BIO 224 Midterm Review L1-5-2 PDF

General Concepts: 1.​ What is an animal? 2.​ Animal Characteristics 3.​ Animal Diversity 4.​ Animal Origins 5.​ Animal Classification 1.​ Animal Origins 1.​ What is an animal? Common ancestor for all of kingdom animalia = c...

General Concepts: 1.​ What is an animal? 2.​ Animal Characteristics 3.​ Animal Diversity 4.​ Animal Origins 5.​ Animal Classification 1.​ Animal Origins 1.​ What is an animal? Common ancestor for all of kingdom animalia = colonial flagellated protist in Precambrian. Animal = non-human animals. How do we know this? All members of the ​ Similarity to the modern colonial flagellated species. animalia kingdom. ​ Morphological and molecular evidence support this. Animal vs Plant Cell 1.​ Animal Characteristics Animal = no cell wall. No CENTRAL vacuole, just vacuoles. ​ Multicellular eukaryote Cell wall = provides tissue stability (lacks cell wall) Plants = cell wall and central vacuole. ​ Heterotroph ​ Motile ​ Sexual or asexual reproductivity ​ Has nerves and Tissue Stability in Animals muscles Why is it different from plants? --> Because animal cells do 1.​ Animal Diversity not have a cell wall. What makes an animal 'diverse'? How is stability achieved in tissues by animals? ​ Extracellular junctions ​ Diverse species ​ Cell junctions ​ Diverse habitats These junctions maintain cell shape, structure, and function. ​ Diverse characteristics Types of Junctions: 1.​ Anchoring junction- attach proteins to join cells together. 2.​ Tight junction- prevents things from passing through cells. Holds cells very close together. 3.​ Gap junction- allows for cell-cell communication, as well as ion exchange. TERMS FROM THIS LECTURE: ​ Protostomes ​ Deuterostomes ​ Spiral cleavage ​ Radial cleavage ​ Blastopore ​ Gastrulation ​ Vegetal Pole ​ Diploblast ​ Triploblast ​ Endoderm ​ Mesoderm ​ Ectoderm ​ Tissues ​ Body Symmetry ​ Radial symmetry ​ Bilateral symmetry ​ Segmentation ​ Body Cavity ​ Acoelomate ​ Pseudocoelomate Main Concept: Classifying Animals Animal Body Plans Sexual Reproduction Animal Body Plans Influences on animal body plans: ​ Embryonic development pattern ​ Germ cell layers ​ Body symmetry ​ Body cavity type Sexual Reproduction ​ Most animals undergo some form of sexual reproduction. Process: ​ Germ line cells undergo meiosis --> haploid gametes are produced. ​ Gametes fuse (fertilization) --> diploid zygote is formed. Asexual Reproduction Examples: ​ Budding in hydra ​ Fragmentation in echinoderms ​ Parthenogenesis in insects PROTOSOMES ​ Exhibit spiral cleavage. ​ Each cells developmental path is determined as the cell is produced. ​ Each blastomere CANNOT become a complete organism by itself. ​ Determinant Cleavage: develops into function NOT organism. DEUTEROSTOMES ​ Exhibit radial cleavage. ​ Developmental path is undetermined. ​ Each cell can for a complete organism by itself, meaning cells can be removed. ​ Indeterminant cleavage: can develop into complete organism. Sexual Reproduction Process: Timeline- Fertilization --> Zygote --> Cleavage --> Morula --> Blastula ZYGOTE: Zygote cleavage is formed following fertilization. ZYGOTE CLEAVAGE --> division of cells in the early embryo. Undergoes rapid cell cycles with NO significant growth. Zygote then develops into a compact cell mass --> MORULA MORULA: Morula derives into a hollow sphere of single layer of cells --> BLASTULA Gastrulation: Follows cleavage. Blastula --> Gastrulation --> Gastrula Begins at the vegetal pole. Blastula invaginates. Undergoes differentiation into 2 or 3 germ layers. GERM LAYERS: ​ Ectoderm (outer) ​ Mesoderm (middle) ​ Endoderm (inside) Why is there different germ layers? Germ layers differentiate to form tissues and organs. Definitions: Tissues- groups of similar differentiated cells specialized for particular functions. DIGESTIVE SYSTEM POLARITY: Blastopore always develops first. But the ends (poles) of the blastopore differ between Protostomes and Deuterostomes. Protostomes: mouth is developed first (vegetal pole), anus forms later. Deuterostomes: anus is developed first (vegetal pole), mouth forms later. Vegetal pole is the bottom of the blastopore and gastrulation ALWAYS begins here. PROTOSTOMES