Physiology Midterm 1 Flashcards
What is physiology?
The science of the function of living systems
What is function?
“Why does the system exist or why does the event occur?
What is process?
How does a system work/the physiological mechanisms
What is homeostasis?
maintenance of a relatively stable internal environment (especially the ECF), oscillation around a set point
Who coined the term homeostasis and wisdom of the body?
Walter Cannon
Study of homeostatic mechanisms?
Physiology
Failure to compensate for change?
Disease
Study of the failure to compensate for disease?
Pathophysiology
What is local control?
Cells near site of change initiate response (working muscle = metabolites cause vasodilation at that site, not the whole body)
What is reflex control?
Cells at a distant site control response; uses the neural and/or endocrine systems. (blood pressure increase sensed by baroreceptors in aorta and caratid arteries = brain evaluates change and initiates response_
Components of response loop
stimulus, sensor, input signal, integrating centre, output signal, target, response
Negative feedback?
homeostatic, stabilizes variable, response coutneracts stimulus, shutting off response loop
Positive feedback?
NOT homeostatic, reinforces stimulus, sends variable further from setpoint, usually dramatic things
Feedforward control
Anticipates change, boots up system to be ready for change (seeing food = increase salivation and stomach motility in anticipation of a meal, or getting pumped before a race)
What are electrical signals and what cells are the restricted to?
changes in membrane potential and restricted to nerve and muscle cells
What is the most common form of cell to ell communication in the body?
chemical signals
What are target cells?
Cells that respond to signals
Endocrine signalling?
hormone/chemical released into bloodstream and distributed throughout body
Neural signalling?
electrical signal travels down neuron; reaches end and is translated to chemical signal (neurotransmitter) which transmits information to the next cell
neuro endocrine signalling?
electrical signal travels down neuron; reaches end and is secreted into blood
What cells respond to a signal
Only those that have RECEPTORS (presence of receptor determined by genetic expression)
Where are receptors located?
Proteins inside the cell or project to outside the membrane
Lopphobic.hydrophilic ligans bind where?
Surface receptor proteins
Lipophilic/hydrophobic ligans bind where?
intracellular receptors
How many transmembrane folds do GPCRs have?
7
Signal transduction steps?
Signal molecule binds to membrane receptor protein activating intracellular signal molecules which alter target proteins and create a response
Kinase?
Add phosphates
IP3?
Made from PI, GPCR that uses phospholipase C as an amplifier enzyme, releases calcium from intracellular stores
DAG?
made from PI, GPCR, uses phospholipase C as amplifier enzyme, activates protein Kinase C, phosphorylates proteins
Ca2+ in cell to cell signaling?
Binds to calmodulin and other proteins to alter enzyme activity, exocytosis, muscle contraction, cytoskelton movement, channel opening
cAMP in cell to cell signalling?
Amplified by adenyl cyclase and activates PKA and binds to protein ion channels, effects are phosphorylation of proteins and alters channel opening
How can same signal have different effects in different cell types?
Several different types of receptors
How are receptors like enzymes?
Exhibit saturation, specificity, competition for their ligands
How can cells change their response to signals?
By changing receptor number or sensitivty
How do cells increase receptor number?
Increase gene regulation (up regulation)
How do cells decrease receptor number?
Internalize surface receptors (down regulation)
How do cells change receptor sensitivity?
Phosphorylation
Agonist?
Similar molecule that activates receptor, giving the same response, MIMICS it
Antagonist?
molecule that is similar enough to native ligand to bind to receptor, but not activate it, BLOCKER
Cannon’s 4 postulates?
- Nervous system has a role in maintaining fitness of the internal environment (coordinates responses that regulate blood volume, blood pressure, osmolarity, etc) 2. some systems are under tonic control 3. some systems are under antagonistic control 4. one chemical signal can have different effects in different tissues
Tonic control?
Regulates physiological parameters in an up down fashion (blood vessel diameter)
Antagonistic control?
2 systems compete for control over parameter. Whichever has the greater tone will have the greater effect
Where a sensors/detectors/receptors often located?
in the ECF
Central receptors?
Specialized cells/structures CLOSE TO THE BRAIN that convert stimuli into electrical signals (eyes, ears, nose, tongue
Peripheral receptors?
Specialized cells/structures OUTSIDE the brain that convert stimuli into electrical signals (baroreceptors, thermoreceptors, chemoreceptors, etc)
Simple endocrine reflex?
Int/ext change, endocrine system senssor-integrating centre, output signal is a hormone, target, response
Simple neural reflex?
int/ext change, receoptor, input signal:sensory neuron, nervous system:integrating centre, efferent neuron, target, response
A complex neuro-endocrine reflex
Int/ext change, receptor, input signal: sensory neuron, nervous system integrating center, efferent neuron or neurohormone, endocrine integrating centre, output signal #2: hormone, target, response
Difference in specificity in neural reflex and endocrine reflex?
Each neuron terminates on a single target cell or on a limited number of target cells. Endocrine reflex sends hormone to most cells in the body, and only those with a recpetor respond.
Difference in speed between neural and endocrine reflex?
Very rapid versus much slower
Duration of action in neural vs. endocrine reflex
Very short. Responses of longer duration are mediated by neuromodulators. vs. Responses usually last longer than neural responses.
Intensity of a neural reflex is related to?
Each signal is identical in strength. Stimulus intensity is correlated to increased frequency of signalling.
Intensity of endocrine reflex is related to?
Amount of hormone dumped into system
Evolution in animals in nervous systems?
Jellyfish “nerve net,” flatworm’s cerebral ganglia and nerve cords, earthworm’s primitive brain and ventral nerve cord ganglia…CEPHALIZATION…fish with a small forebrain, birds with bigger forebrain, mammals with large, folded forebrain
Development of vertebrate CNS?
