Physiology two Flashcards
What is an endocrine gland, and hormone ?
Endocrine gland
- endocrine glands are ductless
- secrete chemical messengers (hormones) into the blood to communicate with target cells throughout the body.
Hormones
- Chemical messengers released by endocrine cells, or by specialised neurons into the blood
- made in glands or cells
- transported by blood
- bind with target tissue receptors
- activates physiological response
- Cells which are influenced by a particular hormone, are that hormones target cells.
- act at even a low concentration and have slow/prolonged effects
- minor changes in the chemical structure of a hormone has profound effects upon its action
Describe how hormones cause an effect in their target cells
Hormones
- Bind with its specific target receptor/receptors
- actions are greatly amplified at the target cell
- rapidly degraded by target cells or removed from the blood by kidneys or liver and excreted
Trophic hormone - regulates hormone secretion by another endocrine gland
- receptors can be located on the cell membrane, in cytoplasm or in the cell nucleus
- receptor protein number can be altered on the target cell
Describe the properties of peptide and protein hormones ?
Protein hormones
Majority of hormones are of this type
- hydrophyllic
- stored in secretory granules
- transported in free form
- Hormones of the hypothalamus, anterior pituitary, pineal gland, parathyroid, digestive trac, liver, kidney, heart
- have receptors on cell surface
With respect to hormones what is synergism, competition and permissiveness ?
Hormones
Synergism
- Action of one hormone compliments another (eg insulin and growth hormone, both are protein anabolic)
Competition
- Structurally similar substances compete with each other for a receptor site - which has many applications in medicine
- Agonist -ephedrine mimics the action epinephrine
- Antagonist - beta-blockers, antagonise the ability of adrenaline/noreadrenaline by binding to receptors
Permissiveness
- Facilitation of the action of one hormone by another eg cortisol is nessary for the action of glucagon.
Describe the mode of action of peptide/protein hormones ?
Protein and peptide hormones
- receptors are located on the surface of the cell
- cause their effect most often via secondary messengers inside of target cell
- cAMP most common secondary messenger
Describe the physiology and mode of action of steroid hormones ?
Steroid hormones
adrenal cortex and gonads
Physiology
- lipophillic (combines with fats)
- synthesised in cholesterol not stored within the cell
- travel in bound form with proteins mostly (99% bound)
Mode of action
- receptors are inside the target cell
- activation of specific genes
- eg hormones from adrenal cortex cortisol, aldosterone, gonads and vitamin D3
- can be given orally as they are absorbed by the GI tract.
Describe the physiology and mode of action of amide hormones ?
Amide hormones
They are derivatives of the amino acid tyrosine
catecholomines and thyroid hormones
- stored until they are excreted
- catecholamines have cell membrane receptors and 50% travel bound in blood
- thyroid hormones behave more like steroid hormones with intracellular receptors which activate genes
Provide three different causes of common endocrine disorders ?
Endocrine disorders
- hypersecretion
- hyposecretion
- abnormally low target cell receptiveness to the hormone (receptor defect, intracellular cell signalling defect).
Describe the location and action of the hypothalamus ?
Hypothalamus
- Located below the thalamus
- process sensory information from the internal and external environment
- mediates response via ANS and endocrine system
- It secretes hormones which have a profound effect upon the pituitary gland hpothalmo-pituitary axis
Describe the location and action of the pituitary gland?
Pituitary gland
Located below the hypothalamus and connected by a stalk - the hypothalamus controls all three lobes but in different ways
Posterior lobe ( Neurohypophysis, pars nervosa)
- neural link
Anterior lobe (Adenohypophysis, pars distalis)
- vascular connection
Intermediate lobe (Pars-intermedia)
- vascular connection
Hypothalamic control of the anterior pituitary gland ?
Anterior pituitary
- The hypothalamus controls the anterior pituitary by secreting hormones into the hypophyseal portal tract.
- hypothalamus regulates the secretion of the anterior pituitary
- anterior pituitary secretes goanadotropin realeasing hormone GnRH, Corticotropin releasing hormone CRH and Thyrotropin releasing hormone TRH as some examples
Describe the hypothalamic control of the posterior pituitary ?
