Chapter 7 – Nervous system

1. Chapter 7 – Nervous system Ms. Harborth Anatomy and physiology

2. Structural classification • Central nervous system (CNS) – consists of the brain and spinal cord. Command center • Peripheral nervous system (PNS) – part of body outside of CNS. • Spinal nerves – carry impulses to and from spinal cord • Cranial nerves – carry impulses to and from the brain

3. PNS • Sensory (afferent) – carries impulses FROM sensory organs TO the brain • Motor (efferent) – carries impulses FROM the brain TO effector organs, muscles, and glands. • Somatic nervous system – control skeletal muscles • Autonomic nervous system – regulates automatic events (smooth and cardiac muscle) • Sympathetic • Parasympathetic

4. Nervous tissue • Supporting cells of CNS “neuroglia” • Astrocytes – barrier between neurons and capillaries • Microglia – phagocytes that “clean” • Ependymal cells – beat cilia to circulate cerebrospinal fluid • Oligodendrocytes – form myelin sheaths Supporting cells of PNS: • Schwann cells – form myelin sheaths • Satellite cells – protective, cushioning cells • Neurons • Cell body (Nissl substance & neurofibrils) • Processes (fibers) • Myelin sheath, Schwann cells (PNS), nodes of Ranvier • Dendrites (toward cell body) • Axons (away from cell body) • Axonal terminals, neurotransmitters, synaptic cleft, synapse

5. Astrocyte Ependymal cells Oligodendrocyte Microglial cell

7. Multiple sclerosis • Immune system gradually destroys myelin sheaths, converting to scleroses (hardened processes)

8. Vocab • Nuclei – clusters of cell bodies in the CNS • Ganglia – small collections of cell bodies found in the PNS. • Tracts – bundles of nerve fibers in the CNS • Nerves – bundles of nerve fibers in the PNS • Whitematter – myelinated fibers in the CNS • Graymatter – unmyelinated fibers and cell bodies in the CNS

9. Classification of neurons • Functional (direction of nerve impulse) • Sensory (afferent) neurons – neurons carrying impulses from sensory receptors to the CNS. Cell bodies are found in ganglion outside of CNS. • Cutaneous sense organs, proprioceptors • Motor (efferent) neurons – neurons carrying impulses to viscera and/or muscles and glands. Cell bodies are in the CNS. • Association neurons (interneurons) – connect motor and sensory neurons in neural pathways.

10. Classification of neurons • Structural • Multipolar neuron – several processes extending from cell body. • All motor and association neurons • Bipolar neuron – axon and dendrite extend from cell body • Rare. Found in some special sense organs. • Unipolar neuron– short, single process that usually divides into proximal and distal fibers. Axon conducts nerve impulses both toward AND away from the cell body. • Sensory neurons found in PNS ganglia

11. Neuron physiology • Nerve impulse – • Irritability • 1. Inactive neuron is polarized (more negative inside) • 2. Stimulus excites neuron, permeability increases • 3. Depolarization Action Potential • 4. Repolarization • Saltatory conduction – occurs on myelinated nerves FASTER • Cold and continuous pressure hinder conduction • Conductivity • When action potential reaches axonal endings, tiny vesicles fuse with axonal membranes, rupture, and releases neurotransmitters which start impulse in next neuron • Electrochemical event • animation

12. Neuron physiology • Reflex Arc • Autonomic reflexes • Regulate activity of smooth muscles, heart, and glands. • Ex: salivary reflex and pupillary reflex. • Somatic reflexes • Reflexes that stimulate skeletal muscles • Minimum of five elements: • Sensory receptor • Afferent neuron • Integration center • Efferent neuron • Effector organ

13. Central Nervous System • Embryonic development: • Neural tube develops • 4th week – anterior end of neural tube expands and brain formation begins. Central canal of neural tube becomes 4 ventricles

14. Functional Anatomy of the Brain • Cerebral Hemispheres • Diencephalon • Cerebellum • Brain Stem

15. Cerebral Hemispheres • Gyri: elevated ridges of tissue • Sulci: shallow grooves • Fissures: deeper grooves which separate large regions of the brain • Hemispheres separated by longitudinal fissure • Lobes are named for cranial bones that surrounding them

