Lecture 7 - Muscle Physiology

Question 1

Skeletal muscle functions?

Answer 1

Producing body movements
Generating heat
Stabilizing body positions

Question 2

Cardiac muscle functions?

Answer 2

Involuntary movement of the heart

Question 3

Smooth muscle functions?

Answer 3

Involuntary movement of organs and blood vessels.

Control of blood vessels, airways, digestive tract, urinary tract.

Question 4

Four properties of muscular tissue that enable muscle to function and contribute to homeostasis?

Answer 4

Excitability
Contractility
Extensibility
Elasticity

Question 5

Excitability

Answer 5

Ability to respond to stimuli

Question 6

Contractility

Answer 6

Ability to contract forcefully when stimulated

Question 7

Extensibility

Answer 7

Ability to stretch without being damaged

Question 8

Elasticity

Answer 8

Ability to return to an original length

Question 9

Three types of muscle tissues?

Answer 9

Skeletal, cardiac, and smooth muscle.

Question 10

Skeletal muscle

Answer 10

Inserted onto bone via connective tissue; tendons and ligaments.

Long cylindrical cells
Many nuclei per cell
Striated
Voluntary
Rapid contractions

Question 11

Cardiac muscle

Answer 11

Found in walls of the heart, specifically the myocardium.

Branching cells, branched fibers
1-2 nuclei per cell
Striated
Involuntary
Medium speed contractions

Question 12

Smooth muscle

Answer 12

Lines hallow organs.

Fusiform cells
1 nuclei per cell
Non-striated
Involuntary
Slow, wave-like contractions

Question 13

Muscles can only do two things: ________ and _______.

Answer 13

contract and relax

Question 14

Fascia

Answer 14

Dense sheet or broad band of irregular connective tissue that surrounds muscles.

Question 15

Epimysium

Answer 15

A sheath of fibrous elastic tissue surrounding a muscle, outmost layer.

Separates 10-100 muscle fibers into fascicles.

Question 16

Perimysium

Answer 16

Surrounds numerous bundles of fascicles.

Question 17

Endomysium

Answer 17

Separates individual muscle fibers from one another.

Question 18

Tendon

Answer 18

Cord that attaches a muscle to a bone.

Question 19

Aponeurosis

Answer 19

Broad, flattened tendon.

Question 20

Neurons that stimulate skeletal muscle to contract are ________.

Answer 20

somatic motor neurons

Question 21

The ____ of a somatic motor neuron typically branches _______. Each branch extending to a _______ skeletal muscle fiber.

Answer 21

1. axon
2. many times
3. different

Question 22

The __________ fibers is set before birth. Most of these cells last a lifetime.

Answer 22

number of skeletal muscle

Question 23

Skeletal muscle structure from largest to smallest unit.

Answer 23

1. muscle bellies
2. muscle fibers
3. myofibrils
4. myofilaments
5. sarcomeres
6. actin & myosin

Question 24

Muscle belly is covered by connective tissue called _________.

Answer 24

epimysium (outer layer)

Question 25

Bundles of muscle fibers called fascicles are surrounded by ________.

Answer 25

perimysium (middle layer)

Question 26

Within fasciculi are individual muscle fibers surrounded by _________.

Answer 26

endomysium (inner layer)

Question 27

Sarcolemma

Answer 27

Plasma membrane of a muscle cell

Question 28

Transverse (T-tubules)

Answer 28

Tunnel in from the plasma membrane. Muscle action potentials travel through the T-tubules.

Question 29

Sarcoplasm

Answer 29

Cytoplasm of a muscle fiber. Includes glycogen used for synthesis of ATP and myoglobin which binds O2 molecules. (Myoglobin releases O2 which is needed for ATP production)

Question 30

Myofibrils

Answer 30

Thread-like structures which have a contractile function.

