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19th LectureFri 27 Feb 2009

Vertebrate PhysiologyECOL 437 (MCB/VetSci 437)Univ. of Arizona, spring 2009

Kevin Bonine & Kevin Oh

Movement & MuscleChapter 18

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Housekeeping, Fri 27 February 2009

ReadingsToday: Ch 18Mon: Ch 19Wed: Ch 19 & 20LAB Wed 04 Mar: Dickinson et al. 2000Fri 06 Mar: Ch 21 (gas transport)

Lab discussion leaders: 04 Mar1pm – Deedra, Franz3pm – AJ, Kareem

Lab discussion leaders: 25 Mar1pm – Sam3pm – Karri, Jason

Fri 13 Feb = Exam 1

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Movement and Behavior

Nervous System and Muscle

integration, control, feedback

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Dipsosaurusdorsalis

Callisaurusdraconoides

Phrynosomaplatyrhinos

Thanks to Duncan Irschick and Steve Reilly

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~Behavior Initiation

Bring together nervous, endocrine, muscular systems, etc.

Complex

Reflexes / Learned / Plasticity

Respond to situation(s)Parallel Processing Complicated

NeuronalCircuitry

Animal Behavior,Neurobiology

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Simple Reflexes – basis of neuronal circuitry

Reflex Arc, Stereotypic Behaviore.g., stretch reflex (patellar tendon)

- Tonic tension in muscle- Important for

maintenance of posture via negative feedback

- Only 2 neurons required

- monosynaptic reflex

Stretch receptor activates1a-afferent neuron

Alpha-motor neuron activates quadriceps

Sherwood 1997 (see 11-1 in Eckert)

(ventral)

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Simple ReflexesStretch receptor = muscle spindle organ

- contains intrafusal fibers(as opposed to extrafusal)

- Sensitive to stretch (stretch -> APs)

- Need to be reset for new muscle length- Gamma-efferent neurons innervate

spindle

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1. 1a-afferent neuron2. Alpha-motor neuron3. Gamma-motor neuron

c. Contracted musclewithout ‘reset’ musclespindle

Sherwood 1997 (see 11-1 in Eckert)

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Simple Reflexes +Other neurons become involved as well:- 1a-afferents inhibit antagonist muscle

(Knee flexor ~hamstring)- Conscious decision to bend leg etc.

- Limb

Fig. 11-2Randall et al. 2002

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Silverthorn 2001

Stretch Reflex

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11Hill et al. 2004 Fig 18.7

12Hill et al. 2004 Fig 18.7

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Silverthorn 2001

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Silverthorn 2001

Golgi Tendon Reflex:

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Law of Nerve-Specific Energy

ventral

dorsalAction Potentials

and Graded Potentials don’t convey specific information.

Rather, the geographic connections, summation of different inputs, and modulation are important for correct response Fig. 11-12

Randall et al. 2002

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CPG = central pattern generator-neuronal network producing repetitive output

Walking, swimming, flying, breathing

Toad walking with no afferents - awkward- flaccid muscles

Sensory feedbackHigher centers can override

Some patterns at level of spinal cord if stimulateinitially (cats on treadmill)

Peripheral vs. Central Control

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Silverthorn 2001

18Hill et al. 2008 Fig 18.11

Central Pattern Generators in Cat Spinal Cord

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Design of a robot salamander that walks and swims Figure 18.12

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Activating muscles

NERVOUS SYSTEM CONTROL:

•cerebral cortex•frontal, parietal,temporal, occipital lobes

•Cerebellum•basal ganglia•brain stem•spinal cord•peripheral nerves

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Silverthorn 2001

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Major Motor Areas,IncludingPRIMARY MOTOR CORTEX

Hill et al. 2004, Fig 18.15&16

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Basal Ganglia(plans&initiates movement)

Cerebellum(fine-tunes execution)

Hill et al. 2004, Fig 18.19

Parkinson’s Disease(akinesia, too much inhibition of motor function, mediated by dopamine)

Huntington’s Disease(chorea, not enough inhibition of motor function)

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http://salmon.psy.plym.ac.uk/year1/ETHEXPT.HTM#Egg%20retrieval

Herring Gull Egg Retrieval

- prefer the larger of two eggs of the same colour- prefer the speckled egg over an unspeckled egg of the same colour- prefer natural coloured(brown speckled) eggs over brown unspeckled eggs - prefer green speckled eggs over green unspeckled eggs - prefer green eggs over brown eggs (Baerends & Kruijt)

Fixed Action Patterns…

Greater preference

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Research Proposal Tips:

-Physiology and science should be subject, not researchers and experiments-Having interesting question or problem helps give direction and focus-More physiology-Subheadings often helpful

-Synthesize, not serial book reports-Abstract, role is summary of entire paper, not an intro to the intro

-Avoid Pronouns (its, these, this, …which, there are)-Passive voice to be avoided (e.g., Avoid passive voice)-Leading and following zeroes (0.5, .5, .50)

-Page numbers-Citation format (J. of Physiology, instructions to authors, [full journal names])

-Turn in old, graded work with each new version

-Peer editing (read quickly, then read for content and writing, comments helpful)

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MuscleA. SarcomereB. Cross-bridge cyclingC. Length-tension relationshipD. Excitation-contraction couplingE. Force-Velocity curves, PowerF. Fiber TypesG. Motor Units/RecruitmentH. EnergeticsI. FatigueJ. Repair and Regeneration

Vertebrate Physiology 437

- Smooth and Cardiac introduction

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Uses: - most observable animal behavior - most visceral function- generally act by shortening

Muscle

Classification: - striated

- smoothskeletal or cardiac

All muscle movement based on myofilaments (actin and myosin) sliding past each other…

