Action potential Flashcards
the only movement of ions through the membrane is ___________ , as demonstrated by the open channels between the potassium symbols (K+ ) inside and outside the membrane.
diffusion of potassium ions
The Resting Membrane Potential Is Established by the :
Diffusion Potentials,
Membrane Permeability, and
Electrogenic Nature of the Sodium-Potassium Pump
high ratio of potassium ions inside
to outside
35 : 1
Nernst potential corresponding to
this ratio is ___________ because the logarithm of 35 is 1.54, and this multiplied by −61 millivolts is __________
94 millivolts.
The ratio of sodium ions from
inside to outside the membrane is 0.1, which gives a calculated Nernst potential for the inside of the membrane of _________
+61 millivolts
Is Used to Calculate the Diffusion Potential When the Membrane Is Permeable to Several Different Ions
The Goldman Equation
sodium potassium pump transport :
3 sodium to the outside
2 potassium into the cell
continual loss of positive ions inside the membrane
further negativity of about -4 millivolts
In the normal nerve fiber, the
permeability of the membrane to potassium is about ______ as great as its permeability to sodium. Using this value in the Goldman equation gives a potential inside the membrane of −86 millivolts, which is near the potassium potential
100 times
when u talk about membrane potential, consider the:
- concentration and charge of ions
- permeability of cells
which are rapid changes in the membrane potential that spread
rapidly along the nerve fiber membrane.
Each action
potential begins with a sudden change from the normal resting negative membrane potential to a positive potential and ends with an almost equally rapid change back to the negative potential.
action potentials
NEURONAL ACTION POTENTIAL stages:
- RESTING STAGE
- before action potential occurs - DEPOLARIZATION STAGE
- membrane becomes permeable to sodium ions - REPOLARIZATION STAGE
- voltage gated ions start to close
The membrane is said to be “polarized” during this stage
Resting Stage
membrane suddenly becomes permeable to sodium ions, allowing tremendous numbers of positively charged sodium ions to
diffuse to the interior of the axon.
The normal “polarized”
state of −90 millivolts is immediately neutralized by the inflowing positively charged sodium ions, with the potential rising rapidly in the positive direction—a process called depolarization.
DEPOLARIZATION STAGE
Within a few 10,000ths of a second after the membrane becomes highly permeable to
sodium ions, the sodium channels begin to close and the potassium channels open to a greater degree than normal.
Repolarization Stage
are transmitted via an action potential. It is a very rapid changes in the membrane potential. And begins with a resting potential which turns to becoming positive potential, then end
with resting potential again.
Neuronal signals
are necessary for both DEPOLARIZATION and
REPOLARIZATION of the neuronal membrane during the action potential.
Voltage-gated sodium channels
also play an important
role in the increasing the rapidity of repolarization of the membrane for potassium.
voltage-gated sodium channels
both voltage-gated channels are addition to the
_______ & __________ which establish the resting membrane potential of the membrane.
sodium-potassium pump
sodium-potassium leak channels
SUMMARY OF THE EVENTS THAT CASUSES THE
ACTION POTENTIAL
- Resting State
- Onset of Action Potential
- End of Action Potential
- before action potential, there is a conductance of
potassium ions which are about 100 times as
greater as the conductance of sodium ions. - Cause by the greater leakage of potassium ions
than sodium ions through leak channels.
Resting State
- voltage-gated sodium channels become activated
instantly allowing about 5000 volts increase in the
permeability which was identified as sodium
conductance. - result to voltage gating of potassium channels
causing them to slowly open
Onset of Action Potential
End of Action Potential
- Return to a resting membrane potential state
- potassium channels are closed back to its original
state - It only happens after a delay
-The voltage-gated sodium channels opens when there is a rise in the membrane potential (specifically, -90 mv to 0)
-The rise and the opening of the voltage-gated sodium channels cause a further rise of membrane potential.
-The rise of the membrane potential, allows a rapid in-flow of ions. An example of
POSITIVE FEEDBACK CYCLE.
