PAS 505 Lecture 1 - Cell Membrane & Muscle

Inversely

Total body weight correlates __________________ with body fat.

more

If you have __________ body fat, you have less body water.

Females, because they have more body fat.

Do males or females have less body water? Why?

Fluids

___________ makes up over half of total body mass.

Na+

Most abundant cation in plasma

Cl-

Most abundant anion in plasma

Na+

Most abundant cation in interstitial fluid

Cl-

Most abundant anion in interstitial fluid

K+

most abundant cation in ICF

PO43-

Most abundant anion in ICF

55-60

Fluids make up _______________% of total body mass in most adults.

2/3

_____ of total body fluids is intracellular fluid (ICF)

1/3

_____ of total body fluids is extracellular fluid (ECF)

80

_____% or most of extracellular fluid is interstitial fluid

20

______% of extracellular fluid is plasma (liquid in blood vessels)

more body fat and less body fluid

Older adults have __________ body fat and __________ body fluid

infants

which age group has less body fat and more fluids (70-80% of body composition)

integral proteins

embedded in & anchored to cell membrane by hydrophobic reactions, very difficult to remove

transmembrane proteins

type of integral protein spanning lipid bilayer one or more times

peripheral proteins

loosely attached to membrane by electrostatic interactions, not covalently bound to membrane components

lipid

water

Phospholipid cell membrane Highly permeable to __________-soluble substances Low permerability to __________-soluble substances

simple diffusion

Passive net "downhill movement" of material from high to low concentration w/o help from a membrane protein

facilitated diffusion

Diffusion utilizing help from a membrane-bound protein

Channel-mediated transport and Carrier-mediated transport

2 types of facilitated diffusion

channel-mediated transport

Either open at all times or "gated" & can be specific or non-specific for a substance

carrier-mediated transport

At low solute concentrations, many binding sites are available and the rate of transport increases as concentration increases. The available binding sites become scarce, and the rate of transport levels off. Finally, when all of the sites are occupied, saturation is achieved (Transport Maximum (Tm)).

stereospecificity

specific solute binding site on carrier protein

competition

chemically related solutes may compete for binding

saturation

limited number of binding sites on carrier proteins

primary active transport

This type of transport requires direct ATP energy

secondary active transport

Type of transport. ATP is not directly used, but supplied indirectly by downhill Na+ movement providing energy for uphill movement of other solute. Na+ moves down its electrochemical gradient (downhill) & another solute moves against its gradient (uphill).

cotransport

uphill solute moves in same direction as Na+

countertransport

uphill solute moves in opposite direction as Na+

depolarization

Process in which the membrane potential becomes less negative

hyperpolarization

Process in which the membrane potential becomes more negative

inward current

flow of positive charge into the cell

outward current

flow of positive charge out of cell

threshold potential

membrane potential at which occurence of the AP is inevitable

overshoot

When the Action potential reaches above 0 and goes more positive towards its peak

undershoot

Time period in which the membrane potential dips lower than the RMP

refractory period

Time frame where another normal AP cannot occur; consists of absolute & relative periods

absolute refractory period

Time frame in which there is 100% no chance of depolarization occurring

relative refractory period

Time frame in which depolarization will only occur with a stronger than normal stimulus

1. Each normal AP for a given cell looks identical

2. Propagation- AP at one site causes depolarization at adjacent sites

3. All or none- if an excitable cell is depolarized to threshold in a normal manner, then occurrence of an AP is inevitable.

3 basic characteristics of an AP

activation ; inactivation

At rest, the ______________ gate is closed and ___________________ gate is open

activation ; Inactivation

During the upstroke, depolarization causes the _________________ gate to open. _________________ gate remains open.

inactivation

During the peak of AP, the _______________ gate closes

repolarization

After AP, there is _____________________, where no more Na+ coming in and more K+ going out

electrical

Electrical or chemical synapse: current flows via gap junctions between cells

chemical

Electric or chemical- Causes the VGCC to open. Ca influx causes neurotransmitter release by exocytosis NT diffuses across cleft, binds to postsynaptic membrane receptor & produces membrane potential change on postsynaptic cell

Excitatory (EPSPs)

Synaptic inputs depolarizing postsynaptic cells, bringing the membrane potential closer to threshold & closer to firing an AP

opening Na+ and K+ channels

What produces a EPSP?

