chapter 13

Question 1

The first layer of protection for the central nervous system is

Answer 1

the hard bony skull and vertebral column.

Question 2

The second protective layer of the CNS

Answer 2

is the meninges, three membranes that lie between the bony encasement and the nervous tissue in both the brain and spinal cord

Question 3

The final protective layer of the CNS is

Answer 3

cerebrospinal fluid

Question 4

The spinal cord is located within

Answer 4

the vertebral canal of the vertebral column

Question 5

meninges (me-NIN-jēz; singular is meninx [MĒ-ninks])

Answer 5

three distinct protective, connective tissue coverings that encircle the spinal cord and brain.

Question 6

From superficial to deep the menegies are .

Answer 6

the (1) dura mater, (2) arachnoid mater, and (3) pia mater

Question 7

epidural space (ep′-i-DOO-ral),

Answer 7

a space between the dura mater and the wall of the vertebral canal

Question 8

There is a cushion layer of fat in the

Answer 8

epidural space

Question 9

Dura mater (DOO-ra MĀ-ter = tough mother).

Answer 9

The most superficial of the three spinal meninges is a thick strong layer composed of dense irregular connective tissue.

Question 10

Arachnoid mater (a-RAK-noyd MĀ-ter; arachn- = spider; - oid= similar to).

Answer 10

This layer, the middle of the meningeal membranes, is a thin, avascular covering comprised of cells and thin, loosely arranged collagen and elastic fibers

Question 11

Between the dura mater and the arachnoid mater is a thin _________ which contains interstitial fluid.

Answer 11

subdural space

Question 12

Pia mater (PĒ-a MĀ-ter; pia = delicate).

Answer 12

This innermost meninx is a thin transparent connective tissue layer that adheres to the surface of the spinal cord and brain.

Question 13

Within the pia mater are

Answer 13

many blood vessels that supply oxygen and nutrients to the spinal cord.

Question 14

denticulate ligaments (den-TIK-ū-lāt = small tooth),

Answer 14

Triangular-shaped membranous extensions of the pia mater suspend the spinal cord in the middle of its dural sheath

Question 15

Extending along the entire length of the spinal cord, the denticulate ligaments

Answer 15

protect the spinal cord against sudden displacement that could result in shock.

Question 16

Between the arachnoid mater and pia mater is a space,

Answer 16

the subarachnoid space, which also contains shock-absorbing cerebrospinal fluid.

Question 17

Why does the spinal cord not extend to the end of the spine

Answer 17

Elongation of the spinal cord stops around age 4 or 5, but growth of the vertebral column continues. Thus, the spinal cord does not extend the entire length of the adult vertebral column.

Question 18

the cervical enlargement,

Answer 18

extends from the fourth cervical vertebra (C4) to the first thoracic vertebra (T1). Nerves to and from the upper limbs arise from the cervical enlargement.

Question 19

the lumbosacral enlargement,

Answer 19

extends from the ninth to the twelfth thoracic vertebra. Nerves to and from the lower limbs arise from the lumbar enlargement.

Question 20

Inferior to the lumbar enlargement, the spinal cord terminates as a tapering, conical structure called the __________which ends at the level of the _______________

Answer 20

conus medullaris

intervertebral disc between the first and second lumbar vertebrae (L1–L2) in adults.

Question 21

Arising from the conus medullaris is the _______________which is ______________

Answer 21

filum terminale (FĪ-lum ter-mi-NAL-ē = terminal filament),

an extension of the pia mater that extends inferiorly, fuses with the arachnoid mater and dura mater, and anchors the spinal cord to the coccyx.

Question 22

In a spinal tap (lumbar puncture),

Answer 22

a local anesthetic is given, and a long hollow needle is inserted into the subarachnoid space to withdraw cerebrospinal fluid (CSF)

Question 23

Spinal nerves are

Answer 23

the paths of communication between the spinal cord and specific regions of the body.

Question 24

How many pairs of nerves are at each segment of the spine

Answer 24

There are 8 pairs of cervical nerves (represented in Figure 13.2 as C1–C8), 12 pairs of thoracic nerves (T1–T12), 5 pairs of lumbar nerves (L1–L5), 5 pairs of sacral nerves (S1–S5), and 1 pair of coccygeal nerves (Co1).

Question 25

Two bundles of axons, called roots,

Answer 25

connect each spinal nerve to a segment of the cord by even smaller bundles of axons called rootlets

Question 26

The posterior root and rootlets contain

Answer 26

only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the central nervous system.

Question 27

spinal (dorsal root) ganglion

Answer 27

A swelling in the posterior root which contains the cell bodies of sensory neurons.

Question 28

The anterior root and rootlets contain

Answer 28

axons of motor neurons, which conduct nerve impulses from the CNS to effectors (muscles and glands).

Question 29

cauda equina

Answer 29

The roots of these lower spinal nerves angle inferiorly alongside the filum terminale in the vertebral canal like wisps of hair.

Question 30

As spinal nerves branch from the spinal cord,

Answer 30

they pass laterally to exit the vertebral canal through the intervertebral foramina between adjacent vertebrae.

Question 31

The spinal cord extends

Answer 31

from the medulla oblongata of the brain to the superior border of the second lumbar vertebra.

Question 32

A transverse section of the spinal cord

Answer 32

reveals regions of white matter that surround an inner core of gray matter

Question 33

The white matter of the spinal cord consists primarily of

Answer 33

bundles of myelinated axons of neurons.

Question 34

The anterior median fissure

Answer 34

a wide groove on the anterior (ventral) side of the spinal cord

Question 35

The posterior median sulcus is

Answer 35

a narrow furrow on the posterior (dorsal) side of the spinal cord

Question 36

The gray matter of the spinal cord is shaped like the letter H or a butterfly; it consists of

Answer 36

dendrites and cell bodies of neurons, unmyelinated axons, and neuroglia.

