UF Bio 2 Exam II

Are animals and plants relatives?

Yes, but very distant

What is an animal? (7)

~Eukaryotic

~Multicellular

~Heterotrophic

~Internal digestion

~Motility

~Muscles

~Neuronal signaling

Trade-offs and Tinkering (4)

~This is what evolution is all about!

~Mechanisms are rarely optimal for any single function

~They are compromises between multiple competing functions and the product of evolution and development

~Evolution does not engineer the optimal condition, it tinkers with preexisting structures and pathways

Evolution of Multicellularity Generated (6)

~An internal extracellular fluid (ECF)

~The internal environment is divided into ICF and ECF compartments by cell membranes

~Most of body water is inside cells

~Total body water for Humans is about 60% by weight

~Multicellularity and the ECF permitted division of labor in cells

~But each cell still needs to make ATP

Cellular Respiration Equation

C6H12O6 + O2 --> CO2 + H2O + energy (heat + ATP)

Nine Levels of Organization

~Atom

~Molecule

~Macromolecule

~Organelle

~Cell

~Tissue

~Organ

~Organ System

~Organism

4 Major Tissue Types

~Epithelial-Barriers between compartments and the environment and often transport

~Connective-Connects, supports, binds, or separates other tissues or organs

~Muscle

~Nervous

Homeostasis (6)

~The maintenance of a similar internal state despite external fluctuations

~Body conditions need to be kept within certain ranges compatible with life

~Homeostasis occurs in cells and in the ECF

~The ECF 'buffers' or shields cells from harsh environmental conditions

~Regulates body conditions through negative feedback loops

~The term originated from Claude Bernard who was studying glucose regulation

Percentages of fluid in each compartment (4)

~Intracellular fluid- 67%

~Extracellular fluid- 26%

~Intravascular fluid (blood plasma)- 7%

~Cerebrospinal fluid- Less than 1%

Medicine and Physiology (3)

~Tightly linked

~Circadian rhythms influence patterns of hormones, brain activity, etc

~One of the five Nobel prizes are awarded for "Physiology or Medicine"

Variables regulated in the ICF and ECF of most animals (5)

~Concentration of energy-rich molecules

~Concentration of oxygen

~Concentration of waste

~Concentration of water, salt, and other electrolytes

~pH

Regulation vs Conformity (5)

~Regulators are homeotherms AKA endotherms (Like dogs)

~Regulators can control their internal environment regardless of external environmental change to a large extent

~Conformers are Poikilotherms AKA ectotherms (Like lizards and snakes)

~Conformer are dependent upon the changes in the external environment

~Animals can be regulators or conformers for many different conditions such as temperature and body salt concentrations (osmolarity)

Metabolic Rate (5)

~The rate at which an organism converts chemical bond energy to heat

~Measures energy consumption

~This equals total energy expenditure

~For endotherms, as external temperature increases, metabolic rate first decreases, then remains steady, then increases again

~For ectotherms, as external temperature increases, metabolic rate increase slightly on a curve

Negative Feedback Loop

When the controlled variable deviates from the set point, an error signal in the control mechanism activates an effector that causes a compensatory response that returns the controlled variable

The Hypothalamus (5)

~Your handy sensor and control mechanism

~Center of homeostasis control

~Links the nervous system with various output points

~The hypothalamus receives information about the internal environment from many regions of the body

~Two responses are the Autonomic Response and the Endocrine Response

Autonomic Response vs Endocrine Response (3)

~The Autonomic Response affects the nervous system- Fight or flight/ rest or digest

~The Endocrine Response affects hormones- ACTH, Growth hormone, FSH/LH, Prolactin

~These both affect behaviors- Shivering, drinking, hunger, finding food, sleep

Endocrine Hormones

Act in a negative feedback loop with the hypothalamus and anterior pituitary to down-regulate stimulation

Positive Feedback Loop (2)

~Causes effectors to amplify the influence that creates an error signal

~Sometimes progressive deviations from a set-point are needed

1st vs 2nd Law of Thermodynamics

~1st Law of Thermodynamics- Conservation of energy

~2nd Law of Thermodynamics- Entropy

3 main mechanisms by which the hypothalamus controls effectors

~The receptor

~The control center

~The effector.

Animals and CO2 (2)

~Animals also need to get rid of CO2

~CO2 forms an acid in body fluids and must be eliminated constantly

Systems that work together to deliver O2 and CO2 throughout the body (7)

~Respiratory and Circulatory systems

~Every cell in the body needs to get O2 and get rid of CO2, but not every cell is in contact with the environment!

