Muscle Contraction and Physiology

Homeostasis

• Animals must deal with constantly changing environments, both external and self-imposed (endogenous).
• Homeostasis occurs when animals maintain a suitable internal environment.
• Homeostasis is the active regulation and maintenance of a stable internal physiological state despite external changes.

Factors in Homeostasis

• Skin temperature
• Breathing rate
• Heart rate
• Sweating
• Heat production

Importance of Homeostasis

• Allows animals to invade "physiologically unfriendly" environments.

Essential Components of Homeostasis

• Sensors: Receptors for temperature, pH, and touch.
• Effectors: Muscles and sweat glands.
• Response: Heat production.
• All essential components are tied together in a negative feedback loop.

Thermostat Example of Homeostasis

• Stimulus: Cold
• Sensor: Thermostat
• Effector: Heater
• Response: Heat

Response to Environmental Changes

• Organisms fall into two categories: conformers (do not maintain homeostasis) and regulators (do maintain homeostasis).
• Environmental changes proceed at different rates and evoke different responses.
• Minutes to Hours: Physiological adjustment, almost instantaneous and easily reversed (Exercise, Temperature, Sun-Light).
• Weeks to Months: Acclimatization, slower over many days and reversible (Altitude, Day length).
• Geologic Time: Evolutionary change, selection on new traits and non-reversible (New Habits, Climate change).

Cellular Homeostasis

• All organisms are made of a single cell or an ensemble of cells.
• Cells are defined by membranes.

Membranes

• Separate the inside of the cell from the outside.
• Surround many internal structures.
• Composed of lipids, proteins, and carbohydrates.
• Membranes contain two phospholipid layers

Phospholipid Layers

• Hydrophilic: Polar head group
• Hydrophobic: Nonpolar tails
• Phospholipids arrange themselves spontaneously into a bilayer.

Membrane Phospholipids

• Membrane is fluid
• Individual fatty acid chains can flex or bend.
• Fluidity depends on the fatty acids present – double bonds, length of tails
• Saturated fatty acid chains without double bonds result in phospholipids with a straight structure that favors tight packing.
• Unsaturated fatty acids have one or more double bonds that introduce kinks in phospholipids, reducing tightness and packing.
• Cold-water species have more double bonds to maintain fluid membranes.

Plasma Membrane Characteristics

• It is critical for homeostasis.
• It is a feature in all cells.
• Defines the cell boundary
• Separates internal contents from surrounding environments
• Plasma membrane is a selective barrier.
• Certain items can move freely, others only under certain conditions, others cannot

Reasons for Limited Permeability

• Lipid bilayer is hydrophobic - prevents ion movement.
• Many macromolecules are too large.
• Gases, lipids, and small polar molecules can cross.
• Selective permeability is key to maintaining homeostasis.

Passive Transport

• Facilitated diffusion.
• Water moves in & out of cells via osmosis.
• Membrane allows passage of water but not solute.
• Aquaporins are protein channels allowing for facilitated diffusion.

Active Transport

• Movement against a concentration gradient.
• Passive transport works only with the right concentration gradient direction.
• Nutrients are higher on the outside to lower on the inside.
• Waste is higher on the inside and lower on the outside.

Kinds of Active Transport

• Primary active transport uses energy of ATP.
• For example, the sodium-potassium pump (Na+/K+ ATPase).
• Steps 1 & 2: Three sodium ions are pumped out of the cell against their concentration gradient.
• Steps 3 & 4: Two potassium ions are pumped into the cell against their concentration gradient.
• Antiporter: Ions moving in opposite directions.
• Symporter: Co-transporter, ions move in the same direction.
• Secondary active transport uses ATP indirectly.
• Protons are pumped across the membrane by primary active transport.
• The proton pump generates an electrochemical gradient, with a higher concentration of protons outside the cell and a lower concentration of protons inside the cell.
• An anti-porter uses the proton electrochemical gradient to move a different molecule out of the cell against its concentration gradient.

Physiological Control in Animals

• Homeostasis is maintained by the endocrine and nervous systems.

