Section 2: Autonomic and Endocrine System Flashcards
Organisation of nervous sytems: CNS and PNS
CNS:
Brain
Spinal cord
PNS: Cranial nerves Spinal nerves Ganglia Peripheral nerves
Sensory vs motor neurons
Sensory neurons: afferent, carry into body
Motor neurons: efferent, carry away from body. Multi-polar in structure
Via cranial and spinal nerves
Types of motor (efferent) neurons
Somatic (voluntary) –> Skeletal muscle
Autonomic (involuntary) –> Sympathetic or parasympathetic –> cardiac muscle, smooth muscle, glands
The alarm response
Increased heart rate and force of contraction
Dilation of pupils
Decreased salivation
Dilation of bronchi –> breathe faster
Contraction of arrector pili muscles and increased secretion from sweat glands (skin)
Constriction of blood vessels, especially in skin
Decreased digestion (gut)
Increased blood sugar, blood pressure (liver) and water retention (kidneys)
The relaxation response
Decreased heart rate and force of contraction
Contraction of pupils
Increased salivation
Constriction of bronchi –> breathe slower
Dilation of peripheral blood vessels (skin)
Increased digestion (gut)
Autonomic Nervous System (ANS)
Controls body’s internal response
ANS - Sympathetic division
Responses associated with exercise, emotion, excitement
Alarm response
ANS - Parasympathetic division
Responses associated with repletion, rest, relaxation
Relaxation response
ANS: Autonomic vs somatic - sensory input
Autonomic: Mainly interoceptors (internal sensing)
Somatic: Special senses and somatic senses
ANS: Autonomic vs somatic - control of output
Autonomic: Involuntary from limbic system, hypothalamus, brain stem and spinal cord
Somatic: Voluntary from cerebral cortex (outer cortical brain)
ANS: Autonomic vs somatic - motor neuron pathway
Autonomic: Two-neuron pathway (pre-ganglionic and post-ganglionic)
Somatic: One-neuron pathway
ANS: Autonomic vs somatic - neurotransmitters
Autonomic: Acetylcholine
- Pre-ganglionic axons
- Post-ganglionic parasympathetic
- Post-ganglionic sympathetic to sweat glands
Autonomic: Norepinephrine
- Post-ganglionic sympathetic fibres other than to sweat glands
Somatic: Acetylcholine
ANS: Autonomic vs somatic - effectors
Autonomic: Smooth muscle, cardiac muscles, glands
Somatic: Skeletal muscle
Raynaud disease
Excessive stimulation following emotion stress/exposure to cold
Chronic vasoconstriction
Fingers and toes become ischemic –> could kill cells in long term
Therefore important for responses to be inducible
Hypothalamus - functions
Control internal organs via ANS and pituitary gland
Regulates behavioural patterns, circadian rhythms and sleep/wake cycles
Controls body temp
Regulates eating and drinking behaviour
Endocrine system - main organs
Hypothalamus
Pituitary
Adrenal glands
HPA axis - controls other organs in endocrine system
Types of hormones
Circulating hormones - distant target cells
Local hormones (paracrines and autocrimes)
- Paracrine hormones - nearby target cell
- Autocrine hormones - same target cell
Mechanism of action of lipid-soluble hormones
- Lipid soluble hormone diffuses into cell
- Activated receptor-hormone complex alters gene expression
- Newly formed mRNA directs synthesis of specific proteins on ribosomes
- New protein alters cell’s activity
Mechanism of action of water-soluble hormones
- Binding to receptor activates G protein which activates adenylate cyclase
- Activated adenyl cyclase converts ATP to cAMP
- cAMP serves as a second messenger to activate protein kinases
- Activated protein kinases phosphorylate other enzymes
- Phosphorylated enzymes catalyse reactions that produce physiological responses
- Phosphodiesterase inactivates cAMP
Parts of the adrenal gland
From superior to inferior:
Capsule
Adrenal cortex
Adrenal medulla
Enhancing the alarm response
Pre-ganglionic neuron joins to post-ganglionic neurons
Modified post-ganglionic neurons act as secretory cells - secretes epinephrine and norepinephrine into bloodstream when stimulated
Adrenal medulla - hormones, stimulated by, principal actions
Hormones: Epinephrine (adrenaline) and norepinephrine
Stimulated by: ACh from sympathetic pre-ganglionic neurons
Principal actions: Enhance sympathetic autonomic alarm response
Adrenal cortex - hormones, stimulated by, principal actions
A:
Hormone: Mineralo-corticoids (e.g. aldosterone)
Stimulated by: Increased K+ and angiotensin II in blood
Principal action: Increase blood Na+ and water and decrease blood K+ –> increased blood V and pressure
