FISIOLOGIA DE LA UNIDAD MOTORA Josep Valls Solé Hospital Clínic

Concepto de unidad motora La unidad motora está formada por: una motoneurona del asta anterior, su axón y las fibras musculares que inerva

Electromiografia de inserción Potencial de unidad motora

Motoneurona alfa Activación fisiológica del cuerpo de la motoneurona Renshaw Inhibición presináptica Ib Interneurona Ia (antagonista) Interneuronas propiospinales Aferentes grupo II Tractos descendentes córtico- retículo- vestíbulo- rubro- espinales Activación anormal de la unidad motora Cambios en la excitabilidad neuronal después de lesión nerviosa Anormalidades en la excitabilidad de axones terminales.

EPSP threshold AHP Histogram of motor unit discharges Motor response Silent period Rebound

Mecanismos de rebote post-inhibición y de inhibición post-facilitación

H wave MEP dorsal root ganglion Ia fibre motor axons H wave stimulus Supraespinal innervation dorsal root ganglion Ia fibre motor axons H wave stimulus H wave recording

A C 50 ms S B ms S Figure 2

Período de silencio en la musculatura tenar

Size of the Vp of the thenar muscles at different levels of force Stimulus at the wrist Size of voluntary potential Stimulus at the axilla Force Kimura J. Electrical activity in voluntarily contracting muscle. Arch Neurol, 1977; 34: 85-88

CHANGES OCCURRING AFTER A PERIPHERAL NERVE LESION Schwann’s cell nucleus muscle fiber node of Ranvier axon cell body basal lamina myelin Wallerian degeneration mycroglial cells K+ Ca++ Protein Na+ growing cone basal lamina tube Schwann’s cell band of Bungner

Abnormal regeneration after a nerve lesion

MN1 MN2 MN1 MN2 cortical motoneuron cortico- spinal tract two different muscles innervated by the same nerve two motor axons going to the same muscle spinal motoneuron motor axon muscle

Musculo-cutaneous nerve territory Innervation of a single large muscle Ulnar nerve territory Innervation of many muscles with antagonistic functions muscle afferents motor axon flexor muscle

EMG hypothenar 1 month Recordings of regenerating axonal activity from 6 patients who suffered ulnar nerve injury 3 months

Recording with needle in hypothenar 3 months Left ulnar nerve Recording with needle in hypothenar Wrist 55.5 Elbow 62.0

Action potential recorded at the wrist 18 months Action potential recorded at the wrist to surface stimulation of the Vth digit 5 ms Motor Response ? SNAP

Possibilities of abnormal nerve regeneration Montserrat et al. Muscle Nerve, 1990; 13:501-507 α motoneuron α motoneuron dorsal root sensory cell α motoneurons ephapsis branching hypothenar muscles digital nerve

Needle recording in hypothenar muscle Surface ring electrodes stimulation of the digital nerves of the Vth finger JGJ 12 months Ephaptic transmission or axonal reflex Motoneuronal response 50 ms 20 ms 24 mA 38 mA

JBV. Electromyographic activity observed at rest Hypothenar First interosseous 10 ms 0.2 mV JBV. Electromyographic activity observed at rest in ulnar nerve innervated muscles in the right hand