Neuroanatomy PDF

 NEUROANATOMY BASHIR MUHAMMAD HUMAN ANATOMY DEPARTMENT FACULTY OF BASIC MEDICAL SCIENCES FACULTY OF BASIC MEDICAL SCIENCES BAUCHI STATE UNIVERSITY, GADAU Dec, 2024 2  Neuroscience is the field of scien...

 NEUROANATOMY BASHIR MUHAMMAD HUMAN ANATOMY DEPARTMENT FACULTY OF BASIC MEDICAL SCIENCES FACULTY OF BASIC MEDICAL SCIENCES BAUCHI STATE UNIVERSITY, GADAU Dec, 2024 2  Neuroscience is the field of science that focuses on the study of the nervous system study of the nervous system – from structure to function, development to degeneration, in health and in disease.  Branches of neuroscience Neuroanatomy. Neurophysiology. The nervous system is the part of an animal's body Neuropharmacology. that coordinates its voluntary and involuntary Behavioral neuroscience. actions and transmits signals between different Developmental neuroscience. Cognitive neuroscience. parts of its body. Systems neuroscience. Molecular neuroscience. NEUROANATOMY AND UNDERSTANDING NEUROANATOMY relies on possessing a fundamental knowledge of the brain’s architectural (structural) components and associated peripheral nervous system. The nervous system is to send and receive information.  It controls, regulate and communicates throughout the rest of the body. “Body’s Control Center It is the center of all mental activity including thought, learning, and memory. Together with the endocrine system, the nervous system is responsible for regulating and maintaining homeostasis. Function of Nervous System The central nervous system consists of the brain and spinal cord. The principal roles of the CNS are to integrate and coordinate incoming and outgoing neural signals and to carry out higher mental functions. What is neuron? Neurons are the structural and functional units of the nervous system specialized for rapid communication. The function of each neuronal component is unique; different parts of the neuron are associated with different functions. DNA transcription occurs only in the soma, while protein synthesis, which involves polysomes and endoplasmic reticulum, occurs both in the soma and in dendrites.  Structure of a neuron Soma / Perikaryon/cyton. Neurites - Axon and Dendrite. Myelin sheath- Fatty cell wraped around an axon. Myelin, layers of lipid, and protein substances form a myelin sheath around some axons, greatly increasing the velocity of impulse conduction. Axon ending- Where electro-chemical signal is converted to a chemical message.  Neurons communicate with each other at synapses, points of contact between neurons. The communication occurs by means of neurotransmitters, chemical agents released or secreted by one neuron, which may excite or inhibit another neuron, continuing or terminating the relay of impulses or the response to them  Structural classification 1. Unipolar 2. Bipolar 3. multaipolar Functional classification 1. Sensory 2. motor 3. Associated or interconnected  Neurotransmitters production DOPAMINE is an important transmitter in the motor system ACHE memory and neuromuscular SEROTONIN, which is an important distributor for the sensory channels in the CNS and in the expressions of emotion NORADRENALIN increases the reaction excitability in the CNS and the sympathetic neurons in the spinal cord. Glutamate GABA  The neuroglial cells are the supporting systems for the neurons which protect and nourish the neurons. Neuroglia (glial cells or glia), approximately five times as abundant as neurons, are non-neuronal, non-excitable cells that form a major component (scaffolding) of nervous tissue, supporting, insulating, and nourishing the neurons. Some glial cells function primarily as the physical support for neurons. In the CNS, neuroglia include oligodendroglia, astrocytes, ependymal cells, and microglia (small glial cells). Others regulate the internal environment of the brain, especially the fluid surrounding neurons and their synapses, and nutrify neurons In the PNS, neuroglia include satellite cells around the neurons in the spinal (posterior root) and autonomic ganglia and neurolemma (Schwann) cells. To surround neurons and hold them in place To supply nutrients and oxygen to neurons To insulate one neuron from another To destroy pathogens and remove dead neurons THE BRAIN  What is brain The brain is the crown jewel of the human body. Seat of central nervous system encase in a cranium  The brain is divided into two anatomically symmetrical hemispheres by the longitudinal fissure – a major sulcus that External Structure runs in the median sagittal plane. Externally, the cerebrum has a highly convoluted appearance, consisting of The falx cerebri (a fold of dura mater) sulci (grooves or depressions) and gyri descends vertically to fill this fissure. (ridges or elevations). The two cerebral hemispheres are connected by a white matter structure, called the corpus callosum. PARTS OF THE BRAIN  The cerebrum The cerebrum is the largest part of the brain, located superiorly and anteriorly in relation to the brainstem. The cerebrum is located within the bony cranium. It extends from the frontal bone anteriorly to the occipital bone posteriorly Main sulci of the cortex Lateral sulcus – groove separating the frontal and parietal lobes from the temporal lobe. Lunate sulcus – groove located in the occipital cortex. The main gyri are: Precentral gyrus – ridge directly anterior to central sulcus, location of primary motor cortex. Postcentral gyrus – ridge directly posterior to central sulcus, location of primary somatosensory cortex. Superior temporal gyrus – ridge located inferior to lateral sulcus, responsible for the reception and processing of sound. Lobes of the Cerebrum The cerebral cortex is classified into four lobes, according to the name of the corresponding cranial bone that approximately overlies each part. The frontal lobe is located beneath the frontal bone of the calvaria and is the most anterior region of the cerebrum. It is separated from the parietal lobe posteriorly by the central sulcus and from the temporal lobe inferoposteriorly by the lateral sulcus. The association areas of the frontal lobe are responsible for: higher intellect, personality, mood, social conduct and language (dominant hemisphere side only).  NEURO CASE Frontotemporal disorders; are forms of HALLMARK OF SCHEZOPHRENIA dementia caused by a family of brain diseases known as frontotemporal lobar degeneration (FTLD). Broca aphasia from a lesion in areas 44 and 45 on the left hemisphere. This disorder is known as transcortical motor Frontal lobe lesion – a diverse range of presentations, often personality and behavioural changes occur and an inability to solve problems develops. 1/1/2025 BRAIN DEFAULT NETWORK 24 Parietal Lobe Functions The parietal lobe is found below the parietal bone of the calvaria, between the frontal lobe anteriorly and the occipital proprioception’ lobe posteriorly and he parietal lobe is separated by the central sulcus and parietooccipital sulcus, respectively. Other functions Cognition (episodic memory) Information Processing Touch Sensation (Pain, Temperature, etc.) Understanding Spatial Orientation Movement Coordination Speech Visual Perception Reading and Writing Mathematical Computation Damage or injury to the parietal lobe Temporal Lobe The temporal lobe sits beneath the temporal bone of the calvaria, inferior to the frontal and parietal lobes, from which it is separated by the lateral sulcus. The cortical association areas of the temporal lobe are accountable for memory and language – this Includes hearing as it is the location of the primary auditory cortex. Temporal lobe lesion – presents with recognition deficits (agnosias) e.g. auditory agnosia: patient cannot recognise basic sounds, prosopagnosia: failure to recognise faces.  Occipital Lobe The occipital lobe is the most posterior part of the cerebrum situated below the occipital bone of the calvaria. It rests inferiorly upon the tentorium cerebelli which segregates the cerebrum from the cerebellum. The parietooccipital sulcus separates the occipital lobe from the parietal and temporal lobes anteriorly. Occipital lobe lesions – visual field defects: contralateral hemianopia or quadrantanopia with macular The primary visual cortex (V1) is located within the sparing. occipital lobe and hence its cortical association area is responsible for vision  Functional organization of the cerebrum Serial processing model; information is performed in serial fashion such that cortical cell form a series of hierarchal levels. Parallel processing model; information is analyzed in series of parallel pathways e.g vision, motion e.t.c Distribution processing model: distribute system theory; describes the brain as a complex interconnected system in which a nerve can participate in numerous pathways. Internal Structure  Internal Structure The cerebrum is comprised of two different types of tissue – grey matter and white matter: Grey matter forms the surface of each cerebral hemisphere (known as the cerebral cortex), and is associated with processing and cognition. White matter forms the bulk of the deeper parts of the brain. It consists of glial cells and myelinated axons that connect the various grey matter areas. Layers of the cerebral cortex  The blood supply to the cerebrum can be simply Vasculature classified into 3 distinct paired arterial branches: Anterior Cerebral Arteries – branches of internal carotid arteries, supplying the anteromedial aspect of the cerebrum. Middle Cerebral Arteries – continuation of internal carotid arteries, supplying most of the lateral portions of the cerebrum. Posterior Cerebral Arteries – branches of vertebral arteries, supplying both the medial and lateral sides of the cerebrum posteriorly.  