Microsoft PowerPoint - Brain Lecture 3_2011.pptxThe Nervous System Neuron
Nucleus Cell body Dendrites – they are part of the cell body of a neuron that collect chemical and electrical signals from g other neurons at synapses and convert them into electrical activity along the thin membrane that encloses the cell. Axon (maybe mylinated) Synapses – junction between two neurons:
• Chemical Synapses • Electrical Synapses
The Synapse: The Processor
A synapse is where two neurons communicate electrically or chemically. A chemical synapse is a small gap that exists between the terminals of one neuron and the dendrites of another into the dendrites of another, into which neurotransmitters are released. At an electrical synapse, two neurons are physically connected to one another via gap junctions. Gap junctions make it possible for an electrical signal in one neuron to pass directly to another.
Chemical synapses are far more common than the electrical ones. Electrical synapses in mammalian CNS, are mainly found in specialized locations where normal functions requires highly synchronized activity between the neighboring neurons.
Although gap junctions are relatively rare between adult mammalian neurons, they are very common in a large variety of non-neural cells, including smooth cardiac muscle cells, epithelial cells, some glandular cells, glia, etc. They are also common in many invertebrates.
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Inactive
Excitatory
Inhibitory
Simple Neural Network • What would happen if inputs from axons 1 & 2 was excitatory?
• What would happen if inputs from axons 1 & p 2 was inhibitory?
• What would happen if input from axon 1 was excitatory and from axon 2 was inhibitory?
Neurotransmitter It is a chemical substance that is released by one neuron and binds to a receptor of another neuron, altering the flow of altering the flow of electrical current or internal biochemical events within the 2nd
cell.
There are many kinds of receptors for a single neurotransmitter. http://cvlab.epfl.ch/research/medical/neurons/
Neurotransmitter
It's not the structure of the compound that makes it a neurotransmitter. It's really its function. For example, glutamate, which is a simple amino acid, is the main excitatory neurotransmitter y in the brain. Obviously it's not an excitatory neurotransmitter when it‘s incorporated into other proteins. And the same substance might be a neurotransmitter in the brain and a hormone elsewhere in the body. – can become quite confusing!
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Neurotransmitters and hormones are chemicals secreted inside our brain, and are largely responsible for our behaviour and attitude but they are not the same!
The most notable difference between a neurotransmitter and a hormone pertains to the point of its release inside the body. Also they are different depending on their release mechanism.
A hormone is a compound produced by endocrine gland and is
Neurotransmitters & Hormones
A hormone is a compound produced by endocrine gland and is released directly into the bloodstream where it easily finds its target cells at a small distance from the point of release.
Neurotransmitter is a compound released by a nerve terminal when the nerve is triggered by an electrical impulse.
Hormones can be synthesized, whereas it is impossible to make neurotransmitters. They are made inside the body only.
Important Neurotransmitters Neurotransmitter Usual action Secreted by: Associated with:
Acetycholine Excitatory Cells of the motor cortex, the motor neurons to skeletal muscles, some neurons in the basal ganglia.
Muscle contraction, arousal, aggression
Glutamate Excitatory Cells in the sensory pathways into the CNS, cortex
Learning, memory
Norepinephrine Excitatory Cells in the brain stem Levels of activity, arousal
Glycine Inhibitory Cells in the spinal cord. Joint movement, arthritis, depression
Dopamine Inhibitory Cells in the substantia nigra of the midbrain, target is cells in the basal ganglia.
Control of movement and posture, mood, dependency.
GABA (gamma- aminobutyric acid)
Inhibitory Cells in the spinal cord, cerebellum, basal ganglia, cortex.
Motor control, regulates anxiety.
Serotonin Inhibitory Cells in the core of the brain stem
Pain pathways, mood.
Simple Reflex Arc • Input from skin receptor
• Processed in spinal cord by interneuron - or
• Output to muscle
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Processing at Higher Levels
Motor Pathways • supplemental and premotor cortex • primary motor cortex b l l• basal ganglia
• thalamus • cerebellum • brain stem
Sensory Memory Working Memory ( h t t )
Long-Term Memory
(shot-term memory)
Very short in duration ( <1 s) Acts like buffer for
sensory stimuli (5 senses)sensory stimuli (5 senses) Cannot be maintained like
other types of memory by rehearsing.
Short-term working memory appears to operate phonologically. For instance, whereas English speakers can typically hold seven
Short-Term (working) Memory
Duration: 10-15s , <1 min
Ability to remember and process information at the same time typically hold seven
digits in short-term memory, Chinese speakers can typically remember ten digits. This is because Chinese number words are all single syllables, whereas English are not.
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R3T-5V6
repetition and association it can convert to long-term memory.
Involves prefrontal lobe of the brain.
Classification of Long-Term Memory
Episodic vs Semantic Memory
• Semantic memory is for facts, while  episodic memory is the memory for  events/experiences. 
• Episodic memories are very dynamic.
Semantic Memory
Interesting to know!
