BIPN 105 Midterm 1

Oscilloscope

Used to detect how electrical voltage changes over time

Axis usually volts / time

Measures voltage

Y axis gain (Range) → sensitivity

Large signal requires large range, thus sensitivity is low

Small signal requires small range, thus sensitivty is high

X axis gain (Timebase) → Sweep speed (time/div)

Sets how long oscilloscope will record for

Large signal (couple min) would sweep slowly to detect event

Small signal (couple ms) would sweep fast

Examples of Oscilloscope use

To detect Electromagnetic fields (EMFs), get closer to EMF noise increases

To measure electrical activity in a nerve, able to stimulate nerve past threshold thus generating AP (utilize preamplifier to see activity better before reaches oscilloscope)

To measure skeletal muscle contractions (utilize transducer which converts mechanical event to voltage)

Why must we calibrate the transducer

Through calibration equation must convert volts into appropriate units

Analog to digital mismatch

Computers take discrete samples whereas in real life its a series of continuous events

To reproduce more accurate results, it may be best to take as many samples to reproduce real life

Types of Filters

Band Pass

AC couple

DC Couple

Band pass filter

Band pass: only allows a certain band of frequencies to pass, removes unwanted frequencies found below and above signal we want to record (reduces noise)

(high pass/low cutoff, low pass/high cutoff)

AC couple filter

sets non /slowly changing parts of signal to 0, only allows fast changing parts go through unchanged (primarily used for fast events and to set baseline to 0)

DC couple filter

all parts of single unchanged (looks exact same as before, and used when turn off AC couple, primarily used for slow events)

Grounding

low resistance circuit, that passively spreading electricity goes into

Decreases amount of stimulus artifact (passive) that reaches recording electrodes

Permeable membrane

Solutes and solvent cross and at equilibrium both compartments are the same (same conc and same volume level)

Semi permeable membrane

ONLY solvent can cross

Diffusion

Movement of molecules from high to low concentration (both solute and solvent move)

Osmosis

Movement of solvent across semi-permeable membrane from high (low solute conc) to low solvent concentration (high solute conc)

only solvent moves

What generates osmotic pressure?

Solute particles generate osmotic pressure driving solvent towards it

What is Hydrostatic pressure

Physical push exerted by a fluid against a surface or container wall.

• When hydrostatic pressure builds up on the concentrated side of a membrane, it pushes water back in the opposite direction.

• Equilibrium occurs when the magnitude of the opposing hydrostatic pressure equals the osmotic pressure, stopping any net movement of water.

Osmotic pressure vs Hydrostatic pressure

Osmotic pressure pulling water

Hydrostatic pressure is pushing water out

What is this equation

What is this equation?

What does osmolarity = ?

conc of solute particles = osmolarity = S/V

S= # of particles

V = volume of distribution

Molarity

a measure of the concentration of a whole solute in a specific volume of solution

What is the difference between osmolarity and molarity

Osmolarity measures dissociated particles in solution, whereas molarity measures whole solutes

Not all solutes dissociate in solution, describe the differences

Non electrolyte and electrolyte solutes

Non-electrolyte solutes

Molecules that don’t dissociate into multiple particles

Thus, Molarity = osmolarity , 150mM sucrose = 150mOsm

EX: sucrose, urea, proteins, etc…

Electrolyte solutes

Molecules that dissociate into multiple particles

molarity dissociation # = osmolarity, 150 mM NACl * 2 = 300 mOsm

Terms to compare solutions/osmolarity

Isoosmotic, generate same osmotic pressure

Hypoosmotic, generates lower osmotic pressure (A is hypoosmotic to B)

Hyperosmotic, generates higher osmotic pressure (B is hyperosmotic to A)

Perm selective membrane

Solvents can cross, solutes have different permeabilities based on Permeability coefficient (P)

Moving down concentration gradient vs against concentration gradient

Conc gradient - high to low

Against gradient - low to high (utilizes energy

What is tonicity

Predicts water flow

Isotonic

no net water flow (water is crossing, but same amount is crossing generating no difference)

Hypotonic

A is hypotonic to B

Hypertonic

B is hypertonic to A (meaning B has higher conc of non permeable solutes)

Predict what will happen if a cell is put into solutions with different tonicities

Isotonic soln see no volume change

Hypotonic solution, water goes into cell, swells too much resulting in lysis

Hypertonic solution, water goes out of cell, cell shrinks

RBCs

no nucleus, few internal structures, little lipid bilayer bags of hemoglobin (Hb)

Cell membrane of RBCs are perm selective (Water and urea can easily cross, whereas other solutes cannot)

What is hemmatocrit test

Put blood solution in centrifuge, will find plasma (water & solutes), buffy coat (WBCs, platelets), RBC at bottom

% of RBCs in blood sample

Hct = vol of RBCs/ total volume

What would happen to hematocrit levels if blood is put into solutions with different tonicities?

