HSF Lect. Exam 3

skeletal, cardiac, smooth

3 basic types of muscle

By moving (sliding) microfilaments

how do muscles contract and shorten?

Microfilaments

What makes up muscle microanatomy?

attached to bone or skin (some facial muscles)

Where are skeletal muscles located?

walls of heart

Where are cardiac muscles located?

walls of hollow organs (other than heart)

where are smooth muscles located?

Skeletal muscle

single, very long, cylindrical, multinucleated, obvious striations

cardiac muscle

Branching chains of cells, uninucleate, striations, intercalated disks

Smooth muscle

Single, fusiform (torpedo shape), uninecleate, no striations

skeletal and cardiac

What two muscle cells have striations?

cardiac and smooth

What two muscle cells are uninucleated?

Skeletal

CT components: Epimysium, perimysium, and endomysium

Cardiac

CT components: Endomysium is attached to fibrous skeleton of the heart

Smooth

CT components: Endomysium

Surrounds cells, group of cells, and bone. Keeps everything together

What does the CT in skeletal muscle do?

holds heart in place, floats in space

What does the CT in cardiac muscle do?

can twist and cause motion, CT not as intense

What does the CT in smooth muscle do?

Skeletal muscle

Voluntary movement via nervous system, no rhythmic contraction

slow to fast

skeletal: speed of contraction depends on what muscle

Cardiac

Involuntary, internal heart pacemaker, nervous system controls, hormones

beats at a certain pace bc it makes sure theres enough time to squeeze out all the blood

Why is the speed of contractions in cardiac muscle slow?

Smooth

Involuntary, nervous system controls, hormones, chemicals, stretch

relies on environmental cues, controlled precise movement

Why is the smooth muscle speed of contraction very slow?

Microfilaments

skeletal muscles are striated bc of obvious stripes from ____

surrounded and bundled

Skeletal muscle is ____ and ____ by CT

Endomysium

around single muscle fiber

perimysium

Around fascicle of fibers

epimysium

around entire muscle

fascia

outside of epimysium

Endomysium, Perimysium, Epimysium, Fascia

Components of skeleton muscle CT

muscle

“mys” & “sarco”

transmit force

What does fascia do?

obvious stripes of microfilaments

What causes strations?

fiber, endomysium, perimysium, epimysium, tendom

each indiv. muscle ___ contracts on its own → fascicles transmits squeezing force to ___ → transmits force to ___ → fascicles transmit ____ → transmits force to ____ → produces movement.

blends

Epimyisum __ with tendon

Tendons

Cordlike structures made mostly of collagen

Aponeroses

Sheetlike structures attach muscles indirectly to bones, cartilage, or CT coverings Ex. Epicranius

bc of the way it contracts, wrings itself out → squeeze

Why do we want smooth m. lining hollow organs?

slow and sustained (lasts a while - dont get fatigue)

bc smooth m. can contract the way it does, the contractions are

varicosities - network of ganglia around smooth m. that releases neurotransmitters

Instead of neuromuscular junctions, smooth muscle has ___. What does it do?

squeeze the tube

If smooth muscles lined up in circular fashion, we can?

flextitude - bend up/down

If smooth muscles lined up in longitudinal fashion, we can?

dense bodies, gap junctions, caveolae

Indiv. smooth m. fiber will contract on its own, what prevents that?

Dense bodies

link with proteins filaments, tie each muscle with itself and neighbors, maintain shape, allow cell to wring itself out

Gap junctions and Caveolae

link smooth m. so they can communicate - contract at same time

auto-rhythm - heart usually beats at 100beats/min, brings down to 70

Autonomic nervous system in Cardiac m. allows what?

makes sure everything contracts as one to pump blood!!!

branching Cardiac m. are linked by gap junctions and intercalated disks, why is this super important?

wrapped up in bundles, long strand

How is cardiac m. arranged in heart?

creates extra tension - helps force out extra blood

Why is the bottom of the heart coiled?

maintains posture and body position

What is the MAIN function of the skeletal muscle?

stabilizes joints, generates heat (keeps up warm)

What are the other functions of skeletal m. other than maintaining posture?

