Biomechanics test 3 review

Stress (axial or shear) is defined as

force divided by area

The slope of a stress – strain curve describes

Stiffness

A material that deforms easily under low forces is

compliant

The maximum amount of deformation that a material can withstand and still return to its original shape when the load is removed is the

yield point

A material that exhibits both a viscous and elastic response to loading is

viscoelastic

The purely elastic response of a spring to loading is described by

Hookes law

The viscous response of a material is modeled using a

dashpot or damper

The energy returned by a viscoelastic material is the

 

area underneath the unload region of the stress – strain curve

When a load is suddenly applied to a viscoelastic material it initial deforms rapidly. After this rapid initial deformation the material slowly continues to deform. The second slow deformation is called

creep

strain is defined as

the amount of deformation caused by a force

A collection of lamellar bone layers is referred to as

 

an osteon or Haversian system

Based upon the peak stresses experienced in strenuous activity the load-bearing bones are

 

2 – 4 times stronger than they need to be to prevent damage

The physiological strain range for the long bones is

 

400 – 3000 microstrain

Bone is stronger when loaded fast than it is when load slow. This is due to:

 

viscoelasticity

The objective of adaptive bone remodeling is to maintain the bone cell structural alignment and mineral density such that typical daily loads produce strains of

 

400 – 1000 microstrain

Following a bout of excessive bone loading, disinhibition triggers bone remodeling with ____ after the bout of excessive loading.

 

within minutes

The primary function of articular cartilage is to

 

minimize wear

Repeated impact to the leg caused which of the following changes to Radin’s rabbits

 

cancellous bone became brittle, the cartilage was thin or nonexistent, and cortical bone increased thickness

Muscular preactivation is defined as

 

the activation of a muscle prior to some known impact event

The minimum time for the neuromuscular system to respond to a stimulus is

 

80 – 200 ms

cancellous bone is

spongy bone, lighter, more porous inner layer, contains bone marrow

cortical bone is

compact bone, the hard dense outer layer of bones

The muscle cell membrane is called the

sarcolemma

Which protein contains distal Ig, PEVK, and proximal Ig regions

titin

The elastic protein structure that connects myosin to the z disks is

titin

The exchange of Na⁺ and K⁺ ions across the cell membrane produces a

 

muscle fiber action potential

The muscle membrane potential goes from the negative resting value to a positive value because of

 

Na⁺ ions flow into the cell at a faster rate than K⁺ ions flow out of the cell

Before the muscle is activated, titin bears the entire passive load of

12 pN

The crossbridge stalls at what force?

6 pN

When Ca++ bonds to troponin

 

it causes a configurational change in actin

The metabolic cost and force obtained in one cycle of actin-myosin concentric cross-bridge formation is

1 ATP and 4-6 pN

The metabolic cost and force obtained in one cycle of actin-myosin eccentric cross-bridge formation is

1 ATP and 8-12 pN

In a single cycle of a concentric actin-myosin cross-bridge the muscle fiber will

 

shorten ~5nm

The increase in steady-state force following the stretch of an active muscle when compared to activation at the same length without a preceding stretch is

 

residual force enhancement

In an eccentric contraction additional resistance to stretch of muscle fiber is provided by

titin

In an eccentric contraction the myosin arm

 

attempts to rotate forward to shorten the fiber

The total force (crossbridge & titin) generated in one cycle of an isometric contraction is

8 pN

a passive load is

the force a muscle experiences when stretched beyond its resting length, even without active contraction

The highest force generated for a frog semitendinosus occurs at sarcomere lengths of

 

2.0 – 2.2 μm

The overlap of actin-myosin cross-bridges causes the force to

decrease

The technique often used to determine sarcomere length is

 

laser diffraction

The muscle force – velocity curve was first described by

 

Archibald V. Hill

According to the force – velocity curve

as the speed of a muscle contraction increases, the force it can generate decreases, and vice versa.

Po in the force – velocity equation stands for

isometric maximum force

Increasing the concentric velocity causes the number of acti-myosin motors to decline from

 

80 - 20

Maximum eccentric force is

 

1.6 – 2.0 times isometric max

Which of the following structures are damaged by excessive eccentric contractions

desman filaments

titin filaments

sarcolemma is torn apart

The stretch-shorten cycle is

 

an eccentric contraction followed by an immediate concentric contraction

A stretch-shorten cycle yields a more powerful concentric contraction because of

stored elastic energy

a stretch reflex

the concentric phase begins at a higher force level

the use of two joint muscles

To calculate the additional work done following a stretch-shorten cycle

 

compute the area under the force – length graph for the concentric phase

Increasing the velocity of stretch during a stretch-shorten cycle will

 

cause an increase in additional work done on the concentric phase

The series elastic component in Hill’s three component model represents

 

tendon, bend of myosin arms, and titin

The parallel elastic component in Hill’s three component model represents

tendon, passive cross-bridges, endomysium, perimysium, epimysium, titin, desman and the dragging of passive tissues by active cross-bridges

