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UNCW Anatomy and physiology > Spinal Cord and Spinal Nerves > Flashcards

Spinal Cord and Spinal Nerves Flashcards

1
Q

what are the 3 basic functions of the spinal cord

A
  1. contains neuronal circuits that mediate spinal reflexes
  2. site for integration ( summing) of nerve impulses that arise locally or arrive from the periphery and brain
  3. provides pathways by which sensory nerve impulses reach the brain and motor nerve impulses pass from the brain to motor neurons
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2
Q

What protects the spinal cord?

A

Two types of connective tissue, bone and meninges, plus the cushion of cerebrospinal fluid (CSF), surround and protect the delicate nervous tissue of the brain and spinal cord.

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3
Q

Where is the spinal cord located?

A

The spinal cord is located within the vertebral (spinal) canal of the vertebral column. The vertebral foramina of the vertebrae, stacked one on top of the other, form the canal.

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4
Q

What are the meninges?

A

The meninges (singular is meninx) are connective tissue coverings that encircle the spinal cord and brain. There are three layers:

  1. Dura mater
  2. Arachnoid membrane
  3. Pia mater
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5
Q

Epidural space

A

is located between the

bony wall of the vertebral canal and the outer surface of the dura mater. It is filled with fat and blood vessels.

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6
Q

Dura mater

A

The dura mater, the outermost meninx, is

dense connective tissue forming a tube enclosing the spinal cord. It extends to the S-2 vertebra, where it closes.

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7
Q

Subdural space

A

The subdural space lies deep to the dura

mater, between it and the arachnoid membrane. It contains a small amount of interstitial fluid

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8
Q

Arachnoid membrane

A

The arachnoid membrane is the

middle meninx formed by delicate collagen and elastin fibers. It is avascular

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9
Q

Subarachnoid space

A

Deep to the arachnoid membrane,

between it and the pia mater, is the subarachnoid space. It is filled with cerebrospinal fluid (CSF

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10
Q

Pia mater

A

The pia mater, the inner-most meninx, is a thin

connective tissue that adheres to the surface of the spinal cord, anchoring blood vessels to it.

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11
Q

What are the denticulate ligaments?

A

The denticulate ligaments are thin extensions of the pia mater that anchor to the dura mater, effectively suspending the spinal cord within the CSF of the subarachnoid space

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12
Q

External anatomy of the spinal cord

A

roughly cylindrical and

slightly flattened in its anterior-posterior dimension

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13
Q

differential growth of the spinal cord

A

– Early in development the spinal cord fills the
entire vertebral canal. By the time of birth, the tip of the cord reaches only to level L3-4. At age 4-5 the cord had reached its adult length and ceases to grow. Differential growth of the vertebral column, continuing until adult stature is reached, is responsible for the disparity in length between the vertebral canal and the spinal cord of the adult

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14
Q

Adult length of the spinal cord

A

In the adult, the spinal cord extends from the

foramen magnum of the occiput, where it is continuous with the medulla of the brain, to vertebral level L2.

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15
Q

Enlargement of the spinal cord

A

The cervical enlargement, from C4-T1, represents
the origins of spinal nerves to and from the extremities. The lumbar enlargement, from T9-T12, represents the origins of spinal nerves to and from the lower extremities.

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16
Q

Conus medullaris

A

– Below the lumbar enlargement is the conus

medullaris, the conical tapering end of the adult spinal cord, ending at L2.

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17
Q

Cauda equina

A

Some nerves that arise from the spinal cord must
pass inferiorly through the vertebral canal before reaching the appropriate intervertebral foramen for exit. These wisps of nerve roots passing inferiorly through the lower vertebral canal are collectively known as the cauda equina (horse’s tail).

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18
Q

Filum terminale

A

From the tip of the conus medullaris is the filum
terminale, an extension of the pia mater that attaches inferiorly to the inside of the coccyx, thus anchoring the spinal cord within the vertebral canal

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19
Q

Segments (#) of the spinal cord

A

The spinal cord is functionally divided into 31
segments; from each “segment” emerges a pair of spinal nerves. Therefore, there are 31 pairs of spinal nerves: 8 cervical. 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal

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20
Q

Internal anatomy of the spinal cord

A

In cross section, gray matter of the spinal cord

is shaped roughly like the letter “H” or a butterfly, and is surrounded by white matter.

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21
Q

Gray matter of the spinal cord

A
  1. Neuronal cell bodies
  2. Unmyelinated axons and dendrites of association and
    motor neurons
  3. Neuroglia
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22
Q

white matter of the spinal cord

A

The white matter consists of bundles of myelinated

axons of sensory, association, and motor neurons called tracts.

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23
Q

Central canal of the spinal cord

A

The gray commissure is the cross-bar of the “H”
allowing communication between the two sides, and bearing in its middle the central canal, which runs the length of the spinal cord and communicates with the fourth ventricle of the brain.

