Phys. Unit 4
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| Central nervous system components | spinal cord and brain
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| What nervous system is divided into | central and peripheral systems
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| peripheral nervous system components | afferent and efferent
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| How much of the blood is in the brain/ | 15-20% of total blood supply
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| Weight of brain and percent of total body weight | 1.5 kg and about 2% of weight of 70 kg man
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| What secretes cerebrospinal fluid? | choroid plexuses
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| What is the blood-brain barrier? | A tissue complex made by the ependyma neuroglia and controls rates of entry and types of substances allowed in
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| Direction of afferent NS? | Sensory organs to CNS
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| Direction of efferent NS? | CNS to Motor organs
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| Myelination description | Schwann cells secrete mylin (fat) sheath around axon that insulates the axon and increases velocity of transmission of impulses; have Nodes of Ranvier
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| Two types of NS cells | Neurons and neuroglia
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| What is basic communication unit of NS? | Neuron
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| Part of neuron that receives stimulus | Dendrites
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| What synthesizes proteins and neurotransmitters? | Cell body
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| Where is the action potential initiated? | In the cell body in the initial segment, or Hillock Area
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| Most common type of neuron | interneurons (200,000)
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| Least common type of neuron | afferent (1.0)
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| Afferent neuron size | long dendrites, short axons
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| Efferent neuron size | short dendrites, long axons
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| Interneurons size | short dendrites, and either long or short axons
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| Number of neurons and neuroglia | neurons- 10%
neuroglia- 90%
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| Size of neurons and neuroglia | neuroglia are smaller, neurons are larger
volume is occupied in 50/50 neurons/neuroglia
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| Somatic Division definition | only skeletal muscles (voluntary) activities; fast transmission; always excitatory; uses ACH
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| Transmission at synapse | most chemical (neurotransmitter), a few electrical
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| Synapses definition | 1. can be excitatory(facilitatory) or inhibitory
2. inputs (divergent and convergent)
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| How many synapses does a spinal neuron have? | 15 x 10^3
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| How many synapses does a cranial neuron have? | 100 x 10^3
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| Autonomic Division definition | involuntary activities; parasympathetics and parasympathetics; innervates smooth, cardiac muscles; uses 2 neurons and ganglion; uses ACH and norepinephrine
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| What division is the major controller of homeostasis? | autonomic division
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| What is the name for adrenal secretions? | neurohormones
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| Adrenal Medulla secretions? | 20%- norepinephrine
80%- epinephrine
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| Sympathetic division secretions? | 20%- epinephrine
80%- norepinephrine
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| Cholinergic receptors | 1. Nicotinic: respond to nicotine; found on other neurons and skeletal muscle
2. muscarinic- respond to mushroom toxin; found on smooth and cardiac muscle, as well as glands
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| What binds cholinergic receptors? | ACH
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| Adrenergic receptors | 1. Alpha- excitatory or stimulatory
2. Beta- inhibitory
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| What binds to adrenergic receptors? | epinephrine or norepinephrine(does not bind to beta receptors)
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| Exceptions to receptors | Cardiac muscle-norepinephrine binds to beta receptors (excitatory response)
**(NE is not supposed to bind to beta receptors and not excitatory)
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| Resting membrane potential (Vm) | -70 mV
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| Depolarization definition | 1. Apply excitatory stimulus
2. Na channels open and K channels close
3. Na influx and cell becomes more positive (30-40 mV)
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| Repolarization definition | 1. K channels open, Na channels closed
2. K efflux and cell becomes more negative (-80 mV)
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| Hyperpolarization definition | 1. Apply an inhibitory stimulus
2. K channels open, Na channels close
3. K effux, cell becomes more negative than resting potential (Vm)
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| Threshold value | -55 mV
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| Equilibrium potential values | 1. K+: -90 mV (more inside cell)
2. Na+: +60 mV (more outside cell)
3. Cl-: -70 mV (do not contribute to membrane signals)
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| Types of potentials | graded and action
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| Graded potential | 1. created by subthreshold stimulus
2. amplitude/size depends on strength of stimulus
3. transmitted decrementally
4. useful in local or short distances
5. can be summed up to make an action potential
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| Action potential | 1. characteristic of excitable membranes-neurons, muscles, glands
2. caused by rapid changes using voltage-sensitive ion channels
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| Threshold voltage value | +15 mV
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| Magnitude or size of AP determined by what? | independent of stimulus strength, but determined by number of Action Potentials fired/unit of time
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| Refractory periods | 1. Absolute: during all of the depolarization and part of repolarization phase
2. Relative: during late part of the repolarization; can restimulate with supra-threshold stimulus only)
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| Where is summation of a signal done on a neuron? | Hillock area because it has the lowest threshold value
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