CHAPTER 45 ~ Neurons and Nervous System

Question 1

two types of cells in neuron system

Answer 1

neurons and glial cells

Question 2

neurons

Answer 2

excitable and generate action potentials

Question 3

glial cells

Answer 3

support neurons physically, immunologically and metabolically. There are oligodendrocytes in CNS and Shwann cells in PNS that myelinate. And astrocytes in blood brain barrier

Question 4

effectors

Answer 4

who nervous system communicates to; are muscles, glands, etc

Question 5

simplest neuronal network consists of

Answer 5

a sensory neuron connected to a motor neuron connected to a muscle cell.

Question 6

Afferent neurons

Answer 6

carry information INTO nervous system –> info comes from sensory neurons, so afferent neuron is usually a sensory neuron

Question 7

Efferent neurons

Answer 7

carry commands to physiological and behavioral effectors such as muscles and glands => motor neuron

Question 8

Interneurons

Answer 8

integrate and store info; communicate between afferent and efferent neurons

Question 9

ganglia

Answer 9

clusters of neurons, (can have different functions throughout body), usually one pair is larger and more central = brain

Question 10

CNS

Answer 10

Brain + Spinal cord; site of MOST info processing, storage, and retrieval

Question 11

PNS

Answer 11

neurons that extend or reside outside brain and spinal cord (bring info TO CNS though)

Question 12

dendrites

Answer 12

projections that sprout from cell body of neuron; bring inputs from other neurons or sensory cells to the body

Question 13

axon hillock

Answer 13

integrates info from dendrites and initiates or inhibits action potentials based on these inputs. Lots of Na+ channels here.

Question 14

axon

Answer 14

carry action potentials away from cell body and towards the synapse with target cell

Question 15

axon terminal

Answer 15

forms synapses with target cell

Question 16

membrane potential

Answer 16

difference in voltage across plasma membrane

Question 17

resting potential

Answer 17

in an unstimulated neuron; -60mV

Question 18

action potential

Answer 18

caused by the sudden opening and closing of ion channels (Na+ and K+) causing large, swift changes in membrane potentials.

Question 19

at resting potential:

Answer 19

K + leak channels always open, voltage Na+ and K+ closed –> -60 mV (HIGH K+ inside, HIGH Na+ outside)

Question 20

during Depolarization:

Answer 20

K+ leak channels and Sodium/potassium pump both open, SOME Na+ voltage open, K+ closed –> -50 mV (threshold) when ALL Na+ open, cell becomes more positive as action potential fires –> +50 mV

Question 21

during Repolarization/Hyperpolarization:

Answer 21

K+ leak and sodium/potassium pump open, Na+ voltage close, K+ voltage open, K+ FLOOD OUT = membrane potential becomes negative again + undershoot

Question 22

threshold potential

Answer 22

opens up voltage gated ion channels 5-10 mV above the resting potential

Question 23

refractory period

Answer 23

voltage Na+ channels cannot open again for 1-2 milliseconds = no action potential (in Na+ voltage channel: activation gates closed, inactivation gates opened)

Question 24

why are action potentials an “all or nothing” event?

Answer 24

because it is a chain reaction; slight depolarization of membrane involves SOME Na+ voltage channels opening, whose influx of Na+ ions triggers further depolarization, which in turn causes MORE Na+ gates to open until membrane reaches threshold and generates action potential –> positive feedback, so action potential always rises to max value

Question 25

saltatory conduction

Answer 25

impulse propagation from node to node–> “jumping”

Question 26

oligodendrocytes

Answer 26

glial cells, myelinate axons in CNS

Question 27

Shwann cells

Answer 27

glial cells, myelinate neurons in PNS

Question 28

astrocytes

Answer 28

glial cells, contribute to blood-brain barrier which protects brain from toxic chemicals in blood; surround smallest blood vessels in the brain; are permeable to fat soluble molecules such as alcohol = drunkness

Question 29

Multiple Sclerosis (MS)

Answer 29

gradual demyelination - destruction of myelin via immune response; affect 400,000 americans, 2.5 million worldwide. Onset ~ 20-40 years old

Question 30

patch clamping

Answer 30

process that allows single ion channels to be studied

Question 31

Mechanism of MS

Answer 31

myelinated fibers demyelinated via inflammatory process, this causes conduction block. Na+ channels redistribute to restore conduction, and remyelination occurs = clinical remission

Question 32

Synapses

Answer 32

an axon terminal that contains many chemical filled vesicles; enable nervous system to process and integrate info.

Question 33

neuromuscular junction

Answer 33

chemical synapse between a motor neuron and a muscle cell

Question 34

Acetylcholine (ACh)

Answer 34

neurotransmitter used by vertebrate neuromuscular synapses

Question 35

Mechanism of Action Potential @ Synapse:

Answer 35

as action potential reaches synapse, Na+ influx triggers opening of Ca2+ voltage gated channels; influx of Ca2+ triggers fusion of ACh-containing vesicles to membrane, releasing ACh into synaptic cleft. ACh binds to receptors on post-synaptic cell, opening Na+ channels and depolarizing motor end plate = Action Potential. ACh-esterase comes and digests ACh, taking back the monomers to the pre-synaptic cell for use in synthesis of new ACh molecules.

Question 36

Acetylcholinesterase

Answer 36

breaks down ACh fused to ACh gated channels on post-synaptic cell. Brings back by-products to pre-synaptic cell to be remade into ACh

Question 37

synapses between motor neurons and muscle cells

Answer 37

are always excitatory = respond to ACh with a graded potential

Question 38

if receptor on post-synaptic cell is a Cl- channel opened by a neurotransmitter..

Answer 38

Cl- influx = hyperpolarization of cell and thus no action potential

Question 39

synapse is EXCITATORY

Answer 39

if post-synaptic neuron responds by chemical stimulus by depolarizing

Question 40

synapse is INHIBITORY

Answer 40

if post-synaptic neuron responds by hyperpolarizing

Question 41

ACh –> Na+ –> depolarization = excitatory

Question 42

GABA or Glycine –> Cl- –>hyperpolarization = inhibitory

Question 43

all excitatory/inhibitory inputs go to axon hillock, excitatory and inhibitory inputs summed over space and time - if resulting combined potential depolarize axon hillock to threshold…

Answer 43

axon fires action potential

Question 44

Spatial summation

Answer 44

adds up simultaneous influences of synapses at diff sites of post synaptic cell

Question 45

Temporal Summation

Answer 45

adds up post-synaptic potentials generated at same site in rapid sequence

Question 46

ionotropic receptors

Answer 46

ion channels; neurotransmitter binding to these receptors cause a direct change in ion movement across the plasma membrane of post-synaptic membrane = these proteins enable fast, short-lived responses

Question 47

metrabotropic receptors

Answer 47

not ion channels, but induce signalling cascades in postsynaptic cell that secondarily lead to changes in ion channels = response is slower and longer-lived tan those by ionotropic receptors