comparison of somatic and autonomic nervous systems
-Autonomic motor neurons, both sympathetic and parasympathetic, conduct nerve impulses from the central nervous system to smooth muscle, cardiac muscle, and glands.
-So named because this part of the nervous system was thought to be self‐governing or spontaneous.
Somatic Sensory Neurons
1. somatic senses (tactile, thermal, pain, and proprioceptive sensations)
2. special senses (sight, hearing, taste, smell, and equilibrium).
-All these sensations normally are consciously perceived.
Somatic Motor Neurons
-If somatic motor neurons cease to stimulate a muscle, the result is a paralyzed, limp muscle that has no muscle tone.
-Mostly, these neurons are associated with interoceptors.
-Examples of interoceptors are chemoreceptors that monitor blood CO2 level and mechanoreceptors that detect the degree of stretch in the walls of organs or blood vessels.
Interceptors are not consciously perceived all of the time:
-Two examples of perceived visceral sensations are pain sensations from damaged viscera and angina pectoris (chest pain) from inadequate blood flow to the heart. Input that influences the ANS also includes some sensations monitored by somatic sensory and special sensory neurons. For example, pain can produce dramatic changes in some autonomic activities.
Autonomic motor neurons
Changes in the diameter of the pupils, dilation and constriction of blood vessels, and adjustment of the rate and force of the heartbeat.
Function & damage to ANS
-example: 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.
autonomic motor pathways
-The first neuron (preganglionic neuron) has its cell body in the CNS; its myelinated axon extends from the CNS to an autonomic ganglion.
-The cell body of the second neuron (postganglionic neuron) is also in that same autonomic ganglion; its unmyelinated axon extends directly from the ganglion to the effector (smooth muscle, cardiac muscle, or a gland).
-Alternatively, in some autonomic pathways, the first motor neuron extends to specialized cells called chromaffin cells in the adrenal medullae (inner portions of the adrenal glands) rather than an autonomic ganglion.
In comparison: (the axon of a single, myelinated somatic motor neuron extends from the central nervous system (CNS) all the way to the skeletal muscle fibers)
-autonomic motor neurons release either ACh or norepinephrine (NE) as their neurotransmitters.
2. the parasympathetic division.
-primarily concerned with processes involving the expenditure of energy.
-often called the fight‐or‐flight division.
-activities result in increased alertness and metabolic activities in order to prepare the body for an emergency situation.
-a rapid heart rate, faster breathing rate, dilation of the pupils, dry mouth, sweaty but cool skin, dilation of blood vessels to organs involved in combating stress (such as the heart and skeletal muscles), constriction of blood vessels to organs not involved in combating stress (for example, the gastrointestinal tract and kidneys), and release of glucose from the liver.
-primarily concerned with activities that conserve and restore body energy.
-replenishes nutrient stores.