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1090 > Synapses, Neurotransmitters & Hormones > Flashcards

Synapses, Neurotransmitters & Hormones Flashcards

1
Q

How does information flow in an action potential?

A

Information flows within a neutron via electrical signals.

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2
Q

How does information flow in synapses?

A

Information flows between neurons via electrical/chemical signals.
(Mainly chemical)

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3
Q

What are synapses?

A

Synapses = the gap between neurones where signals are passed from one to the other.

The neuron that is passing the signal is called the pre-synaptic neuron and the neuron that is receiving the signal is called the post synaptic neuron.

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4
Q

What are the features of electrical synapses?

A

Electrical synapses have a flow of electrical signal.

  • Very small gap between two neurones (2-4 nm)
  • The facing membranes have large channels that allow ions to move directly from one cell to the other
  • Transmission from one neuron to the next is similar to action potential conduction along the axon
  • Very fast – no time delay
  • Rare in human CNS (eye movements)
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5
Q

What are the features of chemical synapses?

A
  • Specialized structures for transmitting chemical signals from one neuron (presynaptic neuron) to another (postsynaptic neuron)
  • There is a gap between the axon of one neurone and the dendrite of the next one, which is called synaptic cleft
  • Small gap but much larger than gap junctions (20-40 nm)
  • Each neurone has many (typically ca 1000) synapses
  • Much slower (ca 1ms) than electrical synapses
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6
Q

What are the 6 steps in chemical synapses?

A
  1. Action potential arrives at presynaptic membrane
  2. Voltage-gated Ca2+ channels open, Ca2+ diffuses into cell
  3. Synaptic vesicles fuse with membrane, releasing neurotransmitter molecules into synaptic cleft
  4. Transmitter binds to postsynaptic receptors, opening ion channels
  5. If channel is for Na+:
    → depolarization = Excitatory Postsynaptic Potential (EPSP)

If channel is for Cl-:
→ hyperpolarization = Inhibitory Postsynaptic Potential (IPSP)

  1. EPSP/IPSP propagated along membrane
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7
Q

What are post-synaptic receptors?

A
  • Receptors are membrane proteins that bind neurotransmitters
  • Each receptor type can bind only to a specific neurotransmitter
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8
Q

What is the lock and key principle?

A

When a transmitter molecule binds to the receptor, the receptor changes shape, causing an ion channel to open.

This results in depolarization or hyperpolarization of the postsynaptic membrane
Depolarization: EPSP - Excitatory effect on post-synaptic neuron
Hyperpolarization: IPSP - Inhibitory effect on post-synaptic neuron

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9
Q

What are the different types of receptors?

A

(Don’t need to remember the names/ details of the receptors – just that some are fast, and some are slow)

The fast receptors can open the channel immediately because they already have the right key.

The slow receptors need another protein involved to open the channel.
Both are important because they can make the post synaptic neuron excited or inhibited.

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10
Q

What is the difference between temporal and spatial summation?

A

Temporal summation occurs when a single pre-synaptic neuron fires many times in succession, causing the post-synaptic neuron to reach its threshold and fire. Spatial summation occurs when excitatory potentials from many different pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire.

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11
Q

What is temporal summation?

A

When many ESPSs/IPSPs occur at the same time on the same cell.

At some point, it receives a signal from the pre-synaptic neuron.
It gets a little bit excited (as seen by the peak on the first graph) but not enough to reach the threshold for an action potential.

However, if the same cell sends a second signal, this time there is a larger amplitude and it might reach the threshold for an action potential.
When the signal reaches the threshold, an action potential is generated, and it might trigger another synapses on another cell and the communication is transferred from one neuron to a second neuron, to a third neuron.

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12
Q

What is spatial summation?

A

When many axons converge in one post synaptic neuron.

If there was only one response (as seen on the first two signals) the signal might not reach the threshold.

But if both signals arrive at the same time, the signal is much higher and reaches the threshold for an action potential.

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13
Q

What is summation?

