Muscular System 2

myofibrils

What are muscle fibers full of?

sarcolemma

_________: (structure of muscle fiber) plasma membrane

transverse tubules

_________: (structure of muscle fiber) tunnel-like extensions of the sarcolemma

sarcoplasm

_________: (structure of muscle fiber) cytoplasm

myoglobin

_________: (structure of muscle fiber) a cytoplasmic protein that binds oxygen

glycogen

_________: (structure of muscle fiber) a polymer of glucose

sarcoplasmic reticulum (SR)

_________: (structure of muscle fiber) a network of membranous sacs around the myofibrils. The SR stores calcium ions.

• has membranous sacs encircling each myofibril

• loaded with CALCIUM

• release of CALCIUM triggers myofibril contraction

contractile, regulatory, structural

What are the three kinds of proteins myofibrils are built from?

contractile proteins

_________: (type of protein) generate force during contraction

regulatory proteins

_________: (type of protein) switch the contraction process on and off

structural proteins

_________: (type of protein) align the thick and thin filaments properly, provides elasticity and extensibility, and links the myofibrils to the sacrolemma

myosin

_________: (type of contractile protein)

• thick filament

• functions as a motor protein which can achieve motion

• Convert ATP to energy of motion

• Projections of each myosin molecule protrude outward (myosin head)

actin

_________: (type of contractile protein)

• thin filaments

• Actin molecules provide a site where a myosin head can attach

• tropomyosin and troponin are also part of the thin filament 

• In relaxed muscle

• Myosin is blocked from binding to actin

• strands of tropomyosin cover the myosin-binding sites

• Calcium ion binding to troponin moves tropomyosin away from myosin-binding sites

• allows muscle contraction to begin as myosin binds to actin

titin

_________: (type of structural protein)

• stabilizes the position of myosin

• accounts for much of the elasticity and extensibility of myofibrils

• extends from z disc to m line

dystrophin

_________: (type of structural protein)

• MOST CLINICALLY IMPORTANT

• links actin in outermost myofilaments to transmembrane proteins and eventually to fibrous endomysium surrounding the entire muscle cell

• transfers forces of muscle contraction to connective tissue around muscle cell

• genetic defects in dystrophin produce disabling disease muscular dystrophy

binds to actin

Whats the function of regulatory proteins?

tropomyocin

_________: (type of regulatory protein)

• covers myosin-binding sites, keeps myosin from engaging actin

troponin

_________: (type of regulatory protein)

• binds to tropomyocin

• in the presence of Ca++, it causes tropomyosin to uncover myosin binding sites, allowing contraction to begin.

Myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere, progressively pulling the thin filaments toward the center of the sarcomere, leading to shortening of the entire muscle

What happens in the presence of Ca++?

1. Myosin heads hydrolyze ATP and become reoriented and energized. 2. Myosin heads bind to actin, forming cross-bridges. 3. Myosin cross-bridges rotate toward the center of the sarcomere (power strike). 4. As myosin heads bind to ATP, the cross-bridges detach from actin.

List the steps of the presence of calcium in Ca++?

Rigor Mortis

_________: hardening of muscles and stiffening of body beginning 3 to 4 hours after death.

• Deteriorating SER releasing Ca++

• Deteriorating sarcolemma allows Ca++ to enter cytosol

• Ca++ activates myosin-actin cross-bridging

• muscle contracts, but cannot relax

• ATP is not produced after death, so muscles don’t relax. -fibers also remained contracted until myofilaments begin to decay.

Ca++ is released and channels close, then troponin holds tropomyocin in position to block myosin-binding sites on actin

What happens when muscles are relaxed?

Ca++ release and channels open, Ca++ binds to troponin, which changes the shape of the troponin-tropomyosin complex

What happens when muscles are contracted?

1. ACh is released from a synaptic vesicle 2. ACh binds to Ach 3. Muscle action potential is produced 4. ACh is broken down

How does someone trigger a muscle contraction?

1. Release of acetylcholine 2. Activation of ACh receptors. 3. Production of muscle action potental. 4. Termination of ACh activity

How does a nerve impulse elicit a muscle action potential?

neuromuscular junction (nmj)

_________: (terminology) interface of the motor nueron and muscle fiber

synaptic cleft

_________: (terminology) gap that separates the two cells

neurotransmitter

_________: (terminology) chemical released by the initial cell communicating with the second cell 

synaptic vesicles

_________: (terminology) sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (Ach)

motor end plate

_________: (terminology) the region of the muscle cell membrane opposite the synaptic end bulbs. Contains acetylcholine receptors

Botulinum toxin

_________:

Blocks release of ACh from synaptic vesicles
 No signal, no contraction....
May be found in improperly canned foods
 A tiny amount can cause death by paralyzing respiratory
muscles
Used as a medicine (Botox®)
 Strabismus (crossed eyes)
 Blepharospasm (uncontrollable blinking)
 Spasms of the vocal cords that interfere with speech
 Cosmetic treatment to relax muscles that cause facial
wrinkles
 Alleviate chronic back pain due to muscle spasms in the
lumbar region

Curare

_______:

 A plant poison used by South American Indians on
arrows and blowgun darts
 Causes muscle paralysis by blocking ACh receptors
inhibiting Na+ ion channels
 Derivatives of curare are used during surgery to relax
skeletal muscles

Anticholinesterase

______:

Slow actions of acetylcholinesterase and removal of
ACh
Can strengthen weak muscle contractions
 Ex: Neostigmine
 Treatment for myasthenia gravis
 Antidote for curare poisoning
 Terminate the effects of curare after surgery