Endocrine System

• Releases hormones, a chemical substance released into the bloodstream, circulates throughout the body, and exerts influence on distant cells.
• Response is slow and widespread.
• Works via negative feedback.
• Endocrine cells are organized into endocrine glands such as the thyroid gland or adrenal gland.
• Glands are ductless – release hormones into capillaries among endocrine cells.
• Target cells possess receptor molecules that recognize the hormone and can bind the hormone.
• Only cells and tissues with the receptor can respond.

Nervous System

• Composed of neurons (nerve cells).
• Signals are fast and targeted.
• Neurons typically make contact with the target cell

Long Distance Signaling

• Release of a hormone into the bloodstream affects distant cells.
• For example, if the stimulus is high glucose, say right after a meal, the sensor would be pancreas cells and the effector would be insulin.

Nervous System Composition

• The fundamental unit is the neuron.
• Stimuli are received by the dendrites and cell body.
• Synaptic stimuli are summed at the axon hillock, where an action potential is triggered.
• Action potentials are conducted to the axon terminal, where they cause the release of neurotransmitters that are stored in vesicles.
• Neurotransmitters bind to receptors on the postsynaptic cell membrane, creating a new signal in the postsynaptic neuron.
• Network of interconnected cells & neuron/nerve cell

Neuron Resting Membrane

• The Na+ -K+ pump moves Na+ ions out of the cell and K+ ions into the cell.
• K+ channels allow K+ ions to "leak" out of the cell, resulting in a negative resting potential on the inside relative to the outside of the cell.
• Membrane potential can be measured with small glass electrodes.
• When a neuron is excited, the inside becomes less negative, or depolarized.
• Depolarization starts in dendrites in response to a neurotransmitter and travels to the cell body.
• If depolarization at the axon hillock exceeds the threshold voltage (potential), then the cell fires an action potential.
• Some input depolarizes the cell membrane at the axon hillock above the threshold potential
• Voltage-gated Na+ channels open, and Na+ rapidly enters the cell, causing a positive spike in the membrane potential; K+ channels open more slowly.
• As the voltage rises +40 mV, Na+ channels close and are inactivated and voltage- gated K+ channels remain open, allowing K+ ions to leave the cell and causing the membrane potential to become more negative.
• If an overshoot in the amount of K+ ions that leave the cell causes the cell membrane to be hyperpolarized this results in a refractory period.
• Gradually, the membrane returns to resting as access K+ ions are returned to the cell assisted by Na+ - K+ pumps.
• The period during which the inside membrane voltage falls below, and then returns to the resting potential.
• A neuron cannot fire a second action potential because voltage-gated Na+ channels are closed/inactive and voltage-gated K+ channels are open.
• Action potentials propagate along the axon by sequentially opening and closing adjacent voltage-gated Na+ and K+ channels.
• They are self-propagating and travel in only one direction

Saltatory Propagation

• Synaptic transmission begins with action potential conduction to the axon terminal.
• Depolarization of the axon terminal opens voltage-gated Ca2+ channels.
• Vesicles respond by fusing with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.
• Neural transmitters bind with receptors on the postsynaptic cell that are ligand-gated ion channels, opening the channels to allow and ions and causing a change in membrane potential.
• Neural transmitters are actively real absorbed into the presynaptic terminal and stored in vesicles until the next action potential arrives.
• Signals can be excitatory or inhibitory
• Binding of neurotransmitters to postsynaptic cells results in an opening of ion channels to generate postsynaptic potential.
• If the cell is depolarized: potential is excitatory EPSP, opening of ligand-gated Na+ channels
• If the cell is hyperpolarized: potential is inhibitory IPSP, opening ligand-gated Cl- or K+ channels
• Signals or pass between neurons are junctions called synapses.

Sensory Transduction

• Chemoreceptors
• Mechanoreceptors
• Vertebrate photoreceptors.
• Hearing relies on mechanoreceptors.

Respiration & Circulation

• All eukaryotic organisms require O2 for ATP production.
• Single-celled organisms and simple multicellular animals exchange compounds with the environment via diffusion.
• Larger animals rely on a combination of diffusion and bulk flow for gas exchange.
• Bulk flow has two steps: ventilation(movement of a medium (air or water) over a respiratory surface (lung or gill) and circulation(movement of body fluids, containing dissolved gases (require pumps)
• The goal of gas transport is to deliver oxygen to the mitochondria in the cells.

