Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
93 Cards in this Set
- Front
- Back
|
Neurons |
Nerve cells carry electrical signals rapidly and have the ability to carry them over long distances. Most release neurotransmitters |
|
|
Emergent properties |
COMPLEX PROCESSES THAT CANNOT BE PREDICTED FROM WHAT WE KNOW ABOUT THE INDIVIDUAL NERVE CELLS AND CONNECTIONS. ie. consciousness and intelligence |
|
|
What are the 2 parts of the nervous system? |
-Central nervous system: brain and spinal cord -Peripheral nervous system: Sensory/afferent neurons and efferent/motor neurons |
|
|
Afferent neurons |
sensory neurons. Carry sense information such as temperature to the central nervous system. Somatic senses are typically pseudounipolar and myelinated, and smell and vision are bipolar and unmyelinated. |
|
|
efferent neurons |
motor neurons. Branches are typically divided many times and are known as collaterals. The axon branches have enlarged endings known as axon terminals, and many have enlarged regions along the axon known as varicosities for the release of neurotransmitter. |
|
|
What pathway does information flow follow? |
Stimulus to sensor to input signal to integrating center to output signal to target to response. |
|
|
What can efferent neurons be divided into? |
-Somatic motor neurons: control the skeletal muscle by voluntary control -Autonomic neurons: Control smooth and cardiac muscle, exocrine glands, some endocrine glands, and some types of adipose tissue. |
|
|
Autonomic division |
Also called the visceral nervous system. Controls contraction and secretion of internal organs. Can be further divided into: Sympathetic (fight or flight) and parasympathetic (rest and digest) branches |
|
|
Enteric nervous system |
Network of neurons in walls of the digestive tract. Frequently controlled autonomically and can also function autonomously. |
|
|
What are the main type of nervous system cells? |
-Neurons: basic signalling units. Functional unit -Glia: Support cells. Out number neurons by 5:1 |
|
|
How are neurons built? |
Nerve cell. Have Dendrites (receive the incoming signal) and axons (carry outgoing information) |
|
|
Multipolar neuron |
Many axons and dendrites. CNS and efferent multipolar cells look different |
|
|
Pseudounipolar neuron |
The cell body is located off to one side pf a single axon. Typically in the somatic sensory division. |
|
|
bipolar neuron |
single axon and single dendrite off the cell body. Mainly for smell and vision |
|
|
Anaxonic neuron |
lack identifiable axon, but have numerous branched dendrites. |
|
|
Interneurons |
Lie within the CNS. Variety of forms with complex branching processes that allows communication with many neurons. |
|
|
Collaterals |
Branches off of efferent neurons |
|
|
Axon terminals |
enlarged endings for neurotransmitter release |
|
|
Cell body |
Control center with nucleus and organelles to direct cell activity. Most neurons have this, and the cell body takes up 1/10 of the total volume of the cell. This part is essential because it contains the DNA. |
|
|
Dendrites |
Incoming information is received. They increase the surface area of the neurons allowing communication with multiple neurons.
|
|
|
Dendrite spines |
Increase the surface area and in the brain, they can make their own proteins. They can change size and shape in response to input such as from learning, memory, and pathologies. |
|
|
Axons |
Carry outgoing signalls. Most peripheral neurons have the axon extending from the axon hillock. Often branch to form collaterals. Each collateral ends in an axon terminal containing mitochondria and membrane bound vesicles filled with neurocrine molecules. At the end of an axon in the peripheral, chemical messengers are released. In the CNS, electrical signals are continuous because there are only gap junctions between them. |
|
|
Axonal transport |
Proteins packaged in cell body of the endoplasmic reticulum and are moved down the axon. |
|
|
slow axonal transport |
Moves material via axoplasmic or cytoplasmic flow. This is only for components not rapidly consumed by the cell itself. |
|
|
Fast axonal transport |
Moves ~400mm/day. Uses stationary microtubules as tracks along which transported vesicles and the mitochondria "walk" with the help of foot like motor proteins binding and unbinding with the help of ATP. Can go in 2 directions: anterograde (cell body to axon terminal) or retrograde (axon terminal to cell body) |
|
|
Synapse |
Where an axon terminal meets the target cell. Where presynaptic and postsynaptic cells communicate. Can be classified as either electrical or chemical depending on the type of signal that is passed |
|
|
Presynaptic cell |
The neuron delivering the signal |
|
|
Postsynaptic Cell |
Receives signal |
|
|
