Spinal Cord Reflexes Flashcards
What are reflexes and what are there major characteristics?
- Automatic Responses to sensory stimuli
- Characteristics:
- Homeostatic responses
- Rapid
- Unconscious (Involuntary)
- Unlearned
- Stereotyped
What are differences between the two fundamental types of reflexes?
Autonomic (visceral)
- Effector is smooth muscle, cardiac muscle or glands
- Generally not consciously perceived
Somatic
- Effector is skeletal muscle
- Consciously perceived
*Some reflexes can fall in both categories
Somatic Reflexes are modified by __________
higher brain centers.
NOTE: Higher brain centers can modulate reflexes but they are NOT necessary for these reflexes. So circuit for relfexes really lies in the peripheral nervous system
Characteristics of Somatic Reflexes
The fundamental circuit for movement (voluntary & involuntary)
Provide the building blocks for complex , voluntary behaviors
Are coordinated and modulated by the cortex and brainstem
Examples of Somatic Reflexes
Stretch Reflex (myotatic reflex)
Withdrawal (Flexor) Reflex
Crossed-Extensor Reflex
Plantar (Babinski) response
The stretch reflex is also known as ___________
Tendon reflexes
Myotatic
Monosynaptic
*This is the simpliest reflex
Crossed- extensor reflex is coupled with which reflex?
Withdrawal reflex
Which reflex changes with development?
Plantar (Babinski) Response
What are the components of the reflex arc and what is the function of each?
- Sensory Receptor
* structures that detect and respond to sensory stimuli - Afferent (Sensory) Neuron
* conducts impulses from sensory receptor to CNS - Central Integrator (spinal cord synapses):
- Monosynaptic (direct contact between afferent and efferent neuron)
- Polysynaptic
- Efferent Neuron (motor neuron)
* transmitter of impulses from integrating center to effector - Effector Organ
* muscle or gland which responds to the efferent neuron
What are the components of the central integrator?
Spinal cord and all of the synapses that happen in that spinal cord
Are there interneurons found between monosynaptic spinal cord synapses?
No
What are the steps to the patella tendon/ knee jerk reflex? What type of reflex is this?
- Sensory receptor: muscle spindle
* When you hit the tendon, the muscle stretches. The sensory receptor senses a stretch in the muscle and sends action potentials through axons and stimulates the alpha-motor neuron which then causes a contraction in the muscle that was stretched. - Sensory Neuron: Type Ia fiber
* Found in dorsal root ganglion - Central Intergration: 1 synapse: Ia to Aα
* Synapses on motor neuron in ventral horn - Efferent Neuron: Α-motor neuron
* Synapses on the same skeletal muscle that gave off the sensory neuron - Effector organ: Skeletal muscle
*The patella tendon/knee jerck reflex is a stretch reflex
Spinal reflexes activate ___________ units.
Myotatic units
Whay are mytotactic units?
-
A group of agonist and antagonist muscles, which function together as a unit because they share common spinal-reflex responses.
- The agonist muscle may act in series or in parallel
- Muscles around a joint act in concert
- Divergent connection of spindle afferents establish strong neural linkages between muscles acting around a joint so that muscle do not act independent of each other.
Are stretch reflexes monsynaptic or polysynaptic?
Monosynaptic
*Though the main reflex arc is monosynaptoc, we will also have a disynaptic input. This is necessary to inhibit the antagonis muscle.
How does the stretch reflex arc inhibit the antagonist muscles?
The cell body sends out a collateral that handles this function
What are the two types of sensory receptors in skeletal muscle? What type of receptors are these?
Muscle Spindles
- Detect Stretch
- Located within the muscle
- Initiated rapid contraction of a rapidly stretched muscle
- Innervated by Ia and II fibers
Golgi Tendon Organs
- Detects muscle tension
- Located in tendon at muscle-tendon junction
- Initiates release of tension in contracted muscle
- Innervated by Ib fibers
Muscle spindles are composed of _________ fibers.
Intrafusal
Skeletal muscle is made up of _________ fibers.
Extrafusal
What are characteristics of muscle spindles?
