Midterm 2 Study Flashcards
Mechanisms of intercellular communication
- Direct communication
- gap junctions
- membrane (tunneling) nanotubules
-mechanosignals - Indirect communication
- chemical messengers
Connexons
- subunits that form a channel (gap junctions)
- pore size is very small
- permits passage of sugars, amino acids and ions between cells
- found in all cells except mature skeletal muscle
Gap junction
First type of direct intercellular communication
Includes connexons and intercalated disks
Intercalated disks
Type of gap junction in cardiac muscle
- allows for rapid and propagation of action potentials for rhythmic contractions
- smaller than connexons
- can be acutely regulated (deactivated/activated) by dephosphorilation/phosphorylation
Nanotubes
Membrane nanotubes are a form of direct intercellular communication
- formed from the plasma membrane
- longer than gap junctions
- have larger pore diameter
- transfer nucleic acids, even small organelles between cells
-might be a way to transfer cellular components from stressed to healthy cells 
Mechanosignal transduction
Conversion of mechanical Stimuli into a cellular response 
Direct physical stress to cells, eliciting a chemical or metabolic response
Ex. mechanical stress to muscle fibres from weightlifting, resulting in increased protein synthesis
Indirect intercellular communication via chemical messengers
When you have 2 cells but nothing is directly connecting them
- paracrine
- neurotransmitters
- hormones (hydrophilic and phobic messengers)
Paracrine
Chemical messenger
- clotting factors, growth factors
- lots of chemical messengers can
Act in a paracrine manner, or endocrine manner 
- ex. Estrogen
Neurotransmitters
Chemical messengers
Characteristics
1. Synapse distance is SHORT
Neurotransmitter signal must be tightly controlled.
- Not too many molecules released
- need an auto shut off.
Hormones
 Chemical messengers
- can be water or lipid soluble must cross boundaries(membranes)
- have specific target receptors
Hydrophilic messengers
- water loving
- ex. Insulin, epinephrine, serotonin
- stored in secretory cell
- dissolves in plasma
NO NEED FOR CARRIER!
Secreted by fusing secretory vesicles to membrane and releasing
Hydrophobic messengers
- water hating or lipid living
Ex. Steroid and sex hormones
-storage is typically more limited - cannot dissolve in plasma
- NEEDS A CARRIER
crossing a lipid membrane is not a barrier
Receptor specificity
- Cells express many types of receptors
- There may be 100s or 1000s receptors on a cell surface
- Amount of receptor is controllable(can be regulated up or down)
Goal of chemical signal transduction
To change overall profile of cellular protein/enzymatic activity
Components of CCN
Control and communication network includes
- the central nervous system (brain and spinal chord
- the peripheral nervous system
(Somatic nervous system, autonomic nervous system)
Overview of the nervous system
Sensory input in peripheral nervous system to central nervous to motor output in peripheral nervous system
Sensory input
- input from sensory receptors
- responding to external stimuli
- in skin, muscles and joints
- in internal organs
Motor output
In peripheral nervous system
Somatic nervous system
And autonomic nervous system
Autonomic nervous system
Regulates involuntary activities such as heart rate breathing
Parasympathetic
Sympathetic
Parasympathetic
Governs body during restful conditions
Rest and digest
Sympathetic
Prepares body for stressful or emergency situations
5 major cell types in the adult human
- Neurons
- Oligodendrocytes and Schwann cells
- Astrocytes
- Microglia
- Epedymal cells
Signal transduction Lipophilic/ hydrophobic messenger acting on cell
- Enters cell through diffusion
- binds to hormone receptor complex - Attached to hormone response element, which binds to dna
- One hormone receptor complex can cause many mRNA to be formed
- mRNA exits the nucleus into the cytoplasm of cell
- Many proteins are formed from each mRNA
Signal transduction
Hydrophilic messenger
1- the first messenger binds to the receptor on cell surface
2- GDP to GTP
- GTP binds to adrnylate Cyclades
3- Atp to cAMP (the second messenger)
4- activates protein kinase, resulting in cascade of activations of another protein
5 - protein + ATP —> protein p + adp
6- this produces a response in cell
G-protein
Turn signal transduction on and off in hydrophilic messengers
Responsible for moving the signal from outside the cell to inside it
Each activates adenylatr Cyclase
Signal amplification and total products
