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Lecture 3

Lecture 3 - Cells of the Nervous System

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University of Toronto Mississauga
Ayesha Khan

PSY290H5S – Introduction to Physiological Psychology Lecture 3 – July 17, 2013 Introduction to today’s class (not apart of slides) - The two major categories of cells o Neurons o Glia  have the capacity to produce neurotransmitters, but more involved in support activity and functioning of neurons Neurons - Basic unit of the nervous system (peripheral nervous system) - Function: allow for Communication (within PSN as well as CNS) - How do they differ from other cells? o Structurally: if you look at a neuron, it has a specific kind of shape, that is different from all other cells in the body o The structure of the neuron allows it to communicate information - Three main functions: o Reception  receiving information from another cell o Conduction  involves changes that occur within the neuron itself o Transmission  taking the information and moving it one way or another - Communication: o Chemical  in the form of neurotransmitters o Electrical  allow for chemical information to occur - Four structural regions that represent the neurons communication functions o Dendrites – receiving chemical messages from other neurons o Cell body (soma) – contains the nucleus, which is important as it houses genetic material  containing chromosomes that codes for proteins that codes for the functioning of neurons* o Axon – action potentials are occurring (change in the voltage of the neuron)  Excitation  increasing likelihood of action potential occurring  Inhibition decrease the likelihood of action potential occurring o Axon terminal (terminal button) The Neural Membrane - Allows for entry or exit of various kinds of chemicals into the cell - Made up of phospholipid bi- layer (2 layers made of lipids and phosphates) PSY290H5S – Introduction to Physiological Psychology Lecture 3 – July 17, 2013 - Rely on channels to gain entry or exit of the cell - Channels are constantly changing – - These channels that are embedded, they need to use the receptors to gain accessed to the cell - How does the neuron get to the point of an action potential?  when the inside of the cell is headed towards a positive direction o If charge inside the cell is heading in a positive direction it means: o (1) There must be a lot of positive ions coming inside the cell o (2) Depolarization Selective Permeability - Lipids – fats - Phosphates head - What is able to gain entry, and exit of the cell? - If there is a chemical that comes around, and that chemical structure is made up of fat, it has very EASY access into the cell o Fat dissolves in fat - If it is a charges particle (neg or pos charge), think about water and oil, it won’t mix o Wont cross the membrane - Ion – has a chemical charge o Maintain the charge of the neuron based on the constant movement of ions in and out of the cell o When talking about the charge, you talk about the charge INSIDE the cell, relative to the OUTSIDE Selective Permeability - Phospholipids bi-layer o Makes the membrane selectively permeable o The only thing that can diffuse in the layer, is something that is also fat - Ion channels (passive diffusion) o Channels in which ions can flow in and out of the cell through passive diffusion - Voltage-dependent channel (require electrical changes) o Dependent on voltage, that is maintained across the cell membrane o These require electrical changes o These channels open and closed based on what the voltage is inside the cell - Ligand-gated channels (require a “ligand”) o Example of a ligand is a neurotransmitter PSY290H5S – Introduction to Physiological Psychology Lecture 3 – July 17, 2013 o Only opens when a neurotransmitter comes in and attached itself - Within the cell, there are a lot of metabolic changes that are occurring o Sodium, potassium o Movement of sodium and potassium in and out of the cell which go though pumps - Sodium-potassium pumps (require energy) o Are positively charged - Calcium pumps (require energy) o Are positively charged Three Fiber Types Compose the Cytoskeleton of Neurons - Neural membrane reuiqes structural support - There are 3 kinds of filaments that are important o Microtubule o Neurofilament o Microfilament - Neurotransmitters can be made in the (1) cell body and (2) axon terminal - (1) Cell body – needs to be packaged in vesciles o Microtubules is important for the movement - (2) Axon terminal – require the building block o Microtubules is important in transporting the raw ingredients that will make up the neurotransmitters when they get to the axon terminal - Movement: o Anterograde transport – Away from the cell body o Retrograde transport – Towards the cell body Alzheimer’s Disease - Most common form of dementia - Dementia – Loss of memory, judgment and reasoning, and changes in mood, behaviour, physical and communicative abilities - How does this occur? o Loss of neurons and synapses in the cerebral cortex - In particular, Cortical gyri shrink o Neurons are starting to die, and so the tissue starts to shrink as well - Ventricles become enlarged because they start to take up more space PSY290H5S – Introduction to Physiological Psychology Lecture 3 – July 17, 2013 - Formation of Plaques o Degenerating axons and dendrites - Amyloid precursor protein is found in the synapse, very important for function and movement, and maintaining healthy functioning of