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The Nervous System

The Nervous System. Ch. 12-17. The Nervous System Introduction. Composed of Brain Spinal Cord Nerves 2 Major Subdivisions CNS (Central Nervous System) Brain, Spinal Cord PNS (Peripheral Nervous System) Cranial and Spinal Nerves 2 Major Subdivisions Afferent  incoming pathways

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The Nervous System

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  1. The Nervous System Ch. 12-17

  2. The Nervous System Introduction • Composed of • Brain • Spinal Cord • Nerves • 2 Major Subdivisions • CNS (Central Nervous System) • Brain, Spinal Cord • PNS (Peripheral Nervous System) • Cranial and Spinal Nerves • 2 Major Subdivisions • Afferent incoming pathways • Efferent  Outgoing pathways

  3. Neurons • Remember neuron structure: • The Cell Body or Soma • Contains a nucleus surrounded by cytoplasm along with all other organelles found within a cell • The Dendrites • Extensions from Cell Body/Soma • Receives information • The Axon • Single, long extension from Cell Body/Soma • Branch out into telodendria and end at synaptic/axon terminals

  4. Structure of a Neuron

  5. The Synapse • Each synaptic/axon terminal is part of a synapse • Site where the neuron communicates with another cell • Presynaptic Cell: sends the message (usually a neuron) • Postsynaptic Cell: receives the message (any cell type) • After a series of electrical signals is transmitted through the neuron, the axon/synaptic terminals release chemicals or neurotransmitters to the dendrite of another cell to continue the message

  6. Synaptic Cleft Synapse

  7. Neuron Video • http://www.youtube.com/watch?v=r71RoIkftd4

  8. Neuroglia • Higher quantity and variation in CNS than PNS • Central Nervous System • Ependymal Cells • Astrocytes • Microglia • Oligodendrocytes • Peripheral Nervous System • Schwann Cells • Satellite Cells

  9. CNS Neuroglia Ependymal Cells Microglia Removes cell debris, wastes, and pathogens by phagocytosis • Line ventricles in the brain and spinal cord • Aid in producing, circulating and monitoring of cerebrospinal fluid

  10. CNS Neuroglia Astrocytes Oligodendrocytes Myelinate axons Provide structural framework • Provide structural support • Regulate ion, nutrient, and dissolved gas concentrations • Absorb and recycle neurotransmitters • Form scar tissue after injury

  11. PNS Neuroglia Schwann Cells Satellite Cells Surround neuron cell bodies Regulate gas, nutrient, and neurontransmitter levels • Surround all axons • Responsible for myelination • Participate in repair process after injury

  12. Synaptic Activity • Messages move from 1 location to another in the form of action potentials along neurons • Also known as nerve impulses • Messages move across the synapse • Can be electrical • Can be chemical (use of neurotransmitter)

  13. Electrical Synapses • Presynaptic and postsynaptic cell membranes are locked together • Local electrical currents and directly transferred from cell to cell = • very rapid electrical impulse • Efficient action potential transfer from cell to cell

  14. Chemical Synapses • Presynaptic and postsynaptic cell membranes are NOT locked together • Message not guaranteed to be transferred to the next cell  dependent on the amount of neurotransmitters released • Different neurotransmitters: • Acetocholyne: found at neuromuscular junction • Norepinephrine: excitatory effect, adrenaline • Dopamine: Parkinson’s disease (rigidity of muscles) • Serotonin: attention, emotion, responsible for depression • GABA: reduce anxiety

  15. Spinal Cord and Spinal Nerves Chapter 13

  16. Spinal Cord Anatomy • Posterior/Anterior/Lateral Horn of Gray matter • Anterior Median Fissure • Posterior Median Sulcus • Spinal Nerve (Posterior/Anterior Roots) • Spinal Ganglion

  17. Spinal Cord Anatomy • Adult – 18 inches in length • Only reaches down to L1-L2 • Spinal Meninges: specialized membranes that surround the spinal cord • Dura Mater • Arachnoid • Pia Mater • Bacterial or vial infections of the Meninges  Meningitis

  18. PiaMater Meninges • Meshwork of connective tissue • Dense area of vessels Dura Mater Arachnoid Filled with cerebrospinal fluid (SPF)—shock absorber Spinal tap • Tough, fibrous outermost layer • Collagen fibers • Covered with blood vessels and adipose tissue • Epidural Space

  19. Nerve Plexuses • Complex interwoven network of nerves  Plexus. • Cervical Plexus • C1-C5 (muscles of neck, thoracic cavity) • Brachial Plexus • C5-T1 (muscles of pectoral girdle and upper limb) • Lumbar Plexus • T12-L4 • Sacral Plexus • L4-S4

  20. Day 2

  21. Refluxes Chapter 13

  22. Reflexes • Rapid automatic responses to a specific stimuli made by a receptor • Preserve homeostasis • Rapid adjustments • The Reflex Arc: wiring of a single reflex • Beings at the receptor • Ends at peripheral effector (ex: muscle fiber)

  23. Reflexes • Sensory Receptors • Proprioreceptors: provide info about body position and muscle control • Vestibular Receptors: provide a sense of equilibrium • Cutaneous Receptors: touch, pressure, heat and cold • Photoreceptors: respond to light • Chemoreceptors: respond to taste • Nocioreceptors: pain receptors

  24. Reflexes • Arrival of a stimulus and activation of receptor (pain) • Activation of a Sensory Neuron (action potential along axons of neurons  spinal cord) • Information Processing (neurotransmitter released and sensation related to brain) • Activation of Motor Neuron (axons carry action potential back towards the origin of pain) • Response of Peripheral Effector (release of neurotransmitter to skeletal muscle fiber contraction pulls hand away from pain) • http://www.youtube.com/watch?v=wLrhYzdbbpE

