Faculty Collaboration Database

Afferent mechanisms for the reflex response to imposed ankle movement in chronic spinal cord injury. Exp Brain Res 2002 Jul;145(1):40-9

Date

06/19/2002

Pubmed ID

12070743

DOI

10.1007/s00221-002-1080-2

Scopus ID

2-s2.0-0036080606 (requires institutional sign-in at Scopus site)   39 Citations

Abstract

We have reported earlier that externally imposed ankle movements trigger ankle and hip flexion reflexes in individuals with spinal cord injury (SCI). In order to examine the afferent mechanisms underlying these movement-triggered reflexes, controlled ankle movements were imposed in 17 SCI subjects. In 13 of these subjects, reflex torques were recorded at the hip, knee and ankle in response to 5 ankle movement ranges, and 4 movement speeds. Subjects were tested using both ankle plantarflexion and dorsiflexion movements. The principal outcome measure, peak hip flexion torque of the induced reflexes, was used for comparing the effects of movement range and speed on the reflex response. We found that movement-triggered reflexes were sensitive to the angular range of ankle deflection, but insensitive to the velocity of the movement. Movement amplitudes sufficient to trigger hip and ankle flexion were routinely associated with increases in ankle passive force, suggesting that force-sensitive receptors participated in the reflex response. However, increases in angular range also corresponded to increases in muscle length, making it difficult to distinguish whether the response was triggered by a load-sensitive receptor (e.g., Golgi tendon organ or muscle free nerve ending) or a position-sensitive receptor responsive to absolute ankle angle (e.g., muscle spindle secondary afferent). The absence of velocity dependence of the reflex suggested that spindle Ia afferents were not major contributors. These results suggest movement-triggered reflexes originate in muscle receptors that are sensitive to either absolute muscle length, to muscle force or to both. Although receptors that are sensitive to absolute muscle length cannot be excluded with certainty, the finding that reflex responses require that ankle movements elicit an increase in passive force argues for a prominent role of nonspindle mechanoreceptors, such as group III/IV muscle afferents. These afferents are activated preferentially as muscles are stretched to near maximum length, and they appear to have potent reflex effects in spinal cord injury.

Author List

Schmit BD, Benz EN, Rymer WZ

Author

Brian Schmit PhD Professor in the Biomedical Engineering department at Marquette University

MESH terms used to index this publication - Major topics in bold

Adolescent
Adult
Afferent Pathways
Ankle
Chronic Disease
Hip
Humans
Knee
Mechanoreceptors
Movement
Muscle Contraction
Muscle Spindles
Muscle, Skeletal
Physical Stimulation
Proprioception
Reflex
Reflex, Stretch
Skin
Spinal Cord
Spinal Cord Injuries
Torque
Weight-Bearing