Spinal Nerves and Reflex Activity

Question 1

Structure of Nerve

Answer 1

• 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

Question 2

Spinal Nerves

Answer 2

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)

Question 3

Spinal Nerves: Roots

Answer 3

• Ventral Roots - contain motor (efferent) fibers
  
  • fibers innervate skeletal muscles
• Dorsal Roots - contains sensory (afferent) fibers
  
  • conduct impulses from peripheral receptors

Question 4

Spinal Nerves: Rami

Answer 4

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

Question 5

Spinal Nerves: Plexuses

Answer 5

• Cervical Plexus
• Brachial Plexus
• Lumber Plexus
• Sacral Plexus
• Advantage: damage to one spinal segment does not completely paralyze any limb segment

Question 6

All ventral rami except __-__ form interlacing nerve networks called _______

Answer 6

• T2-T12
• Plexuses

Question 7

Ventral rami of T2-T12 as _______ ____ supply muscles of the rib, anterolateral thorax, and abdominal wall

Answer 7

intercostal nerves

Question 8

Cervical Plexus

Answer 8

formed by ventral rami of C1-C4

• innervates skin and muscles of the neck, ear, back of head, and shoulders

Question 9

Phrenic Nerve

Answer 9

• Major motor and sensory nerve of the diaphragm irritation - hiccups
• Damage - paralysis of diaphragm

Question 10

Brachial Plexus

Answer 10

• Formed by ventral rami of C5-C8 and T1
• Innervates the upper limb
• Major Branches:
  
  • Axillary
  • Musculocutaneous
  • Radial - largest branch
  • Median
  • Ulnar

Question 11

Injury to the brachial plexus

Answer 11

paralysis of entire upper limb

Question 12

Median Nerve compression

Answer 12

carpel tunnel syndrome

Pincer grasp affected

Question 13

Injury to the ulnar

Answer 13

striking the “funny bone”

Question 14

Radial Nerve Trauma

Answer 14

Improper use of crutch, wrist drop or “Saturday night paralysis”

Question 15

Lumbar Plexus

Answer 15

• 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)

Question 16

Sacral Plexus

Answer 16

• 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

Question 17

Injury to the proximal portion of the sciatic nerve

Answer 17

Sciatica

stabbing pain radiates over the course of the sciatic nerve

Question 18

Injury to the common fibular

Answer 18

Foot Drop

Dorsiflexion is lost and foot dangles in planter flexion

Question 19

Calf muscles affected

Answer 19

Injury to tibial nerve

Question 20

Anesthetics -

Answer 20

Pudenal nerve - episiotomy

Question 21

The area of skin innervated by the cutaneous branches of a single spinal nerve

Answer 21

Dermatome

most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness

Question 22

__ dermatomes for 31 spinal nerves

Answer 22

30

Question 23

All spinal nerves except __ participate in dermatomes

Answer 23

C1

Question 24

*Dermatome Map*

Answer 24

Question 25

A reactivation of the chickenpox virus in the body, causing a painful rash

Answer 25

**Shingles**

Question 26

A rapid, involuntary, predictable motor response to a stimulus

Answer 26

**inborn (intrinsic) reflex**

Question 27

Result from practice or repetition

Answer 27

**Learned (acquired) reflexes**

Question 28

By Complexity...

Answer 28

* Monosynaptic vs. Polysynaptic * ipsilateral vs. contralateral

Question 29

**Reflex Arc**

Answer 29

1. **Receptor -** site of stimulus action 2. **Sensory Neuron -** transmits afferent impulses to the CNS 3. **Integration Center -** either monosynaptic (1 synapse) or polysynaptic (2 or more) within the CNS 4. **Motor Neuron -** conducts efferent impulses from the integration center to an effector organ 5. **Effector -** muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting

Question 30

**Stretch/Extension/Patellar Reflexes**

Answer 30

* maintain muscle tone in large postural muscles * all stretch reflexes are **monosynaptic** and **ipsilateral** * **2 neurons**

Question 31

**Flexor/Withdrawal Reflexes** (typical reflex arc)

Answer 31

* initiated by painful stimulus * **3 neurons** * **Polysynaptic** * **Ipsilateral**

Question 32

**Crossed-Extensor Reflexes** (step on a tac) Intersegmental reflex

Answer 32

* **Contralateral** * **3 or more neurons** * **Polysynaptic**

Question 33

Same side vs. Opp. side

Answer 33

Sensory and motor neurons - **ipsilateral** vs. Association (Grey commissure) - **Contralateral**

Question 34

**Superficial Reflexes**

Answer 34

* **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