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Nervous System

Nervous System. Notes. Functions of the Nervous System. Sensory input- gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration to process and interpret sensory input and decide if action is needed Motor Output

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Nervous System

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  1. Nervous System Notes

  2. Functions of the Nervous System • Sensory input- gathering information • To monitor changes occurring inside and outside the body • Changes = stimuli Integration to process and interpret sensory input and decide if action is needed Motor Output A response to integrated stimuli The response activates muscles or glands

  3. Functions of the nervous system

  4. Structural Classification of the Nervous System • Central Nervous System (CNS) • Brain • Spinal Cord Peripheral Nervous System (PNS) Nerves outside the brain and spinal cord spinal nerves cranial nerves

  5. Functional Classification of the PNS • Sensory (afferent) division • Nerve fibers that carry information to the CNS Motor (efferent) division Nerve fibers that carry impulses away from the CNS 2 subdivisions: Somatic Nervous system = voluntary Autonomic Nervous system = involuntary

  6. Organization of the Nervous System

  7. Nervous Tissue: support cells • Support cells in the CNS are grouped together as “neuroglia” • Function: to support, insulate, and protect neurons.

  8. Support Cells • Astrocytes: • Abundant, star-shaped cells • Brace neurons • Form barrier between capillaries and neurons • Control the chemical environment of the brain Microglia: Spiderlike phagocytes Dispose of debris

  9. Astrocytes

  10. Microglia

  11. Support Cells • Ependymal Cells • Line cavities of the brain and spinal cord • Circulate cerebrospinal fluid Oligodendrocytes Wrap around nerve fibers in the CNS Produce myelin sheaths Satellite Cells: protect neuron cell bodies Schwann Cells: form myelin sheath in the Peripheral nervous system

  12. Ependymal Cells

  13. Oligodendrocyte

  14. Satellite and Schwann Cells

  15. Neurons • Neurons- nerve cells • Cells specialized to transmit messages • Major regions of neurons • Cell body- nucleus and metabolic center of the cell • Composed of Nissl substance (specialized rough e.r.) • Neurofibrils-intermediate cytoskeleton, maintains cell shape. • Processes- fibers that extend from the cell body • Dendrites- conduct impulses toward the cell body • Axons-conduct impulses away from the cell body. Color page: Functional Classification of Neurons

  16. Neuron

  17. Neurons • Axons end in axonal terminals • Axonal terminals contain vesicles with neurotransmitters • Axonal terminals are separated from the next neuron by a gap • Synaptic cleft- gap between adjacent neurons • Synapse- junction between nerves. • Myelin Sheath- whitish, fatty material covering axons • Schwann Cells produce myelin sheaths in jelly roll-like fashion • Nodes of Ranvier- gaps in myelin sheath along the axon.

  18. Neuron Cell Body Location • Most neuron cell bodies are found in the CNS • Gray matter- cell bodies and unmyelinated fibers • Nuclei- clusters of cell bodies within the white matter of the CNS • Ganglia- collections of cell bodies outside the CNS • Sensory(afferent) neurons • Carry impulses from the sensory receptors to CNS • Cutaneous sense organs • Proprioceptors-detect stretch or tension • Motor (efferent) neurons • Carry impulses from CNS to viscera, muscles or glands. • Interneurons (associated neurons) • Found in neural pathways in the CNS • Connect sensory and motor neurons

  19. Neuron Classification • Multipolar Neurons- many extensions from the cell body • Bipolar neurons- one axon and one dendrite • Unipolar neurons- have a short single process leaving the cell body

  20. Neuron Classification

  21. Functional Properties of Neurons • Irritability • Ability to respond to stimuli • Conductivity • Ability to transmit an impulse

  22. Nerve Impulses • Resting neuron • The plasma membrane at rest is polarized • Fewer positive ions are inside the cell than outside the cell • Depolarization • A stimulus deploarizes the neuron’s membrane • A depolarized membrane allows sodium to flow inside the membrane • The exchange of ions initiates an action potential in the neuron

  23. Nerve Impulses • Action Potential • If the action potential (nerve impulse) starts, it is propagated over the entire axon • Impulses travel faster when fibers have a myelin sheath • Repolarization • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane • The sodium-potassium pump, using ATP, restores the original configuration

  24. Nerve Impulses

  25. Transmission of a Signal at Synapses • Impulses are able to cross the synapse to another nerve. • Neurotransmitter is released fro a nerve’s axon terminal • The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter • An action potential is started in the dendrite

  26. Axonterminal Actionpotentialarrives Axon oftransmittingneuron Vesicles Synapticcleft Receivingneuron Synapse Transmitting neuron Neurotrans-mitter bindsto receptoron receivingneuron’smembrane Vesiclefuses withplasmamembrane Neurotrans-mitter is re-leased intosynaptic cleft Neurotransmittermolecules Synaptic cleft Ion channels Receiving neuron Neurotransmitterbroken downand released Neurotransmitter Receptor Na+ Na+ Ion channel opens Ion channel closes Transmission of Signal

