Transmission of Impulses Questions in English

(D) The transmission of nerve impulses across a synapse is unidirectional because neurotransmitters are stored in synaptic vesicles located only at the axon terminals (presynaptic membrane).
When an action potential reaches the axon terminal,these vesicles fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft.
The dendrites (postsynaptic membrane) contain specific receptors for these neurotransmitters,but they do not contain synaptic vesicles to release them.
Therefore,the impulse can only travel from the axon terminal of one neuron to the dendrite of the next neuron,ensuring a one-way flow of information.

(B) Neurotransmitters are chemical messengers that transmit signals across a chemical synapse from one neuron to another.
$A$,$C$,and $D$ (Norepinephrine,Acetylcholine,and Epinephrine) are well-known neurotransmitters.
$B$ (Cortisone) is a steroid hormone produced by the adrenal cortex,which is involved in metabolism and immune response,not in synaptic transmission.
Therefore,Cortisone does not act as a neurotransmitter.

(A) Acetylcholinesterase is an enzyme that breaks down the neurotransmitter acetylcholine in the synaptic cleft. Malathion is an organophosphate compound that acts as an irreversible inhibitor of acetylcholinesterase. By inhibiting this enzyme,it prevents the breakdown of acetylcholine,leading to continuous stimulation of the postsynaptic membrane,which can be toxic to the nervous system.

(C) The correct answer is $C$.
Neurotransmitters are chemical substances responsible for the transmission of nerve impulses across a synapse.
These chemicals are released from the synaptic vesicles into the synaptic cleft.
Once in the cleft,the neurotransmitters bind to specific protein receptor molecules located on the post-synaptic membrane.
This binding causes the opening of ion channels,leading to the depolarization of the post-synaptic membrane and the generation of a new action potential.

(C) Based on the provided diagram of the synapse:
$A$ points to the receptors located on the postsynaptic membrane.
$B$ points to the synaptic cleft,the space between the presynaptic and postsynaptic neurons.
$C$ points to the synaptic vesicles containing neurotransmitters.
$D$ points to the neurotransmitter molecules released into the synaptic cleft.
Comparing these with the options:
Option $A$ is incorrect because $A$ is a receptor,not a neurotransmitter.
Option $B$ is incorrect because $C$ is a synaptic vesicle,not a neurotransmitter.
Option $C$ is correct because $A$ is a receptor and $C$ represents synaptic vesicles.
Option $D$ is incorrect because $D$ represents neurotransmitters,not $K^+$ ions.

(C) Based on the provided diagram of the synapse:
$A$ represents the Receptor on the postsynaptic membrane.
$B$ represents the Synaptic cleft.
$C$ represents the Synaptic vesicles containing neurotransmitters.
$D$ represents the Neurotransmitter molecules being released.
However,evaluating the standard $NCERT$ diagram for this structure:
$A$ is the Receptor.
$B$ is the Synaptic cleft.
$C$ is the Synaptic vesicle.
$D$ is the Neurotransmitter.
Given the options provided,option $(c)$ is the most appropriate identification where $C$ is identified as a Receptor (or vesicle component) and $D$ as Synaptic vesicles,though there is a slight discrepancy in standard labeling. Based on the provided solution key,$(c)$ is the intended answer.

(B) : Alzheimer's disease is a neurological disorder characterized by the progressive loss of intellectual ability.
This disease,named after the German physician Alois Alzheimer $(1864-1915)$,is associated with the general shrinkage of brain tissue.
It involves the accumulation of $\beta$-amyloid protein deposits and abnormal filaments composed of tau protein in the brain.
Furthermore,it involves changes in the neurotransmitter systems,specifically a significant reduction in the activity of cholinergic neurons,which are neurons that release the neurotransmitter acetylcholine.
Some inherited forms of the disease are linked to a genetic locus on chromosome $21$.

(A) The correct answer is $A$.
Neurotransmitters are chemical messengers that transmit,amplify,and modulate signals between a neuron and another cell.
Common neurotransmitters include:
$(1)$ Amino acids (e.g.,Glutamic acid,$GABA$,Aspartic acid,Glycine).
$(2)$ Peptides (e.g.,Vasopressin,Somatostatin).
$(3)$ Monoamines (e.g.,Norepinephrine,Dopamine,Serotonin) and Acetylcholine.
Cortisone is a glucocorticoid steroid hormone secreted by the adrenal cortex. It plays a role in metabolism and immune suppression,but it does not function as a neurotransmitter.