Synaptic cleft |
Narrow space between the presynaptic and the postsynaptic cell. Has a matrix with fibers to hold it in place. Most are chemical The CNS contains electrical, connected by gap junctions, and are bidirectional. These are also faster than chemical synapses |
|
|
Growth cones |
Special tips that embryonic nerve cells have that allows them to find the correct location connect with. |
|
|
What does the survival of the neuronal pathways depend on? |
The neurotrophic factors secreted by the glial cells. It helps to maintain neurons and guide them during repair and development. |
|
|
Glial cells |
10-50x more than neurons. These communicate with neurons and provide biochemical support. These all respond to neurotransmitters and neuromodulators. The peripheral NS has 2 types and the CNS has 4 types -PNS: Schwann cells, and satellite cells -CNS: Astrocytes, microglia, ependymal cells, and oligodendrocytes. |
|
|
Damaged neurons |
-Damage to a cell body results in cell death -If axon is severed, there are steps for repair: 1) Axon cytoplasm leaks out at the injury site until membrane is sealed 2) Segment of the axon still attached to the cell body swells as organelles and filaments brought in by axonal transport accumulate 3) Schwann cells near an injury site send out chemical signals to tell the cell body injury has occurred. 4) The distal segment transmission ceases and slowly begins to collapse because it is deprived of a protein source. The myelin begins to unravel. 5) Scavenger microglia and phagocytes ingest debris. This can take 1 or more months. -This is not likely to occur in the CNS, only the peripheral nervous system |
|
|
What are excitable tissues? |
Nerve and muscle tissue |
|
|
What are factors influencing membrane potential? |
-Uneven distribution of ions -Differing membrane permeabilities to those ions (ie. the resting membrane potential for potassium is greater than when there is an action potential) |
|
|
Nernst equation |
Describes membrane potential that would result if membrane was permeable to only one ion -potassium: Ek - -90 mV -The actual resting membrane potential (-70 mV) is more positive than Ek because of the sodium leaks. |
|
|
Goldman-Hodgkin-Katz (GHK) Equation |
Predicts membrane potential using multiple ions. Mainly assumes Na, K, and Cl for mammalian cells. |
|
|
How does ion movement create signals? |
-Changes the membrane potential 1) Resting membrane potential (-70 mV) 2) Depolarization occurs because there is an influx of Na 3) Repolarization occurs (ie Na-K ATPase pumps 3Na out and 2K in) 4) Hyperpolarization (membrane potential becomes more negative than the resting membrane potential because step 3 continues) 5) Resting membrane potential is restored (sodium leak channels) |
|
|
What are the 4 major types of selective ion channels in the neuron? |
-Na channels -K channels (large role in resting membrane potential) -Ca channels -Cl channels -There are also less selective channels such as monovalent cation channels, which can allow both Na and K to pass through. |
|
|
Conductance |
The ease which ions can flow through a channel. Varies with gating state and channel protein isoform. Larger neurons allow for faster (because of the decrease in resistance due to the larger diameter) Faster in myelinated neurons |
|
|
What are the 3 categories of gated ion channels? |
-Mechanically gated: Sensory neurons. Open to physical forces -Chemically gated: Most neurons. Respond to a variety of ligands (such as neurotransmitters or modulators) -Voltage gated: Respond to changes in membrane potential. Na and K voltage gated channels are very important for initiation and conduction of electrical signals along the axon. |
|
|
Mechanically gated channels |
Sensory neurons. Open to physical forces |
|
|
Chemically gated channels |
Most neurons. Respond to a variety of ligands (such as neurotransmitters or modulators) |
|
|
Voltage gated channels |
Respond to changes in membrane potential. Na and K voltage gated channels are very important for initiation and conduction of electrical signals along the axon. |
|
|
Activation |
Channel opening, the speed can vary. -Some channels can spontaneously inactivate. Like an elevator door with a button to close, it will close sooner or later regardless of whether you are standing in the elevator or not |
|
|
Current |
flow of electrical charge carried by an ion. The direction depends on the electrochemical gradient -The net flow will hyperpolarize or depolarize the cell -Potassium usually flows out, while sodium, chlorine and calcium ions usually flow in. |
|
|
Ohm's Law |
The current flow is proportional to electrical potential differenct (in Volts) between 2 points and inversely proportional to the resistance of the system for current flow I = V/R |
