Endocrine/Nervous Flashcards
Endocrine vs. Exocrine
Ductless, secretes hormone directly into the bloodstream vs. via ducts such as sebaceous glands
Gland
An organ specializing in secretion of substances for further use in the body or excretion of substances for elimination ex. liver excretes bile pigments
Hormone
A chemical produced in one location that exerts its effect in a place far removed form the source ( via the bloodstream )
Steroid Hormones
Water insoluble, diffuse through the membrane and bind to receptors inside the cell, act directly at the level of the nucleus. Ex. androgens (testosterone), estrogen, corticosteroids.
Protein Hormones
Long chain polymers of amino acids, do not enter the cell but rather bind to cell membrane receptors and exert their effect via an intermediary (2nd messenger system) like cyclic AMP. ex. insulin; hypothalamic releasing factors.
Amine Hormones
Small molecules, do not enter the cell but rather bind to cell membrane receptors and exert their effect via an intermediary (2nd messenger system) like cyclic AMP ex. thyroxine, norepinephrine.
What is homeostasis maintained by?
The neuroendocrine control centre which is the hypothalamus by way of its control of the master gland ( pituitary gland.)
ADH
Source: Hypothalamus but stored in the post pit
Target/Action: Collecting ducts in the kidneys retain 30% more water from the filtrate= increase in BP and contraction of arteriolar smooth muscle resulting in vasoconstriction= increase in BP
ADH Patho
- Alcohol depresses ADH production from the hypothalamus and release by the post pit= increased urine volume= dehydration
- ADH deficiency may result in diabetes insipidus
Oxytocin
Source: Hypothalamus but stored in post pit
Target/Action: Promotes contraction of uterine smooth muscles during child birth=parturition and stimulates the mammary glands to letdown milk ( suckling stimulates oxytocin release) Both are positive feedback loops.
HGH
Source: Ant pit but production/release is controlled by hypothalamus’s GHRF and inhibition is controlled by the hypothalamus’s GHIF
Target: All body tissues
Action: Osteoblasts promotes deposition of bone matrix in bone tissue, protein synthesizing tissue (muscles/ tissue repair), carb catabolism (glycogen breakdown into glucose in cells causing blood glucose levels to rise)
HGH Patho
Overproduction/Hyperexcretion: pituitary giantism/acromegaly
Underproduction/Hyposecretion: pituitary dwarfism
Prolactin
Source: Ant pit but release is stimulated by PRH from the hypothalamus
Target: Mammary glands
Action: starts and maintains milk production, suckling stimulates PRH production, positive FBL
TSH
Source: Ant pit but release is controlled by TRF from hypothalamus
Target: Thyroid Gland
Action: Causes the thyroid gland to produce T3 and T4 which together make up thyroid hormone.
TH
Source: Thyroid Gland
Target: Cells
Action: Controls basal metabolic rate or cellular operations rate ( rate of aerobic cellular respiration in mitochondria resulting in things such as growth and heat production)
Thyroid Patho
- Congenital Underproduction: cretinism which is a condition where the nervous system is underdeveloped due to deficiency in thyroid hormones resulting in mental delay
- Adult Underproduction: hypothyroidism which is an autoimmune disease. S/S include: weight gain, water retention, lethargy, hypertension, decrease basal metabolic rate. treated by exogenous thyroxine.
* Goiter: thyroid enlargement usually due to lack of dietary iodine. - Adult Overproduction: hyperthyroidism which is also an autoimmune disease. S/S include: antibodies stimulate thyroid hormone release, exophthalmos or protruding eyes, thin or hyperactive dt increase basal metabolic rate, 40-50 year old females
What other hormone does the thyroid release?
Calcitonin: stimulates osteoblast activity which will overall decrease blood calcium levels
Parathyroid Glands
Parathormone: stimulates osteoclast activity which removes Ca+2 and PO4 from bones resulting in increase in blood calcium levels, also promotes calcium absorption from the small intestine and decreases calcium excretion from kidneys.
Adrenocorticotropic hormone
Source: ant pit but release is controlled by CRF from hypothalamus
Target: Adrenal Cortex
Action: Causes the adrenal cortex to release glucocorticoids, mineralocorticoids and sex hormones (gonadocorticoids) response to long term stress
Glucocorticoids
Ex. cortisol
Mobilize energy stores, protein and fat breakdown, suppress inflammatory reaction, healing and repair.
