E109 Final

the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties

• stimulus
• sensor
• integration center
• set point
• effector organ

• a control system which has only feed-forward behavior responds to its control signal in a pre-defined way without responding to how the load reacts
• characteristically, is fast and simple, and response is not modulated

• a control system that acts when a gap between the actual value and a reference value of a system parameter is used to reduce the gap
• characteristically, slow and complicated, and response is modulated

• positive feedback is a process in which the effects of a small disturbance on a system can include an increase in the magnitude of the perturbation
• characteristically, is very fast
• requires an external shutoff

• when body temperature gets below lower threshold, two paths are -
• 1) detection by cutaneous thermoreceptors leads to shivering in skeletal muscles via somatic motor neuron from hypothalmus
• 2) if blood gets too cold, detection by hypothalmic thermorecptors leads to vasocontriction of cutaneous blood vessels via sympathetic neurons

• when body temperatur gets above higher threshold, two paths are-
• 1) detection by cutaneous thermoreceptors leads to sweat release from sweat glands via sympathetic neurons
• 2) if blood gets too hot, detection by hypothalmic thermoreceptors leads to vasodilation of cutaneous blood vessels via sympatheric neurons

• set points can change throughout the day
• for example, body temperature set point can rise during the day and lower at night
• circadian rhythms are any biological process that displays an endogenous, entrainable oscillation of about 24 hours

• dorsal root ganglion
• autonomic ganglion
• dorsal and ventral horn
• white and gray matter

the dorsal root houses the cell bodies of neurons in afferent spinal nerves of the PNS

• gray matter is unmylinated
• white matter is mylinated
• ascending and descending tracts run through white matter

serves as the integrating center and relay station for sensory and motor signals

serves as the integrating center for thermoregulation and homeostasis

• specialized endocrine tissue associated with the sympathetic nervous system
• secretes primarily epinephrine which activates B1 and B2 receptors on target cells

• adreneric receptors are a class of G protein-coupled receptors that are targets of catecholamines, especially norepinephrine and epinephrine
• alpha
• beta1
• beta2

• alpha - norepinephrine
• beta1 - norepinephrine and epinephrine
• beta2 - epinephrine

• central nervous system - brain and spinal cord
• peripheral nervous system - neurons outside the CNS

• two main divisions - somatic and autonomic
• three divsions of the autonomic system -
• 1) sympathetic
• 2) adrenal sympathetic
• 3) parasympathetic

• interneuron runs from brain in white matter to motor neuron, synapsing at the ventral horn
• motor neuron releases ACh at synapse with skeletal muscle, which has nicotinic receptors sensitive to ACh

• interneuron runs from brain in white matter to another interneuron, synapsing at the ventral horn
• ACh and nictotinic receptor activate interneuron at autonomic ganglion
• interneuron innervates with smooth muscle, releasing norepinephrine which activates adreneric receptors (a type of G-protein coupled receptor)

• both sympathetic and parasympathetic preganglionic neurons release ACh onto nicotinic receptors on the postganglionic cell
• most postganglionic sympathetic neurons secrete NE onto adreneric receptors on target cell
• most postganglionic parasympathetic neurons secrete ACh onto muscarinic receptors on target cell

• released by postganglionic sympathetic neurons  
• activates alpha and beta1 receptors
• alpha receptors allow for localized response

• released by adrenal medulla
• activates beta1 and beta2 receptors
• beta2 receptors allow for systemic response

• interneuron innervates with another interneuron in the autonomic ganglion, releasing ACh which activates nicotinic receptors
• this interneuron innervates with smooth muscle, releasing ACh which activates muscarinic receptors, a type of cholinergic receptor

