Test: Assertion & Reason :Neural Control and Coordination - NEET MCQ

The axon terminal of the neuron contains many membrane bound vesicles called synaptic vesicle, 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 passes the axon terminal, its synaptic vesicles release their stored chemicals to the synaptic cleft. These diffuse through the cleft to reach the membrane of the next neuron, stimulating the latter. This causes the nerve impulse to be transmitted along the next neuron.

Topic in NCERT: Transmission of Impulses

Line in NCERT: "Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses."

To maintain the unequal distribution of Na⁺ and K⁺ ion, the neurons use chemical energy in the form of ATP to actively transport Na⁺ ion out of cell and more K⁺ inside the cell.

Topic in NCERT: NEURAL CONTROL AND COORDINATION

Line in NCERT: "The electrical potential difference across the resting plasma membrane is called as the resting potential."

Transmission of nerve impulse across synapses is accomplishe by neurotransmitter because synapses comprises of a synaptic cleft between the end of one nerve fibres and the beginning of the next

Topic in NCERT: Transmission of Impulses

Line in NCERT: "Chemicals involved in the transmission of impulses at chemical synapses are called neurotransmitters."

The axonal membrane of neuron is more permeable to potassium ions (K⁺) and nearly impermeable to sodium ions (Na⁺). In a resting state, neuron does not conduct any impulse as the fluids outside the cell membrane carry a relatively high positive charge while the fluids inside the cell membrane carry a less positive, or relatively negative charge.

Topic in NCERT: Generation and Conduction of Nerve Impulse

Line in NCERT: "the axonal membrane is comparatively more permeable to potassium ions (K*) and nearly impermeable to sodium ions (Na+)."

There are two types of synapses, namely, electrical synapses and chemical synapses. 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. 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 and electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system

Topic in NCERT: Transmission of Impulses

Line in NCERT: "Electrical synapses are rare in our system."

Based on the number of axons and dendrites, the neurons are divided into three types, i.e, multipolar (with one axon and two or more dendrites; found in the cerebral cortex), bipolar (with one axon and one dendrite, found in the retina of eye) and unipolar (cell body with one axon only; found usually in the embryonic stage).

Myelinated nerve fibres are present in spinal and cranial nerves. Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon, and is commonly found in autonomous and the somatic neural systems. The conduction of impulses is faster in myelinated nerve fibre (or medullated nerve fibre) because when an impulse travels along a medullated nerve fibre, it does not proceed uniformly along the length of the axis cylinder, but jumps from one node of Ranvier to the next. This is called the saltatory conduction of impulses.

Topic in NCERT: NEURON AS STRUCTURAL AND FUNCTIONAL UNIT OF NEURAL SYSTEM

Line in NCERT: "Myelinated nerve fibres are found in spinal and cranial nerves."

impulse, i.e., resting, the axonal membrane is comparatively more permeable to potassium ions (K⁺) and nearly impermeable to sodium ions (Na⁺). Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm. Consequently, the axoplasm inside the axon contains high concentration of K⁺ and negatively charged proteins and low concentration of Na⁺. These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3 Na⁺ outwards for 2 K⁺ into the cell. As a result, the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and therefore, is polarised.

Topic in NCERT: Generation and Conduction of Nerve Impulse

Line in NCERT: "The outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and therefore is polarised."

Action potential occurs in response to stimulation of nerve fibre as a result of various stimuli like touch, smell, pressure and chemical changes

Topic in NCERT: Transmission of Impulses

Line in NCERT: "When a stimulus is applied at a site... the membrane at the site A becomes freely permeable to Na+. This leads to a rapid influx of Na+ followed by the reversal of the polarity at that site, i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. The polarity of the membrane at the site A is thus reversed and hence depolarised. The electrical potential difference across the plasma membrane at the site A is called the action potential, which is in fact termed as a nerve impulse."

The plasma membrane of the neuron is polarised due to the high out flow of Na⁺ ions to outside and low intake of K⁺ ion. Na⁺ ions outflow by the ion channel of plasma membrane and K⁺ ions inflow by it. This creates a difference in the positive potential across the plasma membrane. The membrane is less positive inside which is normally termed as negative inside w.r.t. outside.

Topic in NCERT: Generation and Conduction of Nerve Impulse

Line in NCERT: "Neurons are excitable cells because their membranes are in a polarised state. Different types of ion channels are present on the neural membrane. These ion channels are selectively permeable to different ions."

Signals from the axon terminal of presynaptic neuron are transmitted to the dendrites of the postsynaptic neuron with the help of chemicals known as neurotransmitters.

Topic in NCERT: Transmission of Impulses

Line in NCERT: "Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses."

Neurons are excitable cells. Excitability is the ability of nerve cells to generate an electrical impulse in response to stimulus. When a nerve fibre receives stimulus, the potential across the membrane is reversed at the point of excitation. It means, the inner side of plasma membrane of the cell becomes more positively charged with respect to the outer side of plasma membrane. This change in polarity is called action potential. This condition of reverse polarity is said to be depolarised.

Topic in NCERT: Generation and Conduction of Nerve Impulse

Line in NCERT: "Neurons are excitable cells because their membranes are in a polarised state."

The brain stem consists of pons varoli, medulla oblongata, mid brain and diencephalon. It is the connection between brain and spinal cord. It contains centres for controlling many vital activities, e.g. respiratory centres, vasomotor centres, salivary centres etc. It also carries nerve tracts between the spinal cord and the higher brain structure.

Topic in NCERT: Hindbrain

Line in NCERT: "The medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions."

Medulla oblongata consists of accumulation of nerve cells act as vital centres of many autonomic reflexes like vomiting, coughing and sneezing.

Topic in NCERT: Hindbrain

Line in NCERT: "The medulla contains centres which control respiration, cardiovascular reflexes, and gastric secretions."

Hind brain consists of cerebellum located dorsally to medulla oblongat and pons varoli. It contains centres for maintenance of posture and equilibrium of the body and for the muscle tone. All activities of the cerebellum are involuntary but may involve learning in their early stages.

Topic in NCERT: Hindbrain

Line in NCERT: "The hindbrain comprises pons, cerebellum and medulla."