lecture #21date ______ n chapter 48 ~ nervous system
TRANSCRIPT
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Lecture #21 Date ______Lecture #21 Date ______
Chapter 48 ~ Nervous System
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Nervous systemsNervous systems
Effector cells~ muscle or gland cells
Nerves~ bundles of neurons wrapped in connective tissue
Central nervous system (CNS)~ brain and spinal cord
Peripheral nervous system (PNS)~ sensory and motor neurons
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Structural Unit of Nervous SystemStructural Unit of Nervous System
Neuron~ structural and functional unit Cell body~ nucelus and organelles Dendrites~ impulses from tips to neuron Axons~ impulses toward tips Myelin sheath~ supporting, insulating layer Schwann cells~PNS support cells Synaptic terminals~ neurotransmitter releaser Synapse~ neuron junction
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Simple Nerve CircuitSimple Nerve Circuit
Sensory neuron: convey information to spinal cord
Interneurons: information integration Motor neurons: convey signals to
effector cell (muscle or gland) Reflex: simple response; sensory to
motor neurons Ganglion (ganglia): cluster of nerve cell
bodies in the PNS Supporting cells/glia: nonconductiong
cell that provides support, insulation, and protection
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Neural signaling, INeural signaling, I
Membrane potential (voltage differences across the plasma membrane) Intracellular/extracellular ionic concentration difference K+ diffuses out (Na+ in); large anions cannot follow….selective
permeability of the plasma membrane Net negative charge of about -70mV
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Neural signaling, IINeural signaling, II Excitable cells~ cells that can change membrane potentials (neurons, muscle) Resting potential~ the unexcited state of excitable cells Gated ion channels (open/close response to stimuli): photoreceptors; vibrations in air
(sound receptors); chemical (neurotransmitters) & voltage (membrane potential changes) Graded Potentials (depend on strength of stimulus): 1- Hyperpolarization (outflow of K+); increase in electrical gradient; cell becomes more
negative 2- Depolarization (inflow of Na+); reduction in electrical gradient; cell becomes less
negative
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The Resting PotentialThe Resting Potential
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Neural signaling, IIINeural signaling, III Threshold potential: if stimulus reaches a
certain voltage (-50 to -55 mV)…. The action potential is triggered…. Voltage-gated ion channels (Na+; K+) 1-Resting state •both channels closed 2-Threshold •a stimulus opens some Na+
channels 3-Depolarization •action potential
generated •Na+ channels open; cell becomes positive (K+ channels
closed) 4-Repolarization •Na+ channels close, K+
channels open; K+ leaves •cell becomes negative
5-Undershoot •both gates close, but K+ channel is slow; resting state restored
Refractory period~ insensitive to depolarization due to closing of Na+ gates
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The Action PotentialThe Action Potential
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Neural signaling, IVNeural signaling, IV
“Travel” of the action potential is self-propagating Regeneration of “new” action potentials only after refractory period Forward direction only Action potential speed: 1-Axon diameter (larger = faster; 100m/sec) 2-Nodes of Ranvier (concentration of ion channels); saltatory conduction;
150m/sec
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Synaptic communicationSynaptic communication
Presynaptic cell: transmitting cell Postsynaptic cell: receiving cell Synaptic cleft: separation gap Synaptic vesicles: neurotransmitter
releasers Ca+ influx: caused by action
potential; vesicles fuse with presynaptic membrane and release….
Neurotransmitter
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Signal transmissionSignal transmission
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NeurotransmittersNeurotransmitters
Acetylcholine (most common) •skeletal muscle
Biogenic amines (derived from amino acids)
•norepinephrine •dopamine •serotonin
Amino acids Neuropeptides (short chains of amino acids)
•endorphin
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Vertebrate PNSVertebrate PNS
Cranial nerves (brain origin)
Spinal nerves (spine origin)
Sensory division Motor division
•somatic system voluntary, conscious control •autonomic system √parasympathetic
conservation of energy √sympathetic
increase energy consumption
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The Vertebrate BrainThe Vertebrate Brain Forebrain
•cerebrum~memory, learning, emotion•cerebral cortex~sensory and motor nerve cell bodies •corpus callosum~connects left and right hemispheres •thalamus; hypothalamus
Midbrain •inferior (auditory) and superior (visual) colliculi
Hindbrain •cerebellum~coordination of movement •medulla oblongata/ pons~autonomic, homeostatic functions