* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture #13 – Animal Nervous Systems
Clinical neurochemistry wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Neural modeling fields wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Neuroregeneration wikipedia , lookup
Metastability in the brain wikipedia , lookup
Axon guidance wikipedia , lookup
Neural engineering wikipedia , lookup
Optogenetics wikipedia , lookup
Patch clamp wikipedia , lookup
Multielectrode array wikipedia , lookup
Signal transduction wikipedia , lookup
Development of the nervous system wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Evoked potential wikipedia , lookup
Node of Ranvier wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Neurotransmitter wikipedia , lookup
Membrane potential wikipedia , lookup
Neuroanatomy wikipedia , lookup
Action potential wikipedia , lookup
Synaptogenesis wikipedia , lookup
Biological neuron model wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Synaptic gating wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Nervous system network models wikipedia , lookup
Electrophysiology wikipedia , lookup
Single-unit recording wikipedia , lookup
Resting potential wikipedia , lookup
Molecular neuroscience wikipedia , lookup
End-plate potential wikipedia , lookup
Lecture #13 – Animal Nervous Systems 1 Key Concepts: • Evolution of organization in nervous systems • Neuron structure and function • Neuron communication at synapses • Organization of the vertebrate nervous systems • Brain structure and function • The cerebral cortex • Nervous system injuries and diseases??? 2 All animals except sponges have some kind of nervous system • Increasing complexity accompanied increasingly complex motion and activities • Nets of neurons bundles of neurons cephalization 3 First split was tissues; next was body symmetry; echinoderms “went back” to radial symmetry 4 Derived radial symmetry and nerve network 5 Cephalization • The development of a brain • Associated with the development of bilateral symmetry • Complex, cephalized nervous systems are usually divided into 2 sections Central nervous system (CNS) integrates information, exerts most control Peripheral nervous system (PNS) connects CNS to the rest of the body 6 7 Critical Thinking • What is the functional advantage of cephalization??? 8 Critical Thinking • What is the functional advantage of cephalization??? 9 Cephalization • The development of a brain • Associated with the development of bilateral symmetry • Complex, cephalized nervous systems are usually divided into 2 sections Central nervous system (CNS) integrates information, exerts most control Peripheral nervous system (PNS) connects CNS to the rest of the body 10 PNS CNS PNS 11 Specialized neurons support different sections • Sensory Transmit information from the sensory structures that detect the both external and internal conditions • Interneurons Analyze and interpret sensory information, formulate response • Motor Transmit information to effector cells – the muscle or endocrine cells that respond to input 12 Critical Thinking • Which type of neuron would have the most branched structure??? Sensory neurons Interneurons Motor neurons 13 Critical Thinking • Which type of neuron would have the most branched structure??? Sensory neurons Interneurons Motor neurons 14 Neuron structure is complex 100 billion nerve cells in the human brain! 15 16 17 Basic Neuron Structure • Cell body • Dendrites • Axons • Axon hillock • Myelin sheath • Synaptic terminal 18 Cell Body • Contains most cytoplasm and organelles • Extensions branch off cell body 19 Dendrites • Highly branched extensions • Receive signals from other neurons 20 Axons • Usually longer extension, unbranched til end • Transmits signals to other cells 21 Axon Hillock • Enlarged region at base of axon • Site where axon signals are generated Signal is sent after summation 22 Myelin Sheath • Insulating sheath around axon • Also speeds up signal transmission 23 Synaptic Terminal • End of axon branches • Each branch ends in a synaptic terminal Actual site of between-cell signal generation 24 Synapse • Site of signal transmission between cells • More later… 25 Supporting Cells - Glia • Maintain structural integrity and function of neurons • 10 – 50 x more glia than neurons in mammals • Major categories Astrocytes Radial glia Oligodendrocytes and Schwann cells 26 Glia – Astrocytes • Structural support for neurons • Regulate extracellular ion and neurotransmitter concentrations • Facilitate synaptic transfers • Induce the formation of the blood-brain barrier Tight junctions in capillaries allow more control over the extracellular chemical environment in the brain and spinal cord 27 Glia – Radial Glia • Function mostly during embryonic development • Form tracks to guide new neurons