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MindMap Gallery Chapter 2 - Basic Functions of Cells
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Chapter 2 - Basic Functions of Cells
Physiology, Human Health 9th Edition, mainly includes the basic structure and material transport function of cell membranes, electrical activity of cells, contraction of muscle cells, etc.
Edited at 2024-02-08 16:18:34
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Chapter 2 - Basic Functions of Cells
- Avatar Character Relationship Chart
Avatar 3 centers on the Sully family, showcasing the internal rift caused by the sacrifice of their eldest son, and their alliance with other tribes on Pandora against the external conflict of the Ashbringers, who adhere to the philosophy of fire and are allied with humans. It explores the grand themes of family, faith, and survival.
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basic functions of cells
Basic structure and material transport function of cell membrane
Structure and chemical composition of cell membrane
The cell membrane is mainly composed of lipids, proteins and a certain amount of sugars. The molecular arrangement structure of the cell membrane is a liquid mosaic model. The basic content of this theory is: the cell membrane is based on a liquid lipid bilayer as a framework, in which different physiological functions are embedded. protein
(1) Lipid bilayer
Membrane lipids are divided into three categories: phospholipids account for 70%, followed by cholesterol, and a small amount of glycolipids
One end of each phospholipid molecule is the hydrophilic polar group phospholipid and base, facing the outer or inner surface of the membrane; The two longer fatty acid hydrocarbon chains (hydrophobic non-polar groups) in the phospholipid molecules are opposite each other inside the membrane.
Lipid bilayers are stable and fluid
(2) Cell membrane proteins
Functions of cell membrane proteins:
1. Participate in the transmembrane transport of substances
2. Participate in information transmission
3. Related to energy conversion
Cell transport function
(1) Passive transport
Transport across cell membranes along concentration differences without consuming energy is called passive transport.
1. Simple diffusion
It refers to the transmembrane diffusion of substances from the high-concentration side of the plasma membrane to the low-concentration side through the gap between lipid molecules.
The substances transported by simple diffusion are all fat-soluble (non-polar) substances or a small number of uncharged polar small molecule substances. Such as: oxygen, carbon dioxide, nitrogen, steroid hormones, ethanol, urea, glycerol, water, etc.
2. Facilitated diffusion
It refers to the transport of non-lipid-soluble small molecule substances or charged ions across the membrane along the concentration gradient or potential gradient with the help of transmembrane proteins.
(1) Facilitated diffusion through channels
The solutes transported through the channel are almost all ions, so this type of channel protein is also called an ion channel
Important basic features:
Ion selectivity
Each channel only has a high permeability to one or a few ions, and has little or no permeability to other ions.
Gating properties
1. Voltage-gated channel
These channels are regulated by membrane potential
2. Chemically Gated Channels
Such channels are regulated by certain chemicals inside and outside the membrane
3. Mechanically gated channel
This type of channel is regulated by mechanical stimulation, usually when the plasma membrane senses stretch stimulation and the channel develops or closes.
4. Ungated channel
There are a few channels that are always open, such as potassium leak channels on nerve fibers.
water channel
The simple transport speed of water is very slow, and the water phase pores only allow water molecules to diffuse through in a single file.
(2) Facilitated diffusion via carrier
It refers to the transmembrane transport of water-soluble small molecule substances along the concentration gradient mediated by carrier proteins.
Features:
1. Structural specificity
Various carriers can only recognize and bind substrates with specific chemical structures
2. Saturation phenomenon
Since the number and transport rate of carriers in the cell membrane are limited, when the concentration of transported substrate increases to a certain level, the rate of substrate diffusion will reach a maximum.
3. Competitive inhibition
If two substances with similar structures can bind to the same carrier, competitive inhibition will occur between the two substrates. Among them, solutes with lower concentrations or larger Michaelis-Menten constants (that is, the substrate concentration at which the transport rate reaches half of the maximum transport rate) are more likely to be inhibited.
(2) Active transport
It refers to the transport of certain substances across membranes against the concentration gradient or potential gradient with the help of membrane proteins and energy provided by cell metabolism.
