Answer:
Since this question has multiple subquestions in it, I will give you the answer to them as follows:
1. Which neuron would activate a muscle? They are called multipolar neurons, they are found mostly originating from the CNS itself and they are multipolar because when a neuron stimulates a muscle, one signal from just one terminal is not enough; it requires the stimulation from several neurnal terminals.
2. Which neuron would be found in the retina of the eye? A bipolar neuron. This is because these neurons will fulfill a double function: to activate the muscles of the retina, and also they will convey messages taken by the sense of sight, towards the brain for interpretation and integration.
3. Which neuron is a sensory neuron found in a reflex arc? The answer again is a unipolar neuron. These neurons will not reach the brain itself, but rather the reflex arc site on the spinal cord. Their task is to relay sensations from the site that has been stimulated to the spinal cord and from there to the affected place, with the correct response.
4. Which neuron is never myelinated? Again the answer is the bipolar neurons found connecting the retina and the eyes. The reason is that these neurons are capable of relying fast messages to and from the brain, whereas in myelinated ones, messages go slower due to the myeling sheaths.
5. Which neuron is typically involved in the special senses of sight and smell? Once more the answer is the bipolar neurons that are most commonly found connecting the different organs of these two senses. Since these have such unique capabilities: relying information for integration and sensory and motor responses, their action potentials travel fast, and have a short distance to go.
Anatomical and physiological barriers provide the crucial first line of defense against pathogens. These barriers include intact skin, vigorous mucociliary clearance mechanisms, low stomach pH and bacteriolytic lysozyme in tears, saliva and other secretions.
The agents that cause disease fall into five groups: viruses, bacteria, fungi, protozoa, and helminths (worms). Protozoa and worms are usually grouped together as parasites, and are the subject of the discipline of parasitology, whereas viruses, bacteria, and fungi are the subject of microbiology.
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