Spinal Cord Reflexes Flashcards
What are Reflexes?
Automatic Response to sensory stimuli
What are the characteristics of reflexes?
Homeostatic responses
Rapid Unconscious (involuntary)
Unlearned S
terotyped (same in every body)
What autonomic (visceral) reflexes
- effector is smooth muscle, cardiac muscle, or glands - generally not consciously perceived
What are somatic reflexes?
- Effector is skeletal muscle
- Consciously perceived
Pupillary light Reflex What type of reflex is this?
Autonomic reflex
Cough Reflex
What type of reflex is this?
Mixed reflex (both autonomic and somatic)
Withdrawal Reflex
What type of reflex is this?
Somatic Reflex
What are somatic reflex modified by?
By higher brain center
- fundamental circuit for movement (involuntary and voluntary)
- Provide the building blocks for complex, voluntary behaviors
- are coordinated and modulated by the cortex and brainstem
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Stretch reflex, withdrawal reflex, crossed extensor reflex, and plantar response are examples of what type of reflex?
Somatic reflex
Stretch Reflex (myotatic)
Also called, deep tendon reflex or monosynaptic reflex Knee Jerk Reflex
- Sensory receptor - muscle spindle
- Sensory neuron- cell body in DRG - Type 1a fiber
- Central integration: 1 synapse: 1a to Aa
- Efferent Neuron: A- motor neuron
- Effector organ: skeletal m.
These two reflexes are coupled
Withdrawal Reflex (Flexor) AND Crossed-Extensor Reflex
Plantar (Babincki) Reflex
changes with development
What are the components of the reflex are?
- Sensory Receptor
- Afferent (Sensory) Neuron
- Central Integrator (spinal cord and synapse)
- Efferent Neuron (motor neuron)
- Effector Organ
Sensory Receptor
structures that detect and respond to sensory stimuli
Afferent (sensory) neuron
conducts impulse from sensory receptor to CNS
Central Integrator
Monosynaptic (direct contact between afferent and efferent neuron; no interneurons) vs polysynaptic
Efferent neuron
transmitter of impulse from integrating center to effector
Somatic reflexes is always going to involve the motor neuron
Effector organ
muscle or gland which responds to the effector
Myotatic units are activated by ?
Activated by Spinal Reflexes Myototic units are a group Agonist and antagonist muscle from common spinal reflex response, function together
How do agonist muscles behave?
In parallel
How do Muscles around a joint behave?
In concert
What establishes a strong neural linkage between muscles acting around a joint so that muscle do not act independent of each other?
Divergent connection of spindle afferents
What is Reciprocal Inhibition?
Even though the main arc in monosynaptic, you will have a disynaptic unit that synapses with a inhibitory intermotornueron in spinal cord and then makes a synapse with the alpha motor neuron and goes to the antagonist muscle
What are muscle spindles?
- detect stretch
- located within the muscles
- initiated rapid contraction of a rapidly stretched muscle
- innervated by Ia and II fibers
What is a goggle tendon organ (Proprioceptors)?
- detect muscle tension
- located in tendon at muscle-tendon junction, encapsulated, connected to 10-15 muscle fibers
- initiates release of tension in contracted muscle
- innervated by a single large afferent Ib fibers (entwined in the weave of collagen fibers that compose the receptor)
- in series with muscle fibers
What are twi types of muscle spindles (Proprioceptor)?
Some respond to the speed of the stretch and others respond to the strength of the stretch
What are muscle spindle fibers composed off?
Intrafusal fibers
Whats are the intramural fibers of a muscles embedded in?
Skeletal muscle bundles also known as extrafusal fibers (these are the main cells of contraction.
What are the characteristics of a muscle spindle?
