Studying the brain

- Draw a neuron. From memory. (Easy enough.)


Flip to where you were in your notes last. We had a general discussion of the nervous system last. We have a few slides on the rest of this PowerPoint re: studying the brain and then we will go into studying the neuron. Look at the PowerPoints ahead of time. There's a handful of ways to study the live brain. Lesions are where you can destroy the brain and kill the patient. Lesion means damaging the brain somehow. Destroying tissue. There's also ablation where you physically scramble the tissue. We lesion brains of mice, rabbits, monkeys, though not as often to humans. Why would you want to lesion a part of the brain? If you destroy a part of the brain you can see if it works or not, right? So you can try to destroy the section of the brain and see if something is changed.

EEG - Electroencephalogram

Encephalo means head, and gram means chart. This measures electrical activity. In the picture, the baby besides looking quite terrified, they look for activity in the brain when they feed in sides, so they find that the sound is criss-crossed with the ears and they were able to figure this out with EEG. And this is the surface of the brain, the very routine surface stuff. This is the electrode on the picture, and there will be several others on the skull. OpenEEG Project.

CT (computer tomography) scan - a series of x-ray photographs taken from different angles and combined by computer into a composite representation of a slice through the body also called CAT scans. X-rays are rudimentary and do not give you fine detail, it's good for finding big tumours and other structural problems.

PET scan - positron emission tomography. They inject a radioactive dye that means that positrons will collide with this radioactive compound. It tends to measure metabolic activity. This makes sense since they are injecting a dye into your blood stream, so it's seeing where you are using up that dye. So when the brain is being activated, the dye is being demanded and its shown up. They do mass-average of the changes of these. Scan that measures the change in blood flow. There's also caps for PET that would cover surface-area activities. It looks like a skydiving helmet.

MRI - magnetic resonance imaging. MRI is used to determine structural changes in your body. It is able to look at very fine detail of structures. Computer tomography does big structures, and MRI does fine detail. You give your patient a dye, kind of like in PET scans, and this dye is slightly magnetic and slightly radioactive, and when you are placed under the magnet of the MRI machine, it causes the electrons to form in all the same directions so that they can pick up the charge from the EM field, and so the electrons are able to be used for imaging. They do not always give you a dye. You go inside the entire machine. The picture on the PowerPoint shows the ventricle- an abnormal ventricle will indicate that you have schizophrenia, and it's a hole in the center of your brain that is full of fluid, which pushes the tissues of the brain against the skull and causes shortcircuiting in your brain processes, and so this is a physical cause of schizophrenia. Your brain floats, and it is sitting in cerebral spinal fluid. The cerebrospinal fluid shows up in the MRIs of the brain in the dark areas. Your brain is floating in a little pool, it touches nothing, and this keeps it safe. When they have campaigns on television, they'll say don't shake a baby, because that will cause the brain to get concussions and the baby will be killed. That's what a concussion is- when there's an inflammation due to concussion. The meninges encases the brain and spinal column, and it is what seals the brain inside the pocket of fluid. Meningitis is where the brain has too much pressure, then, and there are seizures and die. Get shots for Meningitis, you should do it, they give it to you for free in college.


The basics of the Nervous System

Major structures of the nervous system: CNS, somatic, autonomic, two hemispheres: 4 lobes, contralateral input & output, primary sensory areas, motor areas, localization of functions.

Neurons and synapses

There are three types of neurons: sensory, motor, and interneurons. Sensory neurons first. Sensory neurons are afferent nerves. They have the job of sending information to the brain. All nerves are one-way. All of them. The signal of the nerve goes from the dendrite to the axon terminal. And if it is a nerve flowing towards the brain, it is always an afferent neuron. In this case, on the PowerPoint, it is the one in red going from the finger tip sending a signal through the spinal cord and to the brain. One thing to note, all of your senses, your body senses, are processed by the spinal cord first, but your vision, hearing, and smell is processed directly in the brain, and it is processed immediately. It's a major survival issue: they are processed first for a good reason.

Motor neurons are efferent nerves. They output from the brain and spinal cord to the muscles and glands. They are the "effort". They are always output neurons. So in the PowerPoint image, it's the blue neurons, going from the spinal cord to the muscles of the body.

