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  • Created by: Jennifer
  • Created on: 29-04-12 14:30

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
  • Posture/balance
  • 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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