Neuroanatomy Notes PDF

Neuroanatomy Midterm Notes I.​ Neurons ​ Neuroglia - cells in the nervous system that are uninvolved in neural transmission ○​ For structure and support ○​ Non-excitable ○​ Make up 90% of the brain’s total mass Neuroglia Types...

Neuroanatomy Midterm Notes I.​ Neurons ​ Neuroglia - cells in the nervous system that are uninvolved in neural transmission ○​ For structure and support ○​ Non-excitable ○​ Make up 90% of the brain’s total mass Neuroglia Types ​ Astrocytes - scaffolding; electrical insulators; prevents spread of neurotransmitters and excessive build up of potassium; stores glycogen; serves as the structure for the blood brain barrier ​ Oligodendrocytes - forms myelin sheath in CNS; can form up to 60 intermodal segments; found in nerve cell bodies ​ Schwann Cells - forms myelin sheath in PNS ​ Microglia - scattered within CNS; increase secondary to injury; phagocytic; derived from macrophage outside the nervous system ​ Ependymal Cells - lines brain and spinal cord cavities; forms single layer of cuboidal or columnar cells; contains microvilli and cilia; contributes to the flow of cerebrospinal fluid ​ Neuron - basic functional and anatomical unit of the nervous system ○​ Nerve cell bodies + processes ○​ Excitable ○​ Specialized for the reception of stimuli and the conduction of impulses ○​ Make up 10% of the brain’s total mass ​ Dendrite - a neurite responsible for receiving information from the body and conducting it toward the cell body; end projections are called dendritic spines Info from body → Dendrite → Cell Body ​ Axon - a neurite responsible for conducting impulse away from the body and towards somatic tissues; arises from axon hillock Impulse from cell → Axon → Somatic Tissues ​ Nucleus - cluster of cell bodies within the brain but external to the cerebral cortex ​ Ganglion - cluster of cell bodies outside of the central nervous system ​ Nissl Substance - RNA and proteins aggregated with rough endoplasmic reticulum; involved in protein synthesis and cellular metabolism, varies in quantity and distribution across different neurons Neuron Types By: Number, Length, and Mode of Branching of Neurites 1.​ Unipolar Neurons - one neurite that divides into two branches a short distance from the cell body; one branch enters the CNS, the other branch enters the PNS Ex. Dorsal root ganglion cells 2.​ Bipolar Neurons - an elongated cell body with one neurite projecting from each end. Ex. retinal bipolar, sensory cochlear, and vestibular ganglia 3.​ Multipolar Neurons - one long axon with multiple dendrites projecting from it Ex. fiber tracts of the brain and spinal cord, motor cells of the spinal cord By: Size of Neuron 1.​ Golgi Type I - characterized by a single long axon Ex. Fiber tracts of brain and spinal cord, peripheral nerves, motor cells of spinal cord 2.​ Golgi Type II - short axon with star-like dendrites Ex. Cerebral and cerebellar cortex By: General Function 1.​ Motor (Efferent) - convey motor impulses from CNS to effector organs 2.​ Sensory (Afferent) conduct impulses from somatic tissues towards CNS 3.​ Association/Interneurons - integrate sensory and regulate motor impulses By: Order 1.​ Upper Motor Neuron - first-order neurons that carry movement-initiating electrical impulses 2.​ Lower Motor Neuron - transmit signals from upper motor neurons towards effector muscles Neuron Structure and Cytology Internal Structures and Cytology ​ Cytoplasm - composed of granular (Nissl) and agranular (Golgi complex) endoplasmic reticulum ​ Endoplasmic Reticulum - filled with ribosomes ​ Ribosomes - manufacture and release proteins ​ Lysosomes - intracellular scavengers; formed by budding off of the golgi apparatus ​ Mitochondria - contains enzymes that are involved in the Krebs cycle and cellular respiration; produce energy ​ Golgi complex - smooth endoplasmic reticulum; temporarily holds protein produced by Nissl substance; important in formation of synaptic vesicles at axon terminals ​ Centrioles - paired; involved in cell division ​ Neurofibrils - main component of cytoskeleton; determine shape of nerve cell External Structures ​ Dendrite - receives somatic and/or external stimulus and brings information towards the cell body ○​ Cytoplasm is rich in Nissl granules, mitochondria, microtubules, and microfilaments ○​ Increases surface area of the cell body for the reception of axons and other neurons ​ Axon - receives stimulus from the cell body and transmits it toward somatic tissues ○​ Vary in length ○​ Covered in a plasma membrane called axolemma ○​ Arises from axon hillock ○​ Houses axoplasm inside ○​ Axon Terminals - enlarged, distal ends of the axon ​ Myelin Sheath - lipid-rich insulating material surrounding the axon ○​ Produced by Schwann Cells in the PNS ○​ Produced by Oligodendrocytes in the CNS ​ Nodes of Ranvier - portions of the axon that are unmyelinated ○​ Expedites impulse conduction via saltatory conduction ​ Axon Terminal - most distal end of the axon, transfers impulse to another neuron or effector organ ​ Axon Hillock - cone-shaped initial segment of the axon; absence of Nissl substance; most excitable part of the axon Types of Synapses according to Site and Location 1.