ACTION POTENTIAL DOES NOT OCCUR UNTIL
THRESHOLD POTENTIAL HAS BEEN REACHED
A sudden rise from -90mv to -65mv causes an explosive development of the action potential
is when sodium ions are greater than the number of the potassium ions leaving the neurons
threshold potential
NEW ACTION POTENTIAL CANNOT OCCUR WHEN
MEMBRANE IS STILL DEPOLARIZED FROM PRECEDING ACTION POTENTIAL
why?
After action potential is initiated, sodium ion channel are INACTIVATED
any amount of stimulation cannot open the inactivated gates. It can only be opened when the membrane potential is back to its:
original resting membrane potential
2 Things Presends:
- Absolute Refractory Period
- Relative Refractory Period
- action potential cannot be elicited
- Around 2500 impulses per second are transmitted
Absolute Refractory Period
- allows refractory period is stronger than normal
stimulus to excite nerve fiber. (for action potential
to be initiated)
Relative Refractory Period
Action potential elicited at any point in a
membrane would usually excite adjacent portions,
which results to
PROPAGATION
Transmission along neuron or muscles is called
_______
(Undergoes an all-or-nothing principle)
neuronal or muscular impulse
Re-establishing Sodium and Potassium Ionic Gradients After Action Potentials are Completed – Importance of Energy Metabolism
Transmission of each impulse along the nerve fiber reduces infinitesimally the concentration differences of sodium and potassium
It is necessary to re-establish the sodium and potassium concentration differences across the membrane
As sodium enters the cell so does water. When the pump does not work normally, the cell will then swell.
problem in sodium channel pump
Large Nerve Fibers Are Myelinated and Small
Ones Are
Unmyelinated
Surrounding the larger axons is a thick myelin sheath
deposited by _______
Schwann cells (sphingomyelin)
At the juncture between two successive Schwann cells, a small noninsulated area only 2 to 3 micrometers in length remains where ions can still flow with ease between the extracellular fluid and the axon interior
nodes of Ranvier
the membrane of the axons is used for conduction of
action potential
“Saltatory” Conduction Occurs in
Myelinated Fibers
is when ions flows with ease through nodes of Ranvier. Thus, the neuronal impulse “jumps” from node to node along the fiber
Saltatory
Saltatory conduction is of value for two reasons:
Increased velocity.
Energy conservation.
- by causing depolarization process jump along
intervals, there is an increase of velocity neuronal
transmission from 5 to 50 folds.
Increased velocity.
around _________ of the body mass is around skeletal muscle and around 10% is smooth muscles and cardiac muscles where it’s principles of contraction revolve around nerve fibers
40%
- changes in ions require energy in the form of ATP
- Saltatory conduction conserves energy for axon.
Energy Conservation
Conduction Velocity Is Greatest in
Large, Myelinated Nerve Fibers.
-the velocity increases with the fiber diameter in myelinated fibers
(in unmyelinated, square root increase only)
Velocity of action potential conduction nerve fiber varies from 0.25 m/s to 100 m/s in __________ & ______ fibers respectively.
unmyelinated and myelinated
electrical to chemical using _____ in contraction of muscle
calcium ions
needed as it conserves energy, since
both muscle contraction and muscle relaxation is very dependent with ATP.
saltatory conduction
living tissue.
has its own stroma (made of calcium and phosphate)
hard tissue to support body
contradict with the pull of gravity
(from mechanical to chemical signal)
Bones
In the muscle the specific area where there is a communication of the nerve is in the _____________,
where the mode of communication become electrical to chemical and the involvement of calcium to initiate muscle contraction.
myofibril
Muscle contraction and relaxation is very dependent on
ATP
-We grow because we first had our __________.
- we are able to move our joints because of our ______________
cartilage
________________is avascular.
So, if you damaged the it, it will be hard to generate because of the lack of its lack of blood
vessels.
cartilage
__________common in older people, because the cartilage suffers from the wear and tear of the body.
The cartilage will thin out or will be gone causing to have a friction on the joints.
