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Physo Exam 1
Week 2 Info
| Question | Answer |
|---|---|
| What is the main system for homeostasis? | Nervous system |
| What are the 2 major control systems of the body? | Nervous and endocrine system |
| What does the CNS consist of? | Brain and spinal cord |
| What does the PNS consist of? | Nerves that extend between the CNS and the rest of the body |
| What are glial cells/neuroglia? | Support neurons through physical and metabolic mechanisms (nerve glue) |
| What is the cell body? | Contains the cell nucleus and ribosomes and recieves info from dendrites |
| What are dendrites? | Highly branched outgrowths from the cell body that receive info |
| What happens in dendrite surface area increases? | Increased capacity to recieve signals from many other neurons |
| What is an axon? | A long process that transmits electrical signals |
| The initial segment (axon hillock)... | Is where the vell body connects to the axon |
| What is the trigger zone? | Site where electrical signals that travel away from cell body are generated |
| Where are chemical messengers released to affect neighboring cells? | Axon terminals |
| What are axon collaterals? | Side branches on the main axon that release chemical messages |
| What are axons covered with? | Myelin |
| What is myelin made up of? | Glial cells that wrap around axon |
| What is the purpose of myelin? | To permit efficient signal conduction over long distances |
| What do Schwann cells do? | Make myelin in the PNS |
| What do oligodendrocytes do? | Make myelin in the CNS |
| One oligodendrocyte can wrap... | A small part of many axons |
| What is Nodes of Ranvier? | The axon's plasma membrane is exposed in spaces between adjacent sections of myelin to the extracellular fluid |
| What are Nodes of Ranvier characteristics? | Uninsulated and enriched in ion channels, also participates in rapid conduction of action potential |
| What is axonal transport? | Movement of materials and organelles neccessary for maintenance of neuronal structure and function |
| What is Anterograde transport? | From cell body towards axon terminals via kinesin |
| What is Retrograne transport? | From axon terminal towards cell body via dynein |
| What do afferent neurons do? | Carry toward something |
| What do efferent neurons do? | Carry away from something |
| What are interneurons? | Integrate info between affrent and efferent |
| Afferent neurons transfer info from where to where? | The peripheral tissues and organs to the CNS |
| What is found outside the CNS? | Cell bodies and axons |
| What only enters the CNS? | The terminals of the central process |
| Efferent neurons transfer info out of where to where? | Out of the CNS to muscles, glands, and other neurons |
| What is always in the CNS? | Dendrites and cell body |
| Why do the axons end in peripheral tissues? | So they are where they can cause muscle contraction, secretions, or other effects in the body |
| Interneurons are contained... | Completely within the CNS |
| What is the most abundant type of neuron? | Interneurons |
| How are afferent and efferent neurons organized in the PNS? | Bundled together with blood vessels and connective tissue to form nerves |
| What is a synapse? | Junction between 2 neurons |
| What happens at most synapses? | Signal between neurons is passed by chemicals called neurotransmitters |
| What is a presynaptic neuron? | A neuron that sends signals to the synapse |
| What is a postsynaptic neuron? | A neuron that receives the signals |
| What are the 4 major types of glial cells in the CNS? | 1. Oligodendrocytes 2. Astrocytes 3. Microglia 4. Ependymal cells |
| What are astrocytes? | Star-shaped cells that provide structural and metabolic support for neurons. Also interact with blood vessels to form blood-brain barrier |
| What are microglia? | Small motile cells that provide immune defense |
| What are ependymal cells? | Glia that line fluid-filled cavities within the brain and spinal cord and regulate the flow of cerebrospinal fluid |
| Where does the development of nervous system begin? | Division of precursor/stem cells |
| What is a growth cone? | A specialized enlargement of the top of extending axon |
| What is the function of a growth cone? | Integrates the info conveyed by the receptors to the various guidance signals inducing the changes in the cytoskeleton associated to axon navigation |
| What is neuroplasticitY? | The capacity of the brain to recognize pathways, create new connections, and create new neurons in response to stimulation or injury |
| Can axons only regenerate in the PNS or CNS? | PNS |
| Living cells produce... | Electrochemical gradients and currents across their membranes |
| How are electrochemical gradients produced? | By non-equal distribution of ions in extracellular and intracellular fluids |
| How are currents produced? | By allowing ions to move across membrane |
| What is the resting membrane potential? | When a neuron is not excited |
| How are ECF and ICF measured? | ECF is zero, and ICF is measured relative to that |
