Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science

1. Hewitt/Lyons/Suchocki/YehConceptual Integrated Science Chapter 19 HUMAN BIOLOGY I— CONTROL AND DEVELOPMENT

2. This lecture will help you understand: • Organization of the Human Body • Homeostasis • The Brain • The Nervous System • How Neurons Work • How Fast Can Action Potentials Travel? • Endorphins • The Senses—Vision, Hearing, Smell and Taste, Touch • Hormones • Reproduction and Development • The Skeleton and Muscles

3. Organization of the Human Body The many processes that occur in our body require coordination. Cells achieve this coordination by working together in structures with varying levels of complexity: tissues, organs, and organ systems.

4. There are 10 major organ systems in the human body: Nervous Endocrine Reproductive Sensory Muscular and skeletal Circulatory Respiratory Digestive Immune Excretory Organization of the Human Body

5. Homeostasis Homeostasis is maintenance of a stable internal environment. Examples: • Temperature control • Oxygen level of blood • Amount of water in the body • Concentration of ions inside and outside cells • Blood pH

6. The Brain Certain functions are associated with certain parts of the brain

7. The Brain The brain stem controls involuntary activities such as heartbeat, respiration, and digestion. The cerebellum controls balance, posture, coordination, and fine motor control.

8. The Brain The cerebrum: • Largest part of the brain • Takes in information from the senses • Controls all conscious, voluntary activities • Left hemisphere controls the right side of the body and vice versa • Performs information processing in the cerebral cortex (the thin, wrinkled layer covering the cerebrum)

9. The Brain The cerebrum’s four lobes: • Frontal lobes—reasoning, control of voluntary movement, speech • Parietal lobes—temperature, touch, taste, and pain • Occipital lobes—visual information • Temporal lobes—sound, language comprehension

10. The Brain The control of certain cognitive functions is dominated by either the right or left cerebral hemisphere: Left hemisphere: math, reasoning, language, detail-oriented activities Right hemisphere: spatial relations, emotional processing, music

11. The Brain Thalamus: receives information from many parts of the brain, sorts it, and passes important data on to the cerebral cortex Hypothalamus controls: • Emotions, such as pleasure and rage • Bodily drives, such as hunger, thirst, sex drive • Body temperature and blood pressure • Internal clock • Release of hormones

12. The Brain CHECK YOUR NEIGHBOR What part of your brain allows you to consciously hold your breath? What part makes you finally take a breath? Explain your answer to your neighbor.

13. The Brain CHECK YOUR ANSWER Your cerebrum allows you to decide to hold your breath. Your brainstem protects you by making you take a breath eventually.

14. The Nervous System The nervous system consists of two parts: • Central nervous system—brain and spinal cord • Peripheral nervous system—all of the other nerves in the body And two cell types: • Neurons—receive and transmit electrical impulses • Glial cells—support, protect, and insulate neurons

15. The Nervous System A typical neuron consists of extensions called dendrites, a cell body, and an axon. The dendrites receive information from other neurons or cells. The axon transmits information.

16. The Nervous System Depending on the origin and destination of their messages, neurons are divided into three categories: • Sensory neurons carry messages from the senses to the central nervous system. • Interneurons, found only in the central nervous system,connect neurons to each other. • Motor neurons carry messages from the central nervous system to the rest of the body.

17. The Nervous System There are two types of motor neurons: • Somatic nervous system: controls voluntary actions • Autonomic nervous system: controls involuntary muscles and other internal organs

18. The Nervous System Within the autonomic nervous system are two divisions: • Sympathetic: fight-or-flight response • Parasympathetic: operates in times of relaxation

19. How Neurons Work Neurons use electrical signals in the form of changes in voltage, or electric potential, across the cell membrane. The electric potential across the membrane is called the membrane potential. The inside of a neuron is normally negatively charged and the outside is normally positively charged. The resting potential is about -70 mV.

20. How Neurons Work A neuron must be stimulated in order to fire. A neuron is stimulated when its membrane potential is increased. If the membrane potential reaches a certain threshold value, sodium channels open, sodium ions rush into the cell, and the membrane potential spikes, creating an action potential.

21. How Neurons Work Once the spike occurs, the sodium channels close and potassium channels open, and the membrane potential returns to resting value.

22. How Neurons Work Action potentials are all-or-nothing events. A neuron either fires or it doesn’t. A neuron cannot fire “harder” in response to a stronger stimulus. But it can fire more frequently.

23. How Neurons Work Action potentials travel down the axon to signal to a target cell. How is the action potential propagated down the axon? Once an action potential has occurred in one part of the axon membrane, there’s a brief period when the area cannot be stimulated again. This prevents the action potential from moving backwards.

24. How Neurons Work Myelin sheaths speed the movement of a signal by insulating the axon. The disease multiple sclerosis causes the body to destroy myelin.

25. How Neurons Work At the end of its axon, the neuron connects with a target cell—either another neuron or a cell that does something (such as a muscle cell). The connections between neurons and their target cells are called synapses.

26. How Neurons Work In electrical synapses, ions flow directly from a neuron to a target cell through channels called gap junctions. Electrical synapses transmit action potentials rapidly and are found in places like heart muscle.

