EXSC 224 Lecture 2: Lecture 2 - 8/23

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University of South Carolina
Exercise Science
EXSC 224

Neurons - nerve cells ● Neurons have a resting membrane potential ● Primary cell in the nervous system ● Cell body - biosynthetic center and receptive region ○ *Also called the Soma* ○ Nissil bodies = Rough ER ■ Only called this is NEURONS ■ Rough ER does protein synthesis ○ Has nucleus - makes neurotransmitters (which usually secrete protein/ amino acid) ○ Well-developed Golgi apparatus ■ Modify the proteins made in rough ER ■ Package protein in vesicles ○ Mitochondria - lots, has rough and smooth ER ■ Oxygen is used to produce ATP ○ High metabolic rate ○ Glucose - only use this for fuel (NOT fats) ○ Axon hillock - Cone-shaped area from which the axon arises ■ Segway between cell body and axon ■ Generates action potential if stimulous is big enough ■ Converts stimulus to impulse (AP) ○ Cytoskeleton (neurofibrils and neurofilaments) ■ Microtubules and ATP transports vesicles produced in cell body down the axon ■ Gives neuron it’s shape ○ Clusters of cell bodies are called ■ 1. Nuclei in the CNS ● Lots of nuclei present ■ 2. Ganglia in the PNS ● Only sensory neurons have ganglia, motor neurons don’t! ● Processes - Extensions from the cell body (dendrites and axons) ○ In CNS - tracts ■ Tracts are clusters of axons within CNS ○ In PNS - nerves ■ Axons within the PNS ○ Neurilemma ○ Schwann cell - one internode ○ Node of Ranvier ○ Terminal branches - axon terminals/secretory region ● Dendrites - receive signals from other neurons ○ Receptive/input region from both sensory components or other neurons ○ Short, tapering, and diffusely branched ■ Allow for a large surface area for which neurons can synapse onto ○ Convey input toward the cell body ■ Graded potentials - at the synapses (between neuron to neuron) ● Between dendrites and incoming information into neuron ● Axon - conducting region of a neuron ○ Generates and transmits impulses (aka. axon potentials) ○ One axon per cell arising from the axon hillock ■ Axon hillock generates the AP that travels down the length of the axon ● AP = impulse or nerve impulse ○ Numerous terminal branches - knoblike axon terminals ■ Synaptic knobs or boutons (where neurotransmitter is secreted) ■ Can branch enough to synapse onto hundreds of dendrites ● Myelin Sheath - dont need to know a TON about myelin ○ Oligodendrocytes and Schwann cells - myelin fills the volume of these ○ Axons have proteins, ion channels (Na/K pumps, Na & K pumps) ■ NO ion channels or pumps can cross the membran where myelin wraps around axon ○ Myelin wraps around axon in segments, there are gaps between wrappings ○ Space between myelin wrapping is called Node of Ranvier ○ Membrane at node of Ranvier is DIFFERENT from membrane inside schwann cell ○ AP jumps from one Node of Ranvier to the next ○ Segmented protein-lipoid sheath around most long or large-diameter axon ○ Functions: ■ 1. Protect and insulate the axon - more difficult to injure axon ● Acts as a scaffold to repair axons that have been injured ■ 2. Increase speed of nerve impulse transmission ○ When in the PNS ■ Concentric layers of Schwann cell membrane ■ Not all neurons are myelinated!! ■ Lu gherrics disease - dead neurons ○ When in the CNS ■ Formed by processes of oligodendrocytes ● Wrap around multiple axons ■ Nodes of Ranvier are present ● Thinnest fibers are unmyelinated ○ White matter - dense collections of myelinated fibers ■ Occasionally, some axons are sometimes not myelinated ○ Gray matter - mostly neuron cell bodies and unmyelinated fibers ■ NOT MYELINATED ■ Cell body and dendrites are never myelinated ● Neuron function - ○ 1. Neurons are highly irritable/ excitable ■ There is a resting membrane potential, we can disrupt this resting membrane potential ○ 2. Respond to adequate stimulus by generating an action potential (AP) ○ 3. AP is always the same regardless of stimulus ■ All the same size and duration ● Principles of Electricity (Ions) ○ 1. More positive charges outside cell than inside cell ○ 2. Energy is required to separate opposite charges across a membrane ○ 3. If opposite charges are separated, the system has potential energy
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