Spinal Nerves and The Peripheral Nervous System- Wilson Flashcards
Peripheral nerve lesions produces what types of sensory symptoms?
- anesthesia (no sensation)
- hypothesia (reduced sensation)
- parasthesia (abnormal sensation)
Peripheral nerve lesions produces what types of motor symptoms?
- flaccid paralysis (low motor neuron injury)
- paresis (partial paralysis or muscle weakness)
- muscle atrophy (wasting of muscle)
What are the ways peripheral nerves may be lesioned?
A. compression -entrapment syndromes -joint dislocations -fractures -vessel aneurysms -herniated discs B. Cutting and tearing C. Evulsion (avulsion) to pull out D. Repetitive motion E. Bacterial or viral infections (polio and leprosy) F. Neuropathy (diabetes)
How many cranial and spinal nerves are there? Which part of the nervous system do they each represent?
12 cranial nerves - CNS
31 spinal nerves - PNS
What are the different types of spinal nerves? List their region and the number of nerves located in the region?
8 cervical nerves 12 thoracic nerves 5 lumbar nerves 5 sacral nerves 1 coccygeal
Why are there 8 cervical nerves although there are 7 cervical vertebrae?
Nerves go above and below the vertebrae. If we consider the skull as an extra vertebrae we will have 8 cervical nerves.
What is the functional unit of the nervous system?
neuron
What are the neuronal structures assigned to the following functions?
- where neurons receive info from other neurons (whether excitatory or inhibitory)
- all data converges at this site; contains a nucleus
- beginning of axon that will carry info to the next neuron
dendrites: receptive sites
Soma: integrator
Axon hillock
Axons can go bidirectionally. True or false?
FALSE!!
Axons only go in one direction as action potentials can only go in one direction.
-either to the CNS or away from the CNS
Neurons only have 1 axon. True or false?
TRUE!!!
What are the different types of tissue that receive innervation?
muscle: contraction
glands: secrete
neurons: excite or inhibit
What happens to the action potential if there is cutting, severing, or injection of anesthesia ?
the action potential will not go to completion and propagation of the action potential is blocked
What types of cells compose most of the nervous system?
supporting cells
Neurons have lot of mitochondria. True or false?
True
they need lots of energy
What are cells in the CNS and PNS that produce myelin?
- Schwann cells in the PNS
- Oligodendricytes in the CNS
What are the functions of myelin?
- insulates the electrical activity of axons
- increase conduction velocity (propagation of action potential is faster)
- impulse propagation is more energy efficient (
There are multiple schwann cells for a single neuron and the same applies to oligodendricytes. True or false?
FALSE!!!
There is only one schwann cell for a single neuron.
Oligodendricytes are able to myelinate numerous axons?
Guillian-Barre Disease and multiple sclerosis are both demyelinating diseases. How are they different in terms of the types of cells they affect?
Guillian-Barre Disease affects schwann cells (PNS).
Multiple sclerosis affects oligodendricytes (CNS).
What type of neurons make up the sensory part of the PNS?
pseudo-unipolar neurons
it is a general sensory neuron found in ganglia
Motor neurons are primarily found where?
spinal cord
Histologically if you cut the brachial plexus cross-sectionally do you expect to see dendrites, axons, or cell bodies?
brachial plexus is a nerve
nerves are bundles of axons
So NO dendrites or cell bodies should be seen in this cross-section.
In the PNS, nerves are covered by what 3 connective tissue sheaths?
- every individual axon is covered bu an endoneurium
- bundles of axons are covered by perineurium
- an entire neuron is covered by epineurium
What are the connective tissue surrounding the axons in the CNS?
There are NO CONNECTIVE TISSUE surrounding axons in the CNS.
Thus axons in the CNS do not regenerate (no axonal regeneration) after injury but rather form glial scars.
Why are schwann cells and connective tissue important for regeneration of damaged axons?
They guide growth cones from the axonal stump back to the target tissue and thus they are able to find the original myelin and endoneurium.
Why do nerve lesions produce oftens times are RANGE of motor and/or sensrory symptoms?
Nerves of the PNS contain hundreds to millions of nerve fibers which each may serve a different function.
