NEET Practice Questions (MCQs) with Answers & Solutions

The magnitude of the vector product is $ab\sin\theta$. If two vectors are parallel, $\theta = 0^\circ$ or $\theta = 180^\circ$. In both cases, $\sin\theta = 0$. Therefore, the magnitude of the vector product is zero, making it a zero vector. The text states: 'd(r $\times$ p)/dt = r $\times$ dp/dt + dr/dt $\times$ p. Now, the velocity of the particle is v = dr/dt and p = m v. Because of this d(r $\times$ p)/dt = r $\times$ dp/dt + v $\times$ mv. The term v $\times$ mv is zero as the vector product of two parallel vectors vanishes.'

At a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Therefore, option o3 is incorrect.

The axon is a long fibre, the distal end of which is branched. Each branch terminates as a bulb-like structure called synaptic knob which possess synaptic vesicles containing chemicals called neurotransmitters. These neurotransmitters are crucial for impulse transmission across a synapse.

When an impulse (action potential) arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane, releasing neurotransmitters into the synaptic cleft.

At 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. Electrical synapses are characterized by direct current flow and do not involve neurotransmitters or a significant synaptic cleft. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse.

Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. They are released from the pre-synaptic neuron, diffuse across the synaptic cleft, and bind to receptors on the post-synaptic neuron, thereby continuing the impulse.

The axon terminals contain vesicles filled with these neurotransmitters. These vesicles are vital for the storage and eventual release of neurotransmitters.

A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron.

At electrical synapses, electrical current can flow directly from one neuron into the other. At a chemical synapse, chemicals called neurotransmitters are involved in the transmission of impulses. This highlights the fundamental difference in their transmission mechanism.