The Brain & Nervous System. History Known to relate to thought and behavior for over 3500 years –...
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Transcript of The Brain & Nervous System. History Known to relate to thought and behavior for over 3500 years –...
The Brain & Nervous System
History
• Known to relate to thought and behavior for over 3500 years– Edwin Smith Surgical
Papyrus
• Greeks thought the brain– Was the seat of the mind– Was responsible for
intelligence– Cooled the blood
Trepanning
• Practiced since at least 6500 BCE
• Still used in limited cases– Subdural Hematomae– Most recent psychological
use from 2000
• Used for– Mental Illness– Increased “brainpower”
History
• Descartes believed in dualism– Mind was in but not of
the Brain– Interacted at the Pineal
Gland
• Vesalius– Found nerves
transmitted sensation and motion
– Nerves were not hollow
History
• Galvani first discovered that the nervous system used electricity
• Touched a frog leg with a charged scalpel, which caused a leg twitch
Structure
• The nervous system breaks down into two basic parts– Central Nervous System (Brain & Spinal Cord)– Peripheral Nervous System (Everything Else)
• PNS further divides into– Somatic (voluntary) and Autonomic (involuntary)– Autonomic subdivides into sympathetic and
parasympathetic
Peripheral Nervous System
• Somatic System is everything that is voluntary– Arms, Legs, Eyes, etc.
• The one exception is a reflex arc– Bypasses the brain– Reaction at spinal cord– Action is quicker than
nerve impulse to brain
Peripheral Nervous System
• Autonomic subsystem controls automatic/smooth muscles– Heart, Lungs, etc
• Sympathetic promotes “fight or flight” responses– Dilates pupils, increases heart rate, inhibits peristalsis
• Parasympathetic promotes “rest & digest”– Constrict pupils, slow heart rate, constricts bronchi
• Sympathetic & parasympathetic are opponent systems
Neurons
• The brain and all nerves are made up of neurons– The largest is over 3 feet long
• Every neuron is made up of a– Dendrite– Cell Body– Axon– Axon Terminals
Neurons
• Neurons fire electrically– Have an action potential
• Start off polarized– Excess of Na+ & Cl- outside, K+ inside– Resting potential is around -70 mV
• Depolarization occurs when channels open– Ions flow in and out– Firing occurs around -45 mV
• Neural firings occur at a threshold• All or none• Intensity = rate of fire
Neurons
• After firing, neurons enter a refractory period• Absolute refractory period– Impossible to evoke another firing– Na+ channels are inactive
• Relative refractory period– Requires stronger than normal stimulus
Neurons
Neurons
• Some neurons are myelinated– White matter (vs. Gray matter)
• Insulation– Hops from one uninsulated part to another– Nodes of Ranvier
• Demyelinating diseases– MS, transverse myelitis, Guillan-Barre, etc– Vision problems, weakness, odd sensations, loss of
coordination
Neurons
• Neurons don’t touch• Synapse is a gap
through which communication occurs
• Axons release a transmitter
• Dendrites pick it up
Neurotransmitters
• Neurons communicate with neurotransmitters– Acetylcholine (muscle movement, arousal, reward)– Dopamine (motivation, punishment/reward)– Epinephrine/Norepinephrine (adrenaline, allergy)– Serotonin (mood)– Endorphins (opiods)– GABA (mood, anxiety)– More than 40 others (and homologues)
• Lock-and-Key model• Video
Drugs
• Some drugs work by exciting/antagonize production– Nicotine (acetylcholine)– SSRI (seretonin)
• Some drugs are better keys than neurotransmitters– Heroin (Endorphins)– Cocaine (Dopamine)– Alcohol (GABA)
The Brain
• Divided into two hemispheres– Connected by Corpus
Callosum
• Various lobes & structures– Mirrored in each
hemisphere– E.g. “left & right _____”
• Watch
Brain Structures
• Brainstem• Thalamus• Cerebellum• Limbic System• Cerebral Cortex
Brainstem
• Basic life functions• Medulla (pith/marrow)
– Heart– Lungs
