The cells of the nervous system

Transcription

1 The cells of the nervous system LESSON N.9 - PSYCHOBIOLOGY

2 because of the location and volume as compared to our body, the brain has always been a matter of conjecture about its fundamental role in the control of our behavior. However it is only in the last two centuries, with a sudden acceleration in the last 20 years, thanks to the advent of modern neuroscience that we have begun to understand more deeply the basics of its and then our, functioning. Neurons Synapses and Ionic channel

3 The peripheral nervous system consists of the: Nerves: Set of axons bundled together which extend for the whole body and transmit the information to the muscles or sensory surfaces. These are in turn divided into: cranial nerves spinal nerves autonomic nervous system

4 Cranial nerves The 12 pairs of cranial nerves are sensory systems and head engines and are directly connected to the brain. 3 (I II VIII) are sensory pathways to the brain 5 (III IV VI XI XII) are motor pathways from the brain 4 (V VII IX X) are both sensory and motor

5 Spinal nerves For the whole length of the spinal cord there are 31 pairs of spinal nerves that are combined to the spinal cord at regular intervals through the openings in the spine. Every nerve is formed by the fusion of two distinct branches (roots). The ventral root consists of motor projections ranging from the spinal cord to the muscles The dorsal root consists of sensory projections ranging from the body to the spinal cord The spinal nerves are named according to the vertebra to which are connected: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, coccygeal 1

6 THE ANS Clusters of neurons called autonomic ganglia are located in various parts of the body. Their name comes from the belief that they could act independently from the brain, but we now know that they are still regulated by the CNS through the called preganglionic neurons. By contrast the ganglion neurons that innervate the rest of the body are called postganglionic. THE ANS is formed by three main sections: The sympathetic: the ganglionic projections are contained in the spinal cord and innervate the sympathetic chain that through postganglionic. Performs an action of activation on the entire body (increases blood pressure, dilated pupils, increased heart rate) The parasympathetic: its preganglionic are located above and below the sympathetic, while the postganglionic are scattered throughout the body, usually near the organ controlled. Generally it acts as opposed to the sympathetic system The enteric: is similar to a crosslinked system in the walls of the digestive organs, and is controlled both by the sympathetic and parasympathetic, but also indirectly from the CNS

7 The central nervous system is formed by: BRAIN SPINAL CORD

8 Exploring the brain

9 Exploring the brain

10 Brain development

11 The role of pruning At birth, the neurons in the visual and motor cortices have connections to the superior colliculus, spinal cord, and pons. The neurons in each cortex are selectively pruned, leaving connections that are made with the functionally appropriate processing centers. Therefore, the neurons in the visual cortex prune the synapses with neurons in the spinal cord, and the motor cortex severs connections with the superior colliculus. This variation of pruning is known as large-scaled stereotyped axon pruning. Neurons send long axon branches to appropriate and inappropriate target areas, and the inappropriate connections are eventually pruned away. Regressive events refine the abundance of connections, seen in neurogenesis, to create a specific and mature circuitry. Apoptosis and pruning are the two main methods of severing the undesired connections. In apoptosis, the neuron is killed and all connections associated with the neuron are also eliminated. It is believed that the purpose of synaptic pruning is to remove unnecessary neuronal structures from the brain; as the human brain develops, the need to understand more complex structures becomes much more pertinent, and simpler associations formed at childhood are thought to be replaced by complex structures.

12 Important subcortical structures

13 White matter fibers Diffusion Tension Imaging (DTI) is used to study the white matter fibers in the brain

14 Comparison+between+Nissl+and+Golgi+t echniques

15 The Brodmann areas Brodmann areas have been discussed, debated, refined, and renamed exhaustively for nearly a century and remain the most widely known and frequently cited cytoarchitectural organization of the human cortex. Many of the areas Brodmann defined based solely on their neuronal organization have since been correlated closely to diverse cortical functions. For example, Brodmann areas 1, 2 and 3 are the primary somatosensory cortex; area 4 is the primary motor cortex; area 17 is the primary visual cortex; and areas 41 and 42 correspond closely to primary auditory cortex. Higher order functions of the association cortical areas are also consistently localized to the same Brodmann areas by neurophysiological, functional imaging, and other methods (e.g., the consistent localization of Broca's speech and language area to the left Brodmann areas 44 and 45). However, functional imaging can only identify the approximate localization of brain activations in terms of Brodmann areas since their actual boundaries in any individual brain requires its histological examination.

