W1 L2 (Homeostasis and Neuronal Biology) Flashcards
Homeostasis
The ability of a cell or organism to regulate and control its internal conditions typically using feedback systems
Set point
The state of which the body attempts to return to when there is a change from this given state, ie the desired state
Physiological Range
A steady state or range at which the body operates most efficiently
Why is it that feedback loops are used to oppose change in the set point, but high blood pressure and body weight seem to represent new set points?
There is not a very good understanding as to why pressure and weight are allowed to fluctuate so much. Weight gets out of hand when hormonal systems get out of whack. High blood pressure is accommodated due to the elasticity of vessels, however, this can lead to rupture, plaque builds up, or even wall thickening.
How do you distinguish between a response that is orderly and one that is disorderly?
An orderly response attempts to bring the controlled variable back to the set point ex. (blood pressure). While a disorderly one creates chaos in an attempt to eliminate the factor that is affecting the set point ex. (body gets super hot with a fever to try to make itself inhospitable for the bacteria). If all goes well the fever goes down if not then the disease will persist.
What does it mean that neurons are polarized?
Neurons are physically and chemically polar. The information flows in one direction and they are designed this way. Information is received at the dendrites, integrated at the soma, and travels down the axon to the synaptic terminal where it reaches its target.
Are glial cells connective tissue or nervous tissue? Or are they both, since glial cells support and protect the neurons and are within the nervous system?
They give support to neurons however they are considered nervous tissue and not connective tissue; they are also separate from neurons. Connective tissue typically has extensive extracellular matrix proteins, and many cells such as fibroblasts and chondrocytes.
Anterograde axonal transport
A mechanism where proteins travel from the soma to various parts of the cell in the normal direction of flow
Retrograde axonal transport
A mechanism where proteins travel from parts of the neuron back to the soma in reverse direction of flow
How does anterograde and retrograde axonal transport contribute to the polarization of the neurons?
Anterograde or retrograde axonal transport have to be in place in order to polarize the cell by moving proteins to maintain an electrical difference. Also, moving many proteins to and from the far corners of the neuron is energetically expensive, and represents one of the many reasons why the nervous system needs a constant supply of oxygen and glucose.
Physiology in Latin
Physio=Nature Logica=Study
Why can’t the body’s cells live independently?
The majority of body cells can’t live on their own because they aren’t exposed to the external environment. For example, a muscle cell can’t exchange nutrients externally because it is isolated from the external environment.
Internal environment (ECF)
The body’s aqueous extracellular environment, which consists of the plasma and interstitial fluid and which must be homeostatically maintained for the cells to make life-sustaining exchanges with it
What allows isolated cells to exchange essential nutrients?
The Internal Environment (ECF) which surrounds them
Intracellular fluid
The fluid contained within all of the body’s cells
Extracellular fluid
The fluid outside of the cells and inside the body
What two things are ECF composed of?
Plasma and interstitial fluid
How are is plasma like a train track?
All of the important nutrients that must be used, digested, excreted etc., are put into the plasma by cells and released into the interstitial fluid surrounding the desired location.
What are stem cells and what are the two types?
Cells which can renew themselves through division. Embryonic stem cells have the ability to become many types of cells and adult stem cells which are used for repair can replicate the type that they are.
Explain the relationship between homeostasis, cells, and body systems
Homeostasis is essential for the survival of cells; cells make up body systems; body systems maintain homeostasis.
List the 7 homeostatically maintained components of the internal environment and explain why
- Concentration of oxygen and carbon dioxide- Oxygen is needed for reactions, carbon dioxide must be removed to stop the acidity from rising 2. Concentration of nutrients- Cells need nutrients 3. Concentration of waste products- Accumulation of waste products is toxic 4. Concentration of water, salt, and electrolytes- Cells don’t work when swollen or shriveled 5. Temperature- Too cold and cells slow down, too hot and cells denature 6. pH-Cells only function within a certain pH range as enzymes may denature 7. Volume and pressure- The plasma must be in ideal conditions or transport throughout the cell won’t take place
What are the 3 steps of a homeostatic control system to maintain homeostasis?
- Detection of deviation (Receptor) 2. Integration of this information (Control center) 3. Make adjustments to return to normal (Effector)
Homeostatic control system
A functionally interconnected network of body components operating to maintain the range of a given variable in the internal environment within a certain range
Intrinsic controls
A control mechanism causes a change in the organ itself to regenerate equilibrium. Ex. Relaxing of de-oxygenated muscle leads to increased oxygenated blood flow through certain vessels to this muscle.
Extrinsic controls
Regulatory mechanisms initiated outside an organ that alter the activity of the organ; accomplished by the nervous and endocrine systems. Ex. Nervous system works on heart and vessels to maintain desired blood pressure.
