Dr. Grubb Flashcards
1
Q
Name the main types of neurones
A
1) Unipolar
2) Pseudo-unipolar cell
3) Bipolar cell
4) Multi-polar cells
2
Q
Describe unipolar neurons
A
Single axon coming out of cell body
3
Q
Describe bipolar cell
A
Both axon and dendrite coming out of the cell body
- E.g. retinal bipolar cell which connects photoreceptors at back of retina to ganglia cells at the front - interneurons
4
Q
Describe multipolar cells
A
Axons and very highly-branches dendrites
- Spinal motor neuron
- Hippocampal pyramidal cell
- Purkinje cell of cerebellum - controlling fine movement, very intricate
5
Q
Describe the pseudo-unipolar cell
A
- Central axons periferal branches
- Only one process out of the cell body
- Eg. Sensory nerves taking information to CNS from tissues skin deep tissue
6
Q
What is an afferent nerve
A
carries information towards the CNS (sensory)
7
Q
What is an efferant nerve
A
carries information towards the periphery (towards muscles, glands etc)
- Motor
8
Q
What are interneurons?
A
- Within the CNS (excitatory, inhibitory, local, relay)
- Process sensory info and make decision
9
Q
What are the three main types of glial cells?
A
1) Oligodendrocyte - myelination
2) Schwann cells- myelination
3) Astrocyte
10
Q
Describe oligodendrocyte
A
- Only found in CNS (brain and spinal cord)
- It can send out processes that can wrap round 20-40 different axons
11
Q
Describe schwann cell
A
- Peripheral nervous system sensory/motor nerves
- Wrap round nerves - single schwann cell per nerve
12
Q
Describe Astrocyte
A
- Really important
- Support cell
- Several functions
- Connection between blood supply and neurons
- Movement of nutrients eg glucose from capillary to neuron
- Removal of waste products like broken down NTs
- Buffer NTs
- Take up K+ ions which can accumulate outside cells when neuronal activity is quite high
13
Q
Name the 8 main functions of glial cells
A
Structural support
Axonal insulation
Removal of debris
Buffering of K+ ions
Removal of neurotransmitters
Guide axonal migration
Contribute to blood-brain barrier
Nutritive function
14
Q
Describe neurulation
A
- Ectoderm called neural plate on dorsal surface of embryo is destined to become neural tissue
- Neural plate envaginates to form the neural groove
- Neural groove pinches off and becomes internalised to neural tube
- Neural crest cells migrate to form peripheral ganglia - separate nerve cells
- Brain forms from ectoderm (same as skin)
15
Q
What does endoderm form
A
Gut, liver, lungs
16
Q
What does mesoderm form
A
Connective tissue, blood vessels and muscles
17
Q
What does the ectoderm form
A
CNS and peripheral nervous systems, epidermis (skin)
18
Q
What is spina bifida
A
- Incorrect invagination
- Improper closure of neural fold
- Abnormality at base of spinal cord
19
Q
What different type of cells do neural crest cells develop into?
A
- Melanocyte
- Glial
- Sensory
- Sympathoadrenal
- Parasympathetic
- Entoric
20
Q
What is cehalisation
A
- Neural tube to three vesicle stage - forebrain, midbrain and hindbrain
- ## Five vesicle stage
21
Q
Name the two flexure types
A
- Cephalic
- Cervical
(- Pontline (in 5 vesicle))
22
Q
What will the following become when developed?