Posterior pituitary
- The hypothalamus controls the posterior pituitary through the supra optic and paraventricular nuclei which secrete hormones stored and released from the posterior lobe of the pituitary
Posterior pituitary hormones
- oxytocin
- Antidiuretic hormone ADH, vasopressin
Describe the stimulus and target of ADH (antidiuretic hormone or vasopressin) ?
ADH vasopressin
Released from the posterior pituitary
Stimulus
- increase in plasma osmolality (electrolyte balance)
- reduction in extracellular fluid volume
Action
- renal tubles and blood vessels
- renal tubules increase water reabsorption
- effect on blood vessels vasoconstriction (eg vasopressin)if released in a large amount
What happens in Diabetes Insipideus; a lack of ADH action ?
Vasopressin and Dibetes
It occurs frequently in cats, dogs, laboratory rats
Characterised
- polyuria, urine of low osmolality
- nocturia and incontinence
Cause
- Central diabetes insipidus posterior pituitary gland dose not secrete enough ADH hormone
- Nonphrogenic diabetes insipidus -ADH is secreted but the kidneys do not respond - receptor defect
Treatment = Desmopressin acetate a drug which acts in a similar way to ADH.
Describe the release, stimulus, target and effect of oxytocin ?
Oxytocin
Oxytocin is released by the posterior pituitary gland
Stimulus
- cervical and uterine stretch
- suckling detected by hypothalamic neurons
Target
- uterus and lactation tissue
Effect
- contraction of smooth muscle in the uterus during partuition
- let down reflex milk ejection + contraction of milk glands
- hormone of love influences social bonding
- influences urge to nurse pups
What is the effect of the intermediate lobe (Pars intermedia) ?
Pars intermedia
- predoment cells are melanotrophs
- secrete melanocyte stimulating hormone (MSH)
- effect = melanin pigment synthesis, controlling skin colour, in lower vertebrates camoflage.
Hyperplasia and neoplasia of the Pars Intermedia is common in older horses.
Where is growth hormone secreted from ?
Growth hormone is secreted by somatotrophs of the anterior pituitary.
What are the effects of growth hormone ?
Growth hormone
Secreted by the somatrophs of the anterior pituitary gland
- protein anabolic hormone = promotes protein deposition in tissues.
- Increases the growth of the skeletal frame until the growth plates close over
- enhances the utilization of fat for energy, rather than carbohydrates raising glucose levels within the body
The effect of growth hormone is said to be carried out via Somatomedins (insulin like growth factor IGF-1)
How is growth hormone regulated, name some factors which stimulate its secretion ?
Regulation of growth hormone
Growth hormone is regulated by IGF-1 and the hypothalamus
Increased by
- increase in blood amino acids
- increase sex hormones
- grehlin from stomach
- deep sleep and physical activity
Decreased secretion due to age and obesity
Review the Growth hormone summary table -
What is the effect of having too litle growth hormone ?
Not enough growth hormone results in
- pituitary dwarfism via desruction of the pituitary gland
- neoplastic, degenerative, inherited
- common in larger dog breeds Great dane, German Sheppards
- Slow growth first 2-3 months
- menatl retardation
- retained puppy hair coat, infantile genitalia, delayed dental eruption
What is the effect of having too much growth hormone ?
Excess gowth hormone in adults results in Acromegaly
- Feline acromegaly occurs in older cats, more frequently in males
- GH secreting tumur of the anterior pituitary
- increased muscle mass
- may result in diabetes mellitus
- growth of jaw, toungue and forehead
What is the main function of the pineal gland ?
Pineal gland
- translator of photoperiod
- produces melatonin
- allows seasonally productive animals to detect daylength changes
- induces sleep in diurnal animals + promotes activity in nocturnal animals
Describe the physiology of the thyroid gland, its location and what it secretes ?
Thyroid gland
- Located in upper third of the neck
- situated anterior to the trachea, just below the larynx
- it has two lobes connected by a narrow isthmus
- in non-mammalian species it is a discrete cluster of cells
Secretes thyroxine T4 and thyronnine T3
- contains two cell types
- thyroid hormone secreting cells - arranged as thyroid follicles
- C cells secrete calcitonin
- histologically follicle is lined by a single layer of cuboidal epithelial cells, well vascularised
- follicles filled with colloid which stores thyroid hormones
Describe the synthesis of thyroid hormones ?
