Neuroscience Introduction
History of brain/mind
- plato though mind was in brain, aristotle thought mind was in heart
- we now understand biological/psychological connection between brain and mind
- phrenology: 1800's- Franz Gall suggested that bumps on your head represent your abilities and personality traits
- he was right that human brains are modular: different parts have different functions
Neural Communication
our information processing system is made up of neural cells
- 20 billion in brain, 100's of billions in glial cells
- glial cells support neurons
- astrocytes: provide nutrition to neurons
- oligodendrocytes and Schwann cells: insulate neurons
- they create a myelin sheath covers axon which accelerates speed of messages
- cell body: life support for neuron
- dendrites: receive messages
- axon: passes message from cell body to other neurons, muscles, glands
- myelin sheath: covers axon, provides protection and increases speed
- terminal branches of axon: goes to dendrites of other cells
aphasia-- impairment caused by damage to broca's area (speaking) or Wernicke's area (understanding)
- action potential: electrical charge (from ions)
- caused by pumping, flowing movement of positive ions through cell's membrane
- too much water can flush out these ions and destroy the system-- death!
- threshold= the level of stimulation required to trigger a neural response
- refractory period: after a neuron fires, there is a moment of readjustment before it can fire again
- always fires in same direction, at same intensity (toilet analogy)
- Synapse: junction between axon tip of sender and dendrite of receiver, tiny gap= synaptic gap
- re-uptake: neurotransmitters are reabsorbed into the sending neurons
Neurotransmitters
Neurotransmitters are the chemicals that are released from the axon terminal of one neuron to the receptor sites (on the dendrites) of another neuron.
They are released in response to an action potential, which sends a biological-electrical shock down the axon. At the end of the axon, the neurotransmitters are released, and they travel across the synaptic gap. They hit the receptor on a dendrite of another neuron, and attach to receptor sites. The receptor sites can identify different types of neurotransmitters. Once it identifies the neurotransmitter, it passes the message on to the next neuron through the same process.
Here are some of the most basic, prominent neurotransmitters.
Acetycholine-- ACH= learning, memory, muscle action
They are released in response to an action potential, which sends a biological-electrical shock down the axon. At the end of the axon, the neurotransmitters are released, and they travel across the synaptic gap. They hit the receptor on a dendrite of another neuron, and attach to receptor sites. The receptor sites can identify different types of neurotransmitters. Once it identifies the neurotransmitter, it passes the message on to the next neuron through the same process.
Here are some of the most basic, prominent neurotransmitters.
Acetycholine-- ACH= learning, memory, muscle action
- alzheimer's disease: hippocampus (which is responsible for memories) dies off
- black widow spider bite: venom releases all of you acetycholine at once, you cramp up all over
- botulism, curane darts: stop acetycholine from being transmitted-- causes paralysis
Seratonin= mood, slee, arousal, hunger
- food coma, staying up late and getting delerious+giggly, milk before bed, ecstasy
- ecstasy lowers seratonin levels permanently-- causes depression
- anti-depressants bring seratonin levels up slowly, in a controlled way
Dopamine= movement, learning, attention, emotion
- schizophrenia, parkinson's, drugs that give you a sense of euphoria
Norepinephrine= alertness and arousal
GABA= inhibitory neurotransmitter
glutamate= excitatory, involved in memory, often overstimulating (in MSG)
Lock & Key mechanism: neurotransmitters bind to receptors of receiving neuron in a lock+key shape
- agonist= synthetic molecule that mimics neurotransmitter: fits closely enough to receptor site to activate a response to another similarly-shaped, naturally occurring neurotransmitter
- example: morphine imitates endorphins because its molecule is similarly shaped
- antagonist= fits into receptor site but does not activate the receiver, simply blocks the path
- curare poison blocks the receptor designated for ACh, so ACh can't get through and you become paralyzed
Nervous System on a large scale
nerves= neural cables containing axons
- part of peripheral nervous system-- muscles, glands, sensory organs
- central nervous system is only the brain and the spinal cord, it is where messages are received, processed and then sent back out
- peripheral nervous system is throughout the body. It includes sensory organs, glands, muscles
- autonomic-- controls self-regulated action of internal organs and glands (heartbeat)
- sympathetic: arousing-- provides activation and energy when needed
- parasympathetic: calming-- helps conserve energy, controls blood flow to sex organs and is constantly telling them to stay calm
- somatic-- controls voluntary movements of skeletal muscles
- peripheral nervous system connects the central nervous system with the rest of the body
Types of Neurons
- sensory neurons: carry messages from peripheral system to central system
- motor neurons: carry messages from central system to peripheral system
- interneurons: connect sensory and motor neurons
- reflexes- burning hand example: reflex happens without aid of brain, controlled by nervous system alone= sensory--> interneuron--> motor neuron in less than 1 sec
- in the brain, the nervous system is less like a chain and more like a web
Endocrine system-- secretes chemical messages through hormones
- hormones can be chemically identical to neurotransmitters, but take much longer to send
- messages stay in place longer: example- still feeling stressed after finishing a test
- pituitary gland: growth hormones and controls release of other hormones (master gland)
- nervous system directs endocrine secretions, which then affect the nervous system
The Brain
Techniques to study the Brain
Brain Lesion= destroy part of brain tissue and observe effects
Clinical Observation= observe people with brain injuries/diseases
Electroencephalogram (EEG)= glue electrodes to scalp, measure electrical waves in brain
PET scan= inject patient with radioactive sugar, scan brain while they do tasks
MRI= use magnetic and radio waves to make images of the brain
fMRI= shows functions of brain by taking multiple MRI pictures mere seconds apart
Brain Structures
Frontal Lobe: planning, decisions, judging, speaking, process memory, personality
Clinical Observation= observe people with brain injuries/diseases
Electroencephalogram (EEG)= glue electrodes to scalp, measure electrical waves in brain
PET scan= inject patient with radioactive sugar, scan brain while they do tasks
MRI= use magnetic and radio waves to make images of the brain
fMRI= shows functions of brain by taking multiple MRI pictures mere seconds apart
Brain Structures
- brainstem= spinal cord swells and enters the skull
- nerves from one half of the brain connect to the other side of the body
- medulla controls heart rate and breathing, coughing, sneezing, hiccups etc.
