Lecture # 22: The Autonomic Nervous System (Chapter 15) Objective s: 2- Define the autonomic nervous system, and compare its anatomy with that of the somatic motor division of the peripheral nervous system. 3- Compare and contrast the sympathetic and parasympathetic divisions of the autonomic nervous system. 1- Distinguish between somatic and autonomic reflexes. Autonomic neurons in the enteric nervous system of the digestive tract
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Lecture # 22: The Autonomic Nervous System (Chapter 15) Objectives: 2- Define the autonomic nervous system, and compare its anatomy with that of the somatic.
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Lecture # 22: The Autonomic Nervous System (Chapter 15)
Objectives:
2- Define the autonomic nervous system, and compare its anatomy with that of the somatic motor division of the peripheral nervous system.
3- Compare and contrast the sympathetic and parasympathetic divisions of the autonomic nervous system.
1- Distinguish between somatic and autonomic reflexes.
Autonomic neurons in the enteric nervous system of the digestive tract
Thalamus
Postcentral gyrus of cerebrum
Precentral gyrus of cerebrum
Cerebe- llum
Somatic sensory receptors
Visceral sensory receptors
Sensory (afferent) Division
Hypo- thalamus
Autonomic Nervous System
Somatic Nervous System
Autonomic ganglion
It is a rapid involuntary response triggered by the CNS for the purpose of maintaining homeostasis.
Reflex:
1- Somatic Reflex: It is a reflex resulting in the contraction of an skeletal muscles.
2- Autonomic or Visceral Reflex:
Baroreceptors sense increased blood pressure1
Glossopharyngeal nerve transmits signals to medulla oblongata (brain stem)
2
Vagus nerve transmitsInhibitory signals to cardiac pacemaker
3
Heart rate decreases reducing blood pressure4
BP
BP
For example, high blood pressure is controlled by a baroreflex.
It is an unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and the response of visceral effectors (contraction of cardiac muscle, smooth muscle or in the secretion of glands).
The ANS is responsible of the Visceral Reflexes
Upper motor neuron in precentral gyrus of cerebrum
Lower motor neuron in anterior gray horn of spinal cord
Somatic Nervous System:1- The entire distance from the CNS (spinal cord) to the effector is spanned by one neuron.
Somatic effectors(skeletal muscles)
CNS
AcetylcholineMyelinated fiber
2- Only acetylcholine is employed as neurotransmitter.
Autonomic Nervous System:1- The entire distance from the CNS spinal cord) to the effector is spanned by two neurons. 2- Only acetylcholine is employed as neurotransmitter in the preganglionic neuron, but postganglionic neurons can employ either acetylcholine or norepinephrine.
Autonomic ganglion
Preganglionic neuron
Postganglionic neuron
AcetylcholineAcetylcholine or Norepinephrine
Denervation hypersensitivity : It is an exaggerated response of cardiac and smooth muscle if autonomic nerves are severed damaged.
The heart beats at its own intrinsic rate of about 100 beats/min. The parasympathetic tone holds the resting heart rate down to about 70 to 80 beats/min.
Divisions of the Autonomic Nervous SystemThe ANS has two divisions. Both divisions innervate the same target organs
2- The ParasympatheticDivision
1- The SympatheticDivisionIt adapts the body for physical activities: exercise, trauma, arousal, competition, anger, or fear(fight or fly). It increases:
It reduces the activity of:1- Digestive system2- Urinary system
Cephalic Phase of Gastric Activity Parasympathetic division
CNS
Regulation of Gastric Activity by Autonomic or Visceral Reflexes
The nervous and endocrine systems collaborate to increase gastric secretion and motility when food is eaten and to suppress them when the stomach empties.
Stimuli:
Vagus nerve (parasympathetic) stimulates gastric secretion even before food is swallowed.
Sight, smell, taste, or thought of food
The Cephalic Phase is directed by the CNS and prepares the stomach to receive food.
Mucous cells
Chief cells
Parietal cells
Mucus
Pepsinogen
HCl
ACh
+
Intestinal Phase of Gastric ActivityIt begins when chyme first enters the duodenum.
Stretch receptors and chemoreceptors in the duodenum trigger the Enterogastric Reflex.
Sympathetic nerve
The medulla oblongata stimulates sympathetic neurons that send inhibitory signals to the stomach.
_
Stimuli:Distention of the duodenum by the chyme.Decrease in the pH of the duodenum by the chyme.
Response:
Mucous cells
Chief cells
Parietal cells
Mucus
Pepsinogen
HCl
XXX
The net result is that immediately after the chyme enters the duodenum, gastric contractions decrease, and further discharge of chyme is prevented, giving the duodenum time to neutralize and digest the acidic chyme.