Download Role of Muscles

Neuromuscular
Fundamentals
Anatomy and Physiology of
Human Movement
420:050
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Outline
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Introduction
Structure and Function
Fiber Arrangement
Muscle Actions
Role of Muscles
Neural Control
Factors that Affect Muscle Tension
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Introduction
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Responsible for movement of body and all of its
joints
Muscles also provide
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Protection
Posture and support
Produce a major portion of total body heat
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 - muscles work in groups
rather than independently to achieve a given joint
motion
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Muscle Tissue Properties
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Irritability or Excitability - property of muscle being
sensitive or responsive to chemical, electrical, or
mechanical stimuli
Contractility - ability of muscle to contract & develop
tension or internal force against resistance when
stimulated
Extensibility - ability of muscle to be passively
stretched beyond it normal resting length
Elasticity - ability of muscle to return to its original
length following stretching
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Outline
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





Introduction
Structure and Function
Fiber Arrangement
Muscle Actions
Role of Muscles
Neural Control
Factors that Affect Muscle Tension
5
Structure and Function
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Nervous system structure
Muscular system structure
Neuromuscular function
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Figure 14.1, Marieb & Mallett (2003). Human Anatomy. Benjamin
Cummings.
Nervous System Structure
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Integration of information from millions of
sensory neurons  action via motor neurons
Figure 12.1, Marieb & Mallett (2003). Human Anatomy. Benjamin
Cummings.
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Nervous System Structure
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Organization
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Brain
Spinal cord
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Nerves
Fascicles

Neurons
Figure 12.2, Marieb & Mallett (2003).
Human Anatomy. Benjamin Cummings.
Figure 12.7, Marieb & Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Nervous System Structure
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Both sensory and motor neurons in nerves
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Figure 12.11, Marieb & Mallett (2003). Human Anatomy. Benjamin
Cummings.
Nervous System Structure

The neuron: Functional unit of nervous tissue (brain,
spinal cord, nerves)
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Dendrites: Receptor sites
Cell body: Integration
Axon: Transmission
 Myelin sheath: Protection and speed
 Nodes of Ranvier: Saltatory conduction
 Terminal branches: Increased innervation
 Axon terminals: Connection with muscular system
 Synaptic vescicles: Delivery mechanism of “message”
 Neurotransmitter: The message
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Dendrites
Cell body
Axon
Myelin sheath
Node of Ranvier
Terminal ending
Terminal branch
Figure 12.4, Marieb & Mallett (2003). Human
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Anatomy. Benjamin Cummings.
Figure 12.8, Marieb & Mallett (2003). Human Anatomy.
Benjamin Cummings.
Terminal ending
Synaptic vescicle
Neurotransmitter:
Acetylcholine (ACh)
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Figure 12.19, Marieb & Mallett (2003). Human Anatomy.
Benjamin Cummings.
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Structure and Function
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Nervous system structure
Muscular system structure
Neuromuscular function
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Classification of Muscle Tissue
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Three types:
1. Smooth muscle
2. Cardiac muscle
3. Skeletal muscle
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Skeletal Muscle: Properties
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Extensibility: The ability to lengthen
Contractility: The ability to shorten
Elasticity: The ability to return to original
length
Irritability: The ability to receive and respond
to stimulus
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Muscular System Structure
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Organization:
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Muscle (epimyseum)
 Fascicle (perimyseum)

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Muscle fiber (endomyseum)
 Myofibril
 Myofilament
 Actin and myosin
Other Significant Structures:
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Sarcolemma
Transverse tubule
Sarcoplasmic reticulum
Tropomyosin
Troponin
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Figure 10.1, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
Figure 10.4, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
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http://staff.fcps.net/cverdecc/Adv%20A&P/Notes/Muscle%20Unit/sliding%20filament%20theory/slidin16.jpg
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Figure 10.8, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
Structure and Function
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Nervous system structure
Muscular system structure
Neuromuscular function
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Neuromuscular Function
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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
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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
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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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Figure 12.9, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
Nerve Impulse

What is depolarization?
-Reversal of the RMP from –70 mV to +30mV
Propagation of the
action potential
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Figure 12.9, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
Nerve Impulse