Mineralocorticosteroids
Ex. Aldosterone
Promotes Na+ retention by kidneys= increase in BP, promotes K+ and H+ secretion at DCT of kidney tubules, for example loss of blood
Sex Hormones
Steroid hormones mostly testosterone
Adrenal Medulla
Not controlled by pituitary but by the nervous system.
Hormones: Norepinephrine and epinephrine
Actions: Fight or flight response, increase in HR BP and resp. rate, bronchiolar dilation (more air in), sweat gland activity (cooling), arrestor pili contraction, pupil dilation, blood shunts from skin and gut to muscles (mobility)
Adrenal Patho
- Overproduction: esp. cortisol results in cushing syndrome S/S: buffalo hump and moon facies
General Adaptation Syndrome (GAS)
The bodies general response to unrelieved stress, cannot be diagnosed.
Three Step Response:
1. Alarm Reaction: mostly adrenal medulla hormones (fight or flight)- epinephrine, but ACTH and thyroid hormones are also released by their glands.
2. Resistance Stage: corticosteroid levels increase to deal with the long term stress
3. Exhaustion Stage: adrenal glands lose ability to cope with stressor causing collapse and death
Normally adrenal hormones feed back to the hypothalamus to inhibit further release once the stressor is relieved (negative feedback). In this case, the stressor is not relieved so the positive feedback occurs preventing normal levels of these hormones and instead relating in more Ne/epinephrine and corticosteroids to be released.
FSH and LH
Sex hormones
Melanocyte Stimulating Hormone (MSH)
From the pars intermedia
Target: Melanocytes in skin epidermis
Action: Promotes normal production of melanin (skin pigment) and acts as a neurotransmitter.
* NOT MELATONIN
Pancreas
Both exocrine and endocrine
Exocrine: acinar cells produce enzymes
Endocrine: Alpha- produces glucagon which breaks down glycogen into glucose in the liver Beta- Produces insulin which synthesizes glycogen from glucose in the liver and also promotes trans membrane movement of glucose into cells and Delta- produces somatostatin (GHIF) All three cell types are found within the islets of langerhans.
Diabetes Mellitus: Type 1 S/S
-Cause is insulin non production or insulin deficiency (Juvenile Onset) Insulin Dependant
S/S:
-Increase in blood glucose levels (hyperglycemia)
-H2O osmotically pulled from tissues
-increase in BP
-Kidneys excrete excess H2O and glucose= sugar in urine and dehydration, also electrolyte imbalances
-Cells become glucose starved therefore fats are used as an energy source=ketone bodys produced resulting in fruity smelling breath, lethargy, weight loss, and blood pH drops.
Long Term Effects of DM 1
- Atherosclerosis: increased fat transport so more fatty deposits in arteries= risk of MI, strokes, and pulmonary embolisms
- Microangiopathy: Blood capillaries become weak
- Ulceration because of poor healing due to poor vascularization and sugary blood results in infection= amputation
- Blindness due to retinal blood vessel breakage
- Glomeruli in kidneys are affected= chronic renal failure
How DM 1 Affects the Nervous System
Peripheral neuropathy: decreased or increased sensitivity to stimuli therefore decreased pain perception
Causes of Type 1 DM
- Genetic Predisposition: Inherited defect of the immune system triggered by an environmental stimulus. There are 18 genes associated with DM 1 production but some people have protector genes that would inhibit them from getting DM 1.
- Viral: Genetic defect in the immune systems on switch. The immune system does not turn on when the virus is present so the virus then attacks the beta cells destroying them.
- Autoimmune: Genetic defect in the immune systems off switch. The immune system turns on to attack the virus but does not turn off when its supposed to so it attacks the beta cells themselves.
DM 1 is and inherited defect of the immune system that interacts with environmental factors
Causes of Type 2 DM
- Genetic Predisposition: The genes that carry this trait are different from the genes that carry DM1
- Environmental Triggers: The genetic predisposition interacts with triggers such as obesity, excess calorie intake or not burning enough calories. This results in resistance to insulin
Major environmental trigger is glucotoxicity because too much glucose may be toxic to beta cells Therefore, if it goes undetected the beta cells become damaged making the body cells less responsive to glucose. = result is resistance to the action of insulin and insulin deficiency.
