The Vertebrate Brain
The head of the central nervous system is the vertebrate brain. The three pound organ has three main parts: the forebrain, the midbrain, and the hindbrain.
The Midbrain
The largest part of the vertebrate brain is the cerebrum, which is located in the midbrain and is split between the two cerebral hemispheres of the brain. It is the center for learning, emotion, and perception and it manages calculation, contemplation, and memory; it is also in control of skeletal muscle contraction. The two hemispheres of the cerebrum communicate via the corpus callosum, which is a tract of connected nerve fibers.The cerebellum, which lies just below the cerebrum coordinates movement, balance, and motor skills. Sensory information is received here to tell the brain information about joints and the lengths of muscles. Motor commands are monitored here. For example, hand-eye coordination resides here. The cerebral cortex is a thick tissue stack around the cerebrum and the cerebellum.
The frontal lobes lie right behind the forehead and are the main short term memory storage site.
The motor cortex is in the back part of the frontal lobe and controls voluntary movements.
The parietal lobes enact the five senses, such as taste, smell, and touch.
The Somatosensory cortex gets information about the five senses, body temperature, and movement.
The occipital lobes process visuals and are responsible for mentally recalling images from memory. Any damage to these lobes can result in blindness, as these lie just behind the eyes.
The temporal lobes receive information from the ears, specifically information from hearing which enables noise processing. The underside of these lobes manage memory retrieval.
The Inner Brain
The Inner brain holds three important structures and is the most protected part of the brain.
The hypothalamus is the main emotional center of the brain and holds the chemicals that cause severe emotions, such as dopamine and growth hormones.
The thalamus is a midway where information goes when it is traveling to and back from the spinal cord and the cerebrum.
The hippocampus is a small, complex brain structure that processes learning and the formation of memories, thus why it is pertinent in Alzheimer’s disease and other forms of dementia. The hippocampus is a vital part of the limbic system, which includes structures that regulate emotions, feeding, and the fight versus flight response. This explains why as a patient’s Alzheimer’s progresses, they ultimately lose the ability to function: examples include outbursts of emotions, inability to eat, and immobility. The hippocampus itself is made mostly of pyramidal cells which are the cell body, nerve fibers, dendrites, and an axon. Dendrites are branched extensions that receive signals from neurons and the axon sends signals toward the synapse, which is the place where neurons communicate. The hippocampus is hidden within the temporal lobe, which sits just above the cerebellum. There are two hippocampi within the human brain, with one in each cerebral hemisphere. The hippocampus is crucial for converting short-term memory to long-term memory and is additionally helpful with spatial awareness. Damage to the hippocampus is indicated in Alzheimer’s disease. Age in general is related to a decrease of hippocampus activity and implicated in hippocampus shrinkage, which thus leads to impaired memory.
Neurotransmitters
Brain nerve cells communicate via electrical and chemical signals. Nerve cells have dendrites, which are branched extensions that receive signals from neurons and the axon is the part of the nerve cell that sends signals toward the synapse, which is the place where the neurons communicate. When synapses reach the end of the nerve, little sacs, called vesicles, release chemicals. Those chemicals are called neurotransmitters and they jump to receptors on the cell beside it. There are both excitatory and inhibitory neurotransmitters, which activate or hinder a cell’s activity, respectively. A shortage of Acetylcholine, an excitatory neurotransmitter which oversees hormone secretion and muscle contractions, is linked to Alzheimer’s disease, so it is one of the factors tested in a work-up.
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