Chapter 13 Part 2) PNS Flashcards

1
Q

Spinal Nerves

A
  • We have 31 pairs of Spinal Nerves.
    • All are mixed nerves
    • Named from the point of origin on the spinal chord
  • Supply all body parts except head and part of the neck (cervical nerves)
  • Regions
    • Cervical Nerves) 8 Pairs (C1-C8)
      • The first seven nerves exit superior to C vertebrae
      • C8 exits inferior to C7
      • C7 has one nerve above and below it
    • Thoracic Nerves) 12 pairs (T1-T12)
    • Lumbar Nerves) 5 pairs (L1-L5)
    • Sacral Nerves) 5 pairs (S1-S5)
    • Coccygeal Nerves) 1 Pair (Co1)
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2
Q

Spinal Nerve Roots

A
  • Each Nerve is connected to the spinal chord via two roots
  • Ventral Roots
    • Contain Motor (effrent) fibers from ventral horn motor nuerons
    • Innerviate Skeletal muscles
  • Dorsal Roots
    • Contain sensory (affrent fibers) from sensory nuerons in dorsal root ganglia
    • Conduct impules from perpherial receptors
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3
Q

Spinal Nerve Branches

A
  • Spinal Roots become longer as you go down the chord
    • Lumbar and Sacral roots are very long (cauda equina)
  • Spinal Nerves are very short
    • only extend about 1-2 cm before they branch
  • Diffrent branches of Spinal Nerves
    • Dorsal Ramus) smaller branch from dorsal roots
    • Ventral Ramus) larger branch from ventral roots
    • Menigeal Branch) tiny branch that reenters the vertebral canal to innervate menigenes and blood vessels.
  • Rami Communicates
    • Communicate signals
    • contain autonomic nerve fibers that join ventral rami in thoraic region
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4
Q

Innervation Of Specific Body Regions

A
  • Spinal Nerve Rami and branches supply innervation to entire somatic region (skin and muscle) from neck down
    • Dorsal Rami) supply posteior body trunk
    • Ventral Rami) Supply rest of the trunk and the limbs
  • Diffrences between roots and Rami
    • Roots
      • are more medial and form the spinal nerve
      • Each is purly sensory or purly motor
    • Rami
      • More distal and form branches
      • Carry both sensory or motor fibers
  • All Ventral Rami (except T2-T12) branch and rejoin to form complicated networks called Nerve Plexuses
    • only ventral rami
  • Fibers cross over in plexus
    • Means one nerve will have more than one fiber type
    • damage to one nerve does not mean entire paryalsis.
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5
Q

Cervical Plexus

A
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6
Q

Brachial Plexus

A
  • Gives rise to virtually all of the nerves that innervate the upper limb
    • Orginates from Ventral Rami of C5-8 and most of T1 (may also come from C4 or T2)
  • Four Major Branches
    • Roots) Five Ventral rami rami (C1-T1) form…
    • Trunks) Upper, middle and lower trunk unit to form…
    • Divisions) Anterior and Posterior, unit to form…
    • Cords) Lateral, Medial, and Posteior
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7
Q

Five Important Nerves of the Brachial Plexus

A
  • Cords of brachial plexus give rise to nerves of the upper limb. There are 5 important ones
  • Axillary) Innerviates Deltiod, Teres minor, and skin and joint capsule of the shoulder
  • Musculocutaneous) Innerviates Biceps Brachii, Brachialis, coracobrachialis, and skin of lateral forearm
  • Median) Innerviates skin, most Flexors, forarm Pronators, Wrist and Finger Flexors, and Thumb oppostion muscles
  • Ulnar) Innervates Flexor muscles, and skin of medial hand.
  • Radial) Innercates essentially all extensor muscles, supinators, and posteiror skin of limb
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8
Q