Feedback
Response after a change has been made
Feedforward
Anticipation of a change that is imminent
Negative feedback
A change in a variable triggers a response that opposes the change and returns the variable to the stable set point. Ex. Temperature regulation
Steps of a negative feedback loop
- There is a change in the controlled variable 2. The sensor detects the change from the desired set point or physiological range and sends a signal to the integrator 3. The integrator calls upon an effector to return to the desired state “Know, Compare, Adjust”
Sensor “Security Gaurd”
A cell that detects a given property and records or responds to it
Control Center/Integrator “Boss”
The part of the process that receives information from the sensor and compares it with that of the set point or physiological range. The integrator also calls upon the effector to initiate a return to the set point
Effector “Sniper”
Receives message from the integrator and initiates a change back towards the set point
Thermoregulatory Control
The process by which the body maintains a constant internal temperature. 1. Temperature monitoring nerve-cells in the hypothalamus detect a change from 37 degrees Celsius 2. Temp monitoring cells signal to nerve cells in the control center 3. The control center cells activate heating (sweating) or cooling (shivering) mechanisms to return to the set point 4. The heating or cooling continues until the setpoint is reached at which point the temperature monitoring cells stop the effector
Negative feedback vs Positive feedback respond to stimulus
Neg- The response to the stimulus decreases the stimulus Pos- The response to the stimulus increases the stimulus
Positive feedback
A mechanism where a stimulus and a response in a system increase the output of each other and thus further the system from the equilibrium or stable point. Ex. During child birth contractions increase and oxytocin creates a positive-feedback loop
Heatstroke
A harmful positive feedback loop in which the body’s temperature regulating system has been rendered useless and the body’s temperature continues to rise and damage the control center
3 example of when homeostasis isn’t absolute constancy
- Heart rate changes from beat to beat 2. Body temperature rises as the day gets warmer 3. Our hormones change with each month (women especially) and with age
Feed forward example-Insulin
When a meal is eaten insulin is released which promotes the cellular uptake and storage of nutrients as to not have too many nutrients in the blood (high glucose levels)
2 times when homeostasis has extreme variability
- Weight-eventually hormones get out of whack and weight continues to be gained 2. Blood pressure-The elasticity of the vessels allows for blood pressure to rise to unhealthy levels where permanent damage can be done
Homeostatic imbalance: Diabetes
In a diabetic, the endocrine system has difficulty maintaining the correct blood glucose levels, so diabetics must closely monitor their blood glucose levels
The 3 primary methods of intercellular communication are:
- Gap junctions- Ions/Molecules exchange without ever crossing the ECF 2. Surface markers- Certain proteins on cells allow them to communicate, especially important in destroying foreign invaders 3. Extracellular chemical messengers- Hormones, neurotransmitters, paracrine’s, and neurohormones are released into the ECF and reach the target cell where their message is delivered
Types of intercellular communication
Homeostatic Order
A homeostatic response is a response to the set point changing in an orderly fashion which works back towards the setpoint
Homeostatic Order Example: Standing up too fast
- Stand up too fast
- Blood pressure drops and feel light-headed
- Blood rate increases in response
- Blood pressure is restored
Homeostatic Disorder
A response to a change in the setpoint that brings the controlled variable further from the setpoint
Homeostatic Disorder Example: Fever
- Bacterial Infection or Fever
- Toxins are in body
- Thermogenesis ensues (the process of producing heat)
- Bacteria die
This response moves away from the set point however it is beneficial
Paracrines
The effect is on local cells and they don’t reach the blood stream because they are disabled by local enzymes. They are distributed by diffusion. Ex. Histamine which draws blood with fighting tools to affected areas.
Hormones
Specific long-range messengers secreted into the blood stream by endocrine glands with specific targets. Only sites with receptors are affected by them.
Neurotransmitters
A short range chemical messenger that is released in response to an action potential.
Neurohormones
Released into the blood by neurosecretory neuron into the blood stream to reach a long range target
Signal transduction
The sequence events in which chemical messengers come from the ECF to reach their target in or on a target cell
Lipid soluble molecules such as hormones/steroids pass through the membrane by…
Dissolving through the bilayer and targeting their intracellular receptor
Water soluble molecules such as protein hormones pass through the membrane by __________
They don’t!!!! They bind to surface proteins and have their message relayed to the inside of the cell
The two ways for an extracellular messenger to get its message across is to
- Cross across the membrane by diffusion or opening channels
- Initiating a secondary messenger by binding to a protein on the surface of the cell
Chemically Gated Channels (Voltage-Gated ion channels) in neurons
In the neuron chemically gated channels in the synaptic membrane allow ions to cross and cause an action potential.
