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What is the main function of the nervous system?

The nervous system controls the body through electrical and chemical signals. Its roles include both sensory and motor functions, as well as the control of basic life processes.

The nervous system involves both voluntary and involuntary control.


What are the defining features of a neuron?

Neurons are the functional units of the nervous system. They synapse with other neurons and transmit electrical and chemical signals.

The main components of a typical neuron are dendrites, a cell body, and an axon.


In the diagram of a human neuron shown here, the structure labeled A represents the nucleus of the cell. What part of the neuron does the label B represent?

The cell body

The cell body is the region of the neuron that holds the nucleus.


In the diagram of a human neuron shown here, the structure labeled D represents:

The dendrites

Dendrites are projections that extend from the cell body of a neuron. These structures receive information from adjacent neurons and carry it toward the cell body.


In the diagram of a human neuron shown here, the structure labeled C represents:

The axon

The axon is a relatively long projection along which signals can propagate away from the cell body. The end of the axon, or axon terminal, can send chemical signals to an adjacent neuron through a gap known as a synapse.



A synapse is a region where one nerve cell adjoins another. Here, signals can pass between the two, generally from the axon of the presynaptic cell to the dendrite of the postsynaptic one.

Synapses can be electrical or chemical. On the AP Biology exam, synapses tested are generally chemical.


Which part of the neuron contains the nucleus, as well as organelles like the endoplasmic reticulum and mitochondria?

The cell body or soma serves as the location for the nucleus and organelles.

The region of the cell body immediately next to the axon is called the axon hillock. Here, incoming signals are summed (added together) and create an action potential if they surpass a certain threshold.


Which part of the neuron receives incoming signals from previous neurons in the form of neurotransmitter-containing vesicles?

Dendrites receive signals from adjacent neurons.

A neuron releases neurotransmitters, held inside membrane-bound vesicles, into the synapse in a calcium-dependent process. These vesicles reach the dendrites of another cell and activate its receptors.


Which part of the neuron ends in a single terminal and can release neurotransmitters?

The axon releases neurotransmitters at its terminal.

These NTs can range from glutamate to acetylcholine, but all must be held in membrane-bound vesicles. Calcium influx promotes the fusion of these vesicles to the cell membrane, allowing their contents to be sent into the synapse.


What is the axon hillock, and what function does it serve?

The axon hillock is the region of the cell body situated immediately before the axon.

Incoming signals from the dendrites meet here, are summed, and create an action potential if they are greater in magnitude than a certain threshold.


sensory neuron

A sensory neuron receives information from a peripheral receptor, then transmits it as an electrical signal to the spinal cord. This information could relate to the external environment or the body's interior.

Sensory neurons are also called afferent neurons. Afferent structures always travel toward the organ or system in question; here, afferent neurons travel toward the spinal cord.


motor neuron

A motor neuron transmits an electrical signal from the spinal cord to an effector muscle to initiate movement.

Motor neurons are also called efferent neurons. Efferent structures always travel away from the organ or system in question; here, efferent neurons travel away from the spinal cord.


Name the two divisions of the nervous system.

The nervous system is broadly divided into the central nervous system (CNS) and the peripheral nervous system (PNS).


What two components does the central nervous system include?

The central nervous system (CNS) includes the brain and the spinal cord.


Name two main structures of the peripheral nervous system.

The peripheral nervous system (PNS) includes spinal nerves and cranial nerves.

In the PNS, neurons are organized into peripheral structures called ganglia.


Name the two divisions of the peripheral nervous system.

The PNS is divided into the somatic and the autonomic nervous systems.

The somatic system involves the conscious movement of skeletal muscles, while the autonomic system deals with the involuntary functioning of internal organs.


What is the function of the somatic nervous system?

The somatic nervous system is generally associated with voluntary skeletal muscle movement. However, it also includes sensory neurons that transmit signals to the central nervous system.

Sensory neurons are afferent, meaning that they carry signals toward the spinal cord. Motor neurons are efferent and travel from the spinal cord to effector muscles.


What is the function of the autonomic nervous system?

