Exercise Physiology Exam 2 Questions

What is a motor unit?

a motor neuron and all the muscle cells it services

What type of charge do muscles have in a resting state?

Negative

Why are multiple muscle cells activated by one neuron?

If there was only one muscle cell per neuron, you would have an increased number of neurons which means you would need more muscle to carry your weight and this cycle would continue

How do neurons communicate with each other and muscle cells?

Neurons release neurotransmitters

What are neurotransmitters?

Chemicals released by neurons which can cause excitation, facilitation, or inhibition

What are neuron activations or excitations?

Waves of depolarization caused by Na+ influx

What causes neuron and muscle excitations?

Na+ influx

What are the 2 types of Na+ gates that allow Na+ influx?

Chemical gates and electrical gates

Where are chemical gates found?

nerve cell bodies, dendrites, and in muscles at the nerve synapse

How are chemical gates opened?

neurotransmitters

Where are electrical gates found?

neuronal axons and distal to synapses in muscle cells

How are electrical gates opened?

when the resting membrane potential exceeds a voltage threshold

How often can impulses be sent down an axon?

As fast as the nerve can repolarize

How are neurons repolarized?

Na+K+ pumps are used and require ATP

What do Na+K+ pumps do?

they switch which ions are going in and out (Na+ out and K+ in)

What is facilitation?

raising the resting membrane potential a little; it increases the chance of activation

What is inhibition?

lowering the resting membrane potential below normal; decreases the chance of muscle activating

What are the most common excitatory neurotransmitters?

Norepinephrine and acetylcholine

What are the most common facilitory neurotransmitters?

Norepinephrine and acetylcholine

How does noepinephrine pack a double punch?

It activates the adrenal medulla which releases epinephrine aka adrenaline

What is the most common inhibitory neurotransmitter?

GABA

How do drugs work as facilitators?

act like a "skeleton key" and open gates

What is spatial summation?

neurotransmitter releasing from more than one neuron

What is temporal summation?

altering the frequency of a nerve firing to ensure sufficient amounts to cause depolarization

What is rate of coding?

temporal summation in muscles

What is tetanus?

when muscle achieves mximal temporal summation

How can facilitation and inhibition operate?

directly on the motor neuron or can influence spatial or temporal summation

What is coordination?

learning of fine motor skills

What does coordination involve?

inhibition and facilitation

Why do we have inhibition?

It acts as a safety net for muscle groups

What is a maximum volutary contraction?

the max amount of weigh a muscle group can lift under conscious effort

What is max contraction

the max amount of weight a muscle group can lift under electrical stimulation

Which is greater: max contraction or max voluntary contraction?

max contraction because theres no inhibition

What is nerve failure?

a nerve fails to activate its target through some mechanism other than inhibition

what is fatigue?

when a nerve fails to activate a muscle

What are the 3 causes of nerve failure?

Neuron doesn't repolarize, neuron doesnt release neurotransmitter, and branch point failure

What causes a neuron to not repolarize?

not enough ATP to activate the Na+K+ pump

What causes a neuron to not release neurotransmitter?

if not enough neurotransmitter can be made, the neuron will run out

What is branch point failure?

when longer branches of neurons cant repolarize as fast as the shorter branches

How are muscles divided?

Divided into motor units

What is the optimum muscle length?

2 inch

Why is optimum muscle length short?

Electrical resistance

How are cells arranged in muscles?

Cells are arranged in stories in muscles and also are spread out over the muscle

Why are cells arranged like they are in muscles?

It helps produce more force because more of the muscle can contract and also it helps prevent wear and tear because the muscle contracts evenly.

What do capillaries have to do with muscle cell arrangment?

Muscle cells are spread out in the muscle because capillaries are also spread throughout the muscle. If the cells were next to each other they wouldnt be nourished as well

What happens to axons when they are damaged?

They regrow, but not like they were before. They grow to the closest cell without a nerve

Why do some athletes not return to 100% after an injury?

The axons regrow in a different configuration as before and can group together

What is a muscle fiber?

a bundle of rod like structures called myofibrils

What is the sarcoplasmic reticulum?

a network of tubes that surrounds myofibrils

What are sacromeres?

a series of myofibrils

What are the basic functional contractile unit of a muscle?

sarcomeres

What are the two basic parts of a sarcomere?

thick and thin filaments

How is muscle work accomplished?

thin filaments slide over thick filaments

How do filaments move during isometric work?

they don't move

How do filaments move during concentric work?

