Neuroanatomy: Introduction to the Central Nervous System PDF

Introduction to Neuroanatomy: The Central Nervous System Schedule Gross Neuro tissue Brady Little, DVM, MSc - Brain - Spinal cord Neurologic Function...

Introduction to Neuroanatomy: The Central Nervous System Schedule Gross Neuro tissue Brady Little, DVM, MSc - Brain - Spinal cord Neurologic Function - Reflexes - Conscious Motor Efferent (UMN / LMN) - Proprioception - Nociception - Special senses (eyes / ears) - Cerebellum Clinical Application / Review (3 lectures)  Outline of Topics Anatomy of the Brain Central Nervous System Blood Supply Meninges, Ventricles, and Cerebral Spinal Fluid (CSF) TEXT: Veterinary Clinical Neuroanatomy Handbook. Digital copy is on canvas For supplemental understanding / explanation  Two types of CNS tissue: 1) Gray matter Neuron cell bodies Located in the cortex of cerebrum & cerebellum and cerebellum Collections of Cell bodies in the CNS are called “Nuclei” Recall that collections of neuron cell bodies in the periphery are called “Ganglia” 1) White matter Axons (and supporting cells) Centrally located in the cerebrum & cerebellum Collections of axons in the CNS are called “Tracts” Recall that collections of neuron axons in the periphery are simply called “nerves”.  Cross Section of spinal cord: location of Grey and White matter are reversed The brain and brainstem from a dorsal perspective Anatomical terms of the Brain  Cerebrum Comprised of two hemispheres which communicate via a tract called the corpus callosum (CC). Surface has a wrinkled appearance due to numerous convolutions. Gyri – elevated folds of the convolutions (singular Gyrus) Sulci – depressed grooves (singular Sulcus) Surface is comprised of gray matter (“cerebral cortex”) Darker “orange” tissue (mostly peripheral) JOB of the CEREBRUM 1) Conscious Perception of senses 2) Thoughts and reasoning 3) Initiation of consciousness movement. NOTE: Reflex pathways do not utilize the cortex. Corpus Callosum  Three Regions of the Cerebrum: 1) Cerebral cortex Outer layer of gray matter - Sensory fields – conscious perception of stimuli - Motor areas – voluntary initiation of skeletal muscle - Association areas – integration of sensory information; memory, reasoning, verbalizing, judgment, and emotion “GREY matter” 2) Basal nuclei (a.k.a. basal ganglia) Inner layer of Grey matter (cell bodies within the deeper regions of the cerebrum - Regulation of movement (example: balance, posture) 3) Internal capsule (3, 5) White matter Projection of tracts from the brain stem (thalamus) to the cerebrum All Sensory information (except smell) is directed to the cortex via the thalamus The outer cortex has been torn away to demonstrate the deeper regions of the cerebrum. Lateral view of a brain dissected to show axonal connections between the thalamus (4) and a cerebral grey matter (2). These are connected by the internal capsule (3 and 5).  Functions of the Thalamus (Th) “Relay Station” filtering information between the BRAIN → BODY All conscious sensory input (except olfaction) is relayed through the thalamus before reaching the cerebral cortex via the Internal Capsule (IC) Also associated with wakefulness IC IC IC IC IC CC IC Th Th  Five cortical lobes of each cerebral hemisphere can be externally visualized: In humans, specific named Gyrus are used to demarcate lobes. In animals, it is more common for lobes to be named for the major bones of the skull adjacent. 1. Occipital 2. Parietal 3. Frontal 4. Temporal 5. Piriform  Occipital Lobe Conscious perception of visual information – Cortical event, not an ocular event! – Reception Vs. Perception (The occipital lobe has widespread connections to other parts of the brain as well) Occipital Lobe Lesions associated with the visual cortex of the occipital lobe may produce cortical blindness (cannot perceive visual inputs) Can happen even if the rest of the visual components are intact Not all stimulus from light is directed to the occipital lobe for perception of an image (some tracts are directed to the brain stem for reflexes). Explains why pupillary light reflexes can be normal in a cortically blind individuals since the PLR pathway projects to the brainstem (NOT to the occipital lobe) Occipital lobe lesions also cause absent Menace response. Menace is not a reflex and requires cortical perception of a menacing gesture.  