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Chapter 48: Nervous Systems 1. What are the 3 main fcns of the nervous system? - Sensory input – stimulus – PNS - Integration– brain & spinal cord – CNS - Motor output – response –PNS Figure 48.3 Overview of information processing by nervous systems Sensory input Integration Sensor Motor output Effector Peripheral nervous system (PNS) Central nervous system (CNS) Protected by bone Chapter 48: Nervous Systems 1. What are the 3 main fcns of the nervous system? - Sensory input – stimulus – PNS - Integration– brain & spinal cord – CNS - Motor output – response –PNS 2. How does a reflex work? Figure 48.4 The knee-jerk reflex 2 Sensors detect a sudden stretch in the quadriceps. 3 Sensory neurons convey the information to the spinal cord. Cell body of sensory neuron in dorsal root ganglion 4 The sensory neurons communicate with motor neurons that supply the quadriceps. The motor neurons convey signals to the quadriceps, causing it to contract and jerking the lower leg forward. Gray matter 5 Sensory neurons from the quadriceps also communicate with interneurons in the spinal cord. Quadriceps muscle White matter Hamstring muscle Spinal cord (cross section) Sensory neuron Motor neuron 1 The reflex is initiated by tapping the tendon connected to the quadriceps (extensor) muscle. Interneuron 6 The interneurons inhibit motor neurons that supply the hamstring (flexor) muscle. This inhibition prevents the hamstring from contracting, which would resist the action of the quadriceps. No brain involvement = faster response Chapter 48: Nervous Systems 1. What are the 3 main fcns of the nervous system? - Sensory input – stimulus – PNS - Integration– brain & spinal cord – CNS - Motor output – response –PNS 2. How does a reflex work? 3. What cells make up the nervous system? - Neurons – functional unit of the nervous system - Supporting cells (glia) - Astrocytes, radial glia, oligodendrocytes, & Schwann cells - provide nutrition & support Figure 48.5 Structure of a vertebrate neuron Dendrites Cell body Nucleus Synapse Signal Axon direction Axon hillock Presynaptic cell Postsynaptic cell Myelin sheath Cell body – has nucleus Dendrites – bring signal to cell body Synaptic terminals Axon – takes signal away from cell body Axon hillock – cell body region where impulse is generated & axon begins Myelin – sheath that insulates axons made of supporting cells - PNS – Schwann cells secrete myelin - CNS – oligodendrocytes secrete myelin Synapse – junction between neurons or neuron & muscle or gland Chapter 48: Nervous Systems 1. What are the 3 main fcns of the nervous system? 2. How does a reflex work? 3. What cells make up the nervous system? - Neurons – functional unit of the nervous system - Supporting cells (glia) - Astrocytes - regulate extracellular concentration of ions & neurotransmitters - Form tight junctions between cells that line capillaries of brain & and spinal cord - Blood-brain barrier – restricts passage of substances into CNS - Can act as multipotent stem cells - Radial glia - Forms tracts for neurons to migrate in formation of neural tube - Can act as multipotent stem cells - Oligodendrocytes & Schwann cells Students -Test Monday means LL due Monday -Bozeman – 21, 22, 23, 37, 39, 41, 45 -Crash Course – 21, 26, 32, 33 -Phones in bin…muted or off…please & thank you!, Figure 48.8 Schwann cells and the myelin sheath Node of Ranvier Layers of myelin Axon Schwann cell Axon Myelin sheath Nodes of Ranvier Schwann cell Nucleus of Schwann cell Node of Ranvier – space between Schwann cells on axon 0.1 µm Chapter 48: Nervous Systems 1. 2. 3. 