  27. The Reflex Arc • Reflex-rapid, predictable and involuntary response to a stimulus • Occurs over pathways called reflex arcs • Reflex arc- direct route from a sensory neuron, to an interneuron to an effector

  28. Types of Reflexes and Regulation • Somatic Reflexes • Activation of skeletal muscles • EXAMPLE: when you move your hand away from hot stove. • Autonomic Reflexes • Smooth muscle regulation • Heart and blood pressure regulation • Regulation of glands • Digestive system regulation • Patellar or knee jerk, 2-neuron reflex arc

  29. CENTRAL NERVOUS SYSTEM • CNS develops from the embryonic neural tube • The opening of the neural tube becomes the ventricles • Four chambers within the brain • Filled with cerebrospinal fluid

  30. Regions of the Brain • Cerebral hemispheres (Cerebrum) • Diencephalon • Brain Stem • Cerbellum

  31. Cerebrum • Fissures (deep grooves) divide the cerebrum into lobes • Surface lobes of the cerebrum • Frontal Lobe • Parietal Lobe • Occipital Lobe • Temporal Lobe

  32. Cerebrum • Specialized areas of the cerebrum • Primary somatic sensory area • Receives impulses from the body’s sensory receptors • Located in the parietal lobe • Primary motor area • Sends impulses to skeletal muscles • Located in frontal lobe • Broca’s area • Involved in our ability to speak

  33. Cerebrum • Cerebral areas involves in special senses • Gustatory area (Taste) • Visual area • Auditory area • Olfactory area

  34. Cerebrum • Interpretation areas of the cerebrum • Speech/language region • Language comprehension region • General interpretation area • Layers of the cerebrum • Gray matter- outer layer in the cerebral cortex composed mostly of neuron cell bodies • White matter- fiber tracts deep to the gray matter • Corpus callosum connects hemispheres • Basal nuclei= islands of gray matter buried within the white matter

  35. Diencephalon • Sits on top of the brain stem • Enclosed by the cerebral hemispheres • Made of 3 parts • Thalamus • Hypothalamus • Epithalamus

  36. Thalamus • Surrounds the third ventricle • The relay station for sensory impulses • Transfers impulses to the correct part of the cortex for localization and interpretation

  37. Hypothalamus • Under the thalamus • Important autonomic nervous system center • Helps regulate body temperature • Controls water balance • Regulates metabolism • An important part of the limbic system (emotions) • The pituitary gland is attached to the hypothalamus

  38. Epithalamus • Forms the roof of the third ventricle • Houses the pineal body (an endocrine gland) • Includes the choroid plexus=forms cerebrospinal fluid

  39. Brain Stem • Attaches to the spinal cord • Parts of the brain stem • Midbrain • Pons • Medulla oblongata

  40. Brainstem • Midbrain • Mostly composed of tracts of nerve fibers • Has two bulging fiber tracts—cerebral peduncles • Has four rounded protrusions—corpora quadrigemina • Reflex centers for vision and hearing

  41. Brainstem • Pons • The bulging center part of the brain stem • Mostly composed of fiber tracts • Includes nuclei involved in the control of breathing • Medulla Oblongata • The lowest part of the brain stem • Merges into the spinal cord • Includes important fiber tracts • Contains important control centers • Heart rate control, blood pressure regulation, breathing, swallowing, vomiting

  42. Reticular Formation • Diffuse mass of gray matter along the brain stem • Involved in motor control of visceral organs • Reticular activiating system plays a role in awake/sleep cycles and consciousness

  43. Cerebellum • 2 hemispheres with convoluted surfaces • Provides involuntary coordination of body movements

  44. Protection of the Central Nervous System • Scalp and skin • Skull and vertebral column • Meninges • Cerebrospinal fluid (CSF) • Blood-brain barrier

  45. Meninges • Dura mater • Double-layered external covering • Periosteum-atached to inner surface of the skull • Meningeal layer-outer covering of the brain Folds inward in several areas • Arachnoid layer • Middle layer • Web-like • Pia mater • Internal layer • Clings to the surface of the brain

  46. Cerebrospinal Fluid (CSF) • Similar to blood plasma composition • Formed by the choroid plexus • Forms a watery cushion to protect the brain • Circulated in arachnoid space, ventricles and central canal of the spinal cord • HYDROCEPHALUS-condition where CSF accumulates and exerts pressure on the brain if not allowed to drain

  47. Blood-Brain Barrier • Includes the least permeable capillaries of the body • Excludes many potentially harmful substances • Useless as a barrier against some substances • Fats and fat soluble molecules • Respiratory gases • Alcohol • Nicotine • Anesthesia

  48. Traumatic Brain Injuries • Concussion • Slight brain injury • No permanent brain damage • Contusion • Nervous tissue destruction occurs • Nervous tissue does not regenerate • Cerebral edema • Swelling from the inflammatory response • May compress and kill brain tissue

  49. Cerebrovascular Accident (CVA) • Commonly called a stroke • The result of a ruptured blood vessel supplying a region of the brain • Brain tissue supplied with oxygen from that blood source dies • Loss of some functions or death may result

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