- Imbedded within skeletal muscle bundles
- Encapsulated within a collagenous membrane
- Contains small, modified muscle cells (intrafusal fibers)
- Coupled to sensory (Ia, II) sensory fibers
- Innervated by gamma (γ) motor neurons
What is the role of gamma motor neurons in muscle spindles?
Regulate sensitivity of muscle spindles
What are the types of intrafusal fibers?
2 Types (3-15/spindle)
- Nuclear Chain (length of stretch)
- Nuclear Bag
- static bag (length of stretch)
- dynamic bag (speed of stretch)
NOTE: Intrafusal fibers don’t contribute to overall tension they just regulate the sensitivity of spindles
Which intrafusal fiber type detects length of stretch?
Nuclear Chain
Static bag
Which intrafusal fiber type detects speed of stretch?
Dynamic bag
The distal part of intrafusal fibers contain _______
Contractile fibers (actin and myosin)
Muscle spindle is localized within the __________.
Perimysium
As muscle dexterity increases, spindle density ____________ (increase/decreases).
Increases
What are the differences between group Ia and Group II sensory fibers?
Group Ia fibers:
- make annulospiral endings around central region of intrafusal fibers
- Innervate nuclear bag and nucear chain fibers
- Group Aα fibers (large, highly myelinated)
Group II fibers
- Tend to make flower spray endings
- Innervate nuclear chain and static nuclear bag fibers
- Group Aβ fibers
Firing patterns of Ia fibers respond primarily to _________ (rate/length) and II Fibers respond primarily to __________(rate/length).
Rate; length
Gamma motor neurons account for ________% of motor neurons.
30
Ia nerves innervate which fibers?
Nuclear chain fiber
Nuclear bag fiber (dynamic)
Nuclear bag fiber (static)
II nerves innervate which fibers?
Nuclear chain fiber
Nuclear bag fiber (static)
Static gamma-motor neurons innervate which fibers?
Nuclear chain fiber
Nuclear bag fiber (static)
Dynamic gamma-motor neurons innervate which fibers?
Nuclear bag fiber (dynamic)
What are characteristics of Golgi tendon organs?
- Found at the junction of the muscle fibers and the tendon
- In series with muscle fibers
- Innervated by a single large afferent fiber (Ib), which is entwined in the weave of collagen fibers that compose the receptor
- Encapsulated
- Connected to 10-15 muscle fibers
Where are golgi tendon organs found?
In tendon not muscle.
*Tension in tendon immulates tension found in muscle
What is the firing pattern of Ib fibers?
Ib has a dynamic and static response
- Dynamic response: rate of tension increase induces rapid firing in Ib fibers
- Static response: low level steady state firing that is closely proportional to the muscle tension
A golgi tendon reflex is also known as ___________
Reverse myotactic reflex
What are the stages of a golgi tendon reflex?
- Tension on tendon activates sensory neuron
- Sensory neuron stimulates interneuron
- Interneuron inhibits motoneuron
- Tension on tendon is reduced
The flexion withdrawal reflex is also known as__________
Polysynaptic reflex
Flexion withdrawal flex is in response to stimuli where?
On the skin
Flexion withdrawal reflex is elicited by__________
Various cutaneous receptors (temp, pressure, proproceptors, unexpected stimulus to skin
Flexion withdrawal reflex coordinates the contraction of _________ and inhibition of ___________ around affected joint/
Flexor muscles; extensor muscles
Polysynaptic flexor reflexes involve activation of group _____ afferents.
III
What are the stages of polysynaptic flexor reflexes?
- Activation group III afferents
- Afferent innervates excitatory interneuron in lumbar spinal cord segment
- Collateral branches of group III travel up spinal cord to higher lumber regions
- Activation of excitory interneurons innervating alpha-motor neurons to flexor muscles in higher spinal segments.
Flexor reflex is coupled to crossed-extensor reflex. What effect does this have?
uLimbs of other parts of the body will be extended to maintain balance and posture.
The withdrawal-crossed extensor reflex lasts a bit longer than other reflexes. How?
Involves circuits of excitatory interneurons that re-excite each other.
*Allows flexor activity to be maintained
What is muscle tone?
- Passive partial contraction of muscles
- Resistance to passive stretch during resting state
- Maintained by muscle spindles
- Provides a tonic innervation of muscle required for muscle health
- The excitability of the stretch reflex is used as a measure of tone.