Injuries to Brachial Plexus

A
  • Brachial Plexus) common injury
    • severe injuries can weaken or paralize the entire upper limb
    • Injuries may occur if upper limb is pulled to hard which streatches the plexus
  • Median Nerve) injury makes it difficult to use thumb and pointer finger to pick up small objects
    • Carpal Tunnel) median nerve is compressed
  • Ulnar Nerve) Damage can lead to sensory loss or paryalsis
    • Can’t make a fist
    • Funny Bone) spot where nerve rest against medial epicondyle
  • Radial Nerve) Damage results in wrist drop, or inabiluty to extend wrist.
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9
Q

Lumbosacral Plexus

A
  • Lumbar and Sacral Plexuses have signifigant overlap
  • Create Lumbosacral plexus
    • serve mostly the lower limbs
    • Also sneds some branches to the abdomen, pelvis, and buttocks
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10
Q

Lumbar Plexus

A
  • Arises from L1 to L4
  • Innervates thigh, abdominal wall, and psoas muscle.
  • Important Nerves
    • Femoral Nerve) innervates quadriceps and skin of anterior thigh and medial surface of leg
    • Obturator Nerve) passes through the obturator foramen to innervate adductor muscles.
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11
Q

Sacral Plexus

A
  • Arises from L4-S4
  • Serves the buttock, lower limb, pelvic structres and perinuem
  • Sciatic Nerve
    • Longest and thickest nerve of the body
    • Innervates hamstring muscles, adducot magnus, and most muslces in leg and foot
    • Composes of the Tibial and Common Fibular Nerve
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12
Q

Injuries to Lumbosacral Plexus

A
  • Femoral Nerve) Damage can be caused by a herniated disc of spine
  • Oburator Nerve) Impared nerve can cause pain in the medial thigh
  • Sciatical) Stabbing, radiating pain over the course of the sciatic nerve
    • Leg cannot be flexed because hamstrings are paralyzed
    • Foot and Ankle cannot move at all and drop into permenant plantar flexion called footdrop
  • Tibial nerve (of siatic) paralyzes calf muscles
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13
Q

Anterolateral Thorax and Abdominal Wall

A
  • Ventral Rami of T1-T12 nerves are intercostal nerves that supply muscles of the ribs, anterilateral thorax, and abdominal wall
    • Also supply skin
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14
Q

Back Innerviation

A
  • Innerviated by Dorsal Rami of many branches
    • Each branch innervates a stript of muscle
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15
Q

Dermatomes

A
  • Area of Skin Innercated by a single spinal nerve
    • all spinal nerves except C1 innervates the skin in some way
    • In patients with spinal chord injures damaged nerves can be pinpointed by determining damaged dermatome
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16
Q

Innervation Of Joints

A
  • Hilton’s Law) any nerve serving a muscle that produces a movemt at a joint also innervates that joint and skin over that joint.
17
Q

Segemental Level of Motor Control

A
  • Lowest Level in the motor heirechy
  • Consists of Reflexes and Automatic movments
    • relays info to spinal chord
  • Central Pattern Generators) Cirtuts that control locomotion and specific, often-repeated motor activity.
18
Q

Projection Level

A
  • Projection motor pathways send information to lower motor neurons and keep higher command levels informed of what is happening
  • Consists of
    • Upper Motor Neurons) Initate direct (pyramidal) system to produce voluntart skeletal muscle movments
    • Brain Stem Motor Areas) Oversee indrect (extrapyramidal) system to control reflex and CPG controlled activities.
19
Q

Precommand Level

A
  • Nuerons in the cerebellum and basal nuclei
    • regulate motor activity
    • precisly start or stop movment
    • corrdiante movments with posture
    • Block unwanted movments
    • Moniter muscle tone
20
Q

Reflexes (Two Types)

A
  • Inborn (intrinsic) relfex: Reflex that is not learned (innate)
    • ex) posture, visceral activities
    • Can control the body wihtout communication with the body
    • Can be modified by learning and conscious effort
  • Learned (acquired) reflexes: Learned from pratice or learning
    • Ex: Driving Skills
  • The distinction between inborn and learned reflexes is not clear as most inborn reflexes can be relearned
21
Q