Acetylcholine, norepinephrine, epinephrine, dopamine, glutamate, serotonin

The neurotransmitters that control/contribute to an EPSP

Inhibitory (IPSPs)

Synaptic inputs hyperpolarizing postsynaptic cells; membrane potential moves away from threshold & farther from firing an AP

opening Cl- channels

What produces IPSP?

spatial summation

2+ inputs arrive at postsynaptic site at the same time. If both +, they combine to produce greater depolarization, and AP. If one is - and the other +, they cancel each other out.

temporal summation

2 presynaptic inputs arrive at postsynaptic cell in rapid succession (not both at once). These inputs overlap in time, and summation occurs

Acetylcholine

NMJ. Released from preganglionic and most post ganglionic neurons in PSNS and all preganglionic neurons in SNS.

Norepinephrine, epinephrine, & Dopamine

Biogenic amines that tyrosine is a common precursor. Which one is secreted is dependent on which enzyme is present to break it down. These enzymes are COMT and MAO.

serotonin

Biogenic amine produced from tryptophan. Brain and GI tract neurons. Is a precursor to melatonin in pineal gland.

histamine

Biogenic amine synthesized from histidine. Catalyzed by histidine decarboxylase. Neurons of hypothalamus, mast cells of skin & GI tract.

glutamate

Excitatory neurotransmitter in CNS. Spinal cord and cerebellum. Receptors- NMDA, and GTP-binding proteins (G proteins)

Glycine

Inhibitory neurotransmitter. Brain & spinal cord. Increases Cl- conductance of the postsynaptic cell membrane- hyperpolarization.

GABA

AA & inhibitory neurotransmitter in CNS. Made from glutamic acid, catalyzed by glutamic acid decarboxylase

Motor unit

A motor neuron innervates one set of muscle fibers

Motor neuron pool

A pool consists of many motor neurons, each of which innervates a motor unit with the muscle

Thick filaments

Myosin- have actin binding site (cross bridge) and also a site that binds and hydrolizes ATP

thin filaments

Composed of actin, tropomyosin, & troponin

actin

2 strands twisting in a helical structure. Contains myosin binding sites

Tropomyosin

cover the myosin binding sites at rest

Troponin

Complex of 3 globular proteins. T- binds to tropomyosin, I-Inhibits, C- where Ca binds

T tubules

Muscle cell membrane that goes deep into muscle fiber. Carries AP depolarization from cell surface to interior. Make contact with SR terminal cisternae and contain voltage sensitive proteins called DHT receptor

sarcoplasmic reticulum

Store the Ca for when depolarization occurs.

No striation (no organized sarcomeres) Found in walls of hollow organs & vasculature Produce motility and maintain tension

3 Qualities of smooth muscle

multiunit and unitary

2 types of smooth muscle

multiunit

Multiunit or unitary smooth muscle: little or no coupling between cells.

iris, lens ciliary muscles, vas deferens

Location of multiunit smooth muscle cells (examples)

multiunit

Multiunit or unitary smooth muscle: Densely innervated by postganglionic fibers of ANS

Unitary

Multiunit or unitary smooth muscle: contains gap junctions between cells

GI tract, bladder, uterus, ureter

Location of unitary smooth muscle cells (examples)

unitary

Multiunit or unitary smooth muscle: Contracts in a coordinated contraction

unitary

Multiunit or unitary smooth muscle: Spontaneous pacemaker or slow waves

50-60

Fluids make up _______________% of total body mass in most adults.

troponin C

What is the ca2+ binding protein in skeletal muscle?

calmodulin

What is the ca2+ binding protein in smooth muscle?

think and thin filaments

What composes the A band of a sarcomere?

thin filaments

What composes the I band of a sarcomere?

end of sarcomere that runs down the I band

What are the Z disks of a sarcomere?

runs down H zone and links thick filaments

What is the M line of a sarcomere?

thick myosin only

What is the H zone of a sarcomere?

ryanodine receptor

What receptor allows the release of Ca2+ from the sarcoplasmic reticulum?

dihydropyridine receptor

What receptor is located in T tubules?

Ca2+

During muscle excitation, what stimulates the release of ACh?

T: attaches to tropomyosin

I: inhibits actin & myosin interactions

C- binds Ca2+ ions

What do the three proteins of troponin do?

end plate potential reaching threshold

What causes the activation gates to open?

peak of AP

When does the inactivation gate close?

calsequestrin

What protein allows for high concentration of Ca2+ in the sarcoplasmic reticulum of skeletal muscle?

detaches from actin

What does ATP binding to myosin head do?

pulls the myosin head back

What does the hydrolization of ATP to ADP & Pi do?

release of inorganic phosphate

What causes a power stroke in skeletal muscle contraction?