Exam 2: Ch 5 Book Background Info

Question 1

what is a neuron

Answer 1

a nerve cell that communicates information using a combination of electrical and chemical signals

convey electrical signals rapidly and accurately to organize and direct physiological responses

Question 2

most neurons are ____ excitable

Answer 2

electrically

Question 3

what does being electrically excitable mean

Answer 3

electrical signals can be generated across the plasma membrane

these signals are transmitted across the cell’s length without losing signal strength b/c of the movement of ions

Question 4

glial cells

Answer 4

supportive cells of the nervous system that fill the spaces between neurons

10-50x more glia than neurons

Question 5

what does the nervous system do

Answer 5

collects and processes information, analyzes it, and generates outputs to control responses

Question 6

why is studying neurons useful

Answer 6

electrical properties easily studied with tools from the physical sciences

neurons function similarly in all animals so results from one species are applicable to many others

Question 7

neurons process info in a complex manner but in doing so they rely on a surprisingly _____ number of basic physical and chemical properties

Answer 7

small

Question 8

soma

Answer 8

cell body of a neuron

responsible for metabolic maintenance

Question 9

nerve processes

Answer 9

thin fibers that arise from the soma

2 types: dendrites and axons

Question 10

dendrites

Answer 10

branched nerve processes that extend from the soma and serve as receivers that gather signals from other neurons

transmit signals toward the soma

Question 11

cells with a complex dendritic tree…

Answer 11

typically receive input from many other neurons

Question 12

axons (nerve fibers)

Answer 12

a specialized nerve process that conducts signals away from the soma

may be very long (spine to muscles)

Question 13

axon terminal

Answer 13

a region at the end of the axon that allows signals to be sent simultaneously to many other neurons (to glands, to muscle fibers)

Question 14

many vertebrate axons are surrounded by supporting cells that provide an insulating layer called the ….

Answer 14

myelin sheath

Question 15

during embryonic development and maintenance through life…

Answer 15

dendrites and the axon grow outward from the soma

maintenance of these fibers depends on a steady flow of proteins and other constituents that are synthesized in the soma and transported down the processes

Question 16

what happens if an axon in an adult animal is severed?

Answer 16

degenerates back to the soma within days or weeks

Question 17

regeneration of axons in mammals

Answer 17

limited to nerves in the periphery of the body

in cold-blooded vertebrates some regeneration may happen in the CNS

Question 18

damaged neurons in invertebrates

Answer 18

many times they will regenerate and reestablish connections with their original targets

Question 19

what does a spinal motor neuron do?

Answer 19

carries signals from soma in spinal cord to skeletal muscle fibers

Question 20

spike-initiating zone

Answer 20

an area located at or near the junction between the axon and soma (axon hillock)

integrates signals from many input neurons to determine whether an action potential is created

actions potential originate in the spike-initiating zone

Question 21

action potential (spike, nerve impulse)

Answer 21

voltage across plasma membrane rapidly rises then falls

Question 22

where does the axon carry the action potential?

Answer 22

from the spike-initiating zone to the axon terminals, which transmit the signal to other cells

Question 23

axon hillock

Answer 23

the junction between the axon and soma

the spike-initiating zone is often found here

Question 24

much of the physiological behavior of the neuron depends on ______ _____ ____ such as ____ and _____

Answer 24

passive electrical properties

capacitance and resistance

Question 25

neurons also possess active electrical properties that allow them to...

Answer 25

conduct electrical signals without loss of strength depends on the presence of proteins in the plasma membrane called voltage-gated ion channels

Question 26

voltage-gated ion channels

Answer 26

proteins in the cell membrane that allow ions to cross in a regulated fashion located in regions of specialized signaling function open when the plasma membrane is depolarized to make an AP

Question 27

what voltage-gated ion channels are found in the axonal membrane

Answer 27

Na and K

Question 28

what voltage-gated ion channels are found in the axon terminals

Answer 28

Ca

Question 29

the axon of a sensory neuron is called?

Answer 29

an afferent fiber

Question 30

what does afferent fiber mean

Answer 30

it conducts signals inward toward higher processing centers in the brain

Question 31

interneuron

Answer 31

the most numerous type of neuron found only in the CNS link and carry information between other neurons

Question 32

synapse

Answer 32

a specialized region between the axon of a neuron and the dendrites of another

Question 33

types of effector organ

Answer 33

muscles and glands

Question 34

efferent neuron

Answer 34

neurons that carry information from the processing regions of the CNS outward to effectors

Question 35

neuronal circuit

Answer 35

afferent neurons, interneurons, and efferent neurons

Question 36

a cell that passes information to a particular neuron is said to be _____

Answer 36

presynaptic

Question 37

a cell that receives information transmitted across a synapse is said to be _____

Answer 37

postsynaptic

Question 38

most synaptic transmission is carried by chemical _________

Answer 38

neurotransmitters

Question 39

neuronal circuit cockroach example

Answer 39

afferent neurons in the wind receptors in the tail contact large interneurons in the CNS the interneurons contact efferent motor leg neurons stimulus causes the cockroach to run away

Question 40

the plasma membrane of the postsynaptic neuron's dendrites and soma contain...

