Motor Systems Flashcards

Question

What areas project to the motor cortex?

Answer 1

Cortical areas including prefrontal, parietal, and temporal associated areas ## Footnote These areas provide inputs that affect the activation of the motor cortex.

Answer 2

Stretch - muscles Waithdrawal - cutaneous receptors

Answer 3

Smooth: 30-200 um Cardiac: 50-100 um Skeletal: up to 0.3m ## Footnote Smooth muscle fibers can vary in length but typically fall within this range.

Answer 4

Mono-nucleated, central nucleus. Spindle-shaped, tapered ends, non-striated Location: lining of the respiratory, cardiovascular, digestive, and reproductive tract Under involuntary control (autonomic NS) ## Footnote Smooth muscle is characterized by its unique structure and locations in various body systems.

Answer 5

Mono-nucleated mainly, some van be multinucleated (<5) Striated; branched Located in linign of the heart Self contractile + under involuntary control (autonomic NS) ## Footnote The branched structure of cardiac muscle allows for effective contraction and communication between cells.

Answer 6

Voluntary movement It is elongated & striated, attached to skeleton ## Footnote Skeletal muscle is responsible for movements that are consciously controlled by the somatic nervous system.

Answer 7

Muscle organ -> fascicles (bundles of fibers) -> muscle fibers (cell) -> myofibrils (organelles) ## Footnote This hierarchical structure allows for efficient force generation and contraction.

Answer 8

Alternation of dark & light bands ## Footnote Striations are due to the arrangement of thick and thin filaments within the muscle fibers.

Answer 9

Sarcomere: - interdigitated thick + thin filaments - each myofibril has as many as 20,000 sarcomeres in repeated subunits - thin filaments project from Z bands, thick prject from centre ## Footnote The sarcomere consists of interdigitated thick and thin filaments and is the basic unit of muscle contraction.

Answer 10

Pulled closer together to shorten myofibril ## Footnote This shortening is due to the sliding filament mechanism facilitated by cross-bridges between thick and thin filaments.

Answer 11

F actin, tropomyosin, troponin ## Footnote These components work together to facilitate muscle contraction and regulate interactions with myosin.

Answer 12

Fine, thin elastic filaments connecting ends of thick filaments with Z disks ## Footnote Connectins provide elastic properties to the muscle and help maintain structural integrity.

Answer 13

Myosin (thick) and actin (thin) filaments ## Footnote Myosin and actin are essential for muscle contraction.

Answer 14

Calcium is released from cisternae of the sarcoplasmic reticulum, diffuses along myofibrils and binds to troponin -> cross-bridge formation ## Footnote This binding enables cross-bridges to form and muscle contraction to occur.

Answer 15

Released very rapidly: 20-50 ms Reuptake also rapid: cross-bridge decrease (80-200ms) ## Footnote This rapid release is crucial for effective muscle contraction.

Answer 16

Twitches due to limited calcium release ## Footnote it allows enough time for calcium reuptake and muscle relaxation.

Answer 17

Tetani due to more calcium released -> can be helpful for powerful contractions ## Footnote This results in less time for reuptake and relaxation, leading to summation or fused contraction.

Answer 18

True ## Footnote Tetanus affects the nervous system, causing overactivation of motor neurons.

Answer 19

Troponin-tropomyosin complexes on thin fils block binding sites on actin, myosin heads ADP bound (cocked) low [Ca2+] in sarcoplasm, no cross bridges between thick + thin

Answer 20

Muscle fibre activated via T-tubule AP, Ca2+ released from cisternae of SR. Ca2+ binds troponin -> conformational changes exposes binding sites to cocked myosin heads (cross bridge formation)

Answer 21

Mech energy from dephos ATP stored in cocked mysoin released -> power stroke. Longitudinal forces pull thick + thin fils into greater overlap (~0.06um), shortening fibre Myosin heads shed bound ADP, resume relexed state but still bound by cross bridges

Answer 22

ATP binds myosin so it detaches from actin binding site, released to form another cross bridge -> sustained contraction

Answer 23

Thick fil: dephos of ATP -> ADP energy stored in heads (recocked) Thin fil: high [Ca2+] system remains activated + contraction persists, low [Ca2+] it retrurns to retsing state so myosin heads cocked but cannot form cross-bridges

Answer 24

100% overlap when contracted, no overlap when fully stretched. Dictated by number of cross-bridge connections available: - too stretched -> less available -> less force - too contracted -> all are occupied -> no additional force available

Answer 25

Anti-gravity + postural e.g. standing walking - mainly slow twitch (type I) - resitant to fatigue, small amounts tension for long periods of time - aerobic metabolism, many mt & capillaries, myoglobin rich

Answer 26

Shorter bursts activity, less mt, less myoglobin - mix of fast (type II) & slow twitch

Answer 27

- slow contraction (50-110ms) - small force (20g tet. tension) - resistant to fatigue (ox metab, many mt, good blood supply) - recruited first in contraction

Answer 28

- fasct contraction (25-45ms) - intermediate force (20-60g tet tension) - resistant to fatigue (ox metab + anaerobic - intermediate recuitment order

Answer 29

- Very fast contraction (<10ms), fast myosin isoform - High force (50-150g), has many large muscle fibres - Fatigue easily (anaerobic metab, glycogen store, few mt) - Recruited last during contraction

Answer 30

Genetic disposition Training & exercise can enable fibres to shift between type -> hybrids ## Footnote Hybrid fibre types do exist - express more than one MHC type

Answer 31

Motor/premotor cortex, axons extend to brai stem + spinal cord - pyramidal cells - glutamatergic transmission - various pathways

Answer 32

* Corticospinal tract * Corticobulbar tract * Corticopontine tract * Rubrospinal tract * Reticulospinal tract

Answer 33

Cholinergic transmission

Answer 34

Proximal-distal rule

Answer 35

Cholinergic transmission, large neurons, cell bodies are covergence of sensory fibres, interneuorns & descending pathways (many inputs) Originate in SC + axons extend down to skl muscle, located in central horn of the spinal cord and cranial nerve nuclei in the brainstem ## Footnote Organised in MN pools - groups fo MNs that supply individual muscles, arranged in longitudinal columns spannig several segments

