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Chapter 48: Nervous Systems
What are the 3 main fcns of the nervous system? Sensory input – stimulus – PNS Integration– brain & spinal cord – CNS Motor output – response –PNS
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Figure 48.3 Overview of information processing by nervous systems
Sensor Effector Motor output Integration Sensory input Peripheral nervous system (PNS) Central nervous system (CNS) Protected by bone
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Chapter 48: Nervous Systems
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?
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Figure 48.4 The knee-jerk reflex
Sensory neurons from the quadriceps also communicate with interneurons in the spinal cord. 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. 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. 4 5 6 The reflex is initiated by tapping the tendon connected to the quadriceps (extensor) muscle. 1 Sensors detect a sudden stretch in the quadriceps. 2 Sensory neurons convey the information to the spinal cord. 3 Quadriceps muscle Hamstring muscle Spinal cord (cross section) Gray matter White matter Cell body of sensory neuron in dorsal root ganglion Sensory neuron Motor neuron Interneuron Figure 48.4 The knee-jerk reflex No brain involvement = faster response
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Chapter 48: Nervous Systems
What are the 3 main fcns of the nervous system? Sensory input – stimulus – PNS Integration– brain & spinal cord – CNS Motor output – response –PNS How does a reflex work? 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
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Figure 48.5 Structure of a vertebrate neuron
Dendrites Cell body Nucleus Axon hillock Axon Signal direction Synapse Myelin sheath Synaptic terminals Presynaptic cell Postsynaptic cell Cell body – has nucleus Dendrites – bring signal to cell body 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
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Chapter 48: Nervous Systems
What are the 3 main fcns of the nervous system? How does a reflex work? 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 Oligodendrocytes & Schwann cells
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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!,
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Figure 48.8 Schwann cells and the myelin sheath
Nodes of Ranvier Schwann cell Nucleus of Schwann cell Axon Layers of myelin Node of Ranvier 0.1 µm Node of Ranvier – space between Schwann cells on axon
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Chapter 48: Nervous Systems
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 Reference electrode Voltage recorder –70 mV
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Figure 48.10 Ionic gradients across the plasma membrane of a mammalian neuron
CYTOSOL EXTRACELLULAR FLUID [Na+] 15 mM [K+] 150 mM [Cl–] 10 mM [A–] 100 mM [Na+] 150 mM [K+] 5 mM [Cl–] 120 mM – + Plasma membrane [A-] – DNA, RNA, proteins What happens when Na+ comes in & K+ leaves?
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Figure 48.11 Modeling a mammalian neuron
Inner chamber Outer chamber –92 mV +62 mV Artificial membrane Potassium channel K+ Cl– 150 mM KCL 150 mM NaCl 15 mM NaCl 5 mM KCL Na+ Sodium channel – (a) Membrane selectively permeable to K+ (b) Membrane selectively permeable to Na+ As K+ leaves, the cell loses (+) charge It becomes more (-) As Na+ enters, the cell gains (+) charge It becomes more (+)
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Chapter 48: Nervous Systems
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?
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Figure 48.12 Graded potentials and an action potential in a neuron
+50 –50 –100 Time (msec) 4 5 6 Threshold Resting potential Hyperpolarizations Depolarizations Membrane potential (mV) Stimuli Stronger depolarizing stimulus Action potential (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K+. The larger stimulus produces a larger hyperpolarization. (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+. The larger stimulus produces a larger depolarization. (c) Action potential triggered by a depolarization that reaches the threshold. Hyperpolarization K+ channels open Slight depolarization Na+ channels open More depolarization More Na+ enters Threshold achieved (-55 mV) LOTS of Na+ channels open NEURONS ARE ALL OR NONE!!
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Chapter 48: Nervous Systems
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?
