Aspects of Muscle Physiology & Neurophysiology
Kinesiology and Biomechanics
April 16, 2013
Structure of the Skeletal Muscle
Structural Basis For Muscle Contraction And Relaxation
Excitation of Nerve and Skeletal Muscle Fibers
Sliding Filament Theory
Energy Sources for Muscle Contraction
Muscle Fiber Types
The Motor Unit
Nerve Fibers
Joint, Tendon and Muscle Receptors
Kinesiology
Nervous System
CNSPNS
Sensory PortionMotor Portion
Organization of Muscles
superficial and deep fascia
Muscle Epimysium
FasciculusPerimysium
Muscle FiberEndomysium
MyofibrilMyofilament
Structure of the Skeletal Muscle
Organization of Muscles
superficial and deep fascia
Muscle Epimysium
FasciculusPerimysium
Muscle FiberEndomysium
MyofibrilMyofilament
Structure of the Skeletal Muscle
Organization of Muscles
superficial and deep fascia
Muscle Epimysium
FasciculusPerimysium
Muscle FiberEndomysium
MyofibrilMyofilament
Structure of the Skeletal Muscle
Organization of Muscles
superficial and deep fascia
Muscle Epimysium
FasciculusPerimysium
Muscle FiberEndomysium
MyofibrilMyofilament
Structure of the Skeletal Muscle
Structural Basis For Muscle Contraction And Relaxation
Structural Basis For Muscle Contraction And Relaxation
Nerves and Muscle
• Excitable = depolarized• Excitable and propagates along the
membrane = ACTION POTENTIAL
Excitation of Nerve and Skeletal Muscle Fibers
Membrane Potential
• Resting Membrane Potential• Action Potential
• Depolarization• Repolarization
Excitation of Nerve and Skeletal Muscle Fibers
Membrane Potential
• Resting Membrane Potential• Action Potential
• Depolarization• Nerve impulse – nerve fiber• Muscle impulse – muscle fiber
• Repolarization – active process, re-establish RMP
Excitation of Nerve and Skeletal Muscle Fibers
Membrane Potential
• Cell membrane is relatively impermeable to certain ions
• The cell can actively move ions across the membrane to maintain a required resting potential
Excitation of Nerve and Skeletal Muscle Fibers
ACTION POTENTIAL
• Depolarizes the membrane and establishes a difference in electrical potential between active and inactive regions CURRENT FLOW
Excitation of Nerve and Skeletal Muscle Fibers
NEUROTRANSMISSION
• Neurons send control signals to other neurons or muscles releasing small chemicals (neurotransmitters)
• Nerve impulse synapse neurotransmitter are released• EXCITATORY depolarization• INHIBITORY hyperpolarization negative
potential of postsynaptic membrane postsynaptic neuron inactive
• (AP of inhibitory impulses = facilitatory impulses; NT released in the presynaptic ending of inhibitory neuron produces hyperpolarization of the postsynaptic membrane)
Excitation of Nerve and Skeletal Muscle Fibers
NEUROTRANSMISSION
• Neurons send control signals to other neurons or muscles releasing small chemicals (neurotransmitters)
• Nerve impulse synapse neurotransmitter are released• EXCITATORY depolarization• INHIBITORY hyperpolarization negative
potential of postsynaptic membrane postsynaptic neuron inactive
Excitation of Nerve and Skeletal Muscle Fibers
Myoneural Junction
• Contains mitochondria manufacture neurotransmitters (ACTH)
• Nerve impulse release of ACTH receptors of the muscle fiber increases the permeability of ions muscle cell depolarizes muscle action potential
