PSL300 Section 4: CNS and Senses (PDF)

Welcome to PSL300 Section 4 CNS and Senses n Instructor Douglas Tweed n n The slides contain all the testable material in my lectures: I will test you only on facts and concepts in my slides. n n You are responsible for everything in the slides except for text printed gray. n...

Welcome to PSL300 Section 4 CNS and Senses n Instructor Douglas Tweed n n The slides contain all the testable material in my lectures: I will test you only on facts and concepts in my slides. n n You are responsible for everything in the slides except for text printed gray. n n Watch the lectures, where I explain concepts in the slides at greater length. n n Read Silverthorn’s Human Physiology for further explanation of concepts in the slides.  CNS Central Nervous System PSL 300 University of Toronto  Question of the day Why are only 4% of the neurons in your brain firing right now?  Outline n Overview of the CNS n Anatomy Energy supply n n Spinal cord n n Segmental structure n Nuclei and tracts n Spinal reflexes n Brain n n 6 divisions n y Brain stem n Cerebrum Overview of the CNS The central nervous system (CNS) is the brain and spinal cord Brain Spinal cord  Neurons outside the CNS make up the peripheral nervous system n The peripheral nervous system, or PNS, includes all neurons, and cell bodies parts of neurons, outside the CNS. some have in PNs n in CWS & dentrites/axon n The PNS comprises the somatic nervous system, for controlling voluntary action via skeletal muscle, and the autonomic nervous system, for visceral functions such as heart rate and breathing. n Part of the autonomic system is the enteric nervous system, which controls digestion and movements of the gut. It gets input from spinal cord, but can also work independently.  Most neurons are in the CNS Microscopion S in as neuronmajority n The brain has ~86 billion neurons, and the spinal cord ~1 billion. n n Estimates for the enteric nervous system range from 100–600 mil- muchles lion, and the total for the PNS is likely not much more. n n CNS and PNS also have cells called glia, which support and protect neurons, and are about as numerous. Dr Susana Herculano found 4 volunteers and turned their brains into what she called “brain soup”. I’m impressed that the 100 bn was basically right. But Dr H and the media went on about how “staggering” the discrepancy is and how we’re much stupider than we thought, with just 86 bn neurons. She said 14 bn is a lot — it’s the number of neurons in the entire brain of a baboon, so saying 86 bn is basically the same as 100 bn is like saying a baboon has no brain at all, which is rude.  The CNS contains ventricles filled with cerebrospinal fluid CSF Macroscopion dir Ventricle 2 Lateral ventricles -> backwards ( Third ventricle Connectes Fourth ventricle Central canal of spinal cord it's contineous  Front view of the ventricles Lateral ventricles E Third ventricle Fourth ventricle Central canal of spinal cord Your head is like a coconut. -  The CNS includes gray and white matter n Gray matter consists of nerve cell bodies, unmyelinated axons, and dendrites. The cell bodies are arranged either in layers (in parts of the brain) or in clusters called nuclei (singular: nucleus).avey clusteafter in n White matter consists of myelinated axons running in bundles called tracts. n n In the peripheral nervous system, clusters of neurons are called ganglia (singular: ganglion), and bundles of axons are nerves. PNS CNS nerves tracts axons Myelin is made by oligodendrocytes in the CNS and by Schwann cells in the PNS. ganglia nuclei bodies  Compared to other organs, the CNS uses a lot of energy n The brain has just ~2% of the body’s mass, but gets 15% of the blood pumped by the heart. n It consumes half the body’s glucose. it's energy efficient tho · (compared to computers  Compared to computers, the CNS uses very little energy Watson n It runs on ~40 watts, like a lightbulb, whereas computers that try to mimic it, such as IBM’s Jeopardy-playing computer Watson, need much more — ~200,000 watts. www.legendary.com  The CNS saves energy by limiting communication between neurons n Neurons communicate with each other by sending action poten- tials (spikes) down their axons, but those action potentials take a lot of energy. n The energy supply to the CNS can support only a low rate of firing, e.g. in cortex it permits an average rate per cell of just one spike every 6 s. At any moment, only ~4% of your neurons are firing. n n That is, communication is expensive, and so the CNS has to use it sparingly. Spinal Cord  The spinal cord has 31 segments, each with a pair of spinal nerves afferent into norcal roots - incoming sensory 1 of the sequent back Dorsal root Ganglion front sellbodies Spinal of RNS nerve nerve Ventral root neutral roots merrez CNS- body efferent (outgoing) > - PN n Each spinal nerve has a dorsal root, which carries afferent (i.e. incoming, sensory) signals. The dorsal root ganglion contains the cell bodies of the neurons carrying these signals. n The ventral root carries efferent (i.e. outgoing) signals from the CNS to the body, including motor signals (i.e. to skeletal muscles). n n Dorsal means toward the back; ventral means toward the belly.  