Histology of the nervous system Flashcards
Lecture 4
intercellular neuron
communication within the cell - chemical
intracellular neuron
communication between cells through gap junctions - electrical
sensory information flow
from sensory receptors to the CNS (somatic and visceral)
motor information flow
from CNS to effector tissues/organs (somatic and visceral)
interneurons
form communication and integration network between sensory and motor neurons
dendrites
part of a neuron, involved in input (afferent communication)
- Nissl body
- cytoskeleton
- mitochondria
axon
part of a neuron, involved in output (efferent communication)
- hillock - site of origin of axon
- initial segment - between hillock and start of myelin, site of action potential generation
- terminal - site of synapses
- no Nissl body
soma (cell body)
integrate electrical signals, synthesize macromolecules
- prominent nucleolus
- large golgi apparatus
- NIssl body (composed of RER and ribosomes)
- cytoskeleton
- mitochondria
neuron structure
1) dendrite
2) soma (cell body)
3) axon
chemical synapse
conduction of impulse achieved by release of chemical substance (neurotransmitter)
neurotransmitter diffuses across synaptic cleft to stimulate post synaptic cell
electrical synapse
gap junctions, ions diffuse between cells
occurs in cardiac and smooth muscle, crystalline lens
chemical synapse structure
1) presynaptic membrane (axon) - vesicles contain neurotransmitters
2) postsynaptic membrane (dendrite) - receptors on plasma membrane
- asymmetric = excitatory
- symmetric = inhibitory
axonal transport
materials move along microtubules and neurofilaments in a bidirectiona manner
kinesin
anterograde transport - carries material from nerve cell body to periphery (towards synpase)
dynein
retrograde transport - carries material from axons and dendrites to nerve cell body (away from synapse)
differences between axons and dendrites
- dendrites are shorter with larger diameter
- dendrites are unmyelinated
- dendrites have larger surface area for synaptic input due to extensive branching and dendritic spines (knob-like projections)
bouton terminal (nerve to nerve)
single synapse from axon
boutons en passant (nerve to nerve)
multiple synapses from a single axon
neuromuscular junction (nerve to muscle)
en plaque motor end plate
multipolar neurons
single axon, two or more dendrites
- pyramidal cells (golgi type I neurons)
- purkinje cells
- stellate cells (golgi type II neurons)
- granule cells
pseudo-unipolar neurons
axon/dendrite are fused
bipolar neuron
single axon, single dendrite
pyramidal cells (multipolar)
golgi type I neurons
- soma is pyramid-shaped
- in cerebral cortex
- long axons, leave grey matter
purkine cells (multipolar)
- flask-shaped soma
- in cerebellar cortex
- lots of dendrites
stellate cells (multipolar)
golgi type II neurons
- start-shaped soma
- in cerebral and cerebellar cortex
- axons stay in grey matter
granule cells (multipolar)
- small stellate cells
- in cerebellum
- like grains of sand
pseudo-unipolar neurons
primary sensory neurons, pseudo because they don’t only go in one direction, one axon, one dendrite
bipolar neurons
associated with special senses
- retina
- ear and olfactory epithelium
glial cells
found in CNS and PNS, non-neuronal (not involved in signalling), involved in metabolic function
schwann cells
glial cells in PNS
- electrochemical insulation
- myelinate axons
- envelope and nurture unmyelinated axons
satellite cells
glial cells in PNS
- electrical insulation
- surround cell bodies of neurons
- metabolic exchanges
myelin sheath
insulator that directly surrounds an axon
- neurilemma is continuous with myelin sheath, includes nucleus and cytoplasm of Schwann cell
- basal lamina is external to neurilemma
myelin sheath development
1) membranes fuse together
2) portions not squeezed = clefts of Schmidt-Lanterman
3) myelin protein in major dense lines (cytoplasm)
segmentation of myelin sheath
one axon, many schwann cells
oligodendrocytes
neuroglia of the CNS
- produce and maintain myelin sheath
- small cells with a few processes, each process forms an internode
- no basal lamina or neurilemma
astrocytes
neurglia of CNS
- start-shaped
- largest of neuroglial cells
- fibrous: white matter, few long processes, many intermediate filaments
- protoplasmic: grey matter, numerous short processes, few intermediate filaments
microglia
neuroglia of CNS
- phagocytic
ependymal cells
neuroglia of CNS
- line fluid-filled cavities of CNS (ventricles and central canal of spinal cord)
- produce CSF (choroid plexus)
