Karteikarten
Nerve Tissue
Karten in diesem Stapel (102)
- 1What are the two signaling systems used to controls functions of cells that make up the body?1. Endocrine system
-Release of soluble signaling molecules into blood
-Relatively slow
-Diffuse targeting
2. Nervous system
-Rapid and Specific - 2What is a nerve?A bundle of neurons
- 3What is the nervous system?-Trillions of nerves
-Network
>Brain and Spinal cord: Central Nervous System
>Periphery: Peripheral Nervous System (PNS)
-Communicate using both electrical and chemical signals - 4What is the basic unit of nerves?Neuron (nerve cell)
- 5What is the afferent neuron?Sends signal into CNS (affect behaviour) from Peripheral nervous system
- 6What is the Efferent Neuron?Sends signal out of CNS (affects muscle) to Peripheral nervous system
- 7What is an interneuron?Can be inhibitory or excitory- determines if nerve fires
Fires if excitory - 8How are signals passed around from sensory receptor to muscle, gland or neuron?Afferent neuron brings to CNS where interneurons are either excitory or inhibitory. If excitory the nerve fires signal to efferent neuron down to site (muscle or gland)
- 9What is the structure of Neurons?Many sizes and shapes
Cell body (soma) and two types of processes
1. Dendrites
2. Axons - 10What do dendrites do?-Neurons may have as many as 400,000
-Huge surface area
-Large distribution area
-Allows integration of signals from many inputs - 11What are Axons?-Long projection/process -1 micrometer to 1 meter
-Up to 10,000 times longer than the cell body is wide
-Arises from initial segment or axon hillock
(trigger zone that generates electrical signal)
-Signals usually propagate away from cell body along axon - 12What is an Axon Terminal?-Responsible for release of neurotransmitter
(Diffuses across gap to reach target cell, Synapse)
-Some cells have axon varicosities (swellings) - 13How does signal transduction work?-Dendrites must be able to accept information
-Cell body must be able to integrate signals from dendrites
-Axon must be able to conduct electrical signal (action potential)
-Axons that have low resistance have increased efficiency (aka if they have large diameter and are myelinated)
-Axon terminal must contain neurotransmitters (requires axonal transport) - 14What is the structure of myelin?20-200 layers of plasma membranes
- 15What forms myelin on peripheral neuronal axons?Schwann cells
- 16What forms myelin sheathes on central neuronal axons?Oligodendrocytes
- 17Do myelinated neurons conduct action potentials most rapidly?True
- 18How is the Node of Ranvier visible on an axon stained with osmium tetroxide?The myelin sheath is stained while the underlying axon does not take up this stain. Node of Ranvier shown in area of unstained axon
- 19What is axonal transport?-Not electrical signaling
-Kinesin transports secretory vesicles (with protein, lipids ect) from cell body through axon
-Dynein transports recycled membrane vesicle back to cell boxy through axon - 20What is the Synapse?-Anatomically specialised junction between two neurons
-Signal generally transmitted via neurotransmitters
-Primarily between axon terminal of one neuron and a dendrite or cell body of a second neuron
-(sometimes between two dendrites, or a dendrite and a cell body, or two axon terminals) - 21How is communication between two neurons explained?A single neuron postsynaptic to one cell can be presynaptic to another cell
- 22How do synapses work?Pre-synaptic neuron influences metabolic or electrical activity in post-synaptic neuron
-Excitatory or inhibitory synapses
-Electrical synapse- extremely rapid
(cardiac and smooth muscle)
(rare in mammalian nervous system)
-Chemical synapse
The synapse is the point of communication between two neurons that operate sequentially - 23How do nervous systems achieve diversity and flexibility?Diversity in synaptic form
- 24What are glial (glue) cell?-90% of the cells in the CNS
-Account for 50% of CNS volume
-Surround the soma, axon and dendrites of neurons
-Provide physical and metabolic support - 25How is multiple sclerosis work?Immune system convinces itself myelin sheath is foreign
- 26What are some examples of Glial cells?-Oligodendrocytes (Schwann cells in PNS)
-Astrocytes
-Microglia
-Ependymal cells - 27What do Astrocytes do?-Regulates composition of ECF