​ Axodendritic - between an axon terminal of one neuron and the dendrites of another neuron ❖​ Most common ❖​ Usually excitatory 2.​ Axoaxonic - connection between two axons ❖​ Usually presynaptic inhibition (modulates transmitter release in postsynaptic neurons) 3.​ Axosomatic - between an axon terminal of one neuron and the soma of another neuron ❖​ Usually inhibitory 4.​ Dendrodendritic - connection between two dendrites ❖​ Can be excitatory or inhibitory Nerve Fibers - name given to an axon or dendrite of a nerve cell 1.​ Nerve Tracts - bundles of nerve fibers within CNS 2.​ Peripheral Nerves - bundles of nerve fibers within PNS ❖​ Collective term for cranial and spinal nerves ❖​ Surrounded by connective tissue ❖​ May be myelinated or unmyelinated  ❖​ May be efferent or afferent II. Gross Anatomy of the Head Scalp ​ Skin - thick; hair bearing with sebaceous glands ​ Connective Tissue - fibrofatty; branches of internal and external carotid and other veins found in this layer ​ Aponeurosis - thin; connects frontal and occipital bellies of occipitofrontalis muscle ​ Loose Areolar Tissue - contains some arteries and emissary veins ​ Periosteum - periosteum covering the surface of the skull Arterial Supply ​ Supratrochlear - branch of the ophthalmic artery of the internal carotid that supplies the forehead ​ Supraorbital - branch of the ophthalmic artery that exits through the supraorbital foramen ​ Superficial Temporal ​ Posterior Auricular ​ Occipital Arteries - originate from the external carotid artery Venous Drainage ​ Supratrochlear ​ Supraorbital ​ Superficial Temporal ​ Posterior Auricular ​ Occipital Veins Sensory Supply ​ Trigeminal Nerve (CN V) ○​ Ophthalmic (V1) ○​ Maxillary (V2) ○​ Mandibular (V3) ​ Cervical Plexus Face - contains many sweat and sebaceous glands Skull ​ Sutures - immobile joints ​ Sutural ligaments - connective tissue between sutures Cranium  ​ 1 frontal ​ 2 parietal ​ 1 occipital ​ 2 temporal ​ 1 sphenoid ​ 1 ethmoid Vault Base Facial Bones ​ 2 zygomatic ​ 2 maxillae ​ 2 nasal ​ 2 lacrimal ​ 2 palatine ​ 2 inferior conchae ​ 1 mandible ​ 1 vomer Exits of the Cranial Nerves from the Skull Exits Nerves Cribriform Plate Olfactory Nerve (CN I) Optic Foramen Optic Nerve (CN II) Superior Orbital Fissure Oculomotor (III) Trochlear (IV) Trigeminal Ophthalmic (CN V1) Abducens (VI) Foramen Rotundum Trigeminal Maxillary (CN V2) Foramen Ovale Trigeminal Mandibular (CN V3)  Stylomastoid Foramen Facial Nerve (CN VII) Internal Auditory Canal Vestibulocochlear (CN VIII) Facial Nerve (CN VII) Glossopharyngeal (CN IX) Jugular Foramen Vagus (CN X) Accessory (CN XI) Hypoglossal Canal Hypoglossal (CN XII) III. Central Nervous System A.​ Brain ➔​ Left brain - responsible for language, logic, analytic thought, reasoning, math, science ➔​ Right brain - responsible for recognition, visual perception, general behavior, imagination, music and art Clinical Relevance: Stroke Left Hemisphere Stroke Right Hemisphere Stroke ★​ Right side hemiplegia/ paresis ★​ Left side hemiplegia / paresis ★​ Right side sensory loss ★​ Left side sensory loss Speech and language impairments: Visual-perceptual impairments : ★​ Broca’s aphasia - motor impairment ★​ Left side unilateral neglect ★​ Wernicke’s aphasia - cognitive impairment ★​ Agnosias - inability to process sensory ★​ Global aphasia - total impairment information ★​ Visuospatial disorders ★​ Disturbances of boy image and body scheme ★​ Difficulty processing visual cues ​ Forebrain ○​ Cerebrum/Telencephalon ​ Cerebral cortex ​ Central Sulcus - landmark demarcating precentral and postcentral gyri ○​ Precentral Gyrus - contains motor cells that initiate movement on contralateral side of the body; anterior to central sulcus  ○​ Postcentral Gyrus - receives sensory information from contralateral side of body; posterior to central sulcus ​ Precentral Sulcus ​ Postcentral Sulcus The precentral and postcentral sulci lie parallel to the central sulcus ​ Lateral Sulcus/ Sylvian Fissure - found inferior and lateral; separates temporal lobe ​ Parieto-occipital Sulcus - approx. 