fabio - exam 2

length-tension relationship

- # of cross-bridges determines amount of force that can be developed - increasing or decreasing length (from its ideal resting length) decreases force production - passive tension from stretch of elastic components - active tension from contractile components - total length tension curve is a combination of both passive and active tension and varies considerably between muscles of different structure and function

periosteum

- A dense fibrous membrane covering the surface of all bone - Permeated by blood vessels and nerve fibers

bending

- a combination of tension (convex side) and compression (concave side) - no strain along the neutral axis - the further the stresses are from the neutral axis the greater they are

ductility

- a property that allows a material to undergo a relatively large deformation before failure - failure by flow => deforms slowly => ex. bubble gum

brittleness

- a property that allows a material to undergo a relatively small deformation before failure - failure by fracture => deforms all at once => ex. glass

effects of aging on muscles

- aging process (hormonal changes) - disuse - other factors such as nutrition, pathology, and medications

force and velocity have an inverse relationship

- as velocity increases force production decreases - eccentric relationship is not as smooth as concentric

disuse and immobilization of muscles

- atrophy (decrease in fiber size and number) - loss of endurance and strength capabilities - during rigid casting isometric exercises cannot offset or reverse the atrophy - type one fibers atrophy earlier and more significantly with immobilization - early mobilization and dynamic exercises are key to limiting atrophy

toe region

- collagen fibers straighten out and become taut - change in length of a structure with minimal stress

stress relaxation

- deformation is constant while force decreases - the stress in a structure decreases with time while deformation is held constant

plastic region

- deformation with permanent injury to the tissue

elastic or linear region

- deformation without permanent injury to the tissue - linear change between stress and deformation

composition of ligaments and tendons

- dense, connective tissue - parallel collagen fibers - sparsely vascularized - few cells (fibroblasts) - abundant ECM

modulus of elasticity or young's modulus

- describes how stiff a material is - the stiffer the material the steeper the sloop

the roles of tendons

- dynamic restraint (with muscle) - connects muscle with bone - transmits tensile loads from muscle to bone to produce joint motion - enables the muscle belly to be at optimal distance with joint

tension

- equal and opposite loads are applied outward from the surface (pulling the two ends) - structure lengthens and narrows - tensile strain and stress result inside the structure - tensile fractures occur in bones with more cancellous (trabecular, spongy) bone - yielding is caused by the debonding of the osteons at the cement lines and microfractures

compression

- equal and opposite loads are applied toward the surface (pushing the two ends) - results in compressive stress and strain inside the structure - structure shortens and widens - yielding in bone is indicated by the cracking of osteons - compression fx are commonly found in vetebrae

fast twitch (type two B) fibers

- fast contraction - fatigue easily - larger, stronger, and more powerful

creep

- force is constant while deformation increases - the structure continues to deform while the load or stress remains constant - can be increased by increase time, load, or temp.

angle of pennation

- if a fiber attaches parallel to a tendon then the angle is 0 and all force is transmitted to the tendon - for angles greater than 0, less force is transmitted to the tendon - at an angle of 30 deg, 86% of force is transmitted to the tendon (totally worth the pennation) - most muscles have pennation angles 0-30 deg - pennation muscles produce greater maximal force than fusiform muscles of similar volume because they cannot fit more fibers into a given length of muscle - force increases even though less force is transmitted since physical CSA increases significantly

how temperature effects muscles

- increased temperature increases conduction velocity, frequency of stimulation, and muscle force production - greater enzymatic activity (increasing efficiency of muscle contraction) - increased elasticity of collagen which enhances extensibility of the muscle tendon unit Can increase temperature by warming up (increased blood flow) and metabolism (energy released in muscle contraction and friction of the contractile components) At low temperatures (50 deg), max shortening velocity and isometric tension are inhibited due to decreased pH (acidosis)

how training effects muscles

- increases CSA of all fibers (hypertrophy and strength) - percentage of fibers changes depending on the kind of training - stretching => inhibits the spinal effect (increases muscle contraction) and enhance the Golgi effect (inhibits contraction and enhances relaxation in response to muscle tension)

fast twitch (type two A) fibers

- larger - extensive SR for rapid release of Ca2+ - lots of glycolytic enzymes - less extensive blood supply - fewer mitochondria - fast contraction (intermediate glycolytic activity) - relatively fatigue resistant (oxidative)

