Biology 102 (4-12-07)

Erick Santos Biology 102 April 12, 2007 Biology 102 (4/12/007) Lecture: A week from this Saturday, the Biology Lab will be open. Review of Exam #2

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Filtration of Blood Arterial blood P pushes H2O + Small molecules (filtrate: salts, glucose, etc.) in capillaries out of glomerulus’s  lumen of Bowman’s Capsule  lumen of renal; tubules. Secretion Addition of plasma solutes to the filtrate Primarily takes place in the Proximal and Distal tubules. Very selective Active + passive transport

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Reabsorption Selective transport of substances across from tubule to interstitial fluid

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Proximal + Distal + Loop of Henle Reabsorbed: sugar, vitamins, organic nutrients, water In the Renal Cortex Reabsorption (Taken out of fluid in the Secretion (Out of blood into the urine) kidneys) HCO3- (pH) NH3 Nutrients H+ (pH control) K+ Toxins (liver) H2O NaCl Transport Properties of Descending Limb/ Loop of Henle

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In Medulla Permeable to water, but not salt (Descending loop of Henle) Reabsorption of water by osmosis Increase [NaCl] in filtrate Osmolarity of extracellular fluid increases from outer to inner medulla Transport Properties of Ascending Limb In Medulla

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Permeable to salt but not to water NaCl into extracellular fluid in thin segment (diffusion) and thick segment (active) o Increased osmolarity of extracellular fluid + decreased osmolarity of filtrate in thick segment In Cortex Reabsorption (movement of things from Secretion the filtrate into the body fluid) NaCl K+ HCO3H+ H2O Transport Properties of Collecting Duct

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In Cortex and Medulla Permeable to water Gradient of osmolarity in medulla o Reabsorption of H2O by osmosis Bottom of duct is permeable to urea  some urea diffuses into extracellular fluid (recycled as it enters the ascending limb). Loop of Henle Loop of Henle acts as a counter- current system 2

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o Creates a increasing [NaCl] gradient from outer to inner medulla Vasa Recta carrying blood in opposite direction to descending limb of Henle o Carry reabsorbed water and solutes out of kidneys Figure 51.10 The loops of Henle create a concentration gradient in the tissue fluid of the renal medulla by a countercurrent multiplier mechanism. Urine flowing down the collecting ducts to the ureter is concentrated by the osmotic resorption of water caused by the concentration gradient in the surrounding tissue fluid.

Hormonal Regulation 1. Antidiuretic Hormone 2. Juxtaglomerular Apparatus 3. Atrial Natriuretic Factor

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1) Antidiuretic Hormone (ADH) (=Vasopressin) Produced- Hypothalamus Stored + released- posterior pituitary 3

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Osmolarity > 300 mosm/L  released Target- distal tubules + collecting ducts Effect- increase permeability to water + promote thirst + helps maintain blood volume + constriction of peripheral blood vessels. Decreased osmolarity + increased blood pressure  negative feedback  decrease ADH release Alcohol can inhibit release of ADH Figure 51.14 2) Juxtaglomerular Apparatus (JGA) Near afferent arteriole Decrease blood P or V o Renin secreted by JGA, when the blood volume or pressure goes down below a certain limit. o Conversion of angiotensinogen  angiotensin II 1. Constrict blood vessels + increase reabsorption of H2O and NaCl by proximal tubules 2. Stimulate adrenals- produce aldosterone • Increase Na + + H2O reabsorption at distal tubules + stimulate thirst • Increase blood pressure/ volume 3) Atrial Natriuretic Factor (ANF) Released by walls of atria with increased blood volume and pressure o Inhibits release of rennin o Inhibits NaCl reabsorption in collecting ducts o Reduces aldosterone release o Decrease the blood pressure and volume

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Circulation and gas exchange in mammals Anatomy (Circulatory system of mammals)

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Fully divided ventricle- four chambered heart Double circulation- pulmonary and systemic circuits o Same in birds and crocodiles Advantages

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Gas exchanges in maximized Full separation of O2- rich and O2 poor blood Arterial and venous circuits can work at different pressures Arterial blood receives the highest oxygen content Ability to maintain higher blood pressure to sustain E-expensive tissues Heart

