Module 14.1 Overview of the Autonomic Nervous System Flashcards
: What is the Autonomic Nervous System (ANS)?
The Autonomic Nervous System (ANS) is the involuntary arm of the peripheral nervous system (PNS), also known as the visceral motor division. It oversees most vital functions including heart rate, blood pressure, and digestive and urinary processes autonomously without conscious control.
How is the ANS divided?
The ANS is divided into two divisions, the sympathetic and parasympathetic nervous systems. These two systems constantly work together to maintain homeostasis.
What are the functions of the ANS and Visceral Reflex Arcs?
The ANS manages vital processes through visceral reflex arcs. A sensory stimulus leads to a predictable motor response. Sensory signals from viscera and skin are sent by afferent sensory neurons to the brain or spinal cord and integrated by the CNS. Motor impulses from the CNS are sent out via efferent neurons in cranial and spinal nerves, usually leading to autonomic ganglia in the PNS. Autonomic ganglia send impulses via other efferent neurons to various target organs, triggering a motor response.
What are the main differences between the motor divisions of the PNS?
The somatic motor division neurons innervate skeletal muscle, leading to voluntary muscle contractions that are initiated consciously. On the other hand, autonomic motor division neurons innervate smooth muscle cells, cardiac muscle cells, and glands, producing involuntary actions.
How do ANS motor neurons differ from somatic motor neurons?
Unlike somatic motor neurons that directly innervate their target, ANS motor neurons require a two-neuron circuit. The initial efferent neuron, known as the preganglionic neuron, has its cell body residing within the CNS and all its axons release acetylcholine. The postganglionic neuron, on the other hand, has its cell body residing in an autonomic ganglion in the PNS. Its axons travel to target cells and trigger specific changes (either inhibitory or excitatory responses) by releasing either acetylcholine or norepinephrine.
What are the main structural and functional differences between the sympathetic and parasympathetic nervous systems?
In the sympathetic nervous system, preganglionic axons are usually short and postganglionic axons are usually long. Conversely, in the parasympathetic nervous system, preganglionic axons are long while postganglionic axons are short.
What are the characteristics of the sympathetic nervous system?
The sympathetic nervous system is also known as the thoracolumbar division because the preganglionic cell bodies originate in the thoracic and upper lumbar spinal cord. The sympathetic ganglia are generally located near the spinal cord. Preganglionic axons synapse with postganglionic neuron cell bodies, and the postganglionic axons proceed to the target.
What is the role of the sympathetic nervous system?
The sympathetic nervous system is often referred to as the “fight or flight” division of the ANS. It prepares the body for emergency situations, plays a vital role in maintaining homeostasis when the body is engaged in physical work, and mediates the body’s responses to emotion.
What are the characteristics of the parasympathetic nervous system?
The parasympathetic nervous system, also known as the craniosacral division, has preganglionic cell bodies located within the nuclei of several cranial nerves in the brainstem and the sacral region of the spinal cord. Cranial nerves innervate structures of the head and neck, thoracic viscera, and most abdominal viscera. Sacral nerves innervate structures within the pelvic cavity. The cell bodies of postganglionic neurons are usually located near the target organ, requiring only a short axon to make a connection. This division is often referred to as the “rest and digest” division and plays a role in digestion and in maintaining the body’s homeostasis at rest.
How do the parasympathetic and sympathetic nervous systems work together?
The actions of the parasympathetic division directly antagonize those of the sympathetic division. Together, they maintain a delicate balance to ensure homeostasis is preserved.
What is the difference between pre- and postganglionic neurons?
A ganglion is a cluster of neuronal cell bodies. The prefixes “pre-” and “post-” mean “before” and “after,” respectively. Therefore, a preganglionic neuron is the neuron that comes before the ganglion, and a postganglionic neuron is the one whose cell body is located within the ganglion, and whose axon comes after the ganglion.
