Chapter 12

Front 1

integration

Back 1

- processes that produce coherency and result in harmonious function
- cellular = process within cells
- whole animal = selective combination and processing of sensory, endocrine, and CNS in ways that promote harmonious functioning
- nerve and endocrine cells

Front 2

control systems

Back 2

- system that sets the level of a particular variable that is being controlled
- information from sensors to determine signals to the effectors
- negative feedback
- whole animal integration = processing to promote homeostasis
- nerve cells and endocrine cells control the way other cells function

Front 3

nervous

Back 3

- short term
- local
- control homeostasis
- allow response to stimuli
- secrete substances
- receptors on target cells

Front 4

endocrine

Back 4

- long term
- long distance
- widespread, prolonged activities

Front 5

hormone

Back 5

- chemical substance
- secreted by endocrine

Front 6

neuron

Back 6

- cell specially adapted to generate electrical signal in form of an action potential
- dendrite, integration, conduction, and output
- functional unit of nervous system
- generate and transmit electrical signals
- extreme longevity = amitotic

Front 7

synapses

Back 7

- specialized cell-cell contact points

Front 8

dendrites

Back 8

- branching processes where synaptic input occurs
- bring information in

Front 9

neurotransmitters

Back 9

- exert specific physiological effects on the postsynaptic cell by binding to neurotransmitter receptors
- contained in terminal buton

Front 10

cell body

Back 10

- part of neuron where signal integration and impulse generation occur
- processes originate
- also called soma

Front 11

axon

Back 11

- conduction component
- serving to propagate action potentials along its length
- takes information out

Front 12

axon hillock

Back 12

- axon arises from soma
- free of nissl bodies

Front 13

axon initial segment

Back 13

- specialized area commonly the site of action potential initiation

Front 14

presynaptic terminals

Back 14

- place where neuronal output occurs
- axon ends
- form synapses with other neurons or cells

Front 15

innervate

Back 15

- excitatory or inhibitory response or stimulus

Front 16

nervous system

Back 16

- extended network of neurons
- sensory functions, integrate arriving signals, generate nerve impulse, transmit signals
- central and peripheral nervous system
- fine rapid movements of discrete muscles

Front 17

neuron types

Back 17

- afferent = relay sensory signals to integrative centers of CNS
- efferent = relay control signals from CNS to target cells
- interneurons = entirely within CNS
- motor = outgoing axons exit the CNS and innervate muscle interneruons synaptically excite

Front 18

endocrine cells

Back 18

- signals broadly distributed
- release hormones into blood
- receptor proteins to elicit specific response
- target cells = certain tissues or organs that respond
- slow and broadcast

Front 19

reflex

Back 19

- simple, stereotyped behavioral response to distinct stimulus

Front 20

neuron classification

Back 20

- classified according to number of processes
- unipolar, bipolar, mutlipolar
- unipolar - CNS, bipolar - sensory, multipolar - CNS vertebrates

Front 21

multipolar

Back 21

- 3 or more processes
- most common in humans in CNS
- purkinje cells and pyramidal cells

Front 22

bipolar

Back 22

- 2 processes = axon and dendrites
- rare in humans but may occur as receptor cells
- olfactory and retinal cells

Front 23

unipolar

Back 23

- also called pseudounipolar
- chiefly in ganglia
- single short process
- divides into a T process
- peripheral process associated with sensory central processes enters CNS

Front 24

myelin

Back 24

- multiple wrappings of insulating glial cells membrane that increase speed of transmission

Front 25

transport mechanism

Back 25

- ATP dependent motors
- kinesin = + end directed (anterograde)
- dynein = - end directed (retrograde)
- microtubule binding domain, cargo domain, body domain
- run inside axons

Front 26

anterograde

Back 26

- toward axonal terminal
- neurotransmitters, mitochondria, cytoskeletal elements, and etc.
- kinesin is motor

Front 27

retrograde

Back 27

- toward perikaryon
- organelles returned for degradation and intracellular communication
- dynein is motor

Front 28

neuroglial cells

Back 28

- supporting cells of nervous system
- also called glial cells
- take care of and support neurons
- Schwann cells
- olgiodendrocytes
- CNS has multiple axons

Front 29

Schwann cells

Back 29

- support axon in PNS
- 1mm allows action potential to move without losing voltage
- unmyelinated = wrapped a few times, multiple axon per cell
- myelinated = wrapped multiple times, 1 axon per cell