shear stress

- load is applied parallel to the surface of the structure - shear stress and strain result inside the structure - the structure deforms internally in an angular manner (right angles on the plane surface become obtuse or acute) - tensile or compressive loads also produce shear stress

torsion

- load is applied that causes a twist about the axis and a torque is produced within the structure - shear stresses are distributed over the entire structure proportional to their distance from the neutral axis - max tensile and compressive forces act on a plane diagonal to the neutral axis - it is pulled horizontally and vertically as compression, tension, and shear work together - bone will fail first in shear and then in tension => first crack is parallel to the neutral axis => second crack forms along the plane of max tensile stress (diagonal)

summation

- mechanical responses to successive stimuli that add to the initial response - the greater the frequency of stimulation the greater the tension produced in the muscle up to a maximum

prestretching

- more work can be performed when it contracts immediately after being quickly stretched eccentrically - energy is stored in the elastic and contractile components - activates the stretch-shortening cycle

muscle activity and bone

- muscular contraction alters stress distribution on bone - eliminates or reduces tensile stress by creating a neutralizing compressive stress

PNS

- nerve processes that extend from the brain and spinal cord - provides input to CNS - provides output from CNS - 12 pairs of cranial nerves and their branches - 31 pairs of spinal nerves and their branches

nerve root problems

- nerve roots move with spinal motion and should therefore be able to glide easily - chronic irritation with fibrosis around nerve roots can lead to 'microstretching' injuries because the nerve cannot glide as it should ex. herniated disk - one nerve root is compressed quickly from a single area (lateral compression) ex. spinal stenosis - pressure applied circumferentially at a slow, progressive rate (circumferential compression)

nerves and tensile injuries

- nerves are very strong in tension (severe intraneural tissue damage occurs long before a nerve breaks) - usually associated with severe accidents stress strain curve: - extended toe region - followed linear elastic region (maxes at 20%) - perineurial sheaths rupture at 25-30% elongation (complete structural failure) - plastic region follows - variations in nerves exist and injury may increase stiffness and decrease elasticity

double-crush syndrome

- neural axon distal to long standing compression site is more susceptible to injury - likely due to depletion of axonally transported proteins distal to the compression site

multiple levels of nerve root compression

- patients with multiple levels of compression have more pronounced symptoms - compression at two levels may induce a nutritionally impaired region between the two sites (blood flow and CSF supply nutrition) - also affects nerve conduction and may be enhanced if distance between sites is greater

slow twitch (type one) fibers

- smaller - more extensive blood vessel system - more mitochondria - large amounts of myoglobin - slow contraction speed - fatigue resistant (high oxidative capacity)

spinal nerve roots

- spinal cord ends at L1 at the conus medullaris - the bundle of lumbar nerve roots is called the cauda equina dorsal root: - inclosed by a multilayered CT sheath and an epineurium - root sleeve becomes tighter as the nerve root approaches the intervertebral foramen - increased risk of 'entrapment' syndrome' at the intervertebral foramen than more central in the cauda equina

musculotendinous unit

- spring-like elastic component (tendons) are in series with the contractile component (contractile proteins) which are in parallel with another elastic component (the epi, peri, or endomysium) - stretch produces tension (stored energy) in the elastic components (tendons) which recoils when the stretch is released - viscoelastic properties allow for further elongation (creep) and a decrease in tension (stress-relaxation) when a stretch is heal for a period of time

the roles of ligaments

- static restraint - connects bone with bone - augments mechanical stability of joints - guides joint motion - prevents excessive motion

ultimate failure load

- the absolute load (force) that causes a structure to fail. This may not mean complete failure of a structure, but it will result in at least partial disruption. - examples: completely breaking a plastic fork or partially tearing a ligament

three-point bending

- the break will occur at the middle IF it is homogenous, symmetrical and without defect.... but most things aren't - ex. 'boot top' fx

viscoelasticity

- the time dependent mechanical property of a material - includes creep and stress-relaxation - amount and rate of force application matter

four-point bending

- two forces couple together to produce equal moments - break will occur at the weakest point

compression of spinal nerve roots

- vascular impairment is present even at low pressure levels - full restoration of blood flow does not occur until compression is removed completely - while compressed, nerve roots will get nutrition via diffusion from the cerebrospinal fluid but doesn't compensate for the loss of nutrition from the vascular supply - compression can increase vascular permeability leading to intraneural edema which can increase the endoneurial fluid pressure which can then impair blood flow => edema usually persists after the removal of compression => leads to the formation of fibrosis and slow recovery => edema forms even at low pressure levels - sensory fibers slightly more susceptible to compression than motor fibers

microvascular system in nerves

- well-vascularized structure with networks in all three layers of CT - impulse propagation and axon transport depend on local O2 supply - large vessels approach the nerve at many locations (a redundancy). creates a back up system incase one vessel goes down.

