2. Sistema Nervioso Autonomo
O El sistema Nervioso Autónomo es
la parte del Sistema Nervioso
que es responsable de la
homeostasis
O Excepto por el musculo
esquelético, que tiene su
inervación del sistema nervioso
somato motor, la inervación
para los otros órganos es
suplida por el Sistema Nervioso
Autónomo .
3. O Terminaciones nerviosas están localizadas en el
musculo liso (ej., vasos sanguíneos, pared intestinal,
vejiga urinaria), musculo cardiaco y glándulas (ej.,
glándulas sudoríparas, glándulas, salivales).
4. O Aunque la supervivencia es posible sin el Sistema
Nervioso Autónomo, la habilidad para adaptarse a
los estresores ambientales y otras amenazas está
severamente comprometida.
5. O La definición clásica del Sistema Nervioso
Autónomo es la de las neuronas
preganglionares y postganglionares dentro de
las divisiones simpáticas y parasimpáticas.
O Esto es equivalente a definir el sistema
nervioso somatomotor como las motoneuronas
craneales y motoneuronas espinales.
O Una definición moderna del SNA toma en
cuenta las vías descendentes de varias
regiones del encéfalo y el tallo cerebral asi
como vías aferentes viscerales que regulan el
nivel de actividad en los nervios del simpático y
parasimpático.
6. SIMPATICO Y PARASIMPATICO
O EL SNA tiene dos divisiones
mayores: el sistema nervioso
simpático y el sistema nervioso
parasimpatico. Como se
describirá algunos órganos blancos
son inervados por ambas divisiones
del SNA y otros son controlados por
uno solo.
O Además el SNA incluye Sistema
Nervioso Entérico dentro del
sistema gastrointestinal.
7. Sistema Simpático
O Este sistema nos prepara para la acción. Este
es el sistema que media en la respuesta de
estrés hormonal. Las conductas de lucha y de
huida están mediadas por el sistema
simpático.
O La sudoración excesiva o hiperhidrosis en
manos, axilas o cara se relaciona con una
hiper estimulación del sistema simpático.
8.
9. Acción del sistema nervioso simpático en
distintos órganos
OEn el ojo: dilata la pupila
OEn la salivación: la producción de saliva se reduce
OEn los pulmones: dilata los bronquios
OEn el corazón, aumenta la velocidad del latido
OEn los vasos sanguíneos: los constriñe
OEn las glándulas sudoríparas: las estimula
OEn el riñón: disminución de la secreción de orina
OEn el pene: promueve la eyaculación
OEn el aparato digestivo: inhibe los movimientos
involuntarios de contracción del estómago.
10. Sistema Parasimpatico
O Se origina en el tronco del encéfalo.
O Sus funciones son más diferenciadas.
O Es responsable de la regulación de
órganos internos del descanso de la digestión y
las actividades que ocurren cuando el cuerpo está
en reposo como el sueño.
11. Actividades mediadas por el sistema
parasimpático:
OEl lagrimeo – en el ojo, la pupila se contrae
OEn los pulmones: contrae los bronquios
OEn la salivación: la producción de saliva aumenta
OEn el corazón: disminuye la frecuencia cardíaca
OEn el aparato digestivo aumenta los movimientos e
contracción del estómago
ODisminuye la tensión arterial
OEn el riñón: aumento de la secreción de orina
OAumenta el almacenamiento de combustible
OAumenta nuestra resistencia a las infecciones
Notas del editor
The autonomic nervous system (ANS) is the part of the nervous system that is responsible for homeostasis. Except for skeletal muscle, which gets its innervation from the somatomotor nervous system, innervation to all other organs is supplied by the ANS. Nerve terminals are located in smooth muscle (eg, blood vessels, gut wall, urinary bladder), cardiac muscle, and glands (eg, sweat glands, salivary glands).
Although survival is possible without an ANS, the ability to adapt to environmental stressors and other challenges is severely compromised (see Clinical Box 17–1). The ANS has two major divisions: the sympathetic and parasympathetic nervous systems. As will be described, some target organs are innervated by both divisions and others are controlled by only one. In addition, the ANS includes the enteric nervous system within the gastrointestinal tract. The classic definition of the ANS is the preganglionic and postganglionic neurons within the sympathetic and parasympathetic divisions. This would be equivalent to defining the somatomotor nervous system as the cranial and spinal motor neurons. A modern definition of the ANS takes into account the descending pathways from several forebrain and brain stem regions as well as visceral afferent pathways that set the level of activity in sympathetic and parasympathetic nerves. This is analogous to including the many descending and ascending pathways that influence the activity of somatic motor neurons as elements of the somatomotor nervous system.
Although survival is possible without an ANS, the ability to adapt to environmental stressors and other challenges is severely compromised (see Clinical Box 17–1). The ANS has two major divisions: the sympathetic and parasympathetic nervous systems. As will be described, some target organs are innervated by both divisions and others are controlled by only one. In addition, the ANS includes the enteric nervous system within the gastrointestinal tract. The classic definition of the ANS is the preganglionic and postganglionic neurons within the sympathetic and parasympathetic divisions. This would be equivalent to defining the somatomotor nervous system as the cranial and spinal motor neurons. A modern definition of the ANS takes into account the descending pathways from several forebrain and brain stem regions as well as visceral afferent pathways that set the level of activity in sympathetic and parasympathetic nerves. This is analogous to including the many descending and ascending pathways that influence the activity of somatic motor neurons as elements of the somatomotor nervous system.
In contrast to -motor neurons, which are located at all spinal segments, sympathetic preganglionic neurons are located in the IML of only the first thoracic to the third or fourth lumbar segments. This is why the sympathetic nervous system is sometimes called the thoracolumbar division of the ANS. The axons of the sympathetic preganglionic neurons leave the spinal cord at the level at which their cell bodies are located and exit via the ventral root along with axons of - and -motor neurons (Figure 17–2). They then separate from the ventral root via the white rami communicans and project to the adjacent sympathetic paravertebral ganglion, where some of them end on the cell bodies of the postganglionic neurons. Paravertebral ganglia are located adjacent to each thoracic and upper lumbar spinal segments; in addition, there are a few ganglia adjacent to the cervical and sacral spinal segments. These ganglia form the sympathetic chain bilaterally. The ganglia are connected to each other via the axons of preganglionic neurons that travel rostrally or caudally to terminate on postganglionic neurons located at some distance. This arrangement is seen in Figures 17–2 and 17–3
The parasympathetic nervous system is sometimes called the craniosacral division of the ANS because of the location of its preganglionic neurons (Figure 17–3). The parasympathetic nerves supply the visceral structures in the head via the oculomotor, facial, and glossopharyngeal nerves, and those in the thorax and upper abdomen via the vagus nerves. The sacral outflow supplies the pelvic viscera via branches of the second to fourth sacral spinal nerves. Parasympathetic preganglionic fibers synapse on ganglia cells clustered within the walls of visceral organs; thus these parasympathetic postganglionic fibers are very short.