Presentation on theme: "Communication Within the Nervous System"— Presentation transcript:
1 Communication Within the Nervous System Chapter 4Communication Within the Nervous System
2 The Exchange of Information Types of information exchange:Axodendritic - from the axon of one neuron to the dendrite of anotherAxosomatic - from axon to cell bodyAxoaxonic - from axon to axonDendrodendritic - from dendrite to dendrite
4 The Resting Membrane Potential Factors involved:Channel proteins - provide channels for the passage of substances from one side of the membrane to the otherReceptor proteins - recognize and bind to neurotransmitters or other chemicalsPump proteins - exchange one type of substance for anotherPolarity - intracellular fluid in more negatively charged than the extracellular fluid which has more positively charged ions;Difference in polarity is called resting membrane potential
5 The Resting Membrane Potential Forces affecting the membrane potentialDiffusion - refers to the movement of molecules from an area of higher concentration to an area of lower concentrationElectrostatic pressure - attraction of opposite-polarity molecules and repulsion of same-polarity moleculesSodium-potassium pump - an active protein mechanism which excludes 3 Na+ ions for every 2 K+ ions taken into the cell
6 Influence of Diffusion and Electrostatic Pressure on the Movement of Ions into and out of the Neuron (More negatively charged)
7 The Action PotentialAlso called the spike potential or firing of the neuronThe action potential only refers to depolarization of an axonAll-or-none law - the strength of the action potential is independent of the intensity of the stimulus that elicits itProcess:Depolarization to threshold levelReversal of membrane polarityRe-polarization to the resting potentialRefractory period
8 The Action Potential: Depolarization to Threshold Level Excitatory stimulus - A stimulus which causes depolarization due to the influx of Na+.Rate Law – the greater the intensity of the stimulus, the faster the rate of firingThreshold -The level of stimulation required for the neuron to fireVoltage-gated ion channels - sensitive to changes in cell membrane potential.Channels open to Na+ ions when threshold is reachedFollowed by the opening of K+ channels.The K+ ions are expelled by the electrostatic charge from the Na+ ions which have entered the cell.
9 Action Potential: Repolarization to Resting Potential The process of recovery of the resting membrane potential.The Refractory PeriodAbsolute refractory period - The time during which the neuron is insensitive to further stimulation.Relative refractory period -The time following the absolute refractory period during which a neuron can generate another action potential but only by a stronger than normal stimulus.
10 Propagation of the Action Potential along an Unmyelinated Axon Action Potential in action
11 The Neural ImpulseNeural impulse -The propagation of an action potential along an axon.The axon depolarizes in a sequential fashion from the axon hillock to the presynaptic terminal.The neural impulse occurs only one way because of the absolute refractory period.Speed of transmission varies due to thickness of the axon, presence or absence of myelination, and number of synapses.
12 The Neural Impulse: Saltatory Conduction Occurs on myelinated neurons only at the nodes of Ranvier.Faster than unmyelinated neuronsAn unmyelinated neuron of 1.5 mm conducts about 1 m/sec whereas a myelinated neuron of the same size conducts about 100 m/secRequires less energy than unmyelinated neurons since depolarization only occurs at the nodes of Ranvier.
13 Propagation of the Action Potential Along a Myelinated Axon Action Potential in action
14 Synaptic Transmission: Neurotransmitter Release Neurotransmitter – chemical stored in the synaptic vesicles that when released transmits messages to other neurons, muscles, or blood vesselsSynaptic transmission occurs when neurotransmitter molecules pass across the synaptic cleft and depolarize or hyperpolarize the postsynaptic membrane.Hyperpolarized – the charge across the cell membrane is more negative than normalNeurotransmitter molecules are carried across the synaptic cleft by diffusion.
16 Synaptic Transmission: Neurotransmitter Release Transmitter-gated ion channels – are sensitive to a specific neurotransmitterA neurotransmitter will have either an:Excitatory (EPSP) affect – which results from depolarization produced by neurotransmitter molecules on a postsynaptic membraneMany Na+ enter and few K+ leaveInhibitory (IPSP) affect – which results from hyperpolarization produced by neurotransmitter molecules on a postsynaptic membraneMany K+ leave or many Cl- enter
17 Synaptic Transmission: Summation Effects Is the result of multiple inputs, EPSP and IPSP, on neuronsSpatial summation - the combined effects of neurotransmitters binding to different locations on the postsynaptic membrane at a particular moment in timeTemporal summation - the combined effects of neurotransmitters binding over time
18 Synaptic Transmission: Presynaptic Effects Release of neurotransmitters is not automatic and can be influenced by several processes:Presynaptic inhibition - A decrease in the release of neurotransmitters caused by the action of another neuron.Presynaptic facilitation - The enhanced release of neurotransmitters caused by the action of another neuron.Autoreceptors (inhibition) - stimulation of autoreceptors by a released neurotransmitter causes a decrease in subsequent neurotransmitter release
19 Axoaxonic Synapse and Presynaptic Inhibition and Facilitation Synaptic Transmission: Presynaptic EffectsAxoaxonic Synapse and Presynaptic Inhibition and Facilitation
20 Synaptic Transmission: Postsynaptic Receptors Types of postsynaptic receptors:Ionotropic -These receptors’ ion channels are opened quickly by the direct action of a neurotransmitter.Metabotropic -These receptors’ ion channels are opened indirectly by a second messenger.Second messenger - A chemical that causes changes inside the cell in response to a neurotransmitter that leads to ion channel changes.
22 Synaptic Transmission: Termination of Neurotransmitter Effects Termination of synaptic transmissionDiffusion - transmitter substance floats away from the synapseEnzymatic degradation -The transmitter action is deactivated by an enzymeReuptake -The transmitter substance is returned to the presynaptic neuron
24 Agents of Synaptic Transmission: Large-Molecule Neurotransmitters Peptides - Small chains of amino acidsNeuropeptides - peptides that function as neurotransmittersendogenous opioidsoxytocinantidiuretic hormone (ADH)cholecystokinin (CCK)substance POxytocin
25 Agents of Synaptic Transmission: Large-Molecule Neurotransmitters NeuromodulatorsA type of chemical that modifiesthe sensitivity of cells to neurotransmitters orthe amount of neurotransmitter releasedDiffuse throughout an areaDopamineSerotoninHistamineCaffeine, nicotine
26 Hormones and the Endocrine System Hormone - A chemical produced by the endocrine glands that is circulated widely throughout the body via the bloodstream.Pheromone - A chemical released into the air, rather than into the bloodstream, that affects other members of a speciesAlthough hormones have similar actions to neurotransmitters, they are distinguished from neurotransmitters because they are released into the general circulation and not directly onto a target organ.
29 Electrical Synaptic Transmission Anaxonic neuron - a neuron without an axon.- Communication is dendodentritic- The synapse is called electrical synapse.- Gap junction is the namefor the space between thedendrites of two neurons- Connexon is a specializedprotein channel throughwhich ions move acrossgap junctions.