Dermatomes, Naming tracts, Motor Reflexes

Question 1

What are the two maps of afferent nerves that convey cutaneous sensation

Answer 1

1. Dermatomes

2. Peripheral nerve fields

Question 2

How are dermatomes helpful

Answer 2

Each spinal nerve contains sensory neurons that serve a specific segment of the body, so if there is reduced sensation on a specific section of the skin then there could be damage to that specific spinal nerve.

Question 3

What is shingles and how does it relate to the spinal nerves/dermatomes

Answer 3

• Acute infection of the PNS caused by herpes zoster (virus that causes chicken pox)
• After infetion w/ chicken pox/herpes zoster the virus retreats to the posterior root ganglion. When the pt become immunocompromised/stressed the virus leaves the ganglion and travels down the sensory neurons of the skin. The virus then causes pain/blisters on the skin coinciding w/ dermatomal distribution of the infected posterior root ganglion.

Question 4

How does the herpes zoster virus travel from the posterior ganglion to the sensory neurons of the the skin

Answer 4

By fast axonal transport

Question 5

What are the 2 types of descending pathways for skeletal muscle output and how do they differ

Answer 5

1. Direct=originate in the cerebral cortex, and is responsible for precise voluntary movement of skeletal muscle
2. Indirect= originate in the brainstem, responsible for involuntary skeletal muscle movement, ie maintaining posture, responding quickly to visual stimuli

Question 6

Define a reflex

Answer 6

a fast, involuntary, unplanned sequence of actions that occur in response to a particular stimulus they can be innate or learned

Question 7

What are the two types of reflexes based on the site of stimuli integration

Answer 7

1. Spinal reflex= integration take place in grey matter of spinal cord
2. Cranial reflex= integration take place in the spinal cord

Question 8

What are the 2 types of reflexes based on the type of muscles involved and how do they differ

Answer 8

1. Somatic= involve contraction of skeletal muscles, we use this clinically
2. Visceral= involve contraction of smooth muscle, usually not perceived, and not easily initiated in clinical setting

Question 9

What is another name for visceral reflexes

Answer 9

Autonomic reflexes

Question 10

What is a reflex arc

Answer 10

a very specific (for each reflex) pathway followed by nerve impulses that produce a reflex

Question 11

What are the reflex arc components

Answer 11

1. Sensory receptor
2. Sensory neuron
3. Integrating center
4. Motor neuron
5. Effector

Question 12

Where is the integrating center for reflexes

Answer 12

grey matter of CNS

• if spinal reflex it integrates in spine
• if cranial reflex it integrates in the brain stem

Question 13

What parts of the body are typically effectors in a reflex arc

Answer 13

muscles or glands

Question 14

Define a monosynaptic reflex arc

Answer 14

simplest reflex consisting of the integrating center and one synapse between sensory neurons and a motor neuron

Question 15

Define a polysynaptic reflex arc

Answer 15

Most common reflex arch, it involves 2 types of neurons and more more than 1 CNS synapse

Question 16

Describe a stretch reflex

Answer 16

It is a feedback mechanism that controls muscle length, and prevents injury from over stretching, by causing muscle contraction

Muscle spindle(stretch receptors) sense muscle stretch the motor neuron is activated and muscle contracts and antagonistic muscles relax

Question 17

What is clinically relevant stretch reflex

Answer 17

Patellar reflex

Question 18

Describe a tendon reflex

Answer 18

It is a feedback mechanism to control muscle tension by causing muscle relaxation when muscle force becomes too extreme

Golgi tendon organs (tension receptors) are in tendons at the musculotendinous junction, it is activated by stretching, which causes inhibitory neuron to be simulated, the motor neuron is hyperpolarized, the muscle relaxes and ipsilateral muscles contract

Question 19

Describe the flexor and crossed extensor reflexes

Answer 19

Flexor reflex= withdraw reflex that moves a limb to avoid pain also known as nociceptive withdraw reflex

Crossed extensor reflex= synchronized extension of the joints of the of one limb contralaterally to flexor reflex that helps maintain balance during the flexor reflex

Question 20

Describe the plantar flexion reflex

Answer 20

results from the stroking of the lateral outer margin of the sole which causes Babinski sign= dorsiflexion of the great toe wit or without lateral fanning of the other toes

• Should disappear after 1.5 years old, if it is still around after that it is abnormal.
• Normal after 1.5= is curling under of toes

Question 21

What does hyperactive reflexes suggestive of

Answer 21

central nervous system disease

Question 22

What does hypoactive reflexes suggestive of

Answer 22

damage to relevant spinal segments, muscle diseases, neuromuscular junction or loss of sensation

Question 23

Define discriminative touch

Answer 23

ability to feel exactly what body part is being touched

Question 24

Define 2 point discrimination

Answer 24

ability to distinguish the touching of two different points on the skin which are close together

Question 25

Define paraplegia

Answer 25

paralysis of lower limbs

Question 26

Define hemisection

Answer 26

partial transection of the spinal cord on either the L or R side

Question 27

Define myelitis

Answer 27

inflammation of spinal cord

Question 28

Define paresthesia

Answer 28

abnormal sensation such as burning, pricking….