Luke Anatomy Lecture Exam 3

About how many skeletal muscles are there?

About 600

3 Kinds of Muscles

Skeletal, Cardiac, Smooth

Skeletal Muscles Convert...

Chemical energy in ATP to motion

Functions of Muscles

Movement, Stability, Control of Openings and passageways, Heat Production

Origin of Muscle

Proximal and non-moveable

Insertion of Muscle

Distal, Moveable

Agonist

Prime mover, muscle that produces the most force during a movement

Synergist

Muscle that aids prime mover

Antagonist

Opposes prime mover

Fixator

Holds bone in place

Innervation of the muscle refers to

The identity of the nerve that stimulates it

Muscles of Chewing

Temporalis, Masseter, Medial Pterygoid, Lateral Pterygoid

Suprahyoid group does...

Aspects of chewing, swallowing, vocalizing

Infrahyoid group does...

Fixes hyoid bone from below

Allow suprahyoid muscles to open mouth

Muscles of Respiration

Diaphragm - innervated by phrenic nerve

External intercostal

Internal intercostal

Skeletal Muscles are...

Voluntary, striated muscle attached to one or more bones

Endomysium

Connective tissue surrounding a muscle cell

Perimysium

Connective tissue around muscle fascicles

Epimysium

Connective tissue surrounding entire muscle

Fascicle

Group of muscle fibers

Myofiber

Muscle cell

Myofibril

Long protein bundles that occupy main portion of sarcoplasm

Myofilaments

Thick filaments, myosin

Thin filaments, actin

Myosin Heads

Attach to thin filaments (actin) during contraction

Sarcoplasm

Cytoplasm of a muscle fiber

Sarcoplasmic Reticulum

Smooth ER that forms a network around each myofibril

Terminal Cisternae

Dilated end-sacs of Sarcoplasmic Reticulum which cross the muscle fiber from one side to the other

T-Tubules

Tubular infolding of the sarcolemma which penetrate through cell

Triad

A T-tubule, plus one cisternae at either end

Sarcomere

Segment of the myofibril from z line to z line

Sarcomeres do what?

Contract muscle cells

Thick and thin filaments stay the same length, the zone of overlap just increases

Thick filaments are shaped like

A golf club

Myosin heads are directed in what way?

Outward in a helical array around the bundle

Actin Protein

Forms main part of thin filaments

Tropomyosin

Molecules that wrap around the actin

Troponin

Small calcium-binding protein on each tropomyosin molecule

Elastic Myofilaments

Allowing muscle to recoil after being stretched

Titin

Large springy protein

Anchor each thick filament to z line

Prevents over stretching

Striations

Result from zones of overlap among protein filaments

For a muscle to move it must be...

Stimulated by a nerve

Somatic Motor Fibers

Axons that lead to the skeletal muscle

Nerve fibers branch out to...

Multiple muscle fibers

Each Muscle fiber is supplied by...

Only one motor neuron

Neuromuscular Junction

Point of contact between a motor neuron and a skeletal muscle cell

Synapse

Point where nerve fiber meets target cell

Motor Unit

A motor neuron and all of the muscle fibers it innervates

Average Motor Unit Size

200 muscle fibers per motor unit

Small Motor Unit Size

3-6 muscle fibers per motor unit

Fine degree of control

Slow twitch muscle fibers

Large Motor Unit Size

1,000 muscle fibers per motor unit

More strength than control

Fast twitch muscle fibers

Steps of Excitation

Electric signal comes from nerve fiber

Allows calcium to rush down into synaptic knob

Causes release of Ach (Acetylcholine) into synaptic cleft

Opens up sodium channel, which flows into the cell

Depolarizes muscle fiber

Excitation-Contraction Coupling

Electrical signal moves down T-Tubule and allows for release of calcium into sarcomere

Starts contraction

Myosin head pulls on...

Thin filaments and binds to them

When myosin head binds to thin filaments, that is called...

Cross Bridge

To not allow contraction, what is myosin head blocked by?

