In: Anatomy and Physiology
Answer :
Normally we can idetify objects touched in the absence of light by a mechanism known as to Steriognosis (also known as haptic perception or tactile gnosis ) is the ability to percieve and recognize the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temparature etc, Steriognosis tests determine whether or not the parietal lobe of the brain is intact. Typically these tests involved having the human identify the common objects (e.g, key, comb) placed in their hand without any visual cues.
Asteriognosis is the failure to identify the objects by touching in the absence of visual or auditory information. It may be caused by disease of the sensory cortex or posterior columns, People suffering from Alzeimer's disease show a reduction in steriognosis. Asteriognosis can be caused by damage to the posterior association areas of the parietal, temporal, or occipital lobes or the post central gyrus of either hemisphere.
Mechanism of Neural Pathway
The dorsal column-medial lemnicus pathways is also known as posterior column-medial lemnicus pathway ( PCML). It is the sensory pathway of the central nervous system, is carring sensations of :
This transmits information from the body to the primary somatosensory cortex. This somatosensory cortex situated in the post central gyrus of the parietal lobe of the brain. The pathway recieves information from the sensory receptors throughout the body, and carries this in nerve tracts in the white matter of the dorsal columns of the spinal cord to the medulla, where it is continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted through the somatosensory cortex.
There are three groups of neurons that are involved in the pathway.
The first-order axons make contact with second-order neurons of the dorsal column nuclei (the gracile nuclei and the cuneate nucleus) in the lower medulla.
Sensory information from the upper half of the body is recieved at the cervical level of the spinal cord and carried in the cuneate tract, and information from the lower body is recieved at the lumbar level and carried in the gracile tract. The gracile tract is medial to the more lateral cuneate tract.