Flat neural tissue converges, with the epidermis forming a covering, the neural plate border forming neural crest cells, and the nueral tube formed by the folding
Neural crest cells?
Will migrate throughout the body and contribute to many structures, including peripheral nervous system
Neural tube forms?
CNS
Human CNS at 4 weeks?
Anterior end of neural tube specialized into 3 regions
Human CNS at 6 weeks
Neural tube differentiated into major brain regions present at birth
At 6 weeks, hind brain differentiates into?
Medulla, cerebellum, and pons
At 6 weeks, forebrain differentiates into?
Diencephalon and cerebrum
11 weeks into human CNS development
Growth of cerebrum much more rapid that of other regions
Human CNS at birth
Cerebrum covers most of other brain regions; convoluted surface due to rapid growth in confined space
Meninges in order from superficial to deep
Dura mater, arachnoid mater, pia mater
Protection and support for CNS?
Surrounded by bony cage, 3 layers of connective tissue, fluid between layers –CSF
CSF is secreted from?
Choroid plexus in the 3rd and 4th ventricle
How is CSF made?
Ependymal cells pump out ions, which draw water out of plasma, making CSF
Oligiodendrocytes
form myelin sheaths within CNS
microglia
immune cell lineage–phagocytic
astrocytes
regulate local extracellular fluid by releasing chemicals
ependymal cells
create barriers between compartments
How often is CSF recycled/flushed and how much is made per day?
4x per day and 500 mL
Compared to blood, CSF has
Lower K+, Ca2+, HCO3-, glucose, nad pH, similar Na+, and VERY LOW PROTEIN AND NO BLOOD CELLS
How is CSF reabsobred into venous blood?
arachnoid villi
Circulation of CSF?
Lateral ventricles, third ventricles, fourth ventricles, through Foramen of Magendie and Luschka to arachnoid villi to superior sagittal sinus/dural sinus, venous return to heart. At the fourth ventricle, some of the CSF is exchanged with the central canal of spinal cord…some also goes back into 4th ventricle here, too
How are tight junctions promoted in the CNS?
Astrocyte foot processes secrete paracrine factors that promote tight junction formation, which prevent solute movement between endothelial cells
What can readily cross the blood-brain barrier?
Lipid soluble molecules like ethanol
What types of substances will only cross the blood-brain barrier if specific transports/carriers are present on endothelial cells of capillaries within CNS?
Hydrophilic substances like ions, amino acids, peptides, and proteins
How is the blood-brain barrier important for phamacological practices?
Allows for the design of drugs that cannot or can cross the barrier, depending on what you want. Anti-histamine doesn’t cross, so doesn’t make you drowsy, but WANT l-dops to cross using an AA transporter to become dopamine for Parkinson’s disease
Can neurons use anaerobic metabolism?
NO…obligate aerobes
Can oxygen readily corss the blood-brain barrier?
YES!!
How much of the body’s glucose does the body consume, and how does it access it?
Consumes approximately half of body’s glucose consumption, and the capillaries of CNS express high levels of glucose transporters (GLUT-1)
How much of the CO goes to the brain to supply oxygen and glucose?
15%
Purpose of spinal cord?
Major path for information flow between CNS and skin, joints, muscles and contains neural networks involved in locomotion
4 regions of spinal cord?
Cervical, thoracic, lumbar, and sacral
Sympathetic neuron axons leave the spinal cord at what levels?
Thoracic and lumbar
Parasympathetic neurons’ axons leave the spinal cord at what levels?
Brain stem and sacral regions
Ascending and descending tracts consist of what type of matter?
WHITE matter (myelinates axons)
Dorsal columns are part of what tracts and purpose of them
Part of ascending tracts an send information of touch/pressure and proprioreception from the 4 regions
Spinocerebellar column is part of what type of tract and its purpose?
Ascending tracts and is used for proprioreception/posture/coordination
Spinothalamic column is part of what type of tract and its purpose?
Ascending tract and for pain/temperature
Corticospinal tracts are part are part of what type of tract and purpose?
DESCENDING tracts for for VOLUNTARY movement
Spinal reflex?
Stimulus. sensory information to spinal cord, integrating centre is an interneron, command to muscles/glands, response…Initiates response without input from the brain (but does send some sensory information there for perception)
Purpose of corpus callosum>
Axons that allow communication between sides of the brain
Parts of the diencephalon>
Thalamus, pineal gland, hypothalamus, and pituitary gland (:interbrain, in between brain)
What is the oldest, most primitive part of the brain?
Brainstem
Brain stem contains structures dervied from embryonic regions____?
Hind and midbrain
How many spinal nerves originate at brain stem?
11 OF 12
Cranial nerve x?
VAGUS nerve
Reticular formation is located where?
Brain stem
Purpose of reticular formation?
Diffuse network of neurons that is involved in processes such as arousal/slepp, muscle tone, coordination of breathing, and blood pressure
Function of gray matter in medulla?
Involved in control of many involuntary functions–blood pressure, breathing, swallowing, vomiting
Function of medulla’s white matter?
Ascending somatosensory tracts, descending corticospinal tracts, and site of decussation (crossing over) for most neurons in corticospinal tract
Diencephalon is located?
Between brain stem and cerebrum
Purpose of thalamus?
Relays and integrates sensory info from lower parts of CNS, ears, eyes, motor info from cerebellum
Purpose of hypothalmus?
Tiny region, but major centre for homeostasis–contains centres that drive behaviour related to hunger, satiety, thirst, and influences autonomic responses, and endocrine responses
Purpose of pineal gland?
