Chp 10 & 11- Muscle Physiology, Muscles

Excitability

able to conduct an action potential (change of charge across membrane)

contractility

protein filaments that contain actin and myosin

elasticity

ability to stretch and recoil

functions of skeletal muscle

1. movement 

2. posture

3. production of body heat (through energy usage)

layers to get to muscle (superficial to deep)

1. skin

2. hypodermis

3. deep fascia 

what is deep fascia?

dense irregular connective tissue that surrounds the entire muscle. also called epimysium.

tendon

dense regular connective tissue that weaves into periosteum of bone and connects muscle to bone.

tendon sheath

surrounds tendon to protect from friction and pressure

aponeurosis

flat tendon found at the head and abdomen

layers of muscles

1. epimysium (around muscle)

2. perimysium (around muscle fascicle)

3. endomysium (around muscle fiber)

4. myofibril

muscle fascicle 

makes up muscle. Contains bundles of muscle cells surrounded by perimysium

muscle fiber

contains myofibrils surrounded by endomysiium

myofibrils

made of myofilaments, either actin (thin) or myosin (thick)

sarcolemma

cell membrane of cell

t-tubule

invaginations in sarcolemma and conducts action potential into sarcoplasm and excited sarcoplasmic reticulum

sarcoplasm

cytoplasm of cell. Abundance of mitochondria and smooth endoplasmic reticulum

sarcoplasmic reticulum

smooth endoplasmic reticulum that stores Ca2+

sacromere

unit of contraction and consist of 1 dark band and ½ light band on each side of dark band

myosin description

• myosin head: actin-binding sites

• Breaks down ATP, head pivots, and binds to actin

• myosin and actin binding= cross bridge

A-band description

Contains many myosin stacked with heads pointing away from the center and overlapping actin myofilament

actin description

• I-band is stacked with actin

• has binding sites for myosin

• contains tropomyosin and troponin

Tropomyosin

wrapped as a spiral around actin to cover actin binding sites at rest

troponin

attaches to tropomyosin, Ca2+, and actin

As Ca2+ levels increase in sarcoplasm, what happens to tropomyosin and troponin

Ca2+ binds to troponin. Troponin changes structure and tropomyosin is moved off actin-binding sites and myosin is able to bind.

what role does calcium have in contraction

Ca2+ binds to troponin and moves tropomyosin off actin-binding sites to allow myosin to bind and contract the muscle

what is the role of ATP in muscle contraction

myosin head binds and splits ATP. This recockes the myosin head and swivels it and it movrs actin to the center of the sacromere to shorten the cell

how does muscle relaxation occur

through the breakdown of acetylcholine by acetylcholinesterase

motor neuron

where action potential comes from

axon hillock

where the action potential originates

axon terminal of motor neuron

contains acetylcholine. the neurotransmitter “carries” impulse across synaptic cleft

synaptic cleft

space b/w axon terminal and muscle cell

motor end plate

has receptors (chemically-gated channels) for neurotransmitters

events at neuromuscular junction

1. action potential travels down neuron

2. reaching the axon terminal, Ca2+ rushes into terminal

3. Ca2+ triggers exocytosis of acetylcholine

4. Ca2+ diffuses across synaptic cleft

5. Ach binds to receptor on motor end plate

6. Binding causes Na+ to rush into muscle (chemically gated)

7. Na+ is positive= change of charge across membrane 

8. charge propagates down sarcolemma down t-tubules 

9. Ach is broken down by acetylcholinesterase to stop action potential 

motor unit

1 neuron and the muscle fiber it innervates

large motor unit

large # of muscle cells/neurons and large motor movements. Posture and muscle tone 

small motor unit

small # of muscle cells/neurons and fine motor movement. g=finger and toes movement.

More contraction needed= ___ amount of motor units.

more

recruitment

increasing # of active motor units

All-Or-None law

each muscle cell will contract to it’s maximum ability

muscle tone

some motor units are active at any times and other are not. Allows for certain muscles, like for muscle down, to not fatigue

hypotonic

decrease in muscle tone

flaccid paralysis

occurs w/peripheral nerve damage. Muscles become limp

hypertonic 

increase in muscle tone 

spastic paralysis

occurs when there is CNS damage. lack of inhibition of muscle movement and causes muscles ti become rigid

atrophy

loss of muscle myofibrils and occurs when muscles are not used or lose of nueron stimulation (denervation)

irreversible atrophy 

muscle fibers replaced by fibrous tissue if muscle is nerve used 

hypertrophy 

increased diameter due to increases myofibrils. Increases mitosis, SER, phosphocreatine. Occurs when muscles are used excessively 

anabolic steroids

build up of muscle proteins

Power stroke

Hydrolysis of ATP and binding of actin causing ADP + P and swiveling of myosin head

