23 nervous system Flashcards
central nervous system components
brain
spinal cord
relay neurons
peripheral nervous system components
cranial nerves spinal nerves peripheral nervs sensory neurons motor neurons
grey matter
peripheral in brain called nuclei
central in spinal cord, butterfly shape
consists of : enrve cell bodies, dendrites, axons terminals, non-myelinated axons and neuroglia
The anterior and posterior prongs are referred to as ventral
horns (VH) and dorsal horns (DH), respectively. They are
connected by the grey commissure (GC)
white matter
cnetarl in brain and peripheral in spina cord
consists of myelinated material
contains nerve fibres that form ascending
and descending tracts
where the blood vessels
on outer connective layers at ventral fissure
neurons
many dendrites, single axon
main body called soma
witnin the PNS
often myelinated
Myelin in PNS and CNS
In the CNS, the myelin for the axon is produced by, and is
part of, an oligodendrocyte
• in the PNS, the myelin is produced by, and is part of, a
Schwann cell
4 types of neurons
Motor
Location: CNS to periphery
Function: to send signals to effector tissues
Sensory
Location: Periphery towards CNS
Function: to send environmental signals to integrative
centre
Integrative
Location: CNS
Function: collate all information
Anaxonic
Location: retina (some parts of CNS)
Function: act as relays
neuron structure
multipolar neuron: 1 axon multiple dendrites. most common.
bipolar: one axon one dendrite.
unipolar: sinle process leading away from the soma.
anaxonic neuron: many dendrites but no axon
neurons
pseudounipolar (unipolar), bipolar, and
postsynaptic autonomic neuron cell bodies are
located outside the CNS
• Purkinje and pyramidal cells are restricted to the
CNS; many of them have elaborate dendritic
arborisations that facilitate their identification
• The majority of nerves in the CNS are interneurons
movement in neuron
uses kinesin forward and dyenin backward. microtubule took off end and added on to front for movement down axon.
Anterograde and retrograde vesicles use microtubule
‘shuttle’ system to move from soma to synapse and back.
5 different types of synapses
a. Axodendritic or axosomatic
- directly to the plasma membrane of nerve or cell
b. Axodendritic
- axon terminal synapses with a dendritic spine
c. Axoaxonic
- synapse at the axonic bouton
- The axoaxonic synapse may enhance or inhibit the
axodendritic (or axosomatic) synapse
d. Dendro-dendritic
e. Axo-axonal
- impinging dendritic/axonal synapse usually inhibits
other inputs
peripheral nerves connective tissue layers
Paraneurium Fascia that separates nerves from surrounding structures Epineurium Dense irregular connective tissue Separates different types of nerves and fills spaces between fascicles Perineurium Specialised connective tissue – transport proteins Maintains ionic composition Surrounds clusters of axons (fascicle) Endoneurium Loose connective tissue Surrounds single nerve cells
peripheral nerves 3 types
sensory, integrative and motor
THE BIGGER THE DISTANCE BETWEEN NODES OF RANVIER
THE FASTER THE CONDUCTION
myelination
- The axon sitting in a groove is surrounded by a Schwann cell
- The mesaxon membrane initiates myelination by
surrounding the embedded axon - A sheet-like extension of the mesaxon membrane then wraps
around the axon, forming multiple membrane layers - Cytoplasm is extruded from between the two apposing
plasma membranes of the Schwann cell, which then become
compacted to form myelin (19-20 rounds)
inner and outer mesaxon
Outer mesaxon: invaginated plasma membrane extending
from the abaxonal surface of the Schwann cell to the myelin
Inner mesaxon: extends from the adaxonal surface of the Schwann cell (the part facing the axon) to the myelin
oligodendracyte in CNS
Cytoplasmic processes from the oligodendrocyte cell
body form flattened cytoplasmic sheaths that wrap
around each of the axons
• The relationship of cytoplasm and myelin is
essentially the same as that of Schwann cells
• Difference: wraps around more than one axon
simultaneously
unmyelinated nereve cells
slwoer propagation of action potential
astrocytes
control flow of nutrients in the CNS
star like
have perineural feet that contain gap junctions
regulate nerve ipulses by releasing glutamate near to node of ranvier
contributes to BBB
microglial cell
large cell with elongated nucleus. mop up damaged nerve cells when they sense an increase in potassium. associated with alz
ependymal cell
line the spinal canal
look similar to comulmnar epithelial cells
ependymal cell functions
• Synthesise and secrete CSF in the ventricles (choroid plexus)
• Cilia move cerebrospinal fluid (CSF) through the ventricles to
the spinal cord
• Microvilli absorb CSF for removal of pathogens
- Present to microglial cells and astrocytes
- Modified tight junctions between epithelial cells control fluid
release into brain
- Molecular and cellular contents of brain can be monitored – ‘spinal
tap’
MS
• Remitting and relapsing disease
• Caused by autoimmune degradation of myelin
- [Probably against EBV]