Secretes hormone melaatonin–involved on circadian and seasonal rhythms
What’s a key differnce between a local/paracrine factor regulator and a hormone?
Local regulators diffuse to neighbour cells; hormones travel hroughout the body to distant target cells
In signal transducction, ligand binding to a cell surface receptor results in information transfer in for of _____ from upstream and downstream pathways?
Alterations in protein confirmation (phosphates and CA2+ change protein confirmation)
A 2nd messenger participates in signal transduction pathway by…
Relaying a message from inside of membrane to cytoplasm
Glucagon acts via a GPCR that acts by increasing levels of cyclic AMP. What is the 1st and 2nd messengers?
1st = glucagon, amplifier = adenyl cyclase, 2nd messenger = cAMP
Four lobes of brain?
Frontal, parietal, occipital, and temporal
How many hemispheres in brain?
2
FUrrow or groove in brain?
Sulcus (plural = sulci)
Convolution?
Gyrus
Three regions of cerebral gray matter?
Cerebral cortex, basal ganglia/nuclei, and limbic system
Purpose of basal ganglia/nuclei?
Motor coordinatoin
Purpose of cerebral cortex?
Outermost part of cerbrum, mostly higher brain functions
Purpose of limbic system?
Emotions
Functional areas of cerebal cortex?
Sensory areas that translate sensory input into perception (awareness), motor areas that control skeletal muscles, and association areas that integrate info from sensory and motor areas
Frontal lobe contains what?
Primary motor cortex, premotor cortex/motor association area, and the prefrontal association area
Parietal lobe contains?
Primary somatic sensory cortex and sensory association area that receives info from muscoskeletal system, visceral, and taste buds
Occipital love contains?
Visual association area and visual cortex
Temporal lobe contains?
Auditory cortex and auditory association area
Another name for primary motor cortex in frontal lobe?
Precentral gyrus
Another name for primary somatosensory cortex in parietal lobe?
Postcentral gyrus
Neural pathways extend from sensory areas to association areas to…?
integrate stimuli into perception
Small body parts with LOTS of control have what size on the somatotopic map?
Bigger area of the motorcortex, like face and hands
Places that have lots of sensation need what size in the somatosensory somatotopic map?
Big regions…like the lips and hands, but NOT the toes/libs
Scientist credited with hte burnty toast cure to epilepsy?
Wildred Penfield
Neural pathway for voluntary movement?
Primary motor cortex sends signal to contract. Signal is carried in the anterior corticospinal tract, where at the caudal end of the medulla, most of the corticospinal neurons cross to opposite sides of the body. Finally, the primary motomeuron crosses over at the bottom and synapses onto the somatic motor neuron which will synapse onto the skeletal muscle
The blood brain barrier…
consists of cerebral capillaries that are more tightly sealed than other capillaries in the body and involved a relationship between glial cells called astrocytes and endothelial cells of cerebral capillaries
The dorsal root ganglia contain…
Cell bodies of somatosensory neurons
How can the spinal cord act as an integrating centre with cc to brain?
Step on a tack…withdrawal reflex is a simple neural reflex, but crossed extensor reflex requires input from the brain
Examples of stimulus processing that occur consciously?
Vision, hearing, taste, smell, equilibrium, touch, temperature, pain, itch, proprioreception
Stimulus processing that occurs subconsciously?
Somatic stimuli (muscle length and tension and proprioreception) and visceral stimuli (blood pressure, distension of GI tract, blood glucose concentrations, internal body temperature, osmolarity of body fluids, ling inflation, pH of CSF, and pH and O2 of blood
Example of how a sensory pathway works
Stimulus (some form of physical energy) acts on a receptor. Receptor trasduces stimulus into intracellular signal (typically a change in membrane potential). If change in MP reaches threshhold, APs travel along afferent neuron for either subconscious processing or conscious processing in correct region in cortex
Sensory receptors for pain, touch, temp?
Free nerve endings…NO MYELIN
Sesory receptors for cutaneous touch?
Pacinian corpuscle…nerve endings enclosed in connective tissue capsules
Receptors for special senses?
Usually cells that release neurotrasnmitter onto sensory neurons…like hair cells
Chemoreceptors respond to? Examples?
Respond to chemicals…examples area O2, pH, carious organic molecules such as glucose
Mechanoreceptors?
Respond to pressure (baroreceptors), cell stretch (osmoreceptors), vibration, acceleration, sound
Photoreceptors respond to?
Pohtons of light
Thermoreceptors respnd to?
Varying degrees of heat and cold
Stimulus to a sensrry neuron usulally does what?
Opens or closes ion channels in receptor cell membrane directly or via a 2nd messenger…mostly open cation channels for hyperpolarization but sometimes open K+ channels for hyperpolrization
What are receptive fields?
Stimuli that fall within a certain area that activate cutaneous receptors (patch of skin) or photoreceptors (light falling on an area of the retina)
How many afferent neurons are needed in pathway to CNS?
2…first order/primary that is directly associated with stimuli and second order/secondary that relays information from first neuron
Convergence of sensory info?
Several primary sensory neurons converge onto a secondary neuron, convergence allow for summation of multiple stimuli at hte secondary sensory neuron, making it more likely to reach AP. Perceived as one signl because the 2 separate points cannot be discriminated
Smaller receptive fields results in?
The stimuli will activate separate pahteays to teh brain and the two points are perceived as distinct stimuli
Visceral sensory info mostly travels via what?
Vagus nerve fibres
Visceral sensory info is integrated where?
Brainstem…usually subconscious, although fullness and pain can reach consciousness
Olfactory info is sent?
Directly to the olfactory cortex/bulb
Equilibrium sensory info is usually sent?
To the cerebellum
Somatic senses, hearing and vision sent to?
