Test 4 Flashcards
What is homeostasis?
Process by which body’s substances and characteristics (such as temperature and glucose level) are maintained at their optimal level
What is ingestive behaviour?
Eating or drinking
What is a system variable?
variable that is controlled by a regulatory mechanism
- Ex: temperature in a heating system
What is set point?
optimal value of the system variable in a regulatory mechanism
What is a correctional mechanism?
In regulatory process, mechanism that is capable of changing value of system variable
- Provides negative feedback: process whereby the effect produced by a correctional mechanism serves to diminish or terminate the corrective action
What is a satiety mechanism?
brain mechanism that causes cessation of hunger or thirst, produced by adequate and available supplies of nutrients or water
When does thirst occur?
- Not enough blood circulating in the body (volumetric thirst)
- There is too much salt in the blood (osmometric thirst)
What is hypovolemia?
• When there is not enough blood circulating in the body
What does low blood flow cause?
Causes the release of renin, which triggers a hormone signalling cascade that promotes thirst, among other things, by activating hypothalamic neurons near the anteroventral tip of the third ventricle (the AV3V region), where the blood brain barrier is weak
- Hormones in the blood can seep into the CSF
What is tonicity?
The relative concentration of dissolved solutes (ex: salt) on either side of a semipermeable membrane
- It is used to describe the direction and extent of water diffusion across the membrane
What is an isotonic solution?
similar solute concentrations are present inside and outside the cell
- The cell will neither gain nor lose water
What is a hypotonic solution?
solute is less concentrated outside the cell than in, so water will enter the cell
- Because only water can move, water begins to enter the cell to try to equilibrate the concentration
What is a hypertonic solution?
solute is more concentrated outside the cell than in, so water will leave the cell
- Water will leave the cell to try to dilute the solution outside the cell
What are osmoreceptors?
neurons that detect changes in cell size, which corresponds to interstitial solute concentration
- The membrane potential and release of NT from osmoreceptor cells relates to the volume of these cells
What is glycogen?
Polysaccharide referred to as animal starch
- constitutes the short-term store of nutrients
What is insulin?
Pancreatic hormone that facilitates conversion of glucose into glycogen, entry of glucose and amino acids into cells of the body, and transport of fats into adipose tissue
What is glucagon?
Pancreatic hormone that promotes conversion of liver glycogen into glucose and conversion of adipose triglycerides into fatty acids
What is a triglyceride?
Form of fat storage in adipose cells (fat cells)
- Constitutes the long-term store of nutrients
What is glycerol?
Substance (also called glycerine) derived from breakdown of triglycerides, along with fatty acids
- Can be converted by liver into glucose
What is a fatty acid?
Substance derived from breakdown of triglycerides, along with glycerol
- Can be metabolized into sugars by most cells of body except for brain
What is grehlin?
Peptide hormone released by the empty stomach that increases eating
- also produced by neurons in the brain
What is the duodenum?
First portion of small intestine attached directly to the stomach
- the presence or absence of food in the duodenum regulates the release of grehlin from the stomach
What is leptin?
A circulating hormone that is secreted by adipocytes (fat cells)
- Thought to signal the size of peripheral energy stores in the body
- As fat cells grow, there is a concomitant increase in leptin levels in the blood stream
- The leptin provides a negative homeostatic feedback signal that decreases hunger
- Exogenous administration of leptin temporarily decreases meal size in healthy people
What is glucoprovation?
Dramatic fall in amount of glucose available to cells (detected in liver and brainstem)
- Can be caused by excess insulin signalling or by drugs that inhibit glucose metabolism
- Creates intense hunger
What is lipoprivation?
Dramatic fall in level of fatty acids available to cells (detected in liver and brain)
- Usually caused by drugs that inhibit fatty acid metabolism, but it can also relate to too little body fat
What is hypoglycemia?
Low blood sugar
- When the brain senses that it does not have enough glucose (sugar) to support normal brain function (via glucose-sensing neurons in various regions of the brain), it launches an emergency cascade of effects
What is hyperglycemia?
