Class 16 - Muscle Tissue

Question 1

Characteristics of ALL muscle cells (5)

Answer 1

1. Excitability - to outside stimuli (chemical signals, stretch, electrical changes across plasma membrane)
2. Conductivity - Local electrical excitation sets off wave of excitation that travels along muscle fiber.
3. Contractility - shortens when stimulated
4. Extensibility - capable of being stretched between contractions
5. Elasticity - Ability to “bounce back” to original testing length after stretching

Question 2

4 characteristics of collagen in muscle (4)

Answer 2

1. Stretches slightly under tension and recoils when released
2. Resists excessive stretching, protecting from injury
3. Returns muscle to resting length
4. Contributes to power output and muscle efficiency

Question 3

Components of a muscle fiber (7)

Answer 3

1. Sarcolemma - plasma membrane of a muscle fiber
2. Sarcoplasm - cytoplasm of a muscle fiber
3. Myofibrils - Long protein cords occupying most of sarcoplasm
4. Glycogen - carbohydrate stored to provide local energy for exercise
5. Myoglobin - red pigment; provides some local oxygen for immediate muscle activity
6. Many mitochondria
7. Nuclei - 30 to 80 per mm. Help fiber repair

Question 4

Sarcoplasmic reticulum

Answer 4

smooth ER that forms network around each myofibril

Question 5

Terminal cisterns

Answer 5

dilated end-sacs of SR which cross muscle fiber. Act as calcium reservoir. Calcium bound to calequestrin.

Question 6

Transverse (T) tubules

Answer 6

Tubular infoldings of the sarcolemma which penetrate through cell and emerge on other side.

Each has two terminals cisterns associated with it on either side

Question 7

Myoblasts

Answer 7

Muscle stem cells that fused to form each muscle fiber early in development, each contributing one nucleus

Question 8

Satellite cells

Answer 8

Unspecialized myoblasts remaining between the muscle fiber and endomysium.

Help regenerate damaged skeletal muscle tissue

Question 9

What are myofibrils composed of? + 3 types

Answer 9

Muscle filaments (myofilaments)

1. Thick filaments
2. Thin filaments
3. Elastic filaments

Question 10

Thick myofilaments

Answer 10

Made of several hundred myosin (motor protein) molecules

Each molecule shaped like golf club: two chains intertwined to form tail and globular head
Heads direct outward with bare zone in between

Question 11

Thin myofilaments + 3 composing proteins

Answer 11

1. Fibrous (F) actin - two intertwined strands of globular (G) actin subunits, each with an active site that can bind to head of myosin molecule
2. Tropomyosin - each blocks six or seven active sites on G actin subunits
3. Troponin - calcium-binding protein on each tropomyosin molecule

Question 12

Elastic myofilaments

Answer 12

Made of huge springy protein called titin.

Runs thru core of thick filament and anchors it to Z disc at M line.
Helps stabilize and position thick filament
Prevents overstretching and provides recoil

Question 13

What are the two contractile proteins and two regulatory proteins of myofilaments?

Answer 13

Contractile: Myosin and actin

Regulatory: Tropomyosin and troponin (binds calcium, moves tropomyosin off actin active sites)

Question 14

Dystrophin

Answer 14

Protein which links actin in outermost myofilaments to membrane proteins that link to endomysium

Transfers forces of muscle contraction to connective tissue and ultimately tendon
Genetic defects produce muscular dystrophy

Question 15

A band + 2 components

Answer 15

Darkest part where filament thick filaments overlap hexagonal array of thin filaments

1. H-band - less dark, middle of A band. Thick filaments only.
2. M line - dark, transverse protein in middle of H band

Question 16

I band + 1 component

Answer 16

Light band of striations.

Z disc - protein complex that provides anchorage for thin filaments and elastic filaments.

Question 17

Sarcomere

Answer 17

Segment from Z disc to Z disc. Functional contractile unit of muscle fiber.

Question 18

Muscle contraction process

Answer 18

Muscles shorten because individual sarcomeres shorten - Z discs are pulled together as thick/thin filaments slide past each other.

Dystrophin and linking portions also pull extracellular proteins, pulling extracellular tissue

Question 19

Denervation atrophy

Answer 19

Shrinkage of paralyzed muscle when nerve remains disconnected

Nerve stimulation is ESSENTIAL to muscle contraction

Question 20

Somatic motor neurons + somatic motor fibers

Answer 20

Nerve cells whose cell bodies are in the brain stem/spinal cord while their axons (somatic motor fibers) lead to skeletal muscle

Each nerve fiber branches out to multiple muscle fibers, but each muscle fiber is supplied by only one motor neuron

Question 21

Motor unit + 4 characteristics of their muscle fibers

Answer 21

One nerve fiber and all the muscle fibers innervated by it

Muscle fibers are:
1. dispersed throughout the muscle
2. contract in unison
3. Produce weak contraction over wide area
4. Require other motor units to take turns with to sustain long-term contractions

Question 22

Avg motor unit fibers/fascicles + 2 types

Answer 22

Avg motor unit contains 200 muscle fibers in up to 100 fascicles

1. Small motor unit - provides fine degree of control (hand or eye muscles controlled by units with only 3-5 fibers each)
2. Large motor units - provide more strength than control (quadriceps femoris and gastrocnemius controlled by motor units with ~1,000 fibers)

Question 23

3 components of neuromuscular junction

Answer 23

1. Synapse/NMJ - point where nerve fiber meets target cell; each terminal branch of nerve fiber within NMJ has separate synapse with muscle fiber
2. Axon terminal - swollen end of nerve fiber. Contains synaptic vessels with acetylcholine
3. Synaptic cleft - narrow gap between axon terminal and sarcolemma

Question 24

Postsynaptic membrane folds

Answer 24

Increase surface area of the neuromuscular junction, maximizing the number of ACh receptors.

Question 25

Basal lamina

Answer 25

Encloses entire NMJ. Thin layer of collagen and glycoprotein separating muscle fiber and nerve endings from surrounding connective tissue

Passes thru synaptic cleft

Question 26

Acetocholinesterase (AChE)

Answer 26

Enzyme that breaks down ACh, allowing for muscle relaxation

Found in sarcolemma, lamina, and synaptic cleft.

Question 27

Electrophysiology

Answer 27

Study of electrical activity of cells

Electrical activity depends on concentration differences in ions of ICF and ECF

Question 28

Polarized membrane and normal K+ Na+ concentrations

Answer 28

Contains a net negative charge

Normal resting cell:
More K+ inside (ICF), more Na+ outside (ECF)

Question 29

Electrical potential/voltage and resting membrane potential

Answer 29

Electrical potential - Any difference in charge between two points

RMP - the natural state of the plasma membrane with a polarized negative charge

Question 30

2 actions of a stimulated cell + action potential definition

Answer 30

1. Ion channels open, allow Na+ into cell, causing depolarization (increased positive charge in cell)
2. Additional ion channels allow K+ out of cell, causing repolarization

Action potential - voltage shift of cell membrane

Question 31

Cholinesterase inhibitors, tetanus, flaccid paralysis, botulism

Answer 31

Cholinesterase inhibitors - Found in some pesticides. Bind to acetocholinesterase and prevent degradation of ACh causing spastic paralysis (continual contraction)

Tetanus - form of spastic paralysis where glycine of spinal cord ceases to prevent motor neurons from producing unwanted contractions

Flaccid paralysis - state in which muscles are limp and cannot contract. Curare competes for ACh receptor sites

Botulism - food poisoning which causes blockage of ACh release, causing flaccid paralysis