Active transport of Ca2+

Occurs at sarcoplasmic reticulum and requires ATP

Na+/Ka+ pump

Resets cell’s resting membrane potential. 3 Na+ out, 2 K+ in. needs ATP

Detachment of myosin head from actin

muscle cell stays contracted without ATP

Rigor mortis

Muscle cell stays contracted because of complete depletion of ATP

Phosphocreatine

• Present in muscle cell

• Supplies ATP for 15 secs of rigorus muscle activity

Equation for creatine phosphate

Phospho~creatine + ADP ←→ creatine + ATP

Glycogen

stored in sarcoplasm. polysaccharide and an ATP source

Anaerobic

• No oxygen

• Lactic acid + 2 ATP

• fast glycolytic fibers

Aerobic (cellular respiration)

• Oxygen 

• H2O + CO2 + 38 ATP + heat

• slow oxidation fibers

• Occurs at mitochondrion 

• O2 comes from blood

Myoglobin

protein binds to O2 and holds inside muscle causing it to appear red

Fatigue

Not enough ATP/O2 and causes low ADP, low ATP, low pH, high lactic acid

oxygen debt

Not enough O2 to meet needs

what does recovery allow 

Oxygenated myoglobin to get rid of lactic acid build up and replenish glycogen and make new phosphocreatine 

Twitch

1 motor unit response to 1 action potential

myogram

graph of twitch (tension vs. time)

latent period 

only a few milliseconds. The time between transmission of action potential and shortening of muscle cell

contraction period

time is takes for a muscle to shorten

relaxation 

time is takes for muscle fibers to relax

refractory period

the very short time a muscle cell cannot be stimulated again. 1/100 of a second

summation

if muscle is stimulated after refractory by before it has completely relaxed, the 2nd contraction is greater than 1st

Muscle cell contraction is relative to ___

amount of intracellular Ca2+

Tetanus

sustained muscle contraction w/no relaxation

treppe

using the same stimulus, muscle will contract more forcefully after contraction several times. also occurs in cardiac muscle

isotonic contraction

constant tension, muscle shortens

isometric contraction

tension increases, muscle does not shorten

Description of cardiac muscle

• lots of mitochondrion 

• contains shorter and thicker sarcomeres

• intercalated discs (gap and mechanical junctions)

• self-excitation 

• longer contraction and refractory periods

• no regeneration 

• can use lactic acid, always requires O2

Description of smooth muscle

• Surrounds organs

• No sacromere, myofibrils or troponin

• contains actin and myosin

• very long contraction, relaxation delayed 

• stretch-relaxation response 

• Can have gap junction

• Greatest capacity for regeneration

origin

less movable bony attachment of muscle

insertion

generally the more moveable bony attachment

Agonist/ prime mover

major muscle that produces desired action 

anatagonists

action opposite of prime mover. They stretch while prime contracts 

Synergists

Assists prime mover. Same action, less powerful

Fixators

stabilize the point of origin

How do you name a muscle

1. location

2. shape

3. direction of fibers

4. # of origins

5. size

6. actin

7. origin + insertion

Facial muscles description

• Orbicularis oris, orbicularis oculi, buccinator, zygomatic muscle

• inserts in skin

• innervated Facial CN VII

• Flaccid paralysis : Paralysis of 1 side of face

sternocleidomastoid

contraction causes neck flexion

scalense

neck flexion and can lift rib cage

trapezius

neck extension

Pectoralis major

• flexion

• adduction

• medial rotation of shoulder (prime mover)

latissimus dorsi + teres major 

• Extension

• Adduction

• Medial rotation of arm (prime mover)

Rotator cuff

• Subscapularis (Medial rotation)

• Infraspinatus + teres minor (lateral rotation)

• Supraspinatus (abduction) 

Deltoid

• Abduction

• Extends and flexes muscle bc of attachment at clavicle and scapula

Biceps branchii

• Origin at shoulder

• Insertion at elbow

• Flexion at elbow

Brachialis

Prime mover of elbow flexion

Triceps branchii

• Extends elbow

• Long head adducts shoulder

Rectus abdominis + Linea alba

• Flex spinal column

External, internal oblique + transverse abdominis

• Compress abdomen to hold organs in place

Erector spinae

Major of 3 major muscle groups of back and extends trunk

iliopsoas (iliacus + psoas major) 

Prime mover for hip flexion

rector femoris

• spans 2 joints

• hip flexion

vastus laterlais, medialis, intermedius

• Knee extension

• femoral nerve innervates