Treatment DM 1
Insulin injections or use of insulin pump. 10% of all cases
Treatment DM 2
Diet, exersize, oral hypoglycaemic drugs and insulin. 90% of all cases
Myelin
Fatty cell membrane coating of some axons
3 Functions of Myelin
- Insulates and protects the myelinated axons
- Allows for saltatory impulse transmission
- Acts as a tunnel for regeneration (PNS: if severed pieces are close together, CNS: generally produces molecules that inhibit regeneration
Neuroglial Cells: 4Types in CNS
Supporting cells found in CNS
- Astrocytes: star shaped, binding/ spatial organization, reabsorption of K+ and one neurotransmitters, produce scar tissue, part of blood/brain barrier-screens substances moving from blood to brain.
- Microglia: transform into phagocytes
- Oligodendrocytes: produce myelin sheath in CNS not PNS
- Ependymal Cells: Lines CNS cavities (choroid plexuses of brains ventricles) circulates CSF using cilia.
Cells in PNS
- Schwann Cells: Produce myelin sheath
2. Satellite Cells: Function like Astrocytes
Steps in Impulse Transmission Along an Axon
- Nerve cell is at resting potential which is -70mV. This is maintained by Na+/K+ pumps (3 Na out for every 2 K in to counteract the leakage of K+ gates).
- Stimulus opens both Na+ and K+ voltage gated channels. Na+ rapidly diffuses into the cell reducing cell charge difference from -70mV to +30mV= depolarization but only if the threshold potential of -40mV is reached first.
- K+ diffuse out of the nerve cells single gated K+ channels open while Na+ channels become inactivated = repolarization.
- Hyperpolarization occurs when K+ continues to diffuse out while Na+ channels are resetting because the K+ gates are leakier.
- All K and Na channels close
- Refractory period occurs when Na/K pumps re-establish resting potential so that a new impulse can be generated.
- When Na+ channels open they stimulate neighbouring Na+ channels causing impulse transmission
All or None
A neutron either fires completely or not at all. Firing only occurs if the stimulus causes depolarization to the threshold potential (minimum voltage re’q to trigger an action potential)
Saltatory Transmission
The impulse “jumps” from node of ranvier to node of ranvier because it cannot enter the nerve cell through the myelin sheath. -Very fast. De-/Re+ only occur at the nodes where Na+ and K+ gates are exposed.
Electrical Synapses
- Different from chemical synapses due to their cell to cell contact via connexons (b/w glial cells and b/w cardiac cells).
- Connexons are gap junctions that connect adjacent cells via transmembrane proteins to allow ion movement (intercalated discs).
Steps in Nerve Impulse Transmission Across a Synapse
- Action potential arrives at pre-synaptic membrane causing voltage gated Ca+2 channels to open.
- Ca diffuses into the axon bulb
- This causes neurotransmitter containing synaptic vesicles to fuse with the presynaptic membrane
- The neurotransmitter is dumped into the synaptic cleft via exocytosis
- Neurotransmitter diffuses across the synaptic cleft to the postsynaptic membrane
- When enough neurotransmitter molecules bind to specific receptor sites on post synaptic membrane, a new impulse is generated unless threshold potential is not reached.
- Stimulus termination: specific enzymes break down neurotransmitters and the presynaptic membrane reuptakes the
Summation at the Synapse
Balance between neuroexcitatory and neuroinhibitory transmitters. The summation of the two will either allow or inhibit the postsynaptic membrane to depolarize. NE transmitters usually cause it to depolarize and NI transmitters usually cause it to hyper polarize (inhibiting depolarization)
- Some hallucinogenic drugs mimic these chemicals
Sensory
From receptor to CNS, also known as afferent neurons
Motor
From CNS to effector, also known as efferent neurons
Interneurons
Connect sensory to motor, much of CNS
Multipolar
One axon and 2 or more dendrites, esp CNS, most common
Bipolar
One axon, one dendrite on opposite sides ex retinas of eyes.
