Aspects of Muscle Physiology & Neurophysiology

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

Structural Basis For Muscle Contraction And Relaxation

Nerves and Muscle

• Excitable = depolarized• Excitable and propagates along the

membrane = ACTION POTENTIAL


Membrane Potential

• Resting Membrane Potential• Action Potential

• Depolarization• Repolarization


Membrane Potential

• Resting Membrane Potential• Action Potential

• Depolarization• Nerve impulse – nerve fiber• Muscle impulse – muscle fiber

• Repolarization – active process, re-establish RMP


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


ACTION POTENTIAL

• Depolarizes the membrane and establishes a difference in electrical potential between active and inactive regions CURRENT FLOW


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)


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


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


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



Exposure of the attachment site

Formation of Cross bridges


Power StrokeEnergy stored is used to

move myosin head

ATP binds to Myosin head

Rephosphorilation of ATP


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


Glycogen- Lactic Acid System

• Source of energy: • Glycogen

2 mechanism• Anaerobic Stage• Aerobic Stage


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


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 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


• 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 RECEPTORS

• Stimulated by being deformed• Depending on the location and

magnitude of the deforming force acting on the joint


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


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


Muscle Spindle

• EXTRAFUSAL fibers (regular muscle fibers)

• INTRAFUSAL fibers (3-10 small muscle fibers)


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”


SENSORY PART

• Primary:

• Annulospiralsupplies the nuclear bag and chain

• Secondary:

• Flower Spray supplies the nuclear chain only


MOTOR PART• Nuclear Bag mm spindle

• Plate Endings• Nuclear chain mm spindle

• Train Endings


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


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

Aspects of Muscle Physiology & Neurophysiology

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