Secondary messengers
Chemical messengers that can’t enter the cell bind to surface proteins and have their message relayed through to the desired intracellular protein where the instructions are carried out.
“Fast” synapses
Change the confirmation of an ion gated channel and therefore the permeability and ion fluxes across the membrane.
“Slow” synapses
Have responses mediated by secondary messengers and therefore take longer. Secondary messengers may trigger long-term postsynaptic cellular changes believed to be linked to neuronal growth and development, as well as possibly playing a role in learning and memory.
Neuron
A nerve cell or the fundamental unit of the nervous system. Diverse phenotype and have many functions, shapes, and sizes.
How many neurons are there in the brain?
10^11
Gila Cells
The glue of the nervous system, they surround neurons and provide support for them, they are the most abundant cell type in the nervous system. Non-excitable, no information stored, and don’t process information.Types of glial cells include oligodendrocytes, astrocytes, ependymal cells, Schwann cells, microglia, and satellite cells.
Neuronal membrane
A specialized membrane in nerve cells that is highly excitable and communicate electrically
Oligodendrocytes
A type of Gila cell that forms the insulating myelin sheaths around the axons of the CNS.
Microglia
The brains defense system are phagocytic scavengers
Ependymal Cells
Produce cerebrospinal fluid, line cavities, and are the neural stem cells used to make new neurons and gila cells. Cila on these cells contribute to moving cerebrospinal fluid throughout ventricles in the brain.
Astrocytes
- Star shaped
- Mop up transmitters and extracellular potassium
- Function in support
- Form neural scar tissue
- Take up degraded Gaba and Glutamate limiting the effect of these substances
How can microglia damage neurons?
Microglia when overactive can do damage to neurons by releasing harmful chemicals, this is a factor in many neurodegenerative diseases ex. Alzheimers, Aids, MS, and dementia.
Types of neurons
Why are Gila cells and not neurons common in brain cancers?
Gila cells are mature cells capable of cell division which makes rapid cell division a possibility. Neurons, however, are unable to divide.
Describe the 2 non-neuronal brain cancers
- those that metastasize (spread) to the brain from other sites and
- meningiomas, which originate from the meninges, the protective membranes covering the central nervous system.
What are the 4 ways that the nervous system is protected?
- Enclosure in the bony cranium and the vertebral column
- Protective and nourishing membranes called the meninges
- The brain “floats” in CSF (cerebrospinal fluid)
- A highly selective blood-brain barrier limits access of blood-borne detriments
Explain polarization of a neuron
The cell membrane separates the inside of a cell from the outside, and all chemicals that get into and out of the cell must go through it. The cell membrane of a neuron is polarized meaning that there is an electrical difference across the cell membrane due to these chemicals.
Dendrites
A short branched extension of a nerve cell along which impulses received from other cells at synapses are transmitted to the cell body. They make up most of the cells volume.
Soma
Non processing cell-body of a neuron
Presynaptic vs postsynaptic neuron
A presynaptic neuron is a neuron (nerve cell) that fires the neurotransmitter as a result of an action potential entering its axon terminal. A postsynaptic neuron in a neuron (nerve cell) that receives the neurotransmitter after it has crossed the synapse and may experience an action potential if the neurotransmitter is strong enough.
Axon Hillock (The last stop before the axon)
The last site in the soma where membrane potentials from synaptic inputs are propagated before they are transmitted to the axon.
Axon
The long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells. They can be 100micrometers to 1 meter long.
Synaptic cleft
The space between neurons at a synapse where a nerve impulse is carried across by neurotransmitters.
Myelin Sheath
A concentric membrane insulating the axon
Nodes of Ranvier
Sections of unmyelinated axon
Schwann cell
A glial cell that wraps around the axon and myelinates it (only in the peripheral nervous system)
What cells myelinate axons in the peripheral and central nervous system respectively.
Peripheral=Scwann Cells
Central=Oligos
What is myelinogenesis and what are the four stages?
This is the process of myelin sheath being proliferated on the axon by Schwann cells in the PNS and oligodendrocytes in the CNS, it begins in the embryo.
Stage 1: Axon contact
Stage 2: Glial cell gene production
Stage 3: Axon ensheathment
Stage 4: Maturation
Rapid control pathway vs Slow control pathway
-How they are set up and where they are found
Rapid- A hardwired and fixed pathway where an electrical signal travels down the axon triggering neurotransmitters that go directly to the target cell. This form of a pathway is used for our reflexes and motor control.
Slow- An electric signal triggers neurotransmitters to be released by a gland into the bloodstream where they travel to a far away target cell. Cells that have receptors for the neurotransmitters bind them and those that don’t are unaffected. This form of a pathway is used for far away targets, for targeting a region, and for hormonal regulation.