~Gases have to travel a LONG way and through different phases

~Gases need to travel passively between air and liquid

~O2 and CO2 are referred to as the respiratory gases

~Exchange of O2 and CO2 between animal and environment are urgent in most vertebrates

~All molecular O2 and CO2transport is passive by diffusion, which is not as straightforward between phases

Dissolution of Gases (4)

~Gases dissolve into body fluids in proportion to their partial pressures

~Gases freely mix in air, but also dissolve into water

~Gases dissolve into liquid much like ions or glucose (sugar in your tea)

~They do not appear as tiny bubbles; bubbles are gases not in solution (beer!)

Pressure of Oxygen at Sea Level

At sea level, oxygen is 21% of air and total pressure is one atmosphere (1 atm), therefore the pressure exerted by oxygen is 0.21 x 1 atm = 0.21 atm

Gases in air (6)

~In air, partial pressure is the pressure exerted by a single gas

~In air, the partial pressure of a single gas is proportional to its percent concentration

~Pressure falls with increasing altitude

~O2 diffuses until equilibrium reached-at high elevations that means lower O2 levels in the blood

~Gases still follow laws of diffusion, but not necessarily according to concentration, since when at equilibrium, O2 concentration in water is 1/20th concentration in air

~At sea level, air contains about 20% O2 but water contains only about 0.8% O2

Resting Ventilation in Humans vs Fish (6)

~Resting ventilation means O2 uptake

~In humans, the cost of resting ventilation is 1-2% of total metabolism

~But it's about 10% for fish

~There are no endothermic water breathers

~O2 needs increase as O2 availability decreases, so animals with high metabolic rate are air breathers

~O2 solubility decreases as external temperatures increase

CO2 vs O2 (4)

~CO2 is usually easier to eliminate than O2 is to obtain

~The concentration gradient of CO2 from air-breathers to the environment is always large

~Relative to O2, CO2 is more soluble in water and is easy for aquatic animals to exchange

~Venous blood is about 5% CO2 and the atmosphere is only 0.03% CO2

Fick Equation (7)

~Diffusion of gases follows this

~Q = DA[(P1- P2)/L]

~Q is the rate of diffusion

~D is a constant that depends on the diffusing substance, the medium and temperature

~A is the area of the respiratory membrane

~P1-P2 is the difference in partial pressure of gas on either side of the membrane

~L is the diffusion distance across the membrane

Oxygen diffusion through tissue (6)

~Oxygen can only diffuse through so much tissue

~August Krogh analyzed O2 diffusion over tissue distances and found that 0.5mm is greatest distance over which O2 can diffuse and meet metabolic needs

~Diffusion alone can support life only over short distances

~Diffusion of O2 in water can generally support aerobic metabolism up to 0.5 mm

~Many small animals do not need gas transport organs

~Gases can diffuse easily within the lung (and in tissues), but it's a long journey from there

Fluid Diffusion (2)

~Fluid accumulation in the lungs must be controlled to keep diffusion distances below 1 mm

~Even small accumulations of fluid (pulmonary edema) can be very dangerous

Flatworms

Flatworms (e.g. Planaria) have nervous and digestive systems, but no respiratory system

Sponges (3)

~Sponges also lack a respiratory system

~Sponges use choanocytes to move water through the internal cavity

~All cells are close enough to O2 source that gases are able to diffuse

Gills vs Lungs

~Gills protrude into water

~Lungs invaginate into the body

Air Movement and Circulation (4)

~Insects have a series of branching air tubules in their bodies called tracheae that are not ventilated (air movement)

~Perfusion (circulation) can take care of respiratory needs in some animals

~Amphibians and some other taxa can use cutaneous respiration, which Functions in both air and water, but skin must be kept moist

~Fish have gills allowing high SA, high ventilation, and high perfusion

Direction of Blood Flow

The direction of blood flow affects efficiency of oxygenation (Can be concurrent or countercurrent gas exchange)

Air-Breathers (3)

~Endotherms

~Most air-breathing vertebrates use tidal ventilation in lungs where air flows in and out the same path

~Mammals, including humans, use tidal ventilation with very thin diffusion distances

Lungs (3)

~Animal lung diversity gives us information about how lungs evolved, since the mammalian lung is 10x the surface area of the amphibian lung

~The lung starts as an out-pocket from the endoderm (digestive system)

