In anatomy, we performed a laminectomy. We removed the posterior vertebral structures to reveal the spinal cord, about the diameter of the thumb. We opened up the dura (outer meninges that forms a fibrous protective layer), a continuous white sheath that covers both spinal cord and brain. At each intervertebral level, four roots come off the spinal cord to form bilateral spinal nerves. The ventral root is where all the motor fibers exit the spinal cord to control muscles and glands. The dorsal root is where sensory fibers enter into the spinal cord. Several spinal nerves in the lumbar and cervical regions were surprisingly large, about the diameter of a pinky. How could something the size of a thumb contain nerves that occupied so many pinkies? The answer turns out to be that nerves within the spinal cord are highly myelinated, which maintains conduction speed without the need for a large diameter. Once the neurons fan out from the spinal cord, however, not all of these nerves are myelinated and therefore must be thicker. We also saw the aptly named cauda equina (horse’s tail). The spinal cord stops at L4 but the spinal nerves must exit from the lower vertebrae. The spinal nerves flow down the vertebral foramen fibers forming a horse’s tail!
This week in lecture we learned about the cerebellum (from the Latin for “little brain”) and basal ganglia. The cerebellum is located in the posterior inferior (back/lower) portion of the skull under the occipital lobe and contains an estimated 50 billion neurons in the cerebellum—more than in the entire rest of the brain and spinal cord combined! These cells can be thought of as writing computer programs to determine muscle activity and timing. One program, for example, might determine the sequence of firing hand muscles to grasp a cup. “Anyone who has had one too many cold ones knows what happens when you lose cerebellum function,” noted Doctor J. Alcohol affects the the purkinje neurons of the cerebellum first, causing the characteristic drunk stumble.
The cerebellum uses the same neural architecture to process different inputs. For example, whether information is coming from the vestibular (balance) apparatus, or coming from proprioceptive information of the big toe, the information ascends to the densely packed purkinje neurons. The purkinje cells form massive planar dendritic trees that stack together in parallel. Purkinje cells have the same branching pattern as fan coral. Information received from the nervous system is sent along parallel fibers that travel perpendicular to the purkinje dendritic trees, synapsing along the way. This allows an immense amount of connectivity.
Cerebellar lesions, for example from a stroke, are devastating. Simple tasks become near impossible as the victim has difficulty timing an action. We practiced various cerebellar tests including the finger-to-nose test where you ask patients to reach out to your finger and touch their noses. They will have an intention tremor as they near the end of the action. Doctor J commented, “Do not use their nose as the endpoint. A stroke patient will poke his/her eyes out. Use the chin.”
We had two lectures on the basal ganglia, cell bodies deep in the brain that are involved in filtering information passing through the thalamus (relay station) to the cerebral cortex. While the cerebellum’s outputs dictate the timing of muscle firings, the basal ganglia determine which muscles need to be activated. Lesions of the basal ganglia, for example Parkinson’s disease, cause debilitating rest tremors (tremors while not performing an action). We learned that stripes of tape on the floor can help Parkinson’s patients with stability. The visual cues of the tape are thought to override the abnormal baseline thalamic input. This simple addition has huge benefits for the patient and caretakers, for example, when the patient tries to get out of bed to the bathroom. “This is an easy way to help keep a Parkinson’s patient out of the hospital.”
Doctor J brought out a VHS cassette showing various tremors, reflexes, and symptoms of patients with neurological disorders. “It might be old, but it’s the best display of these symptoms.” It took two IT staff 15 minutes to get it playing. We saw symptoms and movements associated with Parkinson’s disease and Huntington’s disease. The video was apparently worthwhile; the next day, a classmate shadowing an internist diagnosed a 40-year-old patient with Parkinson’s.
Our patient case: Martha, a 62-year-old female with Parkinson’s disease accompanied by her daughter Janine. The class quickly fell in love with Martha. She was witty, humble, and kind. Martha was diagnosed about eleven years ago with Parkinson’s after presenting with balance issues, difficulty writing, and a rest tremor in her hands. The neurologist explained there are two stages of Parkinson’s. “The first stage involves movement and dexterity. Typically two decades after diagnosis, patients enter a second phase characterized by significant cognitive deterioration. There are drugs, for example carbamoyl-levodopa, that are effective at treating the tremor and movement disorders.”