out from the neural tube (neural tube develops into the CNS) • Can also function as stem cells to replace glia and neurons (so can astrocytes) This function is limited in nature; major line of research 28 Glia – Oligodendrocytes (CNS) and Schwann Cells (PNS) • Form the myelin sheath around axons • Cells are rectangular and tile-shaped, wrapped spirally around the axons • High lipid content insulates the axon – prevents electrical signals from escaping • Gaps between the cells (Nodes of Ranvier) speed up signal transmission 29 The nerve signal is electrical! • To understand signaling process, must understand the difference between resting potential and action potential 30 Resting Potential • All cells have a resting potential Electrical potential energy – the separation of opposite charges Due to the unequal distribution of anions and cations on opposite sides of the membrane Maintained by selectively permeable membranes and by active membrane pumps Charge difference = one component of the electrochemical gradient that drives the diffusion of all ions across cell membranes 31 Neuron Function – Resting Potential • Neuron resting potential is ~ -70mV At resting potential the neuron is NOT actively transmitting signals Maintained largely because cell membranes are more permeable to K+ than to Na+; more K+ leaves the cell than Na+ enters An ATP powered K+/Na+ pump continually restores the concentration gradients; this also helps to maintain the charge gradient 32 Resting Potential Ion Concentrations 1. Cell membranes are more permeable to K+ than to Na+ 2. There is more K+ inside the cell than outside 3. There is more Na+ outside the cell than inside • Both ions follow their [diffusion] gradients 33 Critical Thinking • If both ions follow their diffusion gradients, what is the predictable consequence??? 34 Critical Thinking • If both ions follow their diffusion gradients, what is the predictable consequence??? 35 Resting Potential Ion Concentrations • A dynamic equilibrium is predictable, but is prevented by an ATP powered K+/Na+ pump 36 Neuron Function – Resting Potential • Neuron resting potential is ~ -70mV At resting potential the neuron is NOT actively transmitting signals Maintained largely because cell membranes are more permeable to K+ than to Na+; more K+ leaves the cell than Na+ enters An ATP powered K+/Na+ pump continually restores the concentration gradients; this also helps to maintain the charge gradient 37 Resting Potential Ion Concentrations • ATP powered pump continually transfers 3 Na+ ions out of the cytoplasm for every 2 K+ ions it moves back in to the cytoplasm • This means that there is a net transfer of + charge OUT of the cell 38 Resting Potential Ion Concentrations • Thus, the membrane potential is maintained • Cl- and large anions also contribute to the net negative charge inside the cell 39 REVIEW Neuron Function – Resting Potential • Neuron resting potential is ~ -70mV At resting potential the neuron is NOT actively transmitting signals Maintained largely because cell membranes are more permeable to K+ than to Na+; more K+ leaves the cell than Na+ enters An ATP powered K+/Na+ pump continually restores the concentration gradients; this also helps to maintain the charge gradient Cl-, other anions, and Ca++ also affect resting potential 40 Gated Ion Channels Why Neurons are Different • All cells have a membrane potential • Neurons can change their membrane potential in response to a stimulus • The ability of neurons to open and close ion gates allows them to send electrical signals along the extensions (dendrites and axons) Gates open and close in response to stimuli Only neurons can do this! 41 Gated Ion Channels Why Neurons are Different • Gated ion channels manage membrane potential Stretch gates – respond when membrane is stretched Ligand gates – respond when a molecule binds (eg: a neurotransmitter) Voltage gates – respond when membrane potential changes 42 Gated Ion Channels Why Neurons are Different • Hyperpolarization = inside of neuron becomes more negative • Depolarization = inside of neuron becomes more positive Either can occur, depending on stimulus Either can be graded – more stimulus = more change in membrane potential • Depolarization eventually triggers an action potential = NOT graded 43 Depolarization eventually triggers an action potential – action potentials are NOT graded 44 Action Potentials ARE the Nerve Signal • Triggered whenever depolarization reaches a set threshold potential • Action potentials are all-or-none responses of a fixed magnitude Once triggered, they can’t be stopped There is no gradation once an action potential is triggered • Action potentials are brief depolarizations 1 – 2 milliseconds • Voltage gated ion channels control signal 45 Critical Thinking • If the action potential is of a fixed magnitude, how do we sense different levels of a stimulus??? 