Thyroid hormone sysnthesis
Iodine and tyrosine is required for thyroid hormone synthesis
- stored extracellular in colloid of follicles
- all aspects of thyroid hormone synthesis and secretion enhanced by TSH from the anterior pituitary
- lack of iodine in inland areas restricts animals growth
How are thyroid hormones secreted and transported around the body ?
Thyroid hormone transport
- 93% of released hormone from gland is T4
- 7% is T3
- Over 99% of thyroid hormones are bound with plasma proteins
- the thyroid hormones are released to tissues slowly by the plasma proteins
- slow onset; long duration of action
- affects all almost all tissues of the body
- T3 in free form is the active hormone within the body
- most T4 is converted to T3 in peripheral tissues via deiodination.
Describe the mechanism of action of thyroid hormones ?
Mechanism of action of the thyroid gland
- activates nuclear transcription of a large number of genes resulting in the synthesis of many proteins
- increase in number of protein enzymes, structural proteins, transport proteins, and other substances are synthesised in virtually all cells of the body
- increase in functional activity throughout the body
Describe the physiological functions of thyroid hormones ?
Thyroid hormone actions
- increase cellular metabolic activity - increases 02 consumption
- calorigenic effect produces heat
- sets bodys basal metabolic rate BMR (may increase 60-100%)
- mainatins level of metabolism for normal function
Effect
- increases number and activity of mitochondria
- increase Na+K+ pump
- permissive action on catecholamines (increase of cardiac output)
- rate of utilization of food is increased
- generally elevated in endoderms
What is the effect of thyroid hormones on growth and nervous function ?
Thyroid hormone effect on growth
- essential for normal growth stimulates GH secretion
- nessary for normal gonadal functions
- frogs=metamorphosis
Thyroid hormone effects on the central nervous system
- Crucial role in the devlopment of CNS during foetal development + after birth, hatch
- Essential for normal CNS activity in adult animals
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How is the secretion of thyroid hormones regulated ?
Regulation of thyroid hormone secretion
Under control of the hypothalamic pituitary thyroid axis
- TRH thyrotropin releasing hormone hypothalamus
- acts upon the anterior pituitary which sectrets TSH to increase secretion of T3 and T4
- T3 and T4 provide negative feedback on the secretion of TSH and TRH
Cold = enhances secretion highly adaptive in newborn animals
Starvation = reduces secretion
Describe the abnormalities of thyroid function ?
Abnormal thyroid function
Normal thyroid function = euthyroidism
Hyperactive thyroid gland
- elevated BMR
- poor heat tolerance, increased appetite, increased HR
- excessive mental alertness
- frequently observed in older cats dur to adenomas benign tumors
Hypoactive thyroid gland
- frequently caused by thyroiditis, increased TSH and desensitization
- low BMR, sluggish, low heart rate, dull mentation
- poor tolerance to cold
- weight gain
- patchy fur
- reduced apetite
Describe the location and physiology of the adrenal glands ?
Adrenal glands
Comprised of a central medulla (nervous tissue), and outer cortex in most mammals
Located on the top of the kidney
What dose the adrenal medulla stimulus, target and secretion ?
Adrenal medulla
Stimulus
Sympathetic nervous system stimulation, fight or flight response, hypoglycaemia, decrease in BP or cold exposure
Target
Heart, smooth, muscle, pancreas and eye
Secretion
Catecholamines = adrenaline / epinephrine (90%) and noradrenaline / norepinephrine
What are the effects of the secretions from the adrenal medulla ?
The effects of the adrenal medulla
Short term stress response.
- effects are carried out via alpha and beta receptors
- incresaed cardiac output
- arteriole constriction
- increase in blood sugar levels
- increase plasma fatty acids
- dilation of pupil
- combat short term acute stress
Pheochromocytoma = Is a tumur of the adrenal gland causing excessive secretion of catacholamines
What hormones dose the adrenal cortex produce and from where ?
Adrenal cortex
Essential for life - secrete steroid hormones (have lipid droplets contain cholesterol)
Adrenocortical hormones mostly transported in bound form and act upon intracellular receptors
Zona Glomerulosa - mineralocorticoids
Zona Fasciculata - glucocorticoids
Zona reticularis - sex steroids (source of sex hormones in castrated animals)
Describe the actions of glucocorticoids ?
