Human Phys unit 1

• Homeostasis is when a living organism maintains relatively stable internal conditions, despite external changes
• Homeostasis is important for survival, allowing organisms to maintain an optimal internal environment for cellular functions
• Negative feedback contributes to homeostasis
• Negative feedback: Body senses a change and activates mechanisms to negate or reverse it

Negative Feedback Loop Components

• Receptor: structure that senses change in the body
• Integrating Center/Control Center: processes information and directs the response, commonly the brain
• Effector: cell/organ that carries out the corrective action to restore homeostasis
• Example: Body temperature regulation

Positive Feedback

• Self-amplifying cycle
• Leads to greater change in the same direction
• Beneficial examples: childbirth, blood clotting, protein digestion, nerve signal generation
• Harmful examples: vicious circle of runaway fever
• Matter and energy flow down gradients

Gradients

• Gradient: difference in chemical concentration, charge, temperature, or pressure between two points.
• Pressure gradient: blood flowing from high to low pressure
• Concentration gradient: chemicals flow from high to low concentration
• Electrical gradient: ions flow from high to low charge
• The combination of charge and concentration gradient is called "electrochemical gradient."
• Thermal gradient: heat moves from areas of high to low temp

Plasma Membrane

• Primary gatekeeper of materials into and out of the cell
• Phospholipids (75%): arranged in bilayer with hydrophilic phosphate heads and hydrophobic tails, drift laterally
• Cholesterol (20%): holds phospholipids still and stiffens membrane
• Glycolipids (5%): contribute to glycocalyx (carbohydrate coating on cell surface)

Membrane Proteins

• Transmembrane Proteins: pass through the membrane, have hydrophilic and hydrophobic regions and are sometimes glycoproteins (carbohydrate attached)
• Peripheral Proteins: adhere to one face of the membrane

Peripheral Protein Functions

• Receptors: bind chemical signals to trigger internal changes, production of a second messenger may form
• Enzymes: catalyze reactions including digestion of molecules
• Channels/Carriers: allow certain solutes and water to pass through membrane ("leaky” or "gated")
• Some carriers require energy, called "pumps"
• Gated Channels: open only at certain times (voltage, ligand, or mechanical)
• Cell-identity markers: glycoproteins acting as identification tags
• Cell-adhesion molecules (CAMs): mechanically link cells and extracellular material

Glycocalyx

• "Fuzzy” outer layer of cell membrane with glycoproteins and glycolipids
• Functions as cell "fingerprint" or ID tag, protection (cushions the cells) and immunity to infection.

Selective Permeability

• Allowing some things through, but preventing others

Passive Transport

• Filtration: particles are driven through membrane by physical pressure, kidneys filter wastes from blood
• Simple diffusion: net movement of particles from high to low concentration if the membrane is permeable (impacted by temp, molecular weight, concentration gradient, surface area, permeability)
• Osmosis: net flow of water through a selectively permeable membrane, water goes down its concentration gradient towards solutes, aquaporins increase osmosis
• Facilitated diffusion: carrier moves solute down its concentration gradient (solute attaches, carrier changes, solute releases)

Active Transport Mechanisms

• Primary active transport: carrier moves solute through membrane up its concentration gradient using ATP, often called "pumps"
• Secondary active transport: carrier moves solute through membrane using ATP indirectly, another pump establishes required concentration gradient
• Vesicular transport: movement of particles of fluid droplets through the plasma membrane by endocytosis or exocytosis
• Endocytosis: uses vesicles to bring material into cell
• Exocytosis: uses vesicle to release material out of cell
• Active Transport: requires energy, consumes ATP
• Passive Transport: requires NO energy

Simple Diffusion Factors

• Increase: Temperature, concentration gradient, surface area, permeability
• Decrease: Molecular weight

Methods of transport, carriers

• No Carriers: filtration, simple diffusion, osmosis
• Carrier-Mediated: facilitated diffusion, primary active transport, secondary active transport
• Vesicular: endocytosis, exocytosis

Transport Proteins

• Saturation: all carrier molecules are occupied, demand increases make no difference
• Transport maximum is the point at which all carriers are occupied and the rate of transport plateaus
• Specificity: solute (ligand) can only bind to specific carrier
• Glucose carrier cannot transport fructose
• Uniport: carrier that moves one type of solute
• Symport: carrier that cotransports two or more solutes simultaneously in same direction.
• Antiport: carrier that countertransports two or more solutes in opposite directions

