Gracile projection to the cat medial accessory olive: Ultrastructural termination patterns and convergence with spino-olivary projection

The inferior olivary body or nucleus forms the ovoid projection which extends almost the whole length of the medulla oblongata, from the lower margin of the pons Varolii to within a short distance of the level of the decussation of the anterior pyramids. It is separated from the latter by a groove through which emerge the roots of the hypoglossal nerve. On its outer margin it is separated from the line of the roots of the glossopharyngeal and pneumogastric nerves by a shallow depression. Transverse vertical and longitudinal sections of the medulla show the olive to be a highly convoluted sac of grey matter open, at its hilum, towards the mesial plane. (It has two accessory nuclei of smaller size, an internal and a posterior accessory olive, which, as they are really parts of the larger nucleus, do not call for special consideration here.) The fibres of the hypoglossal nerve pass through its substance, but do not become, as was at one time supposed, and as has been recently again affirmed by Vincenzi, connected with the olive. On its median aspect lies the interolivary stratum or fillet. Anteriorly lies the anterior pyramid, posteriorly the formatio reticularis.

Download Full-text

Reduction of rostral dorsal accessory olive responses during reaching

Journal of Neurophysiology ◽

10.1152/jn.1996.76.6.4140 ◽

1996 ◽

Vol 76 (6) ◽

pp. 4140-4151 ◽

Cited By ~ 32

Author(s):

K. M. Horn ◽

P. L. Van Kan ◽

A. R. Gibson

Keyword(s):

Receptive Fields ◽

Evoked Response ◽

Active Movement ◽

Light Touch ◽

Reaching Task ◽

Highly Sensitive ◽

Lower Amplitude ◽

Limb Posture ◽

Accessory Olive ◽

Stimulation Of

1. Rostral dorsal accessory olive (rDAO) neurons are sensitive to light touch but have little or no discharge during active movement. We hypothesize that sensitivity of the rDAO is reduced during movement. To test this hypothesis, we evaluated sensitivity of rDAO neurons as cats reached out and retrieved a handle. On selected trials, mechanical or electrical perturbations to the forelimb were presented, and responses of rDAO neurons to the disturbances were recorded. 2. All rDAO units were highly sensitive to somatosensory stimuli during periods of stance. The cells responded to stimuli such as touch to hairs or light taps to the platform on which the cat was standing. 3. Discharges of rDAO neurons showed little or no synchronization to any aspect of the reaching task. rDAO neurons failed to fire to mechanical perturbations of the food handle during retrieval or hold phases of the task, even when their receptive fields included the surface of the paw in contact with the handle. 4. Electrical stimulation of the skin produced the greatest evoked response at all rDAO recording sites when the cats were at stance. Stimulation at any time during the reaching task, including periods of holding and licking, produced lower-amplitude evoked responses. The reduction in evoked response could be large and was restricted to the limb performing the task. 5. The data support the hypothesis that the cutaneous sensitivity of the rDAO is reduced during behavior. However, the inhibition does not appear to be tailored to specific times during the task or to neurons with specific receptive field locations on the actively moving limb. The reduction in sensitivity is as likely to be dependent on limb posture as on movement. We conclude that the rDAO discharge provides the cerebellum with information about vibration or contact during stance; it does not provide reliable information about undisturbed or disturbed movement. Climbing fiber input from rDAO might be useful in the preparation to make a movement, but it is probably not useful for correction of movement errors.

Download Full-text