1) 1a
2) 1b
3) 2
4) 3a
5) 3b
6) 4 - Lowest area
A
1) Cerebral cortex
2) Thalamus and hypothalamus
3) Midbrain - pain control
4) Pons and cerebellum (‘little brain’) - linking to motor function
5) Medulla oblongata - vegetative functions
6) Spinal cord
23
Q
What is the corpus callosum
A
Carries information from the left side to the right side of the brain for you to integrate functions between each side
24
Q
What is interesting about the growth rate of the spinal cord and vertebre
A
The spinal cord doesn’t grow as fast - bottom of the cord is then further up the vertebral column
Cauda equina - horses tail ‘leash of nerves’
25
Name 6 types of sensory neurones
- Mechanoreception, pain, temperature, proprioception - limbs and trunk
- Proprioception - jaw
- Olfaction
- Gustation
- Audition, Vestibular labyrinth
- Vision
26
What is a dorsal root ganglia
- Single unipolar neuron in the human body CNS, pseudo-unipolar
- Cell body with single axon then central branch going into spinal cord and axon with terminal
- All sensory neurons have this basic structure
27
Name the layers of skin
- Dermis
- Epidermis (separated by the epidermal-dermal junction)
- Hairy/Glabrous ( with papillary ridges & septa of the stratum corneum) skin
28
Name the nerves that innervate skin
- Hair receptors - wrap round the end of hairs to detect movement
- Meissner's corpuscle - detect pressure
- Ruffini's corpuscle - detect pressure but deeper
- Pacinian corpuscles - detect vibrations (low frequency)
- Bare nerve endings - fine myelinated and unmyelinated nerves at the top which - pain detection - no specialisation
- Merkel's receptor - superficial - only in hairy skin
29
State the ABC nerve fibre types and their function
```
Aalpha - Motor - somatic, proprioception
Abeta - Touch, pressure, vibration
Agamma - Motor, spindles
Adelta - Pain - reflex, temp
B - Pregangllionic sympathtic
C (Dorsal Root) - Pain - slow pain, dull ache, inflammation, sensitised nerve endings
C (Symp) - postganglionic synpathtic
```
30
How does velocity and axon diameter change going down the list?
They get smaller diameters meaning smaller in velocity
31
What are all A fibres?
Myelinated
32
State the numerical classification of just sensory nerves (number - ABC class - size - modality - diameter - conduction velocity)
I - Aalpha - Large - proprioceptive - 13 to 20 - 80 to 120
II - Abeta - medium - touch, pressure - 6 to 12 - 25 to 75
III - Adelta - small - pain (fast), temperature - 1 to 5 - 5 to30
IV - C - pain (slow) - 0.2 to 1.5 - 0.5 to 2.5
33
Describe nociceptor endings
- Pain endings
- Poorly differentiated
- Contain varicosities (small swellings) containing many mitochondria
- Between varicosities are thin axonal threads containing neurofilaments
34
Describe types of thermal nociceptors (4)
1) Cool receptors - Adelta/III - skin cooling - 25 celsius
2) Warm receptors - Adelta/III - skin warming - 41 celsius
3) Heat nociceptors - C/IV - hot temperatures - 46 to 52 celsius
4) Cold nociceptors - C/IV - cold temperatures -
35
Describe the responses of nerve to two different stimuli
1) Rapidly adapting - pacinian corpuscle - one action potential when stimulus is applied, one when released as layers slide over each other
2) Slowly adapting - pain receptors - burst of AP which slows down but is maintained for stimulus duration
36
How can you measure density of innervation?
Two-point discrimination test
| - bring pins closer and closer as whether they think its one or two pins
37
Which corpuscle detects higher frequencies, Meissner's or pacinian?
Pacinian - it is found lower in the skin
38
Why are we segmental
Came from segmental ancestors
- nerves come from left and right into each vertebrae of the spine
- Pairs of nerves at each segment
39
What happens to thermo & mechano-nociceptors following tissue damage
- Damaged tissue releases inflammatory mediators via WBH or mast cells (histamine)
- Some bind to receptors on the sensory nerve endings to change its sensitivity to different stimuli - eg tooth sensitive to heat, biting
- through signalling pathways they become sensitised to mechanical or thermal stimuli of transducer
- Ion channel thermal transducer
- PRIMARY HYPERALGESIA
40
Name 6 inflammatory mediators
- PGs - prostaglandins - PGE(little 2), PGI(little two)
- Bradykinin
- 5-HT - serotonin
- Histamine
- Neuropeptides
- Purines eg. ATP
41
Why do receptive fields overlap?