Question 37

The gray commissure (KOM-mi-shur)

Answer 37

forms the crossbar of the H of the gray matter

Question 38

the central canal

Answer 38

extends the entire length of the spinal cord and is filled with cerebrospinal fluid. At its superior end, the central canal is continuous with the fourth ventricle (a space that contains cerebrospinal fluid) in the medulla oblongata of the brain.

Question 39

Anterior to the gray commissure is the anterior white commissure, which

Answer 39

connects the white matter of the right and left sides of the spinal cord.

Question 40

In the gray matter of the spinal cord and brain, clusters of neuronal cell bodies form functional groups called

Answer 40

nuclei.

Question 41

The posterior gray horns contain

Answer 41

axons of incoming sensory neurons as well as cell bodies and axons of interneurons

Question 42

The anterior gray horns contain

Answer 42

somatic motor nuclei, which are clusters of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles.

Question 43

The lateral gray horns contain

Answer 43

autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle, and glands.

Question 44

The anterior and posterior gray horns divide the white matter on each side into three broad areas called

Answer 44

funiculi

Question 45

tracts

Answer 45

distinct bundles of axons having a funiculus origin or destination and carrying similar information. These bundles, which may extend long distances up or down the spinal cord

Question 46

Sensory (ascending) tracts consist of

Answer 46

axons that conduct nerve impulses toward the brain

Question 47

Tracts consisting of axons that carry nerve impulses from the brain are called

Answer 47

motor (descending) tracts.

Question 48

How does the does the spinal cord allow sensory input and motor output to be processed by the spinal cord

Answer 48

1. Sensory receptors detect a sensory stimulus.
2. Sensory neurons convey this sensory input in the form of nerve impulses along their axons, which extend from sensory receptors into the spinal nerve and then into the posterior root. From the posterior root, axons of sensory neurons may proceed along three possible paths (see steps 3, 4, and 5).
3. Axons of sensory neurons may enter the posterior gray horn and then extend into the white matter of the spinal cord and ascend to the brain as part of a sensory tract.
4. Axons of sensory neurons may enter the posterior gray horn and synapse with interneurons whose axons extend into the white matter of the spinal cord and then ascend to the brain as part of a sensory tract.
   5, Axons of sensory neurons may enter the posterior gray horn and synapse with interneurons that in turn synapse with somatic motor neurons that are involved in spinal reflex pathways. Spinal cord reflexes are described in more detail later in this chapter.

Question 49

How does the spinal cord allow motor outouts to be processed by the spinal cord

Answer 49

1.Motor output from the spinal cord to skeletal muscles involves somatic motor neurons of the anterior gray horn. Many somatic motor neurons are regulated by the brain. Axons from higher brain centers form motor tracts that descend from the brain into the white matter of the spinal cord. There they synapse with somatic motor neurons either directly or indirectly by first synapsing with interneurons that in turn synapse with somatic motor neurons.
2. When activated, somatic motor neurons convey motor output in the form of nerve impulses along their axons, which sequentially pass through the anterior gray horn and anterior root to enter the spinal nerve. From the spinal nerve, axons of somatic motor neurons extend to skeletal muscles of the body.
3. Motor output from the spinal cord to cardiac muscle, smooth muscle, and glands involves autonomic motor neurons of the lateral gray horn. When activated, autonomic motor neurons convey motor output in the form of nerve impulses along their axons, which sequentially pass through the lateral gray horn, anterior gray horn, and anterior root to enter the spinal nerve.
4. From the spinal nerve, axons of autonomic motor neurons from the spinal cord synapse with another group of autonomic motor neurons located in the peripheral nervous system (PNS). The axons of this second group of autonomic motor neurons in turn synapse with cardiac muscle, smooth muscle, and glands. You will learn more about autonomic motor neurons when the autonomic nervous system is described in Chapter 15.

Question 50

Sensory input is conveyed

Answer 50

from sensory receptors to the posterior gray horns of the spinal cord

Question 51

motor output is conveyed

Answer 51

from the anterior and lateral gray horns of the spinal cord to effectors (muscles and glands).

Question 52

the amount of white matter decreases

Answer 52

from cervical to sacral segments of the spinal cord.

Question 53

why does the amount of white matter decreases from cervical to sacral segments of the spinal cord.

Answer 53

(1) As the spinal cord ascends from sacral to cervical segments, more ascending axons are added to spinal cord white matter to form more sensory tracts. (2) As the spinal cord descends from cervical to sacral segments, the motor tracts decrease in thickness as more descending axons leave the motor tracts to synapse with neurons in the gray matter of the spinal cord.

Question 54

Describe the characteristics of the cervical segment of the spinal cord

Answer 54

Relatively large diameter, relatively large amounts of white matter, oval; in upper cervical segments (C1–C4), posterior gray horn is large but anterior gray horn is relatively small; in lower cervical segments (C5 and below), posterior gray horns are enlarged and anterior gray horns are well developed.

Question 55

Describe the characteristics of the thoracic segment of the spinal cord.

Answer 55

Small diameter due to relatively small amounts of gray matter; except for first thoracic segment, anterior and posterior gray horns are relatively small; small lateral gray horn is present.

Question 56

Describe the characteristics of the lumbar segment of the spinal cord.

Answer 56

Nearly circular; very large anterior and posterior gray horns; small lateral gray horn is present in upper segments; relatively less white matter than cervical segments.

Question 57

Describe the characteristics of the sacral segment of the spinal cord.

Answer 57

Relatively small, but relatively large amounts of gray matter; relatively small amounts of white matter; anterior and posterior gray horns are large and thick.

Question 58

Describe the characteristics of the coccygeal segment of the spinal cord.

Answer 58

Resembles lower sacral spinal segments, but much smaller.

Question 59

Spinal nerves

Answer 59

are associated with the spinal cord and, like all nerves of the peripheral nervous system (PNS), are parallel bundles of axons and their associated neuroglial cells wrapped in several layers of connective tissue.