synapses o This protein is able to convert into -amyloid protein in Alzheimer’s disease o If there is high level of -amyloid, the functioning of the synapse starts to deteriorate and deregulate Tau Phosphorylation Leads to Cell Death - Neurons in general start to collapse o The structural support starts to diminish - In a healthy brain, Tau is very important for holding microtubules in place - In alzheimers disease, Tau becomes elevated (where Tau increases in number) - As a consequence of the presence of Tau (in a healthy brain), you have phosphate groups that come and bind to that protein o Basically helping Tau to do its job - Therefore amount of Tau start to increase, meaning the number of phosphates that bind are also increasing - This allows and gets in the way of healthy movement and therefore results in tangles o Movement of particles/ neurotransmitters is not able to occur and the neuron starts to fold because of all these disruptions and ultimately collapse The Neural Cell Body - Contains all the organelles found in the cell including different kinds of structures where protein production becomes very important - The smooth ER is important for protein production - Rough ER is important for protein production - The nucleus is where the gene comes from for protein production - Golgi apparatus – important for packaging of proteins - Mitochondrion – energy source - Ribosomes – key for protein production PSY290H5S – Introduction to Physiological Psychology Lecture 3 – July 17, 2013 - Micotrubules important for movement in the cell body and axon itself Axons and Dendrites - Axons important for communication - Local circuit neuron o It is a very small neuron, not able to have an axon that projects far away o Small distance away - Projection neurons o Have axons so long o Works further and further away due to the length of axon - Fundamental concept: o Synapse will always act the same way regardless if it a local circuit or projection Neurons - Structural Features of Neurons o Cell body (soma) contains nucleus and other organelles o Dendrites – branches that serve as locations at which information from other neurons is received o Axons are responsible for carrying neural messages to other neurons  Vary in diameter and length  Many covered by myelin Myelin - Is essentially fatty tissue that will cover axons in majority of neurons - Allows for axons to be smaller in diameter without decreasing transmission speed o Efficient in which it is faster - Presence of myelin adds “space” to the nervous system - No ion channels in myelinated areas Structural Variations in Neurons - Unipolar o Single branch extending from the cell body, fairly lengthy o Tend to have a characteristic appearance, almost as if the cell body is off to the side and long looking axon - Bipolar o Two branches extending from the neural cell body: one axon and one dendrite o Cell body in the middle, axon extending out of it - Multipolar o Many branches extending form the cell body; usually one axon and many dendrites o Have lots of dendrites branching PSY290H5S – Introduction to Physiological Psychology Lecture 3 – July 17, 2013 - For test  be able to describe, one example of location and example of function Structural and Functional Classification of Neurons Functional Variations in Neurons - Sensory Neurons o Specialized to receive information from the outside world o Are taken from our sensory organs o Moving info to an afferent direction - Motor neurons o Synapsing with muscles found all over the body o Transmit commands from the CNS directly to muscles and glands o Glands are important in production and various kind of secretion - Interneurons o Act as bridges between the sensory and motor systems o Collects sensory information and passes it to a motor direction o Lots are found in the spinal cord Glia - Macroglia: Largest of the glial cells o Astrocytes  Found in the CNS  Tend to have the most ray of function they participate in PSY290H5S – Introduction to Physiological Psychology Lecture 3 – July 17, 2013  Nutriential support, structural support for nucleus,  Isolation of the synapse (neurotransmitters are going where they should go)  Debris clean up  start to leave scar tissue (disadvantage)  Blood-brain barrier  Participation in chemical signaling o Oligodendrocytes  Found in the CNS  Myelination of axons  important in te speed in which neural messaging exists o Schwann cells  Dominate in the PSN  Myelination of axons - Microglia: smallest of the glial cells o Found in the CNS o Debris cleanup Astrocytes - When you look at a neuron, it is surround by multiple astrocytes - There are glia cells than neurons in the nervous system - Results in a structural matrix, otherwise the neuron would just be floating around in the fluid - Astrocytes are important in holding neuron in place - Nutriential support is important because capillary o Blood flows through the capillary, has glucose, oxygen and other nutrients that important for the survival or neuron o Blood brain barrier, prevents toxins circulating in the blood, where the astrocytes realizes that this is a foreign neuron - Toxins get into the brain by tricking these astrocytes, allowing the access into the neuron - As they are cleaning up the debris, most of the time they will leave scar tissue - Have the ability to release their own neurotransmitters o Excitatory neurotransmitter  glutamate – have the ability to produce action potential in post synapti
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