Anatomical terms of neuroanatomy
This article describes anatomical terminology, used to describe the central and peripheral nervous systems - including the brain, spinal cord, nerves. Neuroanatomy, like other aspects of anatomy, uses specific terminology to describe anatomical structures; this terminology helps ensure that a structure is described with minimal ambiguity. Terms help ensure that structures are described depending on their structure or function. Terms are derived from Latin and Greek, like other areas of anatomy are standardised based on internationally accepted lexicons such as Terminologia Anatomica. To help with consistency and other species are assumed when described to be in standard anatomical position, with the body standing erect and facing observer, arms at sides, palms forward. Anatomical terms of location depend on the location and species, being described. To understand the terms used for anatomical localisation, consider an animal with a straight CNS, such as a fish or lizard. In such animals the terms "rostral", "caudal", "ventral" and "dorsal" mean towards the rostrum, towards the tail, towards the belly and towards the back.
For a full discussion of those terms, see anatomical terms of location. For many purposes of anatomical description and directions are relative to the standard anatomical planes and axes; such reference to the anatomical planes and axes is called the stereotactic approach. Standard terms used throughout anatomy include anterior / posterior for the front and back of a structure, superior / inferior for above and below, medial / lateral for structures close to and away from the midline and proximal / distal for structures close to and far away from a set point; some terms are used more in neuroanatomy, particularly: Rostral and caudal: In animals with linear nervous systems, the term rostral is synonymous with anterior and the term caudal is synonymous with posterior. Due to humans having an upright posture, their nervous system is considered to bend about 90°; this is considered to occur at the junction of the diencephalon. Thus, the terminology changes at either side of the midbrain-diencephalic junction.
Superior to the junction, the terminology is the same as in animals with linear nervous systems. Inferior to the midbrain-diencephalic junction the term rostral is synonymous with superior and caudal is synonymous with inferior. Dorsal and ventral: In animals with linear nervous systems, the term dorsal is synonymous with superior and the term ventral is synonymous with inferior. In humans, however the terminology differs on either side of the midbrain-diencephalic junction. Superior to the junction, the terminology is the same as in animals with linear nervous systems. However, inferior to the midbrain-diencephalic junction the term dorsal is synonymous with posterior and ventral is synonymous with anterior. Contralateral and ipsilateral referring to a corresponding position on the opposite left or right side and on the same side respectively. Standard anatomical planes and anatomical axes are used to describe structures in animals. In humans and most other primates the axis of the central nervous system is not bent.
This means that there are certain major differences that reflect the distortion of the brains of the Hominidae. For example, to describe the human brain, "rostral" still means "towards the face", or at any rate, the interior of the cranial cavity just behind the face. However, in the brain "caudal" means not "towards the tail", but "towards the back of the cranial cavity". Alternative terms for this rostro-caudal axis of the brain include antero-posterior axis. "Dorsal" means "in the direction away from the spinal cord i.e. in the direction of the roof of the cranial cavity". "Ventral" means downwards towards floor of the cranial cavity and thence to the body. They lie on the superior-inferior or Dorsoventral axis; the third axis passes through the ears, is called the left-right, or lateral axis. These three axes of the human brain match the three planes within which they lie though the terms for the planes have not been changed from the terms for the bodily planes; the most used reference planes are: Axial, the plane, horizontal and parallel to the axial plane of the body in the standard anatomical position.
