The Nervous System. Chapter 9

Transcription

1 The Nervous System Chapter 9

2 Objectives To identify the basic structure of a neuron. To explain the main components of the nervous system. To compare and contrast the central nervous system and the peripheral nervous system. To differentiate between the somatic and autonomic nervous systems.

3 Functions of the Nervous System Sensory input (gathering information): to monitor changes occurring inside and outside the body o Changes = stimuli Integration: to process and interpret sensory input and decide if action is needed Motor output: a response to integrated stimuli o The response activates muscles or glands

4 Functions of the Nervous System

5 Structure of a Neuron Neuron= Nerve Cell Reacts to physical/chemical changes in surroundings Transmit information through nerve impulses to other neurons and other cells.

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7 Anatomy of a neuron video

8 Nervous Tissue Neuroglia o Definition: all support cells in the CNS (Central nervous system) o Function: to support, insulate, and protect neurons Neurons o Function: transmit messages o Major regions of neurons Cell body nucleus and metabolic center of the cell Processes fibers that extend from the cell body o Dendrites conduct impulses toward the cell body o Axons conduct impulses away from the cell body

9 CNS vs. PNS CNS (Central Nervous System): o Brain o Spinal Cord PNS (Peripheral Nervous System): o Cranial nerves o Spinal Nerves

10 PNS Contains a sensory division and a motor division. Sensory Division: o Contains sensory receptors that convert info into a nerve impulse and transmit it back to the CNS to make sense of it. o Monitors environmental changes such as light and sound o Detects changes in homeostasis ( ex: temperature, oxygen level)

11 Motor Division Utilize peripheral neurons to carry impulses from the CNS to an effector which will cause a response o Ex: muscle contraction, gland secretion, etc.

12 Motor Division Somatic Nervous System: o Controls skeletal muscle and voluntary movement. Autonomic Nervous System: o Controls effectors that are involuntary Ex: heart, smooth muscle, certain glands

13 Objectives To identify and explain the 3 different structures of neurons. To compare and contrast sensory, motor, and interneurons and explain a general pathway. To determine the functions of the 5 types of neuroglia.

14 Types of Neurons Multipolar: o Many processes stemming from cell body. o *most neurons in brain and spinal cord are multipolar

15 Types of Neurons Bipolar: o Only two processes (one at each end. o *found in eyes, nose, ears..

16 Types of Neurons Unipolar: o One single process extending from cell body. o one side of axon is the peripheral process associated with body part, other side is the central process that enters brain or spinal cord. o Cell bodies create a tissue mass called ganglia.

17 Types of Neurons

18 Neuron Classification Sensory Neurons (afferent): o Carry impulses from PNS to CNS o Contain receptor ends at the tips of dendrites o Changes outside the body stimulate receptor ends triggering an impulse o *Most are unipolar

19 Neuron Classification Interneurons (association): o Completely in brain or spinal cord. o Link neurons together. o *multipolar

20 Neuron Classification Motor Neurons (efferent): o carry impulses out of brain or spinal cord to the effector and stimulate response.

21 General Pathway

22 Neuroglial Cells *More numerous than neurons, support neurons in different ways. Microglial Cells: o Phagocytize bacterial cells and cellular debris Oligodendrocytes: o Provide insulating layers of myelin Astrocytes: o Provide structural support o join parts (ex: neuronà capillary) o help regulate concentrations of nutrients and ions o Form scar tissue in the CNS Ependymal Cells: o Forms membrane that covers specialized brain parts and forms inner linings within the brain and spinal canal Schwann cells: o Forms myelin sheath around axons.

23 Nervous Tissue: Support Cells

24 Nervous Tissue: Support Cells

25 Nervous Tissue: Support Cells

26 Nervous Tissue: Support Cells

27 Nervous Tissue: Support Cells

28 Neuroglial Cells

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30 Myelin A lipid that sometimes coats axons o White matter = myelinated axons in CNS o Gray matter = cell bodies & unmyelinated axons in CNS Produced by some neuroglial cells Insulates neurons & increases efficiency of nerve impulses

31 Objectives To explain how a nerve impulse occurs. To determine what types of stimuli elicit an action potential. To explain different things that inhibit an action potential. To understand components of a neuron that contribute to impulse velocity.

