Anatomy & Physiology Unit 2

M10-18

Somatic Nervous System

The branch of the nervous system that causes voluntary contraction of skeletal muscles through the corticospinal tract and lower motor neurons originating in the ventral (anterior) horn of the spinal cord.

Autonomic nervous system

The branch of the nervous system that controls involuntary contraction of cardiac muscle, smooth muscle, and glandular tissue, capable of both exciting and inhibiting target effectors.

Preganglionic Neuron

The first neuron in the two-neuron autonomic pathway; its cell body originates in the lateral horn of the spinal cord or brainstem and extends to a ganglion to synapse with a second neuron.

Preganglionic Axon

The axon of a preganglionic neuron; myelinated in the sympathetic division (giving white rami their appearance) and long in the parasympathetic division.

Ganglion (ganglia)

A collection of neuronal cell bodies outside the CNS where the preganglionic neuron synapses with the postganglionic neuron

Postganglionic Neuron

The second neuron in the two-neuron autonomic pathway, extending from the ganglion directly to the target effector organ.

Postganglionic Axon

The axon of a postganglionic neuron; unmyelinated (forming gray rami in the sympathetic division), relatively long in sympathetic pathways, and short in parasympathetic pathways.

Acetylcholine

The neurotransmitter released at synapses between preganglionic and postganglionic neurons in both divisions, as well as between parasympathetic postganglionic neurons and target effectors.

Dual Innvervation

The arrangement where a visceral target organ receives nerve inputs from both the sympathetic and parasympathetic divisions to adjust effector activity based on bodily needs.

Referred Pain

The phenomenon where visceral pain sensations are consciously felt in unexpected somatic body surface areas because visceral sensory fibers enter the same spinal cord segments as somatosensory fibers from those surface areas.

Plexus

A complex web of intermingled parasympathetic preganglionic and sympathetic postganglionic axons traveling together to their destination organs.

Cardiac Plexus

An autonomic plexus containing nerve fibers that travel to the heart.

Esophageal Plexus

An autonomic plexus containing nerve fibers that travel to portions of the esophagus.

Pulmonary Plexus

An autonomic plexus containing nerve fibers that travel to the lungs and bronchi.

Abdominal Aortic Plexuses

A collection of autonomic networks along the abdominal aorta that supply abdominal organs

Celiac Plexus

An autonomic plexus carrying fibers to organs of the foregut (from the inferior esophagus through the first two parts of the duodenum, liver, pancreas, and gallbladder)

Superior mesenteric Plexus

An autonomic plexus carrying fibers to midgut organs (from the third part of the duodenum through the first two-thirds of the transverse colon).

Inferior mesenteric plexus

An autonomic plexus carrying fibers to hindgut organs (from the last two-thirds of the transverse colon to the rectum).

Hypogastric Plexus

An autonomic plexus supplying pelvic organs, including the urinary bladder and reproductive organs.

Parasympathetic Division

The division of the autonomic nervous system associated with "rest and digest" functions, which conserves energy, replenishes energy stores, and oversees routine maintenance.

Craniosacral

A term referring to the parasympathetic division because its preganglionic neurons originate in brainstem cranial nerve nuclei (CN III, VII, IX, X) and sacral spinal cord levels S2–S4.

Vagus Nerve

CN X; The primary parasympathetic cranial nerve that supplies preganglionic fibers to organs throughout the thorax and most of the abdomen.

Pelvic Splanchnic Nerves

Preganglionic parasympathetic fibers originating from sacral spinal cord levels S2–S4 that supply the distal alimentary tract and pelvic organs.

Thoracolumbar

A term referring to the sympathetic division because its preganglionic neurons originate from the lateral horns of thoracic and upper lumbar spinal cord segments (T1–L2).

Sympathetic Chain (trunk)

A continuous network running parallel alongside both sides of the vertebral column containing connected ganglia.

Sympathetic Chain Ganglia

Swellings along the sympathetic chain where preganglionic neurons synapse with postganglionic neurons.

Norepinehprine/Epinephrine

Signaling molecules where norepinephrine is released by most sympathetic postganglionic axons onto effectors, and both epinephrine and norepinephrine are secreted as hormones into the blood by the adrenal medulla.

Superior, middle, inferior cervical ganglion

Sympathetic chain ganglia in the neck that receive ascending preganglionic fibers from upper thoracic levels to innervate structures in the head, neck, and thorax.

