Physiology Chapter 12 The Spinal Cord, Spinal Nerves and Spinal Reflexes

When an anesthetic blocks the function of the ventral rami of the cervical spinal nerves, which areas of the body will be affected?

Muscles and skin of the neck, the skin of the superior portion of the chest, and the diaphragm (phrenic nerve)

Identify the basic characteristics of polysynaptic reflexes

Polysynaptic reflexes includes at least one interneuron, and thus by definition more than one neuron. There is a longer delay between stimulus and response when compared to monosynaptic, however, polysynaptic responses can be more complicated. They can include several muscle groups at once.

Indicate whether the following fibers make up the white rami or gray rami:

Preganlionic fibers connecting a spinal nerve with a sympathetic ganglion in the thoracic and lumbar region of the spinal cord WHITE Postganglionic fibers connecting a sympathetic ganglion in the thoracic or lumbar region with the spinal nerve GRAY

A typical spinal cord has how many pairs of spinal nerves, and where does the spinal cord end?

31 pairs of spinal nerves and the cord ends between L1 and L2

Define nerve plexus, and list the major nerve plexuses.

A nerve is woven network of nerves that have sensory and motor functionality. Functions include muscle contraction, coordination, sensation of pain, temperature and pressure. The five plexuses are Cervical, Brachial, Lumbar, Sacral, and Coccygeal

What is reflex?

A reflex is a rapid automatic response triggered by a specific stimuli. It is involuntary.

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

A. Activation of a receptor i. Tapping your patellar tendon with a reflex hammer stretches fibers in the quadriceps muscle B. Activation of sensory neuron i. Distortion of the stretch receptors then stimulates sensory neurons ii. Sensory neurons extend into the spinal cord and synapse on motor neurons that control motor units in the stretched muscle C. Information processing in the CNS i. Occurs at the cell body of the motor neuron ii. In this example basically determining if there is sufficient stimulus to activate the motor neuron D. Activation of a motor neuron i. once activated and action potential propagates to the effector E. Response of a peripheral effector i. Skeletal muscle fibers of the stretched muscle contract ii. Extends knee in a brief kick

List the components of a reflex arc. slides 78-80

Activation of a receptor by stimulus, activation of a sensory neuron, information processing in the CNS, activation of a motor neuron and finally response of a peripheral effector.

Explain the cause of shingles.

Also known as herpes zoster, shingles viral inflammation of the sensory ganglia of spinal and cranial and is associated with vesicular eruptions within areas of the dermatomes supplied by the corresponding spinal nerve. Shingles is caused by the reactivation of the poxvirus causing chicken pox.

Where does the most complex neural processing occur?

BRAIN

Injury to which nerve plexuses would interfere with the stability to breathe?

Cervical

Describe a dermatome.

Dermatomes are areas of skin supplied by sensory neurons that arise from a spinal nerve ganglion. Dermatomes and the associated major cutaneous nerves are shown here in a ventral view. There are eight cervical nerves, twelve thoracic nerves, five lumbar nerves and five sacral nerves. There are 8 cervical nerves, 12 thoracic nerves and 5 lumbar nerves and 5 sacral nerves. Each of these nerves relays sensation, including pain, from a particular region skin to the brain. Along the thorax and abdomen the dermatomes are like a stack of discs, with each section each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different. The dermatomes run longitudinally along the limbs, so that each half of the limb has a different dermatome.

Differentiate between divergent and convergent neural circuits.

Divergent circuits spread information from one neuron to several as it branches Convergent is when several neurons synapse on a single postsynaptic neuron

Which ramus innervates the skin and skeletal muscles of the back?

Dorsal Ramus

Name the major nerves associated with the brachial plexus.

Radial, Ulnar, Median, Supscapular, Medial pectoral and lateral pectoral nerves

Identify and describe the three spinal meninges.

Dura mater- outermost covering of the spinal cord, of which the external surface is simple squamous epithelium. It is fibrous due to collagen fibers oriented along longitudinal axis of the spinal cord. Arachnoid mater- is the middle meningeal layer which also has a simple squamous epithelium. It is attached to the inside of the dura mater. There are villi-like projections of the arachnoid mater, which protrude into the dura mater. The subarachnoid space extends between arachnoid membrane and outer surface of the Pia mater, in which CSF flows. There are also trabeculae in this space, which are fibrous filaments that connect the two layers Pia mater- innermost meningeal layer made of meshwork of elastic and collagen fibers, and is firmly bound to underlying neural tissue. It's impermeable to fluid and is attached to the dura mater. The ligaments provide stability by cushioning lateral movement of spinal cord. At the level of the conus medullaris, the Pia extends and becomes the film terminal (Within the lumbar cistern) and eventually fuses with coccyx as part of coccygeal ligament

Describe the composition of the gray matter of the spinal cord?

Gray matter has cell bodies of neurons, neuroglia, and UNmyelinated axons. There is a small central canal within gray matter. Spinal neurons within gray matter are either efferent neurons (axons enter ventral roots), projection neurons (axons join white matter tracts), or interneurons (axons remain within gray matter). Structural features include the posterior median sulcus and anterior median fissure.

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

White matter

Define a nerve plexus trunk and cord.

check question 22 for this

Describe the brachial plexus.

