13.8 Reflexes

Question 1

what’s a reflex action

Answer 1

an automatic, rapid, involuntary response to a stimulus/change in the internal/external environment that occurs without the need for conscious thought

Question 2

whys the reflex arc quicker

Answer 2

because it consists of fewer synapses

Question 3

what’s the order of the reflex arc

Answer 3

stimulus
receptor
sensory neurone
relay neurone
motor neurone
effector
response

Question 4

why are reflexes important (5)

Answer 4

automatic so they don’t have to be learnt so can help with survival from birth

rapid so can reduce injury or damage to tissues

in survival can allow the animal to instinctively find food and escape from predators

enable homeostasis control eg shivering

help with things like posture and balance

Question 5

what are reflex tests and why are they used

Answer 5

they are tests carried out by doctors which have a specific predictable automatic response
they allow a doctor to determine if a persons nervous system is functioning properly & if there’s an injury

Question 6

what are the two main reflex tests

Answer 6

blink reflex & knee jerk reflex

Question 7

what are the two types of blinking reflex

Answer 7

optical & corneal reflexes

Question 8

what type of reflex is the knee jerk reflex and what do doctors use it to look for

Answer 8

it’s a spinal reflex (the neural circuit only goes up to the spinal cord and not the brain)
it’s used to check for nervous problems or cerebellar disease

Question 9

describe the knee jerk reflex and

Answer 9

The knee jerk reflex is a spinal reflex - the nervous pathway passes through the spinal cord as opposed to the brain. It is a reflex action that straightens the leg when the patella tendon is tapped.

involved in - coordinated movement and balance
caused by - unexpected increase in the length of the quadriceps
causes - the quadriceps to contract this straightens the leg.

Question 10

why does the body have the knee jerk reflex

Answer 10

as it allows you to maintain balance and posture with minimal conscious thought or effort.

Question 11

what neurone does the knee jerk reflex not use

Answer 11

relay neurone

Question 12

describe the knee jerk reflex

Answer 12

Doctor strikes the patellar tendon (by tapping just under the knee cap) - this is the stimulus. This makes the patellar tendon stretch
• The stimulus initiates a reflex arc which causes the extensor muscle on top of the thigh to contract
• At the same time, a relay neurone inhibits the motor neurone of the flexor muscle, causing it to relax
these muscles work antagonistically causing the leg to kick upwards, unless there are nervous problems

Question 13

what’s the corneal reflex

Answer 13

It’s the Involuntary blinking of the eyes when the cornea is touched- this is the stimulus. It’s used to protect the cornea from dust, moving insects, other foreign bodies

Question 14

what’s the optical reflex

Answer 14

It’s the involuntary blinking and pupil constricting when the eye is subjected to very bright light-this is the stimulus. It’s used to protect the lens and retina

Question 15

what type of reflexes are the optical and corneal reflexes

Answer 15

they are cranial reflexes- they occur in the brain and not the spinal cord

Question 16

when do doctors use the blinking reflex tests and what conclusions can be drawn from them

Answer 16

Doctors use the blinking reflex when examining unconscious patients
• If the reflex is present, then it indicates that the lower brain stem is functioning
• If the corneal reflex is absent, the patient may be diagnosed as brain dead