Warm-Up

1. Outline pages 222-230 Warm-Up

2. The Nervous System Chapter 7

3. Master controlling and communicating system of the body • Monitor changes (stimuli) both inside and outside of the body • Gathered information is called sensory input • Processes and interprets the sensory input and makes decisions about what should be done at every moment • This is called integration Functions

4. Effects a response by activating muscles or glands (effectors) via motor output

5. Does not work alone to regulate and maintain body homeostasis • Endocrine system is a second important regulating system • Produces hormones • Typically brings about its effects in a more leisurely way

6. Structural Classification • Central nervous system (CNS) • Brain and spinal cord • Occupy the dorsal body cavity and act as the integrating and command centers of the nervous system • Interpret incoming sensory information • Issue instructions Organization of the Nervous System

7. Peripheral nervous system (PNS) • Parts of the nervous system that are outside of the CNS • Consists mainly of the nerves that extend from the brains and spinal cord • Spinal nerves carry impulses to and from the spinal cord • Cranial nerves carry impulses to and from the brain • Serve as communication lines

8. Concerned only with PNS structures • 2 subdivisions • Sensory (afferent) division • Consists of nerve fibers that convey impulses to the CNS from sensory receptors located through the body • Somatic (afferent fibers) – impulses from the skin, skeletal muscles and joints • Visceral fiber (visceral afferents) – impulses from the visceral organs Functional Classification

9. Motor (efferent) division • Carries impulses from the CNS to effector organs, the muscles and glands • Effect a motor response • Two subdivisions • Somatic nervous system – voluntary nervous system • Autonomic nervous system (ANS) – involuntary nervous system • Sympathetic • Parasympathetic

11. Nervous Tissue: Structure and Function

12. Two Principal Types of Nervous Cells • Supporting cells • Neurons Background Information

13. Neuroglia – supporting cells in the CNS that are “lumped together” • Many types of cells that support, insulate and protect the neurons • Glia – different types of neuroglia that have a special function Supporting Cells

14. Astrocytes • Star shaped • Account for nearly half of the neural tissue • Form a living barrier between capillaries and neurons and play a role in making exchanges between them • Help control the chemical environment in the brain • Microglia • Spiderlike phagocytes • Dispose of debris Types of Glial

15. Ependymal • Line the cavities of the brain and the spinal cord • Helps circulate the cerebrospinal fluid • Oligodendrocytes • Wrap their flat extensions tightly around the nerve fibers • Produce fatty insulating covering called the myelin sheaths • Glia do not transmit nerve impulses • Never lose their ability to divide • Most brain tumors are gliomas

16. Supporting Cells in the PNS come in two major varieties • Schwann cells • Form the myelin sheaths around the nerve cells that are found in the PNS • Satellite cells • Act as protection, cushioning cells

17. Also called nerve cells • Highly specialized to transmit messages • Have a cell body containing the nucleus and is the metabolic center of the cell • No centrioles • Very abundant are the • Nissl substances – specialized RER • Neurofibrils – intermediate filaments that are important in maintaining cell shape Neurons

18. Extending from the cell body there are one or more slender processes (fibers) • Vary in length • Dendrites – convey incoming messages (electrical signals) towards the cell body • May have hundreds of branching dendrites • Axons – generate nerve impulses and typically conduct them away from the cell body • Only has one • Arise from the axon hillock • Occasionally branch to give off a collateral branch • Branch profusely at their terminal end to form the axon terminals

19. Terminals contain the neurotransmitters in tiny vesicles which are released when stimulated • Synaptic cleft separates the one neuron for the next • The functional gap is the synapse • Myelin – whitish, fatty material with a waxy appearance surrounds most nerve fibers • Protects and insulates the fibers along with increasing the transmission rate

20. Outside the CNS, the myelination is done by Schwann cells • A myelin sheath results from the myelination • Most of the Schwann cell cytoplasm ends up just beneath the outermost part of its plasma membrane and is called the neurilemma • Remains intact (for the most part) when a peripheral nerve fiber is damages, it plays an important role in fiber regeneration • Nodes of Ranvier form where there are gaps between the adjacent Schwann cells • In the CNS, the oligodendrocytes form the myelin sheaths. • Coil around as many as 60 different nerve fibers at a time • Lack neurilemma