A

Summation, which includes both spatial and temporal summation, is the process that determines whether or not an action potential will be generated by the combined effects of excitatory and inhibitory signals, both from multiple simultaneous inputs (spatial summation), and from repeated inputs (temporal summation).

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14
Q

What happens after the EPSPs/IPSPs reaches the axon hillock?

A

Once EPSPs/IPSPs reach axon hillock:

If the net charge (sum of EPSPs + IPSPs) is below threshold (

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15
Q

What is a neurotransmitter?

A

A chemical released by one neuron that affects another neuron or an effector organ (e.g., muscle, gland, blood vessel)

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16
Q

What are the key features of neurotransmitters?

A
  • Neurotransmitters are produced in the presynaptic neuron
  • Localised to vesicles in the presynaptic neuron (they are stored in vesicles and not free to move around)
  • Neurotransmitter molecules that leak from their vesicles are immediately destroyed by enzymes
  • Released from the presynaptic neuron under physiological conditions
  • Some of them will bind with auto receptor. The rest bind to post synaptic receptors.
  • . If there is still neurotransmitter in the synaptic cleft, they will be removed by two different mechanisms: reuptake or enzyme degradation
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17
Q

Why is re-uptake essential?

A

Continued presence of neurotransmitters in the synaptic cleft would lead to persistent EPSPs or IPSPs – even without further action potentials in the pre – synaptic neuron
(The neurotransmitters in the cleft that haven’t been used will continually activate the post synaptic neuron)
Many mood related disorders are influenced by not enough/too many neurotransmitters.

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18
Q

How are neurotransmitters “cleaned out” from the synaptic cleft?

A
  1. Moved back into the pre-synaptic or other cells by transporters (re-uptake)
  2. Degraded/ neutralised by enzymes
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19
Q

Name 4 ways in which neurons can communicate?

A
  • Point to Point Communication
  • Hormonal Communication
  • Interconnected neurons of the ANS
  • Diffuse modulatory systems
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20
Q

What is Point to Point Communication?

A

One neuron communicates directly with another neuron (not very common).
Restricts synaptic communication.

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21
Q

What is hormonal communication?

A

The neurotransmitters aren’t involved, hormones are involved instead. One cell is producing and releasing the hormones into the blood stream where it can travel all over the body and affect our behaviour.

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22
Q

What are the interconnected neurons of the ANS?

A

Simultaneously controls responses in many internal organs.
Only related to the autonomous nervous system – a system where one cell is communicated with a chain of cells and they can simultaneously control many processes.

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23
Q

What are diffuse modulatory systems?

A

Some cells are releasing neurotransmitter and they are broadcasting signals to large portions of our brain. This is heavily related to the way you eat, sleep, think, whether you are happy or not etc.
Specific neurotransmitter. Regulate arousal, mood, motivation, sexual behaviour, emotion, sleep etc.

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24
Q

What methods of neuronal communication are restricted and which ones are spread with wider influence?

A

Restricted: Point to point communication

Spread – Wider Influence: Hormonal communication, Interconnected neurons of the ANS and Diffuse modulatory systems.

25
Q

What are some features of diffuse modulatory systems?

A
  • Messages that must be widely broadcast through the brain use diffuse modulatory systems
  • The brain uses many of these mechanisms each requiring a specific neurotransmitter
  • Connections are widely dispersed throughout the brain
  • Important in motor control, memory, mood, motivation, and metabolic state
  • Heavily involved in many psychiatric disorders
26
Q

Where is the core of each diffuse modulatory system located, to what extent does each neuronal have an effect and how are the neurotransmitters released?.

A
  • Core of each system has a small number of neurons, located in the brainstem
  • Neurons of the diffuse system arise from the central core
  • Each neuron has tremendous effect because it can connect to as many as 100,000 neurons
  • Neurotransmitters are released into the extracellular fluid and can diffuse to many neurons
27
Q

What is the Noradrenergic Locus Coeruleus?

A

It’s a type of modulatory system.

The Locus Coeruleus is the core of one of the modulatory systems, in the brain stem.

