Chapter 9

Is skeletal muscle striated?

yes it's striated

Is skeletal muscle branched?

no

Is skeletal muscle voluntary or involuntary?

voluntary

Does skeletal muscle need nervous stimulation?

yes

What is excitability?

ability to receive and respond to stimuli by changing membrane potential

What is contractility?

ability to shorten forcibly when stimulated

What is extensibility?

ability to extend or stretch

What is elasticity?

ability to recoil and return to resting length

What are the four functions of muscle?

movement, posture, joint stability, heat production

What is a muscle?

an organ that consists of many muscle cells, connective tissue wrapping, blood vessels, and nerve fibers

What is a fascicle?

bundle of muscle cells that is separated from the rest of the muscle by a connective tissue sheath

What is a muscle fiber?

an elongated multinucleate contractile cell, with striated appearance

What is a myofibril?

rodlike structures inside muscle fibers that contain myofilaments

Is cardiac muscle striated?

yes it's striated

Is cardiac muscle branched?

yes

Is smooth muscle striated?

no striations

Is smooth muscle branched?

no

Is cardiac muscle voluntary or involuntary?

involuntary

Is smooth muscle voluntary or involuntary?

involuntary

What is a sarcomere?

Contractile unit of striated muscle

What is the H zone?

segment with no thin filaments (thick only)

What is the M line?

anchoring site for thick filaments

What is the Z disc (line)?

anchoring site for thin filaments, aka the dividing line

What are thick filaments made of?

myosin protein

What are thin filaments made of?

actin protein

What happens during the sliding filament theory?

thin filaments slide across thick filaments, H zone disappears with contraction, then z discs get closer to m line with contraction

stages of skeletal muscle contraction

1. motor neuron excitation, 2) stimulation by acetylcholine, 3) excitation-contraction coupling, 4) cross-bridge cycling

Steps of muscle fiber excitation

1. action potential, 2) voltage-gated calcium channels open, 3) release of acetylcholine, 4) ACh receptors at neuromuscular junction, 5) ACh binds ti receptors, sodium enters, end plate potential, 6) acetylcholinesterase degrades ACh

What is action potential?

a massive, all-or-none, depolarization of a cell's membrane

What is excitation-contraction coupling?

events that transmit action potential along sarcolemma lead to sliding of myofilaments

Steps of Excitation-Contraction Coupling

1. The action potential (AP) spreads from the cell membrane into the T tubules.

2. Voltage-sensitive proteins stimulate release of Ca2+ from SR

3. Calcium binds to troponin on thin filaments

4. Contraction begins by cross bridge cycling

steps of cross bridge cycle

1. Cross bridge formation, high-energy myosin head attaches to actin thin filament active site

2. Power stroke, myosin head pivots, pulls thin filaments to M line

3. Cross bridge detachment, ATP attaches to myosin head, causing detachment

4. Cocking of myosin head, ATP cocks myosin head into high-energy state

What is a motor unit?

one motor neuron and all the muscle fibers it innervates

Which muscle fiber type is both involuntary and not branched?

a) Skeletal muscle

b) Cardiac muscle

c) Smooth muscle

c) Smooth muscle

Which structure of a sarcomere serves as the anchor for thin filaments?

a) H zone

b) I band

c) M line

d) Z disc

d) Z disc

Select the true statement about muscle contraction in the sliding filament model.

a) The A band gets shorter

b) The Z discs get closer to the M line

c) Myosin thin filaments pull on the thick filaments

d) Cross bridges only break when the muscle relaxes

b) The Z discs get closer to the M line

How does the body stop the stimulation of muscle fibers by acetylcholine?

a) ACh breakdown by acetylcholinesterase

b) ACh reuptake by motor neurons

c) Inactivation of ACh receptors at the end plate of the neuromuscular junction

c) Inactivation of ACh receptors at the end plate of the neuromuscular junction

What is triggered when the action potential reaches the end of the T tubules?

a) Calcium is released from the sarcoplasmic reticulum

b) Sodium flows into the sarcoplasm

c) Calcium flows into the motor neuron axon terminal

d) Calcium is moved back into the sarcoplasmic reticulum

a) Calcium is released from the sarcoplasmic reticulum

What would happen to the cross-bridge cycle if there was no ATP available?

a) The myosin head would not be able to attach to the actin filament > flaccid muscle

b) The myosin head would not be able to release from the actin filament > rigid muscle

b) The myosin head would not be able to release from the actin filament > rigid muscle

From what two sources can higher tension be produced by a skeletal muscle?

a) Higher frequency stimulation

b) Lower frequency stimulation

c) Higher recruitment of motor neurons

d) Lower recruitment of motor neurons

a) Higher frequency stimulation