22. Clusters of neuron cell body and collections of nerve fibers • In the CNS, the cell body clusters are called nuclei • Protected in the skull and vertebral column • Do not routinely undergo cell division • Carries out most of the metabolic functions • In the PNS, small collections of cell bodies are called ganglia • Found in few sites • In the CNS, bundles of nerve fibers are called tracts • White matter – dense collections of myelinated tracts • Gray matter – mostly unmyelinated fibers and cell bodies • In the PNS, bundles of nerve fibers are called nerves

23. Functional • Groups neurons according to the direction the nerve impulse is traveling relative to the CNS • Sensory (afferent) neurons – carry impulses from sensory receptors to the CNS • Cell bodies are always found in a ganglion outside the CNS • Keep use informed about what is happening both inside and outside the body • Dendrite endings are usually associated with specialized receptors that are activated by specific changes occurring nearby. Neuron Classification

24. Complex receptors may be discussed later; we will focus on the simpler type of sensory receptors found in the skin (cutaneous sense organs), muscles and tendons (proprioceptors). • The pain receptors (which are bare dendrite endings) are the least specialized cutaneous receptors as well as the most numerous. • Proprioceptors detect the amount of stretch (tension) skeletal muscles, their tendons and joints • These allow the body to make the proper adjustments to maintain balance and normal posture.

25. Motor (efferent) neurons carry impulses from the CNS to the viscera and/or muscles and glands • The cell bodies of motor neurons are always located in the CNS • Association neurons (interneurons) connect the motor and sensory neurons in neutral pathways • Their cell bodies are always located in the CNS

26. Page 268-269 • Multiple Choice 1-3 • Write the questions and correct answers • Short Answer Essay Question 5 • Write the question and answer in complete sentences Warm-Up

27. Structural Classification • Based on the number of processes extending from the cell body.

28. Multipolar neurons – many extensions from the cell body • Most common type • All motor and association neurons Figure 7.8a

29. Bipolar neurons – one axon and one dendrite • Rare in adults • Found only in some special sense organs Figure 7.8b

30. Unipolar neurons – have a short single process leaving the cell body • Divides almost immediately into proximal and distal processes • Unique because only the small branches at the end of the peripheral process are dendrites • Axons conduct impulses towards and away from the cell body • Sensory neuron found in the PNS ganglia Figure 7.8c

31. 2 Major Functional Properties of Neurons • Irritability – ability to respond to stimuli • Conductivity – ability to transmit an impulse • The plasma membrane at rest is polarized • Fewer positive ions are inside the cell (K+) than outside the cell (Na+)

32. Stimuli excite neurons to become active and generate an impulse • Most neurons are excited by neurotransmitters released by other neurons • Regardless of the type of stimuli received, the result is the permeability properties of the cell’s plasma membrane change for a very brief period • Normally, the membrane is not very permeable to Na+; however, when stimulated the sodium channels open and Na+ diffuses into the cell • The difference between the charges is a membrane potential Starting a Nerve Impulse

33. Depolarization – a stimulus depolarizes the neuron’s plasma membrane at a certain site • A graded potential may result or if strong enough the graded potential can become an action potential (nerve impulse) Figure 7.9a–c

34. The Action Potential • If the action potential (nerve impulse) starts, it is propagated over the entire axon • All-or-None response • Almost immediately, repolarization occurs • The membrane permeability changes again • K+ rush out of the neuron and restores the electrical conditions at the membrane to the polarized, or resting, state • The sodium-potassium pump restores the original configuration • This action requires ATP • These events spread along the entire neuronal membrane

35. The impulse continues to move toward the cell body • Impulses travel faster when fibers have a myelin sheath because the impulse leaps from node to node because no current can flow across the axon membrane where there is myelin • This is called saltatory conduction Nerve Impulse Propagation Figure 7.9d–f

