VPHY E1

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what do all cells have?

cell membrane, cytoplasm, nucleus

cytoplasm

cytosol (ICF), organelles (ER, golgi, etc)

cell membrane (plasma membrane)

phospholipid bilayer
contains protein, carbohydrates, lipids

body water by weight

male - 60%, female 55%
made up of ICF ~2/3, ECF ~1/3

extracellular matrix/fluid

water, carbohydrates, protein
ECF ~1/3 of body fluid; made up of 20% blood plasma (vascular), 80% interstitial (btwn) fluid

high [Na+], [Cl-], [Ca2+]

intracellular fluid

high [K+]

selective permeability of cell membranes

degree substance will diffuse across lipid bilayer

permeable: gases, ethanol (small uncharged polar)

slightly permeable: urea, water (small uncharged polar)

impermeable: large uncharged polar molec (glucose, fructose), ions, charged polar molecules (AA, ATP, proteins, NA)

simple diffusion

non-carrier mediated, "downhill" movement of some molec across membrane; w/o energy

high [solute] -\> low [solute]

diffusional driving force

proportional to the concentration gradient

osmosis

net diffusion of water across a membrane

high [h2o] -\> low [h2o]
low [solute] -\> high [solute]

what are the requirements for osmosis?

semipermeable membrane (to water)
at least 1 osmotically active solute (membrane impermeable)
conc gradient exists (osmotic pressure)

osmotic pressure

force needed to counteract osmosis; inc [solute], inc OP of soln

determined by total [solute] and M/m

one mole (mol)

6.02 x 10^23

molarity (M)

moles of solute/liters of solution

molality (m)

moles of solute/kg of solvent

osmolality/osmolarity (Osm/OsM)

the total molality of the solution \= the sum of the molalities of all solutes present

predicts what direc osmosis will occur

tonicity

total [solutes] ; water follows solute as long as conc grad and permeable mem

isotonic

when the concentration of two solutions is the same

hypotonic

bathing medium has lesser tension than inside of cell
lower conc outside (outside

hypertonic

solution with the greater concentration of solutes

lower conc inside (outside\>inside); water moves out, cell SHRINKS

what are the types of membrane transport proteins?

pumps (ATPases), channels (transporters), carriers

what are the characteristics of membrane transport proteins?

specificity (only carry some molec)
competition (for same R' or transporter)
saturation (\#; transport max)

passive transport

facilitated diffusion; E not required
downhill transport (hi to lo)
all channels & some carriers (uniporters)

facilitated diffusion

uses thermal E of diffusing molecs
involves net transport from hi to lo

active transport

must do work to move; energy required
uphill transport (lo to hi); against conc grain
primary active transport (pumps) and secondary (some carriers)

primary active transport

active transport that relies directly on the hydrolysis of ATP; all pumps

ATP-powered pumps

require metabolic energy (ATP); largest and slowest

always move solutes UPHILL against ec gradient

secondary active transport

movement of solute due to pre-exist EC grad from primary AT; symporters and antiporters

1 solute releases E to move other up; atleast one uphill against + one downhill

coupled (sodium/glu cotransporter), uphill of target + downhill of Na+/K+

ion channels

fastest; facilitated diffusion, downhill
mediates - changes in Vm
transmembrane proteins that conduct ions, specific, gated

what are the 3 types of ion channels?

voltage gated, ligand gated, mechanically gated

uniporter

single type solute transported; passive, downhill

transporters (carriers)

intermediate speed, widest variety
uniporter, symporter, antiporter

symporter (cotransporter)

2 or more ions or molecules transported in same direction

antiporter (exchanger)

moves multiple molecules in opposite directions across the cell membrane

sodium pump (Na+/K+ ATPase)

creates ionic grad across membranes; electrogenic pump - hyperpolarizing effect

3 Na+ out / 2 K+ in

vesicular transport

transport of large particles and macromolecules across plasma membranes

endocytosis

enter cells; taken in

exocytosis

exit cells

what contributes to establishing the RMP?