32 Cell Membrane Potential The membrane is electrically charged, polarized due to Na+ and K+ ions o Greater concentration of sodium ions outside and potassium ions inside. o Potassium ions pass through more easily o Active transport (sodium/potassium pump) maintains balance This is essential in the propagation of a nerve impulse.

33 Resting Potential When a nerve cell membrane is undisturbed, the membrane remains polarized staying more negative on the inside and positive on the outside.

34 Threshold Potential If the nerve cell detects a change in light/temp/ pressure it effects the resting potential and the membrane begins depolarizing. o Sodium channels open and + ions flow in, making the inside less negative. Change in potential is proportional to the intensity of the stimulation. Stimulation + more stimulation before initial stimulation subsides is called summation. Once the threshold is reached, an action potential occurs.

35 Action Potential Definition: change in neuron membrane polarization and return to resting state Nerve Impulse: chain of action potentials from neuron to neuron

36 Action Potential Depolarization: a decrease in membrane potential Repolarization: increase in membrane potential, causes membrane to become negatively charged again Action Potential 1. Stimuli (temperature, light, pressure, other neurons) decreases membrane potential 2. When threshold potential (~55 mv) is reached, stimulus is big enough to cause neuron to send a signal.

37 Action Potential Continued 3. Reaching threshold potential triggers Na+ and K+ channels (located in nodes of Ranvier) to open and equalize charges 3a. Na+ channels open faster, causing rapid depolarization. 3b. As K+ channels open slowly, membrane becomes more polarized, Na+ rushes out. 4. Further parts of axon are triggered and action potentials propagate down length of axon causing nerve impulse. 5. Results in neurotransmitters being released into synapse

38 Action Potential

39 Action potential video

40 Impulse Conduction Unmyelinated nerve = impulse conducted over the entire surface. Myelin insulates and prevents ion flow, would prevent conduction if it were continuous and didn t have the nodes of ranvier. Myelinated nerve= impulse jumps from node to node and creates a saltatory response and is much faster than unmyelinated.

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42 All- or- None Nerve impulses create an all or none response. Once the stimulus reaches threshold, it generates an action potential.

43 Objectives Identify the different components of a reflex arc. Explain different autonomic reflexes found throughout the body.

44 Reflexes Ordinarily, a receptor sends a signal to the brain where the brain coordinates a response. What happens when you touch something hot?

45 Reflex Arcs Reflex: a rapid, predictable, and involuntary response to a stimulus Reflex Arc: Direct route from sensory neurons, to an interneuron, to an effector. o Interneuron: neuron between the primary sensory neuron and the final motor neuron. A reflex is a rapid action that happens without thought and does not involve the brain.

46 Reflex Arc 1) Receptor- sense organ in skin, muscle, or other organ 2) Sensory Neuron- carries impulse towards CNS from receptor 3) Interneuron- carries impulse within CNS 4) Motor Neuron- carries impulse away from CNS to effector 5) Effector- structure by which animal responds (muscle, gland, etc).

47 Steps in a Reflex Arc 1. Stimulus: A receptor receives a stimulus 2. Afferent Pathway: Receptor sends message to integrating center (CNS) via a sensory neuron 3. Integration: CNS makes correct connection between sensory neuron and motor neuron; usually involves an interneuron 4. Efferent Pathway: Motor neuron carries message from CNS to effector 5. Response: Effector carries out appropriate response

48 Reflex Arc

49 Reflex arc video

50 Types of Reflexes Somatic reflexes: Activation of skeletal muscle o Example: when you move your hand away from a hot stove Autonomic reflexes: Regulation of smooth muscle; regulation of cardiac muscle, regulation of glands o Example: Heart rate and blood pressure regulation; digestive system regulation; regulation of fluid balance

51 NeurotransmiLers Definition: chemicals that transmit signals from neurons to a target cell across a synapse NTs can be either excitatory (excite) or inhibitory (inhibit) Each neuron generally synthesizes and releases a single type of neurotransmitter

52 Neurotransmitter Acetylcholine Dopamine Role in the Body Excitatory. Used by spinal cord neurons to control muscles; used by neurons in the brain to regulate memory. In most instances, acetylcholine is excitatory. Inhibitory. Produces feelings of pleasure when released by the brain reward system. GABA (gamma-aminobutyric acid) Glutamate Glycine The major inhibitory neurotransmitter in the brain. The most common excitatory neurotransmitter in the brain. Inhibitory. Used mainly by neurons in the spinal cord. Norepinephrine Serotonin Mostly excitatory, can be inhibitory in a few brain areas. Acts as both neurotransmitter and hormone. In PNS, part of fight or flight response. it is part of the flight-or-flight response. In brain, regulates normal brain processes. Inhibitory. Involved in many functions including mood, appetite, and sensory perception.