36. Impulses are able to cross the synapse to another nerve via neurotransmitters • Neurotransmitters are released from a nerve’s axon terminal when the action potential reaches it • The neurotransmitters diffuse across the synapse and the dendrite of the next neuron has receptors that are stimulated by it • An action potential is started in the axon hillock and travel down the axon • The electrical changes caused by this is very brief because the neurotransmitters are reabsorbed into the axonal terminal or broke down by enzymes Electrochemical Event

37. How Neurons Communicate at Synapses Figure 7.10

38. Rapid, predictable and involuntary responses to stimuli • Once it begins, it always go in the same direction • Occur on reflex arcs – neural pathways • Involve both the CNS and PNS • Two types • Somatic reflexes – stimulate the skeletal muscles • Autonomic reflexes – regulate the activity of the smooth muscles, the heart and glands Reflexes

39. Minimum of 5 elements • Sensory receptor – react to a stimulus • Effector organ – organ or gland stimulated • Sensory and motor neurons – connect the two above • Synapse – the CNS integration center • 2-neuron reflex arc • Most simple type • Example is the patellar reflex

40. Most are more complex and involve synapses between one or more association neurons in the CNS • 3-neuron reflex arc (flexor, or withdrawal, reflex) • limb is withdrawn from a painful stimulus • Consists of 6 elements • The more synapses there are, the longer the reflex takes to happen • Many spinal reflexes involve only the spinal cord neurons and occur without brain involvment • Can be tested to help determine nervous system disorders

41. Cerebral hemisphere (cerebrum) Gyri (gyrus) Sulci (sulcus) Fissures Lobes Sensory Primary motor area Corticospinal (pyramidal tract) Motor Basal nuclei (basal ganglia) Speech area Vocabulary 3

42. Central Nervous System

43. During embryonic development • The neural tube is the first part of the CNS to appears • 4th week – anterior end of the neural tube begins to expand – brain formation begins • the posterior to the brain the neural tube becomes the spinal cord • The central canal of the neural tube becomes enlarged in four regions of the brain to form the ventricles Development

44. Description • About the size of 2 fistfuls • Pinkish gray • Wrinkled • Texture of cold oatmeal • Little over 3 pounds • Largest and most complex mass of nervous tissue in the body • 4 major regions • Cerebral hemispheres • Diencephalon • Brain stem • Cerebellum

45. Paired cerebral hemispheres (cerebrum) • Superior part of the brain • Largest area of the brain • Enclose and obscure most of the brain stem • Surface is covered with gyri separated by sulci • Fissures separate the large regions of the brain • Longitudinal fissure separates the cerebral hemispheres • Divide each cerebral hemisphere into lobes (named for the cranial bones that lie over them) Cerebral Hemisphere

46. Functions • Speech • Memory • Logical and emotional response • Consciousness • Interpretation of sensation • Voluntary movement

47. Diencephalon (interbrain) Thalamus Hypothalamus Limbic system Pituitary gland Mammillary bodies Epithalamus Pineal body Choroid plexus Olfaction Warm-Up 2/22

48. Somatic sensory area (in parietal lobe) - receives impulses from the body’s sensory receptors • Occipital Lobe – visual area • Temporal lobe – auditory area and olfactory area • Primary motor area (in frontal lobe) – sends impulses to skeletal muscles • Broca’s area (in one cerebral hemisphere) – involved in our ability to speak • Frontal lobe – higher intellectual reasoning and socially acceptable behavior

49. Cerebral cortex is the outermost gray matter of the cerebrum • Houses the previously discussed functions of the cerebrum • Cerebral white matter is composed of fiber tracts carrying impulses to or from the cortex • Corpus callosum connects the cerebral hemispheres • There are basal nuclei deep within the white matter of the cerebral hemispheres • Help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex.

50. On top of the brain stem • Enclosed by the cerebral hemispheres • 3 major structures • Thalamus • Hypothalamus • Epithalamus Diencphalon