Isotonic solution = no change in Hct

Hypotonic solution = increase in Hct (if lysis occurs decrease in Hct)

Hypertonic solution = decrease in Hct

TOTAL VOLUME DOESN”T CHANGE ONLY VOLUME OF RBCs

low HCT Anemia

Causes: Bleeding (lose RBCs), low iron (need iron to make HB (found within RBC) and for maturation of RBCs), pregnancy (expansion of plasma volume), RBC breakage (hemolytic anemias, immune attack on RBC), some type of kidney disease (decrease Erythropoietin “EPO” production, main hormone triggers production of RBC in bone marrow)

high HCT Polycythemia

causes: dehydration (decreased plasma volume), hereditary overproduction of RBC, low blood oxygen (high altitude, etc), blood packing, EPO injections

Derivation of Osmometer equation

1) V= W + B

V= total volume of RBC

W = volume of water in RBC (can be changed by osmotic forces)

b = “osmotically inactive volume”, can’t cross membranes such as proteins and solutes (can’t be changed by osmotic forces)

Rearrange to W = V-b

2) C = [solute] inside of an RBC

C= S/ W

S = # of particles

W = volume of water in RBC

S = W * C (S is constant since # of particles is same due to assumption solutes cant cross RBC membrane)

S= W C = Wo Co (normal state, isotonic blood solution)

Stick V-b in place for W

3) (V-b) C = (Vo- b) Co

Osmometer equation

Describes changes in RBC volume when put into different tonicity solutions

Anatomy of a neuron (nerve cell)

Dendrites, cell body, Hillock, Axon, Terminals

Dendrites

main input

Cell body

Has nucleus

Hillock

APs start

Axon

carries Action potentials towards other cells

Terminals

Axon branches to contact multiple cells

What happens if stimulus reaches threshold?

Will generate AP, AP will travel down axon and once it reaches the terminal, causes Ca2+ to rush into cell activating synaptic vesicles and releasing neurotransmitters into synaptic cleft

Why do neurons have membrane potential?

They have Sodium/Potassium ATPase pumps along the membrane that maintain ion concentration gradients across.

Typical cell membrane concentration

Find K+, anions, proteins inside cell

Find Na+, Ca2+, Cl- outside cell

Ions go down conc gradient unless utilize form of energy to go against conc gradient

Chemical and Electrical potential

K+ leaves the cell from high to low conc (Chemical potential), the cell will become more negative, which starts to pull K+ back into the cell (Electrical potential)

Nernst equation (Calculates equilibrium potential)

Tells you how much voltage need across membrane to balance chemical potential, no net flow of ion across membrane

Goldman equation (calculates membrane potential for all ions)

Why is it that at rest the permeability of K+ is larger than Na+?

Membrane potential at rest is much closer to K+ due to there being more K+ leak channels

Intracellular recording

Good for recording one neuron

Lec 3, 6:18

Define terms depolarize, repolarize, hyperpolarize

Depolarize: membrane potential past (Vrest)

Repolarize: membrane potential back to (Vrest)

Hyperpolarize: membrane potential below (Vrest)

Threshold potential

Vm at which an AP is initiated

APs are all or nothing

What is the purpose of Vt?

Serves as a noise filter and neurons use frequency modulation to code information (cant increase AP size instead increase frequency of AP)

AP phases

Depolariztion

1. Na+ channel activates

2. Large force drives Na+ into cell

3. Na+ influx depolarizes past threshold generating AP

Repolarization

1. Na+ channel inactivation (time dependent, very fast)

2. K+ channel activation

3. K+ flows out of cell

Hyperpolarization

1. Excess permeability/current of K+ (drives membrane potential below Vrest)

Return to Vrest

1. K+ channel deactivation (voltage dependent, not time dependent)

2. Na+ channel deactivation (voltage dependent, required to remove inactivation)

3. Leak channels are the only activated channels bring back to Vrest

-APs are local events that spread along the membrane

-As APs spread, they regenerate/don’t get smaller

-Very small # of ions cross during AP

-Repolarization not due to ATPase pumps, too slow, instead K+ pumps causing K+ to leave the cell

-If membrane stays depolarized Na+ channels stay inactivated must repolarize to remove inactivation

Refractory period

How long a neuron must wait before it can fire a second AP

Absolute refractory period

Period in which no amount of stimulus will be able to fire another AP since Na+ channels are still inactivated (to remove inactivation must have repolarization)

Relative refractory period

Period in which you are able to fire another AP, however only if 2nd stimulus is big enough (Na+ inactivation removed and still have high Pk (some K+ haven’t deactivated)

AP spread

At rest, neuron is negative inside and positive outside, if stimulate axon and generate AP now negative outside and positive inside (accumulating Na+ inside cell), depolarization will spread across (by activating Na+ channels)

What affects spread of AP (conduction velocity)

Greater the diameter the greater velocity

Myelination (acts as insulation, preventing passive spread (very fast) depolarization from dropping below threshold)

Saltatory conduction

-AP jumps node to node, AP regenerated node to node, AP spread faster

What are the different types of fibers?

