College aantekeningen
College aantekeningen en afbeeldingen
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- Wageningen University (WUR)
College aantekeningen en afbeeldingen.
[Meer zien]Voorbeeld 4 van de 57 pagina's
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Brain, Hormones and MetabolismLecture 1
- CNS = neuronal tissue encased by bones of skull and spinal column
- PNS = nerves and most of the sensory organs located outside skull and spinal column
- Different types of neurons:
o Unipolar = one cell body with nucleus and one axon
o Bipolar = cell body in the middle and two myelinated sheats.
o Pseudo-unipolar = cell body on a stolk, an axon and hand side, no myelin sheats
o Multipolar = axon with a lot of dendrites and myelin sheath.
- Functions of neurons:
o Multipolar neurons: motor neurons, impulses from the spinal cord to skeletal and
smoot muscles. Two types of motor neurons: from spinal cord to muscle → lower
motor neurons. And those between the brain and spinal cord → upper motor
neurons.
o Pseudo-unipolar and bipolar neurons: sensory neurons activated by sensory input to
the brain.
o Unipolar neurons: from the brain to spinal cord.
- Axon collaterals = axon can divide into several branches.
- Neural plasticity = configuration of synapses on dendrite changes continuously as dendrites
change shape, synapses come and go.
- Supporting cells in CNS = neuroglia.
- Astrocytes (are also neuroglia) = located close by synapses. Astrocytes contain glucose and
produce lactate = source of energy for neurons. Astrocytes play a role in phagocytosis,
nourishment (glycogen and lactate) and is a nerve glue (involved in formation of new
synapses and pruning surplus synapses). More functions:
o Control composition of neuronal extracellular fluid → role in epilepsy (changed
neuronal excitability)
o Surround synapses → limiting dispersion of neurotransmitter
o Communication between neurons
o Swelling in case of brain damage → edema
o 17% of brain’s glial cells
- >60% of brain tumors are of astrocyte origin → astrocytoma. It can develop into
glioblastoma (5 year survival is 5%).
- Microglia (also neuroglia) = resident macrophages of the brain, phagocytosis, and migrate to
site of injury and they are a key component in neural pain system. They play a role in
maintenance of synapses → may interfere with Alzheimer disease and other dementias. 7%
of brain’s glial cells.
- Microglia and brain cancer → microglia are not static, can suppress brain tumour
progression. Tumour can polarize microglia after which they switch role → become
immunosuppressive and facilitate brain tumour growth (support angiogenesis, metastasis
and relapse).
- Oligodendrocytes (also neuroglia) = involved in formation of myelin sheath. Loss in
oligodendrocytes is linked to onset of Schizophrenia. 75% of brain’s glial cells, most
abundant!! Oligodendrocytes can assist multiple neurons.
- Myelin sheath = insulation of axons. Myelin = 80% lipid and 20% protein. The axon is not
completely covered by myelin sheath → nodes of Ranvier.
- Multiple sclerosis = defect in myelination → oligodendrocyte function.
- Myelinization by Schwann cells:
o Schwann cells surrounds cell cytoplasm
o Makes layers around the axon
, o When the myelinization is finished, the cytoplasm is gone. High lipid content and low
protein content.
o Schwann cells is supporting one axon. On both sides of the node of Ranvier → 2
Schwann cells.
- Functions of Schwann cells:
o Re-growth axon → is more simple in PNS than in CNS.
o Support non-myelinated axons → one Schwann cell support multiple axons.
- New ideas about Schwann cells:
o They are capable of providing myelin to multiple axons
o Loss of Fbxw7 gene → loss of E3 ubiquitin ligase component → enhances
myelinating potential of Schwann cells, making thicker.
- When peripheral axons are damaged, they can easier adapt than the brain axons → due to
the organization of Schwann cells → support re-growth.
- Horizontal, sagittal, coronal plates of the brain.
- Frontal lobe, parietal lobe, occipital lobe and temporal lobe.
- Gyri (folds) and sulci (spaces) → increase in cortex volume → the more gyri and sulci → the
more complex the brain → more extensive learning and memory capacity.
