The Nervous System - Part 3

The Nervous System - Part 3

• The autonomic nervous system (ANS) regulates smooth muscle, cardiac muscle, and certain glands.
• The ANS usually functions without conscious control; however, brain regions like the hypothalamus and brain stem regulate it.
• Somatic motor neurons connect the central nervous system (CNS) directly to skeletal muscle.
• Somatic motor pathways consist of one neuron.
• Autonomic pathways involve two neurons: a preganglionic neuron and a postganglionic neuron that synapse in an autonomic ganglion.
• The ANS has two divisions: sympathetic and parasympathetic.
• Most organs receive dual innervation from both systems; one division usually stimulates, while the other inhibits.
• Somatic motor neurons release acetylcholine (ACh).
• Autonomic motor neurons release either acetylcholine (ACh) or norepinephrine (NE).
• Pre-ganglionic neurons release ACh.
• Postganglionic neurons can release either norepinephrine (NE) or acetylcholine (ACh) depending on the division of the ANS.
• Sympathetic division neurons leave the CNS at thoracic and lumbar levels of the spinal cord.
• Parasympathetic division neurons leave the CNS at the brainstem and sacral levels of the spinal cord.
• Sympathetic is often referred to as the "fight or flight" response.
• Parasympathetic is often referred to as the "rest and digest" response.
• The fight-or-flight response involves pupil dilation, increased heart rate and blood pressure, airway dilation, and constriction of nonessential organ blood vessels.
• The rest-and-digest response includes slowing of digestion, urine production, and digestive activities, blood vessel dilation of organs involved in exercise, and relaxation of the urinary bladder.
• The balance between sympathetic and parasympathetic activity is known as "tone", regulated by the hypothalamus.
• The hypothalamus typically turns up sympathetic tone while simultaneously turning down parasympathetic tone.
• The SLUDD responses (Salivation, Lacrimation, Urination, Digestion, Defecation) are primarily parasympathetic responses.
• The parasympathetic division decreases heart rate, airway diameter, and pupil diameter.
• Engaging in regular exercise can help manage stress by releasing endorphins, increasing dopamine levels, and increasing other mood-boosting molecules like serotonin and oxytocin.