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Nervous System
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Function of the Nervous System
• Receive sensory information, interpret it, and send out appropriate commands to form a response
• Composed of neurons (functional unit of the nervous system)
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Nervous System Endocrine System
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Divisions of the Nervous System
• Central Nervous System (CNS) – processes, interprets and stores information, composed of the brain and spinal cord
• Peripheral Nervous System (PNS) – peripheral nerves that carry signals to and from the CNS
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Divisions of the Nervous System
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Structure of a Neuron
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Schwann Cells and Myelin
• Schwann cells are supporting cells that produce myelin (lipid insulator)
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Types of Neurons
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Three Types of Neurons
• Sensory Neurons – Convey signals to the CNS from sensory receptors
• Interneurons – Located within the CNS, integrate data and then relay signals to other neurons
• Motor Neurons – Convey signals from the CNS to effector cells
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Reflex Arc
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Reflex Arc (Neural Circuit)
Stimulus (External or Internal)
Sensory Receptor Cell
(5 Types)
Interneuron (Brain and Spinal
Cord)
Motor Neuron (Efferent)
Sensory Neuron (Afferent)
Response (Behavior, Secretion)
Effector (Muscle, Gland)
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The Synapse
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The Synapse
• Site of communication between an axon (or synaptic) terminal of one neuron and another cell
• Transmission of information between neurons occurs across synapses
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Molecular Mechanism of Synaptic Function
How Cone Snails Paralyze Fish
When Cone Snails Attack
Watch the following three videos on synaptic function:
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What do you already know about action potentials?
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Nerve Impulse Animation
Watch the following video:
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Membrane Potential
• Neurons, like most cells, have an electrical charge difference (membrane potential)
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Resting Potential • At rest, the membrane potential is -70mV
(resting potential) - maintained by the Na+/K+ pump
• At rest, the neuron is said to be “polarized”
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Threshold (“All or None”) • A neuron remains at rest until it receives a
stimulus strong enough for the membrane to reach a voltage of ~ -55 mV (threshold)
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Action Potential (Nerve Impulse)
• An action potential is the rapid reversal of electrical charge of the neuron membrane (depolarized)
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Steps of an Action Potential
1. Stimulus causes Na+ gated ion channels to open and Na + rushes into the cell (initiation of action potential and depolarization)
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Steps of an Action Potential 2. As Na + gated channels close, K + gated
channels open allowing K + to rush out of the cell (repolarization)
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Steps of an Action Potential
3. Na + /K + pump restores resting potential by pumping Na + ions back out of the neuron and K + ions into the neuron (refractory period)
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How Nerves Work Animation
Crossing the Divide: Neurotransmitters and the
Synapse
Watch the following two videos:
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Release of Neurotransmitters
• As the action potential reaches the axon terminal, it causes Ca2+ gated channels to open allowing Ca2+ ions to rush into the cell
• Causes synaptic vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft
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Release of Neurotransmitters
• Neurotransmitters (ligand):
– bind to receptors on the postsynaptic cell
– cause ion channels to open
– Initiate an action potential by changing the membrane potential (depolarization
• Esterases: enzymes that breaks down and recycles neurotransmitters in the synaptic cleft
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Neurotransmitters
• Chemical messengers that transmit nerve impulses (or action potentials) across the synapse
• Neurotransmitters can be stimulatory (excitatory) or inhibitory
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Neurotransmitters
Stimulatory Inhibitory
Acetylcholine
Epinephrine GABA
Serotonin
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Acetylcholine
• Stimulatory neurotransmitter released at the neuromuscular junction
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GABA
• Inhibitory neurotransmitter released between neurons
• Motor control, vision, regulates anxiety
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A little bit more about the nervous system…..
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Evolution of Nervous Systems
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Brain Evolution in Vertebrates
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Vertebrate Brain
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