- reticular formation: controls arousal, introversion/extroversion
- thalamus= brain's sensory switchboard- sensory info routed to brain through thalamus
- cerebellum (little brain): voluntary movements and coordination, balance
- limbic system= system of neural structures at border of brainstem and cerebrum
- emotions, fear, agression, food and sex
- amygdala= nut shaped structure at the end of the hippocampus- fear and agression
- hypothalamus- sits below thalamus, controls body maintenance- hunger, thirst, temp
- controls pituitary gland, the reward center of the brain
- hippocampus= processes memory (makes new memories)
- cerebral cortex= layer of neural cells covering hemispheres-- information processing
- white matter= axons, gray matter= dentrites, processing
- frontal lobe: motor cortex
- parietal lobe: sensory cortex
- temporal lobe
- occipital lobe: vision
Frontal Lobe: planning, decisions, judging, speaking, process memory, personality
- motor cortex= back strip- voluntary movement
- phineas gage- metal rod through his frontal lobe, personality change
- movement of body mapped out in motor cortex
- body parts that need more articulation have more neuron space (hands, lips)
Parietal Lobe: back rear of head- integrates sensory input, body position, spatial understanding, sense of direction, language, math, visual processing-- color, shape, form, movement, 3D
- sensory cortex= more sensitive parts have more neural space
- homunculus- way of visualizing amount of brain devoted to different body parts
- damage to lobe-- contralateral neglect: forget that you have a certain body part, difficulty with language, writing math
- Einstein's brain was normally sized, except for a huge parietal lobe
Occipital lobe: visual processing, damage makes you blind
- unconscious v. conscious visual processing
- horizontal v. vertical lines
- movement, color (damage- black and white), detail vision
Temporal Lobe: above and behind ears- auditory info
- hippocampus juts in to the lobe
- face recognition in the right temporal lobe
Connecting the Brain
association areas--used for higher functions (learning, memory, thinking, speaking)
Corpus callosum--bands of neurons that connect the two hemispheres
Language
complex, requires many different parts of the brain (centered in left hemisphere)
--- Note: languages that rely on tone are centered in both halves of the brain
- visual cortex: receives written words as visual stimulation
- Angular gyrus: transforms visual into auditory code= language recognition, internal monologue
- damage: written language becomes unrecognizable, difficulty naming things/tip of the tongue phenomenon
- Wernicke's area: interprets auditory code (reception, understanding, expression)
- damage: makes written language look foreign, can't understand spoken language
- Broca's area: controls speech muscles (motor cortex)
- damage: stuttering while speaking, but can still sing!
Hemispheres/Split Brain
Split Brain: some epilepsys are triggered by abnormal electric signals reverberating between the two hemispheres of the brain
- to separate the hemispheres and stop the reverberation, surgeouns sever the corpus callosum
- tested first on cats: cutting the hemispheres apart made no noticeable difference
Effects of Splitting the Brain
- left visual field goes to right brain and vice versa, creating full visual picture
- in a normal brain, the spheres can communicate to make this exchange possible
- in severed patients, each hemisphere does its own thing! (example: drawing)
--Hemispheric specialization: theory of left brain dominance in 1960's
- left: language, math, logic, details, analysis, decisions
- right: imagination, music, spatial understanding, faces and pictures
- intuitive decisions and "big picture", holistic view of problems
Now, a special note about language-- an ability for which both halves of the brain work together
- left: literal interpretations
- right: subtle inferences (ability to form stories when given a few seemingly unrelated words), ability to modulate speech for sentence flow, understanding jokes and making connections
- languages like Mandarin, which rely heavily on tone, use the right brain (music!)
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