Answer 36

Axial/proximal muscles ## Footnote e.g. axial, shoulder

Answer 37

Distal muscles ## Footnote e.g. wrists & digits

Answer 38

Motor neuron & the skeletal muscle fibre it innervates - forms basic unit of contraction - has 10s to 1000s of muscle fibres ## Footnote CNS controls motor units, not single muscle fibres

Answer 39

1) firing rates of MUs (summation of twitches + tetani) 2) recruitment of MUs Recruitment is major mechanism at low force levels, follows size principle ## Footnote size principle - small MNs always activated before large MNs

Answer 40

Small MNs recruited first due to small SA (Henneman) Smaller MNs have: - high density electrical inputs (small SA) - high electrical input reistance -> will exceed AP threshold, recurited before large MN ## Footnote Provides graded muscle contraction depending on force needed.

Answer 41

Alpha - supply extrafusal muscle fibres, large soma, fast/large myelinated axons -> control muscle force generation Gamma - supply itrafusal fibres (spindle), smaller soma, smaller/slower myelinated axons -> control muscle spindle responsiveness ## Footnote Beta supply intra and extrafusal, more rare

Answer 42

- Non-fatigable fibres used for most tasks, fatigable fibres used sparingly - Increments in contractile force (recruitment) roughly proportional to current force ○ Fine movements : small increments ○ Grosser movements : larger increments

Answer 43

Dysfunction of motor neuron axons.

Answer 44

Guillain-Barré Syndrome.

Answer 45

Preceding infection produces antibodies that target peripheral myelin Associated w/ bacterial/viral infections such as gastroenteritis, EBV, Zika.

Answer 46

Numbness, pain in distal limbs, facial weakness, respiratory failure, paralysis. Can be diagnosed w/ CSF analysis & nerve conudction analysis. Treatments: IV immunoglobins, plasma exchange, supportive care, rehabilitation. ## Footnote 5% die, 15% w/ disability

Answer 47

Dysfunction of the synapse between motor neuron and muscle fiber.

Answer 48

An autoimmune attack on skeletal muscle affecting signal transmission at the neuromuscular junction. Mostly affects women aged 20-40

Answer 49

Antibodies specific to nAChR a-subunit on muscle membrane - main immunogenic region between a.acids 67-76 Can also be: Congenital - transfer of AChR antibodies across placenta from mother Inherited - mutations that affect gating, mutated a-subunit of nAChR (V249F), 2 residues below Leu gate

Answer 50

* Receptors internalized by endocytosis. * Destruction/simplification of endplate, complement attack reduces junctional folds, synapse widened * Block of ACh binding sites (antibody binding), sompetitive antagonism

Answer 51

A progressive skeletal muscle degeneration/weakness. Is X-linked recessive for mutant dystrophin. Primarily affects boys, diagnosed w/ Gowers sign, life expectancy = 22 years

Answer 52

Links actin cytoskeleton to extracellular matrix, providing support and membrane stabilization.

Answer 53

Palliative care BUT early clinical trials of antisense oligonucleotides show motor function improvement. -> induces exon skipping in mutated dystrophin exon

Answer 54

1) Dysfunction of motor neuron cell body (motor neuron diseases) 2) Dysfunction of motor neuron axons (peripheral neuropathies) e.g. GBS 3) Dysfunction of synapse between MN & muscle fibre (neuromuscular) e.g. MG 4) Dysfunctions of muscle fibres (myopathies) e.g. DMD

Answer 55

Relay neurons (interneurons), sensory neurons, motor neurons ## Footnote Relay neurons are entirely within the CNS, while sensory neurons have axons that transmit sensory information, and motor neurons have cell bodies that send signals to muscles.

Answer 56

Segmented ## Footnote The segmentation of the spinal cord corresponds to the arrangement of spinal nerves.

Answer 57

Recurrent inhibition of the same motor neuron pool - input is collateral axons of MN ## Footnote Renshaw cells provide negative feedback control to reduce contraction of synergistic muscles and are important for descending control.

Answer 58

Organized into 10 layers Classify the grey matter of the spinal cord based on the arrangement of neurons

Answer 59

Motor neurons, interneurons, sensory neurons ## Footnote Interneurons link sensory and motor neurons and are essential for reflexes and neural circuits.

Answer 60

Axons ## Footnote White matter contains myelinated axons that facilitate communication between different parts of the CNS.

Answer 61

Contains cerebrospinal fluid ## Footnote The central canal is a fluid-filled space that helps protect and nourish the spinal cord.

Answer 62

Contains interneurons that link to specific functional motifs ## Footnote These interneurons play a crucial role in coordinating reflexes and motor patterns.

Answer 63

Retrograde labelling shows MN pools clustered along ristrocaudal axis. MNs innervating axial + distal muscles located along mediolateral axis of ventral horn. ## Footnote - proximal muscles controlled by MNs close to midline - distal muscles controlled by more lateral MNs

Answer 64

+: can link interneurons to specific functional motifs -: expression of functional motifs can be flexible depending on behavioural state

Answer 65

Prevent synergistic & antagonistic muscles working against each other, receive input from muscle spindle receptors -> function to inhibit antagonistic MN motor pool ## Footnote - reduce antagonistic muscle contraction - important for stretch reflex

Answer 66

Prevents excessive muscle elongation, receive excitation from golgi tendon organs (sense stretch) - Ib afferents. --> function to inhibit same MN motor pool, non-reciprocal inhibition ## Footnote - reduce cotraction of synergistic muscles - important for tendon reflex

Answer 67

+: based on neurodevelopment, used to identify distinct cell types -: can't always map neuronal function to distinct genetic sub-types ## Footnote 11 progenitor domains give rise to cardinal classes w/ unique TFs - RCs make up 5% of V1 class - Ia inhib from V1 (inhibit flexors) & V2B (inhibit extensors)

