Chapter 32 Neural Control Sections 1-6

1. Chapter 32Neural ControlSections 1-6

2. 32.1 In Pursuit of Ecstasy • Ecstasy (MDMA) is a psychoactive drug, similar in structure to methamphetamine • Drugs like MDMA flood the brain with signaling molecules and saturate receptors, disrupting neural controls • Repeated doses of MDMA may alter and even kill neurons in the brain • A bad reaction to MDMA can cause death

3. Meth and Ecstasy methamphetamine Ecstasy (MDMA)

4. Effect of Ecstasy

5. 32.2 Evolution of Nervous Systems • Interacting neurons give animals a capacity to respond to stimuli in the environment and inside their body • Neuron • A cell that can relay electrical signals along its plasma membrane and can communicate with other cells by specific chemical messages • Neuroglia • Support neurons functionally and structurally

6. Nerve Nets • Cnidarians are the simplest animals that have neurons, which are arranged as a nerve net • Nerve net • A mesh of interconnecting neurons with no centralized controlling organ

7. Cnidarian Nerve Net A nerve net (highlighted in purple) controls the contractile cells in the epithelium.

8. Bilateral, Cephalized Invertebrates • Flatworms are the simplest animals with a bilateral, cephalized nervous system • Cephalization • The concentration of neurons that detect and process information at the body’s head end • Ganglion • A cluster of neuron cell bodies that functions as an integrating center

9. Nerve Cords • Annelids and arthropods have paired ventral nerve cords that connect to a simple brain, and a pair of ganglia in each segment for local control • Chordates have a single, dorsal nerve cord; vertebrates have a brain at the anterior region of the nerve cord

10. Flatworm Cephalization pair of ganglia pair of nerve cords connected by lateral nerves

11. Insect with a Simple Brain brain nerve cords with ganglia

12. ANIMATED FIGURE: Bilateral nervous systems To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

13. Three Types of Neurons • Sensory neuronsdetect stimuli and signal interneurons or motor neurons • Interneurons process information from sensory neurons and send signals to motor neurons • Motor neuronscontrol muscles and glands

14. The Vertebrate Nervous System • Central nervous system(CNS) • Brain and spinal cord (mostly interneurons) • Peripheral nervous system(PNS) • Nerves from the CNS to the rest of the body (efferent) and from the body to CNS (afferent) • Autonomic nerves and somatic nerves control different organs of the body

15. Nerves • A nerve consists of nerve fibers bundled inside a sheath of connective tissue • Peripheral nerves are divided into two functional categories • Autonomic nerves regulate the body’s internal state; they control smooth muscle, cardiac muscle, and glands • Somatic nerves monitor body’s position and external conditions; they control skeletal muscle

16. Central Nervous System Brain Spinal Cord Peripheral Nervous System (cranial and spinal nerves) Autonomic Nerves Somatic Nerves Nerves that carry signals to and from smooth muscle, cardiac muscle, and glands Nerves that carry signals to and from skeletal muscle, tendons, and the skin Sympathetic Division Parasympathetic Division Two sets of nerves that often signal the same effectors and have opposing effects Stepped Art Figure 32-3 p543

17. Sensory stimuli, as from the nose, eyes, and ears Temporary storage in the cerebral cortex Input forgotten SHORT-TERM MEMORY Emotional state, having time to repeat (or rehearse) input, and associating the input with stored categories of memory influence transfer to long-term storage Recall of stored input LONG-TERM MEMORY Input irretrievable Stepped Art Figure 32-25 p559

18. Brain cranial nerves (twelve pairs) cervical nerves (eight pairs) Spinal Cord thoracic nerves (twelve pairs) ulnar nerve (one in each arm) sciatic nerve (one in each leg) lumbar nerves (five pairs) sacral nerves (five pairs) coccygeal nerves (one pair) Figure 32-4 p543

19. Take-Home Message: What are the features of animal nervous systems? • Cnidarians and echinoderms have a simple nervous system, a nerve net with no central integrating organ. • Bilateral animals have three types of neurons: sensory neurons, interneurons, and motor neurons. • Flatworms have paired ganglia that serve as an integrating center. Other invertebrates have more complex brains. • Bilateral invertebrates usually have a pair of ventral nerve cords. In contrast, the chordates have a dorsal nerve cord. • The vertebrate nervous system includes a well-developed brain, a spinal cord, and peripheral nerves.

20. ANIMATION: Vertebrate nervous system divisions To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

21. 32.3 Neurons: The Great Communicators • Neurons have special cytoplasmic extensions for receiving and sending messages • Dendrites receive information from other cells • Axonssend chemical signals to other cells • Sensory neurons have an axon with one end that responds to stimuli; the other sends signals • Interneurons and motor neurons have many dendrites and one axon

22. Three Types of Neurons receptor endings peripheral axon cell body axon axon terminals cell body axon cell body axon axon terminals dendrites dendrites