Tropomyosin

This is when muscle is relaxed

Steps to Contraction

1. Calcium binds to troponin and moves tropomyosin out of the way

2. Myosin heads binds to actin and creates a Cross Bridge

3. Power Stroke - 1 ATP per Power Stroke

4. ATP comes and allows it to release and repower the myosin head

5. Another power stroke (until tropomyosin blocks it)

Steps of Relaxation

1. Cessation of nervous stimulation and ACh release

2. AChE (Acetylcholinesterase) breaks down ACh to stop connection and contraction (AChE is always free floating in synaptic cleft)

3. Calcium ions are lost and tropomyosin slides back into position, blocking myosin head

2 Main Pathways of ATP Synthesis

Anaerobic Fermentation and Aerobic Respiration

Anaerobic Fermentation

Enables cells to produce ATP in the absence of oxygen

Yields little ATP and toxic lactic acid, a major factor in muscle fatigue

Aerobic Respiration

Requires continuous supply of oxygen

Produces far more ATP than Anaerobic Fermentation

Less toxic end products - CO2 and H2O

Phosphagen System

Provides nearly all energy used for short bursts of intense activity

Uses ATP and CP (Creatine Phosphate) collectively

About 6 sec sprint

When phosphagen system is exhausted, muscles shift to

Anaerobic Fermentation

How can muscles obtain glucose

Muscles obtain glucose from blood and their own stored glycogen

In absence of O2, glycolysis can generate a net gain of...

2 ATP for every glucose molecule consumed

Pyruvate turns into...

Lactic Acid

Glycogen-Lactic Acid System

Pathway from glycogen to lactic acid

Produces enough ATP for 30-40 seconds of maximum activity

Aerobic Respiration produces...

36 ATP per glucose

After about ____ seconds, the respiratory and cardiovascular systems catch up and deliver O2 to muscles fast enough for aerobic respiration

40

What sets limits on endurance?

Depletion of glycogen and blood glucose, along with loss of electrolytes through sweating

Muscle Fatigue

Progressive weakness and loss of contractility from prolonged use of the muscles

Lactic Acid does what?

Lowers pH of sarcoplasm

Endurance is determined in large part by...

VO2 Max (Maximum O2 Uptake)

VO2 Max

Point at which the rate of O2 consumption reaches a plateau

Proportional to body size

Peaks around age 20

Males > Females

Oxygen Debt

Heavy breathing that continues after exercise

Replaces O2 reserves that were depleted in 1st minute of exercise

How is the phosphagen system replenished?

Synthesize ATP and use it to donate some to phosphate groups back to creatine until resting levels of ATP and CP (creatine phosphate) are restored

Oxidising Lactic Acid

Conversion back to glucose to replenish glycogen stores in muscle

Classes of Muscle Fibers

Slow Oxidative (SO) - slow twitch

Fast Glycolytic (FG) - fast twitch

Slow Oxidative (SO)

Slow-twitch, red, type I fibers

Aerobic Respiration

Abundant in mitochondria, myoglobin, capillaries

High Endurance

Big blood supply

Fast Glycolytic (FG)

Fast twitch, white, type II fibers

Anaerobic Fermentation

Low in mitochondria, myoglobin, capillaries

Low blood supply

Fatigue quickly

Great for power, bad for endurance

Strength Training Muscle Growth is...

Cellular enlargement

Mostly targets fast twitch fibers

Muscle fibers synthesize more myofilaments and myofibrils and grow thicker

Endurance Training produces more...

Mitochondria, blood capillaries, and glycogen

Required Properties of Cardiac Muscle

Contraction with regular rhythm

Muscle cells of each chamber must contract in unison

Contractions must last long enough to expel blood

Must be highly resistant to fatigue

Cardiac Muscle can contract without...

Any nervous stimulation, involuntary muscle

Contains a built-in pacemaker that rhythmically sets off a wave of electrical excitation

Autonomic nervous system DOES send nerve fibers to the heart to do what?

Increase and decrease heart rate

Cardiac Muscle has...

Very slow twitches

Maintains tension for about 200-250 milliseconds

Cardiac Muscle Uses...

Aerobic respiration almost exclusively

Has especially large mitochondria

Pyruvate helps to start...

The Krebs Cycle

Krebs Cycle is part of...

Aerobic Respiration