muscle 1.4

Question 1

in one single motor unit muscle fibers are..

Answer 1

all the same

Question 2

does a muscle have only 1 fiber type

Answer 2

no it has all 3 motor unit types

Question 3

2 factors of total muscle tension development

Answer 3

1) amount of tension developed by each fiber
(frequency-tension relation, length-tension relation, fiber diameter, fiber type, fatigue)

2) number of fibers contracting at any time (number of fibers per motor unit, number of active motor units)

Question 4

small motor units vs large motor units

Answer 4

small motor units : total tension the muscle produces increases in small steps by activating more motor units

large motor units : total tension the muscle produces increases in large steps by activating more motor units

Question 5

size of a motor neuron

Answer 5

the diameter of the neuronal cell body (diamteter of its axon)

type 1 smallest diameter = smallest tension
type 2a slightly larger diameter= larger tension
type 2x biggest diameter =greatest tension

Question 6

what makes the smaller diameters in muscle fibre types produce less tension?

Answer 6

there is the same number of sodium ions entering to cause excitatory synapse, but the difference is there greater depolarization
-motor units are spread out over a smaller surface in muscle fibre types with smaller diameters

Question 7

what determines the velocity that a single muscle fiber shortens

Answer 7

1) the load on the fiber -> load on the whole muscle
2) the speed of the myosin type expressed in the fiber -> type of motor units in the muscle

when you increase motor unit recruitment, the load decreases on each motor unit which increases both force and velocity

Question 8

what happens if there is denervation atrophy

Answer 8

neuron to the skeletal muscle was destroyed

-progressively smaller in diameter and amount of contractile proteins they contain will decrease

Question 9

what happens if there is disuse atrophy

Answer 9

when the muscle is not used for a long period of time

-same thing, smaller diameter, amount of contractile proteins decrease

Question 10

what happens when you exercise the muscle

Answer 10

increase amount of contractile activity, increase in size (hypertrophy), changes in capacity of ATP production and subtype of myosin they express

Question 11

low intensity/long duration exercise leads to

Answer 11

• increase number of mithochondra in all muscle fibers
• myosin composition MAY shift in fast fibres from 2X to 2A
• increase in number of capillaries

all increase ability to sustain muscle contraction through OXIDATIVE metabolism

Question 12

high intensity exercise

Answer 12

• increase in diameter (hypertrophy) due to satelite cell activation and increased synthesis of actin and myosin filaments -> more fibrils
• myosin in fast fibers could shift 2a to 2b
• increase synthesis of glycolytic enzymes

Question 13

can you increase strength without hypertrophy?

Answer 13

yes increase synchronous of muscle units, enhance ability to recruit fast glycolytic motor neurons

Question 14

can you change proportions of fibers in a muscle

Answer 14

can change fibres 2A to 2x but not from type 1 to 2

Question 15

tone

Answer 15

resistance training can enhance tone

• more myofibrils are activated during RT, more energy being used = good for weight loss
• RT enhances background motor unit firing
• better at recruiting large motor units

Question 16

transient hypertrophy

Answer 16

increase in muscle size that develops immediately following exercise (transitioning quickly)

Question 17

chronic hypertrophy

Answer 17

increase in muscle size due to long term strength training, muscle fibres increase size and increased recruitment of muscle fibres and activation

neural adaptations happen first then hypertrophy

Question 18

insulin like growth factor 1, anabolic steroids (androgens), myostatin

Answer 18

androgens influence on muscle strength and growth

myostatin is produced by skeletal muscle cells, it is a regulatory protein which inhibits muscle hypertrophy through negative feedback effect

-myostatin bad if you want to get big

-some people have myostatin deficiency

Question 19

effects of aging

Answer 19

maximum force a muscle can generate decliness 30-40% between 30-80 years old

• average fibre diameter decreases, less PA
• intensity and duration of exercise in older individuals doesnt produce as much change

Question 20

what causes exercise-induce muscle soreness

Answer 20

thought to be structural damage to the muscle cells and their membrane which activates the inflammation response

-releases histamines that activate endings of pain neurons in the muscle

eccentric produces most muscle soreness

Question 21

acute muscle soreness

Answer 21

pain due to ischemia (not enough blood flow; oxygen to the muscle) or accumulation of hydrogen ions or lactate

Question 22

doms

delayed onset muscle soreness

Answer 22

post - 12,24,48 hours after exercise

nothing to do with lactate, lactate gone after an hour

Question 23

creatine kinase

Answer 23

structural member of the M LINE

• when the muscle is damaged it is torn apart and released
• CK is often used as a marker for muscle damage

Question 24

what does strained muscle leads to

Answer 24

scar tissue

has collagen overtop which does not allow the muscle to stretch as nicely

Question 25

antagonist

Answer 25

groups of muscles that produce oppositely directed movements at joint

Question 26

fulcrum

Answer 26

point on which a lever rests or is supported and on which it pivots

Question 27

first class lever

Answer 27

fulcrum is between load and effort

eg. semispinalis doing flexion and extension at head

Question 28

second class lever

Answer 28

fulcrum at the end near the load

eg. soleus doing plantar flexion and dorsiflexion

Question 29

third class

Answer 29

fulcrum at the start near the effort

eg. biceps doing flexion and extension

skeleton is a lever and fulcrum system

Question 30

mechanical equilibrium of forearm

Answer 30

downward load x distance from the elbow = isometric tension exerted by the muscle X distance from the elbow

Question 31

muscle cramps

Answer 31

involuntary tetanic contractions of skeletal muscles

AP’s firing higher rates than normal, sensory receptors and motor neurons in the area activated

caused by : electrolyte imbalances in extracellular fuid, over exercise, dehydration, chemical imbalances, hormonal imbalances, cholesterol lowering medications

-spicy foods reduce excess AP = less cramping

Question 32

muscular dystrophy

Answer 32

genetic disease

• progressive degeneration of skeletal and cardiac muscle fibres
• absence of proteins that make up the costameres in striated muscle

Question 33

costameres

Answer 33

clusters of structural and regulatory proteins that link the Z disks of the outermost myofibrils to the sarcolemma and extracellular matrix

-allow you to have lateral transmission from sarcomere to extracellular matrix

help stabilize the muscle

Question 34

myasthenia gravis what is it? whats it caused by? treatment?

Answer 34

neuromuscular disorder charcterized by muscle fatigue and weakness that progressively worsened as the muscle is being used

caused from destruction of nicotinic Ach receptors proteins of the motor end plate, mediated by antibodies of a persons own immune system

treatment is adminestering acetylcholinesterase inhibitors, suprress immune function with glucocorticoids and removal of the thymus