13.8 Reflexes

Question 1

what is a reflex

Answer 1

an involuntary response to a sensory stimulus

Question 2

explain the steps of a reflex arc

Answer 2

1. receptor = detects stimulus and creates AP in sensory neuron
2. sensory neuron = carries impulse to spinal chord
3. relay neuron = connects sensory neuron to motor neuron within spinal chord/brain
4. motor neuron = carries impulse to effector to produce appropriate response

Question 3

describe the spinal chord

Answer 3

• column of nervous tissues running up the back
• surrounded by the spine for protection
• pairs of neurons emerge at intervals along the spinal chord

Question 4

describe the knee-jerk reflex

Answer 4

• spinal
• helps maintain posture and balance
• absence may indicate nervous problems and multiple oscillation of the leg may be sign or cerebellar disease

1. leg tapped below the kneecap
2. patellar tendon stretches and acts as stimulus
3. extensor muscle on thigh contracts
4. relay neuron inhibits motor neuron of flexor muscle causing it to relax
5. contraction of coordinated muscle and relaxation of antagonistic flexor causes leg to kick

Question 5

describe the blinking reflex

Answer 5

• cranial
• occurs when cornea is stimulated and acts to protect cornea from damage due to foreign bodies
• also occurs when sounds greater than 40-60db are heard or bright light is seen
• absence suggests bran stem isn’t functioning therefore patient is brain dead

1. cornea is irritated
2. impulse sent along sensory neuron
3. passes through relay neuron in lower brain stem
4. impulses sent to branches of motor neuron
5. eyelids close

Question 6

what is the optical reflex

Answer 6

blinking as a reaction to over-bright light

Question 7

how do reflexes increase chances of survival

Answer 7

• by being involuntary responses (brain can deal with more complex responses as decision-making areas sent involved so prevents brain being overloaded)
• not having to be learnt (present at birth so provide immediate protection)
• extremely fast (normally only 1/2 synapses)
• many are everyday actions e.g. keeping us upright and controlling digestion