The overlap of receptive fields allows us to detect the precise position of stimuli on the skin surface.
42
Describe the prostaglandin synthesis pathway
Membrane phospholipids----cPLA(little2) Ca2+ dependant--->Arachidonic acid-----Cox-1 constitutive, Cox-2 inducible----> PGG(little2)/PGH(little2) which makes:
- PGI(little2) - Prostacyclin
- PGE(little2)
- PGD(little2)
- PGF(little2alpha)
43
What do prostaglandins do?
- Sensitisation
| - Excitation
44
Name the function of:
1) PGE2
2) PGI2
1) PGE2 sensitises nerve endings to mechanical and thermal stimuli
2) PGI2 directly excites a subpopulation of nociceptors ALSO sensitises nerve endings to mechanical and thermal stimuli
45
Mechanism of nonsteroidal anti-inflammatory drugs (NSAIDs)
- Group of drugs most widely sold - aspirin, ibuprofen
- Inhibit Cox 1 and 2 as Cox 1 is enhanced in damaged tissues meaning reduced synthesis of prostaglandin
- Upregulation of Cox 2
- This means less hyperalgesia thus decreasing pain
46
Where are the cell bodies of sensory neurons contained
Dorsal root ganglion
47
Name the 5 spinal regions and their number of segments
- 8 Cervical segments
- 12 Thoracic segment
- 5 Lumbar segments
- 5 Sacral segments
- 3 Coccygeal segments
(Curvy, Thick Ladies Suck Cock)
48
Describe segmental dermatomes
- Dermatome maps show the innervation territory of all nerve fibres entering the spinal cord at a single segmental level.
- Originally investigated by looking at responses to a stimulation of different parts of the body
49
Name the structures of the brain (9)
Cerebral cortex, corpus callosum, thalamus, midbrain, cerebellum, pons, medulla, spinal cord
50
What is in gray, white matter and the spinal cord
Gray matter contains neuronal cell bodies and some axons
White matter carries axons (white due to myelin)
Spinal cord has fluid-filled central canal
51
What is the difference between the dorsal and ventral root?
Dorsal carries sensory information in whereas ventral is the one that carries motor information out
52
Which part of the spinal cord is sensory and which motor?
Posterior - sensory
| Anterior - motor
53
What is the small swelling on the dorsal root?
Dorsal root ganglion - all the cell bodies from sensory pseudounipolar cells are found here
54
Why's white matter white?
Myelination
55
Where do different sensory fibres terminate in the spinal cord (which lamina)
Aalpha/Abeta fibres - IV
Adelta - majority (80% I, V. superficial. The rest terminate in V
C - II
Separation between modalities
56
Describe a reflex withdrawal
- Pain mediated reflex
- Adelta - fast pain
- E.g. hot candle
- Activate heat sensitive ion channels in nerve endings
- 52 degrees c
- AP travel along afferent sensory nerve to dorsal horn of spinal cord
- Polysynaptic reflex
- Adelta fibre synapses in lamina I, with an interneuron that activates projection to motor region of spinal cord, to motor neurons that activate flexor muscles of arm
57
What are the two ascending pathways?