Utilize: ATP, Ca2+, ~APs

walls of hollow organs

(Myo-, Sarco- = musclerelated)

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Structure:

Skeletal Muscle

- muscle attached to bone(skeleton) via tendons

- muscle comprises elongate,multinucleate, muscle fibers

- multinucleate muscle fibersderived from combination of manymyoblasts (embryonic muscle cells)

- within each muscle fiber are many parallel myofibrils

- each myofibril contains sarcomeresarranged in series (end-to-end)

- sarcomere is functional unit ofmuscle

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Sarcomere

Z-disk at each end of sarcomere

Sarcomeres in adjacent myofibrils are alignedleading to striated appearance

Actin thin myofilaments attachedto each Z-disk

Myosin thick myofilaments in between actins (6,3)

Actin and Myosin overlap is what allows muscle contraction

(6,3)

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Sarcomere

Z-disk (actin attaches)

Areas within sarcomere given names:

I-band (actin only) A-band (myosin length)

H-zone (myosin only)

M-line (midpoint of myosin)

During muscle contraction, myosin thick filaments slide past actin thin filaments toward Z-lines

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Which regions change length and which remain the same as the sarcomere shortens?

Z-disk (actin attaches)I-band (actin only) A-band (myosin length)

H-zone (myosin only)

M-line (midpoint of myosin)

During muscle contraction, myosin thick filaments slide past actin thin filaments toward Z-lines

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Sarcomere Composition

Actin composed of:individual molecules of G-actin (globular)united into chains called F-actin (filamentous) which form a two-stranded helix

In the groove of the two F-actin strands is tropomyosin,which also has globular troponin molecules attached to it

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Sarcomere Composition

Myosin composed of:2 heavy chains with

globular heads2 essential light chains2 regulatory light chains

Myosin molecules spontaneously aggregate into complexes with the heads at the ends and the tails toward the middle

The light chains are involved in the speed of contraction(important for different muscle fiber-types)

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Sarcomere Function

Cross-bridges form transiently between myosin head and actin filament(actomyosin) Sarcomere shortens

during contraction

Sliding Filament Theory

Actin and Myosin molecules slide past each other, but don’t themselves change length

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Cross Bridges and Force Production

Myosin head binds to actin (actomyosin), then pulls myosin toward z-line thereby shortening sarcomere (= contraction)

Vander et al., 2001

Cross-bridge forces are additive.Same force all along myofibril.

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Sarcomere Function

Number of Cross-bridges (and therefore contraction magnitude) increased with appropriate overlap of actin with myosin heads

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Length-Tension Relationship

Normal muscle function at or near the plateau (1.8-2.2)

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Length-Tension Relationship

Why lose force production at short end?

What constrains muscle length in the body?

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39Hill et al. 2004, Fig 17.12

Length-Tension Relationship

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Vander et al., 2001

Myosin head has to be able to detach and bind again to actinfurther along in order to continue to generate forceDetachment requires ATP bind to myosin head

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Vander et al., 2001

Cross Bridges and Force ProductionATP required for the (3)dissociation of actin and myosin (else rigor mortis)

Myosin acts as an ATPase, hydrolyzing ATP to ADP + Pi (4) (Energy of ATP hydrolysis “cocks” the myosin head)

Myosin releases ADP and Pi (very slowly (2)unless bound to actin) ATP binds to myosin

Actomyosin complex forms (= crossbridge) (1)

Cross bridge stronger when Pi released, then myosin head rotates

Movement about 10-12 nm

Cycle repeats until Ca++ resequestered or run out of energy

ATP hydrolysis

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San Diego State University College of Sciences Biology 590 - Human Physiology

Actin Myosin Crossbridge 3D Animation*

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Hill et al. 2004, Fig 17.5

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Regulation of Contraction

CALCIUM & the cross bridge

Need free Ca2+ in cytosolto get contraction

Calcium binds troponinwhich is attached to tropomyosin on actin

This causes conformational change in tropomyosinexposing actin binding sites for myosin heads (not shown)

Without calcium, contraction is inhibited

Vander et al., 2001

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Excitation-Contraction Coupling, from the beginning…

1. AP from CNS arrives at neuromuscular junction.

2. ACh released into synapse.

3. ACh binds to nicotinic receptors on motor endplate.4. Ion channels for K+ and Na+ open; greater Na+ influx leads to depolarization and AP in muscle plasma membrane

EPP = Endplate Potential(~Excitatory Post-Synaptic Potential or EPSP)

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Excitation-Contraction Coupling, the middle I…

5. Change in membrane potential (AP) reaches deepinto the muscle cell via transverse tubules (T-tubules; one per Z-disk)

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Excitation-Contraction Coupling, the middle II…

6. T-tubules have voltage sensitive proteins called dihydropyridine receptors

8. Calcium stored in the SR. Released into the cytosol via the ryanodine receptor channel when the RR is mechanically triggered by the voltage sensitive dihydropyridine receptor.

7. Dihydropyridine receptors in the T-tubules are mechanically linkedwith ryanodine receptors (RR) on sarcoplasmic reticulum (SR)

The ends of the SR adjacent to the T-tubule are called terminal cisternae (w/ calsequestrin)

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Excitation-Contraction Coupling, the last bit…

9. Calcium triggers release of more calcium from some ryanodine receptors that are not linked to dihydropyridine receptors

10. Calcium binds to troponin leading to actomyosin complex…

Called calcium-induced calcium release

11. After repolarization, calcium actively (requires ATP) movedback into SR where much of it is bound to calsequestrin

12. Muscle relaxes as long as ATP is present to allow actomyosin complex to dissociate

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Sherwood, 1997

Review of EC Coupling and Muscle Contraction