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Chapter 49

Chapter 49. Nervous Systems. Overview: Command and Control Center. The circuits in the brain are more complex than the most powerful computers The vertebrate brain is organized into regions with different functions. FYI: The Human Brain has: 100 billion neurons

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Chapter 49

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  1. Chapter 49 Nervous Systems

  2. Overview: Command and Control Center • The circuitsin the brain are more complex than the most powerful computers • The vertebrate brain is organized into regionswith different functions FYI: The Human Brain has: 100 billion neurons 1000 trillion synapses 110,000 miles of nerve fibers 100,000 miles of blood vessels It makes up ~2% of the body weight. It uses ~20% of the O2 we breathe It is 77% water

  3. Animals are multicellular and most groups respond to stimuli using systems of neurons

  4. Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells • The cnidarians, have nerve nets: a series of interconnected nerve cells • Sea stars have a nerve net and radial nerves in each arm connected to a central nerve ring.

  5. Fig. 49-2a Radial nerve Nerve ring Nerve net (a) Hydra (cnidarian) (b) Sea star (echinoderm)

  6. Bilaterally symmetrical animals exhibit cephalization;the clustering of sensory organs at the front end of the body • Cephalized flatworms, have a central nervous system (CNS) with a brain and spinal cord.

  7. Fig. 49-2b Eyespot Brain Brain Nerve cords Ventral nerve cord Transverse nerve Segmental ganglia (c) Planarian (flatworm) (d) Leech (annelid)

  8. Fig. 49-2c Annelidsand arthropodshave segmentally arranged clusters of neurons called ganglia Brain Ganglia Anterior nerve ring Ventral nerve cord Longitudinal nerve cords Segmental ganglia (e) Insect (arthropod) (f) Chiton (mollusc)

  9. Fig. 49-2d • Vertebrates have a hollow dorsal nerve cord. Brain Spinal cord (dorsal nerve cord) Sensory ganglia (h) Salamander (vertebrate)

  10. In vertebrates • The CNS is composed of the brain and spinal cord • The peripheral nervous system (PNS) is composed of nerves and ganglia

  11. Organization of the Vertebrate Nervous System • The spinal cord conveys information from the brain to the PNS • The spinal cord also produces reflexes independently of the brain • A reflexis the body’s automatic response to a stimulus. It does not involve the brain. • For example, a doctor uses a mallet to trigger a knee-jerk reflex (patellar reflex)

  12. Fig. 49-3 Cell body of sensory neuron in dorsal root ganglion Gray matter Quadriceps muscle White matter Hamstring muscle Spinal cord (cross section) Sensory neuron Motor neuron Interneuron

  13. Invertebratesusually have a ventral nerve cord while vertebrateshave a dorsal spinal cord • The spinal cord and brain develop from the embryonic nerve cord

  14. Fig. 49-4 Peripheral nervous system (PNS) Central nervous system (CNS) Brain Cranial nerves Spinal cord Ganglia outside CNS Spinal nerves

  15. The central canal of the spinal cord and the ventriclesof the brain are hollow and filled with cerebrospinal fluid • The cerebrospinal fluid is filtered from blood and functions to cushionthe brain and spinal cord

  16. The brain and spinal cord contain • Gray matter, whichconsists of neuron cell bodies, dendrites, and unmyelinated axons • White matter, whichconsists of bundles of myelinated axons. It is white because of the myelin sheaths about the axons.

  17. Fig. 49-5 Gray matter White matter Ventricles

  18. Glia in the CNS • Gliaare cells that support neurons. They have numerous functions • Ependymal cells promote circulation of cerebrospinal fluid • Microglia protectthe nervous system from microorganisms • Oligodendrocytes and Schwann cells form the myelin sheaths around axons

  19. Astrocytesprovide structural support for neurons • Radial gliaplay a role in the embryonic development of the nervous system

  20. Fig. 49-6 PNS CNS Neuron VENTRICLE Astrocyte Ependy- mal cell Oligodendrocyte Schwann cells Microglial cell Capillary (a) Glia in vertebrates 50 µm (b) Astrocytes (LM)

  21. The Peripheral Nervous System • The PNS transmits information to and from the CNS and regulates movement and the internal environment • In the PNS, afferentneurons transmit information to the CNS and efferentneurons transmit information away from the CNS • 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

  22. Fig. 49-7-1 PNS Afferent (sensory) neurons Efferent neurons Autonomic nervous system Motor system Hearing Locomotion

  23. The PNS has twofunctional components: • The motor system carries signals to skeletal muscles and is voluntary • The autonomic nervous system regulates the internal environment in an involuntary manner

  24. The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions • The sympathetic and parasympathetic divisions have antagonistic effects on target organs

  25. 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

  26. Fig. 49-7-2 PNS Afferent (sensory) neurons Efferent neurons Autonomic nervous system Motor system Hearing Sympathetic division Parasympathetic division Enteric division Locomotion Hormone action Gas exchange Circulation Digestion

