Friday, 19 April 2024 ------------------------ Hello. All is well. Finishing chapter three, we cover brain imaging and the endocrine system. There are three main methods of brain imaging: radioactive, magnetic, and electrical. Radioactive methods include computerized tomography (CT) scans and positron emission tomography (PET) scans. CT scans are done by X-ray. They're a structural scan, useful for spotting tumors and atrophy. PET is a functional scan, looking at brain activity. We do this by injecting a radioactive substance in the bloodstream, known as a tracer, that can tells us where blood is flowing in the brain, which is an approximation of brain activity. It's mostly replaced by fMRI, but it's still useful in some cases when combined with a CT scan. For magnetic methods, we've got magnetic resonance imaging (MRI), and functional magnetic resonance imaging (fMRI). MRI works by exposing the brain to a magnetic field, causing hydrogen atoms to move. When the magnetic field turns off, the atoms return to their original position, and in the process, send an electromagnetic signal which differs dependent on the density of tissue. fMRI works similarly, but we look at oxygen and blood flow. Finally, electroencephalography (EEG) tracks overall electrical activity in the brain. With millisecond accuracy, it can tell us the frequency (waves per second) and amplitude (wave height) of brainwaves. It's done by putting a bunch of electrodes on the head. Side note, do you think electroencephalography is difficult to spell? It is for me, but by splitting it up loosely by its syllables or by smaller word units, it becomes surprisingly easy. In this case, I split it like this: Electro-encep-halo-graphy. See? Easy peasy lemon squeezy. That's that, now it's time to discuss the endocrine system. This system helps regulate bodily functions by using the bloodstream to send chemical messengers across the body. Not neurotransmitters but hormones. We begin with the hypothalamus (hypo-thala-mus). Quick recall exercise: The hypothalamus is structure within the limbic system. Remember the limbic system is a subcortical structure in the forebrain. The limbic system also includes the hippocampus, important for learning and memory, and the amygdala, important for emotions. We also have the thalamus as a subcortical structure, the sensory and motor signal synchronizer, the composer of consciousness perhaps? In the forebrain, we also have the cerebral cortex with its four lobes: the frontal lobe, the parietal lobe, the temporal lobe, the occipital lobe. First one, in the front and middle-top, has the over thinker prefrontal cortex, and primary motor cortex, the second at the back-top has the somatosensory cortex, the third on the sides has auditory cortex, and the last in the back has primary visual cortex. The midbrain was the little nugget, I forgot the name, but it had responsibilities of sleep-wake-cycle, arousal, alertness, and some other structures for dopamine and movement. The hindbrain has the brainstem with the pons (bridge) and the medulla (autonomic functions). We also have the cerebellum in the hindbrain. I think I forget to mention its function yesterday, but it basically does movement and coordination stuff. I remember Temple Grandin saying hers was smaller, reducing performance fir physical activities such as skiing. Quickly, spinal cord, automatic reflexes at top, 30 functional segments, connecting to PNS, efferent fibers send out motor signals, afferent fibers send in sensory signals. Autonomic system has sympathetic and parasympathetic system working together for equilibrium of biological conditions or homeostasis. What was the other one called, hmm, somatic nervous system, responsible for sensory and motor signals, like pressure on skin, moving your fingers. I mainly remember all this by visualizing the brain, the illustrations the book had for the CNS and PNS, and associating stuff, like walnut for the cerebral cortex, onion to signify layers, the midbrain like a little nugget, hindbrain as the behind brain, you get the idea. I generally don't like to remember arbitrary things, but for example, I do remember the axon fiber bundle connecting the hemispheres is called corpus callosum by thinking of the band as a white pale corpse. In actuality, corpus refers to collection of something I think, you remember corpus linguistics we talked about earlier? Might be better association. Anyway, callosum I imagine as the caloric sum of the band, being 200 million, which is the amount of axons it has. The longitudinal fissure I remember easily by the name itself as I understand those words more. But I think it's better to learn connections and processes. It's to remember reality more accurately. Labels and boxes are essentially an abstraction. Knowledge is confined by its context. Back to the endocrine system, the hypothalamus instructs the pituitary gland. This gland is known as the master gland, responsible for a wide range of hormones and controlling other glands. The thyroid gland, situated in the neck, secretes hormones for growth, metabolism, appetite regulation. The adrenal glands, above the kidneys, secrete epinephrine and norepinephrine, regulating stress-response. The gonads secrete sexual hormones for reproduction, regulating sexual motivation and behavior. Ovaries for females(estrogen and progesterone), and testes for males (androgens like testosterone). The pancreas secretes insulin and glucagon to regulate blood sugar levels. Hormonal imbalances cause all sorts of issues, like diabetes, when insulin is low or non-reactive, causing high blood sugar levels. Not very nice.