B:
Hormone: Glucocorticoids (e.g. cortisol)
Stimulated by: ACTH from pituitary, which is stimulated by CRH from hypothalamus
Principal actions: Resistance reaction to stress, dampens inflammation and depresses immune responses
What do the hypothalamus and pituitary gland regulate
Development
Metabolism
Homeostasis
Portal system between hypothalamus and pituitary gland
Capillaries - portal vein - capillaries
Negative feedback effects on pituitary gland
Elevated cortisol inhibits release of ACTH by anterior pituitary corticotrophs (cortisol –> anterior pituitary)
Elevated cortisol inhibits release of CRH by hypothalamic neurosecretory cells (cortisol –> hypothalamus)
Resistance reaction: Actions and consequences of glucocorticoids - Protein breakdown
Increase protein breakdown mainly in muscle fibres
Amino acids released into bloodstream may be used for synthesis of new proteins and ATP production
Resistance reaction: Actions of glucocorticoids - Gluconeogenesis
Liver cells convert some amino acids or lactic acid to glucose, which neurons and other cells can use for ATP production
Resistance reaction: Actions of glucocorticoids - Lipolysis
Breakdown of triglycerides and release of fatty acids from adipose tissue into blood
Resistance reaction: Actions of glucocorticoids - Resistance to stress
Increased glucose and ATP combat stresses, e.g. exercise, fasting, fright, temp extreme
Resistance reaction: Actions of glucocorticoids - Vasoconstriction
Blood vessels become more sensitive to hormones that cause vasoconstriction –> rise in blood pressure
Resistance reaction: Actions of glucocorticoids - Anti-inflammatory
Inhibit white blood cells that participate in inflammatory responses (to limit tissue damage by them)
Retards tissue repair and slow wound healing
Resistance reaction: Actions of glucocorticoids - Immune depression
High glucocorticoid conc depress immune responses
Used therapeutically following organ transplants to retard graft rejection
Fight-or-flight response vs resistance reaction
Fight-or-flight is a faster response and only lasts a short while, whereas resistance reaction is slower and lasts longer (stage 2)
Fight-or-flight response
Immediate burst
Initiated by nerve impulses from hypothalamus to sympathetic division of ANS
Adrenal medulla involvements (epinephrine and NE)
Resistance reaction
Slower, longer lasting
Associated with hypothalamus - pituitary - adrenal cortex
Initiated in large part by hypothalamic releasing hormones
Corticosteroid (cortisol) production
The stress response
Sympathetic autonomic activation (stage 1)
Mobilise resources for immediate physical activity
Glucose and oxygen consumption
Alertness and activity
Reduce tissue damage (stage 2)
Ward off danger or flee!
Links between neuroendocrine and immune systems
Neuroendocrine —hormones (e.g. cortisol)—> immune
Neuroendocrine —autonomic nerves—> immune
Immune —cytokines (immune hormones)—> neuroendocrine
Short-term remedial action
Threat system arousal:
- Blood (energy)
- Muscle (motor)
- Vigilance (sensory)
Dampen unnecessary:
- Digestion
- Immunity
Types of stresses
Eustress (acute):
- Prepares us to meet certain challenges
- Helpful, beneficial
Distress (chronic):
- Associated with undesirable events
- Potentially harmful
How is the spinal cord connected to the brain
Through the foramen magnum of the occipital bone
Encircled by bones of vertebral column
What does PNS consist of
All nervous tissue outside the CNS
e.g. nerves, ganglia, sensory receptors
What is a nerve
A bundle of hundreds to thousands of axons plus associated CT and blood vessels that lie outside the brain and spinal cord
Number of cranial and spinal cords
12 pairs of cranial nerves emerge from brain
31 pairs of spinal nerves emerge from spinal cord
What are ganglia
Small masses of nervous tissue, consisting primarily of neuron cell bodies located outside of the brain and spinal cord
Closely associated with cranial and spinal nerves
What are enteric plexuses
Extensive networks of neurons located in walls of organs of GI tract
What is a sensory receptor
A structure of the nervous system that monitors changes in internal or external environment
Nervous system - functions (3)
Sensory function
Integrative function
Motor function
Nervous system - sensory function
Sensory receptors detect internal or external stimuli
This sensory info is then carried into the brain and spinal cord through cranial and spinal nerves
Nervous system - integrative function
