neurones and all that Flashcards
what are the basic cellular unit of the nervous system
neurones
what are the basic components that all neurones have (4)
- Dendrites
- Cell body/soma
- Axon
- Presynaptic terminal
what are the cell types of the CNS
neurones
differentiated glia
how much of CNS cells are accounted for by neurones
half - rest are glial cells
what are neurones specialised for
electrical signalling
how do neurones receive inputs
via dendrites which transmit
to the cell body (soma)
how do neurones transmit info
via axons and action potentials are propagated from the axon
hilock
when are neurones mainly formed
during development
how do neurones look with H&E stain
haemotoxylin - it stains nucleic acid blue
eosin - stains proteins red
which stain stains myelin
Luxor fast blue (LFB)
which stain stains stains Nissl (RER)
Cresol violet (CV
how do neurones communicate
via synapses
2 types
what are the 2 types of synapses
chemical and electrical
what are chemical synapses
the main type
via neurotransmitters
what are electrical synapses
less abundant
via direct flow of ions
enable synchronised electrical activity
examples of electrical synapses
- brainstem - breathing
- hypothalamus - hormone secretion
where are excitatory synapses often concentrated
on dendritic spines
describe chemical synaptic transmission
- axon potential depolarises synaptic terminal membrane
- opening of voltage gated calcium channels leads to calcium influx
- calcium influx triggers neurotransmitter release
neural plasticity
changes in neuronal/synaptic structyre and function in response to neural activity
basis of learning and memory
why is spine remodelling important
linked to neural activity
how do neurones differ
size
morphology
neurotransmitter content
electrical properties
where are glial cells found
surround the soma (cell body), axon and dendrites of neurones
what do glial cells provide
they provide neurones with physical & metabolic support
what are the 5 types of glial cells
- oligodendrocytes
- Schwann cells
- astrocytes
- microglia
- ependymal cells
what are oligodendrocytes
the myelinating cells of the CNS
unique to vertebrates
function of myelin
to insulate axon segments to increase the speed of conduction along the axon
what are myelin sheath segments interrupted by
nodes of ranvier - saltatory conduction
are myelinated axons thicker or thinner than normal
thicker
where are myelinated axons mostly found
in somatic nerves i.e. in fast
sensory/motor systems e.g. muscle & spinal systems
where are unmyelinated axons usually found
d in post-ganglionic autonomic
fibres, fine sensory fibres, olfactory neurones & interneurons - essentially where speed is not necessary e.g. hypothalamus (hormonal)
what are nodes of ranvier
the spaces between adjacent
sections of myelin where the
axons plasma membrane is
exposed to extracellular fluid
what do oligodendrocytes provide
metabolic support for axons in CNS - they are able to transport
metabolic products directly into axons
describe myelin sheath
formed by wrapping of axons by 20 - 200 layers of highly moligodendrocyte processes (membranes)
highly compacted - 70% lipid, 30% protein
myelin specific proteins eg myelin basic protein can be used as ‘markers’
how many axons can each oligodendrocyte myelinate
each oligodendrocyte may branch to form myelin on as many as 40 axons
what are microglia
specialised macrophage-like cells that perform immune functions in the
CNS
what do microglia originate from
from yolk sac progenitors that migrate into CNS
where do microglia proliferate
at sites of injury and then migrate to sites of damage - phagocytic
what are microglia like in the cortical grey matter
they are more ramified (branched)
how can microglia be bad
by being too sensitive causing excessive inflammation & destruction of dendritic spines
how do microglia contribute to synaptic plasticity
they “eat” unwanted dendritic spines
functions of microglia
immune surveillance
phagocytosis - debris/microbes
synaptic plasticity - pruning of spines
good (m2 ) and bad (m1) microglia
what are astrocytes
star like cells
most numerous glial cells in the CNS
highly heterogenous - not all star shaped
common “marker” GFAP
sub types of astrocytes
protoplasmic - found in grey matter
fibrous - found in white matter
astrocyte functions
- help regulate the composition of the extracellular fluid in the CNS by
removing K+ ions & neurotransmitters (e.g. glutamate) around synapses - take up glutamate then convert it to glutamine and release it,
then neurones can take it up and convert it back to glutamate for reuse - stimulate the formation of tight junctions between the cells
that make up the walls of capillaries found in the CNS - this forms the
BLOOD-BRAIN BARRIER, which is a much more selective filter for
exchanged substances that is present between the blood and most other
tissues - help form the blood-brain barrier by foot-processes closely applied
around capillaries - sustain the neurones metabolically e.g. by providing glucose
and removing ammonia
specialised astrocytes
radial glia - important for brain development
bergmanm glia- found in the cerebellum, support purkinje cell
dendrites & synapses