Unipolar
One cell process, most common in dorsal root ganglions
Wraps of nerves
Epineurium: Wraps neuron, collagen rich
Perineurium: Wraps fascicle, collagen rich
Endoneurium: Wraps axon/dendrite outside of myelin sheath, collagen rich
Nuclei vs Ganglion
Nuclei: cluster of nerve cell bodies in CNS
Ganglion: cluster of nerve cell bodies in PNS
Reflex Arc Components
Receptor, afferent/sensory neuron, interneuron, efferent/motor neuron, effector
Reflexes
Rapid, autonomic, stereotypical responses used to
a) control visceral organs (neural stimulation of adrenaline release.
b) react to external stimuli to prevent further injury (pain withdrawal)
Reflex Examples
- Patellar reflex- lower leg extension
- Biceps/Triceps jerk reflex
- Abdominal Reflex- pin
- Corneal reflex- blinking tearing
- Plantar and Babinski reflex- run pin along sole of foot (Plantar= normal adult curls toes, Babinski= normal infant extends toes)
Crossed Extension Reflex
When one limb with draws, the opposite limb extends in order to protect.
- Accidentally step on a tack with right foot
- Info is transmitted along a sensory neuron to dorsal root and interneuron of spinal cord and back along motor neuron from interneuron and ventral root to hamstring muscles to flex knew of the right leg (withdrawal from pain=simple reflex)
- Simultaneously, motor impulses run to the quadriceps muscles of the left leg in order to extend it so that the body weight is supported when the right knee flexes.
Meninges
Dura mater= superficial
Arachnoid mater= middle
Pia mater= deep
Hydrocephalus
Buildup of CSF in brain which can be drained by a cerebral shunt.
Meningitis or encephalitis
Inflammation of the brains meninges which is very dangerous because expansion is very limited in the adults brain. Sore neck is a symptom.
Cerebrum
Occipital: vision
Parietal: motor and sensory areas
Temporal: hearing and smell (olfaction)
Frontal: personality, thought patterns, behaviour, reasoning
Insula: deep to frontal, parietal and temporal… Taste and integrates ANS functions
Cerebellum
Balance, muscular activity, motor coordination. Mainly LEARNING how to do certain actions such as crawling/ walking etc.
Thalamus
Distribution/relay centre with info to/from the brain being gathered and transferred to appropriate regions= gateway to the cerebral cortex. Filters
Hypothalamus
- regulates core body temperature
- helps regulate BP (ADH and ACTH->aldosterone) and HR
- electrolyte balance (Na+, K+ due to aldosterone) and H2O balance via ADH.
- sleep/wake cycle (suprachiasmatic nucleus relays light info from the eyes to the pineal gland)
- hunger/thirst
- controls pituitary, plus hormone/ RF production
- forms part of the limbic region
Pineal Gland
Sleep/ wake cycle via melatonin. More melatonin is released at night due because it is influenced by light stimulating the suprachiasmatic nucleus of the hypothalamus.
*Patho- Jet lag and night shifts
Brainstem
Midbrain, pons, medulla oblongata
Medulla Oblongata
- Regulates HR/BP via cardioaccelleratory/cardioinhibitory center (cardiac center)
- Regulates BP via vasomotor center (more or less vasoconstriction)
- Regulates ventilation/breathing (resp centre)
- contains other reflex arcs such as vomiting coughing sneezing and peristalsis
Reticular Activating System
- Parts of medulla oblongata and thalamus
- screens unwanted/unneeded stimuli
Limbic System
- Parts of cerebrum, thalamus, hypothalamus, etc
- Feelings, emotions, pleasure and anger
Blood Supply to the Brain
Circle of willis- cerebral arterial circle, aneurysms mainly occur here
Cerebrovascular Accident
Stroke which is caused by thrombosis, embolism, aneurysm.
Thrombosis
complete or partial blockage of an artery due to a build up of fatty plaques (atherosclerosis) which form a thrombus.. Can happen at the junction before the common carotid artery splits. Treatment: carotid endarterectomy
Embolism
Mobile fatty plaque or clot is an embolus: gets caught in a blood vessel in the brain, may have originated from the heart dt A fib (Cardiac arrhythmia with quivering atria)
Aneurysm
A type of hemorrhagic stroke, ballooning and breakage of a blocked vessel ( usually in the circle of willis in young)
Epidural Hematoma
Blood accumulates between dura mater and skull plate. Usually arterial bleeding (acute). Tx: relieve Intracranial pressure by drilling a burr hole; surgical repair of vessels.
Subdural Hematoma
Blood accumulates between dura mater and brain. Usually venous bleeding (acute, sub acute, or chronic) Tx: relieve Intracranial pressure by drilling a burr hole; surgical repair of vessels.