(1) Primary active transport
A process in which cells directly use the energy generated by metabolism to transport substances against concentration gradients or potential gradients.
The substrates for primary active transport are usually charged ions, so the membrane proteins or carriers that mediate this process are called ion pumps
1. Sodium-potassium pump (sodium pump)
It has ATPase activity itself, and the sodium pump is also called Na-K dependent ATPase.
Under normal circumstances, for every molecule of ATP decomposed, 3 Na can be pumped out and 2 K can be pumped in at the same time. Since this activity of the sodium pump causes a net increase in extracellular positive ions and an increase in potential, the sodium pump is also pumped biosodium pump
Physiological significance:
Causes high intracellular K, which is necessary for many metabolic reactions in the cytoplasm
Maintain intracellular osmotic pressure and cell volume
The Na and K transmembrane concentration gradient formed by the sodium pump activity is the basis for cell electrical activities such as action potential or resting potential.
The electrogenic effect of sodium pump activity can increase the negative value of the potential within the membrane and directly participate in the formation of the resting potential.
The Na transmembrane concentration gradient established by sodium pump activity can provide potential energy reserve for secondary active transport.
2. Calcium pump
3.Proton pump
(2) Secondary active transport
The active transport of certain substances does not come directly from the decomposition of ATP, but uses the concentration gradient of Na or H ions established by the primary active transport mechanism. While Na or H ions diffuse along the concentration gradient, other substances go against the concentration gradient. or potential gradient transport across membranes.
1. Same-way transport
Secondary active transport in which the transported ions or molecules all move in the same direction
For example, glucose absorption in the small intestinal mucosal epithelium and reabsorption in the proximal renal tubule epithelium are achieved through sodium-glucose symporters.
2.Reverse transport
Secondary active transport in which the transported ions or molecules all move in opposite directions
Such as Na -Ca2 exchanger, Na -H exchanger
(3) Membrane vesicle transport
Macromolecules and particulate matter entering and leaving the cell do not directly pass through the cell membrane, but are wrapped by the membrane to form vesicles. The transport is completed through a series of processes such as membrane wrapping, membrane fusion and membrane separation, so it is called membrane vesicle transport.
(1) Coming out of the cell
1. Continuous exocytosis
It refers to the process in which secretory vesicles spontaneously fuse with the cell membrane when cells are quiet, so that macromolecular substances in the vesicles are continuously discharged from the cell.
2. Regulated exocytosis
It refers to the process in which secretory vesicles stored in certain parts of the cell fuse with the cell membrane when cells are induced by certain chemical signals or electrical signals, and the vesicle contents are expelled from the vesicles.
(2) Enter the cell
1.devour
The process by which transported substances enter cells in solid form
2. Swallow and drink
The process by which transported substances enter cells in liquid form
cell signal transduction
cell electrical activity
1. Resting potential (RP)
(1) Measurement and concept of resting potential
The reference electrode is placed in the extracellular fluid, which is grounded to keep it at a zero potential level; the measuring electrode is a glass electrode with an extremely fine tip that can be inserted into the cell without significantly damaging the cell. The membrane potential of various types of cells is negative in the quiet state.
Glossary
polarization
At rest, both sides of the cell membrane are in a stable state of positive outside and negative inside.
hyperpolarization
The state or process of increasing resting potential
depolarization
The state or process of reducing the resting potential
reverse polarization
A state in which the membrane potential becomes positive and the polarity on both sides of the membrane is reversed.
repolarization
The process by which the cell membrane returns to its resting potential after depolarization
(2) The generation mechanism of resting potential
1. The concentration difference and equilibrium potential of ions on both sides of the cell membrane
K efflux is the main reason for the formation of resting potential
The concentration difference of ions on both sides of the cell membrane is the direct driving force for ion diffusion across the membrane.
The transmembrane electric field formed by the diffusion potential has exactly the opposite effect on the movement of charged ions across the membrane than the concentration difference, and will prevent the ions from continuing to diffuse.