vs DEUTEROSTOMES Mesoderm Origin: P: Mesoderm differentiates near the blastopore. (bottom) D: Mesoderm originates from outpocketings. (top) GERM LAYERS Diploblastic animals (2) = animals that have 2 germ layers. Ecto- and Endo- derm. Triploblastic animals (3) = animals that have 3 germ layers. Ecto-, Endo-, and Meso- derm. ENDOderm: ​ Innermost layer ​ Forms gut lining; digestive tract MESOderm: ​ Between other layers (middle) ​ Forms body wall muscles and structures between gut and external covering; muscles and skeleton ECTOderm: ​ Outermost layer ​ Forms external covering (skin) and nervous system. EMBRYONIC DEVELOPMENT DIFFERENCES Protostomes Deuterostomes Cleavage pattern Spiral Radial Cell fate Determinant Indeterminant Digestive tract polarity Mouth from blastopore Anus from blastopore Mesoderm origin Differentiates near blastopore Originates from outpocketings Coelom origin Schizocoelom Entercoelom BODY CAVITY What is a body cavity? ​ A body cavity separates the gut from the body wall. ​ AKA coelom Deuterostome body cavity: Fluid-filled cavity between the intestines and the body wall. Protostome body cavities: Acoelomate- no body cavity, influences material diffusion Pseudocoelomate- false body cavity. Fluid filled or organ filled space between endoderm and mesoderm. BODY SYMMETRY Radial Symmetry: can be divided equally by any longitudinal plane. (diploblastic) Bilateral Symmetry: can be divided along a vertical plane at the middle. (triploblastic) Segmentation: Repeated structures along the anterior-posterior axis. Why? Movement and specialization. UNIFYING CONCEPTS Physiological processes must: ​ Obey the laws of physics and chemistry ​ Be tightly regulated usually. (homeostasis)  Terms from this Main Concept: Homeostasis Lecture: What is Homeostasis? ​ Negative Why is it necessary? Feedback What are methods of homeostasis? ​ Positive What is thermoregulation? Feedback ​ Feedforwa rd ​ Endother m What is Homeostasis? ​ Ectotherm ​ Regulation of the body's internal environment at ​ Homeothe or near a stable level. rm ​ Homeostasis regulates a physiological variable ​ Heterothe within a narrow range around a set point. rm Why is it necessary? ​ To allow an organism to reach optimal Thermoregulation physiological performance. Endotherm VS Ectotherm Homeostatic Methods ​ Location of needed body heat ​ Negative feedback loops ​ Positive feedback loops Endotherm = heat from internal ​ Feedforward physiological sources ​ If environment decreases, 1.​ Negative Feedback metabolism increases to warm Variable rises above the set point. up. Mechanisms of - feedback return variable back to set ​ Physiological and behavioural point. responses to changes in skin Minimizes difference between current level and set and core temperature. point. ​ Use negative feedback loops to maintain balance between 1.​ Positive Feedback heat loss and gain. Moves variable away from the set point. Used to quickly increase/decrease a process. Ectotherm = heat from external Eventually shut off by negative feedback. environment ​ If environment decreases, 1.​ Feedforward body temp also decreases. Future needs are anticipated. ​ Most aquatic invertebrates Physiology is adjusted in advance. Often involves learning and complex behaviours.  ​ Some use behavioural responses to regulate body temp. Homeotherm VS Heterotherm ​ Constant VS variable body temp. Homeotherms = maintains body temp at a constant level Heterotherms = vary between self-regulating their body temp and allowing environment to affect it. KEY TERMS FROM THIS LECTURE: ​ Thermoregulation ​ Organismal performance ​ Hypothalamus ​ Thermal acclimatization ​ Torpor ​ Vasoconstriction ​ Vasodilation Main Concept: Thermoregulation ​ Thermoregulation in Ectotherms ​ Thermal Acclimatization ​ Thermoregulation in Endotherms ​ Torpor Thermoregulation ​ Maintaining body temperature at a level that provides optimal physiological performance. Allows every body cell to function at optimal level. Organismal Performance: The rate and efficiency of an animals biochemical, physiological, and whole-body processes. Ectotherms ​ Obtain heat energy primarily from the external environment. Endotherms ​ Obtain heat energy primarily from internal reactions Thermal Acclimatization What? ​ A structural or metabolic change in the limits of tolerable temperatures as the environment alternates between warm and cool seasons. Why? ​ Allows animal to attain good physiological performance. ​ Increase in specific enzymes that work better at different temps. ​ Could change phospholipid saturation and cholesterol. Temperature Regulation- Endotherms ​ Changes in skin temperature causes changes in core temperature and body's attempt to thermoregulate.  ​ Thermoreceptors detect change in temp. (Hypothalamus = 'body thermostat') Hypothalamus: maintains core homeostatic functions. Skin and Endothermy Skin = organ of heat transfer How? ​ Blood vessels of skin regulate heat loss by vasoconstriction or vasodilation. ​ Skin = water impermeable. ​ Fatty tissue layer under blood vessels in skin limit the amount of heat loss. PROCESS: (FALL IN TEMP) 1.​ Thermoreceptors signal a fall in core temp. 2.​ Hypothalamus triggers compensating responses. 3.​ Signals are sent through the autonomic nervous system to restore temp. 4.​ Constriction occurs and reduces the flow of blood to the skin's capillary network. PROCESS: (INCREASE IN TEMP) 1.​ Thermoreceptors detect a increase in core temp. 2.​ Hypothalamus sends signals through ANS. 3.​ Signals relax smooth muscles of arterioles. 4.​ Vasodilation occurs, increasing blood flow. Temperature Variations ​ Temp. set point in many birds and mammals vary in daily and seasonal patterns. ​ Cooler conditions = lower set point; TORPOR TORPOR: A state of physical or mental inactivity; lethargy. KEY TERMS FROM THIS LECTURE: ​ Cells ​ Tissues ​ Organs ​ Organ systems ​ Epithelial tissue ​ Connective tissue ​ Muscle tissue ​ Nervous tissue ​ Glands ​ Skeletal muscles ​ Cardiac muscles ​ Smooth muscles Friday, January 31, 2025 9:32 AM ○​ Afferent ○​ Efferent ○​ Interneurons ○​ Dendrites ○​ Axons ○​ Myelin ○​ Glial cells ○​ Schwann cells Main Concept: Animal Body Organization & Nervous System ​ Layers of Organization ​ Animal Organ Systems ​ Tissue Types ​ Neuron Types ​ Neuron Structure ​ Glial Cells Organization of the Animal Body 1.​ Cells; specialized/organized into tissues. 2.​ Tissues; group of cells with the same structure and function. Work as a unit to carry out activity. 3.​ Organs; assembly of tissues integrated into a structure. Carry out a specific function. 4.​ Organ system; Group of organs that carry out related steps in a major physiological process. Cell properties in tissue = determine structure and function of tissue. Tasks of Organ Systems: ​ Acquire nutrients ​ Synthesize molecules. ​ Sense and respond to environment ​ Protect the body ​ Reproduce. Tissue Types: 1.​ Epithelial 2.​ Connective 3.​ Muscle 4.​ Nervous Epithelial Tissue ​ Sheetlike layers of cells. ​ Cover body surface and internal organs. ​ Lines cavities and ducts within body. ​ 5 types of epithelial tissue. 1.​ Simple Squamous ​ Layer of flattened cells. ​ Function = diffusion 1.​ Stratified Squamous ​ Several layer of flattened cells. ​ Function = abrasion protection 1.​ Cuboidal ​ Layer of cubelike cells. ​ Function = secretion and absorption 1.​ Single columnar ​ Layer of tall slender cells with nuclei at base. ​ Function = secretion, absorption, protection 1.​ Simple pseudostratified ​ Single layer of columnar cells of differing heights. ​ Function = protection, mucus secretion and movement. Connective Tissue ​ Consists of cell networks and extracellular matrix ​ Supports other body tissues ​ Transmits mechanical forces ​ Acts as a filter ​ 6 types of connective tissue 1.​ Loose connective tissue ​ Support, elasticity, diffusion. 1.​ Cartilage ​ Support, flexibility, joint movement 1.​ Adipose tissue ​ Energy reserves, insulation, padding 1.​ Fibrous Connective Tissue ​ Strength, elasticity. 1.​ Bone ​ Movement, support, and protection (Also Blood; substance transport) ​ 11 MAJOR Organ Systems: ​ 1.​ Respiratory 2.​ Digestive 3.​ Reproductive 4.​ Excretory 5.​ Nervous 6.​ Endocrine 7.​ Muscular 8.​ Skeletal 9.​ Integumentary 10.​Circulatory 11.​Immune Nervous Tissue ​ Neurons communicate information between body parts. ​ Glial Cells Muscle Tissue ​ 3 types 1.