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Biology 30

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  1. Biology 30 Providence Christian School 2013-14 Mr. Schooten

  2. Unit A: The Nervous & Endocrine Systems Chapters 11-13

  3. Chapter 11: The Nervous System Section 11.1 Structures and Processes of the Nervous System

  4. Homeostasis – the tendency of the body to maintain a relatively constant internal environment • The nervous system regulates body structures and processes to maintain homeostasis despite changes in both the internal and external environment.

  5. A. Organization of the Nervous System a. Central Nervous System (CNS) • Located centrally – consists of the brain and spinal cord • Integrates and processes information sent by nerves

  6. b. Peripheral Nervous System (PNS) • Located peripherally – consists of nerves that carry sensory messages to the CNS and nerves that return information to muscles and glands • Divided into two systems • Somatic system • Sensory receptors in the head and extremities • Under conscious control or voluntary • Autonomous system • Controls glandular secretions as well as smooth and cardiac muscles • Not under conscious control or involuntary • Has two divisions, sympathetic and parasympathetic, that work against each other to regulate involuntary processes such as heartbeat and peristalsis

  7. Organization of the Nervous System

  8. B. Cells of the Nervous System a. Glial Cells • The support cells for neurons (glial is Greek for ‘glue’) • Nourish the neurons • Remove waste • Defend against infection • Provide a supporting framework #1, 5, and 6 are types of glial cells

  9. b. Neurons • The basic structural and functional units of the nervous system, organized into tissues called nerves that are made up of hundreds of neurons • Three main types of neurons form the basic impulse-transmission pathway of the entire nervous system: • Sensory neurons gather information from sensory receptors (ie. senses) and transmit the information to the CNS • Interneurons act as a link between sensory and motor neurons by processing and integrating incoming information and relaying outgoing motor information • Motor neurons transmit information from the CNS to the effectors such as muscles, glands, and other organs

  10. c. Special Case: The Reflex Arc • Reflex arcs are simple connections of neurons that allow for sudden, reflexive behaviours such as blinking your eye when an object comes towards it. • Very few neurons are used to transmit messages • A reflex arc moves directly to and from the brain or spinal cord before the part of the brain involved with voluntary control has time to process the sensory information

  11. C. The Structure of a Neuron • In general, each neuron contains: • Dendrites • Short, branching terminals that receive impulses from sensory receptors or other neurons and relay the impulse to the cell body • Cell body (soma) • Contains the nucleus and performs metabolic reactions • Processes input from dendrites, and if input is large enough, relays it to the axon which begins an impulse

  12. Axon • Conducts impulses away from the cell body where it branches into many fibres • The axon terminal releases chemical signals to the receptors or dendrites of neighbouring cells. • Some axons are covered in a fatty insulating layer called the myelin sheath (myelinated) • the myelin sheath is made up of Schwann cells, a type of glial cell, and protects the neuron and speeds the rate of impulse transmission • Myelinated neurons form the white matter in the CNS and unmyelinated neurons form the gray matter. Most PNS neurons are myelinated.

  13. D. UnmyelinatedNerve Impulse • Luigi Galvani (1737-1798) discovered the electrical nature of nerve tissue by using two metal rods and some wire to cause a frog’s leg to twitch. In 1952, A.L. Hodgkin and A.F. Huxley performed experiments on the giant axon of a squid to determine more about the mechanisms by which nervous tissue transmitted electrical information.

  14. Nerve conduction differs from electrical conduction along a wire in that it depends on movement of ions across the cell membrane of the axon. • In a resting neuron, the inside (cytoplasmic) of the membrane is negatively charged relative to the extracellular side. The separation of charge across the membrane is potential energy, called membrane potential. • The potential difference across the membrane in a resting neuron is called the resting membrane potential and is -70 mV (millivolts). This potential provides the energy for a nerve impulse.

  15. In order to generate and maintain a resting membrane potential of -70 mV, three mechanisms contribute to polarization: • Large negatively charged protein molecules are found in the intracellular fluid but not outside the cell and are too large to pass through the membrane. • The membrane is nearly impermeable to some smaller negative charged ions such as chloride ions that are also inside the cell • The main mechanism is the sodium-potassium exchange pump • This system uses energy from ATP to remove sodium ions and bring potassium ions into the cell. Three sodium ions leave for every two potassium ions that enter, thereby decreasing the net positive charge on the inside of the cell • Mechanism found in Figure 11.12 on pg. 374

  16. E. Action Potential • A nerve impulse consists of a series of action potentials • In myelinated neurons, action potentials exist only at the gaps in the myelin sheath, the nodes of Ranvier, because the myelin insulates the membrane elsewhere • When the transmembrane potential is reduced to less than the resting potential of -70 mV, the membrane is depolarized. • If it is depolarized past the threshold potential a significant change occurs called an action potential

