AP Biology : Understanding Afferent and Efferent Neurons

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understanding Afferent And Efferent Neurons

Which of the following correctly pairs the signal to the type of nervous pathway?

Possible Answers:

Blinking follows an efferent pathway

Cold water on your hand follows an efferent pathway

Breathing follows an afferent pathway

A bug walking on your leg follows an efferent pathway

Walking follows an afferent pathway

Correct answer:

Blinking follows an efferent pathway

Explanation:

Efferent pathways carry signals away from the central nervous system. Essentially, they are signals that your brain sends to tell your body to do something, like blinking. Afferent signals come from outside stimuli and tell your brain what they are sensing, such as temperature. Afferent neurons bring stimuli to the brain, where the signal is integrated and processed. The brain then coordinates a response via efferent signals back to the rest of the body.

Example Question #1 : Understanding Afferent And Efferent Neurons

Where do motor outputs from the brain exit the spinal cord?

Possible Answers:

Dorsal root

Ventral root

Anterior root

Posterior root

Intervertebral foramen

Correct answer:

Ventral root

Explanation:

The ventral root of the spinal cord is located anteriorly, while the dorsal root is located posteriorly. Afferent neurons enter the spinal cord through the dorsal root, carrying signals from the body to the brain. Efferent neurons exit the spinal cord from the ventral root before interfacing with their target muscles.

Example Question #1 : Understanding Afferent And Efferent Neurons

Which of the following answers explains the typical succession of neuronal communication from receiving sensory input to generating a muscle response?

Possible Answers:

Interneuron, efferent neuron, afferent neuron

Afferent neuron, interneuron, efferent neuron

Efferent neuron, interneuron, afferent neuron

Afferent neuron, efferent neuron, interneuron

Correct answer:

Afferent neuron, interneuron, efferent neuron

Explanation:

The typical response pattern is that a sensory afferent neuron receives the external stimulus and communicates with an interneuron. The information is then interpreted, and a response is sent through efferent motor neurons to the appropriate portion of the body. Afferent neurons communicate information from the stimulus to the brain/spinal cord. Efferent neurons communicate information from the brain/spinal cord to the appropriate portion of the body.

Example Question #4 : Understanding Afferent And Efferent Neurons

If you touch a hot pan, __________ neurons tell your brain "it's hot!" and __________ neurons are used to quickly move your hand away

Possible Answers:

afferent . . . efferent

peripheral nervous system . . . central nervous system

efferent . . . afferent

parasympathetic . . . sympathetic

sympathetic . . . parasympathetic

Correct answer:

afferent . . . efferent

Explanation:

Afferent neurons are sensory neurons that carry nerve impulses from sensory stimuli towards the central nervous system and brain, while efferent neurons are motor neurons that carry neural impulses away from the central nervous systme and towards muscles to cause movement.

In this case, the afferent neuron would carry sensory information from your hand to your brain, letting it know your body is touching something hot. Your brain would then process this information and use efferent neurons to tell the arm muscle to contract and move your hand away.

Example Question #2 : Understanding Afferent And Efferent Neurons

Afferent neurons are often associated with __________ function, while efferent neurons are often associated with __________ function.

Possible Answers:

sensory or input . . . motor or effector 

motor or effector . . . sensory or input

sensory or effector . . . motor or input

motor or input . . . sensory or effector

Correct answer:

sensory or input . . . motor or effector 

Explanation:

A good way to remember afferent vs. efferent neurons is: Afferent Arrives, Efferent Exits.

Afferent neurons are neurons whose axons travel towards (or bringing information to) a central point, while an efferent neuron is a cell that sends an axon (or carries information) away from a central point. For example, if the central point in question is the brain, sensory neurons are afferent because they send information to the brain, while motor neurons are efferent because they carry information from the brain to effector organs like muscles or glands. It is crucial to keep in mind exactly which structure is the current focus of the discussion, since the terms "afferent" and "efferent" are relative to the direction of information transmission.

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