W3 notes Flashcards
Synesthesia
Synesthesia is a condition where individuals experience a mingling of the senses
E.g. grapheme-colour synesthesia is when the perception of numerals and letters is associated with the experience of colours
patient george case
A man known as patient George is one of 2 people known to have acquired synesthesia after suffering damage to the thalamus (stroke in the left thalamus)
He reported experiencing an intense sensory-emotional experience as a result of hearing the brass theme from James Bond
Hearing the music led to greater neural activation in widespread areas of the brain including the auditory cortex, somatosensory cortex, motor cortex, thalamus, hippocampus, and particular regions of the insula, cerebellum, and prefrontal cortex
neurons
Neurons→nerve cells which are the building blocks of the nervous system
glia
the supporting cells in neurons
neural communication process
First step takes place within a single neuron and involves the generation of an electric signal
Second step takes place between 2 neurons and involves the release of a chemical messenger from 1 neuron that affects the activity of the second
-This is why the nervous system is often referred to as the body’s electrochemical communication system
cell body
Like other cells, a neuron has a large central mass or cell body, and within the cell body, it has a nucleus
structure of neuron outer membrane
Like other cells, neurons feature an outer membrane, which surrounds the neuron and forms a barrier between the fluid outside the cell (extracellular fluid) and the fluid inside the cell (intracellular fluid)
neural membrane
Neural membrane is composed of fatty materials that do not dissolve in water, so even though it is only 2 molecules thick, it’s able to hold apart the water-based fluids on either side
Pores within the membrane act as channels that allow chemicals to move into or out of the cell
axons vs dendrites
Neurons have 2 types of branches that extend from the cell body to allow the neuron to perform its information-processing and communication functions
The branches known as axons are responsible for carrying info to other neurons, while the branches known as dendrites receive input from other neurons
Each neuron has only one axon
terminal
At its farthest point from the cell body, an axon bulges to form a terminal
Inside an axon terminal, you can see hollow spheres known as synaptic vesicles, which contain molecules of chemical messengers
glia
Glia make it possible for neurons to do their job effectively and provide a structural matrix for neurons, ensuring that the neurons stay in place
Other glia are mobile, allowing them to move to a location where neurons have been damaged to clean up debris
Glia form tight connections with the blood vessels serving the nervous system
-This forms a blood-brain barrier that prevents many toxins circulating in the blood from exiting into brain tissue where neurons could be harmed
psychoactive drugs
Psychoactive drugs, are substances capable of penetrating the blood-brain barrier with ease
blood brain barrier
Gilia form tight connections with the blood vessels in the nervous system, preventing many toxins from entering the brain
Glia also help hold neurons in place and form the myelin on some axons
Sometimes offers too much protection to the brain and chemotherapy agents can’t get past it to treat tumours
myelin
In vertebrates, glia wrap around some axons, forming an important layer of insulation called myelin
Myelin makes neural signalling fast and energy efficient
By speeding up the transmission of neural signals and contributing to quicker recovery between signals, myelin increases the amount of info a neuron can transmit per second by a factor of 3000
function of different types of glia
One type of glia forms the myelin in the brain and the spinal cord, and a 2nd type forms the myelin in the remainder of the nervous system
-They behave differently from each other when damaged
–Glia in the brain and the spinal cord form scar tissue, inhibiting repair to the damaged nerves
—Because of this feature, we consider damage in the CNS to be permanent
Damaged glia in the PNS do not form scar tissue and instead help the damaged axons regrow
-As a result, nerve damage in these areas can heal
The last area of the nervous system to be myelinated is the…
prefrontal cortex, which is involved with judgement and morality
Until myelin in this area is mature, these neurons don’t work efficiently, which’s why adults and teens make different decisions
neuron
A neuron is a sophisticated communication and information-processing system that receives input, evaluates it, and decides whether to transmit info to neurons downstream
1st step of neuron communication
In the 1st step of neuron communication, it takes place in the signalling neuron’s axon, the neuron generates an electrical signal known as action potential
This signal travels the length of the axon from its junction with the cell body to its terminal
2nd step in neural signalling
In the 2nd step, which takes places between 2 neurons, the arrival of an action potential at the axon terminal of the first neuron signals at the release of chemical messengers, which float across the extracellular fluid separating the 2 neurons
These chemicals influence the likelihood that the second neuron will respond with its own action potential, sending the message along
electrical signaling
When a neuron is not processing information we say that it’s at rest
When a cell is at rest, the difference between the readings from the interior of the axon and the external fluid is known as the resting potential
Neurons can respond to incoming chemical signals by becoming either …
depolarized or hyperpolarized
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The word polarized means “far apart” and being depolarized means we have moved closer together, being hyperpolarized means we have moved farther apart than before
depolarization
In the case of neurons, depolarization means that the difference between the electrical charges of the extracellular and the intracellular recordings is decreasing
hyperpolarization
Hyperpolarization means that the difference is increasing
what happens when a neuron is depolarized?