  17. This threshold potential for most neural cells is close to -55 mV. It is an “all-or-none” event because nothing changes if the potential remains between the threshold potential and the resting potential. • When the threshold is reached, voltage-gated sodium channels open to make the membrane very permeable to sodium ions, allowing sodium to rush in because of the concentration gradient • Within a millisecond or less the potential difference across the membrane is +35 mV • This causes voltage-gated potassium channels to open and potassium ions rush out of the cell according to the concentration gradient • The membrane is thus repolarized to a potential of -90 mV. • The sodium-potassium exchange pump then restores the potential to the resting potential of -70 mV • The membrane cannot be stimulated to undergo another action potential for a few milliseconds which is called the refractory period

  18. F. Myelinated Nerve Impulse • When the sodium ions rush into the axon through the voltage-gated sodium channels during an action potential, they spread out in both directions within the axon. • These sodium ions reach neighbouring nodes of Ranvier and depolarize to threshold and stimulates an action potential at the next node of Ranvier • The impulse only travels in one direction, however, since one of the neighbouring nodes of Ranvier is still in the refractory period • This process of one action potential stimulating the next is a nerve impulse

  19. Action potentials “jump” from one node of Ranvier to the next so it is called saltatory conduction, which is Latin for jump or leap. • In unmyelinated neurons action potentials can occur everywhere along the axon so the impulse is much slower (about 0.5 m/s compared to up to 120 m/s in myelinated neurons)

  20. Multiple Sclerosis • Multiple sclerosis is caused by a body’s immune system breaking down the myelin sheath surrounding the axons in the CNS which prevents neurons from efficiently carrying impulses between the brain and body. • Symptoms include blurred vision, loss of balance, muscle weakness fatigue and slurred speech

  21. G. Signal Transmission across a Synapse • When an impulse reaches the terminal of a neuron it must jump a gap or a synapse in order to have the impulse continue. The synapses between motor neurons and muscle cells are called neuromuscular junctions. • Chemical messengers called neurotransmitters carry the neural signal from the presynaptic cell across the synaptic cleft to the postsynaptic cell.

  22. When an action potential arrives at the synaptic terminal it causes sacs, called synaptic vesicles, which contain neurotransmitters to fuse with the membrane of the axon. • The contents of these vesicles are released into the synaptic cleft and diffuse across the synapse in between 0.5 ms to 1 ms and reach the dendrites of the postsynaptic cell. • The neurotransmitters bind to specific receptor proteins in the postsynaptic membrane which triggers ion-specific channels to open. • Sodium ions rush in and depolarizes the postsynaptic membrane stimulating an action potential. • Neurotransmitters can have excitatory or inhibitory effects and the cell body must integrate all incoming signals. If the combined effects are excitatory enough, an action potential will be generated through the axon and the impulse will be carried on. • Enzymes break down neurotransmitters after they have had their effect in order to inactivate it so it can be reabsorbed by the presynaptic cell.

  23. Neurotransmitters • Some common neurotransmitters include: • Dopamine • Linked to sensations of pleasure, such as eating • Serotonin • Involved in mood control • Endorphins • Act as natural painkillers in synapses in the brain • Norephinephrine • Readies the body to respond to danger or other stressful situations

  24. Chapter 11: The Nervous System Section 11.2 The Central Nervous System

  25. The CNS is the structural and functional centre for the entire nervous system. It is composed of grey matter and white matter • Grey matter is found around the outside areas of the brain and forms the H-shaped core of the spinal cord. • White matter forms the inner region of some areas of the brain and the outer area of the spinal cord.

  26. A. The Spinal Cord • A column of nerve tissue that extends out of the skull from the brain down through a canal within the backbone • A vital communication link between the brain and the PNS • Sensory nerves carry message from the PNS to spinal cord and motor nerves relay messages from the brain to the effectors • The primary reflex centre, coordinating incoming and outgoing neural information • The spinal cord is protected by cerebrospinal fluid, soft tissue layers, and the spinal column or backbones (vertebrae)

  27. B. The Brain • Plays a central role in maintaining homeostasis and is the centre for intelligence, consciousness, and emotion • It is very fragile and has a gelatin-like consistency. It is protected by the skull and the meninges, three layers of tough, elastic tissue within the skull and spinal column that enclose the brain and spinal cord. • Can be divided into three general regions: the hindbrain, the midbrain, and the forebrain.