-Provides glucose, remove ammonia
-Induce formation of tight junctions in blood brain barrier
-Guide neuronal growth and development - 28What do Microglia do?Macrophage-like cell
- 29What do Ependymal cells do?Epithelial-like cells that line fluid filled cavities and produce CSF (cerebral spinal fluid)
- 30How do nerves grow and regenerate?-Complicated and slow
-Stem cell- neuron/glia
-Sends out projections
-Growth cone forms the tip of developing axon
-Axon seeks out effector target
-Peripheral axon re-growth 1mm/day - 31What are excitable cells?Ability to generate and transmit an electrical signal (action potential)
- 32What are excitable tissues?Regions of the body that contribute to transmission of electrical signals
1. Sensory Receptors
2. Neuron Cell bodies
3.Axons
4.Muscles - 33What are Sensory Receptors?-Pressure, Pain, heat, light, sound, smell
-Specialized endings of afferent neurons
-Unfortunate overlap with the definition of a ligand-specific signaling molecule
-Generate signal (receptor potential) that can activate the neuron and thus signal to CNS - 34What are the specific types of mechanosensory stimulation transduced by?Tactile (Meissner's) corpuscle (light touch)
Tactile (Merkle's) corpuscles (touch)
Free nerve ending (pain)
Lamellated (Pacinian) corpuscle (vibration and deep pressure)
Ruffini corpuscle (warmth) - 35What alters activity in a sensory unit?Peripheral events
Communicates information into the CNS - 36What do axons do?-Specialized part of the excitatory neuron
-Conduction of electrical signal
-Polarized communication
(sensory receptor or cell body decide whether to send a signal)
(one end of axon contains the switch)
(the other has the functional effector unit (muscle, gland etc) - 37How do muscles work?-Have ability to contract
-Electrical signal received and converted into mechanical function - 38What does Smooth muscle do?-Peristaltic movement of gut
-Blood vessels and airway diameter
-Subconscious control - 39What does skeletal muscle do?-Attached to bones via tendons
-Conscious and reflex activation - 40What is Resting Membrane Potential?All cells under resting conditions have an electrical potential difference across their plasma membranes
-Inside of cell negatively charged
-Outside positively charged
-By convention extracellular fluid is zero
-70 mV - 41What mV does a paralyzed neuron have?-90 mV
- 42What is Ohm's Law?The effect of voltage (V) and resistance (R) on current (I) is expressed in Ohm's law
I=V/R
If resistance is high, current is low - 43What is a cell membrane lipid according to Ohm's law?Insulator (high resistance)
- 44What is Cytoplasm and extracellular fluid water and ions according to Ohm's law?Conductor (low resistance)
- 45When does electrical force increase?With quantity of charge and with decreasing distance of charge separation
- 46Why do Resting membrane potentials develop?Proteins make a cell function (large molecules that carry charge and cannot cross plasma membrane)
Charged proteins contribute to approx 10mV to membrane potential - 47What is Gibbs-Donnan Effect?Accounts for the effect of charged particles near semi-permeable membranes
-Cations want to get into the cell - 48What Establishes resting membrane potential?Na+/K+ pump establishes concentration gradient generating a small negative potential; pump uses up to 40 percent of the ATP produced by that cell
- 49Where is the Resting Membrane Potential used?-Neuronal Signaling
-Synaptic transmission
-Muscle Contraction
-Pacemaker activity
-Non excitable (secretion and absorption e.g. Insulin secretion)
(Cell to cell signaling) - 50What was predicted by the Nernst Equation?Ion will always seek its equilibrium potential, the membrane potential at which a given ion is in electrochemical equilibrium
- 51How to find equilibrium potential for ion?Potassium channels open, K+ diffuses down concentration gradient. Potential difference established,
Electrical gradient pulls back against K+. Electrochemical gradient pulls back against K+. Electrochemical gradient established. When force of electrical attraction equals that of concentration gradient we have equilibrium potential for that ion - 52What is an electrochemical gradient?Net chemical concentration gradient + net electrical gradient
