examples of reflex actions

knee- jerk reflex

- is a spinal reflex
1. the patella (kneecap) is tapped, stretched out the patella tendon
2. stimulus initiates a reflex that causes the extensor muscle (on top of the thigh) to contract
3. at the same time:
relay neurone inhibits the motor neurone of the flexor muscle, causing it to relax
4. contraction of the externer muscle and relaxation of the flexor antigonistic hamstring muscle causes the leg to kick

why is this reflex needed?

- balance
- posture
absence of this reflex:
may indicate nervous problems
can be a sign of cerebellar disease

blinking reflex

- is a cranial relfex
1. sensory nerve endings in the corneal are stimulated by stimuli (e.g touch)
2. nerve impulse is sent along the sensory neurone to a relay neurone in the CNS
-> impulse is passed from the relay neurone to the motor neurone
-> motor neurone sends impulse to the effectors (orbicularis oculi muscles)
the muscles contract causing the eyelids to close, preventing damage

how do reflexes increase the chances of survival?

- they're involuntary
no need for decision making
- are innate
born with the reflex actions, no need to learn, instant protection
- very fast
reflex arc is short