Martha explained that it took a while to find the right balance. Too much of these powerful drugs can also cause tremors. She takes her medications every four hours or as needed if the tremors get worse. “If I do not take my medications, I have this terrible slowness,” explained Martha. “I want to walk but my feet do not move. They just twitch up and down with the rest of my fidgety body. My body does not respond to my mind.”
Asked to describe her typical day and what she wanted others to know about Parkinson’s, Martha responded, “Oh, I still do lots of stuff. I cannot drive, but I love to garden and cook. Everything just takes longer for me. Appreciate that it is difficult for me to get to an appointment or brunch at 10:00 am. It takes me several hours with the help of Janine to get ready.”
What was her greatest concern? She immediately responded, “That I will become dependent on Janine.” She explained that Janine was the only family member who was a significant help. A student asked Janine, “How has this changed your life?” Janine responded, “She is the center of my world. I wouldn’t change it. I wish people understood that her disease has not destroyed everything of her. There is a whole life after diagnosis. It doesn’t stop there.”
Friday afternoon, we practiced motor and reflex tests on each other. Reflexes are elicited by sudden changes in muscle length. Swinging a reflex hammer at a tendon causes a sudden increase in the length of the tendon, which sends this stretch information to reflex centers in the spinal cord. Upper motor neurons communicate with these centers for a net inhibitory effect. Therefore, an upper motor neuron lesion may result in hyper-reflexia (e.g., doctor gets hit in the nose by the patient’s foot). As we practiced on each other, two student-examinees shouted, “I got the clonus!” Clonus is when a muscle undergoes a series of involuntary contraction-relaxation cycles after a sudden change in the fiber length. The hospitalist told them not to get too excited about a few beats of clonus: “Wait until you are on the hospital wards.”
Seven students stuck around to speak to the physician. One of our classmates had suffered a stroke at age 10. He reluctantly volunteered to have his reflexes tested. We quickly identified hyper-reflexia in his left lower extremity (left leg below the knee). For the patellar reflex (knee), the leg straightened at the knee and then kept going up towards the ceiling. After that we saw more than 5 seconds of sustained clonus. This is entered on a chart as “Grade 4+” (2+ is normal). Further, the physician elicited the “Babinski sign” by moving a pen along the underside (“plantar” surface) of the classmate’s foot. His toes fanned out, which is normal for a baby under six months old. After six months, this reflex is typically eliminated as upper motor neurons suppress the primitive response. We thanked our good friend and classmate.
The next day, Doctor J held a group “question and answer” session. The class gets into six-person groups to answer challenging questions. Each group is required to hold up an answer. Doctor J would then delve into why Group 1 picked “C” whereas Group 2 erroneously picked “D”. Type-A Anita did not attend stating, “I feel humiliated when I go to these question/answer sessions and he pimps me about why I got the question wrong.”
Lunch outside with nine classmates: A woman checked CNN headlines about the missile strike on Syria on her phone and yelled that Trump was a warmonger. Type-A Anita added, “On top of this, Gorsuch was confirmed. We are going back to the Stone Ages.” The topic somehow turned to race relations. A classmate chimed in, “Ben Carson got appointed only because he is black.” A female classmate from a rural conservative family opined, “America has our class divisions but we are by far the most tolerant country compared to anywhere else.” Immediate reactions stormed in. “This is because Western culture portrays whites as heros and blacks as criminals,” a female Asian student asserted. “It is the West’s fault that other countries are not tolerant because they watch our movies and pop culture.” The discussion settled down after someone brought up the livestream of April the Giraffe (a pregnant resident of an animal park in New York).
Statistics for the week… Study: 8 hours. Sleep: 8 hours/night; Fun: 1 night. Example fun: After class, we played soccer with Ph.D. students in the rain followed by burgers and beers.