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11 Cards in this Set
- Front
- Back
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ANS - (a motor subdivision of the Peripheral nervous system) is also called the involuntary nervous system |
- operates below conscious level - largely maintains the stability of thebody’s internal environment - affects such things as heart rate, blood pressure, pupil size, digestive secretions, urine release |
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ANS operates via |
reflex arcs (similar to reflexes used by Somatic NS) |
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Autonomic reflex arc involves 5 STEPS |
1. Autonomic sensory neurons in visceral organs and blood vessels- detect change in internal environment 2. Carry info via autonomic sensory neuron to CNS 3. Integration center in CNS (mostly in hypothalamus and brainstem) or within walls of gastrointestinal tract 4. Autonomic motor neurons (2 motor neuron chain) carry info from CNS to effector tissues 5. Effector is smooth muscle, cardiac muscle or gland that responds to motor impulse |
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Autonomic motor pathway |
involves 2 neurons in sequence - second neuron has its cell body located in the ganglion |
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ANS has 2 divisions |
sympathetic (SD) and parasympathetic (PD) |
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1. Preganglionic neuron cell bodyoriginates in different regions: (SD VS PD) |
SD - thoracic and lumbar spinal cord PD - brainstem and sacral spinal cord Note: ~90% of PD preganglionic axons are found within the vagus nerve (X) |
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2. Ganglia are located in different areas: (SD VS PD) |
SD -ganglia lie close to spinal cord so preganglionic fibers are short -postganglionic fibers are longer to extend to the effector PD -most ganglia are within wall of the effector organ so preganglionic fibers are long -postganglionic fibers are shorter |
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3. Neurotransmitters used differ (SD VS PD) |
Both divisions - preganglionic neurons release acetylcholine (ACh) SD - most postganglionic neurons release norepinephrine (NE) at synapses with their effectors PD - postganglionic neurons release ACh at synapses with their effectors Adrenal medulla - is considered a sympathetic organ- receives SD preganglionic stimulation - in response, the medullary cells secrete the hormones epinephrine and NE into blood |
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4 |
SD -“flight or fight” division becomes dominant during vigorous activity PD - “rest and digest” division isdominant during resting periods |
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5. Receptors used: |
SD - effectors have “adrenergic” receptors - response of effector organ depends on the receptor type present: Alpha (α) or Beta (β) type - effect of NE or epinephrine can be stimulatory or inhibitory depending on the subclass of α or β receptor present on the organ PD - effectors have “cholinergic” receptors of 2 types: (i.) Nicotinic receptors are found on postganglionic neurons (both SD and PD) and on hormone-producing cells of adrenal medulla Note: Skeletal muscle has nicotinic receptors (i.e. at neuromuscular jct). - response to ACh is always stimulatory (ii.) Muscarinic receptors are found at all effector organs innervated by postganglionic cholinergic neurons - effect of ACh can be stimulatory or inhibitory depending on the subclass of muscarinic receptor present on the organ |
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Control of Autonomic Function
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Activity of the ANS is regulated by CNS controls
Hypothalamus is main integration center for ANS - coordinates heart activity, blood pressure, body temperature, water balance and endocrine activity -Spinal cord and medullary centers mediate reflex activity - Cerebral cortex can influence ANS via connections with the limbic system (emotional input) |