​ Skeletal muscles ​ Long contractile cells; muscle fibers. ​ Move body parts and maintain posture 1.​ Cardiac muscle ​ Short contractile cells with a branched structure. ​ Forms the heart. 1.​ Smooth muscle ​ Spindle shaped contractile cells. ​ Forms layers surrounding body cavities and tubes. Glands Function; secretory structures derived from epithelia. 2 TYPES 1.​ Exocrine ​ Secretions expelled outside of the body (by a duct). 1.​ Endocrine ​ Ductless. Neuron types 1.​ Afferent (sensory) ​ Conduct info. from sensory receptors. 1.​ Interneurons ​ Integrate information from afferent into a response. 1.​ Efferent (motor) ​ Carry response signals to effectors --> carry out a response. A basic neuron circuit is made up of all three neuron types. Glial Cells ​ Astrocytes and Schwann cells ​ Support/provide nutrients to neurons. ​ Provide electrical insulation ​ Scavenge foreign matter/debris. Astrocytes; maintain ion balance in surrounding neurons Schwann cells; form insulating layers (myelin) around axons. Neuron Structure Dendrites = receive signals and integrate/transmit them toward 'spike initiation zone (SIZ)'. Axons = conduct signals away from SIZ to another neuron or effector. Nervous System ​ Functions result from the activities of neurons and glial cells. ​ Nerves provide a common pathway between different structures and CNS. ​ CNS = ganglia and brain. Functions of Nervous System: ​ Reception ​ Integration ​ Transmission ​ Response Main Concept: Synaptic Transmissions ​ Synapses ​ Neurotransmitters ​ Receptor types ​ Electrophysiology ​ Graded Potentials ​ Summation ​ Evolution of the Nervous System ​ Divisions of the Nervous System Synapses ​ Site where a neuron communicates with another neuron or effector  ​ 2 types of neurons Electrical Synapse in depth: 1.​ Presynaptic cell; sends a signal. ​ Gap junctions directly connect cytoplasm 2.​ Postsynaptic cell; receives a signal. of each cell. ​ Ions flow between cells. 2 types of synapses ​ Rapid flow of current. ​ Excitatory only. ​ Electrical synapse Impulses pass directly from presynaptic Chemical Synapse in depth: cell to postsynaptic cell. ​ Pre- and postsynaptic neurons separated ​ Chemical synapse by synaptic cleft. Neurotransmitter released by presynaptic ​ Neurotransmitter is stored in vesicles cell diffuses across synaptic cleft. within the axon terminals of presynaptic Binds to receptors in the plasma membrane neuron. of postsynaptic cell. What are Neurotransmitters? Release of Neurotransmitters ​ All bind to a receptor protein in post-synaptic membrane. ​ Influx of calcium through voltage-gated ​ Have several different receptors channels. ​ Can stimulate or inhibit an effector cell. ​ Calcium causes vesicles to move, fuse, and release neurotransmitters Acetylcholine into the cleft. ​ Stimulates skeletal muscle contractions. ​ Neurotransmitter binds to post ​ Inhibits cardiac muscle contraction. synaptic receptors- channels open. ​ Allows for integration of multiple presynaptic inputs. 2 types of Acetylcholine Receptor Proteins 1.​ Ionotropic receptors 2.​ Metabotropic receptors Main concept: Sensory Systems KNOW THE CHART ON ​ Environment detection ​ Sensory inputs SLIDE 12 OF LECTURE 9!! ​ Sensory transduction ​ Sensory receptors ​ Mechanoreceptors ​ Photoreceptors Detecting the Environment ​ Important in order to maintain homeostasis Sensory Inputs  ​ Sensory systems begin Sensory Receptors with sensory receptors; (transducers) formed by ​ Respond to stimuli in their receptive fields. the dendrites of afferent How? neurons. ​ By undergoing a change in receptor ​ These detect sensory potential, this varies with the magnitude of info., convert it to neural the stimulus. activity, then pass info Why? along neurons to the CNS. ​ Change in receptor potential is caused by changes in rate of conduction of cations Sensory Transduction across plasma membrane. ​ Occurs when stimuli Sensory Receptors; Structural Forms (3) cause changes in ​ Specialized cell that synapses with an membrane potential in the afferent neuron. sensory receptors. ​ Peripheral endings of an afferent neuron. ​ If receptors are available to the stimulus, the cell 1.