Chapter 3 CNS Gross Anatomy Chris Rorden University of South Carolina Norman J. Arnold School of Public Health Department of Communication Sciences and Disorders

Key Objective To be able to identify the level of the CNS by recognizing the landmarks in transverse, horizontal, and coronal sections Brain, brainstem, spinal cord Requires practice and drill Use book, atlases and software Look for shape, size, location and proximity to other features.

Pyramidal Tract Changes Ventricular Changes Easy to spot changes Pyramidal Tract Changes Cortical + Subcortical Ventricular Changes All levels – including fourth ventricle and brainstem Changes in shape of brainstem and spinal cord

Horizontal and Coronal Views Crucial anatomy Horizontal and Coronal Views Pyramidal Tracts Cerebellum Thalamus Internal Capsule Basal Ganglia Putamen Globus Pallidus Caudate Nucleus Hippocampus Fornix Ventricles Corpus Callosum Optic tract Insula

Aka ‘Corticospinal tract’. Pyramidal tract Corona Radiata Aka ‘Corticospinal tract’. Massive bundle of axons that contect cortex to spinal cord. Mostly voluntary motor control. http://library.med.utah.edu/kw/hyperbrain/syllabus/syllabus10.html

M1 is principle origin for pyramidal tract. Primary Motor Cortex M1 is principle origin for pyramidal tract. Spatial organization (homunculus) M1: movement S1: sensation

Pyramidal Cells Neurons in layers V and VI send axons long distances. Layer V of M1 the pyramidal cells are extremely large. (Betz cells). Dendrites go into superficial layers. Axon travels down pyramidal tract.

Corona Radiata Near the motor cortex, we refer to the fibers of the pyramidal tract as being in the ‘corona radiata’.

Internal Capsule Near the basal ganglia, the pyramidal tract forms the central body (genu) of the internal capsule. Internal capsule and neighboring basal ganglia often injured by small strokes.

Peduncles Pes Pedunculi (part of Cerebral peduncle) A P A P

Motor Fibers in the Pons A Corticospinal Tract A P

Motor Fibers in the Medulla Pyramidal Tract P A

Motor Fibers in the Spinal Cord Lateral Corticospinal Tract Pyramidal Tract A

CSF Lateral Ventricles Third Ventricle Fourth Ventricle Cerebral Aqueduct Lateral Ventricles Third Ventricle Fourth Ventricle

Ventricles

Look for relationships and shapes of structures Sections of the Brain Note whether views are Axial (Horizontal) Views Coronal Views Less need for familiarity with sagittal view Look for relationships and shapes of structures

Cerebellum Heavily folded appearance – huge number of neurons.

Thalamus Difficult to see on MRI scan – similar contrast to nearby white matter Major portion of diencephalon

Thalamus Sensory information is relayed to the cortex via the thalamus. Auditory, somatic, visceral, gustatory and vision (but not smell) each have dedicated nuclei in thalamus. Not just relaying information: thalamic nuclei have reciprocal connections with cortex. Regulates level of awareness - damaged can lead to coma.

Thalamus: medial, posterior to basal ganglia Cleft for Internal Capsule Head of Caudate Nucleus Thalmus Putamen Amygdaloid Nucleus Tail of Caudate Nucleus Lateral View

Thalamus Not seen on the more anterior coronal slices.

Basal Ganglia Basal Ganglia (CN+Putamen referred to as striatum) Caudate nucleus near lateral ventricle Putamen (yellow): superficial Globus pallidus (green): deep Nucleus accumbens: (not shown – junction of CN and Putamen) Function: initiating action. Involved with parkinson disease. Also involved with motivation, addiction.

Basal Ganglia Coronal slices

Papez Circuit A Hippocampus, fornix and mammillary body crucial for long term memory. A difficult structure to visualize. P

Hippocampus Hippocampus: coronal view reveals folded shape. Fornix also visible in this view.

Corpus Callosum Massive white matter bundle that connects the two hemispheres

Sometimes surgically severed to treat epilepsy Corpus Callosum Sometimes surgically severed to treat epilepsy ‘Split brain patients’ Connections mostly homotopic

The optic tract Lesions at different locations lead to different forms of visual field cuts. Important diagnostic tool to infer brain injury. Lateral Geniculate Nucleus (Thalamus) V1 Primary Visual Cortex

Visual Defects Field defects reveal anatomical injury Monocular blindness Monocular quadrantanopia Bitemporal hemianopia Homonymous hemianopia Upper quadrantanopia Lower quadrantanopia

V1 Primary visual cortex (V1) lies in calcarine fissure. Complete damage leads to Homonymous hemianopia. Partial damage leads to scotomas

V1 – retinotopic mapping V1 is retinotopic: distorted spatial map of visual scene Fovea has massively over represented.

Insular Cortex Insula: below the portions of the frontal, temporal, and parietal lobes Insula: damage to this area has been linked to verbal dyspraxia Dyspraxia: a dysfunction of motor planning in the absence of muscular weakness or muscular dysfunction In the insula, it would be damage producing the simplest verbal gestures Parahippocampus: emotional memory center

Insular Cortex Sometimes referred to as Insular Lobe Operculum (lids) separate the insula and the superficial cortex. Temporal Operculum (inferior bank) Parietal Operculum (posterior+superior) Frontal Operculum (anterior+superior)