Question

In: Anatomy and Physiology

Describe the various neural pathways involved in picking up a penny in the dark and how...

Describe the various neural pathways involved in picking up a penny in the dark and how do these pathways work?

I know the pathways are motor, sensory, and integrative, but I need help piecing it all together. Thanks

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Expert Solution

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 :

  • Fine touch
  • vibration
  • two-point discrimination
  • position from the skin and joints.

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.

  • First order neurons : These are sensory neurons located in the dorsal root ganglia, that send their afferent fibers through the two dorsal columns : cuneatefasciculus (cuneate tract) and gracile fasciculus ( gracile tract).

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.

  • The second oreder neurons send their axons to the thalamus. The axons of the second order neurons of the gracile and cuneate nuclei are known as the internal arcuate fibers. When these fibers crossed over the midline at the sensory decussation in the medulla, they form the medial lemniscus. This is connects with the thalamus.
  • The third order neurons are in the ventral nuclear group in the thalamus and fibers from these ascend to the post central gyrus.

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.


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