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-Anatomy of the nervous system -- macrostructure -showing page 1-6 out of 6

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Anatomy of the nervous system -- macrostructure
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CNS
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Brain and spinal cord
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PNS
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Nerves outside the CNS
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Includes autonomic
and somatic
nervous systems
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Autonomic nervous system
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Controls involuntary muscles
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Sympathetic:
expands energy
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Parasympathetic:
conserves energy (calms)
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Somatic nervous system
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Controls voluntary muscles and conveys sensory info to the
CNS
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The autonomic nervous system
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The autonomic nervous system sends and receives messages to regulate the
automatic functions of the body
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Includes groups of specialized neurons, called
autonomic ganglia
, that are founds
throughout the body
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Innervated by neurons that come from the CNS
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Preganglionic:
comes from the CNS and innervate ganglia
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Postganglionic:
project from ganglia to the rest of the body
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Divided into two subsystems:
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Sympathetic nervous system:
a network of nerves that prepares the
organs for rigorous activity
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Increases heart rate, blood pressure, etc.
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Comprised of ganglia on the left and right of the spinal cord
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The sympathetic nervous system mostly uses
norepinephrine
as its
neurotransmitter
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“Fight or flight” response
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Parasympathetic nervous system:
facilitates vegetative, non emergency
response
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Decreases functions activated by the sympathetic nervous system
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Comprised of long preganglionic axons extending from the spinal
cord and short postganglionic fibers that attach to the organs
themselves
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Postganglionic axons of the parasympathetic nervous system
mostly release
acetylcholine
as a neurotransmitter
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Dominant during our relaxed stage
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“Rest and digest”
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Somatic nervous system
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Somatic
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Consists of axons conveying messages from the sense organs to the CNS
and from the CNS to the muscles
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12 pairs of cranial nerves
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31 pairs of spinal nerves
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8 cervical (neck)
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12 thoracic (trunk)
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5 lumbar (lower back)
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5 sacral (pelvic)
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1 coccygeal (bottom)
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Connected at regular intervals to the spinal cord
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One member of each pair for each side of the body
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Each nerve consists of the fusion of two different distinct branches, or
roots, with different functions
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Dorsal root:
carry sensory info
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Ventral root:
carry motor info
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spinal cord:
part of the CNS found within the spinal column
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Communicates with the sense organs and muscles, except those of the head
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Cell bodies of the sensory neurons are located in clusters of neurons outside the
spinal cord, called the
dorsal root ganglia
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Comprised of:
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Grey matter:
located in the center of the spinal cord and is densely
packed with cell bodies and dendrites
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White matter:
composed mostly of myelinated axons that carry
information from the grey matter to the brain or other areas of the spinal
cord
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Each segment sends sensory information to the brain and receives motor
commands
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CNS-- brain and spinal cord
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Key terms
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Tract:
a set of axons in the CNS that are part of a projection pathway
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Nerve:
a set of axons in the periphery, either from the CNS to muscle or
gland, or from sensory organ to CNS
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Nucleus:
a cluster of neuron bodies within the CNS
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Ganglion:
a cluster of neuron cell bodies, usually outside the CNS
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The brain
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Three major divisions of the brain
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Hindbrain
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Midbrain
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Forebrain
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Gross anatomy
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Cerebral hemispheres
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Frontal
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Parietal
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Occipital
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Temporal
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White matter
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Mostly fiber tracts (myelin)
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Grey matter
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Mostly cell bodies and dendrites
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Support systems
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Meninges
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Three membranes that surround the brain and spinal cord
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Dura mater
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Arachnoid
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Pia mater
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The brain has no pain receptors, but the meninges do
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Swollen blood vessels in the meninges are a key cause of migraine
headaches
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Ventricular system
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The
central canal
is a fluid filled channel in the center of the spinal cord
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The
ventricles
are 4 fluid filled cavities within the brain
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Cerebrospinal fluid (CSF)
is a clear fluid found in the brain and spinal
cord
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Provides “cushioning” for the brain
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Reservoir of hormones and nutrition for the brain and spinal cord
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Removes metabolic waste from the interstitial fluids of nervous
tissues and returns it to the blood stream
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CSF is produced by filtering of the blood via a specialized membrane
called the
choroid plexus
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CSF circulates through the ventricles to eventually emerge into the
subarachnoid space where it is reabsorbed into the blood
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Vascular system
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Interrupted blood supply is critical for normal oxygenation of the brain
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Multiple routes for blood to get into the CNS
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Carotid arteries-- branch off the iota
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Vertebral arteries
