Neuroanatomy PDF

Isabella Ronchi Ñëürøåñåtømÿ The prosencephalic vesicle is going to divide into the diencephalon and telencephalon. The cerebral hemispheres need to be able to host a lot of neurons, therefore the telencephalic vesicles grow large. The two telencephalic vesicles gro...

Isabella Ronchi Ñëürøåñåtømÿ The prosencephalic vesicle is going to divide into the diencephalon and telencephalon. The cerebral hemispheres need to be able to host a lot of neurons, therefore the telencephalic vesicles grow large. The two telencephalic vesicles grow rostrally, bend dorsally, and then grow posteriorly and inferiorly, acquiring a C- shaped appearance. In the meantime, they envelop the diencephalic vesicle in the middle. The diencephalon is not any longer in series with the telencephalon, but it is in parallel. While they grow, they meet the bones of the skull. The lobes of the cortex take their name from the bones they are closer to the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. Because of the change in shape of the vesicles, the cavity (lateral ventricle) within each of the telencephalic vesicles, also acquire a C-shaped appearance. The lateral ventricles have a frontal horn, a central horn, and an inferior horn, which all converge to the atrium. Communication between the third ventricle and the lateral ventricles takes place at the level of the intraventricular foramen. The third ventricle then communicates with the fourth ventricle through the aqueduct of Sylvius. Phylogenetically speaking, the brain is not homogenous. In cyclostomata there is a primitive pallium, and the cortex is poorly developed. In amphibians, the cortex starts to differentiate into the archipallium and the paleopallium. In reptiles the archicortex changes its position and the paleocortex becomes bigger; the neopallium appears. In mammals the neocortex expands so much that the archicortex and paleocortex get squeezed medially and ventrally at the level of the telencephalic vesicles. The paleocortex corresponds to areas of the cortex that process olfactory information, so it was much more important for less developed mammals. In humans, small and located inferiorly and ventrally. Ontogenesis retraces phylogenesis. The oldest portion of the cortex, the hippocampus, is in the floor of the inferior horn of the fourth ventricle. At the initial phases of embryonic development, the oldest part of the cortex is located dorsally, but it moves ventral and medial into the temporal lobe leaving behind a trail of fibres (fornix) to maintain communication with the region of the basal forebrain and the mammillary nuclei of the  Isabella Ronchi hypothalamus. The choroid fissure, in which the choroid plexus is forming, acquires a C-shape within the concavity of the arch formed by the fornix. In the region of the basal forebrain is the origin of the corpus callosum, which keeps the two hemispheres in communication. The corpus callosum contains commissural fibres that run horizontally. Because of the bending of the two telencephalic vesicles, they surround the diencephalic vesicle, and they fuse with it. The cortex can now project directly to the brainstem without crossing the diencephalon. During this process of bending and fusion, the region of the telencephalon that proliferates gives rise to the ganglionic/basal eminence or corpus striatum. At some point, neurons of the cortex form connections with the neurons of the brainstem and the spinal cord, so their axons must pass through the ganglionic eminence. At the same time the thalamus starts to project to the cortex and the axons of neurons of the thalamus need to pass to the ganglionic eminence. This bundle of ascending and descending fibres forms the internal capsule, that crosses the corpus striatum. Part of the basal eminence remains medial (caudate nucleus) to the internal capsule and part remains lateral (putamen). The internal capsule has an anterior limb, a genu and a posterior limb. The retrolenticular division and the sublenticular division are portions of the interal capsule that pass below or behind the lenticular nucleus. With completion of development, only the ventral portion of the diencephalon (that corresponds to the hypothalamus) remains visible. Expansion of the cerebral hemispheres is not uniform. A portion of the wall of the telencephalic vesicle as the other: it is the insula or hidden lobe. The cortex adjoining it grows over it, making it invisible from outside. The portions of the parietal, temporal and frontal lobes that join together to cover it are called opercula. The putamen is located -  Isabella Ronchi Further expansion of the cerebral hemispheres leads to formation of sulci that separate lobes and gyri of the cortex. The three major sulci are: the central sulcus (of Rolando) separates the frontal lobe from the parietal lobes, the lateral sulcus (of Sylvius) separates the temporal lobe from the others, the calcarine sulcus is in the occipital lobe. On the medial surface the limbic lobe separated by the adjoining lobes by several sulci and grooves. The limbic lobe includes areas of the frontal, parietal and temporal lobes. It consists of the cingulate gyrus and the parahyppocampal gyrus. The parahyppocampal gyrus terminates with a U-shaped region called uncus. The cingulate gyrus is in close relationship with the corpus callosum. In the frontal lobe, the precentral gyrus contains the primary motor cortex. The most anterior part of the In this area, there are the superior, middle and inferior frontal gyri. The superior frontal gyrus contains the premotor cortex, for orientation, eye and head movements. The inferior frontal gyrus is divided into an opercular part, a triangular part and an orbital part. A lesion in the frontal lobe results in loss of motor function and changes in personality. In the parietal lobe, posterior to the central sulcus, is the postcentral gyrus, that contains the primary somatosensory cortex. The rest of the parietal lobe is divided into the superior perietal lobule and inferior parietal lobule, which is subdivided into the supramarginal gyrus and the angular gyrus. The superior parietal lobule is important for body scheme, while the inferior parietal lobule is important for language. In the temporal lobe there are the superior, middle and inferior temporal gyri. The superior temporal gyrus contains the primary auditory cortex, surrounded by the secondary  Isabella Ronchi auditory cortex. A lot of the temporal cortex is involved in understanding what we see. The occipital lobe is all devoted to vision. On the medial aspect of the occipital lobe there is the calcarine sulcus and the cortex around it is the primary visual cortex. The calcarine sulcus divides the cortex around it into the cuneus superiorly and the lingual