chapter 2: cells of the nervous system Flashcards
cells present in nervous system
neurons
neuroglial cells = glia
CNS consists of
gray matter: contains cell bodies of neurons, embedded in neuropil
white matter: long processes of neurons, surrounded by myelin sheath
classification of neurons by Erlanger and Gasser
myelinated Aα, β, γ, δ, B fibers
unmyelinated C fibers
classification of neurons by Lloyd and Hunt
Aα = type Ia Aβ = type Ib or II Aδ = type III C = type IV
neuroglial cells: central neuroglia are …
astrocytes
oligodendrocytes
ependyma
microglia
cytoplasm of astrocytes
contains intermediate filaments (neurofilaments) composed of glial fibrillary acidic protein (GFAP)
2 types of astrocytes
fibrous astrocytes: in white matter and GFAP- filaments
protoplasmatic astrocytes: in gray matter
functions of astrocyte
- surround capillary blodd vessels with perivascular end feet
- other end feet connect to pia mater
- connections to ependymocytes in ventricular system
- synapses and nodes of Ranvier absorb neurotransmitters (excitatory and inhibitory)
excitatory and inhibitory neurotransmitters are …
+: glutamate, acetylcholine, noradrenaline, serotonin and dopamine
-: GABA, glycine, dopamine
characteristics of oligodentrocytes
- small nuclei
- small rim of cytoplasm: contain granular endoplasmic reticulum and polyribosomes
- few long thin processes
- filaments are absent, but has numerous microtubules
3 types of oligodendrocytes
- interfascicular oligodendrocytes
- satellite oligodendrocytes
- third type contacts the nodes of Ranvier
ependyma =
the simple cuboidal/ columnar epithelium than lines the ventricular system
3 types of cells in ependyma
- ependymocytes
- tanycytes
- choroidal epithelial cells
characteristics of resting microglial cells
- small, elongated nuclei
- not a lot of cytoplasm
- several short- branched processes with spiky appedages
- enevly spaced throughout gray and white matter
- no overlapping or intertwining
reactive microglial cells
- formed from resting microcglial cells
- are distended with lipid- rich phagocytosed material
neuroglial cells: peripheral neuroglia are …
Schwann cells = neurolemmocytes
Schwann cells
- elongated nuclei
- ensheath all axons in all parts of the PNS
- each axon is suspended in the cytoplasm of its Schwann cell by a dubble layer of surface membrane
- 1 Schwann cell ensheaths either 1 myelinated axon or surrounds several unlyelinated axons
- gaps between the cells = nodes of Ranvier
neurons are…
cells specialized for sending and receiving chemically mediated electrical signals
their axons carry the encoded output of information fron the region containing their cell bodies to other parts of the nervous system
basic concepts of neurons
- cell body with nucleus
- cytoplasma = perikaryon
- neurite = any neural process (axon or dendrite)
- neuron doctrine = each neuron is a structural and functional unit
different shapes and sizes of neurons
- size of cell body: 5 μm- 135 μm
- neurons occur in ganglia (PNS) and in laminae and nuclei (CNS) together they are principal cells
- small local circuit neurons = interneurons
types of neurons
- multipolar neurons
- unipolar neurons
- bipolar neurons
myelin sheath =
apposed layers of glial plamsa membranes
- begins near origin of axon & ends short of its terminal branching
- laid down by neuroglial cells
- interruptions are nodes of Ranvier
saltatory conduction
- AP jumps from one node to the next
- signaling is faster in a myelinated exon than in an unmyelinated axon
- the greater the diameter of a nerve fiber, the faster the conduction of the nerve impulse
synapses =
a point of functional contact between 2 neurons or between a neuron and and effector cell
presynaptic neurite = synaptic terminal
has synaptic vesicles that contain neurotransmitters
neurotransmitters can be excitatory or inhibitory
excitatory: stimulates postsynaptic cell
- -> EPSP: excitatory postsynaptic potential = depolarization
inhibitory: inhibits postsynaptic cell
- -> IPSP: inhibitory postsynaptic potential = hyperpolarization
neuromodulator =>
modifies the responsiveness to transmitters
what is axonal transport?
enzymes, membrane lipoproteins, cytoplasmic structural proteins
what is anterograde transport?
- from cell body to synapses
- 2 rates: slow pace or fast pace
what is retrograde transport?
- from synaptic terminals to cell body
- absorbed proteins from extracellular space
- rate is variable
what are the responses of neurons to injury?
- breakdown of axons and myelin sheath distal to an injury site