Question 60

The 31 pairs of spinal nerves are named and numbered according to

Answer 60

the region and level of the vertebral column from which they emerge

Question 61

The first cervical pair of spinal nerves emerges from the spinal cord

Answer 61

between the occipital bone and the atlas

Question 62

Spinal nerves C1–C7 exit the vertebral canal

Answer 62

above their corresponding vertebrae.

Question 63

Spinal nerve C8 exits the vertebral canal

Answer 63

between vertebrae C7 and T1

Question 64

Spinal nerves T1–L5 exit the vertebral canal

Answer 64

below their corresponding vertebrae.

Question 65

From the spinal cord, the roots of the sacral spinal nerves (S1–S5) and the coccygeal spinal nerves.

Answer 65

enter the sacral canal, the part of the vertebral canal in the sacrum

Question 66

spinal nerves S1–S4 exit the sacral canal via

Answer 66

the four pairs of anterior and posterior sacral foramina, and spinal nerves S5 and Co1 exit the sacral canal via the sacral hiatus.

Question 67

The posterior and anterior roots unite to form a spinal nerve at the

Answer 67

intervertebral foramen.

Question 68

Because the posterior root contains sensory axons and the anterior root contains motor axons, a spinal nerve is classified as a

Answer 68

mixed nerve

Question 69

Each spinal nerve and cranial nerve consists of

Answer 69

many individual axons and contains layers of protective connective tissue coverings

Question 70

Individual axons within a nerve, whether myelinated or unmyelinated, are wrapped in

Answer 70

endoneurium (en′-doˉ -NOO-rē-um; endo- = within or inner; -neurium = nerve), the innermost layer.

Question 71

Groups of axons with their endoneurium are held together in bundles called

Answer 71

nerve fascicles, each of which is wrapped in perineurium (per′-i-NOO-rē-um; peri- = around), the middle layer.

Question 72

The outermost covering over the entire nerve is the

Answer 72

epineurium (ep′-i-NOO-rē-um; epi- = over). It consists of fibroblasts and thick collagen fibers.

Question 73

Three layers of connective tissue wrappings protect axons:

Answer 73

Endoneurium surrounds individual axons, perineurium surrounds bundles of axons (nerve fascicles), and epineurium surrounds an entire nerve.

Question 74

A short distance after passing through its intervertebral foramen,

Answer 74

a spinal nerve divides into several branches. These branches are known as rami

Question 75

The posterior (dorsal) ramus (RĀ-mus; singular form) serves

Answer 75

the deep muscles and skin of the posterior surface of the trunk.

Question 76

The anterior (ventral) ramus serves

Answer 76

the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk.

Question 77

meningeal branch (me-NIN-jē′-al).

Answer 77

This branch reenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges

Question 78

The branches of a spinal nerve are

Answer 78

the posterior ramus, the anterior ramus, the meningeal branch, and the communicating rami.

Question 79

Axons from the anterior rami of spinal nerves, except for thoracic nerves T2–T12,

Answer 79

do not go directly to the body structures they supply.

Question 80

plexus

Answer 80

networks on both the left and right sides of the body that join with various numbers of axons from anterior rami of adjacent nerves.

Question 81

The principal plexuses are the

Answer 81

cervical plexus, brachial plexus, lumbar plexus, and sacral plexus. A smaller coccygeal plexus is also present

Question 82

The anterior rami of spinal nerves T2–T12

Answer 82

do not enter into the formation of plexuses and are known as intercostal nerves or thoracic nerves.

Question 83

After leaving its intervertebral foramen, the anterior ramus of nerve T2 innervates the

Answer 83

intercostal muscles of the second intercostal space and supplies the skin of the axilla and posteromedial aspect of the arm.

Question 84

Nerves T3–T6 .

Answer 84

extend along the costal grooves of the ribs and then to the intercostal muscles and skin of the anterior and lateral chest wall

Question 85

Nerves T7–T12 supply

Answer 85

the intercostal muscles and abdominal muscles, along with the overlying skin.

Question 86

dermatome

Answer 86

The area of the skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal (V) nerve

Question 87

Knowing which spinal cord segments supply each dermatome makes it possible to

Answer 87

locate damaged regions of the spinal cord

Question 88

The cervical plexus (SER-vi-kul) is formed by

Answer 88

the roots (anterior rami) of the first four cervical nerves (C1–C4), with contributions from C5 (Figure 13.8). There is one on each side of the neck alongside the first four cervical vertebrae.

Question 89

The cervical plexus supplies

Answer 89

the skin and muscles of the head, neck, and superior part of the shoulders and chest. The phrenic nerves arise from the cervical plexuses and supply motor fibers to the diaphragm. Branches of the cervical plexus also run parallel to two cranial nerves, the accessory (XI) nerve and hypoglossal (XII) nerve.

Question 90

the Lesser occipital nerve

Answer 90

originates from C2 and is a sensory branch that serves the Skin of scalp posterior and superior to ear.

Question 91

Great auricular nerve

Answer 91

originates from C2-C3 and is a sensory branch that serves the Skin anterior, inferior, and over ear, and over parotid glands.

Question 92

Transverse cervical branch

Answer 92

a senxory branch that Originates from C2-C3 and serves the Skin over anterior and lateral aspect of neck.

Question 93

Supraclavicular branch

Answer 93

A sensory branch originating from C3-C4 that serves the Skin over superior portion of chest and shoulder.

Question 94

Ansa cervicalis

Answer 94

Motor branch that Divides into superior and inferior roots.

Question 95

Superior Root

Answer 95

Motor branch that originates at C1 and controls the Infrahyoid and geniohyoid muscles of neck.

Question 96

Inferior Root

Answer 96

Motor branch that originates at C2-C3 and controls the Infrahyoid muscles of the neck

Question 97

Phrenic

Answer 97

Motor branch that originates at C3-C5 and controls the diaphragm

Question 98

Segmental branches

Answer 98

Motor branches that originate at C1-C5 and control Prevertebral (deep) muscles of neck, levator scapulae, and scalenus medius muscles.

