Chapter 9: Skeletal muscle tissue and muscle organization

muscles that form the walls of the abdominal and pelvic cavities

This group, the oblique and rectus muscles, is located between the first thoracic vertebra and the pelvis. These muscles move the chest wall during breathing (inspiration and expiration), compress the abdominal cavity, and rotate the vertebral column. In the thoracic area, the ribs separate these muscles, but over the abdominal surface, the muscles form broad muscular sheets. There are also oblique and rectus muscles in the neck. Although they do not form a muscular wall, they are included in this group because they share a common embryological origin. The diaphragm is within this group because it is embryologically linked to other muscles of the chest wall.

Pennate muscles

-fibers are arranged like a feather. The muscle fibers sit at an angle and attach to a tendon that runs the length of the muscle -contains more muscle fibers than a parallel muscle of the same size

fixator muscle

Muscle that functions as a joint stabilizer -When agonists and antagonists contract simultaneously, they are acting as fixators, stabilizing a joint and creating an immovable base

You are watching a movie with your roommate. In one scene, a person is shot with a dart dipped in a chemical that blocks the action of acetylcholine. Your roommate does not understand why the person then falls down. How do you explain this to your roommate?

Muscle tone is involved in maintaining body position while standing. The administration of a chemical that blocks the action of acetylcholine would prevent action potentials crossing from nerves to skeletal muscles. ACh is needed to generate an action potential and thus is needed for a muscle contraction. If ACh is not available, the muscles could not contract, and there would be no muscle tone. Without muscle tone, the person falls.

epimysium

Outer layer of skeletal muscle. a layer of dense irregular connective tissue surrounds the entire skeletal muscle. The epimysium separates the muscle from surrounding tissues and organs and is connected to the deep fascia

2 regulatory proteins of thin filaments

tropomyosin and troponin

what two proteins help regulate the interaction between actin and myosin

tropomyosin and troponin

Rigor Mortis

extended muscular contraction and rigidity that occurs after death, as the result of calcium ion release from the sarcoplasmic reticulum (SR). the lack of ATP does not allow the criss bridges too detach from the myosin active sites, and the muscles lock in the contracted position

muscles of facial expression are divides into 5 groups

mouth, eyes, scalp, nose, and neck and are all innervated by the facial nerve 7 (VII)

unipennate muscle

muscle fibers are arranged on the same side of the tendon

How do muscles sustain long periods of contractions?

powerful contractions cannot last long because the individual muscle fibers song use up their energy reserves. To delay the onset of fatigue during periods of sustain contractions, motor units are activated on a rotating basis. therefore, some motor units are resting and recovering while others are actively contracting

The endomysium consists of a delicate network of _________ fibers

reticular fibers

The plasma membrane in skeletal muscle cell is called the

sarcolemma

Myofibrils are organized in repeating units called _____________

sarcomeres

Cytoplasm in a skeletal muscle cell is called the

sarcoplasm

surrounding each myofibril is the ___________ __________

sarcoplasmic reticulum (SR)

What is shivering, and why do you do it when you are cold?

shivering is an involuntary contraction of skeletal muscles that occurs when you are cold. These muscle contractions utilize ATP, which produces heat, which in turn helps to maintain body temperature.

Slow fibers (red fibers)

slow fibers are specialized to continue contracting for expended periods of time, long after a fast muscle fatigues. They fatigue slowly because their mitochondria continue producing ATP throughout the contraction process. They have: 1) a smaller diameter than fast fibers 2) take 3x as long to contract after stimulation 3) contains a larger number of mitochondria than fast muscles

At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium come together to form a _______

tendon

on each side of a T-tubule, the tubules of the SR enlarge, fuse, and form expanded chambers called _________ _________

terminal cisternae

aponeurosis

broad tendon-like sheets that may serve as the origins or insertions of skeletal muscle

Transverse tubules (T-tubules)

-deep indentations in the sarcolemma that form a network of narrow tubules that extend deep into the sarcoplasm. -the sarcolemma and these T-tubules conduct electrical impulses, called action potentials, to stimulate muscle fiber contraction

sliding filament theory

-explains the physical changes occurring between thick and thin filaments during contraction -the concept that a sarcomere shortens as the thick and thin filaments slide past one another

Circular muscles

-guard entrances and exits of long internal passageways, such as the digestive and urinary tracts -the fibers are concentrically arranged around an opening -when the muscle contracts, the diameter of the opening decreases.

