Lecture 15 (Exam 3)

Biology 409 with Wibbles at University of Alabama - Birmingham

About this deck

By: John Bouldin
Created: 2010-11-11
Size: 54 flashcards
Views: 7

About StudyBlue

STUDYBLUE makes things that make you better at school. Things like online flashcards with photos and audio. Things like personalized quizzes and friendly reminders about when (and what) to study next. Think of it as a digital backpack™: access to all of your study materials online and on your phone. STUDYBLUE exists to make studying efficient and effective for every student, for free. Join us.

“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy

Sign up (free) to study this.

Thick filament

several hundred myosin molecules

What are the two subunits of myosin shaped like?

golf clubs
the head acts as a bridge between myosin and actin

What are the two active sites on the head of a myosin molecule?

1. actin binding site
2. myosin ATPase site for binding and cleaving ATP

Thin filament

composed of actin, tropomyosin, and troponin

Actin helix

composed of actin molecules (which are globular
proteins) each molecule has a binding site for a myosin head

Tropomyosin

thread-like proteins that lie end to end
they wrap around the actin helix

Tropomyosin purpose

acts as a regulatory protein for muscle contraction by covering the binding sites on actin

Troponin

regulatory protein for muscle contractions

What is troponin composed of?

troponin T, troponin I, and troponin C

Troponin T

binds to tropomyosin

Troponin I

binds to actin

Troponin C

binds to Ca++

Troponin purpose

forms a complex with tropomyosin which can cover the actin binding sites
i.e. the troponin-tropomyosin complex

Status of relaxed muscle

intracellular Ca++ is low
so the troponin/tropomyosin complex covers binding sites on actin helix
prevents any "crossbridging" between actin and myosin

First step of muscle contraction

increase in intracellular Ca++

Second step of muscle contraction

troponin-tropomyosin complex undergoes aconformational change that uncovers binding sites on actin helix

Third step of muscle contraction

heads of myosin molecules then attach to binding sites on actin

Fourth step of muscle contraction

Attachment of myosin head triggers conformational change in myosinthat causes head to "tilt" (power stroke)
Tilting moves actin filament along myosin filament
thus shortening the sarcomere.
Tilting also releases ADP from myosin head

Fifth step of muscle contraction

ATP molecule now binds to myosin head.
ATP binding causes head to detach from binding site on actin helix
ATP is then cleaved to ADP, causing the head to return to the non-tilted conformation.

How many times does the process of muscle contraction occur?

repeatedly as long as Ca++ is present

"Walk along" theory of muscle contraction

the idea of myosin heads pulling themselves along actin fibers to contract muscles

Rigor Mortis

stiffness of muscles occurring approximately 3 to 12 hours afterdeath

Rigor Mortis cause

Ca++ leaks into ICF and stimulates contraction
Existing ATP is utilized but without new ATP being generated, there is no way for the myosin to detach from the actin to relax the muscle

Neuromuscular junction

location where motor neuron innervates each skeletal muscle fibers

Neuromuscular junction components

1. axon terminal of motor neuron
2. "Motor end plate" of muscle

Neuromuscular junction mechanism

action potential in neuron
Ca++ influx into axon terminal
release of acetylcholine to nicotinic receptors on motor end plate, opening ligand gated ion channels allowing large amounts of Na+ and small amounts of K+ in
generating an "end plate potential"

End-Plate Potential

graded potential
larger than EPSP of neuron (+50 to +75 mV)

this initiate action potentials in adjacent areas of cell membrane
ensures that a single action potential will cause a twitch in the muscle fiber

What are end-plates stimulated by?

acetylcholine

Drug that blocks release of acetylcholine in neuromuscular junction

Botulinum toxin (less than 1 billionth of a gram can be lethal)
paralyzes diaphragm
19,000 liters is enough to kill 3x the population of Earth

Non-fatal usages of botulinum toxin

muscle relaxer
botox injections
specific voice disorders
reduces migraines
prevents excessive sweating

Drug that increases release of acetylcholine in neuromuscular junction

Black widow spider venom
muscle spasms followed by fatigue

Drugs that block nicotinic receptors

Curare- plant extract used in poison arrows
Alpha-bungarotoxin- venom in some poisonous snakes

Transverse Tubules (T-tubules)

conduct the action potential deep into fiber

T-tubule purpose

extension of cell membrane, but they run perpendicular from
surface deep into the center of muscle fiber.They carry action potential which stimulates sarcoplasmic reticulum

Sarcoplasmic reticulum

specialized ER for intracellular storage of Ca++

What is the ratio of Ca++ in the SR to the cytosol at rest?

10,000 : 1

How do T-tubules and SR interact?

causes release of Ca++ from lateral sacs of SR

Purpose of SR

releases Ca++ to initiate muscle contraction

Ca++ is pumped back into SR when at rest

Smooth muscle

found in the walls of many viscera
forms ciliary and iris muscles of eye, piloerector muscles in skin, etc

Structure of Smooth Muscle

composed of small muscle fibers

each cell has a single nucleus
contains actin and myosin but not organized into myofibrils

Diameter and length of smooth muscle fibers

2 to 5 um in diameter20 to 500 um in length

Why are there no striations in smooth muscle?

there are no myofibrils

Where is actin attached to in smooth muscle?

dense bodies

Why are smooth muscles specialized for slow prolonged contractions?

no t-tubules and poorly developed SR

Smooth Muscle Contraction

Ca++ from the ECF binds to intracellular Ca++ receptor (the receptor is “calmodulin”)
Ca++/calmodulin complex activates the enzyme “myosin kinase”
that then activates myosin.Once activated, the myosin then binds to actin and undergoes a power stroke

General Characteristics of Smooth Muscle Contraction

slower more prolonged strokes
uses less energy
forms an electrical “syncytium”

some is autorhythmic

Pharmacology relating to smooth musclem

Calcium channel blockers such as “verapamil” block the influx of Ca++ intosmooth muscle cells. Used for vasodilation, lowering blood pressure, and reducing angina

Cardiac Muscle

found only in heart
hybrid between skeletal and smooth muscle

Cardiac muscle/skeletal muscle similarities

It contains myofibrils (so it is striated).
Ca++ activates contraction by binding to troponin C.It has well-developed sarcoplasmic reticulum and t-tubules
quick powerful contractions

Cardiac muscle/smooth muscle similarities

autorhythmic
cells are connected via gap junctions, forming electrical syncytium

Unique to cardiac muscles

relatively short and branched muscle fibers (cells) which normally containone or two nuclei
Individual cells are connected to one another by “intercalated discs

Intercalated discs

specialized cell membranes containing gap junctions and desmosomes

Cardiac action potential

long duration (250 msec)
display a "plateau" which allows for a prolonged muscle contraction (300 msec)

Reason for plateau in cardiac muscle

Ca++ channels are slow to open and close
steady influx of Ca++ at peak of potential causes the plateau

About this deck

By: John Bouldin
Created: 2010-11-11
Size: 54 flashcards
Views: 7

About StudyBlue

“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy