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Human Physiology > ANS & Limbic system > Flashcards

ANS & Limbic system Flashcards

1
Q

Describe the limbic system. What does it control (function)?

A

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

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2
Q

What are the major structures of the limbic system?

A
  • Olfactory bulb
  • Hippocampus
  • Amygdala
  • Hypothalamus
  • Cingulate gyrus
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3
Q

Describe the behavioural responses to these motivational states:
- hunger
- thirst
- cold/hot
- feeling tired
- rage
- fear
- sexual arousal
- pain

A
  • search for food and feeding
  • search for water and drinking
  • change location, clothing, thermostat
  • resting and sleeping
  • fight
  • flight
  • reproduction
  • avoidance of stimulus
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4
Q

How is pain under the control of the limbic system?

A
  • 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)
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5
Q

What is congenital pain insensitivity?

A

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

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6
Q

What are the functional categories of the limbic system and what are they composed of?

A
  1. Input and processing areas:
    - hippocampus
    - amygdala
  2. Output area
    - hypothalamus
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7
Q

Describe the Hippocampus

A
  • 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
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8
Q

Describe the Amygdala

A
  • 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
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9
Q

Describe the Hypothalamus

A
  • 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.
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10
Q

What are the ways that the hypothalamus maintains homeostasis?

A
  1. Direct regulation of homeostasis
    - control of endocrine output from pituitary gland
    - regulates output from the autonomic nervous system (ANS)
  2. Indirect regulation of homeostasis
    - coordination of motivational behaviours
    Regulation occurs through negative feedback
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11
Q

What are the input/ output from the hypothalamus

A

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

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12
Q

What are the parts of the pituitary gland (hypophesis)?

A
  • anterior pituitary
  • posterior pituitary
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13
Q

Describe the anterior pituitary gland

A

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

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14
Q

Describe the posterior pituitary gland

A

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)

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15
Q

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

A
  1. Autonomic: -metabolic rate -cutaneous vasoconstriction - shivering
    Endocrine: - TSH, Thyroxine from thyroid gland
    Behavioural: - clothing - new location - thermostat
  2. Autonomic: metabolic rate (SNS), digestion (PNS)
    Endocrine: thyroxine leptin
    Behavioural response: feeding (searching, smelling, tasting and eating)
  3. Autonomic: -blood pressure - body temp
    Endocrine: -melatonin (from pineal gland) - ADH - ACTH (cortisol)
    Behavioural: sleep
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16
Q

Describe the setpoint regulation by the hypothalamus

A

Regulation of homeostasis
- control of endocrine output from pituitary gland
- regulates output from the autonomic nervous system (ANS)
- behavioural regulations
- done through negative feedback

17
Q

Describe the autonomic nervous system. What are the three main divisions of the ANS?

A
  • 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)
18
Q

What is the main overall function of the ANS? What do the SNS and the PSNS/ PNS help to regulate?

A
  • 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
19
Q

How does the ANS exert its action?

A

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

20
Q

Describe the difference between the autonomic (ANS) and somatic nervous systems (SNS)

A

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

21
Q

What is the organization of the ANS?

A
  • 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*
22
Q

What is the long reflex?

A

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

23
Q

What is the short reflex?

A

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

24
Q

Difference between SNS and PNS?

A
  • most organs have dual innervation, with antagonistic effects SNS vs PSNS
    exceptions:
  • blood vessels
  • sweat glands
  • piloerector muscles
  • kidney
  • adrenal medulla
25
Q

Describe the adrenal gland

A
  • 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
26
Q

What are the neurotransmitters of the Sympathetic and Parasympathetic nervous systems?

A

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

27
Q

Describe the receptors of the ANS?
Location
Receptor
Agonist
Antagonist
Action
Mechanism

A
  1. PNS and SNS ganglia
    Nicotinic (N2)
    - Ach (NT), - Nicotine
    Hexamethonium
    Ligand gated ion channels
    Opens Na+/K+ channels, produces fast EPP, produces fast EPSPs
  2. 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
  3. 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
  4. 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
28
Q

Summary of the receptors in the nervous system:

A

Somatic: motor neuron cholinergic
PSNS: entirely cholinergic
SNS: - preganglionic cholinergic - postganglionic adrenergic - exception: all cholinergic = adrenal gland (preganglion neuron cholinergic)

29
Q

Describe the autonomic neuroeffector junction

A
  • 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
30
Q

What are the effects of the ANS on organs?

A

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

31
Q

What is the sympathetic tone in blood vessels?

A
  • 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
32
Q

What happens when the sympathetic nervous system is innervated?

A

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

33
Q

What happens when the parasympathetic nervous system is innervated?

A
  1. 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
  2. Digestion
    increases bile secretion -> liver
    increases motility and secretion -> stomach + intestines
    releases enzymes and insulin -> pancreas
    - increases digestion and absorption of nutrients
  3. Adrenal glands, kidneys, and bladder
    No PSNS innervation of the adrenal gland
    release urine -> contracts bladder
34
Q

How does the sympathetic and parasympathetic nervous systems innervate the reproductive organs?

A

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

35
Q

Describe the autonomic control of the heart

A
  • 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

Human Physiology (13 decks)

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