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A section through a mouse vertebra at 200x magnification

The vertebrae that make up our spine have the critical task of housing and protecting the spinal cord, a thin bundle of nervous tissue hooked up directly to the brain. The spinal cord in part transmits movement information from the brain to the muscles. In fact, the function of the spinal cord can be divided into segments based on the muscles they control: Nerves from the lower vertebrae in the neck help extend the elbows and flex the wrists, while nerves from the lower back vertebrae assist in extending the legs and toes. Spinal cord injury can result in different degrees of paralysis depending on which segment was affected.

Image by  Dr. Michael Nelson and Samantha Smith, University of Alabama at Birmingham.



Commensal Life on Fire Urchins

Fire urchins are named for their red and orange colouration, as well as the burning sting they deliver if touched. Several species of crustaceans have evolved alongside these urchins and live their entire lives amongst their host’s spines. The commensal animals take advantage of the urchin’s bright warning colours and toxicity, which provides a safe haven away from predators. Although they generally do not harm their host, the shrimp may remove spines from a small area of the urchin to perch on.

Coleman’s Shrimp (Periclimenes colemani)

Fire Urchin (Asthenosoma varium)

Zebra Crab (Zebrida adamsii)

Images: Raymond on Flickr, Candice Pratt via Wikimedia Commons, Klaus Stiefel on Flickr

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