Anatomy Unit 3 PDF

CNS DIVISIONS Forebrain 1. Telencephalon: all 5 lobes plus basal ganglia, including the caudate and putamen (striatum), globus pallidus, and subthalamic nuclei a. Frontal: precentral gyrus b. Parietal: postcentral gyrus c. Occipital: calcarine fissure...

CNS DIVISIONS Forebrain 1. Telencephalon: all 5 lobes plus basal ganglia, including the caudate and putamen (striatum), globus pallidus, and subthalamic nuclei a. Frontal: precentral gyrus b. Parietal: postcentral gyrus c. Occipital: calcarine fissure d. Temporal: superior temporal gyrus e. Insular f. Cavity of the telencephalon: lateral ventricle, extends to all lobes 2. Diencephalon: thalamus and hypothalamus a. Hypothalamus is connected to the pituitary stalk via the infundibulum b. Cavity of the diencephalon: 3rd ventricle Midbrain 1. Mesencephalon: a. Cerebral peduncles: contains descending motor fiber tracts b. Substantia nigra: functions with the basal ganglia system c. Red nucleus: origin of rubrospinal tract d. Motor nuclei of CN III and CN IV e. Tectum: contains the superior and inferior colliculi (corpora quadrigemina) f. Cavity of the mesencephalon: cerebral aqueduct Hindbrain 1. Metencephalon: a. Pons: ascending and descending fiber tracts, heavily interconnected with the cerebellum via middle cerebellar peduncle. Origin of cranial nerves V-VII b. Cerebellum: interior, posterior, and flocculonodular lobes are separated by primary and posterolateral fissures. Connected to the brainstem by cerebellar peduncles 2. Myelencephalon: a. Medulla: contains numerous ascending and descending motor fiber tracts. Sensory relay nuclei (nucleus cuneatus and gracilis). Origin of CN IX, X, XII. i. Pyramidal decussation takes place at the spinomedullary junction b. Cavity of the metencephalon and myelencephalon: 4th ventricle SPECIALIZATIONS OF THE MENINGES 1. Arachnoid: contains subarachnoid space which houses CSF, arachnoid granulations allow CSF to enter venous circulation by extending the arachnoid into the dura and venous sinuses 2. Dura: falx cerebri and cerebelli separate hemispheres in the cerebrum and cerebellum. The falx tentorium separates the occipital and temporal lobes from the cerebellum and brainstem  a. Dural venous sinuses: superior and inferior sagittal, straight, transverse, and sigmoid. Superior sagittal will collect CSF from arachnoid granulations and feed it back into venous circulation CIRCLE OF WILLIS *note the relationship of the ACA to the lower extremities, and the MCA to the trunk, upper extremities, and face FEATURES OF THE CORTEX 1. Divisions: a. Neocortex: 95%, 6 layers b. Allocortex: more variable lamination patterns as seen in the olfactory cortex (paleocortex) and hippocampus (archicortex) 2. Cortical lamination patterns: a. Layer I: molecular layer, contains few cells, mostly horizontally oriented dendrites and axons b. Layer II: external granular layer, receives input from layer III. Contains smaller neurons and few pyramidal cells c. Layer III: external pyramidal layer, sends input to layer II via commissural and association fibers. Contains medium sized pyramidal cells  d. Layer IV: internal granular layer. Receives thalamic input. Mainly stellate neurons, few pyramidal cells e. Layer V: internal pyramidal layer. Gives rise to cells that terminate on subcortical structures and the spinal cord. Many large pyramidal cells and Betz cells f. Layer IV: multiform layer, contains many cell types. Includes pyramidal cells that project to the thalamus 3. Types of cortical connections: a. Association fibers: connect portions of the cortex in the same hemisphere, including axons from layer III that terminate in layer II. Can be long or short b. Commissural fibers: connect adjacent hemispheres. Majority are found in the corpus callosum, also found in the anterior and posterior commissures. c. Projection fibers: axons from layer V or VI that project to deep parts of the cerebrum i. Corticostriatal: layer V→ caudate nucleus or putamen ii. Corticorubral: layer V→ red nucleus iii. Corticopontine: layer V→ pons iv. Corticobulbar: layer V→ brainstem motor nuclei (CN III-VI, IX-XII) v. Corticoreticular: layer V→ reticular formation vi. Corticospinal: layer V→ ventral horn spinal cord vii. Corticothalamic: layer VI→thalamus SPINAL CORD FEATURES 1. Same meninges as the brain: dura, arachnoid, and pia mater 2. Anterior median fissure: divides the anterior white matter into halves 3. Posterior median fissure: divides the posterior white matter into halves 4. Cervical and lumbosacral enlargements: correspond to the additional motor nuclei needed to supply the upper and lower extremities 5. Conus medullaris: the lowermost tapering of the spinal cord 6. Cauda equina: end of the true spinal cord at L2-3, spinal nerves branch off but there is no true spinal cord 7. Filum terminale: anchors the tip of the spinal cord to the coccyx FEATURES OF THE THALAMUS 1. Ventral posterolateral (VPL): 3rd order