2. extent of transporter saturation (transporter affinity and ligand concentration)
3. rate of transporter confirmational change
how does a hypotonic solution change a cell?
cell swells
how does a hypertonic solution change a cell?
cell shrinks
how does an isotonic solution affect a cell?
no change
what is the difference between isotonic and isosmotic?
isotonic: non-penetrating solutes
isosmotic: non-penetrating plus penetrating solutes (non-penetrating: ions, penetrating: urea)
1 mole of NaCl is how many osmoles?
2 osmoles (Na + Cl)
how many osmoles is 1 mole of glucose?
1 osmole
what is the osmolarity of extracellular fluid?
300 mOsm
define equilibrium potential
when there is a concentration difference but no voltage difference, i.e. both sides have the same net charge
"The equilibrium potential is the voltage across a cell membrane that exactly balances the force in the concentration gradient of a permeable ion"
define the nernst equation
Ex = (58/z)log10 ([X1]/[X2]) where X1 = extracellular concentration, X2 = intracellular concentration and z = valence electron (eg. Ca = 2). The nernst equation yields the equilibrium potential of a single ionic species
define the log10 of 0.1, 1, 10 and 100
0.1: -1
1: 0
10: 1
100: 2
define diffusion potential
a transient charge due to certain ions diffusing faster than other ions. this charge dissapears as the equilibrium potential is reached.
true/false: [K] is always greater inside the cell than outside
true
define the resting potential
it is not a transient diffusion potential. it is a steady potential due to ions having moved across the membrane.
membrane potential moving away from 0 mV in the negative direction
define hyperpolarization
membrane potential more negative than the resting value
what would happen if the Na/K ATPase pump did not work?
the membrane potential would slowly reach 0 mV
list the steps of an action potential
1. increase in Na permeability driven by electrical and concentration gradients
2. membrane moves closer to 0 mV
3. Voltage gated Na channels open causing more Na channels to open via positive feedback (rising stage)
4. potential overshoots reaching 40 mV causing voltage gated K channels to open and K leaves the cell
5. falling phase - first driven by concentration gradient then by electrical gradient. Na channels close (voltage gated) leading to Na inactivation
6. hyperpolarization
7. resting potential
define absolute refractory period
brief period after the AP when a second threshold stimulus or suprathreshold stimulus cannot elicit a second AP due to voltage gates being closed.
why type of stimulus will not cause an AP?
a stimulus that is applied slowly--"Adaption"
define Adaption
a property of the neuron and is due to accomodation of ion channels
define rheobase
magnitude of the lease intense stimulus that can elicit a response
define utilization time
duraction required to elicit a response by a stimulus with a rheobase magnitude
define chronaxie
duration required to elicit a response from a stimulus that has a magnitude that is twice the rheobase magnitude
a drug that makes a cell more excitable will shift the graph which direction?
to the left
define electrotonic currents
passive currents that do not propagate
what prevents an AP from traveling backwards along an axon?
Na inactivation
list the events that occur during an AP in a motorneuron to an AP in the sarcolemma of a muscle cell
1. AP reaches presynaptic terminal causing an influx of Ca
2. ACh is released into the synapse
3. ACh binds AChR in postsynaptic motor endplate
4. chemically regulated Na and K channels open causing Na influx and K efflux across the motor endplate
5. Endplate potential is generated and opens voltage-regulated Na channels in the sarcolemma immediately surrounding the motor endplate causing an AP in the sarcolemma
list 5 characteristics of End Plate Potentials (EPPs)
1. only occur following an AP in a motorneuron
2. not spontaneous
3. confined to endplate region
4. amplitude: 10 mV
5. lead to an AP in adjacent region of the membrane
list 6 characteristics of Miniature EPPs
1. occur at rest
2. spontaneous
3. confined to endplate region
4. follow release of the contents of one synaptic vesicle
5. amplitude 1-2 mV
6. undergo summation
what are the products of ACh metabolism?
acetate: enters circulation
choline: taken up by presynaptic terminal to form ACh again
what effect does curare have?
binds to AChR so ACh cannot bind. Muscle AP does not occur
what effect does botulinum toxin have?
blocks ACh release causing flacid paralysis
what effect does organophosphatase have?
blocks the action of ACh, muscle cannot relax causing spastic paralysis leading to suffocation followed by flacid paralysis due to ATP depletion.
define Titin
largest protein. stretches when filaments contract. Runs from Z-line to M-line and stabilizes thick filaments
define Nebulin
runs along entire length of thin filament and acts as a scaffold
what areas of the sarcomere change length during contraction?