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Circle of Willis is a confluence of arteries of these arteries that can
maintain perfusion of the brain even if narrowing or a blockage limits flow
through one part
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The blood brain barrier (BBB)
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Arteries branch out into fine arterioles and eventually into fine capillaries that
permeate the brain tissue
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The BBB is a mechanism that surrounds the brain vasculature and blocks most
chemicals from entering
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Brain cells are very sensitive and relatively finite in number
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BBB needs to block incoming viruses, bacteria, or other harmful
material from entering
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Selectively permeable, but not impermeable
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Active transport is the protein-mediated process that expands energy to pump
chemicals from the blood into the brain
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Can be problematic for therapeutic interventions
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Incomplete at several brain regions
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Area postrema (“chemical trigger source”)
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Mechanism for removal of toxic substances via vomiting reflex
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Median eminence
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Mechanisms for hormones entering the blood
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Anatomy of the nervous system-- microstructure
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Most critical cell types
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Glia and neurons
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The neuron doctrine has two key principles:
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Contiguous cells
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Neurons and other cells that are independent structurally,
metabolically, and functionally
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Information is transmitted from cell to cell across tiny gaps
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Synapses
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Neurons and glia
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Like other cells in the body, neurons and glia contain:
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Membrane
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Nucleus
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Mitochondria
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Ribosomes
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Endoplasmic reticulum
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Glia
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~50% of the cells in the CNS:
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Macroglia
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Astrocytes
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Oligodendrocytes
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Microglia
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Radial glia
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Especially important during early development
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Ependymal cells
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Specialized role for creating CSF in the choroid plexus
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Schwann cells-- the “oligos of the periphery”
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2 types
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Myelinating
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1 schwann cell per axon
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Non-myelinating
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Help maintain neuron’s health
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Serve structural and functional purposes
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Classic view of their roles:
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Support structure of brain tissue
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Astrocytes
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Help form the BBB
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Astrocytes
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Formation of the myelin sheath of axons
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Oligodendrocytes and schwann cells
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Guide the migration of neurons and the growth of
their axons and dendrites during embryonic
development
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Radial glia
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Isolation of junctional surfaces of synapses
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Astrocytes
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Repair processes following damage or injury to
nerves
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Microglia
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Contemporary views of their roles:
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Control local blood flow
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Help form new synapses
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Help in dendritic pruning and synapse refinement
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Receive synapses from neurons
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Absorb and release important neurochemicals,
including neurotransmitters
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Generate electrical potentials (maybe even action
potentials)
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Glia can engage in mitosis (neurons can’t)
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Neurons
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The human brain contains approximately 100 billion neurons
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There may be almost as many unique cell types
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There is tremendous genetic, molecular, and morphological diversity
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Leads to functional diversity
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All neurons have these major components:
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Dendrites
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soma/cell body
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Axon
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Presynaptic terminals
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A
motor neuron
has its soma in the spinal cord and receives excitation
from other neurons and conducts impulses along its axon to a muscle
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A
sensory neuron
is specialized at one end to be highly sensitive to
stimulation
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Large diversity
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Vary in size, shape, and function
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Dendrites
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Surface is lined with receptor proteins responsible for bringing
information into the neuron
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Some dendrites also contain
dendritic spines
that further branch
out and increase the surface area of the dendrite
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The greater the surface area of the dendrite, the more
information it can receive
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Terms used to describe the neuron:
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Projection neuron:
those whose axons project outside the brain
structure where their soma resides
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Afferent axon:
refers to bringing information into a
structure
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Efferent axon:
refers to carrying information away from a
structure
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Interneurons:
those whose dendrites and axons are completely
contained within a single structure
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The synapse
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Presynaptic membrane
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Postsynaptic membrane
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Synaptic cleft
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Other key features:
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Information flow
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Anterograde (classic view)
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Retrograde
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Synaptic vesicles
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Dendritic spines
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Prominent site for synapses
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Receptors
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Postsynaptic
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Presynaptic