Body systems unit 2
What is a ligand?
a molecule which selectively binds to a specific sit on another molecule
What is a receptor?
A protein with a site to which the signalling chemical can bind. The binding causes changes in the receptor which stimulates a response to the signal.
Compare and contrast enzymes vs receptors
Enzymes: The active site is vacant, the substrate binds to it, the substrate is converted to the product, and the product is released.
Receptors: the ligand binding site is vacant, binding causes changes to the receptor, a message is conveyed to the cell, and the signalling chemical is released
What is quorum sensing?
A form of cell signalling in bacteria. Chemical signals are secreted at low rates by all cells and diffuse freely between them. If a certain number of signalling molecules are present, more signals will be received by the cell, and changes in the activity of the cell are triggered. Group behaviour is more powerful than individual action.
Hawaiian bobtail squid quorum sensing
The bacterium vibrio fischeri which has a symbiotic relationship with the squid and provides bioluminescence will only produce light if there is high cell density and high concentration of autoinducer.
What are hormones?
chemical signalling molecules produced by ductless endocrine glands in the body and transported throughout the bloodstream. They work to promote or inhibit (regulate) specific processes in target cells.
What are neurotransmitters?
chemicals thaat transmit signals across a synapse between two neurons in the nervous system. It is released from the presynaptic neuron and binds to receptors in the plasma membrane of the postsynaptic neuron. It excites or inhibits transmissions of impulses.
What are cytokines?
small proteins that act as signalling chemicals. They are secreted by many cells. Multiple cells can secrete the same cytokine or can secrete more than one type of cytokine. The bind to plasma membranes of nearby cells and cause cascades of signalling, leading to changes in gene expression and cell activity.
What are calcium ions?
ions used for cell signalling in muscle fibres and neurons.
How do calcium ions travel through neurons?
they diffuse into neurons through voltage-gated channels and cause presynaptic neurons to release a neurotransmitter into the synapse.
How to calcium ions travel through muscles?
they are released from a specialized endoplasmic reticulum (sarcoplasmic reticulum) causes proteins on muscle fibres to change position. This protein (troponin) normally blocks binding sites to prevent msucle contraction, but when they are moved out of the way contraction can happen.
3 types of hormones
Steroids (testosterone), amines (epinephrine), and peptides (oxytocin & insulin)
4 types of neurotransmitters
amines (adrenaline, serotonin, dopamine, acetylcholine), Amino Acids, polypeptides, and gases (Nitric oxide)
Localized signalling
One cell secretes molecules on a nearby target cell in the extracellular fluid (or by synaptic signalling). Example includes neurotransmitters diffusing across the synapse.
DIstant signalling
molecules are transporte long distances in the body from the cells that secrete them to target cells. Examples include hormones such as LH being secreted in the brain and then transported to the ovaries or testes.
How do transmembrane receptors work?
Ligands bind to the receptor (in the membrane), causing the change in shape of the receptor and the signal being relayed across the membrane to the cytoplasm. The ligand binding site is hydrophilic, while the parts that traverse the membrane are hydrophobic, areas near the phosphate heads are also hydrophilic.
How do intracellular receptors work?
These receptors are soluble proteins in the cytoplasm. Intracellular receptors have hydrophilic amino acids so they remain dissolved in the fluids of the cytoplasm or nucleus.
What is a signal transduction pathway?
A sequence of interactions triggered in the cell ater a signalling chemical binds to the receptor.
Types of responses triggered by chemical signalling
Regulation of protein activity, protein synthesis, and enzyme activity. Rearrangement of the cytoskeleton of the cell, and death of the cell.
Acetylcholine and ligand gating
When acetylcholine binds to transmembrane receptors, the channel undergoes a change in conformation and opens, allowing sodium ions to flow across the membrane.