53 Drugs Interfere with Neurotransmission Drugs can affect synapses at a variety of sites and in a variety of ways, including: o Increasing number of impulses (firing of nerves) o Release NT from vesicles with or without impulses o Block reuptake of neurotransmitters or block receptors o Produce more or less NT o Prevent vesicles from releasing NT

54 Three Drugs (of many) which affect Neurotransmission Methamphetamine Nicotine Alcohol

55 Methamphetamine Meth alters Dopamine transmission in two ways: o Enters dopamine vesicles in axon terminal causing release of NT o Blocks dopamine transporters taking dopamine back into the transmitting neuron Result: More dopamine in the synaptic cleft o This causes neurons to fire more often than normal resulting in a euphoric feeling.

56 Methamphetamine Problems o After the drug wears off, dopamine levels drop, and the user crashes. The euphoric feeling will not return until the user takes more methamphetamine. o Long-term use of meth causes dopamine axons to wither and die. o Note that cocaine also blocks dopamine transporters, thus it works in a similar manner.

57 Nicotine Similar to methamphetamine and cocaine, nicotine increases dopamine release in a synapse. However, the mechanism is slightly different Nicotine binds to receptors on the presynaptic neuron

58 Nicotine Nicotine binds to the presynaptic receptors exciting the neuron to fire more action potentials causing an increase in dopamine release. Nicotine also affects neurons by increasing the number of synaptic vesicles released.

59 Alcohol Alcohol has multiple effects on neurons. It alters neuron membranes, ion channels, enzymes, and receptors. It binds directly to receptors for acetylcholine, serotonin, and gamma aminobutyric acid (GABA), and gluatmate.

60 GABA and the GABA receptor GABA is a neurotransmitter that has an inhibitory effect on neurons. When GABA attaches to its receptor on the postsynaptic membrane, it allows Cl ions to pass into the neuron. This hyperpolarizes the postsynaptic neuron to inhibit transmission of an impulse.

61 Alcohol and the GABA Receptor When alcohol enters the brain, it binds to GABA receptors and amplifies the hyperpolarization effect of GABA. The neuron activity is further diminished. This accounts for some of the sedative affects of alcohol.

62 The Adolescent Brain and Alcohol The brain goes through dynamic change during adolescence, and alcohol can can seriously damage long and short-term growth processes. Frontal lobe development and the refinement of pathways and connections continue until age 16, and a high rate of energy is used as the brain matures until age 20. Damage from alcohol at this time can be long-term and irreversible.

63 The Adolescent Brain and Alcohol In addition, short-term or moderate drinking impairs learning and memory for more in youth than adults. Adolescents need only drink half as much as adults to suffer the same negative effects.

64 Drugs that Influence NeurotransmiLers Change in Neurotransmission Effect on Neurotransmitter release or availability Drug that acts this way increase the number of impulses increased neurotransmitter release nicotine, alcohol, opiates release neurotransmitter from vesicles with or without impulses release more neurotransmitter in response to an impulse block reuptake produce less neurotransmitter prevent vesicles from releasing neurotransmitter block receptor with another molecule increased neurotransmitter release increased neurotransmitter release more neurotransmitter present in synaptic cleft less neurotransmitter in synaptic cleft less neurotransmitter released no change in the amount of neurotransmitter released, or neurotransmitter cannot bind to its receptor on postsynaptic neuron amphetamines methamphetamines nicotine cocaine amphetamine probably does not work this way No drug example LSD caffeine

65 CNS (Brain Structure)

66 Regions of the Brain

67 Cerebral Hemispheres (Cerebrum) Structure of cerebrum: Paired (left and right) superior parts of the brain Function of cerebrum: Higher brain function (thought and action)

68 Regions of the Brain: Cerebrum

69 Four (Main) Lobes of the Cerebrum Frontal lobe: problem solving, judgment, motor function (Primary Motor Area), speech (Broca s Area) Parietal lobe: sensation, handwriting, body position (Primary Somatic Sensory Area) Occipital lobe: visual processing system Temporal lobe: memory and hearing

