Final Exam 1 Flashcards
How fast do sounds move?
340m/s
What is frequency?
Vibration rate
How many cycles/unit time
Corresponds to our perception of pitch
Measured in Hz = wl/sec
Human can hear anywhere from 20 -20000 Hz
The higher the frequency, the shorter the wavelength
Doppler Effect
The perceived pitch of a sound is higher as a sound approaches us and lower as the sound moves away from us
Sound is produced at a particular frequency, it is just the perceived frequency that changes.
Amplitude
Difference in intensity of sound (loudness)
Measured in decibels (dB)
Hitting a tuning fork harder or softer changes the loudness but not the frequency. Wavelength is the same, but the amount of air moved is greater when the fork is hit harder
What is tinnitus?
The perceived continuous sound after a loud noise
What is a simple sound?
pure tone - only produces one frequency
ex. tuning fork
But most sounds are complex
Complex sounds
Made up of a combination of frequencies - one fundamental frequency plus many overtones (multiples of the fundamental frequency, each with its own amplitude)
COMPLEX TONES ARE PERIODIC
Noise
Aperiodic complex sounds.
Can the pinna enhance certain frequencies?
It sure can!
Tympanic membrane
Vibrates based on the frequency of sound waves
Ossicles
Malleus, Incus, Stapes
Hammer, Anvil, Stirrup
Stapes hits the OVAL WINDOW
Smallest bones in the body - they amplify vibrations
Eustachian tube
Connects the muddle ear to the nasal-sinus cavity
Ensures that the pressure is equal between the middle and outer ear
Pressure equalization here is important for the ear drum to work efficiently
What connects in the inner ear to the brain?
The auditory nerve (Vlllth cranial nerve)
Inner ear = cochlea + vestibular organ + semicircular canals
Structure of the Organ of Corti
Organ of corti lies on top of the basilar membrane, tectorial membrane lies on top
The organ of corti has inner and outer hair cells with stereocilia
Outer hair cells are connected to the tectorial membrane
Base of the basilar membrane and pitch?
The basilar membrane maximally vibrates in response to high pitches (high frequencies)
Apex of the basilar membrane and frequency?
The apex responds to lower pitches (lower frequencies)
Get the highest neural response in hair cells located at the part of the basilar membranes where the most displacement occurs (depends on the frequency)
Shape of the basilar membrane
Narrow and thick near the oval window (responds to HIGH frequencies)
Thin and broad near the apex (responds to lower frequencies)
How is frequency coded at the Apex?
Not coded in a tonotopic fashion (everywhere else on the BM is coded in a tonotopic fashion)
This is the region sensing frequencies below 200 Hz
Here, the action potential rate is proportional to frequency such that the higher frequencies get more firing.
Volley theory
Inner and outer hair cells
1 row of inner hair cells that are responsible for hearing. these are connected to the tectorial membrane 3500
3 rows of outer cells 12000
Mechanically-amplify low-level sound entering the cochlea
CONNECTED TO THE TECTORIAL MEMBRANE
How to movement of the BM lead to APs?
Displacement of the BM leads to movement of the hair cells against the tectorial membrane. The movement causes the cilia on the hair cells to move - opening channels via the movement of tiplinks (connect stereocilia together)
When the steriocilia bend, they pull open cation channels .
K+ channels open - leads to influx of potassium ions - depolarization - this leads to the activation of voltage gated Ca2+ channels - INCREASE IN NT RELEASE -
When the cilia bend the other way - no channels open - hyperpolarization - decreased NT released
What do the outer hair cells do?
Touch the tectorial membrane
Have afferent and efferent associations with the brain - receive feedback and regulate their activity
Change the stiffness of the regions of the BM - sharpens tuning for some frequencies
What cells do hair cells synapse on?
Bipolar cells!
Each bipolar cell gets input from ONLY ONE hair cell
The axons of the bipolar cells form the 8th cranial nerve
What part of the brainstem do bipolar cells contact in the auditory system?
The ipsilateral (same side brainstem)
-aka the cochlear nucleus
How is the phase of a sound wave codes by the brain?
Bursting pattern of the firing corresponds to the wavelength
Sizing of Wernicke’s area
In righties, it is bigger on the left
In lefties - 70% bigger on the left
Dorsal stream in the auditory pathway
GOES TO THE POSTERIOR PARIETAL CORTEX
Plays a role in auditory control of MOVEMENT (where?)
Ventral stream in the auditory pathway
To further TEMPORAL LOBE areas. Plays a role in identifying auditory stimuli (what?)
How is pitch coded for in the brain?
Tonotopic arrangement - Place coding
1:1 ratio of hair cells to bipolar cells – this makes sure that the brain knows exactly where on the membrane the hair cell was activated - identify the pitch
Which parts of the CNS is the frequency map involved in?