~Lungs (and gills) help increase gas diffusion by increasing area and decreasing distance

Two Mechanisms of Ventilation

~Positive pressure (air gulping)

~Negative pressure (expanding the lungs)

Birds (2)

~Birds are a kind of medium between fish and mammals- counter current gas exchange

~Birds also have very short diffusion distances and large surface area in lungs

Three Different Ways to Breathe

~Human Lungs-Mammals inhale by moving the diaphragm to lower the air pressure in the chest cavity and pull air into the lungs. The human chest cavity is always at a lower pressure than the outside environment

~Bird Lungs-Birds have air sacs that store and pump air through stationary lungs. Unlike in mammals, air flows only one direction through bird lungs. With the help of the air sacs, this allows birds to take in oxygen even during exhalation. Birds can breathe at much higher elevations than mammals because of their more efficient lung structure.

~Grasshopper trachea-Grasshoppers have no lungs and do not use their circulatory system to move oxygen. They transport air directly to tissue cells using tracheal tubes. Grasshoppers use different breathing methods when they are resting, alert, hopping, or flying. The alert pumps its abdomen to change the volume of its air sacs, helping to pump air through the trachea.

Bulk flow over long distances is mediated by (5)

~Circulatory Systems

~Open air to lung-Long distance travel

~Air to blood-Short diffusion through 2 epithelial layers

~Lung to tissue-Long distance travel

~Blood to tissue-Short diffusion through 2 epithelial layers

True Circulatory Systems (3)

~They have a pump, fluid, and conduits (vessels or tubes)

~Not all animals have/need one

~Animals transport O2 in the blood, but they use different methods to bind O2

Hemoglobin vs Hemocyanin (4)

~Hemoglobin is in humans and the majority of other vertebrates

~Hemoglobin is bound to red blood cells and contains iron to carry oxygen that gives oxygenated blood its red color and deoxygenated blood its deep red color

~Hemocyanin is in spiders, crustaceans, and some mollusks, octopi, and squid

~Hemocyanin floats free in the blood and contains copper that gives oxygenated blood its colorlessness and deoxygenated blood its blue

Variation in Circulatory Systems (3)

~Animals also vary in the set up of their circulatory systems

~Closed circulatory system— blood vessels keep circulatory fluid (blood) separate from the interstitial fluid

~Open circulatory system— heart pumps blood though vessels that empty into cavities around organs; found in athropods, molluscs, and some invertebrates

Simplest of the Closed Circulatory Systems (4)

~Fish have the simplest system

~Atrium—receives blood from body

~Ventricle—receives blood from the atrium and sends it to the gills

~Blood is pumped to the gill capillaries and then to the other tissues in series, meaning the blood goes from the gills to the rest of the body without returning to the heart

Amphibian Heart (3)

~Amphibians have a 3-chambered heart

~2 atria (deoxygenated blood enters on the right, oxygenated blood enters left)

~These flow into 1 ventricle for mixed blood

Reptile Heart

Similar to the 3 chambered amphibian heart, but there is an extra valve for the mixed blood to leave the half separated ventricle, bypassing the lungs, and entering the systemic capillaries with the oxygenated blood

Mammal and Bird Hearts (3)

~Mammals and birds have completely separated ventricles= 4 chambers

~Separate pulmonary and systemic systems with oxygenated blood leaving the left ventricle and deoxygenated blood entering the right ventricle

~So advantageous it evolved (at least) twice, so it is a key adaptation for endothermy

Separate Sides of the Mammalian Heart (13)

~Separate sides of the heart keep systemic and pulmonary circuits separate

~Pulmonary:

1.Right atrium

2.Right ventricle

3.Pulmonary arteries

4.Lungs

5.Pulmonary veins

~Systemic

6.Left atrium

7.Left ventricle

8.Aorta

9.Body (arteries, arterioles, capillaries, venules, veins)

10.Vena cavae

Systole and Diastole (5)

~Both atria contract together at the end of diastole

~Both ventricles contract together during systole

~Diastole is the relaxation phase when ventricles relax, the heart fills with blood, and blood pressure is low

~Systole is the contraction phase when AV valves close, ventricles contract, the heart pumps blood, and blood pressure is high

~Systole and Diastole provide blood pressure measurement

Pacemaker Cells (3)

~Specialized cardiac muscle cells form pacemaker potentials and coordinate contraction in the heart

~They make the heart autorhythmic, meaning activation of cells and subsequent contraction occurs automatically

