1 Neuromuscular Fundamentals Anatomy and Kinesiology 420:024.

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Neuromuscular Fundamentals

Anatomy and Kinesiology

420:024

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Outline Introduction Structure and Function Fiber Arrangement Muscle Actions Role of Muscles Neural Control Factors that Affect Muscle Tension

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Introduction Responsible for movement of body and all of its

joints Muscles also provide:

Over 600 skeletal muscles comprise approximately 40 to 50% of body weight

215 pairs of skeletal muscles usually work in cooperation with each other to perform opposite actions at the joints which they cross

Aggregate muscle action:

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Muscle Tissue Properties

Irritability or Excitability

Contractility

Extensibility

Elasticity

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Structure and Function

Nervous system structure Muscular system structure Neuromuscular function

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Figure 14.1, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

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Nervous System Structure

Integration of information from millions of sensory neurons action via motor neurons


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Nervous System Structure Organization

Brain Spinal cord

Nerves Fascicles

Neurons



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Nervous System Structure Both sensory and motor neurons in nerves


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Nervous System Structure

The neuron: Functional unit of nervous tissue (brain, spinal cord, nerves) Dendrites: Cell body: Axon:

Myelin sheath: Nodes of Ranvier: Terminal branches: Axon terminals: Synaptic vescicles: Neurotransmitter:

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DendritesCell body

Axon

Myelin sheath

Node of Ranvier

Terminal branch

Terminal ending


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Terminal ending

Synaptic vescicle

Neurotransmitter: Acetylcholine (ACh)

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Classification of Muscle Tissue Three types:

1. Smooth muscle

2. Cardiac muscle

3. Skeletal muscle

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Muscular System Structure Organization:

Muscle (epimyseum) Fascicle (perimyseum)

Muscle fiber (endomyseum) Myofibril Myofilament Actin and myosin

Other Significant Structures: Sarcolemma Transverse tubule Sarcoplasmic reticulum Tropomyosin Troponin

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http://staff.fcps.net/cverdecc/Adv%20A&P/Notes/Muscle%20Unit/sliding%20filament%20theory/slidin16.jpg

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Neuromuscular Function

Basic Progression:

1. Nerve impulse

2. Neurotransmitter release

3. Action potential along sarcolemma

4. Calcium release

5. Coupling of actin and myosin

6. Sliding filaments

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Nerve Impulse

What is a nerve impulse?

-Transmitted electrical charge

-Excites or inhibits an action

-An impulse that travels along an axon is an ACTION POTENTIAL

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Nerve Impulse

How does a neuron send an impulse?

-Adequate stimulus from dendrite

-Depolarization of the resting membrane potential

-Repolarization of the resting membrane potential

-Propagation

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Nerve Impulse

What is the resting membrane potential?-Difference in charge between inside/outside of the neuron

-70 mV


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Nerve Impulse

What is depolarization?

-Reversal of the RMP from –70 mV to +30mV

Propagation of the action potential


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Nerve Impulse

What is repolarization?

-Return of the RMP to –70 mV


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-70 mV

+30 mV

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Basic Progression:

1. Nerve impulse



4. Calcium release



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Release of the Neurotransmitter

Action potential axon terminals

1. Calcium uptake

2. Release of synaptic vescicles (ACh)

3. Vescicles release ACh

4. ACh binds sarcolemma

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Ca2+

ACh


33Figure 14.5, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

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1. Nerve impulse



4. Calcium release



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Ach

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AP Along the Sarcolemma

Action potential Transverse tubules

1. T-tubules carry AP inside

2. AP activates sarcoplasmic reticulum

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1. Nerve impulse



4. Calcium release


6. Sliding Filaments

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Calcium Release

AP T-tubules Sarcoplasmic reticulum

1. Activation of SR

2. Calcium released into sarcoplasm

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Sarcolemma

CALCIUM

RELEASE

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1. Nerve impulse



4. Calcium release



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Coupling of Actin and Myosin

Tropomyosin Troponin

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Blocked Coupling of actin and myosin

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1. Nerve impulse



4. Calcium release



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Sliding Filament Theory

Basic Progression of Events

1. Cross-bridge

2. Power stroke

3. Dissociation

4. Reactivation of myosin

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Cross-Bridge

Activation of myosin via ATP

-ATP ADP + Pi + Energy

-Activation “cocked” position

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Power Stroke

ADP + Pi are released Configurational change Actin and myosin slide

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Dissociation

New ATP binds to myosin Dissociation occurs

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Reactivation of Myosin Head

ATP ADP + Pi + Energy Reactivates the myosin head

Process starts over Process continues until:

-Nerve impulse stops-AP stops-Calcium pumped back into SR-Tropomyosin/troponin back to original position

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Shape of Muscles & Fiber Arrangement

Muscles have different shapes & fiber arrangements

Shape & fiber arrangement affects

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Shape of Muscles & Fiber Arrangement

Two major types of fiber arrangements

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Fiber Arrangement - Parallel

Parallel muscles

Categorized into following shapes: Flat Fusiform Strap Radiate Sphincter or circular

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Flat muscles

Modified from Van De Graaff KM: Human anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.

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Fusiform muscles

Figure 3.3. Hamilton, Weimar & Luttgens (2005). Kinesiology: Scientific basis for human motion. McGraw-Hill.

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Strap muscles

Figure 8.7. Hamilton, Weimar & Luttgens (2005). Kinesiology: Scientific basis for human motion. McGraw-Hill.

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Radiate muscles


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Sphincter or circular muscles


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Fiber Arrangement - Pennate

Pennate muscles

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Categorized based upon the exact arrangement between fibers & tendon


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Unipennate muscles

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Bipennate muscle

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Multipennate muscles

Bipennate & unipennate produce more force than multipennate

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Muscle Actions: Terminology

Origin (Proximal Attachment):

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Insertion (Distal Attachment):

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When a particular muscle is activated:

Examples: Bicep curl vs. chin-up Hip extension vs. RDL

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Muscle Actions Action:

Contraction:

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Muscle Actions Muscle actions can be used to cause,

control, or prevent joint movement or

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Types of Muscle Actions

IsometricIsometric IsotonicIsotonic

EccentricEccentricConcentricConcentric

MUSCLE ACTION (under tension)MUSCLE ACTION (under tension)

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Isometric action:

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Isotonic (same tension):

Isotonic contractions are either concentric (shortening) or eccentric (lengthening)

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Concentric contractions involve muscle developing tension as it shortens

Eccentric contractions involve the muscle lengthening under tension

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Modified from Shier D, Butler J, Lewis R: Hole’s human anatomy & physiology, ed 9, Dubuque, IA, 2002, McGraw-Hill

What is the role of the elbow extensors in each phase?

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Types of Muscle Actions Isokinetics:

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Movement may occur at any given joint without any muscle contraction whatsoever

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Role of Muscles

Agonist muscles

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Role of Muscles

Antagonist muscles

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Role of Muscles

Stabilizers

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Role of Muscles

Synergist

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Role of Muscles

Neutralizers

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Factors That Affect Muscle Tension

Number Coding and Rate Coding Length-Tension Relationship Force-Velocity Relationship Angle of Pull Uniarticular vs. Biarticular Muscles Cross-sectional Diameter Muscle Fiber Type Pennation

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Number Coding & Rate Coding

Difference between lifting a minimal vs. maximal resistance is the number of muscle fibers recruited (crossbridges)

The number of muscle fibers recruited may be increased by

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Number of muscle fibers per motor unit varies significantly

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Number Coding & Rate Coding As stimulus strength increases from threshold,

more motor units (Number Coding) are recruited & overall muscle contraction force increases in a graded fashion

From Seeley RR, Stephens TD, Tate P: Anatomy & physiology, ed 7, New York, 2006, McGraw-Hill.

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Greater contraction forces may also be achieved by increasing the frequency or motor unit activation (Rate Coding)

Phases of a single muscle fiber contraction or twitch Stimulus Latent period Contraction phase Relaxation phase

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Latent period

Contraction phase

Relaxation phase

From Powers SK, Howley ET: Exercise physiology: theory and application to fitness and performance, ed 4, New York, 2001 , McGraw-Hill.

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Summation When successive stimuli are provided before

relaxation phase of first twitch has completed, subsequent twitches combine with the first to produce a sustained contraction

Generates a greater amount of tension than single contraction would produce individually

As frequency of stimuli increase, the resultant summation increases accordingly producing increasingly greater total muscle tension

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Number Coding & Rate Coding Tetanus

From Powers SK, Howley ET: Exercise physiology: theory and application to fitness and performance, ed 4, New York, 2001 , McGraw-Hill.