Venous drainage Venous drainage of the cerebrum is via a network of small cerebral veins. These vessels empty into the dural venous sinuses – endothelial lined spaces between the outer and inner layers of dura mater. Clinical correlates A cerebrovascular accident (also known as a stroke) is defined clinically as “an abrupt loss of focal brain function lasting more than 24 hours due to either spontaneous haemorrhage into brain substance or inadequate blood supply to part of the brain i.e. ischaemia (thrombosis, embolism)“. Damage to the cerebrum in this matter can give rise to a range of clinical signs. The exact nature of the functional deficit that arises depends on the specific lobe that has been affected: Global lesions – severe cognitive deficits (dementia), patients cannot answer simple questions such as their name, today’s date, where they are etc. 1/1/2025 BRAIN DEFAULT NETWORK 37 CEREBELLUM “LITTLE BRAIN”,  Anatomical Location THE CEREBELLUM The cerebellum is located at the back of the brain, immediately inferior to the occipital and temporal lobes, and within the posterior cranial fossa. The cerebellum, which stands for “little brain”, is a structure of the central nervous system. It is separated from these lobes by the tentorium cerebelli, a tough layer of dura mater. In particular, it is active in the coordination, precision and timing of movements, as well as It lies at the same level of and posterior to the pons, from in motor learning. which it is separated by the fourth ventricle.  The cerebellum consists of two hemispheres which are connected by the vermis, a narrow midline area. Like other structures in the central nervous system, the cerebellum consists of grey matter and white matter: Grey matter – located on the surface of the cerebellum. It is tightly folded, forming the cerebellar cortex. White matter – located underneath the cerebellar cortex. Embedded in the white matter are the four cerebellar nuclei (the dentate, emboliform, globose, and fastigi nuclei).  three ways that the There are cerebellum can be subdivided – anatomical lobes, zones and functional divisions Anatomical Lobes There are three anatomical lobes that can be distinguished in the cerebellum; the anterior lobe, the posterior lobe and the flocculonodular lobe. These lobes are divided by two fissures – the primary fissure and posterolateral fissure. Zones There are three cerebellar zones. In the midline of the cerebellum is the vermis. Either side of the vermis is the intermediate zone. Lateral to the intermediate zone are the lateral hemispheres. There is no difference in gross structure between the lateral hemispheres and intermediate zones Functional Divisions The cerebellum can also be divided by function. There are three functional areas of the cerebellum – the cerebrocerebellum, the spinocerebellum and the vestibulocerebellum. Cerebrocerebellum – the largest division, formed by the lateral hemispheres. It is involved in planning movements and motor learning. It receives inputs from the cerebral cortex and pontine nuclei, and sends outputs to the thalamus and red nucleus. This area also regulates coordination of muscle activation and is important in visually guided movements. Vestibulocerebellum – the functional equivalent to the flocculonodular lobe. It is involved in controlling balance and ocular Spinocerebellum – comprised of the reflexes, mainly fixation on a target. vermis and intermediate zone of the cerebellar hemispheres. It is involved in It receives inputs from the vestibular system, regulating body movements by allowing and sends outputs back to the vestibular for error correction. It also receives nuclei. proprioceptive information. Cerebellar PEDUNCLES Three pairs of peduncles, located above and around the fourth ventricle, attach the cerebellum to the brain stem and contain pathways to and from the brain The inferior cerebellar peduncle contains many fiber systems from the spinal cord (including fibers from the dorsal spinocerebellar tracts and cuneocerebellar tract; The middle cerebellar peduncle also contains inputs from the vestibular nuclei and nerve and efferents to the vestibular nuclei. The middle cerebellar peduncle consists of fibers from the contralateral pontine nuclei. These nuclei receive input from many areas of the cerebral cortex. The superior cerebellar peduncle, composed mostly of efferent fibers, contains axons that send impulses to both the thalamus and spinal cord, with relays in the red nuclei. Afferent fibers from the ventral spinocerebellar tract also enter the cerebellum via this peduncle.  CEREBELLAR CORTEX LAYERS The cerebellar cortex consists of three layers: outer molecular layer; the Purkinje cell layer; and the granular layer. Cells of cerebellar cortex Granule cells, with cell bodies located in the granular layer of the cerebellar cortex, are the only excitatory neurons in the cerebellar cortex. The granule cells send their axons upward, into the molecular layer, where they bifurcate in a T-like manner to become the parallel fibers which form excitatory synapses on these dendrites. Glutamate appears to be the neurotransmitter at these synapses Brush cells (or monodendritic cells) These are small cells present in the granular layer. Each cell gives off a single dendrite the branches of which give a brush-like appearance. The dendrite synapses with mossy fibres. Purkinje cells provide the primary output from the cerebellar cortex. These unique neurons have their cell bodies in the Purkinje cell layer and have dendrites that fan out. The axons of Purkinje cells project ipsilaterally to the deep cerebellar nuclei, especially the dentate nucleus, where they form inhibitory synapses. Basket cells are located in the molecular layer. These cells receive excitatory inputs from the parallel fibers and project back to Purkinje cells, which they inhibit. Golgi cells are also located in the granular layer and within the granule cell layer. They receive excitatory inputs from parallel fibers and mossy fibers. The Golgi cells send their axons back to the granule cells, which they inhibit.  Vasculature The cerebellum receives its blood supply from three paired arteries: superior cerebellar artery(SCA) Anterior inferior cerebellar artery (AICA) Posterior inferior cerebellar artery (PICA) The SCA and AICA are branches of the basilar artery, which wraps around the anterior aspect of the pons before reaching the cerebellum. The PICA is a branch of the vertebral artery. Venous drainage of the cerebellum is by the superior and inferior cerebellar veins. They drain into the superior petrosal, transverse and straight dural venous sinuses. Clinical Relevance: Cerebellar Dysfunction Dysfunction of the cerebellum can produce a wide range of symptoms and signs. The aetiology of cerebellar dysfunction is varied, with a number of possible causes. The most common are stroke, physical trauma, tumours and ageing. The clinical picture is dependent on the functional area of the cerebellum that is affected. Damage to the cerebrocerebellum and spinocerebellum presents with problems in carrying out skilled and planned movements and in motor learning. A wide variety of manifestations are possible: ataxia dysarthria and scanning speech dysmetria Brain stem  THE BRAIN STEM the brainstem is the most inferior portion of the brain, adjoining and structurally continuous with the brain and spinal cord. It is tube-shaped mass of nervous tissue. 3 inches long and as thick as your thumb. It's located under the Cerebrum. Location: The brainstem is located in posterior cranial foss Though small, the brainstem is an extremely important part of the brain, as the nerve connections from the motor and sensory systems of the cortex pass through it to communicate with the peripheral nervous system. SAGITTAL SECTION OF BRAIN Thalamus Superior Mid brain Cerebellum Cerebellar peduncle Pons Medulla  FUNCTIONS OF BRAIN STEM 1. Pathway of tracts between cerebral cortex & spinal cord. 2. Site of origin of nuclei of cranial nerves (from 3rd to 12th). 3. Site of emergence of cranial nerves (from 3rd to 12th). 4. Contains groups of nuclei & related fibers known as reticular formation responsible for:.control of level of consciousness.perception of pain.regulation of cardiovascular &.respiratory systems.  Function of the brain stem The brainstem also plays an important role in the regulation of eating. cardiac, respiratory and sleep cycle. Others; Alertness, Arousal, Blood Pressure Control, Digestion It also plays a role in conduction. All information relayed from the body to the cerebrum and cerebellum and vice versa must traverse the brainstem. Relays Information Between the Peripheral Nerves and Spinal Cord to the Upper Parts of the Brain  The brainstem consists (from above downwards) of the midbrain, the pons and the medulla. The midbrain is continuous, above, with the cerebral hemispheres. The medulla is continuous below, with the spinal cord. Posteriorly, the pons and medulla are separated from the cerebellum by the fourth ventricle The midbrain, pons and medulla are connected to the cerebellum by the superior, middle and inferior cerebellar peduncles, GATE WAY TO SEAT OF KNOWLEDGE IN SUB SAHARAN AFRICA GATE WAY TO CNS NUERAL CONNECTIVITY  GROSS ANATOMY OF MEDULLA OBLONGATA The medulla oblongata is conical in shape. Its broad part joins the pons above and narrow part becomes continuous with the spinal cord. The lower half of the brainstem that contains the cardiac, respiratory, vomiting, and vasomotor centers and regulates autonomic, involuntary functions such as breathing, heart rate, and blood pressure.  