Cell body- is also called a soma. Although the cell bodies of different neurons very widely in size, I'll consist of a single nucleus surrounded by cytoplasm.
Dendrites- processes that branch from the cell body like the limbs on A tree. Dendrites function as receptive sites, providing and in large surface area for receiving signals from other neurons. By definition, dendrites conduct electrical signals toward the cell body.
Axon hillock- A neuron has only one excellent, which arises from the cone shaped region of the cell body called the axon Hillock.
Axon- are thin processes of uniform diameter throughout their length. by definition, axons are impulse generators and conductors that transmit nerve impulses away from their cell body.
Axon terminal- axons branch far less frequently then dendrites, occasionally branches do occur along their length these branches, called axon collateral, extend from the axon more or less right angles. Whether an axon remains undivided or has collaterals, it usually branches profusely at the end called the terminal arborization. For there to be 10,000 of these branches per near aunt is not unusual. They end in knobs called terminal buttons or axon terminals.
Synapse vesicles- The say it which neurons communicate is called a synapse. Most synapses in the nervous system transmit information through chemical messengers. Structurally, synapses are elaborate cell junctions. This section focuses on XO dendrite dick synapse because it's structure is structure is representative of both types of synapses. On the presynaptic side, the terminal button contains synaptic vesicles. These are membrane-bound sax filled with neurotransmitters, the molecules that transmit signals across the synapse.
Star shaped astrocytes are the most abundant glial cells of the CNS. They have many radiating processes with bulbous ends. some of these bulbs cling to the neurons whereas others cling to capillaries. Known functions include 1)regulating neurotransmitter levels by increasing the rate of neurotransmitter uptake and regions of high neuronal activity; 2) signaling increase blood flow through capillaries in active regions of the brain; and 3) controlling the ionic environment around neurons. astrocytes also help synapses warm and developing neural tissue, produce molecules necessary for neural growth, and propagate calcium signals that may be involved with memory.
Microglial cells, the smallest and least abundant neuroglia of the CNS, have elongated cell bodies and cell processes with many potential projections, like thorny bush. They are phagocytes, and macrophages of the CNS. They migrate to, and then and golf, invading microorganisms and injured or dead neurons. Unlike other neuroglia cells, microglia all cells do not originate in the nervous tissue; like other macrophages of the body, they are divided from blood cells called monocytes. The monocytes that become microglial cells migrate to the CNS during the embryonic and fetal periods.
Ependymal cells form a simple epithelium that lines the central cavity of the spinal cord and brain. Here the cells provide a fairly permeable layer between the cerebrospinal fluid that fills the cavity and the tissue fluid that bathes the cells of the CNS. Ependymal cells bear cilia that help circulate the cerebrospinal fluid.
Oligodendrocytes have your branches then astrocytes, as their name implies. They line up in small groups and wrap their cell processes around the thicker axons in the CNS, producing insulating coverings called myelin sheaths.
The two kinds of neuroglia in the PNS our satellite cells and Schwan cells, very similar cell types that differ mainly in location. Satellite cells surround neuron cell bodies with in ganglia. Their name comes from a fancied resemblance to the moons, or satellites, around a planet. Schwann cells surround all axons in the PNS and form Myelin sheaths around many of these axons.
Underlaying the gray matter of the cerebral cortex is the cerebral white matter. It is via the many fibers that form the cerebral white matter that the various areas of the cerebral cortex communicate with both with one another and with the brain stem and spinal cord. Most of these fibers are myelinated and bundled into large trucks. The fibers are classified as commissural fibers, association fiber, or projection fibers, according to where they run.
Cholesteryl fibers cross from one side of the CNS to the other that. The commissural fibers of the cerebrum enter connect corresponding great areas of the right and left cerebral hemispheres, allowing the two hemispheres to function together as a coordinated whole. The largest commissioner is the corpus callosum, a broadband that lies appear to the lateral ventricles, deep with in the longitudinal fissure.
Association fibers connect different parts of the same hemisphere. Short association fibers connect neighboring cortical areas, and long association fibers connect widely separated cortical lobes.
Projection fibers either descend from the cerebral cortex two more Cortile parts of the CNS or a send to the cortex from the lower regions. It is through projection fibers that sensory information reaches the cerebral cortex and motor instructions or leave it. These fibers run vertically, where as most comitia roll and association fibers run horizontally.
Deep to the cerebral white matter, the projection fibers from form a Compact bundle called that internal capsule, which passes between the thalamus and some of the deep gray matter, the basal nuclei ganglia. Superior to the internal capsule, the projection fibers running to and from the cerebral cortex fanout to form the Corona radiata.
