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46 Cards in this Set
- Front
- Back
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What is neurolemma and why is it important? |
Neurolemma is the outer nucleated cytoplasmic layer of the Schwann cell, which encloses the Myelin Sheath (sheath of the Schwann cell). When an axon is injured it aids in the regeneration by forming a regeneration tube that guides and stimulates regrowth of the axon. |
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What is a nucelus with regards to the nervous system? |
A nucleus is a cluster of neuronal cell bodies located in the CNS |
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What is the Ganglion? |
refers to a cluster of neuronal bodies in the PNS, ganglia are closely associated with cranial and spinal nerves. |
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Neurons communicate with one another using two types of electrical signals: |
1. Graded potential allow communication over short distances only. 2. Action Potential allow communication over a long distance within the body. - Action potential in a muscle fiber is called muscle action potential -Action potential in a neuron (nerve cell) s called a nerve action potential (nerve impulse) |
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What is a graded potential? |
Small deviation from the membrane potential that makes the membrane either more polarized (Inside more negative) hyperpolarizing graded potential or less polarized (inside less negative) depolarizing graded potential |
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Perception and the conscious awareness of a sensation is primarily a function of what? |
The cerebral cortex |
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The production of graded potentials and action potentials depends on 2 basic features of the plasma membrane of the excitable cells: |
1. The existence of the resting membrane potential
2. The presence of specific types of ion channels which open and close in response to specific stimuli. |
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What is resting membrane potential? |
The difference in voltage of the fluids inside a cell and outside a cell, which is usually between -70 to -80 millivolts (mV). |
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What are the 4 types of Ion channels? |
1. Leak Channels 2. Ligand-gated channel 3. Mechanically gated channel 4. Voltage-gated channel |
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How does a leak channel function? |
Randomly alternates between open and closed positions. Typically plasma membranes have more potassium leak channels than sodium ion leak channels. thus, the membranes permeability to K+ is much higher than to Na+. found in nearly all cells, including dendrites, cell bodies and axons of all types of neurons. |
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How does a ligand-gated channel function?
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Opens and closes in response to the binding of a ligand (chemical) stimulus including neurotransmitter acetylcholine opens cation channels that allow Na+ and Calcium to diffuse inwards and K+ to diffuse outward. Located in dendrites of some sensory neurone, such as pain receptors and in dendrites and cell bodies of interneurons and motor neurons. |
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How does a mechanically gated channel function? |
Opens and closes in response to mechanical stimulation in the form of vibration (such as sound waves), touch, pressure, or tissue stretching. The force distorts the channel from its resting position, opening the gate. Found in auditory receptors int eh ears, in receptors that monitor stretching of internal organs and in touch and pressure receptors in the skin. |
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How does a voltage-gated channel function? |
Opens in response to a change in membrane potential (voltage). Participate in the generation and conducrion of action potentials in axons of all types of neurons. |
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The membrane potential arises from what 3 major factors? |
1. Unequal distribution of ions in the ECF and cytosol. ECF rich in Na+ & Cl-. Cytosol rich in K+ & anions (Phosphates in ATP & amino acids in proteins. 2.Inability of most anions to leave the cell. 3. Electrogenic nature of the Na+/K+ ATPase. Only a few sodium leak channels so permeability is low, but they do slowly diffuse down their concentration gradient and such leakage could destroy the action potential. The small inward leak of NA+ and outward leak of K+ is offset by the Na+/K+ ATPases (sodium potassium pump). Expels 3 Na+ for every 2 K+ it brings in. |
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What is an action potential (impulse)? |
A sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restores t to the resting state. |
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What are the 2 main phases of an action potential? |
1. Depolarizing phase: The negative membrane potential becomes less negative, reaches zero and then becomes positive.
2. Repolarizing phase: the membrane potential is restored to its resting state of -70mV. |
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What the refractory period? |
The period of time after an action potential begins during which an eexcitable cell cannot generate another action potential in response to a normal threshold stimulus. Unlike action potentials graded potentials do not have a refractory period. |
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What is absolute refractory period? |
Even the strongest stimulus cannot initiate a second action potential. Coincides with the period of the Na+ channel activation and inactivation. Inactivated Na+ channels cannot reopen, they first must return to the resting state. |
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What is a relative refractor period? |
A period of time during which a second action potential can be initiated, but only by a larger than normal stimulus. |
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What is propagation? |
Unlike in graded potentials which is decremental and die out over time action potentials keep its strength as it spreads along the membrane and this mode of conduction is called propagation and depends on positive feedback. |
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What are the two tpes of propagation |
1. Continuous conduction - step by step depolarization and depolarization of each adjacent segment of the plasma membrane.
