Ch13: Spinal Cord & Spinal Nerves

Front 1

Identify the 2 types of connective tissue coverings, as well as the additional protection for the spinal cord

Back 1

Bony vertebrae
Meninges
*cerebrospinal fluid
*fat

Front 2

Describe the function the meninges (singular: meninx) and describe its 3 layers

Back 2

=3 layers of ct, encircle spinal cord & brain
-continuous w cranial meninges (encircle brain)
1 DURA MATER =most superficial layer, forms a sac from level of foramen magnum in occipital bone, where it is continuous w dura mater of brain to 2nd sacral vertebra
2 ARACHNOID MATER = middle meninx
-avascular covering
-web of collage and elastic fibers
-continuous w arachnoid mater of brain
3 PIA MATER =adheres to surface of spinal cord & brain
-thin, transparent ct layer
-squamous to cuboidal cells within interlacing collagen & elastic fibers
-many blood vessels >> supply oxygen & nutrients to spinal cord

Front 3

Describe where the epidural space is and what it contains

Back 3

=space between dura mater and wall of vertebral canal
-contains a cushion of fat and ct >> protect spinal cord

Front 4

Describe where the subdural space is located and what it contains

Back 4

-Between dura mater & arachnoid mater
-contains interstitial fluid

Front 5

Describe where the subarachnoid space is located and what it contains

Back 5

-Between arachnoid mater & pia mater
-contains cerebrospinal fluid >> shock absorber & suspension system for spinal cord & brain

Front 6

Describe the External anatomy of spinal cord: where it extends in adults and infants and its growth

Back 6

Adults -extends from medulla oblongata to 2nd lumbar vertebra
Infants- extends to 3rd/4th lumbar vertebra
***During early childhood, both spinal cord & vertebral column grow longer >> spinal cord stops around age 4-5, but vertebral column continues

Front 7

Identify the location of the cervical and lumabr enlargements and what they contains

Back 7

Cervical enlargement = superior, extends from 4th cervical vertebra to 1st thoracic vertebra, consist of nerves to & from upper limbs
Lumbar enlargement = inferior, extends from 9th to 12th thoracic vertebra, consist of nerves to & from lower limbs

Front 8

What is the Conus medullaris

Back 8

Conical structure where spinal cord tapers off

Front 9

What is the filum terminale?

Back 9

-an extension of pia mater that extends inferiorly and blends with the arachnoid mater and dura mater and anchors the spinal cord to the coccyx
-arises from conus medullaries

Front 10

What is the cauda equine

Back 10

A tail-like array of roots of spinal nerves at the inferior end of the spinal cord

Front 11

How many pairs of Spinal nerves are there are list the segments they are organized in

Back 11

=one of the 31 pairs of nerves that originate on the spinal cord from posterior and anterior roots
>>cervical, thoracic, lumar, sacral, coccygeal nerves

Front 12

What do the posterior/dorsal root and ganglion, and anterior/ventral root contain?

Back 12

Posterior (dorsal) root and rootlets contain only sensory axons >> conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into CNS. Each posterior root has a swelling, the posterior (dorsal) root ganglion, which contains the cell bodies of sensory neurons
anterior (ventral) root and rootlets contain axons of motor neurons, which conduct nerve impulses from the CNS to effectors (muscles and glands)

Front 13

Describe the two grooves that penetrate the white matter of the spinal cord and divide it into right and left sides

Back 13

Anterior median fissure =wide groove on the anterior (ventral) side
Posterior median sulcus = narrow furrow on the posterior (dorsal) side

Front 14

What is the gray commissure

Back 14

=A narrow strip of gray matter connecting the two lateral gray masses within the spinal cord
=butterfly body / crossbar of H

Front 15

What is the central canal?

