Spinal N. & PNS Flashcards
Dr. Wilson lecture
Peripheral nerve lesions may produce?
Sensory symptoms and/or motor symptoms
What are sensory symptoms?
Anesthesia (no sensation)
Hypothesis (partial reduce of sensation)
Parathesisa (abnormal sensation)
What are examples of parathesia?
burning, tingling, and or pins & needle
What are examples of motor symptoms?
Flaccid Parlysis (low motor neuron injury/no tone) Paresis (partial paralysis or muscle weakness
Muscle atrophy (wasting of muscle)
How do lesions form?
Compression
Cutting and tearing
Evulsion (avulsion) - being pulled out
Repetitive motion
Bacterial/viral infections (polio or leprosy)
Neuropathy (diabetes)
How does a nerve become compressed?
Entrapment syndromes
joint dislocation
fractures
Vessel aneurism
Herniated discs
How does a nerve get cut?
Stab, bullet, shrapnel, fractures
What an example of a repetitive motion that can damage a nerve?
Carpel tunnel
How many pairs of spinal nerves do we have?
31 (come of each vertebral level) 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
What is the functional unit of the nervous system?
Neuron
Where is the action potential being initiated?
Axon hillock
Propagation of an action potential along an axon
Resting axon - inside negative charge and outside positive charge (negative resting potential)
action potential - charges change position (reverse)/membrane is leaky
Myelin producing cells
Schwann cells (PNS) - myelinate one portion of one axon
Oligodendrocytes (CNS) - myelinate one portion of multiple axons
Myelin Insulate axons and increase conduction velocity; impulse propagation is more energy efficient
T/F Size a myelin sheath plays no role in speed of AP
False
Thicker the myelin sheath the faster the AP
What is Guillian- Bare Disease?
PNS demyelinating disease that affects Schwann cells?
What is Multiple Sclerosis (MS)?
CNS demyelinating disease that affects oligodendrocytes
What are the three type of neurons that you can identify anatomically?
Multipolar: motor neuron (many dendrites/one axon) - found in spinal cord
bipolar: special sensory neuron (one dendrite/one axon)
psudounipolar: general sensory neuron found in ganglia (single process giving rise to axon) - found in PNS
Schwann cells and connective tissue sheaths are important for what?
regeneration of damaged axons in PNS When a nerve becomes damage -> stump forms -> schwann cells in area die but connective tissue/endoneurium stays in place-> axon regeneration occurs from the stump (guided by the myelin sheath from the live Schwann cells)
Why do axons not regenerate in the CNS?
Because there is no connective tissue in the CNS Glial scars form instead so it prevents regeneration
What are characteristics of the nerves in the PNS
contain hundreds to millions of nerve fibers or axons function of each fiber in a nerve may differ therefore, lesions of the nerve may produce a range of motor and/or sensory symptoms.
What are the three ways you can classify an axon?
- . Efferent or Afferent
- Somatic or visceral
- General or special
Which classification is based on the direction the axon potential travels
Efferent - CNS to periphery- motor/ventral (to skeletal muscle/myotome)
Afferent - PNS to CNS -sensory/dorsal (from skin/dermatome)
Somites give rise to?
Sclerotomes - vertebra
Myotome - muscles (motor innervation)
dermatome - skin (sensory innervation)
The axon leaving the vertebral column at the level of T10 innervates which dermatome?
The umbilicus
The axon leaving the vertebral column at the level of T5(T4) innervates which dermatome?
Nipples
How the axons distributed throughout the body?
Somatic - surface
Visceral - organs
How are nerves embryologically classified ?
General - functions that you find in spinal cord nerves as well as cranial nerves (example is pain) Special - functions found only cranial nerves (example is seeing)
Spinal cord only has which type of function
General function
Which are GSE, GVE, GSA, GVA
GSE (High yield) General Somatic Efferent
somitic skeletal muscle (from myotomes)
GVE General Visceral Efferent
smooth and cardiac muscle and glands ANS
GSA (high yield) General Somatic Afferent
pain, touch, temperature & proprioception (from dermatomes)
GVA General Visceral Afferent
pain, stretch & distention ANS
SVE
branchio- meric skeletal
SSA
vision, hearing & balance
SVA
smell & taste
Grey matter
Cell bodies of neurons
White matter
Axons and myelin sheaths
Parts of gray matter?