gyrus inferiorly. On the ventral surface of the frontal lobe there are orbital gyri, that are in relationship with the orbital cavities. The straight gyri are also in relation with the orbital cavity. There also olfactory bulbs. The anterior and posterior perforated substances are perforated to allow passage of the deep vessels that enter the brain parenchyma from the circle of Willis. The hippocampus is located medially in the temporal lobe. It stretches on the floor of the inferior horn of the lateral ventricle in continuity with the structures of the basal forebrain and mammillary bodies of the hypothalamus through the fornix, a system of white matter. The fornix is located below the corpus callosum. The hippocampus is coiled on itself, because originally it was dorsal and lateral and was squeezed ventral and medial. Medially and dorsally to the hippocampus, there is a choroid plexus in the floor of the inferior horn of the lateral ventricle. The hippocampus (cornu Ammonis) belongs to the hippocampal formation, which contains the dentate gyrus and the subiculum. The hippocampus is important for memory and learning. The subicular cortex is important to receive all the information coming from different areas of the cortex and to feed it to the dentate gyrus and hippocampus. The hippocampus is a very sensitive region of the brain. It is damaged very early in Alzheimer. Damage can be caused by hypoxia, encephalitis, and medial temporal lobe  Isabella Ronchi epilepsy. Bilateral hippocampal damage causes , a memory disorder characterised by inability to retain new information (anterograde amnesia) and a less severe defect in recall of old memories (retrograde amnesia). Hippocampal amnesia affects more severely episodic memory and less semantic memory. Semantic memory is memory for facts (e.g., Kabul is the capital of Afghanistan), while episodic memory is memory for personally experienced events (e.g., remembering where you parked your car this morning). The amygdala is a large deep d in front of the hippocampus and is close to structures related to olfaction and belonging to the limbic system. Together with the limbic lobe, the amygdala belongs to the limbic system, important for emotions, learning, behaviour, learning From the amygdala there is the origin of a bundle of white matter, the stria terminalis, that continues dorsally to the thalamus and then to the forebrain. The Bed nucleus of the stria terminalis is involved in homeostasis, behaviour, fear, defensive responsive, mood disorders The amygdala is involved in mood disorders, that is dysregulation of the feelings of happiness and sadness. Individuals affected by unipolar depressions have increased blood flow in the amygdala and prefrontal cortex. The amygdala modulates the autonomic responses based on learning and previous experiences (especially emotionally charged). It also has a role in anxiety, PTSD, aggressive behaviour, alcoholism, and substance abuse. Klüver- Bucy syndrome is a rare disease due to bilateral lesions of mesial/anterior temporal lobe structures. It leads to memory loss, emotional changes, extreme sexual behaviour. Placidity, indifference It can be caused by trauma, encephalitis, temporal lobe epilepsy, Alzheimer The amygdala was a popular target during the era of psychosurgery, specifically for the treatment of intractable aggression. At the time, psychiatrists believed on prisoners. Brodmann areas to a functional classification. The white matter in the cerebral hemispheres is organised in: o Commissural fibres form the corpus callosum, which keeps the two hemispheres in communication. The corpus callosum connects homologous areas of the two hemispheres. Cranially and caudally, there are two areas of the corpus callosum called forceps minor and forceps major respectively. In between these two there are the radiated fibres. The induseum griseum is a strip of greyish matter,  Isabella Ronchi animals it corresponds to the dorsal hippocampus). In a sagittal view, the corpus callosum can be divided (from posterior to anterior) into the splenium, the trunk, the rostrum and the genu. Between the genu and the anterior column of the fornix there is a thin layer of tissue called septum pellucidum. The septum pellucidum forms the medial wall of the anterior horn of the lateral ventricle. The basal forebrain is located anteriorly and ventrally with the respect to the septum septal nuclei. The anterior commissure is anterior to the fornix. It can be divided into an anterior division and a posterior division. The anterior division connects the two olfactory tracts and olfactory cortexes. The posterior division connects middle gyri of the temporal lobes and the amygdalae and contains fibres from the stria terminalis. When the fibres of the fornix reach the area of the anterior commissure, they slip into pre- commissural fibres, directed to the septal nuclei and into post- commissural fibres that reach the mammillary bodies (of the hypothalamus) and the anterior nuclei (of the thalamus). The hippocampal formation is in relationship with the basal forebrain, which has to do with behaviour and decision making. Between the crura of the fornix there is a commissural system that keeps in communication the hippocampus on the right with the hippocampus on the left (commissure hippocampi). The septal nuclei receive fibres but also project cholinergic axons towards the fornix and the amygdala. In some degenerative pathologies, like Al cholinergic nuclei in the forebrain. The cholinergic projection to the hippocampus is reduced, basal nucleus of Maynert projects to the hippocampus, but also gives rise to an extensive projection to the neocortex. Another important nucleus is the nucleus accumbens, and corresponds to the ventral striatum. The nucleus accumbens is important for the reward systems. The two hippocampal formations are kept in contact by the commissure of the fornix. o Associative fibres connect areas of the same hemispheres. They can be short or long, depending on how far the two gyri to be connected are.  