Question 99

The cervical plexus supplies

Answer 99

the skin and muscles of the head, neck, superior portion of the shoulders and chest, and diaphragm.

Question 100

The roots (anterior rami) of spinal nerves C5–C8 and T1 form

Answer 100

the brachial plexus

Question 101

the brachial plexus

Answer 101

extends inferiorly and laterally on either side of the last four cervical and first thoracic vertebrae (Figure 13.9a). It passes above the first rib posterior to the clavicle and then enters the axilla.

Question 102

As with the cervical and other plexuses, the roots of the brachial plexus are the

Answer 102

anterior rami of the spinal nerves.

Question 103

The roots of several spinal nerves from the brachial plexus unite to form

Answer 103

trunks in the inferior part of the neck.

Question 104

Posterior to the clavicles, the trunks of the brachial plexus diverge into

Answer 104

divisions, called the anterior and posterior divisions.

Question 105

In the axillae, the divisions of the brachial plexus unite to form

Answer 105

cords called the lateral, medial, and posterior cords.

Question 106

The branches of the brachial plexus form

Answer 106

the principal nerves of the brachial plexus.

Question 107

Five large terminal branches arise from the brachial plexus:

Answer 107

(1) The axillary nerve supplies the deltoid and teres minor muscles. (2) The musculocutaneous nerve supplies the anterior muscles of the arm. (3) The radial nerve supplies the muscles on the posterior aspect of the arm and forearm. (4) The median nerve supplies most of the muscles of the anterior forearm and some of the muscles of the hand. (5) The ulnar nerve supplies the anteromedial muscles of the forearm and most of the muscles of the hand.

Question 108

The Dorsal scapular Nerve

Answer 108

Originates at C5 and supplies the Levator scapulae, rhomboid major, and rhomboid minor muscles.

Question 109

The long thoracic nerve

Answer 109

Originates at C5-C7 and supplies Serratus anterior muscle.

Question 110

Nerve to subclavius

Answer 110

Originates at C5-C6 and supplies the subclavius muscle

Question 111

The suprascapular nerve

Answer 111

Originates at C5-C6 and supplies Supraspinatus and infraspinatus muscles.

Question 112

Musculocutaneous

Answer 112

Originates at C5-C7 and supplies Coracobrachialis, biceps brachii, and brachialis muscles.

Question 113

The lateral pectoral nerve

Answer 113

Originates at C5-C7 and supplies the pectoralis major muscle

Question 114

The superior subscapular nerve

Answer 114

Originates at C5-C6 and supplies the Subscapularis muscle.

Question 115

the Thoracodorsal nerve

Answer 115

Originates at C6-C8 and supplies the Latissimus dorsi muscle.

Question 116

the Inferior subscapular nerve

Answer 116

Originates at C5-C6 and supplies Subscapularis and teres major muscles.

Question 117

The axillary nerve

Answer 117

Originates at C5-C6 and supplies the Deltoid and teres minor muscles; skin over deltoid and superior posterior aspect of arm.

Question 118

The median nerve

Answer 118

Originates at C5-T1 and supplies Flexors of forearm, except flexor carpi ulnaris; ulnar half of flexor digitorum profundus, and some muscles of hand (lateral palm); skin of lateral two-thirds of palm and lateral 3½ digits.

Question 119

The radial nerve

Answer 119

Originates at C5-T1 and supplies Triceps brachii, anconeus, and extensor muscles of forearm; skin of posterior arm and forearm, lateral two-thirds of dorsum of hand, and lateral 3½ digits.

Question 120

The medial pectoral nerve

Answer 120

Originates at C8-T1 and supplies Pectoralis major and pectoralis minor muscles.

Question 121

Medial cutaneous nerve of arm

Answer 121

Originates at C8-T1 and supplies Skin of medial and posterior aspects of distal third of arm.

Question 122

Medial cutaneous nerve of forearm

Answer 122

Originates at C8-T1 and supplies Skin of medial and posterior aspects of forearm.

Question 123

The Ulnar nerve

Answer 123

Originates at C8-T1 and supplies Flexor carpi ulnaris, ulnar half of flexor digitorum profundus, and most muscles of hand; skin of medial side of hand, and medial 1½ digits.

Question 124

Erb-Duchenne palsy or waiter’s tip position

Answer 124

The presentation of this injury is characterized by an upper limb in which the shoulder is adducted, the arm is medially rotated, the elbow is extended, the forearm is pronated, and the wrist is flexed

Question 125

Injury to the radial (and axillary) nerve can be caused by

Answer 125

improperly administered intramuscular injections into the deltoid muscle. The radial nerve may also be injured when a cast is applied too tightly around the mid- humerus.

Question 126

Radial nerve injury is indicated by

Answer 126

wrist drop, the inability to extend the wrist and fingers

Question 127

Injury to the median nerve may result in

Answer 127

median nerve palsy

Question 128

median nerve palsy is indicated by

Answer 128

by numbness, tingling, and pain in the palm and lateral 3½. digits.

Question 129

Injury to the ulnar nerve may result in

Answer 129

ulnar nerve palsy

Question 130

ulnar nerve palsy

Answer 130

is indicated by an inability to abduct or adduct the digits, atrophy of the interosseous muscles of the hand, hyperextension of the metacarpophalangeal joints, and flexion of the interphalangeal joints, a condition called clawhand (Figure 13.9c). There is also loss of sensation over the medial 1½ digits.

Question 131

Injury to the long thoracic nerve results in

Answer 131

paralysis of the serratus anterior muscle.The medial border of the scapula protrudes, giving it the appearance of a wing. this condition is called winged scapula

Question 132

Compression of the brachial plexus on one or more of its nerves is sometimes known as

Answer 132

thoracic outlet syndrome.

Question 133

What are the symptoms of thoracic outlet syndrome

Answer 133

The patient may experience pain, numbness, weakness, or tingling in the upper limb, across the upper thoracic area, and over the scapula on the affected side. The symptoms of thoracic outlet syndrome are exaggerated during physical or emotional stress because the added stress increases the contraction of the involved muscles.

