In human beings, certain chemicals which cross the synapse between nerve cells are released from
- A.cell body of nerve cell
- B.nucleus of nerve cell
- C.nerve endings of nerve cell
- D.axon of nerve cell
Correct answer
Explanation
The correct answer is C, nerve endings of nerve cell. Chemical messengers called neurotransmitters are released from the nerve endings, the tips of the axon, into the synapse.
A nerve impulse travels from the dendrites through the cell body and along the axon as an electrical signal. When it reaches the branched endings of the axon, it causes small vesicles to release chemicals such as acetylcholine or dopamine into the tiny gap, the synapse. These cross the gap and bind to the dendrites of the next neuron, starting a new impulse. This is why the signal at a synapse moves in one direction only.
A is wrong: the cell body holds the nucleus and keeps the cell alive, but it does not release neurotransmitters into the synapse.
B is wrong: the nucleus controls the cell's activities and is not the site of chemical release.
D is wrong: the axon carries the impulse as an electrical signal; the chemicals come out only at its endings.
Exam tip: dendrite → cell body → axon → nerve ending → synapse (chemical).
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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