muller cells - specialised radial glia of the retina
function of ependymal cells
- line fluid-filled cavities within the brain (i.e. ventricles) and spinal cord
- regulate the production & flow of cerebrospinal fluid (CSF)
- provides barrier between CSF & brain to allow solute exchange between nervous tissue and CSF
structure of ependymal cells
have cilia, microvilli & desmosomes
motor neurones disease
adult-onset neurodegenerative disease characterised by loss of upper and lower motor neurones
multiple sclerosis
autoimmune demyelinating disease where immune cells attack the myelin sheath of oligodendrocytes
what is an early marker of Alzheimers
the loss of dendritic spines
what are the 3 functional classes neurones are grouped into
- afferent (sensory)
- efferent (motor)
- interneurons (within the CNS
what forms the nerves of the PNS
groups of afferent & efferent neurone axons together with connective tissue and blood vessels
what does nerve fibre refer to
a single axon
what does nerve refer to
a bundle of axons (fibers) bound
together by connective tissue
function of afferent (sensory) neurones
convey information from tissues and organs TOWARDS the CNS
what do afferent neurones have at their peripheral ends (farthest from CNS)
sensory receptors which respond to various physical or chemical changes in their environment by generating electrical signals in the neurone
describe shape of afferent neurones
shortly after leaving the cell body, the
axon divides;
1. one branch (the peripheral process) begins where the dendritic
branches converge from the receptor endings
2. the other branch (the central
process), enters the CNS to from junctions with other neurons
the cell body & long axon (peripheral process) are OUTSIDE the CNS, and
only a part of the central process enters the brain or spinal cord
function of efferent (motor) neurones
convey information AWAY from the CNS to effector cells such as muscle,
gland or other cell types
structure of efferent neurones
cell bodies & dendrites are WITHIN the CNS, and the axons extend OUT to
the periphery
function of interneurones
connect neurons WITHIN the CNS - form the majority of neurons
where are interneurons found
they lie entirely WITHIN the CNS
which cells form myelin sheath in PNS
schwann cells - form individual
myelin sheaths surrounding 1 to
1.5 mm-long segments at
regular intervals along the
axons
where are myelinated axons mostly found
in somatic nerves i.e. in fast
sensory/motor systems e.g. muscle & spinal systems
difference between schwann cells and oligodendrocytes
schwann - myelinate PNS
myleinate single axon
oligodendrocytes - myelinate CNS
myelinate multiple axons
what causes epilepsy
disease of neurones
what causes depression
disease of neurones and glia
what are tracts
a collection of nerve fibers (axons) in the CNS
what is contained in nuclei in CNS
abundance of neuronal cell bodies
what are commissures
tracts that cross midline in the CNS
what is neuropil
the dense network of fine glial processes, neuronal processes (axons and dendrites), and fibrils in the gray matter of CNS
where are cell bodies and supporting cells located in the PNS
ganglia
what are axons bundled into in the PNS
nerves
what is the blood brain barrier (BBB)
A network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain
what is BBB formed from (3)
- endothelial cells
- pericytes (contractile cells that wrap around the endothelial cells of capillaries and venules)
- astrocytes
features of BBB (5)
- Endothelial tight junctions
- Astrocyte end feet
- Pericytes
- Continuous basement membrane, lacks fenestrations (windows)
- Requires specific transported for glucose, essential ions etc
what are CIRCUMVENTRULAR ORGANS
certain parts of the brin that lack the BBB
example of a circumventrular organ
posterior pituitary - they need to be in
contact with the blood for a sensory role to monitor
what is BBB sensitive to
- inflammation
- hypertension
- trauma
- ischaemia
where does CSF circulate
through the subarachnoid space (around the brain and spinal cord)
and within ventricles - offers protection by cushioning brain from gentle
movements)
what does CSF do
offers protection by cushioning brain from gentle movements
what are the 4 ventricles
- Lateral (paired)
- III
- IV
how do ventricles & subarachnoid
spaces connect
via cisterns
describe CSF appearance
a clear, colourless liquid
what does CSF contain
protein, urea, glucose & salts
what is CSF produced by
by ependymal cells in the choroid plexuses of the lateral ventricles
(mainly)
what is choroid plexus
a network of blood vessels in each ventricle of the brain, producing the cerebrospinal fluid.
what is choroid plexus formed from
from modified ependymal cells
they from around a network of capillaries, large surface area
how is CSF absorbed
via arachnoid granulations (VILLI) e.g. in the superior sagittal sinus
what is hydrocephalus
a disease
abnormal accumulation of CSF in ventricular system
often due to a blocked cerebral aqueduct
impact of accumulation of CSF
leads to a build up of pressure which can damage brain tissue since the skull in hard in adults
- In children with soft skull the pressure will cause the soul to bulge and look
abnormal as well as damaging the brain
