PCB4723C Exam 4

three muscle types

skeletal, cardiac, and smooth

striated muscle

skeletal and cardiac

voluntary muscle

skeletal

involuntary muscle

smooth and cardiac

unstriated muscle

smooth muscle

contraction of muscles

locomotory movement, manipulation, propulsion, emptying, heat, sound

skeletal muscle cells are

MUSCLE FIBERS!!! (LARGE!) formed by myoblasts, parallel bundles

myofibrils

NOT MUSCLE CELLS, but contractile elements!!

muscle fibers with a low percentage of myofibrils cannot generate _________

much tension, but can contract at high frequency for long times

myofibrils have both _____ and ____ filaments

thick and thin!

thick filaments

made of myosin, tails are intertwined with globular heads (each head has actin binding site and ATPase)

Thin filaments

Made of actin, tropomyosin forms strands that cover actin binding sites when relaxed. Troponin stabilizes tropomyosin in its blocking position

troponin three subunits

binds to tropomyosin, actin, and Ca2+

Striations in skeletal muscle!!!

A band, H zone, M line, I band, Z line, (+Sarcomere)

A band

consists of a stacked set of thick filaments and portions of thin filaments that overlap them

H zone

(lighter area in middle of A band) has only thick filaments with no overlapping thin filaments

I band

(in center of A band) holds thick filaments together

Z line

(in center of I band) is a flat cytoskeletal disc where thin filaments connect

sarcomere

is the area between two Z lines • Functional unit of skeletal muscle • 2.5 µm in width

during contraction thin filaments do what, which results in what?

thin filaments slide toward the center of the A band, resulting in shortening of the sarcomere

A BAND ALWAYS ____________ SIZE

stays the same

What happens when Ca2+ bonds to troponin?

It changes shape, resulting in binding sites on actin being uncovered.

What do myosin heads do during cross-bridge cycling?

They bind to actin.

What is the power stroke in cross-bridge cycling?

The cross-bridge bends 45 degrees inward, pulling the thin filament with it.

What happens to myosin after the power stroke?

Myosin detaches and attaches to a new site on actin.

How is shortening accomplished in muscle contraction?

By repeated cross-bridge cycles.

Ca2+ links

excitation and contraction

skeletal muscles are stimulated to contract by

ACh (acetylcholine) at neuromuscular junctions being released

after ACh is released at neuromuscular junctions what does it result in

action potential, conducted along the muscle membrane

after ACh is released at neuromuscular junctions and action potential is conducted, what happens

Surface membrane dips deeply into the muscle fiber to form a transverse tubule (T tubule) • Action potential enters the interior of the muscle fiber along the T tubules • Induces permeability changes in the adjacent sarcoplasmic reticulum

Ca2+ is stored where

in the lateral sacs of sacroplasmic reticulum in skeletal muscles

Elevated cytosolic Ca2+ results in

increased binding of Ca2+ to troponin (contraction)

during relaxation where and how is Ca2+ transported

back into sarcoplasmic reticulum by Ca2+-ATPase pumps (reduces levels)

tendons (in vertebrates)

attach muscle to bones

muscles attach to _________ (in arthropods)

ridges that project from the inner face of exoskeleton (apodemes)

Muscles are arranged in ______ pairs

antagostic pairs (flexors and extensors)

flexors

bend limb

extensors

straighten limb

if a muscle fiber is stimulated so rapidly that it has no chance of relaxing between stimuli, what happens and what is this called?

smooth sustained contraction occurs (Tetanus)

what does tetanus look like on a graph?

a bunch of staggered upwards movements until fatigue begins which straightens it out, action potentials looks like up down up down up down

every muscle has optimal _____ at which _____ force can be achieved upon tetanic contraction

optimal length at which maximal force can be achieved

for a muscle to shorten during contraction tension must what

tension > load (forces that oppose movement)

isotonic contraction (flex?)

muscle shortens, tension remains constant, work is done (work=forcexdistance)

isometric contraction (nothing?)

-muscle is prevented from shortening

-tension develops at constant muscle length

-no work is done

Eccentric contraction (extend?)

muscle lengthens during contraction because it is being stretched by external force

if a person is not able to move their leg which of the 3 types of contraction might they be experiencing?

likely isometric contraction as no work is done and the muscle is prevented from shortening

the greater the load _______ velocity

lower

velocity is _______ when load exceeds tension (isometric contraction)

ZERO

hydrostatic skeleton

• A pressurized moving fluid can create largescale movement • Contraction of circular muscles surrounding a closed chamber of body fluid stiffens the body region around it • Longitudinal muscles shorten the chamber upon contraction and lengthen it when relaxed

What is a lever? (skeletal muscle)

A lever is a rigid structure capable of moving around a pivot point (fulcrum)

Bones are levers and joints are fulcrums

what is the power arm?

the part of a lever between the fulcrum and the point where an upward force is applied

what is the load arm?