Appopriate cortex after processing in thalamus
How can brain distinguish different sensations if all APs are identical?
CNS must be able to decode the type of stimulus/modality, location, intensity, and duration
How is sensory modality determined in brain?
Determined by the type of neuron activated and where the pathway terminates in brain
How is location of stimulus decoded in brain?
Coded according to which receptive fields are activated. Example, touch receptors from a particular part of body project to a specific location in somatosensory cortex.
What is lateral inhibition, and how does it work?
Primary neuron response is proportional to stimulus strength. Pathway closest to the stimulus uses branches from its secondary neuron to inhibit its neighbours. Inhibition of lateral neurons enhances pereption of stimulus onto tertiary neuron, making the sensation more easily localized.
How is stimulus intensity coded for?
- number of receptors activated (populartion coding) 2. Frequency of APs coming from individual receptor cells
How does the number of receptors activated code for stimulus intensity?
Different thresholds for stimulation among group of receptors. With low intensity stimulus, most sensitive (lowest threshold) receptors recruited first. As stimulus intensifies, more receptors activated.
How do the frequency of APs code for stimulus intensity?
Frequency of APs increases with stimulus intensity, up to maximum that the axon can transmit. More intense = higher frequency AP
How is a long, strong stimulus coded for?
Lots of receptors potentials for a long duration of time are integrated at trigger zone. Then, the frequency of APs is proportional to stimulus intensity. Duration of a series of APs is proportional to stimulus duration. NT release varies with pattern of APs arriving at axon terminal
Tonic receptors?
Slowly adapt, and respond throughout stimulus. Fire rapidly when first activated, and then slow and maintain their firing as long as the stimulus is present. In general, the stimuli that activate tonic receptors must be monitored continuously by the body, like blood pressure.
Phasic receptors?
Rapidly respond to a stimulus and then turn off if stimulus remains constant. Like smelling cologne at first, but then the smell goes away.
Pain, temp., and coarse touch cross where in the spinal cord and ascend in what tracts?
Cross midline in spinal cord and ascend via dorsal columns
Fine touch, vibration, and proprioreception cross midline where, and ascend in what tracts?
Corss in medulla and ascend in spinothalamic tracts
Cutaneous sensory receptors that are just free nerve endings serve what purpose?
Pain, temperature, and hair movement
Where are free nerve endings for cutaneous sensation located?
Various places, including wrapped around hair root and as nocireceptors
Merkel disk receptive field, location, adaptation, and function?
Small, superficial, slow, and for sustained touch/pressure, texture
Meissner’s corpuscle receptive field, location, adaptation, and function?
Small, superficial, fast, for beginning and end of fine touch/pressure
Ruffini corpuscle receptive field, location, adaptation, and function?
Large, deep, slow, and for sustained gross touch/vibration
Pacinian corpuscle receptive field, location, adaptation, and function?
Large, deep, fast, for beginning and end of gross touch/vibration
Where are nocireceptors found?
In many tissues (not just skin)
What is pain?
A sensation rather than a stimulus
Nocireception is mediated by?
Free nerve endings that express ion channels that respond to a variety of strong stimuli (chemical/mechanical/thermal)
Pain is mediated by a release of what local chemicals, and what do they do?
K+, histamine, prostaglandins, serotonin, and substance P. Wither directly activate nocireceptors or sensitize them by lowering their thresholds (inflammatory pain)
Pain is mediated by what type of channels?
Transient Receptor Potential Channels
What are Transient Receptor Potential Channels?
Expressed on the membranes of many different cells and mediate a cariety of sensations including pain, heat/warmth, cold, some tastes, pressure, vision, osmotic pressure, stretch…
What type of channels are TRP channels?
Relatively non-selective cation channels (Na, Ca, Mg)
TRP V (vanilloid) receptors respond to?
Temperature (receptor subtypes have different ranges), pepper, allicin/garlin, clove oil, thyme, oregano, wasabi, menthol, and peppermint
Pathways for somatic pain?
Spinal reflexes and ascending pathways to cerebral cortex (info also sent to limbic system and hypothalamus, leading to emotional reactions and autonomic responses like nausea, vomiting, and sweating)
Fibre type for fast pain?
Delta fibres…small, myelinated
Fibre type for slow pain?
C fibres…small unmyelinated
How does visceral/referred pain work?
Pain from viscera synapses onto sane 2nd order neuron as a part of skin, so brain cannot distinguish between the skin and viscera, so you feel pain in the area of skin, not the viscera where the pain is originating from
Most primitive sense?
Olfaction
Olfactory pathway?
Olfactory receptor cell (primary neuron) in olfactory epithelium, to Cranial Nerve 1, to secondary neuron on olfactory bulb, to the olfactory tract, to olfactory cortex in temporal lobe
Non-motile cilia on olfactory receptor neuron acts as?
Dendrites for odorant receptors
Olfactory Receptor Neurons are what tpe of neurons?
Bipolar neurons
Axons of olfactor receptor neurons go through?
Gaps in cribiform plate
How many types of odorant receptors does an olfactory receptor neuron expresss?
1
Odarant receptors are?
GPCRs and form one of the largest gene families in vertebrates (3-5% genome)
How is a particular odor interpreted?
Input from 100s of olfactory neurons in combinations
5 BASIC TASTES?
Sweet (carbs…energy?), sour (H+), salty (Na+), bitter (many compounds…warning of possible toxicity), and umami (glutamate, some nucleotides…protein?)
Taste receptors cells are?
Non-neural epithelial cells that frequently come into contact with nocious chemicals, and they are replaced approximately every 10 days
What tastes release ATP onto primary afferent neurons?
Sweet, Umami, and Bitter
How do bitter taste buds transmit information to primary afferent neurons?