Processes sensory info by analysing it and making decisions for appropriate responses - known as integration
Nervous system - motor function
Once sensory info is integrated, the nervous system may elicit an appropriate motor response by activating effectors through cranial and spinal nerves
Nervous tissue is comprised of what types of cells
Neurons and neuroglia, which combine in a variety of ways in diff regions of the nervous system
Neurons - electrical excitability
The ability to respond to a stimulus and convert it into an AP
What is a stimulus
Any change in the environment that is strong enough to initiate an AP
What is an AP
An electrical signal that propagates along the surface of the membrane of a neuron
Parts of a neuron
Cell body
Dendrites
An axon
Types of neurons
Multipolar neurons (most common neuron in brain and spinal cord)
Bipolar neurons
Unipolar neurons
Dual innervation
Most organs have dual innervation - receive impulses from both sympathetic and parasympathetic neurons
Cholingergic neurons
Release ACh
Where is ACh stored
Stored in synaptic vesicles, released by exocytosis
Adrenergic neurons
Release NE
Where is norepinephrine stored
Stored in synaptic vesicles, released by exocytosis
Receptor agonist
A substance that binds to and activates a receptor, in the process mimicking the effect of a natural neurotransmitter / hormone
Receptor antagonist
A substance that binds to and blocks a receptor –> prevents a natural neurotrasmitter or hormone from exerting its effect
Hypothalamus - composed of a dozen or so nuclei in which four major regions?
Mammilary region - most posterior part of hypothalamus
Tuberal region - widest part of hypothalamus
Supraoptic region - superior to optic chiasm
Preoptic region - anterior to supra optic region
Hormones: Down-regulation and up-regulation
Down-regulation: If hormone is present in excess, number of target-cell receptors may decrease. Makes target cell less sensitive to a hormone
Up-regulation: If hormone is deficient, number of target-cell receptors may increase. Makes target cell more sensitive to a hormone
Most common type of endocrine hormone
Circulating hormones - pass from secretory cells that make them into interstitial fluid and then into blood
Local hormones
Act locally on neighbouring cells or on the same cell that secreted them without first entering the bloodstream
Usually inactivated quickly
Types of lipid-soluble hormones
Steroid hormones - derived from cholesterol Thyroid hormones (T3 and T4) - synthesised by attaching iodine to tyrosine Nitric oxide (NO) - hormone and neutransmitter
Types of water-soluble hormones
Amino hormones - synthesized by decarboxylating and modifying certain amino acids
Peptide hormones and protein hormones - amino acid polymers
Eicosanoid hormones - derived from arachidonic acid (fatty acid)
Water-soluble vs lipid-soluble hormones - free?
Most water-soluble hormones circulate in watery blood plasma in a ‘free’ form
Most lipid-soluble hormone molecules are bound to transport proteins
Lipid-soluble hormones: Transport proteins - functions
Make lipid-soluble hormones temporarily water-soluble –> increases solubility in blood
Retard passage of small hormone molecules through filtering mechanism in kidneys –> slows rate of hormone loss in urine
Provide a ready reserve of hormone, already present in bloodstream
The responsiveness of a target cell to a hormone depends on…
Hormone’s conc in blood
Abundance of target cell’s hormone receptors
Influences exerted by other hormones
Hormones - permissive effect
Where actions of some hormones on target cells require a simultaneous or recent exposure to a second hormone
Hormones - synergistic effect
Where effect of two hormones acting tgt is greater or more extensive than effect of each hormone acting alone
Hormones - antogonistic effect
Where one hormone opposes actions of another hormone
The release of most hormones occur in…
Short bursts, with little or no secretion between bursts
Hormone secretion is regulated by…
Signals from nervous system
Chemical changes in blood
Other hormones
Most hormones work via ____ feedback
Negative feedback, but a few operate via positive feedback
Infundibulum
Attaches pituitary gland to hypothalamus
Anterior vs posterior pituitary
Anterior: accounts for ~75% of weight of gland, composed of epithelial tissue
Posterior: composed of neural tissue
Stressor
Any stimulus that produces a stress response
Stress response is controlled by..