The deep gray matter of the cerebrum consist of the basal nuclei (ganglia), involved in motor control; the basil for brain nuclei associated with memory; and the claustrum, a brain nucleus of a known function. The amygdaloid body is also deep gray matter in the cerebrum. It is part of the limbic system and it is included in the discussion of that functional brain system.
Deep within the cerebral white matter lies a group of sub cortical brain nuclei connected collectively called the basal nuclei (ganglia): the caudate nucleus, the putamen and the globus pallidus. The caudate nucleus and the putamen together are called the striatum because some fibers of the internal capsule passing through them create a striated appearance. The caudate nucleus arches just over the thalamus and lies medial to the internal capsule. The globus pallidus and the putamen are located lateral to the internal capsule.
The cauliflower like cerebellum, the second of the brains major parts as we move caudally to rostrally, makes up 11% of the brains mass. The cerebellum is located dorsal to the pond and the medulla oblongata, from which it is separated by the fourth ventricle. Functionally the cerebellum smooths that and coordinates body movements that are directed by other brain regions, and it helps maintain posture and equilibrium.
1. The cerebellum receives information from the cerebrum on the movements being planned. The area of cerebrum that initiates voluntary movements, the motor cortex of the cerebrum, passes information from the cerebral cortex through that Pontine nuclei in the pons to the lateral portion of the anterior and posterior your lobes of the Cerebellum.
2. The cerebellum compares these planned movements with current body position and movement. Information on the equilibrium and head position is relayed from receptors in the inner ear through the vestibular nuclei in the medulla oblongata to the flocculinodular lobe. Information on the current movements of the limbs, neck, and trunk travels from the proprioceptors in muscles, tendons, and joint up the spinal cord to the vermis and medial portions of the interior and posterior lobes.
3. The cerebellum sends instructions back to the cerebral cortex on how to resolve any differences between the intended movements and current position. Using this feedback from the cerebellum, the motor cortex of the cerebrum continuously readjust the motor commands it sends to the spinal cord, fine-tuning movement so that they are well coordinated.
The diencephalon, The third of the four main parts of the brain, forms the central core of the forebrain it is is surrounded by the cerebral hemispheres. The Diencephalon consist largely of three paired structures - the thalamus, the hypothalamus, and the epithalamus. These border the third ventricle and consists primarily of gray matter.
Thalamus- The egg shaped thalamus is a paired structure that makes up 80% of the diencephalon informs the super pro lateral walls of the third Bend chuckle. Thalamus is a Greek word meaning in her room. The thalamus contains about a dozen major nuclei each of which sends axons and particular portion of the cerebral cortex. It why sheep sheet of white matter, the internal medullary lamina divides that thalamus nuclei into three groups: the anterior nuclei, the medial group including the mediodorsal nucleus, and the large lateral nuclear group. The ventral posterolateral nuclei act as relay stations for the sensory information is sending to the primary sensory areas of the cerebral cortex. The medial geniculate body receives auditory input and links to the auditory cortex. The lateral geniculate body receives visual input in transmits the visual cortex.
hypothalamus: the hypothalamus is inferior portion of the diencephalon. It forms inerolateral walls of the third ventricle. On the underside of the brain, the hypothalamus lies between the optic chiasma and the posterior border of the mammillary bodies, rounded bumps that bulge from the hypothalamus floor. Projecting inferiorly from the hypothalamus is the pituitary gland. The thalamus has control of the automatic nervous system. Recall that the automatic nervous system is composed of Peripheral motor neurons that regulate contraction of smooth and cardiac muscle and secretion from glands. The hypothalamus is one of the major brain regions involved in directing the automatic neurons. Regulation of body temperature. The bodies thermostat is in the hypothalamus. Some hypothalamic neurons Monitor blood temperature and receive input from the peripheral thermoreceptors. The hypothalamus initiates the bodies cooling or heating mechanisms as needing. Regulation of hunger and thirst sensations. By sensing a concentrations of nutrients and salts in the blood, certain hypothalamic neurons mediate feelings of hunger and thirst and this aid in maintaining the proper concentrations of these substances. Regulation of sleep-wake cycles. Acting with other brain regions, the hypothalamus helps regulate the complex phenomenon of sleep. The suprachiasmatic nucleus is the body's biological clock. It generates the daily circadian rhythm's and synchronizes the cycles in response to Dirk - light information sent via the optic nerve. In response to such signals, the preoptic nucleus induces sleep. Other hypothalamus nuclei near the mammillary body mediate arousal from sleep. Control of the endocrine system. The hypothalamus controls the secretion of hormones by the pituitary gland, which in turn influences the activity of many other endocrine organs. Control of emotional responses. The hypothalamus lights at the center of the emotional part of the brain, the limbic system. Regions involved in pleasure, rage, and fear are located in the hypothalamus. Control of motivational behavior. The hypothalamus controls behavior that is rewording for example, the hypothalamus influences our motivation for feeding, thereby determining how much we eat, and also influences sex drive and sexual behavior. Formation of memory. The brain nucleus in the mammillary body receives many inputs from the major memory processes structure of the cerebrum, the hippo Campell information.