23. A Motor Neuron Conducting zone Output zone 3 4 axon terminals axon Trigger zone 2 cell body Input zone 1 dendrites

24. ANIMATED FIGURE: Neuron structure and function To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

25. Properties of the Neuron Plasma Membrane • Neurons have electrical and concentration gradients across their plasma membrane – their cytoplasm is more negatively charged than the interstitial fluid outside the cell • Negatively charged proteins and active transport of Na+ and K+ ions maintain voltage difference across a cell membrane, called the membrane potential • An unstimulated neuron has a resting membrane potential of about –70 mV

26. Resting Membrane Potential interstitial fluid 150 Na+ 5 K+ plasma membrane neuron’s cytoplasm 15 Na+ 150 K+ 65

27. Transport Proteins in a Neuron Membrane interstitial fluid 3 Na+ 2 K+ ADP + Pi cytoplasm A Sodium–potassium cotransporters actively transport three Na+ out of a neuron for every two K+ they pump in. B Passive transporters allow K+ ions to move across the plasma membrane, down their concentration gradient. c Voltage-gated channels for Na+ or K+ are closed in a neuron at rest (left), but open when it is excited (right).

28. Take-Home Message: How does a neuron’s structure affect its function? • Sensory neurons have an axon with one end that responds to a specific stimulus and another that signals other cells. • Interneurons and motor neurons have many signal-receiving dendrites and one signal-sending axon. • Transport proteins in the neuron plasma membrane set up electrical and concentration gradients across the membrane of a resting neuron. • A neuron’s axon has special voltage-gated channel proteins that function in the transmission of electrical signals along the axon.

29. ANIMATION: Measuring membrane potential To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

30. 32.4 The Action Potential • When stimulated, neurons and muscle cells undergo an action potential– a brief reversal in the electric gradient across the plasma membrane • During an action potential, membrane potential rises from its resting potential (–70 mV) to a peak of +30 mV, then declines to resting potential

31. Graded Potentials and Reaching Threshold • Stimulation of a neuron’s input zone causes a local, graded potential – a slight shift in the voltage difference across the neuron’s membrane • When stimulus in the neuron’s trigger zone reaches a threshold potential, gated sodium channels open • Voltage difference decreases and starts the action potential

32. An All-or-Nothing Spike • Diffusion of sodium into the neuron has a positive feedback effect – gated sodium channels open in an accelerating way after threshold is reached • Once threshold level is reached, membrane potential always rises to the same level as an action potential peak (all-or-nothing response) • Outward diffusion of K+ causes membrane potential to decline to a bit below its resting value in a small area

33. Propagation of an Action Potential • An action potential is self-propagating – sodium ions diffuse to the adjoining region of the axon, triggering sodium gates one after another • The action potential can only move one way, toward axon terminals – a brief refractory period after sodium gates close prevents the signal from moving backwards

34. Action Potential Membrane Potential +30 action potential threshold level 3 Membrane potential (millivolts) 2 -60 resting level 4 -70 1 0 1 2 3 4 5 6 Time (milliseconds)

35. Neuron at Rest voltage-gated ion channels

36. Threshold Na+ Na+ Na+ Na+ Na+ Na+

37. K+ Channels Open K+ K+ K+ Na+ Na+ Na+

38. K+ Channels Close K+ K+ K+ Na+ Na+

39. ANIMATED FIGURE: Action potential propagation To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

40. Take-Home Message: What happens during an action potential? • An action potential begins in the neuron’s trigger zone. A strong stimulus decreases the voltage difference across the membrane. This causes gated sodium channels to open, and the voltage difference reverses. • The action potential travels along an axon as consecutive patches of membrane undergo reversals in membrane potential.

41. Take-Home Message (cont.) • At each patch of membrane, an action potential ends as sodium channels close and potassium channels open. Potassium ions flow out of the neuron and restore the voltage difference across the membrane. • Action potentials can move in one direction, toward axon terminals, because gated sodium channels are briefly inactivated after they close

42. 32.5 How Neurons Send Messages to Other Cells • An action potential travels along a neuron’s axon to a terminal at the tip • Terminal sends chemical signals to a neuron, muscle fiber, or gland cell across a synapse

43. Chemical Synapses • A synapse is the region where an axon terminal (presynaptic cell) send chemical signals to a neuron, muscle fiber or gland cell (postsynaptic cell) • The synapse between a motor neuron and a skeletal muscle fiber is called a neuromuscular junction

44. Chemical Synapses • Action potentials trigger release of signaling molecules (neurotransmitters) from vesicles in the presynaptic terminal into the synaptic cleft • A motor neuron in a neuromuscular junction releases the neurotransmitter acetylcholine (ACh)

45. Chemical Synapses • Release of neurotransmitters from presynaptic vesicles requires an influx of calcium ions, Ca++ • Postsynaptic membrane receptors bind the neurotransmitter and initiate the response • The neurotransmitter must be cleared from the synapse after the signal is transmitted

46. A Neuromuscular Junction

47. axon of a motor neuron neuromuscular junction Figure 32-9a p548

48. axon terminal of motor neuron plama membrane of muscle fiber synaptic vesicle Ca++ 2 3 4 synaptic cleft Figure 32-9b p548

49. binding site for neurotransmitter (no neurotransmitter bound) ion channel closed Figure 32-9d p548

50. neurotransmitter ion flows through now-open channel Figure 32-9d p548