~The atrioventricular (AV) node conducts the signal slowly to ensure adequate time for chambers to fill

EKG (3)

~What the cycle of cardiac cell activation can be read as

~Waves of depolarization (muscle cell activation) in the heart can be read on the surface of the skin with electrodes

~Waves of depolarization in the heart muscle cells cause electrical potentials on the skin that are measured by EKGs

General Path of Blood in Mammalian Body (4)

~Blood travels from lungs (O2-rich, CO2-depleted) to heart

~Heart pumps blood to tissue (unload O2, upload CO2)

~Blood travels back to heart (O2-depleted, CO2-rich)

~Heart pumps blood back to lungs

Blood Distribution Methods in the Mammalian Body (6)

~Blood flows circularly through the body

~Blood vessels go through further and further branching to reach systemic cells

~Elastic, muscular arteries lead away from the heart

~Arterioles can control where blood flows through smooth muscles

~Distribution of blood flow is tightly regulated by changing vessel diameter via smooth muscle

~If a vessel constricts, then the extra blood flow is divided among the remaining less constricted vessels

Rings of the Artery from Inner to Outer

1)Endothelium

2)Elastin Layer

3)Smooth Muscle

4)Elastin Layer

5)Connective Tissue

Vessel Resistance and Flow =

~Resistance = 1/(r^4)

~Flow = 1/resistance = r^4

Vasodilation and Vasoconstriction (2)

~Vasodilation increases flow and vasoconstriction decreases flow due to dilation or constriction of the artery

~This increases or decreases blood flow to the capillary and venule

Capillaries (2)

~Principle site of gas and small particle exchange in systemic tissues

~They empty into venules, where deoxygenated blood begins flowing back to the heart

Veins (2)

~Veins carry blood back to the heart, store blood volume, and are less muscular than arteries

~They have one-way valves that promote venous return to the heart

Arteriole (3)

~Have high resistance

~Regulate flow into specific tissue capillaries

~Mainly made of smooth muscle

Vessel Blood Flow Path and Diameter in Humans (9)

~Vessel diameter decreases up to capillaries, then increases

~Aorta

~Arteries

~Arterioles

~Capillaries

~Venules

~Veins

~Vena Cava

~But TOTAL cross-sectional area is highest in capillaries!

Ohm's Law (2)

~Relates liquid flow rate to the total surface area of flow

~Q= V x SA

Blood Pressure of Major Vessels in Humans (3)

~Higher blood pressure in arteries, medium blood pressure in capillaries, and low blood pressure in veins

~Less work is required to push blood through large arteries, but more is required for arterioles/capillaries

~Low blood pressure in veins helps explain the evolution of one-way valves

Nervous System (4)

~The main source of integration and communication

~2 categories of cells are neurons and glia

~Neurons generate and transmit electrical signals called action potentials

~Glia provide support and maintain extracellular environment

Neuronal Signaling vs Endocrine Signaling

Neuronal signaling is fast and specific and endocrine signaling is slow and broad

Nerves (2)

~Nerve signal transmission alternates between electrical signaling within cells and chemical signaling between cells

~Nerves are groups of axons, but some axons are pretty big

Glial cells (4)

~Support, nourish, and insulate neurons

~The support metabolism, have immune function, and have electrical insulation

~"Glial" refers to glue

~Make up ~1/2 of mammalian brains and outnumber neurons 10:1

Membrane Potentials (8)

~Ions are unevenly distributed across cell membranes, generating this

~Almost all cells, including neurons, have a higher concentration of Na+ outside than inside and a higher concentration of K+ inside than outside at rest

~Tiny electrodes inserted into cells are used to measure membrane voltages (potentials)

~Ions diffuse according to concentration and electrical gradients

~The Nernst equation provides the electrochemical equilibrium of a certain ion, assuming no other diffusion

~Potassium (K+) is at equilibrium around resting potential

~Larger currents don't increase the action potential magnitude

~Long currents cause repetitive action potentials, but each action potential is the same

Ion Channels (5)

~Ion transport through ion channels in the membrane change voltage, or potentials

~Resting K+ Channels are always open

~Voltage-gated Channels open (transiently) in response to change in the membrane potential

~Ligand-gated Channels open (and close) in response to a specific extracellular neurotransmitter

~Signal-gated Channels open (and close) in response to a specific intracellular molecule

Action Potential Spike (8)

~An action potential spike is an all-or-none event

~A threshold must be reached before a spike occurs

~An action potential spike is caused by opening and closing of voltage-gated ion channels