It contains the medial axes of the brain. Coronal, a vertical plane that passes through both ears, contains the lateral and dorsoventral axes. Sagittal, a vertical plane that passes from between the nostrils, between the cerebral hemispheres, dividing the brain into left and right halves, it contains the medial axes of the brain. A parasagittal plane is any plane parallel to the sagittal plane. Specific terms are used for peripheral nerves. An afferent nerve fiber is a fibre originating at the present point. For example, a striatal afferent is an afferent originating at the striatum. An efferent nerve fiber is one. For example, a cortical efferent is a fibre coming from elsewhere, arriving to the cortex. Note that, the opposite of the direction in which the nerve fibre conducts signals. Specific terms are used to describe the route of a nerve or nerve fibre: A chiasm i
The pectineus muscle is a flat, quadrangular muscle, situated at the anterior part of the upper and medial aspect of the thigh. The pectineus muscle is the most anterior adductor of the hip; the muscle does adduct and medially rotate the thigh but its primary function is hip flexion. It can be classified in the anterior compartment of thigh; the pectineus muscle arises from the pectineal line of the pubis and to a slight extent from the surface of bone in front of it, between the iliopectineal eminence and pubic tubercle, from the fascia covering the anterior surface of the muscle. The pectineus is in relation by its anterior surface with the pubic portion of the fascia lata, which separates it from the femoral artery and vein and internal saphenous vein, lower down with the profunda artery. By its posterior surface with the capsule of the hip joint, with the obturator externus and adductor brevis, the obturator artery and vein being interposed. By its external border with the psoas major, the femoral artery resting upon the line of interval.
By its internal border with the outer edge of the adductor longus. Obturator foramen is situated directly behind this muscle, it forms part of the floor of the femoral triangle. The lumbar plexus is formed from the anterior rami of nerves L1 to L4 and some fibers from T12. With only five roots and two divisions, it is less complex than the brachial plexus and gives rise to a number of nerves including the femoral nerve and accessory obturator nerve; the pectineus muscle is considered a composite muscle as the innervation is by the femoral nerve and a branch of the obturator nerve called the accessory obturator nerve. When it is present, the accessory obturator nerve innervates a portion of the pectineus muscle, entering the muscle on its dorsomedial aspect; the greater nerve to the muscle is the femoral nerve. Unlike the obturator accessory nerve, the femoral nerve is always present and provides the sole innervation for the pectineus muscle in over 90% of cases; the muscle is innervated by the accessory obturator nerve in the 8.7% of cases in which the nerve occurs.
It is one of the muscles responsible for hip flexion. It adducts the thigh. Thigh This article incorporates text in the public domain from page 472 of the 20th edition of Gray's Anatomy Woodburne, Russell. "The Accessory Obturator Nerve and the Innervation of the Pectineus Muscle". Michigan Library Med School: 367–369. Retrieved 2 December 2015. Saladin, Kenneth S. Anatomy & Physiology: The Unity of Form and Function. New York, NY: McGraw-Hill, 2007. Pg.493. Print. Anatomy figure: 12:02-05 at Human Anatomy Online, SUNY Downstate Medical Center - "Muscles of the anterior compartment of the thigh." Anatomy figure: 12:03-04 at Human Anatomy Online, SUNY Downstate Medical Center - "Deep muscles of the anterior thigh." Cross section image: pelvis/pelvis-e12-15—Plastination Laboratory at the Medical University of Vienna
The obturator foramen is the large opening created by the ischium and pubis bones of the pelvis through which nerves and blood vessels pass. It is bounded by a thin, uneven margin, to which a strong membrane is attached, presents, superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely medialward and downward; this groove is converted into the obturator canal by a ligamentous band, a specialized part of the obturator membrane, attached to two tubercles: one, the posterior obturator tubercle, on the medial border of the ischium, just in front of the acetabular notch the other, the anterior obturator tubercle, on the obturator crest of the superior ramus of the pubis Reflecting the overall sex differences between male and female pelvises, the obturator foramina are oval in the male and wider and more triangular in the female. Additionally, unilateral pelvis hypoplasia can cause differences in size between the obturator foramina, there are rare reports of individual pelvises featuring a double obturator foramen in one of the hip bones.
