Nervous System Part 2

1. Nervous System Part 2 IB-202-15 4-24-06 Chapt 48 pp 1022-1028, 1036 (memory), 1040-1041 (Alzheimer’s and Parkinson’s disease)

2. Direct Synaptic Transmission • The process of direct synaptic transmission • Involves the binding of neurotransmitters to ligand-gated ion channels • Neurotransmitter binding • Causes the ion channels to open, generating a postsynaptic potential • After its release from channel, the neurotransmitter • Diffuses out of the synaptic cleft • May be taken up by surrounding cells and degraded by enzymes

3. Table 48.1 • Major neurotransmitters

4. Acetylcholine • Acetylcholine • Is one of the most common neurotransmitters in both vertebrates and invertebrates. Transmitter for neuromuscular synapses in vertebrates (skeletal muscle). • Can be inhibitory or excitatory with other types of muscle.

5. Biogenic Amines • Biogenic amines • Include epinephrine (adrenalin), norepinephrine, dopamine, and serotonin • Are active in the CNS and peripheral nervous system (PNS) • Various amino acids and peptides • Are active in the brain

6. Gases • Gases such as nitric oxide and carbon monoxide • Are local regulators in the PNS

7. Central nervous system (CNS) Peripheral nervous system (PNS) Brain Cranial nerves Spinal cord Ganglia outside CNS Spinal nerves Figure 48.19 • Concept 48.5: The vertebrate nervous system is regionally specialized • In all vertebrates, the nervous system • Shows a high degree of cephalization and distinct CNS and PNS components

8. The brain provides the integrative power • That underlies the complex behavior of vertebrates • The spinal cord integrates simple responses to certain kinds of stimuli • And conveys information to and from the brain

9. Gray matter White matter Ventricles Figure 48.20 • The central canal of the spinal cord and the four ventricles of the brain • Are hollow, since they are derived from the dorsal embryonic nerve cord Mylinated axons interconnecting parts of brain and nerve tracks to spinal cord Grey matter is unmylinated axons, dendrites and nerve bodies.

10. The Peripheral Nervous System • The PNS transmits information to and from the CNS • And plays a large role in regulating a vertebrate’s movement and internal environment • The cranial nerves originate in the brain • And terminate mostly in organs of the head and upper body • The spinal nerves originate in the spinal cord • And extend to parts of the body below the head

11. Peripheral nervous system Somatic nervous system Autonomic nervous system Sympathetic division Parasympathetic division Enteric division Figure 48.21 • The PNS can be divided into two functional components • The somatic nervous system and the autonomic nervous system Autonomic regulates the internal environment in an involuntary manner. Somatic largely voluntary control of muscle in response to external stimuli

12. Parasympathetic division Sympathetic division Action on target organs: Action on target organs: Dilates pupil of eye Constricts pupil of eye Location of preganglionic neurons: brainstem and sacral segments of spinal cord Location of preganglionic neurons: thoracic and lumbar segments of spinal cord Inhibits salivary gland secretion Stimulates salivary gland secretion Sympathetic ganglia Neurotransmitter released by preganglionic neurons: acetylcholine Constricts bronchi in lungs Relaxes bronchi in lungs Neurotransmitter released by preganglionic neurons: acetylcholine Cervical Accelerates heart Slows heart Inhibits activity of stomach and intestines Thoracic Stimulates activity of stomach and intestines Location of postganglionic neurons: in ganglia close to or within target organs Location of postganglionic neurons: some in ganglia close to target organs; others in a chain of ganglia near spinal cord Inhibits activity of pancreas Stimulates activity of pancreas Stimulates glucose release from liver; inhibits gallbladder Stimulates gallbladder Lumbar Neurotransmitter released by postganglionic neurons: acetylcholine Neurotransmitter released by postganglionic neurons: norepinephrine Stimulates adrenal medulla Promotes emptying of bladder Inhibits emptying of bladder Promotes erection of genitalia Promotes ejaculation and vaginal contractions Sacral Synapse Figure 48.22 • The sympathetic and parasympathetic divisions • Have antagonistic effects on target organs

