Anatomy Exam 2

Muscles

• series of soft tissue that attach to skeletal system and provide force for movements and other requirements

Muscle Roles

• Supply force for movement

• Restrain movement

• Control the viscera

• Form sphincters

• Heat production

• Electricity production

What can be sensed by predators?

the electricity produced

Classifying Muscles

Color (red and white)

Location (somatic vs visceral)

Control (voluntary vs involuntary)

Nuclei (multi vs uni)

Striation (striated vs unstriated)

Smooth Muscle

• Unstriated

• Mononucleate

• Cell joined in sheets that wrap around organs to control

• Cells in sheet are electrically couples so innervation spreads through surface

• Visceral

• Involuntary Contractions

• Manages force without fatigue

Cardiac Muscle

• striated

• mononucleate

• joined by intercalated disks

• involuntary

• waves of contraction spread across cells through intercalated disks (nerve or arise within muscle)

Skeletal Muscle

• Voluntary

• Striated

• Multinucleate

• Unbranched fibers from fusion of multiple cells

• Filled with sacromeres

• attach to skeleton to aid movement

Skeletal Muscle Actions

• pulls on the skeleton to create movement

• the origin of a muscle (head) attached to the immobile bone

• the insertion (slip) is attached to the more mobile

• Only pull, cannot push!

• Paired often as antagonistic sets

• Synergistic muscles (work together) doing the same thing

Skeletal Muscle Structure

• Muscle bundles

• Each bundle has muscle cells (or fibers)

• Entire muscle surrounded by epimysium

• Attached to bones via tendons

Why is having more tendon beneficial than muscle?

• less energically costly

• Long connections for short muscles

• Tendons connect to the epimysium

Skeletal Muscle Structure

Each cell packed full of myofibrils

Each cell surrounded by endomysium

Bundles, fasciciles, surrounded by perimysium

Myofibril Structure

• chains of repeating units called sarcomeres

• separated by z bands

• composed of myofilaments: myosin and actin

Resting State

• no stimulation from nervous system

• muscle is soft

• shape maintained by collagenous fibers

• no force generated

• ability to stretch

active state

• nerves stimulate the muscle past a threshold point

• contraction occurs creating a tensile

• this force acts to try and move the bone

• the resistance to this movement is called the load

Muscle contraction theories

Originally thought that the muscles increased in volume

actually sacromeres shortening during contraction

Movement

A band stays constant

I band slides

H zone shortens

Myosin Head

contain binding sites for both ATP and actin

Heads can hydrolyze ATP, releasing a phosphate and energy

Heads change orientation

Myosin pulls actin!

Myosin is then considered an active filament

How do electric eels sting prey

Main and Hunter organs

The sachs organ can be used to fire 10 volt discharges

Flattened electrocytes are stacked into 70 columns

When triggered each cell received a flood of sodium ions, creating electrical gradient

The stacking replaces the (150 mv one electrolyte) to build series (build voltage) and in parallel (current build)

How to alter the function of muscle

• Fiber level

• Whole Muscles

• Whole System

Maximum force that muscle fiber can produce

“the sweet spot”

Slower contraction leads to stronger force, why?

Myosin is unable to bind fast enough onto the actin

Power Equation

Power = energy / time

Power = force (velocity)

Differentiating muscle fibers

• initial color

• Now histochemical and molecular methods

Red muscle

• contain a lot of myoglobin (O2 as well)

• contract slowly but resistant to fatigue

• Useful for high endurance acitivites

White muscle

• low in myoglobin

• contracts rapidly, fatigues easily

• Good for quick reactions

Tonic Fibers

• low contracting

• low force

• sustain that force for long

• useful for postural support

• common in amphibians and non-avian

• Rare in mammals but are in the eyes

Twitch Fibers

• fast contraction/higher forces

• found in all vertebrates

• can be further subdivided into fast and slow

• Fast twitch muscles have been further subdivided in mammals based on fatigue

• This is all relative

Differences in reliances on ATP in both slow and fast?

Slow twitch rely on aerobic respiration

Fast twitch rely on anaerobic respiration

Sequence of activation

slow twitch, fatigue-resistant fast twitch, fatigable-fast twitch fibers

Graded force

Rate modulation- increase or decrease the rate that nerve impulses are delivered to the muscle

Motor unit alteration

Motor Unit

a single neuron and a unique set of fibers it innervates

Cross Sectional area

• the overall length of muscle doesn’t matter in terms of force (not contraction)

• The total force a muscle can produce is proportional to total cross-section of its myofibrils

Two cross-sections

Morphological - overall muscle perpendicular to its length

Physiological- sum of the cross sectional area of all the muscle fibers perpendicular to their lengths

Parallel fibers

• fibers lie along line of force generation

• move lighter loads through long distance

• Your neck muscle

pinnate fibers

• fibers lie oblique to the line of force

• Insert on common tendon

• Pack more myofibrils into area

• greater force productiton

• Cannot shorten as much

• trade-off

• Move heavier loads a short distance, your calf

muscle organ

Use elastic elements such as tendons and connective tissue

Overall force comes from active component (sliding filaments) and elastic component (tendons)

Total tension

active+passive tension combined

Active tension

sliding filaments contracting

Passive

tendons and connective tissue being loaded like a rubber band

Three different contractions

concentric

isometric

eccentric

Homologous Traits

Share a common ancestor

Attachment

Muscles have same attachment sites can be homologous

Function

• can be misleading

• depressor mandibulae and digastric muscle (different structure)

Innervation

• muscle and the innervation

The diaphragm is innervated by phrenic nerve, which forms in the cervical region

Development

• common developmental origin correlates with ancestry

Repeated Trends

• Reduction of muscles when they aren’t needed

• Splitting muscles in regions to increase the complexity of motion

• Bunching muscles around the center of mass

Myomeres

Myomeres arise directly from the myotomes, keeping the segmented structure

arranged in a zig zag patterns that allow each block to influence multiple axial segment

Myosepta

Neighboring blocks connected by this, which extend inwards and attach to the vertebral column

Horizontal septa

Runs the length of the body and divides axial muscles into epaxials and hypaxials

Where do skeletal muscles arise from?

Paraxial mesoderm

How do tetrapods change from fish?

• Axial musculature is reduced and differentiated

• legs take over locomotion

• Hypaxial muscles remain robust: control breathing

• Appendicular muscles expand

• Limbs are more important to locomotion

• Cursorial animals bunch their limb muscles up near the body with utilization of long tendons to reduce weight

Frogs

• appendicular muscles for jumping

• Have robust forelimbs for impact

• Expanded leg musculature

Birds

Sysnsacrum- stabilizes the posterior portion of the vertebral column

Axial musculature in this region is further reduced

Forelimbs are greatly expanded but bunched near body to keep limbs light

Tendons in the legs aid in fine movement of the claws

Branchial Arches

• outer sheet of muscle constrictors straightens the arch

• Deeper adductor muscles bend the arches