2 inches anterior to occipital pole ​ Calcarine Sulcus - located on the medial surface of the hemisphere; ends under the posterior end of the corpus callosum ​ Frontal lobe - responsible for cognitive processes, muscle and movement control, emotional regulation, memory storage; most anterior part of the brain ​ Superior frontal gyrus ​ Superior frontal sulcus ​ Middle frontal gyrus ​ Inferior frontal sulcus ​ Inferior frontal gyrus ​ Temporal lobes - processes auditory information and encodes memory; lies inferior to the lateral sulcus ​ Superior temporal gyrus ​ Superior temporal sulcus ​ Middle temporal gyrus ​ Middle temporal sulcus ​ Inferior temporal gyrus ​ Parietal lobes - responsible for sensory perception and integration; located posterior to the central sulcus and superior to the lateral sulcus ​ Superior parietal lobule ​ Infraparietal sulcus ​ Inferior parietal lobule ​ Parieto-occipital sulcus ​ Occipital lobe - visuospatial processing, distance and depth perception, color determination, object and face recognition, memory formation; located posterior to the parieto-occipital sulcus ​ Medial and Inferior surface of the cerebral hemisphere  ​ Cingulate Sulcus - separates superior frontal gyrus and inferior frontal gyrus ​ Cingulate Gyrus - component of the limbic system, responsible for emotional processing and behavior regulation; arch-shaped structure found above the corpus callosum ​ Callosal Sulcus - separates cingulate gyrus and corpus callosum ​ Corpus Callosum - connect left and right hemispheres together ○​ Rostrum - anterior end of corpus callosum ○​ Genu - curved anterior end that continues inferiorly in front of septum pellucidum ○​ Body - ends as a thickened posterior portion ○​ Splenium - posterior end ​ Septum Pellucidum - thin sheet of gray and white matter that extends from the fornix to the corpus callosum; forms partition between anterior horns of the lateral ventricle ​ Internal Capsule ​ Corona Radiata - merging of the nerve fibers from the nuclear masses; fibers from the posterior aspect radiate towards calcarine sulcus and form the optic radiation ​ Association fibers - white fibers that connect various internal structures of one side of the brain ○​ U fibers / short association fibers ○​ Long association fibers ○​ Cingulum Uncinate fasciculus ○​ Arcuate fasciculus Brodmann Areas - divisions based on the cytoarchitecture (arrangement and connections of neurons) Areas Name Function 3, 1, 2 Primary somatosensory cortex (postcentral gyrus) ​ Localization of touch, temperature, vibration, and pain ​ Sensory perception (2-point discrimination, proprioception) ​ Skilled orofacial movement (e.g. whistling) ​ Motor learning 4 Primary motor cortex (precentral gyrus) ​ Motor movements ​ Contralateral finger, wrist, hand, orofacial movements ​ Learned motor sequences ​ Breathing control ​ Voluntary blinking 5 Somatosensory association cortex ​ Spatial imagery ​ Motor execution ​ Working memory ​ Language processing ​ Line bisection judgment 6 Pre-motor and supplementary motor cortex (superior ​ Voluntary motor activity from sensory input frontal gyrus) ​ Movement planning ​ Programming of motor sequence ​ Speech motor programming 9 Dorsolateral/ anterior prefrontal cortex (DLPFC) ​ Regulation of intellectual function and action ​ Deception and lying 10 Anterior prefrontal cortex ​ Memory retrieval ​ Reasoning ​ Problem solving ​ Planning ​ Processing emotional stimuli 17 Primary visual cortex ​ Visual information processing center 22 Primary auditory cortex / superior temporal gyrus ​ Language and auditory processing 37 Fusiform gyrus / occipitotemporal gyrus ​ Processing color information ​ Face and body recognition ​ Word and number recognition 22, 39, 40 Wernicke’s area ​ Speech fluency and thought cohesion 44,45 Broca’s area ​ Speech praxis Motor Homunculus - topographic representation of the brain’s motor innervations to the body  Sensory Homunculus - topographic representation of the brain’s sensory innervations to the body ○​ Diencephalon ​ Thalamus - integrates visceral and somatic functions, serves as main cell station for all sensory pathways, influences voluntary movement in connection with basal ganglia; ovoid mass of cell bodies located at each side of the 3rd ventricle  ​ Hypothalamus - center of the limbic system, controls and integrates functions of the ANS and endocrine system; plays vital role in homeostasis; extends from optic chiasma to mammillary bodies, forms the floor of the 3rd ventricle ​ Mammillary bodies - aids in recollective memory, pair of small hemispherical bodies on each side of tuber cinereum ​ Subthalamus - involved in muscle control activity; contains superior ends of medial, spinal, and trigeminal lemnisci tracts; collection of nerve cells found are red nucleus and substantia nigra; located inferior to the thalamus and tegmentum, related to the midbrain ​ Lesion: ballismus ​ Epithalamus - connects the limbic system to other parts of the brain ​ Habenular Nucleus - small group of neurons, located medial to the posterior surface of the thalamus; center for integration of olfactory, visceral, and somatic afferent pathways ​ Pineal Body/ Gland - plays large role in sleep and reproductive function regulation; secretes melatonin produced by pinealocytes ​ Midbrain / Mesencephalon - connects pons and cerebellum to the forebrain; connects midbrain to cerebellum via superior cerebellar peduncle; located at the level of the cerebral aqueduct; has basic, tegmentum, and tectum; contains CN III and IV ○​ Tectum - dorsal; midbrain only ○​ Tegmentum - ventral; throughout brainstem ○​ Basis - throughout brainstem ​ Hindbrain ○​ Medulla oblongata / Myelencephalon ○​ Pons / Metencephalon ○​ Cerebellum / Metencephalon - “little brain”, largest part of the hindbrain; located posterior to the 4th ventricle, attached to the brainstem via cerebellar peduncles ​ Peduncles - connections to the brainstem ​ Superior → midbrain ​ Middle → pons ​ Inferior → medulla oblongata ​ Lobes ​ Anterior - propulsive stereotypical movements (locomotion, ambulation); regulation of muscle tone ​ Posterior/ Middle - coordination of movement ​ Flocculonodular - balance and equilibrium; coordination of eye movements ​ Fissures ​ Primary - separates anterior and middle lobes ​ Uvulonodular - separates middle and flocculonodular lobes ​ Horizontal - separates inferior and superior surfaces ​ Arbor Vitae (Tree of Life) - branched appearance, contains small amounts of white matter. White matter consists of 3 fibers: ​ Intrinsic - connects to different regions within the cerebellum ​ Afferent - forms majority of cerebellum, proceeds to cerebellar cortex; enters cerebellum via inferior and middle peduncles ​ Efferent - output of the cerebellum; commences as axons of Purkinje cells; most of these axons pass and synapse with neurons of the cerebellar nuclei ​ Inner white matter → cerebellar white matter; embedded intracerebellar/ deep cerebellar nuclei ​ Intrinsic - originate from Purkinje Cell fibers; terminate in the deep cerebellar nuclei  ​ Efferent (output) - originate from deep cerebellar nuclei and the cerebellar cortex; terminate at extracerebellar locations ​ Afferent (input) - originate from extracerebellar locations and terminate at the cerebral cortex and deep cerebellar nuclei ​ Outer gray matter → cerebellar cortex 4 Masses of Gray Matter (lateral to medial) ​ Dentate nucleus - largest cerebellar nuclei filled with white matter; large part of cerebellar peduncle; functions for finely coordinated movements and movements in the distal limbs ​ Interposed ○​ Emboliform nucleus - ovoid, medial to the dentate nucleus; functions for locomotion and extremity coordination ○​ Globose nucleus - one or more rounded cell groups medial to the emboliform; functions for locomotion and extremity coordination ​ Fastigial nucleus - closer to midline in the vermis and close to the roof of the 4th ventricle; functions for posture, muscle tone, balance, and eye movements ​ Dentate, emboliform, and globose leave via superior cerebellar peduncle ​ Fastigial leaves via inferior cerebellar peduncle Functional Areas: ​ Intermediate Zone (lateral to vermis) - controls muscles of the distal limbs especially the hands and feet ​ Lateral zones of each hemisphere - sequential movement planning of the entire body; conscious awareness of movement errors Vertical Divisions  Zone Cortical Region Cerebellar Nucleus Vermis (median) Vermis Fastigial nucleus Paravermal (intermediate) Medial region of cerebellar Interposed nuclei hemispheres Lateral (hemisphere) Lateral region of cerebellar Dentate nucleus hemisphere Cerebellar Functions General Functions Specific Functions ★​ Maintains posture and balance ★​ Part of the motor system ★​ Maintains muscle tone ★​ Executes smooth sequential movement ★​ Coordinates voluntary motor activity ★​ Controls adjustment, timing, trajectory, and velocity of movement ★​ Exerts its control through brainstem and cerebral cortex ★​ Enables smooth occurrence of voluntary movement with precision and economy of effort ★​ Receives afferent information from the sensory system, cerebral cortex, and spinal cord ★​ Receives afferent stimuli such as balance from the vestibular nuclei Cerebellar Sensory / Afferent Pathways Tract Name Function Origin Destination Corticopontocerebellar Movement planning, initiation, Cerebral cortex; frontal, Cerebellar cortex via pontine nuclei monitoring, and adjustment parietal, temporal, and mossy fibers occipital lobes Cerebero-olivocerebellar Movement planning, initiation, Cerebral cortex; frontal, Cerebellar cortex via inferior olivary monitoring, and adjustment parietal, temporal, nuclei and climbing fibers occipital lobes Cerebroreticulocerebellar Conveys control from cerebral Sensorimotor areas Cerebellar cortex via reticular cortex for movement planning, formation initiation, monitoring, and adjustment Anterior / Ventral Spinocerebellar Conveys motor control from muscles Muscle spindle. GTO, Cerebellar cortex via mossy fibers and joints of UE and LE joint receptors Posterior / Dorsal Spinocerebellar Conveys control from muscles and Muscle spindle, GTO, Cerebellar cortex via mossy fibers joints of the trunk and LE joint receptors Cuneocerebellar Conveys control from muscles and Nucleus cuneatus of Cerebellar cortex via mossy fibers joints of UE and and LE medulla Vestibulocerebellar Conveys information of head Utricle, saccule, Cortex of flocculonodular lobe via position and movement for eye semicircular canals, mossy fibers movement vestibular nuclei Tectocerebellar Reflex head turning due to auditory