nervous system intro Flashcards
plane along midline of the brain
saggital
plane sideways through brain
coronal
plane parallel to midline of brain
parasagittal
plane that goes flat through brain
horizontal
3 main brain areas
forebrain, midbrain, hindbrain
parts of the forebrain
cerebral hemispheres, thalamus, hypothalamus
parts of the hindbrain
pons, cerebellum, medulla
pons function
autonomic system, respiratory and cardiac control
pons function
autonomic system, respiratory and cardiac control
cerebellum function
motor coordination
medulla function
autonomic system, respiratory and cardiac control
what is the ventricular system in brain
cavity filled with cerebrospinal fluid
cerebrospinal fluid function
allows specific substances into brain - blood brain barrier
ventricular system function (3)
physical = provides protection
chemical = maintains ion levels
removes waste products
4 subdivisions of spinal cord (top to bottom)
cervical, thoracic, lumbar, sacral
spinal cord – cervical
cervical enlargement due to large number of motor neurons for the arms
spinal cord – thoracic
autonomic neurons - sympathetic system for heart rate
spinal cord – lumbar
lumbosacral enlargement due to large number of motor neurons for legs
spinal cord – sacral
autonomic neurons for bladder and reproductive organ control
brain tissue – grey vs white matter
grey = neuronal cell bodies and glia
white = neuronal axons wrapped in myelin
brain tissue – grey and white matter locations in brain and spinal cord
brain = grey matter surrounds white matter in centre
spinal cord = mostly white matter with grey matter more centrally
functional divisions of spinal cord (2)
DAVE:
dorsal (sensory information) is afferent (input)
ventral (motor function) is efferent (output)
neurons vs glia
neural circuits/systems
neurons = excitable cells that conduct impulses, integrate and relay info within neural circuit
glia = supporting cells, clear away debris, maintain environment for neurons and homeostasis
neurons + glia = neural circuits
multiple neural circuits = neural systems
methods for studying neurons and glia:
Nissl staining
positive charged dye (cresyl violet) which stains RNA (negatively charged)
allows distinguishing between neurons and glia
stains nucleolus of calls - neurons have Nissl bodies
used to view cytoarchitecture of brain
methods for studying neurons and glia:
Golgi staining
silver chromate
highlights some neurons
used to find out neurons aren’t fully connected - small gaps (synapses)
methods for studying neurons and glia:
immunohistochemistry
used to find locations and densities of different membrane proteins
use target proteins e.g. Nav channels
specific primary antibodies bind to target proteins
secondary antibodies with fluorescent tags bind to primary antibodies and tag changes level of fluorescence when bound
therefore can see areas dense with target proteins
methods for studying neurons and glia:
live imaging of fluorescent dye
can be genetic or injected
neurons expressing desired protein will fluoresce and can be tracked and studied
methods for studying neurons and glia:
electron microscopes
can view synapses and organelles
methods for studying neurons and glia:
retrograde and anterograde tracers
horseradish peroxidase (HRP)
retrograde = moves back to the cell body (backward)
anterograde = move away from cell body (forward)
retrograde:
inject retrograde tracer into neuron and wait for it to reach the brain
section brain to find tracer and find where neuron has gone to
anterograde:
inject anterograde tracer into brain and wait to see where in the body the tracer ends up
4 parts of the neuron
soma
axon
dendrite
presynaptic terminal
(axons and dendrites are neurites)
soma structure - what organelles??