Vesicle Transport Types

• Endocytosis + Exocytosis

Endocytosis Types

• Phagocytosis: engulfing and destroying large particles; "cell eating"
• Pinocytosis: taking in droplets of ECF containing molecules useful in the cell; "cell drinking"
• Receptor-mediated endocytosis: particles bind to specific receptors on plasma membrane

Osmosis details

• Net flow of water through a selectively permeable membrane, water moves down its concentration gradient, towards solutes, aquaporins can increase rates

Concentration terms

• Osmolarity: osmotic concentration; quantity of nonpermeating solutes per liter of solution, osmolarity is a number
• Body fluids: Blood plasma, tissue fluid, and intracellular fluid are 300 milliosmoles per liter (mOsm/L)
• Tonicity: ability of surrounding solution to affect fluid volume and pressure in a cell

Solution Strength

• A description of the relative strength depends on concentration of nonpermeating solutes.
• Hypertonic solution: Has a higher concentration of nonpermeating solutes than ICF (cell loses water and shrivels/crenates)
• Isotonic solution: Concentrations of nonpermeating solutes in ECF and ICF are the same (no change in cell volume)
• Hypotonic solution: Lower concentration of nonpermeating solutes than intracellular fluid (ICF) so cell would absorb water, swell, and burst (lyse)

DNA & RNA

• Deoxyribonucleic acid (DNA): Long, thread-like molecule arranged in a double helix. Located in cell nucleus, two purines: adenine, guanine and two pyrimidines: cytosine and thymine
• The sugar deoxyribose is present, function is instructions (genes) for protein synthesis
• Humans have about 20,000 genes and 46 DNA molecules (chromosomes)
• DNA strands wind around histones to create chromatin, which packs into chromosomes during division

Ribonucleic acids (RNAs)

• Single nucleotide chain located mainly in cytoplasm, with sugar ribose, two purines: adenine, guanine and two pyrimidines: cytosine and uracil
• RNA uses instructions from DNA to create proteins
• There are different types of RNA

Muscle Properties

• Excitability (responsiveness): to chemical signals, stretch, and electrical changes across the plasma membrane
• Conductivity: local electrical excitation sets off a wave of excitation along the muscle fiber
• Contractility: fibers shorten when stimulated
• Extensibility: capable of being stretched between contractions
• Elasticity: returns to its original rest length after being stretched

Skeletal Muscle Characteristics

• Voluntary, striated muscle usually attached to bones, with striations resulting from arrangement of contractile proteins
• Voluntary: subject to conscious control, with connective tissues between layers
• Most skeletal muscles are continuous with tendons
• Muscle, fascicle, muscle fiber/cell, myofibril, myofilament

Muscle Fiber Contents?

• Sarcolemma: plasma membrane of a muscle fiber
• Sarcoplasm: cytoplasm of a muscle fiber
• Transverse (T) tubules: tubular infoldings of the sarcolemma that penetrate through the cell and emerge on the other side
• Mitochondria: many of these! Bean-shaped and tubular shaped
• Nuclei: 30 to 80 per millimeter; serve role in fiber repair (multinucleated)
• Sarcoplasmic reticulum (SR): smooth endoplasmic reticulum that forms a network around each myofibril and acts as a calcium reservoir
• Terminal cisterns: dilated end-sacs of SR which cross the muscle fiber from one side to the other
• Myofibrils: long protein cords occupying most of the sarcoplasm, made of myofilaments that contract and regulate contraction

Myofilaments

• Thick filaments: made of several hundred myosin molecules, with two chains intertwined, heads on one half angle to the left, bare zone with no heads in the middle
• Thin filaments: composed of actin, tropomyosin and troponin, each block six/seven active sites
• Elastic filaments: made of titin. Runs through core of thick filament and anchors it to Z disc and M line
• Function of Sarcomere: the functional contractile unit of a muscle fiber
• Sarcomere Structure: A band, I band, Z disc, H zone, M line, know what is included, where the different proteins are and the location of each component
• Z disc to Z disc = 1 sarcomere

Sarcomere Changes

• 12,000 sarcomeres in 3 cm muscle fiber
• Z discs (Z lines) pull closer together as thick and thin filaments overlap, sarcomeres shorten
• Thick and Thin do not change length
• A band: dark band where thick and thin filaments overlap
• H band: not as dark; middle of A band; thick filaments only
• M line: dark, transverse protein in middle of H band
• I band: light band; thin filaments only
• Z disc (Z line): protein complex that provides anchorage for thin filaments and elastic filaments
• Skeletal muscle cannot contract unless stimulated

Skeletal Muscle Requirements

• If the nerve connection is severed or poisoned, the muscle is paralyzed
• Each nerve fiber supplies a number of muscle fibers, but each muscle fiber is supplied by only one motor neuron
• Motor Unit: one nerve fiber and all the muscle fibers innervated by it, which contracts in unison, motor units take turns contracting for sustained long-term contractions