Isabella Ronchi o Projecting fibres are organised in capsules. In the brain there are the extreme capsule, between the insular cortex and the claustrum; the external capsule between the putamen and the claustrum and the internal capsule. The latter is made of fibres running from the thalamus to the cortex and from the cortex to the thalamus, brainstem and spinal cord. The section of the internal capsule that goes from the thalamus to the cortex is called corona radiata. The basal ganglia are a complex of nuclei located deep in the cerebral hemispheres. The basal ganglia are the caudate nucleus, the putamen and the pallidus. The caudate and the putamen are also called the striatum. The putamen and pallidus together are collectively the lenticular nucleus. All three together they are called corpus striatum. The oldest part of the corpus striatum corresponds to the nucleus accumbens (or ventral striatum) and is located in the basal forebrain. The caudate nucleus has an important relationship with the thalamus: the head of the caudate nucleus is located anterior to the thalamus, while the body of the caudate is located dorsal to the thalamus. The tail of the caudate nucleus runs below the thalamus and laterally. The basal ganglia are important for posture and movement control. The neocortex is organised in 6 layers, numbered from I to VI going from superficial to deep. The cerebral neocortex is largely excitatory. There are two main categories of neurons: pyramidal cells (75-80%) and nonpyramidal cells (or stellate cells). Pyramidal cells are characterised by an apical dendrite that extends to the layers above the cell body. The axon of pyramidal neurons abandons the cerebral cortex (corticofugal axon), but it leaves a recurrent collateral. All pyramidal cells are excitatory. Nonpyramidal cells are mostly located in the granular layers (II and IV). Among nonpyramidal cells, there are inhibitory and excitatory interneurons. Excitatory nonpyramidal cells are spiny, while inhibitory nonpyramidal cells are smooth. Nonpyramidal neurons are important because they modulate the activity of the pyramidal cells. The pyramidal neurons develop from the ventricular zone, while nonpyramidal neurons originate from migration from the ganglionic eminence. Interkinetic nuclear migration in the neuroepithelium leads to a proliferation of progenitor cells, which leave the proliferation cycle and progressively differentiate into neurons or glial cells. When they exit the  Isabella Ronchi proliferation cycle, they move to their final position using apical radial glia. progenitor cells themselves. The differentiating neurons organise in three layers around the lumen of the neural tube. The innermost layer is the ventricular layer (ependymal layer). The majority of the neuron cell bodies cluster in the mantle layer, while the axons are found prevalently in the marginal layer, the outermost. In the cortex, instead, there are six layers. At some point, there is a first wave of migration, meaning that some differentiating cells migrate more superficially in the preplate region, that eventually will become layer I. The axons from the preplate region are located in the intermediate zone, which will become the white matter. In the second wave of migration, other neurons leave the replicative cycle and move to the cortical plate. They split the preplate into two compartments, a marginal zone and a subplate region. The cortical plate correspond two layers V-VI. The later born neurons will have to cross the cortical region to form layers IV, III and II. An additional layer, the subventricular zone, forms for proliferating cells. This process is known as inside-out formation of the cortical layers. Apart from layering, correct expansion of the cortex also has to take place for proper development. The process of gyrification in upper vertebrates is promoted by basal radial glial cells, which impose a tangential migration pathway to neurons and consequent tangential expansion and folding. The basal radial glia add in a fan-like manner to the pre-existing scaffold. The process of migration of differentiating neurons can be disrupted, leading to a defective development of the cortex. Migration takes place thanks to a link between the nucleus, the microtubule network and the centrosome to enable movement. A microtubule cage surrounds the nucleus and links with the centrosome using the microtubule network. The lissencephaly 1 protein functions as a bridge. The nonpyramidal cells reach the layer of the cortex from a different source, the ganglionic eminence. They tangentially migrate within the cortical layers and arrange erall microcircuitry of the cortex cannot function. In primates, cortical interneurons originate also from the ventricular zone. The layers in the neocortex do not have the same thickness in different regions of the cortex, and also different regions of the cortex do not have the same thickness. For instance, sensory information that reaches the cortex from the thalamus end up in layer IV. Layer IV of the primary sensory cortex is much thicker than in the primary motor cortex. Layer V is much thicker in the primary motor cortex, and it contains giant pyramidal cells and is important for the pyramidal tract. Agranular are the areas of the cortex where there are only few granule cells (nonpyramidal cells), while granular contain prevalently nonpyramidal cells.  Isabella Ronchi Homotypical means that all the six layers are represented and well distinguishable, while heterotypical are regions of the neocortex where some of the layers are not as distinguishable. During mammals phylogenesis the paleopallium and archipallium decreased in size, while the neopallium became dominant occupying almost the whole surface of the brain. The human cortex can be divided into: isocortex (the neocortex) and allocortex (paleopallium and archipallium). The paleocortex is the oldest cortical area of the telencephalon which contains 3 to 5 layers of neuronal cell bodies. It includes the olfactory bulb, olfactory tubercle and the piriform cortex. All those cortical and non-cortical areas which are related to the sense of smell are summarised as the rhinencephalon or olphactory brain. The archicortex is constituted by 3 to 4 layers of neurons and contains the hippocampal formation. It includes the dentate gyrus, the cornu Ammonis and the subiculum. The archicortex is basically organised in three layers: the polymorph layer, the granular layer and the molecular layer in the dentate gyrus. In the hippocampus, the granular layer is substituted by the pyramidal layer. The frontal horn of the lateral ventricles is delimited medially by the septum pellucidum, anteriorly by the genu of the corpus callosum, inferiorly by the rostrum of the corpus callosum and laterally by the head of the caudate nucleus. The central part of the lateral ventricles is delimited inferiorly by the dorsal surface of the thalamus, medially by the septum pellucidum and by the corpus callosum. The posterior horn extends llosum. The inferior horn is delimited inferiorly by the hippocampus, superiorly by the tail of the caudate nucleus and stria terminalis, medially by the choroid fissure. Communication between the third ventricle and the lateral ventricles takes place through the interventricular foramina of Monro. They are located on each side at the junction of the roof and anterior wall of the third ventricle. The foramen is bounded anteriorly by the junction of the column and the body of the