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Nervous System and Nervous Tissue. Master control and communication Functions (system level and cell level)  Sensory input – monitoring stimuli  Integration.

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Presentation on theme: "Nervous System and Nervous Tissue. Master control and communication Functions (system level and cell level)  Sensory input – monitoring stimuli  Integration."— Presentation transcript:

1 Nervous System and Nervous Tissue

2 Master control and communication Functions (system level and cell level)  Sensory input – monitoring stimuli  Integration – interpretation of sensory input  Motor output – response to stimuli

3 Dendrites: input Cell body: integration Axon: output PNS CNS

4 Central nervous system (CNS) Form: Brain and spinal cord Function: Integration and command center Peripheral nervous system (PNS) Form: Paired spinal and cranial nerves Function: Carries messages to and from the spinal cord and brain

5 Central Nervous System Peripheral Nervous System Motor (efferent) Sensory (afferent) Somatic (voluntary) Autonomic (involuntary) Parasympathetic (Stop! ) Sympathetic (Action! Go!)

6 INPUTS: Sensory (afferent) division  Sensory afferent fibers – from skin, skeletal muscles, and joints to the brain  Visceral afferent fibers – from visceral organs to the brain OUTPUTS: Motor (efferent) division  Transmits impulses from the CNS to effector organs

7 Somatic nervous system (SNS)  Conscious control of skeletal muscles Autonomic nervous system (ANS)  Regulates involuntary muscle (smooth and cardiac) and glands ▪Sympathetic (Stimulates = Go!) ▪Parasympathetic (Conserves = Stop!)

8 1. Is part of the CNS 2. Is part of the PNS 25

9 1. Includes only the brain 2. Includes the brain and spinal cord 3. Includes the brain, spinal cord and all peripheral nerves 25

10 Neurons  Transmit electrical signals Neuroglia (“nerve glue”)  Supporting cells Neuroglia in the CNS  Astrocytes  Microglia  Ependymal cells  Oligodendrocytes Neuroglia in the PNS  Satellite cells  Schwann cells

11  Structural units of the nervous system  Long-lived (100+ years)  Amitotic (no centrioles = can’t divide)  High metabolic rate (glucose gobblers!)

12 Sensory (afferent)  transmit impulses toward the CNS Motor (efferent)  transmit impulses away from the CNS Interneurons (association neurons)  shuttle signals through CNS pathways

13 (b) (a) Dendrites Cell body Nissl bodies Axon terminals (secretory component) Axon hillock Node of Ranvier Impulse direction Schwann cell Neuron cell body Dendritic spine

14  Contains nucleus and nucleolus  Major biosynthetic center  Focal point for the outgrowth of neuronal processes (dendrites and axons)  Axon hillock – where axons arise

15 Dendrites  Numerous  Short and tapering  Diffusely branched  Contain “spines” where synapses form Axons  One per cell  Long (up to 4 ft. in length)  Form synapses at terminals (release neurotransmitters)  Anterograde and retrograde transport (out and back!)

16  Provide a supportive scaffolding for neurons  Segregate and insulate neurons  Guide young neurons to the proper connections  Promote health and growth  Help regulate neurotransmitter levels  Phagocytosis

17  Most abundant and versatile  Cling to neurons and synaptic endings  Cover capillaries (blood-brain barrier)  Support and brace neurons  Guide migration of young neurons  Control the chemical environment

18  Monitor health of neurons  Transform into macrophages to remove cellular debris, microbes and dead neurons NOTE: Normal immune system cells can’t enter CNS

19 Shape: squamous to columnar (often ciliated) Location: Line the central cavities of the brain and spinal column Function: Circulate cerebrospinal fluid

20  Wrap CNS axons like a jelly roll  Form insulating myelin sheath

21 Schwann cells  Surround axons of the PNS  Form insulating myelin sheath Satellite cells  Surround neuron cell bodies Nodes of Ranvier

22 Myelin Sheath  White, fatty sheath protects long axons  Electrically insulates fibers  Increases the speed of nerve impulses Neurilemma  remaining nucleus and cytoplasm of a Schwann cell

