What 2 functions is the ear specialized for?
- hearing
2. equilibrium
What is the visible part of the ear?
the pinna
What occurs in the middle ear? (primary function)
the amplification of sound waves in preparation for transmission from air to a fluid environment
Whats another words for the ear canal and what does it do?
the external auditory meatus - brings waves to the tympanic membrane
What is the primary function of the external ear?
to gather sound waves and conduct them to the tympanic membrane
What is the middle ear composed of (x4)?
- tympanic membrane (ear drum)
- ossicles (malleus, incus and stapes)
- oval window
- round window
What is the primary function of the inner ear?
the transduction/conversion of sound energy (fluid filled)
What is the inner ear composed of? (X2)
cochlea and vestibular apparatus
What is the external ear composed of?
ear canal (aka external auditory meatus) and pinna
What does the Eustachian tube do?
aka auditory tube, it connects the airfield middle ear with the pharynx (throat) to equilibrate pressure. Normally collapsed however it opens transiently to equilibrate middle ear pressure with atmospheric air
Malleus
aka hammer, first auditory ossicle
Incus
aka anvil, middle/second auditory ossicle
Stapes
aka stirrup, last/third auditory ossicle
What is the cochlea?
a coiled, bony, fluid filled tube in the inner ear through which sound waves trigger nerve impulses
What is the vestibular apparatus?
the receptive organs of the inner ear that contribute to balance and perception of head movement
How do sound waves work?
Don’t move from original position, they bump into adjacent molecules and transfer E which is transmitted in waves that radiate away from vibrating object (like ripples)
How do sound waves spread?
in 3 dimensions in a spherical way
What is amplitude?
intensity/loudness of sound (dB)
What is pitch?
frequency of waves/second (Hz)
What is pitch?
frequency of waves/second (Hz)
- low frequency = low pitch, vv
What exactly is sound?
the brains interpretation of the frequency, amplitude and duration of sound waves that reach the ears
What are infrasound waves?
sound waves with a frequency too low for the human ear to hear (whales, elephants and hippos) – can cause headaches and many other conditions when exposed to them for long periods of time
What are ultrasound waves?
Sound waves with a frequency too high for the human ear to hear (dogs, bats, insects and birds)
What happens when sound waves strike the tympanic membrane?
the membrane vibrates at the same frequency as the sound, which causes movement of ossicles (amplify sound waves) which then cause movement of the oval window (smaller than TM)
- mechanical vibrations from ossicles and oval window are converted into fluid waves
What are the 5 levels of amplification and transduction?
1st: movement of ossicles
2nd: movement of oval window
3rd: fluid waves bending hair cells in the cochlea, generating electrical signals
4th: elec. signals alter neurotransmitter release
5th: NT bind to primary auditory neurons, initiating APs
Which ossicle has the largest force and what does it force it on?
stapes - onto the oval window
What does the oval window do?
its the membrane at the entrance to the cochlea (top) through which the ossicles transmit vibrations (site of conversion of mechanical vibrations to fluid waves) (smaller than tympanic membrane)
What does the round window do?
a membrane covered opening in the inner wall of the middle ear that compensates for changes in cochlear pressure
What does the vestibular duct do?
aka scala vestibuli, is a perilymph filled cavity inside the cochlea of the inner ear that conducts sound vibrations to the cochlear duct
What is the tympanic duct?
aka scala tympani, it contains perilymph and is located at the bottom of the cochlea
What is the cochlear duct?
aka scala media, a fluid filled cavity within the cochlea that vibrates when sound waves strike it, contains endolymph and a high K+ concentration
What are hair cells and where are they located?
they are receptor cells for sound and are embedded in the basilar membrane of the cochlea
What are hair cells and where are they located?
they are receptor cells for sound and are on the organ of corti of the cochlea – located in the ampulla (end of the canal) – tonically active
What are stereocilia?
small hair like projections on the tops of auditory hair cell tips that are embedded in the tectorial membrane, organized from short to tall and surrounded by endolymph
What is endolymph and what does it do?
the fluid that fills the cochlear duct - plays a part in excitation of hair cells
What are tip links and how do they move?
they connect stereocilia of hair cells by protein bridges (move by mechanical stress which can open/close K+ channels)
- tall = open = depolarization = AP
- short = close = hyperpolarization = no AP
What does the vestibular membrane do?
it separates the cochlear duct from the scala vestibuli
Which neurotransmitter is the receptor for depolarization?
