Structure of the Nervous SystemCHAPTER 3

Directions in the Nervous System  Anterior/Rostral = Front  Posterior/Caudal = Back  Dorsal = Top  Ventral = Bottom  Lateral = Toward the side  Medial = Toward the midline  Ipsilateral= Same side  Contralateral= Opposite side Fig. 3.1

Coronal Coronal *Cross Section or *Frontal Section Transverse section at right angles to the neuraxis. Brain Slices and Planes Coronal Fig. 3.2

Sagittal Section Section parallel to neuraxis and perpendicular to the ground. Midsagittal Plane – special type of sagittal section through the corpus callosum separating the hemispheres. Brain Slices and Planes Sagittal Fig. 3.2

Horizontal Section Section made through the brain parallel to the ground. Brain Slices and Planes Horizontal Fig. 3.2

Meninges The MENINGES  Meninges  Dura Mater – tough, flexible outermost layer.  Arachnoid Membrane – middle layer of the meninges. Subarachnoid Space – space between arachnoid membrane and pia mater filled with CSF.  Pia Mater – last layer of the meninges, which adheres to the surface of the brain.

The Ventricular System  CSF surround the brain (protection)  Four ventricles (lateral-2, third and fourth connected by cerebral aqueduct)  Choroid plexus- produces CSF (125 ml/day)  Arachnoid granulations: absorb CSF Figure 3.4  Obstructive hydrocephalus Figure 3.6

Development of the CNS  Begins around 18 th day after conception  A patch of tissue on the dorsal surface of the embryo becomes the neural plate

Development of the CNS Figure 3.7 Neural plate folds to form the neural groove

Development of the CNS  The neural groove then fuses to form the neural tube…  Walls of the neural tube become the CNS  Neural crest becomes the PNS Figure 3.7

Brain Development Figure 3.8  Early and later development of the human nervous system

Cellular Development  Totipotent – earliest cells have the ability to become any type of body cell Stem cells  Multipotent – with development, neural plate cells are limited to becoming one of the range of mature nervous system cells Progenitor cells

Migration of Neurons  Once cells have been created through cell division in the ventricular zone of the neural tube, they migrate  Migrating cells are immature, lacking axons and dendrites  Inside-out migration  Progenitor cells have limited capacity to replicate  First Step: Symmetrical Division  Progenitor -> progenitor  Increases the size of the ventricular zone Figure 3.10

Second: Asymmetrical Division  Asymmetrical division (7 weeks after conception)  First produces radial glia  Cell bodies of RG in the VZ and processes extend to the pia  Guide the migration of new neurons (neurogenesis)  Ends after 3 months development where a progenitor cell divides into one progenitor cell and one brain cell

Cellular Development and Migration  Cajal-Retzius cells  Develop after radial glia  Migrate to just inside the pia (Layer 1)  Orderly migration: Build on each successive layer All end up below C-R

Anatomical Subdivisions

Anatomy Basics Major Division Ventricle Subdivision Principle Structures Midbrain Hindbrain Forebrain Lateral Third Telencephalon Diencephalon Cerebral cortex Basal ganglia Limbic System Cerebral aqueduct Mesencephalon Metencephalon Tectum Tegmentum Fourth Cerebellum Pons Myelencephalon Thalamus Hypothalamus Medulla oblongata

The Forebrain  Largest section of the brain, comprised of the: Telencephalon Cerebral hemispheres Cerebral Cortex Limbic System Basal Ganglia Diencephalon Thalamus Hypothalamus Figure 3.8

The Forebrain  Telencephalon – contains most of the cerebrum. 1. Cerebral Cortex – thin, wrinkled layer of tissue covering the brain consisting of sulci (groove), fissures (big groove), and gyri (convolution). Frontal Lobe Parietal Lobe Temporal Lobe Occipital Lobe Figure 3.8 Figure 3.16