27. How Neurons Work Most synapses are chemical synapses. Chemical synapses allow for a finer degree of control. When the action potential reaches the end of the axon, the neuron releases a chemical messenger called a neurotransmitter into the space between the neuron and the target cell. Neurotransmitters diffuse to the target cell and bind to receptors on the target cell. This opens ion channels in the target cell, changing its membrane potential. The effect of the neurotransmitter may be to make the target cell more likely to fire. Or, the effect may be to make the target cell less likely to fire.

28. How Neurons Work

29. How Fast Can Action Potentials Travel? An action potential’s speed depends on how quickly successive parts of the axon’s cell membrane can be induced to increase to threshold. This is determined by how quickly sodium ions travel downstream. This depends on Ohm’s law: Current = voltage/resistance Thicker axons have lower resistance. Myelinated axons have lower resistance. In myelinated axons, the ability of the action potential to jump from one gap in the myelin sheath to the next makes it faster still.

30. Endorphins Endorphins bind to opiate receptors on neurons. Like opiates, endorphins decrease sensitivity to pain and induce euphoria. Endorphin release is associated with many activities, including “runner’s high,” eating chocolate, and meditation.

31. The Senses—Vision Vision depends on light entering the eye through the cornea and the pupil. The light then passes through the lens, which focuses it on the retina. The retina holds the actual light-sensitive cells of the eye—rods and cones. When light hits these cells, action potentials occur that transmit information to the brain via the optic nerve.

32. The Senses—Vision Rods are very sensitive to light and are responsible for vision in dim light.Rods cannot discriminate colors, so at night we see shades of gray. Cones detect color by responding to red, green, and blue light. Cones also provide us with our ability to see fine details.

33. The Senses—Hearing The ear consists of three parts: the outer, middle, and inner ear. Sound waves vibrate the eardrum.The movement of the eardrum, inturn, moves three middle ear bones—hammer, anvil, and stirrup—in sequence, amplifying the sound.In the cochlea, vibrations bend tiny sensory “hairs,” starting action potentials.

34. The Senses—Smell and Taste Smell and taste rely on chemoreception—a process in which chemicals bind to receptors on the surface of special chemosensory cells. The binding opens ion channels and begins action potentials.

35. The Senses—Touch The sense of touch includes several different senses, including pressure, temperature, and pain. Separate sensory cells detect light touch and heavy pressure. Unlike other touch receptors, pain receptors become more sensitivewith continued stimulation.

36. Hormones Hormones are chemical messengers that give instructions to the body. Hormones are: • Produced in one place in the body • Released into the bloodstream • Received by target cells elsewhere

37. Hormones Protein hormones bind to receptors on the cell membranes of their target cells.

38. Hormones Steroid hormones cross the cell membrane and bind to receptors in either the cytoplasm or nucleus of the target cell. The hormone and receptor then bind to DNA in the nucleus and directly affect gene transcription.

39. Hormones Endocrine organs include: • Hypothalamus • Anterior and posterior pituitary glands • Thyroid • Parathyroid • Adrenal glands • Pancreas • Ovaries • Testes • Pineal gland

40. Hormones

41. Reproduction and Development Eggs and sperm are gametes—haploid cells produced through meiosis. Eggs are large, because they are the result of unequal meiosis—during cell division, the future egg gets almost all of the cytoplasm and the other cells receive very little. These other cells quickly degenerate.

42. Reproduction and Development The ovaries are made up of follicles, developing eggs surrounded by support cells. After ovulation, the egg moves down the oviduct, where fertilization can take place. If the egg becomes fertilized, it completes meiosis. After fertilization, the egg continues to the uterus, where it implants and continues development.

43. Reproduction and Development Sperm are made in the testes, which is located in the scrotum. From the testes, sperm move to the epididymis, where they complete development and become mobile. Each mature sperm has a head that contains DNA, mitochondria, enzymes for penetrating the egg, and a tail.

44. Reproduction and Development The egg is surrounded by the zona pellucida. Once a sperm has reached the egg’s cell membrane, the two membranes fuse. The zona pellucida changes to become impenetrable to additional sperm. This ensures that the fertilized egg does not end up with too many chromosomes.

45. Reproduction and Development CHECK YOUR NEIGHBOR What organ provides oxygen and nutrients to the developing embryo and carries away wastes? Explain your answer to your neighbor.

46. Reproduction and Development CHECK YOUR ANSWER The placenta delivers oxygen and nutrients to the developing embryo and carries away wastes. The placenta also produces the sex hormones estrogen and progesterone throughout pregnancy to prevent further ovulation and maintain the uterus in nurturing condition.

47. The Skeleton and Muscles The skeleton: • Consists of bones and cartilage • Includes 206 bones • Protects the body • Supports and moves the body • Produces red and white blood cells in the bone marrow

48. The Skeleton and Muscles Muscles: • Contract, or shorten • Are connected to our bones via tendons • Pull on our bones, moving us • Can only pull, not push, so we often have pairs of muscles that work in opposition (biceps, triceps)

49. The Skeleton and Muscles How do muscles contract? • A muscle receives a signal from a motor neuron • Motor neurons connect to muscles through a chemical synapse that uses the neurotransmitter acetylcholine • Acetycholine starts an action potential in the muscle cells • The muscle cells contract

50. The Skeleton and Muscles A muscle consists of a bundle of elongated muscle fibers. Each fiber is actually a single cell with multiple nuclei. Each muscle fiber contains myofibrils, which are made of contractile units called sarcomeres. The sarcomeres are made up of actin and myosin, which work together to shorten and contract the muscle.