Unit 2 Study Guide: Autonomics and Anatomy Overview

Autonomic Nervous System

A two-neuron chain consisting of a preganglionic neuron and a postganglionic neuron.

Preganglionic Neuron

The first neuron in the autonomic nervous system chain.

Postganglionic Neuron

The second neuron in the autonomic nervous system chain.

Parasympathetic Nervous System

Part of the autonomic nervous system that promotes digestion, gland secretion, energy conservation, and bladder emptying.

Preganglionic Cell Bodies (Parasympathetic)

Located in the brainstem associated with cranial nerves and in the sacral spinal cord in segments S2-S4.

Postganglionic Cell Bodies (Parasympathetic)

Located in ganglia that lie within or very close to the target organ.

Cranial Nerves (Parasympathetic)

CN III, VII, IX, and X carry parasympathetic fibers.

Sympathetic Nervous System

Part of the autonomic nervous system that increases heart rate, dilates pupils, inhibits digestion, and redirects blood flow to muscles.

Preganglionic Cell Bodies (Sympathetic)

Found in the thoracic and lumbar regions of the spinal cord, specifically from the lateral horn.

Thoracolumbar Division

Spinal cord region that spans from T1 to L2 where sympathetic preganglionic neurons originate.

Postganglionic Cell Bodies (Sympathetic)

Located in paravertebral ganglia (sympathetic trunk) and prevertebral ganglia.

Splanchnic Nerves

Preganglionic fibers that pass through the sympathetic trunk without synapsing and synapse in prevertebral ganglia in the abdomen.

Heart (Autonomic Supply)

Parasympathetic: CN X (vagus); Sympathetic: T1-T5 via sympathetic trunk.

Lungs (Autonomic Supply)

Parasympathetic: CN X (vagus); Sympathetic: T2-T5 via sympathetic trunk.

Stomach (Autonomic Supply)

Parasympathetic: CN X (vagus); Sympathetic: Greater splanchnic nerve (T5-T9) → celiac ganglion.

Upper Duodenum (Autonomic Supply)

Parasympathetic: CN X (vagus); Sympathetic: Greater splanchnic nerve (T5-T9) → superior mesenteric ganglion.

Lower Duodenum (Autonomic Supply)

Parasympathetic: CN X (vagus); Sympathetic: Lesser splanchnic nerve (T10-T11) → superior mesenteric ganglion.

Jejunum and Ileum (Autonomic Supply)

Parasympathetic: CN X (vagus); Sympathetic: Lesser splanchnic nerve (T10-T11) → superior mesenteric ganglion.

First Part of Large Intestine (Autonomic Supply)

Parasympathetic: CN X (vagus); Sympathetic: Lesser splanchnic nerve (T10-T11) and possibly some lumbar splanchnic contribution → superior mesenteric ganglion.

End of Large Intestine (Autonomic Supply)

Parasympathetic: S2-S4 via pelvic splanchnic nerves; Sympathetic: Lumbar splanchnic nerves (L1-L2) → inferior mesenteric ganglion → pelvic ganglia.

Pelvic Viscera (Autonomic Supply)

Parasympathetic: S2-S4 via pelvic splanchnic nerves; Sympathetic: Sacral splanchnic nerves → pelvic ganglia.

Pericardium

The protective sac around the heart.

Fibrous Pericardium

The outermost layer of the pericardium that is tough and non-elastic.

Serous Pericardium

The inner layers of the pericardium, consisting of parietal and visceral pericardium.

Base of the Heart

Located at the sternal angle around T4-T5 vertebral level.

Parietal pericardium

Lines the inner surface of the fibrous pericardium and pericardial cavity.

Visceral pericardium (epicardium)

Lies directly on the surface of the heart.

Inferior surface of the heart

Rests on the diaphragm.

Right border of the heart

Formed by the right atrium.

Left border of the heart

Consists of the left ventricle and left auricle.

Apex of the heart

Located to the left of the sternum in the 5th intercostal space, between the 5th and 6th ribs.

Anterior (sternocostal) surface

Mostly made up of the right ventricle, includes part of the right atrium and a little bit of the left ventricle.

Inferior (diaphragmatic) surface

Formed by the left ventricle and part of the right ventricle.

Posterior surface (base)

Mostly the left atrium, includes a small part of the right atrium.

Tricuspid valve

Located left of the sternum, near the 3rd costal cartilage.

Pulmonary valve

Located left of the sternum, at the 3rd intercostal space.

Mitral valve

Located beneath the sternum, at the 4th and 5th intercostal spaces.

Aortic valve

Located left of the sternum, at the 4th costal cartilage.

Atria

Chambers where blood enters the heart.

Ventricles

Chambers where blood exits the heart.

Right side of the heart

Contains deoxygenated blood.

Left side of the heart

Contains oxygenated blood.

Foramen ovale

Connects the right atrium to the left atrium, with the adult remnant being the fossa ovalis.

Ductus arteriosus

Connects the pulmonary trunk/arteries to the aorta, with the adult remnant being the ligamentum arteriosum.

Normal blood flow through the adult heart

1. Deoxygenated blood enters the right atrium via SVC, IVC, and coronary sinus. 2. Passes through the tricuspid valve into the right ventricle. 3. Right ventricle pumps it through the pulmonary valve into the pulmonary trunk → pulmonary arteries → lungs. 4. Oxygenated blood returns via pulmonary veins to the left atrium. 5. Passes through the mitral valve into the left ventricle.

