The Nervous System

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The Nervous System

• Kenneth P. Hughes, BS, EMT-P

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Objectives

• Function of the Nervous System
• Efferent Afferent Divisions of the PNS
• Anatomy of the Neuron
• Polarization, Depolarization, Repolarization
• Action Potentials Neurotransmitters
• Receptor Sites

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Nervous System Function

• Involuntary activity
• Voluntary activity
• Sensory input

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Review

• Central nervous system
• Brain Spinal cord
• 12 cranial nerves
• Peripheral nervous system
• Nerves and ganglion outside the CNS

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• Cranial Nerves
• Olfactory (S) Nose to brain
• Optic (S) Eye to brain
• Occulomotor (M) Brain to eye muscles
• Trochlear (M) Brain to external eye muscles
• Trigeminal (B) Skin, mucous membranes, teeth to
  brain / Brain to masseter
• Abducens (M) Brain to external eye muscles
• Facial (B) Taste buds to brain / brain to face
• Acoustic (S) Ear to brain
• Glossopharyngeal (B) Throat to brain / brain to
  throat and salivary glands
• Vagus (B) Throat/thoracic organs abdominal
  organs to brain / Vice versa
• Spinal Accessory (M) From brain to shoulder and
  neck
• Hypoglossal (M) From brain to tongue

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Divisions of the PNS

• Afferent
• Sensory organs to the CNS to the brain
• Efferent
• Transmit action potential from CNS to effectors
  organs
• Somatic CNS to skeletal muscle
• Autonomic CNS to glands, smooth muscle
• Sympathetic
• Parasympathetic

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Meet the Neuron

• Cell body (Soma)
• Dendrites branches off of the soma
• Axons Extend from soma to CNS
• Terminals

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The Neuro-Receptor Junction

• Terminal bulbs
• Synapse
• Chemical connections
• Neurotransmitters
• Neurohormones
• Gap junctions
• Mitochondria

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CELL MEMBRANE

• Fluid bi-layer of lipids
• Membrane bound protein
• Net positive charge outside
• Net negative charge inside
• Membrane potential

S-EMTPR-1-1-6
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Propagation of Action Potential

• An action potential at any point on the cell
  membrane acts as a stimulus to adjacent regions
  of the cell membrane
• The excitation process, once started, is spread
  along the length of the cell and on to the next
• A stimulus strong enough to cause a cell to reach
  threshold and depolarize (action potential)
  starts a cascade of depolarization from one cell
  to another

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Types of Synapses

• Chemical
• A neurotransmitter is dumped into the synaptic
  cleft that will stimulate / inhibit / communicate
  with the receptor organ or membrane of the
  postsynaptic membrane
• Electrical
• Gap Junctions

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Release of Neurotransmitters

• Calcium is released when the membrane potential
  changes
• Elevated calcium concentrations in the
  presynaptic membrane area
• Vesicles then fuse with pre-synaptic membrane
• Neurotransmitters are released

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REVIEW

• (http//www.brainexplorer.org/neurological_control
  /Neurological_Neurotransmission.shtml)

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Return of Neurotransmitters

• Diffusion out of the cleft into surrounding
  fluids
• Enzyme destruction
• Acetylcholine Broken down by cholinesterase
• Active transport back into the terminal bulb

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Neurotransmitters Neurohormones

• Catecholamines (sympathomimetics)
• AKA Adrenergic
• Acetylcholine (Parasympathomimetics)
• AKA Cholinergic
• Both inhibitory and excitatory effects can be
  present

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Sliding Filament Theory

• Impulse travels along a motor nerve
• Acetylcholine is released at neuromuscular
  junction
• Action potential travels along membrane
• Calcium is released
• Calcium causes a binding of actin and myosin
• ATP causes heads to cock
• ATP causes return to original location
• Calcium taken back into storage
• Actin and myosin attraction stops

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Other Important Neurotransmitters

• GABA
• Neurotransmitter in the brain that has a
  tranquilizer effect
• Dopamine
• Precursor to norepinephrine
• Causes stimulation in brain and has vascular and
  cardiac effects
• Serotonin
• The feel good neurotransmitter

Parkinson's Disease?
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The Autonomic Nervous System
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The Autonomic NS

• Transmits action potentials from CNS to
• Smooth muscle
• Cardiac muscle
• Certain glands

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Autonomic Nervous System

• Sympathetic division
• function, neurotransmitter
• Parasympathetic division
• function, neurotransmitter

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The Autonomic Nervous System

• Sympathetic
• Thoracolumbar
• Fibers located in the Thoracic and lumbar spine
• Parasympathetic
• Craniosacral
• Fibers located within the brain and sacral spinal
  cord

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Sympathetic Nervous System

• Fight or Flight
• Increased cardiac output
• Epinephrine / Norepinephrine

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Receptors

• The release of the neurotransmitter will
  stimulate the following receptors
• Alpha
• Beta 1
• Beta 2

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Receptors

• Alpha
• Vasoconstriction
• Iris dilation
• Intestinal relaxation
• Intestinal sphincter contraction
• Bladder sphincter contraction

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Receptors

• Beta 1
• Cardio acceleration
• Heart rate
• Automaticity
• Contractility

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Receptors

• Beta 2
• Bronchial dilation

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Paraympathetic NS

• Vegetative Functions
• Digestion
• Defecation
• Urination
• Decreased heart rate

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Neurotransmitters / Receptors

• Acetylcholine
• Receptors
• Muscarinic
• Found at receptor sites at postganglionic
  parasympatheic nerve fibers
• Nicotinic
• Found in the membranes of skeletal muscle

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Other receptors of importance

• Opiate receptors
• Various protein structures
• Mu1, mu2, Kappa, Delta
• Nociceptors
• Pain receptors
• Become increasingly sensitive with increased
  stimulation

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Opiate Receptors and effect of Agonist
http//www.csam-asam.org/pdf/misc/OpiatePharm.ppt
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Summary

• Function of the Nervous System
• Efferent Afferent Divisions of the PNS
• Anatomy of the Neuron
• Neurotransmitters
• The Autonomic NS

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Credits

• PPortions of this presentation were taken from
  the following sources
• GGuyton Hall. Textbook of Medical Physiology,
  9th Ed. W.B. Saunders Company. Philadelphia, PA.
  1996
• MMartini, Frederic. Fundamentals of Anatomy
  Physiology 3rd Ed. Prentice Hall. Upper Saddle
  River, NJ. 1995
• SSanders, Mick. Mosbys Paramedic Textbook, 2nd
  Ed. Mosby. St. Louis, MO. 2000