1) leaky K+ channels
2) Na+/K+ ATPase (sodium pump - electrogenic)
3) fixed anions inside cell

membrane potential (Vm)

potential difference across a cell membrane; always inside relative to outside \= 0

dependent on all ionic conc grad across mem & permeability of each ion

resting membrane potential

typically Vr \= -60 to -80 mV

K+

Ek \= -87 mV
"leaky" channels, always open
Vr ≈ Ek+
intracellular

Na+

extracellular cation
Ek\= +64 mV

Cl-

extracellular
Ek\= -89 mV

Ca2+

extracellular
Ek \= +129 mV

Nernst equation

Ex \= 61/z * log([x]out/[x]in)
ec equil state for a specific ion, balance pt btwn two diff forces acting (chemical and electrical)

can use to work backwards and figure out conc

Nernst potential

Ex \= equil potential (volt) for ion X
Vm \= Ex , no net movement

how to predict net movement of an ion?

existing Vm
Nernst potential Ex
charge on ion

electrical driving force

due to unequal distribution of ions
compare charge and Vm

chemical driving force

concentration gradient

electrochemical gradient

combo, net direction
compare Ex and Vm

chemical signaling

chemicals released from one cell into ECF and then "sensed", target responds via receptor proteins

types: local signaling (auto, para), neurotransmission, endocrine signaling

autocrine signaling

the target cell is also the secreting cell (self signaling)

paracrine signaling

signal released from a cell has an effect on neighboring cells

neurotransmission

the process of transferring information from one neuron to another at a synapse

release of NTs from presyn nerve term; interaction of NTs w postsyn cell mem; removal of NTs from syn cleft

synaptic cleft -\> axon -\> post synaptic cells

endocrine signaling

secreted molecules diffuse thru blood circulation (blood borne), mediated by hormones, longer last effects

what are the types of receptor proteins?

channel-linked (LGIC)
enzyme-linked
G-protein-coupled (infl others)
intracellular (cascade)

what are the 2 divisions of the nervous sytsem?

1. central nervous sytem (CNS)
2. peripheral nervous system (PNS)

what are the 7 major parts of the CNS?

7. cerebrum (cerebral hemisphere)
6. diencephalon
5. midbrain *
4. cerebellum
3. pons *
2. medulla oblongata *
1. spinal cord

what are the 3 broad regions of the brain?

forebrain, midbrain, hindbrain

what are the 2 cell types of the nervous system?

glia and neurons

anatomy of a neuron

dendrites, cell body, axon, nerve terminals

what are the functions of the 4 regions of a neuron?

dendrites & soma -\> syn potentials and integration (receiving info)
axon -\> action potenial conduction
nerve terminal -\> synaptic transmission (transmitting info)

central nervous system

brain and spinal cord

peripheral nervous system

all nervous tissue outside the CNS (nerves and ganglia; 31 pairs of spinal nerves)

includes motor (efferent) and sensory (afferent) sys

divides into autonomic and somatic

what are the functional classes of neurons?

afferent -\> sensory (in)
efferent -\> (somatic and autonomic) motor (out)
interneurons
"projection"

what is the difference between nuclei and ganglia?

nuclei: clusters of neuron bodies in CNS
ganglia: clusters of neuron bodies in PNS

what is the difference between tracts and nerves?

tract: collection of nerve fibers (axons) in CNS
nerves: collection of nerve fibers (axons) in PNS

what are the three classifications of neurons?

functional, morphological, NT released

what are the morphological classes of neurons?

pseudounipolar
bipolar
multipolar

glial cells

support cells of CNS

1. astrocytes
2. oligodendrocytes
3. ependymal cells
4. microglia

what are the predominant glia in humans?