1) Dorsal Column-Medial Lemniscal Pathway - touch pressure
| 2) Anterolateral system - pain/temp
58
What three parts are there to the anterolateral system
Spinothalamic tract
Spinoreticular tract
Spinomesencephalic tracts
59
Describe traits of the dorsal column-medial lemniscal pathway
- Activated by Abeta fibres
- Dorsal column rises from spinal cord
- Afferent fibre makes first synapse in medulla oblongata
- Gracile and cuneate fascicles (nucleus) - carry info from the spinal cord to the oblongata
- Second order fibre crosses the midline - decussation - in the medulla - rises in medial lemniscus tract through pons to the midbrain
- Synapse in thalamus
- Third order fibre continues to somatosensory cortex (touch and pressure pathway terminates)
60
Where are the gracile and cuneate fascicles located
- Dorsal surface of white matter (top little 'hat' of white matter)
61
Describe the anterolateral system
- Pain pathway
- 3 Different pathways - Spinothalamic tract, Spinoreticular tract, Spinomesencephalic tracts
- Common properties - Adelta or C fibres synapsing in spinal cord for crossing over - decussation
- Lateral tracts rise to different part of the higher centre of the brain
- Spinothalamic tract -goes from spinal cord to thalamus - ventral lateral portion or gray matter - meets thalamus at central lateral nucleus & ventral posterolateral nucleus - 3rd order neurons project from lateral to somatic sensory cortex
- Spinoreticular tract - same pathway but extra synapse in reticular formation of pons - Afferent --> spinal reticular tract (to pons) --> (pons to thalamus) --> (thalamus to somatosensory cortex
- Spinomesencephalic tract - Rise to terminate in the midbrain after afferent neuron around aqueduct - periaqueductal gray matter PAG
62
What is descending inhibition of pain
Feel inition pain then reduced - controls endogenous pain
63
Describe the Spinothalamic tract (6 facts)
Pain pathway
Afferent fibres synapse in the superficial dorsal horn
Decussate (cross over midline) at the level of the spinal cord
Ascend in the spinothalamic tract
Synapse in the thalamus
Project to the somatosensory cortex
64
Describe the Spinoreticular tract (7 facts)
.Pain pathway
Afferent fibres synapse in the superficial dorsal horn
Decussate (cross over midline) at the level of the spinal cord
Ascend in the spinoreticular tract
Synapse in the reticular formation
Project to the thalamus and synapse again
Project to the somatosensory cortex
65
Describe the Spinomesencephalic tracts (7 facts)
Pain pathway
Afferent fibres synapse in the superficial dorsal horn
Decussate (cross over midline) at the level of the spinal cord
Ascend in the spinomesenceph-alic tract
Synapse and terminate in the periaqueductal gray matter
Project to the thalamus and synapse again
Project to the somatosensory cortex
66
Name the four lobes and their functions
- Frontal - Consciousness
- Parietal - processing sensory information
- Temporal - auditory
- Occiptal - vision
67
What is somatotopic
Relationship between position on body surface and termination point on brain - shown in homunculus.
Interesting because hand/face is large as larger proportion of processing power is allocated to them as more afferent fibres come from there (two point discrimination test)
68
Name the two principle descending tracts
- Corticospinal tracts
| - Corticobulbar tract
69
Describe corticospinal tracts
- Lateral tract (crosses over in the medulla – 75% of fibres)
- Ventral tract (does not cross over – 25% of fibres)
- Main role is to control limb movements
- From cortex to spinal cord
70
Describe corticobulbar tract
- Projects from motor cortex to the brain stem
| - Main role is to control head and facial movements
71
What is the pain controlling descending tract
- Monoaminergic pathway
- Use NA and 5-HT (serotonin) as neurotransmitters released in vicinity of pain fibres
- Stems from periaqueductal gray matter
- Synapse in the nucleus at nucleus raphe magnus
- Down to spinal cord
- More pain decreases ascending fibres and increases descending fibres to help reduce pain
72
What are cranial nerves?
Pairs of nerves coming off from segments within brainstem similar to pairs of spinal nerves
73
What deficits are associated with basal ganglia lesions
- Abnormal movements (dyskinesias): tremor, e.g pill rolling tremor, chorea (involuntary flicking or writhing), dystonia (slow truncal movement & body distortion)
- Increased muscle tome (cogwheel rigidity)
- Slow initiation of movements (bradykinesia)
74
Describe Parkinson's disease
- Loss of dopaminergic neurones in the pars compacta of the substantia nigra
- Characterised by tremor (pill rolling) cogwheel rigidity bradykinesia
- Net effect is to increase the activity of neurones in the globus pallidus
75
Describe Huntington's disease
- Genetic disorder – autosomal dominant
- Causes loss of GABAergic and cholinergic neurones in the striatum
- Accompanied by secondary degeneration of the motor cortex causing dementia.