Glutamate – when theres sufficient membrane potential to admit calcium
What is the tectorial membrane?
a membrane located above the basilar membrane and serves as a shelf against which the cilia of the auditory hair cells move
What is the basilar membrane?
a structure in the inner ear that undulates when vibrations from the ossicles reach the cochlear fluid
How is amplitude coded (intensity coding)?
by the degree of deflection and opening of ion channels in the stereocilia (AP generated)
How is frequency coded?
by where on the basilar membrane the deflection occurs (location of hair cells)
Where do hair cells synapse?
afferent axons of CN 8
What is the CN8 aka vestibulocochlear nerve and what is it composed of?
the hearing and equilibrium nerve that travels to the brainstem - composed of the vestibular and cochlear nerves
What is the ratio of hair cell : cochlear nerve fiber?
1:1
What makes up the cochlear nerve and what is it?
made up of axons, is the cranial nerve responsible for hearing
Where does the second order neuron travel?
the medial geniculate nucleus
Where is there a frequency map?
the auditory cortex – corresponds to the basilar membrane
What is lateral communication?
the cochlear input being processed on the same side as it was detected
What is contralateral communication?
one side of the brain communicates with the opposite side of the body
What does the anterior canal detect?
detects movement of the head up or down (nodding yes)
What does the posterior canal detect?
movement of the head up and down to the side (ear to shoulder)
What does the lateral canal detect?
the movement of the head from side to side (shaking the head - no)
What are the 3 semi circular canals of the vestibular apparatus, how are they located and what do they do?
perpendicularly located – anterior, posterior and lateral – monitor rotational acceleration in 3 planes
Which organs sense linear acceleration?
utricle and saccule (otolith organs)
What is an otolith?
a structure made up of calcium carbonate and proteins in the vestibule of the inner ear (gelatinous)
What does the utricle detect?
forwards/backwards acceleration
What does the saccule detect?
up/down acceleration
Where are the supporting hair cells located?
the cristae
What is the cupula and where is it located?
provides the sense of spatial orientation (in the ampulla of the 3 semicircular canals)
What is the bony labyrinth?
winding tunnels located in the inner ear
What is the kinocillium?
this is a large hair cell important in the detection of the head’s position. whether the displacement of the stereocilia is towards or away from this determines whether it is excitatory or inhibitory.
What is the equilibrium pathway?
it projects primarily to the cerebellum through the vestibular nerve
Where is the primary site for equilibrium processing?
the cerebellum
What is the collateral pathway?
it runs from the medulla to the cerebellum or upwards through the reticular formation and thalamus
What are the 2 branches of the ANS and what are their main purpose?
sympathetic and parasympathetic – they innervate (supply with nerves) most organs (dual innervation), maintaining homeostasis
What does the parasympathetic nervous system do?
rest and digest – thoracolumbar division – increase gastrointestinal activities while decreasing heart rate and blood pressure
What does the sympathetic nervous system do and what is it also called?
fight or flight – craniosacral division – increase heart rate and blood pressure, mobilize energy stores (glucose from the liver turned into glycogen), pupillary dilation and decreases gastrointestinal and urinary functions
How do the 2 parasympathetic nervous systems relate to one another?
they are antagonistic but complement one another
Which nerve is the most powerful?
Cranial nerve 10
What is the preganglionic neuron and where does it originate?
neuron from the CNS to the effector organs – shorter axon in SNS – originate in the thoracolumbar spinal cord aka lateral horn aka brainstem aka sacral spinal cord
What is the postganglionic neuron?
neuron from ganglion (CNS) to effector organs – shorter axon in PNS
What are the 4 effector organs?
cardiac muscle, smooth muscle, glands and adipose tissue
Where are ganglia linked together?
in the sympathetic chain
What is the sympathetic chain?
a chain of ganglia that runs along each side of the spinal column; part of the sympathetic nervous system.