- Cortex seat of complex cognition.
- Basal ganglia consist of: caudate nucleus, putamen, globus pallidus, substantia nigra → all
involved in movement.
- Substantia nigra = first affected in Parkinson’s disease.
- Learning and memory = hippocampus and mammillary body and fornix
- Emotions = amygdala
- Reward and reinforcement = septal nuclei
- Smell = olfactory bulb
- Attention and cognitive functions = cingulate gyrus
- Communication among cortical lobes → corpus callosum.
- Cortex:
o Exterior dark gray matter (cell bodies, dendrites, blood vessels)
o Underneath white matter (axons with myelin sheets, less cell bodies)
- Cerebrospinal fluid (CSF):
o Protection of the brain.
o Shock absorption.
o Reduces weight brain (floating) from 1400 to 80 grams.
o Medium for exchange of nutrient between brain and blood circulation.
o Produced in lateral ventricles → choroid plexus.
- Absorption of CSF in arachnoid granulations at skull side → take CSF up and release it again
→ takes place at different sites → otherwise the amount of CSF will be too high.
- Obstruction of cerebral aqueduct = hydrocephalus → CSF cannot reach subarachnoid space
where absorption of CSF occurs → CSF will accumulate in ventricles leading to increased
pressure on the brain → can lead to brain damage.
Lecture 2
- Intra- and extracellular fluid:
o Cations + and anions – are distributed unevenly across the neuronal cell membrane
o Steady outward diffusion of K+ through leakage channels
o Na+ barely able to cross cell membrane (inward direction)
o Net result: state of relative negativity on the inner membrane face = the resting
membrane potential (voltage difference of -50 mV to -80 mV, in general -60-70 mV)
- Sodium-potassium pump = continuously pushes Na+ ions out and pulls K+ ions in. Requires
ATP!
- There is also a large negatively charge of proteins in the cell.
,- Membrane is permeable to ions → K+ ions pass back out again through channels down their
conc. gradient. Departure of K+ ions leave the inside of the cell more negative than the
outside. Na+ ions can’t pass back inside.
- Equilibrium potential (-60 mV) → when enough K+ ions have left the cell until -60 mV.
- Electrostatic pressure = pulls back K+ ions out of the cell.
- Nernst equation = predicting the voltage (electrical force) needed for efflux of K+ outside.
May be around resting membrane potential, doesn’t include chlorine and calcium ions.
- Action potential: hyperpolarization.
o Increasing negativity of membrane potential.
o The greater the stimulus, the greater the response.
o Potentials produced by stimulation of membrane diminish as they spread away from
point of stimulation.
- Action potential: depolarization.
o Graded responses.
o Change when stimulus depolarization cell to -40 mV threshold.
o Brief action potential, all-none-property.
o Inside of membrane becomes positive.
o Action potential actively propagated down axon.
o Larger depolarizations produce more action potentials, not larger action potentials
(amplitude is independent of stimulus magnitude)
- Potassium concentration is higher inside the cell (moves outside), sodium concentration is
higher outside the cell (moves inside).
, - Absolute refractory period = temporarily inability to generate action potentials. Sodium
channels are open, another depolarization will not result in another action potential.
Independent of the strength of the signal.
- Relative refractory period = follows the absolute refractory period, Na+ channels have
returned to resting state (closed), some K+ channels are still open and repolarization is
occurring. An action potential can be induced if signal is strong enough.
- Propagation action potential in unmyelinated axons:
o Action potentials are generated at sites immediately to each other, move in one
direction.
o Conduction is relatively slow.
o Conduction velocity varies with axon diameter.
o Leakage of charge from the axon.
- Propagation action potential in
myelinated axons: voltage-gated
Na+ channels open quickly and
briefly active (typical for axon):
o APs generated only at
nodes, inducing a
depolarization followed
by opening of Na+
channels generating
another AP.
o Current flows along the
axon from node to
node.
o Fast transduction.
- Unmyelinated axons →
continuous conduction.
- Myelinated axons → saltatory conduction, less Na+ channels need to be opened.
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