MEDULLA – VENTRAL I. SURFACE Ventral median fissure: Continuation of ventral median fissure of spinal cord Divides the medulla into 2 halves Its lower part is masked by decussation of most of pyramidal (corticospinal) fibers (75%-90%). What Is Pyramid? An elevation, lies on either side of ventral median fissure Produced by corticospinal tract.  Olive: An elevation, lies lateral to the pyramid. Produced by inferior olivary nucleus (important in control of movement).  Nerves emerging from Medulla (4 nerves): Hypoglossal (12th): from sulcus between pyramid & olive Glossopharyngeal (9th), vagus (10th) & cranial part of accessory (11th): from sulcus dorsolateral to olive (from above downwards)  MEDULLA – DORSAL SURFACE The features differ in the caudal part (closed medulla) and the cranial part (open medulla) open medulla closed medulla  Cavity: central canal.  Composed of: CLOSED Dorsal median sulcus: divides the closed MEDULLA medulla : on either sinto 2 halves. Fasciculus graciliside of dorsal median sulcus. Gracile tubercle: an elevation produced at the upper part of fasciculus gracilis, marks the site of gracile nucleus. Fasciculus cuneatus: on either side of fasciculus gracilis. Cuneate tubercle: an elevation produced at the upper part of fasciculus cuneatus, marks the site of cuneate nucleus.  Cavity: 4th OPEN ventricle  On either side, an MEDULLA inverted V-shaped sulcus divides the area into 3 parts (from medial to lateral): 1. Hypoglossal triangle: overlies hypoglossal nucleus. 2. Vagal triangle: overlies dorsal vagal nucleus. 3. Vestibular area: overlies vestibular nuclei. Shown after removing cerebellum  The Pons Pons has a convex anterior surface marked by transversely running fibers which laterally forms a bundle called middle cerebellar peduncle. The Pons. Contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.  PONS – VENTRAL SURFACE  Basilar sulcus: Divides the pons into 2 halves, occupied by basilar artery.  Transverse pontine (pontocerebellar) fibers: Originate from pontine nuclei, cross the midline & pass through the contralateral middle cerebellar peduncle to enter the opposite cerebellar hemisphere.  Nerves emerging from Pons (4 nerves): Trigeminal (5th): from the middle of ventrolateral aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root. Abducent (6th): from sulcus between pons & pyramid. Facial (7th) th & vestibulocochlear (8 ): at cerebellopontine angle (junction between medulla, pons & cerebellum). Both nerves emerge as 2 roots: from medialthto lateral: motor rootth of 7 , sensory root th of 7 vestibular partth of 8 & cochlear part of 8 PONS – DORSAL SURFACE  Separated from the medulla by an imaginary line passing between the caudal margins of middle cerebellar peduncle. On either side, a sulcus divides the area into 2 parts (from medial to lateral):  Medial eminence & facial colliculus: overlies abducent nucleus.  Vestibular area: overlies vestibular nuclei. - Lateral to this sulcus is an elongated elevation, the medial eminence, which is bounded laterally by a sulcus limitans. - The upper end of sulcus limitans presents a bluish-gray coloration and the area is called substantia ferruginosa. Shown after removing cerebellum  MIDBRAIN Associated with vision, hearing, motor control, sleep and wake cycles, alertness, and temperature regulation. Anteriorly, it presents two large bundles of fibers, one on each side of the midline, called crus cerebri. The oculomotor nerve Posteriorly, the midbrain presents four rounded swellings called colliculi. - Superior and inferior colliculi one on each side - Each colliculus is laterally related to a ridge called brachium Parts of the midbrain The midbrain comprises two lateral halves, called the cerebral peduncles; which is again divided into an anterior part, the crus cerebri, and a posterior part, tegmentum, by a pigmented band of gray matter, substantia nigra. The narrow cavity is the cerebral aqueduct, which connects the 3rd and 4th ventricles. The tectum is the part of the midbrain posterior to the cerebral aqueduct;  MID BRAIN – VENTRAL SURFACE  large column of descending fibers (crus cerebri or basis pedunculi), on either side, separated by a depression called the interpeduncular fossa.  Nerve emerging from Midbrain (one): Occulomotor (3rd): from medial aspect of crus cerebri.  MID BRAIN – DORSAL SURFACE  Marked by 4 elevations: 1. Two superior colliculi: concerned with visual reflexes. 2. Two inferior colliculi: forms part of auditory pathway.  Nerve emerging from Midbrain (one): Trochlear (4th): just caudal to inferior colliculus (The only cranial nerve emerging from dorsal surface of brain stem). BRAINSTEM AND CRANIAL NERVES The brainstem gives rise to cranial nerves and provides the main motor and sensory innervation to the face and neck via the cranial nerves. Cranial nerves are those nerves that either arise from brain or brain stem (in pairs). They enervates different organs in head and neck region (with the exception of vagus nerve). Names of cranial nerves Ⅰ Olfactory nerve Ⅱ Optic nerve Ⅲ Oculomotor The cranial nerves nerve are 12 pairs of Ⅳ Trochlear nerve nerves that can be Ⅴ Trigeminal nerve seen on the ventral Ⅵ Abducent nerve (bottom) surface of Ⅶ Facial nerve the brain. Ⅷ Vestibulocochlear Some of these nerve nerves bring Ⅸ Glossopharyngeal information from nerve the sense organs to Ⅹ Vagus nerve the brain; Ⅺ Accessory nerve Ⅻ Hypoglossal other cranial nerve nerves control muscles; other cranial  These 12 cranial nerves carry different fiberes. Most of them are sensory fibers but some are motor and other are mixed as well. Classification of cranial nerves Sensory cranial nerves: contain only afferent (sensory) fibers ⅠOlfactory nerve ⅡOptic nerve Ⅷ Vestibulocochlear nerve Motor cranial nerves: contain only efferent (motor) fibers Ⅲ Oculomotor nerve Ⅳ Trochlear nerve ⅥAbducent nerve Ⅺ Accessory nerv Ⅻ Hypoglossal nerve Mixed nerves: contain both sensory and motor fibers--- ⅤTrigeminal nerve, Ⅶ Facial nerve, ⅨGlossopharyngeal nerve ⅩVagus nerve CONNECTION /TRACT IN THE BRAIN STEM. corticospinal tract (motor) the posterior column medial lemniscus pathway (fine touch, vibration sensation, and proprioception).. spinothalamic tract (pain, temperature, itch, and crude touch). The ascending pathways from the body to the brain are the sensory pathways, including the spinothalamic tract for pain and temperature sensation and the dorsal column, fasciculus gracilis, and cuneatus for touch, proprioception, and pressure sensation. Nerve tracts traveling through the brainstem relay signals from the cerebellum to areas of the cerebral cortex that are involved in motor control. This allows for the coordination of fine motor movements needed for activities Applied neuroanatomy Diseases of the brainstem can result in abnormalities in cranial nerve function, leading to visual and hearing disturbances, changes in sensation, muscle weakness, vertigo, coordination problems, swallowing and speech difficulty, and voice changes. What is Basal ganglia  Basal ganglia: A group of nuclei, act as a unified functional unit.  Basal ganglia: A subcortical nuclei of grey matter located in the interior part of cerebrum / base of the forebrain connected with cerebral cortex, thalamus, and other brain areas.  Play a role in action selection, decision of possible behaviors to execute at a given time  BASAL GANGLIA: NUCLEI Five nuclei :  Caudate Nucleus  Putamen  Globus Pallidus – external & internal segments.  Subthalamic Nucleus  Substantia Nigra- pars compacta,reticulata 81 regulate movements at various stages (e.g. preparation and execution) and influence various types of learning. prepares and aids in movement of the limbs  The globus pallidus involved in the regulation of voluntary movement. regulate movements that occur on the subconscious level. The neurons of this nucleus use an excitatory neurotransmitter, glutamate. The neurons of the subthalamic nucleus are in normal motor function,  Basal ganglia “circuitry” Cortex Striatum Thalamus GPi + SNr Nolte. Essentials of the human brain. Mosby, 2010 Fitzgerald MJT, Gruener G, Mtui E. Clinical Neuroanatomy and related Neuroscience, 6th Ed., W. B. Saunders 2012  Basal ganglia Input 1. Parietal cortex (primary and secondary somatosensory information, secondary visual information), 2. Temporal cortex (secondary visual and auditory information), 3. Cingulate cortex (limbic and emotional status information), 4. Frontal cortex (primary and secondary motor information), 5. Prefrontal cortex.  