- Causes loss of inhibition of globus pallidus
76
What focuses light onto the eye
- Cornea (somewhat)
| - Lens which can change shape to focus light onto fovea, cones most concentrated there
77
What is the retina structure
- Neural network
- Rod and cone cells
- Processing cells
- Ganglion cells whose axons form optic nerve which travels to optic cortex
78
What cells are in the retina
- Photo receptors (rods and cones)
- Retinal bipolar cells
- Amacrine cell
- Ganglion cell
79
What layers make up the retina (closest to light first)
- Nerve fibre
- Ganglion cell
- Inner plexiform
- Inner nuclear
- Outer plexiform
- Outer nuclear
- Photoreceptor outer segments
- Pigment epithelium
80
How can information flow?
- Lateral information flow
| - Vertical information flow
81
What's different about neurons in eyes (rod, cone horizontal and bipolar)
- DON'T USE ACTION POTENTIALS
- Graded changes in membrane potentials induces transmitter release
- (all ganglion and some amacrine)
82
Structures common to rods AND cones
- General layout - outer (collects light), inner and synaptic terminal (which connects to bipolar cells)
- Nucleus
- Mitochondria
- Cillium
- Plasma membrane
83
What features are only found in rods?
- Disks and cytoplasmic space
84
Describe rod cells
- Low light conditions
- B and W (monochromatic)
- Saturate in normal light levels - so cannot work
- More across retina periphery vision eg. star at night falling on adjacent region of fainter light
- High sensitivity, specialised for night vision
- More photopigment, capture more light
- High amplification, single photon detection
- Low temporal resolution (12Hz)
- Slow response, long integration time
- More sensitive to scattered light
85
Describe cone cells
- High conc. in fovea
- Colour
- Invaginations never pinch off and internalise
- Lower sensitivity, specialised for day vision
- Less photopigment
- Less amplification
- Saturate only in intense light
- High temporal resolution (55Hz)
- Fast response, short integration time
- Most sensitive to direct axial rays
86
How do you detect light
- photons of light detected by photopigments
- Opsin proteins - packed into invaginations in cone cells and disks in rods
- Rhodopsin in disks
87
Why are rods better at getting light
- Cones have less invaginations (layers) meaning less photopigment
88
What spectrum of light do our eyes see
Visible light - ~380nm to ~750nm
| Purple to red in increasing wavelength
89
What are the different photopigments
Rods - rhodopsin
Cones - Red opsin
- Blue opsin
- Green opsin
+ 11-cis retinal (vitamin A derivative)
= pigment
90
What are opsins
- Photopigments that detect light
| - GPCR
91
What is a GPCR
- G protein coupled receptors
- Found on cell surfaces
- eg Adrenoceptors
92
How does rhodopsin
- Rather than a chemical ligand they are photo sensitive
- 11-cis retinal causes photo sensitivity as it changes conformational shape (All-trans retinal) when it absorbs light
- Sets of signalling cascade
93
Describe the signally cascade
- Light absorbed by Rhodopsin
- Metarhodopsin II needs to be removed from the All-trans-Retinal to get 11-cis-Retinal
- + Opsin recycles it to rhodopsin
- Changes membrane poyensial (NA+ in)
- Vitamin A important for not getting night time blindness
94
What is the conformational change in rhodopsin
Photo-transduction : Cis to Trans, 11-cis-retinal to all-trans-retinal
95
What happens in cell signalling in the rod outer segment
Light enters visual pigment (rhodopsin) which causes conformational change that activates G-Protein (Transducin) by binding GTP resulting in activation of cGMP Phosphodiesterase regulate (concentration) [cGMP] within the cell which is fundamental in membrane potential of photoreceptor. (5'-GMP is the inactive form). Controls cGMP-gated ion channel (primarily NA+) so more cGMP broken down by cGMP phosphodiesterase means less influx of Na+ and a decrease in membrane potential.