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Membrane potential (mV)
Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Threshold – – – – – – – – + + + + + + + + + + – – Na+ K+ 1 Resting state Undershoot 2 3 4 5 Sodium channel Action potential Resting potential Time Membrane potential (mV) +50 –50 –100 Cytosol
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Membrane potential (mV)
Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Threshold – – – – – – – – + + + + + + + + + + – – Na+ K+ 2 Depolarization 1 3 4 5 Sodium channel Action potential Resting potential Time Membrane potential (mV) +50 –50 –100 Cytosol Resting state
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Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Threshold – – – – – – – – + + + + + + + + + + – – Na+ K+ 1 Resting state 2 Depolarization 3 Rising phase of the action potential 4 5 Sodium channel Action potential Resting potential Time Membrane potential (mV) +50 –50 –100 Cytosol
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Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Threshold – – – – – – – – + + + + + + + + + + – – Na+ K+ 1 Resting state 2 Depolarization 3 Rising phase of the action potential 4 Falling phase of the action potential 5 Sodium channel Action potential Resting potential Time Membrane potential (mV) +50 –50 –100 Cytosol
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Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Threshold – – – – – – – – + + + + + + + + + + – – Na+ K+ 5 1 Resting state 2 Depolarization 3 Rising phase of the action potential 4 Falling phase of the action potential Undershoot Sodium channel Action potential Resting potential Time Membrane potential (mV) +50 –50 –100 Cytosol
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Figure 7.16 The sodium-potassium pump: a specific case of active transport
Cytoplasmic Na+ binds to the sodium-potassium pump. 1 Na+ binding stimulates phosphorylation by ATP. 2 K+ is released and Na+ sites are receptive again; The cycle repeats. 3 Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside. 4 Extracellular K+ binds to the protein, triggering release of the Phosphate group. 6 Loss of the phosphate restores the protein’s original conformation. 5 EXTRACELLULAR FLUID [Na+] high [K+] low CYTOPLASM [Na+] low [K+] high Na+ P ATP ADP P i K+ Maintains charge of -70 mV. NOT THE SAME AS A Na+ or K+ channel.
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Chapter 48: Nervous Systems
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?
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Figure 48.14 Conduction of an action potential
– + Na+ Action potential K+ Axon An action potential is generated as Na+ flows inward across the membrane at one location. 1 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?
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Figure 48.15 Saltatory conduction
Cell body Schwann cell Myelin sheath Axon Depolarized region (node of Ranvier) + + + + + – – – – – 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
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Chapter 48: Nervous Systems
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
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Figure 48.17 A chemical synapse
Presynaptic cell Postsynaptic cell Synaptic vesicles containing neurotransmitter Presynaptic membrane Postsynaptic membrane Voltage-gated Ca2+ channel Synaptic cleft Ligand-gated ion channels Na+ K+ Ligand- gated ion channel Neuro- transmitter 1 Ca2+ 2 3 4 5 6
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Chapter 48: Nervous Systems
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?
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Figure 48.18 Summation of postsynaptic potentials
E1 + E2 E1 + I I Action potential Resting potential Threshold of axon of postsynaptic neuron (a) Subthreshold, no summation (b) Temporal summation (c) Spatial summation (d) Spatial summation of EPSP and IPSP Terminal branch of presynaptic neuron Postsynaptic neuron E2 Axon hillock –70 Membrane potential (mV) Axon hillock determines overall charge. If threshold is met then action potential is fired.
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Na+ K+
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Chapter 48: Nervous Systems
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? Let’s look at some neurotransmitters….
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Table 48.1 Major Neurotransmitters
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Chapter 48: Nervous Systems
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? Let’s look at some neurotransmitters…. How is the nervous system organized?
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Figure 48.19 The vertebrate nervous system
Central nervous system (CNS) Peripheral nervous system (PNS) Brain Spinal cord Cranial nerves Ganglia outside CNS Spinal
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Figure 48.20 Ventricles, gray matter, and white matter
Gray matter – dendrites, unmyelinated axons & neuron cell bodies White matter – myelinated axons Ventricles – filled with CSF (cerebrospinal fluid)
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Figure 48.21 Functional hierarchy of the vertebrate peripheral nervous system
Somatic nervous system Autonomic Sympathetic division Parasympathetic Enteric
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Parasympathetic division Action on target organs:
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 acetylcholine postganglionic neurons: in ganglia close to or within target organs Constricts pupil of eye Stimulates salivary gland secretion Constricts bronchi in lungs Slows heart Stimulates activity of stomach and intestines of pancreas Stimulates gallbladder Promotes emptying of bladder Promotes erection of genitalia Cervical Thoracic Lumbar Synapse Sympathetic ganglia Dilates pupil Inhibits salivary Relaxes bronchi in lungs Accelerates heart Inhibits activity of stomach and intestines Inhibits activity Stimulates glucose release from liver; inhibits gallbladder adrenal medulla Inhibits emptying Promotes ejaculation and vaginal contractions Sacral thoracic and lumbar some in ganglia close to target organs; others in a chain of ganglia near spinal cord norepinephrine Rest & digest Fight or flight
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Students Test & LL – Monday Review session – after school & 7AM Monday Campus Beautification – 9AM tomorrow New seats….say good-bye…& then hello Phones in bins…off or muted….please & thank you! 1st 2nd 4th 7th 8th A 8 5 4 7 B 11 10 6 2 C 9 3 D --- 1 F n= 27 33 28 16 14 avg 87.5 82.5 82.9 84.8 87.9 High 103 105 99 100 Low 61 35 58 67 100+
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