  25. Reflexes • Receptor Density • More dense the receptors = more “sensitive” the area • Upon stimulation… • Phasic: receptors respond with an initial burst of action potentials and rapidly decrease, even though stimulus continues • Tonic: receptors firing at a constant rate as long as the stimulus is applied • Lab on reflexes

  26. The Brain and Cranial Nerves Chapter 14

  27. Human Brain • Contains 98% of neural tissue • Weighs about 3 lbs • Covered by a neural cortex (superficial layer of gray matter • Main Areas • Cerebrum • Cerebellum • Diencephalon • Brain Stem

  28. Cerebrum • Largest portion of the brain • 2 hemispheres • Controls thoughts, sensations, intellect, memory, and complex movements • Lobes (correspond with cranial bones) • Frontal • Parietal • Occipital • Temporal

  29. Cerebrum • Landmarks • Longitudinal fissure (separates the 2 hemispheres) • Central Sulcus (separates the frontal from parietal lobes) • Lateral Sulcus (separates the frontal from temporal) • Parieto-occipital sulcus (separates the parietal from the occipital) • White Matter • Dense region of axons

  30. Cerebrum • Motor and Sensory Areas • Frontal Lobe = Voluntary control of skeletal muscles • Parietal Lobe = conscious perception of touch, pressure, vibration, pain, temperature, and taste • Occipital Lobe = conscious perception of visual stimuli • Temporal Lobe = conscious perception of auditory and olfactory stimuli, speech • All Lobes = Integration and processing of sensory data and motor activities

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  32. Cerebellum • 2nd Largest portion of the brain • 2 hemispheres • 2 Primary Functions • Adjusting Postural muscles of the body • Programming and fine-tuning movements

  33. Other Major Regions of the Brain • Diencephalon: • Thalamus: relay and processing centers for sensory information • Hypothalamus: emotions, autonomic function, hormone production, body temp regulation

  34. Other Major Regions of the Brain • Brain Stem :link between cerebrum and brain stem • Mesencephalon: aka “midbrain”; visual and auditory information • Pons: sleep & respiration • Medulla Oblongata: regulate heart rate, blood pressure, digestion

  35. Ventricles of the Brain • Chambers filled with cerebrospinal fluid (CSF) • Lateral Ventricles (2 in each hemisphere of cerebrum) • Third Ventricle • Interventricular Foramen (connection between the lateral ventricles and third ventricle) • Cerebral Aqueduct • (connection between the third ventricle and fourth ventricle) • Fourth Ventricle • Narrows and opens into the spinal cord

  36. Protection and Support • Protected by • Bones of cranium: mechanical protection (car) • Cranial Meninges: anchor (seat belt) • Dura Mater: outer layer • Arachnoid: middle layer • Pia Mater: surface of brain • Cerebrospinal Fluid: cushions against shocks/jolts (air bag)

  37. Cerebrospinal Fluid (CSF) • Function: • Cushion • Support • Transport nutrients/chemical messengers/waste products • Formation: • Choroid plexus (in all ventricles): specialized cells that produce CSF

  38. Blood Supply to the Brain • Brain requires a tremendous amount of blood • Receives 15-20% of blood pumped by heart • Interruption  unconsciousness/irreversible brain damage • Dependent on constant supply of oxygen & glucose • Receives blood through arteries

  39. Hydrocephalus • Condition with infants • Prior to fusion of cranial bones • Excess CSF (due to blockage or constriction of the meninges)causes the skull to enlarge • Infants suffer some degree of mental retardation

  40. Cranial Nerves • Part of the PNS • Connected to the brain and branch out • 12 of them • Attaches the brain near a sensory or motor neuron • 2 of each

  41. Cranial Nerves • Olfactory Nerves smell • Optic Nerves  Vision • Oculomotor Nerves  Eye Movements • Trochlear Nerves  Eye movements • Trigeminal Nerves  Sensory/Motor to face • Abducens Nerves  Motor eye movements • Facial Nerves  Sensory/Motor to face • Vestibulocochlear Nerves  balance/equilibrium and hearing • Glossopharyngeal Nerves  Sensory/Motor to head and neck • Vagus Nerves  Sensory/Motor to thorax and abdomen • Accessory Nerves Motor to muscles of neck and upper back • Hypoglossal Nerves  Motor for tongue movements

  42. “Oh, once one takes the anatomy final, very good vacations are heavenly”

  43. Sleep

  44. Conscious/Unconscious • Conscious = state of awareness of external stimuli • Unconscious = number of conditions, deep, unresponsive state  drifting into sleep

  45. Levels of Sleep • 2 levels, patterns of brain activity • Slow wave sleep • Deep sleep/non-REM sleep • Entire body relaxed • Cerebral cortex activity at minimum • Heart rate, blood pressure, respiratory rate, energy utilization decline by 30% • Rapid Eye Movement (REM sleep) • Active dreaming • Changes in blood pressure/respiratory rate • Muscle tone decreases • Neurons controlling eye muscles stop regulation = eyes move rapidly as dream events unfold

  46. Sleeping Cycles • REM and Deep sleep alternate throughout the night • Starts with Deep sleep = 1.5 hours • REM last on average 5 minutes • Determined by an EEG • Electroencephalogram: graphic record of the electrical activities of the brain

  47. Alzheimer’s Disease • Loss of cerebral functions • Symptoms appear around 50-60 years old • Can affect younger individuals but is rare • Currently affects 2 million ppl in USA • 100,000 deaths each year • Chromosome 14, 19, and 21 • Majority of Downs Syndrome develop it (21)

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