epithalamus- The epithalamus, the third and most dorsal part of the diet encephalon, forms part of the roof of the third ventricle. It consist of tiny group of brain nuclei and small unpaired knob called the pineal gland. This gland, which derives from epididymal glial cells, is a hormone - secreting organ. Under the influence of the hypothalamus, the pineal gland secretes the hormone melatonin, which signals the body to prepare for the nighttime stage of the sleep-wake cycle.
There are many shallow grooves on the surface of the cerebral hemispheres called sulci. Between the sulci are twisted ridges of the brain tissue called gyri. Some of the deeper sulci divide each cerebral hemisphere into five major lopes: the frontal, parietal the occipital, and temporal lobe's, and the insula.
The frontal lobe is located deep to the frontal bone and fills The anterior cranial fossa. It extends posteriorly to the central sulcus, which separates the frontal lobe from the parietal lobe. The precentral gurus containing the primary motor cortex lies just anterior to the central sulcus. The frontal lobe contains functional areas that planned, initiate, and an act motor movement including eye movement and speech production. The most interior region of the frontal cortex performs higher - order cognitive functions, such as thinking, planning, decision-making, working memory, and other executive functions.
The limbic system is referred to as the "emotional brain." It is responsible for the emotional impact actions, behavior, and situations have on us (our "feelings"); it directs our response to these emotions; and it functions in creating, storing, and retrieving memories, particularly those that elict strong emotions. This functional brain system consists of a group of structures located in the medial aspect of each cerebral hemisphere and the diencephalon. In the cerebrum, the limbic structures form a broad ring ( limbus = headband ), that includes the cingulate gyrus, septal nuclei, part of the amygdaloid body, and the hippocampal formation. In the diencephalon, the main limbic structures are the anterior thalamic nuclei and the hypothalamus. The fornix ("arch") and other fiber tracks link the limbic system together. The limbic system also overlaps the rhinencephelon the portions of the cortex that process olfactory signals. This explains why smells often trigger emotions.
The cingulate gyrus is part of the cerebral cortex located superior to the corpus Callisum. It is linked to all other regions of the cerebral cortex. Through its connections to the sensory regions, the cingulate gyrus mediates the emotional response to the stimuli, such as experiencing painful stimuli as unpleasant. It connects with the hypothalamus and prefrontal cortex function to generate and control visceral and behavioral responses to emotions.
The hippocampal formation, located in the temporal lobe, consist of the hippocampus and the parahippocampal gyrus. These regions encode, consolidate, and later retrieve memories of facts and events. The hippocampal formation receives information to be remembered from the rest of the cerebral cortex; it processes these data and return them to the cortex, where they are stored as long-term memories.
Amygdaloid body is subcortical gray matter that contains the key brain nuclei for processing fear and stimulating the appropriate sympaththetic response to fear. The anygdaloid body also forms memories of experiences based entirely on their emotional impact, especially those related to fear. If people are reminded of these experiences later, the amygdaloid body retrieve some memories and causes them to reexperience the original emotion. This is beneficial because it lets people who make informed decisions about difficult and risky situations, based on memories of past emotional. Says. Hyperactivity in the amygdaloid body and dysfunction in the medial prefrontal cortex and the hippocampus are involved in the extreme response to triggered memory experienced by individuals suffering post-traumatic stress disorder (PTSD).
The meninges are three connective tissue membranes that lie just external to the brain and spinal cord. Their functions are to: cover and protect the CNS. Enclose and protect the blood vessels that supply the CNS. And contain the cerebrospinal fluid.
