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Structure and Function of the Neurologic System

Structure and Function of the Neurologic System. Chapter 14. Overview of the Nervous System. Central nervous system (CNS) Brain and spinal cord Peripheral nervous system (PNS) Cranial nerves Spinal nerves Pathways Afferent (ascending) Efferent (descending).

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Structure and Function of the Neurologic System

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  1. Structure and Function of the Neurologic System Chapter 14

  2. Overview of the Nervous System • Central nervous system (CNS) • Brain and spinal cord • Peripheral nervous system (PNS) • Cranial nerves • Spinal nerves • Pathways • Afferent (ascending) • Efferent (descending)

  3. Overview of the Nervous System • Peripheral nervous system (PNS) • Somatic nervous system • Motor and sensory pathways regulating voluntary motor control of skeletal muscle • Autonomic nervous system • Motor and sensory pathways regulating the body’s internal environment through involuntary control of organ systems • Sympathetic • Parasympathetic

  4. Cells of the Nervous System • Neuron • Variable size and structure throughout the nervous system • Cellular constituents • Microtubules, neurofibrils, Nissl substances, and ribosomes • Some neurons like olfactory neurons continue to divide

  5. Neuron • Three components • Cell body (soma) • Located mainly in the CNS • Densely packed cell bodies in the CNS are nuclei • Densely packed cell bodies in the PNS are ganglia • Dendrites • Receptive portion of the neuron

  6. Neuron • Axons • Carry nerve impulses away from the cell body • Axon Hillock • Cone-shaped, Nissl-free area, where the axon leaves the cell body • Initial segment of the axon • Area of the axon having the lowest threshold for stimulation, so the action potentials begin at this point

  7. Neuron • Axons • Myelin • Segmented layer of lipid material • Insulating substance • Formed and maintained by the Schwann cell • Endoneurium • Delicate layer of connective tissue around each axon • Neurilemma • Thin membrane between the myelin sheath and the endoneurium

  8. Neuron • Axons • Nodes of Ranvier • Regular interruptions of the myelin sheath • Saltatory conduction • The flow of ions between segments of myelin rather than along the entire length of the axon • Divergence • Ability of branching axons to influence many neurons • Convergence • Branches of numerous neurons converging on one or a few neurons

  9. Structural Classification of Neurons • Based on the number of processes extending from the cell body • Unipolar • Pseudounipolar • Bipolar • Multipolar

  10. Functional Classification of Neurons • Sensory • Transmit impulses from sensory receptors to the CNS • Associational • Transmit impulses from neuron to neuron • Motor • Transmit impulses from the CNS to an effector organ

  11. Neuroglia

  12. Neuroglia • “Nerve glue” • Support the neurons of the CNS • Astrocytes • Oligodendroglia (oligodendrocytes) • Microglia • Ependymal cells

  13. Neuroglia

  14. Nerve Injury and Regeneration • Wallerian degeneration • Occurs distal to the cut • Swelling appears • Neurofilaments hypertrophy • Myelin sheath shrinks and disintegrates • Axon portion degenerates and disappears

  15. Nerve Injury and Regeneration • Proximal to the cut • Swelling and dispersal of the Nissl substance • Cell increases in metabolic activity, protein synthesis, and mitochondrial activity • New terminal sprouts project from the proximal segment • Process limited to myelinated axons • Generally only in the PNS • Depends on location, type of injury, the inflammatory response, and scar tissue formation

  16. Neuroglia

  17. Nerve Impulse • Neurons generate and conduct electrical and chemical impulses by selectively changing the electrical portion of their plasma membranes and influencing other nearby neurons by the release of neurotransmitters

  18. Synapses • Region between adjacent neurons is called a synapse • Impulses are transmitted across the synapse by chemical and electrical conduction • Presynaptic neurons and postsynaptic neurons • Connections between pre- and postsynaptic neurons • Axoaxonic • Axosomatic • Axodendritic • Dendrodentritic

  19. Synapses

  20. Synapses • Neurotransmitters • >30 substances • Excitatory (excitatory postsynaptic potential) • Inhibitory (inhibitory postsynaptic potential) • Synaptic boutons • Synaptic cleft • Summation • Temporal summation • Spatial summation

  21. Central Nervous System • Forebrain • Cerebral hemispheres • Midbrain • Corpora quadrigemina, tegmentum, and cerebral peduncles • Hindbrain • Cerebellum, pons, and medulla

  22. Central Nervous System • Reticular formation • Network of connected nuclei that regulate viral reflexes, such as cardiovascular and respiratory function • Together with the cerebral cortex is referred to as the reticular activating system

  23. Central Nervous System

  24. Central Nervous System • Forebrain • Telencephalon • Cerebrum • Gyri, sulci, and fissures • Gray matter and white matter • Cerebral nuclei (basal ganglia)

  25. Forebrain

  26. Forebrain

  27. Central Nervous System • Diencephalon • Epithalamus • Thalamus • Hypothalamus • Subthalamus

  28. Central Nervous System • Midbrain • Corpora quadrigemina (tectum) • Superior and inferior colliculi • Tegmentum • Red nucleus and substantia nigra • Basis pedunculi

  29. Central Nervous System • Hindbrain (metencephalon) • Cerebellum • Pons • Myelencephalon • Medulla oblongata

  30. Central Nervous System

  31. Spinal Cord • Lies within the vertebral canal and is protected by the vertebral column • Connects the brain and the body • Conducts somatic and autonomic reflexes • Provides motor pattern control centers • Modulates sensory and motor function

  32. Spinal Cord

  33. Spinal Cord

  34. Spinal Cord

  35. Reflex Arc • Receptor • Afferent (sensory) neuron • Efferent neuron • Effector

  36. Reflex Arc

  37. Upper and Lower Motor Neurons • Upper motor neurons • Efferent pathways primarily relaying information from the cerebrum to the brain stem or spinal cord • Synapse with interneurons • Lower motor neurons • Neurons having direct influence on muscles • Cell bodies originate in the gray matter of the spinal cord, but their axons extend into the PNS

  38. Neuromuscular Junction

  39. Motor Pathways • Lateral corticospinal • Corticobulbar • Basal ganglia • Vestibulospinal

  40. Sensory Pathways • Anterior spinothalamic • Lateral spinothalamic

  41. Protective Structures • Cranium • Eight bones • Frontal • Occipital • Temporal (2) • Parietal (2) • Sphenoid • Ethmoid • Galea aponeurotica

  42. Protective Structures • Meninges • Protective membranes surrounding the brain and spinal cord • Dura mater • Arachnoid • Pia mater

  43. Meninges

  44. Protective Structures • Cerebrospinal fluid (CSF) and the ventricular system • CSF is a clear, colorless fluid similar to blood plasma and interstitial fluid • 125 to 150 mL • Produced by the choroid plexuses in the lateral, third, and fourth ventricles • Reabsorbed through the arachnoid villi

  45. Protective Structures • Vertebral column • 33 vertebrae • 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal • Intervertebral disks • Nucleus pulposus

  46. Vertebral Column

  47. Vertebral Column

  48. Blood Supply to the Brain • 800 to 1000 mL per minute • CO2 is the primary regulator for CNS blood flow • Internal carotid and vertebral arteries • Arterial circle (circle of Willis)

  49. Blood Supply to the Brain

  50. Blood Supply to the Brain

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