AUTONOMIC NERVOUS SYSTEM
Somatic efferent and ANS Somatic Efferent Control is over skeletal muscles. External environment This division of the PNS responds to some change in the external environment. single somatic efferent neuron Extends from the CNS to the effector (skeletal muscle) Acetlycholine is the NT released at the synapse (motor endplate.)
Autonomic nervous system (visceral efferent) Regulates visceral activities Organs of the thoracic and abdominal regions; sweat and sebaceous glands, etc. No conscious control over visceral activities. Stable internal environment The goal of the ANS is to maintain a stable internal environment.
Autonomic nervous system Regulated by centers in Brain stem and cord 2 efferent neurons One from CNS to ganglion One to visceral effector preganglionic postganglionic CNS ganglion preganglionic postganglionic Acetlycholine (ACh) or norepinephrine (Ne) Are the NTs released at the synapses.
Structure of the ANS Visceral efferent neurons organized into Nerves (neurons) Pre- or postganglionic nerves. Ganglia Where the pre- or postganglionic neurons form a synapse; this is where the postganglionic soma is located. Plexuses Tangles of visceral efferent nerves. Entirely motor Carry motor information to visceral effectors.
1) Efferent neurons preganglionic Soma in brain or cord Myelinated axons Synapses with postganglionic neuron Within a ganglion CNS
1) Efferent neurons Postganglionic autonomic ganglia Somas are located within autonomic ganglia or target organs Unmyelinated axons are found with postganglionic neurons Synapses with effector Usually smooth muscle, heart or gland CNS
1) Efferent neurons Sympathetic division of the ANS has its preganglionic somas in the... thoracolumbar regions of the cord helps body respond to stress This division of the ANS is called the fight or flight division. If the body is under some threat or stress, the sympathetic stimulation goes up. This causes an increase in heart and respiration rate, sweating, blood flow to the CNS and muscles. This causes a decrease blood flow to some visceral organs, such as the intestines and the kidneys. CNS
1) Efferent neurons Parasympatheic division of the ANS has its preganglionic somas in the... craniosacral regions of the cord active under normal conditions This division of the ANS is called the rest and repose division. The parasympathetic division is stimulated under normal or resting conditions, when you want to cover from stress; build up reserves and maintain the body. This causes a decrease in heart and respiration rate, sweating, blood flow to the CNS and muscles. This causes an increase blood flow to some visceral organs, such as the intestines and the kidneys. CNS
Dual innervation The heart, each visceral organ and gland is innervated by both the sympathetic and parasympathetic divisions of the ANS. Although each effector is under the control of both divisions, they are not simultaneously stimulated by both. Which division predominates at any given time is determined by the demands on the body at that time.
2) Autonomic ganglia a) sympatheic trunk or chain ganglia (paravertebral or lateral ganglia) Located close and lateral to the spinal cord. Stimulate primarily... Sympathetic division Preganglionic fibers are short
2) Autonomic ganglia b) prevertebral ganglia (collateral ganglia) Located anterior to the spinal cord. Stimulate primarily... Sympathetic division Preganglionic fibers are short
b) prevertebral ganglia (collateral ganglia) Some examples of prevertebral ganglia Largest Celiac Postganglionic fibers from this ganglion innervate organs of the abdomen; liver, gallbladder, stomach, pancreas, spleen. Superior mesenteric ganglia Innervate the small intestine and part of the large. inferior mesenteric ganglia Innervate most of the large intestine, kidney, bladder and reproductive organs.
2) Autonomic ganglia c) terminal ganglia Located within target visceral organs. Stimulate primarily... Parasympathetic division Preganglionic fibers are very long
3) Plexuses Interlaced networks Similar to the plexuses of the somatic efferent PNS. Tangles of visceral efferent nerve fibers. Solar plexus or Celiac plexus Postgangionic fibers from the celiac ganglion pass through here.
Physiology of the ANS Autonomic fibers release NT at synapse Cholinergic fibers release Ach at the synapse. The preganglionic fibers of the sympathetic division are cholinergic. Ach is released to bind to the postsynaptic (postganglionic) neuron. Adrenergic fibers release norepinephrine (NE) at the synapse. The postganglionic fibers of the sympathetic division are adrenergic.
Responses NE tends to stimulate the effectors. Catechol-O-methyl transferase This enzyme, found in the synaptic gap, breaks down NE. It has a similar function as acetylcholinesterase, but works at a slower rate. As a result some NE tends to diffuse out of the synapse into the surrounding tissues, where it may exert an effect. So the effects of sympathetic stimulation are more wide spread and last longer the parasympathetic stimulation.
Responses Parasympathetic: Both pre- and postganglionic fibers are cholinergic. As Ach is rapidly broken down by acetylcholinesterase, it does not have a chance to diffuse from the synapse. Parasympathetic effects tend to be localized and short in duration.
Visceral Autonomic Reflexes similar to somatic reflexes. Target organs are... smooth muscle Such as digestive system, vessels, reproductive.etc. cardiac muscle gland secretion Heart Salivary, sweat, etc. Visceral Autonomic Reflex Arc receptor afferent neuron association neuron visceral efferent preganglionic neuron visceral efferent postganglionic neuron visceral effector
Visceral sensations conscious sensations Visceral sensations reach the conscious levels of the mind if the a voluntary action is required to deal with the sensation; as in urination or defecation. Control by higher centers Hypothalamus For example; if hypothalamus determines that the the water content of the blood is too low, it will send signals to the higher brain centers to provide a sensation of thirst. Cerebral cortex The cerebrum will respond to the thirst sensation by stimulating drinking behaviors; a voluntary action.