Dura matter- The leathery Dura matter is the strongest of the meninges. where it surrounds the brain, The Dura matter is two layered sheet of dense fibrous connective tissue. The more superficial periosteal layer attaches to the internal surface of the skull bone; the deeper meningeal layer forms the true external covering of the brain. these two layers of the Dura matter are fused together, except where they separate to enclose the blood-filled dural venous sinuses. The dural sinuses collect blood from the brain and conduct it to the large internal jugular vein's of the neck. Largest dural sinus is the superior sagittal sinus in the superior midline.
The arachnoid mater- The arachnoid matter lies just deep to the Dura matter. Between these two layers is a thin potential space called the subdural space, which contains only a film of fluid. The subdural space is referred to as the potential space because although normally it is a thin space it has the potential to fill with substantial amounts of fluid or blood as a result of disease or trauma. Deep to the arachnoid membrane is the wide subarachnoid space, which is spanned by weblike threads that holds the arachnoid matter to the underlying pia mater. This web is the basis of the name arachnoid, which means spider like. The subarachnoid space is filled with cerebrospinal fluid, and is also contains the largest blood vessels that supply the brain. Over the superior part of the brain, the rack annoyed forms not like projections called arachnoid granulation a, or arachnoid villi. The arachnoid granulations project superiorly through the Dura matter into the superior sagittal sinus and into some other dural sinuses, as well.
The pia mater- The pia mater is a layer of delicate connective tissue richly vascularized with fine blood vessels. Unlike the other meningitis, a clings tightly to the brain surface, following every convolution. As it's arteries enter the brain tissue they carry ragged sheaths of Pia mater internally for short distances.
Cerebrospinal fluid (CSF) is a watery broth that fills the subarachnoid space and the central hollow cavities of the brain and the spinal cord. It aids in protecting and nourishing the neural tissue.
CSF provides a liquid medium that surrounds and gives buoyancy to the central nervous system. The brain and the spinal cord actually float in the CSF, which prevents these delicate organs from being crushed under their own weight.
The layer of CSF surrounding the central nervous system resist comprehensive forces and cushions the brain and spinal cord from blows and jolts.
CS of helps to nurse the brain, to remove waste produced by neurons, and to carry chemical signals such as warm owns between different parts of the central nervous system. Also similar in composition to blood plasma from which it arises, CSF contains more sodium and chloride ions and less protein.
CSF is produced in the ventricles of the brain, circulates through the hollow central cavity of the CNS and the sub arachnoid space, and is really sore back into the blood in the dural venous sinuses.
CSF is made in the choroid plexus, capillary-rich membranes located in the roofs of the four brain ventricles. Each Plexus consist of a layer of Ependymal cell's covered externally by the capillary rich pia mater. CSF continually forms from blood plasma by filtration from the capillaries and then passes through the Ependymal cells into the ventricles. After entering the ventricles, the CSF moves freely through these chambers.
Some CS at friends into the central canal of the spinal cord, but most enters the subarachnoid space through the lateral and median apparatus in the walls of the fourth ventricle.
In the subarachnoid space, CSF bathes the outer surfaces of the brain and spinal cord.
CSF then passes through the arachnoid granulation's and enters the blood of the dural venous sinuses.
The spinal cord functions in three ways:
1. Through the spinal nerves that attached to it, the spinal cord is involved in the sensory and motor innervation of the entire body inferior to the head.
2. Through the ascending and descending tracts traveling with and it's white matter, the spinal cord provides a two-way conduction pathway for signals between the body and the brain.
3. Through the sensory and motor integration in it's gray matter, the spinal cord is a major center for reflexes.
The spinal cord runs through the vertebral canal of the vertebral column. The vertebral canal is formed from the successive vertebral foramina of the articulated vertebrae. The spinal cord extends from the foramen magnum at the base of the skulls occipital bone superiorly to the level of the first or second lumbar vertebrae inferiorly. At the inferior end, the spinal cord tapers into the conus medullaris. A long filament of connective tissue, the film terminale extends from the conus medullaris and attaches to the coccyx inferiorly, anchoring the spinal cord in place so that it is not jostled by body movements.
31 pairs of spinal nerves (PNS structures) attached to the spinal cord through dorsal and ventral nerve roots. The spinal nerves lie intervertebral foramina from which they send lateral branches throughout the body. The spinal nerves are named based on the vertebral locations in which they live. The 31 spinal nerves are divided into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal group(s).
Ascending- most of the ascending fibers in the spinal cord carry sensory information from the sensory neurons of the body to the brain.