2. Saltatory conduction - Occurs along myelinated axons action potential appears to leap from node to node between myelin. Thus travels much faster. |
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What are the factors that affect the speed of propagation? |
1. Amount of myelination - Propagate more rapidly along myelinated axons. 2. Axon diameter - Larger diameter axons propagate action potentials faster than smaller ones due to larger surface are 3. Temperature - Propagate slower at lower temperatures |
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What ar the classifications of nerve fibers? |
A fibers B fibers C fiber |
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What are the characteristics of an A fiber? |
Largest in diameter, unmyelinated, The axons of sensory neurons that propagate impulse associated with touch, pressure, position of joints and some thermal and pain sensations are A fibers and axons of motor neurone that conduct impulse to skeletal muscles are as well. |
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What are the characteristics of B fibbers? |
Medium in diameter compared to A and C fibers. Myelinated and exhibit saltatory conduction . Have a some what longer refractory period compared to A fibers. Conduct sensory nerve impulses from the viscera to the brain and spinal cord. Constitute all the axons of the autonomic motor neurone that extend from the brain and spinal cord to the ANS relay stations called autonomic ganglia |
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What are the characteristics of C fibers? |
The smallest in diameter. All unmyelinated. Exhibit the longest refractory periods. These umyelinated axons conduct some sensory impulses for pain, touch, pressure, heat, and cold from the skin and pain impulses from the viscera. Autonomic motor fibers that extend from the autonomic ganglia to stimulate the heart, smooth muscle and glands are C fibers. Function to increase and decrease the heart rate. |
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What is a synapse? |
A region where communication occurs between two neurone or between a neuron and an effector cell (muscle cell or glandular cell) |
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What is a presynaptic neuron? |
(pre=before) refers to a nerve cell that carries a nerve impulse towards the synapse. It is the cell that sends a signal. |
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What is the postsynaptic neuron? |
(post = after) refers to a nerve cell that carries a nerve impulse away from a synapse or an effector cell that response to the impulse at the synapse. |
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What is an electrical synapse and what are its 2 main advantages? |
Action potentials (impulses) conduct directly between plasma membrane of adjacent neurone through structures called gap junctions. 2 main advantage are: faster communication and synchronization |
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What is a chemical synapse? |
Although the presynaptic & postsynaptic neuron are close they do not touch, but are separated by the synaptic cleft and nerve impulse cannot conduct across the synaptic cleft they have to use an indirect form of communication via neurotransmitters that diffuse through the interstitial fluid of the synaptic cleft and binds to the receptor of the postsynaptic neuron. |
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What is an excitatory postsynaptic potential (EPSP) |
A depolarizing postsynaptic potential. Although a single EPSP does not initiate a nerve impulse the post synaptic cell does become more excitable and thus because it is slightly depolarized it is more likely to reach threshold when the next EPSP comes along. |
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What is an inhibitory postsynaptic potential (IPEP) |
A hyperpolarizing postynaptic potential. Generation of an acton potential is more difficult than usual because the membrane potential becomes inside more negative and thus even father from threshold than in its resting state. |
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What are the 3 ways neurotransmitter can be removed? |
1. Diffusion - Diffuse away from the synaptic cleft once released and become out o reach of the receptors of the postsynaptic neuron. 2. Enzymatic degradation - For example the enzyme acetylcholinesterase breaks down acetylcholine in the synapatic cleft 3. Uptake by cells - Actively transported back into the neuron that released them (reuptake)
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What is Spatial Summation? |
Summation of postsynaptic potentials in response to stimuli that occurs at different locations in the membrane of the postsynaptic cell at the same time. Ex: Spatial summation results from the buildup of neurotransmitter released simultaneously by several presynaptic end bulbs. |
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what is Temporal Summation? |
Summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell, but at different times. Ex: Results from buildup of neurotransmitter released by a single presynaptic end bulb two or more times in rapid succession. |
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A single postsynaptic neuron receives input from many presynaptic neurone, some of which release excitatory neurotransmitters and some that release inhibitory ones. The sum of all the excitatory or inhibitory effects at any given time determines the effect on the postsynaptic neurone which may response in the following 3 ways... |
1. EPSP -it the total excitatory effects are greater than the total inhibitory, but less than the threshold level of stimulation. After an EPSP a subsequent stimuli can more easily generate a nerve impulse through summation b/c neuron partially depolarized. 2. Nerve Impulse - Total excitatory effects is greater than the inhibitory and threshold is reached, one or more nerve impulses (action potentials) will be triggers. Impulses continues to be generated as long as the EPSP is at or above the threshold level 3. IPSP - The total inhibitory effects are greater than the excitatory, the membrane depolarizes (IPSP). The result is inhibition of the postsynaptic neuron and an inability to generate a nerve impulse. |
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Neurotransmitter : Acetylcholine |
Released by many PNS neurons and some CND neurons.ACh is an excitatory neurotransmitter at some synapses, such as neuromuscular junction, where the binding of ACh to ionotropic receptors opens cation channels. it is also an inhibitory neurotransmitter where is binds to metabotropic receptors coupled to G proteins to open K+ chanels. |
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Neurotransmitter : Amino Acids |
Glutamate (glutamic acid) and asparate (asparic acid) have powerful excitatory effects. Most excitatory neurons int eh CNS and half the synapses in the brain communicate via glutamate.
Gamma aminobutyric acid (GABA) and glycine are important inhibitory neurotransmitters. GABA is found only in the CNS where it is the most common inhibitory neurotransmitter. Binding to a ionotropic receptor opens Chlorine channels. About half of the inhibitory synapses in the spinal cord use glycine and the other half use GABA |
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Neuotransmitter : Biogenic Amines |
Certain amino acids are modified and decarboxylated (carboxyl group removed) to produce biogenic Amines. Norepinephrine (NE) which pays a role in arousal (awakening from a deep sleep), reaming and regulating mood. Epinephrine like adrenaline. Dopamine (DA) active during emotional responses, addictive behaviours and pleasurable experiences. |
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What are the 5 types of neural circuits? |
1. Simple series circuit 2. Diverging circuit 3. Converging circuit 4. Reverberating circuit 5. Parallell after-discharge circuit |
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What does the central nervous system consist of? |
The brain and the spinal cord
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What does the peripheral nervous system consist of? |
All nervous tissue outside of the CNS |
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What 3 systems is the PNS divided into? |
1. Somatic nervous system 2. autonomic nervous system 3. Enteric nervous system |
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What are the 3 functional classifications of Neurons? |
1. sensory neuron (afferent) 2. Motor neuron (efferent) 3. Interneurons |
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What are the 3 structural classifications of neuron? |
1. Unipolar 2. Bipolar 3. Multipolar |
