10-1 An Overview of the Nervous System

Transcription

1 Nervous System

2 10-1 An Overview of the Nervous System The nervous system controls body functions. It also allows for higher functions such as thinking.

3

4 The Central Nervous System The nervous system consists of two parts: the central and peripheral nervous systems. The central nervous system (CNS) is made up of the brain and spinal cord. Receptors transmit sensory input to the CNS via sensory neurons. The CNS integrates all sensory input and generates appropriate responses. Motor output leaves the CNS in motor neurons.

5 The Peripheral Nervous System The peripheral nervous system (PNS) consists of: spinal nerves cranial nerves The peripheral contains the somatic and the autonomic subdivisions. The autonomic division controls involuntary actions. The somatic division largely controls voluntary actions.

6 What you should know now CNS (Central Nervous System) Brain Spinal Cord PNS Cranial Nerves Spinal Nerves Somatic Deliberately controlled cause action of skeletal muscles Autonomic involuntary movements cause action in Smooth and Cardiac muscle

7 10-2 Structure and Function of the Neuron The fundamental unit of the nervous system is the neuron. This highly specialized cell generates and transmits bioelectric impulses.

8 The Structure of the Neuron All neurons consist of a cell body and two types of processes. Dendrites: conduct impulses to the cell body. Axons: conduct impulses away from the cell body. The terminal ends of axons branch, forming fibers that end in small knobs called terminal boutons.

9 The Myelin Sheath Axons in the CNS and PNS contain an insulating layer, the myelin sheath. It greatly increases the rate of transmission of nerve impulses. Nerve impulses jump over gaps in the sheath, the nodes of Ranvier.

10

11 Nerve Cell Repair Neurons lose the ability to divide. Neurons that die cannot be replaced by existing cells. Undamaged, live neurons can sometimes take over the function of those that are damaged or die.

12 Oxygen Sensitivity of Nerve Cells Neurons have a high metabolic demand. They are highly susceptible to loss of oxygen and glucose. Lack of oxygen in the brain often results in permanent brain damage. The longer the oxygen deprivation, the greater the damage.

13 Build a nerve cell Get some pipe cleaners and build a neuron Include Axon Dendrites Cell body Terminal boutons Is yours myelinated or nonmyelinated

14 What you should know now Structure of a Nerve Cell Body Dendrites Axon Myelinated Nerves Nonmyelinated nerves Nerve Cells are special The can not divide so nerve tissue does not repair

15 Nerve Cell Impulses Nerve impulses result from the flow of ions across their plasma membranes. The electrical potential across the membrane is known as the membrane potential or resting potential.

16 The Action Potential When a nerve cell is stimulated, its plasma membrane increases its permeability to sodium ions. Sodium ions rush in, causing depolarization down the membrane. Depolarization is followed by repolarization. The depolarization and repolarization of the neuron s plasma membrane constitute a bioelectric impulse or action potential.

17 All or nothing: If the influx of Na+ is not enough to reach the +30 mark (action potential) then no signal will be propagated

18 McGraw Hill Nerve Impulse

19 Nerve Cell Transmission Nerve impulses are waves of depolarization. Depolarization in one region increases membrane permeability in adjacent regions. This causes depolarization of the new region.

20 A relay of Neurons: Synaptic Transmission Nerve impulses travel from one neuron to another across synapses. When an impulse reaches the terminal bouton, it stimulates the release of neurotransmitters.

21 Excitation and Inhibition Neurotransmitters may excite or inhibit the postsynaptic membrane. If the number of excitatory impulses exceeds the number of inhibitory impulses, a nerve impulse will be generated.

22 Limiting a Neuronal Response Neurotransmitters are quickly removed from the synapse. They are destroyed by enzymes in the synaptic cleft.

