Back to FlashcardsBiology / LGS A-Level OCR Biology - Unit 5 - Plant and Animal Responses Part 3
Reflex reactions
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Key Terms
Term
Definition
Reflex reactions
Responds to changes in the environment but not involving the brain; Sensory --> relay --> motor; Brain may be informed but doesn't coordinate; Surviva...
Cranial reflex
Nervous pathway passes through the brain
What makes something an reflex arc
Receptor and effector in same place
Blinking reflex
Cranial reflex; Corneal - object touching eyes; Optical - Light hitting back of eye (retina)
Patnway for corneal blinking reflex
Receptor; Sensory neurone on cornea; Sensory centre on pons; Non-myelinated relay neuron passes action potential to motor neurone; Motor neurone passe...
If the corneal blinking reflex is to be overridden
Sensory neurone on cornea; Myelinated relay neurones inform brain; Allows reflex to be overridden (inhibitory neurone) - faster so reflex can be overr...
Related Flashcard Decks
| Term | Definition |
|---|---|
Reflex reactions | Responds to changes in the environment but not involving the brain; Sensory --> relay --> motor; Brain may be informed but doesn't coordinate; Survival; fast, involuntary and not learned (innate) |
Cranial reflex | Nervous pathway passes through the brain |
What makes something an reflex arc | Receptor and effector in same place |
Blinking reflex | Cranial reflex; Corneal - object touching eyes; Optical - Light hitting back of eye (retina) |
Patnway for corneal blinking reflex | Receptor; Sensory neurone on cornea; Sensory centre on pons; Non-myelinated relay neuron passes action potential to motor neurone; Motor neurone passes out of brain to facial muscles |
If the corneal blinking reflex is to be overridden | Sensory neurone on cornea; Myelinated relay neurones inform brain; Allows reflex to be overridden (inhibitory neurone) - faster so reflex can be overridden before it happens |
Knee-jerk reflex | Spinal reflex; Unexpected stretching of quadriceps --> detected by muscle spindles --> causes a reflex reaction (no relay neurone) --> quadriceps contract |
Spinal reflex | Involves the spinal cord rather than the brain |
Muscle spindles | Stretch receptors that detect increase in muscle length |
Class of hormones | Steroid - produced in reproductive organs and adrenal cortex; Peptide - insulin, ADH, adrenaline |
Hypothalamic - anterior axis | Hypothalamus releases hormones (releasing factors); Pass down a portal vessel to anterior pituitary gland; Anterior pituitary gland releases tropic hormones e.g. for thyroid and adrenal |
Tropic hormones | These stimulate other endocrine glands |
Mechanism of steroid hormones | Steroid hormone combines w/ steroid receptor in cytoplasm; Hormone-receptor complex enters nucleus; Complex binds to receptor sites on DNA, activating mRNA transcription; mRNA leaves nucleus; Ribosome translates mRNA into new protein in cytoplasm |
Mechanism of peptide hormones | Adrenaline in the blood binds to membrane bound receptor; Stimulates G-protein to activate Adenyl cyclase; Converts ATP to cAMP; cAMP acts as second messenger by moving into the cell cytoplasm and causing an effect |
Thyroxin | Increases metabolic rate in most cells |
How is thyroxin released | Hypothalamus releases TRH; Travels to anterior pituitary gland and releases TSH; Travels to thyroid through portal vessel and releases thyroxine |
TRH | Thyrotropin releasing hormone |
TSH | Thyroid stimulating hormone |
How are glucocorticoids (cortisol) released | Hypothalamus releases CRH; Travels to anterior pituitary gland and releases ACTH; Travels to adrenal cortex through portal vessel and releases cortisol |
Cortisol | Released as a response to chronic stress | Stimulates breakdown of glycogen |
Coordination of flight or fight | Sensory input; Action potential travels to sensory centres (cerebrum); Signals passed to association areas; If a threat is recognised, cerebrum stimulates hypothalamus; Hypothalamus stimulates sympathetic nervous system and stimulates release of hormones from anterior pituitary gland |
How is the fight or flight response formed | Hypothalamus activates sympathetic nervous system; Impulses activate glands and smooth muscle; Activated adrenal medulla; Secretion of adrenaline into the bloodstream; Hypothalamus also secretes releasing factors e.g. CRH and TRH |
CRH | Corticotropic releasing hormone |
ACTH | Adrenocorticotropic hormone |
Physiological changes in fight or flight response | Pupils dilate - more light enters eyes, retina becomes more sensitive; Heart rate and bp increase; Ventilation depth and rate increases; Less digestion; Blood glucose increases; Metabolic rate increase - faster conversion of glucose to ATP; Endorphins released in brain; Erector pili muscles in the skin contract |
Why do erector pili muscles stand up in fight or flight response | Hairs/ fur stands up - signs of aggression |