astrocytes (CNS - abundant, capillaries, BBB)
oligodendrocytes (CNS - myelin)
Schwann cells (PNS -myelin)

how do oligodendrocytes differ from Schwann cells?

both myelin-producing glial cells;
Schwann cells only form one per internode of myelin sheath in PNS
oligodendrocytes in the CNS form ~15 internodes a cell

excitable cells

electrically excitable to change Vm from RMP to AP (can fluctuate); neurons, muscle cells, carddiac cells

fluctuations in membrane potential

depolarization (more pos)
hyperpolarization (more neg)
repolarization (moves back towards Vr)

depolarization

Vm becomes more positive relative to Vr
increases likelihood of firing AP

movement if Ca2+, Na+

action potenial

propagated electrical "wave" running length of axon; stereotypical; all or none

threshold ~ -55 mV

fixed amplitude ~100 mV (-70 to +30 mV)

shape and duration reflects permeability of Na+/K+

Na channel

"fast"
exists in 3 states: closed at Vr, open when depol, inact
contains 2 volt gates: main & inactivation

K channel

"slow"
exists in 2 states: closed at Vr & open when depol
contains 1 gate: main gate

AP sequence of events

1. Initial depolarizing stimulus reaches threshold
2. Na+ channels open to intake Na+ (depolarizing - fast)
3. K+ channels open to release K+ (repolarizing - slow)
4. Na+ channels inactivate (repolarizing - fast)
5. Both Na+ and K+ channel close (K slower)

rising phase of AP

Na+ channels open, Na+ diffuses in \= depol \= triggers more

falling phase of AP

Na+ channels inactivated, K+ diffuses out
enters refractory period, membrane repolarizes

undershoot of AP

K+ slower to close, still moving out; hyperpol followed by repol

peak of AP

Na+ channel inact begins (Na+ low DF, high perm), gated K+ channels open (K+ high DF, low perm)

absolute refractory period

Na+ channels inact, new stim has no effect on neuron; limits AP freq
unidirectionality of impulse

relative refractory period

due to continued outward diffusion of K+
only strong stim can overcome

"cable properties" of axons

electrical spread is passive when depol doesn't reach threshold and hyperpol
poor electrical conductor -\> attenuation (travels further)

what increases conduction velocity?

axon diameter (lower int resist, depol spreads faster - ions flow easier to next segment)

myelination (insulation)

saltatory conduction

the propagation of AP along myelinated axons from one node of Ranvier to the next; inc conduction velocity

due to internodes (myelin) and nodes of Ranvier

nodes of Ranvier

gaps in the myelin sheath
exposed membrane

myelinated axon vs unmyelinated

unmyelianted: sodium inflow & spreads passively, spreads to adj regions - no internodes
myelinated: prevents inward Na+ current, insulation, AP only produced at nodes of Ranvier

synapse

func connection btwn neuron and cell its signaling
electrical and chemical synapeses

synaptic cleft

gap that separates the presynaptic neuron from the postsynaptic cell; NTs released

presynaptic cleft

neuron that sends message
nerve terminal (vesicles fuse); synaptic vesicles (from chem syn)

postsynaptic cleft

the cell that receives the signal
cell surface receptors (for chem syn)

events in presynaptic cell

1. action potentials reach axon terminals
2. voltage-gated Ca2+ channels open
3. Ca2+ binds to sensor protein in cytoplasm (fusing)
4. Ca2+ protein complex stimulates fusion and exocytosis of neurotransmitter

neurotransmitters

chemical messengers that cross the synaptic gaps between neurons
small-molec, purines, biogenic amines, peptide, endocannabinoids (lipids), gases (NO, CO)

small-molecule NTs

ACh, AA, purines (ATP), monoamines

amino acid NTs

Glutamate, GABA
aspartate, glycine

biogenic amines (monoamines) NTs

try. deriv (catecholamines): epinephrine, dopamine, norepinephrine
trp. deriv: serotonin (5HT)

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