Seizure Disorders
- Epilepsy: diagnosed as 2 or more seizures 24 hours apart. Caused by trauma, stroke, infection, timer, genetics etc.
- Petit Mal Seizure: short periods of unresponsiveness, rapid eye blinking also known as absence seizure.
- Grand Mal Seizure: Classic seizure also known as Tonic-Clonic seizure
Steps to a Seizure
- Aura: momentary visual, auditory, olfactory, gustatory sensation (hallucination)
- Rapid loss of consciousness: grunting, crying, contracting abdominals.
- Tonic clonic spasms: (tonic=rigidity, clonic=alternate contraction/relaxation) Spasms decrease in number over time but not in intensity.
Risks: Remove hazards and cover sharp objects. - Relaxed unconsciousness (one minute to half hour)
- Regaining of consciousness with no recollection of event .
TX- anti convulsive meds
Status Epilepticus
Life threatening medical emergency, one seizure every 5 minutes or 2 or more seizures running together w/o patient regaining consciousness.
Spinal Cord
- 31 pairs of spinal nerves
- all have sensory and motor neurone (mixed nerves)
- 8 cervical, 12 thoracic, 5 lumbar 5 sacral and 1 coccygeal
Spinal Cord Injuries-Cervical
C3 and above- Fatal and/or total respiratory control lost therefore ventilation re’q. Close to medulla oblongata.
C4- Tetra/Quadriplegia, meaning all 4 limbs are affected.
C5- Tetraplegia with some shoulder and elbow function affected, no sensation below clavicles.
C6- Tetraplegia with impaired hand function, no sensation below nipples.
C7/C8- some hand involvement.
Spinal Cord Injuries- Lumbar
Paraplegia, cannot walk (involved with thoracic region too)
Prolapsed Disc
Herniated or slipped disc, gel-like inner nucleus pulposus squeezes spinal nerve if outer rigid annulus fibrosis of fibrocartilage and collagen is ruptured.
Cranial Nerves
- Olfactory- sensory
- Optic- Sensory
- Oculomotor- Motor
- Trochlear- Motor
- Trigeminal- Both
- Abducens- Motor
- Facial- Both
- Vestibulocochlear- Sensory with minor motor role
- Glossopharyngeal- Both
- Vagus- Both
- Accessory- Motor with minor sensory role
- Hypoglossal- Motor with minor sensory role
Olfactory
- Carries sensory impulses to the temporal, frontal and insula lobes; Limbic system.
- Olfactory receptors may be damaged by trauma or affected with age.
- Partial loss of smell=anosmia (sinus problems, trauma, congenital)
Optic
- carries visual impulses from retina to occipital lobes of the brain
- impulses partially cross over =decuss at optic chiasma en route to brain
Oculomotor-All the rest 3
-Operates 4 of 6 extrinsic eyeball muscles, plus iris diaphragm (pupil reflex) and ciliary bodies changing for lens shape during focussing (accommodation)
Trochlear-SO4
-operates superior oblique eyeball muscle via fully system to abduct eyeball.
Trigeminal
-Sensory:face and motor:chew
3 Divisions:
1. Ophthalmic-around eyes and nose=sensory
2. Maxillary- upper jaw=sensory
3. Mandibular- lower jaw= both, chewing muscles
Path: Trigenimal Neuralgia- paroxysmal firing of sensory part of this nerve caused by inflammation… EXTREME PAIN
Abducens-RE6
-Abducts rectus externa=extrinsic eyeball muscle
Facial
Sensory-taste and motor-face (5 branches)
- carries afferent impulses from taste receptors
- motor to facial muscles (expression but not chewing)
- motor to tear glands , salivary glands.
Path: Bells Palsy= paralysis and partial loss of taste on affected side of face caused by herpes infection.
Vestibulocochlear
Vestibular-afferent impulses for equilibrium
Cochlear- auditory impulses for hearing
Glossopharyngeal
- Contains both autonomic and somatic fibers
- carries sensory info from tongue and pharynx (taste and touch)
- motor for swallowing and gag reflex
Vagus
- Contains both autonomic and somatic fibres
- carries sensory from pharynx, larynx, esophagus and visceral organs
- motor=parasympathetic fibers to heart and other organ smooth muscles
- motor for swallowing
Accessory
- helps vagus
- carries efferent impulses to muscles of pharynx, larynx. palate.
- innervates neck, back muscles: trapezius, sternocleidomastoid.
