Your SlideShare is downloading. ×
Upcoming SlideShare
Loading in...5

Thanks for flagging this SlideShare!

Oops! An error has occurred.


Introducing the official SlideShare app

Stunning, full-screen experience for iPhone and Android

Text the download link to your phone

Standard text messaging rates apply



Published on

Published in: Health & Medicine, Technology

  • Be the first to comment

  • Be the first to like this

No Downloads
Total Views
On Slideshare
From Embeds
Number of Embeds
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

No notes for slide


  • 1. THE MOTOR SYSTEM, part I
  • 2. SOMATIC MOTOR SYSTEMMuscles and neurons that control musclesRole: Generation of coordinated movementsParts of motor control Spinal cord coordinated muscle contraction Brain motor programs in spinal cord
  • 3. SOMATIC MOTOR SYSTEMTypes of MusclesSmooth: digestive tract, arteries, related structuresStriated: Cardiac (heart) and skeletal (bulk of body muscle mass)In each muscle there are 100 of muscle fibers innervated by a single axon from the CNS muscle fibers Axon from CNS muscle
  • 4. SOMATIC MOTOR SYSTEMSomatic MusculatureAxial muscles: Trunk movementProximal muscles: Shoulder, elbow, pelvis, knee movementDistal muscles: Hands, feet, digits (fingers and toes) movement Antagonist Synergist Flexors Extensors
  • 5. THE SPINAL CORDThe Lower Motor NeuronLower motor neuron: Innervated by ventralhorn of spinal cordUpper motor neuron: Supplies input to thespinal cord Ventral root Lower motor Ventral horn Spinal neuron nerve Muscle fiber li
  • 6. THE SPINAL CORDAlpha Motor NeuronsTwo lower motor neurons: Alpha and GammaAlpha Motor Neurons directly trigger the contractionof the muscleMotor Unit: muscle fibers + 1 alpha motor neuronMotor neuron pool: all alpha motor neuron thatinnervate a single muscleGraded Control of Muscle Contraction byAlpha Motor NeuronsVarying firing rate of motor neurons (temporalsummation)Recruit additional synergistic motor units.More motor units in a muscle allow for finelycontrolled movement by the CNS
  • 7. THE SPINAL CORDInputs to Alpha Motor Neurons1) Information about muscle lenght2) Voluntary control of movement3) Excitatory or inhibitory in order to generate a spinal motor program 3 1 2
  • 8. THE MOTOR UNITSTypes of Motor UnitsRed muscle fibers: Large number of mitochondria and enzymes, slow to contract, can sustain contractionWhite muscle fibers: Few mitochondria, anaerobic metabolism, contract and fatigue rapidlyFast motor units: Rapidly fatiguing white fibersSlow motor units: Slowly fatiguing red fibersHypertrophy: Exaggerated growth of muscle fibersAtrophy: Degeneration of muscle fibers Normal Crossed innervation innervation slow fast slow fast slow fast Fast like Slow like
  • 9. THE MOTOR UNITSMuscle fiber structure Mitochondria MyofibrilsSarcolemma: external membraneMyofibrils: cylinders that contract after an APSarcoplasmic reticulum: reach of Ca2+T tubules: network that allow the AP to gothrough T tubules Sarcoplasmic reticulum Opening of T tubules Sarcolemma
  • 10. THE MOTOR UNITSThe Molecular Basis of Muscle ContractionZ lines: Division of myofibril into segments by disksSarcomere: Two Z lines and myofibrilThin filaments: Series of bristles. Contains actinThick filaments: Between and among thin filaments. ContainsmyosinSliding-filament model: Binding of Ca2+ to troponin causesmyosin to bind to actin. Myosin heads pivot, cause filamentsto slide
  • 11. THE MOTOR UNITSMuscle contraction Excitation: Action potential, ACh release, EPSP,Alpha motor neurons release ACh action potential in muscle fiber, depolarizationACh produces large EPSP in muscle fibers (via Contraction: Ca2+, myosin binds actin, myosinnicotinic ACh receptors) pivots and disengages, cycle continues untilEPSP evokes action potential. Ca2+ and ATP presentAction potential triggers Ca2+ release, leads to Relaxation: EPSP end, resting potential, Ca2+ byfiber contraction ATP driven pump, myosin binding actin coveredRelaxation, Ca2+ levels lowered by organellereuptake
  • 12. SPINAL CONTROLMuscle spindles: specialized structures inside the skeletal muscle. They informabout the sensory state of the muscle (proprioception)
  • 13. SPINAL CONTROLThe Myotatic ReflexStretch reflex: Muscle pulled tendency to pull backFeedback loop. MonosynapticDischarge rate of sensory axons: Related to muscle lengthExample: knee-jerk reflex (stretching the quadriceps and consequent contraction)
  • 14. SPINAL CONTROLIntrafusal fibers: gamma motor neuronExtrafusal fibers: alpha motor neuron Gamma Loop Provides additional control of alpha motor neurons and muscle contraction Circuit: Gamma motor neuron intrafusal muscle fiber Ia afferent axon alpha
  • 15. SPINAL CONTROLProprioception from Golgi Tendon Organ.In series with the muscle fibers. Information about the tension applied to the muscleReverse myotatic reflex function: Regulate muscle tension within optimal rangeGolgiTendonOrgan
  • 16. SPINAL CONTROLSpinal InterneuronsSynaptic inputs1)Primary sensory axons2)Descending axons from brain3)Collaterals of lower motor neuron axonsSynaptic outputs: alpha motor neuronReciprocal inhibition: Contraction of one muscle set Crossed-extensor reflex: Activation of extensoraccompanied by relaxation of antagonist muscle muscles and inhibition of flexors on opposite sideExample: Myotatic reflex flex flex extend extend