Neurotransmitters of basal ganglia Dopamine pathway: From substantia nigra to caudate nucleus and putamen. Gama amino butyric acid pathway: From caudate nucleus and putamen to globus pallidus and substantia nigra. Acetylcholine pathway: From cortex to the caudate nucleus to putamen. Glutamate: Provide the excitatory signals that balance out the large no. of the inhibitory signals transmitted specially by the dopamin, GABA & serotonin inhibitory transmitters. Dopamine: excites areas of caudate/putamen with D1 receptors to promote the direct pathway, inhibits areas of caudate/putamen with D2 receptors to inhibit the indirect pathway 91 Dopamine: Neuromodulatory neurotransmitter, excites areas of the caudate/putamen with D1 receptors to promote the direct pathway, inhibits areas of the caudate/putamen with D2 receptors to inhibit the indirect pathway Glutamate: Excitatory neurotransmitter Subthalamic nucleus projects glutamate to stimulate the ventrolateral thalamus. Ventrolateral thalamus projects glutamate to stimulate the primary localized motor cortex GABA: Inhibitory neurotransmitter: Caudate/Striatum (direct) projects GABA to inhibit the Gpi GPi projects GABA to inhibit the ventrolateral nucleus Caudate/Striatum (indirect) projects GABA to inhibit the GPe GPe projects GABA to inhibit the subthalamic nucleus Pathogenesis of PD Excitation imbalance Inhibition loss of dopamine inhibition of putamen increases in inhibitory output to GBes decreases inhibitory output of STN increases excitatory output GBis increases inhibitory output to thalamus reduces excitatory drive to cerebral cortex 103 TRACTS  Movement and tracts Movement (motion) is a fundamental and essential property of animal life. The motor system in humans controls a complex neuromuscular network. Reflexes are controlled at the spinal or higher levels Stereo typic repetitious movements , such as walking or swimming, are governed by neural networks i.e Central pattern generators, or local circuits of neurons that are found in spinal cord, brain stem, and cerebellum. Specific, goal-directed movements are initiated at the level of the cerebral cortex.  TRACTS a collection of nerve fibres within the central nervous system, that connects two masses of grey matter, is called a tract. A tract may be defined as a collection of nerve fibres having the same origin, course, and termination. Fiber bundles with a common function are called tracts. Tracts may be ascending or descending.  Types of tracts Naming the tracts If the tract name begins with “spino” (as in spinocerebellar), the tract is a sensory tract delivering information from the spinal cord to the cerebellum (in this case). Eg spino-olivary, spinothalamic etc If the tract name ends with “spinal” (as in vestibulospinal), the tract is a motor tract that delivers information from the vestibular apparatus (in this case) to the spinal cord.eg Olivospinal ,tectospinal etc  Descending tracts/Descending Fiber System The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurons. The lower motor neurons then directly innervate muscles to produce movement.  The motor tracts can be functionally divided into two major groups: Pyramidal tracts – These tracts originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face. Extrapyramidal tracts – These tracts originate in the brain stem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion  Tract_neuronal Order 1st order neuron First order neurons conduct impulses from receptors of the skin and from proprioceptors (receptors located in a join, muscle or tendon) to the spinal cord or brain stem, where they synapse with second order neurons. First order neuron’s cell bodes reside in ganglion (dorsal root or cranial) starts at the cerebral cortex in the somatomotor area.  2nd order neuron 2nd neuron to carry an order could be a sensory stimulus or a motor stimulus. Axon of the 1st order neuron will synapse with the 2nd order neuron at the level of the brain stem, which commonly decussate (crosses over) to the opposite side. The 3rd order The 3rd order neuron is located in the ventral horn of the spinal cord, which will exit with the spinal nerve to supply the muscle.  Motor commands delivery Somatic nervous system (SNS): directs contraction of skeletal muscles Autonomic nervous system (ANS): directs the activity of glands, smooth muscles, and cardiac muscle  Pyramidal Tracts The pyramidal tracts derive their name from the medullary pyramids of the medulla oblongata, which they pass through. These pathways are responsible for the voluntary control of the musculature of the body and face. Functionally, these tracts can be subdivided into two: Corticospinal tracts – supplies the musculature of the body. Corticobulbar tracts – supplies the musculature of the head and neck.  Extrapyramidal Tracts The extrapyramidal tracts originate in the brainstem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion.  Vestibulospinal Tracts There are two vestibulospinal pathways; medial and lateral. They arise from the vestibular nuclei, which receive input from the organs of balance. The tracts convey this balance information to the spinal cord, where it remains ipsilateral. Fibres in this pathway control balance and posture by innervating the ‘antigravity’ muscles (flexors of the arm, and extensors of the leg), via lower motor neurons.  Reticulospinal Tracts The two recticulospinal tracts have differing functions: The medial reticulospinal tract arises from the pons. It facilitates voluntary movements, and increases muscle tone. The lateral reticulospinal tract arises from the medulla. It inhibits voluntary movements, and reduces muscle tone.  Rubrospinal Tracts The rubrospinal tract originates from the red nucleus, a midbrain structure. As the fibres emerge, they decussate (cross over to the other side of the CNS), and descend into the spinal cord. Thus, they have a contralateral innervation. Its exact function is unclear, but it is thought to play a role in the fine control of hand movements  Tectospinal Tracts This pathway begins at the superior colliculus of the midbrain. The superior colliculus is a structure that receives input from the optic nerves. The neurons then quickly decussate, and enter the spinal cord. They terminate at the cervical levels of the spinal cord. The tectospinal tract coordinates movements of the head in relation to vision stimuli.  The ascending tracts The ascending tracts refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex. ascending tracts are also known as somatosensory pathways or systems. Functionally, the ascending tracts can be divided into the type of information they transmit – conscious or unconscious: Conscious tracts – comprised of the dorsal column-medial lemniscal pathway and the anterolateral system. Unconscious tracts – comprised of the spinocerebellar tracts  Conscious tracts The Dorsal Column-Medial Lemniscal Pathway The dorsal column-medial lemniscal pathway (DCML) carries the sensory modalities of fine touch (tactile sensation), vibration and proprioception. There are three groups of neurons involved in this pathway – first, second and third order neurons. The first order neurons carry sensory information regarding touch, proprioception or vibration from the peripheral nerves to the medulla oblongata. There are two different pathways which the first order neurons take  Signals from the upper limb (T6 and above) – travel in the fasciculus cuneatus (the lateral part of the dorsal column). They then synapse in the nucleus cuneatus of the medulla oblongata. Signals from the lower limb (below T6) – travel in the fasciculus gracilis (the medial part of the dorsal column). They then synapse in the nucleus gracilis of the medulla oblongata. Second Order Neurons ` The second order neurons begin in the cuneate nucleus or gracilis. The fibres receive the information from the preceding neurons, and delivers it to the third order neurons in the thalamus. Within the medulla oblongata, these fibres decussate (cros s to the other side of the CNS). They then travel in the contralateral medial lemniscus to reach the thalamus.  Third Order Neurons The third order neurons transmit the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain. They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex.  The Anterolateral System The anterolateral system consists of two separate tracts: Anterior spinothalamic tract – carries the sensory modalities of crude touch and pressure. Lateral spinothalamic tract – carries the sensory modalities of pain and temperature.  The Spinocerebellar Tracts – Unconscious Sensation They transmit information from the muscles to the cerebellum. Within the spinocerebellar tracts, there are four individual pathways:  Posterior spinocerebellar tract – Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum. Cuneocerebellar tract – Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum. Anterior spinocerebellar tract – Carries proprioceptive information from the lower limbs. The fibres decussate twice – and so terminate in the ipsilateral cerebellum. Rostral spinocerebellar tract – Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.  THE BRAIN STEM the brainstem is the most inferior portion of the brain, adjoining and structurally continuous with the brain and spinal cord. It is tube-shaped mass of nervous tissue. 3 inches long and as thick as your thumb. It's located under the Cerebrum Location: The brainstem is located in posterior cranial fossa Though small, the brainstem is an extremely important part of the brain, as the nerve connections from the motor and sensory systems of the cortex pass through it to communicate with the peripheral nervous system. BRAINSTEM AND CRANIAL NERVES The brainstem gives rise to cranial nerves and provides the main motor and sensory innervation to the face and neck via the cranial nerves. Cranial nerves are those nerves that either arise from brain or brain stem (in pairs). They enervates different organs in head and neck region (with the exception of vagus nerve). Names of cranial nerves Ⅰ Olfactory nerve Ⅱ Optic nerve The cranial nerves are 12 pairs of Ⅲ Oculomotor nerve nerves that can be seen on the Ⅳ Trochlear nerve ventral (bottom) surface of the brain. Ⅴ Trigeminal nerve Ⅵ Abducent nerve Some of these nerves bring information from the sense organs Ⅶ Facial nerve to the brain; Ⅷ Vestibulocochlear nerve Ⅸ Glossopharyngeal nerve other cranial nerves control muscles; Ⅹ Vagus nerve Ⅺ Accessory nerve other cranial nerves are connected to glands or internal organs such as Ⅻ Hypoglossal nerve the heart and lungs  These 12 cranial nerves carry different fiberes. Most of them are sensory fibers but some are motor and other are mixed as well. Classification of cranial nerves Sensory cranial nerves: contain only afferent (sensory) fibers ⅠOlfactory nerve ⅡOptic nerve Ⅷ Vestibulocochlear nerve Motor cranial nerves: contain only efferent (motor) fibers Ⅲ Oculomotor nerve Ⅳ Trochlear nerve ⅥAbducent nerve Ⅺ Accessory nerv Ⅻ Hypoglossal nerve Mixed nerves: contain both sensory and motor fibers--- ⅤTrigeminal nerve, Ⅶ Facial nerve, ⅨGlossopharyngeal nerve ⅩVagus nerve Function of the brain stem The brainstem also plays an important role in the regulation of eating. cardiac, respiratory and sleep cycle. Others; Alertness, Arousal, Blood Pressure Control, Digestion It also plays a role in conduction. All information relayed from the body to the cerebrum and cerebellum and vice versa must traverse the brainstem. Relays Information Between the Peripheral Nerves and Spinal Cord to the Upper Parts of the Brain In addition to linking the cerebrum and spinal cord, the brainstem also connects the cerebrum with the cerebellum. The cerebellum is important for regulating functions such as movement coordination, balance, equilibrium, and muscle tone.  