| What is the RMP neuron range? | -40 to -90 mV |
| How is the cell charged? | Inside is negative, outside is positive |
| Ions cannot move freely from inside to outside of cell because... | They cannot diffuse across a lipid membrane |
| What barrier separates cell charges? | Hydrophobic membrane |
| What is responsible for maintaining the ionic difference between the ECF and ICF? | Na+/K+ pump |
| Why does the Na+/K+ pump continuously function? | Ions do not remain in place, they are in a constant flux, flowing through open channels |
| What does an active pump do for living cells? | Counteracts the diffusion of ions through membrane channels and maintains the resting membrane channel |
| Does the Na+/K+ pump require energy? | Yes, in the form of ATP |
| What causes the movement of K+ ions across the membrane? | Concentration and charge |
| What is the equilibrium potential? | The membrane potential at which the electrical flux for K+ balances the concentration flux for K+ |
| The greater the ion concentration difference... | The greater the magnitude of membrane potential needed to balance it |
| How do you calculate the equilibrum potential? | E=61/z*log(Co/Ci) |
| What is the calculated equilibrium potential for K+? | -90mV |
| What is the calculated equilibrium potential for Na+? | +60mV |
| K+ and Na+ concentrations in cell | K+ is higher inside cell, Na+ is higher outside cell |
| When is a cell permeable to both K+ and Na+? | At rest |
| Why is K+ permeability 20-100x larger than Na+ permeablility? | Presence of open K+ leak channels |
| What is the Na+ equilibrium potential close to because of K+ leak channels? | Resting moembrane potentials |
| What is membrane potential? | The voltage difference between the inside and outside of a cell |
| What is equilibrium potential (Ex)? | The voltage gradient across a membrane that is equal and opposite to the concentration force affecting a given ion type |
| What is resting membrane potential? | The voltage difference between the inside and outside of a cell in the absence of exitatory or inhibitory simulation |
| What do graded potentials do? | Transmit info across short distances |
| What do action potentials do? | Transmit info over long distances |
| What is an action potential? | A rapid rise and subsequent fall in membrane potential across a cellular membrane with a characteristic pattern |
| What is depolarization? | The membrane potential becomes less negative than the RMP |
| What is overshoot? | The membrane potential becomes positive >0 |
| What is repolarization? | The membrane potential returns to its resting value (RMP) |
| What is hyperpolarization? | The membrane potential becomes more negative than the RMP (less than approx. -70mV) |
| What is local potential? | Where all electrical info is first generated |
| In a very small area of a neuron membrane, if a Na+ channel is opened for a very brief time, what will happen to the membrane potential? | A few Na+ ions will flow into the cell and slightly depolarize the membrane at that site, creating a local potential |
| What does a local potential do when it is formed? | Depolarize adjacent regions |
| How do graded potentials behave? | Decremental; they decrease in magnitude with distance from the stimulus |
| What initiates graded potentials? | Ligand-gated channels |
| What are 2 other names for graded potentials? | Receptor/synaptic potentials |
| What do action potentials require? | Voltage-gated channels |
| 3 major types of cells that can produce action potentials | -Nerve -Muscle -Endocrine |
| What do voltage-gated ion channels do? | Open and close in response to changes in membrane voltage |
| Voltage-gated channels are closed when the cell is... | At RMP |
| Voltage-gated channels are opened when the cell is... | Sufficiently depolarized |
| What is the key to producing neuronal action potentials? | Voltage-gated Na+ and K+ channels |
| How do voltage-gated Na+ channels open? | Very fast |
| How do voltage-gated K+ channels open | Very slow |
| What is the inactivation gate that voltage-gated Na+ channels have? | Structual feature that limits the flux of Na+ after depolarization opens it |
| What are the steps in generating an action potential? | 1. RMP 2. Depolarizing stimulus 3. Rapid depolarization 4. Overshoot 5. Repolarization 6. Afterhyperpolarization 7. RMP |
| What is the approx. Na+ threshold? | -55mV |
| What causes the beginning of an action potential? | Opening of voltage-gated Na+ channels |
| What is positive feedback? | The response is magnified so that it. can occur much faster |
| What is negative feedback? | The response is decreased or inhibited |
| What is a subthreshold stimuli? | Stimuli that are too weak to open the voltage-gated Na+ channels |
| All action potentials occur maximallyy or not at all so they are called... | All-or-none |
| What are local anesthetics? | Drugs that block voltage-gated Na+ channels |
| If all action potentials are the same size, how do nerve cells distinguish between a large stimulus and a small one? | Depends on the number and patterns of action potentials transmitted per unit of time (frequency) |