Innervates the pectoral girdle and upper limbs. The ventral rami of the spinal nerves C4 to T1 contribute. The nerves originate from trunks, which are bundles of axons made of several spinal nerves. Trunks feed into cords, which are smaller branches. Cutaneous(Skin) nerves are distributed to the hand and wrist.

Describe the various classifications of neural reflexes.

slides 86-89

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

It starts from the sensory receptors then inputs over the spinal nerves then into the reflex centers in the spinal cord and then into the motor output over spinal nerves to effector tissues such as muscle, glands, and adipose tissue.

Describe gray ramus and white ramus.

White ramus communicans to a nearby sympathetic ganglion; the myelinated fibers give the branch a light (white) color. Gray ramus communicans contains postganglionic fibers that innervate glands and smooth muscles in the body wall or limbs and contains unmyelinated fibers, giving the branch a darker gray color.

Which kind of neural circuit processes information in a stepwise fashion, one neuron to another?

SERIAL

Which nerve divides into tibial nerve and common fibular nerve?

Sciatic nerve

Differentiate between sensory nuclei and motor nuclei.

Sensory nuclei are neuronal cell bodies which relays sensory information (via Ans as usual) while motor nuclei issue motor commands to effectors

What purpose does reflex testing serve?

Serves tp provide information about the status of corresponding spinal segments. If the reflex is absent there may be injury within a given segment

After injury her back 22 year old Tina exhibits a positive Babinski reflex what does this imply about her injury?

She may have damage to descending tracts of the CNS.

In the patellar reflex, how does stimulation of the muscle spindle by gamma motor neurons affect sensitivity and reaction time?

Stimulation of the muscle spindle

List the major nerves of the sacral plexus.

Superior and inferior gluteals, the sciatic, the pudendal, and the posterior femoral cutaneous

Where is the cerebrospinal fluid that surrounds the spinal cord located?

The CFS is primarily in the subarachnoid of the spinal cord and in the ventricles of the brain

Define reinforcement as it pertains to spinal reflexes.

The brain can facilitate or inhibit motor and interneurons involved in reflexes. Facilitation is called reinforcement. The example we know is the Jendrassik maneuver to overemphasize the patellar reflex here, we try to pull apart hands the are interlocked together which in turn produces a bigger kick when light trap is applied to the patellar tendon it produces larger response even if person aware of the technique

Describe the anatomical features of a cross section of the spinal cord.

The dorsal root has axons of sensory neurons whose cell bodies are in the dorsal root ganglion. The central root has axons motor neurons. Dorsal and ventral converge to make a spinal nerve. The white matter has both some unmyelinated but more myelinated axons, along with glial cells.

Identify the three layers of connective tissue of a spinal nerve and identify the major peripheral branches of the spinal nerve.

The layers of the spinal nerve are depicted in the graphic below. The dorsal and ventral motor, somaticmotor and sensory information, with the dorsal rams feeding the dorsal trunk (skin and muscles of the back) and the ventral rams feeding the ventral trunk and limbs, through the ventrolateral surface.

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

The lumbar puncture goes into subarachnoid space, and therefore pierces the dura and arachnoid layers. It goes between L3, and L4, or L4 and L5.

Define stretch reflex

The stretch reflex is a monosynaptic. It refers to the distortion of the intrafusal fibers that make up the spindles of specialized skeletal muscle. These spindles are surrounded by larger skeletal muscle fibers. There are gamma motor neurons that innervate each spindle and allow the CNS to alter tension in the intrafusal fibers, which in turn increases or decreases muscle tone. There are also sensory neurons running to the CNS from the bundle. A stretched spindle bundle stimulates more frequent Ads from the sensory neuron which causes the gamma motor neurons coming form the CNS to fire and increase muscle tone of surround skeletal muscles.

Define spinal reflex.

These are reflexes controlled in the spinal cord, which function without input from the brain

Describe the lumbar plexus and sacral plexus.

These plexuses innervate the pelvic girdle and lower limbs. The lumbar goes from T12-L4 while sacral goes from L4-S4 contains the sciatic nerve, which is the largest in diameter and longest in the body

What are the common characteristics of reflexes?

They are rapid; Automatic responses to specific stimuli that often preserve homeostasis by making rapid adjustments in organ or organ system function. There is little variability in the response. The process is called a reflex arc, and often the reflex is an example of negative feedback due to a harmful stimulus.

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

This is a crossed extensor reflex (has stretch and withdrawal components) involving a contralateral reflex arc. When stepping on a track the flexor part of the reflex pulls the affected foot away from ground while interneurons stimulate flexors and inhibits extensors of that foot. At the same time, the motor neurons in the unaffected leg stimulate the extensors while relaxing the flexors which results in straightening of that leg support the shift in weight while pulling away.

Describe the flexor reflex.

This is a withdrawal reflex involving a painful stimulus. The sensory neurons activate interneurons in spinal cord; the interneurons stimulate motor neurons in anterior gray horns in contraction of flexor muscles. At the same time, reciprocal inhibition keeps extensors of the same muscle group, relaxed.

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

This symptom is the result of poliomyelitis, which is an effect of the polio viruses. It destroys nerve cells, and in this case, the motor neurons would be located in the sacral plexus, and may be the sciatic nerve