What is used as a measure of tone?
The excitibility of the stretch reflex
Muscle tone is maintained by ___________ (muscle spindle/ golgi tendon).
Muscle spindle
Which stretch reflexes are clinically assessed? Which nerve fibers contribute to each?
vPatellar reflex (knee jerk) (L2, L3, L4)
vAchilles reflex (ankle jerk) (S1)
vBiceps reflex (C5,C6)
vTriceps reflex (C7,C8)
vBrachioradialis reflex (C5,C6)
Deep tendon reflexes rated at level are considered normal?
1,2, or 3
* Reflexes rated as 0 or 4 are usually considered abnormal
The symptoms below are associated with what type of lesion?
- Weakness (paresis)
- Hypertonia (Rigidity or Spasticity)
- Spastic paralysis
- Hyperreflexia
- Extensor plantar (Babinski) response
- Little or no muscle atrophy
Upper Motor Neuron Lessions
The symptoms below are associated with what type of lesion?
- Paresis or
- Hypotonia (flaccidity)
- Flaccid paralysis
- Hyporeflexia or areflexia
- Fasciculations or fibrillations
- Negative or absent plantar reflex
- Muscle atrophy
Lower Motor Neuron Lesion
Between damage to upper motor neurons and damage to lower motor neurons, which takes linger to be seen?
Damage to upper motor neurons
Spastic paralysis
a feature of altered skeletal muscle performance with a combination of paralysis, increased tendon reflex activity, and hypertonia
spasticity results from the loss of inhibition of motor neurons, causing excessive velocity-dependent muscle contraction.
Flaccid paralysis
an illness characterized by weakness or paralysis and reduced muscle tone without other obvious cause
When muscles enter this state, they become limp and cannot contract.
List conditions that result from CNS/ Upper Motor Neuron Signs
ALS
Brain tumor or injury
Meningitis
Multiple scleoris
Spinal cord tumor or injury
Stroke
What are the two types of hypertonia?
Spasticity
Rigidity
Which type of hypertonia is being described below?
- 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
Spasticity
Which type of hypertonia is being described below?
- 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)
Rigidity
What is the typical lesion site in cases of spasticity?
Corticoreticulospinal tract
What is the typical lesion site in cases of rigidiity?
Basal ganglia, midbrain
Which type of hypertonia is velocity-dependent?
Spasticity
Spasticity usually accompanied by what?
Clonus, hyperreflexia, clasp-knife phenomenon
Rigidity usually accompanied by what?
Tremors (cogwheel)
The 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? When does it occur?
- a series of involuntary, rhythmic, muscular contractions and relaxations.
- Sign of upper motor neuron lesions
- Causes large motions that are usually initiated by a reflex.
- Occurs only when the stretch reflex is highly sensitized by facilitory impulses from the brain.
Lead Pipe Rigidity vs. Cogwheel Rigidity
Leadpipe rigidity is sustained resistance to passive movement throughout the whole range of motion, with no fluctuations.
Cogwheel rigidity is jerky resistance to passive movement as muscles tense and relax.
Babinski Reflex
- Tests the integrity of the cortical spinal tract (CST)
- Stimulation of the lateral plantar aspect of the foot normally results in plantar flexion of toes.
- Initiated by nociceptive (pain) fibers
- Positive (abnormal in adults) Babinski response leads to contraction of toe extensors (usually inhibited by CST).
Why is positive babinski in newborns normal?
Corticospinal pathways are not fully myelinated in newborns and infants.
*Normal up to age 2 yrs
What some signs of cerebellar lesions?
Hypotonia
Depressed tendon reflexes
What role of importance does the cerebellum play?
- Cerebellum controls many important functions including coordination of muscle function.
- Cerebellar receives all proprioceptive information from body
- Indirectly regulates sensitivity and coordination of spinal reflexes
What conditions result from PNS/ Lower motor neuron damage?
- Myasthenia Gravis
- Amyotrophic lateral sclerosis (Lou Gehrig disease)
- Guillain-Barré syndrome
- Muscular Dystrophy
- Bulbar Palsy