23  Both myelinated and unmyelinated fibers are present  Oligodendrocytes insulate up to 60 axons each White matter: dense collections of myelinated fibers Gray matter: mostly soma and unmyelinated fibers

24 1. Schwann cells 2. Ependymal cells 3. Oligodendrocytes 25

25 1. Cell body (soma) 2. Dendrites 3. Axons 25

26 1. Schwann cells 2. Ependymal cells 3. Astrocytes 4. Microglia 25

27 1. Schwann cells 2. Ependymal cells 3. Astrocytes 4. Microglia 25

28  Electrical impulses carried along the length of axons  Always the same regardless of stimulus  Based on changes in ion concentrations across plasma membrane  This is HOW the nervous system functions

29 Voltage (V)  potential energy from separation of charges (+ and -)  For neurons, measured in millivolts Current (I)  the flow of electrical charge between two points Insulator  substance with high electrical resistance  Think myelin sheath!

30 Passive (leakage) channels: always open Voltage-gated channels: open and close in response to membrane potential Ligand-gated (chemically gated) channels: open when a specific neurotransmitter binds Mechanically gated channels: open and close in response to physical forces




34 When gated channels are open:  Ions move along electro-chemical gradients ▪Takes into account charge differences ▪Takes into account concentration differences  An electrical current is created  Voltage changes across the membrane


36 Resting membrane potential (–70 mV)  The inside of a cell membrane has more negative charges than outside the membrane  Major differences are in Na + and K +

37 Depolarization  the inside of the membrane becomes less negative Hyperpolarization  the inside of the membrane becomes more negative than the resting potential Repolarization  the membrane returns to its resting membrane potential

38  Principal means of neural communication  A brief reversal of membrane polarity  All or nothing event  Maintain their strength over distance  Generated only by muscle cells and neurons

39 1. Resting state 2. Depolarization 3. Repolarization 4. Hyperpolarization 5. Return to resting potential

40  Na + and K + GATED channels are closed  Each Na + channel has two voltage-regulated gates  Activation gates  Inactivation gates

41  Na + permeability increases; membrane potential reverses  Na + gates are opened, but K + gates are closed  Threshold: critical level of depolarization (-55 to -50 mV)  Once threshold is passed,action potential fires

42  Sodium inactivation gates close  Voltage-sensitive K + gates open  K + rushes out  Interior of the neuron is negative again

43  Potassium gates remain open  Excess K + leaves cell  Membrane becomes hyperpolarized  Neuron is insensitive to stimuli until resting potential is restored

44 Repolarization  ONLY restores the electrical differences across the membrane  DOES NOT restore the resting ionic conditions Sodium-potassium pump restores ionic conditions  More sodium outside  More potassium inside

45 Na + Potassium channel Sodium channel 1 Resting state 2 Depolarization 3 Repolarization 4 Hyperpolarization Activation gates Inactivation gate K+K+ K+K+ Na + K+K+ K+K+

46    


48 Absolute refractory period (NO WAY! NO HOW!)  Neuron CANNOT generate an action potential  Ensures that each action potential is separate event  Enforces one-way transmission of nerve impulses Relative refractory period (Well, maybe…)  Threshold is elevated  Only strong stimuli can generate action potentials

49 –70 +30 (a) Time = 0 ms(b) Time = 2 ms(c) Time = 4 ms Voltage at 2 ms Voltage at 4 ms Voltage at 0 ms Resting potential Peak of action potential Hyperpolarization Membrane potential (mV))

50 Stronger stimuli generate more frequent action potentials

51 Velocity determined by  Axon diameter ▪the larger the diameter, the faster the impulse  Presence of a myelin sheath ▪Myleinated neurons have much faster impulses ▪Why? Node-jumping! (Saltatory conduction)


53 1. Depolarization 2. Repolarization 3. Hyperpolarization

54 1. The inside is more negative 2. The cell has crossed threshold 3. The inside is more positive