Inferior colliculus
Primary and secondary auditory cortices
Coincidence detection
Occurs in the medial superior olivary nuclus
Receives signals from both the left and the right ears
Helps to identify where a sound came from
Sound shadows
High frequency sounds get blocked and this creates a sound shadow on the distal side of our head
- Sound is perceived as less loud on this shadowed ear and the brain uses this to calculate direction
Low frequency sound localization - Low frequ sounds will bend around our heads quite easily - both ears will perceive the same loudness.
Which type of hearing loss can be corrected?
Conductive hearing loss
Some problem in mechanics ie ossicle failure, eardrum failire
Ear infections are the most common cause of temporary hearing loss in children
Can sensorineural hearing loss be corrected?
Not really - need cochlear implants or auditory brainstem implants
PROBLEM WITH TRANSDUCTION
Gentamicin kills hair cells…high aspirin dose temp dysfunction
Cochlear implants
Some types of hearing loss can be treated with a cochlear implant BECAUSE of the TONOTOPIC arrangement of the BM and of the auditory system
Electrodes inserted into the cochlea
Stimulates BM - required intact auditory nerve and brain structures
What are the Otolith organs?
utricle and saccule
Utricle - detects linear acceleration in the horizontal plane
Saccule detects linear acceleration in the vertical plane
What type of motion to semicircular canals detect?
They detect angular force, like ROTATION
Transduction of info regarding gravity and acceleration of the head
Done by hair cells - they are arranged in specific orientations to respond to acceleration in a particular direction.
Transduction in the semicircular canals
Endolymph resists changes in momentum - activation of hair cells in the ampulla when movements of the head and the fluid are different
- left and right ear respond differently
endolymph initially stays still when the head moves
keeps moving when the head stops
Somatosensation
sense of touch
the ability to feel hot and cold, to recognize an object by touch alone, to respond to pain, etc.
What do receptors for hapis detect?
Fine touch, pressure
Subcutaneous
Hypodermis
Not really part of the skin
Pacinian Corpuscles
Free nerve ending surrounded by an onion-like capsule
Detects vibrations
Rapid deformations of the structure lead to stretching of the free nerve ending - opening of SODIUM Na+ channels
large receptive fields
Fast adapting , RESPOND TO CHANGES IN STIMULUS
FAST ADAPTING
Respond to changes in the stimulus
Slow adapting
Fire whenever the stimulus is present
Merkel’s discs
Densely packed in skin areas with fine spatial resolution
Respond to very light touch
Slow adapting
Great spatial resolution
Meissner’s Corpuscle
More numerous and also densely packed then Merkel’s discs
Fine spatial resolution
FAST adapting - low threshold
Important for determining texture detail and edges
Ruffini’s endings
Respond to indentation/stretches in the skin when body part is moved
SLow adapting
Low spatial resolution
What are the slow adapting touch receptors?
Ruffin’s endings, merkel’s discs
Fast adapting touch receptors?
pacinian corpuscles
Meissner’s corpuscle
Which are the best detectors for Braille?
Merckel’s discs - second is meissner’s corpuscles
Where does somatosensory dorsal ventral combination occur
In the secondary cortex
Purpose of pain?
Withdraw from a source of injury
Promote restorative behaviours (sleeping, grooming, feeding)
Social signal (elicit care-giving behaviour from others)
Pain signal pathway
Tissue damage causes the release of chemicals - activates adjacent nerve fibres - produce NT’s - Activate nociceptors - chemical or temp receptors in the membrane of nerve fibres
CRosses to the contralateral side IN THE SPINAL CORD
where does the pain signal cross to the contralateral side in the spinal cord?
in the spinal cord, before the signal reaches the brain.
Ascending and descending pain pathways
Pain goes up to brain in the primary afferent - synpases on second order neuron and inhibitory interneuron - this can change the perception of pain
WANT TO BLOCK THE ASCENDING PATHWAY WHEN TREATING PAIN
The inhibitory interneuron is very important with the control of pain
Examples of general anaesthetics
GABA a receptor agonist
NMDA receptor antagonist
2-pore K+ channel activator
Prevents brain from processing pain!
C fibres
unmyelinated - thin
- temp and pain receptors
A delta fibres
mylelinated - thickish
tempp and pain
A beta fibres
thick and fast, myelinated fibres
fine touch and pressure sensitive
TRPV1
Nociceptor group - channels ( 1 is a subtype of the group)
Vanilloid receptor - ion channel receptor
Activated by different stimuli - physical, mechanical, chemical, acidic, various ligands, heat
CAPSAICIN (ingredient in hot peppers)
receptor responds to both pain and heat - explains feeling when eating spicy peppers
Can a receptor be activated by both hot and cold?