When a neuron is depolarized by sufficient input, it reaches a threshold for producing an action potential
threshold
A threshold is the point at which an effect (the action potential), is initiated
Once this threshold is reached, the generation of an action potential is inevitable
This involves the opening and the closing of pores or channels in the neural membrane, which in turn allow certain chemicals to move into and out of the cell
These chemicals are in the form of ions or electrically charged particles dissolved in water
when the threshold is reached and channels open, what happens?
When threshold is reached, channels open, allowing only one type of ion, sodium, to rush into neuron (bc of positive electrical charge)
Near the peak of the action potential, channels open that allow another type of ion, (positively charged) potassium, to move across the membrane
resting state
after the production of the action potential, the neuron requires a time-out or refractory period, during which it returns to its resting state
During this period, the cell is unable or unlikely to respond to further input by producing another action potential
action potentials
Action potentials do NOT affect the entire axon all at once
The process just described takes place first in a small segment of the axon where the axon connects to the cell body
propagation
The next step is propagation, or the duplication of the electrical signal down the length of the axon to the axon terminal, where it initiates the release of chemical messengers
Propagation takes place differently in myelinated and unmyelinated axons
action potential in an unmyelinated axon
In an unmyelinated axon, action potentials occur step by step, from one small section of the axon to the next adjacent section, down the entire length of the axon
action potential in a myelinated axon
In contrast, action potentials in myelinated axons are formed only at the sections of the axon membrane between adjacent segments of myelin, known as nodes of Ranvier
propagation in myelinated axons can “_____” the sections covered by myelin
skip
Propagation in myelinated axons
After an initial action potential is generated near the cell body, the current flows beneath a segment of myelin until it reaches a node of Ranvier, where another action potential occurs
By covering the same distance with fewer action potentials, the myelinated axon uses less energy returning to the resting potential than an unmyelinated axon would need
-Once the action potential reaches the axon terminal, the neural communication system switches from an electrical signaling system to a chemical signaling one
synapse
The point of communication between 2 neurons is known as a synapse
At the synapse, neurons do not touch one another physically
They are separated by tiny gaps filled with extracellular fluid
neurotransmitters
Because electrical signals are unable to jump this gap, neurons send chemical messengers instead
These chemical messengers are called neurotransmitters
After interacting with receptors, neurotransmitter molecules are often recaptured by the neuron that released them to be recycled and used again later
receptors
The neurotransmitters released across the synaptic gap come into contact with special channels on the receiving neuron, known as receptors
Receptors work with the neurotransmitters like locks and keys
Only a neurotransmitter with the right shape (the key) can attach itself or bind to a particular receptor (the lock)
reuptake
Once neurotransmitters pop out of the receptor binding site, they drift away from the gap, are broken down by enzymes or return to the axon terminal from which they were released in a process called reuptake
Reuptake is when special channels in the axon terminal membrane known as transporters allow the neurotransmitters to move back into the releasing neuron where they are repackaged for later use
The interaction between neurotransmitters and their receptors can have one of 2 effects on the receiving neuron:
excitation or inhibition
When a neurotransmitter has an excitatory effect…
it slightly depolarizes the receiving neuron, increasing the likelihood that the neuron will reach threshold and initiate an action potential
Recall that depolarization reduces the difference between the electrical environments inside and outside the neuron.
