선린대 로고 선린대학교 물리치료과

1. The more ventral parts if the ventral horn contain laminae VIII and IX of rexed
   • It receives supramaginal and dorsal root fibers
   • It connect with ventral horn motorneurons
2. Somatic nuclei. Lamina IX contains the medial and lateral motor cell columns
   • The medial motor cell column innervates the axial muscles
   • The lateral motor cell column innervates the appendicular muscles

1. Motorneurons of the ventral horn belong to one of two types:
   • a. Large, or alpha, motorneurons
   • b. Small, gamma, motorneurons
2. Characteristics of alpha motorneurons
   • a. In general, large perikarya have large dendritic trees, large axons, or both
     • Ventral motorneurons
     • GSE neurons in the spinal cord and brainstem
     • Special visceral efferent neurons(SVE) 0f the brainstem
     • Lamina IX of the Rexed
     • Lower motorneurons(LMNs)
     • Final common pathway
3. Gamma motorneurons
   • a. The smaller gamma motorneurons of the ventral horn send gamma-sized axons into the peripheral nerves
   • b. The axons of gamma motorneurons end on specialized skeletal muscle fibers contained in muscle spindle

• a. Definition. A motor unit is an alpha motorneuron, its axon, and all of the muscle fibers it innervates
• b. A motor unit is the smallest unit of behavior because the neuron responds on all-or-none principle, the axon conducts on an all-or- none, and muscle fiber responds all-or-none

Motor unit fasciculation

disease may destabilize the membrane of the alpha motorneuron or its axon, causing impulses to arise spontaneously, rather than in response to normal synaptic excitation. Thus motor unit is the anatomical unit, functional, pathologic, and regenerative unit of the neuromuscular system.

Renshaw cell

• The alpha motorneuron send a collateral axon to an interneuron, the Renshaw cell, which sends an inhibitory synapse back to the alpha motorneurons
• Physiological or pathological changes in the balance of excitatory and inhibitory impulses playing on the Renshaw cells and alpha motorneurons may cause the MSRs to be hyperactive or hypoactive, which can be detected when the clinical elicits the MSRs.

1. Ascending pathways run in each of the three columns of white matter, the dorsal, lateral, and ventral
2. Ascending long pathways all transmit information derived from sensory
   • receptors and destined to:
   • a. Produce conscious sensation, somatic or visceral
   • b. Mediate reflexes, somatic or visceral
   • c. Guide the motor centers in the cerebellum, brainstem, diencephalon, basal ganglia, and cortex

Ascending somatosensory pathways that mediate conscious sensation include the :

• a. Lateral spinothalamic tract (pain and temperature)-Neospinothalamic tract
• b. Ventral spinothalamic tract ( touch)-Paleospinothalamic tract
• c. Fasciculus gracilis and cuneatus of the dorsal column (discriminative modalities: touch, form, texture, position sense)

Ascending somatosensory pathways that mediate unconscious sensory function Include the :

• a. Spinocerebellar pathways provide information to the cerebellum for the coordination of volitional movements
• b. Spinoreticular pathways provide information to the brainsrem, tegmentum and reticular formation to mediate somatic and vesceral reflexes

• Information that travels in the spinocerebellar tracts is not consciously perceived
• Used for unconscious adjustments to movement and posture Because the internal feedback tract
• convey descending motor information to the cerebellum prior to information reaching the motor neurons Because the high-fidelity pathways
• convey information from the muscle spindle, golgi tendon organs and cutaneous mechanoreceptor

The cerebellum obtains information about the movements and postural

Adjustments that followed the command. Thus, cerebellum compare the intended motor output with the actual movement output.