Neuromuscular Fundamentals

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Neuromuscular Fundamentals

Anatomy and Physiology of Human Movement

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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

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

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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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: 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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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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Skeletal Muscle: Properties

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 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


34Figure 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 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

Two major types of fiber arrangements Parallel & pennate Each is further subdivided according to shape

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Fiber Arrangement - Parallel

Parallel muscles fibers arranged parallel to length of

muscle produce a greater range of movement

than similar sized muscles with pennate arrangement

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

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Flat muscles 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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Fusiform muscles 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

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

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Strap muscles 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

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

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Radiate muscles Also described sometimes as being triangular, fan-

shaped or convergent Have combined arrangement of flat & fusiform Originate on broad aponeuroses & converge onto a

tendon Ex: Pectoralis major, trapezius


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Sphincter or circular muscles Technically endless strap muscles Surround openings & function to close them upon

contraction Ex: Orbicularis oris surrounding the mouth


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Fiber Arrangement - Pennate

Pennate muscles Have shorter fibers Arranged obliquely to their tendons in a manner

similar to a feather Reduces mechanical efficiency of each fiber Increases overall number of fibers “packed” into

muscle Overall effect = more crossbridges = more force!

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Categorized based upon the exact arrangement between fibers & tendon Unipennate Bipennate Multipennate


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Unipennate musclesFibers run obliquely from a tendon on

one side onlyEx: Biceps femoris, extensor digitorum

longus, tibialis posterior

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Bipennate muscleFibers run obliquely on both sides from

a central tendonEx: Rectus femoris, flexor hallucis

longus

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Multipennate musclesHave several tendons with fibers running

diagonally between themEx: Deltoid

Bipennate & unipennate produce more force than multipennate

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Muscle Actions: Terminology

Origin (Proximal Attachment): 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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Insertion (Distal Attachment): 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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When a particular muscle is activated It tends to pull both ends toward the center Actual movement is towards more stable

attachment Examples:

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

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Muscle Actions 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 Muscle actions can be used to cause,

control, or prevent joint movement or 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

Muscle action (under tension) Isometric Isotonic

Concentric Eccentric

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Isometric action: 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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Isotonic (same tension) contractions involve muscle developing tension to either cause or control joint movement AKA – Dynamic movement

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

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Concentric contractions involve muscle developing tension as it shortens 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 External torque > internal torque Controls movement caused by gravity or other resistance Described as being a negative action

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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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Movement may occur at any given joint without any muscle contraction whatsoever 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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Role of Muscles

Agonist muscles 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

Antagonist muscles 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 Reciprocal Inhibition

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Role of Muscles

Stabilizers 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

Synergist 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

Neutralizers 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

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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

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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 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 of muscle fibers per motor unit varies significantly 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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Greater contraction forces may also be achieved by increasing the frequency or motor unit activation (Rate Coding)

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All or None Principle Motor unit

Single motor neuron & all muscle fibers it innervates

Typical muscle contraction 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

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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

93Figure 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, the muscle begins eccentric action

As load increases, eccentric velocity increases

Eventually velocity = maximum when muscle tension fails

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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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Uni Vs. Biarticular Muscles

Uniarticular muscles 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

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Uni Vs. Biarticular Muscles

Biarticular muscles Cross & act on two different joints

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

Rectus femoris: Knee extension, hip flexion Hamstrings: Knee flexion, hip extension

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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:

Concurrent “lengthening” and “shortening” of muscle

Countercurrent movement: Both ends “lengthen” or “shorten”

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

Hip

Knee

Ankle

Muscles stretched/shortened to extreme lengths!

Implication?

106Figure 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 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

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Cross-Sectional Area

Hypertrophy vs. hyperplasia Increased # of myofilaments

Increased size and # of myofibrils Increased size of muscle fibers

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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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Neuromuscular Fundamentals