28
Q

What are the features of the Locus Coeruleus?

A
  • Makes some of the most diffuse connections in the brain. They can influence almost all of the cortex, subcortical areas and the cerebellum.
  • Involved in regulation of attention, arousal, sleep wake cycles, learning and memory, anxiety, pain, mood and brain metabolism
  • Activated by new, unexpected, non-painful sensory stimuli
  • General arousal to interesting events in the outside world
  • These particular neurotransmitters increase brain responsiveness and speed information processing
29
Q

What is the Serotonergic Raphe Nuclei divided into?

A

It’s divided into two categories, the caudal one (at the bottom) sends the signal into the spine and they are strongly related to pain modulation. The rostral one can influence the activity of the entire cortex and are deeply involved in sleep-wake cycles. Strongly related to mood disorders, depression in particular.

30
Q

What are the features of the Serotonergic Raphe Nuclei?

A
  • Caudal innervate sends information to the spinal cord and modulates pain-related sensation
  • Rostral innervate brain
  • They fire most during wakefulness
  • Part of reticular activating system
  • Involved in sleep wake cycles and stages of sleep
  • Control of mood and emotional behaviours
31
Q

What are the key features of the Cholinergic Basal Forebrain?

A
  • General function not completely understood
  • It seems to be strongly related to Alzheimer’s disease. (First cells to die in the course of Alzheimer’s disease.)
  • Implicated in arousal, sleep wake cycles, learning and memory
32
Q

What are the key features of the Dopaminergic Substantia nigra?

A
  • It targets a lot of areas in the pre-frontal and frontal cortex which is important for our behaviour and decision making.
  • Neurons project from Substantia Nigra to striatum
  • Control voluntary movements
  • Degeneration results in Parkinson’s disease
  • Ventral tegmental area projects to frontal cortex and limbic system
  • Reward system that reinforces adaptive behaviours. The reward system can lead to addiction (substance, gaming, shopping)
  • Involved in motor control, reward and pleasure.
33
Q

What are the causes of some types of depression and how can it be treated?

A

Some types of depression may be due to a lack of serotonin. Patients with depression have a lack of serotonin in the synaptic cleft – not enough neurotransmitter.

(Don’t need to remember this) One of the main anti-depressant drugs is called SSRI. It helps the synaptic transmission by avoiding the reuptake of serotonin.

34
Q

What do many drugs use?

A

Many drugs use neurotransmitters to shape our behaviour.

The drugs either facilitate or inhibit activity at the synapse.

35
Q

How do drugs either facilitate or inhibit activity at the synapse.

A
  • Increasing number of action potentials
  • Release transmitters from vesicles without impulses
  • Producing more neurotransmitter
  • Preventing neurotransmitter release
  • Blocking re-uptake
36
Q

Where is dopamine released?

A

Dopamine is released by the substantia nigra and the nucleus accumbens.

37
Q

Why do people get a pleasant sensation when taking drugs?

A

Almost all abused drugs stimulate dopamine release in the nucleus accumbens.
This is why there is a very pleasant sensation when taking drugs.

38
Q

What are hormones?

A

Hormones = chemicals secreted by endocrine glands

39
Q

What are the features of hormonal communication?

A
  • They control most major bodily functions, from simple basic needs like hunger to complex systems like reproduction, and even emotion and mood
  • Hormones travel through the blood and influence the activity of other glands and organs
  • A hormone can only influence cells that have specific target receptors for that particular hormone
40
Q

What are the 9 general principles of hormonal communication?

A
  1. Gradual, often long-lasting, effect
  2. Change likelihood of behaviour
  3. Hormones and behaviour interact
  4. Many different hormones affect many
    different body parts & behaviours
  5. Produced in small amounts (often in
    bursts)
  6. Many have rhythmic release
  7. Hormones interact with other hormones 9
  8. All vertebrate hormones have similar
    structures, but not necessarily similar
    effects
  9. Can only affect cells with the appropriate
    receptor proteins
41
Q

What is the difference between hormonal communication and diffuse modulatory systems?