fornix and the anterior pole of the thalamus posteriorly. The ventricles are filled with CSF, which appear black in MRI and CT scans, so they can be used as reference points. In other types of weighting (T2), the ventricles may also appear white. Sometimes in the choroid plexuses of the lateral ventricles there can be formation of cysts. They do not give any clinical problems. The diencephalon gives rise to the thalamus (and metathalamus), hypothalamus, epithalamus and subthalamus. During development the diencephalon remains medial to the internal capsule. The thalamus is made of two lateral ovoid structures, that come in contact with each other at the inter-thalamic adhesion. The most posterior and largest portion of the thalamus is the pulvinar region. Between the two thalamic bodies there is the tela choroidea of the fourth ventricle. Close to where the tela choroidea comes in contact with the medial side of the thalamus, there is a stripe of white matter called stria medullaris, through which the epithalamus communicates with other areas of the brain. The stria terminalis runs over the dorsal surface of the thalamus. The anterior pole of the thalamus is in contact with the columns (pillar) of the fornix. Between the thalamic ovoids posteriorly there is the epithalamus, made by the pineal gland and by a small region called trigone of the habenula. The trigone of the habenula gives rise to the stria terminalis and is part of the limbic system. The habenular commission keeps in communication the habenular nuclei on the right and on the left. Ventral to the pulvinar region there are the lateral geniculate bodies, that form the metathalamus. Below the pineal gland, where the cerebral aqueduct opens in the third ventricle, there is the posterior commissure, important for the consensual response of both eyes to a light stimulus. It keeps  Isabella Ronchi in communication the pretectal areas on both sides. Other fibres connect the two superior colliculi and the enter in the medial longitudinal bundle of the brainstem. Below the posterior commissure, where the Sylvian aqueduct opens in the third ventricle, there is a sub- commissural organ, which produces substances to keep the patency of the mesencephalic aqueduct and ventricular system. The sub-commissural organ secretes a protein that binds a compound that needs to be cleared from the CSF. If the mesencephalic aqueduct is closed or narrowed, fluid accumulates in the lateral ventricles and in the third ventricle, leading to hydrocephalus. The grey matter of the thalamus can be divided in many nuclei, based on their position with respect to the internal medullary lamina. They ovoids can be divided into an anterior, a medial and a lateral compartment. Within the core of the medial compartment there is a Y-shaped lamina of white matter called internal medullary lamina. Within the internal medullary lamina there are areas of grey matter that form the intralaminar nuclei. There is also an external medullary lamina, which envelopes the thalamus laterally and separates the rest of the nuclei from the reticular nucleus. Functionally speaking, all the nuclei of the thalamus can be divided into: o Specific nuclei: they project to a specific area of the cortex o Association nuclei: they project to associative areas of the cortex o Non-specific nuclei: they project to many areas (intralaminar nuclei). This is an old definition. The thalamic peduncles are bundles of white matter that connect the thalamus to the cortex. They are part of the corona radiata, the portion of the internal capsule between the thalamus and the cortex. The subthalamus is the continuation of the tegmentum of the midbrain below the thalamus.  Isabella Ronchi Ñëürøåñåtømÿ The spinal nerves are mixed nerves, made of viscerosensory, somatosensory, visceromotor and somatomotor components. The spinal nerves divide into two terminal branches: a dorsal ramus and a ventral ramus. Each of these two branches is still a mixed nerve. There are also collateral branches: the recurrent (or meningeal) branch that re-enters the vertebral canal and the white (T1-L2) and grey rami communicantes. The sinuvertebral nerve (or recurrent branch) is a branch of the anterior ramus, and it contains sensory fibres and sympathetic fibres from the grey rami communicantes. It innervates the intervertebral disc, meninges, ligaments and vertebral periosteum. Facet joints are innervated by the medial branch of the posterior rami, instead. The division between an anterior ramus and a posterior ramus has an embryological reason. The myotomes are divided into an epimere (dorsal) and a hypomere (ventral). Most of the muscles that originate from the epimere are the muscles of the back, while the hypomere gives rise to the muscles of the abdomen and limbs. Posterior rami The posterior rami divide into a medial division and a lateral division, maintaining a segmental distribution. They have a cutaneous area of innervation, but they also supply the intrinsic muscles of the back. Additionally, they innervate the zygapophyseal joints, the posterior portions of the vertebral bodies and some ligaments. o The posterior ramus of C1 (sub-occipital nerve) innervates the sub-occipital muscles. o The posterior ramus of C2 has a large sensitive medial branch, which gives rise to the greater occipital nerve and is responsible for the innervation of the skin on the posterior surface of the head. Occipital neuralgia (C2 neuralgia) is a stabbing pain in the dermatomes of the greater occipital nerve. From an origin in the sub-occipital region, the pain spreads throughout the vertex, particularly the upper neck, back of the head and behind the eyes.  Isabella Ronchi The first cervical nerves also innervate the meninges of the posterior cranial fossa, so infratentorial meningitis is associated with occipital cephalea and reflex retraction of the head, due to contraction of the sub-occipital muscles. Anterior rami The ventral rami form plexuses, so they exchange fibres with one another. The reason for this is that muscles originate from more than one somite, and one somite gives rise to more than one muscle. The plexuses are: The cervical plexus Cervical (C1-C4) the posterior triangle of the neck, between the sternocleidomastoid muscle and by the anterior rami of C1 to C4. The anterior rami divide into an ascending and descending branch (except C1 which only has a descending branch). They come together and exchange fibres forming superior, middle and inferior anastomotic loops. There are also anastomotic branches directed to the hypoglossal (CNXII) and to the accessory of the cervical plexus, but contribute to the brachial plexus. Finally, there are also 4-5 grey rami communicantes. The cutaneous territory includes the neck, part of the shoulder, part