Question 134

The roots (anterior rami) of spinal nerves L1–L4 form the

Answer 134

lumbar plexus

Question 135

in the lumbar plexus

Answer 135

there is minimal intermingling of fibers

Question 136

the Iliohypogastric nerve

Answer 136

Originates at L1 and supplies Muscles of anterolateral abdominal wall; skin of inferior abdomen and buttocks.

Question 137

The Ilioinguinal nerve

Answer 137

Originates at L1 and supplies Muscles of anterolateral abdominal wall; skin of superior and medial aspect of thigh, root of penis and scrotum in male, and labia majora and mons pubis in female.

Question 138

The Genitofemoral nerve

Answer 138

Originates at L1-L2 and supplies Cremaster muscle; skin over middle anterior surface of thigh, scrotum in male, and labia majora in female.

Question 139

The Lateral femoral cutaneous nerve

Answer 139

Originates at L2-L3 and supplies Skin over lateral, anterior, and posterior aspects of thigh.

Question 140

The femoral nerve

Answer 140

Originates at L2-L4 and supplies Largest nerve arising from lumbar plexus; distributed to flexor muscles of hip joint and extensor muscles of knee joint, skin over anterior and medial aspect of thigh and medial side of leg and foot.

Question 141

The obturator nerve

Answer 141

Originates at L2-L4 and supplies Adductor muscles of hip joint; skin over medial aspect of thigh.

Question 142

The lumbar plexus supplies

Answer 142

the anterolateral abdominal wall, external genitals, and part of the lower limbs.

Question 143

Injuries to the femoral nerve are indicated by

Answer 143

an inability to extend the leg and by loss of sensation in the skin over the anteromedial aspect of the thigh.

Question 144

Injuries to the obturator nerve result in

Answer 144

paralysis of the adductor muscles of the thigh and loss of sensation over the medial aspect of the thigh. It may result from pressure on the nerve by the fetal head during pregnancy.

Question 145

The roots (anterior rami) of spinal nerves L4–L5 and S1–S4 form the

Answer 145

sacral plexus

Question 146

The sacral plexus supplies

Answer 146

the buttocks, perineum, and lower limbs.

Question 147

The largest nerve in the body—the sciatic nerve—arises from

Answer 147

sacral plexus.

Question 148

The roots (anterior rami) of spinal nerves S4–S5 and the coccygeal nerves form a small

Answer 148

Coccygeal plexus

Question 149

ancoccygeal nerves

Answer 149

arises from the coccygeal plexus and supplys the skin in the coccygeal region

Question 150

Injury to the sciatic nerve results in

Answer 150

sciatica (sī-AT-i-ka), pain that may extend from the buttock down the posterior and lateral aspect of the leg and the lateral aspect of the foot.

Question 151

The sciatic nerve is actually

Answer 151

two nerves—tibial and common fibular—bound together by a common sheath of connective tissue.

Question 152

Damage to the common fibular nerve causes

Answer 152

the foot to be plantar flexed, a condition called footdrop, and inverted, a condition called equinovarus (e-KWĪ-nō-va-rus).

Question 153

Injury to the tibial portion of the sciatic nerve results in

Answer 153

dorsiflexion of the foot plus eversion, a condition called calcaneovalgus

Question 154

Superior gluteal nerve

Answer 154

originates at L4–L5 and S1 and suplies Gluteus minimus, gluteus medius, and tensor fasciae latae muscles.

Question 155

Inferior gluteal nerve

Answer 155

originates at L5-S2 and suplies Gluteus maximus muscle.

Question 156

Nerve to piriformis

Answer 156

originates at S1-S2 and suplies Piriformis muscle.

Question 157

nerve to quadratus femoris (quod-RĀ-tus FEM-or-is) and inferior gemellus (jem-EL-us)

Answer 157

originates at S1-S2 and suplies Quadratus femoris and inferior gemellus muscles.

Question 158

Nerve to obturator internus (OB-too-rā′-tor in-TER-nus) and superior gemellus

Answer 158

originates at L5-S2 and suplies Obturator internus and superior gemellus muscles.

Question 159

Perforating cutaneous nerve

Answer 159

originates at S2-S3 and suplies Skin over inferior medial aspect of buttocks.

Question 160

Posterior femoral cutaneous nerve

Answer 160

originates at S1-S3 and suplies Skin over anal region, inferior lateral aspect of buttocks, superior posterior aspect of thigh, superior part of calf, scrotum in male, and labia majora in female.

Question 161

Pudendal nerve

Answer 161

originates at S2-S4 and suplies Muscles of perineum; skin of penis and scrotum in male and clitoris, labia majora, labia minora, and vagina in female.

Question 162

Sciatic nerve

Answer 162

originates at L4-S3 and is Actually two nerves—tibial and common fibular—bound together by common sheath of connective tissue; splits into its two divisions, usually at the knee. (See below for distributions.) As sciatic nerve descends through thigh, it sends branches to hamstring muscles and adductor magnus.

Question 163

Tibial nerve

Answer 163

originates at L4-S3 and suplies Gastrocnemius, plantaris, soleus, popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles. Branches of tibial nerve in foot are medial plantar nerve and lateral plantar nerve

Question 164

Medial plantar nerve

Answer 164

suplies Abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis muscles; skin over medial two-thirds of plantar surface of foot

Question 165

Lateral plantar nerve

Answer 165

suplies Remaining muscles of foot not supplied by medial plantar nerve; skin over lateral third of plantar surface of foot.

Question 166

common fibular nerve

Answer 166

originates at L4-s2 and Divides into superficial fibular and deep fibular branch.

Question 167

Superficial fibular nerve

Answer 167

suplies Fibularis longus and fibularis brevis muscles; skin over distal third of anterior aspect of leg and dorsum of foot.

