chapter 15 autonomic nervous system Flashcards
PNS divides into the ?
the motor (efferent) division of the peripheral nervous system (PNS) is divided into a somatic nervous system (SNS) and autonomic nervous system (ANS).
Autonomic Nervous System (ANS) regulates?
is the part of the nervous system that regulates cardiac muscle, smooth muscle, and glands.
These tissues are often referred to as visceral effectors because they are usually associated with the viscera (internal organs) of the body.
Autonomic motor neurons
The autonomic nervous system consists of autonomic motor neurons that regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues (cardiac muscle, smooth muscle, and glands).
Changes in the diameter of the pupils, dilation and constriction of blood vessels, and adjustment of the rate and force of the heartbeat are examples of autonomic motor responses.
ANS tissues compared to skeletal muscle tissues (key differences)
Unlike skeletal muscle, tissues innervated by the ANS often function to some extent even if their nerve supply is damaged.
The heart continues to beat when it is removed for transplantation into another person,
smooth muscle in the lining of the gastrointestinal tract contracts rhythmically on its own, and
glands produce some secretions in the absence of ANS control.
Biofeedback
Biofeedback, in which monitoring devices display information about a body function such as heart rate or blood pressure, enhances the ability to learn such conscious control.
The ANS usually operates without conscious control…. but
practitioners of yoga use techniques of meditation may learn how to regulate at least some of their autonomic activities through long practice.
interoceptors
The ANS can also receive sensory input from sensory neurons as- sociated with interoceptors
interceptors are sensory receptors located in blood vessels, visceral organs, muscles, and the nervous system that monitor conditions in the internal environment.
these sensory signals are not consciously perceived most of the time, although intense activation of interoceptors may produce conscious sensations
ANS two main branches
The ANS consists of two main division (branches): the sympathet- ic nervous system and the parasympathetic nervous system.
Dual innervation
-Most organs receive nerves from both of divisions; sympathetic & parasympathetic
-This arrangement is known as dual innervation.
-usually one division causes excitement & one causes inhibition
NOT always the same direction
-BACK & FORTH SO WE SURVIVE
The sympathetic nervous system
promotes the fight-or-flight response, which prepares the body for emergency situations.
Parasympathetic nervous system
the parasympathetic nervous system enhances rest-and-digest activities, which conserve and restore body energy during times of rest or digesting a meal.
Enteric nervous system
The ANS is also comprised of a third division known as the enteric nervous system (ENS).
The ENS consists of millions of neurons in plexuses that extend most of the length of the gastrointestinal tract.
Its operation is involuntary. Although the neurons of the ENS can function autonomously, they can also be regulated by the other divisions of the ANS.
The ENS contains sensory neurons, interneurons, and motor neurons.
Enteric sensory neurons monitor chemical changes within the GI tract as well as the stretching of its walls.
pathways consist of two motor neurons in series; that is, one following the other
Autonomic motor pathways
Chromatin cells
in some autonomic pathways, the first motor neuron extends to specialized cells called chromaffin cells in the adrenal medullae (inner portion of the adrenal glands) rather than an autonomic ganglion. Chromaffin cells secrete the neurotransmitters epinephrine and norepinephrine (NE)
All somatic motor neurons release only ?
All somatic motor neurons release only acetylcholine (ACh)
Each division of the ANS has two motor neurons?
The first of the two motor neurons in any autonomic motor pathway is called a;
preganglionic neuron
- Its cell body is in the brain or spinal cord; its axon exits the CNS as part of a cranial or spinal nerve. The axon of a preganglionic neuron is a small-diameter, mye- linated type B fiber that usually extends to an autonomic ganglion, where it synapses with a postganglionic neuron.
postganglionic neuron
the second neuron in the autonomic motor pathway. Note that the postganglionic neuron lies entirely outside the CNS in the PNS. Its cell body and dendrites are located in an autonomic ganglion, where it forms synapses with one or more preganglionic axons.
The axon of a post- ganglionic neuron is a small-diameter, unmyelinated type C fiber that terminates in a visceral effector.
Thus, preganglionic neurons convey nerve impulses from the CNS to autonomic ganglia, and postgangli- onic neurons relay the impulses from autonomic ganglia to visceral effectors.
Preganglionic Neurons in the sympathetic division
In the sympathetic division,
the preganglionic neurons have their cell bodies in the lateral horns of the gray matter in the 12 thoracic segments and the first two (and sometimes three) lumbar segments of the spinal cord
For this reason, the sympathetic division is also called the thoracolumbar division
and the axons of the sympathetic preganglionic neurons are known as the thoracolumbar outflow.
Preganglionic Neurons in the parasympathetic division
Cell bodies of preganglionic neurons of the parasympathetic division are located in the nuclei of four cranial nerves in the brainstem (III, VII, IX, and X) and in the lateral gray matter of the second through fourth sacral segments of the spinal cord
Hence, the parasympathetic division is also known as the craniosacral division
and the axons of the parasympathetic preganglionic neurons are referred to as the craniosacral outflow.
Two major groups of autonomic ganglia?
(1) sympathetic ganglia, which are components of the sympathetic division of the ANS,
(2) parasympathetic ganglia, which are components of the parasympathetic division of the ANS.
Sympathetic ganglia are the sites of what?
The sympathetic ganglia are the sites of synapses between sympathetic preganglionic and postganglionic neurons.
Two major types of sympathetic ganglia?
- sympathetic trunk ganglia
- prevertebral ganglia.
Sympathetic trunk ganglia
(also called vertebral chain ganglia or paravertebral ganglia)
lie in a vertical row on either side of the vertebral column.
These ganglia extend from the base of the skull to the coccyx
Postganglionic axons from sympathetic trunk ganglia primarily innervate organs above the diaphragm, such as the head, neck, shoulders, and heart.
Prevertebral ganglia
The second group of sympathetic ganglia, the prevertebral (collateral) ganglia, lies anterior to the vertebral column and close to the large abdominal arteries.
In general, postganglionic axons from prevertebral ganglia innervate organs below the diaphragm.
Parasympathetic ganglia
Preganglionic axons of the parasympathetic division synapse with postganglionic neurons in terminal (intramural) ganglia.
Most of these ganglia are located close to or actually within the wall of a visceral organ.
Terminal ganglia in the head have specific names.
Once axons of sympathetic pre- ganglionic neurons pass to sympathetic trunk ganglia, they may connect with postganglionic neurons in one of the following ways
- An axon may synapse with postganglionic neurons in the ganglion it first reaches.
- An axon may ascend or descend to a higher or lower ganglion before synapsing with postganglionic neurons. The axons of incoming sympathetic preganglionic neurons pass up or down the sympathetic trunk from ganglion to ganglion.
- An axon may continue, without synapsing, through the sympa- thetic trunk ganglion to end at a prevertebral ganglion and synapse with postganglionic neurons there.
- An axon may also pass, without synapsing, through the sym- pathetic trunk ganglion and a prevertebral ganglion and then extend to chromaffin cells of the adrenal medullae that are functionally similar to sympathetic postganglionic neurons.
