BIOL 1051H Chapter Notes - Chapter 12: Voltage-Dependent Calcium Channel, Excitatory Postsynaptic Potential, Inhibitory Postsynaptic Potential

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Neural Physiology Part 2

There are two types of synapse: The electrical synapse is formed via gap junctions that

connect one cell to another. With electrical synapses every action potential is transmitted to the

next cell. This allows for very little control of signal transmission. Therefore, these synapses are

very rare in the nervous system. They are, however, typical of some muscle tissues such as

cardiac muscle. Here the depolarization of one muscle cell will lead to the depolarization of

adjacent muscle cells resulting in a coordinated contraction of the heart itself.

Chemical synapses are much more common in the nervous system. These synapses

involve the release of a chemical at the terminal bouton located at the end of the axon. The

chemical then diffuses across the small synaptic cleft and binds receptor proteins on the

postsynaptic cell. The postsynaptic cell could be a muscle, another, neuron, or a gland.

Neurotransmitter chemicals are synthesized by the neuron in the cell body and

transported to the synaptic bouton. They are stored in small synaptic vesicles which are lined up

along the synapse. The amount of neurotransmitter released is due to the influx of Ca2+

(calcium) at the axon terminal. As the action potential reaches the axon terminal, voltage gated

Ca2+ channels open and allow Ca2+ to move into the presynaptic axon terminal. The Ca2+

then binds the vesicles full of neurotransmitter and causes them to release the neurotransmitter

into the synaptic cleft. The higher the frequency of action potentials, the more Ca2+ ions are

allowed to move into the axon terminal, and the more neurotransmitter molecules are released.

When the postsynaptic cell is a neuron, different things can happen depending on the

type of synapse as well as the location of the synapse on the postsynaptic cell. The

neurotransmitters in this situation will generally bind receptors on the postsynaptic cell which

trigger changes in membrane potential. If the change makes the postsynaptic membrane slightly

more positive, or depolarized it brings the membrane closer to threshold and is therefore an

excitatory postsynaptic potential (EPSP). If the change makes the membrane more negative, or

hyperpolarized it moves the membrane potential farther from threshold and decreases the

chances of an action potential. Thus this is called an inhibitory postsynaptic potential (IPSP).

Location of the synapse is important in that those synapses that are located closer to the axon

hillock have a greater effect than those located farther away or on dendrites as opposed to the

cell body.

The cell membrane on the cell body and dendrites is not the same as the axon and does

not produce action potentials. However, it can be depolarized (polarization decreases usually

due to increased positive charge inside the cell) or hyperpolarized (polarization increases

usually due to increased negative charge inside the cell). This change will take place where a

synapse occurs either on the cell body or dendrites and this membrane change will spread

away from the area of initiation. As the membrane potential spreads from the site of initiation it

will decrease much like the ripple in water after throwing a stone. The impact of any given

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Document Summary

There are two types of synapse: the electrical synapse is formed via gap junctions that connect one cell to another. With electrical synapses every action potential is transmitted to the next cell. This allows for very little control of signal transmission. Therefore, these synapses are very rare in the nervous system. They are, however, typical of some muscle tissues such as cardiac muscle. Here the depolarization of one muscle cell will lead to the depolarization of adjacent muscle cells resulting in a coordinated contraction of the heart itself. Chemical synapses are much more common in the nervous system. These synapses involve the release of a chemical at the terminal bouton located at the end of the axon. The chemical then diffuses across the small synaptic cleft and binds receptor proteins on the postsynaptic cell. The postsynaptic cell could be a muscle, another, neuron, or a gland.

Related Questions

The junction specialized for the transmission between a neuron and another cell is called a (1) _____ ______. Usually, the signal being sent to the receiving cell is carried by chemical messengers called (2) _____. (3) _____ is an example of this type of chemical messenger, which diffuses across the synaptic cleft, combines with protein receptor molecules on the muscle cell membrane, and soon thereafter is rapidly broken down by enzymes. At an (4) ____ synapse, the membrane potential is driven toward the threshold value and increases the likelihood that depolarization and an action potential will occur. At an (5) ____ synapse, the membrane potential is driven away form the threshold value, and the receiving neuron becomes hyperpolarized and is less likely to achieve an action potential. A specific transmitter substance can have either excitatory or inhibitory effects depending on which type of protein channel it opens up in the (6) ____ membrane. (7) ____ are neuromodulators that inhibit perceptions of pain and may have roles in memory and learning, emotional states, temperature regulation, and sexual behavior. (8) ____ ________ at the cellular level is the moment-by-moment tallying of all excitatory and inhibitory signals acting on a neuron. Incoming information is (9) ____ by the cell bodies, and the charge differences across the membranes are either enhanced or inhibited. Some narrow-diameter neurons are wrapped in lipid-rich (10) _______ produced by specialized neuroglial called Schwann cells; each of these is separated from the next by a(n) (11) ________ ________ - a small gap where the axon is exposed to extracellular fluid. A (12) ____ is an involuntary sequence of events elicited by a stimulus. During a (13) _______ ________, a muscle contracts involuntary whenever conditions cause a stretch in length; many of these help you maintain an upright posture despite small shifts in balance. Imbalances can occur at chemical synapses; a neurotoxin produced by Clostridium tetani blocks the release of GABA and glycine, thus freeing the motor neurons from (14) _____ control, which may cause tetanus â a prolonged, spastic paralysis that can lead to death. A. Excitatory H. Stretch reflex B. Inhibitory I. Summed C. Myelin J. Neurotransmitters D. Chemical synapse K. Postsynaptic E. Synaptic integration L. Endorphins F. Exposed node M. Acetylcholine (ACh)