13. The sympathetic division • Correlates with the “fight-or-flight” response • The parasympathetic division • Promotes a return to self-maintenance functions • The enteric division • Controls the activity of the digestive tract, pancreas, and gallbladder

14. Forebrain Midbrain Hindbrain Midbrain Hindbrain Forebrain (a) Embryo at one month Embryonic Development of the Brain • In all vertebrates • The brain develops from three embryonic regions: the forebrain, the midbrain, and the hindbrain Embryonic brain regions Figure 48.23a

15. Embryonic brain regions Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon Mesencephalon Metencephalon Diencephalon Myelencephalon Spinal cord Telencephalon Figure 48.23b (b) Embryo at five weeks • By the fifth week of human embryonic development • Five brain regions have formed from the three embryonic regions

16. Brain structures present in adult Cerebrum (cerebral hemispheres; 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: Cerebral hemisphere Hypothalamus Thalamus Pineal gland (part of epithalamus) Brainstem: Midbrain Pons Pituitary gland Medulla oblongata Cerebellum Spinal cord Central canal (c) Adult Figure 48.23c • As a human brain develops further • The most profound change occurs in the forebrain, which gives rise to the cerebrum

17. In humans, the largest and most complex part of the brain • Is the cerebral cortex, where sensory information is analyzed, motor commands are issued, and language is generated

18. Frontal lobe Parietal lobe Motor cortex Somatosensory cortex Somatosensory association area Speech Frontal association area Taste Reading Speech Hearing Visual association area Smell Auditory association area Vision Temporal lobe Occipital lobe Figure 48.27 • Concept 48.6: The cerebral cortex controls voluntary movement and cognitive functions • Each side of the cerebral cortex has four lobes • Frontal, parietal, temporal, and occipital

19. The Diencephalon • The embryonic diencephalon develops into three adult brain regions • The epithalamus, thalamus, and hypothalamus

20. The hypothalamus regulates • Homeostasis • Basic survival behaviors such as feeding, fighting, fleeing, and reproducing

21. Memory and Learning • The frontal lobes • Are a site of short-term memory • Interact with the hippocampus and amygdala to consolidate long-term memory

22. Many sensory and motor association areas of the cerebral cortex • Are involved in storing and retrieving words and images • Many sensory and motor association areas of the cerebral cortex • Are involved in storing and retrieving words and images

23. (a) Touching the siphon triggers a reflex thatcauses the gill to withdraw. If the tail isshocked just before the siphon is touched,the withdrawal reflex is stronger. Thisstrengthening of the reflex is a simple formof learning called sensitization. Siphon Mantle Gill Tail Head (b) Sensitization involves interneurons thatmake synapses on the synaptic terminals ofthe siphon sensory neurons. When the tailis shocked, the interneurons releaseserotonin, which activates a signaltransduction pathway that closes K+channels in the synaptic terminals ofthe siphon sensory neurons. As a result,action potentials in the siphon sensoryneurons produce a prolongeddepolarization of the terminals. That allowsmore Ca2+ to diffuse into the terminals, which causes the terminals to release more of their excitatory neurotransmitter onto the gill motor neurons. In response, the motor neuronsgenerate action potentials at a higher frequency,producing a more forceful gill withdrawal. Gill withdrawal pathway Touchingthe siphon Gill motorneuron Siphon sensoryneuron Gill Sensitization pathway Interneuron Shockingthe tail Tail sensoryneuron Figure 48.31a, b Cellular Mechanisms of Learning • Experiments on invertebrates • Have revealed the cellular basis of some types of learning

24. The presynaptic neuron releases glutamate. 1 Glutamate binds to AMPA receptors, opening the AMPA- receptor channel and depolarizing the postsynaptic membrane. 2 NO diffuses into the presynaptic neuron, causing it to release more glutamate. 7 Glutamate also binds to NMDA receptors. If the postsynaptic membrane is simultaneously depolarized, the NMDA-receptor channel opens. Ca2+ stimulates the postsynaptic neuron to produce nitric oxide (NO). 6 3 Ca2+ diffuses into the postsynaptic neuron. 4 • In the vertebrate brain, a form of learning called long-term potentiation (LTP) • Involves an increase in the strength of synaptic transmission PRESYNAPTIC NEURON NO NMDA receptor Glutamate AMPA receptor NO P Ca2+ initiates the phos- phorylation of AMPA receptors, making them more responsive. Ca2+ also causes more AMPA receptors to appear in the postsynaptic membrane. 5 Ca2+ Signal transduction pathways Figure 48.32 POSTSYNAPTIC NEURON

