Neuromuscular Fundamentals Anatomy and Physiology of Human Movement 420:050

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

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

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

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

Structure and Function Nervous system structure Muscular system structure Neuromuscular function

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

Nervous System Structure Integration of information from millions of sensory neurons  action via motor neurons Figure 12.1, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Nervous System Structure Organization Brain Spinal cord Nerves Fascicles Neurons Figure 12.2, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings. Figure 12.7, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Nervous System Structure Both sensory and motor neurons in nerves Figure 12.11, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

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

Dendrites Cell body Axon Myelin sheath Node of Ranvier Terminal ending Terminal branch Figure 12.4, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Neurotransmitter: Acetylcholine (ACh) Figure 12.8, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings. Terminal ending Synaptic vescicle Neurotransmitter: Acetylcholine (ACh)

Figure 12. 19, Marieb & Mallett (2003). Human Anatomy Figure 12.19, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Structure and Function Nervous system structure Muscular system structure Neuromuscular function

Classification of Muscle Tissue Three types: 1. Smooth muscle 2. Cardiac muscle 3. Skeletal muscle

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

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

Figure 10.1, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Figure 10.4, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

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

Figure 10.8, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Structure and Function Nervous system structure Muscular system structure Neuromuscular function

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

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

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

-70 mV Nerve Impulse What is the resting membrane potential? -Difference in charge between inside/outside of the neuron -70 mV Figure 12.9, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Propagation of the action potential Nerve Impulse What is depolarization? -Reversal of the RMP from –70 mV to +30mV Propagation of the action potential Figure 12.9, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

Nerve Impulse What is repolarization? -Return of the RMP to –70 mV Figure 12.9, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings.

+30 mV -70 mV

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

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

Figure 12.8, Marieb & Mallett (2003). Human Anatomy. Benjamin Cummings. Ca2+ ACh

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

Ach

AP Along the Sarcolemma Action potential  Transverse tubules 1. T-tubules carry AP inside 2. AP activates sarcoplasmic reticulum

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

Calcium Release AP  T-tubules  Sarcoplasmic reticulum 1. Activation of SR 2. Calcium released into sarcoplasm

CALCIUM RELEASE Sarcolemma

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

Coupling of Actin and Myosin Tropomyosin Troponin

Blocked Coupling of actin and myosin

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

Sliding Filament Theory Basic Progression of Events 1. Cross-bridge 2. Power stroke 3. Dissociation 4. Reactivation of myosin

Cross-Bridge Activation of myosin via ATP -ATP  ADP + Pi + Energy -Activation  “cocked” position

Power Stroke ADP + Pi are released Configurational change Actin and myosin slide

Dissociation New ATP binds to myosin Dissociation occurs

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

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

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

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

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

Fiber Arrangement - Parallel 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.

Fiber Arrangement - Parallel 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.

Fiber Arrangement - Parallel 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.

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

Fiber Arrangement - Parallel Sphincter or circular muscles 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.

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!

Fiber Arrangement - Pennate Categorized based upon the exact arrangement between fibers & tendon Unipennate Bipennate Multipennate Modified from Van De Graaff KM: Human anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.

Fiber Arrangement - Pennate Unipennate muscles Fibers run obliquely from a tendon on one side only Ex: Biceps femoris, extensor digitorum longus, tibialis posterior

Fiber Arrangement - Pennate Bipennate muscle Fibers run obliquely on both sides from a central tendon Ex: Rectus femoris, flexor hallucis longus

Fiber Arrangement - Pennate Multipennate muscles Have several tendons with fibers running diagonally between them Ex: Deltoid Bipennate & unipennate produce more force than multipennate

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

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

Muscle Actions: Terminology 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

Muscle Actions: Terminology 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

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

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

Types of Muscle Actions Muscle action (under tension) Isometric Isotonic Concentric Eccentric

Types of Muscle Actions 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

Types of Muscle Actions 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)

Types of Muscle Actions 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

What is the role of the elbow extensors in each phase? Modified from Shier D, Butler J, Lewis R: Hole’s human anatomy & physiology, ed 9, Dubuque, IA, 2002, McGraw-Hill

Types of Muscle Actions 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

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

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

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

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

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

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

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

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

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)

Number Coding & Rate Coding 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

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

All or None Principle Motor unit Typical muscle contraction 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

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

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

Figure 20. 2, Plowman and Smith (2002) Figure 20.2, Plowman and Smith (2002). Exercise Physiology, Benjamin Cummings.

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

Force – Velocity Relationship When muscle is contracting (concentrically or eccentrically) the rate of length change is significantly related to the amount of force potential

Force – Velocity Relationship Maximum concentric velocity = minimum resistance As load increases, concentric velocity decreases Eventually velocity = 0 (isometric action)

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

Muscle Force – Velocity Relationship Indirect relationship between force (load) and concentric velocity Direct relationship between force (load) and eccentric velocity

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

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

Uni Vs. Biarticular Muscles Cross & act on two different joints May contract & cause motion at either one or both of its joints Advantages over uniarticular muscles

Advantage #1 Can cause and/or control motion at more than one joint Rectus femoris: Knee extension, hip flexion Hamstrings: Knee flexion, hip extension

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

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”

What if the muscles of the hip/knee were uniarticular? Ankle Muscles stretched/shortened to extreme lengths! Implication?

Figure 20. 2, Plowman and Smith (2002) Figure 20.2, Plowman and Smith (2002). Exercise Physiology, Benjamin Cummings.

Quasi-isometric action? Implication? Hip Knee Ankle

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

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

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

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

Muscle Fiber Characteristics Three basic types: 1. Type I: -Slow twitch, oxidative, red 2. Type IIb: -Fast twitch, glycolytic, white 3. Type IIa: -FOG