Download Core Lab #1 - Reflex Responses

Name: __________________________
Biology 3201 – Core Lab #1 – The Nervous System and Reflex Responses
Page Reference: 396-397
Background:
The Nervous System and Reflex Responses (p. 395): In a simple reflex arc, such as the knee jerk, a
stimulus is detected by a (1) receptor cell, which synapses with a sensory neuron. The (2) sensory
neuron carries the impulse from the site of the stimulus to the central nervous system (spinal cord),
where it synapses with an interneuron (3). The interneuron synapses with a motor neuron (4), which
carries the nerve impulse out to an effector, such as a muscle (5), which responds by contracting. A
reflex can prevent damage to tissues and allows the body to conduct tasks, such as walking, without
using the cerebrum.
The structural and functional unit of the nervous system is the neuron. Nerves, which are numerous
neurons held together by connective tissue, make up the PNS. Reflex actions occur when specific
stimulus results in a particular reaction. The nerve pathway between a stimulus and the reflex action is
called a reflex arc.
Lab Intro: http://www.youtube.com/user/Beneslachto#p/u/3/jd-PaVg2wpU
Knee-Jerk Reflex: http://www.youtube.com/user/Beneslachto#p/a/u/2/qpw31bvoLpg
Achilles Reflex: http://www.youtube.com/watch?v=BEQ6BbLLucA&feature=related
Babinski Reflex: http://www.youtube.com/watch?v=kOq5Np0eZ6A&feature=related
Pre-Lab Question: What is the advantage of a reflex arc?
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Lab:
Reflex
Description of the motion observed & the location of the stimulus
Knee-Jerk Reflex - The
reflex tested by tapping just
below the knee causing the
lower leg to suddenly jerk
forward.
Achilles Reflex - Occurs
when the Achilles tendon is
tapped while the foot is
dorsi-flexed. A positive
result would be the jerking
of the foot towards its
plantar surface.
Babinski Reflex - Occurs
when the big toe moves
toward the top of the foot
and the other toes fan out
after the sole of the foot
has been firmly stroked.
Post Lab Questions: please answer on loose leaf and staple to the lab.
1. Why is the region where the stimulus applied varied?
2. Is this a controlled experiment?
3. Does the reflex occur each time the stimulus is applied, or did the specific location of the
stimulus affect the reaction?
4. What is the advantage of having reflex reactions?
5. Why would the knee-jerk reflex be essential for walking?
6. How does the Babinski reflex differ in adults and infants?
7. What is one of the reflexes that newborns exhibit that gradually disappear? What is the
advantage of the reflex?