The Nervous System Chapter Nervous Systems Which animals have nervous systems? (Which do not) What are the basic components of a NS? What kind of fish performs brain operations? What differentiates one animal s NS from another? What is the simplest form of NS? NS Diversity Vertebrate NS Nerve net Cephalization => CNS, PNS Ganglia CNS: brain, spinal cord PNS: sensory and motor
Information Processing Three stages Sensory input, integration, and motor output Neuron (IB = neurone ) 1 Sensory input Sensor Integration 2 What works even after it s fired? 3 Motor output Figure 48.3 Effector Peripheral nervous system (PNS) Central nervous system (CNS) Figure 37.2 Dendrites Neuron NS Function Nucleus hillock Sensory neurons Presynaptic cell Synapse Cell body Signal direction Synaptic terminals Synaptic terminals transmit info from sensory neurons Integration interneurons (most common type) Motor neurons communicate w/ effector cells Neurotransmitter Postsynaptic cell 214 Pearson Education, Inc.
2 3 sensation Quadriceps muscle Reflex Arc info to sp. cord cell body 4 White matter SN synapse w/ MN Gray matter 5 Interneurons Figure 37.5 Neuron diversity Dendrites Cell body Hamstring muscle 6 1 Initiation Spinal cord (cross section) Sensory neuron Motor neuron Interneuron Inhibition Sensory neuron 214 Pearson Education, Inc. Interneurons Portion of axon Form follows function Motor neuron The Action Potential brief, all or none depolarization o/t plasma membrane Na+ and K+ ion channels Sequence: stimulus => Na+ channels open AP subsides and K+ channels open refractory period What did the director say to the young neuron who wanted to be an actor? Conduction of Action Potentials An AP regenerates itself depolarization of neighboring axon membrane speed of the AP: diameter of axon? myelination?
Membrane (mv) +5 1 Hyperpolarizations 1 2 3 4 5 Some stimuli hyperpolarize, some depolarize Depolarization = threshold => What did the stimulus Membrane (mv) +5 1 Depolarizations 1 2 3 4 5 Membrane (mv) +5 1 do to the neuron after they got married? Strong depolarizing stimulus Action 1 2 3 4 5 6 Figure 37.1 Membrane (mv) +5 Hyperpolarizations 1 1 2 3 4 5 (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K + Membrane (mv) +5 1 Depolarizations 1 2 3 4 5 (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na + Membrane (mv) +5 1 Strong depolarizing stimulus 1 2 3 4 5 6 (c) Action triggered by a depolarization that reaches the threshold Action (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K + (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na + (c) Action triggered by a depolarization that reaches the threshold 214 Pearson Education, Inc.
Quiz 1. After the depolarization of an action, repolarization occurs due to the a. closing of sodium activation and inactivation gates. b. opening of sodium activation gates. c. refractory period in which the membrane is hyperpolarized. d. delay in the action of the sodium-potassium pump. e. opening of voltage-gated potassium channels and the closing of sodium channels. Quiz 2. How is an increase in the strength of a stimulus communicated by a neuron? a. The spike of the action reaches a higher voltage. b. The frequency of action s generated along the neuron increases. c. The length of an action (the duration of the depolarization phase) increases. d. The action travels along the neuron faster. e. All action s are the same; the nervous system cannot discriminate between different strengths of stimuli. Copyright 25 Pearson Education, Inc. publishing as Benjamin Cummings Copyright 25 Pearson Education, Inc. publishing as Benjamin Cummings Quiz 5. Action s are normally carried in one direction from the axon hillock to the axon terminals. By using an electronic probe, you experimentally depolarize the middle of the axon to threshold. What do you expect? * a. No action will be initiated. b. An action will be initiated and proceed in the normal direction toward the axon terminal. c. An action will be initiated and proceed back toward the axon hillock. d. Two action s will be initiated, one going toward the axon terminal and one going back toward the hillock. e. An action will be initiated, but it will die out before it reaches the axon terminal. What do you call delinquent glial cells? Copyright 25 Pearson Education, Inc. publishing as Benjamin Cummings
Schwann cells (PNS) Oligodendrocytes (CNS) Supporting Cells (Glia) Make up cells of myelin sheath Node of Ranvier Layers of myelin Glia are supporting cells astrocytes biochemical support blood-brain barrier Schwann oligodendrocytes Schwann cell Myelin sheath Schwann cell Nucleus of Schwann cell Nodes of Ranvier Figure 48.8 5 µm Figure 48.7.1 µm The Chemical Synapse AP ---> terminal => neurotransmitters ---> synaptic cleft Postsynaptic cell Presynaptic cell How do you know when a glia cell is happy? Synaptic vesicles containing neurotransmitter 5 Na+ K+ Neurotransmitter Presynaptic membrane Postsynaptic membrane Ligandgated ion channel Voltage-gated Ca2+ channel 1 Ca2+ 4 2 Synaptic cleft 3 Ligand-gated ion channels Postsynaptic membrane 6
Direct Synaptic Transmission DST: binding of neurotransmitters to ligand-gated ion channels (remember these from cell signaling?) Causes the ion channels to open & starts a postsynaptic PSP can be inhibitory or excitatory Neurotransmitters few NT, many effects Acetylcholine most common nt ex: passes signal from one motor neuron to the next allows muscles to contract inhibitory or excitatory Biogenic amines epinephrine norepinephrine dopamine serotonin Active in the CNS and PNS Caffeine Competitive inhib. of adenosine receptors disrupts IPSP path thus increased epinephrine release by pituitary (epinephrine = adrenaline) also inhibits camp path that breaks down epi., prolonging effects of epi. Prolonged use leads to reduced sensitivity to caffeine reduced caffeine then leads to oversensitivity to adenosine blood pressure drops, blood volume in head increases, leading to headache 12-24 hrs later relieved by aspirin, small dose of caffeine Tetrodotoxin liver of puffer fish, also Rough-skinned newts, blue-ringed octopus, some cone snails fugu tingling sensation too much: irreversibly binds & blocks Na+ channels muscles paralyzed; asphyxiation while conscious no antidote
Painkillers Body makes two natural painkillers: enkaphalins made by descending tract in S.Cord block Ca 2+ channels in pain neuron synapses pain signal transmitted, but does not reach brain endorphins block release of nt s by pain neurons pain sensation never transmitted endorphins released: stress, injuries exercise ( runner s high ) spicy food ( capsaicin high )