Answer 68

Dorsal column: - Skin, muscles & Golgi tendon receptors - Fine touch, tactile discrimination, vibrations, control of fine movements Spinothalamic: - Carry nociceptive, temperature, crude touch & pressure from skin to somatosensory area of thalamus - Responsible for quick withdraw reaction to painful stimulus

Answer 69

Pyramidal: - Lateral corticospinal - Ventral corticospinal Non-pyramidal: - reticulospinal - rubrospinal - vestibulospinal - tectospinal

Answer 70

Originate in upper MN + premotor cortex. Function to control contralateral movements (due to decussation) Lateral: cross over in pyramids, extremity muscles, upper MNs innervate single muscles or small set muscles (fine motor control Anterior/ventral: cross over spinal cord, control in axial muscles (more proximal e.g. neck) ## Footnote Pyramidal

Answer 71

1898 Prus could not stop epileptic motor activity by disturbing pyramids Function to control learned or involuntary movements, muscle tone, posture & reflexes/orienting responses to stimuli.

Answer 72

Controls posture + gross movements, neurons branch extensively contracting many MN pools controlling synergistic muscles. Single axons innvervate muscles on both sides.

Answer 73

Originates in Red Nucleus (pink to Fe/Hb), transmit signals from cerebellum & motor cortex -> controls muscle tone + arm muscles

Answer 74

Receive info from vestibulococlear crania nerve about angular & linear head accelerations, originates from vestibular nuclei in the pons. Medial - stabilises head position by innvervating neck muscles Lateral - controls 'antigravity' muscles, extensor muscles of leg.

Answer 75

Originates in superior colliculus (optic tectum in non-mammalian vertebrates) -> important centre for multisensory & sensorimotor integration Combines info to detect salient stimuli & orient animal towards them

Answer 76

Monosynaptic: Ia afferent fibres excited by muscle elongation SO excite motor neurons from the same and synergistic muscles to contract (one synapse) Disynaptic: Ia afferent fibers excited by muscle elongation SO excite Ia inhibitory interneurons -> Ia inhibitory interneurons inhibit muscle contraction in antagonist muscles

Answer 77

- noiciceptive-ad fibres excite spinal sensory neurons - spinal sensory neurons indirectly promote flexor muscle contraction via inhibitory & excitatory interneuron ## Footnote Polysynaptic

Answer 78

- Spinal sensory neurons contact commissural neurons - Commissural neurons indirectly promote flexor muscle relaxation and extensor muscle contraction Responsible for left-right alternation, same circuitry for locomotion

Answer 79

Produce recurrent inhibition of activated muscles through MN collaterals Also inhibits Ia inhibitory interneurons, so indirectly excites antagonist muscles ## Footnote Double action controlled by des pathways -> single projection onto RCs

Answer 80

Stimulation of Ib sensory afferent induces: - non-reciprocal inhibition of muscle at rest - excitation of muscle during walking Ib interneurons + excitatory interneurons controlled by des pathways according to behavioural state (rest vs walking)

Answer 81

5-10% hereditary, remainder sporadic. Very heterogeneous disease, some mutants cause both ALS & FTD ## Footnote Very rare for ALS causing mutations to occur sporadically.

Answer 82

An umbrella term for a group of neurodegenerative diseases with inconsistent nomenclature ## Footnote Includes conditions like ALS, PLS, PMA, and PBP.

Answer 83

Amyotrophic lateral sclerosis ## Footnote Also known as Lou Gehrig's disease.

Answer 84

~1-2 in 100,000 ## Footnote ALS is considered quite rare.

Answer 85

* Limb/spinal onset * Bulbar onset

Answer 86

Fatal within 2-5 years of symptomatic onset ## Footnote Limited treatment options necessitate urgent research.

Answer 87

* Muscle stiffness * Cramps * Muscle twitching (fasciculations) * Weakness in legs, arms, hands, and feet * Poor grip strength

Answer 88

* Dysphagia (swallowing difficulty) * Pooling of saliva (sialorrhea) * Spasm of vocal cords (laryngospasm) * Slow/slurred speech

Answer 89

Corticospinal tract ## Footnote This leads to degeneration of motor neurons.

Answer 90

Corticobulbar tract

Answer 91

Worse prognosis due to respiratory infections

Answer 92

Selectively killing neurons prematurely and progressive degeneration ## Footnote Neurons are not regenerated.

Answer 93

* Wasting * Weakness * Fasciculations

Answer 94

Episodic memory impairments, 15% develop frontotemporal dementia (FTD) - due to atrophy in frontal & temporal lobes Can also lead to personality changes/language disorders. ## Footnote Episodic memory is the ability to recall past events and experiences, along with the details of when and where they took place

Answer 95

1st ALS mutant discovered, 10-20% FALS, 1-2% SALS, many different mutants (many missense single a.acid subs) SOD1 is copper-zinc superoxide dismutase 1, antioxidant enzyme that normally hydrolyses superoxide radicals - ubiquitous (cytosol, mt, nucleus & ER) Unclear if toxicity due to LoF or GoF ## Footnote New antisense oligomer (ASO treatment) - Tofersen - Administered via CSF injections

Answer 96

~1 in 12 of all cases, most common cause of ALS & FTD Repeat expansion of large hexanucleotide (GGGGCC) - mutation in nc region (intron 1 or promoter) - patients 50% less C9orf72 expression (but not main cause) Expansion still gets TRANSCRIBED, forms folded G quadruplex tricks machiner into thinking it has ATG start codon

Answer 97

Depending on initiation site, 5 different repetitive dipeptides formed on both strands. -> Dipeptide repeat proteins (DPRs), e.g. AP is alanine-proline Also RNA foci formed from transcript in nucleus. BOTH RNA foci & DPRs form inclusions in brain -> toxicity.

Answer 98

ALS affects the whole motor unit, causing motor neuron degeneration and damage to the neuromuscular junction (NMJ) ## Footnote This leads to muscle wastage.