Release NT
Taste transduction for sweet, umami, or bitter
Ligands activate TRC, various intracellular pathways activated, Ca2+ signals triggers ATP formation, ATP released, Primary sensory neuron fires and APs sent to brain
Taste transduction of Sour?
Ligand activates TRC, various intracellular pathways activated, Ca2+ signal triggers exocytosis of NT, NT is released, primary sensor neuron fires, and AP sent to brain
Sweet, umami, and bitter ligands are believed to bind to?
GPCRs
Taste sensory pathway?
Presynaptic taste cell, primary sensory neuron through cranial nerves, medulla (synapse with secondary neuron), thalamux, gustatory cortex in parietal lobe.
Low=frequency waves translate to?
Low-pitched sounds
High-frequency waves translate to?
High-pitched sound
Amplitude of sound wave determines?
Loudness
Sound transduction?
Sound swaves striking outer ear are directed down the ear canal until they hit the tympanic membrane and cause it to vibrate (1st transduction) Tympanic vibrations are transferred to the malleus, incus, and the stapes. Stapes’ vibration pulls and pushes on the oval window to create waves in the fluid-filled cochlea (2nd transduction). As waves move through the cochlea, they push on flexible membranes of the cochlear duct and bend sensory hair cells inside the duct. Movement of cochlear duct open or closes ion channels on hair cell membranes, creating electrical signals (3rd transduction) Electrical signals alter NT release (4th transduction) NT binding to primary sensory neurons initiates AP (5th transduction) that send coded information about sound through cranial nerve and brain
3 fluid-filled channels of cochlea?
Vesitbular, cochlear, and tympanic duct
What 2 ducts on the cochlea are continuous?
Vestibular and tympanic. Cochlear duct is a dead-end tube that connects with the vestibular apparatus
Perilymph?
Fluid in vestibular and tympanic ducts. Similar to plasma (high Na+, low K+)
Endolymph?
Fluid in cochlear duct. Similar to intracellular fluid (low Na+ and high K+)
Organ of Corti?
Found in the cochlear ductm composed of hair cell receptors and support cells. Sits on the basilar membrane and is partially covered by the tectorial membrane
Signal transduction in hair cells for hearing?
In neutral position, tonic rate of APs are sent, MP about -30mV. Waves deflect cilia towards tallest members of bundle, more channels open nd cation ion entry depolarizes the cell. When the tectorial membrane pushesthe cilia away from the tallest members, channels close, and less cation entry hypoerpolarizes cell.
Sensory coding for pitch in cochlea?
Higher frequencies near oval window, and lower frequencies further from oval window.
How is loudness coded for?
How much the hair cells bend = increase the rate of APs = more frequent AP = louder noise
Auditory pathway?
Cochlear nerve, cochlear nuclei in medulla, secondary neurons on pons, nuclei in midbrain and thalamuc before projecting to auditory cortex in temporal lobes. Collateral pathways take info to the reticular formation and the cerebellum
Conductive hearing loss?
No transmission through either external or middle ear, issues with earwax or fluid, can usually be repaired
Central hearing loss?
Damage to neural pathway between ear and cerebral cortex or damage to cortex itself (stroke)…uncommon
Sensorineural hearing loss?
Damage to structures of inner ear/death of hair cells due to loud noises, common in young and old. Hair cells cannot be replaced in mammals
Dynamic component of equilibrium?
Movement of body through space
Static component of equilibrium?
Position of head
Otolith orgrans?
Utricle and saccule, for linear acceleration and head position
Semicircular canals?
Rotational acceleration
Hair cells of semicircular canals are grouped in?
Cristae, within ampulla of canals
Cupula?
Like the tectonic membrane in hearing, a gelatinous mass that embeds hair cells.
Utricle for?
Forward/backward acceleration. Head tilt. Riding in a car
Saccule for?
Vertical displacement…elevator
How do otolith organs sense linear acceleration and head positioN?
Hair cells grouped in maculae, within utricles nad saccules. Otoliths move, the gelatinous otolith membrane slides with them, bending the hair cell cilia and setting off a signal
Afferent fibres that transmit info about a dull ache in your arm are most likely…
Small diamter, unmyelinated (C fibres)
Afferent neurons for fast pain?
Small, myelinated…delta fibres
Heat afferent fibres?
Small diamter, unmyelinated
You’ve stepped on a tack with your bare left foot. What type of receptor would detect this?
Free nerve endings
Pathway for stepping on a tack?
Spinal nerve, dorsal horn gray matter, spinothalamic tract, thalamus, somatosensory cortex
Temperature, pain, and course touch sent via what tract?
Spinothalamic
Fine touch, proprioreception, and vibration sent via what tract?
Dorsal columns
You’re snow blowing. The ____ cutaneous receptors that are stimulated by vibration?
Pacinian (beginning and end) and Ruffini (sustained)
The cutaneous receptors that’d be used for Braille would have _______ receptive fields and ascend to the brain via the _________
small, dorsal columns
Neural pathway for equilibrium?
Vestibular hair cells release NT onto primary sensory neurons of the vestibular nerve. Those sensory neurons either synapse in the vestibular nuclei of the medulla or run without synapsing to the cerebellum, which is the primary site for equilibrium processing. Collateral pathways run from the medulla to the cerebellum or upward through the reticular formation and the thalamus.
Purpose of canal of Schlemm?
Collects aqueous humour and recycles it to the bloodstream. If blocked, there is an increase in intraeye pressure, which can lead to glaucoma
What is the optic disk?
Region where optic nerve and blood vessels leave the eye
Neural pathways for vision?
Optic nerve, optic chiasm, optic tract, thalamic relay, visual cortex (occipital lobe)
What is the pupillary light reflex?
