INTRO TO PSYCH Flashcards
Neurons
Signal changes in the environment, internal states, action plans, etc (86 billion neurons in the brain)
Glia
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)
Ependymal cells
Line fluid-filled ventricles and guide cell migration during brain development
Microglia
Remove debris from degenerating neurons and glia
Vasculature
Arteries, capillaries, veins
Cell membrane
boundary of cell
Lipid bilayer (2 fat layers) which contains proteins, e.g., receptors, channels
Dendrites
Receive input from other neurons
Part of synapses (post-synaptic)
Synapses are connections between neurons
Axon
Provides input to other neurons
Axon hillock
Site of action potential generation
Axon terminal
Part of synapses (pre-synaptic)
Soma
Cell body
– 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”
Electric charge
Positive or negative charge
– 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
Electric field
Created in space around positive source and negative source
Electric potential
– 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
Potential difference
– 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)
Current
Movement of charged particles, e.g., Na+, K+
Ion concentration gradient
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
Membrane potential
Electric potential difference between inside and outside of cell
Reflects charge separation across cell membrane
Resting membrane potential
At “rest”, inside of cell more negative than outside of cell
Resting membrane potential commonly at -65 to -70mV
When channels open, ions move across membrane
Movement of ions depends on electric potential difference
Depolarization
Membrane potential becomes less negative (more positive)
Hyperpolarization
Membrane potential becomes more negative
Ions will diffuse evenly across membrane if:
– There are no other driving forces (e.g., see figure)
– Diffusion direction down concentration gradient
Movement of ions determined by:
– Concentration gradient
– Electric potential difference (membrane potential)
More sodium outside cell and more potassium inside cell
Equilibrium potential (Eion)
Electrical potential difference that exactly balances ionic concentration gradient
K+ key determinant of resting membrane potential
– Leak currents through potassium channels at rest
– Resting membrane potential close to EK because it is mostly permeable to potassium at rest
Voltage-gated ion channels
– Channels open at particular membrane potentials
– Charged protein subunits of channel change conformation based on membrane potential
E.g., sodium channel; potassium channel
Ligand-gated ion channels
– Transmitter/messenger (ligand) opens channel
– Binding of ligand changes channel conformation
E.g., AMPA glutamate receptor (positive ion channel); GABA receptor (chloride channel)
Na+ channels open when membrane depolarizes
– Sodium moves into cell
– Channel stays open for brief period (1ms)
– Cannot be immediately opened again (1ms)
– Channel inactivated (called “absolute refractory period” )
Membrane potential threshold
Critical value of membrane potential at which Na+ channels open, generating an action potential
E.g., around -45mV
Depolarizing phase
– Sodium channels open
– Inward sodium current
Hyperpolarizing phase
– Sodium channels close
– (More) Potassium channels open
– Outward potassium current (resets potential)
Concentration gradients reduced
– 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
Sodium-potassium pump
– Protein that transports Na+ and K+ back across the membrane against their concentration gradient
– Consumes much energy (ATP)
Action potential travels from axon hillock to axon terminal
Orthodromic direction
– 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)