Answer 99

Changes can be observed through physical brain defects or immunohistochemistry ## Footnote Immunohistochemistry allows for the visualization of specific proteins in the tissue.

Answer 100

ALS patients have far fewer visible neurons, with less structure and order ## Footnote This indicates significant neurodegeneration.

Answer 101

Insoluble intraneuronal protein aggregates/inclusions ## Footnote These aggregates are a hallmark of neurodegeneration.

Answer 102

Proteins are ubiquitinated and phosphorylated for proteasome degradation, but the system can become overwhelmed ## Footnote This leads to the accumulation of protein aggregates.

Answer 103

TDP-43 is mislocalized to the cytosol instead of remaining in the nucleus, leading to aggregation ## Footnote This mislocalization is a key feature of ALS pathology.

Answer 104

RAN translation produces repeat-associated non-ATG dipeptides, which form insoluble aggregates ## Footnote This process contributes to the complexity of protein aggregation in ALS.

Answer 105

Rare, ~1-3% of all ALS. Encodes TDP-43, an RNA & DNA binding protein primarily found in nucleus. Many roles in DNA repair & RNA processing: - Regulating transcription, translation, splicing >40 mutations (most missense) linked to ALS, majority in glycine rich region of gene (binding domain).

Answer 106

- Post mortem patient tissue, brains & spinal cord - Clinical imaging e.g. PET - Patient blood/CSF samples - In vitro disease models: ○ Immortalised cell lines (Hela cells, difficult to compare to neuron) ○ Human iPSC-derived neurons (derived from fibroblast) ○ Primary cell cultures from animals - In vivo disease models: ○ Rodents, drosophila, zebrafish, C. elegans

Answer 107

Investigate normal function & investigate whether LoF causes disease

Answer 108

○ SOD1 G93A mice -> SOD1 pathology, motor phenotype ○ TARDBP mutations OR overexpression of human WT TDP-43 ○ C9orf72 GGGGCC expansions ○ Artificial expression of a single C9orf72 dipeptide (e.g. poly-GR) ## Footnote Can use rotor rod test to test mice motor skills, quantify length it takes to fall off

Answer 109

- excitoxicity - neuroinflammation - altered axonal transport ## Footnote Many other different causes.

Answer 110

Too much Glu, binds AMPA/NMDA/kainate Rs causing Ca2+ influx Too much Ca2+: ○ Activation of signalling processes/enzymes e.g. proteases, endonucleases, phospholipases ○ Damage to cytoskeleton, membrane, DNA etc. ○ Mitochondria release toxic free radicals ○ Caspase cleavage -> apoptosis ## Footnote Glu reuptake transport proteins (EAATs) on neurons/astrocytes normally maintain tight control

Answer 111

- Increased Glu in patient plasma & CSF - Reduced expression of glutamate transporters (e.g. EAAT2) on astrocytes in ALS patient motor cortex and spinal cord - Riluzole reduces Glu transmission, only approved ALS drug, modest therapeutic benefit

Answer 112

- Cultured motor neurons particularly vulnerable to excitotoxicity compared to other neuronal subtypes - Patient CSF is toxic to cultured motor neurons -> rescued by glutamate receptor antagonists

Answer 113

EAAT2 knockout exacerbates motor impairments and reduces survival in mSOD1 mice, reverse also true

Answer 114

Motor proteins (kinesins/dyneins) which bind cargoes & transport along MTs (tubulin polymers), powered by ATP hydrolysis Anterograde transport - away from cell body (kinesins) Retrograde transport - towards cell body (dyneins) ## Footnote Can be viewed w/ live fluorescent microscopy

Answer 115

- Mutations in kinesin family proteins linked to ALS (KIR1A, KIR5A) - EM and histopatholoy of ALS patient tissue -> abnormal accumulation of vesicles, lysosomes, mitochondria, neurofilaments, microtubules etc. in motor neurons

Answer 116

* SOD1 and TARDBP mutant mice and cells have axonal transport defects * Cargoes are fluorescently labelled and tracked with live-imaging * Cargoes move more slowly/not at all in ALS models * Recent research shows similar phenotype caused by C9orf72 expansion

Answer 117

Used patient iPSC MNs, fluorescentally labelled mt for live imaging -> fewer mt oving in human C9orf72 Found that poly-GR & -PR reduced mt motility - Immunohistochemistry shows that the C9orf72 dipeptides bind several axonal tranpsort proteins so cant carry out normal function -> defects ## Footnote Fumagali et al, 2021

Answer 118

- Common to all neurodegenerative diseases - Microgliosis in affected brain region: observed by immunohistochemistry/PET imaging, correlated to severity of disease progression - Increased pro-inflammatory cytokines in CSF e.g. IL-1β, IL-6, TNFα, IFN-γ…

Answer 119

More amoeboid shape - suggesting increased microglial activation in SOD1 ## Footnote Using SHOD analysis

Answer 120

Genetic evidence supports key role of microglia in inflammation e.g. TBK1, OPTN1 & VCP mutations Inflam cytokines can be toxic to neurons mSOD1 MNs protected by co-culturing w/ WT microglia BUT mSOD1 microglia toxic to cultured MNs ## Footnote IL-2 treatment can benefit

Answer 121

Large intracellular multiprotein complexes, inflammasome activation -> caspase-1 activation. - Caspase-1 cleaves pro-interluekin-1B -> IL-1B release (inflam cytokine) Linked to other neurodegenerative diseases, NLRP3 inhibition rescues cognition in AD in rodents. ## Footnote NLRP3 binds ASC to activate caspase 1. Activates in response to tissue damage, pathogens or protein aggregation

Answer 122

More IL-1B secretion = more inflammasome activation. GR activates NLRP3 in dose dependent manner by cleaving pro-IL-1B ## Footnote NLPR3 KO rescues mobility in GR mice - suggests NLRP3 contributes to neurodegeneration/ALS symptoms, highlights inflammasome as potential therapeutic target.

Answer 123

The perception of joint and body movement as well as position of the body, or body segments in space ## Footnote Proprioception is crucial for balance and coordination.

