Spinal Chapter 17

Describe the protective structures of the spinal cord:
Bony vertebrae

Meninges: 3 layers
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 layer
-squamous to cuboidal cells within interlacing collagen & elastic fibers
-many blood vessels supply oxygen & nutrients to spinal cord

Cerebrospinal fluid

Describe the External anatomy of spinal cord:
Adults – medulla oblongata to 2nd lumbar vertebra
16-18 inches long 2cm diameter
Infants- extends to 3rd/4th lumbar vertebra
longer in infants

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

What is the Conus medullaris
Conical structure where spinal cord tapers off

What is the filum terminale?
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

What is the cauda equine
A tail-like array of roots of spinal nerves at the inferior end of the spinal cord

How many pairs of Spinal nerves are there are list the segments they are organized in
31 pairs of spinal nerves from posterior and anterior roots

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

Describe the two grooves that penetrate the white matter of the spinal cord and divide it into right and left sides
Anterior median fissure – wide groove on the anterior (ventral) side
Posterior median sulcus – narrow furrow on the posterior (dorsal) side

What is the gray commissure
A narrow strip of gray matter connecting the two lateral gray masses within the spinal cord (butterfly body / crossbar of H)

What is the central canal?
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

Where is the anterior/ventral white commissure
-connects the white matter of the right and left sides of the spinal cord
-anterior to central canal

Describe what the posterior/dorsal gray horns contain
Posterior (dorsal) gray horns contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons

Describe what the anterior/ventral gray horns contain
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

Describe what the lateral gray horns contain
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

Describe what the anterior/central, posterior/dorsal, and lateral white columns contain
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

What is the difference btween tracts and nerves?
tracts are bundles of axons in the CNS, whereas nerves are bundles of axons in the PNS

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

Describe how spinal nerves are connected to the spinal cord
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).

Why is the spinal nerve considered a mixed nerve?
Because the posterior root contains sensory axons and the anterior root contains motor axons

Identify the connective tissue coverings of spinal nerves
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

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

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

What are intercostal/thoracic nerves?
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

Define dermatome. Describe the clinical significance of them
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

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

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

Describe Stretch reflex
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

Describe the function of a Muscle spindle
Slight stretching of a muscle stimulates sensory receptors in the muscle
Monitors changes in length of muscle

Ipsilateral reflex arc
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

Define Muscle tone
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

Define Reciprocal Innervation
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

What is Flexor/withdrawal reflex
Flexor/withdrawal reflex
-in response to a painful stimulus

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

What is a Tendon reflex
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).

Describe the 2 clinically important reflexes
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

Describe homeostatic disruption of spinal function in shingles
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)

Describe homeostatic disruption of spinal function in poliomyelitis aka polio
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

Describe homeostatic disruption of spinal function in meningitis
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

the polio virus can cause skeletal muscle paralysis by destroying neuron cell bodies. Identify the area of the spinal cord that is destroyed anterior horn shingles is a condition characterized by pain, discoloration of the skin, and eruption of skin …

epineurium the outer covering around the entire nerve perineurium surround bundles (fascicles) of axons WE WILL WRITE A CUSTOM ESSAY SAMPLE ON ANY TOPIC SPECIFICALLY FOR YOU FOR ONLY $13.90/PAGE Write my sample endoneurium surrounds individual axons dermatome the skin …

Define PNS and list its components Peripherial Nervous System – Sensory(afferent) Division and Motor (efferent) division Motor division – Somatic NS & Autonomic NS ANS – Parasympathetic and sympathetic Differentiate among a stimulus, a sensation and perception. Stimulus – Changes …

acetylcholine neurotransmitter chemical released at the ends of nerve cells afferent nerve carries messages torward the brain and spinal cord WE WILL WRITE A CUSTOM ESSAY SAMPLE ON ANY TOPIC SPECIFICALLY FOR YOU FOR ONLY $13.90/PAGE Write my sample arachnoid …

Blood-brain barrier Blood vessels (capillaries) that selectively let certain substances enter brain tissue and keep others out. Astrocyte Type of glial (neuroglial) cell that transports water and salts from capillaries. WE WILL WRITE A CUSTOM ESSAY SAMPLE ON ANY TOPIC …

The spinal cord is one of the most delicate structures that nature has enclosed in the bodies of the humans. It is a wonder pathway which consists of the nerves connection and transmitting millions of messages from the brain all …

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