Transmission of Impulses Questions in English

(B) The synaptic knob (also known as the synaptic terminal or bouton) is the bulbous end of an axon terminal.
It contains synaptic vesicles filled with neurotransmitters.
Among the given options,$Acetylcholine$ is a primary neurotransmitter stored in the synaptic vesicles of the synaptic knob.
While other substances like adrenaline or noradrenaline can act as neurotransmitters in specific neurons,$Acetylcholine$ is the most characteristic neurotransmitter associated with general synaptic transmission models in textbooks.

(C) synapse is the junction between two neurons,or between a neuron and a target cell (such as a muscle or gland). It allows the transmission of nerve impulses from one neuron to another or to an effector cell. The motor end plate is specifically the junction between a motor neuron and a muscle fiber,which is a type of neuromuscular junction. Therefore,the general term for the connection between two neurons is a synapse.

(D) In an electrical synapse $(P)$,the membranes of pre-synaptic and post-synaptic neurons are in very close proximity,allowing current to flow directly from one neuron to another.
In a chemical synapse $(Q)$,the membranes of pre-synaptic and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft.
Therefore,the correct sequence is $P$ = Electrical synapse and $Q$ = Chemical synapse.

(C) In the provided diagram of a chemical synapse,the structure labeled $P$ represents the receptors located on the postsynaptic membrane. These receptors bind to the neurotransmitters released from the synaptic vesicles of the presynaptic neuron. This binding triggers the opening of ion channels,leading to the generation of a new action potential in the postsynaptic neuron. Therefore,$P$ is a neurotransmitter receptor.

(D) In a chemical synapse,the transmission of nerve impulses is mediated by chemical substances called neurotransmitters.
These neurotransmitters are stored in synaptic vesicles within the presynaptic neuron.
Common examples of neurotransmitters include $Acetylcholine$,$Adrenaline$,$Noradrenaline$,$Dopamine$,and $Serotonin$.
Since both $Adrenaline$ and $Noradrenaline$ act as neurotransmitters in various chemical synapses,the correct answer is $D$.

(B) In electrical synapses,the membranes of pre-synaptic and post-synaptic neurons are in very close proximity.
Impulse transmission across an electrical synapse is very similar to impulse conduction along a single axon.
Electrical synapses are very rare in our system.
Neurotransmitters are not involved in electrical synapses.
Impulse transmission across an electrical synapse is always faster than that across a chemical synapse.
Therefore,option $B$ is incorrect because it states that electrical synapses are slower,which is false.

(A) The transmission of an impulse across a chemical synapse follows these steps:
$1$. An action potential (impulse) reaches the axon terminal (synaptic knob).
$2$. This depolarization triggers the opening of voltage-gated $Ca^{+2}$ channels,allowing $Ca^{+2}$ to enter the synaptic knob.
$3$. The influx of $Ca^{+2}$ causes synaptic vesicles to fuse with the pre-synaptic membrane and release neurotransmitters into the synaptic cleft via exocytosis.
$4$. These neurotransmitters diffuse across the cleft and bind to specific receptors on the post-synaptic membrane.
$5$. This binding opens ion channels in the post-synaptic membrane,leading to the generation of a new action potential (or graded potential) in the post-synaptic neuron.

(D) In an electrical synapse,the membranes of pre- and post-synaptic neurons are in very close proximity.
Electrical current can flow directly from one neuron into the other across these synapses.
This direct flow of current allows for the transmission of impulses to be very fast,often faster than in a chemical synapse where neurotransmitters must be released,diffuse across the synaptic cleft,and bind to receptors.
Therefore,both the assertion and the reason are correct,and the reason provides the correct explanation for why electrical synapses are faster.

(C) During the transmission of a nerve impulse across a synapse,the neurotransmitters released from the pre-synaptic membrane bind to receptors on the post-synaptic membrane.
These neurotransmitters can cause either depolarization (excitatory post-synaptic potential,$EPSP$) or hyperpolarization (inhibitory post-synaptic potential,$IPSP$) of the post-synaptic neuron.
Therefore,the new potential generated in the post-synaptic neuron may be either excitatory or inhibitory,depending on the nature of the neurotransmitter and the receptor type.

(C) $i$. The elevated and stable body temperature of homeotherms accelerates molecular,enzymatic,and ion channel processes,resulting in faster synaptic transmission compared to poikilotherms.
$ii$. In a chemical synapse,the synaptic cleft has a width of about $20 \ nm$ to $30 \ nm$,not $3.8 \ nm$.

(C) Parkinson's disease is a progressive neurodegenerative disorder that primarily affects movement.
It is caused by the death of dopamine-producing neurons in a specific area of the brain called the substantia nigra.
Dopamine is a neurotransmitter that plays a crucial role in coordinating smooth and controlled muscle movements.
When there is a hyposecretion (reduced production) of dopamine,the brain cannot effectively regulate motor signals,leading to symptoms such as tremors,rigidity,and bradykinesia (slowness of movement).
Therefore,the correct answer is $C$ (Dopamine).

(C) In an electrical synapse, the membranes of pre- and post-synaptic neurons are in very close proximity, typically less than $0.2 \ nm$ apart, allowing for direct flow of electrical current.
Conversely, in a chemical synapse, the gap between adjacent neurons, known as the synaptic cleft, is approximately $20-30 \ nm$ wide.
Therefore, the statement that the gap in an electrical synapse is $20-30 \ nm$ is incorrect, making it the exception.

(C) The transmission of an impulse across a chemical synapse occurs in the following sequence:
$1$. When an action potential reaches the synaptic knob,voltage-gated $Ca^{++}$ channels open,allowing $Ca^{++}$ to diffuse into the synaptic knob from the extracellular fluid $(b)$.
$2$. The influx of $Ca^{++}$ triggers the synaptic vesicles to move toward and fuse with the presynaptic membrane $(a)$.
$3$. The neurotransmitters are then released into the synaptic cleft via exocytosis $(d)$.
$4$. Finally,the neurotransmitters bind to the specific receptors present on the postsynaptic membrane,which may lead to the opening of ion channels $(c)$.
Therefore,the correct sequence is $b \rightarrow a \rightarrow d \rightarrow c$.

(C) chemical synapse is a junction where information is transmitted from one neuron to another via chemical messengers called neurotransmitters.
In a chemical synapse,the membranes of the pre-synaptic and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft.
The width of this synaptic cleft in a typical chemical synapse ranges from approximately $20 \ nm$ to $40 \ nm$.

(C) When an action potential reaches the axon terminal,it triggers the following sequence of events:
$1$. The depolarization of the axon terminal membrane causes the opening of voltage-gated calcium channels.
$2$. Calcium ions enter the terminal,which stimulates the synaptic vesicles to move towards and fuse with the pre-synaptic membrane.
$3$. The neurotransmitters are released into the synaptic cleft via exocytosis.
$4$. These neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the post-synaptic membrane.
$5$. This binding leads to the generation of a new action potential in the post-synaptic neuron.
Therefore,the correct sequence is: Axon terminal $\rightarrow$ Synaptic vesicles $\rightarrow$ Synaptic cleft $\rightarrow$ Post-synaptic membrane $\rightarrow$ Post-synaptic neuron.

(B) In a chemical synapse,the neurotransmitters are released from the synaptic vesicles of the pre-synaptic neuron into the synaptic cleft.
These neurotransmitters then bind to specific receptor proteins located on the membrane of the post-synaptic neuron (post-synaptic membrane) to generate an action potential.