Nervous System 1 Nervous systemNervous System 2 Somatic Nervous System The somatic nervous system consists of peripheral nerve fibers that send sensory information to the central nervous system AND motor nerve fibers that project to skeletal muscle. The picture above shows the somatic motor system. The cell body is located in either the brain or spinal cord and projects directly to a skeletal muscle.Nervous System 3 Autonomic Nervous System is divided into three parts: the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system. The autonomic nervous system controls smooth muscle of the viscera (internal organs) and glands. This picture shows the general organization of the autonomic nervous system. The preganglionic neuron is located in either the brain or the spinal cord. This preganglionic neuron projects to an autonomic ganglion. The postganglionic neuron then projects to the target organ. Notice that the somatic nervous system has only one neuron between the central nervous system and the target organ while the autonomic nervous system uses two neurons.Nervous System 4 Enteric nervous system The enteric nervous system is a third division of the autonomic nervous system that you do not hear much about. The enteric nervous system is a meshwork of nerve fibers that innervate the viscera (gastrointestinal tract, pancreas, gall bladder). Contains approx. 100 million nerves.Nervous System 5 The central nervous system is divided into two major parts: the brain and the spinal cord. The average adult human brain weighs 1.3 to 1.4 kg. The brain contains nerve cells (neurons) and "support cells" called glia. The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams. The vertebral column, the collection of bones (back bone) that houses the spinal cord, is about 70 cm long. Therefore, the spinal cord is much shorter than the vertebral column. Central Nervous SystemNervous System 6 Telencephelon Diencephelon Metencephelon Mesencephelon MyelencephelonNervous System 7 Brain: main partsNervous System 8Nervous System 9 Saggital sectionNervous System 10 Temporal Occipital ParietalNervous System 11 1. Frontal pole 2. Superior frontal sulcus 3. Middle frontal gyrus 4. Superior frontal gyrus 5. Precentral sulcus 6. Longitudinal cerebral fissure 7. Precentral gyrus 8. Postcentral gyrus 9. Central sulcus 10. Postcentral sulcus 11. Occipital pole (From www.vh.org)Nervous System 12 1. Medial frontal gyrus 2. Cingulate sulcus 3. Cingulate gyrus 4. Central sulcus 5. Paracentral lobule 6. Callosal sulcus 7. Isthmus of cingulate gyrus 8. Subparietal sulcus 9. Precuneus 10. Parieto-occipital sulcus 11. Cuneus 12. Calcarine sulcus or fissure 13. Rostrum of corpus callosum 14. Genu of corpus callosum 15. Trunk of corpus callos 16. Splenium of corpus callosum 17. Choroid plexus in interventricular foramen 18. Interthalamic adhesion 19. Habenular trigone 20. Hypothalamic sulcus 21. Pineal body 22. Anterior (rostral) commissure 23. Tectum of midbrain 24. Mamillary body 25. Medial longitudinal fasciculus 26. Choroid plexus of 4th ventricle Nervous System 13Nervous System 14 Some differences between the Peripheral Nervous System (PNS) and the Central Nervous System (CNS): In the CNS, collections of neurons are called nuclei. In the PNS, collections of neurons are called ganglia. In the CNS, collections of axons are called tracts. In the PNS, collections of axons are called nerves. Nervous System 15 In the Peripheral Nervous System, neurons can be functionally divided in 3 ways: Sensory (afferent) -carry information INTO the central nervous system from sense organs. Motor (efferent) -carry information away from the central nervous system (for muscle control). Cranial Nerve -connects the brain with the periphery. Spinal Nerve -connects the spinal cord with the periphery. Somatic -connects the skin or muscle with the central nervous system. Visceral -connects the internal organs with the central nervous system.Nervous System 16 Cerebral Cortex Functions: Thought , Voluntary movement , Language, Reasoning, Perception The word "cortex" comes from the Latin word for "bark" (of a tree). This is because the cortex is a sheet of tissue that makes up the outer layer of the brain. The thickness of the cerebral cortex varies from 2 to 6 mm. The right and left sides of the cerebral cortex are connected by a thick band of nerve fibers called the "corpus callosum." In higher mammals such as humans, the cerebral cortex looks like it has many bumps and grooves. A bump or bulge on the cortex is called a gyrus (the plural of the word gyrus is "gyri") and a groove is called a sulcus (the plural of the word sulcus is "sulci"). Lower mammals like rats and mice have very few gyri and sulci. Nervous System 17 Cerebellum Functions: Movement, Balance, Posture The word "cerebellum" comes from the Latin word for "little brain." The cerebellum is located behind the brain stem. In some ways, the cerebellum is a bit like the cerebral cortex: the cerebellum is divided into hemispheres and has a cortex that surrounds these hemispheres. Nervous System 18 Hypothalamus Functions: Body Temperature, Emotions, Hunger, Thirst, Circadian Rhythms The hypothalamus is composed of several different areas and is located at the base of the brain. It is only the size of a pea (about 1/300 of the total brain weight), but it is responsible for some very important behaviors. One important function of the hypothalamus is