The ascending pathways conduct generals somatic sensory impulses a purely through chains of two or three neurons to various regions of the brain. The first neuron in the pathway, called the first order neuron, is the sensory neuron which extends from the sensory receptor to the spinal cord. The first order neuron synapses in the CNS with another neuron in the pathway, the second order neurons. In some ascending pathway, the second order neuron synapses with a third order neuron. The three main ascending pathways are spinocerebellar pathway, the dorsal column pathway and spinothalamicns of the brain the limbic system? pathway.
The spinocerebellar pathway arises from second-order neurons in the dorsal horn of the spinal cord and terminates on the Cerebellum. This pathway carries information on proprioception from the lower limbs and truck to the cerebellum, which wses this information to coordinate body movements. These fivers either do not decussate or cross twice, undoing the decussation; they project ipsilaterally.
The dorsal column pathway carriess information on fine touch, pressure, and coscious aspects of proprioception. These are discriminative senses- senses that can be localized very precisely on the body surface.
The spinothalamic pathway carries information on pain, temperature, deep pressure, and non-discriminative touch - stimuli we are where of but cannot localize precisely on the body surface in the spinothalamic pathway:
1. Axon of the first order sensory neurons enter the spinal cord, where they are synapse on interneurons in the dorsal gray horn.
Axons of The second order neurons decussate in the spinal cord, enter the lateral and ventral do you lie as the spinothalamic tract, and ascend to the thalamus.
Axons from third order neurons in the thalamus project to the primary Somatosensory cortex on the postcentral gyrus, where the information is processed into the conscious sensations. The brain interprets the sensory information carried by the spinothalamic pathway as unpleasant - pains, burns, cold and so on.
Descending - most descending fibers carry motor instructions from the brain to the spinal cord, to this simulate contraction of the body's muscles and secretion from its glands.
The descending spinal tracts deliver more motor instructions from the brain to the spinal cord. Each pathway contains upper motor neuron's and lower motor neuron's. Upper motor neuron's originate in the gray matter of the brain and send long axons down a descending tracts of the spinal cord. These axons synapse with other motor neurons in the ventral horn of the spinal cord. The axons of the lower motor neuron's exit the ventral root of the spinal cord to innervates the muscles or glands of the body. The descending spinal tracts can be classified into groups 1. direct pathways which are the pyramidal tracks and 2. indirect pathways, essentially all others.
1. The direct pathway's extend without synapsing from the Pyramidal cells in the cerebral cortex in the spinal cord. The Pyramidal cells are the large neurons found in the primary motor cortex of the brain. The long axons of Pyramidal cells from the Pyramidal tracks, also called corticospinal tracks, which control precise and skilled voluntary movements.
That axons of Pyramidal cells, the upper motor neuron's, descend from the cerebral cortex motor cortex through the brain stem to the spinal gray matter - mostly to the ventral horns.
In the ventral horn, the axons either synapse with short interneurons that activates somatic motor neurons or synapse directly on somatic motors neuron, the lower motor neurons.
2. The indirect ascending pathways originate in the sub cortical motor nuclei of the brainstem. Historically, these pathways were thought to be independent of the Pyramidal cells and were called the extraPyramidal tracts, a term still used clinically. It is now known, however that the Pyramidal cells do you project to that influence these pathways; thus, these pathways are referred to as indirect or multi neuron pathways. The indirect motor pathways include the techtospinal tract from the superior colliculus, the vestibulospinal tract from the red nuclear this, and the reticulospinal tract from the reticular formation. These tracts stimulate body movements that are subconscious, course, or postural.
1.Mechanorecetors respond to mechanical forces such as touch, pressure, stretch, vibrations, and itch. One type of mechanoreceptor, called a barotreceptor monitors blood pressure.
2. Thermoreceptors respond to temperature changes.
3. Chemoreceptors respond to chemicals in solution and changes in blood chemistry.
4. Photoreceptors in the eye respond to light.
5. Nociceptors respond to harmful stimuli that result in pain.
General sensory receptors widely distributed receptors are nerve endings of sensory neurons that monitor touch, pressure, vibration, stretch, pain, temperature, and proprioception. Structurally, sensory receptors are divided into two broad groups 1) free nerve endings and 2) encapsulated nerve ending surrounded by a capsule of connective tissue.
1) free nerve endings of sensory neurons invade almost all tissues of the body that are particularly abundant in epithelia and in connective tissue that underlies that epithelia. These receptors are primarily nociceptors and Thermoreceptors scepters responding to pain and temperature. One way to characterize free nerve ending functionally is to say that they Monitor the effective senses, those to which people have an emotional response - and people certainly respond emotionally to pain!