46 Critical Thinking • If the action potential is of a fixed magnitude, how do we sense different levels of a stimulus??? 47 Action Potentials ARE the Nerve Signal • Triggered whenever depolarization reaches a set threshold potential • Action potentials are all-or-none responses of a fixed magnitude Once triggered, they can’t be stopped There is no gradation once an action potential is triggered • Action potentials are brief depolarizations 1 – 2 milliseconds • Voltage gated ion channels control signal 48 Fig. 48.13; p. 1019, 7th Ed. 49 Voltage Gate Activity 1. Resting Potential – Na+ and K+ activation gates closed; Na+ inactivation gate open on most channels 2. Depolarization – Na+ activation gates begin to open – Na+ begins to enter cell 3. Rising Phase – threshold is crossed, Na+ floods into the cell, raising the membrane potential to ~ +35mV 50 51 1. Resting Potential – Na+ and K+ activation gates closed; Na+ inactivation gate open on most channels 52 Voltage Gate Activity 1. Resting Potential – Na+ and K+ activation gates closed; Na+ inactivation gate open on most channels 2. Depolarization – Na+ activation gates begin to open – Na+ begins to enter cell 3. Rising Phase – threshold is crossed, Na+ floods into the cell, raising the membrane potential to ~ +35mV 53 54 2. Depolarization – Na+ activation gates begin to open – Na+ begins to enter cell 55 Voltage Gate Activity 1. Resting Potential – Na+ and K+ activation gates closed; Na+ inactivation gate open on most channels 2. Depolarization – Na+ activation gates begin to open – Na+ begins to enter cell 3. Rising Phase – threshold is crossed, Na+ floods into the cell, raising the membrane potential to ~ +35mV 56 57 3. Rising Phase – threshold is crossed, Na+ floods into the cell, raising the membrane potential to ~ +35mV 58 Voltage Gate Activity 4. Falling Phase – Na+ inactivation gates close, K+ activation gates open – Na+ influx stops, K+ efflux is rapid 5. Undershoot – K+ activation gates close, but not until membrane potential has gone a little bit below resting potential 6. Refractory Period – the Na+ inactivation gates remain closed during stages 4 and 5, limiting the maximum frequency of 59 action potentials Membrane repolarizes 60 4. Falling Phase – Na+ inactivation gates close, K+ activation gates open – Na+ influx stops, K+ efflux is rapid 61 Voltage Gate Activity 4. Falling Phase – Na+ inactivation gates close, K+ activation gates open – Na+ influx stops, K+ efflux is rapid 5. Undershoot – K+ activation gates close, but not until membrane potential has gone a little bit below resting potential 6. Refractory Period – the Na+ inactivation gates remain closed during stages 4 and 5, limiting the maximum frequency of 62 action potentials 63 5. Undershoot – K+ activation gates close, but not until membrane potential has gone a little bit below resting potential 64 Voltage Gate Activity 4. Falling Phase – Na+ inactivation gates close, K+ activation gates open – Na+ influx stops, K+ efflux is rapid 5. Undershoot – K+ activation gates close, but not until membrane potential has gone a little bit below resting potential 6. Refractory Period – the Na+ inactivation gates remain closed during stages 4 and 5, limiting the maximum frequency of 65 action potentials 6. Refractory Period – the Na+ inactivation gates remain closed during stages 4 and 5, limiting the maximum frequency of action potentials 66 67 Fig. 48.13, 7th Ed. Conduction of Action Potential • Electrical signal moves along the axon by depolarizing adjacent regions of the membrane past the threshold • The depolarization effect is NOT directional – the cytoplasm becomes more + in both directions 68 Critical Thinking • If the depolarizing effect is bilateral, why does the signal travel in one direction only??? 69 Critical Thinking • If the depolarizing effect is bilateral, why does the signal travel in one direction only??? 70 Conduction of Action Potential • Electrical signal moves along the axon by depolarizing adjacent regions of the membrane past the threshold • Depolarization zone travels in one direction only due to the refractory period (Na+ gates locked) 71 Speed! • Diameter of axon Larger = less resistance faster signal Found in invertebrates Max speed ~ 100 m/second • Nodes of Ranvier Signal jumps from node to node Found in vertebrates Saves space – 2,000 myelinated axons can fit in the same space as one giant axon Max speed ~ 120 m/second 72 Synapses – the gaps between cells • Electrical synapses occur at gap junctions Action potential is transmitted directly from cell to cell Especially important in rapid responses such as escape movements Also with controlling heart beat (but with specialized muscle tissue) • Most synapses are chemical The signal is