• ACTH is rapidly inactivated by cholinesterase splits ACTH
Excitation of Nerve and Skeletal Muscle Fibers
Conduction of Muscle Impulse to the Interior of the Muscle Fiber
• ENDOPLASMIC RETICULUM• Transverse tubular system (T system) speeds the
transmission of muscle action potential• Sarcoplasmic reticulum storage and release of
calcium ions
• Excitation-Contraction Coupling
• SLIDING FILAMENT THEORY OF MUSCLE CONTRACTION
Excitation of Nerve and Skeletal Muscle Fibers
Sliding Filament Theory
Exposure of the attachment site
Formation of Cross bridges
Sliding Filament Theory
Power StrokeEnergy stored is used to
move myosin head
ATP binds to Myosin head
Rephosphorilation of ATP
Sliding Filament Theory
Cross-bridge release
ATP breakdown; myosin head release
from the actin
Recovery StrokeReturning to resting
position; energy stored in the myosin
head
Anaerobic Metabolism Phosphagen System
Glycogen-Lactic Acid
Aerobic Metabolism Oxidative
Energy Sources of Muscle Contraction
Anaerobic Metabolism Phosphagen System
• Source of energy: • ATP ADP + PO4 + energy (first 5-6 secs)• CrPO4 Cr +PO4 +energy (next 5-10 secs)
• Sudden burst of activity POWER
• 100 meter dash, diving, jumping, weight lifting
Energy Sources of Muscle Contraction
Glycogen- Lactic Acid System
• Source of energy: • Glycogen
2 mechanism• Anaerobic Stage• Aerobic Stage
Energy Sources of Muscle Contraction
AnaerobicGlucose 2 pyrovic acid and 1
ATP (glycolysis)
AerobicPyrovic acid mitochondria
• With oxygen glycogen breakdown ATP
• Without oxygen glycogen breakdown Lactic Acid
Glycogen- Lactic Acid System
• 30-90 seconds of activity • Last longer than the phosphagen system; less
amount of energy• Provides additional power needed for
IMMEDIATE duration• An athlete who use this system has to rest for
48h before engaging to another activity to allow adequate replenishment for the system
Energy Sources of Muscle Contraction
Aerobic (Oxidative) System
• Least amount of ATP• Energy for an indefinite period of time
ENDURANCE• Oxidation of nutrients
• Carbohydrates best absorbed after 2 days• Protein best absorbed after 5 days
• Recovery is greatly affected by the type of diet
Energy Sources of Muscle Contraction
ENERGY SYSTEM SPORTS
Phosphagen System 100 m dash, JumpingWt. liftingDivingFootball dashes
Phosphagen +Glycolytic Lactic acid System
200 m dashBasketballBaseball (home run)Ice hockey dashes
Glycogen-Lactic Acid System
400 m dash, 100 m swimTennissoccer
Glycolytic Acid +aerobic System
800 m dash, 200 m swim, 1500 m skatingboxing2000 m rowing, 1500 m run, 1 mile run, 400 m swim
Aerobic system 10,000 m skating, Cross-country skiing, Marathon, Jogging
MET (Metabolic Equivalent)
• Energy requirements for various activities• Resting oxygen consumption of an individual • Average value at rest: 3.5 mL of O2/kg/BW/min
• Energy cost of any particular activity VARIES depending on the intensity of the activity
Energy Sources of Muscle Contraction
• TYPE I• TYPE IIB• TYPE IIA
Muscle Fiber Types
• Other names?• Muscle fiber diameter?
• Color?• Oxidative enzymes?• Glycolytic enzymes?• Speed of contraction?
• Rate of fatigue?
