BIOS 252 Week 3 Case Study: CNS-PNS
Student Name
Chamberlain University
BIOS-252: Anatomy & Physiology II with Lab
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Date
Week 3 Case Study: CNS and PNS Overview
1. What is the term used to describe the inability to voluntarily move the legs?
The inability to voluntarily move the legs is medically referred to as paraplegia. This condition results from damage to the spinal cord or brain that disrupts communication between the central nervous system (CNS) and the lower body. Paraplegia specifically affects motor control and often impairs sensory function in the trunk, pelvic organs, and lower limbs. The severity of paraplegia can vary depending on the level and extent of neurological damage. It is most commonly caused by traumatic spinal cord injury, multiple sclerosis, or other diseases that affect the CNS.
2. What are the components of a basic reflex arc?
A reflex arc is the simplest neural pathway that mediates a reflex action. It involves a sequence of neural structures working in coordination to produce an involuntary response to stimuli. The basic components are summarized in the table below:
| Component | Description |
|---|---|
| Sensor | Sensory receptors in the skin, muscles, or tendons that detect a specific stimulus. |
| Sensory Neuron | Afferent neurons that transmit impulses from receptors to the spinal cord or brainstem. |
| Integration Center | Located in the gray matter of the spinal cord or brainstem, where the sensory neuron synapses with interneurons or motor neurons. |
| Motor Neuron | Efferent neurons that carry commands from the CNS to the effector organ or muscle. |
| Effector | The muscle or gland that carries out the response (e.g., contracting or secreting). |
This process ensures rapid, automatic responses to potentially harmful stimuli, contributing to the body’s defense mechanism (CK-12, 2014).
3. What is Babinski’s sign, and how does it compare to a normal plantar reflex?
The plantar reflex is tested by stroking the lateral aspect of the sole of the foot. In healthy adults, this stimulus typically results in plantar flexion of the toes—meaning the big toe points downward.
In contrast, Babinski’s sign occurs when the big toe moves upward and the other toes fan outward. This response is normal in infants under 2 years old due to immature nervous systems, but in older children and adults, it suggests pathology in the upper motor neurons or corticospinal tract (Acharya et al., 2022).
| Reflex Type | Hallux Response | Clinical Significance |
|---|---|---|
| Normal Plantar | Downward (flexion) | Indicates intact corticospinal tract |
| Babinski Sign | Upward (extension) | Suggests upper motor neuron damage |
4. Why might Babinski’s sign appear instead of the normal plantar reflex?
Babinski’s sign appears when there is dysfunction or damage in the corticospinal tract (CST)—a crucial descending motor pathway originating in the cerebral cortex and terminating at the spinal cord. Damage to the CST disrupts the normal inhibition of primitive reflexes, such as the Babinski response, leading to their reappearance in adults. Common causes include traumatic spinal cord injury, brain tumors, multiple sclerosis, and stroke.
The presence of this abnormal reflex may prompt further diagnostic testing, including MRI, CT scans, and lumbar punctures, to determine the underlying neurological condition (Acharya et al., 2022).
5. Why is this not an issue with a first-order neuron?
This condition is not attributed to a first-order neuron issue because the Babinski sign is indicative of upper motor neuron lesions, which involve the central nervous system (CNS) rather than peripheral structures. First-order neurons are part of the peripheral nervous system (PNS) and transmit sensory input to the CNS. Damage to these neurons would more likely cause a loss of reflexes, rather than the pathological reflexes seen with CST disruption.
Hence, the Babinski reflex is a valuable tool in localizing CNS pathology and is especially useful in detecting early signs of spinal cord injury or stroke before other symptoms manifest.
6. Where along the spinal cord might a lesion be found in a patient with Babinski’s sign?
A lesion associated with Babinski’s sign would typically be located along the corticospinal tract, which runs from the motor cortex, through the brainstem, and down the spinal cord. These fibers synapse with alpha motor neurons in the anterior horn of the spinal cord. Damage anywhere along this descending pathway can lead to an upper motor neuron lesion, resulting in a positive Babinski sign.
| Location | Possible Lesion Sites |
|---|---|
| Brain | Primary motor cortex or internal capsule |
| Brainstem | Midbrain, pons, or medulla oblongata |
| Spinal Cord | Cervical or thoracic spinal cord regions |
Identification of such lesions through imaging techniques is essential for early intervention and treatment planning.
References
Acharya AB, Jamil RT, Dewey JJ. (2022, July 25). Babinski Reflex. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519009/
CK-12 Foundation. (2014, November 13). Reflexes: Neurons in Action. Retrieved November 12, 2022, from https://www.ck12.org/book/human-biology-nervous-system/section/5.1/
Wikipedia contributors. (2022, June 12). Reflex arc. Wikipedia. Retrieved November 12, 2022, from https://en.wikipedia.org/w/index.php?title=Reflex_arc\&oldid=1092719613
Wikipedia contributors. (2022, November 4). Plantar reflex. Wikipedia. Retrieved November 12, 2022, from https://en.wikipedia.org/w/index.php?title=Plantar_reflex\&oldid=1119913988
BIOS 252 Week 3 Case Study: CNS-PNS
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