Dermatomes, Naming tracts, Motor Reflexes Flashcards
What are the two maps of afferent nerves that convey cutaneous sensation
- Dermatomes
2. Peripheral nerve fields
How are dermatomes helpful
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.
What is shingles and how does it relate to the spinal nerves/dermatomes
- 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.
How does the herpes zoster virus travel from the posterior ganglion to the sensory neurons of the the skin
By fast axonal transport
What are the 2 types of descending pathways for skeletal muscle output and how do they differ
- Direct=originate in the cerebral cortex, and is responsible for precise voluntary movement of skeletal muscle
- Indirect= originate in the brainstem, responsible for involuntary skeletal muscle movement, ie maintaining posture, responding quickly to visual stimuli
Define a reflex
a fast, involuntary, unplanned sequence of actions that occur in response to a particular stimulus they can be innate or learned
What are the two types of reflexes based on the site of stimuli integration
- Spinal reflex= integration take place in grey matter of spinal cord
- Cranial reflex= integration take place in the spinal cord
What are the 2 types of reflexes based on the type of muscles involved and how do they differ
- Somatic= involve contraction of skeletal muscles, we use this clinically
- Visceral= involve contraction of smooth muscle, usually not perceived, and not easily initiated in clinical setting
What is another name for visceral reflexes
Autonomic reflexes
What is a reflex arc
a very specific (for each reflex) pathway followed by nerve impulses that produce a reflex
What are the reflex arc components
- Sensory receptor
- Sensory neuron
- Integrating center
- Motor neuron
- Effector
Where is the integrating center for reflexes
grey matter of CNS
- if spinal reflex it integrates in spine
- if cranial reflex it integrates in the brain stem
What parts of the body are typically effectors in a reflex arc
muscles or glands
Define a monosynaptic reflex arc
simplest reflex consisting of the integrating center and one synapse between sensory neurons and a motor neuron
Define a polysynaptic reflex arc
Most common reflex arch, it involves 2 types of neurons and more more than 1 CNS synapse
Describe a stretch reflex
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
What is clinically relevant stretch reflex
Patellar reflex
Describe a tendon reflex
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
Describe the flexor and crossed extensor reflexes
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
Describe the plantar flexion reflex
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
What does hyperactive reflexes suggestive of
central nervous system disease
What does hypoactive reflexes suggestive of
damage to relevant spinal segments, muscle diseases, neuromuscular junction or loss of sensation
Define discriminative touch
ability to feel exactly what body part is being touched
Define 2 point discrimination
ability to distinguish the touching of two different points on the skin which are close together
Define paraplegia
paralysis of lower limbs
Define hemisection
partial transection of the spinal cord on either the L or R side
Define myelitis
inflammation of spinal cord
Define paresthesia
abnormal sensation such as burning, pricking….
