Psyc 311A, fall 2008 Conference week 3 TA: Jürgen Germann

Transcription

1 Psyc 311A, fall 2008 Conference week 3 TA: Jürgen Germann jurgen.germann@mcgill.ca Overview: 1. Meninges 2. Cerebral cortex-cytoarchitecture 3. Diencephalon (thalamus/hypothalamus) (this replaces the part of reading 1 on the Diencephalon) 4. Basal ganglia 1. Meninges The organs of the central nervous system (brain and spinal cord) are covered by 3 connective tissue layers collectively called the meninges. They support blood vessels and contain cerebrospinal fluid. the pia mater (closest to the CNS structures); it is a delicate thin, transparent membrane that follows the curvature of the cerebral surface arachnoid mater; it is just below the dura mater and has small spider web like filaments that attach to the pia mater creating a little space (subarachnoid space, between arachnoid and pia mater) filled with CerebroSpinalFluid dura mater (farthest from the CNS); it s a thick, durable protective membrane attached to the skull. It consists of two layers and the two layers split to create the large venous channels in which CSF is deposed.

2 2. Cerebral cortex The cerebral cortex that is the grey matter that surrounds the cerebral hemispheres. The Cerebral Cortex is composed of Nerve Cells (: which create the local computational networks) and Glial Cells (: which have supportive functions). There are many different types of nerve cells that have different functions in the CNS. Cytoarchitecture: Studies the local cell arrangement of the cortex in order to classify and distinguish different regions that are suspected to serve different functions. Myeloarchitecture: Studies the local arrangement of myelinated fibers to classify cortical regions. Different Stains being used to make Cytoarchitectonic Maps: -Weigert Stain: Stains the myelin of the Cell Axons. -Nissl Stain: Stains the Cell Bodies. -Golgi Stain: Stains the whole Cell but not all cells in a slice. Subdivisions of Cerebral Cortex: - Archicortex: 3 layered Cortex (Hippocampus) - Paleocortex: 3-5 layered Cortex transition cortex (Parahippocampal Cortex) Together the archicortex and paleocortex constitute the allocortex or heterogenetic cortex

3 - Neocortex: 6 layered cortex. e.g.: most of the Cerebral Cortex of Cerebral Hemispheres. The neocortex can also be referred to as the homogenetic cortex. Korbidius Brodmann (1908/1909) Very renowned scientist in the field of cytoarchitecture (fellow of Oscar and Cecelia Vogt). He created the most widely used cytoarchitectonic map with approximately 50 different areas named with different numbers (noted as Brodmann area [BA] #). The function of the various areas is studied using: - Stimulation of exposed cortex during neurosurgery in awake patients - Recording of electrical potentials during the presentation of different sensory stimuli - In vivo neuroimaging of brain functions with PET, fmri and other imaging techniques.

4 Important remarks A few specific areas you already know: Primary Motor Cortex (cortex lining the caudal precentral Gyrus in particular the rostral bank of the central sulcus / BA 4 / M1) Premotor Cortex (cortex lining the rostral part of the precentral gyrus / BA 6) Primary Somatosensory Cortex (cortex lining the post- central gyrus / BA 3, 1 & 2 / S1) Primary Auditory Cortex (Caudal temporal operculum / cortex lining Heschl s Gyrus/i / Transverse Gyrus/i / BA 41(42), A1) Primary Visual Cortex (Cortex lining the banks of the Calcarine Sulcus / BA 17/ Striate cortex / V1) The primary motor and the premotor areas (BA 4 and 6) do not show a layer IV and are thus called agranular. The two differ because the primary motor cortex has large pyramidal neurons in layer V called Betz cells. Rostral to the premotor cortex the cortex of the pars opercularis (BA 44) shows an ill-defined/inconsistent layer IV and is thus called dysgranular. All primary sensory neocortical areas (S1,A1,V1) have a greatly expanded layer IV (input layer). The large population of granule cells give it a dust-like appearance and cortex with that characteristic is thus called: koniocortex (dust-cortex) The Diencephalon is the part of the cerebral hemispheres that lies in the depth forming the roof of the Brainstem. It is a collection of subcortical nuclei that are arranged around the third ventricle. It has important connections to sensory,

5 motor as well as limbic pathways and acts as a relay station for all senses apart from olfaction and also has important control functions for homeostasis. The lateral walls of the diencephalon are formed by the internal capsule. The ventral surface of the diencephalon is formed by the pituitary gland and mammillary bodies and the optic chiasm. The Diencephalon is composed of the thalamus, the hypothalamus that lies rostroventral to the thalamus, and other structures like the epithalamus (dorsal) and the subthalamus. Thalamus The Thalamus is a bilateral subcortical structure composed of numerous nuclei that have specific connections with the cortex and serve different functions. In most people, a fiber system crosses the midline joining the right and left thalami through the third ventricle. This fiber system can be clearly seen on the medial view of the brain and it is called the Massa Intermedia or Interthalamic Adhesion. Three nuclei you will need to know: - The lateral geniculate body (or nucleus) of the thalamus is in the lateral aspect of the caudal thalamus and it is a relay nucleus for vision projecting to V1. - The medial geniculate body (or nucleus) of the thalamus is in the medial aspect of the caudal thalamus and it is a relay nucleus for audition projecting to A1 (Heschl s gyri). - The anterior nucleus of the thalamus is in the most rostral aspect of the thalamus and it is involved in memory. It receives input from the hippocampus via the fornix and projects via the mammillothalamic tract to the mammillary bodies and also to the cingulate gyrus. It is part of the circuit of Papez.