What is repolarization?
-Return of the RMP to –70 mV
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Figure 12.9, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
+30 mV
-70 mV
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Neuromuscular Function
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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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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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Figure 12.8, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
Ca2+
ACh
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Figure 14.5, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
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Neuromuscular Function
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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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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Figure 14.5, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.
Neuromuscular Function
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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Calcium Release
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AP  T-tubules  Sarcoplasmic reticulum
1. Activation of SR
2. Calcium released into sarcoplasm
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CALCIUM
RELEASE
Sarcolemma
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Neuromuscular Function
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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Coupling of Actin and Myosin
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Tropomyosin
Troponin
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Blocked
Coupling of actin and myosin
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Neuromuscular Function
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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Sliding Filament Theory
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Basic Progression of Events
1. Cross-bridge
2. Power stroke
3. Dissociation
4. Reactivation of myosin
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Cross-Bridge
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Activation of myosin via ATP
-ATP  ADP + Pi + Energy
-Activation  “cocked” position
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Power Stroke
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ADP + Pi are released
Configurational change
Actin and myosin slide
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Dissociation
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New ATP binds to myosin
Dissociation occurs
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Reactivation of Myosin Head
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ATP  ADP + Pi + Energy
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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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Outline







Introduction
Structure and Function
Fiber Arrangement
Muscle Actions
Role of Muscles
Neural Control
Factors that Affect Muscle Tension
52
Shape of Muscles & Fiber
Arrangement
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Muscles have different shapes & fiber
arrangements
Shape & fiber arrangement affects
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Muscle’s ability to exert force
Range through which it can effectively exert force
onto the bones
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Shape of Muscles & Fiber
Arrangement
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Two major types of fiber arrangements
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Parallel & pennate
Each is further subdivided according to shape
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Fiber Arrangement - Parallel
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Parallel muscles
 fibers arranged parallel to length of
muscle
 produce a greater range of movement
than similar sized muscles with pennate
arrangement
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Categorized into following shapes:
 Flat
 Fusiform
 Strap
 Radiate
 Sphincter or circular
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Fiber Arrangement - Parallel
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Flat muscles
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Usually thin & broad, originating from broad, fibrous,
sheet-like aponeuroses
Allows them to spread their forces over a broad area
Ex: Rectus abdominus & external oblique
Modified from Van De Graaff KM: Human
anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Parallel
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Fusiform muscles
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Spindle-shaped with a central belly
that tapers to tendons on each end
Allows them to focus their power onto
small, bony targets
Ex: Brachialis, biceps brachii
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Figure 3.3. Hamilton, Weimar & Luttgens (2005). Kinesiology:
Scientific basis for human motion. McGraw-Hill.
Fiber Arrangement - Parallel
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Strap muscles
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More uniform in diameter
with essentially all fibers
arranged in a long
parallel manner
Enables a focusing of
power onto small, bony
targets
Ex: Sartorius,
sternocleidomastoid
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Figure 8.7. Hamilton, Weimar & Luttgens (2005). Kinesiology:
Scientific basis for human motion. McGraw-Hill.
Fiber Arrangement - Parallel
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Radiate muscles
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Also described sometimes as being triangular, fanshaped or convergent
Have combined arrangement of flat & fusiform
Originate on broad aponeuroses & converge onto a
tendon
Ex: Pectoralis major, trapezius
Modified from Van De Graaff KM: Human
anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Parallel
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Sphincter or circular muscles
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Technically endless strap muscles
Surround openings & function to close them upon
contraction
Ex: Orbicularis oris surrounding the mouth
Modified from Van De Graaff KM: Human
anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Pennate
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Pennate muscles
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Have shorter fibers
Arranged obliquely to their tendons in a manner
similar to a feather
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Reduces mechanical efficiency of each fiber
Increases overall number of fibers “packed” into
muscle
Overall effect = more crossbridges = more force!
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Fiber Arrangement - Pennate
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Categorized based upon the exact
arrangement between fibers & tendon
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Unipennate
Bipennate
Multipennate
Modified from Van De Graaff KM: Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Pennate
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Unipennate muscles
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Fibers run obliquely from a tendon on
one side only
Ex: Biceps femoris, extensor digitorum
longus, tibialis posterior
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Fiber Arrangement - Pennate
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Bipennate muscle
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Fibers run obliquely on both sides from
a central tendon
Ex: Rectus femoris, flexor hallucis
longus
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Fiber Arrangement - Pennate
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Multipennate muscles
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Have several tendons with fibers running
diagonally between them
Ex: Deltoid
Bipennate & unipennate produce more
force than multipennate
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Outline
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
Introduction
Structure and Function
Fiber Arrangement
Muscle Actions
Role of Muscles
Neural Control
Factors that Affect Muscle Tension
66
Muscle Actions: Terminology
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Origin (Proximal Attachment):
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Structurally, the proximal attachment of a muscle
or the part that attaches closest to the midline or
center of the body
Functionally & historically, the least movable part
or attachment of the muscle
Note: The least movable may not necessarily be
the proximal attachment
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Muscle Actions: Terminology
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Insertion (Distal Attachment):
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Structurally, the distal attachment or the part that
attaches farthest from the midline or center of the
body
Functionally & historically, the most movable part
is generally considered the insertion
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Muscle Actions: Terminology
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When a particular muscle is activated
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It tends to pull both ends toward the center
Actual movement is towards more stable
attachment
Examples:
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Bicep curl vs. chin-up
Hip extension vs. RDL
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Muscle Actions
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Action - when tension is developed in a
muscle as a result of a stimulus
Muscle “contraction” term is exclusive in
nature
As a result, it has become increasingly
common to refer to the various types of
muscle contractions as muscle actions
instead
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Muscle Actions
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Muscle actions can be used to cause,
control, or prevent joint movement or
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To initiate or accelerate movement of a body
segment
To slow down or decelerate movement of a body
segment
To prevent movement of a body segment by
external forces
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Types of Muscle Actions
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Muscle action (under tension)
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Isometric
Isotonic
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Concentric
Eccentric
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Types of Muscle Actions
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Isometric action:
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Tension is developed within
muscle but joint angles remain
constant
AKA – Static movement
May be used to prevent a
body segment from being
moved by external forces
Internal torque = external
torque
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Types of Muscle Actions
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Isotonic (same tension) contractions involve
muscle developing tension to either cause or
control joint movement
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AKA – Dynamic movement
Isotonic contractions are either concentric
(shortening) or eccentric (lengthening)
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Types of Muscle Actions
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Concentric contractions involve muscle developing
tension as it shortens
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Internal torque > external torque
Causes movement against gravity or other resistance
Described as being a positive action
Eccentric contractions involve the muscle
lengthening under tension
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External torque > internal torque
Controls movement caused by gravity or other resistance
Described as being a negative action
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What is the role of the elbow extensors in
each phase?
76
Modified from Shier D, Butler J, Lewis R: Hole’s human anatomy
& physiology, ed 9, Dubuque, IA, 2002, McGraw-Hill
Types of Muscle Actions
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Movement may occur at any given joint
without any muscle contraction whatsoever
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referred to as passive
solely due to external forces such as those
applied by another person, object, or resistance
or the force of gravity in the presence of muscle
relaxation
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Outline