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Four chambers o 2 Atria and 2 Ventricles Right Atrium o Receives deoxygenated blood from the superior and inferior Vena Cavas o Pumps blood to Right Ventricle past the Tricuspid Valve (Prevents backflow) Right Ventricle o Sends blood to Pulmonary Circuit via Pulmonary Artery (carries deoxygenated blood) o Backflow is prevented by the Pulmonary Semilunar Valve Left Atrium o Receives blood from the Pulmonary Veins (carries oxygenated blood) o Sends oxygenated blood to the Left Ventricle past the Bicuspid Valve (prevents backflow). Left Ventricle o Sends oxygenated blood to the Systemic Circuit via Aortic Arch 5

o Aortic Semilunar Valve prevents backflow.

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Figure 49.3 The human heart has four chambers. Valves in the heart prevent the backflow of blood

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Layers of the wall of Heart Endocardium- connective + epithelial (protection) Myocardium- cardiac muscle (contraction) Pericardium and Pericardial Cavity Pericardium (protection + support) o Fibrous (outer) o Serous  Parietal (fused to fibrous)  Visceral (=epicardium; adheres to heart’s surface) Pericardial cavity o Between parietal and visceral o Pericardial fluid (reduces friction)

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Blood Supply to Heart Coronary Arteries- opening below aortic semilunar valve Cardiac Veins  Coronary sinus  right atrium

Cardiac Cycle Systole: contraction of the ventricles Diastole: relaxation of the ventricles Sphygmomanometer and stethoscope are used to measure the systolic and diastolic blood pressures. Read about the cardiac cycle Figure 49.4

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Figure 49.5

Control of Heartbeat

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Intercalated disks join cardiac muscle fibers. o Gap junction- spread of action potentials o Desmosomes- reinforce the connections between fibers Sinoatrial (SA) node o Acts as a pacemaker- maintains self rhythm o Near where superior vena cava enters the right atrium Artioventricular (AV) node o Wall between RA and RV o Transmits the action potential from atria to ventricles via: Bundle of His  Bundle Branches (left and right)  Purkinje fibers. o Impulses are delayed  atria contact first; empty before ventricles contact The sinoatrial node controls the cardiac cycle by initiating a wave of depolarization in the atria, which is conducted to the ventricles through a system consisting of the atrioventricular node, the bundle of His, and the Purkinje fibers

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Nervous system controls the rate: o Acetylcholine: slows heart rate o Norepinephrine: speeds heart rate Arteries (caries blood away from the heart) Collagen- provides support for high blood pressure Elastic fibers store energy from blood pressure  recoil during diastole  smoother blood flow Smooth muscle – vasodilatation and vasoconstriction control direction and pressure of blood

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Veins How does blood travel against gravity? 1. Veins in between muscles- squeezing 2. One- way valves- prevent back flow 3. Inhalation (increased volume in thoracic cavity) 4. Leg muscles act as pumps  greater blood volume to heat  as cardiac cells stretch they contact more forcefully (Frank- Starling Law) 5. Smooth muscle in major veins Figure 49.13

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Capillaries (exchange of materials between muscles and blood) Connect arterioles to venules Small diameter (erythrocytes pass in single line) Walls (single layer of endothelial cells) are permeable to water, and lipid-soluble + small molecules (O2, CO2, glucose, Na+, etc.) Some with intercellular clefts (spaces between endothelial cells) Some with fenestrated (pores in plasma membrane) endothelial cells Materials may also move by pinocytosis Some are very selective o E.g., blood-brain barrier (tight junctions between endothelial cells and continuous basal membrane). Others are much less selective o E.g., digestive tract and kidneys As blood moves from arterial side to venous side: o Blood pressure + velocity decreases  Total crossectional area of capillary bed is greater than that of arterioles. o Osmotic potential increases  As blood pressure becomes lower than osmotic pressure (osmotic pressure remains constant throughout the capillary) o Arteriole side of capillary:  Blood pressure > osmotic pressure  Fluids exits o Venule side of capillary:  Blood pressure < osmotic pressure  Fluids enters Read? What is the role of bicarbonate in the capillaries? Figure 49.10 Arteries and arterioles have many elastic fibers that enable them to withstand high pressures. Abundant smooth muscle cells allow these vessels to change their diameter, altering their resistance and thus blood flow.

