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Biology 2331 – A&P I M&H Chapter 11 – Fundamentals of the Nervous System and Nervous Tissue Lecture: Nervous Tissue

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Biology 2331 – A&P I M&H Chapter 11 – Fundamentals of the Nervous System and Nervous Tissue Lecture: Nervous Tissue Biology 2331 – A&P I M&H Chapter 11 – Fundamentals of the Nervous System and Nervous Tissue Lecture: Nervous Tissue Learn and Understand: 1. Like muscle cells, neurons use membrane polarity upset (AP) as a signal therefore keeping their membranes constantly ready (RMP). 2. In order to carry their message, some neurons have axons greater than 1 m in length. 3. Increasing the frequency of action potentials, not its strength, is how the NS controls the intensity of its message. 4. Graded potentials may sum to threshold depolarization causing AP in the neuron. The source of graded potentials is the up to 10,000 synapses with other neurons. 5. Neuroglia help create and maintain the environmental conditions necessary for optimal neuron functioning. Some concepts that you may have to learn on your own: o Differences between sarcolemma action potential and axolemma action potential. o Neuronal pathways and circuits – how is information passed to various parts of the nervous system; convergence, divergence, reverberating, parallel and serial processing of action potentials o Neurotransmitter classification and function. o Classification of axons based on degree of myelination. Some concepts you must know for the next test: o Functions of the nervous system. o Anatomic and functional divisions of the nervous system. o Cells of the nervous system: structural classifications of neurons and their functions; structural classifications of glial cells and their functions o Composition of the myelin sheath: cells involved, role in transmission of action potential; functional differences of myelinated and unmyelinated axons. o Chemical events, ions, gates, channels involved in resting membrane potential at the axolemma; permeability characteristics of the axolemma particularly as it relates to potassium ion. o How the axolemma is depolarized; hyperpolarized. o Consider now graded potential – not discussed when presenting sarcolemma action potential o Threshold o Chemical events, ions, gates, channels involved in action potential at the axolemma o The causes and benefits of the two types of refractory periods. o Stimulus intensity and frequency of action potentials o Speed and event differences between unmyelinated action potential propagation and saltatory conduction. Speed of conduction by different groups of neurons. o Adding to what you already know about chemical synapses consider the function and role of electrical synapses. o Presynaptic inhibition and synaptic potentiation: structures involved; how the events lead to ‘neuromodulation.’ o Summation of graded potentials in the postsynaptic neuron. Some concepts in the chapter that won’t be covered on the next test: Table 11.3 Neurotransmitters and neuromodulators. – no need to try and memorize this table Developmental aspects of neurons. Lecture Outline I. Functions of the Nervous System a. Sensory b. Integration c. Motor d. Higher level functions – some uniquely human e. rapid and specific II. Anatomic Divisions of the Nervous System a. CNS i. Brain ii. Spinal cord b. PNS i. Cranial nerves ii. Spinal nerves iii. Ganglia – gathering of NCBs outside of CNS iv. Plexus – sensory-integration-motor networks outside of the CNS v. Sensory receptors and tissue III. Functional Divisions of the PNS a. Sensory i. Somatic ii. Visceral b. Motor i. Somatic ii. Autonomic 1. Sympathetic 2. Parasympathetic 3. Enteric IV. Cells of the Nervous System a. Neurons i. Parts: 1. Nerve cell body 2. Dendrite 3. Axon 4. unique organelles and adaptations: nissl bodies, axon terminals, axon hillock, axon collaterals 5. Others ii. Permanent tissue – extreme longevity, amitotic iii. Structural and functional classifications: 1. Multipolar – common – Motor 2. Bipolar – least common – Sensory 3. Unipolar/pseudounipolar – common –Sensory 4. Interneurons or association neurons b. Neuroglia i. Astrocyte ii. Ependymal cell iii. Microglia iv. Oligodendrocytes v. Schwann cell (neurolemmacyte) - PNS only vi. Satellite cells - PNS only V. Myelination a. Function of myelin in myelinated axons b. Unmyelinated axons VI. Electrical excitability – RMP, GP, and AP a. Resting membrane potential i. About -70 to -90 mV b. Ionic concentration differences across cell membrane i. Membrane permeability differences ii. Availability of open (leak) channels, ligand-gated channels, voltage-gated channels iii. Negatively-charged cytoplasmic proteins 1. Attracts positively charged potassium ion, repels negatively charged chloride ion iv. Final ion concentration on each side of membrane the result of diffusion, active transport, availability of leak channels, and attractive/repulsive forces – electrochemical equilibrium c. Graded or local potential i. Generated when ligand-gated or mechanically-gated ion channels open or close, temperature changes ii. Can summate iii. Spread under the plasma membrane for short distances then summate or dissipate iv. Depolarization or hyperpolarization 1. When Na+ enters cell or K+ enters and does not leave cell, depolarization occurs 2. When K+ leaves cell and does not reenter or Cl- enters, hyperpolarization occurs d. Action potential VII. Nerve Action Potential a. Basic steps involved i. Graded potential sums to threshold ii. Voltage-gated Na channels open activation gates iii. Voltage gated K channels open but slower than Na activation gates iv. Na enters cell completely depolarizing membrane to +20 mV v. Activation and Inactivation gates on Na voltage gated channels close – no more Na can enter the cell vi. Open voltage gated K channels allow K to leave cell vii. Membrane is repolarized viii. Na/K pump resets ion concentrations to RMP configuration b. Refractory period i. Absolute: activation and inactivation gates on Na voltage gated channels are closed and no graded potentials of any strength will cause the neuron to reach action potential ii. Relative: Na activation and inactivation gates are reset – neuron will reach action potential with graded potential of sufficient strength (must overcome hyperpolarization by K+) c. Propagation of AP i. Unmyelinated or continuous propagation of AP 1. Domain by domain ii. Myelinated propagation of AP 1. Saltatory – occurring only at Nodes of Ranvier 2. Much faster than unmyelinated iii. Nerve fiber groups 1. Group A 2. Group B 3. Group C d. Synapses i. Electrical 1. Gap junctions ii. Chemical 1. Neurotransmitter needed 2. Synaptic delay 3. Neurotransmitters are ligands that open or close ligand-gated ion channels iii. Presynaptic Facilitation and inhibition of neurotransmitter release VIII. Postsynaptic Local Potentials a. Excitatory postsynaptic potential i. Depolarization of postsynaptic membrane b. Inhibitory postsynaptic potential i. hyperpolarization of postsynaptic membrane c. Summation of local potential i. Spatial ii. Temporal iii. Combined – realistic .
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