Wednesday 15 March 2023

Cerebral Structure and Function: BRAINCHECK

Visual cortex
Homonomous hemianopsia
Bitemporal hemianopsia
Motor homunculus
More to follow

Authors' Note: 

   Korbinian Brodmann (1868–1918) was a German neurologist famous for his definition of 52 cerebral cortical areas based on their histological (tissue-architecture) characteristics. Functional correlates were defined for many of these areas, and the primary and subsidiary areas of visual interpretation are often described by their Brodmann numbers. 
   The primary visual cortex, straddling the calcarine (Latin: spur) sulcus (fissure or slit), is located on the inner surface of each cerebral hemisphere's occipital lobe, well protected from injury.

Authors' Note:  Lesions in the occipital, or posterior portion of the brain's cerebral hemispheres are notorious for producing visual disruption. Each side of this sensitive area of brain tissue is targeted at integrating one half of the patient's visual field (to left or right). So for example, a tumour in the right side of the occipital lobe interrupts the signals arriving from the nerve fibres in the right side of the retina in both eyes; the patient's ability to see objects in the well-defined semi-circular zone to his left is eliminated in a fashion that is homonomous, i.e. congruent - both eyes are affected similarly. The resulting pattern of contralateral loss of visual sensation (homonomous hemianopsia) may be mapped by a test known as perimetry (visual-field analysis).


Authors' Note: Loss of sight in half of the visual field in an eye is a medically well-characterized and significant lesion known as hemianopsia, or occasionally hemianopia. An attack on the underlying lesion, often deep within the brain is in the province of neurosurgeons, and often a multidisciplinary team is needed. The bitemporal pattern discussed here, involving the lateral half of each eye's visual field, is less common than homonomous hemianopsia. For further reading on this topic, the Wikipedia article is suggested.

Authors' Note:  The homunculi referred to here are the representations of the human body, well-known to anatomy students, that are mapped out on the "motor strip", symmetric areas of cortex on both sides of the brain that control voluntary movement on the contralateral side of the body. The motor homunculus on each side maps the primary motor cortex, located in the precentral gyrus (fold) of the frontal lobe; analogously, there is a similarly arranged sensory homunculus located nearby in the postcentral gyrus.

Here's a LIST OF LINKS to collections of intriguing poems (over 160 of these!) on medical/dental topics that can now be found on various posts. 

To resume daily titillations on our related blog 'Daily Illustrated Nonsense', click HERE. Once you arrive, you can select your time frame of interest from the calendar-based listings in the righthand margin, and check the daily offerings for any month in the years 2020 to the present. (As of September 2023, there are over 1200 unique entries available on the Daily blog, and most of these are also presented here on 'Edifying Nonsense' in topic-based collections.) The 'Daily' format has the advantage of including some videos and other material that are not shown here on this topic-based blog.

No comments:

Post a Comment