Parietal Lobe Contains the somatosensory cortex – Sensory input from skin, skeletal m., ligaments, tendons and joints – Pain and touch are perceived here – Integration of sensory information to produce a 3D “map” of the body’s location in space (cumulatively called Proprioception)  Parietal Lobe lesion Often leads to loss of conscious proprioception. Defined by deficits in postural reactions during a neurologic exam  Parietal Lobe – less common symptoms Lesions here can produce bizarre abnormalities of spatial perception. Awareness of certain parts of the space around the body is lost or altered. Unilateral lesions produce “hemineglect” (Failure to perceive half of one’s environment) Sometimes manifested by failure to groom one portion of the body.  Frontal Lobe Associated with judgement, behavior and personality. Responsible for initiating voluntary motor functions – This does NOT include fine tuning motor activities (that’s done by the cerebellum)  Frontal Lobe Lesions Lesions produce abnormalities of voluntary movement Clinical signs: delay or inability to initiate movement Unilateral damage results in contralateral clinical signs Contralateral relay: descending motor systems and ascending sensory systems decussate between cortex and target tissue (muscles and receptors) I.e., if the right frontal lobe has a lesion, initiation of movement on the the left side of the body will be affected. May produce alteration in attitude/personality / judgement. “Phineas Gage”  Temporal Lobe Auditory cortex: Perception and interpretation of auditory (cochlear) information Multiple decussations allow information from both ears to reach both auditory cortices cochlea project sensory stimulus to BOTH hemispheres, so destruction of unilateral auditory cortex will not produce deafness (not even in just one ear) Damage to temporal lobe would result in reduced perception of sound.  Piriform Lobe Perception of olfactory information – Only sensation that does NOT relay through the thalamus Strong connections to the limbic system – Important for autonomic (visceral) reflexes and emotional responses – Plays a major role in survival Lesions of this lobe reduce sense of olfaction.  Cerebellum ❑Anatomy: Centrally located vermis, right and left hemispheres White matter is deep to an outer cortex of gray matter ❑ Function: Coordination and fine tuning of movement ** controls Rate, Range and Force of movement** Hemisphere Vermis Hemisphere Dorsal View Mid Sagittal View  Cerebellum (Cont.) Communicates with other parts of the CNS via nerve tracts called the cerebellar peduncles (CP) The brainstem from a dorsal perspective cerebellum is removed.  Brain Stem (key for following slide) What remains after the cerebrum and cerebellum have been removed It is comprised of: Thalamus (T) Relay center for all afferent (sensory) information except smell. Hypothalamus (H) Essential in maintenance of homeostasis; has direct connection to the pituitary gland Optic tracts(OT) /optic chiasm(OC) Epithalamus – connects the limbic system to the rest of the brain (mood regulation) Near and inclusive of pineal gland (PG) melatonin secretion, photo periodicity, circadian rhythms, estrus timing, hibernation, winter coat etc. Corpora quadrigemina - Rostral colliculus (RC) - visual reflexes - Caudal colliculus (CC) - auditory reflexes Pons (P) “bridge” Fibers of the pons form the cerebellar peduncle (CP) (carry signals from cerebrum to cerebellum). All sensory information from spinal cord travel through pons to arrive at the thalamus. Cerebral Peduncles: Collection of fibers in the ventral midbrain, which connect the cerebral cortex with the spinal cord and Pons (and ultimately to the cerebellum). Medulla oblongata (MO) Junction between the brain and spinal cord All ascending/descending tracts pass through the medulla Cardiovascular and respiratory reflexes - Obex (yellow circle) CSF connection between the fourth ventricle and the central canal of the spinal cord  Dorsal View Ventral View CN II CN II OC OT OT T T H PG RC RC CC CC P Cerebral Peduncles CP CP MO CORD CORD  Limbic System Not a discrete anatomical “lobe” Group of structures Function in emotional and survival drives Pathways form a ring around the brainstem and thalamus. Involves connections between: 1. Hypothalamus: homeostasis 2. Amygdala: emotional memory, aggression 3. Hippocampus: short term memory to long term 4. Cingulate gyrus: emotion 5. Thalamus: emotional behavior  The four “F’s” of limbic function: Fighting Feeding Fleeing F______ ornicating  Blood Supply of the Spinal Cord Primary blood supply is from the ventral spinal artery Secondary supply is from the paired dorsal spinal arteries  Arterial Supply Highly anastomotic Basilar a. Unity of L/R vertebral arteries with ventral spinal artery Cerebral arterial circle (a.k.a. circle of Willis) Supplied by the basilar artery and internal carotid arteries in most species The cerebral arterial circle supplies the cerebrum and cerebellum. Ventral view  Internal Carotid aa. Cerebral arterial circle Supplied by the basilar artery and internal carotid arteries in most species Basilar a.  