nervous system

Question 1

what are the 3 functions of nervous system?

Answer 1

1) sensory input
2)integration
3)motor output

Question 2

what is sensory input?

Answer 2

• Response to external and internal stimuli
• Sensory neurons

Question 3

what is integration?

Answer 3

• Interpretation of sensory input
• Decides appropriate response

Question 4

what is motor output?

Answer 4

• Conduction of signals from the CNS to the effector cells
• Motor neurons

Question 5

what are neurons?

Answer 5

• Cells specialized for transmitting electrical and chemical signals

Question 6

what are the 2 components to a neuron?

Answer 6

-cell body
-fiber-like extensions

Question 7

what are the two fiber like extensions in a neuron?

Answer 7

• Dendrites
  o Convey signals towards the cell body
  o Short and numerous
• Axons
  o Conduct impulse away from the cell body
  o Long single processes
  o Some are insulated by a myelin sheath
  o Ends in axon terminal

Question 8

what do axons do?

Answer 8

Relay signals to other cells by releasing neurotransmitters

Question 9

how do neurons communicate?

Answer 9

Neurons communicate via synapses

• Neurotransmitters are released from a pre-synaptic neuron and act on a post-synaptic neuron

Question 10

what are nerve impulses?

Answer 10

Nerve impulses are changes in voltage across the plasma membrane
o Caused by the movement of ions across the membrane (Na+, K+)

Question 11

what is the membrane potential of a resting neuron?

Answer 11

A resting neuron has a membrane potential of about -70 mV
* Inside is more negative than outside!

Question 12

what determines the potential of a neuron?

Answer 12

ion distribution across membrane

Question 13

what are the ions that determine the potential across the membrane of a neuron?

Answer 13

-negatively charged molecules (anions): proteins, amino-acids, sulfate and phosphate, Cl-
-positively charged molecules (cations): K+ and Na+

Question 14

how do charged molecules cross the membrane?

Answer 14

-passive ion channel (open all the time)
-gated ion channel (require a stimulus to open)

Question 15

what are the 2 types of gated ion channels?

Answer 15

-voltage-gated channels
-ligand-gated channels

Question 16

what does the Na+/K+ ATPase pump do?

Answer 16

• Maintains concentration gradients of Na+ and K+ across the membrane
• High Na+ outside and high K+ inside o 3 Na+ pumped out
  o 2 K+ pumped in
  o 1 ATP used

Question 17

true or false, neurons have many passive K+ channels?

Answer 17

true.
* Always open; K+ diffuses down its concentration gradient (created by the Na+/K+ pump) out of the cell

Question 18

how can a stimuli cause changes in membrane potential?

Answer 18

-stimuli opens gated ion channels, changing the charge distribution across the membrane

Question 19

what is hyperpolarization?

Answer 19

• Inside becomes more (-)
• K+ channels open
• K+ diffuses out of the cell

Question 20

what is depolarization?

Answer 20

• Inside becomes more (+)
• Na+ channels open
• Na+ diffuses into the cell

Question 21

what are the 2 types of changes in membrane potential?

Answer 21

hyper polarization and depolarization

Question 22

what is an action potential?

Answer 22

nerve impulse

Question 23

what happens if a depolarization stimulus is strong enough to pass the threshold potential?

Answer 23

an action potential is generated

Question 24

what does an action potential do?

Answer 24

moves along the entire length of the axon and stimulates the release of neurotransmitters from the axon terminal!

Question 25

what are the steps to generate an action-potential?

Answer 25

(1) Resting state
* No gated channels are open; -70mV resting potential (2) Threshold
* Stimuli causes gated Na+ channels to open; Na+ flows in causing depolarization
(3) Depolarization
* If depolarization reaches threshold an action potential will begin
* At threshold, voltage-gated Na+ channels open causing a large influx of Na+ and a large
depolarization
(4) Repolarization
* Na+ channels close and K+ channels open * K+ moves out of the cell
(5) Undershoot
* K+ channels are slow to close allowing more K+ to leave
* Membrane potential is more negative than resting potential

Question 26

what is the refractory period?

Answer 26

neuron is insensitive to stimuli. Constitutes of repolarization and undershoot

Question 27

where does the action potential go?

Answer 27

moves along the length of the axon to the axon terminal

Question 28

true or false, an action potential is a localized electrical event

Answer 28

true (happens in one part of axon)

Question 29

why can an action potential only move in one direction?

Answer 29

-Depolarization in one part of the axon causes depolarization in region right next to it by opening voltage gated Na+ channels

-During repolarization and undershoot (refractory period) a membrane cannot be depolarized so action potential can only move in one direction!

Question 30

what is a synapse?

Answer 30

• Synapse is a space between a presynaptic (transmitting) cell and a postsynaptic (receiving) cell

Question 31

what is a presynaptic cell?

Answer 31

transmitting cell

Question 32

what is a post synaptic cell?

Answer 32

receiving cell

Question 33

what happens at chemical synapses?

Answer 33

neurotransmitters are released from the axon terminal of a presynaptic cell and act on a postsynaptic cell

Question 34

what are the steps that happen at a synapse?

Answer 34

(1) Action potential arrives at the axon terminal
* Depolarization of the presynaptic membrane causes voltage-gated Ca2+ channels to open and Ca2+ to move into the axon terminal

(2) Ca2+ stimulates the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane
* Neurotransmitters are released into the synaptic cleft via exocytosis

(3) Neurotransmitters bind to ligand-gated ion channels on the postsynaptic
membrane

(4) Neurotransmitters are quickly degraded or taken back up by the presynaptic cell

Question 35

how many synapses will postsynaptic neurons form?

Answer 35

Postsynaptic neuron will form synapses with many (hundreds to thousands) presynaptic neurons

Question 36

what are the 2 types of potentials formed on the post synaptic neuron?

Answer 36

-Excitatory postsynaptic potential (EPSP)
-Inhibitory postsynaptic potential (IPSP):

Question 37

what is an Inhibitory postsynaptic potential (IPSP):

Answer 37

• Involve K+ and Cl- channels
• Causes hyperpolarization

Question 38

what is an excitatory postsynaptic potential (EPSP)

Answer 38

• Involve Na+/K+ channels
• Causes depolarization

Question 39

how can we determine whether or not an action potential will be generated in the post synaptic neuron?

Answer 39

Sum of EPSPs and IPSPs determine whether an action potential will be generated

Question 40

what are the summation rules for the post synaptic potentials?

Answer 40

(a) Subthreshold / no Summation
* By the time a single EPSP arrives at the postsynaptic neuron, it may not be large enough to trigger a response
(b) Temporal Summation
* If 2 EPSPs (or IPSPs) from the same presynaptic neuron arrive in rapid succession, the effect is additive
(c) Spatial Summation
* If 2 EPSPs (or IPSPs) from different presynaptic neurons arrive in rapid succession, the effect is also additive
(d) Spatial Summation of EPSP and IPSP
* An IPSP can counter the effect of an EPSP