What are G proteins?
membrane bound protein receptors which bind to GTP, usually activated by the binding of a hormone or other ligand. It is an energy rich nucleotide (like ATP) that helps to transmit other signals when activated
Structure of the G protein
It has coupled receptors with multiple helices that span the plasma membrane and form hydrophobic interactions with the core of the plasma membrane. It binds to the third largest cytoplasmic loop of the receptor. It is composed of 3 subunits (a, b, and y)
How does the G protein work?
if GDP is bound to the G protein (at the a subunit), the protein is inactive. A ligand binds to the binding site on the receptor, causing it to change shape and change the shape in the G protein. GDP detaches and gets exchanged for GTP , activating the G protein. When it is activated, the G protein dissociated from the receptor and binds to an enzyme or other protein, causing further interaction within the cell.
What is epinephrine & what does it do?
it is a hormone released from adrenal glands that circulates in the blood stream and binds to a class of G protein receptors. The effects of epinephrine are preparation for vigorous activity, increase in heart/breathing rate, enabling increased delivery of oxygen and glucose to muscle cells, and vasoconstriction of blood cells.
What is cAMP?
the most common secondary messenger used in cells, and is activated by binding of epinephrine to the G protein coupled transmembrane receptor.
Results of the activation of adenylyl cyclase
its activation results in a boot in the production of cAMP, which leads to the activation of an enzyme which breaks down glycogen. With more glucose around, muscle activity increases.
How is cAMP created?
the G protein activates the adenylyl cyclase enzyme which converts ATP to many cyclic AMP molecules (cAMP)
What are kinases?
Enzymes that add a phosphate group from an ATP to a molecule to phosphorylate it. They are inactively bound to transmembrane receptors. Upon binding they become active.
What are tyrosine kinases?
transmembrane receptors composed of two protein tails. Upon binding the kinases move together to form a dimer and attach phosphate groups to tyrosine parts.
Tyrosine kinase in insulin receptors
Upon binding of insulin the kinases form a dimer which then is phosphorylated. This causes vesicles containing glucose transporters to move the plasma membrane and fuse with it. The transporters inserted in the plasma membrane are channel proteins that allow uptake of glucose into the cell by facilitated diffusion
What is estradiol/what does it do?
It is found in the ovaries, adrenal glands, adipose tissue, and breast tissue. It targets the hypothalamus during ovulation, causing a release of a hormone that triggers the release of LH. It is a steroid hormone that is lipid soluble.
What is progesterone/what does it do?
It is found in the ovaries and targets the endometrium. Binding to a receptor causes transcription of specific genes that cause endometrial cells to divide repeatedly, leading to thickening of the endometrium.
What is positive feedback?
an end product amplifies the starting point to that more product is created. E.g ethylene produced by ripening fruit causes nearby fruits to start ripening.
What is negative feedback?
an increase of the end product shuts off the start of the signalling pathway so that less is produced. E.g. insulin in the control of the blood sugar level
What are neurons/what do they do?
They are the basic structural & functional unit of the nervous system. They respond to physical and chemical stimuli, conduct electrochemical signals, and release chemicals that regulate various body processes.
What are glial cells?
They help support the neurons, nourish them, remove their waste, defend against infection, and provide supporting framework for all the nervous system tissue.
What are dendrites?
They are short-branched fibres that convert chemical information from other neurons or receptor cells into electrical signals. They are numerous and highly branched (increase surface area for info). They carry nerve impulses toward the cell body
What are axons?
they are elongated fibres that trasnmit electrical signals to terminal regions for communication with other neurons or effectors. They carry nerve impulses away from the cell body.
What is the soma (cell body)?
a cell body containing the nucleus and organelles, where essential metabolic processes occur to maintain cell survival (site of metabolic reactions)
What is the myelin sheath?
it is a insulating layer that covers the axon of a nerve cell for protection. It can improve conduction speed of electrical impulses along the axon, but require additional space and energy, composed of glial cells.
What are the nodes of ranvier?
