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Chapter 2

chapter 2

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Ted Petit

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Chapter: Neuroanatomy Psy B65 Cells of the Nervous system: - Neurons/ glia: are the specialized cells of the nervous system and they are specialized in both structure and function : glia: provides support functions and neurons are the communicators - Neurons react and respond to stimuli and they are basis of the behaviour - Neurons also learn and store information about the environment Neurons and Glia: Structure and Function Gross anatomy of the neuron: - Distinctive structural feature of a neuron is its shape - Has (3) components: Dendrites which receive incoming information from other neurons Soma cell body, which contains the genetic machinery and most of the metabolic machinery needed for common cellular functions Axon sending neural information to other neurons: info is passed from the axon to the dendrite across a gap: called synapse - Events that occur in the axon, such as presynaptic (in the axon events) and postsynaptic (events that happen in the dendrite) - Dendrites: has spines that can form synapses themselves with other neurons - Axons are thought to be information senders - Neuron has only one axon: even if it can extend far into many branches - Axon: long thin wire that can pass its message along to many different cells simultaneously - Many axons in the mammalian nervous system are covered with myelin helps to speed the rate of information transfer and to ensure that the message gets to the end of the axon - Terminal button: end of the axon , information is sent from the terminal button across the synapse to the dendrite: info that passes from the axon across the synapse : neurochemical message by neurotransmitters Internal anatomy of the neuron: - Neuron is covered with a membrane - Plasma membrane: consists of a bilayer of continuous sheets of phospholipids that separate 2 fluid (h20 environments one inside the cell and the other side of cell - there is protein and channels that allow the passage of materials in and out of the neurons Structure and function of neurons: - structurally some common neurons are labeled as unipolar, bipolar and multipolar the most common - unipolar neurons have only one process from the cell body - neurons can also be classed as being afferent by bringing the information to the CNS or efferent which is sending information from the brain or away from a structure : neurons are different sizes, shape and function Glia: - important functioning in the CNS - support cells - three different types (3): Astrocytes largest glia, it fills the space between neurons, contact with neurons can affect the growth of neurons , blood brain barrier Oligodendrocytes : makes myelin , wraps around axons in the brain and spinal cord, Schwann cells: myelin provided by this cell provide only one segment Microglia : small in the brain as a result of injury, disease, infection, they are phagocytes which removes debris from the nervous system, debris can accumulate in the brain as a result of injury, excessive activatcation has diseases such as MULTIPLE SCLEROSIS, AND ALZHEIMERS Communication within the Neuron: The Action Potential - Neurotransmitter diffuses across the synapse to interact with the post synapse site: series of electrical events : some send to other neurons, some inhibit info - Electrical events that underlie the transmission/inhibition of information depends on the balance of ions b/w the inside(intracellular) and the outside(extracellular) of the neuron - The inside millivolt charge is less than the charge on the outside: the initial state of the neuron is called: resting potential: this depends on the difference between the concentrations of ions across the neuron membrane - Neurons carry a variety of ions: important ones: Sodium (Na) and Potassium (K) - At rest the OUTSIDE of the neuron has high concentrations of Na and theINSIDE has high concentrations of K How the neuron produces uneven distribution of ions? (2 ways): 1. Permeability of the cell membrane that covers the neuron : Ions cross the membrane through proteins embedded in the membrane: known as ion channels , at rest K nicely goes in the membrane, but Na cant easily enter the neuron , BUT within some time, K would leak out and Na would get in there sneakishly 2. Neurons actively import K and actively export Na through : sodium- potassium pump which requires the neuron to use energy, making sure that there is uneven distribution : sodium potassium pump exchanges three Na ions indife the cell for 2 K ions that are outside the cell - If the resting stage voltage goes down it is known as: depolarization , and action potential occurs - When action potential occurs neurotransmitters are released from the terminal buttons: they occur in one neuron , they result in the neurotransmitter to release COMMUNICATION b/w neurons - As neuron becomes depolarized K channels open , then they leave the neuron , so the neuron returns to resting state : repolarization - Some Ks leak out of the neuron resulting in temporary change in the membrane beyond normal state: hyperpolarization Action potential features: - Cant be triggered - Require the movement of Na: inability to open sodium channels resulting in absolute refractory period: a period of time during which an action potential cant be triggered- All or none : once a neuron becomes depolarized-> sodium channels open up -> and action potential occurs - Relating in myelination of axons : there are small gaps in the myelin - In the myelated neurons the ion channels and sodium potassium pumps occur only at the gaps in myelin - When the action potential reaches the axon it goes to the FIRST gap in the myelin - When deprolarization happens: there is a new action potential in the gap of the myelin - There is jumping of the action potential from one gap to another on the myelin: salutatory conduction : this occurs in the entire length of the axon - Each gap on the myelin generates a new action potential - Neurons with myelination transmission is faster without the myelination Communication b/w Neurons: The synapse: - Neuron: relies on the action potential to transmit information - Within neurons: chemical - Most synapses are: axodendritic that is consisting of axons that form synapses with dedritic spines - The terminal button of an axon has small packages (vesicles) that contain neurotransmitters , the deposit of the vesicle is dropped to the synapse - The release of the neurotransmitter is triggered by the arrival of an action potential at the terminal button of the axon - The action potential causes calcium channels to open and Ca rushes in the neuron, the increase of this causes the neurotransmitter to be released by a process : exocytosis: during this the membrane of the fuses with the axonal mem
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