Nervous Tissue (Parts & Functions)

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CNS/ PNS

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Central nervous system (all nerves in brain & spinal cord)/ Peripheral nervous system (all nerves & receptors outside of brain & spinal cord)

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Afferent

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Sensory going toward CNS from periphery

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Efferent

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Sensory going away from CNS towards muscle

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Autonomic efferent

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involuntary impulses to smooth muscle and glands and cardiac muscle.

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Somatic

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Voluntary muscle impulses to skeletal muscle.

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Function of sensory neurons--

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Afferent (PNS) and ascending (CNS)

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Function of motor neurons--

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Efferent (PNS) and descending (CNS)

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Integrative

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Located within spinal cord and brain

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In PNS there is...

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Sensory afferent and motor efferent neurons.

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In CNS there is...

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Sensory ascending and motor descending neurons

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Nerve

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Bundle of axons in the PNS--cranial nerves & spinal nerves.

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Tract

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Bundle of axons in the CNS

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Functions of neurons/neuroglia

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Neurons conduct impulses, neuroglia are supporter cells.

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Neuroglial cells in CNS

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Astrocytes (blood-brain barrier,
Metabolism of neurotransmitter,
Repairing damaged areas in CNS)

Microglia (phagocytes, digest away debris)

Ependymal cells (ciliated, line spaces in brain)

Oligodendrocytes (makes myelin sheath around neurons)

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Neuroglial cells in PNS

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Schwann cells (makes myelin sheath in PNS)

Satellite cells (support neurons in ganglia--nerve clusters)

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Dendrites

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Receives action potential

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Nissl bodies

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Rough ER in neurons (involved in protein synthesis)

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Why is it important that neuron has alot of nissl bodies?

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Because it functions in synthesis of proteins, important for protein channels in neural cells (especially during muscle contraction)

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Axon terminals

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Contains vesicles with neurotransmitter

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Myelin sheath

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Covers axon--insulation, speeds up action potential, helps conduct nerve impulse.

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Node of Ranvier

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Not covered by myelin sheath, where action potential happens, separates internodes.

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Gray matter

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In CNS, concentration of cell bodies.

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Myelin sheath

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Phospholipid covering around neuron that plays role in conduction & insulation of electrical impulse.

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What makes myelin sheath in PNS? CNS?

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Schwann cells/ Oligodendrocytes

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Differences between how myelin made in CNS and PNS?

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Oligodendrocyes in CNS, Schwann cells in PNS, neuriemma in PNS, not in CNS, myelinates only one part of axon in PNS, many parts in CNS, fewer nodes of Ranvier in CNS, many in PNS

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What is unmyelinated axon?

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One layer instead of many layers

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Unmyelinated axons conduct impulses ______ than myelinated ones.

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Slower

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Example of a demyelinating disease?

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Multiple Sclerosis, poisons (lead, mecury, etc.) can also lead to irreversible nerve damage.

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Are all neurons myelinated in newborn baby?

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No

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White matter

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Group of axons traveling together (In CNS)

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Axon

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Takes electrical impulses away from cell body

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Axon hillock

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Where electrical impulse begins (decides whether or not to fire)

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Astrocyte

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Neuroglial cell of CNS that acts as blood-brain barrier (anything in blood has to go through astrocytes before reaching neurons), also repairs damages in CNS, metabolizes neurotransmitter, potassium balance.

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Oligodendrocytes

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Neuroglial cell of CNS, makes myelin sheath in CNS neurons (has "legs" that wrap around several axons at once and myelinates them)

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Microglia

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Neuroglial cell of CNS, phagocytic cells that digests away debris.

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Ependymal cells

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Ciliated neuroglial cells of CNS that line cavities in brain and spinal cord.

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Difference between axon and dendrite

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Dendrites receives electrical impulse while axon take it away from cell body.

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Significance of axon hillock

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Portion of neuron where action potential begins and makes decision of whether or not to fire it.

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Three advantages of myelin:

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Insulation, saves ATP, speeds up action potential

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Saltatory conduction

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Action potential happens only at nodes of Ranvier in myelinated neurons.

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Are all neurons myelinated?

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Most are

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Bundle of axons in: PNS? CNS?

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Nerves/tracts

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What is resting membrane potential?

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When neuron membrane is it at rest, it's charge is -70 mv, when cell is it normal conditions (sodium concentrated on outside, potassium on inside--outside positive, inside negative)

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Two parts of action potential?

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Depolarization/Repolarization

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Depolarization

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Sodium rushes into cell and changes charge of cell, causing inside of cell to become positive when normally negative.

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Repolarization

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Potassium rushes back out in resopnse to influx of sodium to keep cell at balance. Balanced is resored by potassium taking positive charge with it.

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Purpose of Na+/K+ pump in action potential

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To keep sodium and potassium outside and inside of cell respectively.

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What is all or none response in neuron?

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Once resting membrane potential increases to -55mv, action potential automatically stops and cannot be stopped.

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What is refractory period?

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Period where second action potential cannot be generated.

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Which neurons move the fastest?

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Neurons with most myelin, largest in diameter.

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Different types of nerve fibers:

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A Larger diameter
B Also more myelin
C Slower, less myelin

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Events at cholinergic hillock

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Action potential travels down axon of presynaptic neuron and causes influx of calcium through channels which causes release of neurotransmitter by exocytosis which then travels across synaptic cleft and binds to receptor on membrane pf postsynaptic neuron.

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How many different neurotransmitters are there?

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Hundreds of thousands.

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Where does calcium play role in transmission of impulse across a synapse?

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Calcium causes release of neurotransmitter from vesicles in axon terminal by exocytosis--they then diffuses across synaptic cleft.

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Excitatory neurotransmitter

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One that brings resting potential closer to -55 mv--it will start action potential when binding to receptor on postsynaptic membrane.

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Inhibitory neurotransmitter

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One that move resting potential away from -55 mv--it will not be enough to start action potential.

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What is EPSP?

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Excitatory post synaptic potential

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What is IPSP?

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Inhibitory post synaptic potential

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How is acetylcholine broken down?

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By cholinesterase

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Is acetylcholine only located at neuromusclar junction?

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No, also in autonomic nervous system

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Inhibitory neurotransmitter in brain (most common)

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GABA

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Most common excitatory neurotransmitter in brain

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Glutamate

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Neurotransmitter than acts as natural pain killer:

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Endorphins/ Enkephalins

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Serotonin

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Neurotransmitter that plays a role in sleep and mood.

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Gaseous Neurotransmitter

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Nitric oxide--relaxes smooth muscle

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Examples of voltage-gated channels

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Calcium channels, Sodium/Potassium channels

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Chemical-gated channels

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Neurotransmitter receptors

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Hyperpolarization

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Change in charge of cell membrane's potential that makes it more negative.