The autonomic nervous system is involved in the involuntary control of muscles and glands. It can promote a variety of functions including peristalsis (muscle movement in the intestines), changes in heart rate, dilation and constriction of blood vessels, and more.

The ANS includes two main divisions: the sympathetic nervous system and the parasympathetic nervous system.


Name the two divisions of the autonomic nervous system.

The autonomic nervous system is divided into the sympathetic and parasympathetic systems.

The sympathetic system is commonly known to activate "fight-or-flight" responses, while the parasympathetic system relates to "resting and digesting."


What is the function of the sympathetic nervous system?

The sympathetic nervous system serves to activate certain bodily processes when in cases of stress or danger. It is commonly known as the "fight-or-flight" system.

Broadly, the sympathetic system speeds up heart rate, increases blood flow to muscles, and inhibits digestion.


What is the function of the parasympathetic nervous system?

The parasympathetic nervous system serves to activate certain bodily processes when at rest and in safe conditions. It is especially active after eating and is commonly known as the "rest-and-digest" system.

Broadly, the parasympathetic system slows down heart rate and increases blood flow to the digestive system.


Name four physiological responses triggered by the sympathetic nervous system.

The sympathetic system:

  • increases heart rate
  • increases blood flow to skeletal muscle via vasodilation
  • decreases blood flow to the digestive system via vasoconstriction
  • dilates pupils


Name four physiological responses triggered by the parasympathetic nervous system.

The parasympathetic system:

  • decreases heart rate
  • decreases blood flow to skeletal muscle via vasoconstriction
  • increases blood flow to the digestive system via vasodilation
  • constricts pupils

Other effects include the stimulation of sexual arousal, salivation, and urination.


What are the main neurotransmitters involved in sympathetic activity?

Epinephrine (commonly called adrenaline) and norephinephrine (commonly called noradrenaline) are the main sympathetic neurotransmitters.

Technically, these hormones are only released by the postganglionic synapse, which runs from the ganglion (nerve center) to the target organ. Acetylcholine is released at the preganglionic synapse, which travels from the spinal cord to the ganglion. However, the AP Biology exam typically does not test this distinction.


What is the main neurotransmitter associated with parasympathetic activity?

Acetylcholine is the main parasympathetic neurotransmitter.

In this capacity, acetylcholine promotes "rest and digest" functions. However, note that acetylcholine also has an entirely distinct role in the muscular system, where it promotes skeletal muscle contraction.


During the examination of a subject, it was found that the smooth muscle of her artery walls was temporarily dilated. Is this effect associated with sympathetic or parasympathetic activation?


To discern which division of the autonomic nervous system was active in this patient, we would need to know which artery walls are being described. Vasodilation of the arteries leading to the digestive system would imply parasympathetic activity, while dilation of the arteries that supply skeletal muscle is an effect of the sympathetic system.


When the sympathetic nervous system is activated, which hormone will be present at higher concentrations: insulin or glucagon?

Glucagon will be more highly present.

The release of both glucagon and cortisol is correlated with sympathetic activity. Both hormones act to increase blood glucose levels, making energy more available for fight-or-flight activity.


When the parasympathetic nervous system is activated, which hormone will be present at higher concentrations: insulin or glucagon?

Insulin will be more highly present.

Insulin release from the beta islet cells of the pancreas can be directly promoted by parasympathetic stimulation. More importantly, simply remember that insulin is released after meals to promote the storage of glucose, while the parasympathetic system is also activated after eating to promote digestion.


What function is served by an action potential?

An action potential is an electrical event that allows a signal to propagate down the axon of a neuron.

Action potentials involve a brief variation in membrane potential from its resting value of -70 mV. This process is facilitated by voltage-gated sodium and potassium channels.


Which two gradients combine to dictate the membrane potential of a neuron?

Electrical and chemical gradients combine to form the electrochemical gradient.

The electrical potential is produced by the difference in charge across the membrane, while the chemical gradients are formed by differences in ion concentration between the two sides. Like any gradients, both of these are under pressure to dissipate.