Control of pupil diameter according to intensity of light
Autonomic pupillary light reflex pathway?
Detector: photoreceptors in retina. Afferent: afferent neurons travelling in optic nerve Integrating Centre: Thalamus/brainstem (midbrain). Efferent: motor neurons travelling in oculomotor nerve. Effectors: Smooth muscles regulating pupil diameter–circular/sphincter = constriction (parasympathetic) and radial = dilation/sympathetic
Reflex that dilates the pupil is?
Sympathetic…radial muscles
Reflex that constricts the pupil?
Parasympathetic…sphincter/circular muscles
If light is shined in the left eye, what happens to the left and right pupils? Why?
Both will constrict…consensual reflex because of the crossing over of info in the midbrain
What is phototransduction?
Conversion of light into changes in membrane potential by photoreceptor cells in retina
3 types of photoreceptors?
Rods–monochromatic vision/low light
Cones–colours (red, green, blue)
Modified ganglion cells–mediate pupillary light reflex and circadian/seasonal rhythms (non-visual responses to light)
Purpose of pigment epithelium?
Absorbs excess light
Cellular organization of the retina?
Cone/rod to bipolar cell to ganglion cell, whose axons form the optic nerve
What makes the fovea’s cellular organization different than the rest of the retina’s?
Cones receive light directly because the intervening neurons (ganglion and bipolar) are pushed aside. The fovea is also free of blood vessels.
Convergence in the retina onto rods serves what purpose?
The high degree of convergence of rods onto ganglion cells increases the visual field of the rods, allowing for increased sensitivity to low light. Rods aren’t for fine reading or colour (can’t see colour in low light).
Purpose of cones?
Colour and fine light/reading
What is rhodopsin is composed of what 2 molecules?
Opsin, a protein embedded in the membrane of the rod disks and retinal, the light absorbing of the pigment
When retinal absorbs light, what happens?
The orientation of the double bond flips, allowing retinal to leave opsin (opsin bleaching)
Signal transduction in photoreceptor cells in the dark?
Rhodopsin is inactive cGMP is high, CNG and K+ channels open (Na+ and Ca2+ entering cell), membrane potential is around -40 mV, and there is a tonic release of glutamate onto bipolar neurons
Signal transduction in photoreceptor cells in light conditions?
Activated opsin (retinal leaves, opsin bleaching), active transducin, decreased levels of cGMP, closes CNG channels, cell hyperpolarized, and glutamate release decreases in proportion to amount of light onto bipolar neurons.
Recovery phase in photoreceptor cells?
Retinal converted to inactive form in pigment epithelium cell, and then recombines with opsin to form rhodopsin
Sweet tastes are detected when…
Sugars bind to GPCR expressed by taste receptor cells and intiate a signal transduction cascade leading to Ca2+ influx and release of signal molecule (ATP) that binds to a primary afferent neuron
The olfactory bulb is…
the structure in which secondary neurons that have recieved a neural input from olfactory receptor neurons continue on to the olfactory cortex as the olfactory tract (CN1) NO THALAMIC RELAY!!
The most direct initiator of the pressure wave with in the perilymph of vestibular duct is…
vibration of oval window
How does the pressure wave in the vestibular duct fluid get transduced into stimulation of cochlear hair cells?
Fluid wave pushes on tectorial mebrane, bending cilia embedded in it. Bending of cilia as a result of the fluid waves causes opening or closing of ion channels, a change in NT release and a change in AP frequency to primary afferent neuron
Perceived pitch determined by…
location of activated hair cells on basilar membrane
Perceived volume determined by…
frequency of AP to brain
What is a hormone?
Chemical messenger secreted into the blood by specialized cells
What tpyoe of long-term/ on going things do hormones regulate?
Growth/development, metabolism, regulation of internal environment (temp, water balance, ions), reproduction
Hormones act on target cells by regulating…
Enzyme activity, ion transport across a membrane, and gene expression to protein synthesis
Endogenous means?
Generated from within the body (insulin from beta cells in pancreas)
Exogenous means?
Generated from outside the body (recombinant insulin)
What were the first endocrinology experiments, and who performed them?
Arnold Berthold did experiments on removing chickens’ gonads.
Classical approaches in experimental endocrinology?
Ablate (remove the suspected gland), replace (gland or extract of gland), create a situation of excess, and run biological assats on intact animals and cell/tissue cultures, and introduce putative hormone
Features of Typical Classical Hormones?
- Secreted by a group of cells derived from epithelial tissue that form discrete glands 2. Secreted into blood 3. Travel to distance targets 4. Act at very low concentrations
Exception to the typical hormones?
Non-classic hotmones are not secreted by identifiable glands (endocrine cells of gut, neurons, and immune cells), some molecules clearly identified as hormones are also secreted in CNS, and act as NT, and sometimes hormones act locally (testosterone doing maintenance work in testes)
Exocrine gland?
Secrete out via ducts…still in contact with epithelium
Endocrine gland?
Dump into capillaries…no contact with surface
Ways that equilibrium between free and bound hormone?
- Hormones are inactivated on their way through liver/kidney (major determinant of hormone’s half life) 2. Nonspecific proteases in ECF break them down (peptidases) 3. Hormone-receptor complex can be internalized (endocytosis)
3 ways to classify hormones?
Source, mechanism of action, and chemistry
Mechanisms of hormones?
GPCR, receptor tyrosine-kinases, and intracellular receptors
3 types of hormones?
Peptide/protein, steroids (derived from cholesterol), and amine/amino acid (derived from either tyrosine or tryphtophan)
Largest group of hormones?
Peptide/protein hormones
Half-life of peptide/protein hormones?
A few minutes…sustained responses require continuous release of hormone
Typical responses to peptide hormones?
