chapter 2 lecture disco 4e
TRANSCRIPT
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Chapter 2
Neuroscience and Behavior
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Neurons and Synapses
Types of Neurons
Sensory Motor Interneurons
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SpinalCord
BrainSensoryNeuron
Sensory Neurons
• INPUT From sensory organs to the brain and spinal cord
Drawing shows a somatic neuron
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Motor Neurons
• OUTPUT From the brain and spinal cord to the muscles and glands
SpinalCord
BrainSensoryNeuron
MotorNeuron
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SpinalCord
BrainSensoryNeuron
MotorNeuron
Interneurons
• Interneurons carry information between other neurons only found in the brain and spinal cord
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Parts of a Neuron
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The Cell Body
– round, centrally located structure – contains DNA– controls protein manufacturing – directs metabolism– no role in neural signaling
Contains the cell’s nucleus
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Dendrites
• Information collectors
• Receive inputs from neighboring neurons
• Inputs may number in thousands
• If enough inputs, the cell’s AXON may generate an output
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Dendritic Growth
• Mature neurons generally can’t divide • But new dendrites can grow• Provides room for more connections to other
neurons• New connections are basis for learning
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Axon
• The cell’s output structure
• One axon per cell, 2 distinct parts– tube-like structure – branches at end that connect to dendrites
of other cells
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Myelin Sheath
• White fatty casing on axon • Acts as an electrical insulator • Not present on all cells• When present, increases the speed of neural
signals down the axon
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How Neurons Communicate
• Neurons communicate by means of an electrical signal called the action potential.
• Action potentials are based on movements of ions between the outside and inside of the cell.
• When an action potential occurs, a molecular message is sent to neighboring neurons.
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Action Potential Within a Neuron
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Resting Potential
• At rest, the inside of the cell is at -70 microvolts.• With inputs to dendrites, the inside becomes more positive. • If resting potential rises above threshold, an action potential
starts to travel from cell body down the axon.• Figure shows resting axon being approached by an AP.
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Depolarization Ahead of AP
• AP opens cell membrane to allow sodium (Na+) to enter.
• Inside of cell rapidly becomes more positive than outside.
• This depolarization travels down the axon as leading edge of the AP.
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Repolarization follows
• After depolarization, potassium (K+) moves out restoring the inside to a negative voltage.
• This step is called repolarization.• The rapid depolarization and repolarization produce a
pattern called a spike discharge.
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Finally, Hyperpolarization
• Repolarization leads to a voltage below the resting potential, called hyperpolarization.
• Now, the neuron cannot produce a new action potential.• This is the refractory period.
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Neuron to Neuron
• Axons branch out and end near dendrites of neighboring cells.
• Axon terminals are the tips of the axon’s branches.
• A gap separates the axon terminals from dendrites.
• The gap is called the synapse.
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Neurotransmitter Release
• Action potential causes vesicle to open.
• Neurotransmitter released into synapse.
• Neurotransmitter locks onto receptor molecule in postsynaptic membrane.
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Excitatory and Inhibitory Messages
• Excitatory message — increases the likelihood that the postsynaptic neuron will activate
• Inhibitory message — decreases the likelihood that the postsynaptic neuron will activate.
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Locks and Keys
• Neurotransmitter molecules have specific shapes.
• When NT binds to receptor, ions enter.
• Receptor molecules have binding sites.
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Some Drugs Work on Receptors
• Some drugs are shaped like neurotransmitters.