Bulk Flow/Diffusion

• Ventilation of the lungs with oxygen through breathing.
• Diffusion across the respiratory system (oxygen diffuses from lungs to blood and carbon dioxide from blood to lungs).
• Circulation buys bulk.
• Oxygen and carbon dioxide are transported by the circulatory system to and from cells.
• Diffusion delivers oxygen to cells and takes carbon dioxide into the blood.

Ventilation

• Ventilation can be active or passive.
• The goal is to reduce the formation of static boundary layers.
• Active ventilation involves animal-created ventilatory currents that flow across gas exchange surfaces and uses suction or positive pressure.
• Consumes metabolic energy.
• Passive ventilation relies on environmental air or water currents flowing to and from the gas exchange membrane.
• Does not use metabolic energy

Gas Exchange Organs

• Tube worms, Aquatic salamanders = External gills
• Fish: Internal gills
• Bony fish pump water across gills; some species ventilate by swimming (ram ventilation)
• Fish have unidirectional respiration and concurrent blood flow.

Concurrent Exchange

• Many examples in biology & physics show oxygen and heat being exchanged between two fluids

Land Animal Oxygen Uptake

• Oxygen content of air is much higher than water.
• Oxygen diffuses 8000x faster in air than water.
• Air is less dense and less viscous than water, requiring less energy to pump
• Most land vertebrates use tidal ventilation of lungs (negative pressure draws air in and positive pressure expels air from lungs).

Mammalian Lungs

• Mammals increase their lung volume by actively expanding their thoracic cavity
• Draw oxygen-rich air into lungs (inhalation).
• Expel oxygen-poor air from lungs using passive elastic recoil (exhalation).
• Alveolar sacs are blind-ended and never fully emptied
• The amount of O2 and CO2 in alveoli differs from the environment.
• Lungs contain stale air
• On inspiration, fresh air pushes stale air deeper into the lungs
• At the end of resting inhalation, airways are 12% fresh and 88% stale air.
• Surfactants reduce surface tension in alveoli (for easier inflation of the lungs).
• Alveoli are surrounded by a network of capillaries

Bird Lungs

• Birds use unidirectional ventilation and crosscurrent flow.
• First inhalation draws oxygen-rich air into posterior air sacs.
• First exhalation moves fresh air into the lung.
• The second inhalation moves oxygen-depleted air from the lung into anterior air sacs.
• Second exhalation moves air out of anterior air sacs.

Chemoreceptors

• Chemoreceptors in the brain stem detect CO2 and H+.
• Carotid and aortic bodies detect O2 and H+.
• If CO2 is too high, chemoreceptors in the brain stem stimulate respiratory muscles.

Components of Circulatory Systems

• Animals take oxygen from air and it diffuses into vessels, then this must be transported to the tissues and cells.
• Circulatory systems move fluids by increasing the pressure of the fluid in one part of the body.
• Fluid flow through the body is down the pressure gradient.
• Three main components:
  • fluid that circulates through the system
  • a system of tubes, channels, or spaces
  • a pump or pulsatile structure

Vertebrate Oxygen Transport

• Mammals have 55% plasma, 1% white blood cells, and 45% red blood cells(hematocrit)
• Fish have 65% plasma, 1% white blood cells, and 30% red blood cells
• Hematocrit % is the fraction of blood made up of red blood cells and can affect resistance.
• Hemoglobin reversibly binds oxygen.
• O2 and CO2 can dissolve in plasma and dissolved amount is measure of solubitity which is lower for O2.
• Vertebrates and invertebrates evolved hemoglobin (Hb)
  • Globular protein with 4 subunits (in vertebrates) where each subunit surrounds a heme group containing iron that each binds one O2 molecule.
  • In red blood cells of vertebrates and hemolymph of invertebrates.

