be: Synarthrosis—

immovable Amphiarthrosis—

slightly moveable Diarthrosis—freely

moveable

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.

Synovial joint

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

Types of synovial joints

Gliding (planar) Joint surfaces are flat or slightly curved. E.g. intercarpal, acromioclavicular


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


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


Ellipsoid (condyloid) Joint surfaces are oval

shaped depression/projection.

Allows movement around 2 axes.

E.g. radiocarpal, tempromandibular


Saddle Modified condyloid

—in shape of saddle and rider.

Allows freer biaxial movement.

E.g. base of thumb


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

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


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.

Abduction…not!


Rotation—bone revolves around its longitudinal axis.


Inversion—moving soles of feet (plantar surface) medially.

Eversion—movement of soles away from each other.


Supination—turning palm anteriorly

Pronation—turning palm posteriorly

Part 4—Muscle tissue & homeostasis


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).

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

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


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.


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.

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).

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.

Skeletal Myo Tissue

Three layers of connective tissue protect & strengthen skeletal myo.

1. Epimysium2. Perimysium3. Endomysium

Skeletal Myo Tissue

Epimysium Outermost layer Encircles entire

myo

Skeletal Myo Tissue

Perimysium Surrounds fascicle These fascicles

give meat its “grain” appearance.

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.

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.

Skeletal Myo Tissue

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.


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.


Sarcoplasm is filled with small fibers called myofibrils. Give skeletal myo

its striated appearance.


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.


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.


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)


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.


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


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.


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.


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.


Small amounts of regulatory proteins are part of the thin filament: Tropomyosin Troponin

They cover the myosin-binding sites in a relaxed myo.


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.


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.

What happens when muscles contract?

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


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.


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.


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.


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.


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

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.


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.


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.

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

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.

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).

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.

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.

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


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.


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.

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.

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?

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

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

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.

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.

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.

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.

Role of muscles

Origin—the muscle attachment on the fixed bone. Usually proximal.

Insertion—muscle attachment on the moving bone. Usually distal.

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.

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.

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.

The End

unit 2—principles of support & movement

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