Tectum of brainstem Cerebellar cortex via mossy fibers or visual impulses Cerebellar Motor / Efferent Pathways Name Function Origin Destination Globose-emboliform Rubral Influence ipsilateral motor activity Globose and emboliform Contralateral red nucleus then to nuclei ipsilateral motor neurons in the spinal cord via crossed rubrospinal tract Dentothalamic Influence ipsilateral motor activity Dentate nucleus Contralateral ventrolateral nucleus of thalamus to contralateral motor cerebral cortex Fastigial Vestibular Influence ipsilateral extensor muscle Fastigial nucleus Mainly to ipsilateral and tone contralateral vestibular nuclei, vestibulospinal tract to ipsilateral motor neurons in the SC Fastigial Reticular Influence ipsilateral muscle tone Fastigial nucleus Neurons of reticular formation; reticulospinal tract to ipsilateral motor neurons to SC Cerebellar Disease ​ Vermal and Paravermal ○​ Wide-based gait - walking with feet spaced widely apart ○​ Difficulty with tandem gait - used to diagnose ataxia; difficulty with walking in a straight line ○​ Titubation of head and body - nodding movement ○​ Spontaneous nystagmus - eye movement that occurs without specific triggers  ​ Paravermal and Lateral ○​ Ataxia - poor muscle control resulting in clumsy movements ​ Tremor - occurs in fine movements ​ Decomposition of movement ○​ Ocular movement disorders ​ Pendular nystagmus - rhythmic oscillation of the eyes at the same rate in both directions ​ Jerk nystagmus - rhythmic oscillation of eyes quicker in one direction ○​ Delayed initiation and termination of motor activity ○​ Abnormal stance and gait ○​ Decomposition of movement ○​ Hypotonia - loss of resilience to palpation ○​ Dysarthria - difficulty pronouncing words ○​ Dysmetria - inability to control speed, distance, and ROM necessary to perform smooth movements ○​ Dysdiadochokinesia - inability to perform rapid, alternating movements ○​ Impaired check and rebound - pt unable to return displaced limb to original position with eyes closed ○​ Reflex disturbances ​ Pendular Knee Jerk - reflex continues as a series of flexion and extension Cerebellar Syndromes ​ Vermis Syndrome - typically caused by medulloblastoma ○​ Sx: tendency to fall forward or backward; keeping head in a stray, upright position; difficulty holding trunk erect ​ Cerebellar Hemisphere Syndrome - typically caused by tumors on one cerebellar hemisphere ○​ Sx: usually unilateral, involves muscles on the side of the diseased hemisphere ​ Swaying and falling on the side of the lesion  ​ Dysarthria and nystagmus are commonly observed ○​ Diseases in the lateral part of the cerebellar hemispheres produce a delay in initiating movements and moving all segments together in a coordinated manner ​ Brainstem ○​ Occupies posterior cranial fossa ○​ Stalk-like shape ○​ Composed of midbrain, medulla oblongata, pons Functions: ​ Connects spinal cord and forebrain ​ Conduit of ascending and descending tracts ​ Control of respiratory and cardiovascular systems ​ Contains reticular formation ​ Site and exit of cranial nerves ​ Contains important nuclei of cranial nerves IX-XII B.​ Spinal Cord ➔​ Continuous with the medulla oblongata, begins at the foramen magnum and terminates at the lower border of L1 in adults and in the upper border of L3 in children ​ Conus Medullaris - cone-shaped tapering off of the spinal cord ​ Filum Terminale - prolongation of the pia mater; secures spinal cord onto the coccyx ​ Cauda Equina - collection of spinal nerves resembling a horse’s tail ​ Vertebral Column - holds the spinal cord and roots of the spinal nerves; protects the spinal cord; 33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal) ​ Spinal Cord - Projections of the spinal cord towards the body; 31 spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) Meningeal Coverings (most distal to most proximal) ​ Dura Mater - thick, outermost layer; highly vascularized ​ Arachnoid Mater - middle layer; avascular ​ Pia Mater - thinnest, most proximal layer; follows contours of sulci and gyri; tightly adhered to brain; highly vascularized Ascending / Sensory Tracts  ➔​ Conduct two types of afferent information: ◆​ Exteroceptive - external stimulus (pain, temp, touch) ◆​ Proprioceptive - internal stimulus (information from muscle spindle) ➔​ 1st order neuron - cell body of posterior root ganglion of spinal nerve; receive sensory impulses from receptors and transmit them to SC ➔​ 2nd order neuron - gives rise to axon that decussates and ascends to higher level of CNS; synapses with 3rd order neurons ➔​ 3rd order neuron - transmits impulse from SC to subcortical areas Tract Location Function Decussation Origin Destination Neurons Anterior and Lateral Anterior and lateral white Ant: crude touch and 1-2 levels above via Free nerve endings BA 312 Spinothalamic columns pressure vertebral column (obliquely) Lat: pain and temperature Dorsal Column Medial Posterior white columns Fine touch, Medullary tegmentum BA 312 BA 312 