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central nervous system
brain and spinal cord
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peripheral nervous system
- nerves and ganglia outside of CNS
- 2 divisions: somatic and autonomic
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somatic nervous system
all nerves that control skeletal muscle
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autonomic nervous system
- all nerves that control smooth muscle, cardiac muscle, and glands
- 2 divisions: sympathetic and parasympathetic
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sympathetic nervous system
emergency - fight/flight
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parasympathetic nervous system
housekeeping - maintains normal
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neurons
- highly specialized nerve cells that transmit action potentials
- 3 groups: sensory, motor, association
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sensory neurons
- aka ascending, afferent
- carry APs from external and internal environment to spinal cord or brain
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motor neurons
- aka descending, efferent
- carry APs from brain or spinal cord out to effectors (muscles or glands)
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association neurons
- aka interneurons, internuncial neurons
- connect sensory and motor neurons
- always located in brain or spinal cord
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dendrites
groups of fibers that move APs toward cell body
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cell body
- aka soma, perikaryon
- contains nucleus and all organelles of the neuron
- 3 unique structures: chromatophyllic substance, lipofuscin pigment, neurofibrils
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chromatophyllic substances
- aka nissl body
- rough ER of the neuron
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lipofuscin pigment
fatty substance that gives neurone its yellow color
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neurofibrils
protein tubes that gives cell body its shape
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axon
long, slender projection of a neuron that moves APs away from cell body
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axon hillock
cone shaped region that exits cell body
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initial segment
end of axon hillock
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trigger zone
impulses first start to move down axon
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axon collaterals
- side branches of axon
- always begins after trigger zone but before axon terminal
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axon terminal
end of the axon
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neuroglia
- aka glial cells
- insulate, nourish, support, and protect neurons
- 6 types:
- CNS - oligodendrocytes, astrocytes, microglia, ependymal
- PNS - schwann cells, satellite cells
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oligodendrocytes
- CNS neuroglia
- produce myelin in CNS
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myelin
- fatty covering on axons
- insulates and speeds conduction of APs
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astrocytes
- CNS neuroglia
- make neurotransmitters and maintain proper ion balances for impulse conduction
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microglia
- CNS neuroglia
- phagocytes that destroy bacteria
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ependymal
- CNS neuroglia
- contain cilia that help circulate CSF
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schwann cells
- PNS neuroglia
- produce myelin in PNS
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satellite cells
- PNS neuroglia
- help support cell bodies of peripheral axons
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membrane potential
- more Na+ on outside of membrane
- more K+ on inside of membrane
- negative POPS on inside of membrane
- -70mv charge - polarized
- membrane is 100x more permeable to K+ than Na+
- maintained by sodium-potassium pump, gated channels, and leakage channels
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sodium-potassium pump
- pumps potassium outside to inside
- pumps sodium inside to outside
- 2 K+ move in, 3 Na+ move out
- electrogenic (Na+/K+ move in unequal numbers)
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gated channels
- open and close in response to a stimulus
- more Na+ gated channels
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leakage channels
- always open
- more K+ leakage channels
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excitability
- neurons ability to respond to a stimulus and convert the stimulus into an AP
- if stimulus is threshold, membrane's permeability to Na+ increases because stimulus opens Na+ channels
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stimulus
any condition in the environment that is capable of changing resting potential to some other number
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depolarization
- change in resting potential from -70 to +30
- stimulus opens Na+ gates
- stimulus turns off Na+/K+ pump
- stimulus makes membrane impermeable to K+
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Hodgkin's cycle
- once depolarization hits -55, stimulus no longer required because AP becomes self-generating due to ion movement
- positive feedback loop
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repolarization
- +30 to -70
- Na+ gates begin closing
- K+ gates begin opening
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action potental
a complete depolarization and repolarization of the membrane
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absolute refractory period
- period of time when a second stimulus cannot generate an AP because sodium gated channels are already open
- occurs during depolarization
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relative refractory period
- period of time where sodium gated channels are closing and potassium gated channels are opening
- occurs during repolarization
- a super-threshold stimulus can reopen Na+ gates and generate a 2nd AP
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super-threshold stimulus
an extremely strong stimulus that can reopen Na+ gates during refractory period and generate a 2nd AP
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sub-threshold stimulus
- an extremely weak stimulus that is not capable of depolarizing to -55
- produces slight hypopolarization followed by repolarization
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all or none
- a threshold stimulus always generates an AP
- AP moves from trigger zone to axon terminal at constant and maximum strength
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continuous conduction
AP moves along unmyelinated neuron from point to point
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saltatory conduction
- AP moves along myelinated neuron
- myelin acts as insulator (APs cannot travel through it)
- AP depolarizes and repolarizes at Nodes of Ranvier (neurofibril nodes)
- faster and more efficient
- cell uses less energy
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synapse
- place where 2 neurons come together or where a neuron meets an effector
- 2 types: electrical and chemical
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electrical synapse
- cardiac tissue
- embryo (nervous system not developed)
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chemical synapse
neurotransmitters released to bridge gap caused by synapse
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neurotransmitters
- group of specialized chemicals that allow neurons to communicate with each other or with an effector
- must be located in an axon terminal
- must be able to open gated channels
- must be able to be eliminated after it performs its job
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excitatory NT
- opens Na+ channels
- lower the resting potential of the post-synaptic dendrite from -70 to a number closer to threshold
- makes it easier for future impulse conduction
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inhibitory NT
- opens K+ channels
- hyperpolarize the membrane to make it more negative than -70
- makes it more difficult for future impulse conduction
- *how pain relievers work
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PNS NTs
- acetylcholine (Ach)
- norepinephrine (Ne)
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convergent neuron circuit
- several pre-synaptic neurons converge with one post-synaptic neuron
- ex: NMJ
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divergent neuron circuit
- one pre-synaptic neuron synapses with many post-synaptic neuron
- ex: CNS
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reverberating neuron circuit
- 1st neuron synapses with 2nd which synapses with 3rd
- axon collaterals from 3rd go back to synapse with a previous neuron
- ex: respiratory
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summation
- many axon terminals converge and release NT to generate an AP
- 2 types: spatial and temporal
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spatial summation
rapid depolarization to threshold because axon terminals release NTs at exact same time
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temporal summation
gradual depolarization to threshold because axon terminals release NTs one after the other
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