Body Systems – Part II Chemical Signals – CH 45 Nervous Signals– CH 48 Nervous System – CH 49

1. Body Systems – Part II Chemical Signals – CH 45 Nervous Signals– CH 48 Nervous System – CH 49

2. Chapter 45 Hormones and the Endocrine System

3. Hormone chemical excreted into body fluids - used for communication within an organism - helps maintain homeostasis - modified amino acids and steroids - carried by the circulatory system to target cells Target Cells  equipped to respond to particular hormone; typically have membrane proteins that allow SPECIFIC hormones to bind **So this means that hormones in the blood can cause changes in SOME cells, and other cells will ignore them**

4. Nervous vs. Endocrine System Nervous System  high speed signals; Ex. Jerking your hand away from a flame Endocrine System  slower communication; Ex. Maturation of a butterfly; two parts:

5. Local Regulators Affects activity between neighbor cells; only uses LOCAL targets; there are 3 types: Growth Factors  peptides/proteins stimulate cell growth and development in target cells; includes nerve growth factors Nitric Oxide (NO)  a gas that has multiple functions including acting as a neurotransmitter (when secreted by neurons) and relaxing smooth muscle (when secreted by endothelial cells); it triggers a change in a target cell then breaks down quickly; it is also highly reactive and can be toxic Prostaglandins  modified fatty acids first isolated in semen produced by prostrate; effect the female reproductive system (can cause smooth muscle contractions to help sperm reach egg; also induces uterine contraction in childbirth); aspirin and ibuprofen can inhibit the effects of PGs

6. Local Regulators  divided into 2 groups: • Paracrine act on cells NEAR the secreting cell • Autocrine secreted regulators that act on the secreting cell itself!

7. Synaptic Signaling vs. Neuroendocrine Signaling • Neuroendocrine Signaling specialized neurons called neurosecretory cells secrete chemical signals that diffuse from nerve cell endings into the bloodstream; • these signals are a class of hormones called neurohormones(ex. ADH) • Synaptic Signaling  neurons form specialized junctions called synapses with target cells, such as other neurons and muscle cells; at synapses, neurons secrete molecules called neurotransmitters,which diffuse a very short distance to bind to receptors on the target cell - Endocrine– Ductless(secretes hormones into body fluids) - Exocrine– Uses ducts to send to specific locations (ex. sweat glands)

8. Different types of cells respond differently, so the SAME SIGNAL can bring about a DIFFERENT RESPONSE in various target cells. • Only small amounts of regulators (ex. Hormones) are necessary because the pathway triggers enzyme cascades that can greatly amplify the signal. Signal Transduction Pathway 3 main Processes: - Reception signal binds to a receptor protein - Signal Transduction  causes a change in the target cell -Response causes a change in the receptor cell’s behavior

9. The endocrine system and the nervous system are very closely related • Several chemicals serve as both hormones of the endocrine system and signals in the nervous systems • Ex. Epinephrine (This shows how the two systems are CHEMICALLY related) • Nervous system = neurotransmitter • Endocrine system = “fight or flight” hormone • Each system affects the outputof the other • Ex. Breast feeding – uses interdependent nervous and hormonal signals: • Suckling = simulates sensory cells and nervous signals in the hypothalamus then trigger the release of oxytocin from the pituitary gland; this oxytocin cause the mammary cells to secrete milk

10. Tropic Hormones • Tropic Hormone: have other endocrine glands as their targets

11. Feedback Feedback is COMMON TO BOTH THE ENDOCRINE AND THE NERVOUS SYSTEM!! Positive Feedback: causes a change in the same direction; ex. increasing milk release, labor during childbirth (oxytocin!) Negative Feedback: causes a change in the opposite direction; is responsible for the endocrine system’s ability to regulate homeostasis mechanisms; ex. sweating = cools the body

12. Pancreas • Secretes bicarbonate ions to balance the pH from the acid chyme in the stomach • Alpha cellssecrete glucagon signals the liver to release glucose back into blood stream (increases blood sugar levels); used when someone has not eaten in a while and blood sugar levels are low • Beta cellssecrete insulin signals body cells to take up glucose from the blood (decreases blood sugar levels); used when someone just ate and blood sugar levels are high Exocrine (secrete into ducts) bicarbonate ions and digestive enzymes Endocrine  (ductless) insulin/glucagon antagonists

13. **Insulin and Glucagon are not steroids…they are PROTEIN hormonesmade of AA’s** • Glucagon and Insulin are antagonistic hormonesand work together to regulate the blood sugar levels in the body (recall our other antagonistic hormones are calcitonin and PTH for calcium)