Reflex Arc

A
  1. Receptor) site of stimulus activates
  2. Sensory Nuerson) transmits affrent impules to CNS
  3. Integration Center) Region in CNS
    • Monosynaptic) Between a sensory and a motor nueron (fast)
    • Polysynaptic) Involves multiple synapses going through chains of internuerons.
  4. Motor Neuron) Conducts effrent impulses from integration center to effector nueron
  5. Effector) Muscle Fiber or Gland that responds to impulse.
22
Q

Functional Classification of Reflexes

A
  • Somatic Reflexes
    • Activates skeletal muscles
  • Autonomic (visceral) reflexes
    • Activtae visceral effectors (smooth or cardiac muscle)
23
Q

Spinal Reflexes

A
  • Occur without direct involvment of higher brian centers
    • Brain is still advised of spinal reflex and may affect reflexes
  • Testing of Somatic reflexes is important to asses the condition of the nervous system
24
Q

Muscle Spindle (structure)

A
  • Communicates information about muscle stretch to CNS
  • Two types of affrent endings
    • Anulospiral endings (primary sensory)
      • Ends wrap around spindle
      • Simulated by Rate and Degree of Stretch
    • Flower Spray Endings (secondary sensory)
      • Small axons at spindle ends
      • Stimulated by degree of stretch
  • Muscle Spindles only contract on their end regions
    • end regions are innervated by Gamma (γ) effrent fibers
    • This helps mantain muscle spindle sensitivity
  • Extrafusal fibers are outside of muscle spindle
    • innervated by alpha (α) fibers of large alpha (α) motor nuerons
25
Q

Muscle Spindle Excitment

A
  • Muscle spindles are excited in two ways
  • External Stretch) Applying an external that stretches the entire muscle
    • Ex) carrying a heavy weight or contracting antoganstic muscles
  • Internal Stretch) activation of the gamma motor nuerons
    • Stimulates the distal ends of interfusal fibers which in turn stimulates the middle of the spindle (internal stretch)
  • Strethcing of the Spindle = Increased rate of spinal chord impules
  • α-γ coactivation) makes Extrafusal and Intrafusal fibers contract together
    • Motor impulses are sent to both fibers at once
26
Q

Stretch Reflex

A
  • The brain set’s the muscle’s length via stretch reflex. Stretch Reflex makes sure the muscle says at the proper length
    • Ex) Knee jerk reflex is a reflex that keeps knees from buckling when you stand
  • Stretch Reflex mantains Muscle Tone in postural muscles
    • Causes contraction in respose to stretch
  • How Stretch Reflex works
    • Stretch activates muscle spindle (receptor)
    • Sensory Receptor Directly synapses with alpha motor nuerons
    • Aplha motr nueron cause extrafusal muscle to stretch
  • Reciprocal Inhibition) Affrent (receptive) fiebrs that synapse with internuerons inhibit antoginstic muscles
  • All reflexes are monosynaptic and ipsilateral
    • occur on same side of body
  • Part that inhibits antagonist mucles is polysynaptic
27
Q

Positive Reflex reactions

A
  • Positive Reflex reactions indicate
    • Sensory and Motor connections between muscle and spinal chord are intact and working
    • Strength of response indicates degree of spinal chord excitability
  • Reflexes are hypoactive or absent if damage to peripheral nerve or venntral horn has occured
  • Reflexes are Hyperactive if lesions of corticospinal tract reduce the ability to inhibit reflex.
28
Q

Tendon Reflex

A

*

29
Q

Flexor (Withdrawl) Reflex

A
  • Initiated by a painful stimulus
  • Automatic withdrawl of threatened body part
    • Ipsilateral (onside) and polysnaptic
    • Important to survuval
    • Brain can stop (ex, when needle is coming to arm)
  • A painful stimulus initiates the flexor, or withdrawal reflex, which causes automatic withdrawal of the threatened body part from the stimulus.
30
Q

Crossed Extensor Reflex

A
  • Occurs with flecor reflex in weight bearing limbs (legs) to mantain balance
  • When Withdral reflex occurs extensor reflex occurs on the other side
    • EX) stepping on glass causes withdrawl reflex in that leg and then extensor reflex in other leg to bear weight.