M3: Neural and Hormonal Communication Flashcards
What are hydrophilic hormones?
Hydrophillic hormones are chemical messengers that are released from one cell and travels to another cell (local or distant) and binds to a protein receptor on the cell surface, causing a cellular response.
Chemical messengers are hormones that are secreted from one cell and binds to its target cell to cause a molecular change within the cell. Depending on the make up of the hormone, it binds to different areas of the cell.
Describe the difference between hydrophilic vs hydrophobic messengers.
Hydrophilic messengers cannot pass through the phospholipid bilayer of the cell membrane due to its lipophobic proties, so it binds to target cell surface receptors.
Hydrophobic hormones or lipophillic can pass through the plasma membrane and bind to a the lipophilic hormone receptor inside the cell.
Chemical messagers is used to communuicate between cells locally and distally. Once the messenger is secreted, it need to travel to and bind to the target cell. The successful binding of the messenger to the target cells initiate the appropriate molecular response within the target cell.
What is signal transduction?
Is the transmission of molecular signals from the outside of the cell to the inside.
Hydrophillic receptors of the target cell is crucial for receiving the cell signal from the outside and transmitting it into the cell.
What are the 3 types of receptors for hydrophillic messengers?
- Receptors can serve as ion channels
- can function as enzymes
- can function as G-proteins
Within the body, the individual cells that compose all the tissues, organs, and organ systems must work together to maintain homeostasis through the entire organism. This is acheived through intercellular communiation and is particularly important for the primary regulatory systems of the body: the nervous system and the endocrine system.
- What are the methods in which cell communicates with each other?
1. Via gap junctions
2. Through membrane proteins, which provides direct link up of cells. Eg, T-helper cells and macrophages via specialized membrane receptors allow them to communicate with each other.
-
Extracellualar chemical messengers: 4 types
- paracrines: target local cells
- hormones (insulin, glucagon, leptin, ghrelin,…etc…, pituitary, target distant cells)
- neurohormones (hormones from the brain secreted into circulation. Hypothalamic, pituitary, )
- neurotransmitters: secreted from a neuron to influence the reaction of the adjacent neural cell. Eg, aCH
What cause changes in the membrane potential? What initiates an action potential?
The movement of ions across the plasma membrane through protein channels causes changes in membrane potential.
For example,
When ion gates open, specifically the Na+ gated channels and pumps sodium into the cell which “de-polarizes” the membrane. This generates an electrical charge which initiates an action potential
Neurons at rest is polarized, this means that neurons membrane potential at rest is negative. Depolarization is making the membrane of an neuron more positive, toward zero.
True
The two types of membrane potential are
- Graded potentials
- Action potentials
Compare graded and action potentials
In graded potentials, the magnitude (direction and force) of the potential will be in direct proportion to the strength of stimulus. But for Neuronal action potentials, it is an all or nothing response. Once stimulated or threshold is reached, the potential propagates down the axon.
In brief, graded potential vary in size, while action potential is all or nothing response.
Repolarization vs Hyperpolarization
Repolarization - the membrane potential returns to RMP following a period of depolarization . (As the membrane drop back down to negative due to Na+ being pumped out of the cell. The membrane can soon increase in potential)
Hyperpolarization - (-70mV drops to -90) downward deflection, increased in potential)
What 3 factors maintains the RMP?
- the movement of ions across the plasma membrane
- cell membrane more permeable to potassium
- Na+ K+ atpase pump (pumps out 3 Na+ in exchange for 2 K+)
Depolarization
a change in RMP (-70mV) of a excitable cell, where the cell membrane reduces in its potential as Na+ ions flows into the cell making the cell more positive.
List 3 differences between graded and action potentials.
1) Graded potential gradually decrease as it spreads across. It can also be summed, the stronger the stimulus the greater the strength of graded potential.
Action Potentials: it’s an even spread of electrical change throughout the axon. It can not be summed. It’s either an all or nothing response.
2.
- Graded potentials has two types. It could hyper polarize (become more negative) or depolarizes, become more positive.
Action potential involves 3 phases: depolarization, repolarization and hyperpolarization one after the other.
4.
What causes the action potential ?
The action potential is caused by changes in the permeability to both Na+ and K+ The action potential begins when signals from he dendrites and cell body reach the axon hillock and cause the membrane potential there to become more positive, a process called depolarization.
What is the All or Nothing response and what is it caused by?
It is a response in which an action potential is generated as a result of an influx of Na+ into the cell. It is caused by the depolarization of a neuron by graded potentials to a threshold level.
Three phases occurs during an action potential. In the first phase, rapid depolarization occurs. What contributes to this?
An influx of Na+ crosses the cell membrane. This is caused by rapid depolarization is caused by an increase in permeability of the cell membrane to Na+ due to the opening of voltage-gated Na+ channels.
