Chapter 12: Neurons Flashcards
neurons
functional unit of the nervous system
- generate, transmit, recieve action potentials
parts of a neuron
cell body, dendrites, axon
cell body contains
- nucleus, nucleoli
- lysosomes
- mitochondria
- golgi complex
- lipofuscin pigment
- residues of undigested lysosomal material
- nissal bodies and neurofibrils
nissal bodies
clusters of dark staining granules
neurofibrils are found where?
abundant in cell body, dendrites and axon
dendrites
function
characteristics, for what purpose?
- recieves + relays impulses twd cell body
- many
- contain little spines called gemmules on tips that increase surface area to recieve more axon surfaces
axon conducts impulses away from ________ towards _______ (6)
function
how many per neuron
conducts impulses away from the cell body twds dendrites, axon, or cell body of another neuron, muscle or gland (effector)
- one
parts of axon (6)
- axon hillock: pryamid shaped part on soma
- initial segment: region of axon btwn hillock and begining of myelin sheath, AP is generated
- axolemma: plasma membrane of axon
- axoplasm: cytoplasm of axon
- axon terminal: branches at terminal end of axon
- synaptic buttons: bulbs at terminal, have ACh
how are neurons classified?
according to the # and arrangement of axons and dendrites extending from the soma
monopolar neuron
has 1 process extending from the cell body
- 1 branch serves as an axon
- 1 as a dendrite
bipolar
has 2 processes extending from the cell body
- 1 is an axon
- other is dendrite
multipolar
- most common
- has many processes extending from the cell body
- one is axon
- one is dendrite
can neurons reproduce?
no, they dont have centrioles
% of all neurons in the nervous system are interneurons
90%
types of neuroglia
astrocytes, oligodendrocytes, microglia, ependymal cells, scwann cells, satellite cells
astrocyte
description
associated with blood vessels in the CNS
- irregularly shaped
- many cytoplasmic extensions
oligodendrocytes
function
description
- produce the myelin sheath in the CNS
- controls movement
- smaller than astrocytes
- myelin sheath covers + insulates axons
- can myelinate more than 1 cell
microglia
where does it originate from?
- phagocytes in the CNS thought to have come from macrophages
- comes from monocyte
ependymal cells
function
where is it found
- produce cerebrospinal fluidin CNS
- cuboidal or columnar cells that line ventricles of brain + central canal
schwann cells
function
description
- produce the neurolemma sheath in the PNS
- wraps body around axon 20-30 times
- cytoplasm and nucleus is squeezed into periphery
- outermost layer represents the neurolemma
neurolemma
- noncontinuous
- nodes of ranvier aka sheath of shwann
satellite cells
in PNS ganglia (collection of cell bodies of neurons that lie outside the CNS)
neuroglia in CNS
astrocytes, oligodedrocytes, microglia, ependymal cells
neuroglia in PNS
schwann cells, satellite cells
neuropil represents
neurofilaments, neurfibrils, all cytoplasmic extensions of neuroglia
myelin sheath
description
can have?
multilayered lipoprotein casing that covers the axons of most neurons
- can have unmyelinated axons
what does sheath of schwann do? (2)
insulates the axon and increases the speed of nerve impulse conduction
schwann cells produce____ in the _____
myelin sheath, PNS
outer layer of the schwann cell is called the _____ and is found only around axons in the ____
neurolemma, PNS
what does the neurolemma aid in?
regeneration in an injured axon
what are the gaps in the myelin sheath called?
nodes of ranvier
what happens when there is damage or death to a neurons cell body?
degeneration of attached dendrites + axons
- if nerve fiber is cut, regeneration is only possible if it is covered by schwann cell or neurolemma
- closer damage to CNS, the less likely it will repair
- distal to cute regenerates, leaving and empty meurolemma tube
do spinal cord injuries regenerate?
no
oligodendrocytes form ____ for CNS axons
myelin sheaths
- no neurolemma or regrowth after injury
white matter
aggregations of myelinated axons
- brain: inner
- spinal cord: outer
gray matter
neuron cell bodies, dendrites, bundles of unmyelinated axons and neuroglia
- brain: outer
- spinal cord: inner
spinal cord
gray matter forms an H shaped inner core surrounded by white matter
brain
an outer shell of gray matter covers the cerebral hemispheres
nucleus
mass of nerve cell bodies and dendrites inside the CNS
