Neurons

Question 1

neuron types (3)

Answer 1

• sensory neuron
• interneuron
• motor neuron

Question 2

neuron structure

Answer 2

structural variation:

- can be very long or short

Question 3

neuron components (3)

Answer 3

• cell body
• dendrites
• axon

Question 4

neuron cell body

Answer 4

• maintains the normal cell functions of the neuron

Question 5

neuron dendrites

Answer 5

• receive incoming information

Question 6

neuron axons

Answer 6

• communicate electrical signals across long distances

Question 7

where do electrical signals occur in neurons

Answer 7

• dendrites, cell body, axon, and synapse

Question 8

glial cells (2)

Answer 8

• support and surround neurons to maintain them

- required for proper neuron functioning

Question 9

neural reflex pathways (2)

Answer 9

• simplest neural pathways

- don’t involve brain or consciousness

Question 10

sensory neuron

Answer 10

• afferent neurons that send signals toward the CNS

Question 11

motor neuron

Answer 11

• efferent neurons that send signals away from the CNS

Question 12

sensory receptors and membrane potential (2)

Answer 12

• incoming stimulus causes change in conformation of receptor protein
• causes a signal within the cell that ultimately changes membrane potential

Question 13

what determines signal intensity in neurons (2)

Answer 13

• frequency of action potentials; # of action potentials/time
• more pressure to neuron when there is higher intensity

Question 14

graded potentials (3)

Answer 14

• occurs in dendrites and cell body
• only travel short distances
• vary in magnitude and sign

Question 15

action potentials (3)

Answer 15

• occur in axons
• all or none (always look the same within the cell)
• can be regenerated and conducted along long distances

Question 16

synaptic potentials (2)

Answer 16

• action potentials arriving at synapse

- cause the release of neurotransmitters

Question 17

what causes electrical signals in neurons

Answer 17

• graded, action, and synaptic potentials all result in changes in the membrane potential of the cell

Question 18

depolarization (2)

Answer 18

• becoming more positive

- smaller difference between inside and outside of cell

Question 19

hyperpolarization (2)

Answer 19

• becoming more negative

- bigger difference between inside and outside of cell

Question 20

membrane potential (3)

Answer 20

• voltage differences across the membrane
• always reported as charge inside relative to outside
• in both animals and plants, inside of the cell is more negative than outside at rest

Question 21

Nernst equation

Answer 21

• allows you to calculate the equilibrium potential of any ion

Question 22

how do we predict the direction of ion movement

Answer 22

• compare the equilibrium potential of that ion with the membrane potential of the cell

Question 23

permeability importance (2)

Answer 23

• final membrane potential is a weighted average of the equilibrium potentials of the ions and permeability provides the weighting factor
• increased permeability for an ion will increase its weight/importance

Question 24

why do we only consider Na+, K+ and Cl- in the Goldman equation

Answer 24

• permeability of the membrane to other ions is extremely low under resting conditions

Question 25

permeability and equations

Answer 25

• when permeability to one ion is much higher than to other ions, the Nernst and Goldman equations are the same

Question 26

what is the function of changes in membrane potential (2)

Answer 26

• can act as signals within cells
• occur in many cell types in both animals and plants; animals have nerves and tissues that are specialized for electrical signalling

Question 27

what causes changes in membrane potential

Answer 27

• change in the membrane permeability (channels opening and closing)

Question 28

how is permeability regulated

Answer 28

• gated ion channels

Question 29

how do gated ion channels work

Answer 29

• open and close in response to incoming signals

Question 30

what causes a graded potential

Answer 30

• binding of neurotransmitter to a receptor

Question 31

what sets the size of a graded potential

Answer 31

• depends on amount of neurotransmitter
• more neurotransmitter = more channel opening/closing = larger change in permeability = larger change in membrane potential

Question 32

why can graded potentials only travel short distances

Answer 32

• intracellular resistance and leakage of ions across the membrane cause the signal to degrade with distance; gets weaker as it travels

Question 33

how are action potentials triggered (3)

Answer 33

• graded potentials in the dendrites and cell body alter membrane potential in the axon hillock (trigger zone)
• membrane potential must exceed the threshold potential
• results in action potentials in the axon

Question 34

threshold potential

Answer 34

• 55 mV

Question 35

resting potential

Answer 35

• 70 mv

Question 36

spatial summation (3)

Answer 36

• graded potentials originating at different locations can influence the net change in membrane potential, allowing the neuron to reach threshold
• many positive close together grade potentials can cause the neuron to reach threshold
• positive and negative graded potentials can cancel each other out

Question 37

changes in permeability that occur during the action potential

Answer 37

• large increase in Na+ permeability
• followed by increase in K+ permeability
• occurs due to the opening of voltage-gated channels

Question 38

when do Na+ voltage-gated channels open

Answer 38

• when the membrane is depolarized

Question 39

positive feedback of Na” voltage-gated channels (3)

Answer 39

• positive feedback causes rapid depolarization
• Na+ channel activated gates open -> Na+ enters the cell -> more depolarization -> more gates open
• feedback loops closes after a certain amount of channels close

Question 40

how does Na+ channel density affect neuron function (2)

Answer 40

• higher density of voltage-grated Na+ channels creates lower threshold required to trigger an action potential
• increases excitability

Question 41

how do neurons return to resting MP

Answer 41

• inactivation gate on the VG Na+ channel
• VG K+ channels are not required, but are helpful and are responsible for the hyperpolarization phase of the action potential

Question 42

absolute refractory period (2)

Answer 42

• inactivation gate closed

- no new action potential is possible

Question 43

relative refractory period (3)

Answer 43

• inactivation gate open
• new action potential possible, but less likely because neuron is hyperpolarized
• only occurs in neurons with VG-K+ channels

Question 44

what is the purpose of the refractory periods

Answer 44

• makes it less likely for many action potentials to occur consecutively

Question 45

action potential propogation (2)

Answer 45

• action potentials spread as a wave of depolarization; an electronic current flow
• this triggers actions potentials to be re-generated in nearby regions of the membrane

Question 46

if a neuron is depolarized in the middle of the axon, which direction would the resulting action potential travel? (2)

Answer 46

• in both directions because the inactivation gates are open on both sides
• normally, it will travel toward the synapse due to inactivation gates closing behind it

Question 47

myelin (4)

Answer 47

• formed by Scwhann cells wrapped around axons
• insulates the axon
• allows charge to spread further down the axon without degrading (decreasing below threshold) so that fewer action potentials are needed to send signals
• causes saltatory conduction

Question 48

saltatory conduction

Answer 48

• apparent “leaping” of action potential from node to node

Question 49

synapses (2)

Answer 49

• can be chemical or electrical

- neurotransmitters are rapidly removed from the synapse

Question 50

chemical synapses

Answer 50

• convert electrical signals to chemical signals

- neurotransmitters are released into the synapse when VG Ca+ channels open