The brainstem consists (from above downwards) of the midbrain, the pons and the medulla. The midbrain is continuous, above, with the cerebral hemispheres. The medulla is continuous below, with the spinal cord. Posteriorly, the pons and medulla are separated from the cerebellum by the fourth ventricle The midbrain, pons and medulla are connected to the cerebellum by the superior, middle and inferior cerebellar peduncles, MIDBRAIN Associated with vision, hearing, motor control, sleep and wake cycles, alertness, and temperature regulation. Anteriorly, it presents two large bundles of fibers, one on each side of the midline, called crus cerebri. - The oculomotor nerve Posteriorly, the midbrain presents four rounded swellings called colliculi. - Superior and inferior colliculi one on each side - Each colliculus is laterally related to a ridge called brachium Parts of the midbrain The midbrain comprises two lateral halves, called the cerebral peduncles; which is again divided into an anterior part, the crus cerebri, and a posterior part, tegmentum, by a pigmented band of gray matter, substantia nigra. The narrow cavity is the cerebral aqueduct, which connects the 3rd and 4th ventricles. The tectum is the part of the midbrain posterior to the cerebral aqueduct;  The pons The pons Contains nuclei that relay signals from Pons has a convex anterior surface marked by transversely running fibers the forebrain to the cerebellum, along which laterally forms a bundle called middle cerebellar peduncle. with nuclei that deal primarily with sleep, respiration, swallowing, bladder Parts of the Pons control, hearing, equilibrium, taste, eye a posterior part, the tegmentum, and movement, facial expressions, facial an anterior basilar part sensation, and posture. Main Features - The trigeminal nerve emerges from the anterior surface at its junction. - Presents a basilar sulcus in the midline which lodges basilar artery Posterior surface of the pons is limited laterally by superior cerebellar peduncle. - Lateral to this sulcus is an elongated elevation, the medial eminence, which is bounded laterally by a sulcus limitans. - The upper end of sulcus limitans presents a bluish-gray coloration and the area is called substantia ferruginosa. GROSS ANATOMY OF MEDULLA OBLONGATA Features on the anterior surface of Medulla Oblongata The medulla oblongata is conical in shape. Its broad part joins Anterior median fissure, is an upward continuation of similar the pons above and narrow part becomes continuous with the fissure present on the spinal cord spinal cord. Anterolateral sulcus is an area of hypoglossal nerve The lower half of the brainstem that contains the cardiac, Pyramid is an elevation on each side of the midline between respiratory, vomiting, and vasomotor centers and regulates anterior median fissure and anterolateral sulcus. autonomic, involuntary functions such as breathing, heart rate, - There is a crossing fibers constitute the decussation of the and blood pressure. pyramid. Olive is a prominent, elongated oval swelling that lies in the It is divided into upper part of medulla 1. A lower closed part with central canal and 2. An upper open part posteriorly The elevation is produced by the underlying inferior olivary nucleus. Posterior median sulcus Posterolateral sulcus Gives attachment to the rootlets of 9th, 10th and 11th cranial nerves. Connection /tract in the brain stem the corticospinal tract (motor) the posterior column medial lemniscus pathway (fine touch, vibration sensation, and proprioception). the spinothalamic tract (pain, temperature, itch, and crude touch). The ascending pathways from the body to the brain are the sensory pathways, including the spinothalamic tract for pain and temperature sensation and the dorsal column, fasciculus gracilis, and cuneatus for touch, proprioception, and pressure sensation. Nerve tracts traveling through the brainstem relay signals from the cerebellum to areas of the cerebral cortex that are involved in motor control. This allows for the coordination of fine motor movements needed for activities such as walking or playing video games. Applied neuroanatomy Diseases of the brainstem can result in abnormalities in cranial nerve function, leading to visual and hearing disturbances, changes in sensation, muscle weakness, vertigo, coordination problems, swallowing and speech difficulty, and voice changes. SPINAL CORD  Spinal cord The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain The spinal cord is a cylindrical structure, greyish white in color The spinal cord begins at the occipital bone and extends down to the space between the first and second lumbar vertebrae;  It has a relatively simple anatomical course: The spinal cord arises cranially as a continuation of the medulla oblongata (part of the brainstem). It then travels inferiorly within the vertebral canal, surrounded by the spinal meninges containing cerebrospinal fluid. At the L2 vertebral level the spinal cord tapers off, forming the conus medullaris.  During the course of the spinal cord, there are two points of enlargement. The cervical enlargement is located proximally, at the C4-T1 level. It represents the origin of the brachial plexus. Between T11 and S1 is the lumbar enlargement, representing the origin of the lumbar and sacral plexi. Function of the spinal cord The spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body but also contains neural circuits that can independently control numerous reflexes and central pattern generators. The spinal cord has three major functions: 1- as a conduit for motor information, which travels down the spinal cord, 2- as a conduit for sensory information in the reverse direction, 3- And finally as a center for coordinating certain reflexes  Inferior End of Spinal Cord Conus medullaris - inferior end of spinal cord proper Cauda equina - individual spinal nerves within spinal canal Filum terminale - filamentous end of meninges, "tie-down"  Internal structure shaped like the letter “H” or a “butterfly”. The two “wings” of the butterfly are connected across the midline by the dorsal gray commissure and below the white commissure A transverse section of spinal cord shows white matter in the periphery, gray matter inside, and a tiny central canal filled with cerebrospinal fluid (CSF) at its center. Surrounding the canal is a single layer of cells, the ependymal layer. Surrounding the ependymal layer is the gray matter – a region containing cell bodies  Spinal nerves segment 31 pairs of spinal nerves supply all of the body except head Each nerve is named according to its nearby vertebra  8 cervical (C1-C8)  12 thoracic (T1-T12)  5 Lumbar (L1-L5)  5 Sacral (S1-S5)  1 Coccygeal (C0)  SPINAL NERVE ROOT Ventral Roots The ventral (or anterior) roots constitute motor outflow tracts from the spinal cord. The ventral roots carry the large-diameter alpha motor neuron axons to the extrafusal striated muscle fibers; the smaller gamma motor neuron axons, which supply the intrafusal muscle of the muscle spindles Dorsal Roots The dorsal (posterior) roots are largely sensory. Each dorsal nerve root (except usually C l ) contains afferent fibers from the nerve cells in its ganglion. The dorsal roots contain fibers from cutaneous and deep structures Formation of the Spinal Nerves The spinal nerves are mixed nerves that originate from the spinal cord, forming the peripheral nervous system. Each spinal nerve begins as an anterior (motor) and a posterior (sensory) nerve root. These roots arise from the spinal cord, and unite at the intervertebral foramina, forming a single spinal nerve. RAMI COMMUNICANTES The rami join the spinal nerves to the sympathetic trunk. Only the thoracic and upper lumbar nerves contain a white ramus communicans, but the gray ramus is present in all spinal nerves  The spinal nerve then leaves the vertebral canal via the intervertebral foramina, and then divides into two: Posterior rami – supplies nerve fibres to the synovial joints of the vertebral column, deep muscles of the back, and the overlying skin. Anterior rami – supplies nerve fibres to much of the remaining area of the body, both motor and sensory. The nerve roots L2-S5 arise from the distal end of the spinal cord, forming a bundle of nerves known as the cauda equina. Spinal Nuclei The prominent nuclear groups of cell columns within the spinal cord from dorsal to ventral are marginal zone, substantia gelatinosa, nucleus proprius, dorsal nucleus of Clarke, intermediolateral nucleus and the lower motor neuron nuclei. TRACTS OF THE SPINAL CORD Ascending tracts descending tracts DESCENDING TRACTS ASCENDING TRACTS Clinical correlate Lower-Motor- Neuron Lesions TRACTS  Movement and tracts Movement (motion) is a fundamental and essential property of animal life. The motor system in humans controls a complex neuromuscular network. Reflexes are controlled at the spinal or higher levels Stereo typic repetitious movements , such as walking or swimming, are governed by neural networks i.e Central pattern generators, or local circuits of neurons that are found in spinal cord, brain stem, and cerebellum. Specific, goal-directed movements are initiated at the level of the cerebral cortex.  