Interneurons carry information between other neurons only found in the brain and spinal cords. They hand off information. Sensory information goes to the brain, and once it hits the spinal cord, that's the interneuron taking over, and if it is coming back then it's traveling by interneuron first and then to the efferent neurons to the myocytes. There are many other types of neurons: Schwann cells, gleal cells, and you need to know them lightly, so just read over them and there's really more than three main neurons, and if you were getting down to neuroanatomy, there are thousands of different styles of neurons and they all fall into these categories.

Neuron basics

Neuron - a nerve cell, the basic building block of the nervous system. A dendrite- always the branching part that receives information, so dendrites are input. The axon is the extension of a neuron, ending in a branch terminals fibers, through which messages are sent to other neurons or muscles or glands. The axon is a one-way street: it is always from the dendrite to the axon terminals. The Mylein sheath is a layer of fatty tissue that insulates the axon, and increases the transmission of the impulse (20x); impulse hops from one node to the next. Then there's the buttons/buds - axon terminal endings.

Plant cells are almost alwalys rectangular so that they can keep their structure and stay up. Humans, animals, etc., have rounded cells, and so in the nucleus we have DNA and it also manufactures proteins which are the messages that tell the neuron to fire. The nucleus tells the cell to fire when there's the threshold that has built up, but beyond that there's nothing else that the nucleus does in signal transmission.

Dendrites gather information, they receive inputs, and the inputs may be thousands for a single neuron, and it's not just waiting for one single cell, it's tallying thousands of different cells and information, and it's channeling all of this down, and once it gets all of that, it sends one message down the axon to the button and down to another neuron. It gathers thousands and sends only one. If you get enough information coming in, an axon may generate an output.

Dendritic growth. Dendrites can grow but only when they are new and immature. Every once in a while, and it's very rare, a branch or dendrite will die, and the rest of the cell will be healthy, and the dendrites will reallocate to pick up new information from other terminal buttons that were being cut off, so there's constantly this formation of new communication links but not always are you building new dendrites.

There's one axon per cell. This is for the basic neurons -there are some neurons that have really weird stuff, but you'd study that in neurosurgery class. One axon sends one message all the way down to its buttons. There's an "all or none" law. The Myelin sheath increases the speed of neural signals down the axon. They are made from fat. The fatty tissue can be reabsorbed by the body when there's nerve damage. When you are under too much stress, your body will consume that and convert it to Myelin sheaths and it will help reduce the stress. It speeds up the process 20 times- remembr this.

How neurons communicate

Action potential (or impulse) is the electrical signal that runs down the length of the neuron. Action potentials are based on the exchange of ions across the membrane of the axon. The whole point of an action potential is to send that message, to relay it.

Outside of the cell: potassium+, sodium+, chlorine-.
Inside of the cell: potassium+, sodium+, chlorine-. You have a positive side on the inside, and a positive charge on the outside.

The cell is at the resting state there's a positive equilibrium between both the inside and outside between potassium+, sodium+, and chlorine-. The cell membrane only allows certain things to cross. In order to change the charge, the battery - via electrolysis, as ions run across the surface, and so this is in essence the same thing. As ions cross the membrane, it creates this friction of electrical charge. The neurons are like little batteries, and people can be hooked up to a light bulb and you can run a light bulb and charge it (see "The Prestige").

Messages moving down the axon move in sections at a time. So it starts at the cell body and moves all the way down. It does not go "boom" message, so it starts at one end and runs it down to the other. While there is a charge exchange at the axon, the other sections are still getting ready. The action potential is when it is charging, and the cell body is resting, and the rest of the axon is getting ready, and it slides down that axon. This is what happens with the charge: first it starts at -70 mV resting potential, and when the charge hits and the message is sent, there's an exchange of ions, and once it hits the 35 mV peak the charge drops down and the ions exchange, and then it goes down to -75 mV as the refractory period and then it goes down to normal again, the resting stage, at -70 mV. It goes from -70 mV to 35 mV to -75 mV for the refractory period (hundredths of milliseconds). So there's: