The nasociliary nerve is a branch of the ophthalmic nerve. It is intermediate in size between the two other main branches of the ophthalmic nerve, the frontal nerve and the lacrimal nerve, is more placed; the nasociliary nerve enters the orbit between the two heads of the lateral rectus muscles and between the superior and inferior rami of the oculomotor nerve. It passes across the optic nerve and runs obliquely beneath the superior rectus muscle and superior oblique muscle to the medial wall of the orbital cavity, it passes through the anterior ethmoidal opening as the anterior ethmoidal nerve and enters the cranial cavity just below the cribriform plate of the ethmoid bone. It supplies branches to the mucous membrane of the nasal cavity and emerges between the inferior border of the nasal bone and the side nasal cartilages as the external nasal branch. A branch of the ophthalmic nerve in the superior orbital fissure, passing through the orbit, giving rise to the communicating branch to the ciliary ganglion, the long ciliary nerves, the posterior and anterior ethmoidal nerves, terminating as the infratrochlear and nasal branches, which supply the mucous membrane of the nose, the skin of the tip of the nose, the conjunctiva.
The nasociliary nerve gives off the following branches: ethmoidal nerves anterior ethmoidal nerve posterior ethmoidal nerve infratrochlear nerve long ciliary nerve communicating branch to the ciliary ganglion PLICA is a mnemonic used to remember these branches. Since both the short and long ciliary nerves carry the afferent limb of the corneal blink reflex, one can test the integrity of the nasociliary nerve by examining this reflex in the patient. Both eyes should blink when either cornea is irritated. If neither eye blinks either the ipsilateral nasociliary nerve is damaged, or the facial nerve is bilaterally damaged. If only the contralateral eye blinks the ipsilateral facial nerve is damaged. If only the ipsilateral eye blinks the contralateral facial nerve is damaged; this article incorporates text in the public domain from page 888 of the 20th edition of Gray's Anatomy Anatomy figure: 29:03-08 at Human Anatomy Online, SUNY Downstate Medical Center - "A deeper dissection of the right orbit from a superior approach."
Lesson9 at The Anatomy Lesson by Wesley Norman cranialnerves at The Anatomy Lesson by Wesley Norman MedEd at Loyola GrossAnatomy/h_n/cn/cn1/cnb1.htm
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron or to the target effector cell. Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine; the word "synapse" – from the Greek synapsis, meaning "conjunction", in turn from συνάπτεὶν – was introduced in 1897 by the English neurophysiologist Charles Sherrington in Michael Foster's Textbook of Physiology. Sherrington struggled to find a good term that emphasized a union between two separate elements, the actual term "synapse" was suggested by the English classical scholar Arthur Woollgar Verrall, a friend of Foster; some authors generalize the concept of the synapse to include the communication from a neuron to any other cell type, such as to a motor cell, although such non-neuronal contacts may be referred to as junctions. Synapses are essential to neuronal function: neurons are cells that are specialized to pass signals to individual target cells, synapses are the means by which they do so.
At a synapse, the plasma membrane of the signal-passing neuron comes into close apposition with the membrane of the target cell. Both the presynaptic and postsynaptic sites contain extensive arrays of a molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on an axon and the postsynaptic part is located on a dendrite or soma. Astrocytes exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission. Synapses are stabilized in position by synaptic adhesion molecules projecting from both the pre- and post-synaptic neuron and sticking together where they overlap. There are two fundamentally different types of synapses: In a chemical synapse, electrical activity in the presynaptic neuron is converted into the release of a chemical called a neurotransmitter that binds to receptors located in the plasma membrane of the postsynaptic cell; the neurotransmitter may initiate an electrical response or a secondary messenger pathway that may either excite or inhibit the postsynaptic neuron.
Chemical synapses can be classified according to the neurotransmitter released: glutamatergic, GABAergic and adrenergic. Because of the complexity of receptor signal transduction, chemical synapses can have complex effects on the postsynaptic cell. In an electrical synapse, the presynaptic and postsynaptic cell membranes are connected by special channels called gap junctions or synaptic cleft that are capable of passing an electric current, causing voltage changes in the presynaptic cell to induce voltage changes in the postsynaptic cell; the main advantage of an electrical synapse is the rapid transfer of signals from one cell to the next. Synaptic communication is distinct from an ephaptic coupling, in which communication between neurons occurs via indirect electric fields. An autapse is a chemical or electrical synapse that forms when the axon of one neuron synapses onto dendrites of the same neuron. Synapses can be classified by the type of cellular structures serving as the pre- and post-synaptic components.
The vast majority of synapses in the mammalian nervous system are classical axo-dendritic synapses, however, a variety of other arrangements exist. These include but are not limited to axo-axonic, dendro-dendritic, axo-secretory, somato-dendritic, dendro-somatic, somato-somatic synapses; the axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue. It is accepted that the synapse plays a role in the formation of memory; as neurotransmitters activate receptors across the synaptic cleft, the connection between the two neurons is strengthened when both neurons are active at the same time, as a result of the receptor's signaling mechanisms. The strength of two connected neural pathways is thought to result in the storage of information, resulting in memory; this process of synaptic strengthening is known as long-term potentiation. By altering the release of neurotransmitters, the plasticity of synapses can be controlled in the presynaptic cell.
The postsynaptic cell can be regulated by altering the number of its receptors. Changes in postsynaptic signaling are most associated with a N-methyl-d-aspartic acid receptor -dependent long-term potentiation and long-term depression due to the influx of calcium into the post-synaptic cell, which are the most analyzed forms of plasticity at excitatory synapses. For technical reasons, synaptic structure and function have been studied at unusually large model synapses, for example: Squid giant synapse Neuromuscular junction, a cholinergic synapse in vertebrates, glutamatergic in insects Ciliary calyx in the ciliary ganglion of chicks Calyx of Held in the brainstem Ribbon synapse in the retina Schaffer collateral synapse in the hippocampus The function of neurons depends upon cell polarity; the distinctive structure of nerve cells allows action potentials to travel directionally, for these signals to be received and carried on by post-synaptic neurons or received by effector cells. Nerve cells have long been used as models f
The ciliary muscle is a ring of smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It changes the shape of the lens within the eye, not the size of the pupil, carried out by the sphincter pupillae muscle and dilator pupillae; the ciliary muscle develops from mesenchyme within the choroid and is considered a cranial neural crest derivative. The ciliary muscle receives parasympathetic fibers from the short ciliary nerves that arise from the ciliary ganglion; the sympathetic postganglionic fibers are part of cranial nerve V1, while presynaptic parasympathetic fibers to the ciliary ganglia are from the oculomotor nerve. The postganglionic sympathetic innervation arises from the superior cervical ganglia. Presynaptic parasympathetic signals that originate in the Edinger-Westphal nucleus are carried by cranial nerve III and travel through the ciliary ganglion via the postganglionic parasympathetics fibers which travel in the short ciliary nerves and supply the ciliary body and iris.
Parasympathetic activation of the M3 muscarinic receptors causes ciliary muscle contraction, the effect of contraction is to decrease the diameter of the ring of ciliary muscle. The zonule fibers relax and the lens becomes more spherical, increasing its power to refract light for near vision; the parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book. The ciliary fibers have circular and radial orientations. According to Hermann von Helmholtz's theory, the circular ciliary muscle fibers affect zonular fibers in the eye, enabling changes in lens shape for light focusing; when the ciliary muscle contracts, it pulls itself forward and moves the frontal region toward the axis of the eye. This releases the tension on the lens caused by the zonular fibers; this release of tension of the zonular fibers causes the lens to become more spherical, adapting to short range focus. Conversely, relaxation of the ciliary muscle causes the zonular fibers to become taut, flattening the lens, increasing the focal distance, increasing long range focus.
Although Helmholtz's theory has been accepted since 1855, its mechanism still remains controversial. Alternative theories of accommodation have been proposed by others, including L. Johnson, M. Tscherning, Ronald A. Schachar. Contraction and relaxation of the longitudinal fibers, which insert into the trabecular meshwork in the anterior chamber of the eye, cause an increase and decrease in the meshwork pore size facilitating and impeding aqueous humour flow into the canal of Schlemm. Open-angle glaucoma and closed-angle glaucoma may be treated by muscarinic receptor agonists, which cause rapid miosis and contraction of the ciliary muscles, opening the trabecular meshwork, facilitating drainage of the aqueous humour into the canal of Schlemm and decreasing intraocular pressure; the word ciliary had its origins around 1685–1695. The term cilia originated a few years in 1705–1715, is the Neo-Latin plural of cilium meaning eyelash. In Latin, cilia means upper eyelid and is a back formation from supercilium, meaning eyebrow.
The suffix -ary occurred in loanwords from Middle English, Old French, Latin. Taken together, cili-ary pertains to various anatomical structures in and around the eye, namely the ciliary body and annular suspension of the lens of the eye. Accommodation reflex Ciliary body Cycloplegia Presbyopia Lens, zonule fibers, ciliary muscles—SEM
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
Zonule of Zinn
The zonule of Zinn is a ring of fibrous strands forming a zonule that connects the ciliary body with the crystalline lens of the eye. These fibers are sometimes collectively referred to as the suspensory ligaments of the lens, as they act like suspensory ligaments; the ciliary epithelial cells of the eye synthesize portions of the zonules. The zonule of Zinn is split into two layers: a thin layer, which lines the hyaloid fossa, a thicker layer, a collection of zonular fibers. Together, the fibers are known as the suspensory ligament of the lens; the zonules are about 1–2 μm in diameter. The zonules attach to the lens capsule 2mm anterior and 1 mm posterior to the equator, arise from the pars plana region of the ciliary epithelium and pass forward related to the lateral surfaces of the ciliary process of the pars plicata; when colour granules are displaced from the Zonules of Zinn, the irises fade. In some cases those colour lead to Glaucoma Pigmentosa; the zonules are made of fibrillin, a connective tissue protein.
Mutations in the fibrillin gene lead to the condition Marfan syndrome, consequences include an increased risk of lens dislocation. The zonules of Zinn are difficult to visualize using a slit lamp, but may be seen with exceptional dilation of the pupil, or if a coloboma of the iris or a subluxation of the lens is present; the number of zonules present in a person appears to decrease with age. The zonules insert around the outer margin of both anteriorly and posteriorly; this article incorporates text in the public domain from page 1018 of the 20th edition of Gray's Anatomy Diagram at unmc.edu Diagram at eye-surgery-uk.com Diagram and overview at webschoolsolutions.com Histology image: 08011loa – Histology Learning System at Boston University
The otic ganglion is a small parasympathetic ganglion located below the foramen ovale in the infratemporal fossa and on the medial surface of the mandibular nerve. It is functionally associated with the glossopharyngeal nerve and innervates the parotid gland for salivation, it is one of four parasympathetic ganglia of the neck. The others are the submandibular ganglion and the pterygopalatine ganglion; the otic ganglion is a small, oval shaped, flattened parasympathetic ganglion of a reddish-grey color, located below the foramen ovale in the infratemporal fossa and on the medial surface of the mandibular nerve. It is in relation, with the trunk of the mandibular nerve at the point where the motor and sensory roots join, it surrounds the origin of the nerve to the medial pterygoid. Laterally, mandibular nerve The preganglionic parasympathetic fibres originate in the inferior salivatory nucleus of the glossopharyngeal nerve, they leave the glossopharyngeal nerve by its tympanic branch and pass via the tympanic plexus and the lesser petrosal nerve to the otic ganglion.
Here, the fibres synapse, the postganglionic fibers pass by communicating branches to the auriculotemporal nerve, which conveys them to the parotid gland. They produce secretomotor effects, its sympathetic root is derived from the plexus on the middle meningeal artery. It contains post-ganglionic fibers arising in the superior cervical ganglion; the fibers pass through the ganglion without relay and reach the parotid gland via the auriculotemporal nerve. They are vasomotor in function; the sensory root is sensory to the parotid gland. The motor fibers supplying the medial pterygoid and the tensor palati and the tensor tympani pass through the ganglion without relay; the ganglion is connected to the chorda tympani nerve and to the nerve of the pterygoid canal. These pathways provide an alternate pathway of taste from the anterior two thirds of the tongue; these fibers do not pass through the middle ear. Frey's syndrome in which salivation will induce perspiration at the parotid region, accompanied by erythema.
This article incorporates text in the public domain from page 897 of the 20th edition of Gray's Anatomy Shimizu T. "Distribution and pathway of the cerebrovascular nerve fibers from the otic ganglion in the rat: anterograde tracing study". J. Auton. Nerv. Syst. 49: 47–54. Doi:10.1016/0165-183890019-1. PMID 7525688. Cranialnerves at The Anatomy Lesson by Wesley Norman
An axon, or nerve fiber, is a long, slender projection of a nerve cell, or neuron, in vertebrates, that conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit information to different neurons and glands. In certain sensory neurons, such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body, from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons. Nerve fibers are classed into three types – group A nerve fibers, group B nerve fibers, group C nerve fibers. Groups A and B are myelinated, group C are unmyelinated; these groups include both sensory fibers and motor fibers. Another classification groups only the sensory fibers as Type I, Type II, Type III, Type IV. An axon is one of two types of cytoplasmic protrusions from the cell body of a neuron.
Axons are distinguished from dendrites by several features, including shape and function. Some types of neurons have no transmit signals from their dendrites. In some species, axons can emanate from dendrites and these are known as axon-carrying dendrites. No neuron has more than one axon. Axons are covered by a membrane known as an axolemma. Most axons branch, in some cases profusely; the end branches of an axon are called telodendria. The swollen end of a telodendron is known as the axon terminal which joins the dendron or cell body of another neuron forming a synaptic connection. Axons make contact with other cells—usually other neurons but sometimes muscle or gland cells—at junctions called synapses. In some circumstances, the axon of one neuron may form a synapse with the dendrites of the same neuron, resulting in an autapse. At a synapse, the membrane of the axon adjoins the membrane of the target cell, special molecular structures serve to transmit electrical or electrochemical signals across the gap.
Some synaptic junctions appear along the length of an axon as it extends—these are called en passant synapses and can be in the hundreds or the thousands along one axon. Other synapses appear as terminals at the ends of axonal branches. A single axon, with all its branches taken together, can innervate multiple parts of the brain and generate thousands of synaptic terminals. A bundle of axons make a nerve tract in the central nervous system, a fascicle in the peripheral nervous system. In placental mammals the largest white matter tract in the brain is the corpus callosum, formed of some 20 million axons in the human brain. Axons are the primary transmission lines of the nervous system, as bundles they form nerves; some axons can extend up to more while others extend as little as one millimeter. The longest axons in the human body are those of the sciatic nerve, which run from the base of the spinal cord to the big toe of each foot; the diameter of axons is variable. Most individual axons are microscopic in diameter.
The largest mammalian axons can reach a diameter of up to 20 µm. The squid giant axon, specialized to conduct signals rapidly, is close to 1 millimetre in diameter, the size of a small pencil lead; the numbers of axonal telodendria can differ from one nerve fiber to the next. Axons in the central nervous system show multiple telodendria, with many synaptic end points. In comparison, the cerebellar granule cell axon is characterized by a single T-shaped branch node from which two parallel fibers extend. Elaborate branching allows for the simultaneous transmission of messages to a large number of target neurons within a single region of the brain. There are two types of axons in the nervous system: unmyelinated axons. Myelin is a layer of a fatty insulating substance, formed by two types of glial cells Schwann cells and oligodendrocytes. In the peripheral nervous system Schwann cells form the myelin sheath of a myelinated axon. In the central nervous system oligodendrocytes form the insulating myelin.
Along myelinated nerve fibers, gaps in the myelin sheath known as nodes of Ranvier occur at evenly spaced intervals. The myelination enables an rapid mode of electrical impulse propagation called saltatory conduction; the myelinated axons from the cortical neurons form the bulk of the neural tissue called white matter in the brain. The myelin gives the white appearance to the tissue in contrast to the grey matter of the cerebral cortex which contains the neuronal cell bodies. A similar arrangement is seen in the cerebellum. Bundles of myelinated axons make up the nerve tracts in the CNS. Where these tracts cross the midline of the brain to connect opposite regions they are called commissures; the largest of these is the corpus callosum that connects the two cerebral hemispheres, this has around 20 million axons. The structure of a neuron is seen to consist of two separate functional regions, or compartments – the cell body together with the dendrites as one region, the axonal region as the other.
The axonal region or compart