Question 168

Deep fibular nerve

Answer 168

suplies Tibialis anterior, extensor hallucis longus, fibularis tertius, and extensor digitorum longus and extensor digitorum brevis muscles; skin on adjacent sides of great and second toes.

Question 169

The sacral plexus supplies

Answer 169

the buttocks, perineum, and lower limbs.

Question 170

The spinal cord has two principal functions in maintaining homeostasis:

Answer 170

nerve impulse propagation and integration of information.

Question 171

The white matter tracts in the spinal cord are highways for

Answer 171

both sensory and motor nerve impulse propagation.

Question 172

The gray matter of the spinal cord

Answer 172

receives and integrates incoming and outgoing information.

Question 173

Usually the name of the sensory or motor tracts takes on this order

Answer 173

First word: Directional term that indicates the position of the tract on the white matter
Second word: compound word the first part of the word indicates the origin of the tract (for example cortico stands for cerebral cortex) for sensory tracts the first part of the second word is almost always spino because sensory tracts always originate in the spinal cord The second part of the word describeswhere the tract ends

Question 174

The name of a tract often indicates

Answer 174

its location in the white matter and where it begins and ends.

Question 175

Nerve impulses from sensory receptors propagate up the spinal cord to the brain along two main routes on each side:

Answer 175

the spinothalamic tract and the posterior funiculi.

Question 176

The spinothalamic tract (spī′-nō-tha-LAM-ik) conveys nerve impulses for sensing

Answer 176

pain, temperature, itch, and tickle.

Question 177

The posterior funiculi convey nerve impulses for

Answer 177

touch, pressure, vibration, and conscious proprioception (the awareness of the positions and movements of muscles, tendons, and joints).

Question 178

The cerebral cortex, the outer part of the brain, plays a major role in

Answer 178

controlling precise voluntary muscular movements.

Question 179

Motor output to skeletal muscles travels down the spinal cord in two types of descending pathways:

Answer 179

direct and indirect

Question 180

The direct motor pathways, also called pyramidal pathways, include

Answer 180

the lateral corticospinal (kor′-ti-kō-SPĪ-nal), anterior corticospinal, and corticobulbar tracts (kor′-ti-kō-BUL-bar).They convey nerve impulses that originate in the cerebral cortex and are destined to cause voluntary movements of skeletal muscles.

Question 181

Indirect motor pathways, also called extrapyramidal pathways, include the

Answer 181

rubrospinal (ROO-brō-spī-nal), tectospinal (TEK-tō-spī-nal), vestibulospinal (ves-TIB-ū-lō-spī-nal), lateral reticulospinal (re-TIK-ū-lō-spī-nal), and medial reticulospinal tracts. These tracts convey nerve impulses from the brainstem to cause automatic movements and help coordinate body movements with visual stimuli.

Question 182

The second way the spinal cord promotes homeostasis is by

Answer 182

serving as an integrating center for some reflexes.

Question 183

A reflex is a

Answer 183

fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus.

Question 184

When integration takes place in the spinal cord gray matter, the reflex is a

Answer 184

spinal reflex

Question 185

If integration occurs in the brainstem rather than the spinal cord, the reflex is called a

Answer 185

cranial reflex.

Question 186

somatic reflexes involve

Answer 186

contraction of skeletal muscles.

Question 187

autonomic reflexes

Answer 187

involve responses of smooth muscle, cardiac muscle, and glands.

Question 188

The pathway followed by nerve impulses that produce a reflex is a

Answer 188

reflex arc (reflex circuit).

Question 189

What are the five functional components of a reflex arc

Answer 189

1. sensory receptor
2. Sensory neuron
3. Integrating center
4. Motor neuron
   5 effector

Question 190

What is the role of a sensory receptor in a reflex arc

Answer 190

The distal end of a sensory neuron (dendrite) or an associated sensory structure serves as a sensory receptor. It responds to a specific stimulus—a change in the internal or external environment—by producing a graded potential called a generator (or receptor) potential (described in Section 16.1). If a generator potential reaches the threshold level of depolarization, it will trigger one or more nerve impulses in the sensory neuron.

Question 191

what is the role of the sensory neuron in a reflex arc

Answer 191

The nerve impulses propagate from the sensory receptor along the axon of the sensory neuron to the axon terminals, which are located in the gray matter of the spinal cord or brainstem. From here, relay neurons send nerve impulses to the area of the brain that allows conscious awareness that the reflex has occurred.

Question 192

What is the role of the integrating center in a reflex arc

Answer 192

One or more regions of gray matter within the CNS acts as an integrating center. In the simplest type of reflex, the integrating center is a single synapse between a sensory neuron and a motor neuron. A reflex pathway having only one synapse in the CNS is termed a monosynaptic reflex arc (mon′-ō-si-NAP-tik; mono- = one). More often, the integrating center consists of one or more interneurons, which may relay impulses to other interneurons as well as to a motor neuron. A polysynaptic reflex arc (poly- = many) involves more than two types of neurons and more than one CNS synapse.

Question 193

what is the role of the motor neuron in a reflex arc

Answer 193

Impulses triggered by the integrating center propagate out of the CNS along a motor neuron to the part of the body that will respond.

Question 194

What is the role of the effector in a reflex arc

Answer 194

The part of the body that responds to the motor nerve impulse, such as a muscle or gland, is the effector. Its action is called a reflex. If the effector is skeletal muscle, the reflex is a somatic reflex. If the effector is smooth muscle, cardiac muscle, or a gland, the reflex is an autonomic (visceral) reflex.