70 Regions of the Brain: Cerebrum

71 Regions of the Brain: Diencephalon

72 Regions of the Brain: Diencephalon

73 Diencephalon Structure: sits on top of brain stem; enclosed by cerebral hemispheres

74 Diencephalon Three parts Thalamus: relay station for sensory impulses Hypothalamus: autonomic nervous system center; involved in emotion o Helps regulate body temperature o Controls water balance o Regulates metabolism Epithalamus: houses the pineal gland (involved in sleep); forms CSF (Cerebrospinal fluid)

75 Regions of the Brain: Diencephalon

76 Brain Stem Structure: Attached to the spinal cord Midbrain o Mostly composes of tracts of nerve fibers o Function: reflex center for vision and hearing Pons o Structure: bulging center part of the brain stem o Function: control of breathing Medulla Oblongata o Structure: most inferior part of the brain stem; merges into spinal cord o Functions: heart rate control, blood pressure regulation, breathing, swallowing, vomiting

77 Regions of the Brain: Brain Stem

78 Cerebellum Structure: looks like a little cerebrum, sits inferior to cerebrum, posterior to brain stem Function: provides involuntary coordination of body movements

79 Regions of the Brain: Cerebellum

80 Ventricles Structure: four chambers within the brain filled with cerebrospinal fluid o Lateral Ventricles: within Cerebrum o Third Ventricle: in Diencephalon o Fourth Ventricle: between pons and cerebellum

81 Ventricles Functions 1. Transport of waste and nutrients 2. Protects cerebrum from trauma 3. Contain signaling molecules that direct development and function

82 Spinal Cord Anatomy and PNS

83 Spinal Cord General Info Structure: extends from foramen magnum of skull to the first two lumbar vertebra

84 Spinal Cord Anatomy

85 Spinal Cord Anatomy Internal gray matter mostly cell bodies; surrounds central canal o Central canal is filled with cerebrospinal fluid Exterior white matter - axons

86 Spinal Cord Anatomy

87 Peripheral Nervous System (PNS) Definition: nerves and ganglia outside the central nervous system Ganglia: mass of nerve cell bodies Nerve: bundle of neuron fibers

88 PNS: Classification of Nerves Mixed nerves: both sensory and motor fibers Sensory (afferent) nerves: carry impulses toward the CNS Motor (efferent) nerves: carry impulses away from the CNS

89 PNS: Cranial Nerves Definition: 12 pairs of nerves that serve the head and neck

90 PNS: Cranial Nerves I Olfactory nerve sensory for smell II Optic nerve sensory for vision III Oculomotor nerve motor fibers to eye muscles IV Trochlear motor fiber to eye muscles V Trigeminal nerve sensory for the face; motor fibers to chewing muscles VI Abducens nerve motor fibers to eye muscles VII Facial nerve sensory for taste; motor fibers to the face VIII Vestibulococlear nerve sensory for balance and hearing

91 PNS: Cranial Nerves IX Glossopharyngeal nerve sensory for taste; motor fibers to the pharynx X Vagus nerves sensory and motor fibers for pharynx, larynx, and viscera XI Accessory nerve motor fibers to neck and upper back XII Hypoglossal nerve motor fibers to tongue

92 Spinal Nerves Structure: formed by the combination of the ventral and dorsal roots of the spinal cord o 31 pairs of spinal nerves arise from the spinal cord Cauda equina: collection of spinal nerves at the inferior end

93 Autonomic Nervous System Definition: involuntary nervous system Function: regulates activities of cardiac and smooth muscles and glands Two subdivisions o Sympathetic divisions o Parasympathetic division

94 Sympathetic Division (E) Sympathetic Function fight or flight o Response to unusual stimulus o Takes over to increase activities o Remember the E division: Exercise, excitement, emergency, and embarrassment Neurotransmitters o Norepinephrine o Epinephrine

95 Parasympathetic Division (D) Parasympathetic function housekeeping activities o Conserves energy o Maintains daily necessary body functions o Remember as the D division: digestion, defecation, and diuresis Neurotransmitter o Acetylcholine

96 Difference between Somatic and Autonomic Nervous System Nerves o Somatic: one motor neuron o Autonomic: preganglionic and postganglionic nerves Effector organs o Somatic: skeletal muscle o Autonomic: smooth muscle, cardiac muscle, and glands Neurotransmitters o Somatic: acetylcholine o Autonomic: acetylcholine, epinephrine, or norepinephrine

97 Review video (show on review day!!)