• sympathetic -
• 1) increase heart beat frequency and stroke volume
• 2) increase or decrease arteriole diameter
• 3) increase bronchiole diameter
• 4) decrease GI motility
• 5) decrease endocrine pancreas insulin secretion
• 6) decrease exocrine pancreas enzyme secretion
• 7) increase sweat secretion from sweat glands
• 8) decrease urination from bladder
• 9) responsible for ejaculation in males
• parasympathetic -
• 1) decrease heart beat frequency
• 2) decrease bronchiole diameter
• 3) increase GI motility
• 4) increase endocrine pancreas insulin secretion
• 5) increase exocrine pancrease enzyme secretion
• 6) increase urination from bladder
• 7) responsible for erection in males

• hypothalamus - thermoregulation, water balance, eating behavior
• pons (upper brainstem) - bladder control, blood pressure control, respiratory control
• medulla oblongata (lower brainstem) - respiratory control

an involuntary and rapid response to a stimulus

• part of somatic nervous system
• example of a monosynaptic reflex
• stimulus of hammer hitting knee causes a stretch in the patellar tendon
• stretch is detected by muscle spindle organ
• integration center at the spike initiating zone of the efferent neuron
• efferent neuron innervates with two skeletal muscles, causing quad to contract and hamstring to relax
• can still feel the stimulus because an interneuron sends a signal to the brain, in particular the somatic sensory cortex
• example of feed-forward control since the efferent response does not vary with afferent input

• part of parasympathetic nervous system
• example of polysynaptic reflex
• as urine fills bladder, bladder walls increase in tension
• increased tension is sensed by stretch receptors which and activates two interneurons in the dorsal horn
• one interneuron activates a motor neuron and other activates a parasympathetic neuron
• first internueron inhibits the motor neuron (which usually has a train of APs aka tonic activity via somatic pathway) that maintains tension in the external sphincter, a skeletal muscle; result is relaxation and opening of this sphincter
• other interneuron activates parasympathetic neuron, which then activates smooth muscle of bladder, causing it to contract or squeeze
• both micturition reflex pathways can be inhibited by descending signals from the brain, an ability that is undevelpoed in infant
• sympathetic nervous system can also influence smooth muscle of bladder via N and NE (cannot influence external sphincter because it is skeletal muscle)

• change in stored energy = intake or production - excretion or metabolism
• also be written as - change in stored energy = energy intake - energy used

• glucose -> G6P ->glycolysis ->pyruvate
• if PO2 low, pyruvate goes into lactic acid cycle (anaerobic respiration)
• if PO2 high, pyruvate goes converted into acetyl CoA within mitochondria (all of the above happens in the cytosol)
• acetyl CoA -> citric acid cycle -> e- and H+ -> ETC
• one glucose yields 30-32 ATP molecules in aerobic metabolism
• fatty acids can enter chain as acetyl CoA
• process requires O2 and produces CO2

• alpha and beta cells of the pancreas serve as sensors and integrating centers for energy balance
• high plasma glucose activates beta cells, which promotes insulin secretion 
• low plasma glucose activates alpha cells, which promotes glucagon secretion; low glucose also means beta cells are not stimulated

• pathways happen via second messenger in the liver
• glycogenesis - glucose transformed into glycogen
• lipogenesis - glucose transformed into triglycerides
• glycolysis - ATP production
• glucose transport - increased permeability to glucose
• glycogen and triglycerides can leave liver and circulate to cells and adipose tissue for storage

• pathways happen via second messenger in the liver
• glycogenolysis - glycogen transformed into glucose
• glyconeogenesis - amino acids transformed into glucose

• pathways happen via second messenger
• can increase permeability of both to glucose
• glycolysis and lipogenesis and in the adipose
• glycolysis, glycogenesis, lipogenesis, and protein synthesis in the muscles

• after a meal (fed state), storage of glucose drops blood glucose levels, so that storage is downregulated in a negative feedback loop
• without a meal in a while (feed state), release of glucose raises blood glucose, so that release is downregulated in a negative feedback loop  

• type 1 - autoimmunse disease that destroys beta cells; resulting hyperglycemia damages kidneys, eyes, and nervous system
• type 2 - systemic cells are less sensitive to insulin; also results in hyperglycemia