neurons in the dorsal column-medial lemniscus pathway and lateral spinothalamic tract. Interconnected with postcentral gyrus. Body sensation 2. Lateral geniculate nucleus (LGN): thalamic relay for CN II. Vision 3. Ventral posteromedial (VMP): thalamic relay for sensory info from face (CN V) Face sensation 4. Medial geniculate nucleus (MGN): thalamic relay for auditory information (CN VIII) Audition  5. Ventral anterior and ventral lateral (VA/VL): relays for basal ganglia circuits. Both project to motor or premotor cortices. VL is the only thalamic relay for the cerebrocerebellar circuit. Both motor 6. Centromedian nucleus (CM): source of input to the striatum (caudate and putamen) Motor SENSORY TRACTS (3) 1. Dorsal column-medial lemniscus pathway: carries general touch, pressure, and vibration. Note that fasciculus gracilis ascends medially to fasciculus cuneatus a. 1st neuron: located in the dorsal root ganglia. Their central processes or axons ascend in either the nucleus gracilis (T6 and below) or nucleus cuneatus (T5 and above) b. 1st neuron synapses on a 2nd in the nucleus gracilis or cuneatus in the caudal medulla and crosses the midline. c. The 2nd neuron ascends in the medial lemniscus pathway until it reaches a 3rd neuron in VPL d. The 3rd neuron in VPL ascends to the primary somatosensory cortex (postcentral gyrus of the parietal lobe) 2. Lateral spinothalamic tract: carries information about pain and temperature a. 1st neuron is located in the dorsal root ganglia. Its central process reaches a 2nd neuron in the dorsal horn of the spinal cord in either lamina II (substantia gelatinosa) or lamina IV (nucleus proprius) b. The 2nd neuron crosses the midline within the anterior white commissure which is anterior to the central canal. This neuron will ascend as the lateral spinothalamic tract c. The 2nd neuron reaches VPL, where it synapses on a 3rd neuron that will project to the primary somatosensory cortex **note that the dorsal column-medial lemniscus pathway and lateral spinothalamic tract both cross the midline at different levels, which affects the hemisection in which modalities are lost 3. Dorsal spinocerebellar tract: mediates unconscious proprioception. Information never reaches the cerebral cortex a. 1st neuron is located in the DRG, its central process enters the dorsal horn of the spinal cord and synapses on a 2nd neuron in lamina VI (nucleus dorsalis) b. The 2nd neuron in the dorsal horn ascends on the same side as the dorsal spinocerebellar tract to the cerebellum via the inferior cerebellar peduncle MOTOR TRACTS (2) 4. Lateral corticospinal tract: mediates motor function a. Axons of neurons in the precentral gyrus (primary motor cortex) descend on the internal capsule b. From the internal capsule, neurons descend to the cerebral peduncle in the midbrain  c. From the midbrain, neurons descend to the pons and medullary pyramids d. 90% crossover of motor commands occurs at the pyramidal decussation. These 90% of fibers cross over to the contralateral side and descend through the lateral white matter of the spinal cord as the lateral corticospinal tract where they will innervate lower motor neurons in the ventral white horn e. The remaining 10% of fibers that did not cross over will descend as the anterior corticospinal tract. Descend within the anterior white matter and cross the midline at the level of the spinal cord where they will innervate their respective lower motor neurons 5. Rubrospinal tract: another mediator of motor function. The rubrospinal tract fibers are immediately anterior to the lateral corticospinal tract fibers. a. Axons originate in the red nucleus of the midbrain. These axons cross the midline immediately below the red nucleus as they descend through the brainstem b. Axons that crossed over at the brainstem take position in the lateral white matter of the spinal cord. They will innervate lower motor neurons in the ventral white horn. BROWN SEQUARD SYNDROME: what happens to motor and sensory function if half of the spinal cord is transected? It depends on the level of the lesion, but specific deficits are to be expected. However, all deficits will be lost below the level of the lesion. 1. Touch, pressure, vibration, and conscious proprioception will be lost on the ipsilateral side as they are traveling through the dorsal column and axons are carrying information on the same side (they have NOT crossed the midline yet) 2. Similarly, unconscious proprioception will be lost on the ipsilateral side because these fibers do not cross the midline. 3. Pain and temperature sensation will be lost on the contralateral side as these fibers cross the midline at the level of the spinal cord. They will not be able to reach the opposite side. 4. Deficits in motor function, conveyed by the lateral corticospinal tract and rubrospinal tract, on the ipsilateral side. Although axons originate on the contralateral side, they cross over at the level of the brainstem, so they bypass the lesion. ***note that if the lesion is at or below L2, these deficits will affect the respective lower limb. If above C5, they will affect the upper and lower limb, as well as the trunk. CN I: Olfactory Sensory only Nasal mucosa to Passes through cribriform olfactory bulb to primary plate of ethmoid olfactory cortex CN II: Optic Sensory only Retina to skull to LGN Passes through optic canal CN III: Oculomotor Motor only Oculomotor nucleus in Passes through the superior  midbrain to exit skull orbital fissure CN IV: Trochlear Motor only Trochlear nucleus of Passes through the superior midbrain (posterior orbital fissure surface in brainstem) CN V: Trigeminal Sensory/motor Emerges from the pons V1: thru sup. Orbital fissure to regions of the head V2: thru foramen rotundum V3: thru foramen ovale CN VI: Abducens Motor only Abducens nucleus in Superior orbital fissure pons to exit skull CN VII: Facial Sensory/only Anterior ⅔ tongue into Passes through internal skull acoustic meatus CN VIII: Sensory only From Passes through internal Vestibulocochlear cochlea/semicircular acoustic meatus canals to MGN CN IX: Glossopharyngeal Sensory/motor Sensory from posterior Passes through the jugular ⅓ tongue foramen Motor neurons from medulla to pharynx CN X: Vagus Sensory/motor Sensory from Passes through jugular thorax/abdomen/pelvis foramen Motor from medulla to muscles of palate/pharynx/larynx CN XI: Spinal Accessory Motor only Axons from cervical Enter skull through foramen spine to trapezius and magnum, exit through the sternocleidomastoid jugular foramen CN XII: Hypoglossal Motor only From the hypoglossal Passes through hypoglossal nucleus to the tongue canal AUTONOMIC NERVOUS SYSTEM: uses a 2 neuron chain 1. The first neuron is located in the brainstem or spinal cord, forming a synapse on a postganglionic cell 2. The postganglionic cell located in a peripheral ganglia projects to smooth muscle, cardiac muscle, or a gland Sympathetic division: 1. Preganglionic neurons form a vertical column in the lateral horn of the spinal cord between T1-L2, known as the intermediomedial column  2. Postganglionic neurons are located in a peripheral ganglia adjacent to the vertebral column a. Sympathetic trunk/paravertebral chain: extends from the cervical spine to base of the coccyx. Ganglia are connected to spinal nerves via rami communicans, and connected to ganglia above and below b. Prevertebral ganglia: located anterior to the vertebral column, exist as the celiac, superior mesenteric, and inferior mesenteric ganglia 3. Pathway: the preganglionic cell can connect with the postganglionic cell in one of 4 ways a. Establish contact at the same spinal cord level b. Establish contact at a different level of the spinal cord c. Pass through the sympathetic trunk to reach one of the three prevertebral ganglia d. Pass through the sympathetic trunk to reach the adrenal medulla, which will secrete epinephrine Parasympathetic division: 1. Preganglionic neurons are either located in the brainstem and associated with cranial nerves III, VII, IX, or X, or between S2-S4 2. Postganglionic neuron is found in one of five peripheral ganglia a. Ciliary ganglion: contacted by preganglionic axons of CN III, involved in visual control. Controlled by Edinger Westphal nucleus b. Pterygopalatine ganglion: contacted by preganglionic axons of CN VII, targets the lacrimal gland or mucous glands of oral/nasal cavities c. Submandibular ganglion: contacted by preganglionic axons of CN VII, targets the parotid gland d. Otic ganglion: contacted by preganglionic axons of CN IX, targets the parotid gland e. One of many terminal ganglia, located adjacent to their target organs. Contacted by preganglionic axons of S2-S4 or CN X BASAL GANGLIA: includes the caudate, putamen, globus pallidus, subthalamic nucleus, and substantia nigra. **caudate+putamen=striatum Direct pathway: “re-entrance circuit”, axons extend from the ENTIRE cortex and BACK to the MOTOR cortex, THEN become the lateral corticospinal tract 1. Input from cerebral cortex descends on the striatum (corticostriatal projection) 2. From the striatum, axons project to the globus pallidus internal segment (GPi) 3. From GPi, axons project to the thalamus, either VA or VL 4. From VA or VL, project to the motor cortex Indirect pathway: The cerebral cortex relays in the basal ganglia, then inputs relay to the motor cortex, where they will have an inhibitory effect 1. Input from cerebral cortex projects to the striatum 2. From the striatum, axons project to the globus pallidus external segment (GPe)  3. From GPe, axons project to the subthalamic nucleus **GPe ONLY projects to the subthalamic nucleus 4. From the subthalamic nucleus, axons project to GPi 5. From GPi, will project back to the thalamus (VA/VL) 6. From VA or VL, axons project back to the motor cortex Substantia nigra: 1. Compact part sends dopamine to the striatum. Dopamine has a permissive