Question 195

A stretch reflex operates as follows

Answer 195

1. Slight stretching of a muscle stimulates sensory receptors in the muscle called muscle spindles (shown in more detail in Figure 16.4). The spindles monitor changes in the length of the muscle.
2. In response to being stretched, a muscle spindle generates one or more nerve impulses that propagate along a somatic sensory neuron through the posterior root of the spinal nerve and into the spinal cord.
3. In the spinal cord (integrating center), the sensory neuron makes an excitatory synapse with, and thereby activates, a motor neuron in the anterior gray horn.
4. If the excitation is strong enough, one or more nerve impulses arises in the motor neuron and propagates, along its axon, which extends from the spinal cord into the anterior root and through peripheral nerves to the stimulated muscle. The axon terminals of the motor neuron form neuromuscular junctions (NMJs) with skeletal muscle fibers of the stretched muscle.
5. Acetylcholine released by nerve impulses at the NMJs triggers one or more muscle nerve impulses in the stretched muscle (effector), and the muscle contracts. Thus, muscle stretch is followed by muscle contraction, which relieves the stretching.

Question 196

in an ipsilateral reflex

Answer 196

sensory nerve impulses enter the spinal cord on the same side from which motor nerve impulses leave it.

Question 197

all monosynaptic reflexes are

Answer 197

ipsilateral

Question 198

muscle tone

Answer 198

the small degree of contraction present while the muscle is at rest.

Question 199

Although the stretch reflex pathway itself is monosynaptic (just two neurons and one synapse),

Answer 199

a polysynaptic reflex arc to the antagonistic muscles operates at the same time.

Question 200

how does a polysynaptic reflex occur

Answer 200

This arc involves three neurons and two synapses. An axon collateral (branch) from the muscle spindle sensory neuron also synapses with an inhibitory interneuron in the integrating center. In turn, the interneuron synapses with and inhibits a motor neuron that normally excites the antagonistic muscles

Question 201

The following atatement describes which type of innervation? when the stretched muscle contracts during a stretch reflex, antagonistic muscles that oppose the contraction relax

Answer 201

reciprocal innervation

Question 202

Reciprocal innervation prevents

Answer 202

conflict between opposing muscles and is vital in coordinating body movements.

Question 203

The stretch reflex operates as a

Answer 203

feedback mechanism to control muscle length by causing muscle contraction.

Question 204

the tendon reflex operates as a feedback mechanism to control muscle tension

Answer 204

by causing muscle relaxation before muscle force becomes so great that tendons might be torn.

Question 205

Like the stretch reflex, the tendon reflex is

Answer 205

ipsilateral

Question 206

The sensory receptors for a tendon reflex are called

Answer 206

tendon (Golgi tendon) organs (shown in more detail in Figure 16.4), which lie within a tendon near its junction with a muscle.

Question 207

In contrast to muscle spindles, which are sensitive to changes in muscle length, tendon organs detect and respond to .

Answer 207

changes in muscle tension that are caused by passive stretch or muscular contraction

Question 208

A tendon reflex operates as follows

Answer 208

1. As the tension applied to a tendon increases, the tendon organ (sensory receptor) is stimulated (depolarized to threshold).
2. Nerve impulses arise and propagate into the spinal cord along a sensory neuron.
3. Within the spinal cord (integrating center), the sensory neuron activates an inhibitory interneuron that synapses with a motor neuron.
4. The inhibitory neurotransmitter inhibits (hyperpolarizes) the motor neuron, which then generates fewer nerve impulses.
5. The muscle relaxes and relieves excess tension.

Question 209

The tendon reflex causes

Answer 209

relaxation of the muscle attached to the stimulated tendon organ.

Question 210

The flexor reflex causes

Answer 210

withdrawal of a part of the body in response to a painful stimulus.

Question 211

the flexor reflex or withdrawal reflex, operates as follows

Answer 211

1. Stepping on a tack stimulates the dendrites (sensory receptor) of a pain-sensitive neuron.
2. This sensory neuron then generates nerve impulses, which propagate into the spinal cord.
3. Within the spinal cord (integrating center), the sensory neuron activates interneurons that extend to several spinal cord segments.
4. The interneurons activate motor neurons in several spinal cord segments. As a result, the motor neurons generate nerve impulses, which propagate toward the axon terminals.
5. Acetylcholine released by the motor neurons causes the flexor muscles in the thigh (effectors) to contract, producing withdrawal of the leg. This reflex is protective because contraction of flexor muscles moves a limb away from the source of a possibly damaging stimulus.

Question 212

The flexor reflex, like the stretch reflex, is

Answer 212

ipsilateral—the incoming and outgoing impulses propagate into and out of the same side of the spinal cord.

Question 213

nerve impulses from one sensory neuron ascend and descend in the spinal cord and activate interneurons in several segments of the spinal cord, this type of reflex is called an

Answer 213

intersegmental reflex arc

Question 214

Through intersegmental reflex arcs,

Answer 214

a single sensory neuron can activate several motor neurons, thereby stimulating more than one effector

Question 215

How does a crossed extensor reflex work

Answer 215

1. Stepping on a tack stimulates the sensory receptor of a pain-sensitive neuron in the right foot.
2. This sensory neuron then generates nerve impulses, which propagate into the spinal cord.
3. Within the spinal cord (integrating center), the sensory neuron activates several interneurons that synapse with motor neurons on the left side of the spinal cord in several spinal cord segments. Thus, incoming pain signals cross to the opposite side through interneurons at that level, and at several levels above and below the point of entry into the spinal cord.
4. The interneurons excite motor neurons in several spinal cord segments that innervate extensor muscles. The motor neurons in turn generate more nerve impulses, which propagate toward the axon terminals.
5. Acetylcholine released by the motor neurons causes extensor muscles in the thigh (effectors) of the unstimulated left limb to contract, producing extension of the left leg. In this way, weight can be placed on the foot that must now support the entire body. A comparable reflex occurs with painful stimulation of the left lower limb or either upper limb.

Question 216

Unlike the flexor reflex, which is an ipsilateral reflex, the crossed extensor reflex involves a

Answer 216

contralateral reflex arc

Question 217

how does a contralateral reflex arc work

Answer 217

Sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side. Thus, a crossed extensor reflex synchronizes the extension of the contralateral limb with the withdrawal (flexion) of the stimulated limb.

Question 218

the patellar reflex can be blocked by

Answer 218

damage to the sensory or motor nerves supplying the muscle or to the integrating centers in the second, third, or fourth lumbar segments of the spinal cord.

