Reflex & Voluntary Control of Posture & Movement Flashcards
Define reflex activity
subconscious response brought about by PNS stimulation
Reflex arc is
the basic unit of integrated reflex activity/nervous pathway for a reflex action
5 components of a reflex arc are?
- Receptor/Sense/End organ
- Sensory/Afferent neuron
- Integration center
- Motor/Efferent neuron
- Effector organ
Define effector organ
the structure in which response to stimulus occurs
Name reflexes classified according to their function
Extensor/anti-gravity reflex
Flexor/protective reflex
Give two examples of monosynaptic reflex.
Knee-jerk reflex
Stretch reflex
Differentiate monosynaptic from polysynaptic reflexes
Monosynaptic have only one synapse between the sensory neuron and the motor neuron at the integration center
Polysynaptic reflexes involved interneurons inbetween the sensory and motor neuron
Classic example of polysynaptic reflex
withdrawal reflex
Difference between autonomic and somatic reflexes
Autonomic - made of autonomic fibers, involve smooth and cardiac muscle
Somatic - made of somatic nerve fibers, involve skeletal muscle (for flexion and extension at joints)
State the types of reflexes based on clinical significance
Superficial reflexes (mucous membrane reflexes like corneal reflex and conjunctival reflex and skin reflexes) Deep reflexes (ellicited from structures deep to skin like tendons) Visceral reflexes (include oculocardiac reflex, carotid sinus reflex, & pupillary reflex)
What are pathological reflexes?
Those ellicited only in pathologic conditions
State the conditions under which individuals show positive Babinski sign.
- UMN lesions
- In infancy because pyramidal tracts are unmyelinated
- During deep sleep
Name three types of pathological reflexes
- Babinski reflex
- Clonus
- Pendullar movements
What is clonus?
Repeated, jerky involuntary movements when deep reflex is initiated, instead of it being smooth and continuous
What stimulus causes ankle clonus and what is the response?
Sudden dorsiflexion of foot initiates repeated plantar flexion as calf muscles repeatedly contract
What are the properties of reflexes?
*Hint: there are 7
- One-way conduction / Bell-Magendie law
- Reaction time
- Summation
- Definite recruitment
- After discharge
- Rebound phenomenon
- Fatigue
Define a subliminal stimulus
One that is not enough to initiate a reflex; threshold is below conscious perception
What are the two types of summation in a reflex arc?
Spatial summation
Temporal summation
Differentiate spatial summation from temporal summation.
Spatial summation involves more than one efferent nerve fiber supplying the same muscle such that when a subliminal stimulus is applied separately to each, there is no response, but when all are stimulated at once, it causes the muscle to contract
Temporal summation refers to one nerve fiber supplying a muscle. When subliminal stimulus is applied, there is no response, but when it is applied continuously, then over time it is summated to cause contraction of the muscle.
How is sublimal fringe related to spatial summation?
It’s a phenomenon in which the tension developed when nerve fibers are stimulated all together at once is greater than if they are stimulated separately. Spatial summation requires that nerve fibers must have subliminal stimulus applied so that there can be a response.
Sublimal fringe is an effect of spatial summation.
*NOTE: applies to nerve fibers that DO NOT overlap
How is occlusion different from sublimal fringe?
While sublimal fringe the tension developed is greater when both fibers are stimulated at the same time, in occlusion, the tension developed is greater if both fibers are stimulated separately than if they they are stimulated all at once.
Occlusion is a result of overlapping fibers while sublimal fringe is seen in non-overlapping fibers
Define recruitment.
successive activation of muscle fibers (motor units) to increase force of contraction
Factors affecting reaction time.
- Velocity of conduction
- Synaptic delay
- Length of axon
Where is the first place fatigue occurs in a reflex arc?
Integration center
Reciprocal innervation is a result of …
reciprocal innervation
Describe the crossed extensor reflex.
Seen in UMN lesions, it’s when in one limb extension and flexion of a group of muscles occurs, and in the opposite limb, the opposite group of muscles are extended and flexed
Factors that cause increase in gamma motor neuron discharge.
Sudden unexpected movements
Stress and anxiety
Stimulation of skin especially by noxious stimuli
Descending excitatory input from brain
What does ‘alpha-gamma coactivation’ imply?
When excitatory signals descend through spinal cord from brain, both alpha and gamma motor neurons are activated
What’s the difference in the effects of activation of gamma and alpha motor neurons on muscle contraction?
When gamma motor neurons are activated, they don’t cause a direct contraction. Instead, they cause shortening of intrafusal fibers = stretch of nuclear bags of spindles = impulses initiated in Ia fibers = reflex contraction of muscle
When alpha motor neurons are activated, they directly cause contraction because they innervate the extrafusal fibers which unlike the intrafusal fibers are strong and plenty enough to cause contraction
State the two kinds of afferent fibers to muscle spindles
- only one primary ending (group Ia fibers)
2. up to 8 secondary endings (group II fibers)
Give the functions of Ia afferents and group II afferents?
Ia fibers detect velocity of change in muscle length (dynamic response)
Group II afferents detect static response (which does not involve change in length)
Hyperactive reflex means what part of the reflex arc is damaged?
The descending fibers in the spinal cord involved in inhibition are no longer inhibiting the alpha motor neurons
Differentiate afferent Ia and II sensory endings from group Ib fibers?
*BOTH ARE MYELINATED
Ia and II fibers
-are found in stretch spindles
Ib fibers
-are find in Golgi tendon organs
The receptor for the inverse stretch reflex is the…
Gogli tendon organ
True or false: Golgi tendon organs have high threshold.
False: Golgi tendon organs have a low threshold
3 factors determining discharge of alpha motor neurons.
- Stretch spindle discharge
- Golgi tendon organ discharge
- Reciprocal innervation
Describe the mechanism of the withdrawal reflex.
- Noxious stimulus is applied and nociceptors shoot off signals
- Signals travel through primary sensory neurons
- Primary sensory neurons synapse with interneurons
- Interneurons synapse with alpha motor neurons
- alpha motor neurons go to supply the ipsilateral flexors’ extrafusal fibers causing flexion
- at the same time collateral branches cause inhibition of extensors (reciprocal inhibition)
*at the same time the primary sensory neuron synapses with ipsilateral alpha motor neurons, it also synapses with the contralateral alpha motor neurons which sends signal up spinal cord to causes contraction of contralateral antigraviy muscles to prevent person from losing balance.