• Reticular (net) Formation– Arousal/Alertness– Consciousness– Pain
• Pons (bridge)– Gathering of cranial
nerves
Thalamus
• “Inner Chamber”• Acts as a sensory relay
station• Not as well understood• Implicated in Korsakoff’s
syndrome and Hereditary Familial Insomnia
Cerebellum
• “Little Brain”• Motor Control
– Damage does not cause paralysis
• Active in motor learning– Unconscious/Automatic
actions
• Signals move unidirectionally– Unlike all other parts of
brain
Limbic System
• Amygdala (Almond)– Emotionally significant stimuli (reward/fear)– Stimulation -> Agression; Destruction -> Placid
• Hypothalamus (Under Thalamus)– Body maintenance– Hunger, thirst, sex, temperature– Adjacent to pituitary– Three F’s (Fighting/Fleeing, Feeding, Sex)
Hypothalamus Damage
Limbic System
• Amygdala (Almond)– Emotionally significant stimuli (reward/fear)– Stimulation -> Agression; Destruction -> Placid
• Hypothalamus (Under Thalamus)– Body maintenance– Hunger, thirst, sex, temperature– Adjacent to pituitary
• Hippocampus (Seahorse)– Necessary for long-term memory formation– Think “Memento”
Cerebral Cortex
• Frontal Lobes• Sensorimotor Cortex• Parietal Lobes• Temporal Lobes• Occipital Lobes
Occipital Lobe
• Back of the brain– Above Cerebellum
• Controls visual processing
• Highly specialized Cell groups– Line Angles
• Incredibly basic• “Seeing stars”
Temporal Lobes
• Specific visual processing– Faces
• Hearing– Auditory nerve connects
• Episodic/Declarative memory– “And then, this happened”
• Left side involved in speech/language– Broca’s area = speech
production– Wernicke’s area = speech
comprehension
The Man Who Mistook His Wife for a Hat
• Temporal Lobe damage -> prosopagnosia– Face blindness
• Cannot connect faces to semantic information about people
• May not recognize a person until they speak
• Oliver Sacks
Parietal Lobes
• Integrates sensory information
• Numeracy– What is the relationship
between 8 and 2?
• Where and how of vision– Spatial relations– Action saliency
• Hemispatial neglect– Right lobe usually
Sensorimotor Cortex
• Between parietal & frontal lobes
• Governs movement and sensation
• Areas relate to sensitivity and fine motor control– Not size
• Phantom limb syndrome
Frontal Lobes
• Involved in planning– Consequences– Moral judgment– Response inhibition
• Similarity judgments• Doesn’t mature until
early/mid twenties• Underactive in ADHD
patients
Integrating It All
• Occipital lobe processes shapes
• Temporal lobe tells me it’s a dog– Registers barking
• Parietal lobe tells me it’s angry and running towards me
• Limbic system tells me to run– Engages my sympathetic
nervous system
• Motor cortex works my legs
Lateralization
• Brain divides into left & right hemispheres– Lateralization = specialization of hemispheres
• Left is logical, right is intuitive– Grammar & literal meaning on left, prosody and
intonation on the right• The brain is wired contra-laterally– Left controls right & vice-versa
• Left-handed people are less lateralized– Cause & effect unclear
Lateralization Test
• Mark which of the following you would prefer (not necessarily ability)– A) Major in Logic– B) Write a Letter– C) Fix things at home– D) Major in Art
• Mark which of the following you would prefer (not necessarily ability)– A) Be a movie critic– B) Learn new Words– C) Improve your skills in a game– D) Create a new toy
• Mark which of the following you would prefer (not necessarily ability)– A) Improve your strategy in a game– B) Remember people’s names– C) Engage in sports– D) Play an instrument by ear
• Mark which of the following you would prefer (not necessarily ability)– A) Review a book– B) Write for a magazine– C) Build new shelves at home– D) Draw a landscape or seascape
• Mark which of the following you would prefer (not necessarily ability)– A) Analyze market trends– B) Write a movie script– C) Do carpentry work– D) Imagine a new play
