Reflexes Flashcards
What is a reflex?
An involuntary, stereotyped (same type of response is provoked with the same type of stimulus) response to a stimulus
What are reflex circuits?
Begin with receptors
End with effectors
Do not reach consciousness
What type of circuits are reflex circuits?
Simplest circuits in the nervous system
What are tendon jerk reflexes?
Muscle contractions produced by muscle stretch
What can tendon jerk reflexes be evoked from?
Many muscles where tendon is accessible
What does tapping a tendon do?
Stretches muscle to which it is attached
What does tapping a tendon elicit?
A monosynaptic reflex that produces contraction of the stretched muscle
What are the basic elements of a reflex circuit?
Element Example of tendon jerk reflex
- adequate stimulus e.g. tendon tap (muscle stretch)
- Receptor e.g. muscle spindle
- Afferent (sensory) neurone) e.g. La primary afferent
- Central synapses e.g. monosynaptic
- Efferent (motor) neurone e.g. alpha- motorneurone
- Effector e.g. skeletal muscle
What accompanies the tendon jerk reflex?
La reciprocal inhibition
What is simultaneously evoked with the tendon jerk reflex?
Inhibition of antagonist muscle
What is la reciprocal inhibition mediated by?
An interneurone- la inhibitory neurone
What type of pathway is the tendon jerk and la reciprocal inhibition?
Disynaptic (2 synapses)
How does la reciprocal inhibition operate?
In each direction between antagonistic muscles at a joint- hence reciprocal inhibition e.g. stretch of quadriceps muscle causes inhibition of hamstring muscle
What are excitation of muscle spindles responsible for?
Stretch reflex
What is the tendon jerk reflex useful for?
Clinically, but is a response to an artificial stimulus
What is the stretch reflex?
Normal function of the monosynaptic reflex circuit
What does prolonged stretch produce?
Prolonged contraction
What to stretch reflex act to maintain?
Constant muscle length
What is an example of a closed loop in the vestibulo-occular system?
Moving your finger but trying to concentrate on moving finger
What is an example of a open loop in the vestibulo-occular system?
Looking at finger while moving head
What do both the open and closed loop do in the vestibulo-occular system?
Stabilise the visual image
What is visual pursuit?
Movements of object relative to eyes
What is a control reflex?
Closed loop
Control some physiological variable e.g. stretch reflex control muscle length
What does a stimulus trigger in a control reflex?
Actions which feedback on stimulus e.g. stretch of muscle leads to a reflex response (muscle contraction) which returns the muscle to its original length
What is a protective reflex?
Open loop
What does a protective reflex not affect?
Stimulus e.g. flexion withdrawal reflex
What is a protective reflex accompanied by?
Crossed extensor reflex (both are polysynaptic)
What are flexor reflex and crossed extensor reflex mediated by?
Chains of interneurons- polysynaptic (many synapses)
What do excitatory and inhibitory interneurones produce?
Appropriate actions on different motoneurone pools
What is an example of pathways showing divergence?
Motoneurones with actions at hip
what is the carotid sinus baroreceptor reflex?
Autonomic reflex regulating blood pressure
What does the carotid sinus baroreceptor reflex control?
Heart rate and force of contraction (cardiac output)
Diameter of blood vessels (peripheral resistance)
What are the two ways to change blood pressure
BP= CO x TPR
I.e. Cardiac output or total peripheral resistance
What do reflexes involve?
Both somatic and autonomic nervous systems
What is the somatic nervous system involved in with regards to reflexes?
(Skeletal muscles)
Spinal cord/ brain stem- mainly control movement of limbs and eyes
What is the autonomic nervous system involved in with regards to reflexes?
(Smooth muscles)
Mainly control physiological system
Why does the responses being automatic and rapid well suit reflex responses?
Well suited to processes of continuous regulation e.g. baroreceptor
Suited to rapid protextice responses e.g. flexion withdrawal reflex
Why are reflex circuits used by higher centres?
Spinal reflex circuits are used descending systems to control movement