The gray matter is mainly in the middle of the cord whita back Dorsal root Dorsal horn Ganglion Ventral horn front Ventral root n It has a butterfly shape, with a dorsal and a ventral horn on each side.  The gray matter consists of sensory and motor nuclei viceral somatio dorsal Visceral - Somatic sensory sensory nuclei nuclei ventra Somatic Autonomic motor efferent nuclei nuclei autonomic & somatic n Sensory nuclei are in the dorsal horn because sensory signals ar- rive on the dorsal root. Somatic sensory nuclei get signals from skin; visceral sensory nuclei get signals from the viscera (internal organs). n n Efferent nuclei are ventral. Autonomic efferent nuclei send com- mands to glands and smooth muscle; motor nuclei send commands to skeletal muscle.  White matter consists of axon tracts n Ascending tracts (green) carry sensory signals to the brain. They are mainly dorsal, because sensory signals arrive at the dorsal horn. n n Descending tracts (pale blue) carry signals from the brain. They are mainly ventral, where outgoing signals leave the CNS. n re may n Propriospinal tracts (not shown), stay in the spinal cord. wor di never reach Brain up  In a spinal reflex, the cord responds to stimuli without consulting the brain normally brain makes To brain decision Sensory input but to itit needdmade Interneuron Juna 3 Motor a output it's pu doesn'twait sponse t n An example is the knee-jerk reflex: the physician’s rubber hammer stretches a ligament below the kneecap. Sensory fibers carry the news of this stretch into the dorsal horn. n n These fibers send branches up to the brain, but also excite neur- ons in the ventral horn that send signals out to leg muscles to contract and counter the stretch. Brain  The brain has 6 major divisions Cerebrum Pons Diencephalon Cerebellum Medulla continuation Midbrain of spinal cord th Conce it reaches Skill (  Medulla, pons, and midbrain make up the brain stem center of brain ↑ the Thalamus (not part of the brain stem) Midbrain Pons Cranial nerves Medulla n The brain stem is the main control center for many autonomic functions and reflexes, such as breathing, swallowing, vomiting, and regulating blood pressure. n n Cranial nerves III–X and XII arise from the brain stem. Cranial nerves are ones that enter or leave the brain rather than the spinal cord There alpart) Fields (2007) Sci Am Mind  The diencephalon is the thalamus, hypothalamus, pituitary and pineal cerabrum Corpus callosum Thalamus Pineal gland Hypothalamus Pituitary gland n The thalamus processes information going to and from the cere- into here bral cortex. all most all senses send n n The hypothalamus regulates behavioral drives, and endocrine and autonomic homeostasis. n Pituitary and pineal secrete hormones.  The cerebrum has 2 hemispheres connected by the corpus callosum Cortex White matter X it is thought Corpus Basal ganglia grey matt nuclear callosum I can be join , the hemispheres a opposite matter ot 2 L hemisphere R hemisphere n The cerebral gray matter includes the outer layer called the cortex, the limbic system (shown in a later slide), and the basal ganglia (which help control movement). n n Corpus callosum is a large bundle of myelinated axons. The 2 hemispheres' functions differ, i.e. we have cerebral lateralization Speech Writing Analysis by touch Language Spatial analysis and math L hemisphere R hemisphere  Each hemisphere has 4 lobes Frontal Parietal Occipital ⑪ Temporal near temple Each hemisphere also has a cingulate gyrus, which is part of the limbic system Frontal - Parietal Cingulate gyrus ↓ Occipital Temporal  The limbic system is an evolutionarily old group of brain regions Thalamus (not part of the Cingulate gyrus limbic system) 2 Come on ead side Hippocampus 2 Amygdala n It includes the cingulate gyrus, amygdala, and hippocampus. n n It is concerned with motivation, emotion, and memory, e.g. monkeys with amygdala lesions, unlike normal monkeys, are not frightened of snakes. Reading in Silverthorn’s Human Physiology n 8th edition: Please read the subsections “The CNS Is Divided into Gray Matter and White Matter” (starting on page 274) and “Neural Tissue has Special Metabolic Requirements”, and Sections 9.4 and 9.5, and the subsection “The Cerebral Cortex is Organized into Functional Areas” (pages 289−290). Reading in Silverthorn’s Human Physiology n 7th edition: Pages 277–280 (“The CNS Is Divided into Gray Matter and White Matter”), Figures 9.3(a) and 9.4(a), and pages 283–293, from the start of “Neural Tissue has Special Metabolic Require- ments” to the end of “The Spinal Cord and Brain Inte- grate Sensory Information”. n 6th edition: Page 293 (“The CNS Is Divided into Gray Matter and White Matter”), Figures 9.3(a) and 9.4(a), and pages 297–308, from the start of “Neural Tissue has Special Metabolic Requirements” to the end of “The Spinal Cord and Brain Integrate Sensory Information”.