Osteoarthritis
In growing years cartilage is very active, but at around __________ years old it will slowly lose its activity and capacity.
20-25
3 types of cartilage:
- Hyaline Cartilage
- Elastic Cartilage
- Fibrocartilage
where the cartilage is residing
Lacuna
in some areas of the body is
composed of glycosaminoglycans. Which will
potentially/eventually solidify and become bone.
extracellular matrix
Composed mostly of type II collagen
and glycosaminoglycans; appear homogenous, glassy
Attract water that provides resilience
and allows diffusion of metabolites
throughout avascular cartilage tissue
Hyaline cartilage
the cartilage cells
able to survive because of the
extracellular matrix which contains the nutrients.
Chondrocytes
fibers in pinna of the external ear
Elastic Cartilage
Firm, solid tissue that resembles dense connective tissue
Pubic symphysis, annulus fibrosus of intervertebral
discs, menisci
Fibrocartilage
Cartilage is avascular- thus it relies heavily on the ____________ of nutrients from the vessels of the
perichondrium or to the surrounding tissues
Also attributes to the slow and limited ability to heal
and repair when injury occurs.
active diffusion
mainly occurs during
embryonic and fetal development and childhood and
this slowly decreases in adolescence and in adults
almost little to no growth
Growth of the cartilage
TWO TYPES OF GROWTH IN THE CARTILAGE
- Appositional growth
- Interstitial growth
where in the chondroblasts (cartilage producing cell) located in the perichondrium produce cartilaginous matrix and thicken the cartilage from the periphery.
Once the chondroblast became
incasing matrix they become chondrocyte.
Appositional growth
chondrocyte in the middle of the
cartilage divide and each daughter cell starts to secrete cartilaginous matrix around itself eventually becoming separated from each other by a newly produce cartilaginous matrix
Interstitial growth
a group of chondrocyte that arose
from a single chondrocyte during interstitial growth
Isogenous cells
Osteoprogenitors: Pool of mesenchymal stem cells,
stellate to squamous morphology
Give rise to osteoblasts
Osteoprogenitors
Active: Cuboidal to columnar with basophilic cytoplasm and euchromatic nuclei and distinct
nucleoli
b. Inactive: Squamous
Secrete osteoid
Innermost layer of periosteum; endosteum
Osteoblasts
convert mechanical to chemical stimulus.
Mechanotransduction
Osteoblasts encased in calcified matrix
mature and become osteocytes
Maintain bony matrix; mechanotransduction
Main cell body in lacunae, cell processes in canaliculi
Osteocytes
Large, multinucleated macrophage derivative
Howship lacunae
Osteoclasts
Dense connective tissue
Deliver neurovascular supply to the bone,
allow tight attachment of the muscles and
other structures to the bone
Outer surfaces of most compact bones
Periosteum
Resembles simple squamous epithelium
composed of inactive osteoblasts, osteoprogenitors, and osteoclast
Source of new osteoblasts and osteocytes
Inner surfaces of compact bones, canals;
outer surfaces of all sponge bones
Endosteum
it is where blood is produce
Marrow space
Mechanical support, protection,
weight transfer, mineral
storage
Outer surfaces of the
bones
Compact bone
Weight transfer, quick mineral turnover
Inner portion of the bones
Sponge bone
Site of blood formation and fat storage, lighten
the weight of the bone
Spaces in between
the sponge bone TRABECULAE
Marrow space
Dense outer portions of the bone
Weight bearing, weight transfer, protection, site for
muscle attachment
Peripheries of most bone; thicker in the
diaphysis of long bones
compact bone
has
- concentric lamellae
-initially, it has collagenous fibers running each length
-eventually it will be calcified
-fiber oriented in a very minimal manner so that it can have the
-greatest capacity for weight transfer
-has Cement lines which are Darker staining line
-has Osteocytes in the lacunae
-the dot-like opening between the layers of the lamellae
COMPACT BONES
✓ is composed primarily of plates or branches of bony
tissues
✓ play some role in weight transfer
✓ reduce the weight of the bone
✓ this architecture provides large area for bone
resorption and formation
SPONGE (CANCELLOUS/MEDULLARY) BONE
COMPACT BONE IS ON THE PERIPHERY VS SPONGY
BONE IN THE
MIDDLE OF THE BONE
not a static tissue.
a dynamic tissue and it continues to be
remodeled throughout life.