effect on the striatum, allowing these pathways to take place smoothly. Lack of dopamine leads to Parkinson’s. 2. Reticular part receives striatal inputs and projects to VA and VL of the thalamus, just like GPi. The only difference is that it has no role in the indirect pathway, unlike GPi. Blood supply to the basal ganglia 1. From middle cerebral artery, branches are called the lenticulostriate arteries CEREBELLUM: primary fissure separates anterior and posterior lobes, but anterior is only ⅓ of the cerebellum 1. Peduncles a. Superior peduncles: connect cerebellum to midbrain, contains mostly outputs b. Middle peduncle: comprised of only inputs to cerebellum from the pons c. Inferior peduncle: connects cerebellum to medulla 2. Deep cerebellar nuclei: located deep within the white matter. Inputs come from the cerebellar cortex, outputs begin from one of four of the nuclei, fastigial, globose, emboliform, and dentate 3. Spinocerebellum: more medial aspect of the cerebellum. Functions in error detection and correction with the red nucleus a. Motor signal comes from pons and meets an axon coming from the dorsal spinocerebellar tract (which is the most heavily myelinated, and fastest pathway) b. If correct to a motor pathway is needed, instead of sending corrective information to the thalamus and cortex, it is sent to the red nucleus and down the rubrospinal tract c. Is tested by the finger to nose test 4. Cerebrocerebellum: more lateral aspect of the cerebellum. Functions in motor planning and programming a. Input from cerebral cortex to pons, then to cerebellum b. From cerebellum, axons project to dentate nucleus c. Dentate nucleus projects to VL of the thalamus d. From VL, projects to the lateral corticospinal tract EYE 1. Sclera: outer, connective tissue 2. Choroid separates sclera from cornea 3. Cornea: only in the middle part of the eye, outer covering  a. Bends light (refraction) 4. Iris: contains smooth muscle, inner concentric and contract and constrict pupil (parasympathetic) and dilators under sympathetic control 5. Lens: is always convex, but ligaments can stretch it and make it less convex. More convex=better focus of light onto the retina a. Also bends light (refraction) b. Unaccommodated eye: refraction of light off the retina 6. Ciliary body: contains muscles that control the shape of the lens a. When ciliary muscle contracts, ligaments slack, and lens can take convex shape b. When ciliary muscle relaxes, ligaments pull and lens takes on less convex shape, needed for distance vision 7. Lacrimal apparatus: is stimulated by CN VII and the pterygopalatine ganglia Light transduction 1. At the retina, there are rods (more sensitivity in low light, lower acuity) and cones (better in bright light, convey color). Light stimulates these photoreceptors, relay a message to ganglion cells 2. Ganglion cell axons will become the optic nerve 3. The nasal half of the visual field detects light from the outer part of the visual stimulus, and the temporal half detects light from the inner portion 4. Axons from the right temporal field and the left nasal field will reach the right lateral geniculate nucleus. Axons from the left temporal field and right nasal field reach the left lateral geniculate nucleus. a. So temporal fields will reach the thalamus on the same side as the light originally encountered 5. From lateral geniculate nucleus, the optic radiation projects back to the visual cortex **if the optic nerve was cut on the right side, would lose vision on the right side **if optic chiasm is cut, lose temporal vision on each side (outer parts) GUSTATION 1. General sensation of the tongue a. Anterior ⅔= CN V b. Posterior ⅓= CN IX c. Epiglottis=CN X 2. Taste a. Anterior ⅔ = CN VII b. Posterior ⅓=CN IX c. Epiglottis=CN X Taste transduction 1. Information from CN VII, IX, or X ascends through a vertical column of relay cells in the medulla and projects to the primary somatosensory cortex, more specifically, the gustatory cortex AUDITION 1. Tympanic membrane deflects and moves the ossicles (malleus, incus, stapes), and footplate of the stapes plunges into the oval window cochlea which contains the organ of Corti a. When vibrational wave moves, tectorial membrane shears over the hair cells, which stimulates them b. Impulse is propagated by CN VIII to the brainstem c. Relays on dorsal and ventral cochlear nuclei, giving way to ipsilateral and contralateral projections to the inferior colliculus, MGN of thalamus, and finally primary auditory cortex 2. Fluid in the cochlea moves and at the end, the round window bulges outwards 3. CN V controls tensor tympani, CN VII controls stapedius, which act to contract when noises get too loud Vestibular apparatus: 3 sets of semicircular canals which allow perception of angular rotation of the head. Utricle and saccule are adjacent and detect linear acceleration. Utricle detects this in the horizontal plane, saccule detects this in the vertical plane