Bind to membrane receptors, responses usually rapid (modifying existing enzymes or transport proteins and opening/closing membrane channels), can also have slower effects via changes in gene expression
Peptide hormone synthesis and secretion?
- Product of ribosome is preprohormone (large inactive precursor) 2. Signal sequence directs it to rough ER’s lumen 3. Cleaved into prohormone as it moves through ER/golgi 4. Packaged into vesicles in Golgi, along with enzymes that will carry out cleavage to final active form
3 signal transducction pathways for peptide hormones?
Receptor/second messengers, Receptor/Tyrosine kinase, or G-protein coupled ion channel opening
The perceived volume of a sound is determined by…
the frequency of AP sent by primary afferent neuron and the amount of NT released by sensory hair cell
The vertebrate retina is said to be “inverted” because…
Photoreceptors cells are at back of retina, furthest from light entering the eye, with their light sensing end facing away from entering light
Aps are generated in what cells during vision?
Ganglion cells (local potentials in rods/cones and bipolar cells)
The visual fields of the fovea are…
very small
Would a person with occipital lobe trauma have a normal pupillary light reflex in both eye?
YES! Because of crossing over in midbrain.
Steroid hormones are made in what cells?
Cells that express cholesterol side chain cleavage enzyme…the adrenal cortex, gonads and placenta
Half life of steroid hormones is usually?
1/2 hour to hours to days because they are chemically stable, simple molecules
Steroid synthesis and release?
Cholesterol imported into cell or synthesized in cell. Steroidogenic enzymes in inner mitochondrial membrane or smooth ER determines which steroid the cell makes
Are steroids stored?
No, made on demand by increasing activity of enzymes. Released from cell by simple diffusion.
How do steroid hormones circulate in the body?
Ciruclate bound to proteins, either pecific carriers or albumin
Equilibrium equation for steroid hormones?
Bound to carrier protein free bound to receptor
Steroid hormones in testes?
Testosterone (DHT)
Steroid hormones in ovaries?
Estradiol and progesterone
Steroid hormones in adrenal cortex?
Cortisol (glucocorticoid), aldosterone (mineralocorticoid)
Steroid hormone action?
- Most steroids circulate bound to protein carriers. Only unbound hormones can diffuse into cell. 2. Classic steroid receptors are in cytoplasm or nucleus. 3. Receptor-hormone complex binds to DNA and activates or represses expression of particular genes. 4. Genes transcribed to mRNA that moves out to cytoplasm 5. Translation produces new proteins
Steroid receptor proteins are?
Ligand activated transcription factors
Transcription factors activated by steroids bind to?
Steroid response elements (regulatory sequences upstream of particular genes) New proteins are typically other transcription factors…
Amine hormones are derived from what AAs?
Tryptophan and tyrosine
What are the tyrosine-derived hormones?
Catecholamines and thryroid hormones
What are the catecholamines?
Dopamine, norepinephrine, and epinephrine
What are the thyroid hormones?
Thyoxine and triiodothyonine (need iodine)
What is the purpose of the adrenal medulla?
It is a specialized group of neurons that secrete epinephrine (neurohormone) from the chromaffin cells in adrenal medulla (analogous to postganlionic sympathetic neurons)
In the endocrine system, what does hte hypothalamus do?
Produces neurohormones that are stored in, and secrete by posterior pituitary gland, and produces neurohormones that control release of hormones from anterior pituitary gland
Posterior pituitary gland made from?
Neural tissue (pars nervosa/neurohypophysis) NOT A TRUE GLAND
Anterior pituitary gland made from?
Rathke’s puch…adenohypophysis/pars distalis…TRUE gland
Pathway in posterior pituitary gland??
- Neurohormone is made and packaged in neuron cell body in hypothalamus 2. Vesicles are transported down axon 3. Vesicles containing neurohormone are stored in posterior pituitary 4. Posterior pituitary releases neurohormone into blood
Hormones of posterior pituitary gland?
Oxytocin and vasopressin
Anterior pituitary gland pathway?
- Neurons synthesizing neurohormones in hypothalamus release them into first capillary bed of portal system 2. Portal veins carry neurohormones directly to second capillary bed into anterior pituitary gland 3. Endocrine cells in anterior pituitary releae peptide hormones into second set of capillaries, and peptides exit via venous drainage.
Hypothalaminc hormones?
Dopamine, thyro-tropin releasing hormone, corticotropin releasing hormone, somatostatin (negative), Growth-hormone releasing hormone, gonadotropin releasing hormone
Anterior pituitary hormones?
Prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone, growth hormone, follicle-stimulating hormone, luteinzing hormone
Feedback loop of hypothalamus-pituitary axis involve what 3 integrating centres?
Hypothalamus, anterior pituitary, and endocrine target of pituitary hormone
In a feedback loop of the hypothalamus-pituitary axis, what are the feedback signals?
The hormones themselves
Long loop feedback in hypothalamic pituitary axis?
Hormone acting on the anterior pituitary and/or hypothalamus
Short loop feeback of hypothalamic-pituitary axis?
Trophic hormones acts on hypothalamus
What is a trophic hormone?
A hormone that controls the secretion of another hormone and nourishes the target cell
Synergism in hormones?
Combined effect is greater than the sum of individual effects
Example of synergism in the endocrine system?
Glucagon + epipnephrine + cortisol = huge effect on blood glucose
Permissiveness in endocrine system?
Hormone is required but is not enough for full effect.
Example of permissiveness in endocrine system?
Puberty cannot occur unless thyroid and reproductive hormone are available
Antagonism in endocrine system?
One hormone opposes the action of another
Types of endocrine pathologies?