- But not in a very fast manner, only in a slow
manner
- It will be faster for children, not in adults
❖ In adults, it has to undergo resorption in the osteoblast before you can lay down new bone in the osteoblast
BONE
The histologic features of Trabeculae:
✓ also lined with osteoblast
✓ is lined with bone spicule necessary for weight
transfer, source of quick bone absorption
similar to Lamellar Bone or Compact Bone, the
______________________ bone also has
canaliculi but is arrange in a hair-like fashion within the trabeculae
also has its own cells of osteoclast that participates in
bone resorption
Sponge (cancellous/medullary)
a tissue for red blood
cells as well as white blood cells
Hematopoietic tissue
As an individual grow older, the red marrow that
produces red blood cell eventually reduces in number and it’s going to be replaced by ___________
fatty tissue or yellow marrow
✓ Undergo bone remodeling
✓ In kids, it is normal
✓ The presence of this may be an indication of
a fracture in adults
✓ A red flag in adults, as it can be found in lesions
✓ Malignancies in bodies can be shown as a woven
bone (e.g., osteosarcoma- a bone forming tumor
creating woven bone)
Woven Bone
-forms during development and be remodeled by lamellar bone
-ultra primary or immature bone and the one form near the ossification process
-collagen fibers are unorganized
-osteocytes are scattered about the bony matrix
Woven (primary, immature) bone
❖ most compact and spongy bone in the embryo initially form as a __________
❖ in the adults, ________________ is form in limited areas like sites of healing bone and alveolar processes of the maxilla and mandible
woven bone
Bone tissue that forms through remodeling the woven bone
-Collagen fibers are well-organized
-Osteocytes are regularly arranged and spaced throughout the bony matrix
❖ In between bony matrix found in adult are the
compact and spongy bone
Lamellar (secondary, mature) bone
release by the parathyroid gland and inhibits osteoblast by producing the bony matrix
- but it stimulates the osteoblast (the derivatives of monocytes) via stimulating factor
which increases bone reabsorption by the osteoblast,
ultimately results in elevation of calcium in the body
PTH
released by the parafollicular cells in the thyroid
gland
-inhibits the osteoblast thus no bone reabsorption
-lead to decrease in blood calcium
Calcitonin
These 2 major hormones regulate bone remodeling and blood calcium level
Parathyroid hormone and calcitonin
2 forms of bone formation
- Membranous (intramembranous) ossification
- Endochondral ossification
- Bone formation from the cartilage
- Utilizes the hyaline cartilage model as mold, which is then replaced by bony tissue
- long bones form in this manner.
- As the cartilage model grows, a bony collar forms
around the future diaphysis and blood vessel,
Endochondral Ossification
disc of hyaline that remains in endochondral
ossification
- closes 20-25 yrs old
- epiphyseal plate necessary for bone elongation
- produces hyaline cartilage
Growth plate
The rate of hyaline cartilage replacement with bone
tissue ___________ in adolescence until entire growth plate is calcified
increases
HORMONAL REGULATION :
PTH- Initially stimulates osteoblasts to allow osteoclast to
function thereby also increasing Ca2+
-responsible for activating osteoclast through OSF production
of the Osteoblast.
Calcitonin- inhibits osteoclast function, decreasing blood Ca2
- systemic skeletal bone disease
- looses bone density
- increases susceptibility to fracture
- skeletal deformities due to hormonal imbalance
- more bone resorption than bone building
Osteoporosis