14. Diabetes • Most common endocrine disorder = Diabetes caused by a deficiency in insulin or loss of response to insulin in target cells • Type I diabetes autoimmune disorder; immune system attacks pancreas; occurs in childhood and causes kid to not be able to make insulin; treated with insulin injections or a pump Type II diabetes characterized by deficiency of insulin or reduced responsiveness in target cells; 90% of diabetics are type II; can usually be managed by diet and exercise; caused by genetics and obesity

15. Hypothalamus • Integrates the endocrine and nervous systems • A good example of how they are structurally related is the NEUROSECRETORY CELLS located in the hypothalamus • It is part of the lower brain ** It is important in homeostatic regulation (ex. body’s thermostat, regulates hunger/thirst, role in sexual/mating behaviors) ** It regulates the Pituitary Gland ** The neurosecretory cells of the hypothalamus secrete two hormones: oxytocin and ADH

16. Pituitary • Located at base of the brain • Referred to as “Master Gland” because it regulates so many other endocrine functions • It obeys orders from the hypothalamus • Has 2 discrete parts: • Anterior Pituitary (front) • Posterior Pituitary (back)

17. Posterior Pituitary • Posterior Pituitary Hormonesmade by hypothalamus but secreted by posterior pituitary; these hormones act on specific structures rather than affecting other endocrine glands • Stores and secretes two hormones: • 1. Oxytocin acts on muscles of uterus; induces contractions during childbirth and controls milk secretion during nursing • 2. Antidiuretic Hormone (ADH) acts on the kidneys; causes kidneys to increase water retention thus decreasing urine volume; helps regulate the osmolarity of the blood

18. Anterior Pituitary • Secretes hormones directly into blood • Hypothalamussecretes two kinds of hormones: • Releasing hormones makes anterior pituitary secrete its hormones • Inhibiting hormones makes anterior pituitary STOP secreting hormones • The anterior pituitary secretes many hormones…

19. Anterior Pituitary Hormones • Growth Hormone (GH) promotes growth directly and also stimulates growth factors • Human Growth disorders are related to GH production: • Too much GH (hypersecretion) = gigantism • Too little GH (hyposecretion) = pituitary dwarfism; this can be treated using growth hormones from cadavers • Insulinlike Growth Factors (IGF) stimulate bone and cartilage growth • Prolactin (PRL) similar to GH; produces a variety of effects in different vertebrates (so scientists think this is an ANCIENT HORMONE); mammals = stimulates mammary gland growth and milk synthesis; freshwater fish = salt and water balance

20. Anterior Pituitary Hormones • Follicle-stimulating Hormone (FSH) stimulates production of ova and sperm • Luteinizing Hormone (LH) stimulates ovaries and testes ** Gonadotropins = stimulate the activity of male and female gonads; FSH and LH are examples

21. Anterior Pituitary Hormones • Thyroid Stimulating Hormone (TSH) stimulates the thyroid gland (releases thyroid hormone which increases metabolic rate, raising body temp) • Adrenocorticotropic Hormone (ACTH)  stimulates the production and secretion of steroid hormones by the adrenal cortex (part of the adrenal gland) • Melanocyte-stimulating Hormone (MSH) regulates the activity of pigment-containing cells in the skin; has a role in fat metabolism • Endorphins body’s natural opiates; inhibit the perception of pain

22. Thyroid Gland • Consists of 2 lobes on the trachea • Thyroid hormone increases the metabolic rate, increasing the body temperature • Thyroid has a critical role in vertebrate development & maturation (ex. Human development), homeostasis (blood pressure, heart rate, muscle tone, digestion) • The term “thyroid hormone” refers to two closely related hormones: • Triiodothyronine (T3) causes changes to target cells • Thyroxine (T4)  thyroid secretes mainly T4, but the target cells convert it to T3; this hormone stimulates and maintains metabolic processes • BOTH T3 and T4 affect metabolic processes; important in bioenergetics • CalcitoninLOWERS calcium levels in blood (works antagonistically with PTH)

24. Thyroid Imbalances Include… Cretinism deficiency in development, retarded skeletal/mental growth, develops in infants from hypothyroidism Goiter deficiency of iodine in diet Hyperthyroidism Too much thyroid hormones; symptoms = weight loss, profuse sweating, high blood pressure Hypothyroidism Too little thyroid hormones; symptoms = weight gain, lethargy Cretinism Goiter

25. Parathyroid • Found on the surface of the thyroid; function in homeostasis of calcium ions (very important to the normal functioning of all cells) • Parathyroid Hormone (PTH)raises calcium levels in blood; VERY important! • Calcitonin decreases calcium levels in the blood • PTH and Calcitonin are antagonistic hormonesand work together to regulate the calcium levels in the blood (example of homeostasis)