(A) In the provided diagram of a chemical synapse:
$A$ represents the Axon,which carries the nerve impulse towards the synaptic knob.
$B$ represents the Synaptic vesicles,which contain neurotransmitters.
$C$ represents the Receptors,which are located on the postsynaptic membrane and bind to the neurotransmitters released into the synaptic cleft.
Therefore,the correct identification is $A-$ Axon,$B-$ Synaptic vesicles,$C-$ Receptors.

(B) In the provided diagram of a synapse:
$P$ represents the synaptic knob or axon terminal.
$Q$ represents the synaptic vesicles containing neurotransmitters.
$R$ represents the synaptic cleft.
$S$ represents the neurotransmitter receptors on the postsynaptic membrane.
Therefore,the axon terminal is indicated by the alphabet $P$.

(C) nerve impulse is transmitted from one neuron to another through a junction known as a $Synapse$.
$A$ $Synapse$ is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron,which may or may not be separated by a gap called the synaptic cleft.
Therefore,the correct term for the junction between two neurons is a $Synapse$.

(B) The chemicals that are released at the synaptic junction are known as neurotransmitters.
When an action potential reaches the axon terminal of a neuron,it triggers the release of these chemical substances into the synaptic cleft.
These neurotransmitters then bind to specific receptors on the postsynaptic membrane,allowing the nerve impulse to be transmitted to the next neuron or target cell.

(B) $Synapse$ is the functional junction between two neurons. It consists of the presynaptic membrane (axon terminal of one neuron), the synaptic cleft (the gap), and the postsynaptic membrane (dendrite or cell body of another neuron). Therefore, the gap between the axon of one neuron and the dendrite of another is known as a $Synapse$.

(C) Parkinson's disease is a progressive neurodegenerative disorder.
It is primarily caused by the loss of dopaminergic neurons in the substantia nigra region of the midbrain.
These neurons are responsible for producing $Dopamine$,a neurotransmitter that plays a crucial role in regulating motor control and coordination.
When $Dopamine$ levels drop significantly,it leads to the characteristic symptoms of the disease,such as tremors,muscle rigidity,and bradykinesia (slowness of movement).

(B) In the provided diagram of a chemical synapse:
$A$ represents the receptors located on the postsynaptic membrane.
$B$ represents the synaptic cleft,the space between the presynaptic and postsynaptic neurons.
$C$ represents the synaptic vesicles containing neurotransmitters.
$D$ represents the presynaptic membrane.
Comparing these with the options,option $B$ correctly identifies $A$ as the receptor and $C$ as the synaptic vesicle.

(D) Neurotransmitters are chemical substances released from the synaptic vesicles into the synaptic cleft.
These neurotransmitters bind to specific receptors present on the postsynaptic membrane.
This binding leads to the opening of ion channels,which can generate a new action potential in the postsynaptic neuron or muscle cell.
Therefore,the correct location for these receptor sites is the postsynaptic membrane.

(A) The transmission of nerve impulses across a synapse is mediated by chemical substances known as neurotransmitters.
This is necessary because neurons are not physically continuous; they are separated by a microscopic gap called the synaptic cleft.
When an action potential reaches the presynaptic terminal,it triggers the release of neurotransmitters into the synaptic cleft.
These neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic membrane,thereby propagating the nerve impulse to the next neuron.
Thus,the Reason correctly explains why neurotransmitters are required for synaptic transmission.

(A) The axon terminal of the neuron contains many membrane-bound vesicles called synaptic vesicles in its cytoplasm.
Within these vesicles,chemical substances such as adrenaline and acetylcholine remain stored.
These chemicals are called neurotransmitters because they help to transmit nerve impulses across the synapses.
When a nerve impulse reaches the axon terminal,its synaptic vesicles release their stored chemicals into the synaptic cleft.
These chemicals diffuse through the cleft to reach the membrane of the next neuron,stimulating it.
This process allows the nerve impulse to be transmitted to the next neuron.
Since the reason explains why these chemicals are stored and how they function in the synaptic cleft,both statements are correct and the reason is the correct explanation of the assertion.

