Which statement is incorrect?
a. Cytotoxic T cells release chemicals that destroy targeted cells.
b. Helper T cells enhance the activity of other T cells and B cells.
c. Regulator T cells are believed to play an important role in tolerance to self-antigens.
d. Helper T cells can combine only with host cells bearing both foreign antigen and class I MHC-encoded self-antigens on their surface.
e. The majority of T cells are helper T cells.
D
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The following are the steps involved in transmission at a cholinergic synapse. What is the correct sequence for these events? 1. Chemically-gated sodium channels on the postsynaptic membrane are activated. 2. Calcium ions enter the synaptic terminal. 3. Acetylcholinesterase hydrolyzes acetylcholine. 4. An action potential depolarizes the synaptic terminal at the presynaptic membrane. 5. The
pre-synaptic terminal reabsorbs choline. 6. Acetylcholine is released from storage vesicles by exocytosis. 7. Acetylcholine binds to receptors on the postsynaptic membrane. 8. Calcium ions are removed from the cytoplasm of the pre- synaptic terminal. A) 4, 2, 6, 7, 8, 5, 3, 1 B) 4, 2, 6, 7, 1, 8, 3, 5 C) 2, 4, 6, 7, 1, 8, 3, 5 D) 2, 5, 4, 6, 7, 1, 8, 3 E) 6, 4, 2, 7, 1, 8, 3, 5
The time during which an excitable membrane cannot respond to further stimulation regardless of the stimulus strength is the ________.
Fill in the blank(s) with the appropriate word(s).
Receptors that bind acetylcholine are known as:
A) alpha. B) beta. C) adrenergic. D) cholinergic.
If a physician applies eye drops that inhibit muscle fibers controlled by the parasympathetic division, you would expect
A. no change in the size of the pupil. B. the patient's pupil to constrict. C. the patient's pupil to dilate.