- 53What is chemical concentration gradient?Is a function of the ratio of the concentration on either side of the membrane
=RTln([Ion] A/[Ion] B - 54What is an electrical gradient?It is proportional to the potential difference across the membrane
=zF (Ea-Eb) - 55How is the equilibrium potential for an Ion calculated using the Nernst equation?There is no net movement of ions when the ions are in electrochemical equilibrium across the membrane
- 56What is Nernst Equation?Vion= -(0.0615V/z)log([Ion] in/[Ion] out)
where z= ion charge - 57Where do action potential occur?In excitable cells, Require voltage gated ion channels
- 58What do graded potentials do?Can occur in all cells
Changes in charge across region of membrane - 59What causes Electrical signals?-Caused by transient changes in membrane potentials
-Essential for nerves to process
-Graded potentials - short distance signaling
-Action potentials- long distance signals of nerve and muscle membranes - 60What is the size of a graded potential proportionate to?The intensity of the stimulus
- 61What is an area of depolarisation?Not the whole plasma that is depolarised (only a small area)
- 62When is a cell polarised?Because its interior is more negative than its exterior
- 63What is overshooting?Refers to the development of a charge reversal (past 0 mV)
- 64When does depolarisation occur?When ion movement reduces the charge imbalance
- 65What is Repolarization?Movement back toward the resting potential
- 66What is hyperpolarization?The development of even more negative charge inside the cell
- 67What happens at an excitatory Synapse?Depolarisation occurring at axon hillock
e.g. Ligand-gated Na+ channel - 68What happens at Inhibitory synapse?Hyperpolarization at axon hillock
E.g. Ligand-gated Cl- channels - 69Graded potentials can be:Excitatory: action potential is more likely
Inhibitory: action potential is less likely - 70What is the size of a graded potential proportional to?size of the stimulus
- 71Do graded potentials decay as they move over distance?True
- 72What are action potentials?All cells capable of conducting graded potentials but only excitable cells can conduct Action Potentials
-Rapid
-All or none
-Large Depolarisation followed by repolarization to RMP - 73What do ligand-gated and Mechanically gated ion channels trigger?Graded potentials
- 74What do voltage-gated ion channels?Allow propagation of an Actional Potential
- 75How do Epileptic seizures occur?Channel has lost control and reaches threshold- muscle contracts
- 76What is the threshold potential?-55mV
- 77What are subthreshold potentials?They are just under the threshold potential (stimulus not high enough to reach threshold and hence be an action potential)
- 78Explain an Action PotentialIt is an all or none sequence of changes in membrane potential resulting from an all-or-none sequence of changes in ion permeability due to the operation of voltage-gated Na+ and K+ channels
1. At resting membrane potential (-70mV)
2.Local membrane brought to threshold voltage by a depolarizing stimulus
3.Current through opening voltage-gated Na+ channels rapidly depolarizes the membrane causing more Na+ channels to open
4.Inactivation of Na+ channels and delayed opening of voltage gated K+ channels halts membrane depolarisation (Absolute Refractory Period)
5.Outward current through open voltage-gated K+ channels repolarizes the membrane back to a negative potential
6.Persistent current through slowly closing voltage-gated K+ channels hyperpolarizes membrane towards potassium equilibrium potential. Na+ channels return to inactivated state to closed state (without opening) (REFRACTORY PERIOD).
7. Closure of voltage gated K+ channels returns the membrane potential to its resting value - 79Neuronal signal is unidirectional?True
- 80What is neuronal signal one way?The propagation of the action potential from the dendritic to the axon-terminal end is typically one-way because the absolute refractory period follows along in the wake of the moving action potential
- 81Why do graded potentials decay as they move over distance?Due to K leak
- 82What is Action Potential Velocity?-Depends upon Axon diameter
- 83When does a cell reach threshold for action potential?Enough sodium channels open to create a positive feedback between voltage and channel opening.