4. What are the 3 main fcns of the nervous system? How does a reflex work? What cells make up the nervous system? What is the charge of a neuron? - -70 mV - WHY??? Microelectrode –70 mV Voltage recorder Reference electrode Figure 48.10 Ionic gradients across the plasma membrane of a mammalian neuron EXTRACELLULAR FLUID CYTOSOL [Na+] 15 mM – + [Na+] 150 mM [K+] 150 mM – + [K+] 5 mM – + [Cl–] 10 mM – [Cl–] + 120 mM [A–] 100 mM – + Plasma membrane [A-] – DNA, RNA, proteins What happens when Na+ comes in & K+ leaves? Figure 48.11 Modeling a mammalian neuron –92 mV Outer chamber – 150 mM KCL +62 mV + 5 mM KCL 150 mM NaCl Cl– + – Cl– + Artificial membrane – (a) Membrane selectively permeable to K+ Outer chamber – 15 mM NaCl K+ Potassium channel Inner chamber + Inner chamber + – + – Na+ Sodium channel (b) Membrane selectively permeable to Na+ As K+ leaves, the cell loses (+) charge As Na+ enters, the cell gains (+) charge It becomes more (-) It becomes more (+) Chapter 48: Nervous Systems 1. 2. 3. 4. 5. What are the 3 main fcns of the nervous system? How does a reflex work? What cells make up the nervous system? What is the charge of a neuron? How is neuron polarity altered? Figure 48.12 Graded potentials and an action potential in a neuron Stimuli 0 Threshold 0 –50 0 1 2 3 4 5 Time (msec) (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K+. The larger stimulus produces a larger hyperpolarization. Hyperpolarization K+ channels open Threshold Action potential 0 –50 Resting Depolarizations potential Resting potential Hyperpolarizations –100 +50 Membrane potential (mV) +50 Membrane potential (mV) Membrane potential (mV) +50 –50 Stronger depolarizing stimulus Stimuli –100 Threshold Resting potential –100 0 1 2 3 4 5 Time (msec) (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+. The larger stimulus produces a larger depolarization. Slight depolarization Na+ channels open NEURONS ARE ALL OR NONE!! 0 1 2 3 4 5 6 Time (msec) (c) Action potential triggered by a depolarization that reaches the threshold. More depolarization More Na+ enters Threshold achieved (-55 mV) LOTS of Na+ channels open Chapter 48: Nervous Systems 1. 2. 3. 4. 5. 6. What are the 3 main fcns of the nervous system? How does a reflex work? What cells make up the nervous system? What is the charge of a neuron? How is neuron polarity altered? How is an action potential (nerve impulse) created? Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential Membrane potential (mV) +50 3 0 2 –50 –100 Extracellular fluid Na+ Action potential 5 1 Activation gates Potassium channel + + + + + + + + + + + + + + – – – – – – 1 Resting state 1 Resting potential Time Plasma membrane – – – – – – – – Cytosol Sodium channel 4 Threshold K+ Inactivation gate Undershoot Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential Na+ + + + + + + – – – – + + – – – – K+ Membrane potential (mV) +50 Na+ 3 0 2 –50 –100 2 Depolarization Extracellular fluid Na+ Action potential 5 1 Resting potential Time Activation gates Potassium channel + + + + + + + + + + + + + + Plasma membrane – – – – – – – – Cytosol – – – – – – Sodium channel 1 Resting state K+ 4 Threshold Inactivation gate 1 Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential Na+ Na+ – – – – – – – – + + + + + + + + K+ 3 Rising phase of the action potential Na+ + + + + + + – – – – + + – – – – K+ Membrane potential (mV) +50 Na+ 3 0 2 –50 –100 2 Depolarization Extracellular fluid Na+ Action potential 5 1 Resting potential Time Activation gates Potassium channel + + + + + + + + + + + + + + Plasma membrane – – – – – – – – Cytosol – – – – – – Sodium channel 1 Resting state K+ 4 Threshold Inactivation gate 1 Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential Na+ Na+ – – – – – – – – + + + + + + + + K+ 3 Na+ Na+ + + + + + + + + – – – – – – – – K+ Rising phase of the action potential 4 Falling phase of the action potential Na+ + + + + + + – – – – + + – – – – K+ Membrane potential (mV) +50 Na+ 3 0 2 –50 –100 2 Depolarization Extracellular fluid