Hypoglossal
-carries efferent impulses to tongue muscles for speech, chewing and swallowing.
Plexuses
- complicatied nerve networks involving both spinal and cranial nerves
- there are cervical, brachial, lumbar and sacral plexuses but no thoracic plexuses ( no thoracic enlargements either)
ANS
- controls much involuntary function esp. visceral organs
- Carries only motor impulses
Sympathetic
Uses NE as a neurotransmitter referred to as adrenergic fibres. Fight or flight=speeds things up. Exits spinal cord at thoracic and lumbar region and has ganglionate trunks which are not cell bodies they are bundles made up of inter-motor synapses.
Parasympathetic
Uses ACh as a neurotransmitter referred to as cholinergic fibres. Slows things down. Exits spinal cord at cervical and sacral region.
Sympathetic Effect
HR up, BP up, resp rate up, sweat gland activity increase , bronchioles dilate, pupils dilate, decrease peristalsis/digestive enzyme secretion, gut sphincter constriction, Urinary sphincters relax, arrestor pili contraction.
Parasympathetic Effect
Restores resting rate after the sympathetic response is over.
Adrenergic Receptors
Sensitive to NE/ epinephrine
2 Major Types:
1. Alpha-excitatory
2. Beta-inhibitory/excitatory depending on organ
Therefore, response to NE by an organ could be complex given different cells/tissues present (ex. NE binds to certain beta receptors in the heart to stimulate activity whereas NE binds to certain beta receptors in the bronchiolar smooth muscle to dilate/relax the bronchiole
B-blockers can be used to block NE from beta receptors (ex. general beta blockers block both types of beta receptors to decrease the hearts sensitivity to NE therefore BP and HR decrease= gets rid of hypertension)
Cholinergic Receptors
Sensitive to acetylcholine
2 Types
1. Nicotinic-excitatory
2.Muscarinic- response depends
Mechanoreceptors (touch, pressure):
- Constant Skin Pressure:
a) Merkels Discs- In basal layer of epidermis to sense light pressure and touch
b) Ruffini Endings- deep in dermis, hypodermic and joint capsules to sense deep pressure and stretch - Vibration and Skin Movement:
a) Hair Follicle Receptor- very sensitive to motion or vibrational stimuli but provide little or no info on pressure or constant touch.
b) Smooth Skin Receptors
i) Paccinian Corpuscles- In dermis, hypodermis, tendons and ligaments, respond to higher frequency vibrations (deep pressure and stretch), onion like structures large enough to see
ii) Meissners Corpuscles- In dermal papillae, respond to lower frequency vibrations (light pressure, discriminating touch)
Proprioreceptors
Provide info on body limb position.
Thermal Receptors
Free naked nerve endings of sensory fibers respond to heat and cold with cold receptors located in the upper dermis and hot in the lower dermis
- End Bulbs of Krause: ct coated receptors deeper in dermis,once thought o be cold receptors but not so sure now.
- Free Nerve Endings: Large number of non encapsulated nerve endings in most body tissues including the dermis.
Nociceptors
Respond to pain, hot, cold, itch, and pressure.
Semicircular Canals
Ampullae with sensitive hairs for dynamic equilibrium: respond to rotational movement of the head.
Utricle and Saccule
Subdivisions of vestibule with CaCO3 otoliths suspended in gel on top of stereo cilia for static equilibrium: sensitive to gravity and change in head position
Path of Sound
- Compression waves travel through air or other mediums
- Sound waves are collected and channelled by the pinna and external acoustic meatus of outer ear to tympanic membrane.
- Amplification of signal (10x) by malleus incus and stapes (auditory ossicles) of middle ear.
- Stapes transmits amplified vibrations to oval window on the vestibule at inner ear.
- Pressure waves move through perilymph of the cochleas scala vestibuli and scala tympani and the round window bulges out to relieve fluid pressure within.
- Sounds in the hearing range create pressure waves in the endolymph of the scala media (cochlear duct) and cause specific portions of the organ of court on the underlying basilar membrane to vibrate; sensory hairs on attached hair cells press against the overlying jelly-like tectorial membrane
- Deflected hair cells release neurotransmitter to trigger action potentials in sensory neutrons of the auditory branch of the vestibulocochlear nerve.
- Sensory impulses are received and processed by the auditory cortex of the temporal lobe.
