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Chapter 48 and 49 Name_______________________________ Date: 1. What are neurons? Neurons are nerve cells that transfer information within the body Neurons use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance) 2. What are the three stages in which the nervous systems process information? Briefly describe them. Nervous systems process information in three stages: sensory input, integration, and motor output • Sensors detect external stimuli and internal conditions and transmit information along sensory neurons • Sensory information is sent to the brain or ganglia, where interneurons integrate the information • Motor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity 3. Many animals have a complex nervous system that consists of a CNS and a PNS. What are they? a. A central nervous system (CNS) where integration takes place; this includes the brain and a nerve cord b. A peripheral nervous system (PNS), which brings information into and out of the CNS 4. Draw and label a typical nerve cell below. Make sure to label and briefly describe the following parts: cell body, dendrites, axon, axon hillock, synapse, synaptic terminal, presynaptic and postsynaptic cell, and glia. • Most of a neuron’s organelles are in the cell body • Most neurons have dendrites, highly branched extensions that receive signals from other neurons • The axon is typically a much longer extension that transmits signals to other cells at synapses • An axon joins the cell body at the axon hillock • A synapse is a junction between an axon and another cell • The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters Chapter 48 and 49 • Name_______________________________ Date: Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell) • Most neurons are nourished or insulated by cells called glia Fig. 48-4 Dendrites Stimulus Nucleus Cell body Axon hillock Presynaptic cell Axon Synapse Synaptic terminals Postsynaptic cell Neurotransmitter 5. What is a membrane potential? What is the resting potential? Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential. Messages are transmitted as changes in membrane potential. The resting potential is the membrane potential of a neuron not sending signals Chapter 48 and 49 Name_______________________________ Date: 6. What is the principal cation inside the cell? outside the cell? What does this do to the charge inside and outside of the cell? In a mammalian neuron at resting potential, the concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane These concentration gradients represent chemical potential energy 7. Which side of the membrane has a negative charge? Anions trapped inside the cell contribute to the negative charge within the neuron Key + Na K + Sodiumpotassiu m pump OUTSIDE CELL + OUTSIDE [K ] CELL 5 mM INSIDE CELL + [K ] 140 mM + – [Na ] [Cl ] 150 mM 120 mM + [Na ] 15 mM – [Cl ] 10 mM – [A ] 100 mM INSIDE CELL (a) (b) 8. What pump is used to maintain the gradients across the membrane? Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane Po ch Chapter 48 and 49 Name_______________________________ Date: 9. What change in the permeability of the cell’s membrane to K+ and/or Na+ could cause the cell’s membrane potential to shift from -70mV to -90mV? The opening of ion channels in the plasma membrane converts chemical potential to electrical potential A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell 10. What is hyperpolarization? How does it occur? Membrane potential changes in response to opening or closing of these channels When gated K+ channels open, K+ diffuses out, making the inside of the cell more negative This is hyperpolarization, an increase in magnitude of the membrane potential 11. What is depolarization? How does it occur? Other stimuli trigger a depolarization, a reduction in the magnitude of the membrane potential For example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the cell 12. What is a graded potential? Graded potentials are changes in polarization where the magnitude of the change varies with the strength of the stimulus 13. What is an action potential? What role does a threshold plays in an action potential? Voltage-gated Na+ and K+ channels respond to a change in membrane potential When a stimulus depolarizes the membrane, Na+ channels open, allowing Na+ to diffuse into the cell The movement of Na+ into the cell increases the depolarization and causes even more Na+ channels to open A strong stimulus results in a massive change in membrane voltage called an action potential An action potential occurs if a stimulus causes the membrane voltage to cross a particular threshold An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane Action potentials are signals that carry information along axons Chapter 48 and 49 Name_______________________________ Date: 14. The following diagram shows the changes in voltage-gated channels during an action potential. Label the channels and inactivation gate, ions, and the components of the graph. Name and describe the five phases of the action potential Place numbers on the graph to show where each phase is occurring. After labeling the diagram, you should be able to tell me about the rising and falling phase, the undershoot, and the refractory period. Fig. 48-10-5 Key Na + + K 3 4 Rising phase of the action potential Fa +50 Action potential Membrane potential (mV) 3 0 2 –50 4 Threshold 1 1 5 2 Depolarization Extracellular fluid –100 Sodium channel Resting potential Time Potassium channel Plasma membrane Cytosol Inactivation loop 5 1 Resting state Undersho Chapter 48 and 49 • Name_______________________________ Date: At resting potential 1. Most voltage-gated Na+ and K+ channels are closed, but some K+ channels (not voltage-gated) are open • When an action potential is generated 2. Voltage-gated Na+ channels open first and Na+ flows into the cell 3. During the rising phase, the threshold is crossed, and the membrane potential increases 4. During the falling phase, voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell 5. During the undershoot, membrane permeability to K+ is at first higher than at rest, then voltage-gated K+ channels close; resting potential is restored • During the refractory period after an action potential, a second action potential cannot be initiated • The refractory period is a result of a temporary inactivation of the Na+ channels 15. Where is an action potential generally generated? Why does the action potential only travel in one direction? An action potential can travel long distances by regenerating itself along the axon At the site where the action potential is generated, usually the axon hillock, an electrical current depolarizes the neighboring region of the axon membrane • Inactivated Na+ channels behind the zone of depolarization prevent the action potential from traveling backwards • Action potentials travel in only one direction: toward the synaptic terminals 16. What factors affect the conduction speed of a action potential? The speed of an action potential increases with the axon’s diameter In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase, Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS 17. What are the two types of synapse? What is the difference between the two? At electrical synapses, the electrical current flows from one neuron to another At chemical synapses, a chemical neurotransmitter carries information across the gap junction Most synapses are chemical synapses Chapter 48 and 49 Name_______________________________ Date: 18. How does the signal get transferred from the presynaptic to the postsynaptic neurons across a chemical synapse? In other words, what does the presynaptic neuron synthesize and how does this cause a response in the postsynaptic neuron? The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal The action potential causes the release of the neurotransmitter The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell. Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential 19. What are the two types of postsynaptic potentials? Describe them briefly. a. Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold b. Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from threshold 20. What is a temporal summation? What is spatial summation? What is the difference between the two and what will the combination of them trigger? A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron If two EPSPs are produced in rapid succession, an effect called temporal summation occurs. In spatial summation, EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together The combination of EPSPs through spatial and temporal summation can trigger an action potential Through summation, an IPSP can counter the effect of an EPSP The summed effect of EPSPs and IPSPs determines whether an axon hillock will reach threshold and generate an action potential 21. What is modulated synaptic transmission? What kind of effects can this indirect synaptic transmission have? In indirect synaptic transmission, a neurotransmitter binds to a receptor that is not part of an ion channel Chapter 48 and 49 Name_______________________________ Date: This binding activates a signal transduction pathway involving a second messenger in the postsynaptic cell Effects of indirect synaptic transmission have a slower onset but last longer 22. Complete the chart below. Neurotransmitter Acetylcholine Function • Example Acetylcholine is a common neurotransmitter in vertebrates and invertebrates • In vertebrates it is usually an excitatory transmitter Biogenic amines • Biogenic amines epinephrine, norepinephrine, include epinephrine, dopamine, and serotonin norepinephrine, dopamine, and serotonin • They are active in the CNS and PNS Amino acids • Two amino acids are known to function as major neurotransmitters in the CNS: gammaaminobutyric acid (GABA) and glutamate Neuropeptides • Several • Neuropeptides neuropeptides, include substance P relatively short and endorphins, Chapter 48 and 49 Name_______________________________ Date: • chains of amino acids, which both affect also function as our perception of neurotransmitters pain Opiates bind to the same receptors as endorphins and can be used as painkillers Gases • Gases such as nitric oxide and carbon monoxide are local regulators in the PNS Chapter 49 23. What is a nerve net? A nerve net is a series of interconnected nerve cells More complex animals have nerves 24. Bilaterally symmetrical animals exhibit . Define this term below. Bilaterally symmetrical animals exhibit cephalization Cephalization is the clustering of sensory organs at the front end of the body 25. What are ganglia? Annelids and arthropods have segmentally arranged clusters of neurons called ganglia 26. Sessile molluscs (e.g., clams and chitons) have systems, whereas more complex molluscs (e.g., octopuses and squids) have more systems Sessile molluscs (e.g., clams and chitons) have simple systems, whereas more complex molluscs (e.g., octopuses and squids) have more sophisticated systems 27. What is the job of the spinal cord? The spinal cord conveys information from the brain to the PNS The spinal cord also produces reflexes independently of the brain Chapter 48 and 49 Name_______________________________ Date: 28. The of the spinal cord and the of the brain are hollow and filled with cerebrospinal fluid. The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid 29. What is the difference between gray matter and white matter? a. Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons b. White matter, which consists of bundles of myelinated axons 30. List and briefly describe the types of Glia in the CNS? a. Ependymal cells promote circulation of cerebrospinal fluid b. Microglia protect the nervous system from microorganisms c. Oligodendrocytes and Schwann cells form the myelin sheaths around axons d. Astrocytes provide structural support for neurons, regulate extracellular ions and neurotransmitters, and induce the formation of a blood-brain barrier that regulates the chemical environment of the CNS e. Radial glia play a role in the embryonic development of the nervous system 31. What is the job of the PNS? Describe the difference between afferent neurons and efferent neurons. Describe it’s two functional components. The PNS transmits information to and from the CNS and regulates movement and the internal environment In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS 32. What is the difference between cranial and spinal nerves? Cranial nerves originate in the brain and mostly terminate in organs of the head and upper body Spinal nerves originate in the spinal cord and extend to parts of the body below the head • The PNS has two functional components: the motor system and the autonomic nervous system • The motor system carries signals to skeletal muscles and is voluntary • The autonomic nervous system regulates the internal environment in an involuntary manner Chapter 48 and 49 Name_______________________________ Date: 33. What are the three divisions of the autonomic nervous system? The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions The sympathetic and parasympathetic divisions have antagonistic effects on target organs The sympathetic division correlates with the “fight-or-flight” response The parasympathetic division promotes a return to “rest and digest” The enteric division controls activity of the digestive tract, pancreas, and gallbladder 34. Complete the chart below. The brainstem coordinates and conducts information between brain centers Embryonic Region Brain Region Commonly called Description and Importance Forebrain Telencephalon Cerebrum Outer portion called: cerebral cortex . Brainstem and cerebrum control arousal and sleep. Cerebrum develops from the embryonic telencephalon. The cerebrum has right and left cerebral hemispheres Each cerebral hemisphere consists of a cerebral cortex (gray matter) overlying white matter and basal nuclei In humans, the cerebral cortex is the largest and most complex part of the brain The basal nuclei are important centers for planning and learning movement sequences Diencephalon Diencephalon The diencephalon develops into three regions: the epithalamus, thalamus, and hypothalamus The epithalamus includes the pineal Chapter 48 and 49 Name_______________________________ Date: gland and generates cerebrospinal fluid from blood The thalamus is the main input center for sensory information to the cerebrum and the main output center for motor information leaving the cerebrum The hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducing. Hypothalamus also regulates circadian rhythms such as the sleep/wake cycle. Mammals usually have a pair of suprachiasmatic nuclei (SCN) in the hypothalamus that function as a biological clock Midbrain Mesencephalon Midbrain Part of brainstem. Brainstem and cerebrum control arousal and sleep. core of the brainstem has a diffuse network of neurons called the reticular formation Midbrain contains centers for receipt and integration of sensory information Hindbrain Metencephalon Pons Cerebellum Part of brainstem. Brainstem and cerebrum control arousal and sleep. core of the brainstem has a diffuse network of neurons called the reticular Chapter 48 and 49 Name_______________________________ Date: formation Pons regulates breathing centers in the medulla Cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functions. It is also involved in learning and remembering motor skills Myelencphalon Medulla Part of brainstem. Brainstem and Oblongata cerebrum control arousal and sleep. core of the brainstem has a diffuse network of neurons called the reticular formation Medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion 35. Label the brain below. Chapter 48 and 49 Name_______________________________ Date: 49-9c Cerebrum (includes cerebral cortex, white matter, basal nuclei) Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Medulla oblongata (part of brainstem) Diencephalon: Cerebrum Hypothalamus Thalamus Pineal gland (part of epithalamus) Brainstem: Midbrain Pons Pituitary gland Medulla oblongata Spinal cord Cerebellum Central canal (c) Adult