Regularly occuring gaps between sections of myelin sheath along the axon where nerve cells are transmitted.
What is the neurilemma?
A delicate membrane that surrounds the axon of some nerve cells, it promotes regeneration of damaged axons
What is a nerve impule the result of?
A change in concentration of sodium and potassium ions along the cell membrane
What is resting potential?
the potential difference across a nerve cell membrane when it is not stimulated. It is approximately -70mV.
What is action potential?
The reversal (depolarization) and restoration (repolarization) of the electrical potential across a plasma membrane as a nerve impulse passes along a neuron.
What factors contribute to the membrane potential in neurons?
Sodium potassium pumps, leakage of ions back across the membrane by simple diffusion, and negatively charged proteins inside the nerve fibre.
How does the sodium potassium pump work?
The interior of the pump is open to the inside of the axon, 3 na+ ions enter and attach to binding sites. The release of energy from ATP phorphorylation causes a shape change in the protein, making the pump close. The protein opens to the outside and the na+ ions are released to the outside. 2 K+ ions attach, and ATP makes the protein change shape again to release the K+ ions to the inside.
Leakage of potassium and sodium ions
Leakage contributes to the imbalance of ions across the membrane. The axon membrane has a higher permeability of K+, which leaks out of the cell faster than Na+ leaks in. This unequal distribution and the abundance of negatively charged proteins inside the axon fibre, the membrane potential is -70mV
What is depolarization?
The cell membrane's charge becomes positive. This is caused by positive sodium ions going into the cell (increase on graph)
What is repolarization?
The cell membrane's charge turns to negative, caused by positive potassium ions moving out of the cell. Decrease on graph.
Process of depolarization
An electrical stimulus is carried along the neuron fibre. The Na+ channel gates open, allowing a flow of Na+ ions following the concentration gradient into the cell, making the membrane potential more positive inside.
Process of repolarization
the Na+ gated channels close again, and the voltage gated K+ channels now open, allowing K+ ions to diffuse out of the cell. This makes the inside of the cell more negative again and restores the resting potential
What are oscilloscopes?
An electronic instrument that graphically displays cell potential/signal voltages. Cell potential (voltage produced by ion movement) can be measured using microelectrodes impaled into cells.
What is a nerve impulse?
an action potential that starts at one end of the neuron and travels along the axon to the other end of the neuron. Theye always move in one direction. Once the impulse starts at the dendrite end, the action potential will self-propagate itself to the far end of the axon.
What is a local current (neurons)
the movement of sodium ions from the depolarized part of the neuron to the neighboring part inside the axon and the movement in the opposite direction outside the axon. This area of the axon initiates the next area of the axon to open up the sodium channels and causes the movement of action potential down the axon.
Factors that determine speed of nerve impulses
A bigger diameter of nerve fibres reduces resistance and increases conduction speed as well as protective reactions to danger, mylinated nerve fibres can have much faster nerve impulses than unmylinated ones
What is saltatory conduction?
The rapid, energy-efficient propagation of action potentials along myelinated axons. Action potentials only occur at the unmyelinated nodes of Ranvier (where voltage gated channels are), forcing action potential to jump from node to node. This makes it much faster and reduces degradation of the impulse (allowing for longer distances) as well as energy expenditure.
What is myelination?
Certain neurons being insulated with a myelin sheath. It can improve speed, however it takes up significant space within an enclosed environment. Regions composed of myelinated axon tracts appear as white matter, while other areas appear as grey matter.
What is grey matter made of?
Neuronal cell bodies, dendrites, support cells (glial cells), and synapses
4 types of synapses
synapses between neurons (brain and spinal cord), synapses beyweem neurons and muscle fibres (effectors), synapses between neurons and glands (effectors), and synapses between neurons and sensory receptors of sense organs.
What are effectors?
Effectors are muscles, glands, or specialized cells that produce a specific response in direct reaction to signals from the nerbous system
How does synaptic transmission work?