lilacchinchilla331

1)What type of cell allows the immune system to respond morequickly if the same antigen is encountered a second time?

A)leukocytes

B)memory cells

C)macrophages

D)neutrophils

E)natual killer cells

2)why is the heart divided funtionally into two separate pumpsthat work in series?

A)because arteries carry blood away from the pump and veinsbring blood back to the pump

B)because blood decreases in pressure as it travels throughcirculation

C)because vessles in the vasculature keep blood moving in onedirection'

D)because there are four chambers to the heart

E)none of the above-the heart contracts in unison and is notdivided into two pumps

3)which of the following statements is correct?

A)Na+,K+, Ca2+ and Cl- are all more concentrated in theEXTRACELLULAR fluid

B)Na+, K+, Ca2+ and Cl- are all more concentrated in theEXTRACELLULAR fluid

C)Na+, Ca2+, and Cl- are all more concentrated in theEXTRACELLULAR fluid

D)K+, ca2+ are more concentrated in the EXTRACELLULAR fluid

E)K+, Ca2+ are more concentrated in the EXTRACELLULAR fluid

3)During skeletal muscle contraction:

A)the width of the H-zone decreases

B)the actin heads bind to myosin chain

C)ATP hydrolysis requires Ca2+ as a cofactor

D)tropomyosin changes conformation when Ca2+ binds

E)all of the above occur during skeletal muscle contraction

4)The rapid depolarization phase of myocardial contratile cellaction potential is due to the movement of which ion(s)?

A)Ca2+ flows into the cytosol

B)K+ flow out of the cytosol

C)Na+ flow into the cytosol

D)Ca2+ flow out of the cytosol

E)K+ flow into the cytosol

5)You are a physiology graduate student asked to study theeffect of ion permeability on the initiation of action potentials.You have isolated a cell with resting membrane potential of -70mVand have determined that the cell's threshold voltage is -55mV. Youthen change the cell to make it less permeable to K+ ions(Eions=-90mV)

With all ther condition staying the same, has cell's restingmembrane potential been DEPOLARIZED or HYPERPOLARIZED; and will thecell require a greater or smaller stimulus to reach threshold?

A)hyperpolarize; smaller

B)depolarize;greater

C)hyperpolarize;greater

D)depolarized; smaller

E)none of the above answers are possibe

6)Skeletal muscle cells are UNUSUAL in that they :

A)lack smooth endoplasmic reticulum

B)have no mitochondria

C)depend entirley on anaerobic respiration

D)have MULTIPLE nuclei

E)none of the baove are found in the skeletal muscle cells

7)What is the name for the autonomic nervous system synapses atthe neuroeffector?

A)electrical synapses

B)axon viscosities

C)bidirectional synapses

D)axon varicosities

E)light bulb synapse

8)Which cytokines are involvedin making cells resistant toviruses?

A)colony-stimulating actors

B)interferons

C)erythrpoietin

D)major histocompatibility complex

E)none of the above can make a cell resistant to a virus

9)If a person switiches from normal breathing to more shallowbreathing, whcih statement is true

A)tidal volume decreases

B)alveolar PO2 decreases

C)alveolar ventilation decreases

D)"a" and "b"

E)"a", "b', and "c"

10)Which scenerio supports hyperpolarization of pre-synapticcell?

A)allowing Cl- ions into the cell

B)allowing K+ ions to leave the cell

C)allowing Ca2+ ions into the cell

D)"a" and "b"

E)"a", "b", and "c"

11)The gap junctions in cardia muscle are part of specializedcell junctions that are localized to the__________.

A)transverse tubules

B)intercalated discs

C)Interdigitated fingers

D)desmosomes

E)high-end shppoinf malls

12)What role does myosin light chain kinase (MLCK) play insmooth muscle cell contraction?

A)dephosphorylates myosin

B)phosphorylates actin

C)phosphoylates myosin

D)dephosphorylates actin

E)both "a" and "c"Given that your forearm is 30cm long and yourbiceps inserts 2 cm away from your elbow joint, how much force mustyour biceps exert to hold up a 10kg weight?

A)0.67kg

B)6.0kg

C)20kg

d)150kg

e)600kg

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BIOL 1051H Chapter Notes - Chapter 12: Voltage-Dependent Calcium Channel, Excitatory Postsynaptic Potential, Inhibitory Postsynaptic Potential

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