Answer 124

The perception of external/environmental stimuli acting on the body (e.g touch, vision, sound, smell) ## Footnote Exteroception allows individuals to interact with their environment.

Answer 125

Mechanosensitive ion channels Discovered by Julius & Patapoutian (Nobel prize 2021) Piezo 2 highly expressed in proprioceptive peripheral endings ## Footnote These channels are involved in the perception of mechanical stimuli.

Answer 126

They open. Affects motor coordination, conditional KO in mice where piezo 2 not expressed in dorsal root ganglion proprioceptive neurons -> basic locomotion but impaired limb coordination ## Footnote Normally, these channels are invaginated in the membrane.

Answer 127

Fibers that provide force to the muscle and are stimulated by alpha motor neurons ## Footnote These fibers are responsible for muscle contraction.

Answer 128

Fibers that lay in parallel to EF fibers, do not provide force, and are stimulated by gamma motor neurons ## Footnote IN fibers are part of muscle spindles and provide sensory feedback.

Answer 129

Spindle-like structures made up of intrafusal fibers. - Central MS regions are non-contractile and contain sensory endings (sensory feedback) - Contractile regions of IF fibres used to adjust length. Important to modulate sensory signalling (see gain control section) ## Footnote Muscle spindles are crucial for sensory feedback regarding muscle stretch.

Answer 130

3 types of IF fibres: dyanmic nuclear bag, static nucelar bag, nuclear chain 2 afferent types: Ia sense velocity + length, Il sense length 2 gamma MNs: dyanmic + static ## Footnote Afferent fibers provide information about muscle stretch and rate of change.

Answer 131

Stimulation of alpha motor neurons only suring sustained muscle stretch

Answer 132

Adjust gain of sensory feedback from muscle spindles and keep muscle spindle signals within working range

Answer 133

Muscle spindle length must be adjusted - MS signal changes in muscle length during contraction -> provides sensory feedback for motor control If muscle length change not accompanied by MS length change then sensosry feedback drops to 0

Answer 134

muscle spindle length

Answer 135

Increase gain of static sensory response, active during static postures/slow movements ## Footnote Static gamma fibers play a crucial role in maintaining posture and stability.

Answer 136

Increase gain of dynamic sensory response, active during fast, unpredictable or complex movements ## Footnote Dynamic gamma fibers are essential for quick adjustments during movement.

Answer 137

Muscle length (static) & changes in muscle length (dynamic) Differential modulation of static + dynamic fibres changes sensory feedback by altering balance between static/dynamic response. -> depends on behavioural states ## Footnote Muscle spindles provide critical information about muscle stretch and tension.

Answer 138

Gains dynamically adjusted during behavior, amplifying relevant feedback and suppressing less relevant ones. - proprioceptive feedback -> muscle afferent - tactile feedback -> cutaneous afferent ## Footnote This process helps prioritize sensory information during motor tasks.

Answer 139

Proprioceptive feedback response is amplified; tactile feedback response is inhibited ## Footnote This differential response is important for coordinating movement.

Answer 140

Expressed selectively in intrafusal muscle fibers ## Footnote Erg3 plays a role in muscle spindle function and proprioception.

Answer 141

Provides genetic model of MS degeneration after birth, abolishing sensory feedback - basic walking patterns partially preserved (slow) - fine motor control severely impaired ## Footnote This model is valuable for studying the effects of sensory feedback loss on movement.

Answer 142

Chain of reflexes - series of reflex, foot periodically touches/muscles periodically stretch -> tactile + proprioceptive reafference ncecessary Central pattern generators (CPGs) - rhythm gernated centrally -> sensory reafference not necessary

Answer 143

Brown 1911 in decerebrated cats, leg fixed by clamp, dorsal root cut (no sensory reafference) -> rhythmic flexors (TA) & extensor (GN) alternation emerged soon after dorsal root cut Ficitve motor patterns generated in absence of sensory input in tissue ex vivo. Also observed in vivo after neuromuscular blockers (curarized animals)

Answer 144

Brainstem (resp, chewing, swallowing) Spinal cord (defecation, ejaculation + locomotion)

Answer 145

Expression depends on interaction between 2 main factors: 1. Circuitry - connectivity among cells in the network (synapses/gap junctions) 2. Circuit elements - intrinsic dynamics of individual cells within network ## Footnote Rhythm is emergent property of these interactions

Answer 146

- Distinct CPGs are associated with individual limbs (we know single limbs can generate rhythmic patterns) - Limb coordination (e.g. alternation in walking, near-synchrony in gallop) arises from connectivity among CPGs - Left-right coordination achieved by commissural interneurons crossing the spinal cord midline (extra reading in genetics) - In tetrapod animals (e.g. cats, mice) forelimbs-hindlimbs coordination achieved by long propriospinal descending neurons (LPDNs). - - LPDNs connecting cervical and upper thoracic segments with lumbar spine segments

Answer 147

Rhythm generation via reciprocal inhibition (interaction of excitatory + inhib interneurons) Rhythm provides alternate excitation of extensor + flexor MNs. Downstream interneuron provides reciprocal inhibition of MNs.

Answer 148

Does not account for experimental observations: - complexity of natural + ficitve motor patterns i.e. some activation doesn/t follow strict extensor/flexor alternation - effects of sensory reafference on phase/duration of locomotor patterns

Answer 149

Suggests pattern formation (PF) is an intermediate level between rhythm generator (RG) & MNs RG provides rhythm but PF adjusts specific patterns of MN activations - interacts w/ Ia/renshaw interneurons RG level connects to multiple PF levels -> complex sequential muscle activation ## Footnote extensor & flexor phases can be adjusted w/o affecting cycle duration

Answer 150

Within each limb there are separate CPGs for each set of synergistic muscles - Interactions amongst CPGs generate complex activation patterns - Debate over multilevel vs multiple models contribution to locomotion

Answer 151

Pacemaker - endogenous bursting of V Bistable cells - plateau potentials Half centres (from Brown model) - spike frequency adaptation

Answer 152

2 phases: stance + swing Proprioception controls timing of stance to swing transition. ## Footnote ○ Walking (stance 65%, swing 35%) ○ Running (stance 40%, swing 30%, float 15%)

Answer 153

Controlled by sensory reafference at spinal cord level. - decerebrated cats can adjust locomotor patter at different speeds on treadmill Stance associated w/ extensor muscle activation. Swing associated w/ flexor muscle activation.