2) all encapsulated nerve endings consist of one or more and fibers of sensory neurons enclosed in a capsule of connective tissue all seem to be the Cano receptors, and their capsules serve either to amplify the stimulus or to filter out the wrong types of stimuli. Encapsulated receptors vary widely in shape, size, and distribution in the body. The main types of tactile corpuscles (meissner's), lamellar corpuscles (pacinian), and bulbous corpuscles (ruffini endings), and proprioreceptors.
In tactile corpuscles (meissner's) A few spiraling nerve endings are surrounded by Schwan cells, which in turn are surrounded by an egg shaped capsule of connective tissue. These corpuscles , which occur in the dermal papillary been need the epidermis, are rapidly adapting receptors for fine, discriminative touch. They mainly occur in the sensitive and hairless areas of the skin, such as the soles, palms, fingertips, nipples, and lips.
Scattered throughout the deep connective tissue of the body are lamellar corpuscle (pacinian corpuscles). They occur for example in the hypodermis deep to the skin. Although they are sensitive to deep pressure, they respond only to the initial application of that pressure before they tire and stop firing. Therefore, lamellar corpuscles are rapidly adapting receptors that are best suited to monitor vibration, and on/off pressure stimulus. These corpuscles are large enough to be visible to the unaided Eye- about 0.5-1 mm wide and 1-2 mm long.
Located in the dermis and elsewhere the bulbous corpuscles (Raffini endings), which contain an array of nerve endings enclosed in a thin, flatten capsule. Like lamellar corpuscles they respond to pressure in touch. However, they adapt slowly and thus can monitor continuous pressure placed on the skin.
Virtually all proprioceptors are encapsulated nerve endings that monitor stretch in the locomotory organs. Proprioceptor's include muscle spindles, tendon organs, and joint kinesthetic receptors.
Muscle spindles (neuromuscular spindles) measure the changing length of the muscle as the muscle contracts and is stretch back to its original length. An average muscle contain some 50 to 100 muscle spindles, which are embedded in the perimysium between the fascicles.
I. Olfactory. This is a sensory nerve of smell.
II. Optic. Because it develops as an outgrowth of the brain, the sensory nerve of vision is not a true nerve at all. It is more correctly called a brain tract.
III. Oculomotor. The name oculomotor means I mover. This nerve innervates four of the extrinsic Eye muscles - muscles that move the eyeball in the orbit.
IV. Trochlear The name trochlear at means pulley. This nerve innervates the extrinsic Eye muscle that hooks the through a pulley- shaped ligament in the orbit.
V. Trigeminal. The name triennial means " three fold" which refers to this nerve's three majorbranches. the trigeminal nerve provides general sensory innervation to the face and motor innervation to the chewing muscles.
VI. Abducens. This nerve was so named because it inervates the muscle that abducts the eyeball (turns the eye laterally).
VII. Facial. This nerve innervaters the muscles of facial exprssion as well as other structures.
VIII. Vestibulocochlear. This sensory nerve of hearinf and equilibrium was once called the auditory nerve.
IX. Glossopharyngeal. The name glossopharyngeal means "tongue and pharnyx," structures that this nevre help innervate.
X. Vagus. The name vagus means "vagabond" of "wanderer." this nerve "wanders" beyond the head into the thorax and abdomen.
XI.Accessory. This nerve was once called the spinal accessory nerve. It originates from the cervical region of the spinal cord, enters the skull through the foramen magnum, and exits the skull with the vagus nerve. the accessory nerve carries motor innervation to the trapezius and sternocleidomastoid muscles.
XII. Hypoglossal. The name hypoglossal means "below the tongue." this nerve runs inferior to the tongue and innervates the tongue muscles.
Thirty-one pairs of spinal nerves, each containing thousands of nerve fibers, attach to the spinal cord. These nerves are named according to their point of issue from the vertebral column.
8 pairs of cervical nerves (C1- C8)
The first cervical spinal nerve (C1) lies superior to the first vertebra, whereas the last cervical nerve (C8) esits inferior to the seventh cervical vertabra, leaving six nerves in between.
12 pairs of thoracic nerves (T1- T12)
5 pairs of lumbar nerves (L1-L5)
5 pairs of sacral nerves (S1-S5)
1 pair of coccygeal nerves (designated Co1)
Each spinal nerve connects to the spinal cord by a dorsal root and a ventral root. Each root forms from a series of rootlets that attach along the whole length of the corresponding spinal cord segment. The dorsal root contains the axonal processes of sinsory neurons arising from cell bodies in the dorsal root ganglion.
