BIOL 207: Lab 5
BIOLOGY 207 LABORATORY 5
THE NERVOUS SYSTEM
PART 1: REFLEX ARCS AND CUTANEOUS RECEPTORS.
OBJECTIVES
1. Describe reflex arcs.
2. Describe muscle spindles and discuss their function.
3. Demonstrate reflexes
GENERAL STATEMENT REGARDING SUBJECT MATTER
Reflexes
A reflex is the activation of a muscle response to a stimulus without the involvement of higher brain tissues. This
rapid activation of muscle contraction is necessary to prevent damage to tissues. The simplest form of reflex is
referred to as monosynaptic and it involves only a single synapse within the central nervous system (spinal cord). In
other words, the sensory neuron bringing sensory information into the CNS (dorsal root) directly synapses with a
motor neuron in the spinal cord that can activate a relevant muscle. Activation and contraction of the muscle may be
on the same side of the body as the stimulus (ipsilateral) or on the opposite side of the body (contralateral) or both.
Your job is to investigate some simple reflexes and understand the fundamental processes by which normally
voluntary muscles can be flexed with no input from your brain.
Muscle Spindles
Sensory cell clusters referred to as spindles are present in your skeletal muscles. These spindles are sensitive to the
stretch of the muscle and they can initiate the activation of a muscle to contract if they are stretched too rapidly. The
mechanism by which they activate the muscle involves spindle activation of a sensory neuron(s) that synapses (in the
CNS) with the motor neuron responsible for activating the muscle and thus opposing the potentially damaging stretch.
The knee jerk response is an example of this activation of muscle spindles by stretching, followed by activation of
muscle contraction to oppose that stretch. You will be doing a series of tests on your lab partners to examine their
reflexes.
Cutaneous Receptors
There are numerous receptors in your skin and they come in different varieties. Each type of receptor is specialized
to respond to a particular sensation. Each sensory neuron has a receptive field, or an area of skin that can activate that
particular sensory neuron when stimulated. The area of the receptive field for that sensory neuron depends inversely
upon the density of receptors. In other words, the more receptors you have, the smaller the area served by a particular
receptor. You will be mapping the distribution of the different types of receptors and also determining how close the
receptors are to each other in particular areas of your body. You should find an interesting distribution of receptors of
different types (cold, warm, touch etc.) and also find the actual receptive field for touch receptors varies in size on
different parts of your body. Adaptation
All of us have experienced adaptation of our sensory receptors. After walking into a dark room we begin to see better
after a few minutes (dark adaptation) and after we leave a movie theater and walk into the bright sunshine, it takes a
couple of minutes to see well (light adaptation). Similarly, when we get into a warm shower we adapt to it just like we
do after jumping into a cold lake. Sensory adaptation allows us to ignore constant stimuli. Some types of receptors,
like pain, do not adapt and this is a good thing. You will be testing the adaptation of your sensory system to
temperature.
READING in HUMAN PHYSIOLOGY, 14th Edition, Stuart Ira Fox
Reflex arcs: pp. 238-239
Spindle fibers: pp. 386-390
Cutaneous receptors: pp. 270-274
5.1
, BIOL 207: Lab 5
Sensory adaptation: p. 268
REFLEXES
For these activities, you should work in pairs.
NOTE: YOU WILL NEED A RUBBER MALLET TO DEMONSTRATE EACH OF THESE REFLEXES. USE
THESE MALLETS CAREFULLY. USE THE MINIMUM FORCE NECESSARY TO GET A RESPONSE.
Ex. 5.1A: Knee Jerk Reflex
1. Have the victim (volunteer) sit on the edge of the lab bench with their leg relaxed.
2. Gently strike the kneecap tendon, (the patellar tendon) just below the kneecap.
3. Observe the contraction of the thigh muscle (quadriceps) that opposes the stretch of the muscle.
This contraction is apparent when the leg extends slightly due to muscle action (contraction).
Answer the questions on p. 5.4.
Ex. 5.1B: Ankle Jerk Reflex
1. Have your volunteer kneel on a chair or cushioned surface with the tester behind.
2. Your volunteer must have his or her shoes off for this test.
3. The tester should strike (always gently) the Achilles tendon about the level of the ankle.
4. Observe the extension of the foot.
Answer the questions on p. 5.4.
Ex. 5.1C: Biceps Jerk Reflex
1. Have your volunteer sit next to the desk with the arm completely extended and relaxed.
2. Insert your finger (thumb or other finger) into the indentation (antecubital fossa) below the
biceps and press the tendon.
3. Gently strike the finger with the mallet.
4. Observe the muscle twitch in the biceps.
Ex. 5.1D: Triceps Jerk Reflex
1. Have your volunteer lie on their back with the arm relaxed and laying across the stomach area.
2. Gently hit the triceps tendon about 1.5-2 inches above the elbow
3. Observe the twitch in the triceps muscle.
CUTANEOUS RECEPTORS
In the first set of receptor experiments below, you will be investigating the receptor distribution for sensations of
temperature and touch. You will be mapping these receptors on the inside of your forearm to determine if these
receptors are evenly and equally distributed, if they are more or less distributed in what you might consider a random
distribution, or if they appear to be clustered at different regions in what is called a punctate distribution. When you
do these exercises, keep in mind that each type of sensation is mediated by a different type of receptor.
