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Nervous System

Nervous System. FUNCTIONS: Sensory input. Integration. Homeostasis. Mental activity. Control of skeletal muscles. The Nervous System. Organization of the Nervous System. Central nervous system (CNS) Brain and spinal cord Peripheral nervous system (PNS) Neurons outside the CNS

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Nervous System

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  1. Nervous System FUNCTIONS: • Sensory input. • Integration. • Homeostasis. • Mental activity. • Control of skeletal muscles.

  2. The Nervous System

  3. Organization of the Nervous System • Central nervous system (CNS) • Brain and spinal cord • Peripheral nervous system (PNS) • Neurons outside the CNS • Sensory division • Afferent fibers transmit impulses from receptors to CNS • Motor division • Efferent fibers transmit impulses from CNS to effector organs

  4. Relationship between motor and sensory fibers of the PNS and the CNS

  5. Autonomic Nervous System • Sympathetic • Fight or flight, stress • Excitatory effects elicited by norepinephrine activating beta receptors • Inhibitory effects elicited by activation of alpha receptors

  6. Parasympathetic • Rest and digest • Digestive system activated, heart rate inhibited, blood vessels dilated • Vagus nerve primarily responsible for activating parasympathetic responses

  7. Fig. 8.39

  8. Synapse Specialized site of intercellular communication. 3 Components: 1. Presynaptic terminal 2. Synaptic cleft 3. Postsynaptic membrane

  9. Functional Organization of the Nervous System

  10. The Neuron

  11. Neuroglia

  12. Neuroglia • Accessory cells of the nervous system • Astrocytes • Support tissue in the CNS form blood-brain barrier • Ependymal • Produce and move cerebral spinal fluid • Microglia • Remove cell debris and bacteria from CNS • Oligodendricytes and Schwann cells • Provide insulation around axons of CNS and PNS neurons

  13. Myelinated vs. Unmyelinated Axons

  14. Membrane Potentials • Nervous system functions by establishing concentration gradients and electrical potentials across the membranes • The resting membrane potential of a neuron is negative and is said to be polarized • These gradients are maintained by the sodium potassium pump

  15. Concentration Gradients and Nerve Cell Function

  16. Action Potentials • Muscle and nerve cells are exciteable • When a muscle or nerve cell is stimulated Na+ channels open and Na+ rushes into the cell • This causes a local potential • This local potential may not result in action potential • Doesn’t cross the threshold

  17. If the stimulus is sufficient to cause the local potential to cross the threshold an action potential results • The action potential is the complete depolarization of the cell • The action potential is an all-or-nothing event • If the local potential meets threshold, the cell totally depolarizes and the action potential results • If the potential does not meet threshold, no action potential results

  18. Fig. 8.9

  19. Fig. 8.10

  20. Action Potential Propogation • Unmyelinated neurons propogate signals more slowly than myelinated neurons • Myelination acts as an insulator • Electrical signal will jump from node of Ranvier to node of Ranvier • This is called saltatory conduction • Requires less energy than direct propogation

  21. Propagation of the Action Potential

  22. Synapse • Electrical --rare • Chemical --communication occurs in one direction: presynaptic membrane to postsynaptic membrane --action potential is not always propagated.

  23. Synapse Synapses may occur: • neuron to neuron • neuron to another type of cell (neuroeffector) --neuromuscular junction --neuroglandular junction

  24. The Synapse Fig. 8.13

  25. Neurotransmitters --packaged in synaptic vesicles. Nerve endings of the ANS secrete: • Acetylcholine (ACh)--Cholinergic neuron • Parasympathetic effector • Norepinephrine (NE)--Adrenergic neuron • Sympathetic effector

  26. Neurotransmitters diffuse across the synaptic cleft and bind to receptor on the post-synaptic membrane • This can cause membrane channels (Na+, K+, or Cl-) to open or close depending on the neurotransmitter • If stimulatory, Na+ channels will open • If inhibitory, K+ or Cl- channels will open • Cell becomes more negative, hyperpolarized

  27. Receptors 2 types of cholinergic receptors: • Nicotinic • Preganglionic sympathetic and parasympathetic • Muscarinic • parasympathetic 2 types of adrenergic receptors: • Alpha • Generally inhibitory • Beta • Generally excitatory

  28. Autonomic Reflex Arc 1. Receptor 2. Sensory neuron 3. Association neuron 4. Autonomic motor neuron 5. Visceral effector

  29. Reflex Arc

  30. Knee Jerk Reflex

  31. Converging Circuit

  32. Adult: Brainstem --medulla oblongata --pons --midbrain Diencephalon --thalamus --hypothalamus --epithalamus Cerebrum Cerebellum Central Nervous System

  33. Brainstem • Medulla oblongata • Inferior portion • Regulation of heart rate, venoconstriction, ventilation, swallowing, , etc.. • Pons • Superior to medulla • Bridge between cerebrum and cerebellum • Midbrain • Audio and visual processing

  34. Cerebellum • Integrates motor signals from cerebral cortex with feedback from PNS • Proprioception • Learning tasks

  35. Dienchephalon • Thalamus • Sensory input from PNS passes through thalamus (relay station) • Epithalamus • Pineal gland – sleep cycle, puberty • Hypothalamus • Master gland • Attached to pituitary by infundibulum • Controls much of homeostasis by stimulating or inhibiting pituitary

  36. Cerebrum

  37. Brain Protection: • cranial bones • cranial meninges • cerebrospinal fluid • neuroglia (astrocytes)

  38. The Brain

  39. CEREBRUM • Largest part of the brain; thinking part • Markings: Gyrus (gyri)-- wrinkle, raised area Fissure(s)-- deep, wide groove(s) Sulcus (sulci)-- shallow groove(s)

  40. CEREBRUM Lobes: 1) Frontal 2) Parietal 3) Temporal 4) Insular 5) Occipital

  41. CEREBRUM Displays lateralization: • left hemisphere language; math/science; reason • right hemisphere music/art; spatial relations; insight/imagination

  42. CEREBRUM • sensory areas • motor areas • association areas

  43. white matter (myelin) dorsal column ventral column lateral column gray matter (non-myelin) posterior horn ventral horn lateral horn Spinal Cord-- Composition

  44. Spinal Cord-- White Matter • myelinated axons that travel along the spinal cord. Ascending--up cord to higher levels Descending-- down cord from brain Across the cord

  45. Spinal Cord • Dorsal roots (sensory) • Ventral roots (motor) combine to form spinal nerve. • Dorsal Root Ganglion

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