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BIO 121 Quiz: nevous system

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BIO 121
Jason Wiles

Neural Signaling 1. Reception of info (by a sensory receptor) 2. Transmission by an afferent neuron (to the CNS) 3. Integration by interneurons (in the CNS) 4. Transmission by an efferent neuron (to other neurons or effector) 5. Action by effectors (the muscles and glands) Peripheral Nervous System (PNS): made up of sensory receptors; neurons outside the CNS Response to Stimulus: stimulus  receptor  messenger  effector  response Neurons: receive stimuli; transmit electrical and chemical signals Dendrites: extend from cell body; receive stimuli and sends signals to cell body Axons: extend from body; forms branches; transmits signals into terminal branches (which end in synaptic terminals) • Myellin sheath – surrounds and insulates axons • Schwann cells – form myelin sheath in the PNS o In CNS – sheath is formed by other glial cells • Nodes of Ranvier – gaps in sheath between successive schwann cells Neuron Structure: Nerves and Ganglia • Nerve – several hundred axons, wrapped in connective tissue • Ganglion – mass of neuron cell bodies in the PNS Nerve Structure: Glial Cells – support/nourish neurons; important in neural communication Neural Signals • electrical signals transmit info (along axons) • plasma membrane of resting neuron (not transmitting an impulse) is polarized • inner surface of plasma membrane is () charged (relative to extracellular fluid) Resting Potential • potential difference = -70 mV across membrane • magnitude of resting potential o differences in ion concentrations (Na+, K+) inside cell relative to extracellular fluid o selective permeability of plasma membrane to these ions Sodium-Potassium Pumps: Maintain gradients that determine resting potential; require ATP • transport 3 Na+ our for each 2 K + in KEY CONCEPTS: The resting potential of a neuron is maintained by differences in concentrations of specific ions inside the cell relative to the extracellular fluid and by the selective permeability of the plasma membrane to these ions Action Potential 1 • wave of depolarization that moves down the axon • generated when – o voltage across membrane declines to a critical point (threshold level) o voltage-activated ion channels open o Na+ ions flow into the neuron Action Potential 2 • An all-or-none response o no variation in strength of a single impulse o either membrane potential exceeds threshold level or it does not • Once begun, an action potential is self-propagating Voltage-Activated Ion Channels During an Action Potential: when the axon depolarizes to about -55mV, an action potential is generated Resting Potential. Voltage activated Na+ and K+ channels are closed Depolarization. At threshold, voltage activated Na+ channels open. Na+ entering neuron case further depolarization. Action potential in generated Repolarization. Voltage activated Na+ channels close; voltage activated K+ channels open; K+ diffuse out of cell, restoring negative charge to inside of cell As an action potential moves down an axon, repolarization occurs behind it Return to Resting State. Voltage activated Na+ and K+ channels close KEY CONCEPTS: Depolarization of the neuron plasma membrane to threshold level generated an action potential, an electrical signal that travels as a wave of depolarization along the axon Saltatory Conduction • Depolarization skips along axon from one node of Ranvier to the next o more rapid than continuous conduction o takes place in myelinated neurons • Nodes of Ranvier – sites where axon is not covered by myelin o Na+ channels are concentrated Synapses: junctions bw 2 neurons (or bw neuron and effector); mostly chemical (some are electrical) Nerve Net: interconnected nerve cells from a diffuse nerve net, which controls contraction and expansion of the gastrovascular cavity Planarian Flatworms: • cerebral ganglia • ventral nerve cords • transverse nerves Annelids and Arthropods: • Ventral nerve cord, numerous ganglia o cerebral ganglia (anthropods) Cephalopod Mollusks: • Including octopods o highly developed nervous systems
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