I and H change in length but the filament length does not change during contraction.
list 3 characteristics of Type I myosin
1. slow contraction
2. small diametere
3. less fatigue
list 4 characteristics of Type IIA fibers
1. smaller than IIB
2. use oxidative metabolism
3. less fatigue
4. slower than IIB
list 3 characteristics of type IIB fibers
1. use glycolytic metabolism
2. largest diameter
3. fast
what type of function do Type I fibers serve?
maintaining posture
what type of functions do Type II fibers serve?
perform tasks rapidly with a lot of dexterity
describe the orientation of transverse tubules in cardiac vs. skeletal muscle
cardiac: run parallel to fibers
skeletal: run perpendicular to fibers
what is special about myosin heavy chain alpha?
expressed only in the heart and masseter
what is special about Troponin I?
a unique isoform only expressed in the heart
is nebulin in cardiac muscle?
no.
what is the significance of a long refractory period in cardiac muscle?
prevents the heart from undergoing a tetanic contraction, which would be life threatening.
list the steps in a ventricular action potential
Phase 0: Na influx
Phase 1: K influx, Na efflux
Phase 2: Ca influx, K efflux
Phase 3: K influx, Ca efflux
Phase 4: no net current flow
list 2 sources of calcium in the heart
1. interstitial space
2. SR
list 3 methods of removal of Ca in the heart
1. SR removes Ca via Ca-ATPase pump
2. Membrane bound Ca-ATPase pump pumps Ca out of the cell
3. Na/Ca Exchanger (Secondary active transport mechanism) to pump out Ca and pump in Na, the Na/K ATPase pump maintains the Na concentration
list the steps in smooth muscle contraction initiation
1. Increase in cytosolic Ca
2. Ca + calmodulin
3. Ca/calmodulin + MLCK
4. Phosphorylation of myosin cross bridges
-Activation results when MLCK activity is greater than the phosphatase activity
what is special about the inward flow of positive charged ions in smooth muscle?
uses Ca instead of Na during rising phase of the action potential
list 4 mechanisms that control smooth muscle activation
1. some cell spontaneously generate APs (resting potential is never steady)
2. no NMJ in smooth muscle. motor neuron endings release neurotransmitters in the vicinity of smooth mucles cells
3. hormones can act as NTs
4. local factors such as pH, O2 level, NO and stretching can affect smooth muscle activation
explain the difference between the two types of smooth muscles
Single-Unit: gap junctions, all cells work together, spontaneously activated, stretch-activated
Multi-Unit: each cell activated independently, no spontaneously activated
list the jaw opening muscles
digastric, lateral pterygoid
list the jaw closing muscles
masseter, temporalis, medial pterygoid
what type of fibers predominate in the deep and superficial masseter?
slow fibers, amount of slow fibers increase from bruxing
what general pattern exists among all jaw closing muscles
greater amounts of slow myosin in deep vs. superficial and anterior vs. posterior
what type of efferent nerve fibers are in a muscle spindle?
gamma fusimotor fibers (most common) and beta fusimotor fibers (rare: 1/3 of all spindles)
what type of sensory nerve fibers are in muscle spindles
Ia afferent: primary endings
II afferent: secondary endings
what type of muscle fibers are in muscle spindles?
1. nuclear bag intrafusal (2-3/spindle)
2. nuclear chain intrafusal (4-6/spindle)
- most fibers in a muscle are extrafusal fibers which do the work assoc. with muscle contractions
what is the role of gamma motor neurons in muscle spindle?
sensitivity in shortened muscles. gamma motor neurons cause polar regions of intrafusal fibers to shorten --> stretch of equatorial regions --> restoration of sensitivity
what is the golgi tendon organ?
receptors in skeletal muscles. they are located at the junction between muscle fibers and tendons. they generate signals proportional to the amount of force generated by the extrafusal muscle fibers. Basically tells you how much force the muscle is doing so you don't throw a tea cup over your shoulder when you pick it up.
explain the muscle relationships between carnivores, herbivores and omnivores
Carnivores: large temporalis, jaw closers express superfast myosin
Herbivores: Large masseter, jaw closers express alpha cardiac myosin, no superfast myosin
Omnivores: unspecialized.
what are the three masticatory phases?
Preparatory: transport into the mouth
Reduction: breakdown of food
Preswallowing: bolus formation
what sensory nuclei control mastication?
Trigeminal Sensory Nucleus: projects to cerebellum
Trigeminal Mesencephalic Nucleus: cell bodies of spindle afferents from jaw closers, mechanoreceptors in PDL, gingiva and palate
what are the motor nuclei involved in mastication
Trigeminal Motor Nucleus: alpha and gamma motor neurons of jaw closers
Hypoglossal Motor Nucleus
Facial Motor Nucleus
motor, sensory, and premotor cortex are active during voluntary clenching, but the premotor cortex is not active during what?
gum chewing
explain the jaw-closing reflex
afferent fibers from muscle spindles, cell bodies in mesencephalic nucleus synapse on alpha motor neurons in trigeminal motor nucleus. very fast with basically no modulation from higher centers
explain the jaw-opening reflex
stimulus (touch, pressure) excites afferents that terminate in the spinal trigeminal tract which synapse on interneurons which in turn synapse on alpha motor neurons in trigeminal motor nucleus to innervate jaw openers. polysynaptic reflex, highly modulated for specific stimulus.
explain the difference between facultative group and obligate group of muscles in terms of swallowing
facultative: variable group involved with preparatory and oral phases
obligate: muscles used in the pharyngeal phase of swallowing
list 4 mechanisms that prevent aspiration of food
1. respiration is inhibited
2. larynx and upper esophageal sphincter elevate
3. intrinsic muscles of glottis move vocal cords toward each other
4. bolus moves through sinuses to pharynx
list the sensory and motor nuclei involved in swallowing
