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Lecture 2

BIO310 Lecture 2 & 3.docx

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BLG 144
Tsogbadral Galaabaatar

BIO310H p. 113-117 & 155-157 01/10/13 Lecture 2 & 3 Neurons  Communicate information using a combination of electrical and chemical signals.  Most are electrically excitable electrical signals can be generated across the plasma membrane and transmitted along the length of the cells without loss of signal strength, as a result of the movement of ions.  Individual neurons are most studied of all types because: 1) Their electrical properties can be easily investigated. 2) Neurons function similarly in all types of animals. 3) Neurons process information, while relying on a small number of basic physical and chemical processes. Nervous system  neurons + glial cells = supporting cells  Collects and processes information, analyzes it, and generates output to control the animal’s responses from the simplest to the most complex. Structure, Function, and the Organization of the Neuron  Soma/cell body: responsible for the metabolic maintenance of the cell. Most neurons possess multiple dendrites and a single axon.  Dendrites: branched; receivers that gather signals from other neurons and carry them toward the soma.  Axons/nerve fibers: specialized nerve extensions of the neuron that conduct signals away from the soma.  During the embryonic development of each neuron, the dendrites and the axon grow outward from the soma.  If an axon in an adult animal is damaged, it typically degenerates back to the soma within a few days or weeks. In mammals, regeneration of axons takes place in the periphery of the body. In cold-blooded vertebrates, regeneration of axons takes place within the CNS. Damaged neurons in many invertebrates readily regenerate and reestablish connections with their original targets.  Spike-initiating zone: integrates signals from many input neurons to determine whether the neuron will initiate its own signal action potential (AP). Located at or near the junction between the axon and the soma, a region called axon hillock.  Action potentials/spikes/nerve impulses: the voltage across the membrane rapidly rises and then falls.  The axon carries an AP from its point of origin in the spike-initiating zone to the axon terminals, which transmit the signal to other cells.  Motor neurons: signal travels from the axon terminals to skeletal muscle fibers.  Passive electrical properties: capacitance and resistance  Active electrical properties: allow them to conduct electrical signals without decrement (i.e. with no loss of signal strength). Depends on the presence of voltage-gated ion channels in the plasma membrane.  The axonal membrane is specialized for the conduction of APs by virtue of fast acting, voltage-gated ion channels that selectively allow Na+ and K+ to cross the membrane. In addition, the plasma membrane of the axon terminals contains voltage-gated Ca2+ BIO310H p. 113-117 & 155-157 01/10/13 channels and other specializations that allow neurons to transmit signals to other cells when APs invade the terminals.  Afferent fiber: axon of a sensory neuron; conducts a signal inward toward higher processing centers in the brain.  Efferent neurons: carry information from the processing regions of the CNS outward to effectors.  Synapses: location where information is passed between neurons.  Neuronal circuit: afferent neurons, efferent neurons, and interneurons.  Presynaptic cell: passes information to a particular neuron.  Postsynaptic cell: receives information transmitted across a synapse.  Most synaptic transmission is carried by chemical neurotransmitters, which are released from the axon terminals of the presynaptic neuron.  The plasma membrane of the postsynaptic neuron’s dendrites and soma contains ligand- gated ion channels that bind neurotransmitters and cause the postsynaptic cell to respond to the presence of the chemical signal.  Information is carried in neuronal circuits via alternating chemical and e
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