CNS Anatomy and Organization

Objectives of the Lecture

• The lecture aims to build an anatomical foundation for understanding neurological diseases.
• It revises the organization of the Central Nervous System (CNS).
• The lecture explores the functions of the cerebral cortex and how lesions affect its function.
• It covers the types of white matter, with a focus on the internal capsule and its clinical importance.
• Explores the morphology and organization of the brainstem relative to brainstem lesions.
• Reviews the fundamental anatomy of the cerebellum.
• Details basic cross-sectional and radiological anatomy.

Basic CNS Organization

• The CNS is organized with grey matter on the outer portion and white matter on the inner portion, as opposed to the spinal cord.
• There are 31 pairs of spinal nerves consisting of 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal nerves.
• The rami of spinal nerves are mixed after exiting the spinal nerve.
• Glia supports and nourishes neurons.
• Cell bodies are grouped into nuclei within the CNS, while axons form tracts; in the Peripheral Nervous System (PNS), cell bodies form ganglia and axons form nerves.
• Dorsal refers to motor/efferent functions, ventral refers to sensory/afferent functions.
• Myotomes are specific muscles innervated by motor nerves, Dermatomes sends sensory information from a specific area of skin.

Anatomical Concept Map

• Telencephalon includes the cerebral hemispheres.
• Lateral ventricles are in the telencephalon and connect in the midline via the foramen of Monro.
• The Cerebral cortex is responsible for higher level of control and is grey matter.
• Basal Nuclei are grey matter and are 2 egg-shaped structures on brainstem.
• The Diencephalon refers to the interbrain, made of the thalamus and hypothalamus.
• The third ventricle is the cavity of the diencephalon.
• The hindbrain's cavity is the forth ventricle.
• The dorsal is the pons
• The medulla represents the most distal part of brain.
• The medulla has brainstem.
• The midbrain is between the diencephalon and mesencephalon.
• White matter connects cortical areas and represents association fibres in same hemispheres.
• Commissural fibres connects hemispheres and Corpus callosum connects hemispheres.
• Projection fibers represents ascending and descending and is anteriorly in midbrain or cerebellum
• The cerebral peduncle connects cerebrum to midbrain.
• The superior cerebellar peduncle cerebellum to brain stem with pdeuncles.
• Cerebral hemispheres are the largest, and midline and medial views see diencephalon and midbrain.

Cerebral Cortex Lobes and Areas

• Gyri and sulci are named to identify locations in the cerebral cortex.
• Key sulci include the central sulcus, pre-central sulcus, post-central sulcus, lateral sulcus, superior & inferior frontal sulci, parieto-occipital sulcus, and calcarine sulcus.
• Key gyri include the superior/middle/inferior frontal gyri, supramarginal gyrus, angular gyrus, cingulate gyrus and parahippocampal gyrus.
• The insula lobe hidden below frontal lobe.
• The Lateral view of the name Gyri and Sulci does not reach lateral fissure.
• The Calcarine Sulcus is part of the Medial View of Cerebral Cortex.
• Understand the locations and roles of primary, unimodal, and multimodal cortical areas.

Functional Cortical Areas

• Cerebral cortex handles perception, information processing, decision making, and execution of planned processes.
• Sensory cortical areas perceive basic and detailed sensations.
• More detailed processing and decision-making occur in multimodal association areas.
• The motor cortex is in charge of the response that is executed by the primary motor cortex.
• Sensory pathways go from the sensory areas first to unimodal then to multimodal.
• Changes in the enviroment influences the sensory input.

Functional Cortical Areas

• Primary sensory areas provide basic perception, while unimodal sensory association areas refine this perception.
• Multimodal association areas integrate multiple sensory inputs and make decisions.
• The unimodal motor handles planning of movements and pre-cenral gyrus is primary.

Primary and Unimodal Area Function

• 1ry Somatosensory Cortex (post-central gyrus): tactile information (feel, localize, intensity), receives inputs and initiates direct motor commands
• Unimodal Somatosensory handles stereognosis and graphesthesia.
• 1ry Auditory Cortex: hears simple sounds and pitch and is responsible for integrating sensory inputs.
• Unimodal Auditory recognizes different types/tones of voices.
• 1ry Visual Cortex (either side of Calcarine sulcus): sees colors, edges, light/dark and manages recognizition skills.
• Unimodal Visual Cortex: recognizes visual inputs meaningfully (faces, animals, objects)
• The Supplementary Motor Area focuses on limbs and the Frontal eye field focuses on volunatry eye movements.

Frontal Eye Field Function

• The Frontal Eye Field coordinates extraocular muscles to move eyes to the contralateral side.
• A lesion in the right FEF causes the eyes to deviate to the right and will have preference.