- Encapsulated (collagenous membrane)
- Within perimysium
- Spindle shaped
- coupled to sensory neurons (1a, II)
- sensory fiber
- innervated by gamma motor neurons ; regulated at distal end
NO CONTRIBUTION TO MUSCLE TENSION
Intrafusal fibers with Bulbous center region
Nuclear bag fibers Types:
- static bag
- length of stretch
- dynamic bad
- speed of stretch
Intrafusal fibers with Slender one
nuclear chain fibers Length of stretch
The sarcomeres/contractile fiber part and the nuclei are located where in the spindle?
Distal end and middle, respectively
What modulates the sensitivity of the spindle?
Contraction
As we age what happens to the muscle spindle/skeletal muscle?
You will se more fat within spindle and muscle
Group Ia Fibers
- make annulospinal endings around central region of intramural fiber
- innervate nuclear bag and nuclear chain fibers - Group Aa fibers
- large, highly myelinated Very responsive when the muscle is initially being stretched and then stabilizes it
Group II fibers
- make flower spray endings
- innervate nuclear chain and static nuclear bag fibers
- group alpha-beta fibers
What are gamma motor neurons?
- cell bodies located in the spinal cord ventral horns (just like alpha motor neurons)
- make up 30% of motor neurons
- Type A gamma (5) nerve fibers are smaller than type A alpha (14)
- innervate intrafusal fibers
- receive input from higher centers
What is the purpose of gamma motor neurons?
Adjust spindle sensitivity (they are co-activated with alpha neurons) by stretching the intrafusal fibers during muscle contraction so that they respond to small stretch of muscle = increase gain
Static gamma-motor neurons act on which type of intrafusal fiber?
Nuclear bag fiber (static)
Nuclear chain fibers are acted on by which type of gamma motor neurons?
dynamic gamma motor neurons
Random addition of load to a stretched muscle causes what?
Increase firing of the Ia fiber mainly and II fires mildly-> reflex contraction done by alpha motor neurons This happens because of lack of tension in the muscle
What happen when the person is aware of increase in load?
They are going prepare themselves -> increase tension to hold load -> nothing happens really
What is the firing pattern of Ib fiber?
Ib has a dynamic and static response
Define a dynamic respinse
rate of tension increases induces rapid firing in Ib fibers
Define a static response
Low level of steady state firing that is closely proportional to the muscle tensio. Firing increases and tension increases
Gogli tendon/reverse Myotactic Reflex
- Tension on tendon activates sensory neuron
- Sensory neuron stimulates interneuron
- Interneuron inhibits motor neuron
- Tension on tendon is reduced
What is the Flexion Withdrawal Reflex
It is a polysynaptic reflex
- response to stimuli on the skin (often injurious stimuli)
- elicited by various cutaneous receptors: temperature, pressure, proprioceptors, unexpected stimulus to skin
- coordinates the contraction of flexor muscles and inhibition of extensor muscles around affected joint
Afferent neurons for withdrawal reflex include
Touch/pressure fibers (Group I or II) (As, Alpha-beta)
Pain fibers (Group III or IV) ( alpha-delta, C)
Steps in Polysynaptic Reflex in respinse to stepping on a sharp tack
Activation of group III afferents
Afferents innervate excitatory interneuron in lumbar spinal cord segment
Collateral branches of Group III travel up spinal cord to higher lumbar regions (to flex multi-joints)
Activation of Excitatory Interneurons innervating alpha-motor neurons to flexor muscles in higher spinal segment
During a response to stepping on a sharp tack limbs of other parts of the body will be extended to maintain balance and posture. Why is that?
Because flexor reflex is coupled to crossed extensor reflex
What is the cross extensor reflex?
Collateral cross midline on the spinal cord to synapse with alpha motor neuron on the opposite side of the body (from initial reflex) to complete and opposite reaction
Why is the withdrawal-crossed extensor reflex prolonged whereas the stretch reflex is quick?
Because of reverberating circuits
(They are responsible for maintained flexor activity)
What do Reverberating circuits involve?
Excitatory interneurons that re-excite each other
What is muscle tone?
