INTRO TO PSYCH

Question 1

Neurons

Answer 1

Signal changes in the environment, internal states, action plans, etc (86 billion neurons in the brain)

Question 2

Glia

Answer 2

Regulate chemical content of extracellular space (these glia called “astrocytes”) and Insulate axons of neurons (these glia called “oligodendrocytes” and “Schwann cells”)

10 times more glia than neurons in the thalamus, midbrain and brain

about 1.5 times more glia than neurons in the cerebral cortex)

Question 3

Ependymal cells

Answer 3

Line fluid-filled ventricles and guide cell migration during brain development

Question 4

Microglia

Answer 4

Remove debris from degenerating neurons and glia

Question 5

Vasculature

Answer 5

Arteries, capillaries, veins

Question 6

Cell membrane

boundary of cell

Answer 6

Lipid bilayer (2 fat layers) which contains proteins, e.g., receptors, channels

Question 7

Dendrites

Answer 7

Receive input from other neurons

Part of synapses (post-synaptic)

Synapses are connections between neurons

Question 8

Axon

Answer 8

Provides input to other neurons

Question 9

Axon hillock

Answer 9

Site of action potential generation

Question 10

Axon terminal

Answer 10

Part of synapses (pre-synaptic)

Question 11

Soma

Cell body

Answer 11

– Gene expression and transcription (Nucleus)
– Protein synthesis (Rough ER, Ribosomes)
– Protein sorting (Smooth ER, Golgi Apparatus)
– Cellular respiration/energy (Mitochondria)
– Fluid inside cell called “cytosol”

Question 12

Electric charge

Positive or negative charge

Answer 12

– Atoms contain electrons and protons (and neutrons)
– Positively charged metal ions, e.g., sodium (Na+), potassium (K+), calcium (Ca2+)
– Negatively charged ions, e.g., chloride (Cl–)

Opposites attract and like repels like

Question 13

Electric field

Answer 13

Created in space around positive source and negative source

Question 14

Electric potential

Answer 14

– Energy needed to move positive ion towards positive source of electric field (from A to B)
– Positive ion has more stored energy (electric potential) at site closer to positive source (B)
– Positive ion loses potential energy when it moves towards negative source of electric field

Question 15

Potential difference

Answer 15

– Difference in electric potential energy between two sites
– Measured in volts (V), i.e., energy per unit charge (joules per coulomb)
– Usual range in neurons on the order of millivolts (mV)

Question 16

Current

Answer 16

Movement of charged particles, e.g., Na+, K+

Question 17

Ion concentration gradient

Answer 17

Cell membrane separates ions
– Membrane itself not permeable to ions
Different concentration of ions inside and outside of neuron:
– Called “concentration gradient”
– Ions flow from high to low concentration site
Ion channels selectively permeable to particular ions:
– Channel spans the cell membrane
– Channel provides conduit between inside and outside of cell

Question 18

Membrane potential

Answer 18

Electric potential difference between inside and outside of cell

Reflects charge separation across cell membrane

Question 19

Resting membrane potential

Answer 19

At “rest”, inside of cell more negative than outside of cell

Resting membrane potential commonly at -65 to -70mV

Question 20

When channels open, ions move across membrane

Answer 20

Movement of ions depends on electric potential difference

Question 21

Depolarization

Answer 21

Membrane potential becomes less negative (more positive)

Question 22

Hyperpolarization

Answer 22

Membrane potential becomes more negative

Question 23

Ions will diffuse evenly across membrane if:

Answer 23

– There are no other driving forces (e.g., see figure)
– Diffusion direction down concentration gradient

Question 24

Movement of ions determined by:

Answer 24

– Concentration gradient
– Electric potential difference (membrane potential)

More sodium outside cell and more potassium inside cell

Question 25

Equilibrium potential (Eion)

Answer 25

Electrical potential difference that exactly balances ionic concentration gradient

Question 26

K+ key determinant of resting membrane potential

Answer 26

– Leak currents through potassium channels at rest
– Resting membrane potential close to EK because it is mostly permeable to potassium at rest

Question 27

Voltage-gated ion channels

Answer 27

– Channels open at particular membrane potentials
– Charged protein subunits of channel change conformation based on membrane potential

E.g., sodium channel; potassium channel

Question 28

Ligand-gated ion channels

Answer 28

– Transmitter/messenger (ligand) opens channel
– Binding of ligand changes channel conformation

E.g., AMPA glutamate receptor (positive ion channel); GABA receptor (chloride channel)

Question 29

Na+ channels open when membrane depolarizes

Answer 29

– Sodium moves into cell
– Channel stays open for brief period (1ms)
– Cannot be immediately opened again (1ms)
– Channel inactivated (called “absolute refractory period” )

Question 30

Membrane potential threshold

Answer 30

Critical value of membrane potential at which Na+ channels open, generating an action potential

E.g., around -45mV

Question 31

Depolarizing phase

Answer 31

– Sodium channels open
– Inward sodium current

Question 32

Hyperpolarizing phase

Answer 32

– Sodium channels close
– (More) Potassium channels open
– Outward potassium current (resets potential)

Question 33

Concentration gradients reduced

Answer 33

– To continue generating action potentials, need to re-establish concentration gradients
– I.e., need to move sodium back out of cell, and move potassium back in

Question 34

Sodium-potassium pump

Answer 34

– Protein that transports Na+ and K+ back across the membrane against their concentration gradient
– Consumes much energy (ATP)

Question 35

Action potential travels from axon hillock to axon terminal

Orthodromic direction

Answer 35

– Sodium influx at start of action potential depolarizes membrane just ahead to threshold
– Chain reaction, i.e., action potential generates and regenerates along axon
– Action potential spreads along membrane with conduction velocity of, e.g., 10m/s
(– Action potential can also travel towards cell body, i.e., back propagation, or antidromic)