Introduction
Structure and Function
Fiber Arrangement
Muscle Actions
Role of Muscles
Neural Control
Factors that Affect Muscle Tension
78
Role of Muscles
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Agonist muscles
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The activated muscle group during concentric or
eccentric phases of movement
Known as primary or prime movers, or muscles
most involved
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Role of Muscles
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Antagonist muscles
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Located on opposite side of joint from agonist
Have the opposite concentric action
Also known as contralateral muscles
Work in cooperation with agonist muscles by
relaxing & allowing movement
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Reciprocal Inhibition
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Role of Muscles
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Stabilizers
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Surround joint or body part
Contract to fixate or stabilize the area to enable
another limb or body segment to exert force &
move
Also known as fixators
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Role of Muscles
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Synergist
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Assist in action of agonists
Not necessarily prime movers for the action
Also known as guiding muscles
Assist in refined movement & rule out undesired
motions
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Role of Muscles
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Neutralizers
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Counteract or neutralize the action of another
muscle to prevent undesirable movements such
as inappropriate muscle substitutions
Activation to resist specific actions of other
muscles
84
Outline







Introduction
Structure and Function
Fiber Arrangement
Muscle Actions
Role of Muscles
Neural Control
Factors that Affect Muscle Tension
85
Factors That Affect Muscle
Tension
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Number Coding and Rate Coding
Length-Tension Relationship
Force-Velocity Relationship
Uniarticular vs. Biarticular Muscles
Cross-sectional Diameter
Muscle Fiber Type
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Number Coding & Rate Coding
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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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Activating those motor units containing a greater
number of muscle fibers (Number Coding)
Activating more motor units (Number Coding)
Increasing the frequency of motor unit activation (Rate
Coding)
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Number Coding & Rate Coding
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Number of muscle fibers per motor unit
varies significantly
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From less than 10 in muscles requiring precise
and detailed such as muscles of the eye
To as many as a few thousand in large
muscles that perform less complex activities
such as the quadriceps and gastrocnemius
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Number Coding & Rate Coding

