Autonomic Nervous System Flashcards
Autonomic Nervous System
Control system that acts largely unconsciously; regulates bodily functions such as heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal; regulates reflex responses that people typically take for granted when they’re working properly; involuntary and maintains homeostasis; important to know how developing drug may effect physiological processes
Parts of autonomic nervous system
- Sympathetic nervous system
- Parasympathetic nervous system
- Smooth and cardiac muscle, exocrine glands, some endocrine glands - Enteric nervous system
- Digestive organs only
Autonomic Efferent Pathway
Two neurons in both sympathetic and parasympathetic system
- 1st neuron located in brain or spinal cord
- 2nd neuron is located in ganglia
- “Preganglionic neurons” synapse onto “postganglionic neurons” that innervate target organs
- Release neurotransmitter from “varicosity”
Somatic Efferent Pathway
One neuron system
- Alpha motor neurons project directly from the spinal cord to skeletal muscle
- 1 nerve per muscle fiber
- Release neurotransmitter into traditional “neuromuscular junction”
Autonomic Nerve
Preganglionic fiber from CNS releases preganglionic neurotransmitter at autonomic ganglion; postganglionic fiber branches off of autonomic ganglion and releases postganglionic neurotransmitter from varicosity on effector organ
- Do not always from chain ganglia and to target organ (synapse in same area, travel up and synapse, travel down and synapse, and some make their own ganglion)
Sympathetic Preganglions
Cell body located in the lateral horn of the thoracic and upper lumbar spinal cord; short and synapse in ganglia (clusters of neurons) located just outside of the spinal cord; innervate tissues throughout the body
- T1 to L2
What tissues do sympathetic system innervate?
Eye, lacrimal and salivary glands, lungs, heart, liver, pancreas, stomach, kidney, adrenal glands, small and large intestines, rectum, bladder, and genitalia
Sympathetic Postganglionics
Cell body located in sympathetic chain; long and innervates effector organ; EXCEPTION in adrenal instead preganglionics continue through the ganglia (splanchnic nerves) and innervate adrenal medulla
Parasympathetic Preganglionics
More restricted; located in brain stem and extend via cranial nerves (III, VII, IX, and X); long and extend to series of ganglia very close to visceral target (sometimes synapse on organ); located in sacral spinal cord and extend via pelvic nerve (craniosacral)
What tissues do parasympathetic system innervate?
- Cranial nerve III = eyes
- Cranial nerve VII = lacrimal glands
- Cranial nerve IX = salivary glands
- Cranial nerve X = lungs, heart, stomach, spleen, pancreas, and large and small intestine
-Sacrum innervates large intestine, rectum, bladder, and genitalia
Parasympathetic Postganglionics
Short and reside in ganglia very close to visceral target; activity to the heart, lungs, and abdominal visceral organs travels through the Vagus nerve which synapses; Vagus nerve synapses on very short post ganglionic neurons on heart
Dorsal Motor Nucleus of the Vagus
Neurons within the dorsal motor nucleus of the Vagus (DMV) are parasympathetic motor neurons as they project to the periphery and regulate the tone to most of the subdiaphragmatic organs and thus, regulate feeding, digestion, energy, and glucose homeostasis
Sympathetic Ganglia
- Sympathetic Paravertebral Ganglia
- Sympathetic Prevertebral Ganglia
Sympathetic Paravertebral Ganglia
Run on either side of the vertebral bodies
- Cervical ganglia
- Thoracic ganglia and rostral lumbar ganglia
- Caudal lumbar ganglia and sacral ganglia
Sympathetic Prevertebral Ganglia
- Celiac ganglion
- Aorticorenal ganglion –> in front of aorta and close to kidneys
- Superior mesenteric ganglion
- Inferior mesenteric ganglion
Parasympathetic Ganglia
- Ciliary (cranial nerve III)
- Submandibular (cranial nerve VII)
- Pterygopalatine (cranial nerve VII) - roof of mouth
- Otic (cranial nerve IX)
- In or near the wall of an organ innervated by vagus (cranial nerve X) or sacral nerves (S2, S3, S4)
Dual Innervation
Many organs are innervated by both sympathetic and parasympathetic divisions; “opposite” actions where one branch activates a physiological response and the other inhibits; more precise and faster control
Parasympathetic
- Digestion
- Relaxation
- Metabolism
- “Rest and digest”
Sympathetic
- Stress
- Physical Activity
- Emergencies
- “Fight or flight”
Dual innervation of heart
Parasympathetic system slows heart rate via long preganglionic neurons located in brainstem extend via the Vagus nerve to short postganglionic neurons on heart; sympathetic system increases heart rate and cardiac contractility via short preganglionic neurons located in spinal cord that project to long postganglionic neurons in the sympathetic chain and project to the heart
Pupil Constriction
Increased parasympathetic activity (cholinergic) to circular muscles constrict the iris while sympathetic activity (adrenergic) to radial longitudinal muscles decreases
Pupil Dilation
Decreased parasympathetic activity (cholinergic) to circular muscles dilate iris while sympathetic activity (adrenergic) to radial longitudinal muscles increases
Preganglionic Neurotransmitters
- Primary neurotransmitter for both is acetylcholine (Ach) which classifies all of them as cholinergic neurons
Postganglionic Neurotransmitter Parasympathetic
Always Ach = cholinergic
Sympathetic postganglionic neuron neurotransmitter for enteric neurons, smooth muscle cells, or cardiac cells
Epinephrine and/or norepinephrine = adrenergic
Sympathetic postganglionic neuron neurotransmitter for secretory cells
Ach = cholinergic; muscarinic receptors
Sympathetic postganglionic neuron neurotransmitter for chromaffin cells in adrenal medulla
Ach and then release of epinephrine and norepinephrine from target organ
Nicotinic Cholinergic Receptors (nAchR)
Main receptor types found on both sympathetic and parasympathetic postganglionic neurons; acts as a Na+ and K+ conducting channel; gated not only by Ach but also nicotine