No they are each on separate fibres - different receptors involved
heat r’s - ex = TRPV1
What receptor is responsible for the initial sharp pain?
Vanilloid-like receptor (on large fibres)
activated at a higher temp
Cold receptor
CMR1
TRPm8
activated by menthol
on small fibres
Gate control theory
There is the same inhibitory interneuron involved in some touch and pain signal pathways
Painful stimuli - activate slow small C-fibres which turns OFF the inhibitory interneuron - get activation of the pain pathway- feel the pain
Touch stimuli .ex. rubbing - activates the fast and large alpha beta fibres - activates the inhibitory interneurons - INHIBITION PAIN PATHWAY
Do internal organs have their own pain pathways to the brain?
NO - there is instead referred pain.
They synapse on spinal neurons that receive nociceptive information from body’s surface. So there is one set of neurons but two sets of inputs
Can’t tell the difference between pain in the left arm and pain in the heart.
What is proprioception?
Information about body movement and position
Guides, refines, coordinates movements
Muscle spindles
detects stretch
gOLGI tendon organ
detects the tension at the end of the msucle
what is another word for stretch reflex?
Myotatic reflex
The contraction of a muscle in response to its passive stretching
Corticospinal tract
Pathway between the motor cortex and brain stem/spinal cord’
Most of the axons that form the tract originate from pyramidal cells in layer V of the primary motor cortex
Descend into the brain stem
- most cross over to the contralateral side and continue down the lateral corticospinal tract
- however some stay ipsilateral and continue down the ventral cortical spinal tract,
Motor sequences
how complex behaviours are broken into according to Lashley,
they are movement modules preprogrammed by the brain and produced as a unit. ex. scratching the head
Closed loop control in Executive control of movement
FOR SLOW MOVEMENTS
Uses feedback, maximizes accuracy
Usually involved in slow, smooth, sustained movements
move, adjust, repeat
Open -loop system for executive control of movements
For faster movements - ballistic movements
Preprogammemd control that can be adjusted through learning
high firing rates and velcoities etc
What happens when there is a lesion in the premotor area?
The premotor area coordinates simultanous motor programs - lesions abolish this coordination
All of the movements are still possible, just lose th coordination between them
Primary motor cortex
Responsible for executing skilled movements with fine detail
Complex movements rely on the primary motor cortex
EXECUTES ACTIONS
ex. pincher grasp - highly skilled, requires the primary motor cortex, coordinates
but the power grasp is a low dexterity task and persists even if there is damage to the primary motor cortex.
Which structures are involved in the modulation of movement?
Basal ganglia and the cerebellum
What do the basal ganglia play a role in for movement?
Amplitude and direction of movement
Modulates patterns of activity generated in other cortical regions (MODULATORS)
Guide memory influenced behaviours
Huntington’s
A HYPERKINETIC (fast movements) disorder
Damage to the caudate or putamen nuclei
Leads to unwanted movements (involuntary exaggerated movements - jerking, twitching, etc)
Larger lateral ventricles in these individuals
Genetic - trinucleotide repeat
Parkinson’s
HYPOKINETIC DISORDER (slow/reduced movements)
loss of dopaminergic cells in the substantia nigra
Decreased output to caudate and putamen
Inabability to produce normal movements - hard to initiate movements
Treatments
L-DOPA , deep brain stimulation
Muscular atrophy
Movement disorder
Muscle wasting
Duchenne’s disease - X linked trait, early onset
Myasthenia Gravis
aUTOIMMUNE, movement disorder
Attack of ACh receptors (essential for motor junctions and initiating movements)
Causes muscle weakness (head and face first, speech and breathing later)
Treat with immune system suppressors
Amyloid Lateral Sclerosis (ALS)
Lou Gehrig’s Disease
Destroys motor neurons in the spinal cord and brain stem (without them, cannot move, muscles weaken)
Muscles will waste away without input
Cause is unknown (~10% hereditary)
Aging, toxins, virus, autoimmune, endocrine
Acute flaccid paralysis
Spinal Damage
Affects mainly lower motor neurons
Reflexes absent and muscles waste
Various potential causes
Approaches to spinal cord severing repair
Stem cells, central glial bridge
Neurotrophins - generate a healthy environment
Peripheral nerve bridge
If you have a peripheral nerve injury - help axons regrow
Movement therapy
Following loss of function
Constraint induced
-Strengthen existing pathways (still-functioning pathways)
-Enhance cortex
Brain computer interface therapy
fOLLOWING INJURY
Record brain activity, control muscles or exoskeleton
Train people to move their arm with their brain - have electrodes that report the brain activity - connected to the muscles
Cortex size dedicated to area moved will get larger with therapy/rehab