6 Hypothalamus - Hypothalamus The Hypothalamus is a group of nuclei that form the anterior portion of the walls and floor of the third ventricle. These structures are involved in visceral, endocrine and, metabolic activity as well as emotional behaviour, sleep, thirst, hunger and temperature regulation. The Ventral hypothalamus: Optic Chiasm Decussation of the optic nerves. Hypophysis (Pituitary Gland + Infundibulum) Rostroventral to the Hypothalamus it secretes hormones regulating homeostasis Mammillary Bodies Termination of the Hippocampal Fornix. These structures are connected with the anterior thalamic nucleus via the Mammillothathalamic tract. The other structures (Epi- Subthalamus) Subthalamus Bilateral subcortical nucleus that is found ventral to the thalamus and lateral to the hypothalamus. Epithalamus The Epithalamus that is mainly composed of the Pineal Gland is a structure that is implicated in endocrine functions (circadian rhythm). The Pineal Gland can be seen in the posterior view of the brain just superior to the colliculi of the midbrain.

7 4. Basal Ganglia From an anatomist s point of view (our definition): Basal ganglia are all subcortical structures within the cerebral hemispheres not including the diencephalon (thalamus, hypothalamus ). = Caudate nucleus, putamen, globus pallidus, claustrum, amygdala From a clinician s point of view: Basal ganglia are a collection of large subcortical nuclei that are part of the extrapyramidal (motor) system. The term Extrapyramidal System refers to a

8 system involved in motor function not served by the motor cortex via the corticospinal tract also called pyramidal tract. Damage to this system causes Extrapyramidal syndromes such as muscular rigidity, tremor, motor slowing and, involuntary movements. = Caudate nucleus, putamen, and globus pallidus, together with other subcortical structures such as the subthalamus, substantia nigra, etc. The amygdala and claustrum are subcortical nuclei but they do not participate in motor functions The location of the caudate/putamen/globus pallidus/ amygdala Caudate/putamen/globus pallidus/ amygdala in lateral and medial view

9 Naming issues Corpus striatum (largest component of the basal ganglia) this term is used to describe the: Caudate nucleus, putamen, and globus pallidus. The terms Neostriatum, dorsal striatum or simply striatum refer to the caudate nucleus and putamen that are the phylogenetically newer parts of the corpus

10 striatum. Bridges of gray matter connect the two nuclei. These bridges that indicate the common origin of the two structures are especially pronounced in the anterior limb of the internal capsule between the head of the caudate nucleus and the anterioraspect of the putamen. The terms Pallidum and Paleostriatum refer to the globus pallidus that is different from the caudate nucleus as well as the putamen in both its histology as well as in its anatomical connections. Lentiform nucleus is an anatomical term that describes the p utamen and the globus pallidus together. These two structures although very different histologically they are next to each other in coronal and horizontal sections and they appear as one triangular structure. More details one the different components of the Basal Ganglia: Caudate nucleus (a term derived from a Latin word that means "having a tail"): Head-Body-Tail. This structure is part of the neostriatum. It is a C- shaped structure with an expanded rostral extremity, its head, which tapers down in size to form its body and tail. The head forms a convexity in the lateral floor of the anterior horn of the lateral ventricles. The body forms the lateral wall of the body of the lateral ventricles. The tail occupies a position in the roof of the inferior (temporal) horn of the lateral ventricles. In essence, it follows the curvature of the lateral ventricles from the floor of the anterior horn and the body to the roof of the inferior horn of the lateral ventricles. Putamen: this subcortical structure that is also part of the neostriatum is separated from the caudate nucleus by the anterior limb of the internal

11 capsule. In the frontal lobes, the caudate nucleus and putamen are continuous around the anterior tip of the internal capsule. Globus Pallidus: wedge-shaped structure between the putamen and the internal capsule. The globus pallidus is composed of two segments, a medial and lateral one, that can be easily distinguished in coronal and horizontal sections. *Amygdala: The amygdala is a bilateral structure located in the medial part of the temporal lobe just in the depth of the uncus (the most medial bulging of the parahippocampal gyrus). This structure consists of several sub-nuclei. It is the phylogenetically oldest part of the basal ganglia. The amygdala is found rostral and dorsal to the hippocampus. The tail of the caudate nucleus courses along the roof of the inferior horn of the lateral ventricles and terminates near the amygdala. The stria terminalis, a projection fiber system originating in the amygdala, travels next to the caudate nucleus to terminate in the hypothalamus. The amygdala is a component of the limbic system having primarily olfactory, visceral, endocrine, and behavioural functions. It is a key structure in emotional processes and formation of emotional memories. Since it has no role in motor control it has traditionally been excluded from the clinical definition of the basal ganglia. *Claustrum: this is a small subcortical nucleus that looks like a thin sheet of grey matter medial to the insula and the extreme capsule. The claustrum is lateral to the lentiform nucleus and the external capsule. Its functions are not well understood, although it seems to be related in function to the insula.