Chapter 4: Principles Of Neural And Hormonal Communication Flashcards
Nerve and Muscle cells are excitable tissues
- produce electrical signals when excited
- neurons use these electrical signals to receive, process, initiate, and transmit messages
- electrical signals are critical to the function of the nervous system and all muscles
Polarization
- membrane potential is not 0mv
Depolarization
- potential becomes less polarized than resting potential
Repolarization
- potential returns to resting potential after having been depolarized
Hyperpolarization
- potential becomes more polarized than resting potential
Membrane potential becomes _______ negative during depolarization and _______ negative during hyperpolarization
- less
- more
How are electrical signals produced?
- through ion movement across the plasma membrane
- an event triggers a change in membrane potential
- alters the membrane permeability and consequently alters ion flow across the membrane
- gated channels: voltage-gated, chemically gated, mechanically gated, and thermally gated
Graded Potentials
- has a local change that is the stimulus for a triggering event
- occurs in varying grades or degrees of magnitude or strength
- the stronger triggering event, the larger the resultant graded potential
- spread by passive current flow
Current: any flow of electrical charges
Resistance: hindrance to electrical change movement - die out over short distances
Action Potentials
- large change in membrane potentials (100-mV)
- potential actually reverses
- inside of the excitable cell transiently becomes more positive than the outside
- marked changes in membrane permeability and ion movement lead to an action potential
- voltage-gated Na+ and K+ channels
- changed in permeability and ion movement during an action potential
Restoration of Concentration Gradient
- Na+-KT pump gradually restores concentration gradients disrupted by action potentials
- at the completion of an action potential membrane potential has been restored to resting
- ion distribution has been altered slightly
- action potentials are propagated from the axon hillock to the axon terminals
- release chemical messengers
- once initiated, action potentials are conducted throughout a nerve fiber
- contiguous conduction
- refractory period ensures one-way propagation of action potentials and limits their frequency
- action potential cannot be initiated in a region that has just undergone an action potential
- absolute and relative refractory periods
Action Potential Characteristics
- occur in all-or-none fashion
- strength of a stimulus is coded by the frequency of action potentials
- myelination increase the speed of conduction of action potentials
- fiber diameter influences the velocity of action potential propagation
Synapses
- junction between neurons
Electrical Synapses
- neurons connected directly by gap junctions
Chemical Synapses
- chemical messenger transmits information one way across a space separating the two neurons
- most synapses in the human nervous system are chemical synapses
Neurotransmitter
- receptor combinations always produce the same response
- carries the signal across a synapse
- receptor channels: combined receptor and channel unit
- some synapses excite, whereas others inhibit, the postsynaptic neuron
- excitatory and inhibitory synapses
Neurotransmitters are quickly removed from the synaptic cleft
- after combining t=with the postsynaptic receptor-channel, chemical transmitters are removed and the response is terminated
Grand postsynaptic potential depends on the sum of all presynaptic input activities
- temporal and spatial summation
- cancellation of concurrent EPSPs and IPSPs
- importance of postsynaptic integration
Some neurons secrete neuromodulators in addition to neurotransmitters
- chemical messengers that do not cause the formation of ESPs or IPSPs
- act slowly to bring about long-term changes that subtly modulate the action of the synapse
Presynaptic Inhibition or facilitation can selectively alter the effectiveness of a presynaptic input
Presynaptic Inhibition
- amount of neurotransmitter released is reduced
Presynaptic Facilitation
- release of neurotransmitter is enhanced
Drugs and disease can modify synaptic transmission
- most drugs that influence the nervous system function by altering synaptic mechanisms
Neurons are linked through complex converging and diverging pathways
Convergence
- given neuron may have other neurons synapsing on it
Divergence
- branching axon terminals so a single cell synapses and influences other cells
Intercellular Communication/Signal Transduction
- communication among cells is largely orchestrated by extracellular chemical messengers
- direct intercellular communication is accomplished through gap junctions, possibly through tunneling nanotubes, and through linkup of surface markers
- most common means by which cells communicate with on another
- indirectly through extracellular chemical messengers, or signal molecules
Extracellular Chemical Messengers Types
Paracrines
- local chemical messengers
Neurotransmitters
- very short-range chemical messengers released by neurons
Hormones
- long-range chemical messengers secreted into the blood by endocrine glands
Neurohormones
- hormones released into blood by neurosecretory neruons
Extracellular Chemical messengers bring about cell responses by signal transduction
- incoming signals are conveyed into the target cell, where they are transformed into dictated cellular response
Signal Transduction occurs by different mechanisms
- lipid-soluble extracellular chemical messengers
- water-soluble extracellular chemical
Actions of chemical messenger binding
- messenger binding to a chemically gated receptor-channel opens or closes the channel
- messenger binding to a receptor-enzyme complex activates tyrosine kinase, which phosphorylates designated proteins that lead to the cel’s response
- messenger binding to a G-protein-coupled receptor activates a second-messenger pathway that carries out the cell’s response
Other Actions of Chemical Messengers
- some water-soluble extracellular messengers open chemically gated receptor-channels
- some water-soluble extracellular messengers activate receptor-enzymes
Tyrosine Kinase Pathway - most water-soluble extracellular chemical messengers activate second-messenger pathways via G-protein-coupled receptors
Cytokines act locally to regulate immune responses
- collection of protein signal molecules secreted by cells of the immune system and other cell types
- largely act locally to regulate immune responses
Eicosanoids are locally acting chemical messengers derived from plasma membrane
- group of lipid signal molecules derived from a fatty acid in the plasma membrane of most cell types
- act locally to regulate divers cellular processes throughout the body
Types
Prostaglandins
Thromboxanes
Leukotrienes
Endocrinology
- study of homeostatic chemical adjustments and other activities accomplished by hormone
- hormones are secreted by the endocrine glands into the blood
- types based on solubility and chemical structure: hydrophobic or lipophilic
- mechanisms of synthesis, storage, and secretion of hormones vary according to chemical differences
Hydrophilic hormones…
- dissolve in the plasma
- alter preexisting proteins via second-messenger systems
- cyclic AMP second-messenger pathway
- Ca2+ second-messenger pathway
- amplification by a second-messenger pathway
- regulation of receptors
Lipophilic Hormones…
- are transported by plasma proteins
- by stimulating genes, lipophilic hormones promote synthesis of new proteins
Hormones generally produce their effect by altering intracellular proteins
- location of receptors for hydrophilic and lipophilic hormones
- general means of hydrophilic and lipophilic hormone actions
Nervous vs. Endocrine
- nervous system swiftly transmit electrical impulses to the skeletal muscles and exocrine glands that it innervates
- endocrine system secretes hormones into the blood for delivery to distant sites of action
- the nervous system is “wired” and the endocrine system is “wireless”
- both have their own realms of authority but interact functionally
Neural Specificity…
- result of anatomic proximity
Endocrine Specificity…
- is a result of receptor specialization
Which ion (sodium or potassium) do you think is more important in neuronal physiology?
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In common and usage, how does the definition of a nerve differ from its physiological definition?
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Why are people with multiple sclerosis likely to lose their ability to control skeletal muscles?
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