of the thorax and the parotidean, mastoidal and ear regions. The Erb point is where the 4 superficial cutaneous branches exit accessible for anaesthesia in superficial surgery of the neck and shoulders and thyroid surgery. Its use is most common in carotid endarterectomy. Some muscular branches innervate the prevertebral and lateral muscles of the neck. The sternocleidomastoid and trapezius are innervated by the accessory nerve (XI), specifically by fibres coming from the cervical plexus. Some suprahyoid muscles are innervated by the cervical plexus through the hypoglossal nerve. Some infrahyoid muscles are innervated through the ansa cervicalis. The ansa cervicalis is a loop of nerve fibres from C1 to C3. The ones from C1 enter into the hypoglossus and then leave to form the superior loop. The ones from C2-C3 form directly The descending loop of the ansa cervicalis, without entering other nerves. C1 fibres that remain in the hypoglossal nerve innervate the geniohyoid and thyrohyoid muscles. The ansa cervicalis innervates the omohyoid, sternohyoid and  Isabella Ronchi sternothyroid muscles among the infrahyoid. The ansa cervicalis has a close relationship with the vascular bundle of the neck, made of the common carotid, internal jugular and vagus nerve. The only terminal branch of this plexus is the phrenic nerve, which originates only from C4, C3 and C5. It runs over the anterior surface of the anterior scalenus muscle, between the subclavian artery and vein and then in front of the apex of the lungs. It continues in the mediastinum, along the mediastinal face of the lungs and in front of the hilum of the lung. On its course, it gives sensory branches for the pericardium, peritoneum and pleurae. Most importantly, it gives muscular branches to the diaphragm. The diaphragm is formed by fibres originating from a somite that was originally more cranial and closer to the cervical plexus. Irritation of the diaphragm can give rise to shoulder pain. Diaphragmatic paralysis is due to an interruption due to a lesion of the phrenic nerve caused by mechanical trauma, compression (tumour within the chest cavity), myopathies or neuropathies. Paralysis of the diaphragm produces a paradoxical movement. The affected side of the diaphragm moves upwards during inspiration, and downwards during expiration. A unilateral diaphragmatic paralysis is usually asymptomatic, but if both sides are paralysed, the patient may experience poor exercise tolerance and fatigue. Firstly, the underlying cause must be identified and treated. The second part deals with symptomatic relief, usually with non-invasive ventilation, such as a CPAP machine. The brachial plexus (C5-T1) supraclavicular region, between the anterior scalene and middle scalene. Thoracic outlet syndrome is a group of disorders that occur when blood vessels or nerves in the space between the collarbone and first rib are compressed. Common causes include physical trauma from a car accident, repetitive injuries from a job- or sports-related activities and certain anatomical defects. It can cause pain and loss of sensation in the arms. More distal branches (cords) of the brachial plexus enter the axilla through the axillary inlet. In the axillary cavity there is a relationship with the axillary lymph node, which could irritate the branches of the plexus in case of an inflammation. It is also a possible location for infiltration in cancer. The anterior rami of spinal nerves C5 to T1 are the roots of the plexus. These roots come together to form three trunks. The superior trunk is made of the contributions from C4, C5 and C6. The middle trunk is made of fibres from the C7 root. The inferior trunk is formed by C8, T1 and T2. Each trunk divides into an anterior division and a posterior division. The three posterior divisions come together to form the posterior cord. The radial nerve and the axillary nerve originate as terminal branches from the posterior cord. The superior and middle anterior divisions come together to form the lateral cord, which is going to give rise to the musculocutaneous nerve and the lateral root of the median nerve. The inferior anterior division forms the medial cord and gives rise to the ulnar nerve and medial root of the median nerve. Shoulder dislocation can cause damage to the cords and terminal branches of the  Isabella Ronchi plexus. If the superior trunk is lesioned, for example, it causes a to loss of abduction of the arm, flexion of the forearm, supination of the forearm and extension of the wrist. The superior trunk may also be injured during childbirth, if the shoulder gets stuck. The burner syndrome immediate, severe, burning pain and prickly paraesthesia that radiates from the neck and extends to the arm or fingers. Backpack palsy is caused by incorrect positioning of the backpack, which compress the plexus. If the inferior trunk is injured, the most distal muscles are affected. is characterised by paralysis of the intrinsic muscles of the hand, of the flexors of the wrist, and long flexors of the fingers. There are problems in controlling the lumbricals and dorsal and ventral interossei, which flex the metacarpophalangeal joints and extend the proximal and distal interphalangeal joints. The Pancoast syndrome is most commonly due to cancer in the apex of the lungs. It can lead to weakness and atrophy of the intrinsic muscles of the hand, or pain and paraesthesia of the fourth and fifth digits and the medial aspect of the arm and forearm. Abnormal sensation and pain in the T2 territory may also be an early finding, and the triceps reflex may be lost. Roots, trunks and cords give rise to collateral branches. There is a collateral from the C5 root of the plexus, which gives rise to the dorsal scapular nerve. It innervates the levator scapulae, the rhmoboid major and minor. Weakness in these muscles results in a winged scapula: the scapula protrudes from the objects or pull and push. The winging of the scapula seen with dorsal scapular nerve syndrome is not as severe as seen in injury or paralysis of the serratus anterior muscle, innervated by the dorsoscapular nerve. The long thoracic nerve originates from the roots of C5, C6 and C7. It innervates the serratus anterior rotation of the scapula. It also facilitates abduction of the shoulder. Several muscles are involved in abduction of the shoulder: the supraspinatus (suprascapular nerve) is responsible for the first 15° of movement, the deltoid (axillary nerve) can abduct the arm until 90°, while the serratus anterior and trapezius (accessory nerve) move the arm up to 180°. Only one axillary nerve has a cutaneous territory of innervation, which can help in diagnosing nerve injuring together with weakness and paralysis. The suprascapular nerve and the nerve to the subclavius are