lecture 26 - intro to neurons and resting potential

Question 1

2 functions of neurons/nerve cells

Answer 1

1. building blocks of the nervous system 2. instruments of communication

Question 2

sensory components

Answer 2

monitor environment and internal events

Question 3

integrative components

Answer 3

process and store information

Question 4

motor components

Answer 4

responses to sensory input or commands

Question 5

human brain composed of

Answer 5

100 billion neurons

Question 6

Inputs from other neurons (______ inputs) are received at the ________. The signal spreads _______ to the _____ _____. The ____ conducts ______ ______ away from the _____ (cell body), to the tips of the axon, where their synaptic ______ also called axon _______ communicate with other neurons.

Answer 6

Inputs from other neurons (_sensory_ inputs) are received at the _dendrites_. The signal spreads _passively_ to the _trigger_ _zone_. The _axon_ conducts _action_ _potentials_ away from the _soma_ (cell body), to the tips of the axon, where their synaptic _boutons_ also called axon _terminals_ communicate with other neurons.

Question 7

2 types of signals used in communication and where they are used

Answer 7

electrical signals (dendrites, cell body, axon) + chemical signals (synapses)

Question 8

is the resting potential of most cells in the body positive or negative

Answer 8

negative mate

Question 9

excitable tissue =

Answer 9

suddenly respond to stimuli with a transient change in the resting potential (i.e action potential)

Question 10

excitable tissues include

Answer 10

muscle fibres, neurons, some endocrine cells

Question 11

2 methods for measuring intracellular potentials

Answer 11

• patch clamp technique - microelectrode

Question 12

resting membrane potential (RMP)

Answer 12

electrical potential difference of 50-70mV across the membrane which results from the seperation of charge.

Question 13

more positive inside the cell than out. TRUE/FALSE

Answer 13

FALSE. By definition outside the cell is zero. Because the potential inside the cell is less, it is considered negative.

Question 14

electrons and ions are responsible for the potential difference across the membrane. Yeah or no.

Answer 14

NO! electrons are not. ONLY ions are responsible for the difference in charge.

Question 15

potential outside the cell is defined as being equal to _, meaning that the absolute intracellular potential is usually ________.

Answer 15

potential outside the cell is defined as being equal to _0_, meaning that the absolute intracellular potential is usually _NEGATIVE_. ~-65mV

Question 16

3 things RMP is due too

Answer 16

1. unequal Na+/K+ concentrations inside/outside the cell 2. unequal permeability of the cell membrane to Na+/K+ [3. electrogenic action of NaKATPase] - very small contribution

Question 17

[K+] outside vs. inside cell

Answer 17

HIGHER INSIDE - inside = 100mM - outside = 5mM

Question 18

[Na+] outside vs. inside cell

Answer 18

HIGHER OUTSIDE - inside = 15mM - outside = 150mM

Question 19

[Cl-] outside vs. inside cell

Answer 19

HIGHER OUTSIDE - inside = 13mM - outside = 150mM

Question 20

[Ca2+] outside vs. inside cell

Answer 20

WAY HIGHER OUTSIDE - inside = 0.0002mM - outside = 2mM

Question 21

does calcium affect the RMP?

Answer 21

no it doesn’t because the membrane is not permeable to them at rest

Question 22

does chlorine affect the RMP?

Answer 22

no because Cl- is distributed passively - there are no active Cl- pumps in neurons. This is why it has the same equilibrium potential as RMP (-65mV)

Question 23

What affect to the numerous, negatively charged proteins in the cytosol have?

Answer 23

they DO NOT AFFECT RMP because the membrane is totally impermeable to them

Question 24

how are Na+/K+ concentration gradients maintained?

Answer 24

by the Na+/K+ pumps. 3Na+ out, 2K+ in

Question 25

2 ion channels present in neurons (open/ closed at rest?)

Answer 25

1. non-gated “LEAK” channels - OPEN at rest 2. gated channels (VOLTAGE, LIGAND, MECHANICALLY) - usually CLOSED at rest

Question 26

number of K+ leak channels vs. number of Na+ leak channels at rest. PK+/PNa = ?

Answer 26

PK+/PNa+ = 40/1

Question 27

nervous system =

Answer 27

cns + pns

Question 28

equilibrium potential

Answer 28

net flow of ions is zero, in spite of concentration gradient and permeability. Electrical gradient and concentration gradient are opposing each other. e.g. as each K+ moves out, a negative charge replaces it

Question 29

Nernst equation

Answer 29

calculate the equilibrium potential for each ion Eion = 61.5mV (at 37 degrees c) x log [ion]o / [ion]i

Question 30

what are the equilibrium potentials for 1. K+ 2. Na+ 3. Cl- 4. Ca2+

Answer 30

1. K+ = -80mV 2. Na+ = +60mV 3. Cl- = -65mV 4. Ca2+ = +120mV

Question 31

interpretate the value of Eion of 120mV for Ca2+

Answer 31

you would require an opposing potential of 120mV inside the cell, to prevent entry of Ca2+, if the membrane was fully permeable to it.

Question 32

what are Cl- and Ca2+ important in

Answer 32

synapses

Question 33

fault in Nernst equation

Answer 33

only applies to a situation where the membrane is permeable to only one type of ion (leak channels for just one ion)

Question 34

Glia cells?

Answer 34

leak channels only for K+. therefore, RMP = -80mV

Question 35

the higher the permeability of a membrane to a particular ion, the…?

Answer 35

the greater the ability for this ion to shift the RMP towards its equilibrium position. e.g. small permeability to Na+ is why RMP is much closer to the E of K+.

Question 36

Goldman equation

Answer 36

a way of calculating the RMP by taking into account both the concentration gradients and permeability ratio between Na+/K+

Question 37

what’s this and where would you find it?

Answer 37

multipolar neuron - motor neurons - carry signal from the CNS out to an effector

Question 38

What’s this and where would you find it?

Answer 38

unipolar neuron - sensory neuron (e.g. in the PNS)