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69 Cards in this Set
- Front
- Back
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Sensory Neurons
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Transport nerve signals to spinal cord and brain.
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Synaptic Delay
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Time required to generate Action Potential in postsynaptic cell from presynaptic cell stimulation. .3 to .5 ms.
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Synaptic Fatigue
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Can occur when stimulus rates exceed the ability to recycle and deliver Ach to the synaptic bulb.
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What happens when to synaptic transmission when a neurotoxin blocks the release of Ach from synaptic terminals?
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Stop fusion of vesicles.
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What happens when a toxin such as a spider bite, increase neurotransmitter release?
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Synapse is constantly firing , huge spikes resulting in synaptic fatigue.
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In nerve toxin gases, acetylcholinesterase inhibitors cause what to happen at a neuromuscular junctions?
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Tense up, not able to release anymore.
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Conduction speed of Large, myelinated fibers
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up to 120 m/s
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Conduction speed of Small, myelinated fibers
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3 to 15 m/s
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Conduction speed of small unmyelinated fibers
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0.5 to 2.0 m/s
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Speed at which nerve signal travels along nerve fiber depends on two factors:
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Diameter of fiber
Presence or absence of myelin |
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Actions Potentials started by
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Receptor (chemically) gated
Voltage gated channels |
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Multipolar Neurons
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One axon, multiple dendrites
Most common Includes most neurons of the brain and spinal cord. |
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Bipolar Neurons
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One axon, one dendrite
Olfactory cells of the nasal cavity, certain neurons of the retina, sensory neurons of the inner ear |
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Unipolar Neurons
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Single process leading away from soma, branches like a T.
Pseudonunipolar Carry sensory signals to the spinal cord. |
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Anaxonic Neurons
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Multiple dendrites, no axon.
Do not produce action potentials, communicate through dendrites. Some found in brain, retina, and adrenal medulla. |
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Somatic Sensory Division (PNS)
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Carries signals from receptors in the skin, muscles, bones, and joints.
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Visceral Sensory Division (PNS)
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Carries signals mainly from the viscera of the thoracic and abdominal cavitities, such as the heart, lungs, stomach, and urinary bladder.
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Somatic Motor Division (PNS)
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Carries signal to the skeletal muscles. Produces muscular contractions that are under voluntary control as well as involuntary contractions called Somatic reflexes.
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Visceral Motor Division - Autonomic Nervous System
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Carries signal to glands, cardiac muscle, and smooth muscle. Usually no control over effectors, operates at unconscious level. Visceral reflexes.
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Sympathetic Division
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Visceral Motor Division
Arouse the body for action Ex accelerating heartbeat, increasing respiration, inhibiting digestion. |
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Parasympathetic Division
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Visceral Motor Division
Calming effect. Ex slowing heartbeat, stimulates digestion. |
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Temporal Summation
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1. Intense stimulation by one presynaptic neuron.
2. EPSPs spread from one synapse to trigger zone. 3. Postsynaptic neuron fires. |
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Spatial Summation
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1. Simultaneous stimulation by several presynaptic neurons.
2. EPSPs spread from several synapses o trigger zone. 3. Postsynaptic neuron fires. |
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Ligand Binding
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Chemical
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Action Potential - At Threshold
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Sodium channels open very quickly.
-55 mV Sodium inflow is greater than at any other time. |
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Action Potential - Repolarizing
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Potassium (K) voltage gated channels open
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Potassium (K+) Potential
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-90 mV
Resting membrane is more permeable to K+ than any other ion. |
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Sodium (Na+) Potential
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66+ mV
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Na+K+ pump
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Accounts for 70% of the energy requirement of the nervous system. (ATP)
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ATP
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Adenosine triphosphate, coenzyme used as an energy carrier in the cells of all known organisms.
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Ependymal Cells (CNS)
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Non-typical cuboidal to columnar epithelial cells lining the open spaces in the spinal cord and brain (central canal and ventricles).
Secrete cerebrospinal fluid (CSF) CSF provides cushioning and transport of dissolved gases, wastes, and nutrients Some have cilia to aid in circulation of CSF |
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Astrocytes (CNS)
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Most numerous glial cells
a) Maintain the blood-brain barrier. Astrocyte pseudopodia attach to brain capillaries and regulate their permeability b) Provide structural integrity for CNS c) Make structural repairs following injury d) Direct growth and connections of neurons during development e) Homeostatic mechanisms to regulate interstitial fluid levels of sodium, potassium, CO2, O2, nutrients as well as regulating blood flow and recycling neurotransmitters. |
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Oligodendrocytes (CNS)
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Contact neurons at axons and cell bodies
a) At cell bodies function is unknown b) Oligodendritic processes form sheets of axolemma which wrap around axons forming myelin sheaths (myelination) Myelination results in white matter. Areas wrapped are called internodes while small spaces between myelin are nodes of Ranvier. |
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Microglia (CNS)
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Wandering cells which engulf debris and pathogens much like some white blood cells
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Integral
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Belonging as a part of the whole.
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Diffuse
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To spread about or scatter; disseminate. (perfume)
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Propagate
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To cause to move in some direction or through a medium; transmit. (a wave, for example)
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Gradient
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A series of progressively increasing or decreasing differences in a property.
