Nervous system

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created 8 years ago by rappt2
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1

what types are cells are found in the nervous system?

neuroglia (glial) cells, ependymal cells, microglia, astrocytes

2

neuroglia (glial) cells

regulate the environment around neurons, provide a supporting framework for neural tissue, act as phagocytes; retain ability to divide

3

ependymal cells

line central cavities of the brain and spinal cord, form fairly permeable barrier between the CSF that fills cavities and the tissue fluid bathing cells of CNS; cilia helps to circulate the CSF

4

microglia

protective role in CNS; monitor health of neurons, when neurons are injured migrate toward them; transform into specialized macrophages that phagocytize the microorganisms or neuronal debris

5

astrocytes

most abundant and versatile; play a role in making exchanges between capillaries and neurons, guiding migration of young neurons, and synapse formation; control chemical environment around neurons

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oligodendrocytes

wrap their processes around neuron fibers in CNS, producing myelin sheaths

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Schwann cells

surround and form myelin sheaths around larger nerve fibers in PNS; similar to oligodendrocytes

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satellite cells

PNS neuroglia; surround neuron cell bodies in PNS and have many of the same functions in PNS as astrocytes in CNS

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sensory (afferent) neurons

consists of nerve fibers that convey impulses TO the CNS from sensory receptors throughout the body

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motor (efferent) neurons

transmit impulse FROM the CNS to effector organs - muscles and glands

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interneurons

conduct impulses within the CNS, integrating sensory input or motor output

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cell body (soma)

...

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dendrite

receptive or input regions; very large surface area for receiving signals fom other neurons; finer dendrites are highly specialized for information collection; convey incoming messages toward cell body

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dendritric spine

thorny appendage of a dendrites; points of close contact (synapses) with other neurons

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axon

conducting region of the neuron; generates nerve impulses and ransmits them away from the cell body, along plasma membrane (axolemma)

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axon hillock

cone-shaped area that is the initial region of the axon; in motor neurons nerve impulse is generate at junction of hillock and axon

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synaptic terminal

knoblike distal endings of axon terminal branches where one neuron communicates with another by releasing chemical messages

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synaptic cleft

small space between neurons at a nerve synapse across which an impulse is transmitted by a neurotransmitter

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myelin sheath

speeds up neural impulse conduction; formed by concentric layers of schwann cells (PNS) or oligodendrocytes (CNS)

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nodes of Ranvier

gaps in between Schwann cells; axon collaterals can emerge from the axon here

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resting potential

maintenance of a charge difference between Na+ and K+ of ~70 mV across a selectively permeable membrane; more K+ channels than Na-, loses more positively charged ions than it gains; cell at rest is negative

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membrane concentrations - inside cell

High K+ --> membrane more permeable
high proteins (negatively charged)
low Cl-
low Na+

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membrane concentrations - outside cell

High Na+
High Cl-
Low K+

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sodium-potassium pump

ejects three Na+ from cell and transports two K+ into cell --> stabilizes the resting membrane potential by maintaining the concentration gradient; ATP-driven

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graded potential

short-lived, localized changes in membrane potential that can either be depolarizations or hyperpolarizations; triggered by a change in neuron environment that causes gated ion (Na) channels to open; magnitude varies with stimulus strength and decrease with distance

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depolarization

inside of the membrane becomes less negative

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repolarization

membrane returns to its resting potential

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hyperpolarization

inside of the membrane becomes more negative than resting potential

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steps in graded potential

1. resting membrane exposed to stimulus
2. Na channels open and Na ions enter the cell
3. membrane potential rises = depolarization
4. nearby regions of membrane become depolarized

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what triggers an action potential?

graded depolarization must reach axon hillock and be large enough (10-15 mV) to change membrane potential from -70mV to threshold (-60 to -55 mV)

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threshold

voltage that, if attained at axon hillock is always* cause an action potential; all-or-none principle

32

steps in action potentials

1. depolarization to threshold
2. activation of Na+ channels: gates open, rapid depolarization, Na+ ions rush in, membrane changes from negative to positive
3. at peak (+30mV): Na+ gates close, K+ channels open, repolarization occurs
4. return to normal permeability: K+ channels begin to close when membrane reaches normal resting potential, K+ finish closing when membrane is hyperpolarized

33

AP in myelinated axon

travel very quickly through saltatory conduction - jumps from node to node, not decremental, requires less ATP , less ion movement

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AP in non-myelinated axon

continuous conduction; affects 1 segment of an axon at a time, each segment experiences AP; slower, graded, and decremental

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what types of gated channels are found along axons?

voltage regulated
chemically regulated
mechanically regulated

36

passive channels

always open, more permeable to K+ than Na+ at rest since there are more passive, non-gated K+ channels in the membrane than Na+

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voltage gated

at resting potential, voltage-gated Na+ channels are closed, when membrane is depolarized, conformational changes open the channels

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synapse

junction that mediates information transfer from one neuron to the next, or from a neuron to an effector cell

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electrical synapse

gap junctions; contain protein channels initimately connected the cytoplasm or adjacent neurons and allow ions and small molecules to flow directly from one neuron to the next; rapid transmission

40

chemical synapse

specialized for release and reception of chemical neurotransmitters
two parts - axon terminal of presynaptic neuron that contain synaptic vesicles; neurotransmitter receptor region on membrane of dendrite or the cell body of the postsynaptic neuron

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excitatory postsynaptic potential

graded depolarization of postsynaptic membrane

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inhibitory postsynaptic potential

graded hyperpolarization of postsynaptic membrane; a neuron that receives many IPSP is inhibited from producing an action potential b/c stimulation needed to reach threshold is increased

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summation

to trigger an AP one EPSP is not enough; EPSPs combine to reach treshold

44

acetylcholine (Ach)

causes depolarizaiton in the membrane of skeletal muscles and heart, causes transient hyperpolarization

45

dopamine

amino acid derivative with indirect modulatory effects, rewarding and pleasurable

46

norepinephrine

amino acid derivative with indirect modulatory effects, found in brain and autonomic nervous system

47

serotonin

amino acid derivative with indirect modulatory effects, low levels implicated in depression

48

glutamate

most important excitatory neurotransmitter in brain, important in learning and memory

49

glycine

produces postsynaptic inhibition, poison strychnine block glycine receptors, results in fatal convulsions

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gaba

gamma amino butyric acid; inhibitory neurotransmitter

51

substance P

neuropeptide; important in pain signaling

52

opioids

endorphins, enkephalins - pain control
opiates (morphine) bind to same receptors