Answer 154

Swing initiated when leg extended. Extending hip initiates flexor burst in spinalized cats - effect elicited in MSs in hip flexors

Answer 155

Swing initiated when leg is unloaded - in decerebrated cats loading of ankle extensors inhibits flexor burst - Mediated by Ib afferents

Answer 156

A brain region discovered by Shik, Severin, and Qrlovskij in 1966, involved in locomotion control Low intesnity stim -> walking High intensity stim -> running

Answer 157

MLR firing rates. - Optogenetic stim at 20Hz evokes locomotion vs lower freq at 10Hz is not effective - Firing rates of individual neurons approx prop to locomotion speed

Answer 158

Anatomical and cellular diversity

Answer 159

Pedunculopontine nucleus (PPN) and cuneiform nucleus (CnF)

Answer 160

Excitatory glutamatergic and inhibitory GABAergic neurons Only PPN expresses cholinergic neurons.

Answer 161

Initiate and drive locomotion

Answer 162

Terminate locomotion

Answer 163

Modulate locomotion

Answer 164

CnF evokes a full range of speed from slow to fast locomotion -> firing rate of CnF neurons linearly related to speed PPN only evokes slow locomotion -> firing rate of PPN neurons have complex relationship w/ speed

Answer 165

PPN populations of glutamatergic neurons selectively active in non locomotor behaviours: - rearing, project to spinal cord - grooming & handling , project to basal ganglia Also control posture via body extension ## Footnote Extended posture associated w/ both execution of rearing & locomotion *Body extension is 1st principal component of mouse posture

Answer 166

CPGs via reticulospinal tract

Answer 167

Vestibular system

Answer 168

* Horizontal * Vertical ## Footnote Sensed by hair cells in otoliths -> utricle & saccule

Answer 169

* Medial * Lateral * Superior * Inferior

Answer 170

* Vestibular * Proprioceptive * Motor * Inputs from cerebellum ## Footnote Some vestibular nuclei project to spinal cord via vestibulospinal tracts

Answer 171

* Postural instability * Reduced ability to respond to unexpected perturbations * Increased variability in locomotor pattern (especially at low velocity)

Answer 172

* Yaw * Pitch * Roll ## Footnote Semicircular canacls inc PC, SC & HC

Answer 173

Tone of extensor (antigravity) muscles for posture control. LVN neurons project to spinal cord via lateral vestibulospinal tract.

Answer 174

Extended & stiff limbs in decerebrated cats. Rigidity reduced after lesioning of LVN

Answer 175

During locomotion ## Footnote Highest during extensor muscle contraction

Answer 176

- Fast EMG response in extensor muscle ~20ms latency - Slower EM co-activation of both flexors + extensors ~50ms latency ## Footnote Effects above are mediated by cell pop in LVN w/ direct projection to spinal cord via vestibulospinal tracts.

Answer 177

* Abolishes EMG fast + slow response * Increases postural instability

Answer 178

Oppose movements to maintain stable balance

Answer 179

They are transiently downregulated during initiation & termination of locomotion

Answer 180

Internal/external stimuli forms a goal. Motor cortex plans how to achieve goal + signals to brain stem/spinal cord to induce muscle effectors Disproved by cortical lesions in cats -> still able tom move about well (clumsy) , Bjursten ## Footnote Evolution - lamprey (common ancestor of jawed & jawless vertebrates) analogous to cat experiment, not evolved cerebral cortex vs mammals but still had functioning movements

Answer 181

Cerebral cortex evolved + enlarged forming parallel system to existing brain features (brain stem) Both cerebral cortex & brainstem capable of independent muscle stimulation. - cortex can also signal brainstem via corticobulbar tract

Answer 182

Looked at reaching/grasping in monkeys after bilateral pyramidotomy (cut CST) After 5 months rehab: Intact: running, walking, whole hand grasping Impaired: independent finger movements to retrieve pellets -> CST signals for distal movement + motor control

Answer 183

- Synapse directly into LMNs -> special to primates (evolution of manual dexterity) - Indirect connections to LMNs via interneurons

Answer 184

Both groups had bilateral CST lesion. If lateral cut -> whole hand grasping, dexterity lost - basic system for posture + locomotion If ventromedial cut -> impaired locomotion + posture - controls extermities (esp hand)

Answer 185

- Mediate control similar to brainstem pathways - Additional capacity for independent finger movement

Answer 186

Monkeys 2 months after incomplete lesion of right pyramid: - affected left hand - skilled food retrieval, intact finger movements ## Footnote Resiliency of parallel model

Answer 187

Control of trunk & limbs for posture, locomotion, orienting towards salient obects, reaching/grasping. Also has circuits for orofacial behaviours -> breathing, swallowing, whisking (mice/rats)

Answer 188

Superior colliculus - provides input from retina to visual layer & outputs to brainstem from motor layer

Answer 189

Receptive fields on retina sensitive to visual stimuli - microtimulation in motor layer causes saccade to correpsonding RF location -> SC has motor map, activated by an RF lcoation -> innervates PPRF

Answer 190

Brainstem has premotor neurons (gaze centres). PPRF (paramedian pontine reticular formation) innervated by SC & frontal eye fields, activates LMNs LMNs: nuclei of cranial nerves III, IV, VI for eye movement.