When the potential difference driving force increases to be equal to the concentration difference driving force, the electrochemical driving force is zero. At this time, the net diffusion amount of the ion is zero, and the potential difference on both sides of the membrane stabilizes. The net diffusion amount of this ion is The potential difference across the membrane at zero time is called the equilibrium potential of the ion.
Nernst formula
2. Relative permeability of the cell membrane to ions at rest
If the cell membrane is permeable to only one kind of ion in the resting state, the measured resting potential should be equal to the equilibrium potential of the ion; if the cell membrane is permeable to concentrated or multiple ions at the same time in the resting state, the resting potential The magnitude of the potential depends on the relative permeability of these ions and the concentration difference of these ions on both sides of the respective membrane.
The measured value of the resting potential is slightly smaller than the K equilibrium potential.
3. Electrogenic effect of sodium pump
The sodium pump can maintain the concentration difference between Na and K on both sides of the cell membrane through active transport, laying the foundation for the cross-membrane diffusion of Na and K to form the resting potential.
For each molecule of ATP decomposed, the sodium pump can move 3 Na out of the cell and 2 K into the cell at the same time, which is equivalent to moving a net positive charge out of the cell, resulting in an increase in the negative value of the intramembrane potential. (So the sodium pump is also called the electrogenic sodium pump)
4. Factors affecting resting potential levels
① Extracellular fluid K concentration: When the extracellular K concentration increases, the K equilibrium potential decreases, and the resting potential also decreases accordingly.
②The relative permeability of the membrane to Na and K: If the permeability of the membrane to K increases, the resting potential will increase (more towards the equilibrium potential of K); if the permeability of the membrane to Na increases , the resting potential will decrease (more towards the equilibrium potential of Na)
③Sodium pump activity level: When the sodium pump activity is enhanced, its electrogenic effect is enhanced and the membrane becomes hyperpolarized to a certain extent; on the contrary, when the sodium pump activity is inhibited, the resting potential can be reduced.
2. Action potential (AP)
(1) Concept and characteristics of action potential
Action potential refers to a rapid membrane potential fluctuation that can propagate to a distance after cells receive effective stimulation based on the resting potential.
Glossary
spike potential
The ascending and descending branches of the action potential together form a spike-like potential change, which is the main part of the action potential and is regarded as a symbol of the action potential.
back potential
Low-amplitude, slow fluctuations in membrane potential following a spike
afterdepolarization potential (negative afterpotential)
The membrane potential in the first part of the after potential is still less than the resting potential
Afterhyperpolarization potential (positive afterpotential)
The membrane potential in the latter part of the afterpotential is still greater than the resting potential.
Features:
①The “all or nothing” phenomenon
If the stimulation does not reach a certain intensity, the action potential will not be generated (none)
When the stimulation reaches a certain intensity, the amplitude of the action potential generated reaches the maximum value of the action potential of the cell, and will not increase as the stimulation intensity continues to increase (full)
②No attenuation of transmission
The amplitude and waveform of the action potential remain unchanged during propagation
③Pulse delivery
Multiple action potentials generated by continuous stimulation are always separated by a certain interval and will not completely merge.
(2) The generation mechanism of action potential
1. Electro-chemical driving force and its changes
According to the definition of equilibrium potential, when the membrane potential is equal to the equilibrium potential of a certain ion, the electrochemical driving force on this ion is zero. The electrochemical driving force of an ion is equal to the difference between the membrane potential and the equilibrium potential of the ion.
2. Changes in cell permeability during the action potential period
Changes in Na and K permeability can cause depolarization or repolarization
Functional state of ion channels
Resting state: It is a state in which the channel is not open when the membrane potential is maintained at the resting potential level.
Activated state: a state in which voltage-gated sodium channels open immediately when the membrane is rapidly depolarized.
Inactivation state: It is a state in which the channel no longer responds to depolarizing stimuli after the inactivation state.
(3) Triggering of action potential
1. Threshold stimulation
Stimulation refers to changes in the environment in which cells are located, including environmental changes of physical, chemical and biological properties.