16 Brain ventricles The four cavities of the human brain are called ventricles. The two largest are the lateral ventricles in the cerebrum; the third ventricle is in the diencephalon of the forebrain between the right and left thalamus; and the fourth ventricle is located at the back of the pons and upper half of the medulla oblongata of the hindbrain. The ventricles are concerned with the production and circulation of cerebrospinal fluid. Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the brain and spine. It is produced in the choroid plexuses of the ventricles of the brain. It acts as a cushion or buffer for the brain's cortex, providing basic mechanical and immunological protection to the brain inside the skull. The CSF also serves a vital function in cerebral autoregulation of cerebral blood flow.

17 Blood supply in the brain Blood supply to the brain is normally divided into anterior and posterior segments, relating to the different arteries that supply the brain. The two main pairs of arteries are the Internal carotid arteries (supply the anterior brain) and vertebral arteries (supplying the brainstem and posterior brain). The anterior and posterior cerebral circulations are interconnected via bilateral posterior communicating arteries. They are part of the Circle of Willis, which provides backup circulation to the brain. In case one of the supply arteries is occluded, the Circle of Willis provides interconnections between the anterior and the posterior cerebral circulation along the floor of the cerebral vault, providing blood to tissues that would otherwise become ischemic

18 Brain meninges The meninges are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid space between the arachnoid mater and the pia mater.the primary function of the meninges is to protect the central nervous system

19 History: Fathers of modern Neuroscience Camillo Golgi Black reaction Santiago Ramon Y Cajal Neuron doctrine vs. reticular theory Charles Sherrington Synapses

20 Nervous cells The soma or cell body incoming information is processed through spatial and temporal summation processes The dendrites (dendritic spines) Axon hillock numerator role The axon synapses

21 Flusso dell informazione nervosa Primary information Secondary information

22 Classification of the neuron The neurons can be classified according to their function: sensory neurons interneurons motoneurons All of these types can in turn be classified in accordance with their morphology (no. Of neurites in the output from the soma) in: multipolar neurons bipolar neurons monopolar neurons

23 Neuroglia In addition to neurons, the nervous system is formed by a second type of cells, called neuroglia or glia. Glia has a smaller morphological and functional complexity and includes only four types of cells: astrocytes microglia oligodendrocytes Schwann cells Initially it was believed that the glia had only structural support functions, but recently has emerged that this is just one of many functions. It has been demonstrated that the Glia can send signals to each other and to the neurons, altering the neural transmission mechanisms.

24 Astrocytes Are cells with a star-shape, with numerous ramifications that go in all directions, at the same time interweaving with neurons and blood vessels. Their functions range from support and communication between the blood vessels and neurons. They are also responsible for the formation of new synapses and dynamic control of local blood flow. Finally they can directly interact with neurotransmitters at post-synaptic level. They receive electrical impulses directly from neurons, but are unable to generate their own impulses.

25 Microglia Microglia has primarily a role of macrophages and nervous environmental protection. During development of the nervous system, through the phagocytosis of dead cells and waste material, it contributes to the modeling of neural structures. In the adult nervous system contributes to the maintenance of homeostasis in response to activating pathogens present at the level of the central nervous system.

26 Oligodendrocytes and Schwann cells They are cells that perform the same function, respectively in the CNS and in the PNS. These glial cells wrap their extended plasma membrane in several coils around the axons forming a layer of myelin that has the function of acting as an insulating sheath, preventing the dispersion of electric fields related to nerve impulses that travel along axons. In particular, the longer axons that have to carry nerve signals over long distances compared to the soma are wrapped with myelin, ensuring in these cases an efficient and fast transmission Myelination takes about years in humans.

27 Oligodendrocytes and Schwann cells Since glial cells have a limited length compared to the length of an axon, axon myelination along the entire length will be discontinuous, formed by myelinated sections (internodes) and short sections devoid of myelin (nodes of Ranvier). Multiple sclerosis is a disease that affects the myelin, slowing down and preventing the transmission of nerve impulses.