Greater contraction forces may also be
achieved by increasing the frequency or
motor unit activation (Rate Coding)
89
All or None Principle
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Motor unit
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Typical muscle contraction
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Single motor neuron & all muscle fibers it innervates
The number of motor units responding (and number of
muscle fibers contracting) within the muscle may vary
significantly from relatively few to virtually all
All of the fibers within the motor unit will fire when
stimulated by the CNS
All or None Principle - regardless of number,
individual muscle fibers within a given motor unit
will either fire & contract maximally or not at all
90
Factors That Affect Muscle
Tension
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Number Coding and Rate Coding
Length-Tension Relationship
Force-Velocity Relationship
Uniarticular vs. Biarticular Muscles
Cross-sectional Diameter
Muscle Fiber Type
91
Length - Tension Relationship

Maximal ability of a muscle to develop
tension & exert force varies depending
upon the length of the muscle during
contraction
Passive Tension
Active Tension
92
93
Figure 20.2, Plowman and Smith (2002). Exercise Physiology, Benjamin
Cummings.
Factors That Affect Muscle
Tension
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Number Coding and Rate Coding
Length-Tension Relationship
Force-Velocity Relationship
Uniarticular vs. Biarticular Muscles
Cross-sectional Diameter
Muscle Fiber Type
94
Force – Velocity Relationship

When muscle is contracting (concentrically or
eccentrically) the rate of length change is
significantly related to the amount of force potential
95
Force – Velocity Relationship
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Maximum concentric velocity = minimum
resistance
As load increases, concentric velocity
decreases
Eventually velocity = 0 (isometric action)
96
Force – Velocity Relationship
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

As load increases beyond muscle’s ability
to maintain an isometric contraction, the
muscle begins eccentric action
As load increases, eccentric velocity
increases
Eventually velocity = maximum when
muscle tension fails
97
Muscle Force – Velocity
Relationship


Indirect relationship between force (load)
and concentric velocity
Direct relationship between force (load)
and eccentric velocity
98
Factors That Affect Muscle
Tension

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Number Coding and Rate Coding
Length-Tension Relationship
Force-Velocity Relationship
Uniarticular vs. Biarticular Muscles
Cross-sectional Diameter
Muscle Fiber Type
99
Uni Vs. Biarticular Muscles

Uniarticular muscles

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Cross & act directly only on the single joint that
they cross
Ex: Brachialis
 Can only pull humerus & ulna closer
together
Ex: Gluteus Maximus
 Can only pull posterior femur and pelvis
closer together
100
Uni Vs. Biarticular Muscles
Biarticular muscles

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Cross & act on two different joints
May contract & cause motion at either one or
both of its joints
Advantages over uniarticular muscles
101
Advantage #1
Can cause and/or control motion at more
than one joint

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
Rectus femoris: Knee extension, hip flexion
Hamstrings: Knee flexion, hip extension
102
Advantage #2

Can maintain a relatively constant length
due to "shortening" at one joint and
"lengthening" at another joint (Quasiisometric)
- Recall the Length-Tension Relationship
103
Advantage #3
Prevention of Reciprocal Inhibition
This effect is negated with biarticular
muscles when they move concurrently
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Concurrent movement:
 Concurrent “lengthening” and “shortening” of
muscle
Countercurrent movement:
 Both ends “lengthen” or “shorten”
104
What if the muscles of the
hip/knee were uniarticular?
Hip
Knee
Ankle
Muscles stretched/shortened to
105
extreme lengths! Implication?
106
Figure 20.2, Plowman and Smith (2002). Exercise Physiology, Benjamin
Cummings.
Quasi-isometric action?
Implication?
Hip
Knee
Ankle
107
Active & Passive Insufficiency


Countercurrent muscle actions can reduce the
effectiveness of the muscle
As muscle shortens its ability to exert force
diminishes


Active insufficiency: Diminished crossbridges
As muscle lengthens its ability to move through
ROM or generate tension diminishes

Passively insufficiency: Diminished crossbridges and
excessive passive tension
108
Factors That Affect Muscle
Tension






Number Coding and Rate Coding
Length-Tension Relationship
Force-Velocity Relationship
Uniarticular vs. Biarticular Muscles
Cross-sectional Diameter
Muscle Fiber Type
109
Cross-Sectional Area


Hypertrophy vs. hyperplasia
Increased # of myofilaments

Increased size and # of myofibrils

Increased size of muscle fibers
110
http://estb.msn.com/i/6B/917B20A6BE353420124115B1A511C7.jpg
Factors That Affect Muscle
Tension






Number Coding and Rate Coding
Length-Tension Relationship
Force-Velocity Relationship
Uniarticular vs. Biarticular Muscles
Cross-sectional Diameter
Muscle Fiber Type
111
Muscle Fiber Characteristics

Three basic types:
1. Type I:
-Slow twitch, oxidative, red
2. Type IIb:
-Fast twitch, glycolytic, white
3. Type IIa:
-FOG
112