chapter 2
DESCRIPTION
Chapter 2. Neuroscience and Behavior. Neurons and Synapses. Types of Neurons. Sensory. Motor. Interneurons. Sensory Neurons. INPUT From sensory organs to the brain and spinal cord. Brain. Drawing shows a somatic neuron. Sensory Neuron. Spinal Cord. Brain. Sensory Neuron. Spinal - PowerPoint PPT PresentationTRANSCRIPT
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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 structureOne 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 NeurotransmittersAcetylcholineDopamine SerotoninNorepinephrineGABAEndorphins
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Acetylcholine (Ach)
Found in neuromuscular junctions
Involved in muscle movementsInvolved 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 FunctioningCigarettes — 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 sleepInvolved 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 activityHuntington’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 HormonesHypothalamus
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