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Nervous System Purpose • • • • Communication Control Process information Gather information Neuron • Cell body – Contains nucleus and most normal cell functions – Receives chemical signal from adjacent neuron • Axon – Transmits electrical impulse to synaptic terminals • Synaptic terminals – Transmits chemical signal to cell body of adjacent neuron Types of Neurons Synapse structure and function Synapse close-up Synapse receptors Membrane Potential • Inside of every cell is negative compared to the outside – Inside • Anions – proteins, amino acids, sulfate and phosphate • Cations – potassium (K+) – Outside • Anions – chloride (Cl-) • Cations – sodium (Na+) • Anions and cations cannot pass through the lipid bilayer – they must pass through selective channels Action Potential • Voltage-gated ion channels – Ions move according to gradient and charge attraction • Potassium (more permeable) • Sodium (less permeable) • Sodium/potassium pump – Requires ATP – Pumps Na+ out of cell and K+ into cell Action Potential Myelin sheath Saltatory Conduction Other Cells of the Nervous System • Support • Nourishment • Protection Neuroglial Cells • Non-neuron cells found in the nervous system – – – – – Schwann – forms myelin sheath in PNS Microglial – protect against microbes Astrocytes – structural and nutritive support Oligodendroglial – forms myelin sheath in CNS Ependymal – line CNS cavities and produce cerebrospinal fluid Three Neuroglial Cell Types Nerve structure • Bundles of myelin covered nerve fibers (axons) covered in connective tissue • Blood vessels Organization • Central nervous system (CNS) – Brain – Spinal chord • Peripheral nervous system (PNS) – Motor neurons – Sensory neurons Path of Impulses Central Nervous System • Brain • Spinal chord Spinal Chord • Function – Transmits signals from brain and other parts of the body – Reflex loop – Simple motor functions (walking, running) • Structure – Gray matter • Cell bodies of motor neurons – White matter • Axons of neurons running up and down spinal chord Spinal Chord Structure Pain Withdrawal Reflex Reflex Loop Hindbrain • Medulla – autonomic functions – Breathing, heart rate, swallowing, blood pressure • Pons – stages of sleep • Cerebellum – coordinates muscles – Receives info from position and stretch sensors Midbrain • Reticular formation – Sensory relays – Sensory filter Forebrain • Thalamus – Transmits info to and from limbic system, senses, cerebrum and cerebellum • Limbic system – Basic emotions, drives and behaviors • Cerebral cortex – Thinking and information processing Cerebrum • Two hemispheres – Connected by corpus callosum (white matter) • Each half divided into 4 lobes – Frontal, parietal, temporal, occipital lobes • Cortex – 3mm layer of gray matter – Extensive folds to increase surface area Cerebrum -- Gross Anatomy Functions of Cerebrum Lobes • Frontal – Voluntary motor functions, planning, mood, smell and social judgement • Parietal – Sensory reception & integration of sensory information • Occipital – Visual center of brain • Temporal – Hearing, smell, learning, memory and emotional behavior Sensory Homunculus • Demonstrates that the area of the cortex dedicated to the sensations of various body parts is proportional to how sensitive that part of the body is. Sensory Association Areas • Association areas interpret sensory information • Somesthetic association area (parietal lobe) – Position of limbs, location of touch or pain, and shape, weight & texture of an object • Visual association area (occipital lobe) – Identify the things we see – Faces are recognized in temporal lobe • Auditory association area (temporal lobe) – Remember the name of a piece of music or identify a person by his voice Motor Control • Intention to contract a muscle begins in motor association (premotor) area of frontal lobes • Precentral gyrus (primary motor area) processes that order by sending signals to the spinal cord • Motor homunculus is proportional to number of muscle motor units in a region (fine control) Language • Includes reading, writing, speaking & understanding words • Wernicke’s area – Permits recognition of spoken & written language & creates plan of speech – Angular gyrus processes text into a form we can speak • Broca’s area – Generates motor program for larynx, tongue, cheeks & lips – Transmits that to primary motor cortex for action Language Centers Aphasia • Any language deficit resulting from lesions in same hemisphere as Wernicke’s & Broca’s areas • Lesion to Broca’s = nonfluent aphasia – slow speech, difficulty in choosing words – entire vocabulary may be 2 to 3 words • Lesion to Wernicke’s = fluent aphasia – speech normal & excessive, but makes little sense • Anomic aphasia = speech & understanding are normal but text & pictures make no sense • Others = understanding only 1st half of words or writing only consonants Lateralization of Cerebral Functions Cerebral Lateralization • Left hemisphere is categorical hemisphere – specialized for spoken & written language, sequential & analytical reasoning (math & science), analyze data in linear way • Right hemisphere is representational hemisphere – perceives information more holistically, perception of spatial relationships, pattern, comparison of special senses, imagination & insight, music