Anatomy Exam 1 Flashcards
Receptor
notes changes in system
Integrator
decides what to do
Effector
produces change
What component of a feedback system is not necessarily found in all control systems?
Integrator
Negative Feedback
Product of reaction inhibits further production of that specific product. Over shoot and under shoot are common features of this mechanism due to delay
Positive Feedback
Product stimulates the production of more product
Five primary functions controlled by positive feedback mechanisms
blood clotting
ovulation
labor
nerve impulse generation
shock cycle
The components of the cell membrane that function as receptor sites are the __
glycoproteins
The components of the cell membrane that make the membrane virtually impermeable to water soluble molecules are the __
phospholipids
Peripheral proteins
cell division, shape, and some enzyme activity
Integral proteins
extend from intracellular to extracellular margins
-channel proteins
-transport proteins
Glycoproteins
protein molecules with associated carbohydrate chains
-cell adhesion
-receptor sites
-immune reactions
Diffusion
movement from high concentration to low concentration based on molecular collisions
Simple diffusion
concentration gradient alone
(membrane not necessarily considered simple diffusion)
facilitated diffusion
gradient + protein carriers
Diffusion through protein channels
- simple diffusion through water-filled channels in protein structure
- selective permeability produced by:
channel charge
channel size - gating of protein channels
Voltage gating
ionic charges produce change
Ligand gating
binding of particles other than transport molecule produces change (e.g. Ca++)
The fact that Ca++ can make the sodium channels of conducting membrane less excitable is an example of
Ligand gating
The fact that changes in the ionic environment of the extracellular fluids can open or close protein channels can be attributed to __
configurational changes in the proteins
Transport of glucose and amino acids is by __
Facilitated diffusion
Factors that influence rates of diffusion transport
- permeability of membrane
lipid solubility
molecular size
molecular weight
kinetic energy - concentration gradient
- temperatur
- number of protein channels present
- ionic charge of substance and of membrane proteins
- pressure gradients, in addition for facilitated diffusion
- number of carriers
- activation of carriers
- rate of transport
rate of binding and release
rate of movement across membrane
Increased ATP levels have
no change of diffusion rates
Osmosis
The diffusion of water across the cell membrane
Hypotonic
Gain of water and swelling of cells
Isotonic
no net movement of water
Hypertonic
loss of water and shrinking of cells
Filtration
The separation of large from small particles using a membrane of set pore size and a pressure gradient
e.g. capillary exchange and kidney function
Dialysis
the separation of large form small particles using a membrane of set port size and diffusion. this mechanism does not play a major role in biological systems
Common feature of all passive mechanisms is __
equilibrium
If a cell containing 99.5% water is placed into a 0.9% NaCl solution, the cell will __
Shrink
If you wanted to deliver more water from the blood into the tissues, you would make the blood more __
hypotonic
Although both filtration and dialysis are mechanisms that utilize membranes with specific pore sizes to separate molecules of different sizes, they differ in that dialysis utilizes___
a concentration gradient
Active transport
movement of materials across a membrane, usually against a concentration gradient, using carrier proteins and cell energy
Primary active transport
carrier proteins and ATP
Secondary active transport
movement along concentration of electrical gradients that were established by primary active transport systems
The sodium/potassium pump would be categorizes as a __
Primary active transport system
The mechanism by which materials are transported across cellular sheets could be used as an example of __
primary and secondary active transport
The Na/K pump would be considered __
A counter transport system
Vmax
- number of carriers
- activation of carriers
- rate of binding
- rate of release
- rate of conformational change
Co-Transport
Two binding sites on the same carrier protein. Sodium is common in many co-transport systems
e.g sodium + glucose or amino acids
Counter transport
Similar to co-transport, but particles are moved in opposite across the membrane
Active transport across cellular sheets
Usually involve active transport into cell on one side of the cellular sheet and passive transport out of the cell on the opposite side of the sheet
e.g. movement of digestive products from the gut lumen into the blood
Characteristics of excitable membranes
- membrane permeable to potassium (100x greater than sodium) movement through sodium and potassium leak channels
- membrane for all practical purposes is impermeable to sodium
3.Na/K pump maintains electrical gradient - Na concentration higher extracellular
- K concentration higher intracellular
- Membrane is impermeable to large intracellular and extracellular anion
- Extracellular charge is Net Positive due to NA+>Anions
- Intracellular charge is Net Negative due to Anions>K+
In the resting state an excitable membrane is __
more permeable to potassium than sodium
The sodium/potassium pump mechanism is the most common physiological active transport system
-Integral proteins act as carriers
- 3 intracellular binding sites for sodium/carrier molecule
- 2 extracellular binding sites for potassium/carrier molecule
-intracellular portion of carrier has ATpase activity
Mechanism of action:
-all sodium and potassium binding sites must be occupied
-once all binding sites are occupied, ATPase activity is initiated
-Energy released from ATP used to produce conformational change that moves potassium into cell and sodium out of the cell
-Movement of ions results in higher sodium concentrations in the extracellular fluids with higher concentrations of potassium in the intracellular fluids
Why doesn’t K move if membrane is permeable to K?
