Ch 10-Muscles

functions of skeletal muscle

body movement
maintenance of posture
protection and support-sphincter muscle
regulating elimination of materials
heat production-AP used

characteristics of skeletal muscle

excitability
conductivity
contractility
elasticity
extensibility

excitability

ability to respond to stimuli by changing membrane potential

Condutivity

sending and electrical charge down the length of the plasma membrane

Contractiility

proteins slide against one another-

muscle cells cause body movement

Extensibility

ability to be stretched and lengthened

proteins slide and reduce overlap

Elasticity

ability of cell to return to original length after shortened or lengthened

what is elasticity dependent upon?

extensibility and contractiility

why is skeletal muscle considered an organ?

many tissue types

CT, bv, nerves, muscle fibers

fasicle

bundle of muscle fibers

how many fascicles in muscle?

many

muscle fibers

muscle cells

Layers of skeletal muscle

epimysium
perimysium
endomysium

epimysium

surrounds entire muscle

DENSE IRREG

perimysium

surrounds fascicles
bv and nerves

DENSE IRREG

Endomysium

surrounds each muscle fiber
insulation, support, binds neighboring cells

AREOLAR

tendon

Connects muscle to bone

common properties of tendons and aponeurosis

attachments of muscle to muscle, skin, bone

made from fibers of epi, peri, endo collective fibers

what type of tissue is in tendons?

dense regular

Aponeurosis

strong sheet of tissue that acts as a tendon to attach muscles to bone

btw frontal and occipital head

what type of tissue is in aponeurosis?

dense irregular

deep fascia

superficial to epimyisum

separates individual muscles, binds muscles with similar functions

bv, nerves, lymph

what type of tissue is deep fasica made of?

dense irregular

superficial fascia

separates muscle from skin

superficial to deep fascia

BARRIER

what type of tissue is superficial fascia made of?

areolar/adipose

blood vessel/nerve properties of skeletal muscle

vasculairzed-removes wastes, delivers oxygen

innervated by somatic neurons-voluntarily control of muscle

sacroplasm

cytoplasm of a muscle cell

what does the sarcoplasm contain?

organelles and cytosol

how are muscle cells multinucleated?

myoblasts fuse together

some become satellite cells-support/repair

sacrolemma

plasma membrane of a muscle cell

T-tubules (transverse tubules)

deep invaginations of the plasma membrane

channels in T-tuble and sacrolemma

VGC allow for electrical signals

voltage sensitive calcium channels

responsive to the electrical signals (action potentials)

IN SARCOLEMMA

myofibrils

bundles of myofilaments enclosed in sarcoplasmic reticulum

How many myofibrils are in each muscle fiber?

100s-1000s

sacroplasmic reticulum

internal membrane complex similar to smooth ER


contains Ca pumps/calcium release channels

terminal cisternae

blind sacs of sarcoplasmic reticulum
serve as reservoirs for Ca ions

triad

two terminal cisternae and a T tubule

calcium release channels

Triggered by electrical signal traveling down T-tubule

calcium released into sarcoplasm

myofilaments

contractile proteins

thick/thin

thick filaments

myosin

heads point towards end of filament

thin filaments

actin, troponin, tropomyosin

troponin

globular protein, Ca binding site, pulls tropomyosin off

tropomyosin

covers myosin binding sites on the actin molecules

f actin

G actins polymerized into a double helix

g actin

myosin binding site

monomer of f actin

sacromeres

myofilaments are organized into repeating functional units

thick/thin filaments

z lines

The ends of the sacromeres that cause contractions of a muscle

ANCHOR FOR THIN FILAMENTS

I bands

light bands

thin filaments
b

what are the I bands bisected by?

Z discs

A band

dark area

thick filaments, some thin
contains H zone and M line

CENTER OF SACROMERE

H zone

Central region of A-band
thick filaments

M line

middle of H band

attachment site for thick filaments

What anchors the thin filaments?

Z disc

What anchors thick filaments together?

M line

connectin

Extends from Z disc to M line

Stabilizes thick filaments

"springlike" properties (passive tension)

dystrophin

Anchors some myofibrils to sarcolemma proteins
Abnormalities of this protein cause muscular dystrophy

Duchenne Muscular Dystrophy (DMD)

defective/insufficient dystrophin

sarcolemma damaged during contraction
-ca enters cell, damage

what age do most patients with DMD survive to?