Lemniscus proprioception, vibratory sense, 2-point discrimination Dorsal and Ventral Lateral columns Ventral: proprioception None GTO, muscle spindle Cerebellar paleocortex Spinocerebellar from LE Dorsal: Proprioception from LE and trunk Cuneocerebellar & Rostral: coordination and posture Spinoreticular Anterolateral column Deep, chronic pain, Immediately after origin Deep, somatic structures Reticular formation 1st order neuron: dorsal afferent path for reticular root ganglion formation 2nd order neuron: gray  matter 3rd order neuron: reticular formation of brainstem Spinotectal Anterolateral columns Spinovisual reflexes Median plane Dorsal horn, RL VIII & 1st order neuron: dorsal IX root ganglion RL: Rex Laminae 2nd order neuron: unknown 3rd order neuron: superior colliculus of midbrain Spino-olivary Ventral funiculus Indirect pathway for Median plane Medial part of laminae 3 Cerebellum via inferior further afferent and 4; central cervical cerebellar peduncle information to reach nucleus cerebellum; proprioception of LE to cerebellum Descending/Motor Tracts ➔​ Conduct efferent information ◆​ Involuntary via the extrapyramidal tracts ◆​ Voluntary via pyramidal tracts ◆​ Autonomic (for ANS) via descending autonomic fibers ➔​ 1st order neuron - cell body in cerebral cortex ➔​ 2nd order neuron - anterior gray column of spinal cord ➔​ 3rd order neuron - lower order neuron in anterior gray horn ➔​ Destination - skeletal muscle through anterior root and spinal cord Tracts Location Function Decussation Origin Destination Neurons Anterior and Lateral Ant: anterior column Ant: gross and postural Ant: Sc; either cervical or BA 312, 4, 6 Anterior horn cells at RL Corticospinal muscle control (proximal upper thoracic depending VIII and IX Lat: lateral column and axial musculature); on destination ipsilateral Lat: cervicomedullary Lat: rapid and skilled junction voluntary movements, fine motor skills in distal musculature; contralateral Reticulospinal Anterior column (pontine) Facilitate or inhibit Pontine RS: formed by Reticular formation at Dorsal horn , RL VIII and and lateral column activity of alpha and uncrossed fibers from brainstem IX (medullary) gamma motor neurons; pons; descend into voluntary and reflex anterior white column activities Medullary RS: formed by Lateral RS: decreases crossed and uncrossed tone, breathing fibers from medulla; descend into lateral white Medial RS: contraction, column increase tone Rubrospinal Lateral column Antigravity muscles; Immediately at origin Red nucleus at tegmentum RL VII and IX, facilitates flexors and interneurons inhibits extensors Vestibulospinal Anterior column Posture and balance; Does not decussate Vestibular nuclei at pons RL VII and VIII, facilitates extensors and and medulla interneurons to alpha and inhibits flexors, quick gamma motor neurons reactions to position changes; controls Medial - from medial antigravity muscles vestibular nuclei of brainstem → descend down SC (crossed and uncrossed) → terminates  at cervical levels Lateral - from lateral vestibular nucleus → terminates in ventral white column Olivospinal Lateral column Proprioception; muscular Inferior olivary nucleus Enters lateral white activity funiculus and terminates in anterior gray column of SC Tectospinal / Superior colliculus of Reflex head turning in Midline after descending Inferior olivary nucleus Anterior horn interneurons Colliculospinal midbrain response to visual stimuli; to anterior median fissure at cervical area head and vision coordination Upper and Lower Motor Neurons and Lesions ​ Motor neurons - carry information from brain or spinal cord; are involved in regulating activity in muscles and glands ○​ Lower motor neurons - located in anterior gray horn of spinal cord; innervate muscles through anterior roots of spinal nerves ​ Somatic motor neurons - extend to skeletal muscle to control movement and muscle tone ​ Special visceral or branchial motor neurons - supply muscles of the head and neck ​ General visceral neurons - supply autonomic nervous system ○​ Upper motor neurons - originate in multiple areas of brain and brainstem; carry information about desired movements and other impulses in descending tracts; descend to various levels of the brainstem and spinal cord to form connections with lower motor neurons Upper Motor Neuron Lesions Lower Motor Neuron Lesions  ★​ Weakness and paralysis ★​ Weakness and paralysis ★​ Hypertonia ★​ Hypotonia;flaccidity ★​ Hyperreflexia; spasticity; positive Babinski ★​ Hyporeflexia sign ★​ Atrophy ★​ Muscle mass maintained ➔​ LMN lesions have multiple possible causes ➔​ UMN lesions are usually secondary to such as: cardiovascular accidents leading to ◆​ Poliomyelitis contralateral symptoms ◆​ Motor neuron disease ◆​ Strokes are named based on location ◆​ Spinal cord injury (SCI) of occurrence, not on location of ◆​ Peripheral nerve injury (PNI) weakness ◆​ Muscle myotonias Ex: right side stroke → left side ◆​ Myasthenia gravis