the structure of an osteon

1. Haversian canal - at the center and contains blood vessels and nerve fibers 2. lamellae - rings of intertwined mineralized collagen fibers that surround the canal - collagen fibers run in alternate directions from lamella to lamella to increase strength in many directions 3. lacunae - small cavities containing one osteocyte 3. canaliculi - small channels connecting the lacuna and Haversian canal 4. cement line - a layer of glycoproteins separating the osteons

sliding filament hypothesis of contraction

1. before contraction, ATP cleaved by myosin head which causes it to extend ('ready' position) 2. myosin head binds to actin site forming a cross bridge 3. binding causes a power stroke (cocked springs) so actin and myosin filaments slide over one another. Shortens the sarcomeres - the greater the # of cross bridges the greater the force generated 4. ADP and P- is released from the head, new ATP binds, head detaches 5. ATP is cleaved by the myosin head, head is extended 6. cycle repeats

bone composition

1. cells (osteocyte) 2. organic matrix - collagen (good in tensile strength) - Glycosaminoglycans or GAGs (cement layers of fibers and surrounds the collagen fibers) 3. water 4. inorganic matrix - hydroxyapatite crystals (good in compressive strength) (calcium and phosphate)

the 3 functions of the nervous system

1. collection of sensory input (identifies changes occurring inside and outside of body using sensory receptors) 2. integration (process, analyses and interprets these changes and makes decisions) 3. motor output (it then effects a response by activating muscles or glands (effectors) via motor output

what are two ways to smoothly increase the force produced by a muscle

1. increase stimulation rate 2. recruit more (and larger) motor units

degeneration of bone

1. loss of bone density observed with aging - reduction of cancellous bone - thinning of cortical bone 2. bone is more brittle 3. depends on age, gender, postmenopause, inactivity, calcium deficiency

the elastic components (distensibility and elasticity) in the muucslotendionous unit are valuable

1. they keep the muscle in readiness for contraction and assure that muscle tension is produced and transmitted smoothly during contraction 2. assure that the contractile elements return to their resting positions when contraction is terminated 3. help prevent passive over-stretch of the contractile elements when these elements are relaxed 4. absorb energy proportional to the rate of force application and to dissipate energy in a time-dependent manner

critical pressures for nerve compression

30-80 mmHg - impairment of blood flow to compressed part of nerve - long-standing or intermittent pressure may induce intraneural edema which may become a fibrotic scar - axonal transport may be impaired thus depleting proteins distally - double-crush syndrome => distal portions of the axon are more susceptible to additional compression due to a lack of proteins (anything distal is at risk) 80-200 mmHg - complete cessation of intraneural blood flow causing ischemia - even after 2 hrs, blood flow is rapidly restored when pressure is released 200-400 mmHg - induces structural damage and rapid deterioration of nerve function with incomplete recovery even after short periods of compression Amount and time of compression matter!!

fatigue in muscles

Causes: - a drop in muscle tension following prolonged stimulation - stimulation frequency outpaces ATP regeneration - fatigue occurs more quickly during tetanus - rest allows ATP to regenerate to restore muscle tension Results in: - lack of coordination of movement (accuracy control and contractile velocity) - redistribution of loads in tissues

mode of nerve compression

Direct compression is worse than indirect compression direct compression => Edge effect: - when you squeeze in the middle the edges experience maximal pressure (tension) - hydrostatic pressure is greatest in the center of compression but it can just flow out - both blood vessels and nerve fibers will show greatest damage at the edges - larger fibers are affected much greater than small fibers indirect compression => - surroundings bolster the nerve supporting it

types of contractions

Eccentric contractions can produce greater force at similar (negative) velocities - greater average force produced per cross-bridge as they are pulled apart (they want to reattach; its not a cycle anymore) - a more rapid reattachment phase of cross-bridge formation - passive tension produced by the elastic components