and artistic skill • Highly correlated with handedness – 91% of people right-handed with left side is categorical • Lateralization develops with age • Trauma more problems in males since females have more communication between hemisphere (corpus callosum is thicker posteriorly) EEG and Brain Waves • Electroencephalogram records voltage changes from postsynaptic potentials in cerebral cortex • Differences in amplitude & frequency distinguish 4 types of brain waves Brain Waves & Sleep • States of consciousness can be correlated with EEG • 4 types of brain waves – – – – Alpha occur when awake & resting with eyes closed Beta occur with eyes open performing mental tasks Theta occur during sleep or emotional stress Delta occur during deep sleep • Sleep is temporary state of unconsciousness – Coma is state of unconsciousness with no possible arousal Stages of Sleep • Non-REM sleep occurs in stages – 4 stages occurring in first 30 to 45 minutes of sleep • stage 1 is drifting sensation (would claim was not sleeping) • stage 2 still easily aroused • stage 3 vital signs change -- BP, pulse & breathing rates drop – reached in 20 minutes • stage 4 is deep sleep -- difficult to arouse – seems to have a restorative effect • REM sleep occurs about 5 times a night – rapid eye movements under the eyelids, vital signs increase, EEG resembles awake person dreams – may help sort & strengthen information from memory Sleep Stages and Brain Waves • Brain waves change as we pass through 4 stages of sleep: alpha, to sleep spindles, to theta and finally to delta waves during deep sleep Cognition • Cognition is mental processes such as awareness, perception, thinking, knowledge & memory – 75% of brain is association areas where integration of sensory & motor information occurs • Examples of effects of brain lesions – temporal lobe -- inability to recognize objects or inability to recognize faces – frontal lobe -- problems with personality Memory • Information management requires learning, memory & forgetting (eliminating the trivia) – Abnormalities • pathological inability to forget have trouble with reading comprehension • can not store new data • can not remember old data • Hippocampus - organizes sensory & cognitive information into a memory – lesions cause inability to form new memories • Cerebellum helps learn motor skills • Amygdala important in emotional memory Emotion • Prefrontal cortex controls how emotions are expressed (seat of judgement) • Emotions form in hypothalamus & amygdala – artificial stimulation produces fear, anger, pleasure, love, parental affection, etc. – electrode in median forebrain bundle in rat or human and a foot pedal • press all day to the exclusion of food (report a quiet, relaxed feeling) • Much of our behavior is learned by rewards and punishments or responses of others to them Peripheral Nervous System • Motor neurons • Sensory neurons Organization of Nervous System Motor Neurons • Carry signals from the CNS to muscles and glands – Somatic – voluntary responses • Skeletal muscles – Autonomic – involuntary responses • Cell bodies found in ganglia – Organs – Glands – Smooth muscles Sensory Neurons • Mechanoreceptor – Hearing, pressure, stretch, movement • Photoreceptor – Light, vision • Chemoreceptor – Olfactory – Taste – Pain Sensory Receptors • • • • Where is the stimulus located? How strong is the stimulus? Stimulus = energy Sensory receptors transfer signal to other neurons • Specialized cells or modified neurons Receiving Sensory Information • Sensory Transduction – Converts received signal to action potential • Amplification – Signal transmitted contains more energy than signal received • Transmission – Action potential • Integration – Information processing Types of Sensory Receptors • Mechanoreceptor – Stretch or bending of plasma membrane • Hearing, pressure, stretch, movement • Chemoreceptor – Binding of specific molecules to protein receptors in plasma membrane • Olfactory, taste, pain • Photoreceptor – Photons hitting specific proteins in plasma membrane • Vision Touch • Mechanoreceptor Parts of the Ear • Outer ear – Pinna and auditory canal • Middle ear – Tympanic membrane (ear drum) – Ossicles (malleus, incus, stapes) • Inner ear – Cochlea Auditory Receptors • Different pitches vibrate different parts of the basilar membrane • The basilar membrane vibrates against hair cells in the cochlear duct • Shape and thickness of basilar membrane effects vibrations Pain Receptors • Chemical receptor – Detects chemicals released during tissue damage – Receives chemical on specialized dentrites Olfactory Receptors • Chemical receptor • Different molecules have different cells with unique receptors for that molecule Photoreceptors • Modified neurons containing light absorbing pigment • Rods – Black and white – Night vision – Pigment – rhodopsin • Cones – Color – 4 types – red, blue and green – Pigment – photopsins Photoreceptor Function • Photoreceptor constantly firing in dark which inhibits post synaptic neuron • Light releases inhibition of postsynaptic neuron Retinal Structure • Rods and cones are not mapped 1:1 to ganglion cells • More cells per ganglion cell equals lower resolution but greater sensitivity • Dogs have 5x the number of rod cells per ganglion cell • Optic nerve exits through the fovea which creates your blind spot