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Figure 49.12 The Starling hypothesis offers an explanation for the exchange of fluids between blood and tissues that is based on the balance between blood pressure and osmotic pressure in the capillaries.

Lymphatic Tissues/ system (filters toxins and pathogens out of your body) Loss of fluid at capillaries returned to blood by lymphatic system o Diffusion of fluid into lymph capillaries o Formation of lymph o Drainage of lymph into circulation from thoracic duct Regulation of blood flow Precapillary sphincters (smooth muscle) control flow from arterioles to capillary beds o Low [O2], high [CO2] or [Metabolic products]  smooth muscles relax

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Figure 49.17 Local autoregulatory mechanisms, hormones, and the autonomic nervous system control Blood flow through capillary beds.

Chemosensors in medulla oblongata (big front part of the brain with chemosensors) Chemosensors + stretch sensors in aorta and carotid arches Nervous/ endocrine systems o Norepinephrine, epinephrine, angiotensin, and vasopressin –> contraction of smooth muscles in arteries and arterioles. o Acetylcholine  relaxation of smooth muscles Figure 49.19

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Connective tissue o Plasma o Cellular elements (Hematocirt: packed cell volume) Figure 49.15 Blood can be divided into a plasma portion (water, salts, and proteins) and a cellular portion (red blood cells, white blood cells, and platelets). All of the cellular components are produced from stem cells in the bone marrow. Erythrocytes (red blood cells)

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Made in bone marrow Transport respiratory gases- hemoglobin A nucleated (not in birds), biconcave- increase area Flexible Stored and recycled in spleen Leukocytes Immune response Can move out of the capillaries into extra cellular fluid Nucleated Platelets Cell fragments and enzymes enclosed in plasma membrane Blood clotting o Formation of a platelet plug o Promote blood clotting Blood clotting 16

a) Injury to lining of blood vessel exposure of connective tissue platelets adhere to connective tissue b) Platelets secrete chemicals that make other platelets adhere – platelet plug forms c) Clotting factors (proteins) released form liver+ platelets + damaged cells  Trothrombin activated to Thrombin d) Thrombin  Fibrinogen polymerized to Fibrin • Fibrin clot with trapped platelets forms

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Lungs in Mammals Restricted in one location  Circulatory system needs to carry gases Inside Thoracic Cavity Inside double – walled sac- Pleural membranes Parietal (adheres to wall of thoracic cavity) Visceral (adheres to lungs) Fluid filled left and right pleural cavities Nasal Cavity

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Filtered Humidified Warmed Sampled

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Pharynx Intersection of esophagus and trachea Glottis – closed when eating

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Larynx (vibrate to produce sound) Reinforced cartilage Voice box – vocal cords

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Trachea (round rings on it), Bronchi, and Bronchioles “C” shaped cartilaginous rings 17

• Branch to and within lungs • Internal pseudo stratified epithelium is ciliated and produced mucus (goblet cells) – tapping and discarding particles including pathogens Fig. 48.10 •

Lungs are invagination of tissue

Alveoli (invaginations) • Air sacs w/ very thin cells – reduce distance for diffusion • Large numbers of terminal bronchioles each w/ many alveoli- increase A • Heavily vascularized w/ capillaries • Production of surfactants – reduce surface tension of water layer inside alveoli  ability to inflate during inhalation Fig. 48. 10 •

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Lung Ventilation Negative pressure breathing (sucking air, not pushing) 1. Contraction of external intercostals and diaphragm  expansion of thoracic cavity 2. Subatmospheric P and surface tension between parietan and visceral pleura  Expansion of lungs  decrease in alveolar P  inhalation Exhalation is mostly passive – relaxation of external intercostals and diaphragm  elastic recoil of lungs and thoracic cavity (alveolar surface tension + elastic fibers) Forcefully exhalation utilizes the internal intercostals + abdominal muscles At rest lungs retain some negative pressure – prevent collapsing Fig. 48.11 Respiratory Pigments / Hemoglobin