​ Free Nerve Endings will react. ​ Stimulus causes a change in MP ​ This generates AP in the axon. Mechanoreceptors ​ Detect mechanical stimuli 1.​ Enclosed Nerve Endings ​ Touch and pressure ​ Stimulus affects the specialized structure, receptors in vertebrates triggering an AP in the afferent neuron. ​ 4 types of tactile stimuli mechanoreceptors in 1.​ 2 Separate Cells human skin ​ Synapse with a axon of afferent neuron. ​ Stimulus changes MP, neurotransmitters Proprioceptors- detect stimuli are released. used by the CNS; monitor and ​ Neurotransmitters trigger AP in axon of an maintain body and limb positions. afferent neuron. Sensory hair cells- Generate action potentials in afferent neurons when the hairs are moved. Photoreceptors ​ Detect light at particular wavelengths. ​ Stimuli is converted to AP's. ​ Signals are turned into light perception.  The Ear Structure Compound Eyes ​ Contain many faceted Pinna; outer ear- concentrates and focuses sound visual units fitted closely waves. together. Middle ear- Malleus, Incas, Stapes, and Oval ​ Light entered is focused Window by a transparent cornea Inner ear- Cochlea, Organ of Corti, and Round and crystalline cone onto Window. photoreceptor cells. ​ Brain receives a Movement: motion-sensitive mosaic image. Sound waves enter at auditory canal. Strike thin sheet of tissue; tympanic Single Lens Eyes membrane/eardrum ​ Light enters through the Vibrates this tissue. cornea, lens concentrates Vibrations are transmitted through one or more the light and bones in the middle ear to the fluid filled inner ear. photoreceptors, in this Hair cells in Organ of Corti send signals to the brain case retina, records the via afferent neurons, when moved. image. ​ Iris muscles adjust pupil The Human Ear; Balance and Orientation size to vary amount of light entering the eye. ​ Used for balance and orientation; perceives ​ Accommodation occurs. position and motion of head. ​ Maintains equilibrium and coordinates head Accommodation: occurs when the and body movements lens changes shape to focus on ​ Consists of 3 semicircular canals, 2 distant and near objects. chambers, utricle, and saccule. Sound Detection Retinal photoreceptors; Rods and ​ Sound = wave of vibrations produced by Cones alternation compression and decompression of air or water. Water is faster than air at Rods sound travel. ​ specialized for detecting ​ Detected by mechanoreceptors in low-intensity light invertebrates ​ Consists of opsin protein ​ Detected by sensory hair cells in vertebrates retinal. ​ Hair cells respond by triggering an AP. Cones ​ specialized for detecting light of diff. wavelengths; colour.  ​ Most mammals = 2 cone types ​ Humans = 3 cone types Both are linked to neurons in the retina. Main Concept: Cont. Sensory Systems Chemoreceptors ​ Provide information about taste (gustation) and smell (olfaction). ​ Work through membrane receptor proteins. ​ Stimulated when they bind with specific molecules. ​ Generate action potentials as channels open, leading to the CNS. Taste: detection of food molecules when coming into CONTACT with receptors. Relies on contact chemoreception. Smell: detection of airborne molecules. Many Sensory adaptation mammals communicate with odours. ​ The effect of a stimulus is reduced if it continues at a constant level. Some Taste and Smell receptors have hairlike receptors adapt quickly and broadly. extensions. These contain proteins that bind environmental Perception molecules. ​ The conscious awareness of our external and internal environments Taste receptor hairs: Derived from microvilli and derived from the processing of sensory contain microfilaments input. Smell receptor hairs: Derived from cilia and contain microtubules. Pheromones ​ Chemicals used in communication in both plants and animals.  ​ Binding of odorant leads to membrane depolarization Nociceptors ​ Detect damaging stimuli interpreted by brain as pain. ​ Located on body surface and interior. ​ Protective mechanisms that adapt very little. Electroreceptors ​ Detect electrical currents and fields. Magnetoreception ​ Detect and use Earth's magnetic field as a source of directional information Main Concept: Animal Locomotion; Skeleton and Muscles ​ Types of animal skeletons ​ Bone tissue ​ Calcium regulation ​ Muscle types ​ Muscle structure ​ Muscle physiology ​ Levers ​ Sarcomeres Animal Skeletons ​ For body support, locomotion, and protection Hydrostatic = limited protection ​ Muscles surrounded by compartment(s) filled with fluid under pressure.  ​ Contraction and relaxation of Bone Tissues muscles change the shape of the animal. ​ Complex organs built from multiple tissues. Exoskeleton = must be shed for body ​ Can be compact or spongy. growth; ecdysis ​ Compact = no spaces ​ Rigid external body covering. ​ Spongy = open into larger spaces; filled ​ Provides support, can protect by marrow. delicate internal tissues. ​ Mineral storage. Calcium and phosphate ​ Body is contained within; deposited and withdrawn from bones. incompressible. Calcium regulation Endoskeleton = exposed to bodily fluids ​ Vertebrate skeleton relies on Ca and H as a byproduct of metabolism. homeostasis. ​ Supports the body by rigid ​ Blood Ca is regulated by endocrine structures; bones. negative feedback loops ​ Protects delicate internal tissues. ​ Primary skeletal system in vertebrates. Muscles ​ 2 types; echinoderms and vertebrates ​ Responsible for movement of body ​ Contain contractile cells. Human Skeleton ​ Contraction based on interaction between ​ Axial skeleton; skull, vertebral support filaments; actin, and myosin; column, sternum and ribcage. motor protein. ​ Appendicular skeleton; shoulder, hip, leg, and arm bones. Types of Vertebrate Muscle 1.​ Skeletal Muscles ​ Bundles of elongated, cylindrical cells; Levers muscle fibres. ​ Formed by a fusion of cells call Proximal = speed myoblasts. Distal = strength ​ Cells held in parallel bundles. ​ Tendons attach to bones. Muscles can attached proximal or distal ​ Extensive networks of vessels to supply from the joint. nutrients. ​ Contraction stimulated by motor neurons. Sarcomere Structure 1.​ Cardiac muscle ​ Contain myofibrils (many 2.​ Smooth muscle sarcomeres) ​ Myofilaments = Myosin, actin All muscle is bioelectric; produces a membrane action potential.  ​ Troponin and Tropomyosin regulate interactions with myosin. (Sliding Filament Theory) Main Concept: Animal Locomotion; Skeletal Muscles ​ Neuromuscular Junction ​ Action Potential Conduction ​ Calcium release ​ ATP function ​ Force and Movement ​ Neural Regulation of Skeletal Muscle Contraction ​ Stretch Activation Neuromuscular Junction ​ Junction between the motor neuron axon terminal and the postsynaptic muscle fibre. ​ Occurs when acetylcholine causes a muscle fibre depolarization. ​ Depolarization results in muscle action potential. Muscle Action Potential Conduction ​ Conducted to the interior of muscle fibre along membrane of t-tubules. ​ Sarcoplasmic reticulum; stores calcium and keeps cytoplasmic calcium conc. low and SR calcium conc. high. ​ Ryanodine receptor; calcium channel is sarcolemma ​ Dihydropyridine receptor; voltage gated channel in t-tubule. It plugs Ryanodine at rest. ​ As action potential is produced, DHPR it changes and unblocks RyR. ​ Causing a diffusion of Ca from reticulum into sarcoplasm along large concentration gradient. Sliding Filament Theory in Action ​ Filaments slide past each other to shorten a sarcomere. ​ Myosin is anchored. It does not change in length. Actin does. Cross Bridge Binding ​ Sliding due to cross bridge binding between filaments. ​ Uses actin and myosin. ​ Actin binding sites are closed by another fiber. ​ When Ca is present, binding sites are open. ​ Head of myosin (fiber head) attaches to actin binding site  ​ Causes a cycle of binding and unbinding = CONTRACTION ATP use: ATP is necessary to attach and detach the actin-myosin bond. UNBIND. It is also needed for the calcium pump on sarcolemma. Crossbridge Cycling: Force and Movement Generation Small molecular movements = muscle shortening. Reflex Arcs ​ Stretch receptors and motor neurons connect in CNS. ​ Operate automatically. ​ Integrated with conscious motor control by CNS. ​ Neural stimulation always shortens skeletal muscles. ​ Muscles = antagonistic pairs (USUALLY) Tetanus ​ Multiple action potentials lead to tetanus. ​ Produces much more force than a twitch. ​ Muscle contracts and stays contracted.