At the dendritic end of the nerve cell, each dendrite collects the nerve impulse from the terminal end of a different nerve cell. Depolarization causes the calcium channels to open (ca2+ rushes in). Ca2+ causes synaptic vesicles to move to the membrane and fuse. Neurotransmitters in the synaptic vesicle diffuse across the synaptic gap and bind with post synaptic receptors. Sodium channels open (Na+ enters) leading to depolarization of post-synaptic neuron (action potential initiated, nerve impulse propagated). Enzymes in synaptic gap break down NT, products are taken up by the pre-synaptic neuron by active transport.
What is a neuromuscular junction?
A synapse between a motor neuron and a muscle cell.
Responses in cells activated by neurotransmitters
In neurons neurotransmitters cause stimulation of inhibition of an electrical signal (nerve impulse). In glandular cells they cause stimulation or inhibition of secretion (exocrine or endocrine). In muscle fibres they cause stimulation or inhibition of muscular contraction/relaxation
What are EPSPs?
Excitatory post-synaptic potentials triggeed by neurotransmitters in the post-synaptic neuron. They trigger depolarization in the post-synaptic membrane.
What are IPSPs?
Inhibitory post-synaptic potentials triggered by neurotransmitters in post-synaptic neurons. IPSPs trigger hyperpoolarization in the post-synaptic membrane.
What is summation?
the combination of graded potentials (EPSPs & IPSPs) in the post-synaptic neuron. If the combination of signals reaches a threshold level, an action potential will be triggered in the post-synaptic neuron.
What is cancellation (summation)?
when excitatory and inhibitory graded potentials cancel each other out and no threshold potential is reached.
What is spatial summation?
when EPSPs are generated from multiple pre-synaptic neurons simultaneously to reach threshold
What is temporal summation?
when multiple EPSPs are generated from a single presynaptic neuron in quick succession.
What does acetylcholine do?
It is commonly released at neuromuscular junctions and binds to receptors on muscle fibres to trigger muscle contraction. It is also commonly released within the autonomic nervous system to promote parasympathetic responses (rest and digest).
How is acetylcholine created?
It is created in the axon terminal by combining choline with an acetyl group (Acetyl CoA and choline). It is stored in vesicles within the axon terminal until released via exocytosis in response to a nerve impulse.
What is a muscarinic AChR?
A type of acetlycholine receptor (where acetylcholine binds to). They mediate a slow metabolic transmission.
What is a nicotinic AChR?
a type of acetylcholine receptor (where acetylcholine binds to). It mediates a fast synaptic transmission of the neurotransmitter.
What does AChE do?
It is an ezyme that hydrolyses acetylcholine to choline and acetic acid, which are inactive as transmitters (happens to avoid overstimulation). The choline is returned to the presynaptic neuron and coupled with acetate to form another acetylcholine. As a result, the ion channel of the receptor protein closes, and the resting potential in the post-synaptic neuron is re-established.
What are exogenous chemicals?
substances which enter the body from an outside source through ingestion, inhalation, or absorption through the skin.
What are neonicotinoids?
An exogenous chemical used as a pesticide. They block acetylcholine nicotine receptors of a cholinergic synapse in the central nervous syte of insects (prevents acetylcholine binding). In insects, they are significantly more toxic too them than mammals. This has caused a reduction in honey-bee populations, a reduction in bird populations (insects are their food). The EU has banned them
What aree psychoactive drugs?
Drugs that affect the brain and personality by either increasing or decreasing postsynaptic transmission.
What are stimulant drugs?
drugs that increase post-synaptic transmission. This includes nicotine, MDMA, and cocaine.
What does cocaine do?
Normally, dopamine is re-uptaken by pumps on the pre-synaptic membrane. However, cocaine blocks the pump, causing dopamine to remain in the synaptic cleft. More dopamine continues to be released, causing enhanced feelings of pleasure which last longer than normal. This can cause feelings of euphoria, increased energy, adddiction, and depression as the body reduces production of dopamine over time.