MultiModal Association Areas (MMAA)

• Responsible for detailed processing, decision-making and integrating sensory units.
• There are 3 main MMAA.
• Posterior MMA (PMAA) located in and around supramarginal gyrus.
• Non dominant impacts Tactile and Visuospatial awarenessInternal, the body affects External Environement
• Dominant handles Mathematic skills, Identifying fingers, Writing and left-right orenetation.
• Anterior MMA in prefrontal cortex, for attention, thinking and decision making
• Impact: Impulse control, behaviors.suppression of inappropriate
• Limbic MMAA loacted in medial temporal lobe handles cingulate gyrus, ortbiofrontal cortex for emotional and memories

Limbic System

• Collection of cortical and subcortical structures on the medial aspect of the brain
• Form a "C" shaped arrangement.
• Limbic Cortex: Cingulate gyrus, Parahippocampal gyrus & Uncus and Orbitofrontal surface, Temporal pole.
• Deep structures: Hippocampal formation – Hippocampus, Dentate gyrus, Subiculum, Amygdala and Fornix.
• Connected structures: Mammillary bodies - via fornix and Thalamus and Hypothalamus – via mammillothalamic tract.

Limbic System Function

• It is important to remember functions of limbic system include such as, stress, motor control.
• Controls stress, emotional, endocrine, sensory stimuli.
• Damage: olfactory impairment, agitiation, uncontrolled emotions, abnormal biological rhythms, abnormal sexual behaviour, memory impairment
• Impact: Thalamus, hypothalamus
• Consolidation & formation of new memeories impacts amygdala.

Language Processing

• Auditory cortex, Wernicke's area, Angular gyrus, Arcuate fasiculus and Broca's area
• Intact comprehension and speed but repetition of words and speed is not.
• Understand language written works and how to apply them
• Expressive Dysphasia means can comprehend but hard to speak- non fluen.t

Somatotopic organization

• Specific areas of the primary somatosensory and motor cortices correspond to specific body areas.
• Areas with fine motor skills/dense sensory innervation have a larger cortical representation (e.g. hands, face).
• This arrangement carries into subcortical areas (internal capsule, thalamus, spinal cord)

Frontal Lobe Functions & Dysfunction

• Precentral gyrus handles execution of voluntary movements, and when there is damage it causes contralateral weakness
• Motor association area handles planning of volunatry movements causing Apraxia.
• Frotnal Lobe controls Eye movements.
• Broca's area handles causes and expressice dysphasia.
• Prefrontal Cortex handles working memory causes decision making.

Parietal Lobe Damage

• Left sided damage: Finger knows, acalculia,
• Right sided damaged: Neglect/inability to recognize body

Temporal/Occipital Lobes

• Temporal handles adutiory functions while Occipital lobe handles vision
• The Wernicke area is important in communication
• Damage in both areas causes the body ability to create function

Basal Nuclei Functions and Classification

• These are a groups of subcortical collections of grey matter and are Telencephalic and pallidum that helps for the motor of the nuecli
• Basal Nuclei: For initiation and maintenance of voluntary movements and inhinit involuntary (unwanted) movements.
• Impairments of the Basal ganglia causes reduced inputs to thalamus causing cognitive and emotional functions and motor memeory.

White Matter

• Association Fibers are areas of cortex with in the cerebral.
• Commisures are are connect hemispheres
• Projection fibres are connecting cortext wit the subcortical
• Three main fibers are Superior longitudinal fasciculus, Inferior longitudinal fasciculus and Arcuate fasciculus.

Projections Fibre

• These projections connect the Cerebral cortex and subcortical areas.
• They also include all the efferent and afferent pathways that include cortex and subcortical.
• Most of these pathways run close together, internal capsule, Corona radiata and cerebral peduncles and cerebellar peduncles and all long tracts running in the brainstem.

Internal Capsule

• Paired White Matter helps motor.
• Anterior Limb: Thalmic radiation, and cortico fibres coming pyramind neurons, and genu that motor pathway
• Posterior Limb has superio radiation carring Somatic.
• Radiation helps carrying aduitory fibers.

All Sensory and Motor projection

• Fibers pass throught eh cerebral Peduncles which helps with internal capsules
• Motor: Sensory, cornoal Radiata Thalamus
• It is important to understant all sensory and information.

Brainstem

• Similar to ther Parts of CNS include grey and white Matter for connecting spinal
• Grey Matter arranged in Niceli
• It important for to rememebr level function as conssenics

Radiology

• Isonde is the brain matter
• Hyper and hypo is bone
• CSF is hyperdose and blood
• CT IS BONE and MRI. Radiological Anatay
• Gray for basel with cortex.
• Ventricular radiology.

Cerebellum

• Consists of 2 cerebellar hemispheres linked by the vermis.
• main lobes (Anterior, Posterior and Flocculonodular)
• Horizontal fissure divides the posterior lobe superior and inferior.
• Attached to the 3 parts of the brainstem by the 3 sets of cerebellar peduncles containing input and output cerebellar pathways.
• Main function is to coordination/supervision of movements using sensory inputs from muscle & joint proprioceptors and feed back into motor cortices.

Cerebellum

• Region: Inferior Vermis and the flocculonodular lobe maintains posture/equilibrium and moves movements.
• Spinalcerebellum: Superioy moves adjantent and allows axial motor.