5.2
BIOLOGY 207 LABORATORY 5
THE NERVOUS SYSTEM
PART 1: REFLEX ARCS AND CUTANEOUS RECEPTORS.
OBJECTIVES
1. Describe reflex arcs.
2. Describe muscle spindles and discuss their function.
3. Demonstrate reflexes
GENERAL STATEMENT REGARDING SUBJECT MATTER
Reflexes
A reflex is the activation of a muscle response to a stimulus without the involvement of higher brain tissues. This
rapid activation of muscle contraction is necessary to prevent damage to tissues. The simplest form of reflex is
referred to as monosynaptic and it involves only a single synapse within the central nervous system (spinal cord). In
other words, the sensory neuron bringing sensory information into the CNS (dorsal root) directly synapses with a
motor neuron in the spinal cord that can activate a relevant muscle. Activation and contraction of the muscle may be
on the same side of the body as the stimulus (ipsilateral) or on the opposite side of the body (contralateral) or both.
Your job is to investigate some simple reflexes and understand the fundamental processes by which normally
voluntary muscles can be flexed with no input from your brain.
Muscle Spindles
Sensory cell clusters referred to as spindles are present in your skeletal muscles. These spindles are sensitive to the
stretch of the muscle and they can initiate the activation of a muscle to contract if they are stretched too rapidly. The
mechanism by which they activate the muscle involves spindle activation of a sensory neuron(s) that synapses (in the
CNS) with the motor neuron responsible for activating the muscle and thus opposing the potentially damaging stretch.
The knee jerk response is an example of this activation of muscle spindles by stretching, followed by activation of
muscle contraction to oppose that stretch. You will be doing a series of tests on your lab partners to examine their
reflexes.
Cutaneous Receptors
There are numerous receptors in your skin and they come in different varieties. Each type of receptor is specialized
to respond to a particular sensation. Each sensory neuron has a receptive field, or an area of skin that can activate that
particular sensory neuron when stimulated. The area of the receptive field for that sensory neuron depends inversely
upon the density of receptors. In other words, the more receptors you have, the smaller the area served by a particular
receptor. You will be mapping the distribution of the different types of receptors and also determining how close the
receptors are to each other in particular areas of your body. You should find an interesting distribution of receptors of
different types (cold, warm, touch etc.) and also find the actual receptive field for touch receptors varies in size on
different parts of your body. Adaptation
All of us have experienced adaptation of our sensory receptors. After walking into a dark room we begin to see better
after a few minutes (dark adaptation) and after we leave a movie theater and walk into the bright sunshine, it takes a
couple of minutes to see well (light adaptation). Similarly, when we get into a warm shower we adapt to it just like we
do after jumping into a cold lake. Sensory adaptation allows us to ignore constant stimuli. Some types of receptors,
like pain, do not adapt and this is a good thing. You will be testing the adaptation of your sensory system to
temperature.
READING in HUMAN PHYSIOLOGY, 14th Edition, Stuart Ira Fox
Reflex arcs: pp. 238-239
Spindle fibers: pp. 386-390
Cutaneous receptors: pp. 270-274
5.1
, BIOL 207: Lab 5
Sensory adaptation: p. 268
REFLEXES
For these activities, you should work in pairs.
NOTE: YOU WILL NEED A RUBBER MALLET TO DEMONSTRATE EACH OF THESE REFLEXES. USE
THESE MALLETS CAREFULLY. USE THE MINIMUM FORCE NECESSARY TO GET A RESPONSE.
Ex. 5.1A: Knee Jerk Reflex
1. Have the victim (volunteer) sit on the edge of the lab bench with their leg relaxed.
2. Gently strike the kneecap tendon, (the patellar tendon) just below the kneecap.
3. Observe the contraction of the thigh muscle (quadriceps) that opposes the stretch of the muscle.
This contraction is apparent when the leg extends slightly due to muscle action (contraction).
Answer the questions on p. 5.4.
Ex. 5.1B: Ankle Jerk Reflex
1. Have your volunteer kneel on a chair or cushioned surface with the tester behind.
2. Your volunteer must have his or her shoes off for this test.
3. The tester should strike (always gently) the Achilles tendon about the level of the ankle.
4. Observe the extension of the foot.
Answer the questions on p. 5.4.
Ex. 5.1C: Biceps Jerk Reflex
1. Have your volunteer sit next to the desk with the arm completely extended and relaxed.
2. Insert your finger (thumb or other finger) into the indentation (antecubital fossa) below the
biceps and press the tendon.
3. Gently strike the finger with the mallet.
4. Observe the muscle twitch in the biceps.
Ex. 5.1D: Triceps Jerk Reflex
1. Have your volunteer lie on their back with the arm relaxed and laying across the stomach area.
2. Gently hit the triceps tendon about 1.5-2 inches above the elbow
3. Observe the twitch in the triceps muscle.
CUTANEOUS RECEPTORS
In the first set of receptor experiments below, you will be investigating the receptor distribution for sensations of
temperature and touch. You will be mapping these receptors on the inside of your forearm to determine if these
receptors are evenly and equally distributed, if they are more or less distributed in what you might consider a random
distribution, or if they appear to be clustered at different regions in what is called a punctate distribution. When you
do these exercises, keep in mind that each type of sensation is mediated by a different type of receptor.
5.2