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All or None Principle

Motor unit

Typical muscle contraction

All or None Principle

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Length - Tension Relationship

Maximal ability of a muscle to develop tension & exert force varies depending upon the length of the muscle during contraction

Active Tension

Passive Tension

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Length - Tension Relationship Generally, depending upon muscle

involved

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Length - Tension Relationship

Generally, depending upon muscle involved

99Figure 20.2, Plowman and Smith (2002). Exercise Physiology, Benjamin Cummings.

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Force – Velocity Relationship When muscle is contracting (concentrically or

eccentrically) the rate of length change is significantly related to the amount of force potential

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Force – Velocity Relationship

Maximum concentric velocity = minimum resistance

As load increases, concentric velocity decreases

Eventually velocity = 0 (isometric action)

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Force – Velocity Relationship As load increases beyond muscle’s ability to

maintain an isometric contraction

As load increases

Eventually

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Muscle Force – Velocity Relationship

Indirect relationship between force (load) and concentric velocity

Direct relationship between force (load) and eccentric velocity

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Angle of Pull Angle between the line of pull of the muscle & the

bone on which it inserts (angle toward the joint) With every degree of joint motion, the angle of

pull changes Joint movements & insertion angles involve

mostly small angles of pull

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Angle of Pull Angle of pull changes as joint moves

through ROM Most muscles work at angles of pull less

than 50 degrees Amount of muscular force needed to

cause joint movement is affected by angle of pull – Why?

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Angle of Pull Rotary component - Acts perpendicular to

long axis of bone (lever)

Modified from Hall SJ: Basic biomechanics, New York, 2003, McGraw-Hill.

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Angle of Pull If angle < 90 degrees,

the parallel component is a stabilizing force

If angle > 90 degrees, the force is a dislocating force

Modified from Hall SJ: Basic biomechanics, New York, 2003, McGraw-Hill.

What is the effect of >/< 90 deg on ability to rotate the joint forcefully?

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Uni Vs. Biarticular Muscles

Uniarticular muscles

Ex: Brachialis

Ex: Gluteus Maximus

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Uni Vs. Biarticular Muscles Biarticular muscles

May contract & cause motion at either one or both of its joints

Advantages over uniarticular muscles

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Advantage #1

Can cause and/or control motion at more than one joint

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Advantage #2

Can maintain a relatively constant length due to "shortening" at one joint and "lengthening" at another joint (Quasi-isometric)

- Recall the Length-Tension Relationship

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Advantage #3

Prevention of Reciprocal Inhibition This effect is negated with biarticular

muscles when they move concurrently Concurrent movement:

Countercurrent movement:

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What if the muscles of the hip/knee were uniarticular?

Hip

Knee

Ankle

Muscles stretched/shortened to extreme lengths!

Implication?

117Figure 20.2, Plowman and Smith (2002). Exercise Physiology, Benjamin Cummings.

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Hip

Knee

Ankle

Quasi-isometric action? Implication?

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Active & Passive Insufficiency Countercurrent muscle actions can reduce the

effectiveness of the muscle

As muscle shortens its ability to exert force diminishes

As muscle lengthens its ability to move through ROM or generate tension diminishes

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Cross-Sectional Area

Hypertrophy vs. hyperplasia Increased # of myofilaments

Increased size and # of myofibrils Increased size of muscle fibers

http://estb.msn.com/i/6B/917B20A6BE353420124115B1A511C7.jpg

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Number Coding and Rate Coding Length-Tension Relationship Force-Velocity Relationship Angle of Pull Uniarticular vs. Biarticular Muscles Cross-sectional Diameter Muscle Fiber Type Reflexes Pennation

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Muscle Fiber Characteristics

Three basic types:

1. Type I:

-Slow twitch, oxidative, red

2. Type IIb:

-Fast twitch, glycolytic, white

3. Type IIa:

-FOG

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Number Coding and Rate Coding Length-Tension Relationship Force-Velocity Relationship Angle of Pull Uniarticular vs. Biarticular Muscles Cross-sectional Diameter Muscle Fiber Type Reflexes Pennation

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Effect of Fiber Arrangement on Force Output

Concept #1: Force directly related to cross-sectional area more fibers

Example: Thick vs. thin longitudinal/fusiform muscle?

Example: Thick fusiform/longitudinal vs. thick bipenniform muscle?

Concept #2: As degree of pennation increases, so does # of fibers per CSA

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1 Neuromuscular Fundamentals Anatomy and Kinesiology 420:024.

Documents

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muscle tension slide

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