Comparing Oxygen and Carbon Dioxide Transport

• In vertebrates, O2 diffuses into blood and binds reversibly to the heme group for transport in RBC.
• CO2 is carried in plasma as bicarbonate (HCO3-) and H+.
• Hemoglobin exhibits cooperative binding, which favors binding at lungs and unloading at tissues.
• Open circulatory systems is where blood flows through a vessel with muscular thickenings that act as a pump and then blood empties into an open body cavity to supply the tissues with nutrients and is then returned to the circulation (insects do not use blood supply for oxygen tranposrtation)
• Closed circulatory systems have blood flowing through connected blood vessels pumped by muscular hearts that supply nutrients.
• Arteriole, Venule, Capillary Bed, Capillary are the Vessel types

Fish Cardiovascular System

• Fish have two-heart chambers and single-circuit circulation where deoxygenated blood enters the artrium from the main vein and then the ventrical, which pumps it into a main artery.

Land Cardiovascular System

• Hearts have more than 2 chambres that sepeate circulation of tissues
• Double-circuit circulation is a feature for these species Efficient gas exchange and O2 delivery
• Air is source of Oxygen, not water
• Higher metabolic rates

Anatomy of 4-Chambered Heart

• Deoxygenated blood enters the right atrium from the inferior and superior vena cava
• Deox. blood passes through the right AV valve and enters the right ventricle
• Deox. blood is pumped into the pulmonary arteries through the pulmonary valve
• Oxygenated blood returns from the lungs to the left atrium
• Oxygenated blood enters the left ventricle through the left AV valve
• Oxygenated blood is pumped by the left ventricle through the aortic valve into the systemic circulation
• Circulation in mammals and birds separated into pulmonary and systemic circuits Allows for: - Increased supply of oxygenated blood to tissues (pumped at high pressure) - Increases uptake O2 gas exvhange surface (due to time and lower pressure)

Heart Muscle Coordination

• Cardiovascular Muscle must have coordinated contracts Cardiovascular Muscle cells differ from skeletal muscle cells:
• Specilized cardiac cells generate ation potentials indpeendently from nervouse system

Depolarization in Pacemaker

• The SA-pacemaker cells generate action potentials that spread through the Atria to contract
• Signals from the Sa Pacemaker reach the AV Nodes, where it actiavtes fires, APs get transmitted by muscles fibres for contration

Animal Energetics

• Metabolic rates are the Overall energy over a timeframe
• Measured in Oxygen Comsumption such as converting glucose to water carbon and atp (C6H12O2+602->6H2)+CO2+ATP)
• AFFECTED BY MANY FACTORS such as:
  • ACTIVITY LEVEL
  • BODY SIZE
  • BODY TEMPERATURE
• Metabolic rate increases with activity that begins with oxgyen risng fast and then slowing, cells resyntheize their atop

Metabolism

• Body and Body Speed effect metabolism
• Animials have chemical and physiological responses to ensure thermal regulation
• Source of Heat, Endotherm generates internally, Ectotherm generated externally
• Response to Enviomental Change, Homeo and Poikilotherm
• Optimal Body temp, Ecto and Endotherms regulate temp with behaviour like sun and shelters
• Endotherms use behaviour as first ling against thermal change

Controlling Blood Flow

• Normaly reduce blood flow to surface
• High, dilation of arteries to skin a) response to cold b) repsonse to hot change
• Heat production uses shivering or non shivering thermogenesis

Heat conversion

• Endotherms adapt by, body size, reduce extremities, fur, and avoid overheating through watter contact

Ectotherms

• They:

  • expend little on themal regulation
  • Invest on groth
  • Short time forgivness

• But also limit Ability to regulate

• limit Burst activity

• limit activity

• Limit Geography

• Thermal regulation relies on a regulatory system is it in?

• At high temperatures metabolic rate may increase

                                       ###Animal Movalemnts
  

• Muscles

• skeletal- striated

• Cardiac

• Smooth

• Multi cellular

• generates atp

• Generates Actin

• Arranged and striped

Explore the intricate events of skeletal muscle cell depolarization and the role of ATP in contraction. Learn about troponin regulation and the distinctions between skeletal and smooth muscle. Understand tetanus and motor control characteristics.