Notes on the subject of ingestive behaviour (eating + drinking) from behavioural neurosciences. Includes the physiology of hunger and thirst, neural mechanisms of hunger and thirst as well as patophysiology.
Homeostasis – the property of either an open system or a closed system,
especially a living organism, that regulated its internal environment so as to
maintain a stable, constant condition under varying external conditions =>
equilibrium of vital functions.
Physiological Regulatory Systems
All organisms have a physiological
control mechanism. Irrespective of
the vital function that needs to be
controlled, these control
mechanisms ALWAYS consist of 4
elements:
1) System variable
2) Set point
3) Detector
4) Correction mechanism
5) Ingestive behaviours/satiety
System variable = vital function that needs to be controlled
Set point = ideal value/range for system variable
Detector = required in case there is a deviation from a set point
Correction mechanism = if there is a deviation from set point, a correction
mechanism is necessary for system variable to come back to set point.
All of these control mechanism always are characterized by negative feedback
processes via which the effect produced by the correction mechanism is
terminated.
,Specifically, when talking about Ingestive behaviour the satiety mechanism is
required! In this case the correction mechanism has to stop before the for
example, fluid levels in your cells are at set point again!
The satiety mechanism behind to inhibit the correction mechanism (for example,
drinking) before the water is completely absorbed in the stomach.
Hypothalamus
Hypothalamus is the highest integration centre which is also linked to the
autonomous nervous system. It is responsible for regulation of vegetative and
endocrine processes. Endocrine = secretion of hormones. Vegetative = regulation
of internal organs.
Basically, hypothalamus is a main control centre that maintains homeostasis. This
is why it is connected to both autonomous nervous system and somatic nervous
system.
, - Somatic nervous system = is the part of the peripheral nervous
system associated with the voluntary control of body movements
via skeletal muscles. The somatic nervous system consists of afferent
nerves or sensory nerves, and efferent nerves or motor nerves.
- Autonomous nervous system = is a division of the peripheral nervous
system that supplies smooth muscle and glands, and thus influences the
function of internal organs. The autonomic nervous system is a control
system that acts largely unconsciously and regulates bodily functions,
such as the heart rate, digestion, respiratory rate, pupillary
response, urination, and sexual arousal. This system is the primary
mechanism in control of the fight-or-flight response.
Regulation of vital function = the detection of deviations from set point is in
hypothalamus. Specific detectors/receptors in hypothalamus are responsible for
detection of different signals:
- Temp. regulation -> thermoreceptors
- Hormone regulation -> receptors for hormones
- Osmolarity -> osmoreceptors
Then based upon the signals received the hypothalamus will send signals to the
effector cells like:
- Muscle cells => vasoconstriction or vasodilation
- Glands => hormones
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