Renshaw cell

named for its discoverer, Birdsey Renshaw (1911- 1948)
German: Renshaw-Zelle

1 Definition

Renshaw cells are inhibitory interneurons of the spinal cord that connect to alpha motoneurons.

2 Anatomy

Renshaw cells lie next to the alpha motoneurons of the anterior gray column (cornu anterius medullae spinalis). They receive input from:

• the descending tracts of supra-spinal origin and
• the axon collaterals of alpha motoneurons

3 Physiology

The neurotransmitter activating Renshaw cells is acetylcholine. Subsequent to their activation, Renshaw cells create an inhibitory postsynaptic potential (IPSP) within the alpha motoneurons by means of inhibitory neurotransmitters glycine and gamma-Aminobutyric acid (GABA). Alpha motoneurons are multipolar neurons so they have a large number of dendrites. The result of their activity is determined by the sum of all excitatory (EPSP) and inhibitory (IPSP) inputs. This means that Renshaw cells have more of a modulating than a pure inhibitory influence on the activity of motoneurons.

3.1 Renshaw cell inhibition

The inhibitory effect of Renshaw cells is called Renshaw cell inhibition. This inhibition prevents overshooting muscle contraction as a result of the muscle's proprioceptive reflex.

Alpha motoneurons create a negative feedback loop by causing cholinergic activation of Renshaw cells. This activation of Renshaw cells inhibits the same alpha motoneurons that activated it. This process is called recurrent inhibition.

see also: neuronal inhibition

4 Clinical significance

Wound infection with Clostridium tetani causes a pathological disturbance of Renshaw inhibition. The bacteria's toxin reaches the spinal cord via retrograde axonal transport through peripheral nerves or via the blood circulation. There it prevents the release of inhibitory neurotransmitters from the Renshaw cells. Breakdown of Renshaw inhibition first causes hyperreflexia. Later the separate muscular twitches merge into one permanent contraction (spasm) because the alpha motoneurons are activated constantly. This permanent contraction is the reason for the typical signs of tetanus: risus sardonicus, opisthotonus, convulsion.

see also: Tetanus, Tetanospasmin