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Transmembrane potential
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Is the separation of electrical charges across a membrane.
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Chemical gradients
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Imbalance of ions across the cell membrane
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Electrical gradients
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Since potassium leaks out of the cell faster than sodium leaks in, the inside of the membrane becomes negatively charged (proteins left behind) while the outside gains positive charge.
The separation of charge across a resistance to charge movement (the membrane) results in a potential difference |
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Electrochemical Gradient
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Sum of the chemical and electrical gradients for a particular ion.
a) They may oppose or reinforce each other. b) Small changes in membrane permeability will result in a large movement of ions down their electrochemical gradients |
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Why is the transmembrane potential important?
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A: Changes in membrane permeability and resultant changes in potential are essential to both axonal transmission of impulses and synaptic transmission of impulses.
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Receptor (chemically) gated channels
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Associated with a membrane receptor. Open and close in response to binding of that receptor. Ex. Ach receptor. Usually occur where synapses occur (dendrites and soma).
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Voltage gated channels
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Open or close in response to changes in membrane potential. Occur on excitable membranes such as axons and the sarcolemma of skeletal and cardiac muscle cells.
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Mechanically gated channels
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Open and close in response to distortion of the cell membrane. Found in touch, pressure and vibration sensors.
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Purpose of graded potentials:
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To inhibit or stimulate action potentials.
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Trigger zone voltage regulated gate
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350 to 500 gates per μm2
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Soma voltage regulated gates
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50 to 75 gates per μm2
Cannot generate an action potential |
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Continuous Propagation—unmyelinated axons
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movement down axon
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Type A Fibers
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Largest myelinated axons. Fastest propagation = 140m/s = 300mph!!!
Carry sensory on position, balance, delicate touch, pressure to CNS; motor neurons going to skeletal muscles |
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Type B fibers
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Smaller myelinated axons. 18m/s = 40mph
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Type C fibers
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Small unmyelinated axons (continuous propagation). 1m/s = 2mph
Motor neurons for smooth muscle, cardiac muscle, glands |
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What happens if you block sodium potentials?
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Blocks sodium channels—therefore blocks action potential generation and propagation in motor neurons. Depending upon concentration of toxin…respiratory paralysis.
Puffer fish toxin |
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What happens if you block Ach?
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No synaptic transmission of impulses….depending upon concentration of toxin…muscular paralysis---respiratory failure…dead. Botulinium toxin is another neurotoxin which blocks the release of Ach from synaptic terminals.
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What happens if you encounter pesticide with acetylcholinesterase inhibitors?
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Most pesticides are acetylcholinesterase inhibitors as well as military nerve gases. Cause acetycholine buildup in the synapse and extended postsynaptic stimulation. At neuromuscular junctions this causes extreme (and permanent) muscular contractions…resp. failure.
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Role of the Na-K pump
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A single action potential does not change the concentrations of Na+ or K+ inside and outside the cell. A relatively insignificant amount of ions move across the membrane. However, at maximum stimulation a neuron can generate 1000 APs per second which can over time deplete chemical gradients if they were not restored by active transport.
One ATP molecule is used to move 3 Na out and 2 K in. (ATP>>ADP) |
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Chloride (Cl-) potential
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-70 mV
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Chloride channels
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1) Inhibitors of EPSPs may open K+ channels (tending to hyperpolarization) or open Cl- channels.
2) Cl- is high outside the cell and would tend to come in, however, Cl- has an equilibrium potential of –70mV. Thus no movement at resting potential. 3) When an EPSP arrives and tends to depolarize the membrane a driving force is created for Cl- to move into the cell (electrical gradient changes), thus countering Na+ entry. More Na+ must enter to counteract the influx of Cl-. |
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When does myelination occur?
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Not completed until early adolescence; variation in physical abilities of children the same age
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Multiple sclerosis
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Caused by patchy loss of myelin in brain and spinal cord
Spasms, weakness in limbs, bladder dysfunction, sensory loss, visual disturbances Slows action potentials, Na+ spreads out at nodes and is not transferred efficiently |
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Synaptic transmission
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1) Electrical (direct cell-cell contact)
2) Chemical (neurotransmitter ) |
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Electrical synapses
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Found in both CNS and PNS and involve actual connections between pre and postsynaptic cells by a membrane protein called connexon) and via gap junctions. Local current can pass from one cell to another. Bi-directional
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Chemical synapses
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Very common.
a) Unidirectional transmission of impulse b) Response of postsynaptic membrane may be either depolarization or hyperpolarization depending upon the nature of the receptor (not the neurotransmitter; Ach may depol or hyperpol depending upon the receptor) |
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Cholinergic synapses
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—synapses where Ach is released.
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Neuromodulators
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Molecules synthesized by the presynaptic cell which alter either neurotransmitter release (presynaptic cell) or action (postsynaptic cell).
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Characteristics of neuromodulators
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A) Neuromodulators are long acting
B) Involve second messengers C) Affect pre/post or both cells D) Released alone or with neurotransmitter |
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External neuromodulators
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Caffeine, theobromide (depolarize axon hillock), nicotine (stimulates postsynaptic receptors).
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Neuronal pools
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A group of interconnected neurons that have specific functions
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