The hypothalamus
Stages of the stress response
- An initial fight-or-flight response (alarm response)
- Extended alarm response
- A slower resistance reaction, and eventually
- Exhaustion
Resistance stage and stressor
Resistance stage helps body continue fighting a stressor long after the fight-or-flight response
This is why heart continues to pound for several mins even after the stressor is removed
Stress response - exhaustion
Due to resources of body eventually becoming depleted they can’t sustain the resistance stage
Prolonged exposure to high levels of cortisol and other hormones
Adrenergic receptors
Bind both norepinephrine and epinephrine
Autonomic tone
The balance between sympathetic and parasympathetic activity
Autonomic tone - regulation
Regulated by hypothalamus, which typically turns up sympathetic tone at the same time it turns down parasympathetic tone and vice versa
Why are effects of sympathetic stimulation longer lasting and more widespread than effects of parasympathetic stimulation
Sympathetic post-ganglionic axons diverge more extensively –> many tissues activated simultaneously
ACh esterase quickly inactivates ACh, but NE lingers in synaptic cleft for a longer period
Epinephrine and NE secreted into blood from adrenal medullae intensify and prolong responses caused by NE
Parasympathetic responses (SLUDD and ‘three decreases’)
Salivation Lacrimnation Urination Digestion Defecation
Decreased heart rate
Decreased diameter of airways
Decreased diameter of pupils
Aldosterone
Major mineralocorticoid
Regulates homeostasis of Na+ and K+ (mineral ions)
Helps adjust blood pressure and volume
Promotes excretion of H+ in urine –> removes acids from body –> prevents acidosis
Corticotropin-releasing hormone (CRH)
Promotes release of ACTH from anterior pituitary –> flows into blood –> stimulates glucocorticoid secretion
Adrenal glands - vascular?
Highly vascularised
Adrenal medulla
Modified sympathetic ganglion of ANS
Cells lack axons and form clusters around large blood vessels
Secrete hormones - epinephrine and NE
Cytokines
Small protein hormones that stimulate or inhibit many normal cell functions, e.g. cell growth and differentiation
Synaptic transmission - steps
- AP arrives at pre-synaptic axon terminal
- V-gated Ca2+ channels open on pre-synaptic terminal
- Ca2+ causes synaptic vesicles to fuse to the cell membrane and release neurotransmitters via exocytosis
- Neurotransmitter diffuses across synaptic cleft
- Neurotransmitter binds to receptors on post-synaptic cell membrane
- Ligand-gated ion channels open on post-synaptic membrane and Na+ flows into post-synaptic cell
- Post-synaptic potential reaches threshold and fires an AP
- Nerve impulses continue to propagate
What is multiple sclerosis
A disease that occurs due to destruction of myelin sheaths –> slows down propagation of nerve impulses
Multiple sclerosis - symptoms
Vary widely depending on amount of nerve damage and which nerve are affected
May experience long periods of remission without any new symptoms
Lose ability to walk independently or at all
Numbness or weakness in one of more limbs - usually occurs on one side of body at a time
Electric-shock sensations with certain neck movements
Tremor, lack of coordination or unsteady gait
Effects of visions - partial or complete loss, double vision
Slurred speech, fatigue, dizziness, tingling, pain in parts of body
Connection of anterior and posterior pituitary to hypothalamus
Anterior: via hypophyseal portal system (vascular connection)
Posterior: via hypothalamic-hypophyseal tract (neural connection)
Anterior and posterior pituitary - response to…
Anterior: releasing and inhibiting hormones from ventral hypothalamus
Posterior: directly to hypothalamic neurons
Hypophyseal portal system
A vascular arrangement in which blood flows from one capillary bed in the hypothalamus to another capillary bed in the anterior pituitary without going through the heart in its journey
Kidneys and sympathetic activation - steps
- Sympathetic nerve activation (as a result of fight/flight response)
- Increase in arteriole resistance –> pressure changes
- Baroreceptors sense change in pressure
- Juxtaglomerular cells in kidney release renin into blood
- Renin acts on angiotensin –> cleaved to angiotensin I via renin –> cleaved to angiotensin II via ACE
- Angiotensin II causes vasoconstriction, increases water retention and stimulates formation of aldosterone
If cells in a particular organ don’t respond to water-soluble hormone prolactin, the most likely reason is…
The cells lack the prolactin surface receptor
What occurs most rapidly when in a situation of immediate alarm
Sympathetic nerve signals affect various body functions
What is produced by hypothalamus to control the anterior pituitary
Releasing and inhibiting hormones
Resistance reaction: Responses
Increased glucose, fatty acids, amino acids
Sensitised vessels
Reduce inflammation
Immune suppression