Directly lateral to its intervertebral foramen, each spinal nerve branches into a dorsal ramus and ventral ramus. Connecting to the base of the ventral ramus are rami communicantes leading to sympathetic trunk ganglia. Each of the branches of the spinal nerve, like the spinal nerve itself, contains both motor and sensory fibers.
A nerve plexus is a network of nerves. The ventral rami of all spinal nerves except T2 - T 12 branch enjoying one another lateral to the vertebral column, forming nerve plexuses. These interlacing networks occur in the cervical, brachial, lumbar, and sacral regions and primarily serve the limbs. Note that these plexuses are formed by ventral rami only. Within the plexuses, fibers from the different ventral rami coverage and diverge and redistribute so that 1) each end branch of the Plexus contains fibers from several different spinal nerves, and 2) fibers from each ventral ramus travel to the body periphery via several different routes or branches.
The cervical plexus is buried deep in the neck, under the sternocleidomastoid muscle, and extends into the posterior triangle of the neck. It is formed by the ventral rami of the first four cervical nerves. The plexus forms an irregular series of interconnecting loops from which branches arise.
The brachial plexus lies partly in the neck and partly in the axilla (armpit) and gives rise to almost all of the nerves that supply the upper limb. The brachial plexus can sometimes be felt in the posterior triangle of the neck just superior to the clavicle at the lateral border of the sternocleidomastoid muscle. The brachioplexus it's warm by the intermixing of the ventral Rami of cervical nerve C5 - C8 and most of the ventral ramus of T1. Additionally, it may receive small contributions from C4 or T2.
The lumbar plexus arises from the first for lumbar spinal nerves L1 - L4 and lies within the psoas major muscle in the posterior abdominal wall. It's smaller branches innervate parts of the abdominal wall and the psoas muscle itself, but the main branches descend to innervate the anterior thigh.
The sacral plexus arises from spinal nerves L4 - S4 and lies immediately Cortile to the lumbar plexus. Because some fibers from the lumbar plexus contribute to the sacral plexus via the Lumbo sacral trunk, the two plexuses are often considered together as the Lumbo sacral plexus. Of the dozen named branches of the sacral plexus, about half serve the buttock and lower limb, where as the rest innervate parts of the pelvis and perineum.
Shingles (herpes zoster) is a vermicelli zoster viral infection of sensory neurons innervating the skin. It is characterized by a rash of scaly, painful blisters usually confined to a narrow strip of skin on one side of the trunk, usually to one or several adjacent dermatomes.
Polio is caused by a virus spread most commonly via fecal contamination or through respiratory droplets or saliva it enters the mouth, multiplies in the gut, and then travels to the motor neurons. The initial symptoms resemble those of flu, including fever, headache, and stiffness of the neck and back, but about 10% of cases progress further, destroying some motor neurons of the spinal cord or brain. The result is loss of the motor functions of certain nerves and paralysis of muscles.
Migraine headaches are extremely painful, episodic headaches that affect 29.5 million Americans. the cause of migraines was long debated, but they are now known to relate the sensory innervation of the brain cerebral arteries by the trigeminal nerve: a signal from the brainstem causes the sensory nerve endings of the ophthalmic division to release chemicals on to the cerebral arteries that they innervate, signaling these arteries to dilate. This dilation then compresses and irritates the sensory nerve endings, causing the headache.
Peripheral neuropathy refers to any pathological condition of the peripheral nerves that disrupts nerve function. If an individual nerve is affected, the condition is called a mononeuropathy; if multiple nerves are involved, it is termed a polyneuropathy. Symptoms of neuropathy very according to the nerve fibers affected. Symptoms of sensory nerve involvement include paresthesia, severe pain, burning, or loss of feeling. If motor fibers are affected, muscle weakness and paralysis result. Peripheral neuropathy's may be caused by trauma to individual nerves or by repetitive use injuries that compress nerves.
The sympathetic division is responsible for the fight or flight response. Its activity is evident during vigorous exercise, excitement or emergencies. A pounding heart, dilated eye pupils, and cold, sweaty skin are signs that the sympathetic division has been mobilized. All of them help us respond to dangerous situations: the increase her rate delivers more blood and oxygen to the skeletal muscles use for fighting or running; why didn't pupils let in more light for a clear vision; and cold skin indicates that blood is being diverted from the skin two more vital organs, such as the brain. Additionally, the small air tubes in the lungs dilate, increasing the uptake of oxygen; oxygen consumption by the body's cells increase; and the liver releases more sugar into the to provide for the increased energy needs of the cells. In this way, the bodies motor are revved up for vigorous activity.
