Neurons Synapses and Signaling Overview Neural Signals Organization

Neurons, Synapses, and Signaling §Overview §Neural Signals §Organization of Nervous Systems

Functions of Nervous Systems § Sensory input-conduction of signals from receptors to integration centers (CNS) § Integration-interpretation of signals and generation of proper response § Motor output-signals to effector cells (muscles, glands), carry out response

Composition of Nervous System Neurons § cells specialized for transmitting electrical and chemical signals § Composed of cell body, dendrites, and axons § Three types: sensory neurons, interneurons, and motor neurons § Arranged into circuits of two or more kinds of neurons: convergent, divergent, and reverberating circuits

Composition of Nervous System con’t. Supporting Cells (glial cells) § Structurally reinforce, protect, insulate and assist neurons § Do not conduct impulses § Outnumber neurons 10 - to 50 - fold § Types: astrocytes (blood-brain barrier), oligodendrocytes, Schwann cells

The Nature of Neural Signals § Signal transmission along a length of a neuron depends on voltages created by ionic fluxes across neuron plasma membranes § All cells have an electrical membrane potential: range from – 50 to – 100 m. V on the inside. § Neurons have about – 70 m. V at rest

Ion Concentrations: § [Na+] 10 x greater outside (main cation outside) § [K+] 30 x greater inside (principal cation inside) § [Cl-] 12 x greater outside § Other anions-100 x inside Selective permeability of the membrane maintains these differences

Action Potential-Nerve Impulse Four phases § Resting phase-no channels open § Depolarizing phase-brief reversal of polarity, Na+ gates open Na+ in, result: § -70 m. V to +30 m. V § Repolarizing phase-Na+ gates close, K+ gates open, K+ out, +30 m. V to – 70 m. V § Undershoot phase (refractory period)-K+ and Na+ are returned to proper concentrations, neuron insensitive to depolarizing stimuli

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Action Potentials § “all-or-none” require a minimum stimulus or threshold § Self-propagating § Saltatory conduction-action potential “jumps” from one node of Ranvier to the next, skipping the myelinated regions of the membrane

Synapses § Tiny gap between terminal of an axon and beginning of a dendrite on the next neuron § Presynaptic cell-transmitting cell § Postsynaptic cell-receiving cell § Two types of synapses: electrical and chemical

4. The neurotransmitter binds to ligand-gated ion channels in the postsynaptic membrane. In this example, binding triggers opening, allowing Na 2. The 3. The elevated Ca 2+ 1 An action and K+ to diffuse depolarization concentration causes synaptic potential arrives, through. opens voltagevesicles to fuse with the depolarizing gated channels, presynaptic membrane, the presynaptic triggering an influx releasing neurotransmitter into membrane. of Ca 2+. the synaptic cleft.

Chemical Synapses § Separated by synaptic cleft § Ca 2+ enters cell stimulating cytoskeleton to move vesicles to the surface of the axonal knob § Neurotransmitter from the vesicle is released into the cleft § Neurotransmitter binds to receptor sites on the postsynaptic membrane, reestablishing the action potential

Electrical Synapses § Electrical synapse § Less common § Travel through gap junctions § Example-giant neuron in crustaceans

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neurotransmitters

neurotransmitters § Neurotransmitters are chemical messengers released into the synaptic cleft by neurons § They maintain signals in the nervous system by binding to receptors on post-synaptic neurons and triggering electrical impulses § They also activate responses by effector organs (such as contraction in muscles or hormone release from endocrine glands) § Neurotransmitters may be either excitatory or inhibitory in their effect (some may be both depending on the receptor they bind to) § Excitatory neurotransmitters trigger depolarisation, increasing the likelihood of a response § Inhibitory neurotransmitters trigger hyperpolarisation, decreasing the likelihood of a response

Endorphins § Endorphins are endogenous neuropeptides produced by the pituitary gland that functions as the body’s natural painkiller

Mouse party § http: //learn. genetics. utah. edu/content/add iction/mouse/ § More info on neurotransmitters § http: //ib. bioninja. com. au/options/option-aneurobiology-and/a 5 neuropharmacology/anesthetics. html

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