When disruptions in insulin signalling can cause high blood sugar, because sugar is not being converted int glycogen or fat
- If left untreated, this causes ongoing weight loss and loss of body fat
What are AGRP/NPY neurons?
They are orexigenic (their activity promotes hunger)
- These neurons are inhibited by leptin and activated by ghrelin
What are POMC/alpha-MSH neurons?
Anorexigenic (their activity inhibits hunger)
- These cells are activated by leptin and inhibited by ghrelin
What is the arcuate nucleus of the hypothalamus?
Nucleus in the base of hypothalamus that contains neurons highly sensitive to circulating levels of leptin
- contains AGRP/NPY neurons and POMC/alpha-MSH neurons, which are involved in feeding and metabolic rate
What is the paraventricular nucleus of the hypothalamus?
Nucleus of hypothalamus that receives inputs from arcuate nucleus
- Contains oxytocin neurons that signal the body has adequate levels of leptin (fat)
What is Prader-Willi syndrome?
a rare chromosomal abnormality in which up to 7 genes are deleted from chromosome 15
- One of these genes is critical for the development/survival of oxytocin-containing neurons in the PVN
- People with this syndrome are born with very low muscle mass and have little interest in eating
- But later, between 2 and 8 years old, these people develop into having no sensations of satiety to tell them to stop eating or to throw up, so they can accidentally consume enough food in a single binge to fatally rupture their stomach
What is leptin resistance?
When people have an elevated leptin set point that they are trying to maintain, and they have a blunted response to increases in leptin levels
What is bariatric surgery?
Aimed at the stomach, small intestine, or both
- The most effective form of bariatric surgery is special form of gastric bypass called the RYGB
- With RYGB surgery, the jejunum is cut and upper end is attached to stomach pouch
- The stomach is physically smaller
What is memory retrieval?
Accessing memories
What is neural plasticity?
the ability of the nervous system to change and adapt
What is intrinsic plasticity?
:The number of action potentials a neuron exhibits in response to an influx of positive current
- Determined by the number and type of ion channels (leak channels and voltage-gated channels) expressed by the neuron
- More action potentials = more excitable
What is synaptic strength?
the amount of positive (or negative) current that enters the postsynaptic neuron when the presynaptic cell has an action potential
- Enduring changes in synaptic strength are referred to as long-term potentiation (LTP) or long-term depression (LTD)
- Can involve pre or postsynaptic changes (in vesicle release and receptor activity)
What is habituation?
reduced physiological or behavioural responding to a repeated stimulus
What is sensitization?
Increased sensitivity to a stimulus
What is long-term potentiation (LTP)?
Long-term increase in the strength of the connection between two neurons (synaptic strength)
- repeated high-frequency stimulation can induce LTP
- LTP is often initiated on the postsynaptic side but retrograde signalling of NO can drive presynaptic modifications
What is long-term depression (LTD)?
Long-term decrease in the strength of the connection between two neurons (synaptic strength)
- persistent low-frequency stimulation can induce LTD
- often initiated on the post-synaptic side but retrograde endocannabinoid signalling can drive presynaptic modifications
What is synaptic plasticity?
A change in the strength of the synaptic connection between two neurons
What is an NMDA receptor?
- An ionotropic glutamate receptor that has a large ion pore
- Na and Ca ions will enter a cell through NMDA receptors, but only when these receptors are bound to glutamate and Mg is not clogging the pore (when it is DEPOLARIZED)
What is the AMPA receptor?
Glutamate receptor that mediates most excitatory fast synaptic currents in the brain
- Ionotropic and opens upon glutamate binding
- It lets in sodium ions which cause EPSPs that depolarizes neurons
What is CaMKII: type II calcium-calmodulin kinase?
An enzyme that is activated by calcium influx through NMDA receptors
- Plays a role in the intracellular signaling cascade that establishes long-term potentiation, by increasing the number of postsynaptic AMPA receptors (in excitatory glutamatergic synapses)
What is classical conditioning?
The pairing of strong synapse with weak synapse is enough to strengthen the connection with the tone
What is associative long-term potentiation?
the increase in synaptic strength that occurs in weak synapses when they are active right around the time when stronger inputs caused the postsynaptic neuron to spike
What is Hebb’s rule?