1) Leak K+ channels create the resting potential, while voltage gated channels are closed

2)The membrane in the axon hillock reaches its threshold—5 to 10 mV above resting potential, opening a few voltage-gated Na+ channels

3)Via positive feedback, more voltage-gated Na+ channels (activation gates) open quickly

4)The influx of positive ions causes more depolarization, the membrane potential is briefly positive, and an action potential occurs

5)The axon quickly returns to a negative potential due to voltage-gated K+ channels open slowly and stay open longer so K+ moves out, and voltage-gated Na+ channels (inactivation gates) close and cannot open again during the refractory period—a few milliseconds

Depolarization vs Hyperpolarization

~Depolarization- potential becomes LESS negative

~Hyperpolarization- potential becomes MORE negative

Gated Channels (4)

~Allows neurons to change their membrane potentials in response to a stimulus

~At resting potential, only leak K+ channels are open

~When depolarized, voltage-gated Na+ channels are open

~When hyperpolarized, chemically-gated K+ channels are open

Action Potentials (4)

~Action potentials travel along the axon

~All-or-nothing

~Self-regenerating, depolarizing adjacent regions of the membrane

~Continuous - one direction, refractory period prevents reversals

Axon Diameter and Myelin Sheath (7)

~Large axon diameter and myelin sheath increase the speed of action potential propagation

~Resistance to current flow is reduced as diameter increases

~Vertebrates use a different strategy; they instead evolved myelin to insulate axons

~Myelination increases speed of signal through saltatory conduction

~Large diameter and myelin are different evolutionary solutions to the same problem

~Without myelination, the optic nerve would have to be the diameter of a telephone wire to conduct signals at the same speed

~Multiple sclerosis is caused by the immune system attacking myelin

Synapses (5)

~Neurons connect with each other via synapses to form complex networks

~Neurons can connect through electrical or chemical synapses

~Synapses cause postsynaptic potentials, which are graded, small and decay with distance

~Multiple synapses add together in time or over space to influence threshold at the axon hillock by a process called summation

~A single postsynaptic neuron can have thousands of synapses

Neurotransmitters (3)

~Synthesized in cell bodies, stored in axon terminals, and stimulated for release by action potentials and calcium

~Neurotransmitters bind to receptor (ligand-gated) channels in the postsynaptic membrane and change ion flow and therefore membrane potential

~They will be recycled back to the cell body

Evolution of Nervous Systems (3)

~More ancient/simple nervous systems are diffuse based on nerve nets and have no "central processing unit" where neurons all talk to each other

~Animals, including flatworms, earthworms, squids, and humans evolved more centralized, cephalized nervous systems

~The areas responsible for integrating information cluster together to make the central nervous system

Nervous System in Vertebrates and Invertebrates (3)

~Most bilaterally symmetrical animals have cephalized nervous systems

~Vertebrate nerve cords are mostly dorsal, while Invertebrates mostly have ventral nervous systems

~Vertebrate nervous systems can be divided into central and peripheral

Central Nervous System (3)

~Large structures such as brain and spinal cord that integrate information

~Brain- anterior enlargement of the CNS

~Spinal cord- contact between brain and PNS, e.g. where reflex processing occurs

Peripheral Nervous System (3)

~All processes and cell bodies of sensory and motor neurons that occur outside the CNS

~Nerve- a bundle of multiple axons in the PNS

~Ganglia- swellings containing aggregates of cell bodies and processes

Reflex Arch (2)

~Starts with somatic sensors, travels via afferent neurons to the CNS and then controls skeletal muscles via the somatic efferent neurons

~This process is unconscious- it bypasses processing in the brain

Response Pathway from Receptors to Effectors (7)

1)Sensory receptors detect change in stimuli

2)The sensory division of the PNS brings info to the CNS

3)Information processing occurs in the CNS

4)The motor division of the PNS carries demands from the CNS

5a)EITHER the somatic nervous system controls skeletal muscle contractions

5b)OR the autonomic nervous system provides autonomic regulation of smooth muscle, cardiac muscle, internal organs, glands, and adipose tissue

6)Effectors are target organs whose activities change in response to neural commands

Autonomic Nervous System (3)

~Includes the Parasympathetic and Sympathetic Nervous System

~The parasympathetic nervous system is known for its "rest and digest" and releases acetylcholine to target organs

~The sympathetic nervous system is known for its "Fight or flight response" and releases norepinephrine to target organs

