? ? ? ? ? ? ? ? + + + + + + + + + + + + + + ? ? ? ? ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? + + ? ? ? ? + + ? ? + + ? ? + + ? ? + + Na+ Na+ K+ Na+ Na+ K+ Na+ Na+ K+ Na+ K+ K+ Na+ Na+ 5 1 Resting state 2 Depolarization 3 4 Falling phase of the action potential Undershoot 1 2 3 4 5 1 Sodium channel Action potential Resting potential Time Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Membrane potential (mV) +50 0 ?50 ?100 Threshold Cytosol Rising phase of the action potential Generation of an Action Potential Generation of an Action Potential Legend for diagram on following slide 1. The activation gates on the Na+ and K+ channels are closed, and the membrane?s resting potential is maintained. 2. A stimulus opens the activation gates on some Na+ channels. Na+ influx through those channels depolarizes the membrane. If the depolarization reaches the threshold, it triggers an action potential. 3. Depolarization opens the activation gates on most Na+ channels, while the K+ channels? activation gates remain closed. Na+ influx makes the inside of the membrane positive with respect to the outside. 4. The inactivation gates on most Na+ channels close, blocking Na+ influx. The activation gates on most K+ channels open, permitting K+ efflux which again makes the inside of the cell negative. 5. Both gates of the Na+ channels are closed, but the activation gates on some K+ channels are still open. As these gates close on most K+ channels, and the inactivation gates open on Na+ channels, the membrane returns to its resting state. Nerve impulses propagate themselves along an axon in a domino-effect fashion A positive feedback mechanism is responsible for propagation of action potentials down the axon. Nerve impulses propagate themselves along an axon in a domino-effect fashion A positive feedback mechanism is responsible for propagation of action potentials down the axon. Action potentials are not propagated ?up? the axon (towards the hillock), only ?down? the the axon ? refractory period Contraction of the squid mantle in response to the simultaneous activation of muscle throughout the mantle by the axons Signal Transmission Speed Transmission speed of an action potential is significantly influenced by two factors Axon diameter Myelination http://www.mbl.edu/publications/pub_archive/Loligo/squid/neuro1.html Saltatory conduction along myelinated axons Insulation precludes ion exchange across the membrane, even through specialized ion channels Communication between neurons; Synapses and signal processing in post-synaptic neurons Synapse types Electrical synapses Chemical synapses Direct synaptic transmission Indirect synaptic transmission Action potential Presynaptic membrane Ca2+ Ca2+ Ca2+ Presynaptic neuron Ca2+ Ca2+ Postsynaptic membrane Postsynaptic neuron 1 Action potential arrives; triggers entry of Ca2+. 2 In response to Ca2+, synaptic vesicles fuse with membrane, release neurotransmitter 3 Ligand-gated Ion channels open When neurotransmitter binds, ion flow causes change in postsynaptic cell potential. Direct synaptic transmission Action potential Presynaptic membrane Ca2+ Ca2+ Ca2+ Presynaptic neuron Ca2+ Ca2+ Postsynaptic membrane Postsynaptic neuron 1 Action potential arrives; triggers entry of Ca2+. 2 In response to Ca2+, synaptic vesicles fuse with membrane, release neurotransmitter 3 Ligand-gated Ion channels open When neurotransmitter binds, ion flow causes change in postsynaptic cell potential. Direct synaptic transmission Postsynaptic Potentials Neurotransmitter causes influx of Na+; generates EPSP (excitory post synaptic potential) Neurotransmitter causes efflux of K+ or influx of Cl-; generates IPSP Magnitude of postsynaptic potentials depends on amount of neurotransmitter released at synapse Various mechanisms terminate effect of neurotransmitter ? diffusion, active transport, glial activity, enzyme activity Often involved in indirect synaptic transmision, usually in CNS Often involved in indirect synaptic transmision Vertebrate CNS and PNS * Vertebrate Nervous System: CNS & PNS Anatomic diagrams of major components of mammalian CNS and PNS * Anatomic diagrams of major components of mammalian CNS and PNS Schwann cell, myenates axons Axons Nerve * * The autonomic nervous system consists of two division that act on body organs with opposing effects. Activation of the sympathetic division correlates with arousal and energy generation; the heart beats faster, the liver converts glycogen to glucose, bronchi of the lungs dilate and support increased gas exchange, digestion is inhibited, and secretion of adrenaline from the adrenal medulla is stimulated. Activity of the parasympathetic division causes approximate the mirror image of this; a calming and a return to emphasis on self-maintenance functions. The Autonomic Nervous System Controls Internal Processes PARASYMPATHETIC NERVES ?Rest and digest? SYMPATHETIC NERVES ?Fight or flight? Constrict pupils Stimulate saliva Slow heartbeat Constrict airways Stimulate activity of stomach Inhibit release of glucose; stimulate gallbladder Stimulate activity of intestines Contract bladder Promote erection of genitals Sacral nerves Lumbar nerves Thoracic nerves Cervical nerves Cranial nerves Dilate pupils Inhibit salivation Increase heartbeat Relax airways Inhibit activity of stomach Stimulate release of glucose; inhibit gallbladder Inhibit activity of intestines Relax bladder Promote ejaculation and vaginal contraction Secrete epinephrine and norepinephrine (hormones that stimulate activity; see Chapter 47) Sympathetic chain: bundles of nerves that synapse with nerves from spinal cord, then send projections to organs The vertebrate CNS develops from the hollow, dorsal, embryonic neural tube. The brain forms from three swellings at its anterior end, which become the hindbrain, midbrain, and forebrain * Pituitary Cerebral peduncles Cerebrum Telencephalon Diencephalon The brain is made up of four distinct structures. Inside view Diencephalon Information relay and control of homeostasis Brain stem Information relay and center of autonomic control for heart, lungs, digestive system Cerebrum Conscious thought, memory Cerebellum Coordination of complex motor patterns Except for the cerebrum, these functions generally apply to mammals in general. The cerebrum in mammals in general, functions in movement, sensory processing, olfaction, communication, learning and memory Human Cerebral Function Coritical function Sensory perception Voluntary control of muscle Language & communication Personality traits Sophisticated mental events; thinking, memory, decision-making, creativity, self-conciousness Many aspects of behavior & intellect in general Basal Nuclei function Organize motor output Cortical structure and function Functional areas in each lobe Primary sensory areas Association areas
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