Human Physiology Exam 2

At chemical synapses in the body, the plasma membrane of the presynaptic and the postsynaptic neurons are ________________________.

• separated by a synaptic cleft  

• connected by gap junctions 

• fused with one another  

• connected by a synaptic knob  

The neurotransmitter that is (always) released at the neuromuscular junction is ________________________.

• norepinephrine 

• acetylcholine 

• glycine

• epinephrine

A single depolarization event at one point on the cell body/dendrite region of the neuron is usually not sufficient to cause depolarization that reaches `threshold` levels at the axon hillock. Therefore, in order for the neuron to fire an action potential, the effects of multiple stimulations must often be added together to reach `threshold` depolarization at the axon hillock. When a neuron is simultaneously stimulated at many different sites on the cell body/dendrites, the effect of all the separate stimulations are added together in what is known as ____________ summation.  

• spatial

• temporal

In the resting state, the inside of the neuron ________________________.

• is negative with respect to the outside of the neuron  

• is positive with respect to the outside of the neuron  

• has an excess of sodium ions  

• has more sodium ions than potassium ions  

Because the plasma membrane can regulate passage of charged particles into and out of the cell, the composition of the fluid in the cell is very different than that of the fluid outside the cell. Which of the following ions is in greater concentration in the fluid outside the cell, compared to the fluid inside the cell?  

• Chloride (Cl-) only 

• Sodium (Na+) only

• Calcium (Ca++). Sodium (Na+) and Chloride (Cl-) 

• Potassium (K+) only  

When the axon hillock depolarizes to threshold, _________________.

• all of the voltage gated ion channels present close at once, causing the cell to depolarize 
  

• all the voltage gated sodium and potassium ion channels are stimulated to open at the same time 

• all the voltage gated sodium and potassium ion channels are stimulated to open, but the potassium channels open more rapidly and inactivate just as the sodium channels are beginning to open 

• all the all the voltage gated sodium and potassium ion channels are stimulated to open, but the sodium channels open more rapidly and inactivate just as the potassium channels are beginning to open 

Which of the following statements regarding action potentials is true?

• An action generated whenever the nerve fiber is stimulated, regardless of how much or how little stimulation is applied to the nerve fiber 

• An action potential is generated only when threshold (or greater) levels of depolarization are achieved at the axon hillock 

• Action potentials travel in both directions along the axon

• The strength of the action potential weakens as the action potential travels along the axon away from its site of origin

Which of the following situations would cause the nerve cell to hyperpolarize? 

• increased flow of potassium ions out of the nerve cell  

• decreased flow of potassium ions out of the nerve cell 

• increased flow of sodium ions into the nerve cell 

• decreased flow of sodium ions into the nerve cell 

At most synapses, excluding gap junction synapses in cardiac and smooth muscle, nerve impulses are carried across synapses by __________________.

• electrical currents

• chemical messengers 

• bicycle couriers

• transport proteins

When a nerve fiber is stimulated, the fiber _______________ as the membrane potential becomes more positive (i.e. moves closer to 0 mV).

• neutralizes 

• hyperpolarizes

• repolarizes

• depolarizes