Sarcolemma

Specialized plasma membrane (lemma = plasma membrane)

sarcomere

Contractile unit of muscle fiber (between 2 muscles, mere = repeated unit)

Myofibrils

Long organelles inside muscle cell; light and dark bands give striated appearance

Light bands (I band)

contains only thin filaments, made of actin anchored to Z disc (zigzag down sarcomere)

Dark bands (A band)

contains thick filaments, made of myosin

Sarcoplasmic reticulum

Specialized smooth endoplasmic reticulum that surrounds myofibril and stores and releases calcium for contraction

Ca²+

What is the ion we need for muscle contraction?

1 sarcomere (Z-s-Z-s-Z)

What is in between Z discs?

Actin

What are Z discs connected by?

H zone (aka middle of sarcomere)

What is in the middle of the Z disc?

Myocin (no actin)

What is connected to the H zone?

dark A bands, light I bands

Myosin overlapping with actin = ? Just actin = ?

Myosin reaches out and grabs actin - needs to link and let go → pulls along and causes two Z discs to come together

Myosin is in the middle, and actin is on the edges. What needs to happen for movement?

Elastic filaments (like springs)

What allows cell to return to normal shape after contraction?

1. cross bridge formation

2. The power stroke

3. cross bridge detachment

4. cocking of the myosin head

What are the steps of muscle contractions?

Engergized myosin head attaches to an actin myofilament, forming a cross bridge

What is step 1 of muscle contraction?

releases blocker protein on myocin, and allows myocin to grab actin

Why is calcium needed in step one?

myosin flex back and pull the actin toward it (need ATP)

What happens in step 2 of muscle contraction?

myocin lets go of actin

What happens in step 3 of muscle contraction?

myocin returns back to normal position or myocin can grab actin again if we need to

What happens in step 4 of muscle contraction?

ATP, Ca²+

This cycle of muscle contraction will continue as long as ___ is available and __ is bound to troponin. HAVE to have both.

protein that is denatured by release of Ca²+ so myosin can grab actin

What is troponin?

Irritability

responsiveness, ability to reveive and respond to stimuli

contractility

ability to forcibly shorten

Extensibility

ability to be stretched

Elasticity

ability to recoil and resume resting length after stretching

motor neuron

Skeletal muscles must be stimulated by what to contract

Motor unit

One motor neuron and all the skeletal muscles stimulated by that neuron (muscle fiber + motor neuron)

partial contractions

Axon of motor neuron go to a specific part of muscle, this allows what?

Keeps us from wasting energy, but also allows ability to do fine motor tasks

Why are partial contractions important?

Neuromuscular junction

association site of axon terminal of the motor neuron and sarcolemma of a muscle (not touching - between neuron and muscle fiber)

Neurtransmitter

Chemical releases by nerve upon arrival of nerve impulse in the axon terminal, actylchoine stimulates skeletal muscle

synaptic cleft

gap b/w nerve and muscle filled with interstitial fluid; does not physically touch

acetylcholine

What is the main neurotransmitter?

the proper receptor

even if you have a neurotransmitter, what do you also have to have?

7 steps

How many steps of Neuromuscular junctions are there?

Step 1

Nerve impulse reaches the axon terminal and the motor neuron (resting kinda above teh synaptic cleft)

Step 2

Calcium channels open, and calcium ions enter the axon terminal

Step 3

Calcium ion entry causes some synaptic vesicles to release acetylcholine (ACh) - (bubbles filled w/ neurotransmitter to push toward surface and pop)

Step 4

ACh diffuses across the synaptic cleft and attaches to receptors on the sarcolemma of the muscle cell (ACh inside bubble released and diffuses across fluid in cleft to cell membrane, receptors pick it up)

• just waits

• can spread out and bind

If we dont have enough receptors the transmitter…?

if theres enough…?

Step 5

If enough ACh is released, sarcolemma becomes temporarily more permeable to sodium ions → more soidum in, than potassium can leave = imbalance = depolarizing membrane

step 6

Depolarization open more soidum channels that allow sodium ions to enter the cell → action potential made → conducts impulses from one end of cell to other

No, unstoppable

Once begun, can action potential stop?

Step 7

Acetulcholinesterase (AChE) breaks down acetylcholine into acetic acid and choline → ENDS muscle contraction

Acetylcholinesterase (AChE)

What ends muscle contraction?

if we want to have multiple contractions, need multiple impulses

One single nerve impulse produces only one contraction, why is this a problem?