In dark conditions - cGMP ions open membrane potential will be depolarised
In light conditions - cGMP ions shut and membrane potential will hyperpolarisation - more negative
96
How can 1 rhodopsin molecule detect light so well
- Signal is highly amplified
- 1 rhodopsin molecul can activate hundres of transducin molecules
- they will activate phophodiesterase for each transducin
- cGMP--->5'GMP happens at 10^3 per second
97
How does the ocular signal past from the rod/cone cells onwards?
The change in membrane potential is present at the synaptic terminal meaning change of NT release from cells onto bipolar cells or horizontal cells to ganglion and optic nerve
98
What is the NT in rods ad cones
Glutamate
99
What is the light receptor activated by
Hyperpolarisation
100
How is the light response terminated? (3)
- Opsin kinase - phosphorylates opsin proteins to stop their actions
- Arrestin which helps to stop the action of these proteins
- Breakdown of GTP to GDP
ACTIVE process
101
What is the light adaptation response
- Initially very negative - hyperpolarisation - then rises to a level part way between the dark level and light level
- Hyperpolarisation occurs due to inhibitory influence of Ca2+ on enzyme guanylyl cyclase (which makes cGMP from GTP) being removed by closure of the ion channels
102
What are the two main types of ganglion cells
- M-type
| - P-type
103
Describe M-type ganglion cells
- Large receptive fields
- Detect gross features
- On & off centre
- Not wavelength selective
104
Describe P-type ganglion cells
- small receptive fields
- detect fine features
- on & off centre
- wavelength selective
105
Describe other ganglion cells
- respond to diffuse light
| - illumination/brightness
106
What is common to all ganglion cells?
- They have circular receptive fields
- They have a centre and an antagonistic surround
- They process information in two parallel pathways
107
How does the retina work as a network?
- On and off centre bipolar cells
108
What happens in the dark in on-centre bipolar cells
- Depolarised cell
- More glutamate release
- mGluR6 (receptor) closes TRPM1 channels
- Em hyperpolarises
109
What happens in the light in on-centre bipolar cells
- Hyperpolarised cell
- Less glutamate release
- mGlu6 receptors cause TRPM1 channels open
- Em depolarises
110
What happens in the dark in off-centre bipolar cells
- Depolarised cell
- Higher glutamate release
- AMPAR open
- Em depol
111
What happens in the light in off-centre bipolar cells
- Hyperpolarised
- Lower glutamate
- AMPAR close
- Em hyperpolarise
112
Whats the difference between AMPAR and mGluR
AMPA receptor ligand gated ion channel, non-selective cation channels but mostly Na+ whereas mGluR is GPCR
113
What do they horizontal cells do?
- Inhibitory interneurons
- GABA inhibitory NT
- Eg. Depolarised light on surround depolarises by NT on AMPAR receptors horizontal cell releases GABA which will bind to GABA(littleA) receptors ionotropic chlorine channels which hyperpolorises so less glutamate release fewer mGluR6 receptors activated so less TRPM6 so it depolarises
114
How do rod and cone cells connect?
Electrical synapses - proteins in membranes of the rod cells that line up with proteins of the cone cells to form gap junctions made of connexins - similar to spread of excitation in the heart.