intraneural connective tissue

Epineurium: - surrounds the entire nerve - a loose structure - cushions the nerve during movements (protects from external trauma and maintains O2 supply via epieneural vessels) - amount varies (more where nerves lie close to bone or pass joints while there is none in the spinal nerve roots) Perineurium: - lamellar sheath that encompasses each fascicle - great mechanical strength - biochemical barrier: isolates the nerve fibers thus preserving an ionic environment of the interior of the fascicles endoneurium: - located inside the fascicles and surrounds a nerve fiber - composed mainly of fibroblasts and collagen - slightly elevates endoneurial fluid pressure compared to surrounding tissues which may increase as a result of trauma leading to edema - this effects microcirculation and function of nerve

fatigue of bone under repetitive loads

Fx - single load that exceeds the ultimate strength of bone - repeated applications of a lower load (fatigue fx) Living bone fatigued is affected by: - amount of load - number of repetitions - frequency of loading Theory of muscle fatigue may cause fatigue fxs as muscle can no longer provide neutralizing tensile or compressive force on bone Resistance to fatigue is greater in compression than in tension

Bone geometry

In tension and compression the load to failure and the stiffness are proportional to the CSA of bone In bending the CSA, distribution of bone tissue around the neutral axis, and length affect the mechanical behavior - bones will be stronger if there is more stuff in the direction of the bending force => shorter bones can withstand higher forces because the bending moment is longer - (BxH^3)/12 => H is cubed!! In torsional loading polar moment of inertia takes into account CSA and distribution about an axis - polar moment of inertia => looks at how far it is from the axis of rotation (thicker = stronger)

two basic patterns of muscle architecture

Long: - sarcomeres are in series - designed for velocity and excursion (proportional to lenght) - ex. sartorius Thick: - sarcomeres are in parallel - designed for force production (proportional to CSA) - ex. quads

the loading rate of bone will affect fractures

Low loading rate = single crack = bone and soft tissue remains intact High loading rat = numerous cracks = bone fragments and extensive soft tissue damage

spinal nerves

Roots unite to form spinal nerves at the intervertebral foramen - posterior root (sensory neurons) - anterior root (motor neurons) Two major branches after the spinal nerve - dorsal ramus (innervates muscles and skin of head, neck, and back - ventral ramus (innervate ventral and lateral parts of these structures and the upper and lower extremities) - they then form interlacing networks (plexuses) with adjacent nerves before innervating structures four major plexuses: - cervical - brachial - lumbar - sacral

isometric muscle contraction

a change in muscle tension without a change in muscle length - no mechanical work is performed - no movement is produced - stabilizes joint and position or posture - muscle work is performed - energy dissipated as head - initial isometric phase to all dynamic contraction - greater tension than concentric due to greater number of cross-bridges developed and activation of more motor units

elasticity

a materials ability to return to its original state following deformation - no permanent deformation - the linear region on the stress-strain curve

econcentric contraction

a theoretical muscle contraction that occurs in two-joint muscles when one joint shortens and the other lengthens

deformation

an absolute change in the length of a material in response to an applied stress

CNS is composed of

brain and spinal cord

bone is biomechanically biphasic composite

combines mineral (a strong, brittle material) and collagen (a weaker, more ductile material) to create a stronger unit that either one alone the two types of bone: 1. cortical => stiffer 2. trabecular => more ductile

isotonic muscle contraction

constant muscle tension with a change in muscle length - occurs when the contraction force matches the total load on a muscle such as during walking, running, or squatting

strain

deformation of a material in response to an applied force expressed as a percentage of a change in length (compared to original) strain = delta L/L

when do muscles typically produce their strongest contractions

during the middle phase of their ROM

connective tissues of muscle

epimysium: - surrounds the entire surface of a muscle belly - separates the muscle from other muscles - tightly woven bundles. of collagen fibers that are stretch resistant perimysium: - divides the muscle into fascicles - tough, relatively thick and stretch resistant - conduit for blood vessels and nerves endomysium: - surrounds individual muscle fibers - relatively dense meshwork of collagen fibers - delicate tissue - the location of metabolic exchange between fibers and capillaries

stress

force/unit area - developed within the tissue as a result of an externally applied force

gradation

gradual increase in tension produced by increased stimulation frequency and the number and size of motor units activated