collaterals of the superior trunk. The suprascapular nerve innervates the supraspinatus and infraspinatus, which are part of the rotator cuff. In particular, the supraspinatus abducts and and the infraspinatus laterally rotates the arm at the shoulder joint. The subclavius stabilises the clavicle during movements of the shoulder and arm. The lateral cord gives rise to the lateral pectoral nerve. This nerve innervates the pectoralis major, for flexion, adduction and medial rotation of the arm at the shoulder joint. The muscles involved in shoulder flexion include the pectoralis major (lateral pectoral nerve), the deltoid (axillary nerve), the long head of the  Isabella Ronchi biceps and the coracobrachialis (musculocutaneous nerve). The medial cord has collaterals too: the medial pectoral nerve, the medial brachial cutaneous nerve and the medial antebrachial cutaneous nerve. The medial pectoral nerve innervates the pectoralis minor, which moves the scapula forward and downward, but also contributes to the innervation of the pectoralis major. The posterior cord has several collaterals: the superior subscapular nerve, the thoracodorsal nerve and the inferior subscapular. The superior subscapular innervates the superior subscapular, which is a medial rotator of the arm. The thoracodorsal nerve innervates the latissimus dorsi and the inferior subscapularis innervates the subscapular muscles and the teres major. The thoracodorsal nerve is vulnerable to injury during surgery in the inferior part of the axilla or during mastectomy. The terminal branches of the brachial plexus are the continuation of the cords. The musculocutaneous nerve is also called perforating nerve of Casserius. It innervates all the muscles in the anterior compartment of the arm. They perform flexion of the arm and forearm and supination of the forearm when the elbow is flexed. After passing in the cubital fossa, the musculocutaneous nerve gives off the lateral antebrachial cutaneous nerve. The median nerve innervates the majority of muscles in the anterior compartment of the forearm and some muscles of the hand, excluding the flexor carpi ulnaris (ulnar n.) and medial belly of the flexor digitorum profundus (ulnar n.). The cutaneous territory if innervation is limited to the palmar side of the hand on the radial side. It also innervates the first three and a half fingers. The tips of the same fingers on the dorsal side are also innervated by the median nerve. It originates from C6, (C5), C7, C8 and T1. It passes through the cubital fossa anterior to the medial epicondyle and enters the anterior compartment of the forearm. Here, it gives off some direct muscular branches to the pronator teres, palmaris longus, flexor digitorum superficialis and flexor carpi radialis. Then it gives off the anterior interosseous nerve, which supplies the deep muscles in the anterior forearm (flexor pollicis longus, pronator quadratus, alteral half of the flexor digitorum profundus). The interosseous nerve lies on the anterior surface of the interosseous membrane between the flexor pollicis longus and flexor digitorum profundus. Then it reaches the hand via the carpal tunnel, where it terminates by dividing into two branches, the recurrent branch, which innervates the thenar muscles, and the palmar digital branch, which inntervates the palmar surface and  Isabella Ronchi fingertips of the lateral three and a half digits and the lateral two lumbricals. The median nerve can be damaged by injury at the elbow. The most common mechanism of injury is supracondylar fracture of the humerus. Almost all the flexors and pronators of the forearm will be paralysed, with weakness of wrist flexion and deviation to the ulnar side at flexion. Additionally, there will be loss of the muscles innervated by the recurrent branch, with loss of thumb abduction, opposition and flexion. the thenar eminence becomes atrophic and the thumb cannot be abducted, giving the appearance of an ape hand. The 1st and 2nd lumbricals will also be paralysed and the patient will be unable to flex at the metacarpophalangeal joint of the index and middle fingers. Flexion of when trying to make a fist. Finally, there will be loss of sensation over all cutaneous areas innervated by the median nerve. The median nerve can also be lesioned at the wrist, especially by lacerations and by carpal tunnel. Wrist and finger flexion will be intact as the anterior interosseous nerve is unaffected. There will be thenar wasting, but no ulnar deviation of the wrist or papal benediction. As for sensory damage, the lateral side of the palm can be preserved as the palmar cutaneous branch can be spared. The flexor digitorum anced by the action of the first two of the pronator teres, so if the passageway is too narrow, the nerve can be compressed. This is called pronator teres syndrome, which causes pain in the volar region of the forearm and some muscle weakness. If the anterior interosseous is damaged, because it innervates the flexors of the thumb and flexor digitorum profundus of the index and middle fingers, the patient cannot flex these fingers. The ulnar nerve receives most of its fibres from segments C8-T1. It has a cutaneous territory, which comprises the fifth finger, half of the fourth finger and the corresponding palmar surface. The ulnar nerve enters the anterior compartment of the arm and runs medially to the brachial artery. It pierces the medial intermuscular septum, which separates the anterior and posterior compartments of the arm. Then it runs superficially behind the medial epicondyle. It innervates most intrinsic muscles of the hand and two muscles in the anterior compartment of the forearm: the flexor carpi ulnaris and the medial half of the flexor digitorum profundus. In the hand it innervates the medial lumbricals, the interossei and the thenar muscles (adductor pollicis and flexor pollicis brevis). Overall, the ulnar nerve is involved in flexion of the wrist, flexion at the interphalangeal joints and metacarpophalangeal joints, abduction and adduction of the fingers. The nerve can be damaged at the elbow, specifically with a medial epicondyle fracture and supracondylar fracture. In this case, all muscles are affected. Flexion of the wrist is still present but with lateral deviation, because the flexor carpi radialis works. Abduction and adduction of the fingers is impossible. The patient cannot grip a paper placed between the fingers, because the interossei are impaired. Wasting of the hypothenar muscles can also be visible. The is when the patient cannot use the adductor pollicis and tries to hold on to the paper by using the flexor pollicis longus. There are two types of claw hand associated with damage of the ulnar nerve. With more proximal lesions, the patient cannot flex the 4 th