Question 219

Absence of the Achilles reflex indicates damage to

Answer 219

the nerves supplying the posterior leg muscles or to neurons in the lumbosacral region of the spinal cord. This reflex may also disappear in people with chronic diabetes, neurosyphilis, alcoholism, and subarachnoid hemorrhages.

Question 220

An exaggerated Achilles reflex indicates

Answer 220

cervical cord compression or a lesion of the motor tracts of the first or second sacral segments of the cord.

Question 221

A positive Babinski sign after age 1½ is abnormal and indicates

Answer 221

an interruption of the corticospinal tract as the result of a lesion of the tract, usually in the upper portion.

Question 222

Abdominal reflex.

Answer 222

This reflex involves contraction of the muscles that compress the abdominal wall in response to stroking the side of the abdomen.

Question 223

abscence of the abdominal reflex is associated with

Answer 223

lesions of the corticospinal tracts. It may also be absent because of lesions of the peripheral nerves, lesions of integrating centers in the thoracic part of the cord, or multiple sclerosis

Question 224

Most autonomic reflexes are not practical diagnostic tools because it is difficult to stimulate visceral effectors, which are deep inside the body. An exception is the

Answer 224

pupillary light reflex,

Question 225

absence of a normal pupillary light reflex may indicate

Answer 225

brain damage or injury.

Question 226

A crossed extensor reflex causes

Answer 226

contraction of muscles that extend joints in the limb opposite a painful stimulus.

Question 227

Monoplegia (mon′-ō-PLĒ-jē-a; mono- = one; -plegia = blow or strike) is

Answer 227

paralysis of one limb only.

Question 228

Diplegia (di- = two) is

Answer 228

paralysis of both upper limbs or both lower limbs.

Question 229

Paraplegia (para- = beyond) is

Answer 229

paralysis of both lower limbs.

Question 230

Hemiplegia (hemi- = half) is

Answer 230

paralysis of the upper limb, trunk, and lower limb on one side of the body,

Question 231

quadriplegia (quad- = four) is

Answer 231

paralysis of all four limbs.

Question 232

Complete transection (tran-SEK-shun; trans- = across; -section = a cut) of the spinal cord means that

Answer 232

the cord is severed from one side to the other, thus cutting all sensory and motor tracts.

Question 233

Hemisection is

Answer 233

a partial transection of the spinal cord on either the right or the left side.

Question 234

After hemisection, three main symptoms, known together as Brown-Séquard syndrome (sē-KAR), occur below the level of the injury:

Answer 234

(1) Damage of the posterior funiculus (sensory tracts) causes loss of proprioception and fine touch sensations on the ipsilateral (same) side as the injury. (2) Damage of the lateral corticospinal tract (motor tract) causes ipsilateral paralysis. (3) Damage of the spinothalamic tracts (sensory tracts) causes loss of pain and temperature sensations on the contralateral (opposite) side.

Question 235

Spinal shock is an immediate response to

Answer 235

spinal cord injury characterized by temporary areflexia (a′-re-FLEK-sē-a), loss of reflex function.

Question 236

Signs of acute spinal shock include

Answer 236

slow heart rate, low blood pressure, flaccid paralysis of skeletal muscles, loss of somatic sensations, and urinary bladder dysfunction. Spinal shock may begin within 1 hour after injury and may last from several minutes to several months, after which reflex activity gradually returns.

Question 237

Spinal cord compression may result from

Answer 237

fractured vertebrae, herniated intervertebral discs, tumors, osteoporosis, or infections.

Question 238

symptoms of spinal cord compression include

Answer 238

pain, weakness or paralysis, and either decreased or complete loss of sensation below the level of the injury.

Question 239

Shingles is

Answer 239

an acute infection of the peripheral nervous system caused by herpes zoster (HER-pēz ZOS-ter), the virus that also causes chickenpox

Question 240

post-polio syndrome.

Answer 240

This neurological disorder is characterized by progressive muscle weakness, extreme fatigue, loss of function, and pain, especially in muscles and joints.

Question 241

Epidural block (ep′-i-DOO-ral)

Answer 241

Injection of an anesthetic drug into the epidural space, the space between the dura mater and the vertebral column, in order to cause a temporary loss of sensation. Such injections in the lower lumbar region are used to control pain during childbirth.

Question 242

Meningitis (men-in-JĪ-tis; -itis = inflammation)

Answer 242

Inflammation of the meninges due to an infection, usually caused by a bacterium or virus. Symptoms include fever, headache, stiff neck, vomiting, confusion, lethargy, and drowsiness. Bacterial meningitis is much more serious and is treated with antibiotics. Viral meningitis has no specific treatment. Bacterial meningitis may be fatal if not treated promptly; viral meningitis usually resolves on its own in 1–2 weeks. A vaccine is available to help protect against some types of bacterial meningitis.

Question 243

Myelitis (mī-e-LĪ-tis; myel- = spinal cord)

Answer 243

Inflammation of the spinal cord.

Question 244

Nerve block

Answer 244

Loss of sensation in a region due to injection of a local anesthetic; an example is local dental anesthesia.

Question 245

Neuralgia (noo-RAL-jē-a; neur- = nerve; -algia = pain)

Answer 245

Attacks of pain along the entire course or a branch of a sensory nerve.

Question 246

Neuritis (neur- = nerve; -itis = inflammation)

Answer 246

Inflammation of one or several nerves that may result from irritation to the nerve produced by direct blows, bone fractures, contusions, or penetrating injuries. Additional causes include infections, vitamin deficiency (usually thiamine), and poisons such as carbon monoxide, carbon tetrachloride, heavy metals, and some drugs.

Question 247

Paresthesia (par-es-THĒ-zē-a; par- = departure from normal; -esthesia = sensation)

Answer 247

An abnormal sensation such as burning, pricking, tickling, or tingling resulting from a disorder of a sensory nerve.