Na+ Action potential 5 1 Resting potential Time Activation gates Potassium channel + + + + + + + + + + + + + + Plasma membrane – – – – – – – – Cytosol – – – – – – Sodium channel 1 Resting state K+ 4 Threshold Inactivation gate 1 Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential Na+ Na+ – – – – – – – – + + + + + + + + K+ 3 Na+ Na+ + + + + + + + + – – – – – – – – K+ Rising phase of the action potential 4 Falling phase of the action potential Na+ + + + + + + – – – – + + – – – – K+ Membrane potential (mV) +50 Na+ 3 0 2 –50 –100 2 Depolarization Action potential 4 Threshold 5 1 1 Resting potential Time Na+ Extracellular fluid Na+ Activation gates Potassium channel + + + + + + + + + + + + + + Plasma membrane – – – – – – – – Cytosol – – – – – – Sodium channel 1 Resting state K+ Inactivation gate Na+ + + + + + + + + – – – – – – – – K+ 5 Undershoot Figure 7.16 The sodium-potassium pump: a specific case of active transport 1 Cytoplasmic Na+ binds to the sodium-potassium pump. EXTRACELLULAR [Na+] high FLUID [K+] low Na+ 2 Na+ binding stimulates phosphorylation by ATP. Na+ Na+ Na+ Na+ [Na+] low Na+ + CYTOPLASM [K ] high 3 K+ is released and Na+ sites are receptive again; The cycle repeats. P ADP Na+ ATP 4 Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside. Na+ Na+ K+ P K+ 5 Loss of the phosphate restores the protein’s original conformation. 6 Extracellular K+ binds to the protein, triggering release of the Phosphate group. K+ K+ K+ K+ P Maintains charge of -70 mV. NOT THE SAME AS A Na+ or K+ channel. Pi Chapter 48: Nervous Systems 1. 2. 3. 4. 5. 6. 7. What are the 3 main fcns of the nervous system? How does a reflex work? What cells make up the nervous system? What is the charge of a neuron? How is neuron polarity altered? How is an action potential (nerve impulse) created? Why does an action potential only travel in 1 direction? Figure 48.14 Conduction of an action potential Axon Action potential – – + + ++ – Na – + + – – + K+ + + – – – – + + K+ + + – – + + + + + – – + – – + – – + – – + – – + Action potential – – + ++ Na + + – – K+ + – – + + + – – – – + + K+ + – – + + – – + Action potential – – + ++ Na + + – – + – – + – + + – 1 An action potential is generated as Na+ flows inward across the membrane at one location. 2 The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K+ flows outward. 3 The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon. + – – + – + + – Domino analogy…. Where does this depolarization & repolarization take place? Figure 48.15 Saltatory conduction Schwann cell Depolarized region (node of Ranvier) Myelin sheath –– – Cell body + ++ + ++ ––– –– – + + Axon + ++ –– – Depolarization jumps down the axon from node to node. Na+ & K+ channels are only found at the node of Ranvier. Action potentials can travel 120 m/sec Chapter 48: Nervous Systems 1. 2. 3. 4. 5. 6. 7. 8. What are the 3 main fcns of the nervous system? How does a reflex work? What cells make up the nervous system? What is the charge of a neuron? How is neuron polarity altered? How is an action potential (nerve impulse) created? Why does an action potential only travel in 1 direction? How does a neuron communicate with another cell? - Chemical synapse - Signal changes from electrical chemical electrical Figure 48.17 A chemical synapse Postsynaptic cell Presynaptic cell Synaptic vesicles containing neurotransmitter 5 Presynaptic membrane Neurotransmitter Postsynaptic membrane Ligandgated ion channel Voltage-gated Ca2+ channel 1 Ca2+ 4 2 Synaptic cleft Na+ K+ 3 Ligand-gated ion channels Postsynaptic membrane 6 Chapter 48: Nervous Systems 1. 2. 3. 4. 5. 6. 7. 8. 