The Forebrain  Telencephalon Primary cortices Visual cortex Auditory cortex Somatosensory cortex Motor cortex Association cortices Associated with all primary cortices Figure 3.16 Figure 3.15 Figure 3.16

Limbic System 2. Limbic System – set of structures involved in learning, memory, and emotion. Major structures of the limbic system include: Limbic Cortex (cingulate!) Hippocampus Amygdala Fornix Mammillary Bodies (part of the hypothalamus) Figure 3.19

Basal Ganglia 3. Basal Ganglia – set of structures involved in processing information for motor movement. Major structures of the basal ganglia motor system include: Caudate Nucleus Putamen Globus Pallidus Figure 3.20

Forebrain: The Diencephalon  Thalamus and hypothalamus  Thalamus  Thalamus:  Dorsal diencephalon  Two lobes connected by the massa intermedia  Many nuclei LGN MGN Cerebellum->VLN-> motor Figure 3.8

Forebrain: The Diencephalon Figure 3.21 Hypothalamus  Below thalamus  Many nuclei  Many diverse behaviours  Endocrine- Pituitary Hypothalamus regulates the autonomic nervous system, controlling the pituitary gland, and integrating species-typical behaviors.

Hypothalamic Portal System  Endocrine system  Hormones are secreted from the hypothalamus through the venous portal system to anterior pituitary  These stimulate hormone release from AP Can control other glands or the hormones are the messengers AP- ‘master gland’ Gonadotropin-releasing hormone causes the anterior pituitary gland to secrete gonadotropic hormones, which play a role in reproductive physiology and behavior  Hypothalamus also releases hormones in the posterior pituitary  oxytocin - stimulates milk ejection and uterine contractions during childbirth  Vasopressin - regulates urine output by the kidneys

The Midbrain Figure 3.8  Also known as the mesencephalon and is comprised of the tectum and tegmentum.  Tectum (roof) – contains the superior (vision) and inferior (auditory) colliculi (singular is colliculus).  Tegmentum (floor) – contains the periaqueductal gray matter, reticular formation, red nucleus, and substantia nigra all of which share a role in motor movement. Figure 3.23c and d

The Hindbrain  The Hindbrain  Contains both the metencephalon and the myelencephalon. Figure 3.8

The Hindbrain Metencephalon – a structure comprised of the cerebellum and the pons. Cerebellum – appears as a mini brain and is involved in motor coordination. Pons – contains part of the reticular formation and is involved in sleep and arousal. Figure 3.23

The Hindbrain Myelencephalon – contains the medulla oblongata containing portions of the reticular formation Is involved in basic life functions, such as respiration and regulation of the cardiovascular system. Figure 3.23

The Central Nervous System  The Spinal Cord  Function: distribute motor fibers to the effector organs of the body (glands and muscles) and to collect somatosensory information to be passed on to the brain  Protected by the vertebral column Composed of 24 individual vertebrae

Primary Components of the Spinal Cord  Spinal Roots – a bundle of axons surrounded by connective tissue that occur in pairs, which fuse and form a spinal nerve  Dorsal Roots – the spinal roots that contain incoming (afferent) sensory fibers  Ventral Roots - the spinal roots that contain outgoing (efferent) motor fibers

The Peripheral Nervous System  Somatic Nervous System  Portion of the PNS comprised of the spinal nerves and cranial nerves involved in transmitting sensory information and controlling voluntary movement. Spinal Nerves Peripheral nerves attached to the spinal cord.  Cranial Nerves Set of 12 motor and/or sensory nerves attached to the ventral surface of the brain.  The Autonomic Nervous System  Portion of the PNS concerned with the regulation of smooth muscle, cardiac muscle, and glands

The Autonomic Nervous System  Sympathetic Division of the ANS Nervous system components involved in arousal and preparing the body for the expenditure of energy. ‘Fight or flight’  Parasympathetic Division of the ANS Nervous system components involved in relaxing the body, often competing with those of the sympathetic division. ‘rest and digest’