30

myoglobin

stores oxygen in muscle cells for ATP production

where is glucose stored

liver and skeletal muscle

creatine phosphate

phosphate from creatine phosphate can be removed and attached to an ADP to generate ATP quickly.

10-15 sec of energy

catalyst in creatine phosphate

creatine kinase

motor unit

A motor neuron and all of the muscle fibers it innervates

small motor units

less than five muscle fibers
-allow for precise control of force output

large motor units

thousands of muscle fibers
-allow for production of large amount of force but not precise control

location of fibers of motor unit

dispersed throughout muscle

synaptic knob

rounded areas on the end of the axon terminals

synaptic vesicles

saclike structures found inside the synaptic knob containing AcH

channels in synaptic knob

ca pumps, VGC Ca

motor end plate

specialized part of a muscle fiber membrane at a neuromuscular junction

many AcH receptors

synaptic cleft

separates knob from motor end plate

Acetylorichase resides here

actetylcholinesterase

an enzyme that breaks down acetylcholine

neuromuscular junction

Location where motor neuron innervates muscle

Has synaptic knob, synaptic cleft, motor end plate

resting membrane potential skeletal muscle

-90mV

Calcium entry at synaptic knob

•Nerve signal travels down axon, opens voltage-gated Ca2+ channels
•Ca2+ diffuses into synaptic knob
•Ca2+ binds to proteins on surface of synaptic vesicles

Release of ACh from synaptic knob

-vesicles merge with cell membrane at synaptic knob: exocytosis
-thousands of ACh molecules released from about 300 vesicles

excitation-contraction coupling

sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber's sarcomeres

end plate potential (EPP)

1. ach receptors open when Ach binds to them
2. Na diffuses into cell, little K out
3. EPP is local but is graded potential
4. opens VGC

How does EPP reach threshold?

by causing nearby voltage-gated Na+ channels to open

depolarization of skeletal muscle

30 mV

the release of Ca from the sarcoplasmic reticulum

Ca interacts with myofilaments triggering contraction

crossbridge cycle

crossbridge formation: binding of myosin to myosin binding site and actin to actin binding site

power stroke: myosin pulls on actin, ADP and Pi released

release of myosin head: ATP binds to myosin head causing its release from actin

reset myosin head: ATP split ADP and Pi, cocks myosin head

what is needed for crossbridge cycling?

Ca and ATP

steps of cross bridge cycle

1. cross bridge formation
2. power stroke
3. cross bridge detachment
4. cocking of myosin head

cross bridge formation

myosin heads attach to the active site on actin

power stroke

action of myosin pulling actin inward (toward the M line)

ADP and P1 released

what happens when ADP is released in crossbridge?

moves actin to m line

POWERSTROKE

what happens when phosphate is released in crossbridge?

bonds get stronger

cross bridge detachment

ATP attaches to myosin head, causing cross bridge to detach

cocking of myosin head

As ATP is hydrolyzed to ADP and Pi, the myosin head returns to its prestroke high-energy, or "cocked" position

hydrolize

break down (a compound) by chemical reaction with water.

muscle relaxation

AP ends, electrical stimulation of SR stops

Ca2+ pumped back into SR
Stored until next AP arrives
Requires ATP

Without Ca2+, troponin and tropomyosin return to resting conformation
Covers myosin-binding site
Prevents actin-myosin cross-bridging

storage of ATP in muscle cells

little

spent after 5 seconds of exertion

myokinase

transfers Pi from one ADP to another, converting the latter to ATP

makes additional ATP rapidly

Ways to generate ATP in skeletal muscle fiber

-Immediate supply via phosphate transfer
-Short-term supply via glycolysis
-Long-term supply via aerobic cellular respiration

Glycolysis

NO OXYGEN NEEDED

breaks glucose into pyruvate
in cytosol

aerobic cellular respiration

REQUIRES OXYGEN

pyruvate oxidaized to CO2-NADH FADH

How much ATP does glycolysis produce?

net gain of 2 ATP

How much ATP does cellular respiration generate?

30