Front 30

oligodendrocyte

Back 30

- CNS
- wrap around multiple glial cells

Front 31

microglial cells

Back 31

- mediate immune responses in neural tissue and may act as phagocytes
- detect bacteria like white cells
- main resident immunological cells of CNS
- derived from nervous tissue

Front 32

astrocytes

Back 32

- line outer surfaces of capillaries in CNS and act as metabolic intermediates
- take up NT from extracellular space
- supply metabolic substrates to neurons
- star shaped glial cells
- majority of cell types in CNS
- regulate ionic conditions in intracellular space
- uptake and/or breakdown some NT
- formation of blood-brain-barrier
- place direct role in signaling the brain = regulate function of neurons
- important in cellular basis of learning
- foot processes against blood vessels

Front 33

oligodendroglia

Back 33

- myelin producing cells of CNS
- myelinate multiple neurons

Front 34

ependymal cells

Back 34

- line ventricle of brain
- cubodial and often have cilia
- produce cerebrospinal fluid

Front 35

ions

Back 35

- atoms or molecules that bear a net charge because they have unequal numbers of protons or electrons

Front 36

current

Back 36

- net movement of charge

Front 37

voltage

Back 37

- separation of positive and negative electrical charges
- potential difference = does work when currents flow
- electrical potential difference

Front 38

resistance

Back 38

- limits current flow
- degree object opposes electrical current
- function of both physical geometry and resistivity

Front 39

capacitance

Back 39

- charged stored per unit of voltage
- ability for body to hold electrical charge
- greater it is = more ions the membrane can separate and store

Front 40

circuit of cells

Back 40

- inside and outside are aqueous solutions
- ions aren't free electrons
- voltage occurs because ion difference separated by phospholipid membrane
- ions carry current
- lipid bilayer = dielectric layer of capacitor, separate charge
- resistance = ion channel

Front 41

transmembrane potential

Back 41

- electrical potentials observed in the cell membrane
- directly determines electrical properties

Front 42

passive electrical properties

Back 42

- passive response = electrical properties don't change
- resistance = lipid bilayer impermeable to ions
- capacitance = insulating properties of bilayer
- govern how voltages change over time and space along axon

Front 43

resting membrane potential

Back 43

- potential difference across the axon membrane
- dependent selective permeability
- electrogenic pump
- diffusion potential
- Donnon equilibrium

Front 44

membrane resistance

Back 44

- restricts current flow across axon membrane

Front 45

depolarization

Back 45

- decrease in absolute value of membrane potential toward zero = less negative

Front 46

hyperpolarization

Back 46

- increase in absolute value of membrane potential away from zero = more negative

Front 47

membrane behaves like resistor and capacitor in parallel

Back 47

- capacitor = blocks ion exchange and allow charge accumulation
- resistor = allows ions to flow across
- current redistributes charge and then flows through
- slows change in voltage on membrane = increase if resistance or capacitance increase

Front 48

passive spread

Back 48

- decremental spread
- electronic conduction
- voltage change decrease exponentially with distance from source

Front 49

Nernst equation

Back 49

- relation between concentration difference of permeating ion across a membrane and membrane potential at equilibrium
- large concentration difference = larger membrane potential
- based on model that treats ions as ideal gas
- driven by electrogenic gradient
- gradient represents 2 influence = voltage gradient and concentration gradient
- voltage gradient = concentration gradient - Donnan equilibrium
- one ion at a time

Front 50

equilibrium potential

Back 50

- electrical force holding ion inside is balanced by chemical force for ion diffusion out

Front 51

sodium potassium ATPase pump

Back 51

- active transport = sodium out and potassium in
- every cell has one
- ATP energy for pumping
- ratio of sodium and potassium = 3:2

Front 52

Donnan equilibrium

Back 52

- passive equilibrium despite strikingly unequal concentrations
- nonpermeating anions inside can lead to unequal concentrations across membrane of permeating ions
- electrochemical gradient equilibrium = 2 solutions separated by membrane permeable to only some ions in solution
- magnitude can be calculated using Nerst equation

Front 53

ionic hypothesis

Back 53

- concentrations of ions inside and outside cell are maintained in steady state by mixture of active transport and passive transport
- determine resting membrane potential

Front 54

2 kinds of active ion transport mechanisms

Back 54

- electroneutral pump
- electrogenic pump

Front 55

electroneutral pump

Back 55

- transport equal quantities of charge inward and outward across membrane and thus changes ion concentrations without generating current

