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 is the main reflex test

Answer 6

knee jerk reflex

Question 7

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

Answer 7

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

Question 8

describe the knee jerk reflex and

Answer 8

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 9

why does the body have the knee jerk reflex

Answer 9

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

Question 10

what neurone does the knee jerk reflex not use

Answer 10

relay neurone

Question 11

describe the knee jerk reflex

Answer 11

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