Simple Reflexes Flashcards
What are the characteristics of a reflex?
They are stereotyped involuntary reactions of the CNS to a specific sensory input.
They produce a rapid response
Give some of the functions of reflexes:
Protective
e.g. cough, limb withdrawal
Postural
walking don’t have to think about walking
Homeostasis
mainly autonomic reflexes e.g. maintain BP
Clinical relevance?
stereotyped so can be used to asses the health of the nervous system
is something isn’t happening you know something is wrong
What are the components of a reflex arch
Sensory receptors (generator potential)
Afferent neurones (Generation of AP pass to the integration centre CNS)
Integration
can involve interneurones that allow for modulation adjusting of the signal if there is a change in the environment
Efferetn neruonnes (interneurones communicate with efferent neurones somatic efferent a motor neurones that innervate SK muscle also autonomic efferents too)
Effectors
glands or muscles bring about a response
What is the myotatic stretch reflex?
Stretch and relax muscle
Increases the length of muscle lengthening intrafusal muscle fibres in the muscle spindle
This distorts sensory nerve endings
If the stretch is large enough mechanically gated Na+ ion channels open causing generation of AP in sensory neurone
AP passes to the spinal cord where it directly synapses with a motor efferent through the release of an excitatory NT
This results in muscle contraction and prevents damage of the SK muscle by over stretching of sarcomeres
Need the contraction to enable you to move weights when you pick stuff up
What is a msucle spindle
spindle shaped structure located in the belly of muscles
Has internal intrafusal muscle fibres with many sensory nerve endings wrapped around them acting as sensory receptors detecting changes in muscle length preventing damage and over stretching
These nerve endings come form the fusion come form a gamma motor neurone
What type of reflex is the knee jerk reflex?
Polysynaptic reflex
Describe the knee jerk reflex
Tap patellar tendon
stretching of the muscle resulting in spindle stimulus sensory afferent AP to spinal cord
Sensory afferent branches in spinal cord
directly synapses with a motor neurone and releases excitatory NT this causes increased activity of the MN and contraction of the quadriceps muscle
The other branch synapses with an interneurone
releases excitatory NT that stimulates the interneurone
Interneurone produces inhibitory NT that inhibits. the a motor neurone supplying the hamstring muscles resulting in relaxation
this results int he leg kicking out
What is a Golgi tendon organ?
Located within tendons
many loosely arranged collagen fibres between which are sensory nerve fibres
Muscle contracts collagen fibres straighten and compress the nerve endings
Polysynaptic reflex the interacts with inhibitory interneurones that then interact with motor efferents
Outline the polysynaptic Golgi tendon organ reflex
tendon pulled on due to increase muscle contraction
collagen fibres straighten pressure on sensory nerve endings threshold met AP generated
passes through sensory afferents to SC synapse with inhibitory interneurone increase activity through release of excitatory NT
increased activity of interneurone release of inhibitory NT, inhibits motor efferent causing muscle relation to prevent damage
What is the function of the Golgi tendon refelx
To prevent damage due to overworking of muscles prevents extreme contractions that could cause muscle to tear or tendon to tear
Withdrawal reflex outline?
Step on pin
activates nociceptors in the foot
SN arrives in cord part of spina cord want rapid withdrawal therefore it branches multiple times
some branches transmit AP to the brain to make it aware you are experiencing pain
other branches interact with excitatory interneurones Inc activity release of excitatory NT increases the activity of motor efferent resulting in contraction of the flexor muscle
some branches also interact with inhibitory interneurones activating them through release of excitatory NT/ Inc activity of interneurones release of inhibitory NT this causes inhibition of motor efferent allowing for muscle relation and limb withdrawal
Must singal other leg to support weight of body when we withdraw this leg via activation of other neruones on the other side of the spinal cord
3rd branch of sensory neurone endings will tigger a series of excitatory interneurones that excite motor efferent located in anterior horn on left side resulting in contraction of quadriceps muscle
4th branch of sensory neurone endings will initially involve excitatory interneurones and then an inhibitory interneurone that inhibits the motor efferent supplying the hamstrings resulting in relaxation
This allows the leg to support the body weight as we withdraw the other leg.
