Lecture 2: Spinal Nerves and Spinal Reflex Flashcards
Dermatomes
specific area of body that is served by a single spinal nerve
Dermatomes are important b/c
loss/ alteration of function in any given dermatome signifies a lesion (damage) to a corresponding root.
Nerve Plexuses
Networks of nerves; network of compound nerve trunks
Nerve plexuses are formed during
development
Four major nerve plexuses:
- Cervical Nerve Plexuses
- Brachial Nerve Plexuses
- Lumbar Plexuses
- Sacral Plexuses
(Lumbosacral Nerve Plexuses)
Cervical Nerve Plexuses
- Innervates neck, torso, diaphragm
- Nerve Roots: C1 - C5
- Major Nerve: Phrenic (controls diaphragm)
Brachial Nerve Plexus
- 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.
Lumbosacral Nerve Plexus
- 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.
Sciatica
results from compression of the sciatic nerve by a distorted lumbar intervertebral disc.
Neural Reflexes
- Rapid, automatic responses to specific stimuli
- preserve homeostasis by making rapid adjustments in the functions of organs and organ systems.
- show little variability.
Does stretch reflex use the brain?
No, an individual can be unconscious.
Neural Reflex Process
- Stimulus
- Receptor
- Afferent Signal (Sensory neuron)
- CNS (internuerons)
- Efferent Signal (motor nueron)
- Response
Classification of Reflexes
- Development
- Nature of Response
- Complexity of Response
- Site of Integration
- Development
- Innate Reflexes: genetically or developmentally programmed.
Ex: Chewing, corneal reflex - Acquired Reflexes: conditioned reflexes, rapid and automatic but learned
Ex: driving reflexes, gaming reflexes
- Nature of Response
- 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
- Complexity of the Circuit
- 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
- Site of Intergration
- 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
Stretch Reflex (Myotatic Reflex)
- regulates skeletal muscle length
- used in postural reflexes which help maintain a normal, upright posture
Stretch Reflex Arc Process(Patellar Reflex)
- Stretch
- Activate Muscle Spindle
- Affernt Pathway
- Spinal Cord
- Efferent Motor Nueron
- Contraction
Muscle Spindles
- 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.
Gamma motor neuron
innervates each muscle spindle.
- controls sensitivity by altering tension in intrafusal fibers
- allows CNS to decrease and increase muscle tone.
- Postural Reflex
- category of stretch reflexes that help us maintain an upright, normal position.
Withdraw reflex
moves the affected body away from the stimulus.
- strong withdrawal reflexes are triggered by a painful stimulus.
- Flexor Reflex
- one type of withdraw reflex
- affects muscles of a limb
Reciprocal inhibition
keeps the extensors relaxed.
Crossed extensor reflex
- the stretch reflex and withdraw reflex involve the ipsilateral reflex arcs (sensory and motor responses on the same side of body)
Crossed extensor reflexes involve a
- 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.
In the clinical world, what are the examples of dermatomes?
Biceps. Triceps, and Patellar reflexes
it provides us with information about the status of the corresponding spinal nerve.
Babinski Test
- 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)
True or False.
The brain can either inhibit or facilitate (reinforcement) spinal reflexes.
True.
inhabitation
inhibitory neurons synapse on the postsynaptic motor neurons. Activation of the inhibitory neurons of the brain will stop action potential signals.
Reinforcement
these pathways indirectly enforce the reflex by causing a nervous system distraction.