and  Isabella Ronchi 5th digits when making a fist, because the lateral side of the flexor digitorum profundus and the lateral lumbricals are weakened. If there is a distal lesion, only the intrinsic muscles of the hand are affected. At rest, the hand of the patient at rest has the two lateralmost fingers flexed, because the lumbricals are weakened by the long flexors are spared. The ulnar paradox refers to the fact that more distal lesions actually have a more deformed appearance. If the ulnar nerve lesion occurs more proximally, the flexor digitorum profundus muscle may also be denervated. As a result, flexion at the interphalangeal joints is weakened, which reduces the claw-like appearance of the hand. Instead, the fourth and fifth fingers are simply paralysed in their fully extended position. When there is a lesion of the T1 root of the plexus, the hand presents itself as a full claw. The radial nerve receives contributions from all the roots of the plexus. It innervates all muscles in the posterior compartments of the arm and forearm. It also has a cutaneous territory in the skin of the arm, forearm and hand. It enters the posterior compartment of the arm passing through a triangular space and leaves an imprint on the back of the humerus. It allows extension and adduction of the arm at the shoulder joint via innervation of the long head of the triceps. It crosses the lateral intermuscular septum and enters the cubital fossa in front of the lateral epicondyle. In the cubital fossa the radial nerve gives off a deep branch, the posterior interosseous, that is responsible for innervation of the muscles in the posterior compartment. It also gives off a superficial branch for cutaneous innervation. The posterior interosseous is involved in extension of the wrist, extension of the digits, abduction of the thumb and supination. It also helps in flexion of the elbow because it supplies the brachioradialis. The radial nerve can be damaged at the level of the axilla. All muscles are affected: the patient cannot extend the forearm, wrist and fingers, with loss of supination. Flexion of the wrist is unopposed, leading to the appearance of a wrist drop. The radial nerve can also be damaged by a fracture of the humeral shaft. The triceps would be weakened but not paralysed, because some of the branches originate more proximally. The muscles of the posterior compartment of the forearm are affected, with the same symptoms mentioned above. The sensory branches to the arm and forearm usually remain intact. The radial nerve can also be lesioned in the forearm. If the superficial branch is damaged, there is no motor damage, but there is sensory loss in the territory of the hand. If the deep branch (posterior interosseous) is damaged, there is no sensory damage but there is motor damage to most of the posterior muscles of the forearm. In this case there would be no wrist drop, because the extensor carpi radialis longus is usually spared The axillary nerve is involved in abduction and lateral rotation of the arm, because it innervates the deltoid and teres minor. It mostly obtains its fibres from the C5-C6 segments. It has a cutaneous territory of innervation in the area of the shoulder.  Isabella Ronchi The lumbar plexus (L1-L4) The lumbar plexus is located in front of the transverse processes of the lumbar vertebrae, within the belly of the psoas major. It is composed of fibres coming from L1, L2, L3, part of L4 and anastomosis from T12. The spinal nerves in the lumbar plexus communicated through anastomotic loops of the anterior divisions, from which short and long collateral branches and two terminal branches. The nerves of the lumbar plexus innervate the large abdominal muscles, the back muscles, the thigh muscles and skin of the lower abdomen, perineum, thigh and leg. The short collateral branches innervate the psoas major, psoas minor and quadratus lumborum. The long collaterals, instead, innervate the large muscles of the abdomen together with the lower intercostals. The nerves that originate from the anastomotic loops are: o The iliohypogastric (T12, L1): innervates the internal obliques and transversus abdominis o The ilioinguinal (L1, L2): innervates the internal obliques and transversus abdominis o The genitofemoral (L1, L2): cremasteric o The lateral cutaneous of the thigh (L2, L3): o The superior root of the femoral and obturator (L2) o The middle root of the femoral and obturator (L3) o The inferior root of the femoral and obturator (L4) The obturator nerve and the femoral nerve are the terminal branches of the lumbar plexus. The obturator crosses in front of the sacro-iliac joint and enters the obturator canal, where it innervates the obturator externus muscle. Then it enters the medial compartment of the thigh, where it innervates all the adductor muscles, the gracile and the pectineus (+ femoral nerve). The obturator also gives rise to cutaneous branches that supply the inferomedial thigh and internal knee. If there is a damage of the obturator nerve, there will be weakness of adduction and lateral swinging of the limb during walking because of unopposed abductors.  Isabella Ronchi The femoral nerve passes below the inguinal ligament and enters the femoral triangle. It gives muscular and cutaneous branches in the anterior compartment of the thigh. It innervates the iliacus, the sartorius, the pectineus, the quadriceps. These are the muscles of flexion of the thigh at the hip joint and extension of the leg at the hip joint. It gives rise to a long cutaneous nerve, the saphenous nerve, which enters into the adductor canal and innervates the medial territory of the leg and foot, including the big toe. If there is a damage to the femoral nerve, there will be impaired flexion at the hip and impaired extension of the leg resulting from paralysis of the quadriceps femoris. The sacral plexus (L4-S3) The sacral plexus is attached to the posterolateral wall of the pelvic cavity. It innervates the muscles of the lower limb, pelvis and perineum. It also supplies the skin over the medial side of the foot, the posterior aspect of the lower limb and most of the perineum. The lumbosacral trunk is made of part of L4 and L5m together with S1-S4. Each anterior ramus has an anterior and a posterior division (except S4). The sciatic nerve is made of two components, the common peroneal (or fibular) nerve from the anterior divisions and the tibial nerve from the posterior divisions. These two components originate separately, come together to form the sciatic nerve and then are separated again into two nerves in the popliteal fossa. Anterior and posterior divisions give rise to collaterals. The posterior divisions give rise to: o Superior gluteal nerve (L4-S1), which innervates the gluteus medius and minimus and tensor