Left ventricle

Pumps blood through the aortic valve into the aorta for systemic circulation.

Blood supply to the heart

The heart receives blood from branches of the ascending aorta.

Left coronary artery

Supplies the left atrium, left ventricle, and most of the interventricular septum.

Right coronary artery

Supplies the right atrium, right ventricle, SA node (in most people), and AV node.

SA node

Associated with the right coronary artery and supplied by the sinoatrial nodal artery, which usually branches from the RCA.

Anterior interventricular artery (LAD)

Branch of the left coronary artery that supplies the anterior interventricular septum and anterior walls of both ventricles; runs with the great cardiac vein.

Middle cardiac vein

Runs with the posterior interventricular artery, drains into the coronary sinus, and is associated with the right coronary artery.

Posterior interventricular artery (PDA)

Typically a branch of the right coronary artery in a right-dominant heart; runs with the middle cardiac vein and supplies the posterior third of the interventricular septum and adjacent ventricular walls.

Great cardiac vein

Runs with the anterior interventricular artery (LAD) and drains blood from areas supplied by the left coronary artery.

AV node

Located in the interatrial septum near the opening of the coronary sinus and usually supplied by the right coronary artery via the AV nodal artery.

Conduction system of the heart

The system that initiates and conducts the heartbeat, starting from the SA node to the AV node and through the Bundle of His.

Sinoatrial (SA) node

Located at the junction of the SVC and right atrium; initiates the heartbeat.

Atrioventricular (AV) node

Located in the interatrial septum, near the opening of the coronary sinus; receives impulses from the atria.

Bundle of His

The pathway that conducts impulses from the AV node into the interventricular septum.

Right bundle branch

Passes through the moderator band to the anterior wall of the right ventricle.

Purkinje fibers

Distribute the electrical signal throughout the ventricular myocardium.

Structures passing through the superior thoracic aperture

Includes trachea, common carotid arteries, subclavian arteries, esophagus, internal jugular veins, subclavian veins, thoracic duct, vagus nerve, and phrenic nerve.

Ribs

There are 12 pairs of ribs; ribs 1-7 are true ribs, ribs 8-12 are false ribs, and ribs 11 and 12 are floating ribs.

Costal groove

The inferior internal border of the rib that protects the intercostal vein, artery, and nerve (VAN).

Structures passing through the inferior thoracic aperture

Includes aorta (T12), esophagus (T10), inferior vena cava (IVC) (T8), thoracic duct (T12), vagus nerve (T10), azygos venous system (T12), and greater splanchnic nerve.

Pleura

There are 2 pleural cavities, one for each lung.

Visceral pleura

Lies directly on the lung surface.

Parietal pleura

Lines the thoracic wall.

Cervical pleura

Extends into the neck above the first rib.

Costal pleura

Lines the inner surface of the ribs.

Diaphragmatic pleura

Covers the diaphragm's superior surface.

Mediastinal pleura

Lines the mediastinum and is continuous with visceral pleura.

Pleural recesses

Regions where parietal pleura contacts itself due to the lungs not completely filling the pleural cavities.

Costodiaphragmatic recess

Located between the costal pleura and the diaphragmatic pleura

Cardiac notch

The area where the left lung deviates from the midline

Intercostal nerves

There are 11 pairs of intercostal nerves

Landmark nerves

T4 = cutaneous innervation at the level of the nipple

Posterior intercostal arteries

Arise from the thoracic aorta

Anterior intercostal arteries

Arise from the internal thoracic artery

Anterior intercostal veins

Drain into the internal thoracic vein

Posterior intercostal veins

Drain into the azygos system, which includes: Accessory hemiazygos vein (superior left), Hemiazygos vein (inferior left)

Azygos vein

Drains into the superior vena cava

Trachea

In the superior mediastinum, the structure just anterior to the esophagus and just posterior to the pulmonary vessels is the trachea

Trachea bifurcation

The trachea bifurcates at T4 vertebra

Carina

The midline ridge at this bifurcation

Aspiration

More likely to enter the right primary bronchus because it is shorter, wider, and more vertical

Bronchial branching

Right lung: 3 secondary bronchi (one per lobe)

Bronchopulmonary segments

Each lung has 10 bronchopulmonary segments

Left lung segments

5 superior, 5 inferior

Right lung segments

3 superior, 2 middle, 5 inferior

Phrenic nerve

Runs anterior to the root of the lung

Vagus nerve

Runs posterior to the root of the lung

Diaphragm

Active in inspiration and the main muscle of quiet (passive) and forced inspiration

External intercostals

Active during inspiration and elevate ribs

Internal intercostals

Active during forced expiration and depress ribs

Innermost intercostals

Same fiber direction and action as internal intercostals, active during forced expiration

Subcostalis

Similar action and fiber direction as internal intercostals, active during forced expiration

Transversus thoracis

Depresses ribs and is active during forced expiration

Rectus abdominis

Flexes trunk and is innervated by intercostal nerves

Quadratus lumborum

Laterally flexes lumbar spine, fixes 12th rib, hikes hip