What is the difference between efferent and afferent axons in the PNS?
efferent axons: take action potentials away from the CNS (motor neurons)
afferent axons: take action potential toward the CNS (spinal cord and brain); these axons are sensory
The developing embryo shows metamerism which is?
blocks of tissue that repeat themselves
What is the relationship between the developing spinal cord and the developing somites and the idea of segmentation?
somites gives rise to:
- sclerotome which form vertebrae
- myotomes: skeletal muscles of the body
- dermatome: skin
they all have segmental organization just like the somites (makes sense)
What axons innervate myotomes and dermatomes?
motor axons innervate myotomes
sensory axons innervate dermatomes
At each vertebral level, each segment of the neural tube innervates the somite (dermatome/myotome) associated with it.
sensory-motor wiring is segmental
The axon that leaves thoracic level T10 goes to the dermatome to the striped skin around what anatomical structure? What about the axons that leaves T4/T5?
umbilical
nipples
A woman with two different sized breast will have different innervations of the breast. True or false?
FALLSEE.
Once an innervation is established (which occurs very early in development even before the development of the breast), it is maintained despite what happens to it.
How does the neural tube innervate the myotomes and dermatomes?
- all the axons that go to the myotome, their central bodies will be located in the ventral portion of the spinal cord (AP going towards muscles)
- all the axons coming from the dermatome to the spinal cord, they carry sensory information to the dorsal part of the spinal cord
How does the neural tube innervate the myotomes and dermatomes?
- all the axons that go to the myotome, their central bodies will be located in the ventral portion of the spinal cord (AP going towards muscles from the ventral part of the spinal cord)
- all the axons coming from the dermatome to the spinal cord, they carry sensory information to the dorsal part of the spinal cord
so dorsal is sensory and ventral is motor
Ventral 1/2 of spinal cord innervates myotomes and is motor.
Dorsal 1/2 of spinal cord innervates dermatomes and is sensory.
Axons can be further divided in categories depending on where they’re going. Axons can be either efferent or afferent. What is the second level of characterization?
somatic (body surface)
visceral (body cavity)
What is meant by the general and specials functions of axons in terms of classification?
general functions are functions that you find in the spinal cord as well as cranial nerves (generalized to the PNS)
special functions are functions that you only find in cranial nerves due to embryological origins (seeing
What are the 8 different classifications of functional components of peripheral nerves?
Spinal cord has only 4 general functions:
GSE: axons innervating skeletal muscle that are derived from myotoms
GVE
GSA : sensory axons coming from the spinal cord that innervate the dermatome (these sensory axons carry information about pain, touch, temperature, vibration, proprioception)
GVA
Describe the typical components of the spinal cord. What gives the spinal cord its gray and white matter appearance?
gray matter= cell bodies of neurons
white matter: due to presence of high concentration of myelinated axons
dorsal horn for sensory neurons
ventral horn for motor and multipolar neurons
spinal cord was derived from the neural tube
What is contained within the dorsal root ganglion AKA spinal gangion?
sensory cell bodies of pseudo-unipolar neurons
If a patient had a lesion of the dorsal root or dorsal root ganglion, would the patient have symptoms of sensory, motor, or both?
patient would have sensory symptoms
If a patient presents with only motor symptoms, where did the lesion occur?
ventral root
What is the mixed spinal nerve?
the dorsal root and ventral root come together to form the mixed spinal nerve
If there is a lesion at the spinal nerve what symptoms will the patient most likely present with?
a combination of sensory and motor symptoms
the spinal nerve is found at the level of the intervertebral foramen
What does the spinal nerve do immediately exiting the intervertebral foramen? Why and is there an embryological basis?
It divides into the dorsal and ventral primary rami.
Yes there is an emrbyological basis.
- differentiation of the myotome into the epimere and hypomere
- epimere is forms true back muscles and innervated by dorsal primary
- hypomere gives rise to all othhr skeletal muscles (muscles in the body wall, muscles in the limbs) and is innervated by the ventral primary rami
What is the difference between the dorsal and ventral primary rami?
dorsal primary rami to innervate the true back muscles (erector spinae and transversospinalis muscles) and the skin overlying those muscles
ventral primary rami follows the course of the ribs to innervate muscles of the body wall and limbs
A lesion in the ventral or dorsal primary rami will produce what kind of symptoms?
a mixture of sensory and motor symptoms
If the ventral primary rami of T6 is lesioned, what part of the dermatome will have a loss of sensation?
dermatome of T6 specifically below the nipple to the axilla region
NOT the back region as the dorsal primary rami has not been lesioned
What spinal nerves do not join other spinal nerves as they run beneath the ribs? What does this mean if they are lesioned?
Spinal nerves T2-T12
If lesioned there will be sensory changes in a dermatome.