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24
Q

nuclei of the spinal cord

A

The gray matter on each side of the cord is subdivided into
regions called horns. Within the gray matter are clusters of neuronal cell bodies called nuclei (centers); each nucleus has a specific function.

25
Q

dorsal horns of the spinal cord

A

The dorsal horns are those sections of the spinal
cord gray matter that project dorsally or posteriorly. They contain nuclei that receive sensory information from the spinal nerves and are therefore involved in sensory functions only. The axons entering the dorsal horns from the dorsal roots and are from those neurons whose cell bodies are located in the dorsal root ganglion found just outside the spinal ford within the intervertebral foramen.

26
Q

ventral horns of the spinal cord

A

The ventral gray horns of the spinal cord project
ventrally or anteriorly. They contain nuclei composed of motor neurons whose axons leave the spinal cord as the ventral roots. These neurons control somatic motor functions only.

27
Q

lateral horns of the spinal cord

A

The lateral gray horns, found between the dorsal
and ventral horns and only in spinal segments T1-L2, and S2-4, contain nuclei of motor neurons. The axons of these neurons exit the spinal cord via the ventral roots. They are involved in autonomic motor functions only

28
Q

columns of the spinal cord

A

The white matter is also arranged into three broad

regions called columns: anterior (ventral), posterior (dorsal), and lateral

29
Q

tracts of the spinal cord

A

Each column is subdivided into distinct bundles of nerve

fibers, called tracts, each having a common origin or destination and carrying similar information.

30
Q

ascending tracts of the spinal cord

A

Ascending tracts are sensory tracts, consisting

of axons that conduct impulses, and therefore information, up the spinal cord to the brain

31
Q

Descending tracts of the spinal cord

A

Descending tracts are motor tracts, consisting

of axons that conduct impulses down the spinal cord to the ventral gray horns.

32
Q

what are the two essential function of the spinal cord

A
  1. Convey impulses between the periphery and the brain

2. Provide integrating centers for spinal reflexes

33
Q

What are reflexes?

A

Reflexes are fast, predictable, autonomic responses to changes in the environment that help maintain homeostasis

34
Q

What are the three essential characteristics of a reflex?

A
  1. Inborn
  2. Unlearned
  3. Unconscious
35
Q

Roots

A

Spinal nerves are the paths of communication between the
CNS and most of the periphery of the body. There are two separate points of attachment called roots that connect a spinal nerve with its segment of the spinal cord.

36
Q

Dorsal root

A 
The dorsal (posterior) root contains sensory neuron 
axons that conduct impulses from the periphery into the dorsal gray horn of the spinal cord
37
Q

Dorsal root ganglion

A

Each dorsal root has a swelling located
within the intervertebral foramen called the dorsal root ganglion. It contains the nerve cell bodies of all the sensory neurons found in that spinal nerve.

38
Q

Ventral root

A 
The ventral (anterior) root contains motor neuron 
axons and conducts impulses away from the spinal cord to the appropriate effectors in the periphery.  The nerve cell bodies of origin for these fibers are within appropriate nuclei found either in the ventral gray horns for somatic motor effectors or in the lateral gray horns for visceral motor effectors.
39
Q

What is a pathway?

A

The route followed by a series of nerve impulses from their origin in one part of the body to their arrival elsewhere is called a pathway. Pathways are specific neuronal circuits and may include only a single synapse (monosynaptic) or more than one synapse (polysynaptic).

40
Q

The simplest kind of pathway in the nervous system is the reflex arc. Regardless of complexity, all reflex arcs must include what five functional components?

A
  1. Receptor
  2. Sensory neuron
  3. Center of integration
  4. Motor neuron
  5. Effector
41
Q

Receptor

A

The receptor is the distal end of a sensory neuron or an
associated sensory structure that responds to a specific stimulus (change in the environment) by initiating a nerve impulse.

42
Q

Sensory neuron

A

The sensory neuron passes the nerve impulse
generated by the receptor to the axon terminals located within the gray matter of the CNS. Its cell body is located in the dorsal root ganglion

43
Q

Center

A

The center of integration is that region of the CNS gray

matter where the synapse(s) associated with the reflex are located.

44
Q

Motor neuron

A

– Impulses triggered by the integrating center are

carried by the motor neuron, whose cell body lies within the gray matter, to the part of the body that will respond.

45
Q

Effector

A 
The effector (muscle or gland) is that structure stimulated 
by the motor neuron and which provides the response of the body to the change in the environment that stimulated the receptor.
46
Q

Describe the stretch reflex.

A

The stretch reflex is a monosynaptic reflex involving only two neurons. It results in the contraction of a skeletal muscle when the muscle is suddenly stretched.

The receptors, found within all skeletal muscles, are called muscle spindles and constantly monitor changes in muscle length.

