Chapter 12 Learning Outcomes

In the lumbar puncture, the lumbar puncture needle penetrates the epidermis, dermis, subcutaneous layer (hypodermis), and then skeletal muscle before reaching the protective spinal covering: the dura mater, then the arachnoid matter, and finally the subarachnoid space, which contains cerebrospinal fluid.

Name the structures and spinal coverings that are penetrated during a lumbar puncture procedure.

Motor nuclei

These type of nuclei issue motor commands to peripheral effectors

Sensory nuclei

This type of nuclei receive and relay sensory information from peripheral effectors

Posterior root

Through which root of a spinal nerve does visceral sensory information arrive?

The white matter columns of the spinal cord, which composed of bundles of myelinated axons.

A disease that damages myelin sheaths would affect which portion of the spinal cord?

Stretch reflex

A monosynaptic reflex that provides automatic regulation of skeletal muscle length

The poliovirus-infected neurons would be in the anterior gray horns of the spinal cord, where the cell bodies of somatic neurons are located.

A person with polio has lost the use of his leg muscles. In which area of his spinal cord would you expect the virus-infected motor neurons to be?

Reflex

A rapid, automatic response triggered by specific stimuli

Dermatome

A specific bilateral sensory region monitored by a single pair of spinal nerves

Spinal reflex

An automatic response triggered by a stimulus that is controlled in the spinal cord and can function w/o input from the brain

Phrenic nerves (innervate the diaphragm)

Damage to which nerve of the cervical plexus would interfere with the ability to breathe?

It is composed of the cell bodies of neurons, neuroglia, and unmyelinated axons.

Describe the composition of gray matter of the spinal cord.

Sensory input travels toward the spinal cord; motor commands travel away from the spinal cord

Describe the direction of sensory input and motor commands relative to the spinal cord.

The limb on the opposite side is extended; this response is called a crossed extensor reflex

During a withdrawal reflex of the foot, what happens to the limb on the side opposite the stimulus? What is this response called?

It is caused by reactivation of the varicella- zoster virus (VZV), the same herpes virus that causes chickenpox. Once reactivated, the virus stimulates painful inflammation of the nerve ganglia and causes skin eruptions in a pattern that corresponds to the affected dermatome.

Explain the cause of shingles.

The response observed is leg extension, and the effectors involved are the quadriceps femoris

In the patellar reflex, identify the response observed and the effectors involved.

Divergent neural circuits

Information spreads from one neuron to several neurons

Flexor reflex

Is an example of a withdrawal reflex that contracts the flexor muscles of a limb in response to a painful stimulus; so, it has a protective function

Convergent neural circuits

Several neurons synapse w/ a single postsynaptic neuron

Rapid, unconscious patterned responses to a physical stimulus that restore or maintain homeostasis

What are common characteristics of reflexes?

- Posterior ramus - Anterior ramus - Rami communicantes

What are the 3 major peripheral branches of a spinal nerve?

- Receptor - sensory neuron - motor neuron - peripheral effector - interneurons may also be present

What are the 4 (sometimes 5) components of a reflex?

- All involve pools of interneurons - involve more than one spinal segment - involve reciprocal inhibition - have reverberating circuits

What are the 4 basic characteristics of polysynaptic reflexes

- Cervical - Brachial - Lumbar - Sacral

What are the 4 major nerve plexuses?

- Development (innate reflexes vs acquired reflexes) - Nature of the resulting motor response (somatic reflexes vs visceral reflexes) - Complexity of the neural circuit involved (monosynaptic reflexes vs polysynaptic reflexes) - Site of information processing (spinal reflexes vs cranial reflexes)

What are the 4 various classifications of neural reflexes?

- Anterior median fissure: a deep groove along the anterior or ventral surface - Posterior median sulcus: a shallow longitudinal groove - White matter: dominated by myelinated fibers - Gray matter: composed of cell bodies of neurons, neuroglia, and unmyelinated axons - Central canal: passageway containing cerebrospinal fluid - Posterior root of each spinal nerve: axons of neurons whose cell bodies are in the posterior root ganglion - Anterior root of each spinal nerve: the axons of motor neurons that extend into the periphery to control somatic and visceral effectors - Posterior root ganglia: contain cell bodies of sensory neurons - Spinal nerves: contain the axons of sensory and motor neurons

What are the 9 gross anatomical features of a cross section of the spinal cord?

- It is made up of extensions of the posterior and anterior roots of spinal segments L2 to S5. - It forms as the vertebral column continues to elongate after longitudinal growth of the spinal cord ceases at about age 4.

What is the significance of the cauda equina?

Provides information about the nervous system's functional status

What purpose does reflex testing serve?

In the PNS and spinal cord

Where does the simplest processing occur?

In the subarachnoid space, which lies deep to the epithelium of the arachnoid mater and superficial to the pia mater.

Where is spinal CSF located?

Anterior ramus

Which ramus carries sensory information from the limbs?

Posterior ramus

Which ramus provides sensory and motor innervation to the skin and skeletal muscles of the back?

T2- T11 and Co1

Which spinal nerves are not part of a nerve plexus?

Nerve plexus

a complex, interwoven network of nerves

Reinforcement (as it pertains to spinal reflexes)

an enhancement of a spinal reflex through the facilitation of motor neurons involved in reflexes