• Females consistently perform better  than males on episodic longterm  memory tasks, especially those  involving delayed recall and  recognition.g However, males and females do not  differ significantly on working  memory and semantic memory tasks. There is also evidence for a negative  recall bias in women, which means  that females in general are more  likely than males to recall their  mistakes.
Construction of Memory Studies have shown that attention significantly affects memory during the encoding phase, but hardly at all during recall.
Thus, distractions or di id d tt ti d i divided attention during initial learning may severely impair subsequent retrieval success, whereas distractions at the time of recall may slow down the process a little, but has little to no effect on its accuracy.
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Construction of Long-term Memory Hippocampal Area
Construction of Long-term Memory Hippocampal Area
“Gatekeeper” for semantic and episodic memory which are stored in episodic memory which are stored in diffuse areas of cortex
Location of spatial memory (GPS unit)
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New Findings/Research about Memory
• Retrieving memory is a creative process; there  is no fixed exact of memory of anything that  just needs to be recalled; every time we have  to recreate the memoryto recreate the memory. 
• Memories are prone to error.
General comment: Be aware of the difference  between association and causal relationship.
Conclusions from Case Study HM: a patient who had  bilateral destruction of his hippocampus (in the medial 
temporal lobe) and had lost shortterm memory
1. The ability to acquire new memories is a distinct cerebral  function that is located in the medial portion of the temporal  lobes.
2. The medial temporal lobes were not required for immediate  memory He could retain some new information as long as hememory. He could retain some new information as long as he  didn’t get interrupted.
3. The medial lobes and the hippocampus can’t be the ultimate  storage sites for longterm memory, because he still had his long term memory from before the injury.
4. There is another kind of memory besides the kind that we  normally think of, which is like memories of events. (He became  better from day to day even without a conscious memory of  doing it.
Methods used to study Brain
– Lesion studies – EEG – ERP – Imaging Studies– Imaging Studies – Animal Studies – Neuropsychological Studies
Lesion Studies • Damage to a particular part of the
brain can result in specific behavioral effects – Examples Amygdala (emotion) Hippocampus (memory) Visual cortex (blindsight) Parietal cortex (attention) Left hemisphere (language)
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• Measures “brain waves” • Gross measure of integrity of the
brain as a system brain as a system – Can be used as a very low level indicator
(is this person alive) – Can also be used to measure behavior Depression
Electroencephalography (EEG)
• How does it work? – Brains produce electricity Neurons do their business basically by acting like
wires El d l d l d b i – Electrodes placed on scalp record brain electrical activity
– Measures include the amount of activity in particular frequency bands Power Activation Activation in a particular frequency range
Event – related Potentials (ERP)
• Definition: – Brain electrical activity that comes from
simultaneous firing of synapses, and is related to a specific eventto a specific event.
• How do you measure them? – Electrodes placed on the scalp record brain
activity – Activity is recorded in response to a specific
discrete event. – Averaging over enough trials gets rid of the
“noise” of the background EEG.
Imaging • Computed Tomography (CT or CAT
Scans) – Uses Xray, Useful for describing
overall brain structure
P E T h (PET)• Positron Emission Tomography (PET) Scans – Good measure of blood flow in brain – Poor resolution – Involves radiation – usually used to compliment rather
than replace the information obtained from CT or MRI scans.
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structure of the brainstructure of the brain
Imaging (continued)
flow in the brainflow in the brain – Example - Working Memory
Neuropsychology
• Behavioral method derived from lesion and animal studies
• These behaviors are associated with parts of the brain from lesion, animal, or imaging studies
• You can measure the function of the brain indirectly – Example: Autism
All of the above? • There are advantages to combining
these methods. What might these be? – Look at behavior to determine what
’ ll you’re really measuring – converging measures
– What if an imaging study shows something different than lesion studies or animal studies always have?
– Complementary resolution advantages
Recording of Electrical Activity of Neurons Classification of EEG Waves
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Beta waves: frequency range from 13-15 to 60 Hz , amplitude of about 30 μV. Beta waves occur when the subject is awake, alert, and actively processing information. Alpha waves: frequency range from 8 to 12 Hz, amplitude of 30 to 50 μV. Alpha waves are typically found in people
h k b h h l d
Interpretation of EEG Waves
who are awake but have their eyes closed and are relaxing or meditating. Theta waves: frequency range from 3-4 to 7- 8 Hz , amplitude of 50 to 100 μV. Theta waves are associated with memory, emotions, and activity in the limbic system. Delta waves: frequency range from 0.5 to 3 or 4 Hz, amplitude of 100 to 200 μV. Delta waves are observed when individuals are in deep sleep or in a coma.
EEG Waves in Sleep
Stages of Sleep Stage 1 • eyes are closed • relaxed • heart rate, respiration “normal” • easily aroused
Stage 2 • arousal more difficult
Stage 3 • sleep is deeper • heart rate, respiration slower
Stage 4 • arousal difficult • heart rate, respiration slowest • seen in sleepwalkers
REM • most skeletal muscles inhibited • eye movements • heart rate, respiration increased • dreaming
Patterns of Sleep Stages