Through the canal the obturator artery, obturator vein and obturator nerve pass out of the pelvis. Obturator internus muscle Obturator externus muscle This article incorporates text in the public domain from page 237 of the 20th edition of Gray's Anatomy Anatomy photo:17:st-0205 at the SUNY Downstate Medical Center - "Major Joints of the Lower Extremity: hip and sacrum" Atlas image: male_urethrogram at the University of Michigan Health System - "Pelvis & Perineum: Male Urethrogram" Photo at vc.cc.tx.us
The obturator canal is a passageway formed in the obturator foramen by part of the obturator membrane. It connects the pelvis to the thigh; the obturator artery, obturator vein, obturator nerve all travel through the canal. An obturator hernia is a type of hernia involving an intrusion into the obturator canal. Obturator fascia This article incorporates text in the public domain from the 20th edition of Gray's Anatomy
Obturator internus nerve
The nerve to obturator internus is a nerve that innervates the obturator internus and gemellus superior muscles. The nerve to obturator internus originates in the sacral plexus, it arises from the ventral divisions of first and second sacral nerves. It leaves the pelvis through the greater sciatic foramen below the piriformis muscle, gives off the branch to the gemellus superior, which enters the upper part of the posterior surface of the muscle, it crosses the ischial spine, reenters the pelvis through the lesser sciatic foramen, pierces the pelvic surface of the obturator internus. Obturator nerve Nerve to quadratus femoris This article incorporates text in the public domain from page 957 of the 20th edition of Gray's Anatomy
Anterior branch of obturator nerve
The anterior branch of the obturator nerve is a branch of the obturator nerve found in the pelvis and leg. It leaves the pelvis in front of the obturator externus and descends anterior to the adductor brevis, posterior to the pectineus and adductor longus, it descends upon the femoral artery, to which it is distributed. Near the obturator foramen the nerve gives off an articular branch to the hip joint. Behind the pectineus, it distributes branches to the adductor longus and gracilis, to the adductor brevis, in rare cases to the pectineus; this article incorporates text in the public domain from page 954 of the 20th edition of Gray's Anatomy medialthigh at The Anatomy Lesson by Wesley Norman Anatomy photo:12:st-0602 at the SUNY Downstate Medical Center
External obturator muscle
The external obturator muscle, obturator externus muscle is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis. It is sometimes considered part of the medial compartment of thigh, sometimes considered part of the gluteal region, it arises from the margin of bone around the medial side of the obturator membrane and surrounding bone, viz. from the inferior pubic ramus, the ramus of the ischium. The fibers springing from the pubic arch extend on to the inner surface of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane; the fibers converge and pass posterolateral and upward, end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip joint and is inserted into the trochanteric fossa of the femur. The obturator vessels lie between the obturator membrane. In 33 % of people a supernumerary muscle is found between the adductor minimus. While this muscle, when present, is similar to its neighbouring adductors, it is formed by separation from the superficial layer of the external obturator, is thus not ontogenetically related to the adductor muscles of the hip.
This muscle originates from the upper part of the inferior pubic ramus from where it runs downwards and laterally. In half of cases, it inserts into the anterior surface of the insertion aponeurosis of the adductor minimus. In the remaining cases, it is either inserted into the upper part of the pectineal line or the posterior part of the lesser trochanter, it has been demonstrated by the course of the posterior branch of obturator nerve that the obturator externus is divided into a superior muscle fascicle and a main belly. The supernumerary muscle described above originates from the superior fascicle, while an anomalous fascicle — derived from the external obturator — originates from the main belly; the "original" external obturator, i.e. without these supernumerary muscular parts occurs in only 20% of cases, the external obturator undergoes ontogenetic variations. The external obturator muscle acts as the lateral rotator of the hip joint; as a short muscle around the hip joint, it stabilizes the hip joint as a postural muscle.
This article incorporates text in the public domain from page 477 of the 20th edition of Gray's Anatomy Cross section image: pelvis/pelvis-e12-15—Plastination Laboratory at the Medical University of Vienna lljoints at The Anatomy Lesson by Wesley Norman PTCentral