Lecture 2: Spinal Nerves and Spinal Reflex

Question 1

Dermatomes

Answer 1

specific area of body that is served by a single spinal nerve

Question 2

Dermatomes are important b/c

Answer 2

loss/ alteration of function in any given dermatome signifies a lesion (damage) to a corresponding root.

Question 3

Nerve Plexuses

Answer 3

Networks of nerves; network of compound nerve trunks

Question 4

Nerve plexuses are formed during

Answer 4

development

Question 5

Four major nerve plexuses:

Answer 5

1. Cervical Nerve Plexuses
2. Brachial Nerve Plexuses
3. Lumbar Plexuses
4. Sacral Plexuses
   (Lumbosacral Nerve Plexuses)

Question 6

Cervical Nerve Plexuses

Answer 6

• Innervates neck, torso, diaphragm
• Nerve Roots: C1 - C5
• Major Nerve: Phrenic (controls diaphragm)

Question 7

Brachial Nerve Plexus

Answer 7

• innervates the petoral girdle, upper limb
• Nerve Root: C5 - T1
• Major Nerve(s): Radial and Ulnar Nerves
  Other nerves: Nerves of arm/neck, upper torso.

Question 8

Lumbosacral Nerve Plexus

Answer 8

• Innervates abdominal muscles, upper leg muscles, skin of the genitalia
• Nerve Roots:
  Lumbar: T12- L4
  Sacral: L4 - S4
  Combine: T12- S4
• Major Nerve(s): Femoral, genitofemoral, sciatic nerve, pudendal nerve.

Question 9

Sciatica

Answer 9

results from compression of the sciatic nerve by a distorted lumbar intervertebral disc.

Question 10

Neural Reflexes

Answer 10

• Rapid, automatic responses to specific stimuli
• preserve homeostasis by making rapid adjustments in the functions of organs and organ systems.
• show little variability.

Question 11

Does stretch reflex use the brain?

Answer 11

No, an individual can be unconscious.

Question 12

Neural Reflex Process

Answer 12

1. Stimulus
2. Receptor
3. Afferent Signal (Sensory neuron)
4. CNS (internuerons)
5. Efferent Signal (motor nueron)
6. Response

Question 13

Classification of Reflexes

Answer 13

1. Development
2. Nature of Response
3. Complexity of Response
4. Site of Integration

Question 14

1. Development

Answer 14

• Innate Reflexes: genetically or developmentally programmed.
  Ex: Chewing, corneal reflex
• Acquired Reflexes: conditioned reflexes, rapid and automatic but learned
  Ex: driving reflexes, gaming reflexes

Question 15

2. Nature of Response

Answer 15

• Somatic Reflexes: involuntary control of skeletal muscle
  Ex: Pain withdrawal reflex
• Visceral Reflexes: autonomic reflexes, control activities of smooth muscle, cardiac muscle, glands, and adipose tissue.
  Ex: Baroreceptor Reflexes, feedforward feeding reflexes

Question 16

3. Complexity of the Circuit

Answer 16

• Polysynaptic Reflex: at least one interneuron between the sensory and motor neurons of a reflex arc. Delays occur between stimulus and response
  Ex: pain withdrawal reflex
• Monosynaptic Reflex: No interneuron between sensory and motor neurons
  Ex: Patellar Knee Jerk Reflex

Question 17

4. Site of Intergration

Answer 17

• Spinal Reflex: the important processing occurs in the spinal cord (does not negate brain involvement)
  Ex: Patellar knee jerk reflex
• Cranial Reflex: the important processing occurs in the brain.
  Ex: Corneal (blink) reflex

Question 18

Stretch Reflex (Myotatic Reflex)

Answer 18

• regulates skeletal muscle length
• used in postural reflexes which help maintain a normal, upright posture

Question 19

Stretch Reflex Arc Process(Patellar Reflex)

Answer 19

1. Stretch
2. Activate Muscle Spindle
3. Affernt Pathway
4. Spinal Cord
5. Efferent Motor Nueron
6. Contraction

Question 20

Muscle Spindles

Answer 20

• sensory receptors involved in the stretch reflex
• consists of bundles of small, specialized skeletal muscle fibers called intrafusal muscle fibers.
• surrounded by larger skeletal muscle fibers responsible for resting muscle tone and contraction of entire muscle.
• gamma motor neurons innervates each muscle spindle.

Question 21

Gamma motor neuron

Answer 21

innervates each muscle spindle.

• controls sensitivity by altering tension in intrafusal fibers
• allows CNS to decrease and increase muscle tone.

Question 22

1. Postural Reflex

Answer 22

• category of stretch reflexes that help us maintain an upright, normal position.

Question 23

Withdraw reflex

Answer 23

moves the affected body away from the stimulus.

• strong withdrawal reflexes are triggered by a painful stimulus.

Question 24

1. Flexor Reflex

Answer 24

• one type of withdraw reflex
• affects muscles of a limb

Question 25

Reciprocal inhibition

Answer 25

keeps the extensors relaxed.

Question 26

Crossed extensor reflex

Answer 26

• the stretch reflex and withdraw reflex involve the ipsilateral reflex arcs (sensory and motor responses on the same side of body)

Question 27

Crossed extensor reflexes involve a

Answer 27

• contralateral reflex arc
  that is an additional motor response that occurs on the opposite side of stimulus.

*Shifts weight to other leg in case of stepping on tact.

Question 28

In the clinical world, what are the examples of dermatomes?

Answer 28

Biceps. Triceps, and Patellar reflexes

it provides us with information about the status of the corresponding spinal nerve.

Question 29

Babinski Test

Answer 29

• stroking foot on later side of stole.
  In infants it is normal for fanny toe, as they get older it will be a curling of the toe. (If no curling toe, it may mean there is damage to the CNS)

Question 30

True or False.
The brain can either inhibit or facilitate (reinforcement) spinal reflexes.

Answer 30

True.

Question 31

inhabitation

Answer 31

inhibitory neurons synapse on the postsynaptic motor neurons. Activation of the inhibitory neurons of the brain will stop action potential signals.

Question 32

Reinforcement

Answer 32

these pathways indirectly enforce the reflex by causing a nervous system distraction.