Adrenal glucocorticoids
- secreted from fasiculata of the adrenal cortex
- main glucocorticoid in mammals is cortisol
- incresaes blood glucose (increase gluconeogensis)
- enhances protein catabolism
- permissive action to catacholamines and glucagon
- anti inflammatory and immunosuppressive effects
- may be used to suppress inflammatory reactions or allergic reactions
Helps to adapt an animal to long term stressors ( such as herd seperation).
Describe the regulation of glucocorticoids
Glucocorticoid regulation
- Regulated by the hypothalamo pituitary adrenal axis
- influenced by stress and circadian rythm
- indiurnal animals highest in the morning and lowest over night - the reverse is true in nocturnal animal
- coricotropin releasing hormone
- ACTH adrenocorticotrophic hormone
Stress causes the release of cortisol - its release is proportional to the stressor
Describe mineralocorticoids secretion and action ?
Mineralocorticoids
Secreted from the Zona Glomerulosa within the adrenal cortex
- aldosterone is the main mineralocorticoid
- affect on Na+, K+ and Cl-
- regulation or stimulus is via angiotensin 2 and elevated ECF
Actions
- Act upon the renal tubules
- stimulation of Na+ reasorption
- regulation of ECF volume
- regulation of blood pressure
- K+ level maintenance in ECF
Describe the causes of Cushings disease, Addison’s disease and Conn’s syndrome ?
All are disorders of the adrenal cortex
Cushing disease
- over secretion of CRH/ACTH (excessive cortisol)
- common in older dogs
- excess plasma glucose, protein shortage and fat deposition in abdomen
Addison’s disease
- adrenocortical insuuficiency
- certain dog breeds - life threatening
Conn’s syndrome
- hypersecretion of aldosterone
- tumor or adrenal hyperplasia
Describe the regulation of aldosterone secretion ?
Describe the pancreas, what it produces and from where ?
The pancreas
The pancreas lies dorsally to the stomach in vertebrate, where it has both an exocrine and endocrine function.
Islets of Langerhans
- endocrine tissue
- alpha = glucagon
- beta = insulin
- delta = somatostatin
- PP cells produce pancreatic polypeptide
All are peptide hormones involved in the control of metabolism
Describe the physiology and actions of insulin
Insulin
Physiology
- circulates in unbound form
- half life 5-8 mins
- anabolic hormone and the liver is the most important target organ
Actions
- stimulates glucose entry to cells
- increases glycogen storage within muscle and adipose tissue (Glut 4)
- inceases glycogen production and storage in the liver
- promotes fat synthesis (glucose fatty acid synthesis in the liver)
- promotes protein synthesis (increase amino acid uptake)
Describe the actions of insulin ?
Describe the factors which act to stimulate the secretion of insulin (6)?
Regulation of insulin
Rising blood glucose above nornal is a powerful stimulator of insulin
Other stimulating factors
- rise in blood amino acid level
- rise in blood fatty acid level
- vagus stimulation
- Some GI hormones (gastrin, CCK, secretin)
- hyperkalemia (high potassium)
Describe the actions of the hormone glucagon ?
Glucagon
Secreted by alpha cells in the pancreas; polypeptide
Actions
- catabolism of nutrients (especially between meals)
- increase in blood glucose levels
- increase FFA blood glucose levels
- promotes conversion of fatty acids to ketone bodies
- increase liver gluconeogenesis
- increase lipolysis
Note. A decrease in glucagon enhances breakdown of live glycogen
Describe the regulation of glucagon ?
Glucagon
Secretion is enhanced by a decrease in blood glucose levels
- exercise
- starvation
- sympathetic stimulation
- glucagon levels vary among species (bird twice as high as mammals)
- elevated levels of amino acids in blood plasma results in an increase in both insulin and glucagon secretion. This ensures there is enough glucose available to utilize the amino acids from a protein rich diet. This is especially important in dogs and cats consuming a diet naturally high in protein.
What are the consequences of having transiently high blood glucose ?
Transiently high blood glucose consequences
- Glycosuria = glucose in urine
- polyuria = frequent urination due to osmotic diuresis
- polydipsia = excessive thirst
Swelling of the lens of the eye due to high osmotic pressure can result in transient blindness
What are the consequences of having chronically high blood glucose ?