The cellular basis of learning involves the strengthening of synaptic connections that are active when the postsynaptic neuron fires an action potential – this is known as:
- Neurons that fire together, wire together – more strongly than before
- The synaptic connection does have to initially exist
What is perceptual learning?
Learning to recognize stimuli as direct entities
- It’s a pattern recognition system
- You’re trying to categorize what you’re seeing
What is motor learning?
Learning to make skilled, choreographed movements
- procedural learning
There is rapid component called between-session learning, where improvements in motor behaviour are seen following a period of the memory consolidation (in part during sleep)
• The cerebellum, thalamus, basal ganglia, and motor cortex are all involved in motor learning
What is relational learning?
Learning relationships among individual stimuli
- stimuli-stimuli learning
What is stimulus-response learning?
Learning to perform a particular behaviour when a particular stimulus is present
- includes classical and instrumental conditioning
What is unconscious memory?
Implicit, non-declarative memory
• Memories that influence behaviour in an automatic, involuntary manner
• Relates to automatic adjustments to perceptual, cognitive, and motor systems that occur beneath the level of conscious awareness
What are consciously accessible memories?
Explicit, declarative memory
• Memories of events and facts that we can think and talk about - includes:
- Episodic memory: personal experiences associated with a time and place
- Semantic memory: encyclopedic memory of facts and general information, often acquired generally over time
What is sensory memory?
Lasts only for a couple seconds or less
- Allows an individual to retain the experience of the sensation slightly longer than the original stimulus
- Occurs in each of the senses
What is short-term memory?
Lasts for seconds to minutes
- Only a small fraction of sensory information enters short-term memory
- The memory capacity of short-term memory is limited to a few items, but the length can be extended through rehearsal
What is long-term memory?
Persists after getting distracted and perhaps even after a nap
- Information will be retained from short-term memory is consolidated into long-term memory
- Long-term memories can be retrieved throughout a lifetime and strengthened with increased retrieval
What is visual agnosia?
Damage to regions of brain involved in visual perception not only impair ability to recognize visual stimuli but also disrupt people’s memory of visual properties of familiar stimuli
- People with visual agnosia can draw by copying pictures, but they can’t perceive it; they just see lines and shapes
- They can only draw shapes when asked to draw from memory
What is instrumental conditioning (operant conditioning/reinforcement learning)?
Learning form the consequences of your actions, from the receipt of reinforcement or punishment
- The likelihood these actions will be repeated depends on whether they were reinforced, punished, or completely inconsequential
What is a reinforcing stimulus?
When it follows a particular behaviour, it increases the likelihood the animal will repeat the behaviour
- Reinforcement makes the behaviour more likely to occur
What is a punishing stimulus?
When it follows a particular behaviour, it decreases the likelihood the animal will repeat the behaviour
- Punishment makes the behaviour less likely to occur
What is the function of direct transcortical connections in learning?
involved in acquiring complex motor sequences that involve deliberation or instruction
What is the function of basal ganglia in learning?
To integrate sensory and motor information from throughout the brain; it is important for habit formation
- as behaviours are repeated again and again, the basal ganglia begins to learn what to do
- Eventually, the basal ganglia take over most of the details of the process, leaving the transcortical circuits free to do something else
• At this point, we don’t need to consciously think about what we are doing
Explain the significance of dopamine input into the striatum
Dopamine neurons in the midbrain (specifically in the substantia nigra and ventral tegmental area) strongly innervate the striatum and signal reinforcement and punishment
What is the role of the striatum?
It seems to regulate people’s priorities
What is Korsakoff’s syndrome?
Permanent anterograde amnesia caused by brain damage, usually resulting from chronic alcoholism
- patients are unable to form new memories but can still remember old ones before the brain damage occurred
What is confabulation?
Reporting of memories of events that did not take place without intention to deceive
- seen in people with Korsakoff’s syndrome
What is memory consolidation?
converting short-term memories into explicit long-term memories
What is anterograde amnesia?
the inability to learn new information or retain new information ‘after’ brain injury
- Memory for events that occurred before the injury remain largely intact
What is retrograde amnesia?
inability to remember events that occurred ‘before’ the brain injury
What is basal-ganglia-dependent learning?