When a neurotransmitter has an inhibitory effect…
it slightly hyperpolarizes the receiving neuron, moving the cell farther from threshold and reducing the likelihood that it will initiate an action potential
Recall that hyperpolarization increases the difference between the electrical environments inside and outside the neuron
agonists
Agonists are drugs that enhance the actions of neurotransmitters
An agonist might enhance the actions of a particular neurotransmitter by increasing its release, blocking its reuptake, or by mimicking the neurotransmitter and activating its postsynaptic receptor
For example, cocaine prevents the dopamine transporter protein from being able to perform its normal reuptake function, resulting in an accumulation of dopamine in the synaptic cleft
Increased activation of postsynaptic dopamine receptors leads to the reinforcing effects of cocaine
antagonists
drugs that inhibit the actions of neurotransmitters
An antagonist might inhibit the actions of a particular neurotransmitter by blocking its release, destroying the neurotransmitter in the synapse, or by mimicking the neurotransmitter and binding to a postsynaptic receptor in a way that prevents neurotransmitter binding
For example, beta blockers, a class of drugs commonly prescribed to individuals who have suffered a heart attack, are antagonists that block certain receptor sites for epinephrine and norepinephrine, weakening the effects of the sympathetic stress response
where do synapses occur
Synapses usually occur in many locations on the dendrites or cell body of the receiving neuron, and the depolarizing or hyperpolarizing current that results from neurotransmitter activity at these synapses drifts to the junction of the cell body and axon
how do you know when a neuron will generate an action potential
If there is sufficient depolarization to reach threshold at this junction, the neuron generates an action potential
If not, it remains at rest
summation
The neuron’s “decision” to generate an action potential or not is called summation; the neuron is adding up all incoming messages and making a decision based on that information
Acetylcholine
Acetylcholine (ACh) is a neurotransmitter found in many systems important to behaviour
ACh is found at the neuromuscular junction, the synapse at which the nervous system commands muscles
Interference with the action of ACh at the muscles can result in paralysis and death, making drugs that act on ACh popular for use as pesticides and as bioweapons
ACh also serves as a key neurotransmitter in the autonomic nervous system, which carries commands from the brain to the glands and organs
ACh is also intimately involved in the brain circuits related to learning and memory
dopamine
Dopamine is involved with systems that govern movement, planning, and reward
Parkinson’s disease, which makes normal movement difficult, results when dopamine-releasing neurons in the brain’s movement circuits begin to die
In addition, dopamine participates in the brain’s reward and pleasure circuits by becoming active whenever we engage in behaviours that promote survival and successful reproduction, such as eating a great meal or having sex
Most drugs that produce addiction, including cocaine and methamphetamine, stimulate increased activity in dopamine circuits
serotonin
Serotonin is involved with systems regulating sleep, appetite, mood, and aggression
Consequently, these behaviours are tightly linked
endorphins
Endorphins, short for endogenous morphine or morphine produced by the body, modify our natural response to pain
In evolutionary terms, it makes sense to have a system that reduces your chances of being disabled by pain during an emergency
All too frequently, however, we underestimate the extent of our injuries until we wake up the next morning feeling sore
“Runner’s high,” in which people who regularly engage in endurance sports experience a sense of well-being and reduced sensation of pain, results from the release of endorphins initiated by high levels of activity
Opioid drugs such as morphine, heroin, and oxycodone (OxyContin) produce their pain-relieving effects by mimicking the action of endorphins at the synapse
neurogenesis
Neurogenesis is the creation of new neurons
neuroplasticity
refers to the ability of neurons to change in structure and function in response to change in structure and function in response to alterations in their environment
cerebrospinal fluid
The brain and the spinal cord are further protected by a clear, plasma-like fluid known as cerebrospinal fluid (CSF)
ventricles
CSF seeps out of the lining of hollow spaces in the brain known as the ventricles
what happens when cerebrospinal fluid circulation gets blocked
CSF is constantly produced, so blockages in its circulation cause the fluid to build up
The result is hydrocephalus, which means “water on the brain”
when you get a blow to the head, what protects it
The cushioning provided by the CSF limits the damage produced by a blow to the head
As a result, single minor concussions are unlikely to produce long-term problems, but medical experts are becoming increasingly concerned about the effects of multiple concussions
spinal cord function
The spinal cord serves as a major conduit for information flowing to and from the brain along large bundles of nerve fibres, carrying sensory info from the body and delivering commands to muscles
sensory neurons
Sensory neurons carry info from the external environment or from the body back to the CNS
motor neurons
Motor neurons carry commands from the CNS back to the muscles and glands of the body
interneurons
Neurons that have neither sensory nor motor functions are called interneurons
cranial nerves
Directly branching from the brainstem are the cranial nerves, which perform the same functions for the head and neck areas that the spinal nerves manage for the remainder of the body
cerebellum
Cerebellum helps us maintain balance and muscle coordination
brainstem
Brainstem contains structures responsible for reflexive behaviours, heart rate, breathing, sleep, balance and movement
medulla
The spinal cord merges with our first brain stem structure, the medulla
Contains large bundles of nerve fibers to and from higher levels of the brain
Manages many functions essential to life, such as heart rate, breathing and blood pressure
pons
Above the medulla is the pons, which serves as a bridge between the higher and lower portions of the brain and connects the cerebellum to the rest of the brain
