Reflexes
Reflex Arc
- A body can respond to danger unconsciously in something known as a reflex.
- A reflex follows these basic steps:
- Receptor detects stimulus and creates an action potential in the sensory neurone.
- Sensory neurone carries impulse to spinal cord.
- Relay neurone connects sensory neurone to motor neurone in the brain or spinal cord.
- Motor neurone carries an impulse to the effector to carry out the appropriate response.
- Effector organ changes in response to stimulus to avoid harm.
- The spinal cord is a column of nervous tissue running up the back, surrounded by the spine for protection. Pairs of neurones join the spinal cord at intervals.
Knee Jerk Reflex
- A neural circuit; it only goes to the spinal cord, bypassing the brain.
- Leg is tapped below the patella, causing the patellar tendon to stretch and this is the stimulus. This initiates a reflex arc causing the thigh extensor muscle to contract. Simultaneously the flexor is relaxed. This causes the leg to kick.
- The absence of this reflex can indicate nervous problems, whereas multiple kicks can be a sign of cerebellar disease.
- This reflex's purpose is to help us maintain posture and stay balanced.
- A cranial reflex; it occurs in the brain, not the spinal cord.
- Causes the eyelids to rapidly close in order to protect the eye when the cornea is stimulated by touch, loud sounds or bright light.
- Corneal reflex if response to touch, Optical reflex if response to light.
- Cornea is irritated by foreign body, triggers an impulse along a sensory neurone, passes through relay neurone in the brain stem, impulse sent along motor neurone to cause the eyelids to close.
- Consensual response meaning both eyelids close even though only one may be irritated.
- Crucial for survival as the avoid the body being harmed/act as damage limitation.
- Involuntary means the decision making brain is not overloaded with information.
- Inate means we don't have to learn them and therefore provide immediate protection.
- Rapid means the reflex arc is very short as few synapses are involved, meaning quicker response to harm.
- Many reflexes help with day to day actions such as standing upright and digestion.
- Measuring time taken to catch a falling object measures reaction time.
- Hold a ruler with a suitable scale at 0 in line with the participants fingers.
- Drop the ruler and calculate reaction time.
- Do multiple attempts under the influence of different substances such as caffeine or heroin.