• Mark which of the following you would prefer (not necessarily ability)– A) Analyze management practices– B) Locate words in a dictionary– C) Put jigsaw puzzles together– D) Paint in oil
• Mark which of the following you would prefer (not necessarily ability)– A) Be in charge of computer programming– B) Study word origins and meanings– C) Putter in the yard– D) Invent a new gadget
• Mark which of the following you would prefer (not necessarily ability)– A) Analyze production costs– B) Desscribe a new product in words– C) Sell a new product on the market– D) Draw a picture of a new product
• Mark which of the following you would prefer (not necessarily ability)– A) Explain the logic of a theory– B) Be a copy writer for ads– C) Work with wood and clay– D) Invent a story
• Mark which of the following you would prefer (not necessarily ability)– A) Be a comparison shopper– B) Read about famous men and women– C) Run a traffic control tower– D) Mold with clay and putty
• Mark which of the following you would prefer (not necessarily ability)– A) Analyze your budget– B) Study literature– C) Visualize and re-arrange furniture– D) Be an artist
• Mark which of the following you would prefer (not necessarily ability)– A) Plan a trip– B) Write a novel– C) Build a house/shack– D) Make crafts your hobby
Lateralization Test
• Add up your “a” and “b” responses– This is your left brain score
• Add up your “c” and “d” responses– This is your right brain score
• A difference of more than 3 indicates strong lateralization– Less than 3 is balanced
• My score is 11 left/1 right
Corpus Callosum
• The hemispheres communicate via corpus callosum– Mostly, not exclusively
• Bundle of nerves that serve as a connector
• Highly specialized
Split Brains
• Sometimes, the corpus callosum must be cut– Last resort in epilepsy
• Allows us to look at how the brain lateralizes
• What might you expect to see?
Split Brains
• Gazzaniga would present one word to each visual field
• Only the word in the right field could be read
• Patients could identify left-field word with left hand– Why?
Split Brains
• What will a split brain patient say is the difference
• Which house will a split brain patient prefer?
Plasticity
• Refers in general to the ability to forge connections
• The brain can cover for itself– Rewire & reorganize
• Easier when younger• Whole specializations
will migrate
Concussions
• A bruise on the brain– Newton’s first law– Contracoup
• Physical– Headache, nausea,
dizziness
• Psychological– Confusion, slurred speech,
impaired reasoning
• Axons can be stretched, twisted, or sheared
Neuroimaging
• For a long time, we could only look at the brain after death or when it was damaged– This has obvious limitations
• Now, we have several ways of looking at brain activity– Lesions– Electroencephalograph (EEG)– Positron Emission Tomography (PET)– (functional) Magnetic Resonance Imaging (fMRI)– Event Related Potential (ERP)
LesionsCutting into the brain and looking for change.
Brain tumors also lesion brain tissue.
58
Lesions
• Removal or destruction of some part of the brain.
• Frontal Lobotomy
EEG
• Records electrical potential along the scalp– “Brain Waves”
• Cheap and easy– Low-res
• Used for biology– Seizures– Sleep disturbances
PET
• Patient is injected with radioactive glucose
• Scanner picks up metabolism– More metabolism =
more activity• Can find damaged
areas– Changes metabolism
• Absolute
(f)MRI
• Measures blood flow– Strong magnet causes
ions in blood to align
• Good spatial resolution• Has a lag time• Indirect• Works on contrast– Changes in blood flow
between states/tasks/subjects
ERP
• Measures neural firings of small groups of neurons
• Can tell us when, but not where
• Named negative/positive plus time– E.g. “N100”
MRI PET
• ERP net
TMS
• Transcranial Magnetic Stimulation• Small magnetic pulse discharges all action
potentials in a confined area– Effectively “knocks out” a part of the brain
• Generally safe– Small risk of seizures
• Allows for direct brain experimentation