Ch 16 Flashcards
Peripheral nerves contain :
Both motor and sensory neurons
Sensory neurons are not subdivided into somatic and autonomic because
There is an overlap in function
Ex. Pain receptors can stimulate both somatic and autonomic reflexes
Somatic :
- skeletal muscle
- conscious and unconscious
- skeletal muscle contracts
- one synapse
- acetylcholine
- receptor molecules : nicotinic
Autonomic
- smooth and cardiac muscle and glands
- unconscious
- two synapses
- acetylcholine by pre ganglionic neurons
- ACH or norepinephrine by post ganglionic neurons
Anatomy of autonomic nervous system
- divided into sympathetic and parasympathetic as well as enteric nervous system
- sympathetic and parasympathetic often supply same organs but differ in a number of features
The enteric system
- nerve plexus within the wall of digestive tract
- contributions between:
* sensory neurons between digestive tract and CNS
* ANS motor neurons between the CNS and digestive tract
Functions of enteric system
- stimulate/ inhibit smooth muscle contraction
- stimulate / inhibit gland secretions
- detect changes in content of opening ( lumen )
- interneurons connect sensory and motor aspects of enteric
Distribution of ANS fibers ( sympathetic)
Sympathetic axons reach organs through:
- Spinal nerves: innervate sweat glands, smooth muscle of blood vessels to skeletal muscle and skin and arrector pili
- Head and neck nerve plexus: innervate sweat glands, smooth muscle of blood vessels to skeletal muscle and skin and arrector pili
- Thoracic nerve plexus :cardiac and pulmonary, heart and lungs
- Abdominopelvic nerve plexus: Celiac, superior mesenteric, hypogastric plexuses. Organs of the abdominal cavity
Distribution of ANS fibers ( parasympathetic)
Parasympathetic axons reach organs through:
- Cranial nerves
- Vagus nerve and thoracic nerve plexus. Heart, lungs, esophagus through esophageal plexus
- Abdominopelvic nerve plexus. Parts of vagus nerve supply stomach and other viscera
- Pelvic splanchnic nerves and nerve plexuses. Colin ( large intestine) urinary bladder, reproductive organ
Sensory neurons In autonomic nerve plexuses:
- part of reflex arcs regulating organ activities
- transmit pain and pressure sensations from organs to CNS
Physiology of the ANS
- acetylcholine: released by cholinergic Neurons
- norepinephrine: released by adrenergic neurons
- certain cells have receptors that combine with neurotransmitters causing a response in the cell
Regulation of the ANS
- autonomic reflexes control most activity of visceral organs, glands and blood vessels
- influenced by hypothalamus and higher brain centres, but the hypothalamus has overall control of ANS
- sympathetic and parasympathetic division influence activities of enteric nervous system through autonomic reflexes
Autonomic reflexes
- parasympathetic reflex via vagus lowers heart rate
- sympathetic reflex via cardiac accelerator nerves cause heart rate to increase
Enteric nervous system
Autonomic and local reflexes
- regulation of activity of digestive tract
- sensory neurons of enteric plexuses supply CNS with info
- autonomic neurons affect responses of smooth muscles and glands
Functional generalizations
- dual innervation to most organs with sympathetic and parasympathetic having opposite effects
- either division alone or both working together can coordinate activities or different structures
