Simple reflexes Flashcards
What is a reflex?
Neural reflexes are stereotyped (predictable) involuntary reactions of the CNS to specific sensory input.
They enable an involuntary, rapid response.
Controlled by somatic and autonomic nervous system.
What are the general functions of reflexes?
Protective - e.g. limb withdrawal, cough reflex.
Postural control - walking
Homeostasis - e.g. blood pressure stability
What is the reflex arc?
Sensory receptor - afferent - intergration - efferent - effector
What are interneurones?
Used for intergration - input into and from the reflex arc.
Communicates with other parts of the nervous system.
What are efferent neurones?
Motor neurones that innervate effectors - take the information from the spinal cord to the effectors.
What are afferents?
Sensory neurones that take information from the body to the CNS.
What are sensory receptors?
Detect the sensory stimulus.
What are effectors?
Carry out an appropriate response.
Glands, muscle - skeletal (somatic), cardiac and smooth (autonomic).
What are simple stretch reflexes?
Myotatic
Important for posture
Adjust the degree of muscle contraction
Sensory receptors - proprioceptors - muscle spindles and golgi tendon organs.
What is the appearance of muscle spindles?
Thin at either end, thick in the middle - spindle shaped.
No striated appearance - sensory nerve endings wrapped around them - afferents.
How are muscle spindles simple?
There are no interneurones involved.
The afferent directly controls the activity of the efferent neurone to innervate the effector.
What is monosynaptic?
Only one synapse
Muscle spindles are monosynaptic.
What is the muscle spindle reflex arc?
Stretch activates the sensory receptor - e.g. a weight.
The weight stretches the muscle, stretches the muscle spindle.
This activates the action potential in the sensory neurones.
Drives increase in motor activity in motor efferent, as synapse has excitatory neurotransmitter.
AcetylCholine released, and muscle contracts to prevent damage.
What is the knee jerk reflex?
Tap below knee stretches the tendons of the quadriceps, activates muscle spindles.
This activates the sensory axons - information to CNS.
Sensory input neurone branches - one goes to contract one of the muscle pairs by the afferent which goes straight to the efferent, one goes to relax the other muscle.
How does muscle relaxation occur from the knee jerk reflex?
The other branch from the sensory input goes to an interneurone, activated and produces inhibitory neurotransmitter.
This prevents the motor efferent from firing.
This happens stimultaneously to the contracting muscle.
Where are Golgi Tendon organs?
In the tendon are sensory neurones with bare nerve endings.
What is the type of interneurone in the Golgi Tendon organ circuit?
Inhibitory
What is polysynaptic?
There are mutiple synapses.
The golgi tendon organ arc is polysynaptic.
What is the Golgi Tendon organ reflex arc?
Contraction stretches the tendon, which activates the GTO.
Action potentials in the sensory neurones, releases excitatory signals to spinal cord.
Interneurone is activated and inhibits the efferent - the muscle stops contracting.
What is the function of the golgi tendon organ?
It is a reverse myotatic reflex.
So it prevents damage due to overwork by over-contracting.
Fine control of muscle tension.
What is the complexity of the crossed extensor reflex?
Same-sided connections for sensory and motor neurones innervating the same leg.
To innervate the other leg, the axons must cross over, interneurones allow this.
Through having separate excitatory and inhibitory pathways can contract and relax the muscles to produce a response.