Answer 191

iDREADDs expressed in NF neurons of superior colliculus in mice. Agonist CNO injected - binds receptor -> K+ channels open inhibitg NF neurons (40% decrease firing rate) - slow orientation

Answer 192

Sensory feedback (reflex) OR Central pattern generator in absence of sensory input: small network of neurons whose activity generates more specific movements w/ correct timing & sequences Whisking persists after frontal cortex lesion -> CPG in brainstem (EMG)

Answer 193

Retrograde tracing - studied inputs to facial nucleus -> vIRT as whisking candidate CPG LMNs: Cranial nerve V - trigeminal Cranial nerve VII - facial Cranial nerve XII - hypoglossal Nucelus ambiguous - airway muscles ## Footnote Vibrissa Intermediate Reticular Formation

Answer 194

EMG -> positive vIRT firing during whisking Is vIRT sufficient? - kaiante injected in vIRT -> whisking rhythm Is vIRT necessary? - electrolytic lesion in vIRT on one side of brainstem -> whisking stopped on corresponding side ## Footnote SO brainstem has premotor CPG that projects to LMNs

Answer 195

Reflexes - stereotyped responses to specific stimuli (automatic) Rhythms - voluntarily controlled, largely autonomous Voluntary movements - under conscious control, intentional, involve choice, learnable -> primary & premotor cortex located in posterior forntal lobe

Answer 196

Nissl stain generated Brodmann areas Area 3b: granular, primary somatosensory cortex Area 4: agranular, includes very large Betz cells, primary motor cortex ## Footnote Motor cortex discovered by Fritz & Hitzig by electrical stimulation of dog forntal lobe -> elicits movement

Answer 197

Frontal area where electrical stimulation elicits somatotopically organised movements at low stimulation intensities, located in precentral gyrus.

Answer 198

Neuron doctrine (Cajal) - individual neurons control individual muscles Spike triggered averging EMG for moneky hand muscles -> each neuron activates several muscles SO M1 not precise muscle map as Leyton & Sherrington proposed (1917) -> many M1 neurons contribute to control of each muscle + each neurons contributes to control of several muscles ## Footnote So NO

Answer 199

Graziano - long duration macrostimulation to one part of M1 -> coordinated behaviours (hand to mouth action) M1 has zones associated w/ function

Answer 200

M1-LMN connections are 100-200uV BUT depolarisation required to evoke AP is ~15mV. Individual neurons cannot cause contraction alone. -> population coding

Answer 201

Each M1 neuron has preferred direction (PD). Firing rate of each MN contributes to an average of many different neurons PD -> population vector Vectors decoded in monkeys, pop vectors closely matched reaching direction. - explains how precise reaching possible despite imprecise individual neurons

Answer 202

Medical device that measures/alters electrophysiological activity of at neuronal population level. Types of BMI function: restore lost sensory & motor abilities, also regulates pathological neural activity + restores lost brain processing capabilities.

Answer 203

Bypasses damaged sensory hair cells by direct stimulation of neurons to auditory nerve. They have microphone, sound analyser (frequency decomposition) & a cochlear stimulator electrode array (stimulates each location on cochlear w/ matching component)

Answer 204

Frequency decomposition - each part is selective to different sound frequency - base tuned for high freq - apex tuned for low freq Sound makes mem vibrate - max vibration depends on tone frequency

Answer 205

40-55% monosyllabic words & 70-90% sentences - due to context? - Most widespread and successful BMI - 2008: 120,000 cochlear implants (worldwide) - Many implantees: >90% on tests of sentence intelligibility (quiet conditions)

Answer 206

Tetraplegia - paralysis of arms & legs Amyotrophic lateral sclerosis Symptoms inc: paralysis, dysarthria & dysphagia Similar to C1 & C7 spinal cord injuries ## Footnote Dysarthria - breathing difficulties Dysphagia - eating difficulties

Answer 207

Electrode array, decoding algorithm & actuator.

Answer 208

Complex movements (spiral) can be decoded from motor cortex activity in monkeys. M1 neurons were recorded & pop vector decoding predicted movements 100ms ahead - potential implications for spinal cord damage tretaments

Answer 209

Monkey M1 recorder w/ utah array - allows recording electrical activity across larger section of the brain joystick task - linear filter used to decode hand movement from M1 activity neural control used to track target -> proof of principle

Answer 210

Patient w/ spinal cord transect C3-C4 (complete tetraplegia) impanted w/ utah array in M1 arm area. Asked to make imagined movements - algorthm trained to decode imagined M1 activity (Serruya method) Neural control tested - some neurons directionally controlled ~80% accruacy +: 1st demonstration of neural control in humans, perfromance increase 70-90% -: limited complexity, unknown level of practical use

Answer 211

Pateints C4 spinal injury, 2 utah arrays implanted in M1 hand area. Imagined handwriting -> asked to handrwite complete sentences, activity recorded + ouput given in real time Algorithm trained to decode characters -> 90 characters per min, 5% error rate (no backspace) +: addresses degrees of freedom limitation, achieve peer typing speed (comparable to texting) -: one participant, needs deciated lab

Answer 212

Brainstem: Facial muscles innervated by many peripheral nerves (facial VII, hypoglossal XII, trigeminal V & laryngeal). LMNs & premotor nuclei located in brainstem Cortical: M1 face area lesion -> pseudobulbar palsy, loss of voluntary control over speech Broca's areas (44-45) involved but not sufficient - Broca's aphasia impaired ability to produce language

Answer 213

ECoG array implanted over left sesnorimotor cortex in patient w/ stroke in Pons age 20. Word & sentence task -> decoded by deep learning algorithm to classify words from neural signals Isolated words 47% correct, sentence decoding had 61% error rate & 26% w/ language modelling - 15 words per min ## Footnote Language model reduced error rate

Answer 214

Electrodes placed directly on brain surface, more invasive but more reliable/recordable signals - cover boths sections of motor cortex

Answer 215

Only limited eye movement remains, can worsen to no movement at all (completely locked in syndrome) Coupled neural recording system to a speaker: measured AP firing rate + mapped it to tone generator (high/low freq sound) - Tasked w/ matching target tone, so had to learn to control firing rate - Provided analogous communication to blinking/yes or no Binary communication translated into word generation via matching tone frequency to letters sequentially -> form sentences. - Intelligible output on 44/107 days Very slow speed, 1.08 characters/minute

Answer 216

- provides insights into neural coding - novel treatments of severe paralysis - proof-of-principle established - progress in refining methods

Answer 217

- studies ar eof single participants - systems cannot be used independently by caregivers - comercialisation required

Answer 218

Saccades Smooth pursuit Vergence Vestibulo-occulomotor movements Optokinetic ## Footnote 6th fixation system holds eyes still during intent gaze

Answer 219

Fovea shift rapidly to peripheral target - variable distance, rapid, both eyes move together. Up to 900 degrees/second - stereotypical waveform w/ smooth increase + decrease in eye velocity. - distance moved determines velocity -> cannot voluntarily change velocity of saccades (only direction + amplitude). - saccades also made to auditory + tactile stimuli.

