Neural Control. Chapter 33 Part 2

Transcription

1 Neural Control Chapter 33 Part 2

2 33.6 A Smorgasbord of Signals Different types of neurons release different neurotransmitters; Parkinson s disease involves dopamine-secreting neurons and motor control

3 Fig a, p. 562

4 Fig b, p. 562

5 Fig c, p. 562

6 Major Neurotransmitters and Their Effects

7 The Neuropeptides Neuromodulators Neuropeptides made by some neurons that influence the effects of neurotransmitters Substance P enhances pain Enkephalins and endorphins are pain killers

8 33.7 Drugs Disrupts Signaling Psychoactive drugs exert their effects by interfering with the action of neurotransmitters Stimulants (nicotine, caffeine, cocaine, amphetamines) Depressants (alcohol, barbiturates) Analgesics (narcotics, ketamine, PCP) Hallucinogens (LSD, THC)

9 PET Scan: Effects of Cocaine

10 Signs of Drug Addiction

11 Key Concepts How Neurons Work Messages flow along a neuron s plasma membrane, from input to output zones Chemicals released at a neuron s output zone may stimulate or inhibit activity in an adjacent cell Psychoactive drugs interfere with the information flow between cells

12 33.8 The Peripheral Nervous System Peripheral nerves carry information to and from the central nervous system Nerves are bundled axons of many neurons Each axon is wrapped in a myelin sheath that increases transmission speed

13 Nerve Structure and Function

14 Nerve Structure and Function

15 Nerve Structure and Function

16 Nerve Structure and Function

17 myelin sheath axon blood vessels nerve fascicle (a number of axons bundled inside connective tissue) the nerve s outer wrapping Fig a, p. 564

18 unsheathed node axon b Jellyrolled Schwann cells of an axon s myelin sheath Fig b, p. 564

19 Na + action potential resting potential resting potential Fig c, p. 564

20 K + Na + resting potential restored action potential resting potential Fig d, p. 564

21 Animation: Nerve structure

22 Animation: Ion flow in myelinated axons

23 Divisions of the Peripheral Nervous System Somatic nervous system Conducts information about the environment to the central nervous system (involuntary) Controls skeletal muscles (voluntary) Autonomic nervous system Conducts signals to and from internal organs and glands

24 Divisions of the Autonomic Nervous System The two divisions of the autonomic nervous system have opposing effects on effectors Sympathetic neurons are most active in times of stress or danger (fight-flight response) Parasympathetic neurons are most active in times of relaxation

25 Divisions of the Autonomic Nervous System

26 eyes salivary glands optic nerve midbrain medulla oblongata heart larynx bronchi lungs vagus nerve cervical nerves (8 pairs) stomach liver spleen pancreas kidneys adrenal glands thoracic nerves (12 pairs) (most ganglia near spinal cord) small intestine upper colon lower colon rectum bladder uterus genitals (all ganglia in walls of organs) pelvic nerve lumbar nerves (5 pairs) sacral nerves (5 pairs) Fig , p. 565

27 Animation: Autonomic nerves

28 33.9 The Spinal Cord Spinal cord Runs through the vertebral column and connects peripheral nerves with the brain Serves as a reflex center Central nervous system (CNS) The brain and spinal cord

29 Protective Features Meninges Three membranes that cover and protect the CNS Cerebrospinal fluid Fills central canal and spaces between meninges Cushions blows

30 White Matter and Gray Matter White matter Bundles of myelin-sheathed axons (tracts) Outermost portion of spinal cord Gray matter Nonmyelinated structures (cell bodies, dendrites, neuroglial cells)

31 Reflex Pathways Reflex An automatic response to a stimulus Stretch reflex, knee-jerk reflex, withdrawal reflex Spinal reflexes do not involve the brain Signals from sensory neurons enter the cord through the dorsal root of spinal nerves Commands for responses go out on the ventral root of spinal nerves

32 Stretch Reflex

33 STIMULUS Biceps stretches. A Fruit being loaded into a bowl puts weight on an arm muscle and stretches it. Will the bowl drop? NO! Muscle spindles in the muscle s sheath also are stretched. muscle spindle neuromuscular junction B Stretching stimulates sensory receptor endings in this muscle spindle. Action potentials are propagated toward spinal cord. E Axon terminals of the motor neuron synapse with muscle fibers in the stretched muscle. F ACh released from the motor neuron s axon terminals stimulates muscle fibers. G Stimulation makes the stretched muscle contract. Ongoing stimulations and contractions hold the bowl steady. D The stimulation is strong enough to generate action potentials that selfpropagate along the motor neuron s axon. C In the spinal cord, axon terminals of the sensory neuron release a neurotransmitter that diffuses across a synaptic cleft and stimulates a motor neuron. RESPONSE Biceps contracts. Fig , p. 567

34 Animation: Stretch reflex

35 Key Concepts Vertebrate Nervous System The central nervous system consists of the brain and spinal cord The peripheral nervous system includes many pairs of nerves that connect the brain and spinal cord to the rest of the body The spinal cord and peripheral nerves interact in spinal reflexes

36 33.10 The Vertebrate Brain The brain is the body s main information integrating organ, part of the CNS During development, the brain is organized as three functional regions: forebrain, midbrain and hindbrain

37 Hindbrain and Midbrain The hindbrain includes the medulla oblongata, the pons, and the cerebellum The midbrain in mammals is reduced The brain stem (pons, medulla, and midbrain) is involved in reflex behaviors