|
|
Resistance |
Force that opposes flow. Comes from 2 places: -Resistance of the cell membrane (Rm) - Internal resistance of the cytoplasm (Ri) The membrane is typically a good insulator, if there are no open ion channels than there is a high R and a low conductance Composition of the cytoplasm and the diameter of the cell will influence the internal resistance (Ri decreases as the diameter increases) |
|
|
Graded potentials |
Variable strength signals that travel over short distances and lose strength as they travel through the cell. Short distance communication. If they are strong enough, at the integrating center, they can initiate an ACTION POTENTIAL. -Depolarize or hyperpolarize in the dendrites or the cell body (less frequent near axon terminals) - Graded because of the amplitude is proportional to the strength of the triggering event -CNS and efferent neurons have this happen when chemical signals from other neurons open chemically gated ion channels - Afferent neurons have mechanical or chemical signals to open the ion channels -Can also occur if channels close, ie if potassium leak channels close than there is a depolarization of the cell (because of the decrease in potassium leaving the cell). -Can be summed |
|
|
Action potential |
Very brief, large depolarizations that travel long distances through the neuron without losing strength. Uniform strength from the trigger zone Voltage gated ion channels open as electrical current passes down the axon allowing additional Na to enter the cell, further depolarizing the axon. This makes sure that it does not lose strength while moving down the axon. This increases the membrane potential by ~100 mV All or none phenomenon Typically leads to a domino effect of another action potential along the axon. |
|
|
local current flow |
When an ion enters a cell it's charge spreads out like a wave from point of entry. Wave of depolarization (since current is the net movement of the +ve electrical charges.) |
|
|
Why do graded potential lose their strength as they travel through the cytoplasm? |
- Current leaks: positive ions can leak out of the cell body, decreasing current and the strength of the signal. -Cytoplasmic resistance |
|
|
Trigger zone |
The area that strong enough graded potentials reach. This is the integrating center of the neuron and has high concentrations of voltage gated sodium channels. In efferent neurons and interneurons this is the axon hillock and the the first part of the axon (initial segment). For sensory neurons it is where the dendrites join the axon. |
|
|
Threshold voltage |
The voltage that a graded potential must meet in order to initiate an action potential. If it is not reached than the graded potential dies out and no action potential is produced typical mammalian neuron cells: -55 mV Muscle cells : ~-75 mV |
|
|
Depolarizing graded potentials |
excitatory, the ability of a neuron to respond to a stimulus and fire an action potential. |
|
|
hyperpolarizing graded potential |
inhibitory, produces no response to the weak stimulus (far away from the threshold) |
|
|
Steps of an action potential |
1) Resting membrane potential (-70 mV) 2) Depolarizing stimulus, the graded potential reaches the trigger zone. Sodium channel activation gates open causing an influx of sodium ions 3)Membrane depolarizes to the threshold (-55 mV). Voltage gated Na and K channels begin to open 4) Rapid Na entry further depolarizes the cell as the action potential moves along the axon (reaches ~ 30 mV) 5) Once positive, the electrical driving force for Na disappears because the sodium channel inactivation gates close, but sodium continues into the cell via the Na concentration gradient (slow), and voltage gated K channels open as Na channels begin to close causing an efflux of K ions 6) The electrical gradient for the K favors the outflux of K. As it moves out of the cell, membrane potential becomes -ve rapidly 7) Once -70 mV is reached (RMP), the membrane is still permeable to K from voltage gates and leak channels, thus the membrane hyperpolarizes to almost -90 mV 8) Voltage gated K channels close, less K leaks out of the cell. The sodium activation gates close and the inactivation gates open 9: The retention of K and the leak of Na brings the axon back to RMP and resting ion permeability (-70 mV) |
|
|
How many gates do sodium channels have? |
Two gates! The activation gate (within the channel) and the inactivation gate (ball and chain). This process only allows unilateral conduction. -RMP: activation gate is closed and inactivation gate is open -Depolarization: Activation swings open and inactivation is still open, thus the channel is completely open and this begins positive feedback to open more Na channels. - Depolarization after ~0.5 ms: Activation is open and inactivation closes to stop the positive feedback loop. -Repolarization: Activation is closed and inactivation is open |