26. Adrenal Gland • Adjacent to kidneys • Two parts: • Adrenal cortex (outside) • Adrenal medulla (inside)

27. Adrenal Medulla(inside) • Close ties to the nervous system – FIGHT OR FLIGHT • Catecholamines – secreted in response to positive or negative stress Norepinephrine sustaining blood pressure Epinephrine heart and metabolic rates (Epi pen for anaphylactic shock); also acts as a neurotransmitter; GOOD EXAMPLE of how the endocrine and nervous systems are chemically related • Mechanism: *Adrenal medulla under control of nerve cells from sympathetic division *Nerve cells excited by stressful stimulus *Acetylcholine released in adrenal medulla, and combines with receptors to release epinephrine

28. Adrenal Cortex (outside) • In contrast to the adrenal medulla, which reacts to nervous input, the adrenal cortex responds to endocrine signals. • Corticosteroids include: • Glucocorticoids glucose metabolism; increases glucose in blood; secreted in response to stress and promotes the synthesis of glucose from non-carbohydrate substrates (ex. fats and/or proteins)  helps with long-term environmental issues • Mineralocorticoids helps inflammatory conditions; effects salt and water balance in kidneys • BOTH help the body deal with LONG TERM stress (whereas epinephrine and norepinephrine deal with SHORT TERM stress)

29. Adrenal Medulla vs. Adrenal Cortex

30. Gonadal Steroids • Controlled by gonadotropins from the anterior pituitary gland • Produced in both males and females (in different proportions); produced in testes in males and ovaries in females; general function = affect growth and development and also regulate reproductive cycles and sexual behavior • 3 major types

31. Types of Gonadal Steroids • Androgens ex. testosterone; development and maintenance of male reproductive system; produced in an embryo to turn the fetus into a male instead of a female; produced during puberty to stimulate secondary sex characteristics (hair growth, low voice) • Estrogens ex. estradiol; effects the female reproductive system and secondary sex characteristics in females • Progestins ex. progesterone; prepares and maintains the uterus which supports the growth and development of an embryo

32. Pineal Gland • Small mass of tissue near the center of the brain • Secretes the hormone melatonin, which regulates functions related to light/dark and seasons marked by changes in day length; related to biological clock rhythms

33. Vertebrate Endocrine System

35. Chapter 48 Neurons, Synapses, and Signaling

36. Nervous System • Neurons (functional unit of the nervous system) arenerve cells that transfer information within the body. • Communication by neurons is based on two distinct types of signals: • long-distance electricalsignals • short-distance chemicalsignals • If an organism does NOT have an integration center, it would not be able to interpret stimuli.

37. -Axons -Long; one per cell body; convey OUTGOINGmessages from the neuron to other cells -Axon hillock– part where the axon joins the cell body -Covered by myelin sheaths(insulated layer) -Synaptic terminals– specialized endings; relay signals from neuron to other cells by releasing chemical messengers called neurotransmitters -Site of contact between a synaptic terminal and a target cell is called a synapse -Presynaptic cell = transmitting cell -Postsynaptic cell = target cell Neurons (nerve cells) -Structural and functional unit of the nervous system -Has a cell body(contains the nucleus) and fiber-like extensions (dendrites and axons) -Dendrites -Short branched; many per cell body; receive INCOMINGinformation and pass it to the cell body

39. -Supporting Cells (called Glia) • -Help support the nervous system and help it function properly • -Originally thought to only have a structural role, but some synaptic interactions do occur between glia and neurons • -In mature CNS, the glia are called astrocytes – they provide metabolic and structural support for neurons • -Help form the blood-brain barrier restricts passage of most substances into the brain which controls the extracellular chemical environment of the CNS (FORMED BY TIGHT JUNCTIONS) • -Oligodendrocytes(in CNS) and Schwann cells(in PNS) are glia that form myelin sheaths around the axons of neurons • -Necessary b/c can’t use regular cell membranes b/c they are made of lipids which are poor conductors of electrical currents; the myelin works better

40. Overview • -Nervous system is made up of living neurons • -Neurons are specialized for the fast transmission of impulses • -Three major overlapping functions: • -Sensory Input  sensory receptors take info from inside body and outside world and convey it to integrations centers • -Integration carried out in the CNS (central nervous system; brain and spinal cord); input is interpreted and body responds appropriately; if there was no integration center, organisms wouldn’t be able to interpret stimuli • -Motor Output conduction of signal from integration center to the effector cells (muscles or glands that carry out the signal) • -Signals are conducted by nerves • -PNS (peripheral nervous system) = nerves that communicate motor and sensory signals between the CNS and the rest of the body • -Information is communicated by both electrical and chemical signals