aka cell body, perikaryon
has the nucleus - organelles for protein synthesis and processing: ribosomes, RER, golgi
golgi is stained with silver chromate
mitochondria have many more neurons than other cells - energy intensive
neurite structure (3 components)
cytoskeleton of microtubules, microfilaments, and neurofilaments
microtubules = longitudinally down neurites, hollow tube of polymers of tubulin
microfilaments = longitudinally and membrane associated, polymers of actin
neurofilaments = long protein molecules wound together - very strong
microtubules and microfilaments are dynamically regulated -> can change length according to needs - polymerisation (grow) and depolymerisation (shorten)
axon structure (4 sections)
axon hillock = wide part which connects to soma
axon initial segment = just below hillock, action potentials generated here, high density of Nav channels
axon collaterals = axon starts to branch
axon terminal (terminal bouton) = end of each collateral
axon - organelles and composition
no RER or free ribosomes - all required proteins have to be made in the soma and transported (uses lots of energy)
membrane composition varies depending on part of axon
<1mm to >1m in length e.g. whole length of a leg
1um - 25um in diameter
main axon is thickest and may be more myelinated, collaterals are thinner
axons with many collaterals = high level of divergence = many cells can be contacted
presynaptic terminal - specialisations
no microtubules
synaptic vesicles
specialised proteins - release of vesicles and detection of action potential
proteins are made in soma and transported here
many mitochondria
synaptic cleft - couple of um wide - very small
types of presynaptic terminal (2)
terminal arbour:
one axon split into many terminals
boutons en passent:
means “buttons in passing”
swelling on axon full of vesicles - not at the end of an axon
axoplasmic transport
can be slow or fast
carry’s a vesicle along an axon
travel down microtubules using kinesin which “walks” down using energy from ATP
anterograde = moves forward from cell body - kinesin
retrograde = moves backward from cell body - dynein (similar to kinesin)
dendrites structure (2 main components)
receive messages from other neurons
dendritic branches –> dendritic arbors :
– can have thousands of synapses, convergence of different inputs from other neurons e.g. Purkinje cells have many dendrites from many sources and combine these
dendritic spines:
increases surface area
creates space for isolated reactions
specific receptors on membrane
very plastic - can get rid of spine, or grow new ones
cognitive impairment caused by disorders where number of sines is abnormal
neuronal classification: structure - number of neurites (3)
number of neurites:
unipolar = 1 neurite (rare) – “pseudo-unipolar” is one neurite from soma which splits into two which have distinct functions, very few purely unipolar neurons
example – dorsal root ganglion - info from skin into spinal cord - myelinated axon comes off from soma and becomes dendritic at the end to sense from skin - performs one specific role
bipolar = single axon and dendrite (uncommon)
example – retinal bipolar cells, pass info from sensory cells to retina, very reliable - info from one area passed onto another, specialised function
multipolar = many neurites (common)
example – Purkinje cell, 150,000 contacts/synapses, majority of neurons are like this, high level of convergence
neuronal classification: structure - dendritic geometry (2)
arrangement of dendrites
stellate = star shaped, e.g. layers of neocortex
pyramidal = distinct apical and basal dendritic trees, pyramidal shaped soma e.g. layers of neocortex or hippocampus
neuronal classification: connections - where do they project
sensory = afferent
motor = efferent
interneuron = largest class - relay or projection neurons connect brain regions, local interneurons have short axons and process info in local circuits
axonal length = local or further away connections
neuronal classification: gene expression
underlies structural differences
defines neurotransmitter expression - inhibitory or excitatory
use fluorescent genes to track these and know which neurons to study
glial cells
fill space around neurons
can proliferate through lift - can always make new ones (neurons only created in specific brain areas)
glial cells: types of cells (3 x 3 categories)
homeostatic:
CNS = astrocytes
PNS = satellite cells
ENS = enteric glia
myelinating:
CNS = oligodendrocytes
PNS = Schwann cells
phagocytic:
CNS = microglia
PNS = Schwann cells and macrophages
what is the ENS
enteric nervous system - related to autonomic
just focused on the gut - gastrointestinal tract
glial cells: astrocyes
homeostatic - control environment surrounding neurons
maintain resting potentials
spatial domains - main cell body surrounded by processes in a star like way, area doesn’t overlap with other glial cells much
glial fibrillary acidic protein (GFAP) = unique marker which can be tracked with immunohistochemistry to find astrocytes
buffer extracellular potassium
form part of the BBB
couple neuronal activity to blood supply - more oxygen when more active (homeostatic)
glial cells: subtypes of astrocytes
don’t need to know them all!
fibrous
protoplasmic
radial glial cells - developmental
muller cells - retina
Bergmann glia - cerebellum
ependymal cells - ventricles and central canal (learn this one)
glial cells: astrocyte function as fuel supply
act as fuel suppliers - glycogen stores of the brain
5-10 minute supply
metabolise glycogen and supply lactate (becomes pyruvate)
convert glucose to glycogen in low activity times, use the glucose in high activity times
astrocytic end feet take up glucose
glial cells: astrocyte tripartite synapse
terminates neurotransmitter activity - instantly stop signal once it has been used
recycles neurotransmitters to presynaptic terminals
astrocytes have receptors too - can respond to neurotransmitters themselves
glial cells: microglia
macrophages of the CNS
phagocytosis - engulf debris, take into cell and process it
secrete growth factors, help myelination, and synaptic pruning
3 states = resting –> activated –> phagocytic
can have harmful roles in neurodegenerative diseases - become phagocytic on healthy cells
glial cells: oligodendrocytes
myelinate axons in the CNS
can myelinate many axons from one oligodendrocyte - 15-30 processes
glial cells: Schwann cells
myelin sheaths in the PNS
provides one myelin segment to one axon per Schwann cell
glial cells: formation and function of myelin sheath
formation:
process of oligo cytoplasm wraps many times around the axon
cytoplasm squeezed out of layers by compaction so just the membrane and a few proteins are left
maintain contact with glial cells for nourishment
function:
insulate the axon
speed up neuronal conduction with saltatory conduction
