Lecture 20- Synapses & Sensory Receptors

Question 1

What is a synapse?

Answer 1

A junction between a synaptic terminal and another cell

Question 2

An action potential is a signal that travels _____ the synapse _______ the neuron.

Answer 2

An action potential is a signal that travels to the synapse in the neuron.

Question 3

What are the types of synapses?

Answer 3

Electrical synapses and chemical synapses

Question 4

What are electrical synapses?

Answer 4

Current flows directly from cell to cell. Less common.

Question 5

True or False: The presynaptic cell synthesizes and stores neurotransmitters.

Answer 5

True

Question 6

How are action potentials passed from presynaptic cells to postsynaptic cells?

Answer 6

Presynaptic action potential triggers voltage-gated calcium ion channels to open which allows neurotransmitters to cross the synaptic cleft.

Question 7

True or False: Neurotransmitters bind to voltage-gated ion channels on the postsynaptic membrane.

Answer 7

False, neurotransmitters bind to ligand-gated ion channels (proteins) on the postsynaptic membrane.

Question 8

Explain the process of chemical synapses.

Answer 8

The presynaptic neuron is the neuron sending the signal. It has an axon terminal that ends near the receiving neuron. The synaptic cleft refers to the tiny space between the presynaptic and postsynaptic neurons.

the presynaptic neuron makes neurotransmitters which are stored in synaptic vesicles.

Action Potential Arrival: When an action potential travels down the axon of the presynaptic neuron, it reaches the axon terminal.

Calcium Influx: This triggers the opening of voltage-gated calcium (Ca2+) channels in the membrane of the axon terminal. Now that these channels are open, the Ca2+ enters the presynaptic neuron.

This influx of calcium causes some of the synaptic vesicles to fuse with the presynaptic membrane.

As a result, the neurotransmitters inside the synaptic vesicle are released into the synaptic cleft.

The neurotransmitters diffuse across the synaptic cleft. They then bind and activate specific postsynaptic receptors.

Question 9

How do postsynaptic potentials work and how are they triggered?

Answer 9

Postsynaptic potentials refer to the change in membrane potential of postsynaptic cells. They are triggered by ligand-gated ion channels.

The neurotransmitters released from the presynaptic neuron bind to the specific receptors and bind to the ligand-gated ion channel, serving as a key that can open and close the gate to allow ions to enter the cell and cause a cellular response (either depolarization or hyperpolarization).

Question 10

What are the two types of postsynaptic potentials and what do they do?

Answer 10

1. Excitatory Postsynaptic Potential (EPSP): Depolarizes (Makes more positive inside)
2. Inhibitory Postsynaptic Potential (IPSP): Hyperpolarizes (Makes more negative inside)

Question 11

What is summation of postsynaptic potentials?

Answer 11

There are often 100s of terminals to dendrite and cell body, some excitatory and some inhibitory. Postsynaptic potential is due to interactions, distance, and neurotransmitters.

Question 12

What is temporal summation?

Answer 12

2+ EPSPs at 1 synapse. The 2nd arrives before the MP resets, causing stronger depolarization and resulting in AP.
(If an excitatory neurotransmitter is released and binds to the receptor, causing EPSP but doesn’t depolarize to reach the threshold for an action potential, in this scenario a rapid 2nd EPSP is released at the same synapse, triggering a second EPSP and increasing the likelihood of AP due to combined stronger depolarization).

Question 13

What is spatial summation?

Answer 13

2+ EPSPs nearly simultaneously. Different synapses. Same postsynaptic neuron. Causes stronger depolarization.

Question 14

What is the distinction between temporal summation and spatial summation?

Answer 14

Temporal summation has to do with time- Leverages timing for a stronger overall effect for a SINGLE synapse.

Spatial summation considers the location of DIFFERENT synapses on the same postsynaptic neuron.

Both cause stronger depolarization and increase the chances of an AP.

Question 15

Where is the neuron’s integration system?

Answer 15

Axon hillock

Question 16

How do EPSP and IPSP interactions work?

Answer 16

The membrane potential at the axon hillock is the summed effects of all EPSPs and IPSPs. The AP results if the sum of these effects reaches the threshold (-55mV).

Question 17

Nervous System Development

Answer 17

NS macro organization is established during development and regulated by gene expression, signal transduction. After birth, the brain develops and continues to remodel.

Question 18

Neuronal Plasticity

Answer 18

Response to activity- neurons that are frequently used become stronger.

Remodeling via competition among neurons for growth supporting factors- molecules that promote the growth and survival of neurons. Neurons that are more active are more likely to attract these factors, allowing them to strengthen their connections and survive. Competition ensures that the most frequently used neural pathways have the resources they need to function effectively.