16. Cerebral Hemisphere • Parietal lobe: posterior to central sulcus • Somatic sensory area – localizes and interprets impulses from sensory receptors. Sensory pathways cross (left -> right, right -> left) • Occipital lobe: visual area • Temporal lobe: auditory and olfactory area • Frontal lobe: Higher intellectual reasoning in anterior part • Primary motor area - Axons of motor neurons form pyramidal (corticospinal) tract which descends to spinal cord. Pathways are crossed. • Broca’s area – speech. Only found in one hemisphere • Speech area – junction of temporal, parietal, and occipital lobes. Sound out words. One hemisphere. • Gray matter (cerebral cortex): cell bodies of neurons • White matter: fiber tracts carrying impulses to or from the cortex • Corpus callosum: large fiber tract that connects cerebral hemispheres. Allows halves to communicate with one another. • Basal nuclei: “islands” of gray matter buried in white matter. Modify instructions sent to muscles.

20. Diencephalon • Thalamus • Encloses third ventricle • Relay station for sensory impulses • Hypothalamus • Regulation of temperature, water balance and metabolism. Regulates pituitary • Limbic system – “emotional-visceral brain”. Thirst, appetite, sex, pain, pleasure centers. • Mammillary bodies – reflex involved in olfaction • Epithalamus • Pineal body • Choroid plexus of third ventricle

21. Diencephalon

22. Brain stem • Midbrain • Cerebral aqueduct – canal that connects third ventricle of diencphalon to fourth ventricle below • Cerebral peduncles – convey ascending and descending impulses • Corpora quadrigemina– reflex centers for vision and hearing • Pons • Mostly fiber tracts, but does have some nuclei involved in controlling breathing • Medulla oblongata • Merges into spinal cord. • Regulate vital visceral activities. Controls heart rate, blood pressure, breathing, swallowing, and vomiting • Reticular formation • Neurons involved in motor control of the visceral organs. RAS (reticular activating system) plays a role in consciousness and awake/sleep cycles. Damage to this area results in coma.

23. Brain Stem

24. Cerebellum • Two hemispheres • Timing for skeletal muscle activity and controls balance/equilibrium • Takes info from eyes, ears and muscles to coordinate movements in a smooth fashion

25. meninges • Three connective tissue membranes covering and protecting brain and spinal cord • Dura mater – outermost layer. Double-layered, forms periosteum and meningeal layer. • Arachnoid mater – span subarachnoid space to attach to innermost membrane • Subarachnoid space filled with cerebrospinal fluid. Arachnoid villi protrude through dura mater. Dural sinuses absorb fluid into blood through arachnoid villi. • Pia mater – delicate layer clings tightly to surface of brain and spinal cord. • Meningitis – inflammation of meninges

27. Cerebrospinal fluid (CSF) • similar to blood plasma. • continually formed from blood by choroid plexuses • continually moving. • Blood-brain barrier – any changes in fluid around brain could be detrimental. Barrier composed of the LEAST permeable capillaries in whole body. Water, glucose and essential amino acids can pass through.

28. Spinal Cord • 17 inches long, thickness of a thumb • Extends from foramen magnum to 1st or 2nd lumbar vertebrae, right below ribs • Caudaequina

30. Peripheral Nervous System • Endoneurium • Perineurium • Fascicles • Epineurium • Nerves are classified by which direction they transmit • Mixed nerves • Afferent (sensory) • Efferent (motor)

31. Cranial nerves • 12 pairs (table 7.1) • Serve head and neck (except vagus nerves – extend to thoracic and abdominal cavities) • I. Olfactory • II. Optic • III. Oculomotor • IV. Trochlear • V. Trigeminal • VI. Abducens • VII. Facial • VIII. Vestibulochochlear • IX. Glossopharyngeal • X. Vagus • XI. Accessory • XII. Hypoglossal

32. Spinal Nerves/ Nerve Plexuses • 31 pairs of spinal nerves formed by combo of ventral and dorsal roots of spinal cord. Named for region of spinal cord from which they arise. • Each spinal nerve divides into dorsal and ventral rami • Dorsal rami serve skin and muscles of posterior body trunk • Ventral rami of T1 – T12 form intercostal nerves • Ventral rami of other spinal nerves form 4 plexuses (Table 7.2)

33. Autonomic nervous system • Motor subdivisions that control automatic activities (cardiac and smooth muscle, and glands) • Sympathetic and parasympathetic • Sympathetic – mobilizes body during extreme situation (fear, exercise, rage, etc.) • Parasympathetic – allows us to “unwind” and conserve energy