25. Alzheimer’s Disease • Alzheimer’s disease (AD) • Is a mental deterioration characterized by confusion, memory loss, and other symptoms

26. 20 m Senile plaque Neurofibrillary tangle Figure 48.35 • AD is caused by the formation of • Neurofibrillary tangles and senile plaques of protein in the brain

27. Parkinson’s Disease • Parkinson’s disease is a motor disorder • Caused by the death of dopamine-secreting neurons in the mid-brain. It is characterized by difficulty in initiating movements, slowness of movement, and rigidity • Transplantation of stem cells that appear to transform into dopamine-secreting cells alleviate the symptoms but thus far no success in humans

28. Sensory and Motor Mechanisms • Chapt 49 (pp 1063-1074)

29. Concept 49.5: Animal skeletons function in support, protection, and movement • The various types of animal movements • All result from muscles working against some type of skeleton

30. Types of Skeletons • The three main functions of a skeleton are • Support, protection, and movement • The three main types of skeletons are • Hydrostatic skeletons, exoskeletons, and endoskeletons

31. Endoskeletons • An endoskeleton consists of hard supporting elements • Such as bones, buried within the soft tissue of an animal • Endoskeletons • Are found in sponges, echinoderms, and chordates

32. The mammalian skeleton is built from more than 200 bones • Some fused together and others connected at joints by ligaments that allow freedom of movement

33. Head ofhumerus key Examplesof joints Axial skeleton Skull Appendicularskeleton Scapula 1 Clavicle Shouldergirdle Scapula Sternum 1Ball-and-socket joints, where the humerus contactsthe shoulder girdle and where the femur contacts thepelvic girdle, enable us to rotate our arms andlegs and move them in several planes. Rib 2 Humerus 3 Vertebra Radius Ulna Humerus Pelvicgirdle Carpals Ulna Phalanges 2Hinge joints, such as between the humerus andthe head of the ulna, restrict movement to a singleplane. Metacarpals Femur Patella Tibia Fibula Ulna Radius Tarsals 3Pivot joints allow us to rotate our forearm at theelbow and to move our head from side to side. Metatarsals Phalanges • The human skeleton Figure 49.26

34. Human Grasshopper Extensormusclerelaxes Bicepscontracts Tibiaflexes Flexormusclecontracts Tricepsrelaxes Forearmflexes Extensormusclecontracts Tibiaextends Bicepsrelaxes Forearmextends Flexormusclerelaxes Triceps contracts • The action of a muscle is always to contract • Skeletal muscles are attached to the skeleton in antagonistic pairs even with exoskeletons • With each member of the pair working against each other Figure 49.27

35. Muscle Bundle ofmuscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z line Lightband Dark band Sarcomere TEM 0.5 m A band I band I band M line Thickfilaments(myosin) Thinfilaments(actin) H zone Z line Z line Sarcomere Vertebrate Skeletal Muscle • Vertebrate skeletal muscle • Is characterized by a hierarchy of smaller and smaller units Muscle fiber composed of many individual embryonic muscle cells fused end to end. Note many nuclei. Sarcomere Figure 49.28

36. A skeletal muscle consists of a bundle of long fibers • Running parallel to the length of the muscle • A muscle fiber • Is itself a bundle of smaller myofibrils arranged longitudinally • The myofibrils are composed to two kinds of myofilaments • Thin filaments, consisting of two strands of actin and one strand of regulatory protein • Thick filaments, staggered arrays of myosin molecules

37. Skeletal muscle is also called striated muscle • Because the regular arrangement of the myofilaments creates a pattern of light and dark bands

38. The Sliding-Filament Model of Muscle Contraction • According to the sliding-filament model of muscle contraction • The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments

39. 0.5 m (a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bandsand H zone are relatively wide. Z H A Sarcomere (b) Contracting muscle fiber. During contraction, the thick andthin filaments slide past each other, reducing the width of theI bands and H zone and shortening the sarcomere. (c) Fully contracted muscle fiber. In a fully contracted musclefiber, the sarcomere is shorter still. The thin filaments overlap,eliminating the H zone. The I bands disappear as the ends ofthe thick filaments contact the Z lines. Correlation of structure as seen with the electron microscope and function. • As a result of this sliding • The I band and the H zone shrink Figure 49.29a–c

40. The sliding of filaments is based on • The interaction between the actin and myosin molecules of the thick and thin filaments • The “head” of a myosin molecule binds to an actin filament • Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere

41. Thick filament Thin filaments 1 Starting here, the myosin head is bound to ATP and is in its low-energy confinguration. 5 Binding of a new mole- cule of ATP releases the myosin head from actin, and a new cycle begins. Thin filament Myosin head (low-energy configuration) The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration. ATP 2 ATP Cross-bridge binding site Thick filament P Actin Thin filament moves toward center of sarcomere. Myosin head (high-energy configuration) ADP Myosin head (low-energy configuration) P i 1 The myosin head binds toactin, forming a cross-bridge. 3 ADP + Cross-bridge ADP P i P i Releasing ADP and ( i), myosinrelaxes to its low-energy configuration, sliding the thin filament. 4 P • Myosin-actin interactions underlying muscle fiber contraction Figure 49.30

42. Tropomyosin Ca2+-binding sites Actin Troponin complex (a) Myosin-binding sites blocked The Role of Calcium and Regulatory Proteins • A skeletal muscle fiber contracts only when stimulated by a motor neuron • When a muscle is at rest the myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin Figure 49.31a

43. Ca2+ Myosin-binding site (b) Myosin-binding sites exposed • For a muscle fiber to contract the myosin-binding sites must be uncovered • This occurs when calcium ions (Ca2+) bind to another set of regulatory proteins, the troponin complex Figure 49.31b

44. Motorneuron axon Mitochondrion Synapticterminal T tubule Sarcoplasmicreticulum Ca2+ releasedfrom sarcoplasmicreticulum Myofibril Sarcomere Plasma membraneof muscle fiber • The stimulus leading to the contraction of a skeletal muscle fiber • Is an action potential in a motor neuron that makes a synapse with the muscle fiber Figure 49.32

45. Skip to figure! • The synaptic terminal of the motor neuron • Releases the neurotransmitter acetylcholine, depolarizing the muscle and causing it to produce an action potential

46. Action potentials travel to the interior of the muscle fiber • Along infoldings of the plasma membrane called transverse (T) tubules • The action potential along the T tubules • Causes the sarcoplasmic reticulum to release Ca2+ • The Ca2+ binds to the troponin-tropomyosin complex on the thin filaments • Exposing the myosin-binding sites and allowing the cross-bridge cycle to proceed

47. Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber. Synapticterminalof motorneuron 1 PLASMA MEMBRANE Synaptic cleft T TUBULE Action potential is propa- gated along plasma membrane and down T tubules. 2 ACh SR 4 Action potential triggers Ca2+ release from sarco- plasmic reticulum (SR). 3 Ca2 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. Tropomyosin blockage of myosin- binding sites is restored; contraction ends, and muscle fiber relaxes. 7 Ca2 CYTOSOL Cytosolic Ca2+ is removed by active transport into SR after action potential ends. 6 ADP P2 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments. 5 Calcium as a regulator of muscle contraction! Figure 49.33

48. Neural Control of Muscle Tension • Contraction of a whole muscle is graded • Which means that we can voluntarily alter the extent and strength of its contraction • There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles • By varying the number of fibers that contract • By varying the rate at which muscle fibers are stimulated

49. Motorunit 1 Motorunit 2 Spinal cord Synaptic terminals Nerve Motor neuroncell body Motor neuronaxon Muscle Muscle fibers Tendon • In a vertebrate skeletal muscle • Each branched muscle fiber is innervated by only one motor neuron • Each motor neuron • May synapse with multiple muscle fibers Figure 49.34

50. A motor unit • Consists of a single motor neuron and all the muscle fibers it controls • Recruitment of multiple motor neurons • Results in stronger contractions