|
|
Refractory period |
Time it takes before another action potential can be fired (1-2 ms). This limits the rate signals can be transmitted and ensures 1-way travel |
|
|
Absolute refractory period |
time required for the sodium channel gates to reset to resting positions |
|
|
Relative refractory period |
Follows the absolute refractory period. Some sodium channels have reset (while some are still open) and the potassium channels are still open. All of the sodium channels can reopen by a stronger than normal graded potential. The threshold is closer to 0 mV |
|
|
Myelination |
Increases speed of conduction by minimizing the current leak, and the amount that the axon is in contact with the ECF Nodes of ranvier are unmyelinated junctions on myelinated neurons. Conduction only happens at nodes. Saltatory conduction is the conduction down a myelinated neuron. It looks like it is jumping down the neuron on the nodes. |
|
|
Nodes of ranvier |
Are unmyelinated junctions on myelinated neurons. Conduction only happens at nodes. |
|
|
Saltatory conduction |
Is the conduction down a myelinated neuron. It looks like it is jumping down the neuron on the nodes of ranvier. |
|
|
Hyperkalemia |
The increase in the concentration of potassium in the blood shifts the membrane potential closer to the threshold and causes action potentials to be fired by smaller graded potentials that usually would not cause action potentials. |
|
|
Hypokalemia |
The decrease in the concentration of potassium in the blood. This hyperpolarizes neurons. Normal graded potentials are not strong enough to start an action potential. This shows up as muscle weakness |
|
|
What does cell to cell communication in the nervous system depend on? |
1) Signal molecules secreted by the neuron 2) Target cell receptors for chemicals 3) Anatomical connections between neurons and targets (synapses) |
|
|
Electrical synapses |
-Pass an electrical signal directly from the cytoplasm of one cell to another through the pores of gap junction proteins. Can flow in either direction except for in rectifying synapses, which can only flow in 1 direction. -These are mainly in the CNS, and in glia, cardiac, smooth muscle, and non-excitable cells using electrical signals. -Advantage: Rapid bidirectional conductions to synchronize the cell activity |
|
|
Chemical synapses |
Most synapses found in the body. These use neurocrine molecules to carry information from one cell to the next cell. The electrical signal is converted into neurocrine signals that cross the synaptic cleft and bind to a receptor on the postsynaptic target cell membrane. |
|
|
What types of chemical signals are there? |
-Neurotransmitters: Act at the synapse and elicit a rapid response. All have a specific receptor type to bind to, except for nitric oxide. -Neuromodulators: Act at both the synaptic and the non synaptic sites and are slower acting -Neurohormones: Secreted into the blood to act on distant targets. |
|
|
Neurocrine receptors |
2 types on chemical synapses: -Receptor channels: ionotropic receptors. mediate rapid responses by altering ion flow. Some are very specific, some are not. -GPCR: Metabotropic receptors. Slower responses because of the second messenger system. Some regulate the open/closing of ion channels. |
|
|
Neurocrine molecules |
7 classes: Acetylecholine, amines, amino acids, peptides, purines, gases, and lipids. |
|
|
Acetylcholine |
-Neurocrine molecule -Neurons that secrete this are cholinergic. -2 main subtypes: Nicotinic (Excitatory) and Muscarinic (excitatory or inhibitory) -Nicotinic are monovalent cation channels for Na and K. Na depolarizes and it increases the chance of an action potential being fired. Bot Na and K move along their electrochemical gradients (K out and Na in), but there is more Na being moved because it has a larger gradient. -Muscarinic are GPCR in the CNS and the parasympathetic. The response varies depending on the receptor type. |
|
|
Amines |
-Neurocrine molecules -Active in the CNS, are derived from single amino acids -Serotonin is made from tryptophan -Histamine: made from histidine -Dopamine, norepinephrine, and epinephrine: made from amino acid tyrosine. Norepi is the major neurotransmitter of the PNS sympathetic division. All can also function as neurohormones -Noradrenergic neurons: Secrete norepi. Two classes, alpha and beta, both are linked to G proteins, but work with different second messenger systems. |
|
|
Amino acids |
