ANS & Limbic system Flashcards
Describe the limbic system. What does it control (function)?
The emotional brain. Focused on emotions and learning.
The limbic system controls:
- emotional behaviour (your emotions) - fear, anger, pleasure, happiness, sadness, etc.
- motivational states - hunger, thirst, fear
- behavioural responses - feeding, drinking, flight response
- memory formation - particularly the association of memories with strong emotions
- learning - particularly from strong emotional situations
*all are required for the basic survival of the individual
What are the major structures of the limbic system?
- Olfactory bulb
- Hippocampus
- Amygdala
- Hypothalamus
- Cingulate gyrus
Describe the behavioural responses to these motivational states:
- hunger
- thirst
- cold/hot
- feeling tired
- rage
- fear
- sexual arousal
- pain
- search for food and feeding
- search for water and drinking
- change location, clothing, thermostat
- resting and sleeping
- fight
- flight
- reproduction
- avoidance of stimulus
How is pain under the control of the limbic system?
- travels to somatosensory cortex
- here, location and intensity of pain is interpreted
- also passes to cingulate gyrus, where emotional and motivational determinants are attached
- damage to the CG - can still feel pain but are not longer bothered by it (no association with emotion)
What is congenital pain insensitivity?
congenital - genetic condition, occurring at birth
Congenital pain insensitivity - condition where the patient does not perceive physical pain
- can feel the difference between hot and cold, between sharp and dull (but don’t feel the pain or damage)
- cannot sense that a hot drink is burning their tongue
- many also have a complete loss of the sense of smell
* due to mutation in SCN9A gene that codes for NaV1.7 (sodium voltage gated channel - needed for action potential) - less to no-function of subunit - reduced or non function of channel
What are the functional categories of the limbic system and what are they composed of?
- Input and processing areas:
- hippocampus
- amygdala - Output area
- hypothalamus
Describe the Hippocampus
- part of input/processing area
- where short term memories are formed and stored as long-term memories
- aging shrinks the hippocampus- impaired memory and risk of dementia
- aerobic exercise increases the size of the hippocampus and improves spatial memory in the elderly
Describe the Amygdala
- part of input/processing area
- plays a role in emotional responses to situations: fear, anger, anxiety, pleasure
- attaches emotions to our memories
- determines how strongly memories are stored, particularly those attached to fear and anxiety
- damaged - leads to reduced fear and increased aggression
- inability to recognize facial expressions
Describe the Hypothalamus
- main output area of the limbic system
- roughly 4g in size -small (your brain is 1.4 kg)
- found beneath the thalamus and above the pituitary
- function: maintain homeostasis
- roles: regulation of metabolism, temperature maintenance, 24h circadian clock, fluid balance, osmoregulation, fight or flight, etc.
What are the ways that the hypothalamus maintains homeostasis?
- Direct regulation of homeostasis
- control of endocrine output from pituitary gland
- regulates output from the autonomic nervous system (ANS) - Indirect regulation of homeostasis
- coordination of motivational behaviours
Regulation occurs through negative feedback
What are the input/ output from the hypothalamus
Sensory inputs:
- retina
- somatosensory
Monitors blood:
- temperature
- osmolality
- glucose levels
- many hormones
Output:
- endocrine: Ant. and Post. pituitary gland
- ANS: brain stem to spinal cord
What are the parts of the pituitary gland (hypophesis)?
- anterior pituitary
- posterior pituitary
Describe the anterior pituitary gland
Signalling occurs through a specialized portal system called the hypothalamic-hypophyseal portal system
Neurosecretory cells secrete:
- releasing hormones
- releasing-inhibiting hormones
Hormones released:
- growth hormone, LH, FSH, ACTH
- TSH, Prolactin
Describe the posterior pituitary gland
Magnocellular neurons:
- cell bodies in hypothalamus
- axon terminals in posterior pituitary
- hormones produced in cell bodies of these neurons are released by the posterior pituitary
Hormones released:
- oxytocin
- antidiuretic hormone (ADH)
Describe the autonomic, endocrine and behavioural responses of the following hypothalamus functions:
1. regulation of body temperature
2. control of energy metabolism and feeding
3. control 24hr circadian rhythm
- Autonomic: -metabolic rate -cutaneous vasoconstriction - shivering
Endocrine: - TSH, Thyroxine from thyroid gland
Behavioural: - clothing - new location - thermostat - Autonomic: metabolic rate (SNS), digestion (PNS)
Endocrine: thyroxine leptin
Behavioural response: feeding (searching, smelling, tasting and eating) - Autonomic: -blood pressure - body temp
Endocrine: -melatonin (from pineal gland) - ADH - ACTH (cortisol)
Behavioural: sleep
Describe the setpoint regulation by the hypothalamus
Regulation of homeostasis
- control of endocrine output from pituitary gland
- regulates output from the autonomic nervous system (ANS)
- behavioural regulations
- done through negative feedback
Describe the autonomic nervous system. What are the three main divisions of the ANS?
- Part of the nervous system that controls the internal (visceral) organs of the body (i.e. the viscera)
- not normally under conscious control
1. Sympathetic nervous system (SNS) - fight or flight
2. Parasympathetic nervous system (PSNS) - rest and digest
3. Enteric nervous system (ENS - the gut)
What is the main overall function of the ANS? What do the SNS and the PSNS/ PNS help to regulate?
- To maintain homeostasis
SNS: - heart rate
- blood pressure and blood flow
- body temp
- airway resistance in the lungs
PNS: - gastrointestinal motility
- secretion by glands
- bladder motility
- sexual function
*generally the SNS and PNS inervate similar organs but tend to have opposing effects (not always) - both help in sex organs in similar effects
How does the ANS exert its action?
By controlling the following:
- smooth muscle in blood vessels, digestive tract
- cardiac muscle and specialized cardiac tissue (e.g. tell to pump harder/faster, etc.)
- Glands; salivary, sweat, adrenal gland, digestive, prostate, etc. *sweat and adrenal gland are only sympathetic, the rest are both
Describe the difference between the autonomic (ANS) and somatic nervous systems (SNS)
Autonomic (ANS):
- largerly involuntary
- controls the internal environment
- regulates activity of intrinsically active organs
- has *dual innervations (SNS and PSNS) - activation and inhibition of responses
Somatic (SNS):
- voluntary
- controls the external environment
- regulates activity of skeletal muscle (active when needed)
- single innervation: input - integration - output
What is the organization of the ANS?
- Homeostasis is the relatively constant condition of the internal environment of the body
- sensory receptors monitor internal environment/ organs
- these receptors send signals back to CNS through sensory afferent fibers
- CNS integration centre interprets signals and activates the hypothalamus*
What is the long reflex?
An autonomic (visceral) reflex arc
- receptors monitor internal and external environments (temperature, blood pressure, and chemistry, etc.)
- sending afferent signals to the CNS for processing at different levels (SNS and PSNS)
- sending efferent signals to effector/ target organs
preganglionic neuron to ganglion to postganglionic neuron to target organ
What is the short reflex?
An autonomic (visceral) reflex arc
- characteristic of the ENS
- no CNS involvement - e.g. stretch receptors in the stomach sense the stretch, signal smooth muscle to contract and increase motility
Difference between SNS and PNS?
- most organs have dual innervation, with antagonistic effects SNS vs PSNS
exceptions: - blood vessels
- sweat glands
- piloerector muscles
- kidney
- adrenal medulla
Describe the adrenal gland
- adrenal gland is innervated by only a preganglionic sympathetic fiber
- there are no postganglionic fibers
- adrenal gland is considered a collection of modified post-ganglionic fibers
- when stimulated, it releases 80% epinephrine (rapid effects) also called adrenaline, and 20% norepinephrine (slower effects)
- innervation comes only from the SNS
What are the neurotransmitters of the Sympathetic and Parasympathetic nervous systems?
Somatic: MN release Ach onto nicotinic (N1) receptors at NMJ
- All pre-G neurons (SNS, PSNS) release Ach onto nicotinic (N2) receptors
- PSNS post-G release Ach onto Muscarinic receptors
Therefore, PSNS is entirely cholinergic (releases Ach)
- Most SNS post-G: release Norepinephrine onto adrenergic receptors, exceptions: sweat glands, piloerector muscles (sympathetic vasodilator fibers to blood vessels in skeletal muscle) these -> Post-G release Ach onto Muscarinic receptors
- other exceptions: adrenal gland - pre-G neurons release Ach that binds to nicotinic receptors onto secondary cells within the medulla - epinephrine is then released into the blood vessels
Describe the receptors of the ANS?
Location
Receptor
Agonist
Antagonist
Action
Mechanism
- PNS and SNS ganglia
Nicotinic (N2)
- Ach (NT), - Nicotine
Hexamethonium
Ligand gated ion channels
Opens Na+/K+ channels, produces fast EPP, produces fast EPSPs - PSNS target organs
Muscarinic (5 subtypes)
- Ach (NT) - Muscarine (mushroom)
- Atropine (from nightshade plants) - used to dilate your pupils
G-protein coupled receptor
Modifies K+ and Ca++ conducatance -> slow EPSPs or IPSPs - SNS target organs
Alpha Adrenergic (2 subtypes 1*predominant, and 2)
Norepinephrine > epinephrine
Phentolamine
G-protein coupled receptor
Modifies K+ and Ca++ conductance -> slow EPSPs or IPSPs - SNS target organs (also)
Beta adrenergic (3 subtypes 1, 2 predominant, 3)
Epinephrine > Norepinephrine
Propranolol
G-protein coupled receptor
Modifies K+ and Ca++ conductance -> slow EPSPs or IPSPs
Summary of the receptors in the nervous system:
Somatic: motor neuron cholinergic
PSNS: entirely cholinergic
SNS: - preganglionic cholinergic - postganglionic adrenergic - exception: all cholinergic = adrenal gland (preganglion neuron cholinergic)
Describe the autonomic neuroeffector junction
- release of NT is similar to that at a chemical synapse or NMJ
1. AP depolarize axon
2. Opens VG Ca++ channels and Ca++ flows into varicosity
3. Vesicles fuse to membrane and release NT
4. NT diffuses to target organ.
Further:
1. NE produced from tyrosine
2. NE is released into synaptic cleft
3. NE has the following fates: - binds to receptors on post-synaptic cell (alpha 1 and beta)
- recirculated into pre-synaptic cell - high affinity uptake
- binds to receptor alpha 2 - pre synaptic membrane, recycled by MAO
- binds to receptor alpha 2 - post synaptic cell - metabolized by catechol-O-methyltransferase (COMT) - diffusion **
- diffusion away from synapse
What are the effects of the ANS on organs?
SNS is mainly involved with fight or flight situations:
- regulating BP and temperature
- activated during exercise
- mass discharge due to divergence of Post-G neurons
PSNS is mainly involved with rest and digest situations:
- conserves and restores energy
- slows HR and decreases BP
- discrete or localized discharge due to less divergence
* PSNS closer to organ, doesn’t need mass discharge vs SNS closer to CNS
What is the sympathetic tone in blood vessels?
- SNS and PSNS are continuously active with 1 AP firing roughly every few seconds (maximal activity is roughly 20 AP/sec)
- this normal resting discharge of APs is called tone or tonic activity
- arteries and veins have only sympathetic innervation - the SNS can cause both vasoconstriction and vasodilation by changing the tonic activity to these vessels
1. To cause vasoconstriction = increased SNS activity -> 10 APs/sec
2. Normal SNS = tonic discharge rate -> 1 AP every few seconds
3. To cause vasodilation = decreased SNS activity -> 0 APs/sec
What happens when the sympathetic nervous system is innervated?
Fight or flight
1. Upper body, heart and lungs
pupil dilates - more light entering eye
mucus and enzymes secreted- thick mucus
increase heart rate and contractility- increase blood output by the heart
relaxes airways- more air in and out of lungs easily
2. Digestion * shuts down digestion
inhibits digestion ->liver + stomach
decreases enzymes and insulin -> pancreas
inhibits digestion -> intestines
inhibits digestion -> intestines
3. Adrenal glands, kidneys and bladder
fight or flight
increases renin secretion -> kidney (release epinephrine - adrenaline)
relaxes bladder - hold in urine
What happens when the parasympathetic nervous system is innervated?
- Upper body, heart and lungs
rest and digest
pupil constricts -> less light entering eye
digestive enzymes and watery secretion -> salivary glands - watery saliva and enzymes for digestion
slows heart rate -> decreases blood output from heart
constricts airways -> lungs - Digestion
increases bile secretion -> liver
increases motility and secretion -> stomach + intestines
releases enzymes and insulin -> pancreas
- increases digestion and absorption of nutrients - Adrenal glands, kidneys, and bladder
No PSNS innervation of the adrenal gland
release urine -> contracts bladder
How does the sympathetic and parasympathetic nervous systems innervate the reproductive organs?
Sexual activity
induces erection -> penis
stimulates contraction -> uterus and vagina (SNS)
engorgement and secretions -> uterus and vagina
* sexual responses are mediated by the coordinated activity of both SNS and PSNS - complement eachother
Describe the autonomic control of the heart
- sympathetic activity elevated during arrhythmias
- target for treatment
- the innervation of the SNS is much more complex than presented in this course:
spinal neurons synapse with ganglion neurons in stellate complex
interneurons determine patterns of activity
spinal neurons target heart regions
loads of unknown still
