Chapter 9 The Nervous System

1. Chapter 9The Nervous System

2. Organs and Divisions of the Nervous System • Central Nervous System (CNS) brain and spinal cord centrally located • Peripheral Nervous System (PNS) nerves extending to outlying parts of the body • Autonomic Nervous System (ANS) regulates automatic or involuntary functions • Sympathetic - “fight-or-flight” • Parasympethetic “rest, feed and breed”

4. Cells of the Nervous System Two Types of Nervous System Cells • Neurons nerve cells conduct impulses • Glia connective tissue cells supporting neurons

5. Cells of the Nervous System Neurons Dendrites conduct impulses to cell body of neuron Cell body main, central part with nucleus Axons conducts impulses away from cell body of neuron

7. Cells of the Nervous System Classification of Neurons according to Function • Sensory or Afferent conduct impulses to the spinal cord and brain; • Motor or Efferent conduct impulses away from brain and spinal cord to muscles and glands • Interneurons conduct impulses from sensory neurons to motor neurons

8. Cells of the Nervous System Glia (neuroglia) Support cells, bringing the cells of nervous tissue together structurally and functionally (like glue) 3 main types of connective tissue cells Astrocytes star-shaped cells that anchor small blood vessels to neurons Microglia smallest of the glial cells that act as phagocytes in the brain Oligodendrocytes form myelin sheaths on axons in the CNS (Schwann cells form myelin sheaths in PNS only)

9. Cells of the Nervous System Disorders of Nervous Tissue Multiple Sclerosis • characterized by myelin loss in central nerve fibers resulting in conduction impairment • most common in younger women Tumors • General name for nervous system tumors is neuroma • Most neuromas are gliomas, glial tumors • Multiple neurofibromatosis - characterized by numerous benign tumors

12. Nerves Nerves are bundles of peripheral axons Tract bundle of central axons White matter brain or cord tissue composed primarily of myelinated axons (tracts) Gray matter brain or cord tissue composed primarily of cell bodies and unmyelinated fibers

13. Nerves Nerve coverings are made of fibrous connective tissue Endoneurium surrounds individual fibers within a nerve Perineurium surrounds a group (fascicle) of nerve fibers Epineurium surrounds the entire nerve

14. Reflex Arcs • Reflex arcs by-pass the brain - occur in the spinal chord in situations requiring immediate response • Nerve impulses are conducted from receptors to effectors • conduction by a reflex arc results in a reflex, i.e.; contraction by a muscle or secretion by a gland • Two-neuron arcs the simplest arc, consisting of sensory neurons synapsing in the spinal cord with motor neurons • Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons

15. Nerve Impulses • Definition -self-propagating wave of electrical activity that travels along the surface of a neuron membrane • Mechanism • A stimulus triggers the opening of Na+channels in the plasma membrane of the neuron • Inward movement of positive sodium ions allows sodium into the cell, and marks the beginning of a nerve impulse

16. The Synapse • Synapse The space between the axon of one neuron (presynaptic) - across the synaptic cleft - and the dendrite of the next neuron (postsynaptic) • Neurotransmitters chemical compounds released from axon terminals of a presynaptic neuron into the synaptic cleft bind to specific receptor molecules of a postsynaptic neuron, opening ion channels, and thereby stimulating impulse conduction by the membrane

18. The Synapse Names of Neurotransmitters • acetylcholine • catecholamines - “fight-or-flight” hormones norepinephrine, dopamine, and serotonin • endorphins, enkephalins, nitric oxide (NO) Parkinson Disease • abnormally low levels of dopamine in motor control areas of the brain • involuntary trembling and muscle rigidity

20. Central Nervous System Major Divisions of the Brain 1.Brainstem- vital functions medulla oblongata, pons, midbrain 2. Cerebellum - movement, posture and balance. Lies under the cerebrum. 3. Diencephalon-sensations, emotions hypothalamus, thalamus (endocrine glands) 4. Cerebrum - higher brain functions consciousness, thought, speech, memory, decision-making, judgment

22. Central Nervous System Brainstem • in ascending order: medulla oblongata, pons, and midbrain (vital functions) • Structure white matter with bits of gray matter scattered through it • Function gray matter in the brainstem functions as reflex centers (for example, for heartbeat, respirations, and blood vessel diameter) sensory tracts in the brainstem conduct impulses to the higher parts of the brain motor tracts conduct from the higher parts of the brain to the spinal cord

23. Central Nervous System Diencephalon • Structure of the hypothalamus Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter • Functions of the hypothalamus • acts as the major center for controlling the ANS • helps control the functioning of most internal organs • controls hormone secretion by anterior and posterior pituitary glands; therefore, it indirectly helps control hormone secretion by most other endocrine glands • controls appetite, wakefulness, pleasure

24. Central Nervous System • Structure of the Thalamus dumbbell-shaped mass of gray matter in each cerebral hemisphere • Function of the Thalamus • Relays sensory impulses to cerebral cortex sensory areas • produces the emotions of pleasantness or unpleasantness associated with sensations

25. Central Nervous System Cerebellum Structure • Second largest part of the human brain • Lies under the cerebrum (largest part of the brain) Function • Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal postures

