Answer:
<u>acetylcholine</u>
Explanation:
In the pre-synaptic knob there are vesicles which contain a transmitter substance called acetylcholine. When an impulse reaches the synaptic knob, it stimulates the vesicles to move towards the pre-synaptic membrane releasing the acetylcholine.
The transmitter substance makes the membrane permeable. The neuromuscular junction contains the sensory neurone(afferent), motor neurones(efferent) and the relay neurones(connector).
In cardiac muscle
a. an action potential spreads throughout the Z discs.
b. intercalated discs connect the muscle fibers together.
c. calcium enters the cell from storage chambers called intercalated discs.
d. potassium is released from the sarcoplasmic reticulum
Answer:
b. intercalated discs connect the muscle fibers together.
Explanation:
Intercalated discs are components of the muscles found in the heart(cardiac muscles).
Intercalated discs join the cardiomyoctes (muscle cells or fibers) together so that they can function as one and transmit signals amongst themselves during the contraction of the heart.
Intercalated discs are made of up desmosomes and gap junctions.
Intercalated discs are found on the lining of the sacromere and can only be seen by using a microscope to observe the longitudinal section of the heart tissue.
Answer:
3. An even number of chromosomes are required for synapsis during prophase I and proper pairing during metaphase
Explanation:
Mules are hybrids of a cross between a female horse and a male donkey. Horses contain 64 chromosomes while donkeys contain 63 chromosomes in their somatic cells respectively. This means that they each produce 32 and 31 chromosomes respectively during meiosis. A mule, hence, contains 32+31= 63 chromosomes in their somatic cells.
This chromosome number in mules are uneven for meiosis to occur because meiotic division requires that an even number of homologous chromosomes pair together in a process called SYNAPSIS during prophase I of meiosis I. This is impossible in a mule because of the uneven number of chromosomes in its cells.
Also, during metaphase of meiosis, the homologous chromosomes need to be properly aligned at the equator for separation to occur. This is also impossible in a mule considering the number of chromosomes that don't add up.
Due to this reason of unevenness in the number of chromosomes present in a mule, meiosis will not occur and if meiosis (gamete formation) does not occur, reproduction cannot take place. Therefore, the mule is a sterile species i.e. cannot produce offsprings via sexual reproduction.