weakness ◆​ Muscular dystrophies Spinal Cord Lesions Complete Cord Lesion ★​ Complete bilateral loss of sensory and motor function ★​ Loss of bowel and bladder (spastic bladder) Central Cord Lesion ★​ Bilateral loss of pain, temperature, and motor function ★​ Preservation of proprioception and discriminatory function ★​ Hyperextension injury Brown Sequard ★​ Hemisection of the spinal cord ★​ Ipsilateral loss of tactile discrimination, pressure, vibration, proprioception, and motor function ★​ Contralateral loss of pain and temperature BELOW level of lesion ★​ Bilateral loss of pain and temperature AT level of lesion Anterior Cord Lesion ★​ Bilateral loss of motor, pain, and temperature function ★​ Deep sensation remains intact ★​ Flexion injury Posterior Cord Lesion ★​ Bilateral loss of deep sensation ★​ Intact motor, pain, and temperature function Cauda Equina Lesion ★​ Lesions below L1 ★​ Flaccid paralysis with no spinal reflex ★​ Flaccid bowel and bladder ★​ EMERGENCY CASE Rex Laminae I Pain and temperature sensations  II Pain modulation and processing III Touch and pressure sensation IV Touch and pressure sensation V Nociceptive & non-nociceptive signal processing VI Proprioception VII Posture and movement regulation VIII Coordination of reflexes and voluntary movements IX Innervate skeletal muscles X Autonomic functions, visceral sensory integration IV. Autonomic Nervous System ➔​ Part of the peripheral nervous system that serves as a control system for below the level of consciousness processes; responsible for involuntary or visceral bodily functions: ◆​ Cardiovascular ◆​ Respiratory ◆​ Digestive ◆​ Urinary ◆​ Reproductive ◆​ Stress response ◆​ Glands ​ Sympathetic nervous system ○​ Body’s fight or flight response; stress response function ○​ Primes body for intense skeletal muscle activity ​ Parasympathetic nervous system ○​ Rest and digest mechanism; maintenance functions ○​ Counterbalances sympathetic function ➔​ Commands reach effector organs via a two-neuron chain ​ Preganglionic neurons ○​ Cell body within grey matter of CNS ○​ Myelinated axon exits CNS ○​ Preganglionic axon passes from CNS via a spinal or cranial nerve  ○​ Terminates in a ganglion ​ Postganglionic neurons ○​ Cell body is found in autonomic ganglion; location is dependent upon division of the ANS ○​ Unmyelinated ○​ Passes from the ganglion to the effector; either stimulated or inhibited Autonomic vs Somatic Nervous Systems Characteristics Somatic Autonomic Sensory Neuron Somatic senses and special senses Mainly from interoceptors located in blood vessels, visceral organs, and nervous system that monitor internal environment Effector Skeletal muscle Cardiac muscle, smooth muscle, glands Control of motor neuron Voluntary control from cerebral Involuntary control from cortex with distribution from basal hypothalamus, limbic system, brain ganglia, cerebellum, brainstem, and stem, and spinal cord; limited control spinal cord from cerebral cortex Motor neuron pathway One motor axon from CNS to Two neuron pathway: effector ★​ One motor axon from CNS to autonomic ganglion (preganglionic) ★​ One motor axon from autonomic ganglion to effector (postganglionic) Neurotransmitter Acetylcholine ★​ Sympathetic ganglionic neurons: release Norepinephrine ★​ Sweat glands: release Ach ★​ All parasympathetic postganglionic neurons release Ach Target tissues Skeletal Smooth muscle, cardiac muscle, exocrine glands Regulation Conscious and unconscious Unconscious movement Reaction to stimulation Contractions Stimulation or inhibition Number of neurons 1 2 Axon sheaths Myelinated Pre: myelinated Post: unmyelinated Parasympathetic and Sympathetic Nervous Systems SNS PNS Fight or flight response Rest and Digest Mobilizes body during activity Conserves body energy Promotes adjustments during exercise; blood flow to - organs decreased, blood flow to muscles increased Threat responses: Illustrated in a person who is relaxed: ​ Increased HR and RR ​ BP, HR, RR are low ​ Glucose released from liver to blood ​ GI tract activity high ​ Skin is cold and sweaty ​ Skin is warm ​ Pupils are dilated ​ Pupils constricted Ganglia close to vertebra Ganglia located close to the viscera of plexus Preganglionic neurotransmitter: ACh (cholinergic), Preganglionic neurotransmitter: ACh (cholinergic), binding to nicotinic receptors → stimulation binding to nicotinic receptors → stimulation effect Afferent fibers going to CNS stimulates posterior Afferent fibers going to CNS stimulates anterior hypothalamus primarily hypothalamus primarily Increase in heart and respiratory rates, and inhibit Decrease heart and respiratory rates, and allow for digestion and elimination digestion and the discarding of wastes Controls BP and keeps the blood vessels in continual Slows the heart state of partial constriction Prompts vessels to dilate if blood pressure is to be Dictates normal activity levels of the digestive and decreased urinary systems Causes ejaculation of semen in males