The minimum stimulus intensity that can cause a cell to generate an action potential is called the threshold intensity or threshold. A stimulus equivalent to a threshold intensity is a threshold stimulus
Stimuli that are greater or less than the threshold intensity are called suprathreshold or subthreshold stimuli
Three parameters of stimulation amount
intensity of stimulation
duration of stimulation
Stimulation intensity-time change rate
2.Threshold potential
The critical value of the membrane potential that can trigger an action potential is called the threshold potential
(4) Propagation of action potential
myelinated nerve fibers
Jump conduction (fast)
unmyelinated nerve fibers
Non-jump conduction (slow)
State changes after cell excitement
(1) Absolute refractory period
During the initial period of time after excitement occurs, no matter how strong the stimulus is, the cells cannot be excited again.
The threshold is infinite and the excitability is zero.
(2) Relative refractory period
After the absolute refractory period, the excitability of the cells gradually recovers, and excitation can occur after receiving stimulation again, but the stimulation intensity must be greater than the original threshold.
A period in which excitability gradually returns from zero to normal
(3) Supernormal period
After the relative refractory period, the induced cells will also experience a period of mildly increased excitability.
At this time, the membrane potential has not yet fully returned to the resting potential and is close to the threshold potential level.
(4) Low normal period
After the supernormal period, some cells show a slight decrease in excitability.
The membrane potential at this time is in a slightly hyperpolarized state
3. Local potential
1. Concept
After cells are stimulated, changes in membrane potential are caused by the active properties of the membrane, that is, the opening of some ion channels, and cannot propagate to long distances.
2.Characteristics
①Gradual potential
Its amplitude is related to the stimulus intensity
②Attenuating conduction
The local potential spreads to the surroundings in an electrotonic manner
③No refractory period
Reactions can be superimposed and totaled, (superimposed time sum, superimposed space sum)
muscle cell contraction
(1) Shrinkage mechanism
Motor nerve endings transmit nerve impulses from the motor end plate to the sarcolemma
The excitement of the sarcolemma is transmitted to the sarcoplasmic reticulum through the transverse tubules, and a large amount of Ca flows into the sarcoplasm.
Ca binds to troponin, troponin and tropomyosin are allosteric, exposing the binding site on actin and the myosin head knot, and the two quickly combine
The ATPase of the myosin head is activated, ATP is broken down and energy is released, and the myosin head and rod flex, pulling actin toward the M line;
The thin myofilaments slide toward the M line between the thick myofilaments, the bright band narrows, the H band narrows or disappears, the sarcomeres shorten, and the muscle fibers contract.
After the contraction, the Ca in the sarcoplasm is pumped back to the sarcoplasmic reticulum, troponin, etc. return to their original state, and the muscle fibers relax.
(2) Factors affecting striated muscle contraction efficiency
Glossary
Isometric contraction
It shows that when the muscle contracts, the length remains unchanged and only the tension increases.
isotonic contraction
It shows that the tension remains unchanged during muscle contraction and only muscle shortening occurs.
1. Front load
refers to the load that a muscle bears before contracting
Preload determines the length of the muscle before contraction, that is, the initial length
Within a certain range, muscle contraction tension (i.e. active tension) increases with the increase in initial length.
2.Afterload
refers to the load endured by the muscle after contraction
3. Muscle contractility
Muscle contractility refers to the intrinsic characteristics of the muscle that are independent of preload and afterload and affect muscle contraction efficiency.
4. Sum of contractions
The sum of contractions refers to the superimposed characteristics of muscle cell contraction and is the main way for skeletal muscles to quickly adjust their contraction efficiency. The spatial summation form is called multi-fiber summation, and the time summation form is called frequency summation.
Glossary
single contraction
When the action potential frequency is very low, a complete contraction and relaxation process occurs after each action potential.
incomplete tetanic contraction
The latter contraction process is superimposed on the diastolic phase of the previous contraction process, and the resulting contraction sum
full tetanic contraction
The latter contraction process is superimposed on the contraction period of the previous contraction process, and the resulting contraction total
sum of frequencies