-neurocrine molecule -several in the CNS -Glutamate: Primary excitatory neurotransmitter of the CNS -Asparate: excitatory neurotransmitter in selected regions of the brain -Gamma-aminobutyric acid (GABA): Main inhibitory neurotransmitter in the brain. Hyperpolarizes by opening Cl channels so Cl can enter the cell. -AMPA receptors: ligand gated monovalent cation channels similar to nicotinic acetylcholine channels. Glutamate binding opens, and depolarization occurs from the Na influx -NMDA receptors: Non selective cation channels that let Na, K, and Ca pass. Opening requires glutamate and change in membrane potential |
|
|
Peptides |
-neurocrine molecule -There are a variety secreted by the NS -ie Substance P: pain pathways -Opioid peptides: enkephalins and endorphins mediate pain relief. -Function as both neurotransmitters and neuromodulators: cholecystokinin (CCK), Vassopressen (AVP), and atrial natriuretic peptide (ANP). -Many peptide neurotransmitters are cosecreted with other neurotransmitters |
|
|
purines |
-Neurocrine molecule -Adenosine, adenosine monophosphate (AMP), and adenosine triphosphate (ATP) can all act as neurotransmitters. -Bind to purinergic receptors in the CNS and other excitable tissues like the heart. |
|
|
How are neurotransmitters released? |
-From synaptic vesicles, released on demand. Some are on the membrane waiting while others are within the presynaptic cell (which also contain mitochondria to make ATP for metabolism and transport). |
|
|
Steps in Neurotransmitter release |
1) An action potential depolarizes the axon terminal 2) Depolarization opens voltage gated Ca channels and Ca enters the cell 3) Ca entry triggers exocytosis of synaptic vesicle contents 4) neurotransmitter diffuses across synaptic cleft and binds with receptors on the postsynaptic cell 5) neurotransmitter binding initiates a response in the postsynaptic cell. |
|
|
What are different methods of neurotransmitter termination |
1) The neurotransmitter can be returned to axon terminals for reuse or transported into glial cells. 2) Enzymes can inactivate the neurotransmitters (ie. acetylcholinesterase breaks down acetylcholine) 3) Neurotransmitters can diffuse out of synaptic clefts |
|
|
Steps for synthesis and recycling of acetylcholine |
1) ACh is made from choline and acetyl CoA 2) In the synaptic cleft, ACh is rapidly broken down by enzyme acetylcholinesterase 3) Choline is transported back into the axon terminal by cotransport with sodium 4)Recycled choline is used to make more ACh. |
|
|
Do stronger stimuli release more or less neurotransmitter? |
More because the release of neurotransmitter is tonically active. |
|
|
Divergence |
When an axon and a presynaptic neuron branches and the collaterals diverfe and synapse on multiple target neurons/cells |
|
|
Convergence |
When a group of presynaptic neurons provide input for a less postsynaptic neurons than the group of presynaptic neurons. |
|
|
Synaptic plasticity |
The ability of the nervous system to change activity at the synapses. This is short term and can facilitate or depress the activity |
|
|
Slow synaptic potentials |
-G protein couple receptors reacting to the binding of neurotransmitter. 2nd messenger system results in opening/closing of ion channels, leading to a change in membrane potential. -This lasts longer than if a neurotransmitter directly opened the channels (second to minutes) -Can also modify proteins or regulate production of new proteins -Growth and development of neurons and mechanisms of long term memory |
|
|
Fast synaptic potentials |
Associated with the opening of ion channels. This begins quickly and only lasts milliseconds The neurotransmitter opens on the postsynaptic membrane allowing ions to move between the ECF and the postsynaptic cell. |
|
|
Excitatory postsynaptic potential (EPSP) |
Depolarizing synaptic potential. Makes cells more likely to fire action potentials. |
|
|
Inhibitory postsynaptic potential |
IPSP. Hyperpolarizing synaptic potential. This makes the cell less likely to fire an action potential. |
|
|
Spatial summation |
Several nearly simultaneous graded potentials, where graded potentials occur from different locations. Not always excitatory, if it is inhibitory, then it is called postsynaptic inhibition. This occurs when presynaptic neurons release inhibitory neurotransmitters. |
|
|
Temporal summation |
When 2 subthreshold graded potentials from the same presynaptic neuron are summed because they arrive at the trigger zone close enough together in time. |
|
|
Presynaptic facilitation |
Input from the excitatory neuron increases the neurotransmitter release by the presynaptic cell |
|
|
Presynaptic inhibition |
Modulation decreases neurotransmitter release. Can be global or selective. -Global: decrease for all the dendrites/axons, so all the target cells are effected -Selective: one collateral is inhibited, but the rest remain normal. |
