STRUCTURAL AND FUNCTIONAL ORGANIZATION OF THE AUTONOMIC NERVOUS SYSTEM Flashcards
Differentiate between the somatic and autonomic parts of the nervous system.
Somatic Nervous System
(1) Controls skeletal muscle
(2) Conscious, voluntary control
(3) Motor pathway: one neuron from CNS to effector
(4) Does include sensory neurons (from skin, skeletal muscles, and special sense organs)
(5) All release the neurotransmitter acetylcholine (Ach)
(6) The axon of a single somatic motor neuron extends from CNS all the way to skeletal
muscle fibers
Differentiate between the somatic and autonomic parts of the nervous system.
. Somatic Sensory Pathways
(1) Relay sensory information from periphery to cerebral cortex
(2) Three neurons in each pathway
(a) Cell body #1 in dorsal root ganglion
(b) Cell body #2 in spinal cord or brain stem
(c) Cell body #3 in thalamus; axon extends to cerebral cortex (somatosensory area in postcentral gyrus)
(3) Most sensory input to right side of body reaches left side of brain (and vice versa)
(4) Example: Posterior column - medial lemniscus pathway senses
(a) Senses touch, pressure, vibration, and conscious proprioception
(5) Example: Spinothalamic pathways
(a) Anterior spinothalamic tracts
1) Light touch sensation
2) Deep pressure sensation
(b) Lateral spinothalamic tract
1) Pain Sensation
2) Temperature (hot vs cold) sensation
Differentiate between the somatic and autonomic parts of the nervous system.
Somatic Motor Pathways
(1) Signals come from:
(a) Upper motor neurons: Via corticospinal tracts
(b) Basal ganglia: Help with muscle tone
(c) Cerebellum: Coordination
(d) Sensory neurons or interneurons via reflexes
(2) Impulses activate lower motor neurons
(a) Cell bodies in anterior gray of spinal cord
(b) Axons –> ventral root –> spinal nerve –> muscle –> voluntary movements
(3) Corticospinal Tract
(a) Upper Motor Neuron
1) Originates in the primary motor cortex (Precentral Gyrus)
2) Synapses with a lower motor neuron of appropriate spinal level
(b) Lower Motor Neuron
1) Exits spinal ventral root to the muscle for movement
Differentiate between the somatic and autonomic parts of the nervous system.
. Autonomic Nervous System
(1) Regulated by hypothalamus and brainstem
(2) Controls viscera: Smooth and cardiac muscle, and sweat and digestive glands
(3) Unconscious, involuntary
(4) Motor pathway: Series of two neurons from CNS to effector
(5) Does include sensory neurons (monitors viscera)
(6) Two divisions: Sympathetic and parasympathetic
(7) Release either acetylcholine (ACh) or norepinephrine (NE)
Name the structural features of the autonomic nervous system.
Divisions of the Autonomic Nervous System
(1) Sympathetic (S) division + parasympathetic (P) division
(2) Most viscera supplied with nerves of both S and P divisions: Dual innervation
(3) S and P have opposite (antagonistic) effects
(a) Heart rate: S stimulates, P inhibits
(b) Digestive organs: S inhibit, P stimulate
(c) S: “flight or flight,” P: “rest and digest”
(4) Some viscera receive only S (not P) nerves:
(a) Sweat glands, many blood vessels, hair muscles
(5) Autonomic Nervous System Pathway
(a) Autonomic motor pathway includes two motor neurons(preganglionic and postganglionic neurons)
(b) Preganglionic neuron from CNS to neuron in autonomic ganglion
(c) Postganglionic neuron from cell body in ganglion to effector
Name the structural features of the autonomic nervous system. Sympathetic Divison (S)
(1) Sympathetic preganglionic neurons
(a) Have cell bodies located in lateral gray of spinal cord segments T1-T12 + L1-L2
(b) Often referred to as the “thoracolumbar division”
(c) Axons emerge from spinal cord via anterior root of spinal nerve (along with axons of somatic motor neurons) and pass through ventral roots of spinal nerves
1) Most synapse with postganglionic neurons at a sympathetic trunk ganglion
2) One sympathetic preganglionic axon can synapse with 20 or more postganglionic neuron cell bodies
(d) Results in widespread S effects occurring simultaneously (viscera respond “in sympathy” with one another)
1) Some extend to adrenal medulla
(e) Release epinephrine and norepinephrine
(2) Sympathetic postganglionic neurons
(a) Cell bodies located in S “trunk ganglia” (2 long chains lateral to vertebrae)
1) Postganglionic axons pass from ganglia to viscera
2) Many axons from these cell bodies pass back into spinal nerves to reach viscera
3) Most leave the cervical sympathetic trunk ganglia serve the head (sweat glands, smooth muscles of eye, blood vessels of face, nasal mucosa, salivary glands)
4) Some cervical supply the heart
5) Some leaving thoracic region serve heart, lungs, bronchi, sweat glands, blood vessels, smooth muscles of hair follicles
(b) Cell bodies located in “prevertebral ganglia” follow along 3 large abdominal arteries
1) Named celiac, superior and inferior mesenteric ganglia
a) Supply abdominal viscera: stomach, intestine, kidneys, liver, spleen
Name the structural features of the autonomic nervous system. Parasympathetic Division (P)
(1) Parasympathetic preganglionic neurons
(a) Cell bodies located in brainstem (nuclei of CN III, VII, IX, and X) and in spinal cord segments S2-S4
(b) Parasympathetic preganglionic axons emerge from the CNS as part of a cranial nerve or anterior root of spinal nerve
1) Vagus nerves (cranial nerves X) carry 80% of all P nerve impulses.
2) Vagus nerves carry both motor and sensory neurons to/from viscera within the thorax and most of the abdominal cavity.
(2) Parasympathetic postganglionic neurons
(a) Cell bodies lie in terminal ganglia which are located within or near the innervated organ; thus, P nerves cause precise, localized (not widespread) effects
(3) Unlike sympathetic nerves, parasympathetic nerves do not reach some viscera
(a) These include sweat glands, arrector pili muscles of hairs in skin, kidneys, spleen, adrenal medullae, and the walls of most blood vessels.
Describe the function of the sympathetic divisions of the autonomic nervous system
Sympathetic Effects:
(1) Fight-or-flight activities
(a) Increase heart rate and contraction, and blood pressure (BP)
(b) Dilate pupils
(c) Dilate airways
(d) Dilate vessels to skeletal muscles, heart, liver and adipose tissue
(e) Constrict blood vessels to nonessential organs: skin, GI tract, kidneys
(f) Mobilize nutrients for energy: glucose and fats
. Describe the function of the parasympathetic division of the autonomic nervous system.
. Parasympathetic Effects:
(1) Rest-and-digest activities:
(a) SLUDD
1) Salivation
2) Lacrimation
3) Urination
4) Digestion
5) Defecation
(b) Decrease heart rate, airway diameter, pupil diameter
