Chapter 37&38. Nervous Systems. EQ: How do animals sense and respond to the world around them?

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1 Chapter 37&38 Nervous Systems EQ: How do animals sense and respond to the world around them?

2 The Nervous System Function? sense the internal and external environment, coordinate actions, transmit response Three components: receptors central nervous system processing effectors response (eg muscles, glands) What kind of fish performs brain operations?

3 Vertebrate NS CNS: brain, spinal cord PNS: sensory and motor

4 Information Processing Three stages Sensory input, integration, and motor output 1 Sensory input Sensor Integration 2 3 Motor output Effector Peripheral nervous system (PNS) Central nervous system (CNS)

5 NS functional unit: Neuron (IB = neurone ) What works even after it s fired?

6 Figure 37.2 Dendrites Neuron Stimulus Nucleus Axon hillock Cell body Presynaptic cell Axon Synapse Signal direction Synaptic terminals Synaptic terminals Neurotransmitter Postsynaptic cell 2014 Pearson Education, Inc.

7 Figure 37.5 Neuron diversity Dendrites Axon Cell body Portion of axon Sensory neuron Interneurons Motor neuron 2014 Pearson Education, Inc. Function follows form

8 Reflex Arc 2 3 sensation info to sp. cord cell body 4 SN synapse w/ MN Gray matter Quadriceps muscle White matter 5 Interneurons Hamstring muscle 6 Spinal cord (cross section) Sensory neuron Inhibition enter 1 Initiation Motor neuron Interneuron

9 Function of the Neuron Action Potential depolarization of the plasma membrane Factors increasing the speed of the AP? axon diameter (bigger = faster) myelination How do you know when a Schwann cell is happy? prevents ion leakage, thus current carried in cytoplasm saltatory conduction cheaper for cell - fewer pumped ions

10 Application: Analysis of AP using Oscilloscope Trace

11 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

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18 Application: Analysis of AP using Oscilloscope Trace Membrane depolarization? Repolarization? Hyperpolarization (overshoot)? Threshold? Refractory period?

19 Quiz 1. After the depolarization of an action potential, 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. Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

20 Quiz 2. How is an increase in the strength of a stimulus communicated by a neuron? a. The spike of the action potential reaches a higher voltage. b. The frequency of action potentials generated along the neuron increases. c. The length of an action potential (the duration of the depolarization phase) increases. d. The action potential travels along the neuron faster. e. All action potentials are the same; the nervous system cannot discriminate between different strengths of stimuli. Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

21 Quiz 3. Action potentials 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 potential will be initiated. b. An action potential will be initiated and proceed in the normal direction toward the axon terminal. c. An action potential will be initiated and proceed back toward the axon hillock. d. Two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock. e. An action potential will be initiated, but it will die out before it reaches the axon terminal. Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

22 Quiz Humans need a supply of energy for processes such as active transport in cells. (a) (b) (c) Explain how humans release energy from digested foods to make it available for processes in cells. Describe one example that occurs in axons for each of the following active transport and facilitated diffusion. Outline how biologists can ensure that research into energy release involving animals is ethically acceptable. [7] [5] [3] Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

23 The Chemical Synapse AP ---> terminal => neurotransmitters ---> synaptic cleft Presynaptic cell Postsynaptic cell Synaptic vesicles containing neurotransmitter Presynaptic membrane 5 Na + K + Neuro- transmitter Postsynaptic membrane Voltage-gated Ca 2+ channel Ligand- gated ion channel 1 Ca Postsynaptic membrane 6 Synaptic cleft 3 Ligand-gated ion channels

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25 Acetylecholine (ACh) TOPIC 6.5 APPLICATION: ACH SECRETION AND REABSORPTION 1. ACh made from Acetyl CoA and choline in axon terminal ACh triggers muscle contraction ACh also part of parasympathetic rest and digest response 2.In synapse, after ACh has been received, Acetylcholinesterase (AChE) rapidly breaks it down. (if not broken down, can lead to paralysis and death) 3.Choline transported back to make more ACh

26 Acetylecholine (ACh) TOPIC 6.5 APPLICATION: NEONICOTINOID PESTICIDES Pesticide applied to roots or leaves herbivores ingest it Irreversibly binds to herbivore ACh receptors Causes prolonged response from the receptors Induces responses or behaviors leading to death

27 Kills pollinating insects Acetylecholine (ACh) EFFECT OF NEONICOTINOID PESTICIDES Some countries recently started restricting use of this pesticide. Maryland became first US state to ban use in May 2016 KLCC 3/26/17

28 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 hrs later relieved by aspirin, small dose of caffeine

29 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

30 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 )

31 Olfaction 2004 NOBEL PRIZE TO RICHARD AXEL AND LINDA B. BUCK odorants bind to hairs of olfactory neurons (O.N.), one receptor type per neuron 400 different ones in humans; > one trillion odors detected O.N. are in olfactory epithelium, lining the nasal cavity O.N. send signal to olfactory bulb. Perception of smell based on combination of receptors activated.