Download Sensory Neuron Processing

ANS and Somatic Motor Control
Dr. Gary Mumaugh – Bethel University
Sensory Neuron Processing
 Sensory Neurons
o Each sensory neuron responds primarily to only one particular type of
stimulus
 This is called it’s normal – Example: photoreceptors, chemoreceptors
 The dendrite of the sensory neuron transduces (converts) the stimulus
into changes in membrane potential.
stimulus >>>>> increased permeability of membrane to sodium >>>>>> depolarization >>>>>> AP
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o The intensity of the stimulus affects:
 The number of sensory neurons that respond
 The frequency of the Aps that are generated by each sensory neuron
o Sensory adaptation to an ongoing stimulus
 Continuous stimulation of a sensory neuron resulted in a decreasing
Response (sensory adaptation)
Somatic Sensory Neurons
o Information reaches consciousness (awareness)
o Exteroreceptors
 Provides information about external environment
 Photoreceptors
 Chemoreceptors
 Olfactory receptors
 Taste buds
 Somatic nociceptors
o Stimulated by chemical mediators or inflammation
 Mechanoreceptors
 Touch and pressure receptors
 Vibration, tickle and itch receptors
 Auditory (cochlear) receptors
 Thermoreceptors
o Proprioceptors (kinesthesia)
 Provides information about position of the head and body in space
 Muscle stretch receptors (muscle spindle fibers)
 Golgi tendon organs
 Joint receptors
 Vestibular apparatus
 Semicircular canals
 Utricle
 Saccule
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Visceral Sensory Neurons (Interoreceptors)
o Information does not reach consciousness, or is only poorly defined and
localized.
o Chemoreceptors
 O2, CO2, H
 Glucose
 Visceral nociceptors – stimulated by chemical mediators of
inflammation
o Baroreceptors
o Visceral stretch receptors
 Example – fullness of bladder or rectum
o Irritant receptors – triggers coughing, sneezing or nausea
Injured Cell Releases >>>>>>>>>> Kinins & Prostoglandins >>>>>>>>>> Pain
Sensory Pathways to the Brain
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Organization of Sensory Pathways
o Sensory nerve fibers (1st order neurons) synapses onto myelinated
interneurons (2nd order neurons) in the CNS
o The 2nd order neurons then:
 decussate (cross over)
 travel in bundles (fiber tracts) upwards through the CNS
 synapse in the Thalamus onto myelinated interneurons (3 rd order
neurons)
o These 3rd order neurons project to many areas of the brain, including the
cerebral cortex.
Third Order Neuron
Thalamus to Cortex
Second Order Neuron
Cord to Thalamus
First Order Neuron
Dorsal Root Ganglion to Cord
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General Characteristics of Visceral Effectors (organs)
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Includes:
o The heart
o All organs containing visceral (smooth) muscle
 GI tract
 Blood vessels
 Lung bronchioles
 Urinary bladder
 Iris of the eye
 Uterus
o Glands
 Sweat glands
 Mucus secreting glands of the reparatory tract
 Salivary glands
 Secretory glands of the GI tract
 Liver
 Pancreas
 Adrenal glands
Exhibits intrinsic activity (automaticity)
o The visceral effectors are not dependent upon nerve stimulation
 Example: heart
Innervated by autonomic motor neurons that act to influence the rate of activity
The Autonomic Nervous System
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Consists of the hypothalamus, descending autonomic fiber tracts and the autonomic
motor neurons
o The hypothalamus continuously (and unconsciously) adjusts the activity of the
visceral effectors to match the person’s activity and energy requirements
Homeostasis
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o The hypothalamus is influenced by the person’s emotional state
o A person’s emotional state indirectly influences the activity of the visceral
organs
Limbic System
There are 2 types of autonomic motor neurons for each visceral effector of the body
This is called dual innervation
o Parasympathetic autonomic motor neurons influence the organs during states
of relaxation
(low energy requirements)
o Sympathetic autonomic motor neurons influence organs during stated of
stress – fight, flight, fright
(high energy requirements)
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General Pattern of Autonomic Outflow of the CNS
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Parasympathetic (Cranio-Sacral) Division
o These neurons are present only in certain Cranial nerves and Sacral spinal
nerves
 III
Oculomotor Nerves
 VII
Facial Nerves
 X
Vagus Nerves
 S2 – S4 Pelvis Nerves
Sympathetic (Thoraco-Lumbar) Division
o The sympathetic motor neurons are present in the spinal nerves that emerge
at the thoracic and lumbar levels.