  27. Fig. 49-8 Sympathetic division Parasympathetic division Action on target organs: Action on target organs: Dilates pupil of eye Constricts pupil of eye Inhibits salivary gland secretion Stimulates salivary gland secretion Sympathetic ganglia Constricts bronchi in lungs Relaxes bronchi in lungs Cervical Slows heart Accelerates heart Stimulates activity of stomach and intestines Inhibits activity of stomach and intestines Thoracic Stimulates activity of pancreas Inhibits activity of pancreas Stimulates glucose release from liver; inhibits gallbladder Stimulates gallbladder Lumbar Stimulates adrenal medulla Promotes emptying of bladder Inhibits emptying of bladder Sacral Promotes erection of genitals Promotes ejaculation and vaginal contractions Synapse

  28. Table 49-1

  29. Concept 49.2: The vertebrate brain is regionally specialized • All vertebrate brains develop from three embryonic regions: forebrain, midbrain, andhindbrain • By the fifth week of human embryonic development, five brain regions have formed from the three embryonic regions

  30. Fig. 49-9 Cerebrum (includes cerebral cortex, white matter, basal nuclei) Telencephalon Forebrain Diencephalon Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain Mesencephalon Midbrain (part of brainstem) Metencephalon Pons (part of brainstem), cerebellum Hindbrain Myelencephalon Medulla oblongata (part of brainstem) Diencephalon: Cerebrum Mesencephalon Hypothalamus Metencephalon Thalamus Midbrain Pineal gland (part of epithalamus) Myelencephalon Hindbrain Diencephalon Brainstem: Midbrain Pons Spinal cord Pituitary gland Forebrain Medulla oblongata Telencephalon Spinal cord Cerebellum Central canal (c) Adult (a) Embryo at 1 month (b) Embryo at 5 weeks

  31. As a human brain develops further, the most profound change occurs in the forebrain, which gives rise to the cerebrum • The outer portion of the cerebrum called the cerebral cortex surrounds much of the brain

  32. The Brainstem • The brainstemhas three parts: the midbrain, the pons, and the medulla oblongata

  33. Fig. 49-UN1 Midbrain Brainstem: Pons Medulla oblongata

  34. The midbrainconducts sensory and motor signals between the spinal cord and higher brain centers. • The ponsregulates breathingrate • The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion • The brainstem and cerebrum control arousal and sleep

  35. Sleep is essentialand may play a role in the consolidation of learning and memory • Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while “asleep”

  36. Fig. 49-11 Key Low-frequency waves characteristic of sleep High-frequency waves characteristic of wakefulness Time: 1 hour Location Time: 0 hours Left hemisphere Right hemisphere

  37. The Cerebellum • The cerebellumis important for coordinationof motor, perceptual, and cognitive functions • It is also involved in learning and remembering motor skills

  38. Fig. 49-UN2 Cerebellum

  39. The Diencephalon • The diencephalon develops into three regions: the epithalamus, thalamus, and hypothalamus • The epithalamusincludes the pineal gland and generates cerebrospinal fluid from blood • The thalamusis the main center through which sensory and motor information passes to and from the cerebrum. • The hypothalamusregulates homeostasisand basic survival behaviors such as feeding, fighting, fleeing, reproducing, and circadian rhythms

  40. Fig. 49-UN3 Hypothalamus Thalamus Epithalamus/Pineal Gland Diencephalon

  41. The Cerebrum • The cerebrumdevelops from the embryonic telencephalon

  42. Fig. 49-UN4 Cerebrum

  43. 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

  44. A thick band of axons called the corpus callosumprovides communicationbetween the right and left cerebral cortices • The right half of the cerebral cortex controlsthe leftside of the body, and vice versa

  45. Fig. 49-13 Right cerebral hemisphere Left cerebral hemisphere Thalamus Corpus callosum Basal nuclei Cerebral cortex

  46. Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functions • Each side of the cerebral cortex has four lobes: frontal, temporal, occipital, and parietal • Each lobe contains primary sensory areas and association areas where information is integrated

  47. Fig. 49-15 Frontal lobe Parietal lobe Somatosensory cortex Motor cortex Somatosensory association area Speech Frontal association area Taste Reading Speech Hearing Visual association area Smell Auditory association area Vision Temporal lobe Occipital lobe

  48. Information Processing in the Cerebral Cortex • The cerebral cortex receives input from sensory organs and somatosensory receptors • Specific types of sensory input enter the primary sensory areas of the brain lobes • Adjacent areas process features in the sensory input and integrate information from different sensory areas • In the somatosensory and motor cortices, neurons are distributed according to the body part that generates sensory input or receives motor input

  49. Fig. 49-16 Parietal lobe Frontal lobe Upper arm Shoulder Trunk Head Knee Leg Trunk Neck Hip Elbow Hip Forearm Elbow Wrist Forearm Hand Hand Fingers Fingers Thumb Thumb Eye Neck Nose Brow Face Eye Lips Genitals Toes Face Teeth Gums Jaw Lips Jaw Tongue Tongue Pharynx Primary motor cortex Primary somatosensory cortex Abdominal organs

  50. Language and Speech • Studies of brain activity have mapped areas responsible for language and speech • Broca’s area in the frontal lobe is active when speech is generated • Wernicke’s area in the temporal lobe is active when speech is heard

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