converted from electrical chemical electrical Neurotransmitters cross the synapse and carry 73 the signal to the receiving cell Chemical Synapses • A multi-stage process Neurons synthesize neurotransmitters, isolated into synaptic vesicles located at the synaptic terminal The action potential triggers the release of neurotransmitters into the synapse Neurotransmitters diffuse across the synapse Neurotransmitter binds to a receptor, stimulating a response (more later) 74 Chemical Synapses 1. Action potential depolarizes membrane at synaptic terminal 2. Depolarization in this region opens Ca++ channels 3. Influx of Ca++ stimulates synaptic vesicles to fuse with neuron cell membrane 4. Neurotransmitters are released by exocytosis 5. Neurotransmitters bind to the receiving cell 75 membrane Chemical Synapses 76 Chemical Synapses REVIEW 1. Action potential depolarizes membrane at synaptic terminal 2. Depolarization in this region opens Ca++ channels 3. Influx of stimulates synaptic vesicles to fuse with neuron cell membrane 4. Neurotransmitters are released by exocytosis 5. Neurotransmitters bind to the receiving cell 77 membrane Chemical Synapses • Direct synaptic transmission Neurotransmitter binds directly to ligand-gated channels Channel opens for Na+, K+ or both • Indirect synaptic transmission Neurotransmitter binds to a receptor on the membrane (not to a channel protein) Signal transduction pathway is initiated Second messengers eventually open channels Slower but amplified response 78 Chemical synapses allow more complicated signals • Electrical signals pass unmodified at electrical synapses • Chemical signals are modified during transmission Type of neurotransmitter varies Amount of neurotransmitter released varies Some receptors promote depolarization; some promote hyperpolarization Signals are summed over both time and space Remember that many, many neurons are 79 responding to any given stimulus Chemical synapses allow more complicated signals • Responses are summed at the axon hillock Action potential is generated and sent down axon; or not 80 Chemical synapses allow more complicated signals • Summation is over both time and space • Excitory and inhibitory signals can “cancel” each other 81 Neurotransmitters – review text and table, but don’t memorize Table 48.1, 7th ed. 82 CNS Organization in Vertebrates • Brain – integrates • Spinal cord – 1o transmits • Both derived from hollow, dorsal embryonic nerve cord Hollow remnants remain in ventricles of brain and central canal of spinal cord Spaces are filled with cerebrospinal fluid that helps circulate nutrients, hormones, wastes, etc Fluid also cushions CNS • Axons are aggregated = white matter 83 84 PNS Organization in Vertebrates • Major role – transmitting information from sensory structures to the CNS; and from the CNS to effector structures Nerves always in left/right pairs that serve both sides of the body 85 PNS Organization in Vertebrates • Cranial nerves originate in brain and connect to the head and upper body Some have only sensory neurons (eyes, nose) • Spinal nerves originate in spinal cord and connect to the rest of the body Contain both sensory and motor neurons 86 Critical Thinking • Can the eyes do anything besides see??? • Can the nose do anything besides smell??? • Can the ears do anything besides hear??? 87 Critical Thinking • Can the eyes do anything besides see??? • Can the nose do anything besides smell??? • Can the ears do anything besides hear??? 88 PNS Organization in Vertebrates • Cranial nerves originate in brain and connect to the head and upper body Some have only sensory neurons (eyes, nose) • Spinal nerves originate in spinal cord and connect to the rest of the body Contain both sensory and motor neurons 89 PNS – Sub-divisions All work together to maintain homeostasis and respond to external stimuli 90 PNS - Somatic • Nerves that transmit signals to and from skeletal muscles • Respond primarily to external stimuli • Largely under voluntary control 91 PNS - Autonomic • Nerves that control the internal environment • Respond to both internal and external signals • Largely under involuntary control • Three sub-divisions Sympathetic – stress responses Parasympathetic – opposes sympathetic Enteric – controls digestive system 92 PNS – Autonomic 93 Autonomic - Sympathetic • Activates flight or fight responses • Promotes functions that increase sensory perception and ATP levels • Inhibits non-essential functions such as digestion and urination 94 Autonomic – Parasympathetic • Returns body systems to base-line function • Promotes digestion and other normal functions • Usually antagonistic to sympathetic division 95 Autonomic – Enteric • Specifically controls the digestive system • Regulated by both the sympathetic and parasympathetic divisions 96 Brain Development 97