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Reflexes, Chapter 13 The Spinal Cord, Spinal Nerves, and Somatic Reflexes

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What is the function of the golgi tendon reflex?
To prevent contracting muscles from applying excessive tension tendons
What are golgi tendon organs?
Encapsulated nerve endings that have at their ends numerous terminal branches with swellings associated with bundles of collagen fibers in tendons
Where are golgi tendon organs located?
Within tendons near the muscle-tendon junction
How does the golgi tendon reflex work?
How does the golgi tendon reflex work?

1. As a muscle contracts, the attached tendons are stretched

2. The increased tension on the tendon results in action potentials being elicited in the sensory neurons in the golgi tendon organs
***Golgi tendon organs have a high threshold and sensitive only to intense stretch

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3. The sensory neurons from the golgi tendon organ pass through the dorsal root to the posterior horn, where they synapse with inhibitory interneurons

4. The inhibitory interneurons then synapse with alpha motor neurons that innervate that muscle to which the golgi tendon organ is attached

5. The sensory neurons stimulate the inhibitory interneurons to release inhibitory neurotransmitters

6. These inhibitory neurotransmitters inhibit the alpha motor neuron, resulting in the muscle being inhibitted (relaxing)

7. This mechanism protects tendons from damage

What is the withdrawal reflex also called?
Flexor reflex
What is the function of the withdrawal reflex?
To remove a limb or other body part from a painful stimulus
How does the withdrawal reflex work?
How does the withdrawal reflex work?

1. Pain receptors (sensory neurons) detect a painful stimulus

2. Action potentials are generated in the pain receptor and transmitted through the dorsal root to the posterior horn.

3. Those sensory neurons then synapse with excitatory interneurons

4. The excitatory interneurons then synapse with alpha motor neurons

5. The alpha motor neurons stimulate muscles (usually flexor muscles) that move the limb away from the source of painful stimulus

6. Collateral branches of the sensory neuron synpase with ascending fibers to the brain, providing conscious awareness of painful stimuli

What is reciprocal innervation?

*A process that is associated with the withdrawal reflex the reinforces the efficiency of the withdrawal reflex

*Affects muscles in the same limb

*Is NOT the same thing as the crossed extensor reflex

How does reciprocal innervation work?

1. During the withdrawal reflex, sensory neurons conduct action potentials from pain receptors to the spinal cord

2. Sensory neurons synapse with excitatory interneurons that are part of the withdrawal reflex (which usually trigger the flexor muscles)

3. Collateral branches of the sensory neurons also synapse with inhibitory interneurons that are part of reciprocal innervation

4. The inhibitory interneurons synapse with alpha motor neurons supplying the extensor muscles, causing them to relax and not oppose the flexor muscles of the with drawal reflex, which are contracting

What is the crossed extensor reflex?

*A process that is associated with the withdrawal reflex the reinforces the efficiency of the withdrawal reflex

*Affects muscles in the opposite limb

*When the withdrawal reflex is triggered, allows weight to be shifted to the other side of the body without falling

*Is NOT the same thing as the reciprocal innervation

How does the crossed extensor reflex work?

1. During the withdrawal reflex, sensory neurons from pain rexeptors conduct action potentials to the spinal cord

2. Sensory neurons synapse with excitatory neurons that are part of the withdrawal reflex

3. The excitatory neurons that are part of the withdrawal reflex stimulate alpha motor neurons that innervate flexor muscles, causing withdrawal of the limb from painful stimulus

4. Collateral branches of the sensory neurons also synapse with excitatory interneurons that cross to the opposite side of the spinal cord as part of the crossed extensor reflex

5. The excitatory interneurons that cross the spinal cord stimulate alpha motor neurons supplying extensor muscles in the opposite limb, causing them to contract and support body weight during the withdrawal reflex

