A laboratory introduction to the human brain
It was quite striking to me how many students in the 2014 NeuroMOOC class of Understanding the Brain appeared to really enjoy the laboratory videos that were included in the class. So I will post versions of those videos here on my blog. I will add more from time to time. But let’s start with those that that were part of NeuroMOOC 2014.
I want to emphasize the respect and gratitude that I feel every time I look at tissue from a dead person. The decision to offer up one’s body for scientific study or training is the epitome of generosity and selflessness. I am in awe of those individuals who did so. Please take a moment to be grateful to tissue donors:
To start with, we are going to look at the central nervous system which is comprised of the brain and the spinal cord.
Now let’s look at the meninges that surround the central nervous system.
Now that we know about the meninges, we can talk about “brain tumors” and “brain cancer”. The important point is that none of these are tumors where neurons multiply out of control. Intracranial tumors arise from either glial cells (mostly astrocytomas from astrocytes or Schwannomas from Schwann cells) or from glandular cells (pinealomas in the case of the pineal gland or pituitary adenomas in the case of the pituitary gland). Importantly, neurons are NOT the source of tumors.
I should mention that there are two other ways in which cancer can affect the brain. First, a tumor may spread or metastasize and invade the brain. This would be a case of a metastatic tumor in the brain. Second, paraneoplastic syndromes occur when a substance made by a tumor or in response to a tumor accesses the central nervous system. I wrote about one such disease in a recent post. The anti-NMDA receptor encephalitis that Susannah Cahalan suffered from is just one of many autoimmune encephalitis diseases. You can find out more at the Autoimmune Encephalitis Alliance. Anti-NMDA receptor encephalitis is the most common of these diseases at the moment. However, these diseases have only recently been recognized and it is likely that there are far more out there than we know about right now.
Problematic pituitary adenomas account for a large minority (up to a quarter) of all intracranial tumors. In fact, tiny pituitary adenomas are common within the general population. We know this because autopsy studies tell us that roughly 15% of people who died of other causes have these small adenomas in their pituitary. In the next video, we look at the location of the pituitary, discuss a common visual symptom of a space-occupying tumor in the pituitary and look at the surgical approach used to remove a pituitary adenoma.
Now we move inside the meninges to the central nervous system. We will start with the simplest part of the central nervous system: the spinal cord. The spinal cord is not simple by any measure but it is a segmented structure and there are a smaller number of motifs present in the spinal cord than in the brain. In this first video on the spinal cord, I show the location of the cord in the vertebral column and go over the spinal cord anatomy briefly.
I was not happy with the view of the cauda equina in the above video. So I shot another video of the spinal cord. This one indeed has a better view of the cauda equina. Please note that these spinal cords do not appear to be human. They likely come from cow or sheep. I inherited these spinal cords when I arrived at University of Chicago more than 20 years ago and unfortunately, the source was not identified.
Now we move into the skull to look at the brain. We’ll start with two areas of the outer rind of the brain – the cerebral and cerebellar cortices.
Typically when someone refers to cortex, they mean cerebral cortex. Humans have a large and particularly capable cerebral cortex. The cerebral cortex derives from the dorsal part of the telencephalic vesicle. Subcortical structures of the telencephalon include the striatum and pallidum (the core structures of the basal ganglia), amygdala, and the claustrum of recent consciousness fame (we’ll look at this in a coming laboratory video). White matter structures of the telencephalon include the corpus callosum, corona radiata, internal (and external and extreme) capsules, fornix (the midline tracts visible at the base of the cap in the video) and the anterior commissure. The point of the following video is to see that all of these telencephalic structures hang together in the telencephalic cap, a term that I coined last year when I figured out this dissection. I like the term and when you watch the video, I expect that you will appreciate how appropriate it is. The telencephalon sits on the diencephalon and brainstem as a cap sits on the head. Use the term and spread it around!
Speaking of the cerebral cortex, the most celebrated region of cerebral cortex is the hippocampus, a region that is required for making declarative memories. Note that hippocampus is part of cerebral cortex but is not part of fancy neocortex which is 6-layered cerebral cortex present in mammals only. In this video, we look at a normal hippocampus. And I also show the hippocampus of a woman who suffered from Alzheimer’s disesase [warning: emotionally challenging].
Within the hindbrain, there is a little brain or cerebellum. The anatomy of the cerebellum is beautiful as it contains one of the most spectacular cell types in the brain, the Purkinje cell. Moreover, the gross anatomical arrangemetn of the cerebellum is revealing of function. You will see that the cerebellum is attached – at the hip, so to speak – to the base of the pons. These two areas are married in function and in anatomy. Check it out:
We humans are highly visual creatures meaning that 1) we care very much about our visual surroundings and 2) we use primarily vision to organize our actions. In this next video, I trace the visual pathways from the retina through the optic nerve, chiasm, and tract and ultimately to the primary visual cortex. Of course, visual processing does not end in primary visual cortex but our introductory video does.
We’ll end this introductory lesson with a look at the blood supply of the brain.
That does it for our first installment. Stay tuned for more.