White rami communicantes

Structures containing myelinated preganglionic sympathetic axons branching from spinal nerves into the sympathetic chain.

Gray rami communicantes

Structures containing unmyelinated postganglionic sympathetic axons traveling from the sympathetic chain back into spinal nerves.

Splanchnic Nerves

Preganglionic sympathetic axons (originating T5–L2) that pass through the sympathetic chain without synapsing to travel anteriorly to prevertebral ganglia

Greater thoracic splanchnic nerve

Arises from T5–T9 levels and travels to synapse in the celiac ganglion.

Lesser thoracic splanchnic nerve

Arises from T10–T11 levels and travels to synapse in the superior mesenteric ganglion.

Least thoracic splanchnic nerve

Arises from T12 level and sends fibers to either the superior mesenteric or inferior mesenteric ganglion.

Lumbar splanchnic nerves

Arise from L1–L2 levels and travel to synapse in the inferior mesenteric ganglion.

Sacral splanchnic nerves

Postganglionic sympathetic fibers emerging from the sacral extension of the sympathetic chain to join the hypogastric plexus.

Prevertebral ganglia

Unpaired sympathetic ganglia located anterior to the vertebral column on the abdominal aorta that control abdominal organs

Celiac ganglia

Prevertebral ganglion associated with foregut organs

Superior mesenteric ganglia

Prevertebral ganglion associated with midgut organs

Inferior mesenteric ganglia

Prevertebral ganglion associated with hindgut organs

Spinal nerve pathway

Sympathetic pathway (originating T1–L2) where fibers synapse in chain ganglia and exit via gray rami communicantes to reach sweat glands, arrector pili muscles, and skin blood vessels

Postganglionic sympathetic pathway

Sympathetic pathway (originating T1–T5) where fibers ascend to cervical ganglia, synapse, and exit directly into cardiac, pulmonary, or esophageal plexuses

Splanchnic nerve pathway

Sympathetic pathway (originating T5–L2) where fibers pass through the chain without synapsing and travel as splanchnic nerves to prevertebral ganglia

Adrenal medulla pathway

Unique sympathetic pathway (originating T8–T12) where preganglionic axons pass directly to neuroendocrine cells in the adrenal medulla without synapsing in an autonomic ganglion

Adrenal gland

Glandular and neuroendocrine organ located superior to the kidneys

Adrenal medulla

The interior portion of the adrenal gland that secretes epinephrine and norepinephrine into the bloodstream during sympathetic stimulation

Vertebral Column

The flexible axis composed of 26 bones (24 individual vertebrae plus the fused sacrum and coccyx) that supports the head, neck, and trunk, allows movement, and encloses the spinal cord

Body of the Vertebral Column

The anterior, weight-bearing solid cylinder portion of a vertebra that supports body weight

Spinous Process

The single midline projection extending posteriorly from the vertebral arch that serves as an attachment site for back muscles and ligaments

Transverse Process

Paired lateral projections arising from the junction of the pedicle and lamina on each side of a vertebra

Superior articular facet

Smooth articular surface on the upward-projecting process of a vertebra that joins with the inferior process of the vertebra above it

Inferior articular facet

Smooth surface on the downward-projecting process of a vertebra that joins with the superior process of the vertebra below it

Vertebral foramen

The large opening enclosed by the vertebral arch and body that houses and protects the spinal cord

Intervertebral foramen

The lateral opening formed between the pedicles of adjacent vertebrae through which a spinal nerve exits

Cervical Vertebrae

The 7 vertebrae (C1–C7) of the neck region, characterized by small bodies and transverse foramina.

Transverse Foramen

Openings present in the transverse processes of cervical vertebrae through which the vertebral arteries pass to supply the brain.

Atlas

The first cervical vertebra C1; lacks a body and features deep superior articular facets that articulate with the occipital condyles to allow nodding ("yes") movement.

Superior articular facet of Atlas

Deep concave surfaces on C1 that articulate directly with the occipital condyles of the skull.

Axis

The second cervical vertebra C2; contains an upright vertical tooth-like process (dens) that acts as a pivot for C1 rotation.

Dens (Odontoid Process)

The vertical pivot process extending upward from C2 around which C1 rotates to produce rotational ("no") movement of the head.

Thoracic vertebrae

The 12 vertebrae (T1–T12) of the chest region that articulate with the ribs via specialized costal facets and demifacets

Costal facets/demifacets

Smooth articular surfaces located on the bodies and transverse processes of thoracic vertebrae for attachment to rib heads and tubercles.