Unlike the sympathetic division, the parasympathetic division is most active when the body is at rest the division is concerned with conserving body energy and directing vital housekeeping activities such as digestion and the elimination of feces and urine. The buzz words to remember our rest and digest. Parasympathetic function is best illustrated by a person who is relaxing after dinner and reading the newspaper. Heart rate and respiratory rates are low - Normal levels, and the gastrointestinal tract is digesting food. The pupils are constricted as the eyes focus for close vision.
The white rami contain all the preganglionic axons traveling to the sympathetic trunk ganglionic. White rami are white because pre-ganglionic axons are myelinated. They occur only in the region of sympathetic outflow from the spinal cord - on sympathetic trunk ganglia between T1 and L2.
The gray rami contain only the postganglionic axons headed for the peripheral structures. Gray rami are gray because postganglionic axons are nonmyelinated. They occur on all the sympathetic trunk ganglia because sweat glands, are yor pili, and blood vessels must be innervated in all body segments.
In the sympathetic innervation of the head, the preganglionic axons originate in the first four thoracic segments of the spinal cord T1 - T4. From there, these axons assigned to the sympathetic trunk to synapse in the superior cervical ganglion. From this ganglion, the postganglionic axons associate with large arteries that carry them to the glands, smooth muscle, and vessels through out the head.
In the sympathetic innervation of thoracic organs, the preganglionic axons originate at spinal levels T1 through T6. Some of these axons synapse in the nearest sympathetic trunk ganglionic, and the postganglionic axons run directly to the organ being supplied. Fibers to the lungs and esophagus take this direct route, as do some axons to the heart. Along the way, The post ganglionic axons pass through the pulmonary, esophagus, and cardiac plexus.
In the sympathetic innervation of abdominal organs, the preganglionic axons originate in the inferior half of the thoracolumbar spinal cord T5 through L2. From there, these axons pass through the adjacent sympathetic trunk ganglia and travel in the thoracic splanchnic nerves to synapse in collateral ganglia in the large plexus on the abdominal aorta. These ganglia include the celiac and superior mesenteric ganglia, along with some smaller ones. postganglionic axons from these ganglia then follow the main branches of the aorta to the stomach, liver, kidney, spleen, and intestines.
In the sympathetic innervation of pelvic organs the pre-ganglionic axons originate in the most inferior part of the thoracolumbar spinal cord T10 to L2, then descend in the sympathetic trunk to the lumbar and sacral ganglia of the sympathetic trunk. Some axon synapse there, and the postganglionic axons run in lumbar and sacral splanchnic nerves to plexuses on the lower aorta and in the pelvis - namely, the inferior mesenteric Plexes, the aortic Plexus, and the hypogastric plexus. Other preganglionic axons, by contrast, passed directly to these autonomic plexuses and synapse and collateral ganglia there - the inferior mesenteric ganglia and inferior hypogastric ganglia. Postganglionic axons proceed from these plexuses to the pelvic organs, including the bladder, and reproductive organs, and the distal half of the large intestine. The sympathetic fibers inhibit urination and defecation and promote ejaculation.
Parasympathetic fibers from the The vagus innervate the visceral organs of the thorax and most of the abdomen. Note that this does not include innervation of the pelvic organs and that the vagal innervation of the digestive tube and's halfway along the large intestine. The vagus an extremely important part the ANS, containing nearly 90% of the preganglionic parasympathetic fibers in the body Functionally, the parasympathetic fibers in the Vagus nerve bring about typical rest - and - digest activities in this role muscle and glands - stimulation of digestion, reduction in the heart rate, and constriction of the bronchi in the lungs, for example.
The preganglionic cell bodies are mostly in the dorsal motor nucleus of that is in the medulla and the preganglionic axons run through the entire length of the vagus nerve. Most postganglionic neurons are confined within the walls of the organs being innervated, and their cell bodies from intramural ganglia.
The vagus nerve is essential to the functioning of many organs. As the vagus descends through the neck and trunk, it sends branches through many autonomic nerve plexuses to the organs being innervated. Specifically, the Vagus sends branches through the cardiac Plexes to the heart, through the pulmonary plexus to the lungs, through the esophageal plexus to the esophagus and into the stomach wall, and through the celiac plexus and the superior mesenteric Plexus to the other abdominal organs. Fibers from both divisions of the ANS parasympathetic and sympathetic, travel to the thoracic and abdominal organs through these plexuses.