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Nerve Cells (Electron microscopy x2,250).
Autonomic nervous system (ANS) • The ANS is a subdivision of the motor division of the peripheral nervous system (PNS), which controls involuntary, unconscious body functions through effector organs that include cardiac muscle, smooth muscle, and exocrine glands. Some functions of the ANS include contraction of the heart and blood vessels, ejaculation, saliva secretion, and release of glucose from the liver. • The autonomic nervous system is made of two components, the sympathetic and parasympathetic branches.
Sympathetic system The sympathetic system has its origin in the thoraco-lumbar part of the spinal cord. The sympathetic system is also called the adrenergic system, because the main neurotransmitter released at effector organs is adrenaline (epinephrine) and noradrenaline ( norepinephrine ). How does the sympathetic nervous system function? • Signals are sent from the hypothalamus and brain stem (medulla and pons) through the spinal cord to the sympathetic chain ganglia. The sympathetic ganglia are only a short distance from the spinal cord. Acetycholine is the neurotransmitter. • Postganglionic fibers send signals from the ganglia to effector organs. Norepinephrine (with a few exceptions) is the neurotransmitter. • The adrenal medulla cells are postganglionic neurons. The adrenal medulla secretes large amounts of norepinephrine and epinephrine directly into the blood when stimulated by acetylcholine from sympathetic preganglionic neurons. This causes a massive generalized systemic effect (i.e. fight-or-flight response) in emergency situations.
Parasympathetic system The parasympathetic system has its origins in the sacral part of the spinal cord and cranial nerves. The parasympathetic system is also called the cholinergic system, because acetylcholine is the main neurotransmitter. How does the parasympathetic nervous system function? • Signals arise in the hypothalamus and brainstem and pass through certain cranial nerves. Most signals pass through the vagus nerve (X or tenth cranial nerve) via preganglionic fibers, which terminate by synapsing with postganglionic fibers at effector organs. A few fibers originate in the sacral part of the spinal cord. • Postganglionic fibers are very short and secrete acetylcholine at their terminal synapses.
THE PERIPHERAL NERVOUS SYSTEM 1. ALL OF THE NERVOUS SYSTEM OUTSIDE THE SPINAL CORD AND BRAIN IS KNOWN AS THE PERIPHERAL NERVOUS SYSTEM (PNS) (Figure 49-8). 2. THE PERIPHERAL NERVOUS SYSTEM CAN BE DIVIDED INTO TWO DIVISION: A. THE SENSORY DIVISION (AFFERENT) B. THE MOTOR DIVISION (EFFERENT) 3. THE SENSORY DIVISION TRANSMITS IMPULSES FROM SENSE ORGANS - SUCH AS THE EARS AND TASTE BUDS- TO THE CENTRAL NERVOUS SYSTEM. 4. THE MOTOR DIVISION TRANSMITS IMPULSES FROM THE CENTRAL NERVOUS SYSTEM TO THE MUSCLES OR GLANDS (EFFECTORS). 5. THE MOTOR DIVISION IS FURTHER INTO: A. THE SOMATIC NERVOUS SYSTEM B. THE AUTONOMIC NERVOUS SYSTEM.
THE SOMATIC NERVOUS SYSTEM 1. The Somatic Nervous System regulates activities that ARE UNDER CONSCIOUS CONTROL, movement of skeletal muscles. 2. Every time you lift your finger or wiggle your toes, you are using the Motor Neurons of the Somatic Nervous System. 3. Many Nerves within this system are part of reflexes and can act automatically. 4. A Reflex Sample: A. Step on a tack with your bare foot. B. Receptors in the skin stimulated. C. The Sensory Neurons carry the impulse to Spinal Cord. D. A group of Neurons in the Spinal Cord AUTOMATICALLY ACTIVATES Motor Neurons. E. These Motor Neurons cause the Muscles (effectors) in your leg to contract, pulling you foot away. 5. Notice that this message did not go to the Brain, but was completed in the Spinal Cord. (REFLEX) 6. THE RECEPTOR, SENSORY NEURON, MOTOR NEURON, AND EFFECTOR THAT ARE INVOLVED IN THIS QUICK RESPONSE ARE TOGETHER KNOWN AS A REFLEX ARC.
THE AUTONOMIC NERVOUS SYSTEM 1. THE AUTONOMIC NERVOUS SYSTEM REGULATES ACTIVITIES THAT ARE AUTOMATIC, OR INVOLUNTARY. 2. The Nerves of the Autonomic Nervous System CONTROL Functions of the body that are NOT UNDER CONSCIOUS CONTROL. 3. The Autonomic Nervous system seems to be concerned with striking a balance or MAINTAINING HOMEOSTASIS IN THE FUNCTIONING OF MANY ORGANS OF THE BODY. EXAMPLES: CONTRACTION IN THE HEART, DIGESTION, HEART RATE, BREATHING, SALIVATION, AND BLADDER. 4. THE AUTONOMIC NERVOUS SYSTEM IS FURTHER SUBDIVIDED INTO TWO PARTS: A. THE SYMPATHETIC DIVISION B. THE PARASYMPATHETIC DIVISION 5. The TWO parts have OPPOSITE EFFECTS on the ORGANS they control(See Table 49-1). 6. Most organs controlled by the Autonomic Division are under control of both Sympathetic and Parasympathetic Neurons. EXAMPLE:Heart Rate is SPEEDED UP by the Sympathetic Nervous System, and it is SLOWED DOWN by the Parasympathetic Nervous System. 7. The Sympathetic Division generally ACTIVATES ORGANS or SPEEDS UP. 8. The Parasympathetic Division generally RETARDS ORGANS or SLOWS DOWN.
to contract -> defecation (sympathetic blocks defecation) More Information The autonomic nervous system is described on Eric Chudler's webpage.
The thalamus directs sensory messages to appropriate higher centers. The hypothalamus is involved in emotion and in drives associated with survival. It also controls the operations of the autonomic nervous system and sends out chemicals that tell the pituitary gland when to "talk" to other endocrine glands.
