8. Temporal summation of presynaptic signals summarizes potentials from
(A) two different excitatory presynaptic neurons
(B) two overlapping depolarization signals of the same synapse
(C) two different inhibitory presynaptic neurons
(D) two overlapping hyperpolarization signals of the same synapse.

4. At the equilibrium potential of X channels, (A) the membrane potential of the neuron is at 0 mV (B) the membrane potential of the neuron is at -90 mV (C) the neuron is at its resting membrane potential (D) a flux of X ion into and out the neuron is equal.

5. Which of following enzymes probably won't express in the noradrenergic neurons? (A) tyrosine hydroxylase (B) Dopa decarboxylase (C) dopamine beta-hydroxylase (D) phenyl ethanolamine N-methyltransferase.

6. The circulation of cerebrospinal fluid is between (A) pia mater and arachnoid mater (B) arachnoid mater and dura mater (C) pia mater and dura mater (D) pia mater and cerebrum.

7. Which of following receptor activations mediate skeletal muscle contraction? (A) adrenergic receptors (B) noradrenergic receptors (C) nicotinic acetylcholine receptors (D) muscarinic acetylcholine receptors.

9. Which of following respiratory status has the lowest intrapleural pressure (Pip)? (A) beginning of inspiration (B) middle of inspiration (C) end of inspiration and beginning of expiration (D) middle of expiration.

10. The percentage of oxygen-saturated hemoglobin in the systemic venous under resting state is about (A) 100 (B) 75 (C) 40 (D) 20.

11. Firings of central chemoreceptors are sensitive directly to increase concentration of (A) H+ (B) O2 (C) CO2 (D) lactic acid.

12. Which of the following changes would most increase the resistance to blood flow in a blood vessel? (A) halving the diameter of the vessel (B) doubling the diameter of the vessel (C) halving the length of the vessel (D) doubling the length of the vessel

13. The QRS complex in an electrocardiogram best represents: (A) depolarization of the atria (B) repolarization of the atria (C) depolarization of the ventricles (D) repolarization of the ventricles

14. Which of the following statements about the cardiac cycle is TRUE? (A) The duration of systole is greater than that of diastole in a subject at rest. (B) During isovolumetric ventricular relaxation, blood flows from the atria into the ventricles. (C) Closure of the atrioventricular valves occurs at the onset of ventricular systole. (D) The QRS complex occurs at approximately the same time as the closure of the semilunar valves.