Chapter 17: Peripheral region Flashcards
PNS
all neural structures distal to the spinal nerves (median nerve, ulnar nerve, etc.).
-Cranial nerves are “peripheral” by definition, but are covered in chapters 19-21
everything that is distal to the spinal nerve
CNS
All structures enclosed by bone.
Spinal region- Nerve roots
nerve roots- motor and sensory, ventral and dorsal (dorsal root ganglion)
Spinal nerve
where sensory, motor, and autonomic come together.
Peripheral region: rami
3 rami branches from spinal nerve as it progresses distally.
- Anterior- has all of the axons that feed arms and legs in front of me
- Posterior- has the sensory and motor and autonomic to the backside of us
- Communicating branches (SNS)- autonomic neurons to and from the synapse.
Peripheral region: plexus
Plexus- cervical, brachial, lumbar, and sacral= all get input only from anterior ramus of every spinal level.
- plexus is distal to spinal nerve and proximal to peripheral nerve.
- Posterior rami just goes back and strip you like a barber pole.
Damage to one spinal nerve
a spinal level is damaged proximal to plexus- dermatomal sensory loss (one whole dermatome), many muscles will be weak but non should be paralyzed (every muscles gets input from many spinal levels).
Damage to one peripheral nerve
Damage to one peripheral nerve- sensory loss- medial nerve completely crushed- thumb, index, middle finger all on palmer side sensory loss (section of dermatome, some but not all of C6 dermatome)
Muscle loss- paralyzed muscle, the final pathway to muscle is cut.
peripheral nerves
Bundles of axons (sensory, motor, autonomic))
3 kinds of connective tissue:
- Endoneurium- surrounds individual axons
- Perineurium- surrounds bundles of axons
- Epineurium- surrounds bundles of fascicles.
around all axons is the perineurium gathers a bundle of axons together and is called a fascicle= a bundle of axons in a peripheral nerve.
-Epineurium is a thick connective tissue coating that gathers all fascicles together in a peripheral nerve.
- a peripheral nerve is a “bundle of bundles” axons- nerve is a whole bunch of axons
- axons is one fiber out of a whole nerve.
Peripheral nerve: fascicle
a bundle of neurons that all have a common destination, fascicle is part of the nerve.
Peripheral nerves-blood supply
Rich blood supply alongside every peripheral nerve.
-Arterial branches following every nerve.
myelinated vs. unmyelinated axons
One simple wrapping is unmyelinated
Cinnamon role is myelinated
Peripheral nerves- cutaneous vs muscular branches
Axons that go to skin (superficial) and muscle (deep)
Axons of peripheral nerves
A- alpha (efferent-extrafusal muscle)- motor neurons
Ia, Ib, II (afferent- proprioception)- tell us about how we are moving
A-beta (afferent- exteroception)- discriminative touch from surface of skin
A-gamma (efferent- intrafusal muscle)- keep spindle sensitie
A-delta (afferent-pain, temperature, viscera)- Sharp and stinging types of pain and cause us to move away (fast pain)
B (efferent-presynaptic autonomic)- preganglionic autonomic efferent)
C (afferent-pain, temperature, viscera)- dull and aching chronic pain (slow pain)
C- (efferent- postsynaptic autonomic)- postganglionic autonomic efferent
nerve plexuses
Cervical plexus- C1 to C4
Brachial plexus- C5-T1
Lumbar plexus- L1-L4
Sacral plexus- L4-S4
- The only plexus that contains parasympathetic nervous system fibers in it.
- At S2-S4 parasympathetic in perineum
Principles of a plexus
- One peripheral nerve gets axons from many different spinal levels
- One spinal level sends axons to many different peripheral nerves.
Peripheral nerves
All peripheral nerves have axons of:
- Motor function
- Sensory function
- Autonomic function
- Usually SNS (trunk, arms, legs)
- PNS in peripheral nerves of perineum
Autonomic is only arms, trunk, and legs
movement is essential for nerve health
- improves blood flow
- facilitates gliding of fascicles and nerves
- facilitates axoplasmic transport
- Anterograde
- Retrograde
- “wrinkling” of axons within endoneurium
- Lack of movement leads to physical stress on neural membrane
Contracture
loss of sarcomere and nerves get trapped in connective tissue. When try and move the connective tissue squeezes nerves and activates them (neuropathic pain) neural tension.
Neuromuscular junction
- voluntary effort generates action potentials
- release Ach (only a gas pedal)
- only excitatory
- “Miniature end-plate potential:
- -at rest
- -muscle health
- “atrophy of denervation
- evidence that our A-alpha motor neurons lack a bit of Ach even when not contracting them, doesn’t cause muscle to contract at all but affects the health of the muscle membrane. Lack of leaking that leads muscle fiber to wither away. When muscle fiber is denervated. Becomes unhealthy= atrophy of denervation.
-Down A-alpha motor neurons
dysfunction of peripheral nerves
Sensory changes:
- Decreased
- Absent
- Abnormal (allodynia)
Sensory changes (order of sensory loss)
- Conscious proprioception and discriminative touch
- Cold
- Fast pain (sharp)
- Heat
- Slow pain (dull)
order of sensation return after compression is relieve is in opposite order of loss.
Dysfunction of peripheral nerves: Autonomic changes
- Loss of sweating
- Loss of “shunting” in superficial arterioles
- Loss of “capacitance” (leads to orthostatic hypotension)
- other
-leaves us to be red indicating there is a lot of blood right underneath the skin.
Dysfunction of peripheral nerves: motor changes
- Paresis
- Paralysis
- If denervation
- -atrophy of denervation
- -fibrillations
atrophy of denervation will have fibrillation potentials ( a single muscle fiber that lost its nerve supply) is a signal of their irritation. cannot see on surface of skin.