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2 alpha and 2 beta Plasma carries a small percentage of O2 Erythrocytes carry most O2 and Hb (hemoglobin) o 4 subunits each with a co-factor (heme group) with an Fe atom o Each Hb carries of O2 molecules Positive cooperativity o Binding of O2 to one subunit changes the conformation of others so they increase affinity for O2. (Reverse if one molecule is unloaded) o Result in sigmoidal curve for Hb saturation graph Fig. 48. 12 (higher slope more hemoglobin) Normal Partial Pressure of (O2) of alveoli is 100 mm Hg  Hb is full saturated PO2 in mixed venous blood is about 40 mm Hg Hb is about 75% saturated (O2 reserve). Tissue I n need of O2 (PO2 < 40 mm Hg)  Hb unloads O2 (large slope of curve indicates ability to provide O2 to tissues). 18

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Hemoglobin/ Bohr • Release of metabolic acids (ex. Lactic acid) in tissues  decrease in pH  O2 unloaded form Hb • Fig. 48.13: fetal hemoglobin is to the right to maternal hemoglobin; b/c fetal hemoglobin has greater affinity towards O2. Myoglobin (in muscles) has the greatest affinity from all. Hemoglobin and Diphosphoglyceric Acid Shifts Hb saturation cure to the right Concentration in erythrocytes increases during exercise or at high altitudes Combines with Hb and decreases its affinity for O2  O2 unloaded from Hb at most Po2S (Partial pressures of oxygen) Respiratory Pigments/ Myoglobin In muscle cells- specially in red fibers One polypeptide chain with Fe Higher affinity for O2 than Hb  downloads and retains O2 Reserve of O2 for muscles when little O2 is available from blood o E.g., deep diving animals

Figure 48.13 There is more than one type of hemoglobin. Fetal hemoglobin has a higher affinity for O2 than does maternal hemoglobin, allowing fetal blood to pick up O2 from the maternal blood in the placenta.

CO2 transport •

In tissues with high [CO2]: 19

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o CO2 + H2O  H2CO3  H+ + HCO3o Reaction is catalyzed in erythrocytes by Carbonic Anhydrase  o Facilitates diffusion of CO2 from tissues to plasma membrane Most CO2 transported as HCO3- in plasma membrane Some CO2 transported as carboxyhemoglobin Loss of CO2 from erythrocytes to alveoli in the lungs shifts the equilibrium so: o CO2 + H2O  H2CO3  H+ +HCO3o HCO3- from erythrocytes is converted to CO2 o HCO3- from plasma enters the erythrocytes

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Control Centers o Medulla oblongata (sets rhythm) o Pons (control centers) Control centers are more sensitive to changes in Pco2 than Po2 CO2 + H2O  H2CO3  H+ + HCO3- leads to lowering of pH. Medulla registers a lower pH in blood or cerebrospinal fluid o Higher depth/ rate breathing Figure 48.15 The breathing rhythm is an autonomic function generated by neurons in the medulla and modulated by higher brain centers.

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Figure 48.16

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O2 severely depleted o O2 sensors in aorta and carotid arteries send stimuli to control centers  raise rate trick- Hyperventilation (breath quickly, so the brain doesn’t respond to the fact that oxygen level is too low) o Trick- Hyperventilation

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Adaptations of Diving Mammals High storage of O2 in blood + muscles Increased blood volume Large spleen- contracts during diving Increased [Myoglobin] Bradycardia- abnormally slow heart action. Vasoconstriction (redirect blood flow) Collapsible lungs Fat droplets on respiratory surfaces

Nervous Systems 1) CNS- Central Nervous Systems Integration- association of stimuli with output Brain: integration of Homeostasis + perception + movement + intellect + emotions Spinal cord: reflexes + transmits information from skin & muscles to brain

2) PNS- Peripheral Nervous System Sensory (afferent: going in): sensory receptors  CNS Motor (efferent: going out): CNS  effector cells o Connects to CNS via cranial and spinal nerves 22

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Motor PNS Voluntary (somatic): signals to skeletal muscles in response to stimuli o Reflexes + voluntary Autonomic: Involuntary (e.g., gastrointestinal + cardiovascular + endocrine) o Parasympathetic- activities that gain + conserve energy (e.g., slow heart beat, stimulate digestion) o Sympathetic- activities that increases expenditure of energy (e.g., accelerate heart beat, glucose production in liver, etc.) Voluntary (Somatic) Signals to skeletal muscles in response to stimuli Autonomic Involuntary (e.g., gastrointestinal + cardiovascular + endocrine) o Parasympthathetic- activities that gain + conserve energy (e.g., slow heart beat, stimulate digestion) o Sympathetic- activities that increase expenditure of energy (e.g., accelerate heart beat, glucose production in liver, etc.) Neurons (individual cells of nervous system)