55 1. Action potentials absolutely fire 2. Action potential can never fire 3. The cell is hyperpolarized

56 Cause: Autoimmune disease with symptoms appearing in young adults (women at highest risk)  UNKNOWN environmental and genetic factors Symptoms: visual disturbances, weakness, loss of muscular control, incontinence Physiology  Myelin sheaths in the CNS are destroyed, producing a hardened lesion (scleroses)  Shunting and short-circuiting of nerve impulses occurs  Alternating periods of relapse and remission

57 Treatment  Drugs that modify immune response Prognosis  Medications can prevent symptoms from worsening  Reduce complications  Reduce disability  HOWEVER, not all drugs work long-term in all patients

58 Junction for cell  cell communication  Neuron  neuron  Neuron  effector cell Presynaptic neuron  Conducts impulses toward the synapse Postsynaptic neuron/cell  Receives signal  May/may not act on signal


60  Less common  Resemble gap junctions  Allow direct ion flow cell  cell Important in the CNS  Neural development  Synchronization of activity  Emotions and memory



63  Most common  Excitatory or inhibitory  Communication by neurotransmitters  Presynaptic neuron releases neurotransmitter  Postsynaptic neuron has membrane-bound receptors  Neurotransmitters must be recycled, removed or degraded after release

64 vesicles containing Neurotransmitter Synaptic cleft Ion channel (closed) Ion channel (open) Axon terminal of presynaptic neuron Postsynaptic membrane Ion channel closed Ion channel open Neurotransmitter Receptor Postsynaptic membrane Degraded neurotransmitter Na + Ca 2+ 1 2 3 4 5 Action potential NOTE: Ion channels are chemically gated, not voltage-gated

65  Acetylcholine (ACh)  Biogenic amines (dopamine, serotonin)  Amino acids (glutamate, GABA)  Peptides (endorphins, enkephalins)  Novel messengers  ATP  Nitric oxide (why Viagra works!)  Carbon monoxide

66 Direct  Alter ion channels  Rapid response  Important in sensory-motor coordination  Ex.) ACh, GABA, glutamate Indirect  Work via second messengers and G-proteins  Slower action  Important in memory, learning, and autonomic nervous system  Ex.) dopamine, serotonin, norepinephrine

67 EPSP: excitatory postsynaptic potentials  Cell is depolarized  Ex.) glutatmate IPSP: inhibitory postsynaptic potentials  Cell is hyperpolarized  Ex.) GABA

68 Will the postsynaptic cell fire? It depends on… Which neurotransmitter is released The amount of neurotransmitter released The length of time the neurotransmitter is bound to receptors If threshold isn’t reached, no action potential

69 Spatial summation  Multiple potentials arrive at the same time  Number of IPSPs v. EPSPs determine if action potential is generated Temporal summation  Multiple potentials arrive at different times  Time intervals determine if action potential is generated

70 NOTE: This is oversimplified. One neuron can receive inputs from thousands of other neurons.

71 Depression  Often linked to altered levels of serotonin  Treated with SSRIs (selective serotonin reuptake inhibitors)  Provides greater signal from less neurotransmitter WARNING: Suicide risk can actually increase in some patients, particularly adolescents and young adults.

72 Addiction  Dopamine is essential in “reward” pathways ▪Triggers pleasurable sensations ▪Involved in both drug and alcohol addiction  Glutamate is essential in memory pathways ▪May trigger relapses

73 BoTox = botulinum toxin  Works by blocking acetylcholine release at neuromuscular junction  Facial muscles can’t contract, wrinkles disappear  Also used for many spastic disorders Local anaesthesia  Most block sodium channels, so action potentials aren’t generated

74 1. True 2. False 25

75 1. True 2. False 3. Too confused to even guess! 25

76 1. Multiple stimuli from one neuron 2. Multiple stimuli from multiple neurons 3. Stimuli separated by time 25

77 1. Dopamine 2. GABA 3. Glutatmate 4. Serotonin 25

78 1. Dopamine 2. GABA 3. Nitric oxide 4. Acetylcholine 25

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