Meninges Central Nervous System needs protection and space for CSF and Vessels - Dura - There are two layers of Dura (2&3) - These 2 layers are never separated from each other except at dural reflections (7) - The deeper dural layer dives between hemispheres and between cerebrum / cerebellum. - The superficial dural layer remains immediately adjacent to the periosteum inside the skull. - Dura of the spinal cord (2”’) is separated from the periosteum (2’) of the vertebrae (8) by a layer of fat in the Epidural space (2”) - Arachnoid (4), Subarachnoid space (9) contains Cerebrospinal Fluid (CSF) - Pia (6) Adhered closely to CNS Skull (1) and Vertebrae (8)  Spinal Meninges Comprised of the same three layers as the cranial meninges Difference between spine and skull: There is an epidural space located between the dura and the bony vertebral canal. Target for epidural anesthesia placement  Epidural space (fat-filled between Subarachnoid space vertebra and Dura) (with trabeculae where we would find CSF) Dura Dural Reflections are formed where the 2 dural layers separate. The space created is called a “Sinus” Inside a Dural Reflection is a “Sinus” Dorsal sagittal sinus Dorsal sagittal sinus: Within the Falx Cerebri Transverse sinus: Within the Tentorium Cerebelli Dorsal sagittal sinus Between the 2 cerebral hemispheres (in the longitudinal fissure) Transverse sinuses Between cerebellum and cerebrum (in the transverse fissure) Dural Reflections - Were two Dural layers separate briefly Falx Cerebri Dural reflection between the two cerebral hemispheres Tentorium cerebelli Ventral View of Dura (brain removed) Transverse dural reflection between the cerebrum and cerebellum  Venous return from the brain and CSF is via the dural sinuses. Arachnoid villi The dural sinuses are spaces formed where the inner and outer dural layers separate. Venous blood and CSF (via arachnoid villi) are collected at the dural sinuses, which Arachnoid ultimately drain into the veins of the head  Arachnoid Subarachnoid space contains Arachnoid trabeculae; (literally means Spiderweb-like beams) Cerebrospinal fluid (CSF) is in this space and provides a fluid cushion of protection and space for vessels to travel.  Pia Mater Innermost meningeal layer. Intimately follows the brain’s gyri and sulci Grossly, PIA is seen a very thin membrane on the surface of the brain after the dura and arachnoid are removed.  Pia Mater Pia mater also Intimately lines the interior spaces of the brain called Ventricles. 2. Lateral Ventricle 3. Third Ventricle 7. Fourth Ventricle 9. Central Canal of Spinal cord  Pai also Intimately lines the brain’s interior spaces called Ventricles. Within the ventricles we can find the choroid plexus is made of specialized capillaries surrounded by PIA mater. Choroid Plexus produces CSF and is only found in the ventricles of the brain. Cerebellar Peduncles 4thV Choroid Plexus 4thV Brainstem – Dorsal View  Ventricular System Cerebrospinal Fluid (CSF) is produced by choroid plexus CSF is circulated through ventricles and central canal and finally reabsorbed into venous blood at the Dural Sinuses. Lateral Ventricle Mesencephalic Aquaduct Region of Cisterna Magna Interventricular Foramen Central Third Ventricle Canal of Fourth Ventricle spinal cord  “Cisterns” are relatively large collections of fluid. Cerebellomedullary cistern (“cisterna magna”) red circles Located between the cerebellum and the brain stem. Enlargement of the subarachnoid space. Near the Atlanto-occipital joint. Can be used for CSF collection  Objectives Understand where cell bodies / axons may be found in the CNS. Identify how the location of cell bodies within the spinal cord change according to their function. Identify each lobe of the cerebral cortex, the basic function of each lobe, and how each can be evaluated clinically. Recognize and name surface features of the CNS and how they correlate with function Refer to the “Brain Lab” presentation that is posted in E*College for a listing of structures that you will be responsible for. Comprehend the brain and spinal cord meninges, including the dural sinuses, dural reflections (i.e., falx cerebri, tentorium cerebellum), subarachnoid and epidural spaces, and differences between cranial and spinal meninges. Recognize the ventricles, blood flow, and CSF location / production of the CNS