41. Cerebrospinal Fluid • Made in the brain by filtering the blood; fills the space in the brain and spinal cord

42. The Nature of Nerve Signals • -Nerve signals are changes in voltageacross the membrane due to movement of ions • -Membrane Potential the potential charge difference between the cytoplasm and the extracellular fluid of a cell • -Resting Potential membrane potential of an unstimulated neuron • -Can measure membrane potential as a voltage; typical animal cell is –50 to –100 mV (the negative means the inside of the cell is negative in charge w.r.t the outside)…in resting neurons, the membrane potential is more negative than the threshold potential The inside of the cell is NEGATIVELY charged in comparison to the outside of the cell

43. -Differences in membrane potential are sustained by the actions of the sodium-potassium pump • -Na+ pumped OUT (3 at a time) • -K+ pumped IN (2 at a time) • -THEREFORE…outside = positive; inside = negative • -Goes against the gradient, so needs to use energy (ATP)  active transport • -Ion channels are selective for specific ions; so a membrane can have different permeability's to different ions • -They determine WHAT can pass through, but not the RATE Sodium Potassium Pump

44. Gated Ion Channels • Gated ion channelsare specialized proteins that span the membrane, and allow ions to diffuse back and forth across the membrane according to their respective gradients. • Chemically-gated ion channels respond to a chemical stimulus (ex. neurotransmitter) • Voltage-gated ion channels respond to a change in membrane potential • Allows only ONE kind of ion to pass through

45. -Graded Potentials magnitude of change depends on the strength of the stimulus (larger stimulus will open more channels) -Hyperpolarization– increase in voltage across the membrane -Open K+ channel; K+ flows out and causes the inside of the cell to become more negative -Depolarization– reduction in the voltage across the membrane -Open a Na+ channel; Na+ flows in and causes the inside of the cell to become more positive

46. -Action Potentials ALL OR NOTHING depolarization -DEPOLARIZATION causes an action potential -Triggered by graded potentials -When it reaches a certain point, the threshold potential(usually 15-20 mV more positive than the resting potential) it causes an action potential (NERVE IMPULSE!); all or none event -Occurs in the axons (not dendrites) -HYPERPOLARIZATION does NOT cause action potentials -Action Potential Mechanism: -Resting State– Na+ and K+ channels closed -Threshold– some stimulus opens Na+ channels; it reaches threshold potential, and therefore more Na+ channels open triggering an action potential -Depolarization- because Na+ channels are open and K+ channels are closed, the inside of the cell becomes more positive -Repolarization– Inactivation gates close the Na+ channels and the K+ channels open; K+ leaves the cell and the inside becomes more negative than the outside -Undershoot– K+ gates remain open because they are slow, but the Na+ gates are closed; resting state is restored very quickly (hyperpolarization happens for a millisecond) SEE Fig. 48.11 pg. 1068explains everything perfectly… Action potentials arise because some ion channels in neurons are voltage-gated ion channels, opening or closing when the membrane potential passes a particular level

48. -Because both gates of the Na+ channel are closed, if another stimulus arrives during this period, it is unable to trigger a change (inactivation gates had not had time to open back up yet)  called refractory period(neuron is insensitive to depolarization) • -It is the number of action potentials per second, not their amplitude, that codes for a stimulus intensity in the nervous system • -Action potentials propagate themselves along an axon (like tipping over the first of a long line of dominoes) • -Factors that affect the speed of the action potentials (how fast they go along the axon): • -Diameter of axon (larger diameter  faster transmission) • -Saltatory conduction action potentials that jump from node to node

49. Synapses • -Communication between cells occurs at synapses • -Synapses– unique cell junctions that control communication between a neuron and another cell; two types: electrical or chemical • -Electrical Synapses • -Allows action potentials to spread from presynaptic cell to postsynaptic cell via gap junctions • -Not as common as chemical synapses • -Chemical Synapses • -Very common • -Chemical synapses are called synaptic clefts; they separate presynaptic cell from postsynaptic cell • -The cleft prevents an action potential from going directly from the pre to the postsynaptic cell • -A series of events converts the electrical signal of the action potential arriving at the synaptic terminal into a chemical signal that travels across the synapse, where it is converted back into an electrical signal in the postsynaptic cell. (electrical signal  chemical signal  electrical signal) Fig.48.16 pg. 1072…

50. ***A series of events converts the electrical signal of the action potential arriving at the synaptic terminal into a chemical signal that travels across the synapse, where it is converted back into an electrical signal in the postsynaptic cell. (electrical signal  chemical signal  electrical signal) • 1. An action potentialDEPOLARIZES the PRESYNAPTICmembrane • 2. The depolarization opens voltage gated channels, allowing Ca 2+ to enter the cell (neuron). • 3. Calcium causes synaptic vesicles to fusewith the pre-synaptic membrane • 4. Neurotransmitters are released into the synaptic cleft • 5. Neurotransmitters bind to the POSTSYNAPTIC membrane • 6. Ion channels open, allowing Na+ and K+ ions to enter the postsynaptic cell