Dorsal horn - sensory
Ventral horn - motor
Typical spinal nerve
dorsal horn -> dorsal rootlets and roots
sensory -> dorsal root ganglion/cell bodies
(psuedounipolar)
Ventral horn -> ventral rootlets and roots
motor
Ventral root + dorsal root -> mixed spinal nerve (mixed of sensory and motor fibers/at the level of intervertebral foramen) -> dorsal primary rami (true back muscle) + ventral rami (follow ribs anteriorly)
What are the true back muscles formed by?
Epimere (from myotome) Innervated by dorsal primary rami
What are muscles in the body wall and limbs formed by?
Hypomere (from myotome) Innervated by ventral primary rami
Which spinal nerves do not join other spinal nerves as they run beneath the ribs?
T2-T12
What happens if T2-T12 become lesioned?
There will be changes in a sensory dermatome
At the level of the limbs what changes about the nerves?
Plexus are formed by ventral primary rami (VPR) only Cervial plexus: C1-C4
Brachial Plexus: C5-T1
Lumbosacral plexus: L1-S4
The plexus divide into what?
They divide into anterior and posterior divisions that innervate flexors and extensors, respectively.
Dorsal muscle mass, during embryology formation of the limb bud, gives rise to what?
Extensor muscle (posterior division)
Ventral muscle mass, during embryology formation of the limb bud, gives rise to what?
Flexor muscles (anterior division)
What are lower motor neurons?
GSE fibers
They are the final common pathway to skeletal muscle
Innervated skeletal muscle: cell bodies found in ventral horn
Lesion of a lower motor neuron causes what?
deprives skeletal muscle of motor control resulting in flaccid paralysis, a loss of reflexes, and muscle atrophy.
Damage to the axillary nerve?
Atrophy of deltoid
At what level does the spinal cord end in an adult?
L2 (in fetus a nerve comes out at every level of the vertebrae/spinal cord extends the length of entire canal)
What are the layers of the meningies?
dura mater - thickest layer
arachnoid mater - denticular ligament attached here
pia (outer layer of cord)
What is the purpose of the lenticular ligament?
Anchor spinal cord
Continuation of the spinal cord past L2?
Filum Terminalis
Formed by Pia mater that continues to the coccyx
What forms the cauda equina?
Growth of vertebrae is faster than spinal cord -> nerves stretch down -> spinal roots form the cauda equina
At what level does the subarachnoid space ends?
S2
What is the function of the filum terminals?
Anchor the spinal cord
What is the space between bone and the dura mater?
Epidural space
What does the epidural space contain?
filled with extradural fat and vertebral venous plexus (that lack values) Only around spinal cord, no epidural space in skull
What do the veins of the epidural space anastomose with?
venous sinuses in skull and body, allowing metastasis from pelvic structures prostate gland) to the CNS
Cerebral spinal fluid is located where?
Subarachnoid space
Spinal Tap
Needle inserted into subarachnoid space to either insert drugs or extract CSF
At what level is spinal tap performed at?
L3/L4
What are the components of a reflex arc?
1) Sensory receptor: dendrites on afferent nerve
2) Afferent nerve: afferent fiber takes in info to CNS 3) Central integration* (sensory fiber integration in ganglion and motor fiber integration in ventral horn) 4) Efferent nerve: efferent fiber takes informal away from CNS 5) Effector
What does a reflex arc describe and how is it detected?
Fundamental circuit of NS
Detected through reflexes
What is an example of a monosynaptic reflex?
Knee jerk, biceps reflex (C5, C6), brachioradialis reflex (C5, C6), triceps reflex (C7, C8)
afferent synapses directly on the efferent neuron
Reflex grading
