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ANIMAL NERVOUS SYSTEM

ANIMAL NERVOUS SYSTEM . Chapter 6. Outline. Overview CNS PNS Neurons: Structure and Function Resting potential Action potential Muscle contraction and twitch Nervous disorders. Nervous systems as a whole.

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ANIMAL NERVOUS SYSTEM

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  1. ANIMAL NERVOUS SYSTEM Chapter 6

  2. Outline • Overview • CNS • PNS • Neurons: Structure and Function • Resting potential • Action potential • Muscle contraction and twitch • Nervous disorders

  3. Nervous systems as a whole • 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 • 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

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

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

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

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

  8. 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

  9. 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

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

  11. Many animals have a complex nervous system which consists of: • A central nervous system (CNS) where integration takes place; this includes the brain and a nerve cord • A peripheral nervous system (PNS), which brings information into and out of the CNS • The transmission of information depends on the path of neurons along which a signal travels • Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brain

  12. Fig. 48-3 Sensory input Integration Sensor Motor output Central nervous system (CNS) Effector Peripheral nervous system (PNS)

  13. CNS: Brain and Spinal Cord • Spinal cord and brain are wrapped in three protective membranes, meninges • Spaces between meninges are filled with cerebrospinal fluid • Fluid is continuous with that of central canal of spinal cord and the ventricles of the brain

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

  15. 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 • 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

  16. 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 • 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

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

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

  19. The vertebrate brain • 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

  20. 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

  21. Fig. 49-UN5 Cerebral cortex Cerebrum Thalamus Forebrain Hypothalamus Pituitary gland Midbrain Pons Spinal cord Medulla oblongata Hindbrain Cerebellum

  22. 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

  23. Fig. 49-UN1

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

  25. 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

  26. Fig. 49-UN2

  27. The Diencephalon • The diencephalon develops into three regions: the epithalamus, thalamus, and hypothalamus • The epithalamus includes the pineal gland and generates cerebrospinal fluid from blood • The thalamus is the main input center for sensory information to the cerebrum and the main output center for motor information leaving the cerebrum • The hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducing

  28. Fig. 49-UN3

  29. The Cerebrum • The cerebrum develops from the embryonic telencephalon • 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

  30. Fig. 49-UN4

  31. 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

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

  33. Evolution of Cognition in Vertebrates • The outermost layer of the cerebral cortex has a different arrangement in birds and mammals • In mammals, the cerebral cortex has a convoluted surface called the neocortex,which was previously thought to be required for cognition • Cognition is the perception and reasoning that form knowledge • However, it has recently been shown that birds also demonstrate cognition even though they lack a neocortex

  34. Fig. 49-14 Pallium Cerebral cortex Cerebrum Cerebrum Cerebellum Cerebellum Thalamus Thalamus Midbrain Midbrain Hindbrain Hindbrain Avian brain to scale Human brain Avian brain

  35. 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

  36. Fig. 49-16a Shoulder Knee Trunk Elbow Forearm Hip Wrist Hand Fingers Thumb Neck Brow Eye Toes Face Lips Jaw Tongue Primary motor cortex

  37. Fig. 49-16b Upper arm Trunk Neck Leg Head Hip Elbow Forearm Hand Fingers Thumb Eye Nose Face Lips Genitals Teeth Gums Jaw Tongue Pharynx Primary somatosensory cortex Abdominal organs

  38. 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

  39. 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

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

  41. 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

  42. 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

  43. 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

  44. 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

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