Motor Unit Details

• Small motor units provide a fine degree of control (eye and hand muscles controlled by motor units with only 3 to 5 muscle fibers each)
• Large motor units provide more strength than control (ex: quadriceps femoris controlled by motor units with 1,000 muscle fibers)
• Neuromuscular Junction (NMJ): Nerve/muscle connection

NMJ Details

• AKA motor end plate, a synapse that includes a gap (the synaptic cleft). The entire site is covered by a basal lamina
• Nerve terminal: End of neuron
• Contains synaptic vesicles filled with neurotransmitter acetylcholine (Ach)
• Muscle part: Called the sarcolemma, which is folded and contains millions of Ach receptors and other ion channels
• Botox blocks this item

Muscle Contraction Phases

• Phase 1: Excitation
• Phase 2: Excitation-contraction coupling links action potentials on the sarcolemma to activation of the myofilaments
• Phase 3: Contraction
• Phase 4: Relaxation
• A nerve signal arrives at the axon terminal and opens voltage-gated calcium channels. Calcium (Ca2+) ions enter the terminal
• Calcium stimulates the synaptic vesicles to release Ach into the synaptic cleft
• Ach diffuses across the synaptic cleft and binds to receptors on the sarcolemma
• Receptors are ligand-gated ion channels. When it opens, sodium (Na+) flows quickly into the cell creating an end-plate potential (EPP)
• Areas of sarcolemma next to the end plate have voltage-gated ion channels that open in response to EPP. Sodium (Na+) ions create an action potential so muscle fiber excites

Contraction Excitation Coupling Steps

• Action potential spreads like ripples
• Excitation reaches T-tubules, spreading the the cell interior
• Action potential open voltage-gates ion channels in the T-tubules. These are linked to calcium (Ca2+) channels, ca2+ escapes the the cytosol
• Ca2+ binds to the troponin of the thin filaments, changes shape, exposes actin sites
• Contraction won't happen until myosin is bound to ATP
• The myofilaments do not shorten within the sliding filament theory
• Thin filament slides over the thick filament and pulls the Z disc behind, causing sarcomeres to shorten
• Myosin head must have an ATP
• Myofilaments have binding relationships

Cycle of Contraction

• Step 1: Hydrolyzes the ATP w/Myosin ATPase in the head itself, releases energy and activates myosin heads
• Step 2: ATP goes to ADP and an extended spring cock-like motion to reach for actin
• Step 3: Active Site on the actin, forming a bridge called a cross-bridge between actin and myosin
• Step 4: Tug of the thin filament, called the power stroke
• Step 5; Releases the ADP and Pi and the myosin reattaches

Relaxation Phase

• 1. Action potential stops 2) The Ach seperates from its receptor
• 3. AchE which separates from its receptor.
• 4. Ca2+ release stops
• 5. free Ca2+ in the cytosol decreases
• 6)Tropomyosin then blocks the active site
• Length-tension: A muscle depends on how stretched or shortened it was before the contraction
• A too short for the resting length a is very weak, if a muscle is too long it's gonna pull
• You can't make either a good result, is the optimum way to do it 64

Twitch

• Twitch: quick cycle of contraction and relaxation when a muscle is directly stimulated; latent, contraction, and relaxation periods.
• Threshold: minimum voltage that causes a muscle twitch or contraction
• Factors for Determining:
• muscle start length: the ideal amount of length produces and
• Fatigue: continual use will decrease which which enzymes
• Hydration: bridge is also a result is a factor that is key for what is going to happen
• Stimuli increase frequency: stimulus delivery delivery increases tension output

Stimulus for Contraction

• Stimuls is what causes stimulus the muscle to vary based on strings from the nerves and strength
• Strength equal Stimulus and what causes the turn to
• Frequency increase increases intensity for dial up is and contract

MME

• Higher voltages exit even more nerve fibers
• MME: motor unit. recruitment summation bring units to the play a part
• Size: recruited first needed

How to Get a Stronger Contraction

• Twitching is by a lot of action and the is a process in this
• Increase stimuli can build and get the tension when there is no full tetanus

Contraction Types

• Incomplete: there is a bit relaxation is where there is a full can be when is and is not able to there is
• Immetric: with with the muscles and with an internal a change
• Istonic: while muscles are now in tension
• Fast and slow twitch there is a pulling for both, but slow is much more common for more endurance and slow
• Fibers: SO one Mitochondria myoglobin or for Fiber :

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