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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 Functional magnetic resonance imaging (MRI) can be used to construct a 3-D map of brain activity

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Chapter 49

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  1. Chapter 49 Nervous Systems

  2. Overview: Command and Control Center • The circuits in the brain are more complex than the most powerful computers • Functional magnetic resonance imaging (MRI) can be used to construct a 3-D map of brain activity • The vertebrate brain is organized into regions with different functions

  3. Fig. 49-1

  4. Each single-celled organism can respond to stimuli in its environment • Animals are multicellular and most groups respond to stimuli using systems of neurons

  5. Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells • The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets • A nerve net is a series of interconnected nerve cells • More complex animals have nerves

  6. Nerves are bundles that consist of the axons of multiple nerve cells • Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring

  7. Fig. 49-2 Eyespot Brain Brain Radial nerve Nerve cords Ventral nerve cord Nerve ring Transverse nerve Nerve net Segmental ganglia (a) Hydra (cnidarian) (b) Sea star (echinoderm) (d) Leech (annelid) (c) Planarian (flatworm) Brain Brain Ganglia Anterior nerve ring Spinal cord (dorsal nerve cord) Ventral nerve cord Brain Sensory ganglia Longitudinal nerve cords Ganglia Segmental ganglia (e) Insect (arthropod) (h) Salamander (vertebrate) (f) Chiton (mollusc) (g) Squid (mollusc)

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

  9. Bilaterally symmetrical animals exhibit cephalization • Cephalization is the clustering of sensory organs at the front end of the body • Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS) • The CNS consists of a brain and longitudinal nerve cords

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

  11. Annelids and arthropods have segmentally arranged clusters of neurons called ganglia

  12. Fig. 49-2c Brain Ganglia Anterior nerve ring Ventral nerve cord Longitudinal nerve cords Segmental ganglia (e) Insect (arthropod) (f) Chiton (mollusc)

  13. Nervous system organization usually correlates with lifestyle • Sessile molluscs (e.g., clams and chitons) have simple systems, whereas more complex molluscs (e.g., octopuses and squids) have more sophisticated systems

  14. Fig. 49-2d Brain Spinal cord (dorsal nerve cord) Brain Sensory ganglia Ganglia (g) Squid (mollusc) (h) Salamander (vertebrate)

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

  16. 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 reflex is the body’s automatic response to a stimulus • For example, a doctor uses a mallet to trigger a knee-jerk reflex

  17. 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

  18. Invertebrates usually have a ventral nerve cord while vertebrates have a dorsal spinal cord • The spinal cord and brain develop from the embryonic nerve cord

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

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

  21. The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid • The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord

  22. 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

  23. Glia in the CNS • Glia have numerous functions • Ependymal cells promote circulation of cerebrospinal fluid • Microglia protect the nervous system from microorganisms • Oligodendrocytes and Schwann cells form the myelin sheaths around axons

  24. Glia have numerous functions • Astrocytes provide structural support for neurons, regulate extracellular ions and neurotransmitters, and induce the formation of a blood-brain barrier that regulates the chemical environment of the CNS • Radial glia play a role in the embryonic development of the nervous system

  25. 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)

  26. Fig. 49-6a CNS PNS Neuron VENTRICLE Astrocyte Ependy- mal cell Oligodendrocyte Schwann cells Microglial cell Capillary (a) Glia in vertebrates

  27. Fig. 49-6b 50 µm (b) Astrocytes (LM)

  28. The Peripheral Nervous System • The PNS transmits information to and from the CNS and regulates movement and the internal environment • In the PNS, afferent neurons transmit information to the CNS and efferent neurons 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

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

  30. 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

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

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

  33. 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

  34. 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

  35. Fig. 49-8a Parasympathetic division Sympathetic 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 Cervical Slows heart Stimulates activity of stomach and intestines Stimulates activity of pancreas Stimulates gallbladder

  36. Fig. 49-8b Sympathetic division Parasympathetic division Relaxes bronchi in lungs Accelerates heart Inhibits activity of stomach and intestines Thoracic Inhibits activity of pancreas Stimulates glucose release from liver; inhibits gallbladder Lumbar Stimulates adrenal medulla Promotes emptying of bladder Inhibits emptying of bladder Sacral Promotes erection of genitals Promotes ejaculation and vaginal contractions Synapse

  37. Table 49-1

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

  39. 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

  40. Fig. 49-9ab Telencephalon Forebrain Diencephalon Mesencephalon Midbrain Metencephalon Hindbrain Myelencephalon Mesencephalon Metencephalon Midbrain Myelencephalon Hindbrain Diencephalon Spinal cord Forebrain Telencephalon (a) Embryo at 1 month (b) Embryo at 5 weeks

  41. Fig. 49-9c Cerebrum (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: Cerebrum Hypothalamus Thalamus Pineal gland (part of epithalamus) Brainstem: Midbrain Pons Pituitary gland Medulla oblongata Spinal cord Cerebellum Central canal (c) Adult

  42. 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

  43. Fig. 49-UN1

  44. The Brainstem • The brainstem coordinates and conducts information between brain centers • The brainstem has three parts: the midbrain, the pons, and the medulla oblongata

  45. The midbrain contains centers for receipt and integration of sensory information • The pons regulates breathing centers in the medulla • The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion

  46. Arousal and Sleep • The brainstem and cerebrum control arousal and sleep • The core of the brainstem has a diffuse network of neurons called the reticular formation • This regulates the amount and type of information that reaches the cerebral cortex and affects alertness • The hormone melatonin is released by the pineal gland and plays a role in bird and mammal sleep cycles

  47. Fig. 49-10 Eye Input from nerves of ears Reticular formation Input from touch, pain, and temperature receptors

  48. Sleep is essential and 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”

  49. 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

  50. The Cerebellum • The cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functions • It is also involved in learning and remembering motor skills

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