Hypertrophy

-the enlargement of stimulated muscle -increase in the size of tissue without cell division As a result of repeated, exhaustive stimulation, muscle fibers develop a greater number of myofibrils and mitochondria, a higher concentration of glycolytic enzymes, and larger glycogen reserves

Convergent muscles

-the fibers in convergent muscles are spread out, like a fan or a broad triangle, with a tendon at the tip -example of this is the prominent pectoralis

Parallel muscles

-the individual fibers may run the entire length of the muscle (biceps), or they may be interrupted by transverse pieces of connective tissue (rectus abdomens) -other parallel muscles have a twisted or spiral arrangement (supinator of the forearm) -most of the skeletal muscles in the body are parallel muscles

3 microscopic physical changes in sarcomere when a muscle contracts

1) the H band and I band get smaller 2) the zone of overlap gets larger 3) the Z lines move closer together

steps that end a muscle contraction

1. Action potential generation stops as ACh diffuses out of the synapse or is broken down by AChE. 2. Sarcoplasmic reticulum recaptures Ca2+ and concentrations of calcium ions in the sarcoplasm decreases 3. active sites covered, no cross-bridge interaction 4. contraction ends 5. muscle relaxation occurs, and the muscle fiber returns passively to resting length

3 types of pennate muscles

1. Bipennate muscle 2. multipennate muscle 3. multipennate muscle

Muscles are grouped into four categories according to their primary actions:

1. agonist 2. antagonist 3. synergist 4. fixators

sequence of events in the process of skeletal muscle contraction:

1. chemicals released by the motor neuron at the neuromuscular junction alter the membrane potential of the sarcolemma. This change sweeps across the surface of the sarcolemma and into the T-tubules 2. the change in the membrane potential of the T-tubules triggers the SR to release calcium (Ca+) ions. This release initiates the contraction

Steps that initiate a muscle contraction

Steps that initiate a muscle contraction: 1. ACh released from axon terminal, then binds to sarcolemma receptors 2. Action potential reaches T-tubule 3. sarcoplasmic reticulum releases Ca2+ 4. Calcium ions bind to troponin, producing a change in the orientation of the troponin-tropomyosin complex that exposes active sites on the thin (actin) filaments. Myosin cross-bridges form when myosin heads bind to active sites 5. Repeated cycles of cross-bridge binding, pivoting, and detachment occur, powered by the hydrolysis of ATP. These events produce filament sliding, and the muscle fiber shortens.

each skeletal muscle has 3 concentric layers, or wrappings, or connective tissue:

1) an outer epimysium 2) a central perimysium 3) an inner endomysium

tendons that form thick, flattened sheets are called ______________

aponeuroses

first-class lever

the fulcrum is positioned between the load and applied force

sarco- means

flesh

3 types of muscle tissue

skeletal, cardiac, and smooth muscle

second-class lever

the load is between the fulcrum and the effort

muscles of the vertebral column

this group includes flexors and extensors of the axial skeleton

What happens to the widths of the A band and I bands during a muscle contraction?

during contraction, the width of the A band remains the same, and the I band gets smaller

When the origins and insertions cannot be determined easily on the basis of movement or position, we use other criteria:

- If a muscle extends between a broad aponeurosis and a narrow tendon, the aponeurosis is the origin, and the tendon is attached to the insertion. -If there are several tendons at one end and just one at the other, there are multiple origins and a single insertion.

Muscle atrophy

-a degenerative process that occurs when skeletal muscle cells are not stimulated for a prolonged period of time -the wasting away of tissues from a lack of use, ischemia, or nutricional abnormalities

multipennate muscle

-a muscle whose internal fibers are organized around several different tendons -the tendon branches within the muscle

synergist muscle

-muscle that assists an agonist in performing that action. -syngergists provide additional pull near the insertion or stabilize the origin. -synergists are often most useful at the start, when the agonist is stretched and relatively weak.