A motor unit is

 

one alpha motor neuron and all of the fibers  that it innervates

The sum of all the muscle fiber potentials from all the active motor units that pass thru the recording zone is the

 

definition of the EMG signal

Which of the following affects the shape and amplitude of the recorded EMG signal

the direction the muscle fiber action potential travels thru the recording zone

the distance the muscle fiber action potential travels from active fibers to the recording electrodes

the horizontal distance the muscle fiber action potential travels along the muscle fiber

The polarity of the recorded EMG signal is affected by

 

the direction the muscle fiber action potential travels thru the recording zone

The amplitude of the recorded EMG signal is affected by

 

the distance the muscle fiber action potential travels from active fibers to the recording electrodes

Synchronization of motor units

occurs when two or more motor units fires at the same time

causes amplification and cancellation

The force generated when a single stimulus is transmitted down the motor neuron is a

 

twitch response

In a ramp contraction when a new motor unit is recruited

as the force exerted by a muscle increases, new motor units are recruited to meet the increasing demand

According to the size principle in a ramp contraction motor units will be recruited as follows

 

slow twitch, intermediate, fast twitch

In addition to fiber type, the size principle can also refer to

the size of the EMG signal for a motor unit

the peak force obtained from a motor unit twitch force 

the diameter of the neuron

In a slow ramp contraction to 45% MVC which motor unit types would be active

 

slow and intermediate twitch only

In a ballistic contraction where the subject is instructed to generate maximum tension as rapidly as follows the motor units would fire at the follow rates

 

slow twitch 60 Hz, intermediate 80 Hz, fast twitch 120 Hz

Electromechanical delay includes

the spread of action potential thru T tubule system

the time for Ca⁺⁺ to be released from the sarcoplasmic reticulum

the time to form an actin – myosin cross-bridge

the time to take of slack (tighten) titin and the tendon

The size principle of recruitment of motor units is attributed to the work of

 

Elwood Heneman

The delay between the start of force and the start of the EMG signal is called the

electromechanical delay

An example of a pure reflex

stretch reflex

Which of the following movements would rely on feedforward control?

 

the impact of a tennis ball with a racket

Feedforward control is

initiating responses before the actual disturbance affects the system, allowing for a smoother and more efficient response.

Which reflex makes a monosynaptic connection?

 

Ia mediated stretch reflex

The reflex latency of a cutaneous reflex is

 

50 – 85 ms

Muscle stiffness is regulated by

golgi tendon organ and the muscle spindle

The smallest force that can be measured by a golgi tendon organ is

 

a twitch force from a single motor unit

In addition to autogenic inhibition the Ib stimulus from the golgi tendon organ causes

 

positive force feedback

The golgi tendon organ monitors

muscle force/tension

Which fiber encircles the dynamic nuclear bag and the static nuclear bag?

 

primary type Ia

The muscle spindle monitors

 

muscle length and velocity

The sensitivity of the muscle spindle is adjusted by

 

gamma neurons

The type Ia neuron causes alpha inhibition via

 

interneurons

When stretching to improve flexibility the goal is to

 

stretch the muscle without causing a stretch reflex

Which of the three muscle spindle components contains specialized muscle tissue that is used to alter sensitivity of the spindle?

dynamic nuclear bag, static nuclear bag and the nuclear chain fiber

Which of the following sensory system is the first to provide information to the CNS under normal balance conditions?

 

somatosensory

Which of the following sensory system is less prone to errors in providing information to the CNS?

vestibular

Toes up and toes down rotation of a floor surface would adversely affect

proprioceptor

The vestibular system provides which of the following to the CNS for regulation of balance?

 

linear and angular accelerations of the head

According to sensory organizational theory the CNS

the core of sensory processing, integrating sensory information from the body and the environment to enable adaptive responses

The reflex latency for a visuo-motor reflex response is

 

approximately 100 ms

The developer of the sensory organization test and NeuroCom is

 

Lewis Nashner

The SOT condition in which the subject must rely on vestibular information is

 

condition 5

The SOT condition(s) in which misleading visual information is given is

 

condition 3 and 6

The SOT condition(s) in which misleading somatosensory information is given is

 

condition 4, 5 and 6

stress is defined as

force over area

strain is defined as

% change in the deformation of an object

compression and bending will produce what kind of fracture?

triangular trapezoidal fracture

tension will produce what kind of fracture?

evulsion fracture

torsion will produce what kind of fracture

spiral fracture