23 Altering Synaptic Transmission Many common chemical substances alter synaptic transmission. Insecticides Anesthetics Antidepressants Caffeine Cocaine

24 Serotonin Prozac : A Serotonin reuptake inhibitor relieves the symptoms of depression by altering the levels of Serotonin at neural synapses

25 What you should know now Function of a Nerve What is an action potential What ions are involved in transmitting the action potential What is depolarization and repolarization How are nerve signals propagated from one neuron to another? Synapses Neurotransmitter

26 10-3 The Spinal Cord and Nerves The spinal cord is part of the central nervous system

27 Spinal Nerves The spinal cord gives off numerous nerves that supply the body. The central portion of the spinal cord is an H- shaped zone of gray matter. It contains nerve cell bodies The white matter contains axons and dendrites.

28 Efferent versus Afferent Afferent nerves carry information to the central nervous system SENSORY NEURONS Efferent nerves carry information from the central nervous system to the body MOTOR NEURONS

29 Interneurons: Hub between Afferent and Efferent Interneurons connect sensory( AFFERENT) and motor neurons(efferent) in the spinal cord. In the reflex arc, sensory impulses from receptors reach effectors without traveling to the brain. Some reflex arcs do not contain interneurons. Think about how a reflex is different from a deliberate movement of your muscles

30

31 Damage to the Spinal Cord Injury to the spinal cord can cause permanent damage. Take a second and think about neurons and why damage to them can lead to long term effects The severity of the injury depends on: its location the extent of the damage

32 What if you could replace neural cells?

33 What you should know now Structure of the spinal cord One main cord of gray matter with axons and dendrites extending out from the cord Afferent from the body to the CNS Sensory Efferent from the CNS to the body Motor

34 Interneurons Connect the afferent and efferent Reflex arc May not have interneurons Evolved for quick response to dangerous situations Damage to the Spinal Cord can lead to paralysis One treatment utilizes stem cells

35 10-4 The Brain The brain is part of the central nervous system. Cranial nerves are attached to the brain. They supply structures in the head and upper body.

36 The Cerebrum The cerebral hemispheres function in integration, sensory reception, and motor action. The cerebrum with its two cerebral hemispheres is the largest part of the brain. The outer layer of each hemisphere is the cortex. The cerebral cortex consists of many discrete functional regions including motor, sensory, and association areas.

37 The Primary Motor Cortex The primary motor cortex controls voluntary movement. Each region of the motor cortex controls a specific body part. A conscious thought stimulates the neurons of the primary motor cortex to generate an impulse.

38 The Primary Sensory Cortex and The Association Cortex The primary sensory cortex receives sensory information from the body. The association cortex is the site of integration and complex intellectual activities.

39 Unconscious Functions Unconscious functions are housed in the: Cerebellum Hypothalamus Brain stem

40 The Cerebellum The cerebellum: controls muscle synergy helps maintain posture Cerebral palsy is the result of severe impairment of the cerebellum. This can be caused by lack of oxygen.

41 The Thalamus and Hypothalamus The thalamus is a relay center. It relays some sensory information to the sensory and association cortexes. The hypothalamus controls many autonomic functions involved in homeostasis. Appetite Body temperature Water balance Blood pressure

42 The limbic system is the site of instinctive behavior and emotion. The Limbic System Stimulation of specific regions within the limbic system may elicit sensations.

43 What you should know now about the Cranial Nerves brain Control senses and movement of head and face Cerebrum Contains 2 hemispheres integration, sensory reception, and motor action. Cerebral Cortex : outer layer ( gray matter) has many discrete areas that carry out sensory, motor, integration

44 Involuntary centers Cerebrum Controls muscle synergy (smooth movements ) Maintains body posture Cerebral palsy is caused by damage to cerebrum and leads to jerky body movements and inability to control motion Thalamus and Hypothalamus Controls autonomic functions and triggers the release of hormones The limbic system Insticts Emotions

45 Cerebrospinal Fluid Cerebrospinal fluid cushions the CNS. It is similar in composition to blood plasma and interstitial fluid. Hydrocephalus occurs in children when CSF does not drain properly into the bloodstream.