the control of body temperature. The hypothalamus acts like a "thermostat" by sensing changes in body temperature and then sending out signals to adjust the temperature. For example, if you are too hot, the hypothalamus detects this and then sends out a signal to expand the capillaries in your skin. This causes blood to be cooled faster. The hypothalamus also controls the pituitary.Nervous System 19 Brain stem Functions: Breathing, Heart Rate, Blood Pressure The brain stem is a general term for the area of the brain between the thalamus and spinal cord. Structures within the brain stem include the medulla, pons, tectum, reticular formation and tegmentum. Some of these areas are responsible for the most basic functions of life such as breathing, heart rate and blood pressure.Nervous System 20 Thalamus Functions: Sensory Integration, Motor Integration The thalamus receives sensory information and relays this information to the cerebral cortex. The cerebral cortex also sends information to the thalamus which then transmits this information to other areas of the brain and spinal cord.Nervous System 21 Limbic System Functions: Emotional Behavior The limbic system (or the limbic areas) is a group of structures that includes the amygdala, the hippocampus, mammillary bodies and cingulate gyrus. These areas are important for controlling the emotional response to a given situation. The hippocampus is also important for memory. Hippocampus Functions: Learning, Memory The hippocampus is one part of the limbic system that is important for memory and learning.Nervous System 22 Basal Ganglia Functions: Movement The basal ganglia are a group of structures, including the globus pallidus, caudate nucleus, subthalamic nucleus, putamen and substantia nigra, that are important in coordinating movement. Midbrain Functions: Vision, Audition, Eye Movement, Body Movement The midbrain includes structures such as the superior and inferior colliculi and red nucleus. There are several other areas also in the midbrain.Nervous System 23Nervous System 24 Speech production and articulation Speech Center (Broca's Area) Detection of sound quality (loudness, tone) Auditory Cortex Complex processing of auditory information Auditory Association Area Language comprehension Wernicke's Area Detection of simple visual stimuli Visual Cortex Complex processing of visual information Visual Association Area Processing of multisensory information Sensory Association Area Receives tactile information from the body Primary Somatosensory Cortex Initiation of voluntary movement Primary Motor Cortex Coordination of complex movement Motor Association Cortex Problem Solving, Emotion, Complex Thought Prefrontal Cortex Broca's Area Wernicke's Area Images courtesy of Slice of Life. Function Cortical AreaNervous System 25 Sizes How many neurons? 100 billion (1011) (how much time to count if 1 per/sec?) 3171 years How big is a neuron? 10μ -100μ (microns) (how long if lined up side by side?) 1000KmNervous System 26 Levels Marr defined 3 levels • Computational (decomposing task) • Algorithmic (procedure to do task) • Implementational (working device to do task) Higher levels independent of lower ones.Nervous System 27 Levels of Organization Molecules (1 Angstrom) Synapses (1μ) Neuron (10 -100 μ) Networks (1mm) Maps (1cm) Systems (10cm) CNS (1m) – the whole organismNervous System 28 Computational Neuroscience • Addresses problems at all the levels • How do the levels mesh together – not known, research problem • Approaches – pure bottom up – pure top-down – co-evolutionNervous System 29 Topographic maps • Neighbouring areas in sensory space are mapped to adjacent neurons (vision, touch, hearing, muscle groups). • Maps are non-linear (e.g. fovea, hands map to larger areas, there can be upper/lower differentiation as well)Nervous System 30 Layers and columns • Many areas show laminar organization. Sheets register with higher and lower sheets. • Both horizontal & vertical organization (e.g. superior colliculus)Nervous System 31 Local networks • Colour constancy • 1D, 2D curvature of shapes in shaded imagesNervous System 32 Basic brain facts • Specialization of function (seems to be true for all brains) – though hard to determine function for frontal cortex in higher mammals. • Connectivity: – each cortical neuron connected to roughly same number other neurons (approx. 3%) – most between cell classes (not within) – forward projections matched by backwardNervous System 33 Neurogenesis • Brain cells do not regenerate – widely held view • New brain cells form and join existing structures and become active.Nervous System 34 Basic brain facts (contd.) • Analog inputs, discrete outputs: inputs are analog, output is discrete (spikes or does not). Spiking depends on thresholds. • Timing: signal interaction depends on timing; time scale of computation must match time scale of events; time scale of output must match time for body parts to move. Nervous System 35 Basic brain facts (contd.) • Parallel architecture – parallel streams of input for a given function. • Action at a distance – neuro-transmitters (through extra-cellular space), hormones can alter neural activity after travelling through circulatory systemNervous System 36 References 1. PS Churchland, TJ Sejnowski, The Computational Brain, MIT Press, 1992. 2. IB Levitan, LK Kaczmarek, The Neuron, 3rd. Ed., Oxford Univ. Press, 2002. 3. Various internet sources.