9. What are the 3 main fcns of the nervous system? How does a reflex work? What cells make up the nervous system? What is the charge of a neuron? How is neuron polarity altered? How is an action potential (nerve impulse) created? Why does an action potential only travel in 1 direction? How does a neuron communicate with another cell? How does a single neuron interpret multiple inputs? Figure 48.18 Summation of postsynaptic potentials Terminal branch of presynaptic neuron Postsynaptic E1 neuron E1 E2 E1 E1 I Membrane potential (mV) Axon hillock Threshold of axon of postsynaptic neuron 0 Action potential Action potential Resting potential –70 E1 E1 (a) Subthreshold, no summation E1 E1 (b) Temporal summation E1 + E2 (c) Spatial summation Axon hillock determines overall charge. If threshold is met then action potential is fired. E1 I E1 + I (d) Spatial summation of EPSP and IPSP Na+ K+ Chapter 48: Nervous Systems 1. What are the 3 main fcns of the nervous system? 2. How does a reflex work? 3. What cells make up the nervous system? 4. What is the charge of a neuron? 5. How is neuron polarity altered? 6. How is an action potential (nerve impulse) created? 7. Why does an action potential only travel in 1 direction? 8. How does a neuron communicate with another cell? 9. How does a single neuron interpret multiple inputs? 10. Let’s look at some neurotransmitters…. Table 48.1 Major Neurotransmitters Chapter 48: Nervous Systems 1. What are the 3 main fcns of the nervous system? 2. How does a reflex work? 3. What cells make up the nervous system? 4. What is the charge of a neuron? 5. How is neuron polarity altered? 6. How is an action potential (nerve impulse) created? 7. Why does an action potential only travel in 1 direction? 8. How does a neuron communicate with another cell? 9. How does a single neuron interpret multiple inputs? 10. Let’s look at some neurotransmitters…. 11. How is the nervous system organized? Figure 48.19 The vertebrate nervous system Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Cranial nerves Ganglia outside CNS Spinal nerves Figure 48.20 Ventricles, gray matter, and white matter Gray matter White matter Ventricles Gray matter – dendrites, unmyelinated axons & neuron cell bodies White matter – myelinated axons Ventricles – filled with CSF (cerebrospinal fluid) Figure 48.21 Functional hierarchy of the vertebrate peripheral nervous system Peripheral nervous system Somatic nervous system Autonomic nervous system Sympathetic division Parasympathetic division Enteric division Figure 48.22 The parasympathetic and sympathetic divisions of the autonomic nervous system Parasympathetic division Sympathetic division Action on target organs: Location of preganglionic neurons: brainstem and sacral segments of spinal cord Neurotransmitter released by preganglionic neurons: acetylcholine Location of postganglionic neurons: in ganglia close to or within target organs Action on target organs: Dilates pupil of eye Constricts pupil of eye Inhibits salivary gland secretion Stimulates salivary gland secretion Constricts bronchi in lungs Sympathetic ganglia Cervical Accelerates heart Slows heart Stimulates activity of stomach and intestines Inhibits activity of stomach and intestines Thoracic Inhibits activity of pancreas Stimulates activity of pancreas Stimulates gallbladder Neurotransmitter released by postganglionic neurons: acetylcholine Stimulates glucose release from liver; inhibits gallbladder Lumbar Stimulates adrenal medulla Promotes emptying of bladder Promotes erection of genitalia Rest & digest Relaxes bronchi in lungs Inhibits emptying of bladder Synapse Sacral Location of preganglionic neurons: thoracic and lumbar segments of spinal cord Neurotransmitter released by preganglionic neurons: acetylcholine Location of postganglionic neurons: some in ganglia close to target organs; others in a chain of ganglia near spinal cord Neurotransmitter released by postganglionic neurons: norepinephrine Promotes ejaculation and vaginal contractions Fight or flight