When you can’t form the conscious explicit memory, but you have a gut instinct
- Might be because of dopamine signalling in the basal ganglia
What is the role of the MEC?
provides learned structural information
What is the role of the LEC?
provides perceived sensory information
What are grid cells?
In the MEC, when animals walk around an open field, the spiking activity of some MEC neurons seem to represent space using a hexagonal grid
- the grid of each cell is slightly rotated relative to its neighbours
- can be used to determine the exact location of the animal
What is grid cell realignment?
When an animal walks into a different room (or to a different side of a very large room), the grid of every grid cell rotates a certain amount
What are border cells in the MEC?
They fire whenever the animal is located near a wall in a particular direction
What are object vector cells?
they fire whenever the animal is a certain distance and direction away from an object (any object)
What is prosody?
Rhythm, emphasis and tone of speech
- typically a function of the right hemisphere
- how info about one’s emotional state is extracted
What is phonagnosia?
A disorder where people have great difficulty recognizing voices
- Results from localized brain damage to the right superior temporal cortex
What is aphasia?
• Refers to a disturbance in understanding, repeating, or producing meaningful speech
- The difficulty must not be caused by simple sensory or motor deficits or by lack of motivation
- The deficit must be relatively isolated, such that they must be capable of recognizing when others are communicating
- The patient must be somewhat aware of what is happening around them
What does damage to the frontal lobe cause in language?
Deficits in speaking
What does damage to the sensory association cortex cause in language?
Deficits in understanding language
What is transcortical sensory aphasia?
Failure to comprehend the meaning of words and an inability to express thoughts with meaningful speech
- Words perception and speaking might be fine (without any comprehension of what is heard or spoken)
- Word repetition (almost constantly repeating after people)
- Reading (without understanding)
- Writing (without understanding)
What is repetitive, fluent aphasia?
You can talk to people and recognize emotions, but you can’t derive meaning from your own or other people’s words
What is conduction aphasia?
Can understand and speak words, but they just lack the ability to repeat the exact words
- You have meaningful, fluid speech and good comprehension
- Damage to the connection between Wernicke’s and Broca’s area known as the arcuate fasciculus
- Disrupts short-term working memory
What is Wernicke’s area?
• Involved in the analysis of speech sounds and in recognition of spoken words
What is pure word deafness?
The result of damage to a small part of Wernicke’s area or disruption of auditory input in the region
- A disorder of auditory word recognition – an inability to comprehend or repeat spoken words
What is Wernicke’s aphasia?
The result of damage to both Wernicke’s area and the posterior language area, which means you have features of transcortical sensory aphasia and pure word deafness
- poor language comprehension
- These people can have fluent speech production, but what they say is meaningless
What is pure Alexia (pure word blindness)?
Damage to the visual word-form area (VWFA) disrupts the ability to perceive written words
- People with this damage cannot read, as they cannot recognize written words
- However, they can write just fine – they just can’t read what they write
What is dyslexia?
People who have difficulty reading
What is whole-word reading?
Reading by recognizing a word as a whole; “sight reading”
What is phonetic reading?
Reading by decoding the phonetic significance of letter strings; “sound reading”
What is surface dyslexia?
An inability to recognize whole words – the person can only read words phonetically
- Irregularly spelled words are difficult for these people to perceive, because sounding them out doesn’t work
What is phonological dyslexia?
reading disorder in which a person can read familiar words but has difficulty reading unfamiliar words or nonwords
What is developmental dyslexia?
Mostly a type of phonological dyslexia, and the problem is largely genetic
- People have great difficulty learning to read and some never become fluent readers, even though they are otherwise intelligent
- They also have trouble with grammar and spelling and have a hard time distinguishing the order of sound sequences
What is direct dyslexia?
When people have very specific deficits in their ability to extract meaning from written words even though they can read out loud
- It is typically seen with larger deficits, like transcortical sensory aphasia where there is limited language comprehension