Question 31

Sarcoplasmic Reticulum (SR)

Answer 31

Membranous sacs that encircle each myofibril. Stores calcium ions (Ca++). Release of Ca++ triggers muscle contraction.

Question 32

Filaments

Answer 32

Function in the contractile process. 2 types - thick and thin filaments. 2 thin filaments for every thick filament.

Question 33

Sarcomeres

Answer 33

Compartments of arranged filaments. Basic functional unit of a myofibril. Segment between two neighboring Z-lines. Each sarcomere is made up of actin and myosin myofilaments. Myosin forms the thick filament. Actin forms the thin filament.

Question 34

Z line/discs

Answer 34

Separate one sarcomere from the next

Question 35

A band

Answer 35

Darker middle part of the sarcomere. Contains both actin and myosin myofilaments (they overlap).

Question 36

I band

Answer 36

Lighter in color and contains only the thin actin myofilaments. Z discs pass through the center of each I band.

Question 37

H zone

Answer 37

Center of each A band which contains thick (myosin) but no thin (actin) filaments. Appears to shorten when muscle contracts.

Question 38

M line

Answer 38

Supporting proteins that hold the thick filaments together in the H zone.

Question 39

What are the two regulatory proteins on actin?

Answer 39

Troponin and tropomyosin

Question 40

Actin

Answer 40

Thin filaments. Actin molecules provide a site where myosin head can attach. Tropomyosin and troponin are also part of the thin filament.

Question 41

Myosin

Answer 41

Thick filaments. Functions as a motor protein which can achieve motion. Convert ATP to energy of motion. Projections of each myosin molecule protrude outward (myosin head).

Question 42

Myofibrils are built from what three types of proteins?

Answer 42

Contractile proteins, Regulatory proteins, and Structural proteins.

Question 43

Contractile proteins

Answer 43

Actin and myosin Generate force during contraction

Question 44

Regulatory proteins

Answer 44

Switch contraction process on and off

Question 45

Structural proteins

Answer 45

Titin - Stabilize the position of myosin. Accounts for much of the elasticity and extensibility of myofibrils. Dystrophin - Links thin filaments to the sarcolemma.

Question 46

Excitation-Contraction Coupling

Answer 46

For voluntary muscle contraction to occur, action potentials must arrive from the motor neuron. This stimulates the release of a neurotransmitter, in most cases of skeletal muscle it is ACh. ACh diffuses across the synaptic cleft, and binds to nicotinic receptors on the post-synaptic muscle cell. If the stimulus is strong enough, action potentials are produced, and the muscle is stimulated to contract.

Question 47

Events leading to muscle fiber contraction (4 steps)

Answer 47

1. A motor neuron releases acetylcholine (ACh). 2. ACh binds to receptors on the sarcolemma. 3. The action potential triggers release of Ca2. 4. The Ca2 binds to troponin on the actin filament, and the troponin pulls tropomyosin off the active sites, allowing myosin heads to attach to the actin filament.

Question 48

Sarcomere _________ is the basis for muscle __________.

Answer 48

1. shortening 2. contractions

Question 49

Shortening happens by __________ the degree of overlap of thick and thin myofilaments in each sarcomere.

Answer 49

increasing

Question 50

The sliding filament mechanism

Answer 50

Myosin heads attach to and walk along thin filaments at both ends of sarcomere. Progressively pulling the thin filaments toward the center of the sarcomere. Z discs come closer together and the sarcomere shortens. Leading to shortening of the entire muscle.

Question 51

Skeletal muscle can contract ______ but ______ easily and must be rested.

Answer 51

1. rapidly 2. tire

Question 52

Skeletal muscle contractions _________ depending on use.

Answer 52

vary in force

Question 53

Cardiac muscle contracts at a ________ rate but can _______ to cope with demand.

Answer 53

1. steady 2. accelerate

Question 54

Smooth muscle contracts in ________, ________ contractions and continues _________.

Answer 54

1. steady, sustained 2. tirelessly