Control of Physiological Systems Flashcards
Where are voluntary control mechanisms initiated?
Cerebral cortex
What are two purposes of voluntary control mechanisms?
Modulation
Reflexes
What systems are involved in involuntary control?
ANS
Endocrine system
What are the four important components in the feedback mechanism of a variable?
Sensor
Set point
Comparator
Effector(s)
What is a sensor for?
Measures current variable/tells you where the variable is now
What is the set point?
Where you want the variable to be
What does the comparator do?
Compares the current variable (measured by sensor) to the set point
What is an effector for?
Alters the variable
How do you calculate the difference signal in a negative feedback system?
a - b
What does ‘a’ represent in a feedback system?
Negative feedback system
Set point
What does ‘b’ represent in a feedback system?
Negative feedback system
Sensor measurement/current variable
What is the difference signal?
Difference between set point and current variable
What is the result if the difference variable is negative in a negative feedback system?
Effector turns ‘off’ as variable is too great
What is the result if the difference variable is positive in a negative feedback system?
Effector turns ‘on’ as variable is too small
What is slack?
Range in the variable between which the effector is not turned ‘on/off’
What is the range in which body pH is maintained?
7.35 - 7.45
What is the range in which body temperature is maintained?
36.1 - 37.2°C
What is the negative response loop?
Stimulus -> receptor/sensor -> afferent pathway -> integrating centre -> efferent pathway -> effector/target -> response -> receptor
What turns off the negative response loop?
Variable reaching set point
What is the discrimination of the comparator?
Difference between the endpoints of a variable
Why can it be dangerous when the set point of a variable changes?
Body does not detect harmful changes in the variable which may affect important metabolic processes/structures
What does anaesthesia affect in feedback systems?
Effector sensitivity
Sensor sensitivity
What must you be careful when using anaesthesia?
Decreased sensitivity of effector = limited response
Decreased sensitivity of sensor = limited detection of variable
Insufficient responses to reestablish homeostasis (= death)
Why are signal delays dangerous in feedback systems?
Cannot respond to changes in internal environment sufficiently quickly (more fluctuation)
What is the name given to the fluctuation of the variable about the set point?
Hunting oscillation
What is the difference between positive and negative feedback?
Negative: response counteracts/removes initial stimulus to shut off response loop
Positive: response builds on stimulus causing further response; external stimulus required to shut off response loop
What is an example of feed-forward control?
Gastric secretions on sight and smell of food
When does feed-forward control occur?
Anticipatory/prior knowledge situations
What type of feedback is childbirth?
Positive
Describe the feedback loop in childbirth
Baby drops lower in uterus to initiate labour
Cervical stretch
Oxytocin release
Uterine contractions
Baby pushed against cervix
Further cervical stretch and cycle repeats until baby is delivered
What does ‘X’ represent in a feedback system?
Positive feedback
Sensor measurement/current variable
What does ‘Y’ represent in a feedback system?
Positive feedback
Set point
How do you calculate the difference signal in a positive feedback system?
X - Y
What is the result if X>Y?
Effector works harder as variable is greater than set point
Variable further increases so X»_space; Y and cycle continues
What are some examples of positive feedback mechanisms?
Action potentials
Blood clot formation
Childbirth
Lactation
What are two examples of negative feedback mechanisms?
Baroreceptor reflex
Osmolarity control
How is an action potential an example of positive feedback?
When threshold is reached, voltage-gated sodium ion channels open causing more depolarisation
More depolarisation causes the opening of more voltage-gated ion channels
Describe the feedback loop of lactation
Suckling stimulates nerve endings
Hypothalamus (integrates information)
Posterior pituitary secretes oxytocin causing milk let down
Anterior pituitary secretes prolactin causing milk production
Cycle stops when baby is satiated/stops suckling
What are receptors (relating to homeostasis)?
Specialised cells/structures that convert various stimuli into electrical signals
Where are central receptors found?
In/close to the brain
What are some examples of central receptors?
Eyes, ears, nose, tongue (special sensation)
Chemo, osmo, thermoreceptors
Where are peripheral receptors found?
Outside the brain
What are some examples of peripheral receptors?
Baroreceptors
Proprioceptors
Mechanoreceptors
Chemoreceptors
Osmoreceptors
Thermoreceptors
What do baroreceptors detect?
Pressure
What do proprioceptors detect?
Position
What do mechanoreceptors detect?
Pain
Vibration
Touch
What do osmoreceptors detect?
Osmolarity
Where is the regulatory centre for blood pressure?
Medulla and brainstem
What system is responsible for controlling blood pressure?
ANS
Describe the feedback mechanism in osmolarity control
Dehydration/increased sodium ion intake increases plasma osmolarity
Detected by osmoreceptors in the hypothalamus
Thirst increased so more water ingested
ADH released from pituitary so increased renal water reabsorption
Plasma osmolarity returns to normal
How do osmoreceptors detect an increase in plasma osmolarity?
Water moves out of cells/osmoreceptors into plasma by osmosis
Cell shrinks
Where is the regulatory centre for breathing?
Pons
Medulla
(Central pattern generator)
What factors (of higher centres) can influence breathing?
Temperature
Emotion
What part of the central pattern generator is affected by higher centres in breathing?
Pons
What are the two centres of the pons involved in breathing regulation?
Pneumotaxic
Apneustic
What are the two groups of the medulla involved in breathing regulation?
Ventral respiratory
Dorsal respiratory
Which centres of the pons do each of medulla groups interact with?
Ventral respiratory group interacts with pneumotaxic centre (two-way)
Dorsal respiratory group interacts with apneustic centre (one-way)
What can affect the central pattern generator in breathing regulation?
Chemoreceptors
Higher centres
Lung receptors
What receptors are present in the lungs involved in breathing control?
Stretch
Irritant
Proprioceptors
Juxtapulmonary
Which muscles are used in ventilation?
Intercostals
Diaphragm
Abdominal
What is detected by chemoreceptors in breathing regulation?
Blood pCO2 and pO2
How does voluntary breathing override normal breathing regulation?
Pyramidal tracts
What are pyramidal tracts?
Upper motor neurons that originate in the cerebral cortex and terminate in the spinal cord or brainstem
What is different about the oscillations (around the set point) when there are signal delays?
There are gaps
What causes Cheyne-Stokes breathing?
Poor oxygenation/blood flow causes delay between respiratory muscles and chemoreceptors
What is Cheyne-Stokes breathing?
Deep and fast breathing followed by apnoea
*What causes muscle tremors in Parkinson’s disease?
Loss of damping of basal ganglia on reticular formation
Due to lack of dopamine (to stimulate basal ganglia)
What does damping do?
Reduce, restrict or prevent oscillations