Synapse elimination- keeps only required- Eliminates weak synapses to ensure remaining connections are strong and reliable.

Question 19

How can synapses be strengthened?

Answer 19

When two neurons are active together frequently, their connection (synapse) between them becomes stronger.

Question 20

What does “use it or lose it” mean?

Answer 20

Synapses that are not used frequently may weaken or even be eliminated.

Question 21

Where is short-term memory held? What links different pieces of information in STM?

Answer 21

Held in the cerebral cortex (outermost layer of brain). The hippocampus links different pieces of information in the STM.

Question 22

Short-Term Memory

Answer 22

Information is held briefly: temporary holding area for information. Located in the cerebral cortex, the hippocampus links different pieces of information in STM. Intermediate step for forming LTM, but is not responsible for long-term storage. Can remember things for seconds to minutes, number of items ~ 7

Question 23

Long-Term Memory

Answer 23

Info stored in cerebral cortex. Temporary links replaced by connections within cerebral cortex.
-> Permanent, theoretically unlimited capacity

Question 24

Long-Term Potentiation

Answer 24

Lasting increase in strength of synaptic transmission. Fundamental process of memory storage and learning.

Question 25

What 2 conditions are required for LTP?

Answer 25

1. High-frequency series of APs
2. Depolarization from another stimulus at same time
   -> Strengthens synapse whose activity coincides with that of another

Question 26

How does LTP affect postsynaptic neurons?

Answer 26

There are 2 types of ligand-gated ion channels in a postsynaptic neuron.

Before LTP- one in membrane, other stored
-> Requires simultaneous depolarization from other source to reach threshold potential

After LTP- both in membrane
-> Stronger depolarization
-> More likely AP

Question 27

Synapse prior to LTP

Answer 27

Glutamate from presynaptic neuron wants to bind to the NMDA receptors but cannot because it is blocked by MG2+. No action potential.

Question 28

Process of Establishing LTP

Answer 28

Depolarization (from different axon)-> NMDA releases MG2+
-> Na+, Ca2+ flow in (not a lot, but some)
-> AMPA receptors enter membrane

Glutamate-> AMPA receptors
-> Na+ in
-> Depolarization
unblocks NMDA-> AP

Question 29

Workshop= Promote LTP

Answer 29

Read book/notes= 1 stimulus-> insufficient for LTP
Sequence, compare and contrast, discuss, etc= >1 stimulus
Promotes LTP
Repeated use= “this is important, keep it and be able to access it” message to your brain

Question 30

What are the 4 steps in the sensory pathway?

Answer 30

1. Sensory reception
2. Sensory transduction
3. Transmission
4. Perception

Question 31

Sensory Pathway

Answer 31

Sensory reception: Sensory receptor detects change

Sensory transduction: E of stimulus is converted to receptor potential - stimulus -> AP
2 options- unstimulated receptor or stimulated receptor
Unstimulated receptor
-> resting potential
Stimulated receptor
-> depolarized-> triggers AP

Transmission: Sensory info travels as AP- receptor-> brain
Larger receptor potential-> more frequent AP

Perception: Brain processes info
Exists only in brain

Question 32

Sensory Pathway- Sensory Reception step

Answer 32

Sensory receptor detects change (eyes, ears, nose detect change in the environment)

Question 33

Sensory Pathway- Sensory Transduction step

Answer 33

Energy of the stimulus is converted to receptor potential. An unstimulated receptor remains at resting potential, while a stimulated receptor is depolarized and the AP is triggered.

The strength of the stimulus is directly proportional with the receptor potential.

Question 34

Sensory Pathway- Transmission step

Answer 34

Sensory information travels as an action potential- receptor to the brain.
Larger receptor potential-> more frequent AP
(If the stimulus is greater, more pressure from the sensory receptor will cause high frequency of action potentials per receptor)

Question 35

Sensory Pathway- Perception step

Answer 35

The brain processes the information from the AP.

Question 36

Types of Sensory Receptors

Answer 36

Characterized by type of stimulus transduced

Chemoreceptors: Chemicals (taste, smell)
Photoreceptors: Vision
Mechanoreceptors: Touch, pressure
Thermoreceptors: Hot/cold

Question 37

Human Eye Functions

Answer 37

Detect light of specific wavelengths at specific positions on retina and pass information to NS
Brain interprets as image

Question 38

Sensory Reception and Processing of Eye (How does light travel)

Answer 38

Light -> photoreceptors -> bipolar cells -> optic nerve -> CNS -> light

Question 39

Pathway of light

Answer 39

Cornea-> iris-> lens-> rods and cones on retina-> bipolar cells-> optic neurons-> optic nerve-> AP-> CNS