Back 15

=space at center of the gray commissure
-extends the entire length of the spinal cord and is filled with cerebrospinal fluid
At its superior end, central canal is continuous w 4th ventricle (a space that contains cerebrospinal fluid) in medulla oblongata of brain

Front 16

Where is the anterior/ventral white commissure

Back 16

-connects the white matter of the right and left sides of the spinal cord
-anterior to central canal

Front 17

Define horns
Describe what the posterior/dorsal and anterior/ventral and lateral gray horns contain

Back 17

Horns = regions of gray matter on each side of the spinal cord

Posterior (dorsal) gray horns contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons

Anterior (ventral) gray horns contain somatic motor nuclei, which are clusters of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles

Lateral gray horns contain autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle, and glands
-Between posterior & anterior gray horns
-are present only in thoracic and upper lumbar segments of the spinal cord

Front 18

Describe what the anterior/central, posterior/dorsal, and lateral white columns contain
***White matter of the spinal cord, like the gray matter, is organized into regions

Back 18

-divided by ant and post gray horns into…
(1) anterior (ventral) white columns
(2) posterior (dorsal) white columns
(3) lateral white columns
Each column in turn contains distinct bundles of axons (=tracts) having a common origin or destination and carrying similar information

Front 19

What is the difference btween tracts and nerves?

Back 19

tracts are bundles of axons in the CNS, whereas nerves are bundles of axons in the PNS

Front 20

What do Sensory (ascending) and motor (descending) tracts consist of?

Back 20

Sensory/ascending tracts consist of axons that conduct nerve impulses toward the brain
Motor/descending tracts consist of axons that carry nerve impulses from the brain
***Both are continuous with sensory and motor tracts in the brain

Front 21

Describe how spinal nerves are connected to the spinal cord

Back 21

Two bundles of axons, called roots, connect each spinal nerve to a segment of the cord by even smaller bundles of axons called rootlets
Posterior (dorsal) root and rootlets contain only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the central nervous system
anterior (ventral) root and rootlets contain axons of motor neurons, which conduct nerve impulses from the CNS to effectors (muscles and glands).

Front 22

Why is the spinal nerve considered a mixed nerve?

Back 22

Because the posterior root contains sensory axons and the anterior root contains motor axons

Front 23

Identify the connective tissue coverings of spinal nerves

Back 23

Endoneurium = innermost layer, connective tissue wrapping around individual nerve axons
Fascicle = bundles of endoneurium-wrapped axons
Perineurium = middle layer, wraps fascicles
Epineurium = outermost layer, cover entire nerve
*At invertebral foramen, dura mater of spinal meninges fuses w epineurium

Front 24

What are rami (singular: ramus) and identify the functions of the 4 types of rami

Back 24

=branches of spinal nerves >> branch off after passing through its intervertebral foramen
Posterior (dorsal) ramus serves deep muscles & skin of posterior surface of the trunk
Anterior (ventral) ramus serves muscles & structures of the upper & lower limbs & skin of lateral & anterior surfaces of the trunk
Meningeal branch supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges
rami communicantes = components of the ANS

Front 25

Define Plexus and describe the anatomical importance of a plexus
List the principal plexuses

Back 25

=a network of nerves, veins, or lymphatic vessels
Axons from anterior rami of spinal nerves (except T2-12) do not go directly to the body structures they supply >> Instead, they form plexuses on both left & right sides of body by joining with various numbers of axons from anterior rami of adjacent nerves
-cervical plexus, brachial plexus, lumbar plexus, sacral plexus, smaller coccygeal plexus

Front 26

What are intercostal/thoracic nerves?

Back 26

Nerves branching off the anterior rami of spinal nerves T2–T12 (these ones do not plexuses)
-directly connect to the structures they supply in the intercostal spaces

Front 27

Define dermatome. Describe the clinical significance of them

Back 27

=an area of skin that receives most of its sensory innervation from one spinal nerve ***C1 is the only spinal nerve without a corresponding dermatome
Practical because knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord.
-ie. If the skin in a particular region is stimulated but the sensation is not perceived, the nerves supplying that dermatome are probably damaged

Front 28

What are the functions of the major sensory and motor tracts of the spinal cord? Give examples

Back 28

Major sensory/ascending tract conveys nerve impulses from spinal cord to brain (thalamus for sensations of pain, T, crude touch, deep P)
Ie. Anterior & lateral spinothalamic tracts
Major motor/descending tract conveys nerve impulses from brain toward spinal cord

Front 29

Describe the 2 types of pathways in which motor output travels down spinal cord to skeletal muscles

Back 29

Direct pathways convey nerve impulses from cerebral cortex to cause voluntary movements of skeletal muscles
Indirect pathways convey nerve impulses from brain stem to cause automatic movements that regulate muscle tone, posture, and balance, and orientation of the head and body

Front 30

Describe Stretch reflex

Back 30

A stretch reflex causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle. This type of reflex occurs via a monosynaptic reflex arc (=reflex can occur by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron)
-ie. Knee jerk

Front 31

Describe the function of a Muscle spindle

Back 31

Slight stretching of a muscle stimulates sensory receptors in the muscle
Monitors changes in length of muscle

Front 32

Ipsilateral reflex arc

Back 32

=pathway of sensory nerve impulses that enters the spinal cord on the same side from which motor nerve impulses leave it
***all monsynaptic reflexes = ipsilateral

Front 33

Define Muscle tone

Back 33

=the small degree of contraction present while the muscle is at rest
>>helps avert injury by preventing overstretching muscles since the stimulus for the stretch reflex is stretching of muscle

Front 34

Define Reciprocal Innervation

Back 34

=when the components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonists
-prevents conflict between opposing muscles
-vital to coordinating body movement
-ie. when a stretched muscle contracts during a stretch reflex, antagonistic muscles that oppose the contraction relax

Front 35

What is Flexor/withdrawal reflex

Back 35

Flexor/withdrawal reflex
-in response to a painful stimulus

Front 36

What is Crossed extensor reflex

Back 36

-help maintain balance
-involves contralateral reflex arc (unlike flexor reflex, which is an ipsilateral reflex arc)

Front 37

What is a Tendon reflex

Back 37

A polysynaptic, ipsilateral reflex that protects tendons and their associated muscles from damage that might be brought about by excessive tension. The receptors involved are called tendon organs (Golgi tendon organs).

Front 38

Describe the 2 clinically important reflexes

Back 38

Patellar reflex (knee jerk) = stretch reflex, involves extension of the leg at the knee joint in response to tapping the patellar ligament
This reflex is blocked by damage to sensory or motor nerves supplying the muscle or to the integrating centers in 2nd,3rd,or 4th lumbar segments of the spinal cord
-often absent in people w chronic diabetes mellitus or neurosyphilis (both cause degeneration of nerves)
Babinski’s Reflex
=Extension of big toe, with or without fanning of the other toes, in response to stimulation of the outer margin of the sole; normal up to 18 months of age and indicative of damage to descending motor pathways such as the corticospinal tracts after that

Front 39

Describe homeostatic disruption of spinal function in shingles

Back 39

Shingles =an acute infection of PNS caused by herpes zoster (virus that also causes chickenpox)
After person recovers from chickenpox, virus retreats to a posterior root ganglion. If reactivated, virus leaves ganglion and travels down sensory neurons of skin >> pain, discoloration, characteristic line of skin blisters (line of blisters indicates distribution (dermatome) of which cutaneous sensory nerve belongs to infected posterior root ganglion)

Front 40

Describe homeostatic disruption of spinal function in poliomyelitis aka polio

Back 40

-fever, severe headache, a stiff neck and back, deep muscle pain and weakness, and loss of certain somatic reflexes >> most serious form= paralysis by destroying cell bodies of motor neurons, specifically those in the anterior horns of the spinal cord and in the nuclei of the cranial nerves
Polio can cause death from respiratory or heart failure if the virus invades neurons in vital centers that control breathing and heart functions in the brain stem

Front 41

Describe homeostatic disruption of spinal function in meningitis

Back 41

Inflammation of meninges due to an infection, usually caused by a bacterium or virus >> fever, headache, stiff neck, vomiting, confusion, lethargy, and drowsiness.
Bacterial meningitis is much more serious and is treated with antibiotics (may be fatal)
Viral meningitis has no specific treatment, usually resolves on its own in 1–2 weeks.
A vaccine is available to help protect against some types of bacterial meningitis