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Sensory o Stimulated by receptors triggered by environmental stimuli Interneuron’s o Receive and transmit stimuli from and to other neurons Motor o Transmit impulses from CNS to effector cells

Supporting Cells (Neuroglial Cells) Do not conduct impulses 23

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Support and orient Protection Insulation Maintain ionic environment Supply nutrients o Schwann cells and oligodendrocytes  Myelin sheath: electrical insulation  Increase speed of impulse propagation o Astrocytes  Blood- Brain barrier at brain capillaries (very selective capillaries, less permeable) Figure 44.3

Neurons are excitable cells Na+/ K+ pump maintains a membrane potential Neurons can change their membrane potential in response to stimuli o Selective opening of gated channels (voltage gated or chemically gated) Figure 44.5

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The resting potential is perturbed when ion channels open or close, changing the permeability of the plasma membrane to charged ions. Through this mechanism, the plasma membrane can become depolarized or hyperpolarized.

Action Potential (AP) Rapid reversal in membrane potential Each cell has a threshold  AP triggered AP’s are only produced by depolarizing stimuli 6 phases (a bunch of steps that lead to an action potential) Resting phase

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Na / K o Expels 3 Na+ for every 2 K+ o Keeps the internal [Na+] lower than outside o Keeps the internal [K+] higher than the outside o Open K+ channels (can only be open) o Gated K+ channels are closed (can be closed or open) K+ moves out, while large negatively charged molecules remain inside Membrane potential in resting neuron: -60 mV

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Figure 44.6

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Depolarization Going to decrease the difference of charge from the inside to the outside o K+ channels remain open o Gated K+ channels are closed o Gated Na+ channels are opened Influx of Na+ Membrane potential is decreased

Biology 102 5-3-07 Action Potential (action potential) = temporary depolarization in the membrane of the cell • Same as in depolarization but more gated Na+ channels are opened o More influx of Na+ o Rapid reversal in membrane potential o Once you hit the threshold you’ll get action potential Repolarization + • K channels remain open • Gated K+ channels are opened 26

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Gated Na+ channels are closed o Efflux of K+ o Returns membrane potential to resting level Undershoot (hyperpolarization) Gated K channels are slower and remain open longer than gated Na+ channels o More efflux of K+ o Hyperpolarization (temporarily more negative than resting) o Refractory period- neuron is insensitive to depolarization +

Refractory period Gated Na+ channels remain closed for 1-2 milliseconds before they can open again. o Neuron is insensitive to depolarization Figure 44.9 An action potential is a rapid reversal in charge across a portion of the plasma membrane resulting from the sequential opening and closing of voltage-gated sodium and potassium channels. These changes in voltage-gated channels occur when the plasma membrane depolarizes to a threshold level.

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Action potential is all or none Amplitude not affected by intensity of stimulus System distinguishes between weak/ strong stimuli based on frequency of stimuli Propagation of Action Potential Strong depolarization in one area  Depolarization above threshold in neighboring areas because Na+ moves through inside the axon AP is regenerated at each new position along the membrane AP moves in only one direction because of refractory period Figure 44.10

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Speed Increase diameter of axon  increase speed Saltatory (jumping) conduction Ions cannot cross the myelinated regions of axon but only at nodes of Ranvier where they induce an AP (Action Potential) Ion channels are concentrate at node of Ranvier AP “jumps” between myelinated regions from one node of Ranvier to next Figure 44.12 In myelinated axons, action potentials appear to jump between nodes of Ranvier, patches of axonal plasma membrane that are not covered by myelin.