Slow oxidative fast oxidative fast glycolytic
Slow-oxidative Fast-oxidative Fast-glycolytic
mitochondria many many few
capillaries many many few
myoglobin content
high high low
myosin ATPase activity
low high high
contraction velocity
slow fast fast
rate of fatigue slow intermediate fast
muscle fiber diameter
small intermediate large
innervating neuron size
small intermediate large
motor unit size small intermediate large
Motor UnitIndividual motor neuron + axon + all muscle fiber
(innervated by a single nerve)
Innervation ratioAverage number of muscle fibers per motor unit in a
given muscleIncrease dissemination of nerve to elicit a muscle
contraction
All-or-none lawEither all or no muscle will contract
The Motor Unit
Gradation Strength of Muscle Strength
increased in strength of contraction of muscle, occurs in 3 ways
• Initially activating motor neuron with smallest innervation ratio activating few muscle fibers
• Increasing the number of motor units activated simultaneously (recruitment)
• Increasing the frequency of stimulation of individual motor unit increasing the % of time of muscle fiber in developing tension
The Motor Unit
Size Principle of Recruitment
Smallest motor neurons FIRST to be recruited; Largest motor neurons are LAST to be
recruited
The Motor Unit
Nerve Fibers
Peripheral nerves contain one or more of the following classes of fibers
• Efferent motor fibers• Motor units conduct nerve impulses from the SC
towards the skeletal muscle (control voluntary muscular activity)
• Afferent sensory fibers• Sensory fibers from the various receptors of the CNS
• Autonomic fibers• Concerned with involuntary control of glandular
activities and smooth muscle
Nerve Fibers
Classification of Motor and Sensory Nerve Fibers (AXONAL DIAMETER)
• TYPE A large, myelinated• Alpha: motor, extrafusal fiber of muscle spindle
• Beta: sensory; afferent to meissner’s corpuscles (touch,
pressure, position and movement sense)
• Gamma: motor, intrafusal fiber of muscle spindle
• Delta: sensory; afferent in monitoring quick pain, temp and
light touch
• TYPE B intermediate, myelinated• TYPE C small diameter, un-myelinated
Nerve Fibers
Classification of Sensory Fibers (FIBER ORIGIN)
• Group Ia• Carry impulses that is located in muscles• Muscle spindle primary receptor
• Group Ib• Carry impulses that is located in tendons• GTO
• Group II• Carry impulses that is located in muscles• Muscle spindle secondary receptor
Nerve Fibers
Specialized receptors in joints, tendons, and skeletal muscles
Detects changes in tension and position of the structure
Joint, Tendon and Muscle Receptors
JOINT RECEPTORS
• Stimulated by being deformed• Depending on the location and
magnitude of the deforming force acting on the joint
Joint, Tendon and Muscle Receptors
GTO (Golgi Tendon Organ)
• Stimulated by STRETCH/TENSION• Group Ib• Within the muscle tendon
• Average of 10-15 muscle fibers are usually connected in direct line series with each GTO
Joint, Tendon and Muscle Receptors
GTO (Golgi Tendon Organ)
• Impulses of GTO nerve arrives at SC excites INHIBITORY neuron, that inhibits A-alpha neurons of the contracting muscle
Eg. PATELLAR REFLEX
Joint, Tendon and Muscle Receptors
Muscle Spindle
• EXTRAFUSAL fibers (regular muscle fibers)
• INTRAFUSAL fibers (3-10 small muscle fibers)
Joint, Tendon and Muscle Receptors
Primary Ia afferent• Primary sensory
endings• Detects the amount
and velocity of stretch• “NUCLEAR BAG”
Secondary II afferent• Secondary sensory
endings• Detect the amount of
stretch• “ NUCLEAR CHAIN”
Joint, Tendon and Muscle Receptors
SENSORY PART
• Primary:
• Annulospiralsupplies the nuclear bag and chain
• Secondary:
• Flower Spray supplies the nuclear chain only
Joint, Tendon and Muscle Receptors
MOTOR PART• Nuclear Bag mm spindle
• Plate Endings• Nuclear chain mm spindle
• Train Endings
Joint, Tendon and Muscle Receptors
MUSCLE SPINDLE
• Inhibitory in Nature
• When muscle is stretched, it send impulses to higher brain and send impulse to endings causing the muscle spindle to RELAX or LENGTHEN.
• Prevents muscle tear
Joint, Tendon and Muscle Receptors
CLINICAL CONDITIONS REGARDING MOTOR CONTROL
Insufficient Muscle Tone
Muscle Weakness and Atrophy
Excessive Muscle Tone
HYPOTONIA
FLACCIDITY
DISUSE ATROPHY
DENERVATION ATROPHY
SPASTICITY
RIGIDITY
Aspects of Muscle Physiology & Neurophysiology
Summer 2013: Kinesiology and Biomechanics
THANK YOU!April 16, 2013