Motor Control Flashcards
What is the purpose of the spinal cord in motor programs?
Executive control over motor neurons
What and where are motor neurons, what do they do?
Alpha motor neurons, in the spinal stem, ventral horn of the spinal cord. They are the final pathway for all motor commands
What higher order structures of the brain generate motor programs?
Association cortex, basal ganglia, cerebellum
In what three areas would one find upper motor neurons? What do they project to?
Cerebral cortex, reticular formation, vestibular nuclei. They project to cranial nerve nuclei and lower motor neurons in the spinal cord
What are the two types of lower motor neurons?
Alpha and delta
How are alpha motor neurons arranged?
Arranged somatotopically in the ventral horn
What is the basic reflex arc?
Sensory neuron –> (dorsal horn) inter neuron–> motor neuron
Are interneurons stimulators or inhibitory?
Inhibitory (renshaw 1a inhibitory interneurons)
What two reflexes are tested clinically?
Superficial reflexes (flexor withdrawal, pain response. Tests brain stem, transcortical and propriospinal pathways) Deep tendon reflexes (stretch and tension reflex using 1a, II, Ib afferent pathways to elicit or inhibit muscle contraction)
What are muscle spindles and what do they detect?
Intrafusal fibers, parallel to extramural fibers and surrounded in CT. They respond to changes in muscle length and velocity by stimulating primary (Ia) and secondary (II) afferent neurons
How do spindle neurons work?
Na/Ca physically gated channels connected to each other by spectrin open when the muscle is stretched, allowing influx of ions and AP to travel through the axon
The patellar tap tests the integrity of what reflex?
The myotactic stretch reflex
What is the jendrassik maneuver?
Holding hands against each other to distract the patient during testing of the myotactic reflex
What is reciprocal innervation?
Relaxation if antagonist muscles during agonist muscle contraction
What is the function of gamma motor neurons? How do they work?
Regular muscle spindle sensitivity by contracting around the muscle ends of the spindles. This tonically (not passively stretches the spindle, making Ia fibers more sensitive)
How are game motor neurons controlled?
Brain and brain stem (as speed and difficulty of the movement increase, spindle sensitivity is increased)
Golgi tendon organs regulate:
Muscle tension
What is the inverse myotactic reflex? How does it work?
IIb fibers in the GTOs stimulate excitatory interneurons to antagonist muscles and inhibitory interneurons to agonist fibers
The flexor withdrawal (crossed extensor) reflex involves what neurons?
Propriospinal, interneurons and a motor neurons
What are two purposes of the propriospinal system?
Integrating intersegmental motor responses (eg walking)
Mediates regulatory impact of upper limb cutaneous stimulation on lower limb motor reflexes
Where are propriospinal neurons located?
Medial and lateral ventral horn
What are medial propriospinal neurons, what do they do?
Long propriospinal axons that span the whole spinal cord. Regulate proximal, axial muscles and posture
What are lateral propriospinal neurons, what do they do?
Short propriospinal neurons that regulate distal muscles for independent control of fine movements
What are some function of upper motor neurons?
Fine motor control, posture balance
The motor cortex forms three tracts. What are they and where do they go?
Corticospinal to the ventral horn of the spinal cord
Corticonuclear to cranial nerve nuclei
Corticoreticular tract to the pontine and medullary reticular formation
What are the four descending motor pathways?
Lateral corticospinal tract
Anterior corticospinal tract
Vestibulospinal tract
Reticulospinal tracts
What is the corticonuclear tract, what does it control?
Motor Neurons that join with the cranial nerve nuclei, control muscles of the face, head and neck
What two tracts does the corticospinal tract turn into? Where does this happen and what kinds of motor neurons are involved?
The lateral and ventral (anterior) spinal tract. This occurs at the pyramids (and decussation of the pyramids) in the medulla. Alpha and gamma motor neurons are involved
Which corticospinal tract contains the 10% of uncrossed neurons and controls posture of the neck and trunk?
Ventral (anterior) corticospinal tract
Which corticospinal tract contains 90% crossed neurons and controls fine movement?
Lateral corticospinal tracts
What are the three extrapyramidal pathways?
Corticoreticular, vestibulospinal, reticulospinal
What is the purpose of the vestibulospinal tract? How does it work?
To maintain posture and balance. Information from semicircular canals, saccule, utricle go to the medulla go to the spinal cord to activate extensors of the lower limb and Flexors of the upper limb
Of the lateral and medial vestibular nuclei pathways, which is purely ipsilateral, courses to the lower limbs and is mainly in the ventral part of the spinal cord?
The lateral vestibular nucleus
Of the lateral and medial vestibular nuclei, which contains pathways both ipsilateral and controlateral and controls mainly thoracic, axial and neck muscles?
The medial vestibular nucleus