Front 56

electrogenic pump

Back 56

- transports unequal quantities of charges inward and outward across membrane and thus generates a net current
- changes concentration to offset passive leaks
- alters resting membrane potential directly via the pump current

Front 57

excitable cells

Back 57

- ability to generate electrical signals
- neurons, muscle fibers, and a few others
- electrical signal = action potential

Front 58

diffusion potential

Back 58

- ion mobility
- not all ions mobile in membrane
- experience frictional force
- magnitude frictional force dependent on size
- absolute ion mobility = average voltage in electric field
- smaller radius have decrease mobility because hydration layer

Front 59

permeabilities and ion channels

Back 59

- potassium leakage channels allow potassium to diffuse across membrane and remain open throughout action potential
- stimulus depolarizes membrane past threshold = voltage gated sodium channels open
- sodium rushes in driving membrane potential toward inside positive = cause depolarization and polarity reversal at riding
- falling phase results from two changes in membrane permeability to ions = first opening sodium channels in membrane permeability and second potassium channels open increasing permeability to potassium
- inactivation = abruptly decreases permeability to Na
- at conclusion = highly permeable to K producing characteristic undershoot and Na recover from inactivation

Front 60

ionic permeability

Back 60

- plasma membranes selectively permeable
- sodium, calcium, chloride is very low
- potassium is high
- permeability due to molecular weight, hydration layer, charge

Front 61

2 types of Na channels

Back 61

- transient
- persistent

Front 62

transient Na channel

Back 62

- inactivated by tetrodotoxin in puffer fish or saxitoxin in red marine dinoflagellates
- once activate = automatically inactive
- rectified = resistance and conductance vary with voltage
- depolarization in action potential
- 3 conformations = open, closed, inactive
- rapidly activating and inactivating
- mediates action potential in rising phase

Front 63

persistent Na channel

Back 63

- noninactivating
- enhances depolarization

Front 64

molecular structure of Na channels

Back 64

- sequence homology = evolved from common ancestral peptide
- 4 domains containing 6 membrane spanning segments
- aqueous channel pore
- voltage sensor
- P loop
- cytoplasmic loop
- voltage dependent conformational change
- major alpha protein forms channel
- single polypeptide chain

Front 65

4 domains contain 6 membrane spanning segments

Back 65

- contain predominantly hydrophobic AA side chains that can form alpha helices and cross lipid bilayer of membrane

Front 66

voltage sensor

Back 66

- membrane spanning segment 4
- charged and close to membrane
- collection positively charged AA
- rotates and slides outward in depolarization

Front 67

P loop

Back 67

- connect segment 5 and 6
- helps mediate ion selectivity
- lines pore of ion channel

Front 68

cytoplasmic loop

Back 68

- between domain 3 and 4
- mediate inactivation of Na channel
- block channel from cytoplasmic side = ball on a string

Front 69

Hodgkin cycle

Back 69

- positive feedback leads to depolarization
- threshold = high enough decrease in membrane potential for all Na channels to open
- more that open = more that open
- describes effects of depolarizing an excitable membrane in which permeability to Na is voltage dependent
- only rising phase of action potential

Front 70

3 processes of Hodgkin cycle

Back 70

- opening voltage gated Na channels increase PNa
- increased Na flow
- further membrane depolarization

Front 71

calcium channels

Back 71

- 4 domains with 6 membrane spanning segments
- P loop
- voltage selector

Front 72

4 types of calcium channels

Back 72

- low threshold
- high threshold
- rapidly inactivating
- purkinje cells

Front 73

low threshold

Back 73

- transient
- rapidly inactivating
- threshold negative to 65mV
- involved in cardiac pacemaker activity, growth regulation, and trigger contraction
- low abundance in myocardium
- not sensitive to calcium blockers

Front 74

high threshold

Back 74

- long lasting large sustained conductance
- slowly inactivating
- threshold about -20mV
- activated by strong depolarization
- underlies Ca spikes of dendrites
- synaptic transmitter release in skeletal muscle, brain, and cardiovascular
- responsible for plateau phase = slow inward current
- trigger release of internal calcium
- regulated by cAMP dependent protein kinase
- sensitive to Ca blockers

Front 75

rapidly inactivating

Back 75

- neural type
- activated by strong depolarization
- threshold -20mV
- presynaptic terminals and involved in NT release from presynaptic cell
- not sensitive to Ca blockers

Front 76

purkinje cells

Back 76

- activated by strong depolarization
- slow inactivation
- transmitter release from purkinje cells
- found in purkinje fibers in electrical conduction system of heart