- Can be regulated to open/close
115
Why do rod and cone cells connect
- Cones cannot get enough photons of light as they have less pigment than rod cells which can also amplify signal
- To operate in intermediate conditions eg twilight
116
What do amacrine cells do
Moderate interaction of rod bipolar cells
117
Describe red-green colour blindness
- Recessive gene
- X-linked
- Effects males but females can be carriers
- Anomalous - pigment itself is abnormal, red (protanomaly) and green cones (deuteranomaly) affected (greens more than reds) (blue is called tritanomaly)
- Dichromatopsia - cones absent (1 or 2), red (protanopia) and green (deuteranopia
118
How do you work out the decibel scale
Sound pressure (dB) = 20log(Pt/Pr)
```
Pt = test pressure
Pr = reference pressure (just audible sound (1-3kHz))
```
119
What's the range of the dB scale
4dB to >120dB
120
What defines pitch
Frequency - Hertz (Hz)
121
Name the parts of the ear
Eardrum, Malleus, Incus, Stapes, Semicircular canals, Auditory nerve, Vestibular nerve, Endolymphatic sac, Eustachian tube, Cochlea
122
How do we hear
1) Sound enters the external auditory canal
2) Moves eardrum in and out
3) These pass vibrations onto the three bones of the middle ear - malleus, incus and stapes
4) They carry on to the inner ear, semicircular canals & cochlea
5) Movement of hairs in organ of Corti shearing effect up against techtorial membrane
5) Information is passed down the auditory nerve
123
Describe the cochlea
- spiral 'shell' shaped
- made up of 3 different fluid filled chambers
- Scala vestibuli - entrance, first one
- Scala media
- Scala typani
124
Describe the round and oval window
Push in on oval pushes round window out
125
What scala media
Different composition - high K ion concentration
Tympani-media side is basilar membrane - contains organ or Corti
Vestibuli-media side is Reissner's membrane
126
Where is the organ of corti found
On the basilar membrane
127
What makes up the organ of corti
- 3 rows of outer hair cells
- 1 row of inner hair cells
- Support cells -
- Afferent nerve fibres
- Tectorial membrane
128
Describe the anatomy of the cochlear hair cells
- Rows of stereocilia & kinocilium - held together with small protein strands called tiplings
- NT - Glutamate
- Afferent and efferent fibres connected by ribbon synapses
- Tight junctions between cells - prevents leaking that would affect the K+ concentration of the scala media
129
What happens when you listen to v. loud music?
- Tiplings break
| - Stereocilia become very disordered
130
Describe hair cell innervation
- 3 rows of outer hair cells
- 1 row of inner hair cells
- 3,000 hair cells in each cochlea
- 33,000 cells in spiral ganglion
- 90% of sensory fibres innervate single row of inner hair cells: 10 sensory fibres per hair cell
- Also efferent innervation: involved in efferent innervation of hair cells
131
How can you tune sound
Location in the cochlea
Length of stereocilia
Electrical tuning
Different parts of the basilar membrane have different natural resonance frequency as it starts narrow base (high) and gets wider apex (low)
132
What's the role of the tectorial membrane in detecting the sound
- Sits on top of hairs
| -
133
Describe hair cell properties
1) Membrane potential
- Depolarised at rest (-60mV)
2) Directionally sensitive:
- towards kinocilium = depolarisation
- away from kinocilium = hyperpolarisation
3) Mechanically tuned
- location in cochlea
- hair bundle length varies
4) Electrically tuned
- sinusoidal Em response
134
How does the movement of hairs affect nerve impulses?
- One direction causes a depolarisation and an increased impulse frequency
- The other causes a hyperpolarization and a decreased impulse frequency
- Sine curve of nerve potentials (up and down)
135
How is the sinusoidal membrane potential changed in hair cells
-57mV baseline
- Depolarised at -60mV
- Hyperpolarisation at ~-40mV
Depolarisation caused by K+ ions entering the cell through the stereocilia which causes voltage gated Ca2+ channels to open. As Ca2+ enters it binds to a Ca2+ sensitive K+ channel, which causes K+ ions to leave down their electrochemical gradient. Potential repolarizes assisted by voltage-gated K+ channels. Calcium pumped out by calcium pumps or pumped into mitochondria cells. Hair cells return to being straight again.
Opposite happens when they go down causing K+ channels to close at the top meaning a slight hyperpolarisation
136
Entry of which ion usually causes a depol
Na2+