Somatic Nervous System (3)

~Acetylcholine is the neurotransmitter released in response to stimuli for targeting organs

~The sensory (afferent) nervous system is the sensory input

~The motor (efferent) nervous system is the motor output

Three Types of Muscle

~Cardiac Muscle Cell-Specialized for pumping blood

~Skeletal Muscle Cell-Specialized for rapid and voluntary contraction and relaxation

~Smooth Muscle Cell-Specialized for slow involuntary control; can contract for long periods without fatigue; most efficient use of ATP

Sliding Filament Mechanism (2)

~All types of muscle generate 'pulling' forces by the same sliding mechanism

~Actin and myosin-like proteins mediate cell division, cell motility, and organelle transport in many cell types

Organization of Actin and Myosin (3)

~Organization of actin and myosin of muscle cells give them a striated appearance

~Skeletal muscle is also striated due to the arrangement of actin and myosin into sarcomeres

~Cells-called muscle fibers- are large and multinucleated, made up of many myofibrils

Sarcomere (3)

~The unit that has actin and myosin filaments and contracts

~In a single sarcomere, the actin filament is the longer, thinner band and the myosin filament is the shorter, thicker band

~Actin and myosin slide past each other during a contraction

Thin Filaments

Composed of actin, tropomyosin, and troponin

Muscle Coordination (4)

~Muscles coordinate through stimulation from the somatic nervous system

~Blocked myosin binding sites link stimulation and contraction

~Each muscle cell is innervated by one neuron

~Neurons talk to muscle cells through neuromuscular junctions

How do neurons talk to muscle? (7)

~Through neuromuscular junctions

1)Action potential reaches end of axon

2)Voltage-gated calcium channels open

3)Calcium stimulates synaptic vesicle fusion with presynaptic membrane

4)Acetylcholine is released and binds to ligand-gated channels on the muscle membrane

5)Sodium enters the muscle causing a strong EPSP (excitatory postsynaptic potential)

6)Threshold is reached and voltage-gated sodium channels start an action potential

Action Potentials in a Muscle Fiber (7)

~Action potentials in a muscle fiber travel deep within the cell to each microfibril

~T tubules descend into the cytoplasm

~T tubules run close to the sarcoplasmic reticulum which release Ca2+ ions when depolarized

~The action potential activates voltage-gated T-tubule receptors, which are linked to receptors in the sarcoplasmic reticulum, initiating Ca2+ release

~Calcium binds to troponin, which then exposes myosin binding sites by moving tropomyosin

~Myosin uses ATP to pull actin and shorten each sarcomere

~Action potentials cause contraction in muscle fibers (muscle cells)Sl

Which is the correct sequence of signals starting with an action potential in a motor neuron and ending with calcium release in the skeletal muscle? (6)

1) Voltage-gated Na channels

2) Voltage-gated Ca channels

3) Neurotransmitter

4) Ligand-gated Na channels

5) Voltage-gated Na channels

6) Voltage-gated Ca channels

Skeletal Muscle (2)

~Critical for most behaviors, including breathing, moving, and talking

~They are under the control of the somatic nervous system

Skeletal Systems

The rigid supports to which muscles attach and pull on to produce movement

Muscle for Movement (4)

~Muscles work in opposing pairs

~Muscles can only contract and relax

~For bidirectional movement- muscles contract on either side of a joint via tendons

~Complex movements like walking require many pairs of opposing pairs

Cardiac Muscle (5)

~Cardiac muscle is only located in the heart

~It is striated

~It is controlled by the autonomic nervous system

~Similar to skeletal muscle in striations and contraction mechanism (T-tubules, sarcoplasmic reticulum, Ca2+)

~Cardiac myocytes (muscle cells) have four specializations for pumping blood

Four Specializations of Cardiac Myocytes for Pumping Blood

1.Intercalated discs mechanically connect adjacent cells

2.Gap junctions allow APs to move between adjacent cells

3.Pacemaker cells endogenously generate action potentials

4.Action potentials last 100-500 ms preventing tetanus

Gap Junctions (2)

~Made of membrane proteins that allow small molecules to diffuse between adjacent cells

~Allow for fast propagation of signals

Pacemaker and Conducting Cells (4)

~Initiate and coordinate heart contractions

~Heartbeat is myogenic thanks to pacemaker cells

~The autonomic nervous system can alter the rate of contraction, but it is not necessary for their function

~The mechanism of contraction within the cell is the same as in skeletal muscle