38 The Forebrain Cerebrum Main processing center in humans Evolved as an expansion of the olfactory lobe Thalamus and hypothalamus Important in thirst, temperature regulation, and other responses related to homeostasis

39 Development of the Human Brain

40 Fig (a-c), p. 568

41 forebrain midbrain hindbrain Fig (a-c), p. 568

42 Protection at the Blood-Brain Barrier Blood-brain barrier Protects the CNS from harmful substances Tight junctions form a seal between adjoining cells of capillary walls Some toxins (nicotine, alcohol, caffeine, mercury) are not blocked

43 The Human Brain Cerebellum Has more interneurons than other brain regions Involved in balance, motor skills and language Cerebrum Divided into two hemispheres, coordinated by signals across the corpus callosum Each hemisphere deals with the opposite side of the body

44 Major Brain Regions of Vertebrates

45 olfactory lobe forebrain midbrain hindbrain FISH AMPHIBIAN REPTILE BIRD shark frog alligator goose Fig a, p. 569

46 Fig b, p. 569

47 part of optic nerve corpus callosum hypothalamus thalamus pineal gland location midbrain cerebellum pons medulla oblongata Fig b, p. 569

48 Animation: Sagittal view of a human brain

49 33.11 The Human Cerebrum Each cerebral hemisphere is divided into frontal, temporal, occipital and parietal lobes Cerebral cortex Outermost gray matter of the cerebrum Controls voluntary activity, sensory perception, abstract thought, language and speech Distinct areas receive and process signals

50 Lobes of the Brain

51 frontal lobe (planning of movements, aspects of memory, inhibition of unsuitable behaviors) primary motor cortex primary somatosen sory cortex parietal lobe (visceral sensations) Wernicke s area Broca s area temporal lobe (hearing, advanced visual processing) occipital lobe (vision) Fig , p. 570

52 Animation: Receiving and integrating areas

53 Functions of the Cerebral Cortex Specific areas of the cerebral cortex correspond to specific body parts or functions Examples: The body is spatially mapped out in the primary motor cortex of each frontal lobe Association areas are scattered throughout the cortex, but not in motor or sensory areas

54 The Primary Motor Cortex

55 Association Areas Integrate Inputs

56 Motor cortex activity when speaking Prefrontal cortex activity when generating words Visual cortex activity when seeing written words Fig , p. 570

57 Connections With the Limbic System The cerebral cortex oversees the limbic system Limbic system Governs emotions, assists in memory, correlates emotional-visceral responses Includes the hypothalamus, hippocampus, amygdala, and cingulate gyrus

58 Limbic System Components

59 (olfactory tract) cingulate gyrus thalamus hypothalamus amygdala hippocampus Fig , p. 571

60 Making Memories The cerebral cortex receives information and processes some of it into memories Memory forms in stages Short-term memory lasts seconds to hours Long-term memory is stored permanently Skill memory involves the cerebellum Declarative memory stores facts and impressions

61 Stages in Memory Processing

62 Sensory stimuli, as from the nose, eyes, and ears Temporary storage in the cerebral cortex Input forgotten SHORT-TERM MEMORY Recall of stored input Emotional state, having time to repeat (or rehearse) input, and associating the input with stored categories of memory influence transfer to long-term storage LONG-TERM MEMORY Input irretrievable Fig , p. 571

63 Sensory stimuli, as from the nose, eyes, and ears Temporary storage in the cerebral cortex Input forgotten SHORT-TERM MEMORY Recall of stored input Emotional state, having time to repeat (or rehearse) input, and associating the input with stored categories of memory influence transfer to long-term storage LONG-TERM MEMORY Input irretrievable Stepped Art Fig , p. 571

64 33.12 The Split Brain Investigations by Roger Sperry into the importance of information flow between the cerebral hemispheres showed that the two halves of the brains have a division of labor Typically, math and language skills reside in the left hemisphere; the right hemisphere interprets music, spatial relationships, and visual inputs

65 Visual Information and the Brain

66 Left Half of Visual Field Right Half of Visual Field COWBOY COW BOY pupil optic nerves retina corpus callosum left visual cortex optic chiasm right visual cortex Fig , p. 572

67 Animation: Path to visual cortex

68 Split-Brain Studies

69 33.13 Neuroglia The Neurons Support Staff Neuroglial cells make up the bulk of the brain The adult brain has four types of neuroglial cells Oligodendrocytes make myelin Microglia have immune system functions Astrocytes secrete various substances, take up neurotransmitters, assist in immune defenses, and stimulate formation of the blood-brain barrier Ependymal cells line brain cavities

70 Astrocytes

71 About Brain Tumors Unlike neurons, neuroglia continue to divide in adults, and can be a source of primary brain tumors (gliomas) Exposure to ionizing radiation such as x-rays, or to chemical carcinogens, increases risk

72 Key Concepts About the Brain The brain develops from the anterior part of the embryonic nerve cord A human brain includes evolutionarily ancient tissues and newer regions that provide the capacity for analytical thought and language Neuroglia make up the bulk of the brain

73 Animation: Action potential

74 Animation: Human brain development

75 Animation: Organization of the spinal cord

76 Animation: Primary motor cortex

77 Animation: Regions of the vertebrate brain

78 Animation: Structures involved in memory

79 Animation: Synapse function

80 Animation: Synaptic integration

81 ABC video: New Nerves

82 Video: In pursuit of ecstasy

83 Video: Brain stem

84 Video: Limbic system dissection