What is the synaptic cleft?
the tiny gap between the pre and postsynaptic neurons at a chemical synapse (where neurotransmitters diffuse)
Excitatory neurotransmitters
excites post-synaptic transmissions. This includes acetylcholine, dopamine, and glutamate. It results in an influx of NA+ ions into the postsynaptic membrane, making it more positive and making it easier for depolarization (results in EPSP)
inhibitory neurotransmitters
neurotransmitters that inhibit post-synaptic transmissions. This includes GABA and dopamine. It results in an influx of Cl- ions into the postysynaptic membrane and hyperpolarization. The membrane is more negative, making it more difficult to depolarize (makes IPSP)
What are sedative drugs?
drugs that decrease post-synaptic transmission. These include alcohol, benzodiazepines, and THC.
What does alcohol do?
Normally, GABA inhibits post-synaptic transmission, and glutamate increases post-synaptic transmission by binding to receptors. With alcohol, it increases the effect of GABA, causing it to remain bound for longer. It also prevents glutamate from stimulating the post-synaptic neuron by binding to glutamate receptors. It causes a dopamine release that causes worsened reaction speeds, memory impairment, relaxtion, etc.
What is consciousness?
the qualitative feelings of perception, together with the deeper processes of reflection, communication, and thought. It is agreed on that consciousness is an emergent property from the complex interaction of individual neurons in the brain.
What is an EEG?
electroencephalograms are a brainscanning technology that measures brain activity in microvolts. The tiny discs on the scalp detect tiny electrical charges that result from activity in the brain cells and appear on a graph.
what is an fMRI?
a functional MRI measures changes in blood flow through the brain. It can indicate which regions of the brain are most active. Oxyhemoglobin responds differently to magnetic fields than deoxygenated hemoglobin. Areas that are being used require more oxygen (more blood flow) and computers can see that using different colours. It is an indirect measure, however is non-invasive.
What is an anesthetic?
a varied group of molecules that affect neural pathways in different ways. Many affect the receptors found in synapses.
What is a local anesthetic
it causes numbness (loss of sensation) in an area of the body
What is a general anesthetic?
it causes unconsciousness and therefore a lack of sensation throughout the body. They block long-distance communication, affecting the transmission of impulses from receptors and the central nervous system
What is the skeletal system? What does it do?
It is a framework that provides support and protection for body organs. Skeletons can be internal (endoskeleton) which consist of numerous bones, or external (exoskeletons) which are comprised of connected segments. Skeletons provide a surface for muscle attachment, allowing for movement of the organism.
Exoskeletons and bones as levers
Bones are connected to other bones by ligaments, and bones are connected to muscles by tendons. The skeleton acts as a system of levers, where each joint acts as a fulcrum. The force applied is called the effort. Bones can change the size and direction of a force.
What are synovial joints?
capsules that surround the articulating surfaces of two bones. They function to maintain structural stability by allowing selective movements.
What is the joint capsule?
A part of synovial joints. It seals the joint space and provides stability by restricting the range of possible movements.
What is cartilage?
Part of synovial joints. It lines the bone surface to facilitate smoother movement, as well as absorbing shock and distributing load.
What is synovial fluid?
A part of synovial joints. It provides oxygen and nutrition to the cartilage, as well as lubrication to reduce friction.
Six main types of synovial joints
plane joints, hinge joints, pivot joints, condyloid joints, saddle joints, ball and socket joints.
The knee as a pivotal hinge joint
The knee's range of motion is like a hinge joint, however it allows some pivotal movement. The femur and tibia do not actually make contact with eachother when moving. Cartilage and synovial fluid protect and lubricate the knee joint to reduce impact harm. Strong ligaments hold the knee in place.
What are ligaments?
they are tough cords composed of the fibrous protein collagen, preventing aberrant movements to avoid dislocations.