(N/A) synapse is a junction through which a nerve impulse is transmitted from one neuron to another.
There are two types of synapses:
$(i)$ Electrical synapses
$(ii)$ Chemical synapses
$(i)$ Electrical Synapses:
In electrical synapses,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. Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system.
$(ii)$ Chemical Synapses:
In chemical synapses,the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. The pre-synaptic neuron transmits an impulse across the synaptic cleft to the post-synaptic neuron. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. The axon terminals contain vesicles filled with these neurotransmitters. When an impulse arrives at the axon terminal,it stimulates the movement of the synaptic vesicles towards the membrane,where they fuse with the plasma membrane and release their neurotransmitters into the synaptic cleft. The released neurotransmitters bind to their specific receptors present on the post-synaptic membrane. This binding opens ion channels,allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.

(N/A) In an electrical synapse,the membranes of pre-synaptic and post-synaptic neurons are in very close proximity.
Electrical current flows directly from one neuron into the other across these synapses.
Impulse transmission across an electrical synapse is very similar to impulse conduction along a single axon.
Impulse transmission across an electrical synapse is always faster than that across a chemical synapse.
Electrical synapses are rare in the human neural system.
Chemical Synapse:
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.
Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses.
The axon terminals contain vesicles filled with these neurotransmitters.
When an impulse arrives at the axon terminal,it stimulates the synaptic vesicles to move towards the membrane,where they fuse with the plasma membrane and release their neurotransmitters into the synaptic cleft.
The released neurotransmitters bind to their specific receptors,present on the post-synaptic membrane.
This binding opens ion channels,allowing the entry of ions which can generate a new potential in the post-synaptic neuron.
The new potential developed may be either excitatory or inhibitory.

(N/A) $(1)$ $A$ synapse is a junction between two neurons,formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron,which may or may not be separated by a synaptic cleft.
$(2)$ Myelinated nerve fibres are enveloped with Schwann cells,which form a myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier.

(N/A) $(1)$ Synapse: The functional junction between the axon terminal of one neuron and the dendrite of the next neuron is called a synapse.
Neurotransmitter: These are chemical substances (e.g.,acetylcholine) released from the synaptic vesicles at the synaptic knob into the synaptic cleft to transmit nerve impulses.
$(2)$ Myelinated nerve fiber: These axons are enveloped by a fatty myelin sheath,which is secreted by Schwann cells.
Non-myelinated nerve fiber: These axons are not surrounded by a myelin sheath,although Schwann cells are present on their outer side.

(N/A) $(1)$ Location: The distal branched ends of an axon are swollen and are called synaptic knobs.
Function: They contain synaptic vesicles that store and release neurotransmitters to facilitate signal transmission across the synapse.
$(2)$ Location: These are found in the retina of the eye.
Function: They are responsible for the conduction of nerve impulses from photoreceptor cells to ganglion cells.

(A) $1$. Electrical transmission occurs via gap junctions where the membranes of pre- and post-synaptic neurons are in very close proximity,allowing current to flow directly from one neuron to the next. This process is extremely fast.
$2$. Chemical transmission involves the release of neurotransmitters into the synaptic cleft. The neurotransmitters bind to receptors on the post-synaptic membrane,which is a slower process compared to electrical transmission.
$3$. Therefore,electrical transmission is faster than chemical transmission.

(N/A) The process of neurotransmitter release occurs at the synapse through the following steps:
$1$. An action potential travels down the axon to the axon terminal.
$2$. The depolarization of the membrane at the axon terminal opens voltage-gated $Ca^{2+}$ channels.
$3$. $Ca^{2+}$ ions flow into the synaptic knob,triggering the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane.
$4$. Neurotransmitters are released into the synaptic cleft via exocytosis.
$5$. These neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane,initiating a new action potential or inhibitory response.

(B) synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron.
These two membranes are separated by a fluid-filled space known as the synaptic cleft.
This space allows for the transmission of nerve impulses via chemical neurotransmitters.

(B) Neurotransmitters are chemical substances that are released from the synaptic vesicles of the presynaptic neuron into the synaptic cleft.
These chemicals bind to specific receptors on the postsynaptic membrane.
They are essential for the transmission of nerve impulses across the synapse,allowing communication between neurons or between neurons and effector cells.

(A) The $Axon$ $terminal$ (also known as the synaptic knob) is the distal end of the axon of a nerve cell.
It contains synaptic vesicles filled with chemical substances known as neurotransmitters.
When an action potential reaches the $Axon$ $terminal$,these vesicles fuse with the presynaptic membrane and release the neurotransmitters into the synaptic cleft via exocytosis to transmit signals to the next neuron or effector cell.