5 functions of skeletal muscle

-produce skeletal movement -maintain posture and body position -support soft tissues -regulate the entry and exit of material -maintain body temperature

How to skeletal muscle cells differ from typical cells?

-skeletal muscle fibers are large compared with the cells of other tissues -skeletal muscle fibers are multinucleate

sarcomeres

-smallest functional units of muscle fibers -thick and thin filaments give the sarcomere a banded appearance

sarcoplasmic reticulum (SR)

-surrounds each myofibril -a membrane complex similar to the smooth endoplasmic reticulum of other cells

bipennate muscle

-the muscle fibers are on both sides of the tendon

How do slow fibers get their required oxygen from for aerobic metabolism?

1. Skeletal muscles containing slow muscle fibers have a larger network of capillaries than muscles dominated by fast muscle fibers. This means that there is greater blood flow to the muscle, and the red blood cells can deliver more oxygen to the active muscle fibers. 2. Slow fibers are red because they contain the red pigment myoglobin (MĪ-ō-glō-bin). This globular protein, like hemoglobin (the oxygen-binding pigment found in red blood cells), binds oxygen molecules. As a result, slow muscle fibers contain large oxygen reserves that are mobilized during a contraction.

4 groups of axial muscles

1. muscles of the head and neck that are NOT associated with the vertebral column 2. muscles that move the vertebral column (intrinsic muscles of the back) 3. muscles of the rib cage and the lateral walls of the abdominal and pelvic cavities 4. muscles that form the floor of the pelvic cavity

skeletal muscles of the human body are arranged into one of four patterns

1. parallel muscles 2. convergent muscles 3. pennate muscles 4. circular muscles

3 types of skeletal muscle fibers in the human body

1. slow (red) 2. fast (white) 3. intermediate fibers the fiber types differ in how they obtain ATP to fuel their contractions

2 factors determine the amount of tension produced in a muscle contraction

1. the frequency of stimulation and 2. the number of motor units involved

motor unit

A single motor neuron and all of the muscle fibers it innervates

neuromuscular junction (NMJ)

A synapse between a neuron and a muscle cell

A single thin filament contains 4 proteins:

F-actin, nebulin, tropomyosin, and troponin

third-class lever

The applied force is between the load and the fulcrum

cross-bridges

The binding of myosin heads that project from the surface of thick filaments at the active sites of thin filaments in the presence of calcium ions

all or none principle

The principle that when a neuron fires, it fires with the same potency each time; a neuron either fires or not—it cannot partially fire, although the frequency of firing can vary.

Distribution of fast, slow, and intermediate fibers

The percentage of fast, slow, and intermediate fibers varies from one skeletal muscle to another. Muscles contain a mixture of fiber types, but the fibers within one motor unit are of the same type. The percentage of fast versus slow fibers in each muscle is genetically determined and can change depending on the type and amount of physical exercise.

Why do some motor units control only a few muscle fibers, whereas others control many fibers?

The size of a motor unit is an indication of how fine the control of movement. In the eye muscles, where precise control is important, a motor neuron may control just a few fibers. In large leg muscles, where there is less precise control, a single motor neuron may control a thousand muscle fibers.

How do motor units of the eye differ from a motor unit of the leg?

The smaller the size of a motor unit, the finer the control of movement will be. In the eye, where precise muscular control is critical, a motor neuron may control only two or three muscle fibers. We have less precise control over power-generating muscles, such as our leg muscles, where a single motor neuron may control up to 2000 muscle fibers.

muscles of the perineal region and pelvic diaphragm

These muscles extend between the sacrum and pelvic girdle to support organs of the pelvic cavity, flex joints of the sacrum and coccyx, and control movement of materials through the urethra and anus

Muscles of the head and neck include

These muscles include those that move the face, tongue, larynx, and eyes. They are responsible for verbal and nonverbal communication, such as laughing, talking, frowning, smiling, and whistling. This group is also involved in chewing, swallowing, and moving the eyes.

