When a gazelle suddenly notices a cheetah, several physiological changes occur. What is the best description of how the message is initially transferred from the gazelle's senses to stimulate the fight-or-flight physiological changes? (1 point) electrical impulses from the brain to the muscles to prepare the organism for the response

gene expression of important proteins to initiate the physiological response of the muscles

hormones released by the adrenal gland to set off a physical chain reaction in the organism

tangible dendrite communication from cell to cell that accumulates into muscle contractions

18.
Ivan Pavlov performed experiments on dogs in which he presented food to them accompanied by the sound of a bell. After doing this repeatedly, the dogs began to salivate when a bell was rung, even if no food was being presented.

In a similar fashion, scientists perform an experiment in which a harmless-looking machine with electrodes is attached to each human participant in the study. Pleasant images are shown to each participant accompanied by a slightly painful electric shock. The participants then react with fear when they see the pleasant images again even if there is no machine to deliver an electric shock.

The researchers find that one participant, Catalina, remembers the images very well but is not afraid when they are presented again. She has not been conditioned. Which of the following is the most valid hypothesis the scientists would want to investigate about Catalina's brain? (1 point)

Catalina may have damage to the amygdala, which is responsible for emotional memory but not explicit memory.

Catalina may have damage to the hypothalamus, which forms connections between the left and right hemispheres of the brain, integrating emotional memory with explicit memory.

Catalina may have damage to the occipital lobe, which controls vision, as the images are not being properly integrated with emotional memory.

Catalina may have damage to the part of the cerebrum that is responsible for emotional memory but not the part of the cerebrum responsible for explicit memory.

19.
The all-or-none principal applies to (1 point)
axons
dendrites
saltatory conduction

1 only

1 and 3

1, 2, and 3

2 and 3

20.
If the nodes of Ranvier were closer together, what effect might this have? (1 point)
The action potential would travel faster.
The action potential would travel slower.
The current would not be able to remain above threshold.

1 only

2 only

1 and 3

2 and 3
21.
In golden hamsters, a tau mutation causes their circadian cycle to be 20 hours instead of the wild-type 24 hours. When a part of the tau-mutation hamsters' brain was replaced with one from a wild type, normal circadian rhythms resumed. When this same part of the brain was removed from wild-type hamsters and replaced with one from tau-mutation hamsters, they began a 20-hour circadian cycle. Which part of the brain is this? (1 point)

amygdala

hypothalamus

pineal gland

suprachiasmatic nucleus