lecture 18 Flashcards
Motivation - behaviours (motor activation) occur in response to: -- reflex stimulation – dropping a hot object – automatic -- conscious or willful command (motivated behaviour) - motivated behaviour occurs in response to the body's absolute requirements -- eating when hungry - or by abstract things -- reading a book, going for a swim - motivation = driving force on behaviour
Do sympathetic neurons (and parasympathetic?) function autonomously?
- no, they require input in order to fire
What is the hierarchical control of the autonomic nervous system?
- End organs provide feedback about their state (e.g. brain and oxygen supply via blood)
- spinal visceral sensory neurons (e.g. cranial nerves IX and X)
- feedback inputs on nucleus of solitary tract (in the medulla)
- from here many pathways:
1. loops within the medulla that come straight back out to the end organ (preganglionic neurons in brainstem/spinal cord, primary motor neurons in autonomic ganglia, end organ) (e.g. baroreceptor reflex)
2. parabrachial nucleus (to cortex) (we won’t focus on it)
3. inputs onto hypothalamus
4. inputs onto autonomic centres in brainstem reticular formation - information gets processed in the cortex before descending down through the autonomic nervous system as well
- hypothalamus: the conductor, regulates patterns of autonomic innervation; e.g. after a meal ensures you still have adequate blood perfusion outside of the gut
- amygdala: plays an important role in memory and fear related changes to autonomic nervous system activity
How is the hypothalamus central to conducting the autonomic (and other) response?
Hypothalamus receives:
- contextual information: cerebral cortex, amygdala, hippocampal formation
- sensory inputs: visceral and somatic sensory pathways, chemosensory and humoral signals
Hypothalamus compares input to biological set points and coordinates the visceral motor, somatic motor, neuroendocrine and behavioural responses
How much glycogen can we store?
- a limited amount
How do we store energy?
- as glycogen and as triglycerides
Where do triglycerides get stored?
- in adipose tissue
How much triglyceride can we store in adipose tissue?
- work on the assumption that there is almost a limitless ability to store triglycerides in adipose tissue
Does the body attempt to maintain a level of adiposity and weight?
- yes
- if you starve a rat for a period of time it will maintain its body weight but eventually this will be overcome and it will lose weight (when re-fed it will come back to normal)
- similarly in periods of forced feeding it will maintain weight for a period of time but eventually begin to put on weight
What is being monitored in the body’s attempt to maintain a level of adiposity and weight?
- evidence suggests that it is body fat
- the lipostatic hypothesis
What is key to detecting body fat?
- hypothalamus:
- paroventricular nucleus (PVN)
- lateral hypothalamic area
- arcuate nucleus
What hypothalamic lesions can affect weight?
- lesions of lateral hypothalamus lead to lateral hypothalamic syndrome (too lean)
- lesions of the ventromedial hypothalamus lead to ventromedial hypothalamic syndrome –> obese rats
What is balanced in the maintenance of body weight/fat? How?
- food intake and energy expenditure
- there are key nuclei, and key neurons within those nuclei that are very important for the regulation of feeding behaviour
- energy expenditure can be adjusted in the body through brown adipose tissue – sympathetic innervation of brown adipose tissue causes it to burn energy and release heat, thereby wasting energy. Possible to do this because it is usually stored in the periphery (between scapulae is main store)
What is in the arcuate nucleus?
- two types of neurons that are key in this whole process
- AgRP/NPY neuron make neuropeptide Y, release of this will increase food intake and decrease energy expenditure
- Other neurons make POMC (pro-opiomelanocorpin): a large peptide, opiates, an important one of these is alpha-MSH (melanocyte stimulating hormone), inhibits food intake, more expenditure
- often go to the same second order neurons to regulate behaviour
What does alpha-MSH act on?
- one target is the MC4 receptor in neurons in the lateral hypothalamic area
- inhibits feeding behaviour by activating receptor
What does AgRP act on?
functional antagonist of alpha-MSH
comes along and binds to same receptor to prevent it from doing its drop
therefore activates feeding behaviour