Consequences of chronically high blood glucose
- chronic bladder infections (due to glycosuria)
- oxidative damage of capillary walls
- poor circulation in the back of the eye leading to blindness
- poor circulation can result in thinning skin and hair and infection
- formation of cateracts (glucose converted to sorbitol in the lens)
- ketoacidosis
- vomiting (an emergency situation)
Describe diabetes ?
Diabetes
Diabetes Mellitus
- means sweet
- lack of insulin or its function
- can be associated with glucagon excess
- accumulation of ketone bodies (acidosis)
- cataract
- increased appetite weight loss
- lack of energy
Diabetes Insipidis
- means without sweet
- lack of antidiuretic hormone (ADH, vasopressin)
What is the affect of glucocorticoids on blood glucose level ?
Glucocorticoids
- increases blood glucose level
- protein catabolism and protein mobilisation
Function to combat long term stress and starvation
What is diabetes type one nad two ?
Type 1 and 2 diabetes
Type one insulin dependant
- total lack of insulin
- occurs in many species including cats and dogs
- require exogenous insulin for survival
- arises from autoimmune reaction destroying beta cells
- propensity to develop ketosis
Type two diabetes not insulin dependant
- insulin secretion normal or increased but target cells do not respond
- many factors can cause the disease including genetic, obesety and age
- encourage exercise, low carbohydrate diet high in protein and fibre
Describe the location of the parathyroid gland and what it secretes ?
Parathyroid gland
Location
- dogs and cats beside or within the thyroid gland
- pigs cranial to the thyroid
Secretion
- secretes parathyroid hormone
- acts to increase the plasma concentration of calcium and lower PO4-
Describe the actions of parathyroid hormone ?
Actions of parathyroid hormone
- on kidney increases Ca2+ reabsorption
- on bone stimulates Ca2+ pumping from bone and long term by dissolution of bone
- on intestine indirectly by activating vitamin D3 to absorb Ca2+
Describe how parathyroid hormone is regulated ?
Regulation of parathyroid hormone
Primary signal for PTH is low Ca2+ levels in plasma
parathyroid cells have calcium sensing receptors on their surface.
Discuss calcitonin secretion and actions ?
Calcitonin
Calcitonin is produced by C cells in the thyroid gland of mammals
- by ultimobranchial glands in birds
Action
- decrease Ca2+ level in plasma (weak effect)
- by decreasing Ca2+ secretion from bone
- increase Ca2+ secretion in urine
- secretion of calcitonin is enhanced via a rise in plasma Ca2+
Describe the synthesis and actions of vitamin D ?
Vitamin D
stimulated by sunlight
- indoor, heavily furred animals may need vitamin D suuplementation
Actions - by the active form of vitamin D
- up intestinal absorption of Ca2+
- up intestinal Po43- absorption
- increase bone mineralisation
Vitamin deficiency in young animals causes rickets, and osteomalacia (soft bones) in older animals.
What is parturient paresis ?
Parturient paresis
Excessive demands for calcium (eggs, milk)
- prevent by providing a low Ca2+ and high phosphorus diet to stimulate PTH secretion
- high calcium diet around the time of partuition
- hypocalcemia not enough Ca2+ in blood steam leads to tremors, unconsiousness, coma and even death.
Discuss Atrial naturietic peptide ANP ?
Atrial naturietic peptide
The heart hormone
- stimulated by an increase in blood pressure and a increase in Na+
- acts upon the renal tubules, aldosterone and vascular smooth muscle
Acts to increase Na+ secretion reducing blood pressure
Describe the structure of the eye (outer layers)?
Structure of the eye - three layers
Outer protective layer
- posterier sclera = white tough membranous maintains the shape of the eye
- anterior cornea = transparent first refractive surface
Middle layer uvea
- Choroid = vascular, pigmented
- Tapetum lucidum = light reflective material
- Cilary body = muscular structure
- Iris = pigmented has an opening pupil
Inner layer Retina
Describe the two cavities of the eye ?
Eye cavities
Anterior cavity
Filled with aqueous humor - a clear fluid which supplies nutrients to the cornea and the lens.
