Neurons And Cells Essay

2359 words - 10 pages

Physiological context

Previous to Henneman’s publishing his series of papers, there were three other major constituents that have been well researched and provided the foundations to this paper.

At the commencement of the 20th century, Sherrington was the first person to describe the minute gap between neurons connecting different cells it was termed the ‘synapse’. Over numerous years of studying Sherrington concluded his findings to a theory he stated that “the nervous system acts as a coordinator of various parts of the body and that reflexes are the simplest expressions of the action”(Issue, 2010).

A synapse is a connection for reflex arc function, the neurone theory and the synaptic transmission (Pearce, 2004). Upon this theory from Sherrington, Henneman was able to provide an extension to that presenting a theory of motor control, which is widely accepted by neurophysiologists. At that time Henneman looked beyond the individual units and sought to find answers to how the individual units act together to achieve harmonized control function in complex systems (Henneman, Somjen, & Carpenter, 1965).

Experimental approach

35 cats 9 (average weight 3.2kg) had a tracheal cannula inserted and decerebrated by a small opening in the skull. Fixing the distal left femur stabilized the pelvis; all the nerves innervating the left hind limb were cut except the ones innervating triceps surae. These muscles were dissected back to allow placements of electrodes.

The achillies tendon was freed and attached to a myograph, which consisted of a mechano-electric transducer (Grass model FT10 which fed into a Tektronix type Q unit). The transducer gave a linear signal of up to 10kg tension. The L7 to S1 ventral roots were exposed, the ventral roots were obtained for recording by the incision of small strands. These filaments were mounted on a silver electrode under mineral oil and the discharges of the triceps units were recorded oscillographyically. Filaments that contained 2 to 4 axons with no evidence of conduction blocks were studied.

Data recordings were made using two Grass P5 preamplifiers and a Tektronix RM565 dual beam oscilloscope with split beams. One beam displayed filament discharge, one tension measurement, and one functioned as a base line for the tension measurement. The calibrations were made with hanging weights in a pan from the transducer (Henneman et al., 1965).

Principal findings

The central part of motorneurons and its significance of its size in synaptic transmission, concentrates on the cell bodies (and dendrites) connected to small and large fibres have different functional properties, which can be predicted by their discharge characteristics.

Henneman concluded that the general stretch threshold of motor units is directly associated to the relative size of the action potentials emitted from the axons. From the experiment it was found that larger spikes were interpreted as...

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