Chapter 9 Lecture Notes

Skeletal Muscle

striated, voluntary, slow to fast contraction and tires easily, large range of force

Cardiac Muscle

striated, involuntary, slow to moderate contraction force

Smooth Muscle

non-striated, involuntary, visceral, slow, and sustained movements

Sarcolemma

muscle plasma membrane

Sarcoplasm

muscle cell cytoplasm

Muscle Fibers

elongated components of skeletal and smooth muscle cells

Excitability/Irritability

can excite/stimulate muscle with electricity/chemicals

Contractility

can contract, shorten

Extensibility

lengthen after contraction

Elasticity

can return to normal pre-contracted size

Muscle

discrete organ composed of muscle tissue, blood vessels (bring O2 and nutrients, remove wastes), nerve fibers (nerve ending for every fiber/cell, contraction control), connective tissue (cover and support various parts of muscle)

Origin

muscle attached to the immovable bone

Insertion

muscle attached to the movable bone

Directly

epimysium fused to periosteum of bone

Indirectly

connective tissue wrappings extend beyond the muscle as tendon or apoeurosis

FIber

long,cyndrical cell with multiple nuclei just beneath sarcolemma

Syncytium

multinucleated cells packed tightly

Glycosomes

store glycogen, many in sarcoplasm

Myoglobin

protein, similar to hemoglobin in that it binds to O2

Myofibrils

organelles, densely packed contractile elements, make up ~80% of muscle volume

Sarcomere

area between two Z discs, smallest contractile unit, has thick and thin myofilaments (myosin and actin)

Myosin Tails

two interwoven polypeptide chains

Myosin Heads

two polypeptide chains called cross bridges

Actin

globular subunits that contain active sites where myosin heads attach in muscle contraction

Sarcoplasmic Reticulum (SR)

elaborate smooth ER that surrounds myofibrils

Triad

T tubule and TC pair together

What is the functional characteristic of muscle?

the ability to convert chemical energy to useful mechanical energy (ATP-movement)

How much of the body is made of muscle?

about ½ the body’s mass

What are the three types of muscles?

skeletal, cardiac, smooth

Prefixes that refer to muscle

myo, mys, sarco

What does muscle contraction depend on?

myofilaments actin and myosin

What are the characteristics of muscle?

excitability, contractility, extensibility, elasticity

How do the functions of muscle contribute to homeostasis?

produce movement (body and substances in body), maintain posture, stabilize joints via muscle tone), generate heat during contraction

What are the connective tissue sheaths?

endomysium, perimysium, epimysium

Going from most inner to outer, describe the structures of muscle

fiber → endomysium → fascicle → perimysium → muscle → epimysium

What tissue types make up tendons/ligaments and what wraps around the muscle?

dense regular for tendons and ligaments, loose connective wraps around muscles for support and flexibility

What special structures do muscles have?

myoglobin, SR, T tubules, myofibrils

What is the Z disc?

place where the actin is anchored

Describe the continuation of myosin and actin in a fiber

myosin is continuous throughout, actin has spaces, both are in an alternating arrangement

What are the regulatory units on actin?

tropomyosin and troponin

What is the function of the SR?

regulate cell calcium levels

What feature is unique among the sarcomeres and what is its function?

paired terminal cisternae (TC) are unique, they are pound-like areas of enlarged SR that hold calcium

Where does Ca²⁺ bind?

binds to troponin, which removes the block for myosin to bind to actin

What is the function of T tubules?

to transport nerve impulses to the interior of the muscle fiber, signaling the release oc calcium from the cisternae

Where do nerve impulses travel for transmission into the cell?

go to the sarcolemma fold since the endings are on the outside

Describe the steps for muscle contraction

1. nerve impulse arrives at neuromuscular junction

2. muscle fiber excitation along sarcolemma into T tubules

3. excitation contraction coupling occurs

4. cross bridge cycling occurs where myosin binds to actin and contraction occurs

ACh

acetolcholine, neurotransmitter released from motor neuron and binds to sarcolemma receptors

Describe the process that ACh triggers

it triggers an action potential into the T tubule, which opens voltage gated channels releasing calcium and exposing actin binding sites