TRACTS a collection of nerve fibres within the central nervous system, that connects two masses of grey matter, is called a tract. A tract may be defined as a collection of nerve fibres having the same origin, course, and termination. Fiber bundles with a common function are called tracts. Tracts may be ascending or descending. They are usually named after the masses of grey matter connected by them.  Types of tracts Naming the tracts If the tract name begins with “spino” (as in spinocerebellar), the tract is a sensory tract delivering information from the spinal cord to the cerebellum (in this case). Eg spino-olivary, spinothalamic etc If the tract name ends with “spinal” (as in vestibulospinal), the tract is a motor tract that delivers information from the vestibular apparatus (in this case) to the spinal cord.eg Olivospinal ,tectospinal etc  Descending tracts/Descending Fiber System The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurons. The lower motor neurons then directly innervate muscles to produce movement.  The motor tracts can be functionally divided into two major groups: Pyramidal tracts – These tracts originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face. Extrapyramidal tracts – These tracts originate in the brain stem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion  Tract_neuronal Order 1st order neuron First order neurons conduct impulses from receptors of the skin and from proprioceptors (receptors located in a join, muscle or tendon) to the spinal cord or brain stem, where they synapse with second order neurons. First order neuron’s cell bodes reside in ganglion (dorsal root or cranial) starts at the cerebral cortex in the somatomotor area.  2nd order neuron 2nd neuron to carry an order could be a sensory stimulus or a motor stimulus. Axon of the 1st order neuron will synapse with the 2nd order neuron at the level of the brain stem, which commonly decussate (crosses over) to the opposite side. The 3rd order The 3rd order neuron is located in the ventral horn of the spinal cord, which will exit with the spinal nerve to supply the muscle. Motor commands delivery Somatic nervous system (SNS): directs contraction of skeletal muscles Autonomic nervous system (ANS): directs the activity of glands, smooth muscles, and cardiac muscle  Pyramidal Tracts The pyramidal tracts derive their name from the medullary pyramids of the medulla oblongata, which they pass through. These pathways are responsible for the voluntary control of the musculature of the body and face. Functionally, these tracts can be subdivided into two: Corticospinal tracts – supplies the musculature of the body. Corticobulbar tracts – supplies the musculature of the head and neck.  Extrapyramidal Tracts The extrapyramidal tracts originate in the brainstem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion.  Vestibulospinal Tracts There are two vestibulospinal pathways; medial and lateral. They arise from the vestibular nuclei, which receive input from the organs of balance. The tracts convey this balance information to the spinal cord, where it remains ipsilateral. Fibres in this pathway control balance and posture by innervating the ‘antigravity’ muscles (flexors of the arm, and extensors of the leg), via lower motor neurons.  Reticulospinal Tracts The two recticulospinal tracts have differing functions: The medial reticulospinal tract arises from the pons. It facilitates voluntary movements, and increases muscle tone. The lateral reticulospinal tract arises from the medulla. It inhibits voluntary movements, and reduces muscle tone.  Rubrospinal Tracts The rubrospinal tract originates from the red nucleus, a midbrain structure. As the fibres emerge, they decussate (cross over to the other side of the CNS), and descend into the spinal cord. Thus, they have a contralateral innervation. Its exact function is unclear, but it is thought to play a role in the fine control of hand movements  Tectospinal Tracts This pathway begins at the superior colliculus of the midbrain. The superior colliculus is a structure that receives input from the optic nerves. The neurons then quickly decussate, and enter the spinal cord. They terminate at the cervical levels of the spinal cord. The tectospinal tract coordinates movements of the head in relation to vision stimuli.  The ascending tracts The ascending tracts refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex. ascending tracts are also known as somatosensory pathways or systems. Functionally, the ascending tracts can be divided into the type of information they transmit – conscious or unconscious: Conscious tracts – comprised of the dorsal column- medial lemniscal pathway and the anterolateral system. Unconscious tracts – comprised of the spinocerebellar tracts  Conscious tracts The Dorsal Column-Medial Lemniscal Pathway The dorsal column-medial lemniscal pathway (DCML) carries the sensory modalities of fine touch (tactile sensation), vibration and proprioception. There are three groups of neurons involved in this pathway – first, second and third order neurons. The first order neurons carry sensory information regarding touch, proprioception or vibration from the peripheral nerves to the medulla oblongata. There are two different pathways which the first order neurons take  Signals from the upper limb (T6 and above) – travel in the fasciculus cuneatus (the lateral part of the dorsal column). They then synapse in the nucleus cuneatus of the medulla oblongata. Signals from the lower limb (below T6) – travel in the fasciculus gracilis (the medial part of the dorsal column). They then synapse in the nucleus gracilis of the medulla oblongata. Second Order Neurons ` The second order neurons begin in the cuneate nucleus or gracilis. The fibres receive the information from the preceding neurons, and delivers it to the third order neurons in the thalamus. Within the medulla oblongata, these fibres decussate (cross to the other side of the CNS). They then travel in the contralateral medial lemniscus to reach the thalamus.  Third Order Neurons The third order neurons transmit the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain. They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex.  The Anterolateral System The anterolateral system consists of two separate tracts: Anterior spinothalamic tract – carries the sensory modalities of crude touch and pressure. Lateral spinothalamic tract – carries the sensory modalities of pain and temperature.  The Spinocerebellar Tracts – Unconscious Sensation They transmit information from the muscles to the cerebellum. Within the spinocerebellar tracts, there are four individual pathways:  Posterior spinocerebellar tract – Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum. Cuneocerebellar tract – Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum. Anterior spinocerebellar tract – Carries proprioceptive information from the lower limbs. The fibres decussate twice – and so terminate in the ipsilateral cerebellum. Rostral spinocerebellar tract – Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum. THE LIMBIC SYSTEM  Limbic system – also known as the circle of Papez (or Papez’s Circuit) is considered to be the epicenter of emotional and behavioral expression. The limbic system is a complex set of structures that lies on both sides of the thalamus, just under the cerebrum. This system is composed of several parts, which are found above the brainstem and within the cerebrum. The limbic system connects parts of the brain that deal with high and low functions.  Function of the Limbic System The limbic system is the portion of the brain that deals with three key functions: emotions, memories and arousal (or stimulation). Some of the functions attributed to the so called limbic system are as follows. (a) Integration of olfactory, visceral, and somatic impulses reaching the brain. (b) Control of activities necessary for survival of the animal including the procuring of food and eating behaviour. (c) Control of activities necessary for survival of the species including sex behaviour. (d) Emotional behaviour. (e) Retention of recent memory. Parts of the Limbic System The limbic system includes the hippocampal formation, amygdala, septal nuclei, cingulate cortex, entorhinal cortex, perirhinal cortex, and parahippocampal cortex. (Some experts would also include parts of the hypothalamus, thalamus, midbrain reticular formation, and olfactory areas in the limbic system.)  