sympathetic

(adjective)

Of or related to the part of the autonomic nervous system that under stress raises blood pressure and heart rate, constricts blood vessels, and dilates the pupils.

Related Terms

Examples of sympathetic in the following topics:

  • Sympathetic Nervous System

    • Sympathetic ganglia are the ganglia of the sympathetic nervous system that initiate fight-or-flight, stress-mediated responses.
    • The sympathetic ganglia are the ganglia of the sympathetic nervous system (the red lines in the diagram below).
    • This response is also known as the sympathetico-adrenal response because the pre-ganglionic sympathetic fibers that end in the adrenal medulla—like all sympathetic fibers—secrete acetylcholine.
    • Sympathetic ganglia are the tissue from which neuroblastoma tumours arise.
    • This intercostal nerve shows the sympathetic ganglion at the top left.

  • Divisions of the Autonomic Nervous System

    • The autonomic nervous system (ANS) contains two subdivisions: the parasympathetic (PSNS) and sympathetic (SNS) nervous systems.
    • Sympathetic and parasympathetic divisions typically function in opposition to each other.
    • The sympathetic division typically functions in actions requiring quick responses.
    • Many think of sympathetic as fight or flight and parasympathetic as rest and digest or feed and breed.
    • Distinguish between the parasympathetic and sympathetic subsystems of the autonomic nervous system

  • Autonomic Interactions

    • The sympathetic and parasympathetic autonomic nervous systems cooperatively modulate internal physiology to maintain homeostasis.
    • Sympathetic and parasympathetic divisions typically function in opposition to each other.
    • The sympathetic division typically functions in actions requiring quick responses.
    • Consider sympathetic as fight or flight and parasympathetic as rest and digest or feed and breed.
    • Some typical actions of the sympathetic and parasympathetic systems are listed below.

  • Sympathetic Responses

    • The sympathetic division of the autonomic nervous system maintains internal organ homeostasis and initiates the stress response.
    • Alongside the other two components of the autonomic nervous system, the sympathetic nervous system aids in the control of most of the body's internal organs.
    • The sympathetic nervous system is responsible for regulating many homeostatic mechanisms in living organisms.
    • Some evolutionary theorists suggest that the sympathetic nervous system operated in early organisms to maintain survival since the sympathetic nervous system is responsible for priming the body for action.
    • One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for activity.

  • Preganglionic Neurons

    • Sympathetic preganglionic fibers tend to be shorter than parasympathetic preganglionic fibers because sympathetic ganglia are often closer to the spinal cord while parasympathetic preganglionic fibers tend to project to and synapse with the postganglionic fiber close to the target organ.
    • The sympathetic division has thoracolumbar outflow, meaning that the neurons begin at the thoracic and lumbar (T1–L2) portions of the spinal cord.
    • The sympathetic division (thoracolumbar outflow) consists of cell bodies in the lateral horn of the spinal cord (intermediolateral cell columns) from T1 to L2.
    • Whereas in the parasympathetic division there is a divergence factor of roughly 1:4, in the sympathetic division there can be a divergence of up to 1:20.
    • The site of synapse formation and this divergence for both the sympathetic and parasympathetic preganglionic neurons does, however, occur within ganglia situated within the peripheral nervous system.

  • Autonomic Plexuses

    • Autonomic plexuses are formed from sympathetic and parasympathetic fibers that innervate and regulate the overall activity of visceral organs.
    • Autonomic plexuses are formed from sympathetic postganglionic axons, parasympathetic preganglionic axons, and some visceral sensory axons.
    • It is formed by the superior cardiac branch of the left sympathetic trunk and the lower superior cervical cardiac branch of the left vagus nerve.
    • The pulmonary plexus is an autonomic plexus formed from pulmonary branches of vagus nerve and the sympathetic trunk.
    • This section of the sympathetic trunk shows both the celiac and the hypogastric plexus.

  • Horner's Syndrome

    • Horner's syndrome presents with drooping eyelids and pupil constriction, and is indicative of a problem in the sympathetic nervous system.
    • Horner's syndrome indicates a problem with the sympathetic nervous system, a part of the autonomic nervous system .
    • Partial ptosis: drooping of the upper eyelid from loss of sympathetic innervation to the superior tarsal muscle (Müller's muscle)
    • This happens because a lack of sympathetic stimulation in childhood interferes with melanin pigmentation of the melanocytes of the iris.
    • Sympathetic and parasympathetic innervation of the pupil.

  • The Stress Response

    • The body's stress response is mediated by the sympathetic nervous system and the hypothalmic-pituitary-adrenal (HPA) axis.
    • The body's stress response is mediated by the interplay between the sympathetic nervous system (SNS) and the hypothalmic-pituitary-adrenal (HPA) axis.
    • This response is also referred to as the sympatho-adrenal response of the body owing to the fact that the preganglionic sympathetic fibers that end in the adrenal medulla secrete acetylcholine, which activates the release of adrenaline and noradrenaline from the medulla.
    • This response acts primarily on the cardiovascular system and is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via catecholamines, such as the adrenaline secreted from the adrenal medulla.

  • Adrenal Medulla

    • To carry out this response, the adrenal medulla receives input from the sympathetic nervous system through nerve fibers originating in the thoracic spinal cord from T5–T11.
    • Chromaffin cells are the neuroendocrine cells found in the medulla; they are modified post-synaptic sympathetic neurons that receive sympathetic input.

  • Parasympathetic (Craniosacral) Division

    • Each has three roots entering the ganglion (motor, sympathetic, and sensory roots) and a variable number of exiting branches.
    • The sympathetic root carries postsynaptic sympathetic fibers (general visceral efferent fibers) that traverse the ganglion without creating a synapse.
    • Because of its location, the parasympathetic system is commonly referred to as having craniosacral outflow, in contrast to the sympathetic nervous system, which is said to have thoracolumbar outflow.