Hydrophilic messenger
- One messenger binds to the receptor = 1
- Several G proteins are activated =10
- Each G protein activated adenylatr cyclase =10
- Each adenylatr cyclase activates hundreds of camp mlc =5000 (enzyme is phosphodiesterase)
- Each camp activates a protein kinase = 5000
- Each protein kinase S phosphorylation hundreds of proteins =2500000
Secretion mechanism lipophilic vs hydrophilic
Lipophilic- diffusion
Hydrophilic - secretory cells
Transport of hydrophobic vs hydrophilic messengers in blood
Hydrophilic- dissolved
Hydrophobic- bound to carrier protein
Location of receptor
Hydrophobic vs hydrophilic messenger
Hydrophobic- cytosine or nucleus
Hydrophilic - plasma membrane/cell surface
Signal transduction mechanisms for hydrophilic vs hydrophobic cells
Hydrophilic- open/close ion
- activate membrane bound enzymes
-G- proteins and second messenger systems
Hydrophobic-
Alter transcription of mRNA (alter protein synthesis
Relative time of onset response and duration of response for hydrophilic vs hydrophobic cells
Hydrophilic- fast time, short duration
Hydrophobic - slow time, long duration
Neuroendocrine signalling system
Combines neural and endocrine signalling using neurojormones ex. Norephinephrine and antidiuretic hormone
Secreted by neuron
Messenger- neurotransmitter
Pathway- bloodstream
Target cell- endocrine cells
Specificity- receptors in target endocrine cells
Time to onset- delayed
Duration of effect- longer
Secretory cells nervous vs endocrine system
Nervous- neuron
Endocrine- endocrine cell
Target cell nervous system vs endocrine system (signalling)
Nervous- neuron, muscle, gland
Endocrine- most cell types in the body
Messenger (chemical signalling) nervous vs endocrine
Nervous- neurotransmitter
Endocrine- hormone
Pathway of communication nervous vs endocrine signaling
Nervous- across synapse
Endocrine- via bloodstream
Classic endocrine tissues in the body
-hypothalamus
-anterior pituitary
-adrenal glands
-pancreas
Thyroid
Sex organs
Kidneys
But in fact most tissues have endocrine function
Fluid secretion in intestinal lumen
Maintaining normal fluid levels in the lumen is a matter of chloride and sodium secretion
Chloride and sodium pumps are regulated by a protein kinase (and camp)
Cholera toxin and life threatening diarrhea
Cholera toxin activates G protein for a prolonged period so signal doesn’t turn off
Causes efflux of Cl- and Na+ and loss of 20L/day of water
Cystic fibrosis and cholera
Cystic fibrosis might be evolutionary response to cholera toxin since it causes fluid retention
Neurons built for what
- information flow
- to signal specific target cells with a specific neurotransmitter
- speed
- to be excitatory or inhibitory
- to diverge, converge and form networks
Myelinated vs non myelinated neuron speed
Myelinated- 6-120m/s (quicker)
Non myelinated- 0.5-2m/s (slower) very few of these
What age does remodelling of brains neural network begin
Age 10
Why might teenager be more impulsive
There’s a massive remodelling period and increase in myelination=increase in transmission speeds of neurons)
Oligodendrocytes and Schwann cells
Produce myelin
Oligodendrocytes-
- Found in central nervous system cns
- spam multiple axons
Schwann cells
- do not spam multiple axons
- found in PNS
Astrocytes
Stellate (starlike) morphology
Very important for communication
Have 5 key functions
5 key functions of Astrocytes
1- coordinates overall function of the blood and brain barrier and provides nutrients to feed neurons
2- coordinates function of the brain network (epithelium)
3- coordinates function at the nodes of ranvier
4- participates in/forms tripartite synapses with neurons
5- serve as super hubs for neural network via syncardium formation and calcium signalling (propagated from Astrocyte to astrocyte by gap junctions)
Microglia
Mobile, macrophage like immune cells
Ependymal cells
Line ventricles to form a Barrier
Produce cerebrospinal fluid
The blood brain barrier
Very tight control over what gets through to the brain
(Remember neurons are meant to be very long lived and usually don’t regenerate)
- very good at protection against most bacteria and toxins
What gets through BBB
Mostly very small lipid soluble compounds (fatty acids)
Caffeine
Alcohol
Glucose by specific glucose transporter GLUT1(not insulin sensitive)
Phineas Gage
(1823-1860)
Most of his left frontal lobe was destroyed in accident with tamping iron that went through his skull
He recovered but had a completely different personality
Early evidence that different areas of our brain network to form our personality