The Nervous System: CNS & PNS

Editor's Notes

1. Like a control tower The brain is made up of many specialized areas that work together:• The cortex is the outermost layer of brain cells. Thinking and voluntary movements begin in the cortex.(outer gray matter = cell bodies of neurons, deeper white matter = axons w/ myelin) • The brain stem is between the spinal cord and the rest of the brain. Basic functions like breathing and sleep are controlled here.• The basal ganglia are a cluster of structures in the center of the brain. The basal ganglia coordinate messages between multiple other brain areas.• The cerebellum is at the base and the back of the brain. The cerebellum is responsible for coordination and balance.The brain is also divided into several lobes:• The frontal lobes are responsible for problem solving and judgment and motor function.• The parietal lobes manage sensation, handwriting, and body position.• The temporal lobes are involved with memory and hearing.• The occipital lobes contain the brain's visual processing system. The brain is surrounded by a layer of tissue called the meninges. The skull (cranium) helps protect the brain from injury.
2. CSF (cerebrospinal fluid) fills the subarachnoid space 3 layers of the meninges: dura, pia, and arachnoid Meningitis = infection or inflammation of the meninges
3. Some theorize that frontal lobe size/density denotes higher thinking. Others have concocted an "encephalization quotient," which is the ratio of actual brain mass relative to the predicted brain mass for an animal’s size (based off the assumption that larger animals require slightly less brain matter relative to their size compared to very small animals). By this metric, at least, humans come out on top, with an EQ of 7.5 far surpassing the dolphin’s 5.3 and the mouse’s measly 0.5.     
4. The hippocampus is the part of the brain that is involved in memory forming, organizing, and storing. It is a limbic system structure that is particularly important in forming new memories and connecting emotions and senses, such as smell and sound, to memories. The hippocampus is a horseshoe shaped paired structure, with one hippocampus located in the left brain hemisphere and the other in the right hemisphere. The hippocampus acts as a memory indexer by sending memories out to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary.
5. 33 vertebrae in the human spine spinal cord injuries are permanent and result in paralysis to all muscles below the injured area connects peripheral nerves with brain control
6. Autonomic: Sympathetic revs up (fight or flight) and Parasympathetic calms down (rest and digest)
7. Example is autonomic - you don't process in cerebrum nor consciously control Sensory nerve: carotid body to brain stem Motor nerve: brain stem to ribs/diaphragm
8. There are approximately 100 billion (100,000,000,000) neurons in the human brain. To get an idea of how many 100 billion is, think of this: Assume that you were going to count all 100 billion cells at a rate of 1 cell per second. How long would it take you to count all 100 billion cells? My calculations say it would take about 3,171 years!. Do the math yourself. (Here is a hint on the math: there are 60 seconds in a minute; 60 minutes in an hour; 24 hours in a day; 365 days in a year.) By the way, my calculations did NOT take "leap years" into account. Actually, it would probably take a lot longer than 3,171 years because it takes more than 1 second to say the large numbers. Here is another way to think of 100 billion: Assume the cell body of one neuron is 10 microns wide (this is just an assumption because neurons come in many different sizes. However, 10 microns is small; smaller than the period at the end of this sentence). Ok...if you were able to line up all 100 billion neurons in a straight line, how long would your line be? Check my math!! 1 neuron = 10 microns wide10 neurons = 100 microns wide100 neurons = 1000 microns wide = 1 mm wide1,000 neurons = 10 mm wide = 1 cm wide100,000 neurons = 100 cm wide = 1 m wide100,000,000 neurons = 1000 m = 1 km10,000,000,000 neurons = 100 km 100,000,000,000 neurons = 1000 km (approximately 600 miles) Although all the neurons lined up side by side would stretch 1000 km, the line would be only 10 microns wide...invisible to the naked eye!!! To get an idea of how small a neuron is, let's do some more math: The dot on top of this "i" is approximately 0.5 mm (500 microns or 0.02 in) in diameter. Therefore, if you assume a neuron is 10 microns in diameter, you could squeeze in 50 neurons side-by-side across the dot. However, you could squeeze in only 5 large (100 micron diameter) neurons.
9. Motor neurons are multipolar, with dendrites near the cell body, so ask some students to hold their left hand close to their body. Each person should be about arms length away from the next person. When the leader says "GO," the person at the beginning of the line (an afferent sensory receptor neuron of the PNS) starts the signal transmission by placing his or her "neurotransmitter" into the hand of the adjacent person. Once this message is received, this second neuron (perhaps a spinal cord neuron of the CNS) places its neurotransmitter into the dendrite of the next neuron and lets go of the “giving “ neuron’s transmitters. (Each person’s “terminal button” hand must retrieve their neurotransmitters, which takes energy, just like the re-uptake of an actual neuron.) The third neuron (a brain cell) then places its neurotransmitters into the dendrites of the next neuron (another spinal neuron) and the "signal" travels to the end of the line through an efferent PNS somatic nerve. The transmission is complete when the "signal" goes all the way to the end of the line and an action (contraction of a muscle) occurs. Remember that each "neuron" will pass its own transmitter to the next neuron in line. Each neuron HAS ITS OWN neurotransmitter. What are the parts of a neuron? Measure how long it takes the message to get from the first neuron to the last. Also, measure the distance from the first to the last neuron. Now calculate the speed. How fast did the message travel from first to last neuron? Why do you think the speed of transmission of the model is so slow?
10. Side effects of marijuana: addictive, lung irritation, increased risk of heart attack (elevates heart rate), anxiety/depression & mental illness, impaired judgment, decreased memory/IQ/learning ability, cancer, (?fertility)