A fibers (alpha, beta, gamma, delta) these are large myelinated

C fibers: small and unmyelinated

Sciatic nerve

bundle of different types of axons (find mix of A fibers)

Compound action potential (CAP)

Summation of individual APs, large diameter axons (alpha>beta>gamma>delta) have lower thresholds

Apply very small stimulus → no CAP, likely below threshold

Apply small stimulus → small CAP, likely on A alpha fibers generate AP

As continue to increase stimulus amplitude → CAP increases (recruitment of higher threshold axons)

CAP is not…

an all or nothing action potential, rather the summation of individual APs of multiple neurons

Stimulator

AP generated at (-) stimulating electrode

Extracellular recording

Only records outside voltage, use bipolar recording (subtract voltage at (-) electrode from (+) electrode)

Monopolar vs bipolar recording

Monopolar only utize (-) recording electrode thus stimulus that you see is depolarization at the (-) electrode

Bipolar utilize both (-) and (+) recording electrode, see depolarization event of both recording electrodes

Skeletal muscle are neurogenic since

skeletal muscle cells innervated by A alpha motor neurons that have cell bodies in CNS, send axons all the way to muscle, axons in muscle divide to contact many muscle fibers at the NMJ

NMJ (endplate)

A alpha motorneuron contact postsynaptic cell (skeletal muscle cell), presynaptic terminal contains vesicles, find Ach neurotransmitters inside synaptic vesicles, also find Ca2+ channels (P/Q voltage gated channels) on presynaptic membrane. Neurotransmitters travel synaptic cleft and bind to receptors found on postsynaptic membrane

Which receptors utilized by postsynaptic skeletal muscle cells

Respond to Ach and are sensitive to nicotine, cholinergic nicotinic receptors

Ligand dependent ion channel, requires two Ach to activate (non-specific mixed cation channel)

Is Vrest for skeletal muscle cells closer to Na+ or K+

Vrest is close to equilibrium potential K+, force for K+ is small/greater force for Na+

NMJ function

Nerve AP → Muscle AP (MAP)

A alpha motorneuron, generate AP in hillock, travels to presynaptic terminal, activates Ca2+ channels (P/Q), Ca2+ influx, causes vesicle exocytosis, Ach neurotransmitters released, Ach diffuses across cleft, two Ach bind to cholinergic nicotinic receptors, cholinergic nicotinic receptors activate, postsynaptic depolarization generates Endplate potential (EPP, these are graded potentials), more Ach binds to receptors the greater the EPP, if EPP is greater than threshold generates MAP

How many NMJ in skeletal muscle cell and where do you find them?

Find one NMJ per skeletal muscle cell and they are found in the middle of the cell

Termination of NMJ

Stop exocytosis (Ca2+ diffuses away from vesicles, Ca2+ inside cell is pumped out by ATPase pumps)

ACH dissociates from cholinergic nicotinic receptors, deactivates, EPP dissipates

ACh removed (diffuses away, or enzymatic breakdown by Acetychollineesterase AChE, which converts ACh to choline + acetate)

Recycling

Choline uptake into presynaptic terminal

Choline + Acetyl-coA converted into ACh + Coa by Choline Acetyltransferase (ChAT), ACh put into vesicles by vesicle Ach transporter (VAChT)

How does choline found in synaptic cleft get into cell?

Na+ choline transporter, energy to drive choline into cell is as Na+ comes in following conc gradient (both Na+ and choline enter cell)

Fatigue and Recovery of NMJ

If cell is undergoing high frequency stimulation (deplete ACh storage) and Recovery requires formation of new ACH/vesicles

Synaptic Delay

delay between presynaptic depolarization and postsynaptic depolarization

Things to consider are

release of NT

diffusion across synaptic cleft

two ACh binding to cholinergic nicotinic receptors

Facilitation (can be seen if multiple stimuli are used)

Compare Neurons vs Skeletal muscle

….

What are other NTS/receptors and their functions

….

Why is norepinephrine listed as a NT, but Epinephrine is not

Epinephrine is a hormone not a NT and is released by the adrenal medulla

What is the function of atropine

Blocks muscarinic cholinergic receptors (acts as a antagonist)

What is Myasthenia Gravis

Autoimmune diseases

Muscle organization

Muscle, myofiber (single muscle cell, multinucleated, length entire muscle, one NMJ found in center), myofibril. sarcomere, myofilaments

Myofilaments

Actin (thin filament)

Myosin (thick filament)

Z line

Anchors actin and separates one sarcomere from the next

Bands

A band (myosin + actin/myosin overlap)

I band (only actin)

Sarcomere

Small contractible element built into each myofibril

What happens when muscle contracts?

Myofilaments pull on Z line (either generates tension and shortens muscle)

Where is Ca2+ stored in sarcomere

Sarcoplasmic reticulum (SR), store and release Ca2+ into areas of myofilaments

What is the myofiber membrane called?

Sarcolemma

What channels do you find along the Myofiber membrane and what purpose do they serve?

Find Na+ and K+ channels and fire MAP, which is carried from NMJ (center of muscle) to ends of myofiber