Reflexes

What can the body do when it is in danger?

Respond to situations without conscious thought, causing a faster response, preventing or minimising damage to the body - a reflex action.

What is a reflex?

An involuntary response to a sensory stimulus.

What is the pathway of neurons involved in a reflex action known as?

A reflex arc, most reflexes follow the same steps between the stimulus and the response.

What is the order of neurons in a reflex action?

Receptor → Sensory Neuron → Relay Neuron → Motor Neuron

What is the role of receptors in the reflex arc?

They detect the stimulus and create an action potential in the sensory neuron.

What is the role of sensory neurons in the reflex arc?

They carry the impulse to the spinal chord.

What is the role of relay neurons in the reflex arc?

They connect the sensory neuron to the motor neuron within the spinal chord or brain.

What is the role of motor neurons in the reflex arc?

They carry the impulse to the effector to carry out the appropriate response.

Who is the knee-jerk reflex commonly tested by?

Doctors.

What kind of reflex is the knee-jerk reflex?

A spinal reflex - it only goes up to the spinal chord, not the brain.

What happens when the leg is tapped just below the kneecap (patella)?

It stretches the patellar tendon and acts as a stimulus. This stimulus initiates a reflex arc that causes the extensor muscle on top of the thigh to contract. At the same time, a relay neuron inhibits the motor neuron of the flexor muscle, causing it to relax. This contraction, coordinated with the relaxation of the antagonistic flexor hamstring muscle, causes the leg to kick.

What happens after the tap of a hammer?

The leg it normally extended once and comes to rest.

What may the absence of the knee-jerk reflex indicate?

Nervous problems and multiple oscillation of the leg may be a sign of cerebellar disease.

What are reflexes essential for?

Survival, as they avoid the body being harmed, or reduce the severity of any damage.

How do reflexes increase the chance of survival?

• By being involuntary responses.

• Not having to be learnt.

• Extremely fast.

• Being everyday actions.

How do reflexes being involuntary increase survival chances?

The decision-making regions of the brain are not involved, therefore the brain is able to deal with more complex responses. It presents the brain from being overloaded with situations in which the response is always the same.

How are reflexes not having to be learnt a survival importance?

They are present at birth and therefore provide immediate protection.

How do reflexes being extremely strong a survival importance?

The reflex arc is very short. It normally only involves one or two synapses, which are the slowest part of nervous transmission.

How are reflexes being everyday actions a survival importance?

Many reflexes are what we would consider everyday actions such as those which keep us upright, and those which control digestion.