Lumbar vertebrae

The 5 largest vertebrae (L1–L5) of the lower back, characterized by thick, massive bodies designed to carry the greatest amount of body weight.

Sacrum

A triangular bone formed by the fusion of 5 sacral vertebrae (S1–S5) that articulates with L5 superiorly and the hip bones laterally.

Coccyx

 The tailbone, formed by the fusion of 3 to 5 (typically 4) small coccygeal vertebrae attached to the inferior tip of the sacrum

Spinal Curvatures

Natural anatomical curves of the spine that increase flexibility and weight distribution

Primary Curvatures

The thoracic and sacral curves present at birth (concave anteriorly)

Secondary Curvatures

The cervical and lumbar curves that develop during the first two years of life as an infant learns to hold up its head and walk upright.

Kyphosis

 An abnormal, exaggerated thoracic curvature ("hunchback")

Lordosis

An abnormal, exaggerated lumbar curvature ("swayback")

Scoliosis

An abnormal lateral bending and rotation of the vertebral column

Intervertebral disc

A fibrocartilaginous pad sandwiched between adjacent vertebral bodies to absorb shock and permit movement

Annulus fibrosus

The tough, outer fibrous ring of fibrocartilage surrounding the intervertebral disc

Nucleus pulposus

 The inner gelatinous core of the intervertebral disc that cushions compressive forces

Ligaments

A tough, fibrous band of connective tissue that primarily connects bone to bone and stabilizes joints

Anterior longitudinal ligament

 A wide ligament running down the anterior side of all vertebral bodies that prevents hyperextension of the spine

Posterior longitudinal ligament

A narrower ligament running along the posterior aspect of vertebral bodies inside the spinal canal that resists hyperflexion.

Interspinous ligament

Connective tissue bands running between adjacent spinous processes to resist hyperflexion

Supraspinous ligament

 A strong ligament interconnecting the tips of spinous processes along the posterior spine to support forward bending

Ligamentum Flavum

Elastic ligaments connecting the laminae of adjacent vertebrae that help maintain an upright posture and resist hyperflexion

Ribs

12 pairs of curved flat bones forming the protective lateral walls of the thoracic cage

True Ribs

1-7; Ribs that attach directly to the sternum via their own individual costal cartilages

False Ribs

8-12; Ribs whose costal cartilages do not attach directly to the sternum (Ribs 8–10 connect indirectly via the costal cartilage of the rib above)

Floating Ribs

11-12; A subset of false ribs that have no anterior attachment to the sternum

Costal Cartilage

Bars of hyaline cartilage connecting ribs to the sternum, providing elasticity during breathing

Head of Rib

The posterior end of a rib that articulates with the costal facets/demifacets on vertebral bodies

Neck of Rib

The narrowed region of a rib located immediately lateral to the head.

Articular Facet for Transverse Process (tubercle)

Small bump on the posterior rib lateral to the neck that articulates with the costal facet on a thoracic vertebra's transverse process.

Angle of Rib

The point where the rib shaft bends most sharply anteriorly, forming the most posterior extent of the chest cage.

Shaft (Body of Rib)

The main, flattened, curved portion of a rib extending anteriorly toward the sternum.

Demifacet (On thoracic vertebrae)

A half-facet located on the upper or lower edge of a thoracic vertebral body where a rib head articulates across two adjacent vertebrae.

Sternum

The flat breastbone along the anterior midline of the thorax

Manubrium

The wider, superior segment of the sternum that articulates with the clavicles and first pair of ribs

Body of Sternum

The elongated central portion of the sternum articulating with costal cartilages 2 through 7

Xiphoid Process

The small inferior cartilaginous tip of the sternum that gradually ossifies during middle age

Suprasternal (jugular) notch

The shallow, U-shaped depression located on the superior border of the manubrium.

Clavicular notch

Depressions on the superior-lateral margins of the manubrium where the clavicles articulate

Intercostal nerves

Anterior rami of spinal nerves T1–T11 traveling through intercostal spaces to innervate intercostal muscles, abdominal wall muscles, and chest skin

Intercostal arteries

Blood vessels running along the intercostal spaces to supply blood to the chest wall and intercostal muscles

Intercostal veins

Veins traveling alongside intercostal arteries in intercostal spaces to drain blood from the thoracic wall