Chapter 4: Principles Of Neural And Hormonal Communication

Question 1

Nerve and Muscle cells are excitable tissues

Answer 1

• 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

Question 2

Polarization

Answer 2

• membrane potential is not 0mv

Question 3

Depolarization

Answer 3

• potential becomes less polarized than resting potential

Question 4

Repolarization

Answer 4

• potential returns to resting potential after having been depolarized

Question 5

Hyperpolarization

Answer 5

• potential becomes more polarized than resting potential

Question 6

Membrane potential becomes _______ negative during depolarization and _______ negative during hyperpolarization

Answer 6

• less

- more

Question 7

How are electrical signals produced?

Answer 7

• 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

Question 8

Graded Potentials

Answer 8

• 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

Question 9

Action Potentials

Answer 9

• 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

Question 10

Restoration of Concentration Gradient

Answer 10

• 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

Question 11

Action Potential Characteristics

Answer 11

• 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

Question 12

Synapses

Answer 12

• junction between neurons

Question 13

Electrical Synapses

Answer 13

• neurons connected directly by gap junctions

Question 14

Chemical Synapses

Answer 14

• chemical messenger transmits information one way across a space separating the two neurons
• most synapses in the human nervous system are chemical synapses

Question 15

Neurotransmitter

Answer 15

• 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

Question 16

Neurotransmitters are quickly removed from the synaptic cleft

Answer 16

• after combining t=with the postsynaptic receptor-channel, chemical transmitters are removed and the response is terminated

Question 17

Grand postsynaptic potential depends on the sum of all presynaptic input activities

Answer 17

• temporal and spatial summation
• cancellation of concurrent EPSPs and IPSPs
• importance of postsynaptic integration

Question 18

Some neurons secrete neuromodulators in addition to neurotransmitters

Answer 18

• 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

Question 19

Presynaptic Inhibition or facilitation can selectively alter the effectiveness of a presynaptic input

Answer 19

Presynaptic Inhibition
- amount of neurotransmitter released is reduced
Presynaptic Facilitation
- release of neurotransmitter is enhanced

Question 20

Drugs and disease can modify synaptic transmission

Answer 20

• most drugs that influence the nervous system function by altering synaptic mechanisms

Question 21

Neurons are linked through complex converging and diverging pathways

Answer 21

Convergence
- given neuron may have other neurons synapsing on it
Divergence
- branching axon terminals so a single cell synapses and influences other cells

Question 22

Intercellular Communication/Signal Transduction

Answer 22

• 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

Question 23

Extracellular Chemical Messengers Types

Answer 23

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

Question 24

Extracellular Chemical messengers bring about cell responses by signal transduction

Answer 24

• incoming signals are conveyed into the target cell, where they are transformed into dictated cellular response

Question 25

Signal Transduction occurs by different mechanisms

Answer 25

• lipid-soluble extracellular chemical messengers

- water-soluble extracellular chemical

Question 26

Actions of chemical messenger binding

Answer 26

• 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

Question 27

Other Actions of Chemical Messengers

Answer 27

• 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

Question 28

Cytokines act locally to regulate immune responses

Answer 28

• collection of protein signal molecules secreted by cells of the immune system and other cell types
• largely act locally to regulate immune responses

Question 29

Eicosanoids are locally acting chemical messengers derived from plasma membrane

Answer 29

• 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

Question 30

Endocrinology

Answer 30

• 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

Question 31

Hydrophilic hormones…

Answer 31

• 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

Question 32

Lipophilic Hormones…

Answer 32

• are transported by plasma proteins

- by stimulating genes, lipophilic hormones promote synthesis of new proteins

Question 33

Hormones generally produce their effect by altering intracellular proteins

Answer 33

• location of receptors for hydrophilic and lipophilic hormones
• general means of hydrophilic and lipophilic hormone actions

Question 34

Nervous vs. Endocrine

Answer 34

• 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

Question 35

Neural Specificity…

Answer 35

• result of anatomic proximity

Question 36

Endocrine Specificity…

Answer 36

• is a result of receptor specialization

Question 37

Which ion (sodium or potassium) do you think is more important in neuronal physiology?

Answer 37

-

Question 38

In common and usage, how does the definition of a nerve differ from its physiological definition?

Answer 38

-

Question 39

Why are people with multiple sclerosis likely to lose their ability to control skeletal muscles?

Answer 39

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