Thin filaments slide towards each other

How do filaments move during eccentric work?

the thick filaments try to prevent the thin filaments from sliding apart

How are muscles turned off and on?

Calcium ions

How is myosin attached to actin when muscle is resting?

in a weak binding state

What maintains the weak binding state of myosin and actin during resting?

the troponin complex and Tropomyosin

Where is calcium stored?

sarcoplasmic reticulum

How does calcium get to the Tn-C?

an action potential causes acetylcholine to open a chemical gated Na+ channel. T-tubules spread impulses along the triads and causes depolarization which causes calcium to be released from SR. It goes into the cytoplasm and binds Tn-C

How are muscle contractions turned off?

Calcium is removed

How is calcium removed from muscles?

by using calcium pumps

how do calcium pumps work?

they require ATP and calcium has a higher attraction to them so the calcium wants to leave

What determines the rate of removal of calcium?

The number of pumps and the availability of ATP

Are all skeletal muscles power actions?

No, isometric are not because there is no movement

Power equation

Power = force x velocity

= work/time

= (force x distance)/time

Where does power generate from?

In the cross bridge cycle

What does force magnitude equal?

the number of attached cross-bridge going from 90 - 45 deg

What is contraction velocity related to?

the cross-bridge cycling rate( or the release of ADP release)

How is power production changed?

force, velocity, or both

What are acute changes in force?

changes made during activity

What are chronic changes in force?

long term adaptations made by a person

What are types of acute force modulation?

muscle recruitment, motor unit recruitment, rate coding, alter contractile velocity, control P(i)

What happens during muscle recruitment?

number of muscles is either increased or decreased during a movement

What happens during motor unit recruitment?

different combinations of motor units are used to get the desired amount of force

What happens during rate coding (control sacromere Ca++ concentration)?

there is a direct relationship between % max rate code and % max force of the motor unit; better to have two motor units at 50% than 1 at 100% because it prevents fatigue

What happens when you alter contractile velocity?

inverse relationship between force and velocity; harder to grab a moving object

What happens when you control [P]?

Release of P causes force, the higher the P in the sarcoplasm, the less chance P can be released causing force

What happens when a muscle is too long?

Only a few myosin are in register with the actins

What does optimal muscle length mean?

Each myosin head is in register with an actin

What happens when muscle length is too short?

Some cross-bridges attach to actins from the opposite thin filament and causes a negative force

What controls resting muscle length?

muscle spindles

What are muscle spindles responsible for?

They maintain a certain amount of tension in the resting muscle (not sarcomere length). If tension is altered, sarcomere length will change as a result

What are muscle spindles made of?

Intrafusal muscle fibers

What are intrafusal muscle fibers?

muscle cells which lack sarcomeres in their centers

What happens when you decrease tension on a muscle?

the number of intrafusal cross-bridge attachments will increase causing the intrafusal fibers to contract more which shortens the extrafusal sarcomeres

What happens when you increase the tension on a muscle?

The number of intrafusal muscle fiber decreases, causing the intrafusal fibers to relax, which lengthens the extrafusal sarcomeres

How does stretching effect force?

it decreases force( and power)

How does stretching reduce force?

stretching activates stretch receptors which activate inhibitory interneurons which silence several motor neurons. Silenced motor units fail to activate several motor units.

Why does having less motor units cause less force?

Less motor units = less cross-bridge attachments = decreased force

What happens to tendons and ligaments when you stretch?

They become slack and must be tightened before the muscle can exert force on the bone

What is hypertrophy?

an increase in the number of myofibrils in a muscle cell

What is hyperplasia?

an increase in the number of cells in the whole muscle

What controls hyperplasia and hypertrophy?

satellite cells

What are satellite cells?

single nucleated muscle cells

How do satellite cells come about?

the satellite cells do not fuse with the muscle cell and hangout by themselves

Which cells control muscle growth?

satellite cells

How are satellite cells activated?

by damaging the muscle cells or the connective tissue surrounding the muscle cells

What are the two main types of muscle damage?

mechanical and chemical