5.5 Plant And Animal Responses Flashcards
What is a reflex action?
Response to stimulus that doesn’t involve the brain to coordinate movement, always with a survival value
Explain the blinking reflex - what type of reflex is it? What occurs?
- uses brain but without higher thought processes: CRANIAL
- stimulus, then sensory neurone from cornea carries impulses to sensory centre in pons, which travels through non-myelinated relay neurone to motor centre in pons, and via motor neurone to facial muscles which usually causes both eyes to blink
Describe how the knee jerk reflex works
Coordinated movement and balance
Stimulus - stretching of the quadriceps muscle caused by pressure on the ligament
Receptor - stretch receptors in the quadriceps muscle
Coordinator - the spinal cord
Effector - the quadriceps muscle
Response - contraction of the quadriceps muscle, causing the leg to straighten
Sensory -> motor ( bypasses relay)
What physiological changes occur when adrenaline is released?
- Pupils dilate so more light enters
- Heart rate and blood pressure increases so more oxygen and glucose reaches muscles
- Arterioles to digestive system constricted, to divert blood to muscles
- Blood glucose increases = more energy for muscle contraction
- Erector pills muscles contract = hairs stand up
- Ventilation rate increases to increase gaseous exchange
- Endorphins released = natural painkillers so wounds inflicted do not prevent activity
Describe the pathway of nervous coordination of the fight or flight response
Inputs into cerebrum sensory centres -> signals to association centres -> hypothalamus stimulated -> activates sympathetic nervous system -> activate glands and smooth muscles or activates adrenal medulla to secrete adrenaline into bloodstream. Neuronal activity combines with hormones to constitute fight or flight response.
Describe the pathway of endocrine communication in the fight or flight response
hypothalamus stimulated to secrete hormones into blood which pass down portal vessel to stimulate anterior pituitary gland to release tropic hormones
CRH -> ACTH released from pit -> adrenal cortex secretes corticoids e.g. cortisol to regulate metabolism of carb -> bloodstream
TRH -> TSH released from pit -> thyroid glands secretes thyroxine to increase metabolic rate and make cells more sensitive to adrenaline -> bloodstream
Neuronal activity and hormones combine to carry out response
Describe adrenaline action once it reaches a cell
- Binds to plasma membrane receptor, stimulating G protein to active adenyl cyclase
- Converts ATP to cAMP (second messenger)
- Activates enzyme action
How is heart action modified?
Changing heart rate
Altering force of contractions
Altering stroke volume
What does myogenic mean?
Can initiate its own beat at regular intervals
What do sensory inputs to the cardiovascular centre include?
- Stretch receptors in muscles that detect movement of limbs -> more oxygen needed -> inc heart rate
- Chemoreceptors in carotid arteries, aorta and brain monitor blood pH. If too low, APS sent to centre and inc heart rate
- Baroreceptors in carotid sinus monitor blood pressure. Pressure too high = send APs to centre = dec heart rate
What is the solution if the mechanism controlling the heart fails? E.g. fibrillation occurs
Artificial pacemaker delivered, connected to SAN or to ventricle muscle directly, delivering electrical impulse to heart muscle.
What are some features of smooth muscle?
one nucleus per cell
contracts slowly and regularly
tubular structures : blood vessels, digestive system
circular layer -> segmentation in intestine (spindle shaped)
longitudinal -> wave like contractions (circle cells)
involuntary
What are some features of cardiac muscle?
cells -> long fibres -> branch to form cross bridges between fibres to ensure stimulation spreads evenly
intercalated discs - specialised cell surface membranes fused to produce gap junctions -> allow free ion diffusion
appears striated under microscope
involuntary
What are some features of skeletal muscle?
joints in skeleton
antagonistic pairs
each fibre is multinucleate and surrounded by sarcolemma membrane, and with sarcoplasm and sarcoplasmic reticulum
myofibrils divided into functional subunits called sarcomeres (actin and myosin)
striated appearance
contracts quickly and powerfully
voluntary
Describe the process that occurs at a neuromuscular junction
- APs at end of axon open calcium channels; they enter
- Acetylcholine vesicles move towards membrane and fuse
- Diffuse across gap and bind to receptors
- Sodium channels open and delopolarisation occurs
- Wave of depolarisation passes along sarcolemma and down transverse tubules
What is a motor unit?
muscle fibres contract together (many motor neurones divide and connect to several muscle fibres)
What is the light and dark band?
light: thin filaments, actin
dark: thick filaments, myosin
Describe the structure of actin filaments
two chains of subunits wound around eachother
troponin complexes
tropomyosin wrapped around
Describe the structure of myosin filaments
thick filament, with heads. each molecule has 2 heads
What is the A band, I band and H zone?
A band: between points they overlap
I band: only actin
H zone: only myosin
What happens to sarcomeres during contraction?
- thick and thin filaments slide past one another. H zone gets smaller, Z lines more closer, sarcomere gets shorter. Filaments do NOT change in length. Little/no I band also
How is contraction controlled?
- AP passes along sarcolemma and into muscle fibre
- AP carried to sarcoplasmic reticulum, and causes calcium ion release into sarcoplasm
- Calcium ions bind to troponin, altering shape and pulling it aside (exposes actin binding sites)
- Myosin heads bind to actin = cross bridges form
- Myosin heads move, pulling actin filament past
- Myosin heads detach and can bind again further up
What is the role of ATP in muscle contraction?
- Myosin head attaches to actin
- Power stroke occurs, ADP and Pi are released (part of myosin head acts as ATPase)
- New ATP attaches to myosin head, breaking cross bridge
- Myosin head returns to position as ATP is hydrolysed, releasing energy.