What are collateral ganglion?
splanchnic nerves which travel to the viscera to synapse with a ganglionic neuron; exception to the general anatomy of the SNS
What is the ventral root?
the location of the spinal cord that preganglionic neurons leave before entering the spinal nerve
What is the white ramus?
myelinated; how preganglionic axons leave spinal nerve before entering sympathetic ganglia
What is the gray ramus?
unmyelinated nerves, return from sympathetic ganglion to rejoin spinal nerve
What is the spinal nerve?
carries motor, sensory and autonomic signs between the spinal chord and the body (how postganglionic neurons travel)
What are celiac ganglia?
they innervate the stomach, liver and spleen (top)
What is the superior mesenteric ganglia?
they innervate the small intestine, upper part of the large intestine and kidneys (middle)
What is the inferior mesenteric ganglia?
they innervate the large intestine, urinary bladder and reproductive organs (bottom)
Where do preganglionic neurons of the SNS originate?
thoracolumbar sections of the spinal cord
Where do preganglionic neurons of the PNS originate?
brainstem and craniosacral section of the spinal cord
What is cranial nerve X?
aka the vagus nerve, it is the most powerful nerve and it innervates the lungs, heart, stomach, small intestines and liver
What is cranial nerve lll?
aka oculomotor nerve, it innervates the smooth muscles of the eye
What is cranial nerve Vll?
aka the facial nerve, it innervates the salivary glands
What is cranial nerve lX?
aka the glossopharyngeal nerve, it innervates smooth muscles of the throat (middle ear, Eustachian tube, oropharynx, posterior third of tongue, carotid sinus and carotid body)
What is innervated by the spinal nerves of the PNS?
colon, bladder and reproductive organs
How do sacral differ from somatic spinal nerves?
sacral does not join with the spinal nerve
What are the 2 primary neurotransmitters in the peripheral nervous system?
acetylcholine and norepinephrine
Where is acetylcholine present?
for all ganglionic neurons (pre SNS and PNS and post)
Where is norepinephrine present?
only in sympathetic postganglionic neurons
What is the NT for the somatic (skeletal muscle) nervous system?
acetylcholine
What are nicotinic cholinergic receptors?
they cause cation channels to open which results in depolarization (excitation of postsynaptic cell)
What are cholinergic receptors?
receptors on neurons that bind to acetylcholine
What are adrenergic receptors?
receptors on neurons that bind to norepinephrine (g-protein)
What are muscarinic cholinergic receptors?
receptors coupled with g-proteins effects (either excitatory or inhibitory) depend on the target cell
What. are chromaffin cells?
cells in the adrenal medulla that secrete epinephrine and norepinephrine
What type of receptors do effector organs for the PNS have?
muscarinic cholinergic receptors
What type of receptors does the autonomic postganglionic (sym and para) and skeletal muscle have?
nicotinic cholinergic receptors
What are the 2 main classes of adrenergic receptors?
alpha (1+2) and beta (1,2+3)
Where are alpha receptors located and what do they have an affinity for?
located in effector organs of the SNS, affinity for NE over E
- excitatory and most common receptors
What do beta receptors activate and what do they have an affinity for?
activate cAMP and affinities for NE and E vary
Beta 1 (location, excitatory/inhibitory, affinity)
- located in the cardiac muscle and kidneys
- excitatory
- equal affinity for NE and E
Beta 2 (location, excitatory/inhibitory, affinity)
- located in some blood vessels and smooth muscle
- inhibitory
- greater affinity for E than NE
Beta 3 (location, excitatory/inhibitory, affinity)
- located in adipose tissue
- excitatory
- greater affinity for NE than E
- Energy drawn from fatty acids
What is the neuroeffector junction?
synapses between efferent postganglionic neurons and effector cells/organ in the ANS
Afferent vs Efferent
Afferent: to the brain/spinal cord
Efferent: carry impulses away from the CNS towards muscles to cause movement
What are varicosities?
knoblike swellings of certain autonomic axons containing mitochondria and synaptic vesicles; store and release neurotransmitter in response to action potential in the postganglionic neuron
Where are neurotransmitters stored?
in vesicles
Which nervous system dominates at night?
the parasympathetic NS
Where are NT released?
in varicosities
What is the main regulator of homeostasis?
ANS
What does the hypothalamus do for the ANS?
initiates fight/flight response, activates sympathetic nervous system, contains regulatory centers for body temperature / food intake / water balance (afferent fibers activate organs for fight or flight)
What does the medulla oblongata/pons do for the ANS?
contain centers for cardiovascular / respiratory functions
What are the brainstems regulated reflexes for the ANS?
pupillary light, vomiting and swallowing reflexes
What is the spinal cords reflexes for the ANS?
urination, defecation, erection and ejaculation