Treppe Effect (staircase effect)

graduated series of increasingly vigorous contractions that results when a series of identical stimuli is applied to a muscle - same stimuli but more Ca2+ is available, allowing for more tension

Bone is viscoelastic so loading rate will alter behavior

higher loading rates increase stiffness and strength

when is bone strongest?

it is strongest in compression and weakest in shear

endosteum

lines the inner surface of bones

nerve gliding

mobilizes nerves

size principle

motor units are recruited from smallest to largest allowing fine motor activities and contributing to graduation

eccentric muscle contraction

muscle contracts and lengthening occurs (involuntary and voluntary) involuntarily - when resistance force is greater than max muscle force - maximal tension is developed - greatest chance of DOMs (over other types of contractions) voluntarily - when deceleration of a load or acting as a braking force - down phase of arm curl - walking down stairs - greater chance of DOMs (over other types of contractions)

concentric muscle contraction

muscle contracts and shortening occurs - muscle force is greater than resistance force - up phase of arm curl

the effect of myelinated vs. unmyelinated

myelination increases the speed of conduction of nerve impulses, and insulates and maintains the axon, while the gaps are called nodes of Ranvier. - nerve impulses jump from one node to another (saltatory conduction) - conduction velocity is directly proportional to fiber diameter

PNS is composed of.

nerves and ganglia - cranial and spinal nerves

relaxation time

period from peak tension to zero tension

contraction time

period from the start of tension to peak tension

stess-strain-curve

plots the stress vs. the strain - is used to determine the characteristics and strength of a material

onset rate of compression of nerves

rapid-onset - trauma, disc herniation - fractions of seconds - pronounced effects on edema and impulse propagation - more pronounced edge-zone edema with reduced nutrient transport adjacent to the compression zone slow-onset - months or years - degeneration, stenosis

wolff's law

remodeling of bone is influenced and modulated by mechanical stresses - body weight - weightlessness - immobilization - exercise - plate/implant

twitch

response of a muscle to a single motor nerve impulse

nerves and compression injuries

s/s: - numbness - pain - muscle weakness - irreversible muscle wasting (if greater than 6 wks) mechanical factors are more important at higher pressures: - pressure level - type/mode of compression - time is a secondary factor. there seems to be a minimum amount to time that even a high pressure must act in order to induce damage - may be released to the viscoelastic (time-dependant) properties of a peripheral nerve tissue Ischemia is more important at longer duration low pressures (but still important at high pressures) examples: 1. ulnar nerve entrapment: - numbness, tingling, and pain in arm, elbow, and hand - sometimes hand weakness - 'funny' bone 2. carpal tunnel syndrome: - compression of medial nerve in forearm and hand - pain, weakness, numbness, tingling, and burning in hand - repetitive use

types of bone

spongy bone (trabecular, cancellous) - composed of thin plates (trabecular) in a loose mesh structure - interstitial spaces are filled with red marrow - good in resisting compression and shear compact bone (cortical) - forms the outer shell (cortex) - dense structure - excellent in resisting torque bone is anisotropic!

tetanus

the development of maximal tension as a result of summation beyond which no further increases in stimulation frequency will increase tension

plasticity

the property of a material to permanently deform when it is loaded beyond its elastic range - the yield point when the material no longer acts elastically; stress beyond this point results in permanent deformation - the yield point identifies the strength of a material

ultimate failure stress

the ultimate failure load divided by the cross-sectional area of the tissue

latency period

time from stimulation to the rise in muscle tension (the time it takes to take up slack in the elastic components)

types of nerve pressure

two basic types of pressure application: 1. uniform pressure applied circumferentially - equally squeezed on all sides - ex. carpal tunnel syndrome - decreases the diameter of nerve in the loaded region - tissues are squeezed out from under pressure moving them towards the edges - displacement is maximal at the edges 2. lateral compression - nerves squeezed between two parallel rigid surfaces - ex. sudden blow to a nerve that is against a bone or a spinal nerve between two discs - causes elliptical deformation - nerve is extended in direction perpendicular to the pressure application and compressed in direction of loading - perimeter must increase thus stretching the membrane and affection permeability and electrical properties - may trigger firing of nerves to cause pain sensation

anisotropic

when a material has different levels of strength according to the direction of force application