ReFlex actions &reflex arcs
- Reflex action – rapid, automatic, involuntary response to a stimulus. They are not under conscious control and have survival value.
- Reflex arc – the specific pathway taken by the nerve impulses in a reflex action.
- Characteristics of reflexes:
- Involve a receptor and an effecter
- They are rapid, because they only involve few neurones and synapses
- They are automatic and involuntary, the same stimulus produces the same response each time without the need for a conscious decision
- Roles of reflexes:
- Reduce/avoid damage to tissues
- Escape from predators
- Vital roles in homeostasis
- Finding food/mates
- Types of reflexes and reflex arcs:
- Spinal reflexes – do not involve brain, impulse passes to spinal cord and back out e.g. knee-jerk, withdrawal reflex
- Cranial reflexes – use cranial nerves which run to and from involuntary part of the brain e.g. pupil size, blinking, coughing, sneezing
- Monosynaptic reflex arc – knee jerk, monosynaptic reflex arcs only involve one synapse and two neurones.
- Polysynaptic – withdrawal reflex, polysynaptic reflex arcs involve more than one synapse and three neurones
- The Autonomic Nervous System:
- Consists of two sets of antagonistic nerves:
- Sympathetic nerves – which stimulates the body and prepare it for action
- Parasympathetic nerves – which bring the body, back down to normal.
- In an excited state the sympathetic system dominates and in a relaxed state the parasympathetic system dominates
- Parasympathetic nerves use acetylcholine at the effecter
- Sympathetic nerves use nor-adrenaline at the effecter.
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