Excess/hypersecretion, deficiencieshyposecretion, or abnormal responsiveness of target tissues
Oxytocin, a peptide, is released by neuron terminals in the posterior pituitary gland enters the blood stream and acts on uterine smooth muscle. This substane would be classified as…
A hormone and neurohormone
Acinar cells of the pancreas secrete proteins into the lumen of the small intestine in response to PNS stimulation. These proteins would be considered…
Exocrine secretions
Endocrine cells producing large amounts of peptide hormone would have?
Lots of rough ER and vesicles containing hormone product near plasma membrane
Endocrine cells producing steroid hormone would have?
LOTS of SMOOTH ER
Steroid hormones are made in what cells?
Cells that express cholesterol side chain cleavage enzyme…the adrenal cortex, gonads and placenta
Half life of steroid hormones is usually?
1/2 hour to hours to days because they are chemically stable, simple molecules
Steroid synthesis and release?
Cholesterol imported into cell or synthesized in cell. Steroidogenic enzymes in inner mitochondrial membrane or smooth ER determines which steroid the cell makes
Are steroids stored?
No, made on demand by increasing activity of enzymes. Released from cell by simple diffusion.
How do steroid hormones circulate in the body?
Ciruclate bound to proteins, either pecific carriers or albumin
Equilibrium equation for steroid hormones?
Bound to carrier protein free bound to receptor
Steroid hormones in testes?
Testosterone (DHT)
Steroid hormones in ovaries?
Estradiol and progesterone
Steroid hormones in adrenal cortex?
Cortisol (glucocorticoid), aldosterone (mineralocorticoid)
Steroid hormone action?
- Most steroids circulate bound to protein carriers. Only unbound hormones can diffuse into cell. 2. Classic steroid receptors are in cytoplasm or nucleus. 3. Receptor-hormone complex binds to DNA and activates or represses expression of particular genes. 4. Genes transcribed to mRNA that moves out to cytoplasm 5. Translation produces new proteins
Steroid receptor proteins are?
Ligand activated transcription factors
Transcription factors activated by steroids bind to?
Steroid response elements (regulatory sequences upstream of particular genes) New proteins are typically other transcription factors…
Amine hormones are derived from what AAs?
Tryptophan and tyrosine
What are the tyrosine-derived hormones?
Catecholamines and thryroid hormones
What are the catecholamines?
Dopamine, norepinephrine, and epinephrine
What are the thyroid hormones?
Thyoxine and triiodothyonine (need iodine)
What is the purpose of the adrenal medulla?
It is a specialized group of neurons that secrete epinephrine (neurohormone) from the chromaffin cells in adrenal medulla (analogous to postganlionic sympathetic neurons)
In the endocrine system, what does hte hypothalamus do?
Produces neurohormones that are stored in, and secrete by posterior pituitary gland, and produces neurohormones that control release of hormones from anterior pituitary gland
Posterior pituitary gland made from?
Neural tissue (pars nervosa/neurohypophysis) NOT A TRUE GLAND
Anterior pituitary gland made from?
Rathke’s puch…adenohypophysis/pars distalis…TRUE gland
Pathway in posterior pituitary gland??
- Neurohormone is made and packaged in neuron cell body in hypothalamus 2. Vesicles are transported down axon 3. Vesicles containing neurohormone are stored in posterior pituitary 4. Posterior pituitary releases neurohormone into blood
Hormones of posterior pituitary gland?
Oxytocin and vasopressin
Anterior pituitary gland pathway?
- Neurons synthesizing neurohormones in hypothalamus release them into first capillary bed of portal system 2. Portal veins carry neurohormones directly to second capillary bed into anterior pituitary gland 3. Endocrine cells in anterior pituitary releae peptide hormones into second set of capillaries, and peptides exit via venous drainage.
Hypothalaminc hormones?
Dopamine, thyro-tropin releasing hormone, corticotropin releasing hormone, somatostatin (negative), Growth-hormone releasing hormone, gonadotropin releasing hormone
Anterior pituitary hormones?
Prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone, growth hormone, follicle-stimulating hormone, luteinzing hormone
Feedback loop of hypothalamus-pituitary axis involve what 3 integrating centres?
Hypothalamus, anterior pituitary, and endocrine target of pituitary hormone
In a feedback loop of the hypothalamus-pituitary axis, what are the feedback signals?
The hormones themselves
Long loop feedback in hypothalamic pituitary axis?
Hormone acting on the anterior pituitary and/or hypothalamus
Short loop feeback of hypothalamic-pituitary axis?
Trophic hormones acts on hypothalamus
What is a trophic hormone?
A hormone that controls the secretion of another hormone and nourishes the target cell
Synergism in hormones?
Combined effect is greater than the sum of individual effects
Example of synergism in the endocrine system?
Glucagon + epipnephrine + cortisol = huge effect on blood glucose
Permissiveness in endocrine system?
Hormone is required but is not enough for full effect.
Example of permissiveness in endocrine system?
Puberty cannot occur unless thyroid and reproductive hormone are available
Antagonism in endocrine system?
One hormone opposes the action of another
Types of endocrine pathologies?
Excess/hypersecretion, deficiencieshyposecretion, or abnormal responsiveness of target tissues
Oxytocin, a peptide, is released by neuron terminals in the posterior pituitary gland enters the blood stream and acts on uterine smooth muscle. This substane would be classified as…
A hormone and neurohormone
Acinar cells of the pancreas secrete proteins into the lumen of the small intestine in response to PNS stimulation. These proteins would be considered…
Exocrine secretions
Endocrine cells producing large amounts of peptide hormone would have?
Lots of rough ER and vesicles containing hormone product near plasma membrane
Endocrine cells producing steroid hormone would have?
LOTS of SMOOTH ER