Front 77

potassium channels

Back 77

- multiple types
- 4 identical domains each consisting of 6 membrane spanning regions
- P loop and voltage selector
- tryptoptian and tyrosine form cuff around a pore = pull pore opening
- selectivity filter = glycine, tyrosine, glycine residues

Front 78

delayed rectifying channel

Back 78

- potassium channel
- voltage gated/dependent = rectified
- activated by strong depolarization
- delayed activation and slow inactivation
- mediates action potential repolarization

Front 79

leaky K channels

Back 79

- involved in action potential
- contribute to resting potential

Front 80

inward rectifying channel

Back 80

- nonconducting at + potentials
- allows K to flow into cell
- depolarizing current that is activated by hyperpolarization
- dependent on interaction with phospatdinositol 4,5 biophosphate
- contributes to cell excitability = rhythmic spiking, burst activity
- cardiac muscle, frog skeletal muscle, starfish egg

Front 81

calcium activated

Back 81

- activated by increase in Ca concentration
- mediates action potential repolarization and interspike interval
- long hyperpolarized period
- burst firing due to calcium influx

Front 82

Ia

Back 82

- fast transient
- inactivated channel
- sensory organs
- encode sustained depolarizing stimuli into rate of action potential
- delays onset of firing = lengthens interspike interval

Front 83

chloride channels

Back 83

- plasma membrane and vesicles
- stabilize membrane potential = depolarization in smooth muscle
- some rectified but many aren't

Front 84

action potential

Back 84

- momentary reversal of membrane potential from inside negative to inside positive
- voltage dependent = ion channels produce action potentials that are voltage gated
- inactive Na channels allow unidirectional flow down an axon
- K slow to close = drop below membrane potential
- all or none
- strength duration relationship = length and strength of stimulus determine if you will get past threshold
- triggered by any depolarization of membrane that reaches a critical value of depolarization = voltage threshold
- conduction without decrement = continue with no decrease in voltage
- can't summate

Front 85

action potential results from...

Back 85

- intense, localized increase in permeabilites to specific ions
- voltage and time dependent
- selective = first sodium and then potassium

Front 86

all or none

Back 86

- depolarization below threshold doesn't generate an action potential but all suprathreshold depolarization produce a complete impulse of like amplitude and duration

Front 87

rheobase

Back 87

- minimum current that will produce a response

Front 88

lactency period

Back 88

- period before you have measurable action potential

Front 89

accomodation

Back 89

- adjusts to slowly increasing strength of stimulus

Front 90

adaptation

Back 90

- reduction in sensitivity and action potential generation in presence of constant stimulus

Front 91

refractory period

Back 91

- prevent reexcitation and bidirection propagation
- increased permeability to K doesn't decrease to resting levels until after repolarization

Front 92

absolute refractory period

Back 92

- period from initiation to immediately after the peak
- another action potential can't be generated for 1ms
- inactivation of Na channels resists until membrane potential returns near its negative resting state

Front 93

relative refractory period

Back 93

- period during a stronger than normal stimulus needed in order to elicit action potential after Na recover from inactivity
- generate for a few ms longer
- increase Pk also renders membrane refractory because it represents decreased membrane resistance

Front 94

cardiac muscle action potential

Back 94

- longer duration and a plateau
- Ca channels open in rise and cause plateau when K channels open

Front 95

nonspiking neurons

Back 95

- don't generate sharp "spikes" of action potential
- produce graded membrane - potential changes
- substantially lack voltage gated Na channels
- compact cells with short axons
- photoreceptors, bipolar cells, horizontal cells

Front 96

propagation

Back 96

- conduction velocity of an action potential depends on axon diameter, myelination, and temperature

Front 97

axon diameter

Back 97

- larger diameter conduct more rapidly than small diameter
- conduction velocity increases with axon diameter = longer length constant and thus more distant spread local currents
- membrane surface increase proportionally with axon diameter increase
- axoplasmic resistance decreases proportionally with increase cross sectional area of cytoplasm
- larger axons have lower resistance

Front 98

myelinaton

Back 98

- allow very high conduction velocities with relatively small axon diameters
- saltatory conduction = action potential jumps from node to node without active propagation in the internode
- increase membrane resistance
- decrease membrane capacitance
- greatly increase conduction velocity by increasing axon length constant without increasing time constant
- vertebrates have substantial numbers

Front 99

temperature

Back 99

- increase speeds gating channels
- increase = conduction increase