A

Hormonal communication is very similar to the diffuse modulatory system; the big difference is that the activity of the modulatory system is very fast, and the activity of hormones is not very fast, but it is long lasting.
They don’t initiate a signal but instead change the likelihood of a behaviour. They are produced in small amounts and released into the blood vessels.

42
Q

How are hormones released?

A

Some have a rhythmic release meaning that they are released now and again to keep balance in our organs. Others are released in certain circumstances. They can only target organs and glands.

43
Q

What is the endocrine system and what does it do?

A

All glands of the body and hormones produced by those glands.

By regulating the functions of the organs in the body, these glands help to maintain the body’s homeostasis (cellular metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate, digestion…)

44
Q

Where is the hypothalamus located and what are its features?

A

Hypothalamus is located below the thalamus and forms the walls of the third ventricle. It can be divided into several nuclei: each nucleus has a very specific function.
• Three zones: Lateral, Medial, Perivenular
• Connections are extensive
• Periventricular is most highly connected to the pituitary
• Controls: circadian rhythms and ANS to viscera
• Integrates somatic and visceral responses in accordance with the needs of the brain (Plays a role in keeping a balanced environment for our organs)
• Homeostasis – maintains the body’s internal environment in a narrow physiologic range
• Temperature, blood volume and pressure, pH, oxygen levels

45
Q

What is the pituitary gland connected to and why is it important?
What is the pituitary gland divided into?

A

Pituitary is connected to the base of the hypothalamus.

It’s is the “master gland” of the body. It produces many hormones that travel throughout the body, directing processes or stimulating other glands to produce other hormones.. This gland is also essential for behaviour.

The pituitary is divided into the anterior and the posterior.

46
Q

What are the features of the posterior pituitary gland?

A

• Connected with hypothalamus
The cells in the hypothalamus can directly secrete hormones into the posterior pituitary gland. It can produce oxytocin and vasopressin.
• Neuro-hormones are produced in the magnocellular hypothalamus and released at the pituitary

47
Q

What is oxytocin?

A

Released to initiate uterine contraction or milk let-down.

Can be triggered by somatic, visual or auditory stimuli or inhibited by stress.

48
Q

What is Vasopressin?

A

An antidiuretic hormone.

It regulates blood volume and pressure.

49
Q

What are the features of the anterior pituitary gland?

A
  • Connected with hypothalamus
  • Parvocellular neurosecretory cells release tropic factors that cause the production of hormones in the anterior pituitary
  • It can generate many different hormones which control several aspects of our body.
50
Q

What is love?

A

Love is an increase in oxytocin

51
Q

What is oxytocin?

A
  • Involved in reproductive and social behaviour
  • Stimulates contractions
  • May promote bonding (e.g. Scheele et al 2012) by influencing social distance
  • Triggers the milk let-down reflex
52
Q

What are the similarities between synaptic and hormonal communication?

A

Both bind to receptors.
Both can activate second messengers.
Both effect change in cellular function.

53
Q

What is the difference in signals between the nervous system and the endocrine system?

A

The signals of the nervous system are electrical impulses (action potentials) and the signals of the endocrine system are chemical impulses (hormones).

54
Q

What is the difference in pathways between the nervous system and the endocrine system?

A

The nervous system - transmissions by neurons.

Endocrine system - transported by blood.

55
Q

What is the difference in the speed of information between the nervous system and the endocrine system?

A

Speed of information is fast in the nervous system and slow in the endocrine system.

56
Q

What is the difference in the duration of the effect between the nervous system and the endocrine system?

A

The duration of the effect is short lived in the nervous system and can be short or long lived in the endocrine system.

57
Q

What is the difference in the type of action and response between the nervous system and the endocrine system?

A

The type of action and response is voluntary or involuntary for the nervous system and always involuntary for the endocrine system.

58
Q

What is the difference in the targets of the nervous system and the endocrine system?

A

The target of the nervous system is localised (cells connected to neuronal).

The target of the endocrine system is often distant (many cells can be effected).

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