Answer 40

ligand-gated ion channels that bind neurotransmitters these cause the postsynaptic cell to respond to the presence of the chemical signal

Question 41

all or none signals

Answer 41

signals whose amplitude is invariant APs

Question 42

graded signals

Answer 42

signals whose amplitude is variable depends on stimulus strength or another variable

Question 43

sensory neruons

Answer 43

transmit info collected from external stimuli (sound, light, pressure) or respond to internal stimuli (blood oxygen level, the orientation of the head, position of a joint)

Question 44

motor neurons

Answer 44

carry signals to effector organs cause contraction of muscles or secretion by gland cells

Question 45

central nervous system

Answer 45

brain and nerve cord

Question 46

ganglia

Answer 46

neuronal stomata distributed along the nerve cord typically control local regions of the animal's body

Question 47

vertebrate vs invertebrate spinal cord

Answer 47

vertebrate: located along dorsal midline invertebrate: ventral midline

Question 48

oligodendrocytes

Answer 48

glia found in the CNS

Question 49

schwann cells

Answer 49

glia in the periphery that wrap axons in myelin

Question 50

myelin sheath

Answer 50

an insulating coating around axons that contributes to reliable and rapid transmission of APs

Question 51

functions of glial cells

Answer 51

regulate [K+], pH in fluid filled spaces remove neurotransmitters from extracellular space provide structural and metabolic support

Question 52

glial cell membranes are highly permeable to

Answer 52

K+ coupled by junctions that allow K+ to flow between this flux allows glial cells to take up and redistribute extracellular K+, which could otherwise buildup

Question 53

voltage

Answer 53

electrical potential difference

Question 54

although a stable voltage exists across the plasma membranes of all cells, only the membranes of ______ ______ _____ can respond to changes in their transmembrane potential difference by generating APs

Answer 54

electrically excitable cells ex. neurons, muscle fibers

Question 55

how are membrane potentials measured

Answer 55

as electrical current detected directly by using two electrodes to measure change caused by current flow across the membrane

Question 56

where are the sensing electrodes placed

Answer 56

one in electrical contact with the cytosol the other in contact with the extracellular medium this is so any potential difference can be measured (membrane potential Vm) and amplified and displaced on a recording instrument like a computer or oscilloscope

Question 57

membrane potential Vm units

Answer 57

volts

Question 58

what did Hodgkin and Huxley study in the 40s and 50s

Answer 58

membrane potentials from squid giant axons

Question 59

resting potential (Vrest)

Answer 59

the steady inside-negative potential recorded when no APs or postsynaptic events are occurring expressed in millivolts (usually between -20 - -100)

Question 60

the cytoplasm of the cell is ___potential

Answer 60

isopotential

Question 61

calculate the strength of the electric field across the plasma membrane

Answer 61

E = V/d E = strength of electric field V = volts d = distance in meters (5nm b/c plasma membrane)

Question 62

how to measure passive electrical properties of the plasma membrane

Answer 62

put two microelectrodes into one cell current delivered from a current generator to the current electrode recording electrode records this effect on membrane potenetial

Question 63

current generator effects

Answer 63

current in form of migrating ions flow if from positivity to negativity if positive current, flows into cytosol and out the cell if negative current, positive charge is drawn out of the cytosol and into the electrode

Question 64

hyperpolarization

Answer 64

when the interior of the cell becomes even more negative, which increases the size of the potential difference across the plasma membrane ex. -60 mV to -70 mV

Question 65

depolarization

Answer 65

if the current electrode adds positive charge to the interior of the cell it diminishes the potential difference across the membane ex. -60 mV to -20 mV

Question 66

as the amount of applied positive current increases, the ____ __ ________ also increases

Answer 66

degree of depolarization

Question 67

what can depolarization cause?

Answer 67

some voltage-gated Na+ ion channels to open causes an AP

Question 68

threshold potential

Answer 68

the value of the membrane potential at which an AP is triggered 50% of the time

Question 69

ion selectivity in channels

Answer 69

most channels allow only one or a few ionic species to cross the membrane movement driven by electrochemical gradient

Question 70

what is responsible for the dramatic depolarization during an AP

Answer 70

simultaneous opening of many voltage-gated Na channels when initial depolarization reaches the threshold potential

Question 71

what is responsible for the passive change in membrane potential in response to hyperpolarizing current?

Answer 71

K+ selective leak channels that are always open maintain resting potential and are uniformly distributed in the plasma membrane

Question 72

ligand-gated channels

Answer 72

ion channels that open when messenger molecules like neurotransmitters bind to receptor proteins in the cell surgace

Question 73

electrochemical potential

Answer 73

the voltage difference across the plasma membrane described as Vm (the membrane potential)

Question 74

what does electrochemical potential depend on

Answer 74

concentrations of several ion species inside the cell being different than outside the cell (gradient) ion channels being selectively permeable

Question 75

equilibrium potential

Answer 75

a potential difference across a membrane established by one ion being permeable vs. another impermeable ion formed when a permeable ion diffuses down its concentration gradient until a repulsive electrical potential balances the concentration gradient ex. Cl- impermeable and K+ permeable

Question 76

electromotive force (emf)

Answer 76

force due to electric potential difference across the membrane can offset concentration gradient

Question 77

steady state

Answer 77

system remains invariant maintenance requires no expenditure of energy