Nerves & signaling Ch 37

I. Nerves = A. Cells called neurons bundled together in a sheath of connective tissue

II. Neurons:(fits form to function) A. cells that transmit impulses B. Neuron structure 1. Dendrites : fine branches that receive signals 2. Cell body : nucleus & organelles 3. Axon : transmits signal 4. Synaptic terminal : passes signal to next cell

III. Synapse / synaptic cleft A) Interstitial space between synaptic terminal and next cell B) signaling neuron is the presynaptic cell C) receiving cell is the Postsynaptic cell

IV. Neurotransmitters A. signaling molecules (chemical messengers) B. Carry signal from synaptic terminal to receptors on postsynaptic cell

V. Glia Cells that support neurons Nourish Regulate surrounding interstitial fluid Schwann cells – make myelin in PNS (peripheral nervous system)

VI. Information Processing : three stages 1. sensory input 2. integration 3. motor output

A. Sensory neurons: 1. External a. mechanoreceptors b. chemoreceptors c. photoreceptors 2. Internal a. baroreceptors (pressure) b. pain receptors

B. Divisions of Nervous system 1. CNS = central nervous system…spinal cord and brain 2. PNS = peripheral nervous system.. All other nerves

C. Integrators 1.Found in CNS : central nervous system 2. called interneurons :connect neurons in brain & longitudinal nerve cord 3. process info sent in by sensory neurons

D. Motor output 1. motor neurons transmit signal from CNS to effector cells a. muscle cells b. endocrine cells

VII. Movement Across Cell Membrane A. Simple diffusion 1. very small, not charged B. facilitated diffusion (protein channel) C. active transport –against conc. Grad 1. protein pump or co-transporter

VIII. Resting Potential A. Sodium potassium pump 1. active transport a. 3Na+ out and 2K+ into cell b. creates concentration gradients 1. high Na+ outside High K+ inside B. K+ channels leak ions back out 1. electrical gradient slightly positive outside cell 2. -70 mV potential energy…voltage

2 K+ in for every 3 Na+ out more K+ leaks out than Na+ leaks in

C. Equilibrium Potential = magnitude of voltage across membrane 1. EK =-90 mV 2. ENa = +62 mV 3. Resting potential ≈ -70 mV bcs more K+ leaking 4. Hyper polarization = inside even more negative…increase K diffusing out 5. Depolarization = inside becomes less negative…open Na channels

6. Graded potentials.. different levels of depolarization a. different neuron responses b. no response or action potential c. depolarization signals are summative

Graded potential: High grade: intense or long lasting Low grade: small stimulus, depolarization does not reach trigger zone with high enough energy = no action potential sent down axon High grade: intense or long lasting Signal reaches trigger zone at or above threshold level Action potential send down axon

IX. Action Potential: massive depolarization A. Sum of depolarization signals causes depolarization level to reach threshold B. voltage-gated Na channels open C. positive feed back opens more D. Na flow brings voltage closer to 0mV then above 0mV to be positive E. voltage gated K channels open F. restore negative cytoplasm G. undershoot = too much negative charge inside H. resting potential restored by NaK pumps

Action potential initiation http://www.mind.ilstu.edu/curriculum/neurons_intro/ne urons_intro.php

X.Action potential:quick reversal of polarity http://www.youtube.com/watch?v=7EyhsOewnH4&feature=related A.Action potential is all or nothing B.Na+ flow in as fast as possible for .5ms C.Then Na+ gates shut and K+ gates open

XI. Propagation of action potential http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0014- swf_action_potenti.swf http://www.youtube.com/watch?v=CvktREcRMAo&feature=related A. One patch of membrane activates the Na+ gates next to it by becoming positive inside…..causes more Na+ gates to open B. Propagation is 1 way due to gate inactivation. 1. refractory period = Na gated channels are inactivated

C. Saltatory conduction (leap) 1. Myelin = insulator. 2. space btwn schwann cells =nodes of Ranvier. Nerve impulse jumps between Nodes =faster transmission

XII. Transduction of Action Potential A. Electrical synapse: direct transmission of electric charge via gap junctions =rapid unvarying response (brain) B. Chemical Synapse 1. Depolarization opens Ca+ channels 2. Ca+ causes synaptic vesicles to release neurotransmitters by exocytosis 3. Neurotransmitters diffuse to postsynaptic cell & bind to receptors

C. Neurotransmitters – 2 categories 1. excitatory : causes depolarization (encourages signal transmission) 2. inhibitory : causes hyperpolarization (discourages signal transmission) 3. Ach = acetylcholine (muscle) both excitatory and inhibitory 4. serotonin = mood/ memory/sleep 5. epinephrine/norepinephrine (called adrenalin & noradrenalin in endocrine function)

D. Receptors 1. Most = ligand-gated ion channels a. neurotransmitter = the ligand b. binding of ligand opens the gate c. some let K+ & Na+ pass to depolarize (excitatory) d. some let in Cl- to hyperpolarize (inhibitory)

2) some activate 2nd messenger a) slower longer lastingresponse b) binding n.t. activates G protein c) G protein activates enzyme to make ATP into cAMP d) cAMPs activate protein kinase As e) Kinase As phosphorolate many channels = open them f) many kinase As = amplified signal

E. Transduction = response 1. EPSP=excitatory postsynaptic potential encourages ps cell response 2. IPSP=inhibitory pulls the cell back from threshold (restores resting polarization) 3. integration = summation of EPSP & IPSP determines response of cell a. spatial summation : multiple synapses of same cell receive signal b. Temporal summation : rapidly repeated signal

F. Clearing of synaptic cleft 1. Neurotransmitters cleared by… a. diffusion b. re-uptake into pre-synaptic cell c. enzyme mediated breakdown https://www.youtube.com/watch?v=rWrnz-CiM7A&feature=related#t=3.046506

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