Structure of sarcomere

Z-line Defines boundary of a single sarcomere M-line Runs down center of sarcomere I-band Contains thin filaments only H-zone Contains thick filaments only A-band Contains thick filaments in their entirety without any overlapping portions of thin filaments

tendon

a collagenous band that connects a skeletal muscle to either bone, cartilage, skin, or another muscle

Thin filament

a cytoskeletal filaments in a skeletal or cardiac muscle, consists of actin, troponin, nebulin, and tropomyosin

Fibromyalgia

a disorder characterized by widespread, chronic musculoskeletal pain usually accompanied by fatigue and disturbances in sleep, memory, and mood

Antagonist muscles

a muscle whose action opposes that of the agonist. For example, if the agonist produces flexion, the antagonist produces extension. when an agonist contracts to produce a particular movement, the antagonist stretches, but usually doesn't relax completely.

agonist or prime mover muscles

a muscle whose contraction is mostly responsible for producing a particular movement, such as flexion at the elbow

insertion

a point of attachment of a muscle; the end that is easily moveable

nebulin

a slender strand of protein that extends along the F-actin strand in the cleft between the rows of G-actin molecules -holds the F-actin strand together

Filamentous actin (F-actin)

a twisted strand composed of two rows of 300-400 globular molecules of G-actin

contractile protein component of thin filaments

actin

How do slow fibers primarily obtain ATP?

aerobic metabolism -requires a lot of oxygen

anatomical pulleys

boney structures that change the direction of applied forces

perimysium

central layer of skeletal muscle The connective tissue fibers of the perimysium divide the muscle into internal compartments. Each compartment contains a bundle of muscle fibers called a fascicle. The perimysium contains collagen and elastic fibers, and numerous blood vessels and nerves supply each fascicle.fu

Thick filaments

composed of a bundle of myosin molecules, each made up of a pair of myosin subunits twisted around one another

Fast fibers (white fibers)

contract quickly following stimulation they have: 1) a large diameter 2) densely packed myofibrils 3) large glycogen reserves 4) relatively few mitochondria most of the skeletal muscle fibers in the body are called fast fibers because they contract quickly following stimulation

4 properties of muscle tissue

excitability, contractility, extensibility, elasticity

How do fast fibers primarily obtain ATP?

glycolysis

Intermediate fibers

have properties between those of fast and slow fibers. For example, intermediate fibers contract faster than slow fibers but slower than fast fibers.

origin

in a skeletal muscle, the point of attachment that does not change position when the muscle contracts

How do muscle make ATP

mitochondrial activity and the chemical breakdown of glycogen provide the ATP needed to power muscular contractions

In the body, each bone is a ________ and each joint a ________

lever and fulcrum

What are the cells that lie between the endomysium and the muscle fibers?

mayosatillite stem cells that repair damaged muscle tissue

delayed-onset muscle soreness (DOMS)

muscle pain that follows participation in a particularly long or strenuous activity, begins 24-73 hours later, and involves multiple, microscopic tears in the muscle tissue that cause inflammation, pain, swelling, and stiffness

embryonic cells that fuse to form individual skeletal muscle fibers during development

myoblasts

Myofibrils are made of protein filaments called ____________

myofilaments

contractile protein component of thick filaments

myosin

chemical communication between a neuron and a skeletal muscle fiber occurs at a site called the ______________ _________

neuromuscular junction (NMJ)

myofibrils

organized collections of myofilaments in skeletal and cardiac muscles

function of the sarcoplasmic reticulum

storage and release site of calcium ions (Ca+) and plays an essential role in controlling individual myofibril contraction

triad

the combination of a pair of terminal cisternae plus a T-tubule

G-actin

the globular subunit of the actin molecule -each molecule of G-actin contains an active site where myosin in the thick filaments can bind

endomysium

the inner most layer of skeletal muscle The endomysium surrounds each skeletal muscle fiber, binds each muscle fiber to its neighbor, and supports the capillaries that supply the individual fiber.

muscle tone

the resting tension in a skeletal muscle -Motor units are randomly stimulated, so there is a constant tension in the attached tendon as some motor units contract and others relax

Which band does NOT change throughout a contraction?

the width of the A band remains the same

2 types of myofilaments

thin filaments and thick filaments

Arrange the three types of levers found in the human body in order of decreasing frequency.

third-class lever (most common), followed by second-class lever, and then first-class lever (least common).