False
Spinal cord conducts signals up and down the body passing through gray and white matter, respectively.
True
Cervical and lumbar enlargements are wide points in the cord marking the emergence of motor nerves.
True
Each portion of the spinal cord served by a spinal nerve is called a segment of the cord.
True
Nerve fibers in a given tract in the white matter are similar in origin, destination, and function.
False
Motor signals typically begin in an upper motor neuron in the thalamus.
False
Most nerves are motor nerves.
False
A nerve fiber is enclosed in its own fibrous sleeve called perineurium
True
A ganglion is a swelling along a nerve containing cell bodies of peripheral neurons.
True
A dermatome is a nerve innervating a specific region in the skin.
True
Posterior root ganglia contain somas of unipolar neurons
False
Somatic reflexes are responses of skeletal, smooth and cardiac muscles.
False
The stretch reflex is a tendency of a muscle to stretch when it is overcontracted.
True
A stretch reflex is often accompanied by reciprocal inhibition.
False
The tendon reflex is the inhibition of a muscle contraction that occurs when its tendon is excessively stretched.
True
The cross extension reflex is the contraction of the extensors on one side of the body when the flexors are contracted on the other side
the precentral gyrus of the cerebrum.
The upper motor neurons that control skeletal muscles begin with a soma in
the corticospinal tract.
The signals that control your handwriting travel down the spinal cord in
the anterior horns.
Many upper motor neurons synapse with lower motor neurons in
touch
Which of the following sensory functions involves neurons in the posterior root ganglia?
pelvic.
The spinal cord is divided into all of the following regions except
to protect neurons in both the ascending and descending tract.
The following are all functions associated with the spinal cord except
a fracture of vertebra L4
Which of the following fractures would be the least likely to cause a spinal cord injury
posterior root of a spinal nerve
posterior root of a spinal nerve
This figure shows a detail of the spinal cord, meninges and spinal nerves. What does “1” represent?
arachnoid mater
arachnoid mater
This figure shows a detail of the spinal cord, meninges and spinal nerves. What does “4” represent?
dural sheath and vertebral bones
Epidural anesthesia is introduced in the epidural space between ___ to block pain signals during pregnancy.
anterior horn
anterior horn
This figure shows a cross section of the spinal cord. What does “3” represent?
arachnoid mater and pia mater.
Cerebrospinal fluid fills in the space between
white matter
Which of the following structures is the richest in lipid content?
neurosomas, dendrites, and proximal parts of axons of neurons.
Gray matter contains
Descending tracts
___ carry motor commands from the brain along the spinal cord
thalamus.
Second-order neurons synapse with third-order neurons in the
Endoneurium
___ keep(s) nerve fibers insulated from one another.
Special
___ fibers innervate eyes and ears.
cluster of neurosomas in the PNS.
A ganglion is a
31
There are __ pairs of spinal nerves.
perineurium
perineurium
This figure shows the anatomy of a nerve. What does “3” represent?
brachial plexus
brachial plexus
This figure shows the posterior aspect of spinal nerve roots and plexuses. What does “3” represent?
the cervical enlargement
the cervical enlargement
This figure shows the posterior aspect of spinal nerve roots and plexuses. What does “2” represent?
the thoracic region
The ventral rami of the spinal nerves form nerve plexuses in all regions except
phrenic
The cervical plexus gives origin to the ___ nerve(s
sciatic
Which of the following nerves originates in the coccygeal plexus?
C6
C6
This figure shows a dermatome map. A patient with no sensation in the left thumb would probably have a nerve damaged in
the gracile fasciculus
Which of these is an ascending tract of the spinal cord?
afferent and efferent fibers
A mixed nerve consists of both
posterior (dorsal) root
Which of the following branches of a spinal nerve have somas of solely sensory neurons?
cauda equina.
The bundle of nerve roots that occupy the vertebral canal from L2 to S5 is called the
the viscera.
Somatosensory refers to these sensory signals except the sensory signals from
posterior root ganglion; gray matter
Neurosomas of the posterior root are located in the ___, whereas neurosomas of the anterior root are located in the ___.
nerve; axons
A ___ is a cordlike organ composed of numerous ___.
somatic receptor afferent nerve fiber interneuron efferent nerve fiber skeletal muscle
Which one of the following best describes the order of a somatic reflex?
muscles of the hand
Which of the following groups of muscles have the most muscle spindles?
reflexes are spontaneous actions of the nervous system.
These are all properties of reflexes except
muscle fibers.
A muscle spindle contains mostly
flexor (withdrawal) reflex.
A nurse pricks your finger to type your blood. You flinch at the pain, pulling your hand back. This is called the
monosynaptic
The quickest reflex arcs involve only two neurons, thus forming __ reflex arcs.
parallel after-discharge circuit
The flexor (withdrawal) reflex employs a ____, which maintains a sustained contraction.
an intersegmental reflex.
If a bee sting on the right thigh causes a quick involuntary reaction of the right arm, this would be an example of
gamma motor neurons.
The sensitivity of the muscle spindle is maintained by
alpha motor neurons.
The fibers that carry action potentials to cause skeletal muscle to contract are
stretch (myotatic) reflex.
You go to the movies after a long day and you begin to nod off as soon as the movie starts. Your head starts to lower a little but this reflex causes your head to rise. This is called the
contract and the antagonist muscles, the hamstrings, to relax.
In the patellar tendon reflex arc, the patellar ligament is stretched, which stretches the quadriceps femoris muscle of the thigh. This reflex will cause the quadriceps femoris to
contralateral
A reflex where the sensory input and motor output are on opposite sides of the spinal cord is called a(n) _____ reflex arc.
prevents overcontraction of a muscle.
The tendon reflex
tendon reflex
This reflex shows the least synaptic delay.
proprioceptors.
Tendon organs are

Cite this Reflexes, Chapter 13 The Spinal Cord, Spinal Nerves, and Somatic Reflexes

Reflexes, Chapter 13 The Spinal Cord, Spinal Nerves, and Somatic Reflexes. (2017, Dec 06). Retrieved from https://graduateway.com/reflexes-chapter-13-the-spinal-cord-spinal-nerves-and-somatic-reflexes-essay/

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