Potassium stays in the cell because the charge on the outside of the cell is positive, K is positive so it would repel the outside of the cell
The sodium potassium pump can be activate din non-bioelectric cells when the
water concentration within the cell increases
Charge shift due to change in membrane permeability that allows sodium to enter the cell
Extracellular (anions)>(Na)
Intracellular (Na+K)>(anions)
Propagation of Action Potential
Charge shift across membrane initiated by some form of stimulus – continuation of change in permeability due to charge shift causing a domino effect on permeability from point of stimulation to end of cell.
Immediate Repolarization
Movement of K ions out of cell in response to Na movement into cell
Voltage gated sodium channels
Extracellular activation gate-opens as membrane potential shifts toward the positive (-90mV to -70 mV)
Intracellular inactivation gate - closes as membrane potential shift toward the positive, but with a slight delay
closing of inactivation gate limits the amount of sodium that enters the cell – only allows enough to enter to produce charge shift
Voltage gated potassium channels
Intracellular channel closed when intracellular charge is negative
Intracellular channel opens when membrane potential shift toward the positive - allows for the movement of potassium in the immediate repolarization response
Membrane can continue to depolarize and repolarize in the fashion form __ up to __ times before concentration gradients reach equilibrium
100,000 up to 50 million times
2x increase in (Na) =
8x increase in pump activity
Depolarization is marked by the movement of __
sodium into the cell
Immediate repolarization is marked by movement of __
potassium out of the cell
Immediate repolarization involves
osmosis
When an excitable membrane is in the resting state (RMP) the :
the sodium activation gates are closed and the inactivation gates are open
The movement of ions during depolarization is stopped by the
closing of sodium inactivation gates
The movement of potassium following depolarization will initially produce
the closing of sodium activation gates
Basic features of membrane conduction
- Threshold-liminial stimulus
- All- or -None principle of conduction
- Direction of Propagation: bi-directional (in theory) unidirectional for most practical purposes
When the membrane is stimulated at below threshold levels
the membrane will not depolarize
Calcium channels are
voltage gates
Termed slow channels - 10-20x as long for activation as compared to sodium channels
Calcium channels are more common to __
cardiac and smooth muscle (action of drugs termed calcium channel blockers)
Due to the action of the calcium pump, you would expect to find the concentration of calcium ions to be
lower in the cytoplasm and higher in the extracellular fluids
Calcium ions and sodium channels
-Calcium ions bind to extracellular receptor sites on sodium channels
-Increased voltage change required to open activation gates when Ca++ is bound to protein. 30-50% decrease in Ca++ concentration of the extracellular fluids produces spontaneous opening os sodium channels
-Related to titanic and convulsive muscle contractions in situations where Ca++ regulation is upset
Plateau=
spike + plateau (depolarized state is maintained)
Normal depolarization =
spike
Plateau response in action potentials sequence of events
- fast sodium channels open producing typical spike
- slow calcium channels open maintaining depolarized state- represented by plateau trace
- potassium channels are slow to open, thus delaying repolariztion. potassium channels open when calcium channels close
Plateau typical of smooth and cardiac muscle –
0.2-0.3 second delay
(skeletal muscle= 0.005 seconds in comparison)
Significance of plateau
sustained depolarization period maintains contraction, and delayed repolarization allows for rthymicity
Membrane at rest is always slightly permeable to sodium
-sodium leaks in slowly
-membrane approaches threshold
-threshold is reaches and Na+ channels open
Why delay between depolarizations- Why not continuous depolarization?
Increased K+ outflow during immediate repolarization produces hyper polarization. Therefore, it takes longer for the membrane to again approach the depolarization point
The plateau phase of cardiac and smooth muscle contraction is generated by the
opening of calcium channels
Hyperpolarization is produced by an increase of
the movement of potassium out of the cell
Nerve fiber
axon or dendrite
Epineurium
surrounds entire nerve
Perineurium
surrounds bundles of nerve fibers (fascicles)
Endoneurium
surrounds individual nerve fibers
nerve fibers holds
all or none concept
nerve=
variable numbers of fibers can fire at any one time
Microglia
phagocytes of the nervous system
Oligodendrocytes
myelin sheath of CNS
Astrocytes
blood brain barrier
Ependyma
lining of ventricles of brain and central canal of spinal cord
Neuroglia
supportive cells (nerve glue)
Schwann cells
myelin sheath of PNS, regeneration of neuronal fibers, form “living tube” of myelin around axons
Myelin decreases sodium permeability 5,000x
true
Saltatorial Conduction-depolarization only at the nodes
- increases rate of conduction-impulses “jumps” from node to node
- increases rate or repolarization- repolarization only at nodes
- decreases energy needed for repolarization- less Na+/K+ movement
Relative rates of conduction
unmyelinated 0.5 meter/second
myelinated 100 meters/second
Individual fascicles of a muscle are surrounded by the
perimysium
During the absolute refectory period
the membrane cannot be restimulated
Which of the following is the smallest unit
myofiber
myofibril
myofilament
myofilament
The bundles of contractile proteins in the muscle cell are termed the
myofibrils
Absolute
sodium inactivation gates closed- no additional stimulus can open force them open (as short as 1/2500 second in large myelinated fibers)
Relative
some sodium channels still inactivated, potassium channels open above threshold stimulus can initiate depolarization
Membrane stabilizing factors (anesthetics)
increased extracellular Ca++ - inhibits opening of sodium channels
increased K+- hyperpolarization
Local anesthetics
procaine or tetracaine
block opening of sodium activation gates and prevent depolarization