  28. Hindbrain • Cerebellumis a walnut-shaped structure involved in unconscious coordination of posture, reflexes, and body movements, as well as fine, voluntary motor skills such as those used to play the piano or hit a tennis ball • The medulla oblongata connects the brain to the spinal cord and controls automatic, involuntary responses, such as heart rate, constriction or dilation of blood vessels, rate and depth of breathing, swallowing and coughing • The pons serves as the relay centre between the neurons of the right and left halves of the cerebrum, the cerebellum, and the rest of the brain

  29. Midbrain • It relays visual and auditory information between areas of the hindbrain and the forebrain and plays an important role in eye movement and control of skeletal muscles

  30. Forebrain • The thalamus contains neurons that are connections mainly between the forebrain and hindbrain, and between areas of the sensory system and the cerebellum (except for sense of smell) • The hypothalamus regulates the body’s internal environment by coordinating the actions of the pituitary gland by producing and regulating the release of certain hormones. The hypothalamus controls blood pressure, heart rate, body temperature, basic drives such as thirst and hunger, and emotions. • The cerebrum is the largest part of the brain and is divided into right and left hemispheres which contain centres for intellect, memory, consciousness, and language and interprets and controls responses to sensory information

  31. The meninges protects the CNS by preventing direct circulation of blood through the cells of the brain and spinal cord through the blood-brain barrier. The capillaries that bring blood to the brain and made of tightly fused epithelial cells that block many toxins and infectious agents but allow glucose and oxygen through. Other lipid-soluble substances can also pass through such as nicotine, caffeine, alcohol, heroin and some other drugs.

  32. Approximately 150 mL of cerebrospinal fluid is circulating through the spaces or ventricles within the brain and spinal cord at any time. This fluid is replaced 4 times daily. It transports hormones, white blood cells, and nutrients across the blood-brain barrier and also acts as a shock absorber to cushion the brain.

  33. C. The Structure and Function of the Cerebrum • The cerebral cortex is the outer covering of grey matter on the cerebrum that is responsible for language, memory, personality, vision, conscious thought, and other thinking and feeling activities. • The right and left hemispheres are linked by a bundle of white matter called the corpus callosum. The corpus callosum lets each half of the brain know what the other half is doing.

  34. The right cerebral hemisphere is associated with holistic and intuitive thinking, visual-spatial skills, and artistic abilities.

  35. The left cerebral hemisphere is associated with segmental, sequential, and logical ways of thinking, and to linguistic and mathematical skills. • The process of speech involves two important areas on the left side of the cerebral cortex: • Broca’s area coordinates the muscles for speaking and translates thought into speech • Wernicke’s area stores the information involved in language comprehension

  36. The Stroop Effect – pg. 390

  37. The cerebral cortex is divided into four pairs of lobes: • The occipital lobes receive and analyze visual information • The temporal lobes share in the processing of visual information but are mainly linked to understanding speech and retrieving visual and verbal memories. • The parietal lobes receive and process sensory information from the skin and process information about the body’s position and orientation. • The frontal lobes integrate information from other parts of the brain and control reasoning, critical thinking, memory, and personality

  38. Sheep Brain Dissection

  39. D. Mapping Brain Functions • Positron-Emission tomography (PET) is based on the fact that more active areas of the brain require more energy. A person intakes radioactively-labelled glucose and a scanner monitors glucose consumption within the brain and determines different activity levels • Magnetic Resonance Imaging (MRI) provides structural and functional images of the brain based on a changing magnetic field inducing hydrogen atoms in the brain to emit radio signals that can be detected and translated into an image.

  40. Chapter 11: The Nervous System Section 11.3 The Peripheral Nervous System

  41. The Peripheral Nervous System (PNS) consists of nerves that link the brain and spinal cord to the rest of the body, including the senses, muscles, glands, and internal organs. • The two main divisions of the PNS are the somatic system and the autonomic system.

  42. A. The Somatic System • The somatic system is under voluntary control and its neurons service the head, trunk, and limbs. • It includes 12 pairs of cranial nerves and 31 pairs of spinal nerves which are myelinated. • Each nerve contains both sensory and motor neurons which service the area of the body where they are found.

  43. B. The Autonomic System • The autonomic system is under automatic or involuntary control and either stimulates or inhibits glands or cardiac or smooth muscle. • The hypothalamus and medulla oblongata control the autonomic system by coordinating the sympathetic and parasympathetic divisions of the autonomic system.

  44. The sympathetic nervous system (fight-or-flight) is activated in stressful situations and release a neurotransmitter called norepinephrine which has an excitatory effect on its target muscles. • Sympathetic nerves also trigger the adrenal glands to release epinephrine and norepinephrine which function as hormones that activate the stress response. • It also inhibits some areas of the body such as increasing blood pressure and heart rate while slowing down digestion.

  45. The parasympathetic nervous system (rest-and-digest) is activated when the body is calm and at rest in order to restore and conserve energy. • The parasympathetic nervous system uses a neurotransmitter called acetylcholine to control organ responses.

  46. Depending on the situation and organs involved, the sympathetic and parasympathetic systems work in opposition to each other in order to maintain homeostasis. • Certain drugs act as either stimulants or depressants by directly affecting one of these systems.