• Antagonists: fit the receptor but poorly and block the NT– e.g., beta blockers
• Agonists: fit receptor well and act like the NT– e.g., nicotine
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Types of Neurotransmitters
• Acetylcholine
• Dopamine
• Serotonin
• Norepinephrine
• GABA
• Endorphins
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Acetylcholine (Ach)
• Found in neuromuscular junctions• Involved in muscle movements• Involved in learning and memory
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Disruption of Acetylcholine Functioning
• Curare — blocks ACh receptors– paralysis results
• Nerve gases and Black Widow spider venom — too much ACh leads to severe muscle spasms and possible death
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Disruptions in ACh Functioning
• Cigarettes — nicotine works on ACh receptors– can artificially stimulate skeletal
muscles, leading to slight trembling movements
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Alzheimer’s Disease
• Deterioration of memory, reasoning, and language skills
• Symptoms may be due to loss of ACh neurons
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Dopamine
• Involved in movement, attention, and learning
• Dopamine imbalance also involved in schizophrenia
• Loss of dopamine-producing neurons is cause of Parkinson’s disease
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Parkinson’s Disease
• Results from loss of dopamine-producing neurons in the substantia nigra
• Symptoms include– difficulty starting and stopping voluntary movements– tremors at rest– stooped posture– rigidity– poor balance
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Parkinson’s Disease
• Treatments– L-dopa– transplants of fetal dopamine-producing
substantia nigra cells– adrenal gland transplants– electrical stimulation of the thalamus has
been used to stop tremors
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Serotonin
• Involved in sleep
• Involved in depression– Prozac works by keeping serotonin in
the synapse longer, giving it more time
to exert an effect
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Norepinephrine
• Arousal
• “Fight or flight” response
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Endorphins
• Control pain and pleasure
• Released in response to pain
• Morphine and codeine work on endorphin receptors; involved in healing effects of acupuncture
• Runner’s high— feeling of pleasure after a long run is due to heavy endorphin release
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GABA
• Inhibition of brain activity
• Huntington’s disease involves loss of neurons in striatum that utilize GABA– Symptoms:
• jerky involuntary movements• mental deterioration
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Summary
• Neuron structure• Action potentials• Synapse• Neurotransmitters• Receptors and ions• Agonists and
antagonists
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Parts of the Nervous System
• Central Nervous System (CNS)– Brain and spinal cord
• Peripheral Nervous System (PNS)– Carries messages to and from CNS
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Central nervous system
Peripheral nervous system
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Sympathetic and parasympathetic divisions of the nervous system
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Endocrine System
• Pituitary gland — attached to the base of the brain, hormones affect the function of other glands
• Adrenal glands — hormones involved in human stress response
• Gonads — hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females.
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Brain
• Images
• Brainstem– Hindbrain– Midbrain
• Forebrain– Limbic system– Cortex
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Developing Brain
•Neural tube — beginning of nervous system develops at 2 weeks after conception
•Neurogenesis — development of new neurons
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Hindbrain Structures
• Cerebellum
• Brainstem– medulla– reticular
formation– pons
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Cerebellum• Coordinated, rapid
voluntary movements– e.g., playing the
piano, kicking, throwing, etc.
• Lesions to cerebellum– jerky, exaggerated
movements
– difficulty walking
– loss of balance
– shaking hands
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Medulla
• Breathing• Heart rate• Digestion• Other vital
reflexes– swallowing– coughing– vomiting– sneezing
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Reticular Formation
• Network of neurons in the brainstem (and thalamus)
• Sleep and arousal
• Attention
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Pons• Helps coordinate movements on left and right sides of the body– e.g., postural
reflexes which help you maintain balance while standing or moving
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Forebrain Structures
• Thalamus
• Limbic System
• Cortex
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Thalamus
• Relay station in brain• Processes most
information to and from higher brain centers
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The Limbic System
• Hypothalamus
• Amygdala
• Hippocampus
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Hypothalamus
• Contains nuclei involved in a variety of behaviors– sexual behavior– hunger, thirst– sleep– water and salt balance– body temperature regulation– circadian rhythms– role in hormone secretion
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Hypothalamus and Hormones
Hypothalamus releases hormones or releasing factors which in turn cause pituitary gland to release its hormones
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Amygdala and Emotion
• Identify emotion from facial expressions
Amygdala damage makes this task difficult
(click on picture to advance photos)
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Cortical Specialization
• Localization — notion that different functions are located in different areas of the brain
• Lateralization — notion that different functions are processed primarily on one side of the brain or the other
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Lobes of the Cortex• Frontal lobe — largest lobe, produces
voluntary muscle movements, involved in thinking, planning, emotional control
• Temporal lobe — primary receiving area for auditory information
• Occipital lobe — primary receiving area for visual information
• Parietal lobe — processes somatic information
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Language and the Brain
• Aphasia — partial or complete inability to articulate ideas or understand language because of brain injury or damage
• Broca’s area — plays role in speech production
• Wernike’s area — plays role in plays role in understanding and meaningful speech
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Split brain operation—procedure used to reduces recurrent seizures of severe epilepsy
Corpus callosum—thick band of axons that connects the two cerebral hemispheres