46 Measuring Electrical Activity of the Brain Electrical activity of the brain varies depending on activity level or level of sleep. Electrodes applied to different parts of the scalp detect electrical activity in the brain. This produces an electroencephalogram (EEG). EEGs are used to diagnose brain dysfunction.

47 10-6 Learning and Memory Learning is the acquisition of new information and skills. Memory is the storage and recall of information. Short-term memory retains information for periods of seconds to hours. Long-term memory holds information for periods of days to years.

48 Where are Memories Stored? Memory is stored in multiple regions of the brain: Temporal Lobe Cerebellum Limbic System The hippocampus appears essential for transferring short-term memories into longterm memory.

49 How are Memories Stored? Short-term and long-term memory may involve structural and functional changes in neurons. Short-term memory may involve temporary changes in the function of synapses. Long-term memory may involve permanent structural and functional changes.

50 Maintaining Mental Acuity in Old Age New evidence suggests that brain function can be retained in old age. Connections among brain cells may strengthen over time if individuals remain intellectually challenged. Regular aerobic helps elderly people perform certain mental functions.

51 10-7 Diseases of the Brain Alzheimer s Disease Alzheimer s disease is a progressive loss of mental function. The brains of Alzheimer s patients contains fibrous clumps of protein from degenerated nerve cells. Proteins called beta-amyloid may bind to nerve cells in the brain and cause cell death.

52 Parkinson s Disease Parkinson s Disease is characterized by: Tremors A lack of dopamine in the brain It is caused by progressive deterioration of brain centers that control movement. Drugs and surgery can be used in treatment.

53 Multiple Sclerosis (MS) MS is caused by a destruction of the myelin sheath of nerve cells in the CNS. The damaged myelin results in nerve cell death that leads to: numbness slurred speech paralysis

54 Brain Tumors Two types of tumors develop in the brain tissue: benign malignant Benign tumors do not grow uncontrollably or spread. They can cause problems by placing pressure on areas of the brain. Malignant tumors grow rapidly. They may place pressure on or invade adjacent tissue or other parts of the body. Brain tumors may be related to: Exposure to certain materials or chemicals Heredity Certain viruses

55 What you should know now Detecting disease of the CNS Cerebrospinal fluid It is similar to plasma and bathes the CNS It can be examined for signs of infection Electroencephalogram Measures brain activity Learning and Memory 2 types of memory Short term Temporary changes to neural structure Long term Permanent changes to neural structure

56 Diseases of the brain Alzheimer s Protein plaque build up destroys neurons Parkinson s Tremors caused by lack of dopamine and damage to centers that control movement Multiple sclerosis Damage to schwann cells (sheath) Numbness, speech problems, paralysis Brain Tumors Benign Malignant

57 Chapter 11 The Senses

58 11-1 The General and Special Senses The body contains two types of senses: general and special. Receptors for the senses are grouped into five functional categories: Mechanoreceptors Chemoreceptors Thermoreceptors Photoreceptors Nociceptors

59 11-2 The General Senses Receptors for the general body senses generally fit into two groups: Naked nerve endings Encapsulated receptors Naked nerve endings in body tissues detect Pain Temperature Light touch

60

61 Encapsulated Receptors Encapsulated receptors are naked nerve endings surrounded by one or more layers of cells. Encapsulated receptors detect: pressure light touch muscle extension Receptors play an important role in homeostasis.

62 Adaptation Many receptors stop generating impulses after exposure to a stimulus for some length of time. Muscle stretch receptors and joint proprioceptors do not adapt.

63 11-3 Taste and Smell The special senses include Taste Smell Vision Hearing Balance

64 Taste Buds Taste buds respond to chemicals dissolved in food. They are located principally on the upper surface of the tongue. Food molecules dissolve in the saliva. They bind to the membranes of the microvilli of the receptor cells.