What fibers are called lower motor neurons and are the final common pathway to skeletal muscle? What happens if there are lesions of these fibers?
General Somatic efferent fibers
If lesioned, the skeletal muscle will lose motor control resulting in flaccid paralysis, a loss of reflexes, and muscle atrophy (no muscle tone).
If you do a laminectomy, what do you observe happen to the spinal cord in the regions of the upper limb and lower limbs?
the spinal cord gets larger
cervical enlargement
lumbar sacral enlargement
enlarged because this is where the axons or nerves innervating the limbs are found
limbs have a lot of muscle so ventral roots are very large
a lot of skin in the limbs and therefore the dorsal roots are very large
Ventral primary rami give rise to every muscle EXCEPT treu back muscles. True or false?
TRUE
Plexuses (NERVES) are formed by the ventral primary rami only! What are the different types of plexuses?
- Cervical Plexus C1-C4
- Brachial Plexus C5-T1 (C8): innervate upper limbs
- Lumbosacral Plexus L1-S4: innervate lower limbs
There is a mixing of sensory and motor axons from different levels in a limb plexus.
Limb ventral primary rami divide into anterior and posterior divisions that innervate what?
flexors and extensors for respectively
embryology dictates how the plexuses are formed!!!
When you damage the axillary nerve what superficial muscle will undergo atrophy?
deltoid muscle
The fetus spinal cord extends the length of the spinal canal. True or false?
True!!
At every vertebral level there is a nerve that goes above and below the vertebral level in fetuses.
In the adult, the spinal cord ends at vertebral level L2. Do nerves still come out at sacral and coccygeal levels?
Yes they do. They just stretch to exit where they need to through the intervertebral foramen. Spinal co®d ends but the NERVES continue and they have to continue to exit at the levels they are . supposed to forming the cauda equina.
Below what vertebral level does the spinal roots (nerves) form the cauda equina?
L2
The spinal cord does not sit naked and vulnerable inside this bony vertebral canal. What are the 3 covering of the spinal cord going from outside to inside?
dura mater: tough
arachnoid mater: extremely delicate, which has the denticulate ligament
pia mater: will not see in the cadaver as it is directly attached (welded onto) to the spinal cord
What is the purpose of the denticulate ligament?
it helps to hold the spinal cord in the middle of the vertebral column
found laterally
Just as the spinal cord stops at L2, does the pia mater stop at L2?
NOO
It continues to the coccyx as . the filum terminalis
What is the purpose of the filum terminalis?
it anchors/tethers the end of spinal cord
so you when you want to jump up your spinal cord doesn’t hit you in the nose
it goes all the way to the sacral hiatus
Where is the subarachnoid space and why is it important?
- the space deep to the arachnoid mater
- space between the arachnoid and pia mater
- subarachnoid space ends at S2
- it CONTAINS cerebrospinal fluid
Where is the epidural space? What is so significant about it?
the space outside the dura mater (between bone and the dura mater) is filled with fat but most important it contains veins (VENOUS PLEXUS) which LACK valves
- veins are valveless and anastomose with venous sinuses in skull and body, allowing metastasis from pelvic structures to CNS
- so blood can go any direction
- CANCER from the prostate gland can metastasize all the way to the brain !!!
Where do you insert the needle to do a spinal tap?
below L2 (L3 or L4) into the subarachnoid space to inject drugs (spine anesthesia: all the nerves if the cauda equina would be blocked) or extract CSF (to check for bacterial infection or cancer)
What is simplest circuit of the nervous system?
reflex arc
What are the 5 minimum components to a reflex arc?
- sensory receptor (muscle spindle or pain receptor)
- afferent nerve (sensory neuron carrying info to CNS)
- central integration (integration through synapse)
- efferent nerve (motor neuron taking info to the effector away from CNS)
- effector (muscle)
What nerve does the biceps reflex test examine for its functionality?
testing the musculocutaneous nerve
-causes flexion of the elbow
C5, C6
tapping the tendon
What nerve does the brachioradialis reflex test examine for its functionality?
testing the musculocutaneous nerve
-causes flexion of the elbow
C5, C6
tapping the tendon
What nerve does the tricep reflex test examine for its functionality?
C7, C8
-causes extension of the elbow
tapping the tendon
Which grade of stretch reflexes is normal?
+2
nerve lesion can diminish response +1 or no response at all +3
these are limited to the PNS
exaggerated responses are with CNS
What are the signs of lower motor neuron damage?
flaccid paralysis
decreased or absent reflexes
atrophy of muscles
