1. The basic anatomy of the Central Nervous System (CNS)

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1 Psyc 311A, fall 2008 Conference week 1 Sept 9 th to 11 th TA: Jürgen Germann; jurgen.germann@mcgill.ca Overview: 1. The basic anatomy of the Central Nervous System (CNS) 2. Cells of the CNS 3. Views and Planes of the CNS 4. Directional terms 5. Subdivisions of the cerebral hemispheres: the lobes 1. The basic anatomy of the Central Nervous System (CNS) Cerebrum Brainstem Spinal cord 1

2 Further subdivisions are best seen in a medial view Cerebral hemisphere Diencephalon Midbrain Pons and Cerebellum Medulla oblongata Brainstem Midbrain Pons and Cerebellum Medulla oblongata 2

3 I. CEREBRUM Cerebral Hemispheres Cerebral cortex (Grey matter surrounding the hemispheres) White matter (Myelinated nerve axons connecting different areas in the brain) Subcortical grey matter or Subcortical nuclei (Grey matter within the cerebral hemispheres. e.g. Basal Ganglia) Ventricular system (Cavities in the brain filled with Cerebrospinal fluid: Lateral Ventricles, Foramen of Monro/Interventricular Foramen) Diencephalon The Diencephalon is the part of the Brain that lies within the two cerebral hemispheres and forms the roof of the Brainstem. It has important connections for example to sensory, motor pathways and acts as a relay station for most senses. Thalamus; the largest structure of the Diencephalon Hypothalamus Subthalamus Epithalamus Ventricular system: Third ventricle Grey matter white matter Gray matter (nerve cell bodies) Cortex Subcortical grey matter (Basal Ganglia) White matter (axons, fibre bundles) Efferent = away from a structure Afferent = towards a structure NOTE: the Diencephalon is situated medially to the Sylvian fissure 3

4 II. BRAINSTEM The Brainstem is siutated in between the Diencephalon and the spinal cord of the CNS. It controls bodily functions and special senses. All the white matter fiber tracks connecting the cerebrum with the spinal cord travel within the brainstem. The brainstem also contains a number of nuclei for visceral, special senses and other functions. Ventricular system: fourth ventricle & aqueduct of Sylvius/Cerebral Aqueduct Parts: Midbrain (Mesencephalon) Pons and Cerebellum (Metencephalon) Medula Oblongata (Myelencephalon) THE CEREBELLUM The Cerebellum that is part of the Metencephalon is important for motor coordination and smoothness of motor responses, regulation of muscle tone and maintenance of equilibrium. It is composed of two cerebellar hemispheres that have ipsilateral connections with the body. Major subdivisions of the central nervous system Major components Embryonic componenet Adult derivate Ventricular cavity Brain (Encephalon) Cerebrum Prosencephalon (Forebrain) Telencephalon (Endbrain) Cerebral hemispheres (cortex, white matter and subcortical grey) Lateral ventricles Diencephalon (Interbrain) Diencephalon (thalamus, hypo-, sub-, and epithalamus) Third ventricle Brainstem Mesencephalon (Midbrain) Mesencephalon (Midbrain) Midbrain Cerebral aqueduct (aqueduct of Sylvius) Rhombencephalon (Hindbrain) Metencephalon (Afterbrain) Pons and Cerebellum Fourth ventricle Myelencephalon (Medulla) Medulla oblongata Spinal cord Neural tube Spinal cord Central canal 4

5 Cerebrum Brainstem 2. Cells of the CNS: nerve cells (neuron) Nerve cells consist of a cell body (or soma) with branching dendrites and a long axon. Information flow is from the dendrites to the soma (axon hillock) and down the axon in form of action potentials. There are many different types of nerve cells that have different functions in the CNS. For example pyramidal cells with their long axons form the corticospinal tract, whereas, stellate and granule cells have short axons and form local processing units in the grey matter cortex. Neuronal information is transferred between nerve cells through synapses. Neurotransmitter is released at the axon terminals transferring the signal to the postsynaptic dendrite of another cell. 5

6 Nerve cells Beside nerve cells the brain consists of glial cells, they make up 90% of brain cells. They do not convey neuronal signals but perform many of the protective and supportive functions of the nerve cells. There are many types of glial cells: astrocytes, oligodendrocytes, microglial cells etc. 3. Views and Planes of the CNS 3 views: Lateral view,medial view, Ventral/orbital view 3 planes Horizontal/axial plane/section, Coronal/frontal plane, Sagittal plane Lateral view (what hemisphere?) 6

7 Medial view ventral/orbital view Planes/axes 7

8 Coronal/frontal plane Horizontal/axial plane 8

9 Sagittal plane 4. Directional terms rostral dorsal ventral Brainstem, Spinal cord caudal Cerebral hemisphere, Diencephalon ventral rostral caudal dorsal 9

10 Directional terms Rostral = towards the beak/mouth (rostrum = latin beak ) Caudal = towards the tail (caudum= latin tail ) Ventral = towards the belly (ventrum= latin womb ) Dorsal = towards the back (dorsum = latin back ) ; Can also use superior/inferior; anterior/posterior; those do not change between brainstem and cerebrum The neuronal axis changes between the cerebrum and the brainstem/spinal cord. This is because humans walk upright and thus the cerebrum in tilted by 90 0 compared to other species. Other useful terms: - Unilateral (only on one hemisphere) - Bilateral (on both hemispheres) - Ipsilateral (in the same hemisphere) - Contralateral (in the opposite hemisphere) - Distal (far from a structure) - Proximal (close to a structure) Directional terms lateral medial medial lateral Medial = closer to the midline Lateral = further away from the midline 10

11 5. Subdivisions of the cerebral hemispheres: the lobes Central sulcus Parietoccipital sulcus Sylvian fissure Preoccipital notch 5. Subdivisions of the cerebral hemispheres: the lobes The cerebral hemispheres can be divided into four lobes (frontal, parietal, occipital and temporal). Some scientists though have added a fifth lobe that is the grouping of several medial structures that are involved in memory and emotions. This lobe is called the Limbic lobe. Carpenter in addition refers to the Insula as the Insular lobe. Very few anatomists agree with the separation of the insular cortex into a separate lobe. The determining landmarks to separate the different cerebral lobes are: the Lateral/Sylvian fissure, the Central/Rolandic fissure, the Parietooccipital sulcus, and the Preoccipital notch. The central sulcus forms the boundary between the frontal and parietal lobes. An imaginary line traced between the parietooccipital sulcus and the preoccipital notch delineates the occipital lobe, and an imaginary extension of the Sylvian fissure towards the previously defined imaginary line separates the frontal and parietal lobes from the temporal lobe 11