the part between the fulcrum and the downward force exerted by the load

the lever system of the elbow joint

AMPLIFIES movements of the biceps into larger, more rapid movements of the hand

resilin (elastic protein)

store mucle-generated energy

function of creatine phosphate (vertebrates)

can donate phosphate to form ATP from ADP

phosphagens

creatine phosphate and arginine phosphate (nonvertebrates) ADP to ATP

oxidative phosphorylation

• Takes place in muscle mitochondria • Requires oxygen • Fueled by fatty acids or glucose • Rich yield (~30 ATP per glucose) • Multistep pathway requires more time • Used during light to moderate (aerobic) activity • Myoglobin stores oxygen in muscle fibers

fast-glycolytic fibers can function in anerobic conditions and has ____ resistance to fatigue

LOW RESISTANCE!

glycolysis yield

2 ATP per glucose

fatigue

decreased contractile responses of exercising muscle to stimulation

central fatigue involves

decrease in CNS stimulation of motor neurons

oxygen is needed for recovery of energy systems through oxidative phosphorylation

• Replenishment of creatine phosphate • Conversion of lactate into pyruvic acid and pyruvic acid into glucose • Replenishment of glycogen stores

skeletal muscle fiber types

slow oxidative, fast oxidative, fast glycolytic fibers

slow oxidative fibers (type I)

• 60 - 100 msec to peak tension • Lower myosin-ATPase activity • High resistance to fatigue

fast oxidative fibers (type IIa)

20 - 40 msec to peak tension • Higher myosin-ATPase activity • Intermediate resistance to fatigue

Fast-glycolytic fibers (Type IIb, IId, or IIx)

Similar to fast-oxidative fibers in speed and myosinATPase activity • Low resistance to fatigue • Mostly anaerobic (glycolysis

skeletal muscle has a high degree of

plasticity (can change shape without breaking)

endurance activities improve

oxidative capacity

high intensity activity stimulates

hypertrophy of fast-glycolytic fibers (increases diameter)

what hormone would be blocked to avoid muscle weakening

MYOSTATIN

Testosterone and growth hormone/IGF-I promote synthesis of

myosin and actin filaments

myostatin

negative regulator of muscle growth

disuse atrophy

unused muscle loses mass and strength

damaged muscle =

limited repair is possible due to ability to form new myoblasts

what is needed for flight

high force and high frequency

increased body temp allows for what in terms of ATP and Ca2+ pumps

rapid ATP synthesis and increased Ca2+ pump activity

mitochondria of birds and insects are ____ efficient

more! they allow for higher O2 consumption (flying animals/insects!!)

Flight - synchronous muscle contractions do what

power flight muscle of hummingbirds and large insects (HIGH POWER, LOW EFFICIENCY!)

Flight - asynchronous muscle contractions

longer duration, greater efficiency

afferent and efferent spinal neurons - spinal reflexes are important for

posture and basic protective movements

primary motorcortex

discrete mvoements of hands and fingers and voluntary motor control of the body

brain stem

regulation of overall body posture - involuntary movements of trunk and limbs

cerebellum

coordination and balance (involuntary)

muscle proprioceptors monitor what?

changes in muscle length and tension

muscle length is monitored by

muscle spindles

muscle spindles

monitor muscle length, bundles of specialized intrafusal fibers lying within spindle-shaped connective tissue capsules

changes in muscle tension are detected by

golgi tendon organs

golgi tendon organs

Endings of afferent fibers entwined within bundles of connective tissue fibers in the tendon • Frequency of firing is directly related to tension developed in the muscle • Afferent information reaches the level of conscious awareness of muscle tension

CHANGES IN MUSCLE TENSION

alpha motor neurons in spinal cord

afferent neurons synapse on these in spinal cord (CONTRACTION = result)

gamma motor neurons

initiate contraction of muscular end regions of intrafusal fibers to ADJUST TENSION in muscle spindles

stretch reflex purpose

resist tendency for passive stretch from gravity (UPRIGHT)

smooth muscle

walls of hollow organs and tuber, fibers are smaller and spindle-shaped (single nucleus), sheets,

thick, thin, intermediate filaments

arrangement of filaments

no striations

mechanism of smooth muscle contraction:

During excitation, cytosolic Ca2+ is increased • Ca2+ binds with calmodulin • Ca2+-calmodulin complex binds to and activates myosin light chain kinase (MLC kinase) • MLC kinase phosphorylates myosin • Allows myosin heads to interact with actin and cross-bridge cycling begins

What is unique to smooth muscle?

myosin light chain kinase (MLC kinase)

phasic smooth muscle

contracts in bursts triggered by action potentials that cause raise is cytosolic Ca2+

tonic smooth muscle

partially contracted at all times; varies based on cytosolic Ca2+ levels

multiple individual units must be __________ stimulated by nerves to contract

• Multiple (individual) units must be separately stimulated by nerves to contract

• Contractile activity is neurogenic and phasic

• Can be initiated by the autonomic nervous system

Single-unit muscle fibers are

• Single-unit muscle fibers are self-excitable and contract as a single unit (many together)

• Gap junctions electrically link neighboring cells (functional syncytium)

• Contractile activity is myogenic and may be phasic (pacemaker potentials) or tonic (slow-wave potentials)

• Modified by the autonomic nervous system

smooth muscle contracts slower and uses less energy than ______ muscle

skeletal