Neurohistology Flashcards
neurons
-basic cell unit of the nervous system
-consist of a cell body with projections called dendrites which help with synaptic activity as well as an axon that facilitates long distance communication and est. contact with nerve terminals
-axon is wrapped with myelin
neuroglia
-derived from the ectoderm with the exception of microglia (derived from the mesoderm)
-astrocytes, microglial cells, oligodendrocytes, and peripheral neuroglial cells
embryogenesis of the CNS
-basic structure of the CNS originates in the neural plate, which comes from the ectoderm
-neural plate gives origin to neural groove that gives origin to microscopic structures of the CNS
astrocytes
associated with axons and neurons and blood vessels —> in recent years we have realized the importance of them in neuronal function
oligodendrocytes
-cells that produce myelin
-heavily myelinated axons have rapid conduction vs less myelinated have slower conduction
how is the neural tube divided?
divided into three parts:
-forebrain
-midbrain
-hindbrain
what does the interior of the neural tube give rise to?
the interior gives rise to the brain, midbrain, and spinal cord
adult brain mimics what we see in embryogenesis
brain contains all the physiological functions associated with cognition and behavior
major components of brain
-frontal lobe- largest portion of the brain and critical for many functions like motor organization (motor cortex) and cortical regions with topographic distribution
-prefrontal cortex- controls executive functions, behavior, and personality
-premotor cortex- organizes motor info and organization
-occipital lobe- has cerebral cortex that processes visual info that comes from optic nerves
what happens if you lose the frontal lobe?
-in the 20th century, people with severe mental health disorders would have their frontal lobes removed and they would be calmer since they would lose their personalities and behaviors
-football players who repeatedly get concussions and hit their frontal lobe tend to experience issues with their personalities and behaviors later in life
brain organization
-gray matter- high density of neurons and neuroglia
-white matter- high density of myelinated axons
spinal cord
-contained in the spine, which is the body compartment
-carries sensory info from body to brain and impulses from the brain to the body —> bilateral pathways
Ex. damage to the spinal cord or trauma in neck can cause issues with paralysis since this communication is interrupted
descending info: motor function
Ex. if you want to use your right hand, need to know where your right hand is first (sensory input) —> signal is generated in premotor cortex —> goes to primary motor cortex —> signal goes in white matter down to the spinal cord
left brain —> right side of body
-90% of fibers controlling right hand come from left side of brain
-signals come from the prefrontal cortex but primary motor cortex is on the left side —> signals come down to portion of brainstem where they cross @ pyramidal decussation
corticospinal tract
-one of the most important tracts of the spinal cord
-package of axons with backup function on the same side of hand
symptoms of motor disfunction
weakness, paralysis, stiffness (spasticity), and cramps
ascending info: sensory function
-if you have or need to execute a function the brain needs to know everything about the function
-nerves carrying sensory info from hands and legs —> spinal cord —> carries info to the brain and the first stop is the thalamus
thalamus
distributes info to the frontal lobe and facilitates movement
symptoms of sensory disfunction
pain, lack of sensation, abnormal sensation, and lack of balance
CNS histology
in CNS we frequently include neurons but alone it doesn’t work —> need microglial cells, blood supply, myelin, and astroglial cells
astroglial cells
close contact with neurons and blood vessels
microglia
-microglia and macrophages originated in the mesoderm
-representatives of the immune system in the brain
-no immune privilege in the CNS —> in the CNS microglia and astroglia are part of the innate immunity along with the blood vessels that connect the CNS and bloodstream
what is the main excitatory neurotransmitter?
glutamate
what is the main inhibitory neurotransmitter?
GABA
what happens during embryogenesis?
-during process the brain acquires neurons and neuroglial cells
-during the first year to two years of life, there is not a lot of stimulation so the organization is on the lower side
-after the baby is born, important to provide stimulation otherwise they may have a deficiency in synaptic connectivity
Ex. kids with autism may not have enough stimulation during this time
important factors for development of cerebral cortex
-function of glia like astrocytes that facilitate movement of neurons
-immune system is important —> pregnant women need to be careful not to get sick since it can cause the embryo’s immune system to react
when is the critical period of synaptic development?
in utero to two years of age
when is the adaptation period of synaptic development?
after two years of age
Ex. language imprinted during first two years of life is stronger than a second language acquired as a teenager
adaptation period
-strain on synaptic connectivity
-more susceptible to change
Ex. learn algebra in high school then come to college and stop using it —> synaptic connectivity goes away but you do not lose your primary language
subtypes of glial cells
-astrocytes- help blood vessels and issue long processes called glial processes
-blood vessels- critical for the blood brain barrier, which has macrophages and endothelial cells
-microglia- derived from mesoderm and interact with neurons
how do glial cells help synapses?
-for neurotransmitter to be released, glial cell is controlling the traffic of the neuron and exchange of the neurotransmitter
-synapses are formed or taken away
-synaptic removal is dependent on microglial cells
-synaptic structures use compliment factors and microglia phagocytyse the synaptic structure —> constant process of synaptic modeling
perivascular astrocyte
-healthy tissue that went through injury —> glial cells come to injury and produce growth factors (cytokines and chemokines) for recovery
-some glial cells facilitate regeneration
cajal
-pioneer in histology of CNS
-used photography in the 19th century and exposed film for hours
-he used microscope photography and paint to expose histology
-believed in neurocentric theory that the neuron was the main cell of the CNS
pio del rio-hortega
-instead of drawing neurons, he drew other cells surrounding the neurons
—> found that many neurons were attached to microglia
-fired from lab since he went against what cajal believed
importance of microglia
-main cell mediator of innate immunity in the CNS
-critical for metabolic processes structure of synaptic formation, and direction of transcriptomic function of different areas of the brain
-sensory of injury and disfunction, director of phagocytosis, and necessary for healthy and normal synaptic plasticity
microglia derivation from mesoderm
-1st wave is stem cells from yolk sac that populate brain and liver
-2nd wave is macrophages past embryogenesis —> monocytes are represented in different organs as macrophages throughout life
brain and CNS have lymphatic drainage system
-elements of the CNS are drained into lymphatic drainage system
-facilitates communication between brain and lymphatic chain