Resting Muscle tension
What does muscle tone involve?
- passive partial contraction of muscle
- resistance to passive stretch during resting state
- maintained by muscle spindles
- provides a tonic innervation of muscle required for muscle health
How do you measure tone?
The excitability of the stretch reflex
Dendrastic manœuvre -
ask person to contract a body part thats above where you want to elicit the reflex (pull at or right before tap)
Lesion in a upper motor neuron causes what?
- weakness (paresis)
- hyperopia (rigidity or spasticity)
- Spastic paralysis
- Hypereflexia
- Extensor plantar (Babinski) response
- little or no muscle atrophy
Lesion in a lower motor neuron causes what?
- paresis
- hypotonia (flaccidity)
- flaccid paralysis
- hyporeflexia or areflexia
- fasciculations or fibrillations
- negative or absent plantar reflex muscle atrophy
What is the (Babinski) response
Stimulate sensory receptor on the foot laterally -> Adult gets plantar flexion Child gets dorsiflexion
Whats the difference between fasciculations and fibrillation?
Fasciculations - whole motor unit contracts
Fibrillations - one specific muscle cell contracts
Fasciculations are more noticeable
Amyotrophic lateral Sclerosis (Lou Gehrig disease), Brain tumor, Meningitis, MS, Spina cord injury, and stroke are associated with what type of lesion?
Lower Motor Neuron lesion
Hypertonia involves what two things?
Spasticity and rigidity
Define Spasticity
- Typical Lesion Site: Typically corticoreticulospinal (pyramidal) tract.
- Resistance is pronounced in one direction.
- Resistance is velocity and force dependent.
- Accompanied by clonus, hyperreflexia, clasp-knife phenomenon
Define Rigidity
- Typical Lesion site: Basal ganglia, midbrain
- Increase in muscle tone with resistance to passive movement
- No weakness
- Independent of velocity
- Resistance is uniform in both directions.
- Accompanied by tremors (cogwheel)
Seen in Parkinson’s disease
What is Clasp Knife Spasticity?
Spastic limb initially resists movement and then suddenly releases the tension.
Dysregulated Golgi tendon organ reflex
Loss of regulatory UMNs
What is Clonus?
Pathological oscillation of muscle reflex
How do you test the integrity of the corticospinal tract?
The Babinski Reflex (upper motor neuron)
Initiated by nociceptive (pain) fibers
What is a Positive Babinski response
Abnormal in adults contraction of toe extensors (usually inhibits by Corticospinal tract)
What does the Cerebellum control?
Cerebellar receives all proprioceptive information from body
Indirectly regulates sensitivity and coordination of spinal reflexes
Hypotonia and depressed tendon reflexes are signs for?
Cerebellar Lesion
T/F Positive Bibinski Response in normal in a 1 year old
True.
It is normal in newborns all the way to age 2.
Corticospinal pathways are not fully myelinated in newborns and infants
What resembles a lower motor neuron lesion because the signs it presents are similar to lower motor neuron lesion?
Cerebellar lesion
What are some conditions resulting in PNS/LMN (lower motor neuron) signs?
Myasthenia Gravis
Amyotrophic lateral sclerosis (Lou Gehrig disease) Guillain-Barré syndrome
Muscular Dystrophy
Bulbar Palsy
Assesment of L1, L3, and L4 is done by?
Patellar REflex (knee jerk)
Assesment of S1 is done by?
Achilles reflex (ankle jerk)
Bicep reflex assesses which part of the spinal cord?
C5 and C6
Assesment of C7 and C8 involves what type of test?
Triceps Reflex
Brachioradialis reflex test assess which part of the spinal cord?
C5 and C6
Rating of Deep tendon reflex
Deep tendon reflexes rated 1+, 2+, or 3+ are normal unless
- Asymmetry (left vs. right)
- Dramatic difference between the arms and the legs.
Reflexes rated as 0 or 4+are usually considered?
Abnormal