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Communication at synapses Synapse: Junction between Pre- synaptic (transmitting) cells and a Post- synaptic (receiving) cell Synaptic cleft: space between pre-synaptic membrane and post synaptic membrane

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Electrical synapses Direct transmission via gap junction with connexons (protein tunnels) Fast Action potential (AP) can travel in both directions No summation of inputs Does not allow for large number of synaptic inputs Cannot be inhibitory Little plasticity

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Chemical synapses Better at integration of information

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Transmission at Chemical Synapses AP arrives at presynaptic terminal  o Depolarization  gated Ca2+ channels open  influx of Ca2+ Neurotransmitter is synthesized and packaged into vesicles at axon terminals Presynaptic vesicles fuse to membrane and neurotransmitters are released into synaptic cleft Neurotransmitter binds to receptor in postsynaptic membrane  o Depending on neurotransmitter: depolarization (excitatory: open Na+ channels) or hyperpolarization (inhibitory: open gated K+ or Cl- channels) Neurotransmitters are degraded and recycled Figure 44.13 When a nerve impulse reaches an axon terminal, it causes the release of neurotransmitters, which diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.

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Summation of post- synaptic inputs Happens at Axon hillock o Non insulated and with many ion channels Input excitatory and inhibitory postsynaptic potential spread to Axon Hillock Combination of input postsynaptic potentials may or may not result in AP at Axon Hillock Can occur spatially (simultaneous inputs) or temporally (sequential inputs) Mechanism for integration of information Figure 44.15 Synapses between neurons can be either excitatory or inhibitory. A postsynaptic neuron integrates information by summing excitatory and inhibitory postsynaptic potentials in both space and time.

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Skeletal muscle structure Muscle fibers  myofibrils  myofilaments: o Thin  Action + regulatory proteins o Thick  Myosin Sacromere- organizational units Sarcomere Divided into (based on microscopy): o Z lines- borders o I bands- only thin o A bands- thin + thick (complete myosin) o H zones (center of A)- only thick o M band (center of A and H)- proteins to hold myosin Titin proteins hold myosin in center between Z lines and are elastic Figure 47.3 Skeletal muscles contain numerous myofibrils, which are bundles of actin and myosin filaments. The regular, overlapping arrangement of the actin and myosin filaments into sarcomeres gives skeletal muscle its striated appearance. During contraction, the actin and myosin filaments slide past each other in a telescoping fashion

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Sliding Filament Model Thin filaments ratchet across thick o Z lines pulled together o Sarcomere shortens Myosin cross bridges with actin o Crossbridges form, bend, break o Forming further down Cross bridging requires ATP hydrolysis Block myosin o Tropomyosin: regulatory protein blocking myosin-binding sites on actin at rest o Troponin complex: that accepts Ca2+ and can open myosin binding sites

Sliding Filament Model (continued) 1. Action potential in motor neuron  release acetylchloline a. Release acetylcholine 2. Transverse bundles (deep infolds of plasma membrane) carry depolarization into muscle 3. Sarcoplasmic Reticulum releases Ca2+ 4. Ca2+ binds to troponin a. Thin filament changes shape and exposes myosin binding site 34

b. Muscle contacts 5. Ca out of cytoplasm  for the muscles to relax a. Tropomyosin- troponin blocks myosin 2+

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Duration of muscle contraction is controlled by how long Ca2+ is maintained in cytoplasm Figure 47.4 The molecular mechanism of muscle contraction involves the binding of the globular heads of myosin molecules to actin. Upon binding, the myosin head changes its conformation, causing the two filaments to slide past each other. Release of the myosin heads from actin and their return to their original conformation requires ATP.

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Figure 47.5 The plasma membrane of the muscle fiber is continuous with a system of T tubules that extends deep into the sarcoplasm.

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Figure 47.6 When an action potential spreads across the plasma membrane and through the T tubules, it causes Ca2+ ions to be released from the sarcoplasmic reticulum. The Ca2+ ions bind to troponin and change its conformation, pulling the tropomyosin strands away from the myosin binding sites on the actin filament. Cycles of actinmyosin binding and release occur, and the muscle fiber contracts until the Ca2+ is returned to the sarcoplasmic reticulum

Vertebrate Eye 36

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Structure o Sclera- outer- connective tissue  Cornea- transparent- fixed lens o Choroid- middle layer  Pigmented  Iris- Pupil  amount of light o Retina- inner- photoreceptors Ciliary Body o Produces aqueous humor  helps focus o Vitreous Humor  helps focus Lens  focus o Protein Ciliary muscle  accommodation Figure 45.16 Visual systems vary from the simple eye cups of flatworms, which enable the animal to sense the direction of a light source, to the compound eyes of arthropods, which enable the animal to detect shapes and patterns, to the image-forming eyes of cephalopods and vertebrates.

