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Summary Brain, Hormones and Metabolism HAP-30806
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summary of all lectures of the course Brain, Hormones and Metabolism HAP-30806
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Brain, Hormones and Metabolism lectures summaryWeek 1: intro brain
Lecture 1 – Brain Anatomy
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
General functions:
- Multipolar neurons: bijv. For example the motor neurons of the spinal cord that connect to
muscles, glands and organs throughout the body. Transmit impulses from the spinal cord to
skeletal and smooth muscles -> directly control all of our muscle movements.
Two types of motor neurons:
lower motor neurons: travel from spinal cord to muscle:
upper motor neuron: travel between brain and spinal cord
- Pseudo-unipolar and bipolar neurons: in general sensory neurons activated by sensory input
from the environment
- Unipolar neurons: transmit information from the brain to the spinal cord
Synaptic connections between neurons
- Most neurons have one axon, axon can divide into several branches: axon collaterals
- Neural plasticity: configuration of synapses on dendrite changes continuously as dendrites
change shape, synapses come and go.
Supporting cells – central nervous system (neuroglia)
Astrocytes:
- Phagocytosis
- Nourishment
- Nerve glue, involved in formation new synapses and pruning surplus synapses
- Control composition neuronal extracellular fluid: role in epilepsy (changed neuronal
excitability)
- Surround synapses – limiting dispersion neurotransmitter
- Communication between neurons
- Swelling in case of brain damage – edema
- 17% of brain’s glial cells
- >60% of brain tumors have astrocyte origin (astrocytoma)
- Grade I-IV, grade IV (glioblastoma) has a very poor prognosis (5 year survival 5%)
Microglia:
- Resident macrophages of the brain
- Phagocytosis, migrate to site of injury
- Key component in neural pain system
- Role in maintenance of synapses – interference with this function is related to Alzheimer
disease and other dementias – target for treatment Alzheimer
- 7% of brain’s glial cells
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, - Can suppress brain tumor progression
- Tumor can polarize microglia after which they switch role -> become immunosuppressive
and facilitate brain tumor growth (support angiogenesis, metastasis and relapse)
Oligodendrocytes:
- Myelin sheets – insulation multiple axons
- Myelin – 80% lipid, 20% protein
- Node of Ranvier
- Loss in oligodendrocytes – linked to onset schizophrenia
- 75% of brain’s glial cells
Multiple sclerosis – defect in myelination (oligodendrocyte function) ->
damaged myelin disturbs signal transduction
Supporting cells – Peripheral nervous system (neuroglia)
Schwann cells:
- Myelin from one node of Ranvier to other
- Re-growth axon
- Support non-myelinated axons
- Schwann cells are capable of providing myelin to multiple axons
- Loss of the Fbxw7 gene, an E3 ubiquitin ligase component, enhances the myelinating
potential of SCs, making thicker sheets and sometimes appear to myelinate multiple axons.
Clinical applications characeteristics: facial transplants and regeneration of PNS: regrowth of
peripheral axons facilitated at least in part by Schwann cells.
Major anatomical structures – basal ganglia
- Involved in movement: caudate nucleus, putamen globus pallidus, substantia nigra
- Thalamus, amygdala, subthalamic nucleus
Major anatomical structures – Limbic system
- Fornix, thalamus, stria terminalis, septal nuclei
- Emotional learning: amygdala
- Learning and memory: mammillary body, hippocampus
- Attention and cognitive function: cingulate gyrus
- Smell: olfactory bulb
Corpus callosum: continuous communication among cortical lobes
Cortex: exterior dark grey matter (cell bodies, dendrites, blood vessels) underneath white matter
(axons with myelin sheets)
Function CSF: Protection
- Reduces weight brain from 1400 to 80 g;
- Shock absorption
- Medium for exchange of nutrient etc. between brain and blood circulation
2
,Obstruction cerebral aqueduct – hydrocephalus
In case the CSF cannot reach the subarachnoid space where absorption of CSF occurs (due to for
instance obstruction of the cerebral aqueducts) CFS will accumulate in the ventricles leading to
increased pressure on the brain. Untreated brain damage.
Lecture 2 – Neurophysiology
Communication: Electrical charge across the neuronal membrane
Intra- and extracellular fluid:
- Cations (+) and anions (-) are distributed unevenly across the neuronal cell membrane
- Steady outward diffusion of K+ through leakage channels
- Na+ barely able to cross cell membrane (inward direction)
- Net result: state of relative negativity on the inner membrane face, the resting membrane
potential (voltage difference of -50mV to -80mV, in general -60-70mV)
Membrane Potential: Equilibrium in More Detail
Nernst equation: mathematical function, predicting the voltage (electrical force) needed to just
counterbalance the diffusion force pushing an ion across a semipermeable membrane (from high to
low ion concentration, chemical force)
- K+-ions: Nernst equation predicts required membrane potential to balance the high K+-ion
concentration inside the cell to be close to the resting membrane potential
- Nernst equation does not take into account that membrane is somewhat permeable to other
ions (Cl- and Ca2+)
Neurobiology: The Action Potential
Hyperpolarization:
- Increasing negativity of membrane potential
- The greater the stimulus, the greater the response
- Potentials produced by stimulation of membrane diminish as they spread away from point of
stimulation
Depolarization:
- Graded responses
- Change when stimulus depolarizes cell to -40 mV, threshold
- Brief action potential provoked, all-or-none property
- Inside of membrane becomes positive
- Action potential actively propagated down axon
- Karger depolarizations produce more action potentials, not larger action potentials
(amplitude is independent of stimulus magnitude)
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, Equilibrium:
Absolute refractory period: temporarily inability to generate action potentials: (Na+-
channels open)
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 – threshold for action potential generation temporarily substantially
elevated.
Impulse conduction:
Propagation action potential: unmyelinated axons
- Aps are generated at sites immediately adjacent to each other, move in one direction
- Conduction relatively slow (continuous conduction)
- Conduction velocity varies with axon diameter
- Leakage of charge from the axon
Propagation action potential: myelinated axons
- APs only generated at nodes, including a depolarization followed by opening of Na+ channels
generating another AP, etc.
- Current flows along the axon from node to node
- Fast transduction
- Voltage-gated Na+ -channels open quickly and briefly active (typical for axon)
- saltatory conduction, less Na+ -channels need to be opened -> faster (nodes of Ranvier)
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