65

66 Primary Flavors Taste buds respond to five flavors: Salty Bitter Sweet Sour Umami Taste buds are preferentially responsive to one flavor.

67 The Olfactory Epithelium The olfactory epithelium is a patch of receptor cells that detects odors. It is located in the roof of the nasal cavities. The receptor cells respond to thousands of different molecules. The molecules bind to membrane receptors on the olfactory hairs. This stimulates nerve impulses that are transmitted to the brain via the olfactory nerve. Smell influences our sense of taste, and vice versa.

68

69 11-4 The Visual Sense: The Eye Human eyes are roughly spherical organs located in the eye sockets, or orbits. The eye is attached to the orbit by six small muscles that control eye movement.

70 Anatomy of the Eye The human eye consists of three distinct layers. The outermost layer consists of: the sclera the cornea The middle layer consists of: the choroid the ciliary body the iris

71 The innermost layer is the retina (the lightsensitive layer). The retina contains two types of photoreceptors: Rods: function in dim light provide black-and-white vision Cones Cones operate in bright light and provide color vision. Cones are also responsible for visual acuity. A very small number of the ganglion cells are also sensitive to light.

72

73 Focusing Light on the Retina The cornea and lens focus light on the retina. The shape of the lens is controlled by the muscles in the ciliary body. The curvature of the lens adjusts to focus on items. The cornea cannot adjust for focus. Figure 11-8

74

75 Visual Problems Nearsightedness results when the eyeball is slightly elongated. Farsightedness results when the eyeballs are too short or the lens is too weak Astigmatism occurs when the cornea and lens are slightly disfigured. Laser surgery can correct visual defects. Presbyopia is caused by a decline in the resiliency of the lens. Color Blindness is a hereditary disorder that varies in severity.

76 Laser Surgery

77 Laser Surgery

78 Laser Surgery

79 11-5 Hearing and Balance: The Cochlea and Middle Ear The ear consists of three anatomically separate portions: the outer ear the middle ear the inner ear

80 The Anatomy of the Ear The outer ear consists of the auricle and external auditory canal. Both direct sound to the eardrum. The middle ear consists of the eardrum and three small bones, the ossicles. The ossicles transmit vibrations to the inner ear. The auditory tube equilibrates the pressure inside the middle ear cavity.

81

82 The Eustachian Tube The Eustachian tube helps to equalize pressure in the middle ear. The inner ear contains the cochlea, where the receptors for sound are located.

83 Structure and Function of the Cochlea Hearing requires the participation of several structures. The cochlea is a spiral-shaped, bony structure. It contains three fluid-filled canals. The flexible basilar membrane that supports the organ of Corti separates the middle canal from the lower canal. Hair cells in the organ of Corti are embedded in the relatively rigid tectorial membrane. Sound waves create vibrations in the eardrum and ossicles, which are transmitted to fluid in the cochlea.

84

85 Distinguishing Pitch and Intensity Pressure waves in the cochlea cause the basilar membrane to vibrate. This stimulates the hair cells. Pressure waves resulting from a sound cause one part of the membrane to vibrate maximally. The hair cells stimulated in that region send signals to the brain. The brain interprets signals as a specific pitch.

86

87 Hearing Loss Conduction deafness occurs when the conduction of sound waves to the inner ear is impaired. It may result from a rupture of the eardrum or damage to the ossicles. Nerve deafness results from physical damage to: the hair cells the vestibulocochlear nerve the auditory cortex

88 The Vestibular Apparatus The vestibular apparatus houses receptors that detect body position and movement. It contains: semicircular canals utricle Saccule Fluid movement inside the semicircular canals deflects the cupula lying over the receptor cells. This alerts the brain to head movements. The utricle and saccule contain receptors that respond to: linear acceleration tilting of the head

89

90 11-6 Health and Homeostasis Many general sense receptors play an important role in homeostasis. Noise pollution in our environment affects homeostasis by: disturbing sleep raising stress levels

91