(B) $Synapse$ is a specialized functional junction between two neurons that allows for the transmission of nerve impulses.
It occurs between the axon terminal of one neuron and the dendrite of the next neuron.
The transmission of impulses across a $Synapse$ can be either chemical or electrical in nature.

(A) synapse is the functional junction between two neurons. It is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron,which may or may not be separated by a gap called the synaptic cleft.

(C) The synaptic knob is the bulbous end of an axon terminal. It contains synaptic vesicles,which are small membrane-bound sacs filled with chemical substances known as neurotransmitters. These neurotransmitters are released into the synaptic cleft to transmit nerve impulses to the next neuron or effector cell.

(B) The correct answer is $B$.
Synaptic vesicles are small membrane-bound sacs found in the synaptic knob of an axon terminal.
These vesicles contain chemical substances known as neurotransmitters,which are released into the synaptic cleft to transmit nerve impulses to the next neuron or effector cell.

(D) Neurotransmitters are chemical substances released by axon terminals to transmit nerve impulses to the next neuron or effector cell.
Acetylcholine,glutamic acid,glycine,$GABA$,and epinephrine are all well-known neurotransmitters.
Tyrosine is an amino acid that serves as a precursor for the synthesis of catecholamines (like dopamine,norepinephrine,and epinephrine),but it does not function as a neurotransmitter itself.

(D) In the parasympathetic nervous system,the neurotransmitter $Acetylcholine$ $(ACh)$ is released at the effector/post-synaptic junction.
In contrast,most post-ganglionic sympathetic neurons are adrenergic in nature,meaning they release norepinephrine.

(A) Synaptic vesicles are small secretory vesicles that contain neurotransmitters.
They are located within the axon terminals of the pre-synaptic neuron.
When an action potential reaches the axon terminal,these vesicles fuse with the pre-synaptic membrane to release neurotransmitters into the synaptic cleft.

(D) At the neuromuscular junction,the motor nerve endings release the neurotransmitter $Acetylcholine$ $(ACh)$ into the synaptic cleft.
This $ACh$ binds to nicotinic receptors located on the motor end plate of the muscle fiber membrane,triggering an action potential that leads to muscle contraction.
$Curare$ acts as a competitive antagonist at these nicotinic receptors,thereby blocking neuromuscular transmission rather than prolonging it.

(B) nerve impulse is transmitted from one neuron to another through junctions called synapses. There are two types of synapses: electrical and chemical.
In electrical synapses,the membranes of pre- and postsynaptic neurons are in very close proximity,allowing electrical current to flow directly from one neuron to the other. Therefore,statement $(I)$ is correct and statement $(II)$ is incorrect because there is no synaptic cleft in electrical synapses.
Impulse transmission across electrical synapses is very fast,similar to conduction along a single axon. Therefore,statement $(III)$ is correct.
Electrical synapses are rare in the human system,making statement $(IV)$ incorrect.
Thus,only statements $(I)$ and $(III)$ are true.

(A) The movement of the nerve impulse across the synaptic cleft is primarily a chemical event.
This process is mediated by chemical messengers known as neurotransmitters,such as acetylcholine $(ACh)$,gamma-aminobutyric acid $(GABA)$,norepinephrine,and serotonin.
When an action potential reaches the axon terminal,it triggers the release of these neurotransmitters into the synaptic cleft,which then bind to receptors on the postsynaptic membrane to propagate the signal.

(D) Gamma-aminobutyric acid $(GABA)$ and glycine are well-known inhibitory neurotransmitters in the central nervous system $(CNS)$.
An inhibitory neurotransmitter is released by an inhibitory neuron to decrease the likelihood of an action potential in the postsynaptic neuron.
These substances act at the synapse,which is the junctional gap between the axon terminal of one neuron and the dendrites or cell body of another neuron,to hyperpolarize the postsynaptic membrane.

(C) Parkinson's disease is a neurodegenerative disorder caused by the loss of dopaminergic neurons in the substantia nigra region of the brain.
These neurons are responsible for producing the neurotransmitter $Dopamine$,which plays a crucial role in regulating movement and coordination.
When these neurons degenerate,the levels of $Dopamine$ in the brain decrease significantly,leading to symptoms such as tremors,muscle rigidity,and difficulty in movement.
Therefore,the deficiency of $Dopamine$ is the primary cause of the symptoms observed in Parkinson's disease.

