Theme4. LOWER MOTOR CIRCUITS AND MOTOR CONTROL (v.The lower motor neuron…
Theme4. LOWER MOTOR CIRCUITS AND MOTOR CONTROL
i.Motor functions of the spinal cord. Motor neurons and reflex arcs.
Conveys somatosensorial and visceral information from the body.
Final common pathway for somatomotor and visceromotor systems
Central patterns generator for rythmic movements.
Voluntary Motor cranial verves (Other than III, IV, AND VI pair)
The Hypoglossal Nerves XII
The Accessory Nerves XI unique origin from the spinal cord.
The Glossopharyngeal Nerves IX
Facial Nerves VII
ii.Muscle tone: Muscle stretch reflex, inverse myotaticreflex, and flexor reflex pathways.
The reflex causes the degree of muscle contraction to remain reasonbly constant
Stretch muscle reflexes created by a blow upon a muscle tendon:
Reflex by blow
• Ankle jerk reflex (S1/S2)
• Triceps reflex (C6/C7)
• Extensor digitorium réflex (C6/C7)
• Brachioradialis réflex (C6)
• Bicceps reflex (C5/C6)
• Jaw jerk reflex (CN V)
Golgi tendon organ
Control muscle tension
An encapsulated sensory receptor through which muscle tendon fibers
If excessive load is placed on muscle, Golgi tendon reflex causes relaxation, thereby protecting muscle
Motor neuron is inhibited.
Neuron from Golgy tendon organ fires.
Load is dropped
THE PAIN-WITHDRAWAL (FLEXOR) REFLEX
Circuits to inhibit the antagonist
Diverging circuits to spread the reflex
Circuits to cause after discharge
THE PAIN-WITHDRAWAL (FLEXOR) REFLEX Pathway
3.- Integrating center
4.- Efferent Pathway
2.- Afferent pathway
5.- Effector organs
1.- Sensory receptor (in skin)
iii.Spinal control circuitry and locomotion.
Spinal cord Nerve Anatomy
Associated injuries: Paraplegia
Associated injuries: Tetraplegia
Lumbar sacral coccyx
Allows for the constriction of the pupil when is exposed to bright light.
Serves to regulate the amount of light the retina receives
PHOTOMOTOR REFLEX (MESENCEPHALON)
PONS & MEDULLA:
BLINK AND VESTIBULO-OCULAR REFLEXES
on the center of retinas during head movement.
Grasp Reflex (Palmar and Plantar)
Tonic Neck Reflex
v.The lower motor neuron syndrome.
Loss of muscle tone.
Atrophy: muscle wasting due to denervation and disuse.
Areflexia (loss of reflexes) due to interruption of the efferent (motor) limb of
the sensory motor reflex arcs.
Paresis (weakness) of the affected muscles.
Flaccid paralysis (loss of movement) of affected muscles.
Fibrillations and fasciculations, cause: changes in their excitability and activity respectively
Guillain Barré syndrome
Lower (spinal cord) motor neurons:
(alpha) Motor Neurons:
Are in control of triggering of generation of force by muscles.
(Gamma) Motor neurons
kEEP SPINDLE FIBERS taut, thereby allowing the continued firing of alpha motor neurons