and reflex Causes vasodilation and are responsible for erection of peristalsis in females the penis and clitoris Exerts long-lasting diffuse effects due to NE being: Exerts short-lived highly localized control -​ Inactivated more slowly than ACH -​ An indirectly acting neurotransmitter, using a second messenger system -​ Epinephrine is released into the blood and remains there until destroyed by the liver Referred Pain  ​ Visceral pain afferents travel along the same pathways as somatic pain fibers ​ Pain stimuli arising in the viscera are perceived as somatic in origin ​ Example: heart attack produces a sensation of pain in the superior thoracic wall and the medial aspect of the left arm ​ The same spinal segments (T1-5) innervate both the heart and the somatic regions, the brain perceives pain from the more common somatic regions ​ Heartburn & gallstones ​ Stomach Pain – commonly felt in the epigastrium; give rise to referred pain in dermatomes T5-T9 ​ Appendicular Pain – produced by distention of the lumen or spasm to its muscle; somatic pain is localized to the T12-L1 dermatomes ​ Gallbladder Pain – referred pain is felt in dermatomes T5-T9 ​ Causalgia – painful condition of arm or leg accompanied by trophic changes in the affected skin and nails ANS Injury 1.​ Sympathetic Injuries ○​ Stabbing/ Bullet wounds in the neck ○​ Traction injuries to the first thoracic root of the brachial plexus ​ Can damage sympathetic nerves destined for the stellate ganglion ​ Both listed above can produce a preganglionic type of Horner syndrome ○​ Injuries to the SC or cauda equina can disrupt parasympathetic control of the bladder 2.​ Parasympathetic Injuries ○​ Oculomotor nerve – vulnerable in head injuries and compression by aneurysms in junction between the posterior cerebral and communicating arteries ○​ Facial nerve – can be damaged by fractures of the skull involving the temporal bone; usually affected together with vestibulocochlear nerve ○​ Glossopharyngeal and vagus nerve – at risk in stab and bullet wounds of the neck ○​ Parasympathetic outflow in the sacral region – may be damaged in SC and cauda equina injuries; results in disruption of bladder, rectal, and sexual functions 3.​ Degeneration and Regeneration of Autonomic Nerve ○​ Identical to those found in other areas of the peripheral and central parts of the nervous system 4.​ Urinary Bladder Dysfunction  ○​ Atonic Bladder – bladder becomes greatly distended & overflows due to relaxation of the bladder wall & sphincter urethrae and tight contracting of the sphincter vesicae; occurs during spinal shock ○​ Automatic Reflex Bladder – bladder fills & empties reflexively; normally seen in infants but can occur after spinal shock ○​ Autonomous Bladder – continued dribbling of bladder; occurs when sacral segment of SC is destroyed or cauda equina is severed 5.​ Defecation ○​ SC injuries or cauda equina injuries ​ Patient becomes unaware of rectal distention ​ Parasympathetic influence over peristaltic activity becomes loss is descending colon, sigmoid colon, and rectum ​ Rectum responds to isolation be contracting when pressure within the lumen rises ​ Treatment consist of biweekly enemas 6.​ Erection and Ejaculation ​ bilateral damage to the reticulospinal tracts in the SC above S2 will result in loss of erection and ejaculation Diseases involving the ANS 1.​ Diabetes Mellitus – postural hypotension, peripheral edema, pupillary abnormalities, and impaired swearing 2.​ Horner Syndrome – result from interruption of sympathetic nerve supply to the head and neck; can be caused by MS, syringomyelia, and a cervical rib ○​ Sx include: ​ Constriction of pupil (miosis) ​ Slight drooping of eyelid (ptosis) ​ Enophthalmos ​ Vasodilation of skin arterioles ​ Loss of sweating (anhidrosis) 3.​ Argyll Robertson Pupil – small pupil that doesn’t react to light but does contract with accommodation; caused by neurosyphilitic lesion 4.​ Adie Tonic Pupil Syndrome – pupil has decreased or absent light reflex ○​ Slow/delayed contraction to near vision ○​ Slow/delayed dilatation in the dark  5.​ Frey Syndrome – sometimes follows penetrating wounds of the parotid gland during the healing process ○​ Results in salivary production during sweat secretion stimulus 6.​ Hirschsprung Disease – occurs when myenteric plexus fails to develop in the distal colon which blocks feces passage and makes the proximal colon enormously distended 7.​ Botulinum Toxin – produces atropine-like syndrome with skeletal muscle weakness 8.​ Black Widow Spider Venom – causes a brief release of ACh followed by a permanent blockade 9.​ Anticholinesterase Agents – can be blocked by certain drugs resulting in excessive stimulation of cholinergic receptors ○​ Results in SLUDG syndrome (salivation, lacrimation, urination, defecation, and gastrointestinal distress) Sympathectomy ​ Removal of a sympathetic nerve can be used to treat arterial disease ○​ Raynaud Disease ○​ Intermittent Claudication ○​ Hypertension