-Between 4s and 0.2s for signal to reach brain
Depends on Insulation
-Myelin prevents current leak so current moves further
-Forces AP to leap from node to node
Speeds propagation due to decreased leak resulting in faster initiation of AP at next node - 84What is Saltatorial Conduction?Action potentials jump from one node to the next as they propagate along a myelinated axon
- 85What is the site of action potential?Active node of Ranvier
- 86What is the NMJ?-Specialist synapse
-Signaling interface between nerve and muscle
-Must allow specific and controlled activation of muscle
(rapid and transient)
-Action potential chemically transmitted across synaptic cleft to activate muscle fibre - 87How is skeletal muscle innervated?Motor neurons
-somatic efferent neurons
-alpha
-gamma (innervate muscle spindle which control tension)
Cell bodies in brainstem or spinal cord
Largest diameter neurons in the body (myelinated)
A single alpha motor neuron innervates many muscle fibres - 88What is a single motor unit?Consists of a motor neuron and all of the muscle fibers it controls
- 89What do two motor units consist of?Intermingled fibers of two motor units
- 90What does the terminal bouton mean?Axon terminal
- 91What does the NMJ structure look like?-Motor neuron axon terminal (bouton)
(rich in acetylcholine filled vesicles)
-Synaptic cleft
-Motor end plate (region of muscle fibre plasma membrane that lies directly under the terminal portion of motor neuron axon terminal (nicotinic Ach receptor)
-Ligand-gated ion channels
-Ionotropic Receptors - 92What is Acetylcholine (ACh)?-Major neurotransmitter in peripheral nervous system and the brain
-Cholinergic neurons
-ACh synthesised from choline and acetyl coenzyme A in the cytoplasm of synaptic terminals
-Upon release binds Ach receptors or is broken down by acetylcholinesterase - 93What are some ACh receptors?Nicotinic
-Ligand gated ion channel
-Permeable to both Na+ and K+
-Important in NMJ and certain regions of the brain
(active reward pathways)
Muscarinic
-G protein coupled
-Blocked by Atropine - 94What is the Cholinergic Afferent Motor Neuron?Ach released from pre-synaptic interneuron
Activates Post-synaptic receptor (nicotinic) - 95What happens at the axon terminal?-Action potential arrives
-Axon terminal rich in voltage-gated Ca2+ channels
-Action potential depolarizes membrane causing voltage-gated Ca 2+ channels to open
-Calcium influx into presynaptic interneuron
-Ca 2+ causes neurotransmitter vesicles to fuse with plasma membrane of presynaptic neuron - 96Where is calcium stored?In sarcoplasmic reticulum
- 97How is the neurotransmitter released?Calcium binds synaptotagmin with SNARES that tether vesicles which causes the vesicles to fuse to plasma membrane and it releases Acetylcholine
- 98How does neuromuscular junction work?It is the point of synaptic contact between the axon terminal of a motor neuron and the muscle fiber it controls. Action potentials in the motor neuron cause acetylcholine release into the neuromuscular junction.
Muscle contraction follows the delivery of acetylcholine to the muscle fiber - 99Neuromuscular junction steps1. The exocytosis of acetylcholine from the axon terminal occurs when the acetylcholine vesicles merge into the membrane covering the terminal
2. On the membrane of the muscle fiber, the receptors for acetylcholine respond to its binding by increasing Na+ entry into the fiber, causing a graded depolarization
3. The graded depolarization typically exceeds threshold for the nearby voltage-gate Na+ and K+ channel, so an action potential occurs on the muscle fiber - 100NMJ motor end plate depolarisation?End plate potential (EPP)
Analogous to EPSP (excitatory post-synaptic potential)
Magnitude of an EPP far exceeds that of EPSP due to large surface area of synapse
Single EPP capable of triggering AP in muscle fiber
AP propagates throughout muscle - 101What are the differences between neuronal synapse vs NMJ?Intraneuronal synapses
-receiver inhibitory and excitatory inputs
-These give IPSPs and EPSPs
-Net effect induces graded potentials
-Multiple EPSPs push membrane potential through threshold to generate AP
NMJs
-All NMJs are excitatory
-Single EPP sufficient to induce AP - 102What is excitation-contraction coupling?Action potential in skeletal muscle fiber lasts 1-2ms - over before any signs of mechanical activity begins
-Action potential induces rapid increase in cytosolic calcium due to release from the sarcoplasmic reticulum
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- University Physiology Karteikarten am Nerve Tissue, erstellt von Adrianna Bialecka am 14/10/2024.
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