The genitofemoral nerve refers to a human nerve, found in the abdomen. Its branches, the genital branch and femoral branch supply sensation to the upper anterior thigh, as well as the skin of the anterior scrotum in males and mons pubis in females; the femoral branch is different from the femoral nerve, which arises from the lumbar plexus. The genitofemoral nerve originates from the upper L1-2 segments of the lumbar plexus, it emerges from its anterior surface. The nerve divides into two branches, the genital branch and the lumboinguinal nerve known as the femoral branch, both of which continue downwards and medially to the inguinal and femoral canal respectively; the genital branch enters the inguinal canal. In men, the genital branch supplies the scrotal skin. In women, the genital branch accompanies the round ligament of uterus, terminating in and innervating the skin of the mons pubis and labia majora; the femoral branch passes underneath the inguinal ligament, travelling through the lateral muscular compartment of the femoral canal where it innervates skin of the upper leg.
Passing through the cribriform fascia of the saphenous opening of the fascia lata of the thigh, it supplies the skin of the upper and medial side of thigh. The genitofemoral nerve pierces and passes through the psoas major muscle before bifurcating into a genital branch and a femoral branch midway along its anterior surface. In 25% of cases, the genitofemoral nerve splits into these branches before it enters the psoas major or within the muscle belly of psoas major; this variation causes the split to be occur earlier in the genitofemoral nerve, at the upper rather than mid-portion of the anterior surface of the psoas major. The genitofemoral nerve is responsible for both the sensory and motor portions of the cremasteric reflex, which describes contraction of the cremasteric muscle when the skin of the superior medial part of the thigh is touched. Anatomy photo:36:07-0305 at the SUNY Downstate Medical Center - "Inguinal Region and Testes: Layers of the spermatic cord" Anatomy figure: 40:07-13 at Human Anatomy Online, SUNY Downstate Medical Center - "Muscles and nerves of the posterior abdominal wall."
Posteriorabdomen at The Anatomy Lesson by Wesley Norman
Sensory neurons known as afferent neurons are neurons that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction; the cell bodies of the sensory neurons are located in the dorsal ganglia of the spinal cord. This sensory information travels along afferent nerve fibers in an afferent or sensory nerve, to the brain via the spinal cord; the stimulus can come from extoreceptors outside the body, for example light and sound, or from interoreceptors inside the body, for example blood pressure or the sense of body position. Different types of sensory neurons have different sensory receptors that respond to different kinds of stimuli; the sensory neurons involved in smell are called olfactory sensory neurons. These neurons contain receptors, called olfactory receptors, that are activated by odor molecules in the air. To Olfactory receptors, taste receptors in taste buds interact with chemicals in food to produce an action potential.
Photoreceptor cells are capable of phototransduction, a process which converts light into electrical signals. These signals are refined and controlled by the interactions with other types of neurons in the retina; the five basic classes of neurons within the retina are photoreceptor cells, bipolar cells, ganglion cells, horizontal cells, amacrine cells. The basic circuitry of the retina incorporates a three-neuron chain consisting of the photoreceptor, bipolar cell, the ganglion cell; the first action potential occurs in the retinal ganglion cell. This pathway is the most direct way for transmitting visual information to the brain. There are three primary types of photoreceptors: Cones are photoreceptors that respond to color. In humans the three different types of cones correspond with a primary response to short wavelength, medium wavelength, long wavelength. Rods are photoreceptors that are sensitive to the intensity of light, allowing for vision in dim lighting; the concentrations and ratio of rods to cones is correlated with whether an animal is diurnal or nocturnal.
In humans, rods outnumber cones by 20:1, while in nocturnal animals, such as the tawny owl, the ratio is closer to 1000:1. Retinal ganglion cells are involved in the sympathetic response. Of the ~1.3 million ganglion cells present in the retina, 1-2% are believed to be photosensitive. Problems and decay of sensory neurons associated with vision lead to disorders such as: Macular degeneration – degeneration of the central visual field due to either cellular debris or blood vessels accumulating between the retina and the choroid, thereby disturbing and/or destroying the complex interplay of neurons that are present there. Glaucoma – loss of retinal ganglion cells which causes some loss of vision to blindness. Diabetic retinopathy – poor blood sugar control due to diabetes damages the tiny blood vessels in the retina; the auditory system is responsible for converting pressure waves generated by vibrating air molecules or sound into signals that can be interpreted by the brain. This mechanoelectrical transduction is mediated with hair cells within the ear.
Depending on the movement, the hair cell can either depolarize. When the movement is towards the tallest stereocilia, the Na+ cation channels open allowing Na+ to flow into cell and the resulting depolarization causes the Ca++ channels to open, thus releasing its neurotransmitter into the afferent auditory nerve. There are two types of hair cells: outer; the inner hair cells are the sensory receptors. Problems with sensory neurons associated with the auditory system leads to disorders such as: Auditory processing disorder – Auditory information in the brain is processed in an abnormal way. Patients with auditory processing disorder can gain the information but their brain cannot process it properly, leading to hearing disability. Auditory verbal agnosia – Comprehension of speech is lost but hearing, speaking and writing ability is retained; this is caused by damage to the posterior superior temporal lobes, again not allowing the brain to process auditory input correctly. Thermoreceptors are sensory receptors.
While the mechanisms through which these receptors operate is unclear, recent discoveries have shown that mammals have at least two distinct types of thermoreceptors. The bulboid corpuscle, is a cutaneous receptor a cold-sensitive receptor, that detects cold temperatures; the other type is a warmth-sensitive receptor. Mechanoreceptors are sensory receptors which respond to mechanical forces, such as pressure or distortion. Specialized sensory receptor cells called mechanoreceptors encapsulate afferent fibers to help tune the afferent fibers to the different types of somatic stimulation. Mechanoreceptors help lower thresholds for action potential generation in afferent fibers and thus make them more to fire in the presence of sensory stimulation; some types of mechanoreceptors fire action potentials. Proprioceptors are another type of mechanoreceptors which means "receptors for self"; these receptors provide spatial information about other body parts. Nociceptors are responsible for processing temperature changes.
The burning pain and irritation experienced after eating a chili pepper, the cold sensation experienced after ingesting a chemical such as menthol or icillin, as well as the common sensation of pain are all a result of neurons with these receptors. Problems with mechanoreceptors lead to disorders such as: Neuropa
Cranial nerves are the nerves that emerge directly from the brain, in contrast to spinal nerves. 10 of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and parts of the body to and from regions of the head and neck. Spinal nerves emerge sequentially from the spinal cord with the spinal nerve closest to the head emerging in the space above the first cervical vertebra; the cranial nerves, emerge from the central nervous system above this level. Each cranial nerve is present on both sides. Depending on definition in humans there are twelve or thirteen cranial nerves pairs, which are assigned Roman numerals I–XII, sometimes including cranial nerve zero; the numbering of the cranial nerves is based on the order in which they emerge from the brain, front to back. The terminal nerves, olfactory nerves and optic nerves emerge from the cerebrum or forebrain, the remaining ten pairs arise from the brainstem, the lower part of the brain; the cranial nerves are considered components of the peripheral nervous system, although on a structural level the olfactory and trigeminal nerves are more considered part of the central nervous system.
Most humans are considered to have twelve pairs of cranial nerves, with the terminal nerve more canonized. They are: the olfactory nerve, the optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, accessory nerve, hypoglossal nerve. Cranial nerves are named according to their structure or function. For example, the olfactory nerve supplies smell, the facial nerve supplies motor innervation to the face; because Latin was the lingua franca of the study of anatomy when the nerves were first documented and discussed, many nerves maintain Latin or Greek names, including the trochlear nerve, named according to its structure, as it supplies a muscle that attaches to a pulley. The trigeminal nerve is named in accordance with its three components, the vagus nerve is named for its wandering course. Cranial nerves are numbered based on their rostral-caudal position. If the brain is removed from the skull the nerves are visible in their numeric order, with the exception of the last, CN XII, which appears to emerge rostrally to CN XI.
Cranial nerves have paths outside the skull. The paths within the skull are called "intracranial" and the paths outside the skull are called "extracranial". There are many holes in the skull called "foramina" by. All cranial nerves are paired, which means that they occur on both the right and left sides of the body; the muscle, skin, or additional function supplied by a nerve on the same side of the body as the side it originates from, is referred to an ipsilateral function. If the function is on the opposite side to the origin of the nerve, this is known as a contralateral function. Intracranial course of cranial nerves is important regarding diagnosis of various intracranial lesions like brain tumors and intracranial arterial aneurysms. Dysfunction of one or more cranial nerves indicates stimulation by some lesion. For example an acoustic schwanoma may cause disturbance in hearing but with further growth of tumor it may involve other cranial nerves and the patient may present with pain resembling trigeminal neuralgia when the tumor involves trigeminal nerve or diplopia due to abducent nerve involvement facial palsy with facial nerve compression.
These findings along with cerebellar signs will suggest the diagnosis of a cerebellopontine angle lesion. A patient presenting with ptosis may have a posterior communicating artery aneurysm compressing the oculomotor nerve during its intracranial course. Facial pain in the distribution of any one or all divisions of trigeminal nerve suggests stimulation of trigeminal nerve roots by a near by vessel; the cell bodies of many of the neurons of most of the cranial nerves are contained in one or more nuclei in the brainstem. These nuclei are important relative to cranial nerve dysfunction because damage to these nuclei such as from a stroke or trauma can mimic damage to one or more branches of a cranial nerve. In terms of specific cranial nerve nuclei, the midbrain of the brainstem has the nuclei of the oculomotor nerve and trochlear nerve; the fibers of these cranial nerves exit the brainstem from these nuclei. Some of the cranial nerves have sensory or parasympathetic ganglia of neurons, which are located outside the brain.
The sensory ganglia are directly correspondent to dorsal root ganglia of spinal nerves and are known as cranial sensory ganglia. Sensory ganglia exist for nerves with sensory function: V, VII, VIII, IX, X. There are parasympathetic ganglia, which are part of the autonomic nervous system for cranial nerves III, VII, IX and X; the trigeminal ganglia of the trigeminal nerve occupies a space in the dura mater called Trigeminal cave. This ganglion contains the cell bodies of the sensory fibers of the three branches of the trig
Superior gluteal nerve
The superior gluteal nerve is a nerve that originates in the pelvis and supplies the gluteus medius, the gluteus minimus, the tensor fasciae latae and the piriformis muscles. The superior gluteal nerve originates in the sacral plexus, it arises from the dorsal divisions of the L4, L5 and S1. It leaves the pelvis through the greater sciatic foramen above the piriformis, accompanied by the superior gluteal artery and the superior gluteal vein, it accompanies the upper branch of the deep division of the superior gluteal artery and ends in the gluteus minimus and tensor fasciae latae muscle. The superior nerve starts out in the pelvis and supplies the tensor fasciae latae, the gluteus minimus, the gluteus medius muscle In normal gait, the small gluteal muscles on the stance side can stabilize the pelvis in the coronal plane. Weakness or paralysis of these muscles caused by a damaged superior gluteal nerve can result in a weak abduction in the affected hip joint; this gait disturbance is known as Trendelenburg gait.
In a positive Trendelenburg's sign the pelvis sags toward the normal unsupported side. The opposite, when the pelvis is elevated on the swing side, is known as Duchenne limp. Bilateral loss of the small gluteal muscles results in a waddling gait. Inferior gluteal nerve This article incorporates text in the public domain from page 959 of the 20th edition of Gray's Anatomy Platzer, Werner. Color Atlas of Human Anatomy, Vol. 1: Locomotor System. Thieme. ISBN 3-13-533305-1. Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. 2006. ISBN 1-58890-419-9. Superior_gluteal_nerve at the Duke University Health System's Orthopedics program
A motor neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, whose axon projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs muscles and glands. There are two types of motor neuron -- lower motor neurons. Axons from upper motor neurons synapse onto interneurons in the spinal cord and directly onto lower motor neurons; the axons from the lower motor neurons are efferent nerve fibers that carry signals from the spinal cord to the effectors. Types of lower motor neurons are alpha motor neurons, beta motor neurons, gamma motor neurons. A single motor neuron may innervate many muscle fibres and a muscle fibre can undergo many action potentials in the time taken for a single muscle twitch; as a result, if an action potential arrives before a twitch has completed, the twitches can superimpose on one another, either through summation or a tetanic contraction. In summation, the muscle is stimulated repetitively such that additional action potentials coming from the somatic nervous system arrive before the end of the twitch.
The twitches thus superimpose on one another, leading to a force greater than that of a single twitch. A tetanic contraction is caused by constant high frequency stimulation - the action potentials come at such a rapid rate that individual twitches are indistinguishable, tension rises smoothly reaching a plateau. Motor neurons begin to develop early in embryonic development, motor function continues to develop well into childhood. In the neural tube cells are specified to either ventral-dorsal axis; the axons of motor neurons begin to appear in the fourth week of development from the ventral region of the ventral-dorsal axis. This homeodomain is known as the motor neural progenitor domain. Transcription factors here include Pax6, OLIG2, Nkx-6.1, Nkx-6.2, which are regulated by sonic hedgehog. The OLIG2 gene being the most important due to its role in promoting Ngn2 expression, a gene that causes cell cycle exiting as well as promoting further transcription factors associated with motor neuron development.
Further specification of motor neurons occurs when retinoic acid, fibroblast growth factor, TGFb, are integrated into the various Hox transcription factors. There are 13 Hox transcription factors and along with the signals, determine whether a motor neuron will be more rostral or caudal in character. In the spinal column, Hox 4-11 sort motor neurons to one of the five motor columns. Upper motor neurons originate in the motor cortex located in the precentral gyrus; the cells that make up the primary motor cortex are Betz cells. The axons of these cells descend from the cortex to form the corticospinal tract. Corticomotorneurons are neurons in the primary cortex which project directly to motor neurons in the ventral horn of the spinal cord. Axons of corticomotorneurons terminate on the spinal motor neurons of multiple muscles as well as on spinal interneurons, they are unique to primates and it has been suggested that their function is the adaptive control of the distal extremities including the independent control of individual fingers.
Corticomotorneurons have so far only been found in the primary motor cortex and not in secondary motor areas. Nerve tracts are bundles of axons as white matter. In the spinal cord these descending tracts carry impulses from different regions; these tracts serve as the place of origin for lower motor neurons. There are seven major descending motor tracts to be found in the spinal cord: Lateral corticospinal tract Rubrospinal tract Lateral reticulospinal tract Vestibulospinal tract Medial reticulospinal tract Tectospinal tract Anterior corticospinal tract Lower motor neurons are those that originate in the spinal cord and directly or indirectly innervate effector targets; the target of these neurons varies, but in the somatic nervous system the target will be some sort of muscle fiber. There are three primary categories lower motor neurons, which can be further divided in sub-categories. According to their targets, motor neurons are classified into three broad categories: Somatic motor neurons Special visceral motor neurons General visceral motor neurons Somatic motor neurons originate in the central nervous system, project their axons to skeletal muscles, which are involved in locomotion.
The three types of these neurons are the alpha efferent neurons, beta efferent neurons, gamma efferent neurons. They are called efferent to indicate the flow of information from the central nervous system to the periphery. Alpha motor neurons innervate extrafusal muscle fibers, which are the main force-generating component of a muscle, their cell bodies are in the ventral horn of the spinal cord and they are sometimes called ventral horn cells. A single motor neuron may synapse with 150 muscle fibers on average; the motor neuron and all of the muscle fibers to which it connects is a motor unit. Motor units are split up into 3 categories: Main Article: Motor Unit Slow motor units stimulate small muscle fibers, which contract slowly and provide small amounts of energy but are resistant to fatigue, so they are used to sustain muscular contraction, such as keeping the body upright, they gain their energy via oxidative hence require oxygen. They are called red fibers. Fast fatiguing motor units stimulate larger muscle groups, which apply large amounts of force but fatigue quickly.
They are used for tasks that require large brief bursts on energy, such as jumping or
The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus at the level of the axilla and carries nerve fibers from C5 and C6. The axillary nerve travels through the quadrangular space with the posterior circumflex humeral artery and vein; the nerve lies at first behind the axillary artery, in front of the subscapularis, passes downward to the lower border of that muscle. It winds backward, in company with the posterior humeral circumflex artery, through a quadrangular space bounded above by the teres minor, below by the teres major, medially by the long head of the triceps brachii, laterally by the surgical neck of the humerus, divides into an anterior, a posterior, a collateral branch to the long head of the triceps brachii branch; the anterior branch winds around the surgical neck of the humerus, beneath the deltoid muscle, with the posterior humeral circumflex vessels. It continues as far as the anterior border of the deltoid to provide motor innervation.
The anterior branch gives off a few small cutaneous branches, which pierce the muscle and supply in the overlaying skin. The posterior branch supplies the posterior part of the deltoid; the posterior branch pierces the deep fascia and continues as the superior lateral cutaneous nerve of arm, which sweeps around the posterior border of the deltoid and supplies the skin over the lower two-thirds of the posterior part of this muscle, as well as that covering the long head of the triceps brachii. The motor branch of the long head of the triceps brachii arises, on average, a distance of 6 mm from the terminal division of the posterior cord termination; the trunk of the axillary nerve gives off an articular filament which enters the shoulder joint below the subscapularis. Traditionally, the axillary nerve is thought to only supply the deltoid and teres minor. However, several studies on cadavers pointed out that the long head of triceps brachii is innervated by a branch of the axillary nerve; the axillary nerve supplies three muscles in the arm: deltoid and teres minor.
The axillary nerve carries sensory information from the shoulder joint, as well as the skin covering the inferior region of the deltoid muscle - the "regimental badge" area. The posterior cord of the brachial plexus splits inferiorly to the glenohumeral joint giving rise to the axillary nerve which wraps around the surgical neck of the humerus, the radial nerve which wraps around the humerus anteriorly and descends along its lateral border; the axillary nerve may be injured in anterior-inferior dislocations of the shoulder joint, compression of the axilla with a crutch or fracture of the surgical neck of the humerus. An example of injury to the axillary nerve includes axillary nerve palsy. Injury to the nerve results in: Paralysis of the teres minor muscle and deltoid muscle, resulting in loss of abduction of arm, weak flexion and rotation of shoulder. Paralysis of deltoid and teres minor muscles results in flat shoulder deformity. Loss of sensation in the skin over a small part of the lateral upper arm.
Axillary nerve dysfunction This article incorporates text in the public domain from page 934 of the 20th edition of Gray's Anatomy Axillary_nerve at the Duke University Health System's Orthopedics program
A nerve is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system; each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as Schwann cells that coat the axons in myelin. Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium; the axons are bundled together into groups called fascicles, each fascicle is wrapped in a layer of connective tissue called the perineurium. The entire nerve is wrapped in a layer of connective tissue called the epineurium. In the central nervous system, the analogous structures are known as tracts; each nerve is covered on the outside by a dense sheath of the epineurium. Beneath this is a layer of flat cells, the perineurium, which forms a complete sleeve around a bundle of axons.
Perineurial septae subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium; this forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, meshwork of collagen fibres. Nerves are bundled and travel along with blood vessels, since the neurons of a nerve have high energy requirements. Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid; this acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier. Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation, the amount of endoneurial fluid may increase at the site of irritation; this increase in fluid can be visualized using magnetic resonance neurography, thus MR neurography can identify nerve irritation and/or injury.
Nerves are categorized into three groups based on the direction that signals are conducted: Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from the mechanoreceptors in skin. Efferent nerves conduct signals from the central nervous system along motor neurons to their target muscles and glands. Mixed nerves contain both afferent and efferent axons, thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. Nerves can be categorized into two groups based on where they connect to the central nervous system: Spinal nerves innervate much of the body, connect through the vertebral column to the spinal cord and thus to the central nervous system, they are given letter-number designations according to the vertebra through which they connect to the spinal column. Cranial nerves innervate parts of the head, connect directly to the brain, they are assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included.
In addition, cranial nerves have descriptive names. Specific terms are used to describe their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to "innervate" that section of the body or organ. Other terms relate to whether the nerve affects the same side or opposite side of the body, to the part of the brain that supplies it. Nerve growth ends in adolescence, but can be re-stimulated with a molecular mechanism known as "Notch signaling". If the axons of a neuron are damaged, as long as the cell body of the neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells; this is referred to as neuroregeneration. The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud.
When one of the growth processes finds the regeneration tube, it begins to grow towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect. A nerve conveys information in the form of electrochemical impulses carried by the individual neurons that make up the nerve; these impulses are fast, with some myelinated neurons conducting at speeds up to 120 m/s. The impulses travel from one neuron to another by crossing a synapse, the message is converted from electrical to chemical and back to electrical. Nerves can be categorized into two groups based on function: An afferent nerve fiber conducts sensory information from a sensory neuron to the central nervous system, where the information is processed. Bundles of fibres or axons, in the peripheral nervous system are called nerves, bundles of afferent fibers are known as sensory nerves.
An efferent nerve fiber conducts signals from a motor neuron in the central nervous system to muscles. Bundles of these fibres are known as efferent nerves; the nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body. In vertebrates it consists of two main par