3 A nervous system has three overlapping functions: 1) SENSORY INPUT: signals from sensory receptors to integration centers2) INTEGRATION: information from sensory receptors is interpreted and associated with appropriate responses3) MOTOR OUTPUT: conduction of signals from the integration center to effector cells (muscle cells or gland cells)
8 Two Main Classes of Cells: 1) NEURONS: functional unit of the nervous system transmits signals from one location to another made up of: cell body, dendrites, axon many axons are enclosed by an insulating layer called the MYELIN SHEATH include: sensory neurons,interneurons,motor neurons
13 2) GLIAL CELLS (“GLIA”) - SUPPORTING CELLS 10 to 50 times more numerous than neurons provide structure; protect, insulate, assist neurons example: Schwann cells and oligodendrocytes form myelin sheaths in the PNS and CNS, respectively
20 ACTION POTENTIALS & NERVE IMPULSES all cells have an electrical charge difference across their plasma membranes; that is, they are POLARIZED. this voltage is called the MEMBRANE POTENTIAL (usually –50 to –100 mV) inside of cell is negative relative to outside arises from differences in ionic concentrations inside and outside cell
25 of a nerve cell is approx. –70 mV the “resting potential”of a nerve cell is approx.–70 mV neurons have specialion channels (GATEDION CHANNELS) that allow the cellto change its membrane potential(a.k.a. “excitable” cells)
27 when a stimulus reaches a neuron, it causes the opening of gated ion channels (e.g.: light photoreceptors in the eye; sound waves/vibrations hair cells in inner ear)
28 HYPERPOLARIZATION: membrane potential becomes more negative (K+ channel opens; increased outflow of K+) DEPOLARIZATION: membrane potential becomes less negative(Na+ channel opens; increased inflowof Na+)**If the level of depolarization reaches the THRESHOLD POTENTIAL, an ACTION POTENTIAL is triggered.
29 ACTION POTENTIALS (APs): the nerve impulse all-or-none event; magnitude is independent of the strength of the stimulus
30 5 Phases of an A.P.:1) Resting state2) Depolarizing phase3) Rising phase of A.P.4) Falling phase of AP (repolarizing phase)5) Undershoot
39 **during the undershoot, both Na+ channel gates are closed; if a second depolarizing stimulus arrives during this time, the neuron will NOT respond (REFRACTORY PERIOD) strong stimuli result in greater frequency of action potentials than weaker stimuli
43 How do action potentials “travel” along an axon? the strong depolarization of one action potential assures that the neighboring region of the neuron will be depolarized above threshold, triggering a new action potential, and so on…
56 Electrical Synapses: allow action potentials to spread directly from pre- to postsynaptic cell *connected by gap junctions (intercellular channels that allow local ion currents)**Most synapses are…Chemical Synapses: cells are separated by a synaptic cleft, so cells are not electrically coupled; a series of events converts:elec. signal chem.signal elec.signalHOW???...
57 NEUROTRANSMITTERS: intercellular messengers; released into synaptic cleft when synaptic vesicles fuse with presynaptic membrane specific receptors for neurotransmitters project from postsynaptic membrane; most receptors are coupled with ion channels neurotransmitters are quickly broken down by enzymes so that the stimulus ends
61 the electrical charge caused by the binding of neurotransmitter to the receptor can be: EPSP (Excitatory Postsynaptic Potential): membrane potential is moved closer to threshold (depolarization)IPSP (Inhibitory Postsynaptic Potential): membrane potential is hyperpolarized (more negative)
63 most single EPSPs are not strong enough to generate an action potential when several EPSPs occur close together or simultaneously, they have an additive effect on the postsynaptic potential: SUMMATION-temporal vs. spatial
66 Examples of neurotransmitters: **acetylcholine Neuromuscular junction; can be inhibitory or excitatoryepinephrinenorepinephrinedopamineserotoninendorphins Decrease perception of pain by CNS; (heroin & morphine mimic endorphins)epin. & norep. also function ashormones; “fight or flightresponse”dop. & ser. both affect sleep, mood,attention, learning; LSD &mescaline bind to ser. & dop.receptors
67 Neurotransmitters: Ach ACETYLCHOLINE: triggers skeletal muscle fibers to contract… so, how does a muscle contraction stop???
68 Neurotransmitters: Ach a muscle contraction ceases when the acetylcholine in the synapse of the neuromuscular junction is broken down by the enzyme…..wait for it………………….
69 ACETYLCHOLINESTERASE!! It’s term #4!!!!! ACETYLCHOLINESTERASE = the enzyme the breaks down the neurotransmitter acetylcholine.
70 ACETYLCHOLINESTERASE! ***word #4 on my list!!!1) Okazaki fragments2) plasmodesmata3) ????????4) acetylcholinesterase5) ????????6) rubisco7) oxaloacetate8) islets of Langerhans9) Batesian mimicry10) nodes of Ranvier