- continuously secreted by the ciliary epitheliuminto the posterior chamber after which it enters the anterior chamber
- maintains intraocular pressure
- Glaucoma sustained increase in intraoccular pressure
Posterior cavity
Vitreous humor - gelatinous transparent fluid which acts to maintain the shape of the eye ball
Describe the function of the iris, lens, fovea, tapetum,
Functions
The aim is for the lens and cornea to focus immages onto the retina
Iris = regulates the amount of light entering the eye, has a dilating/constricting muscle
Lens = Suspended by suspensory ligaments and attched to ciliary body. Flexible, biconvex focusses light rays to form an image on the retina
- variable focussing power
Fovea = in primates acts to minimize distortion of light and has the highest visual acuity.
Tapetum = in most nocturanl and domestic animals, choroid has a patch of reflective material which reflects light and helps to improve vision in low light.
Discuss nictitating memebranes
Nictitating membranes
- all domesticated animals have athird eye lid nictitating membrane
- provides extra protection from injury
- retractor muscle contraction pulls the eyelid into the orbital, where the nictating membrane covers the front of the eye to varying degress
- birds have a nictating membrane but no retractor muscle
Describe how the lens functions ?
Describe how rods and cones function ?
Rods and cones - photoreceptors
Outer segment contains a visual pigment - opsin
Rods
- rhodopsin
- visual pigment helps with night vision
- sensitive to light, low acuity, can not discriminante colours
- mostly located in the peripheral retina
Cones
- visual pigment may have different opsins depending upon species
- discriminate different colours
- requires a higher level of illumination
- better visual acuity, day time vision
- concentrated mostly in the fovea region
Describe phototransduction ?
Phototransduction
- when the visual pigment is exposed to light it decomposes to form opsin and all trans retinal
- metarhodopsin 2 generates a nerve action potential
Role of vitamin A = (old hay horses) reduced vitamin A causes night blindness
Describe how photopigments work?
Photopigments
Cone system help for color vision by having different photopigments, each photopigment responds to a different wavelength of light
- ratio of stimulation of different types of cones is interpreted by the brain as a specific colour
- nocturnal animals have mostly rods
- primates three different types of cones
- dogs two types of cones
- birds four populations of cones
- the amount of colours perceived by different species is not clearly understood
Provide a detailed explanation of the visual pathway?
Visual pathway
Ganglion cell axons form the optic nerve
- Primary visual cortex : involved in consciuos visual perception of form, color, motion, orientation and depth
- Supracharismatic nucleus of the hypothalamus, plays a role in the regulation of physiological rythms by light dark cycle
- Pretectal nucleus : plays a role in papillary refelxes of the eye, and reflex orientation of the eye to visual targets
Describe the structures of the ear ?
Hearing
Ear mediates the transduction of sound into action potentials
Outer ear
- pinna (auricle)
- ear canal
- external acoustic meatus funnels sound waves to the middle ear
Middle ear
- Tympanic membrane
- middle ear
Inner ear
- cochlea
- vestibular apparatus
Describe the structures of the middle ear ?
Middle ear
Structures
Tympanic membrane
- thin transparent membrane
- junction between the external and middle ear
- vibrates when sound energy enters the ear
Middle ear
- air filled cavity connected to the nasopahrynx by auditory tube
- contains ossicles (malleus, incus, stapes)
- contains two small muscular structures
Describe the function of the middle ear ?
Function of the middle ear
The ossicles are all connected to each other
The tympanic membrane is connected to the malleus - to the incus to the stapes to the oval window.
The ossicles act to transfer the vibration of the ear drum to the oval window.
Oval window - prevents a significant loss of energy as the sound wave is transferred from the air filled middle ear to the liquid filled inner ear.
- sound wave energy is amplified from outer to inner ear
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Describe the structure of the cochlea ?
Cochlea of the inner ear
The cochlea has three chambers seperated by two membranes
- Basilar membrane (floor of scala media, and organ of corti)
- Organ of corti - has hair like receptor cells
- Reissner’s membrane
Chambers
- dorsally located scala vestibule
- ventrally located scala tympani
- middle scala media
The scala vestibule and tympani contains perilymph
the scala media contains endolymph
Describe how the transmission of sound occurs within the cochlea?
Transmission of sound waves within the cochlea
- vibration of the oval window causes vibrations in the inner ear fluids
- causes a series of traveling waves that begin at the base of basilar membrane and move along its length
- organ of corti movements excites the hair cells
- action potential travels along the eighth cranial nerve to the auditory cortex.
