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Understanding Reflexes: Autonomic and Somatic Responses, Exercises of Neurobiology

An overview of reflexes, their classification as autonomic or somatic, and the functional elements of reflex arcs. It covers various types of reflexes including stretch reflexes, superficial cord reflexes, and pupillary reflexes. Students will learn about the role of receptors, sensory neurons, integration centers, motor neurons, and effectors in reflex responses.

Typology: Exercises

2021/2022

Uploaded on 09/12/2022

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Name _____________________________ Date ____________________ Period __________
Human Reflexes Lab
Introduction:
Neurons communicate in many ways, but much of what the body must do every day is
programmed as reflexes. Reflexes are rapid, predictable, involuntary motor responses
to stimuli and they occur over neural pathways called reflex arcs. Reflexes serve as
immediate, protective responses to potentially harmful stimuli.
Reflexes can be classified as either autonomic or somatic reflexes. Autonomic reflexes
(visceral) are not subject to conscious control. These reflexes activate smooth muscles,
cardiac muscle, and the glands of the body and they regulate body functions such as
digestion and blood pressure. Somatic reflexes include all reflexes that stimulate
skeletal muscles. An example of such a reflex is the rapid withdrawal of your foot from
a piece of glass you have just stepped on.
All reflex arcs have a minimum of five functional elements:
1. The receptor reacts to a stimulus.
2. The sensory neuron conducts the afferent impulses to the CNS.
3. The integration center consists of one or more synapses in the CNS.
4. The motor neuron conducts the efferent impulses from the integration center to an
effector.
5. The effector, muscle fibers or glands, respond to the efferent impulses by
contraction or secretion a product, respectively.
Somatic Reflexes
1.!Spinal Reflexes
a.!Stretch Reflexes- Stretch reflexes are important postural reflexes that
act to maintain!posture, balance, and locomotion. Stretch reflexes are
produced by tapping a tendon, which stretches the attached muscle.
This stimulates muscle spindles (specialized sensory receptors in the
muscle) and causes reflex contraction of the stretched muscle, which
resists further stretching. Even as the primary stretch reflex is
occurring, impulses are relayed to higher brain centers to advise of
muscle length and speed of shortening- information needed to
maintain muscle tone and posture.
i.!Patellar Reflex- The patellar, or knee-jerk, reflex assesses the
L2-L4 region of the!spinal cord. The reflex is processed at this
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Name _____________________________ Date ____________________ Period __________

Human Reflexes Lab

Introduction:

Neurons communicate in many ways, but much of what the body must do every day is

programmed as reflexes. Reflexes are rapid, predictable, involuntary motor responses

to stimuli and they occur over neural pathways called reflex arcs. Reflexes serve as

immediate, protective responses to potentially harmful stimuli.

Reflexes can be classified as either autonomic or somatic reflexes. Autonomic reflexes

(visceral) are not subject to conscious control. These reflexes activate smooth muscles,

cardiac muscle, and the glands of the body and they regulate body functions such as

digestion and blood pressure. Somatic reflexes include all reflexes that stimulate

skeletal muscles. An example of such a reflex is the rapid withdrawal of your foot from

a piece of glass you have just stepped on.

All reflex arcs have a minimum of five functional elements:

  1. The receptor reacts to a stimulus.
  2. The sensory neuron conducts the afferent impulses to the CNS.
  3. The integration center consists of one or more synapses in the CNS.
  4. The motor neuron conducts the efferent impulses from the integration center to an

effector.

  1. The effector, muscle fibers or glands, respond to the efferent impulses by

contraction or secretion a product, respectively.

Somatic Reflexes

1. Spinal Reflexes

a. Stretch Reflexes - Stretch reflexes are important postural reflexes that

act to maintainposture, balance, and locomotion. Stretch reflexes are

produced by tapping a tendon, which stretches the attached muscle.

This stimulates muscle spindles (specialized sensory receptors in the

muscle) and causes reflex contraction of the stretched muscle, which

resists further stretching. Even as the primary stretch reflex is

occurring, impulses are relayed to higher brain centers to advise of

muscle length and speed of shortening- information needed to

maintain muscle tone and posture.

i. Patellar Reflex - The patellar, or knee-jerk, reflex assesses the

L

- L

region of thespinal cord. The reflex is processed at this

level and does not progress to the brain. This reflex is a

monosynaptic, two-neuron, reflex arc

ii. Achilles Reflex - The Achilles, or ankle-jerk, reflex assesses the

first two sacral segments of the spinal cord. The reflex is

processed at this level and does not progress to the brain. The

reflex is monosynaptic, two-neuron, reflex arc.

iii. Biceps Reflex - The biceps-jerk reflex is a more complex, three

neuron reflex (polysynaptic). This reflex assesses C5- C8 and

T1.

b. Superficial Cord Reflexes - The superficial cord reflexes (abdominal

and plantar reflexes) are initiated by stimulation of receptors in the

skin and mucosa. The superficial cord reflexes depend both on brain

participation and on the cord-level reflex arc.

i. Plantar Reflex - The plantar reflex is elicited by stimulating the

cutaneous receptorsin the sole of the foot. In adults, stimulation

of these receptors causes the toes to flex and move closer

together. Damage to the cortocospinal tract (the major

voluntary motor tract, however, produces Babinski’s sign, an

abnormal response in which the toes flare and the great toe

moves upward. In newborn infants, Babinski’s sign is seen

because the nervous system is still incompletely myelinated.

c. Cranial Nerve Reflex Tests - Two reflexes mediated by cranial nerves

are the corneal reflex and gag reflex.

i. Corneal Reflex - The corneal reflex is mediated through the

trigeminal nerve (cranial nerve V). The absence of this reflex is

an ominous sign because it often indicates damage to the brain

stem. This reflex is tested by touching the cornea with a wisp of

absorbent cotton. It causes pain and the eye to tear up. This

reflex will not be tested in class.

ii. Gag Reflex - The gag reflex tests the motor responses of

cranial nerves IX and X. When the oral mucosa on the side of

the uvula is stroked, each side of the mucosa should rise to

some extent. We will not perform this experiment, as vomiting

is a possibility for those with queasy stomachs.

Autonomic Reflexes - The autonomic reflexes include the pupillary reflexes as well as

many others.

  1. Pupillary Reflexes - There are several types of pupillary reflexes- the pupillary

light reflex and the consensual reflex. In both of these reflexes, the retina of the

eye is the receptor, the optic nerve (cranial nerve II) contains the afferent fibers,

some of which synapse at the optic chiasma in the midbrain with other optic

nerve fibers from the opposite eye. As a result, the neurons in the midbrain

process the signal on both sides of the brain. The oculomotor nerve (cranial

nerve III) is responsible for conducting efferent impulses back to the eye, and

the smooth muscle of the iris is the effector. Many CNS centers are involved in

the integration of these responses. Absence of the normal pupillary reflexes is

Data:

Reflex Response

Patellar- normal

Patellar- after

fatigue

Achilles

Biceps

Plantar

Pupillary-

Response to light

Before:

Right eye _____mm Left eye _____mm

After:

Right eye _____mm Left eye _____mm

Difference:

Right eye _____mm Left eye _____mm

Pupillary-

Consensual

response

Draw and label the reflex arc in your lab notebook.