In response to a stretch, a muscle spindle produces one or more action potentials that are propagated along the dendrite of its associated sensory neuron.

From the sensory dendrite the impulse passes along the sensory axon (dorsal root), enters the dorsal gray horn, and synapses with the appropriate motor neuron in the ventral gray horn.

This excitatory synapse stimulates the motor neuron and a second action potential is created that passes from the spinal cord (ventral root), through the appropriate spinal nerve, to innervate the appropriate motor unit.

Stimulation of the motor unit by the motor neuron causes it to contract, thus counteracting the stretch. It is through this mechanism that muscle tone is maintained.

47
Q

Describe how the reciprocal innervation occurs so that the prime mover of the stretch reflex can accomplish its task

A

Since this reflex enters the spinal cord on the same side that the motor impulse leaves it, this reflex is said to be an ipsilateral reflex (all monosynaptic reflexes are ipsilateral).

Although the stretch reflex itself is monosynaptic, an associated polysynaptic reflex to the antagonistic muscle must also be activated.

The incoming sensory information from the stretch also stimulates an association neuron, which in turn inhibits the appropriate motor neurons to the antagonistic muscles.

Without this neuronal activity, the prime mover muscle of the stretch reflex could not counteract the stretch.

This type of neuronal circuit, which provides for the simultaneous contraction of one muscle while inhibiting the antagonistic muscle(s), is called reciprocal innervation.

The reflex adjusts muscle tone, adjusts muscle performance during exercise, and helps prevent overstretching of muscles. The best-known example of the stretch reflex is the patellar reflex.

48
Q

Describe the flexor reflex.

A

The flexor (withdrawal) reflex is a polysynaptic reflex that usually produces and occurs with a crossed extensor reflex.

Suppose you step on a tack: the pain stimulus is received by a pain receptor and the resulting action potential passes along a sensory neuron to the CNS.

At the integration center, the sensory neuron synapses with an association neuron that does several things simultaneously.

Ipsilaterally, the association neuron stimulates the appropriate motor neurons to cause flexion, so that the offended foot can be removed from the tack.

Since many different flexors are required to move the leg, the association neuron must stimulate motor neurons in several segments of the spinal cord. This is an intersegmental reflex.

At the same time, there is reciprocal innervation of the appropriate motor neurons so the ipsilateral extensor muscles are inhibited, thus allowing the flexion movement

49
Q

What is the crossed extensor reflex?

A

The sensory impulses that initiate flexor reflex also initiate a crossed extensor reflex so that balance can be maintained. The axons of association neurons decussate (cross the midline of the spinal cord) through the gray commissure to stimulate motor neurons of the opposite side that initiate extension of the other extremity.

50
Q

What are spinal nerves?

A

Spinal nerves connect the receptors in the periphery to the CNS via sensory neurons, and the CNS to muscles and glands via motor neurons.

51
Q

How are Spinal nerves named?

A

The 31 pairs of spinal nerves are named and numbered according to the region and level of the spinal cord from which they emerge

52
Q

Where do spinal nerves emerge from the vertebral column?

A

The first cervical pair emerges between the atlas (C-1) and the occiput; all other spinal nerve pairs emerge from the vertebral column through the intervertebral foramina between adjoining vertebrae

53
Q

What is the distribution of spinal nerves?

A

8 cervical pairs 5 sacral pairs
12 thoracic pairs 1 coccygeal
5 lumbar pairs

54
Q

How is a spinal nerve formed?

A

A typical spinal nerve is formed by the union of the dorsal and ventral roots from the same side of the spinal cord segment. The union of the spinal roots occurs within the intervertebral foramen through which that spinal nerve passes

55
Q

What is a mixed nerve?

A

The spinal nerve is a mixed nerve since it contains all sensory and all motor components of that particular spinal cord segment.

56
Q

Endoneurium

A

– Each individual nerve fiber, either sensory dendrite

or motor axon, is surrounded by a connective tissue wrap called the endoneurium

57
Q

Perineurium

A

Groups of nerve fibers are arranged into fascicles

(fasciculi) and each bundle is surrounded by another connective tissue wrap called the perineurium.

58
Q

Epineurium

A

All fascicles of a spinal nerve are bound together by

an outermost connective tissue called the epineurium. This layer is a continuation of the dura mater.

59
Q

What are dermatomes?

A

The skin over the entire body, with the exception of the face and top of the head, is supplied by spinal nerves that carry somatic sensory nerve impulses into the spinal cord. All spinal nerves, except C-1, serve a specific and constant segment of the skin. The area of skin that provides sensory input to the dorsal roots of one pair of spinal nerves or to one spinal cord segment is called a dermatome. Because the nerve supplies of adjacent dermatomes overlap to some degree, there may be little loss of sensation if only a single nerve supplying one dermatome is damaged

UNCW Anatomy and physiology (14 decks)

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