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Ileum, caecum and colon of rabbit, showing Appendix vermiformis on fully functional caecum The human vermiform appendix on the vestigial caecum. The appendix was once believed to be a vestige of a redundant organ that in ancestral species had digestive functions, much as it still does in extant species in which intestinal flora hydrolyze cellulose and similar indigestible plant materials. [10]
A vestigial response or vestigial reflex in a species is a response that has lost its original function. In humans, vestigial responses include ear perking, goose bumps and the hypnic jerk . In humans
The formation of goose bumps in humans under stress is considered by some to be a vestigial reflex, [4] though visible piloerection is associated with changes in skin temperature in humans. [5] The reflex of producing goose bumps is known as piloerection or the pilomotor reflex , or, more traditionally, [ 6 ] horripilation .
In humans, the vermiform appendix is sometimes called a vestigial structure as it has lost much of its ancestral digestive function. Vestigiality is the retention, during the process of evolution , of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. [ 1 ]
The postauricular reflex is a vestigial myogenic [5] muscle response in humans that acts to pull the ear upward and backward. [6] Research suggests neural circuits for auricle orienting have survived in a vestigial state for over 25 million years. It is often assumed the reflex is a vestigial Preyer reflex (also known as the pinna reflex). [7] [8]
This suggests that the grasping reflex is vestigial in humans and in other non-fur carrying primates. [11] The reflex is also suggested to create a basis for which the voluntary grasping action originates. This comes from the maturation of higher motor centers, allowing a child to exert more control over the body. [2]
Humans may have physical remnants of a VNO, but it is vestigial and non-functional. [ 2 ] The VNO contains the cell bodies of sensory neurons which have receptors that detect specific non-volatile (liquid) organic compounds which are conveyed to them from the environment.
A list of reflexes in humans. Abdominal reflex; Accommodation reflex — coordinated changes in the vergence, lens shape and pupil size when looking at a distant object after a near object. Acoustic reflex or attenuation reflex — contraction of the stapedius and tensor tympani muscles in the middle ear in response to high sound intensities.