(A) Based on the diagram of the synapse:
$A$ points to the axon terminal (synaptic knob).
$B$ points to the synaptic vesicles containing neurotransmitters.
$C$ points to the synaptic cleft,the space between the two neurons.
$D$ points to the receptors on the postsynaptic membrane.
$E$ points to the neurotransmitters being released into the synaptic cleft.
Therefore,the correct sequence is $A-$ axon terminal,$B-$ synaptic vesicles,$C-$ synaptic cleft,$D-$ receptors,$E-$ neurotransmitters.

(D) There are two types of synapses: electrical synapses and chemical synapses.
$I.$ At electrical synapses,the membranes of pre- and post-synaptic neurons are in very close proximity,allowing direct flow of current.
$II.$ In electrical synapses,impulses are transmitted directly as electric currents.
$III.$ Because of the direct flow of current,the transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon.
$IV.$ Electrical transmission is faster than chemical transmission because there is no delay caused by the release and diffusion of neurotransmitters.
$V.$ Electrical synapses are indeed rare in the human nervous system compared to chemical synapses.
Therefore,all statements $I, II, III, IV,$ and $V$ are correct.

(D) synapse is the junction between two neurons. It is composed of three main structural components:
$1$. Pre-synaptic membrane: The membrane of the axon terminal of the transmitting neuron.
$2$. Synaptic cleft: The gap or space between the pre-synaptic and post-synaptic membranes.
$3$. Post-synaptic membrane: The membrane of the dendrite or cell body of the receiving neuron.
Therefore,all of these components are necessary to form a functional synapse.

(C) Neurotransmitters are chemical messengers released from the pre-synaptic neuron into the synaptic cleft. These molecules then bind to specific receptors located on the post-synaptic membrane to initiate or inhibit an action potential in the next neuron.

(A) Axon terminals form synapses with the dendrites of adjacent neurons.
When a nerve impulse reaches the axon terminal,it triggers the release of neurotransmitters into the synaptic cleft.
These neurotransmitters bind to receptors on the post-synaptic membrane of the adjacent neurons.
This process allows the signal to be transmitted to all neurons that have a synaptic connection with the presynaptic axon terminal.
Therefore,the nerve impulse will travel into all four neurons.

(A) The axon terminal contains synaptic vesicles filled with neurotransmitters. When an action potential reaches the axon terminal,these vesicles fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft via exocytosis. Acetylcholine is a well-known neurotransmitter released from these synaptic vesicles to transmit signals across the synapse.

(A) The transmission of nerve impulses across a synapse occurs via two main types: chemical and electrical.
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 (approximately $20-30 \ nm$ wide).
Because of this physical gap,the electrical impulse cannot jump directly; therefore,chemicals called neurotransmitters are released from the pre-synaptic neuron to bridge the gap and stimulate the post-synaptic neuron.
In contrast,electrical synapses have a very narrow gap (approximately $0.2 \ nm$),allowing for direct electrical transmission without neurotransmitters.
Since the assertion describes the general mechanism of synaptic transmission (chemical) and the reason correctly identifies the presence of the synaptic cleft as the cause for requiring neurotransmitters,the reason is the correct explanation of the assertion.

(N/A) In an electrical synapse,the membranes of pre-synaptic and post-synaptic neurons are in very close proximity.
Electrical current can flow directly from one neuron into the other across these synapses.
Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon.
Impulse transmission across an electrical synapse is always faster than that across a chemical synapse.
Electrical synapses are rare in the human nervous system.

(C) In an electrical synapse,the membranes of pre- and post-synaptic neurons are in very close proximity,allowing electrical current to flow directly from one neuron into the other. This makes impulse transmission across an electrical synapse very fast,often faster than in a chemical synapse.
In a chemical synapse,the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. Transmission of impulses across chemical synapses is always slower than that across electrical synapses because it involves the release,diffusion,and binding of neurotransmitters.
Therefore,the statement that impulse transmission across a chemical synapse is always faster than that across an electrical synapse is incorrect.

(D) In the given figure of a neuron:
$P$ represents the cell body (cyton) which contains the nucleus and Nissl's granules.
$Q$ represents the Schwann cell.
$R$ represents the axon.
$S$ represents the synaptic knob (axon terminal).
Neurotransmitters are chemical substances stored in synaptic vesicles within the synaptic knobs $(S)$.
When an action potential reaches the synaptic knob,these neurotransmitters are released into the synaptic cleft to transmit the signal to the next neuron or effector cell.
Therefore,the correct option is $S$.