Neural Innervation of Effectors
o Somatic Motor Neuron Overflow
 Under voluntary (conscious) control
 Originates in the grey matter of the brainstem, and the ventral gray
horns of the spinal cord (at all levels)
 Releases ACh that excites the skeletal muscle fibers to the part
 Because it releases Ach, it is cholinergic
 Effect of denervation – neurogenic flaccid paralysis
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o Autonomic Outflow
 Functions autonomously (unconscious) control
 Preganglionic (presynaptic) motor neurons
 Myelinated
 Released ACH that excites the postganglionic (post synaptic)
motor neurons (Cholinergic)
 Postganglionic (postsynaptic) motor neuron
 Unmyelinated
 Release a neurotransmitter onto the visceral effector cells
o Parasympathetic post ganglionic motor neurons release
ACH
o Sympathetic post ganglionic motor neurons release
norephinephrine
(Class Drawing – Autonomic Outflow)
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(Class Drawing – Autonomic Innervation of the Heart
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Neural Innervation of Effectors
o Innervation of the Adrenal Medulla
 The adrenal medulla actually consists of
specialized post ganglionic motor
neurons that have no axons!!
 They produce epinephrine.
 They release epinephrine directly
into the adrenal blood vessels,
thus affecting all visceral organs
and the brain.
 The adrenal medulla amplifies a
generalized sympathetic response
Parasympathetic Effects “Rest and Digest” on the Visceral Organs
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Generally inhibits the activity of of most visceral organs to conserve energy
Stimulates anabolic biochemical processes for growth and repair of body tissues
Visualize: The body’s internal state after leisurely enjoying a large dinner and then
relaxing with a movie.
“S L U D D”
o Salivation
o Lacrimation
o Urination
o Digestion
o Defecation
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Sympathetic Effects “Stress” on the Visceral Organs
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Generally increases the activity of most visceral organs to meet the increased
energy demands associated with stress
Stimulates catabolic biochemical processes to increase the availability of O 2 and
glucose to active tissues, and to increase the generation of ATP (cell respiration)
Visualize: The body’s internal state during strenuous exercise
“ E SITUATIONS”
o Exercise
o Excitement
o Emergency
o Embarassment
Clinical Considerations of ANS on the Visceral Organs
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Use of Parasympathomimetic Drugs
Cholinergic
Use of Sympathomimetic Drugs
Adrenergic
Use of Parasympholytic Drugs
Anti-cholinergic
o Examples: the belladona alkaloids
o Widely used to block nasal, salivary and bronchial secretions
 prior to surgery
 in OTC cold medications
Use of Sympatholytic Drugs
Adrogenic Blockers
o Examples: the beta-adrenergic blockers – “beta blockers”
o Widely used to block the physiologic response to stress
The Autonomic Control of the Pupils of the Eyes
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The Iris of the eyes contains antagonistic smooth muscles
o Circular muscle
 Parasympathetic innervation
 Contraction of the circular muscle >>>>>>> pupillary constriction
o Radial muscle
 Sympathetic innervation
 Contraction of the radial muscle >>>>>>> pupillary dilation
The pupils are constricted in response to
o Bright lights
o Near vision
o Quiet reflection
The pupils are dilated in response to
o Dim lights
o Distant vision
o Stress
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Autonomic Actions on Visceral Effectors
“Rest & Digest”
ACh
(Muscarinic Cholinergic)
“Stress”
Epinephrine & Norepinephrine
(Adrenergic, Catecholamines)
Purpose Decreased Energy Demands
Purpose Increased Energy Demands
Liver glycogenesis >> hypoglycemia
Lipogenesis in fat cells
Decreased rate & depth of breathing
Liver glycogenolysis >> hyperglycemia
Lipolysis in fat cells
Increased rate & depth of breathing
(Diaphragm is a skeletal muscle)
Bronchodilation
Decreased bronchial secretions
Increased rate & force of cardiac contraction
Tachycardia
Increased contractility
Vasodilation to heart and skeletal muscle
Causing increased blood flow
Generalized vasoconstriction to the other blood
vessels of the body causing decreased blood flow
to the GI tract and kidneys
Increased blood pressure
Pupillary dilation(Mydriasis)
Decreased salivation
Inhibits emptying of urinary bladder (retention)
Increased CNS alertness
Orgasm (ejaculation)
Increased sweating causing heat loss
(From Increased Cell Respiration)
Bronchoconstriction
Increased bronchial secretions
Decreased rate & force of cardiac contraction
Bradycardia
Decreased contractility
Vasoconstriction to heart and skeletal muscle
Causing decreased blood flow
Generalized vasodilation to the other blood
vessels of the body causing increased blood flow
to the GI tract and kidneys
Decreased blood pressure
Pupillary constriction
Increased salivation
Emptying of urinary bladder
Decreased CNS alertness
Sexual arousal (penile erection)
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