| During an action potential, a second stimulus, no matter how stong, will not produce a second action potential. Why? | When the voltage-gated Na+ channels are already open, they cannot be opened further |
| What is it when the membrane has reached its maximun in an action potential? | Absolute refractory period |
| Innediately after the absolute refractory period, the membrane enters the relative refractory period when some Na+ channels are still inactivated. During this time, a second AP can occur, but only with a larger-than-threshold stimulus. Why? | Because the membrane is still hyperpolarized |
| Absolue refractory period can be observed when membrane is... | Repolarizing |
| If an action potential comes from the left, why can it only travel to the right? | Because the membrane to the right of the AP is at the RMP and the membrane to the left is in the refractory period |
| Do APs travel faster in larger diameter axons or in smaller diameter axons? | Larger diameter axons because larger axons offer less resistance to current |
| Do APs travel faster in myelinated axons or unmyelinated axons? | Myelinated axons because there is less leakeage of charge across the cell membrane |
| How does an AP occur with myelin present? | In myelinated axons,, the Na+ channels are abundant only in the regions between the melin coating, called the nodes of ranvier. Therefore, APs occur only in these places, and they jump from node to node. |
| What is convergence? | Multiple pre-synaptic neurons joining to one post-synaptic neuron |
| What is divergence? | A single pre-synaptic neuron affecting multiple post-synaptic neurons |
| If the postsynaptic cell membrane is depolarized sufficiently to reach threshold... | An action potential will be generated |
| What are electrical synapses/tight junctions? | The pre-synaptic and post-synaptic membranes are connected by gap junctions, and local currents can flow directly through the connecting channels |
| What are chemical synapses? | Signals are transmitted between 2 neurons by diffusible chemical messenger, and chemical messengers are released from the pre-synaptic terminal |
| What is a synaptic cleft? | A gap at the space where the signal from one neuron to the next is transmitted |
| What are synaptic vesicles? | Compartments that store neurotransmitters |
| What is postsynaptic density? | A region of dense chemical receptors |
| How does signaling at a chemical synapse occur? | 1. Presynaptic action potential reaches axon terminal 2. Depolarization of axon terminal opens voltage-gated Ca2+ channels 3. Ca2+ entry into pre0synaptic terminal |
| Are calcium ions higher or lower inside cell? | Lower inside. 10-fold difference |
| What are SNARE proteins? | Where synaptic vesicles are loosely docked in the active zones via interaction with them |
| The fusion of synaptic vesicles causes... | Release of neurotransmitters into the synaptic cleft |
| The neurotransmitters diffuse across the cleft and... | Bind to receptors on the postsynaptic neuron |
| To stop the chemical action, neurotransmitters can... | 1. Transported back into presynaptic axon terminal 2. Diffuse away 3. Be taken up by neighboring cells 4. Be broken down enzymatically |
| At an excitatory synapse... | The postsynaptic membrane is depolarized, and postsynaptic ion channels are permeable to both Na+ and K+ |
| At an inhibitory synapse... | The postsynaptic membrane is hyperpolarized, and postsynaptic ion channels are permeable to Cl- or K+ |
| What is an excitatory post-synaptic potential (EPSP)? | The potential change in the postsynaptic membrane of an excitatory synapse |
| What is an inhibitory postsynaptic potential (IPSP)? | The potential change in the postsynaptic membrane of an inhibitory synapse |
| What is synaptic integration? | Where the actions of EPSPs and IPSPs converge can be summed |
| What is temporal summation? | Adding together of membrane potential change generated at the same synapse in rapid succession |
| What is spatial summation? | Occurs when synapses at different locations on a neuron fire simultaneously |
| Why is synaptic strength significant? | Synapses have the ability to strengthen or weaken over time in response to increases or decreases in their activity |
| What iis a presynaptic/axonic synapse? | When one axon is affected bu the axon of a second neuron |
| What is presynaptic facilitation? | When activity of neuron A results in increased neurotransmitter release from neuron B |
| What are auto receptors? | Presynaptic receptors that are responsive to neurotransmitter released by the presynaptic terminal itself |
| What are the 4 PREsynaptic mechanisms? | 1. Depolarization-induced Ca2+ influx 2. Presynaptic facilitation and presynaptic inhibition 3. Autoreceptor feedback 4. Neurotransmitter availability |
| What are the 4 POSTsynaptic mechanisms? | 1. Temporal and spatial summation 2. Receptor density 3. Receptor type/subtype 4. Receptor activity |
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saradrake46
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