13.8 Reflexes Flashcards
1
Q
what is a reflex
A
an involuntary response to a sensory stimulus
2
Q
explain the steps of a reflex arc
A
- receptor = detects stimulus and creates AP in sensory neuron
- sensory neuron = carries impulse to spinal chord
- relay neuron = connects sensory neuron to motor neuron within spinal chord/brain
- motor neuron = carries impulse to effector to produce appropriate response
3
Q
describe the spinal chord
A
- column of nervous tissues running up the back
- surrounded by the spine for protection
- pairs of neurons emerge at intervals along the spinal chord
4
Q
describe the knee-jerk reflex
A
- spinal
- helps maintain posture and balance
- absence may indicate nervous problems and multiple oscillation of the leg may be sign or cerebellar disease
- leg tapped below the kneecap
- patellar tendon stretches and acts as stimulus
- extensor muscle on thigh contracts
- relay neuron inhibits motor neuron of flexor muscle causing it to relax
- contraction of coordinated muscle and relaxation of antagonistic flexor causes leg to kick
5
Q
describe the blinking reflex
A
- 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
- cornea is irritated
- impulse sent along sensory neuron
- passes through relay neuron in lower brain stem
- impulses sent to branches of motor neuron
- eyelids close
6
Q
what is the optical reflex
A
blinking as a reaction to over-bright light
7
Q
how do reflexes increase chances of survival
A
- 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