Memory The three types of memory are immediate recall, short- term memory, and long-term memory. The hippocampus is involved in converting short-term memory (up to 60 minutes) to long-term memory (several days or more). The Hippocampus The term hippocampal formation typically refers to the dentate gyrus, the hippocampus proper (i.e., cornu ammonis), and the subicular cortex. The hippocampus is another section of the temporal lobe that is responsible for converting short-term memories into long-termed memories. The hippocampus is thought to work with the amygdala for memory storage, and damage to the hippocampus may lead to amnesia (or memory loss). Hippocampus A hippocampal formation is located in the temporal lobe of each cerebral cortex, medial to the inferior horn of the lateral ventricle. Hippocampus means seahorse in Greek. Each hippocampus looks like a seahorse due to the way it is folded during development.  Functions of Hippocampus The hippocampus is the part of the brain that is involved in memory formation, organization and storage. Hippocampus is a limbic system structure that is particularly important in forming new memories and connecting emotions and senses, such as smell and sound, to memories. The hippocampus acts as a memory indexer by sending memories out to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary.  The Cells and layers of hippocampus The hippocampus is composed of multiple subfields. Though terminology varies among authors, the terms most frequently used are dentate gyrus the cornu ammonis literally "Amun's horns", abbreviated CA. The dentate gyrus contains the fascia dentata and the hilus, CA is differentiated into fields CA1, CA2, and CA3 The “horse shoe” appearance of the hippocampus is caused by cell density differentials and the existence of varying degrees of neuronal fibers. The CA regions are also structured depth-wise in clearly defined strata Amygdala General Considerations The amygdala (amygdaloid nuclear complex) is a gray matter mass that lies in the medial temporal pole between the uncus and the parahippocampal gyrus  Fiber connections Its fiber connections include the semicircular stria terminalis to the septal area and anterior hypothalamus direct amygdalofugal pathway to the middle portion of the hypothalamus  Neuron of the amygdala Two distinct groups of neurons,the large basolateral nuclear group and the smaller corticomedial nuclear group The basolateral nuclear group receives higher order sensory information from association areas in the frontal, temporal, and insular cortex. The basolateral amygdala is also connected, via the stria terminalis and the amygdalofugal pathway, to the ventral striatum and the thalamus.  The corticomedial nuclear group of the amygdala, located close to the olfactory cortex, is interconnected with it as well as the olfactory bulb. Connections also run, via the stria terminalis and amygdalofugal pathway, to and from the brain stem and hypothalamus.  Amygdala inputs And Other Structures The amygdala receives inputs from all senses as well as visceral inputs. Visceral inputs come from the hypothalamus, septal area, orbital cortex, and parabrachial nucleus. Olfactory sensory information comes from the olfactory bulb. Auditory, visual and somatosensory information comes from the temporal and anterior cingulate cortices. Major Output Pathways of the Amygdala 1.Ventral amygdalofugal pathway 2.Stria terminalis 3.Directly to the hippocampus 4.Directly to the entorhinal cortex 5.Directly to the dorsomedial nucleus of the thalamus  Ventral Amygdalofugal Pathway The term "fugal" comes from the word fuge—to drive away—as in fugitive. This pathway continues to the anterior olfactory nucleus, anterior perforated substance, piriform cortex, orbitofrontal cortex, anterior cingulate cortex, and ventral striatum i.e part of the caudate, putamen, and the nucleus accumbens septi (nucleus that reclines on the septum). Projections from the ventral striatum are links in a basal ganglia circuit that are important in stimulus-response associative learning.  The ventral amygdalofugal pathway is important because it is a link whereby motivation and drives, through the limbic system, can influence responses. It is also a link whereby responses are learned. In this case this is the link whereby associative learning takes place. That is where responses are associated with appetitive and aversive consequences that is rewards and punishers.  The stria terminalis The stria terminalis connects only to subcortical structures. (Connection to cortical structures is through the ventral amygdalofugal pathway.) The stria terminalis overlaps with the ventral amygdalofugal pathway in that it also connects to the septal nuclei and hypothalamus and thus forms a loop. The stria terminalis also projects to the habenula, which is part of the epithalamus.  Function of the Amygdala Amygdala is the integrative center for emotions, emotional behavior, and motivation. Stimulation of the amygdala causes intense emotion, such as aggression or fear.  Fear Conditioning: An Example of the Role of the Amygdala in Learning  Cholinergic projections from the nucleus basalis to the cortex are thought to arouse the cortex. The reactions involve freezing, elevated blood pressure and heart rate, and it gets twitchy—startles easily.  The auditory system The auditory system is built to allow us to hear. It is remarkable for its sensitivity. It is especially important in humans because it provides the sensory input necessary for speech recognition.  Auditory pathways Auditory messages are conveyed to the brain via two types of pathway: the primary auditory pathway which exclusively carries messages from the cochlea, the non-primary pathway (also called the reticular sensory pathway) which carries all types of sensory messages.  From the cochlear nuclei, small fibers connect with the reticular formation where the auditory message joins all other sensory messages. The next relay is in the non-specific thalamus nuclei before the pathway ends in the polysensory (associative) cortex. The main function of these pathways, also connected to wake and motivation centers as well as to vegetative and hormonal systems, is to select the type of sensory message to be treated first. For instance, when reading a book while listening to a record, this system allows the person to pay attention alternately to the most important task. Visual pathways  Mammals are visual animals: The visual system conveys more information to the brain than any other afferent system. This information is processed within the brain so as to form a set of maps of the visual world. A relatively large proportion of brain tissue is devoted to vision. The visual system includes the eye and retina, the optic nerves, and the visual pathways within the brain, where multiple visual centers process information about different aspects (shape and form, color, motion) of visual stimuli.  The optic nerve transmits the special sensory information for sight. It is one of two nerves that do not join with the brainstem (the other being the olfactory nerve, CN I).  The anatomical course of the optic nerve describes the transmission of special sensory information from the retina of the eye to the primary visual cortex of the brain. It can be divided into extracranial (outside the cranial cavity), and intracranial parts. Extracranial The optic nerve is formed by the convergence of axons from the retinal ganglion cells. These cells in turn receive impulses from the photoreceptors of the eye (the rods and cones). After its formation, the nerve leaves the bony orbit via the optic canal, a passageway through the sphenoid bone. It enters the cranial cavity, running along the surface of the middle cranial fossa (in close proximity to the pituitary gland).  Intracranial (The Visual Pathway) Within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm. At the chiasm, fibres from the nasal (medial) half of each retina cross over, forming the optic tracts: Left optic tract – contains fibres from the left temporal (lateral) retina, and the right nasal (medial) retina. Right optic tract – contains fibres from the right temporal retina, and the left nasal retina. Each optic tract travels to its corresponding cerebral hemisphere to reach the Lateral Geniculate Nucleus (LGN), a relay system located in the thalamus; the fibres synapse here.  Upper optic radiation – carries fibres from the superior retinal quadrants (corresponding to the inferior visual field quadrants). It travels through the parietal lobe to reach the visual cortex. Lower optic radiation – carries fibres from the inferior retinal quadrants (corresponding to the superior visual field quadrants). It travels through the temporal lobe, via a pathway known as Meyers’ loop, to reach the visual cortex. Once at the visual cortex, the brain processes the sensory data and responds appropriately. THE MENINGES BASHIR MUHAMMAD Department of Anatomy Sa’adu Zungur University Bauchi State CRANIAL MENINGES Wednesday, January 1, 2025 226 CRANIAL MENINGES Definition: These are connective tissue membranes covering the brain. Function: they provide the following I. Protection the soft and gelatinous brain. II. Supporting framework for Arteries, Veins and Venous sinuses. III. Enclosed fluid-filled cavity for CSF. Spinal meninges Provide physical stability and shock absorption Three layers Dura mater Arachnoid Pia mater Wednesday, January 1, 2025 228  The Meninges of Brain Cerebral dural mater D (Also called pachymeninx (G. pachy, thick + G. menix, membrane) Cerebral arachnoid mater A (AKA leptomeninx (G. slender membrane). Cerebral pia mater P There exist a potential and real space deep to the dura and arachnoid respectively, the subdural and subarachnoid spaces. No epidural space in skull. Wednesday, January 1, 2025 229 Wednesday, January 1, 2025 230  Cerebral dural mater Characters A thick and