fasciae latae. Damage to the superior gluteal nerve causes weakened abduction of the thigh by the gluteus medius and Trendelenburg sign (the hip deviates to the unaffected side). o Inferior gluteal nerve (L5-S2), which innervates the gluteus maximus. Lesion to the inferior gluteal nerve causes the patient to shift the weight to the side of the deficit, because of loss of hip extension. o Nerve to piriformis The anterior divisions give rise to: o Nerve to obturator internus and superior gemellus o Nerve to quadratus femoris and inferior gemellus o Posterior femoral cutaneous nerve The sciatic nerve is the largest and longest peripheral nerve in the body. It innervates muscles in the posterior compartment of the thigh, leg and foot. It also has a cutaneous territory in the skin of the leg and  Isabella Ronchi foot. It exits the pelvic cavity by passing below the piriformis in the greater sciatic foramen, it enters the gluteal region, the posterior region of the thigh and eventually the popliteal region, where it divides into the fibular nerve and tibial nerve. Piriformis syndrome is caused by a compression of the sciatic nerve by the piriformis muscle. Damage to the sciatic nerve causes impaired extension at the hip, impaired flexion at the knee and loss of dorsiflexion and plantarflexion and inversion and eversion in the foot. Patients with a damaged sciatic nerve cannot walk at all. The gluteal region can be divided into quadrants, and the upper lateral quadrant is considered a safe site for injection, avoiding injury of the sciatic nerve. The sciatic nerve gives off muscular branches in the thigh, particularly to the biceps femoris (tibial and fibular), semimembranosus (tibial) and semitendinosus (tibial). In the thigh the sciatic nerve also contributes to the innervation of the adductor magnus. The sciatic nerve finally reaches the popliteal region, where it divides into the common peroneal and tibial nerves. The tibial nerve is the continuation of the sciatic nerve in the posterior compartment of the leg. The common peroneal nerve distributes to the anterior and lateral compartments, so it arches around the fibula. The superficial peroneal nerve in the lateral compartment innervates the muscles responsible for eversion and plantar flexion of the foot. The deep peroneal nerve (also called tibialis anterior nerve) in the anterior compartment of the leg innervates the extensors, which dorsiflex and invert the foot, and extend the toes. Lesion of the common fibular nerve is the most common lesion of the lower limb. o Damage to the common peroneal nerve: foot drop (loss of dorsiflexion) and inversion of the foot, paralysis of all muscles in the anterior and lateral compartments. There can be sensory deficit to the anterolateral side of the leg and dorsal aspect of the foot. o Damage to the superficial peroneal nerve: loss of eversion of the foot. o Damage to the deep peroneal nerve: foot drop, high stepping gait (to avoid dragging the foot). In this case, the foot is not inverted. The only cutaneous deficit is in the web of skin between the first two toes. The tibial nerve innervates the muscles in the posterior compartment of the leg. These muscles are involved in flexion at the knee, plantarflexion and inversion of the foot. The popliteus muscle unlocks the knee when walking, and it medially and laterally rotates the tibia. The tibial nerve also innervates the intrinsic muscles of the foot in the plantar compartment. The dorsal compartment is innervates by the deep fibular nerve. Damage to the tibial nerve causes loss of plantarflexion and impaired inversion. This leads to difficulty in getting the heel off the ground. On the sensory front, there is loss of sensation in the sole of the foot. The sural nerve originates from the joining of the medial cutaneous branch of the tibial nerve and the lateral cutaneous branch of the common fibular. It runs behind the lateral malleus and continues up to the 5th Acute compartment syndrome occurs when the tissue pressure within a closed muscle compartment exceeds the perfusion pressure and results in muscle and nerve ischemia. It typically occurs following a traumatic event, most commonly a fracture. Tissue pressure exceeds the venous pressure and impairs blood outflow. Lack of oxygenated blood and accumulation of waste products results in pain and loss of sensation. Late manifestations include absence of a distal pulse and extremity paresis, because the cycle of elevating pressure eventually compromises arterial blood flow. If left untreated, the muscles and nerve undergo ischemic necrosis and a limb contracture, called Volkmann contracture, occurs. pressure, via longitudinal incisions along the compartments.  Isabella Ronchi The pudendal plexus (S2-S4) The pudendal nerve is the major somatic nerve of the perineum.. It innervates the skin and skeletal muscles of the perineum, including the external anal and external urethral sphincters. It is involved in micturition, defecation, erection, ejaculation and parturition. Pudendal neuropathy manifests with pain, numbness and hypersensitivity. The other symptoms are voiding dysfunction of the bowels and bladder and sexual dysfunction. The pudendal nerve leaves the pelvic cavity through the lower part of the greater sciatic foramen inferior to the piriformis muscle, passes around the sacrospinous ligament and then enters the anal triangle of the perineum by passing medially through the lesser sciatic foramen. It travels in the pudendal canal. It gives rise to three major terminal branches: the inferior rectal, the perineal nerves and the dorsal nerve of the penis or clitoris. The inferior rectal innervates the external anal sphincters and related regions of the levator ani muscles. It is also the general sensory for the skin of the anal triangle. The perineal nerve supplies skeletal muscles in the superficial and deep perineal pouches. The largest of the sensory branches is the posterior scrotal nerve in men and the posterior labial nerve in women. The dorsal nerve of penis and clitoris is sensory. Pelvic splanchnic nerves originate from spinal nerves S2-S4 and they bring parasympathetic fibres to the regions that cannot be reached by the vagus (descending and sigmoid colon and other viscera in the pelvis and perineum). The inferior hypogastric (pelvic) plexus contains the pelvic splanchnic nerves and the sacral splanchnic nerves, which originate from the paravertebral chain and are sympathetic. The pelvic splanchnic nerves receive fibres from the superior hypogastric plexus. The coccygeal plexus (S5-Co) The coccygeal plexus is located in front of the ischio-coccygeal muscle. It gives rise to the anococcygeal nerves, which are sensory nerves that distribute to the skin of the anal triangle of the perineum.