Spinal Nerves and Reflex Activity Flashcards
Structure of Nerve
- Endoneurium - loose connective tissue that encloses axons and their myelin sheaths
- Perineurium - coarse connective tissue that bundles fibers into fascicles
- Epineurium - tough fibrous sheath around a nerve
Spinal Nerves
31 Pairs of mixed nerves according to their point of issue from the spinal cord
- 8 cervical (C1-C8)
- 12 Thoracic (T1-T12) - intercostal nerves
- 5 Lumbar (L1-L5)
- 5 Sacral (S1-S5)
- 1 Coccygeal (C0)
Spinal Nerves: Roots
-
Ventral Roots - contain motor (efferent) fibers
- fibers innervate skeletal muscles
-
Dorsal Roots - contains sensory (afferent) fibers
- conduct impulses from peripheral receptors
Spinal Nerves: Rami
Each spinal nerve divides into 3 branches or rami
- Dorsal Ramus - the back is innervated by dorsal rami posterior side
- Larger ventral ramus
- Rami Communicans - autonomic pathways join to the ventral rami in the thoracic region
Spinal Nerves: Plexuses
- Cervical Plexus
- Brachial Plexus
- Lumber Plexus
- Sacral Plexus
- Advantage: damage to one spinal segment does not completely paralyze any limb segment
All ventral rami except __-__ form interlacing nerve networks called _______
- T2-T12
- Plexuses
Ventral rami of T2-T12 as _______ ____ supply muscles of the rib, anterolateral thorax, and abdominal wall
intercostal nerves
Cervical Plexus
formed by ventral rami of C1-C4
- innervates skin and muscles of the neck, ear, back of head, and shoulders
Phrenic Nerve
- Major motor and sensory nerve of the diaphragm irritation - hiccups
- Damage - paralysis of diaphragm
Brachial Plexus
- Formed by ventral rami of C5-C8 and T1
- Innervates the upper limb
- Major Branches:
- Axillary
- Musculocutaneous
- Radial - largest branch
- Median
- Ulnar
Injury to the brachial plexus
paralysis of entire upper limb
Median Nerve compression
carpel tunnel syndrome
Pincer grasp affected
Injury to the ulnar
striking the “funny bone”
Radial Nerve Trauma
Improper use of crutch, wrist drop or “Saturday night paralysis”
Lumbar Plexus
- L1-L4
-
Femoral nerve - largest nerve of this plexus
- prime mover of hip flexion and knee extension
- Obturator nerve- passes through obturator foramen to innervate adductor muscles (inner thigh muscles)
Sacral Plexus
- L4-S4
- serves the buttock, lower limb, pelvic structures, and perineum
-
Sciatic Nerve
- longest and thickest nerve in body
- 2 nerves: tibial and common fibular
- Innervates the hamstring muscles, and most muscles in the leg and foot
-
Pudendal Nerve - supplies perineum
- stimulates erection and controls urination
Injury to the proximal portion of the sciatic nerve
Sciatica
stabbing pain radiates over the course of the sciatic nerve
Injury to the common fibular
Foot Drop
Dorsiflexion is lost and foot dangles in planter flexion
Calf muscles affected
Injury to tibial nerve
Anesthetics -
Pudenal nerve - episiotomy
The area of skin innervated by the cutaneous branches of a single spinal nerve
Dermatome
most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness
__ dermatomes for 31 spinal nerves
30
All spinal nerves except __ participate in dermatomes
C1
*Dermatome Map*
A reactivation of the chickenpox virus in the body, causing a painful rash
Shingles
A rapid, involuntary, predictable motor response to a stimulus
inborn (intrinsic) reflex
Result from practice or repetition
Learned (acquired) reflexes
By Complexity…
- Monosynaptic vs. Polysynaptic
- ipsilateral vs. contralateral
Reflex Arc
- Receptor - site of stimulus action
- Sensory Neuron - transmits afferent impulses to the CNS
- Integration Center - either monosynaptic (1 synapse) or polysynaptic (2 or more) within the CNS
- Motor Neuron - conducts efferent impulses from the integration center to an effector organ
- Effector - muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
Stretch/Extension/Patellar Reflexes
- maintain muscle tone in large postural muscles
- all stretch reflexes are monosynaptic and ipsilateral
- 2 neurons
Flexor/Withdrawal Reflexes (typical reflex arc)
- initiated by painful stimulus
- 3 neurons
- Polysynaptic
- Ipsilateral
Crossed-Extensor Reflexes (step on a tac)
Intersegmental reflex
- Contralateral
- 3 or more neurons
- Polysynaptic
Same side
vs.
Opp. side
Sensory and motor neurons - ipsilateral
vs.
Association (Grey commissure) - Contralateral
Superficial Reflexes
-
Plantar Reflex
- downward flexion of toes
- tests for function of corticospinal tracts
-
Babinski’s sign
- Dorsiflexion of hallux and fanning of toes
- present in infants due to incomplete myelination
- in adults, indicates corticospinal or motor cortex damage