dense inelastic membrane that composed of two layers, an inner or meningeal and outer periosteal or endosteal layers It is in loose contact with calvaria, and most strongly adherent to base of skull Wednesday, January 1, 2025 231 Characteristic features of Dura Made up of mainly collagenous CT Outer surface is rough and fibrillated Inner surface is smooth Firmly lines cranial cavity and adhesion is particularly strong at the sutures, cranial base and around foramen magnum. Wednesday, January 1, 2025 232 PERIOSTEAL LAYER OF DURA MATTER Continues with the pericranium through the sutures and foramina. Continues with the orbital periostium through the superior orbital fissure Wednesday, January 1, 2025 233 Wednesday, January 1, 2025 234 Wednesday, January 1, 2025 235  Dura Matter “hard (tough) mother” Epidural space: A POTENTIAL space above dura Because dura is adherent to the skull it is nonexistent. But in vertebra, it is an actual space (occupied by fat and venous sinuses) Where pus, blood and tumor may accumulate Endosteal layer Does not extend to the Spinal Cord Goes out to the ext. surface of bone (periosteum) Meningeal layer Dura matter proper Extends to the Spinal Cord Clinical Note: epidural anesthesia can not ascend to enter the skull. Forms 4 septa (DURAL REFLECTIONS) Restricts ROTATORY displacement of brain Wednesday, January 1, 2025 236 Dura mater In the spinal cord: It Covers spinal cord Tapers to coccygeal ligament Epidural space separates dura mater from walls of vertebral canal Wednesday, January 1, 2025 237 DURAL REFLECTIONS The meningeal layer of dura folds inwards to form four septa that partially divides the cranial cavity into freely communicating spaces which the subdivisions of the brain are lodged. These are CEREBRAL FALX, CEREBELLAR TENTORIUM, CEREBELLAR FALX AND SELLAR DIAPHRAGM Wednesday, January 1, 2025 238 Wednesday, January 1, 2025 239 Four septa Cerebral falx Tentorium of cerebellum－in front there is a gap, the tentorial incisure , for passage of midbrain Cerebellar falx Diaphragma sellae Septa of Dura Matter I. Falx Cerebri Related sinuses (2 layers Sickle shaped fold between fused) hemispheres Superior Sagittal sinus Attachment Upper Fixed margin of falx Anteriorly Internal frontal crests and crista galli Inferior Sagittal sinus Lower Posteriorly Free margin of falx Blend with tentorium cerebelli Straight sinus Along attachment of tentorium cerebelli Wednesday, January 1, 2025 240  II. Tentorium Cerebelli Crescent shaped dural fold located between cerebellum and occipital lobes of cerebral hemispheres Roof over post. Cranial fossa Tentorial Notch For passage of midbrain Attachment Post. Clinoid Process Petrous bone Front of temporal Occipital bone Related sinus Straight sinus Sup. Petrosal Sinus Transverse Sinus Wednesday, January 1, 2025 241  III. Falx Cerebelli Small, sickle shaped fold between Cerebellar hemispheres Attachment to Internal occipital crest Occipital sinus Only sinus related to it Post. Fixed sinus Wednesday, January 1, 2025 242 IV. Diaphragma Sella IV. Diaphragma Sella Small, circular fold Roof of sella turcica Central opening allows passage of Hypophyseal stalk Clinical Note: pituitary tumors will cause this septum to be displaced superiorly can lead to endocrine symptoms (obesity, genital shrinking, etc.) due to the involvement of the pituitary and hypothalamus superiorly can also compress the optic chiasm – leading to bitemporal hemianopsia (or blindness in temporal halves of the visual field, “tunnel vision”) Wednesday, January 1, 2025 243 Wednesday, January 1, 2025 244 Wednesday, January 1, 2025 245  Blunt Trauma to the Head A blow to the head can detach the periosteal layer of dura mater from the calvaria without fracturing the cranial bones. A fracture of the cranial base usually tears the dura and results in leakage of CSF. Because the two dural layers are firmly attached and difficult to separate from the bones. Wednesday, January 1, 2025 246 Tentorial Herniation The tentorial notch is the opening in the cerebellar tentorium for the brainstem. Hence space-occupying lesions, such as tumors in the supratentorial compartment, produce increased intracranial pressure and may cause part of the adjacent temporal lobe of the brain to herniate through the tentorial notch. During tentorial herniation, the temporal lobe may be lacerated by the tough cerebellar tentorium and the oculomotor nerve (CN III) may be stretched, compressed, or both. Wednesday, January 1, 2025 247 Bulging of the Sellar Diaphragm Pituitary tumors may extend superiorly through the aperture in the sellar diaphragm or cause it to bulge. These tumors often expand the sellar diaphragm, producing disturbances in endocrine function early or late. Superior extension of a tumor may cause visual symptoms owing to pressure on the optic chiasm. Wednesday, January 1, 2025 248  Dural Venous Sinus Dural Venous Sinuses are channels formed between the meningeal and endosteal layers of the dura. It drain ALL blood from the brain, Diploe, Orbits and Internal ear via the jugular foramen; continuous with cerebral veins; have no valves; lined with endothelium; no muscles in their walls; Moves via pressure equivalent to internal vertebral venous plexus in the spinal cord as the venous sinuses (usually) lie between periosteal and endosteal layers of the cranial dura. Wednesday, January 1, 2025 249  Sinuses of dura mater Superior sagittal sinus Inferior sagittal sinus Straight sinus Confluence of sinus Transverse sinus Sigmoid sinus Superior petrosal sinuses inferior petrosal sinuses anterior and posterior intercarvenous sinuses Occipital Wednesday, January 1, 2025 250  Superior Sagittal Sinus lies in the median plane in superior border of the falx cerebri 60% of cases ends in right transverse sinus receives superior cerebral veins Clinical Note: these veins are clinically important as they can be torn following a blow to the “front” of the head; this results in a subdural hemorrhage. It contains protrusions from subarachnoid space called arachnoid villi – which return CSF into venous system Wednesday, January 1, 2025 251  Inferior Sagittal and straight Sinus Inferior Sagittal Occupies posterior 2/3 of the free inferior edge of the falx cerebri and ends in the straight sinus. Straight Sinus – formed by the inferior sagittal sinus and great cerebral vein of Galen. runs inferoposteriorly along falx cerebri to tentorium cerebelli Empties into a transverse sinus (usually the left) helps form confluence of sinuses –dilation of the venous channels posteriorly; where the superior sagittal, straight, occipital, and transverse sinuses meet. Wednesday, January 1, 2025 252  Transverse Sinuses Transverse Sinuses – paired sinuses (left and right) pass lateral from the confluence of sinuses form deep grooves in the occipital (and part of the parietal) bones become the sigmoid sinus at the posterior aspect of the petrous temporal bone as they leave the tentorium cerebelli. Blood received by the confluence of sinuses is drained by the transverse sinuses, but rarely equally. Usually the left sinus is dominant (larger). Wednesday, January 1, 2025 253  Sigmoid Sinuses and Occipital Sigmoid Sinuses – paired sinuses with a “S-shaped” course in the posterior cranial fossa they receive the inferior petrosal sinuses directly Occipital Sinus – found posterior to foramen magnum lies in attached border of falx cerebelli communicates inferiorly with internal vertebral plexus drains superiorly in the confluence of sinuses Wednesday, January 1, 2025 254 Wednesday, January 1, 2025 255  Superior AND Inferior Petrosal Sinuses Superior Petrosal Sinuses – paired sinuses that lie superior to the petrous ridge of the temporal bone drain the cavernous sinuses and empty into transverse sinuses. lie in attached margin of tentorium cerebelli Inferior Petrosal Sinuses – paired sinuses that drain directly into the internal jugular vein on either side; also drain the cavernous sinuses Confluence Of Sinuses, a meeting place of the superior sagittal, straight, occipital, and transverse sinuses. Wednesday, January 1, 2025 256  Cavernous sinus large, paired sinuses (2 cm long, 1 cm wide) Position: lies on each side of sella turcica It is located in a dural compartment bounded by the body of the sphenoid bone and the anterior portion of the tentorium. The cavernous sinus extends anteriorly from the superior orbital fissure to the apex of the petrous part of the temporal bone posteriorly. Differ from the other sinuses as they are transversed by numerous trabeculae, which give them a spongy appearance Wednesday, January 1, 2025 257  cavernous sinus Wednesday, January 1, 2025 258  Cavernous sinus It drain through the superior and inferior petrosal sinuses and emissary veins (to pterygoid plexus) receives drainage of the sphenoparietal sinus (along the crest of the lesser wing of the sphenoid), middle cerebral veins, and ophthalmic veins Wednesday, January 1, 2025 259  Relations of cavernous cavernous sinus sinus: Internal carotid artery and abducens nerve run through the sinus (O)Oculomotor and (T)trochlear nerves and (O)ophthalmic and (M)maxillary divisions of trigeminal nerve lie in the lateral wall of the sinus One mnemonic for remembering the contents is "OTOM CAT Wednesday, January 1, 2025 260  Structures that transverse the cavernous sinuses (C) the internal carotid artery and its periarterial nervous plexus (sympathetics) (A)the abducens nerve (CNVI) (O)the oculomotor nerve (CNIII) (T)the trochlear nerve (CNIV) (O)the ophthalmic (V1) and (M)maxillary (V2) divisions of the trigeminal nerve CNIII, CNIV, and the divisions