26. Central Nervous System Cerebrum Structure • Largest part of the human brain • Outer layer of gray matter is the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons • Interior of the cerebrum composed mainly of white matter (that is nerve fibers arranged in bundles called tracts) Function • mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements

27. Central Nervous System Brain Disorders Cerebrovascular Accident (CVA) “stroke” - hemorrhage from or cessation of blood flow through cerebral blood vessels Cerebral Palsy condition in which damage to motor control areas of the brain before, during, or shortly after birth causes paralysis (usually spastic) of one or more limbs

28. Central Nervous System Dementia Syndrome that includes progressive loss of memory, shortened attention span, personality changes, reduced intellectual capacity, and motor control deficit • Alzheimer Disease (AD) - brain disorder of the middle and late adult years characterized by dementia • Huntington Disease (HD) - inherited disorder characterized by chorea (purposeless movement) progressing to severe dementia • HIV - can infect neurons and thus cause dementia

29. Central Nervous System Seizure Disorders Seizure sudden burst of abnormal neuron activity that results in temporary changes in brain function Epilepsy many forms, all characterized by recurring seizures Electroencephalogram (EEG) graphic representation of voltage changes in the brain used to evaluate brain activity

30. Central Nervous System Spinal cord Structure • outer part is composed of white matter made up of many bundles of axons called tracts • interior composed of gray matter made up mainly of neuron dendrites and cell bodies Function • center for all spinal cord reflexes • sensory tracts conduct impulses to the brain • motor tracts conduct impulses from the brain

32. Central Nervous System Coverings and Fluid Spaces of the CNS Coverings • Cranial bones and vertebrae • Cerebral and spinal meninges outermost > innermost: the dura mater, arachnoid mater, and the pia mater Fluid spaces • subarachnoid spaces of meninges • central canal inside cord • ventricles in brain

33. Peripheral Nervous System Cranial Nerves Twelve pairs attached to undersurface of the brain Connect brain with the neck and structures in the thorax and abdomen Spinal Nerves contain dendrites of sensory neurons and axons of motor neurons conduct impulses necessary for sensations and voluntary movements

36. Peripheral Nervous System Peripheral Nerve Disorders Neuritis - nerve inflammation • Sciatica is inflammation of the sciatic nerve that innervates the legs • Neuralgia, or muscle pain, often accompanies neuritis Trigeminal neuralgia recurring episodes of stabbing pain along one or more branches of the trigeminal (5th cranial) nerve in the head Bell’s palsy paralysis of facial features resulting from damage to the facial (7th cranial) nerve Herpes zoster or ‘Shingles’ viral infection caused by chickenpox virus that has invaded the dorsal root ganglion and remained dormant until an episode of shingles produces characteristic painful plaques or vesicles

38. Autonomic Nervous System Composed of Two Divisions 1. Sympathetic Nervous System 2. Parasympathetic Nervous System General Functions • Regulates the body’s automatic or involuntary functions (cardiac, respiratory, digestive, sensory) • Motor neurons (efferent neurons) conduct impulses away from the CNS > cardiac muscle, smooth muscle, and glandular tissue • the 2 systems tend to work in opposites, and many organs are innervated by both.

39. Autonomic Nervous System Sympathetic Nervous System Structure • Originates in the spinal chord • Dendrites and cell bodies of the first neuron (the preganglionic neuron) are located in the thoracic and upper lumbar segments of the spinal cord • Axons from these neurons project to a chain of ganglia located near the spinal chord. • These axons synapse with another neuron (post-ganglionic neuron)in the ganglion. • A chain of sympathetic ganglia is in front of and at each side of the spinal column

40. Autonomic Nervous System Sympathetic Nervous System Function • serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and strong emotions (anger, fear, hate, or anxiety) • group of changes induced by sympathetic control is called the “fight-or-flight” response

41. Autonomic Nervous System Parasympathetic Nervous System Structure • Parasympathetic preganglionic neurons have dendrites and cell bodies in the medulla and the sacral segments of the spinal cord. • Parasympathetic preganglionic neurons project to ganglia located in the head and the thoracic and abdominal cavities close to their target organs • Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one target organ

42. Autonomic Nervous System Parasympathetic Nervous System Function • dominates control of many visceral effectors under normal, everyday conditions i.e: heart rate, blood pressure, respirations, digestion, urination

43. Autonomic Nervous System Autonomic Neurotransmitters Cholinergic Fibers • cholinergic substances produce acetylcholine. • All preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine Adrenergic Fibers • adrenergic substances produce norepinephrine. • All postganglionic axons of the sympathetic nervous system release norepinephrine (noradrenaline)

45. Autonomic Nervous System Autonomic Nervous System as a Whole • Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis • Many visceral effectors are doubly innervated (that is, they receive fibers from parasympathetic and sympathetic divisions) and are influenced in opposite ways by the two divisions.

46. Autonomic Nervous System Disorders of the Autonomic Nervous System Stress-induced disease - prolonged or excessive response to stress can disrupt normal functioning throughout the body • Heart disease • Digestive problems • Reduced resistance to disease Neuroblastoma • highly malignant tumor of the sympathetic nervous system • primarily affects young children