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)
Key Terms
Reflex reactions
Responds to changes in the environment but not involving the brain
Sensory --> relay --> motor
Brain may be informed but doesn't ...
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 toucing 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
If the corneal blinking reflex is to be overridden
Sensory neurone on cornea
Myelinated relay neurones inform brain
Allows reflex to be overriden (inhibitory neurone) - faster so reflex ...
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| 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 toucing 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 overriden (inhibitory neurone) - faster so reflex can be overriden before it happens |
Knee-jerk reflex | Spinal reflex Unexpected stretching of quadraceps --> detected by muscle spindles --> causes a reflex reaction (no relay neurone) --> quadraceps contract |
Spinal reflex | Involves the spinal chord 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/ steriod 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 thryoxin 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 | Stimlates breakdoen 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 symapthetic 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 coversion 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 |
Why are endorphins released in the fight or flight response | Wounds inflicted don't prevent activity |
Why must plants be able to respond to their environment | Cope w/ changing conditions | Avoid antibiotic stress |
How does auxin cause cell elongation (2 marks) | Loosens rigid cellulose framework | Osmotic uptake of water allows cell elongation |
Why do cut plants w/ agar blocks w/ auxin placed on the rhs bend to the lhs | Auxin produced at tip Diffuses laterally to rhs Cells on rhs exhibit greater elongation Bending to the left |
How does auxin act as a selective weedkiller | Rapid cell elongation so plant grows too quickly No extra lignified tissue Stem collapses or loss of extra water from leaves |
What happens when the apex is removed from a plant | Once apex is removed, auxin production stops Apical dominance is stopped Lateral growth is not inhibited and lateral buds develop |
Types of muscle | Skeletal (voluntary) Cardiac Involuntary (smooth) |
Voluntary (skeletal muscle) | Striated Multinucleate Regularly arranged —> contraction in one direction Attached to bone by tendon Tubular Nerves from peripheral, somatic (rapid) |
Cardiac muscle | Specialised striated (parallel myofibrils) Branched fibres Uninucleated Cross bridges allow simultaneous contraction Dark bands - intercalated discs Nerves from autonomic nervous system |
Involuntary (smooth muscle) | Non striated Nerves from autonomic nervous system No reg. arrangement - diff cells can contract in diff directions Fibres are spindle shaped and uninucleated Used in hollow organs (peristalsis) |
Sarcolemma | Plasma membrane that encloses bundles of muscle fibre |
Why may the sarcolemma fold in | Spread impulse throughout sarcoplasm | Contract at the same time |
Sarcoplasm | Shared cytoplasm within muscle fibres |
How are muscle fibres formed | Fusion of several embryonic muscle cells - gap between adjacent cells would be a weakness (That’s why it’s multinucleate) |
Sarcoplasmic reticulum | Modified version of ER | Provides strength and stored Ca^2+ |
Protein filaments | Myosin | Actin |
Muscle organisation | Muscle Fascicles Muscle fibres Myofibrils Protein filaments |
Connective tissue | Tendons |
Light band (I) | Thin actin held together by Z line |
Dark band (A) | Both actin and myosin Entire length of myosin Myosin held together by M line |
M line | Midpoint of myosin | Has no heads |
Z line | Found at the centre of each light band |
Sarcomere | Functional unit of muscle From one Z line to another Sub unit of myofibrils |
Why is muscle considered a tissue | Muscle fibre Blood vessels Nerves Connective cells |