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Summary Physiology
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Physiology (part Buwalda)
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BuwaldaCommunication
Chapter 6: 201-2018, chapter 8: 270-299
Communication: speaking and listening
Ligands: signal molecules → talk to receptor proteins; communication
Receiving information
communication between cells
internal and external stimuli
↓
Sensory systems: sensors pick information up
↓
Brain-integration: decides to take action
↓
Behavioral and endocrine response: tackle the stimulus
➔ Organs receive input from autonomic nervous system → talk back and inform the brain
Central nervous system speaks with endocrine (hormone) system → hormone will be released
through the blood → talks to receptor that is only specific for that hormone
Brain talks with endocrine system → endocrine system talks with immune system → immune system
talks with the brain (nervous system)
Local communication
- Gap junctions: form direct cytoplasmic connections between adjacent cells
communication between cells next to each other
➔ Organizes a movement as one total system
➔ Muscle cells (in intestine)
- Contact-dependent signal: require interaction between membrane molecules on two cells
➔ Natural killer cell
- Autocrine signal: one cell act on the same cell that secreted them
- Paracrine signal: are secreted by one cell and diffuse to adjacent cell
➔ Diffuses over the surface of the stomach
Ligand = signal molecule
Long-distance communication
Long-distance signaling may be electrical signals passing along neurons or chemical signals that travel
through the circulatory system
➔ Secreted into the blood circulation and travel through the whole body
- Hormonous
- Endocrine system (hormones)
- Nervous system (neurons)
Neurotransmitters: chemical secreted by neurons that diffuse across a small gap to the target cell
Hormones: secretd by endocrine glands or cells into the blood. Only target cells with receptors for
the hormone respond to the signal
Neurohormones: chemicals released by neurons into the blood for action at distant targets
➔ Oxytocin, vasopressin: secreted in posterior part in pituitary
Speaking (first messengers)
,Listening by receptor proteins in the cells (membranes / cytosol)
- Ligands: first messengers
- Receptor proteins (in cells: cytosol/membranes)
- Intracellular processes
o Signal pathways: second messengers
- Cellular response
- Behavioral and physiological response
Lipid(fatty) soluble ligands
Steroid hormones: lipophilic, can easily travel through membranes (lipid layer)
- Corticosterone
- Testosterone
- Estradiol
Alter gene transcription
Lipophilic: soluble in lipid environment
Steroid hormones lipophilic
Can bind to cytosolic receptors → travel to nucleus through membrane → bind to DNA, hormone
responsive element in DNA → transcription of gene is activated → mRNA, protein (slow), alter gene
transcription
Antibody can be targeted to specific protein(receptor) (GR) → receptor complex is moving out of the
cytosol into the nucleus → transcription is activated
Water soluble ligands(hydrophilic/lipophobic):
- Neurotransmitters
- Lipophobic hormones (binds to membrane receptors)
o Insulin
o Adrenaline
o Glucagon
➔ Cannot travel through the membrane, they has a transporter that does that for it
Ligand bind to receptor protein that is in the cell → triggers an action (opening an ion channel/
activate G proteins)
Target cell membrane receptors
Guanine nucleotide binding protein(G protein)
- Receptor channel: ligand binding opens or closes the channel (ionotropic)
- G protein-coupled receptor: ligand binding to a G protein-coupled receptor opens an ion
channels or alters enzyme activity (metabotropic)
- Catalytic receptors
o Receptor-enzyme: ligand binding to a receptor-enzyme activates an intracellular
enzyme
➔ Tyrosin kinase: enzyme inside a cell, signal molecule binds to a receptor → tyrosine kinase is
activated and starts to phosphorylate a protein that mediate an action in the cell
o Integrin receptor: ligand binding to integrin receptors alters enzymes or the
cytoskeleton
Agonist: does the same as the internal signal molecule (ligand)(→ response)
Antagonist: blocks the signal → block the ligand to bind to the receptor (→ no response)
Multiple binding sites: receptor proteins
Competitive antagonist always compete for the same binding site
, ➔ Competition for the same binding site
Noncompetitive: Don’t compete with the ligand for the receptor spot where it binds, but bind on a
different place → effect that the own ligand is having
Allosteric: binding on a different spot than own signal molecules do, own signal molecule binds on a
specific place
Communication between neurons
Billions (10^9) neurons in the brain
Neurons with a cell body with a long axon
Dendrites in the cell body → information from other cells projects on the dendrites → touch the
neurons
Neuron is receiving information form a lot of other neurons
Axon can be myelinated (fatty layer around it) → increases the speed of a signal
- Pre-synaptic: where neurotransmitters and vesicles are stored, released when action
potential runs over the axon
- Postsynaptic: neurotransmitter binds to receptors and gives information over
Action potential: membrane depolarization
Action potential arrives at pre-synaptic terminal → causes voltage gated Ca2+ channels to open →
calcium enters cytoplasm of pre-synaptic terminal, there it can bind with proteins that are connected
with vesicles which store the neurotransmitters in synaptic terminal → vesicles are drawn (fuse) in
membrane → calcium interacts with the proteins → neurotransmitters are going to post synaptic
cells
Membrane potential are changing → signaling (electricity)
Outside of cell more positive, more positive loaded ions
Inside of the cell more negatively loaded
Cells are more permeable to K+ than to Na+
Membrane potential: combination of
Ion movement across membranes creates electrical signals
K+ more concentrated on inside
Na+, Ca2+, Cl- more concentrated at the outside
Change in membrane potential does not mean ion concentration gradients are affected significantly
Na+ wants to go inside:
- Inside more negatively
- Concentration Na+ is lower inside
Continuous leakage of ions in and outside the cell → ATP driven pump against stabilizing from K+ and
Na+ ions
Resting membrane potential is maintain by K+ leaks out of the neuron and Na+ leaks in
K+: chemical force somewhat higher than the electrical force needed to counteract this (-90mV)
Neuron is very permeable to K+ Leakage of K+ out of the cell Na+: other way around, but less
permeability for Na+
Equilibrium potential: concentration versus membrane potential
Resting membrane potential ATP driven Na+-K+ pump
➔ The neuron must compensate for K+ and Na+ leaks
For every 3 Na+ ions pumped out, 2 K+ pumped in
➔ Driven by ATP, stored by
Graded and action potentials
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