Vertebrate Eye/ Photoreceptors Rods  light Cones  color a. Most dense at fovea Vitamin A  Retinal Retinal + Opsin (Protein)  1. Rhodopsin- rods 2. Photopsins- cones Respond to light by changing molecular shape 11-cis retinal changes to all trans retinal. 37

Figure 45.12

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Vertebrate Eye/ Photoreceptors At least 3 kinds of cones: blue, green and red (genes coding for different opsins). Light must travel through several; layers of transparent neurons before reaching the photosensors Figure 45.19 Color vision is based on the fact that different cone cells contain different isomers of opsin, which give them different spectral absorption properties.

Vertebrate Eye/ Photoreceptors 1. Outer segments of rods with invaginations of plasma membrane containing rhodopsin- capture photons 2. When exposed to photons a cascade of reactions initiated by G protein signal transduction closes Na+ gates a. Membrane becomes hyperpolarized 3. Photosensory cells release neurotransmitter  alters membrane potential of bipolar 38

cells 4. Bipolar cells release neurotransmitter a. Ganglion cells generated AP 5. Two other layers, horizontal and amacrine, control lateral transmission of signals and adjust sensitivity to light level changes Figure 45.13

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Figure 45.20 The vertebrate retina consists of five layers of neurons lining the back of the eye. The light-absorbing photoreceptor cells are at the back of the retina

Vertebrate Ear •

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o Pinna- receive o Auditory Canal- transmit Middle o Tympanic Membrane- vibrate o Ear bones: Malleus (attached to Tympanic Membrane), Incus, Stapes (attached to Oval Window)- amplify/ transmit o Eustachian tube- connects middle ear to throat- P equilibration Human Ear (continued)

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Inner o Oval Window- vibrations o Cochlea  Divided into three canals by: Reissner’s and basilar membranes o Organ of Corti with hair cells (stereocilia in contact with Tectorial Membrane) o Round Window- absorbs displacement of fluid inside cochlea o Utricle + Saccule + Semicircular canals- Balance Figure 45.10 In mammalian auditory systems, ear pinnae collect and direct sound waves to the tympanic membrane, which vibrates in response to sound waves. The movements of the tympanic membrane are amplified through a chain of ossicles that conduct the vibrations to the oval window. Movements of the oval window create pressure waves in the fluid-filled cochlea.

Human Ear (continued) 40

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1. Basilar membrane bends according to vibrations of oval window transmitted through cochlear fluid 2. Bending of sterocilia of hair cells against Tectorial Membrane causes depolarization or hyperpolarization a. Transmission on AP to Cochlear nerve Proximal end of Basilar membrane (near Oval and Round Windows) is thin an d stiffresponds to high frequency Basilar membrane becomes thicker and more flexible distally- responds to low frequency Different sets of hair cells are activated at different regions of membrane Figure 45.11 The basilar membrane running down the center of the cochlea is distorted by sound waves at specific locations that depend on their frequency. These distortions cause the bending of hair cells in the organ of Corti, which rests on the basilar membrane. Receptor potentials in hair cells cause them to release neurotransmitter, which creates action potentials in the auditory nerve, which conducts the information to the CNS.

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Balance and Equilibrium Semicircular Canals (at right angles to each other) are filled with endolymph. o As endolymph moves it displaces a cupula sitting on top of sterocilia of hair cells of ampullae. Vestibule with 2 chambers: utricle and saccule o Sterocilia of hair cell covered by a layer of gelatin with otoliths of CaCO3 o As head moves, the otoliths move and bend the sterocilia Figure 45.9 Hair cells are also mechanoreceptors. The bending of their stereocilia alters receptor proteins and therefore their membrane potentials. Hair cells are found in the auditory organs and organs of equilibrium such as the lateral line system of fishes and the semicircular canals and vestibular apparatus of mammals.

Gustation Taste buds (some on papillae) contain many taste sensors Pore on taste buds allows molecules to reach microvilli (increased A) on taste sensors Taste buds are replaced every few days Molecular shape+ charge + binding to receptors causes the release of signal molecules that trigger an AP in joining sensory neuron. Detection of sweet, sour, salty, and bitter tastes depends on the combined effect of olfaction and gustation

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