Answer 220

Requires moving target to drive it, much slower than saccades max velocity of 100 degrees/second. - Calculates how fast moving target is + adjusts accordingly. Very different control system to saccades - Eye moves away from target before saccade as latency of pursuit system shorter than that of saccade ## Footnote Pursuit movements begin adjustments earlier

Answer 221

Eye moved in oppsoite directions so image positioned on both fovea. Smooth but disconjugate: - eyes rotate inwards (converge) if object comes closer - eyes rotate outwards (diverge) if object moves further away

Answer 222

Horizontal: adduction (away from nose) & abduction (towards nose) Vertical: elevation & depression Torsional: intorsion (top of cornea towards nose), extorsion (top of onrea away from nose)

Answer 223

4 rectus & 2 oblique: Medial rectus adducts eye, lateral rectus abducts eye. Superior/inferior rectus/oblique muscles control vertical & torsional movements

Answer 224

Abducens (VI), Oculomotor (III) & Trochlear (IV) ## Footnote Nuclei in brainstem

Answer 225

Damage to crainial or extraocular muscles/nerves. Causes fixed image to no longer fall on same locations of both retina. -> double vision

Answer 226

- Damage to abducens nerve -> damage to lateral rectus, loss of abduction beyond midline, causing diplopia - Damage to oculomotor nerve -> loss of eye movements medially or upward from mid-position, leads to drooping eyelid, mydriasis & downward + lateral gaze - Damage to trochlear nerve -> skew deviation (eyes at different vertical positions in orbit), leads to deficits in intorsion/extorsion, elevation/depression + torsional deficit.

Answer 227

Extraocular MNs signal eye position & velocity. Firing rate of MNs increse during saccade in pulse of activity (0->900degree/sec) Baseline MN firing rate changed to reflect new position at end of movement -> step change in intensity ## Footnote height of step = size of saccade height of pulse = speed of saccade

Answer 228

Horizontal - generated by MNs in pontine reticular formation Vertical - generated by MNs in mesencephalic reticular foration (midbrain)

Answer 229

Medium-lead burst - direct connections to oculomotor neurons Long lead burst - drive medium-lead burst cells & receive inputs from higher centres

Answer 230

Omnipause cells fire continuously, except around time of saccaden - GABergic & inhibit medium-lead burst neurons Inhibitory burst - driven by medium-lead burst cells & suppress contralateral abducens neurons ## Footnote Saccadic movement needs both omnipause cells to pause firing & excitation of long-lead burst cells -> stability

Answer 231

Neurons in medial vestibular nucleus & the nucleus prepositus hypoglossi. ## Footnote -> lesions cause drifting of eyes back to central position

Answer 232

Motor signals provided by pontine & mesencephalic burst cells BUT their output controlled by SC SC is a layered, multi-sensory structure on dorsal surface of midbrain -> upper layer receives visual signals from retina + lower layers process multiple signals from other regions of brain. ## Footnote Also called optic tectum, highly conserved & relatively smaller in size as forebrain enlarges in more complex animals

Answer 233

Found in vetsibular nucleus, nucleus prepositus hypoglossi & the pons. - all receive inputs from cerebellum which correlate w/ speed of tracked object Receives major input from visual areas + frontal eye fileds (FEFs)

Answer 234

Superficial layers - more visual, largely sensory Intermediate & deep layers exhibit more sensory-motor control

Answer 235

Primarily visual, main target of retina. >90% of all RGCs project to SC in mice. Supplemented by extensive projection from visual cortex. Notable retinotopic order of inout & processing centres

Answer 236

- Visual (FEF, lateral interparietal cortex) - Auditory/somatosensory (trigeminal complex, barrel cortex, inferior colliculus, nucleus of the brachium of the inferior colliculus) - Recent experience (FEF, M2) - Target value (Substantia nigra) - Saccade control (FEF, cerebellum)

Answer 237

Different layers in SC have mutually aligned maps of space for each sensory modality. Benefits: - allows multi-sensory facilitation -> different inputs dirve one enhanced response (detect biologically relevant events) - simpler transformation from sensory cues to motor commands (e.g. orientation)

Answer 238

- Receive, process & integrate sensory info AND register it spatially - Direct appropriate behaviour e.g. distinct SC stimulation -> orientation & defensive behaviours

Answer 239

Yes - superficial layer neurons code for oculomotor acitivity ~1/2 increases activity if animals going to make saccade to stimulus in its receptive field

Answer 240

Distinct movement-related cells in SC fire prior to saccades of specific size & direction. - Movement related neurons in SC have movement fields - Actual eye movements encoded by population code - individual movement cells have large overlapping fields - Most rostral portion of SC is fixation zone -> maintains fixation/focus. ## Footnote Can command saccade generators in brainstem

Answer 241

Mesencephalic & pontine reticular formations - receive commands from SC

Answer 242

Frontal eye fields (FEF) & lateral intraperietal area (LIP) send provide excitatory projections. Inhib projections form substantia nigra - BUT suppressed by caudate nucleus (excited by FEF) ## Footnote FEF dircetly excites SC + indirectly releases it from suppression bu sub. nigra

Answer 243

TeNT silences all neurons in SC -> increased time taken to attack & capture prey in mice SC involvement in orientation

Answer 244

Technique that uses genetically engineered receptors to modulate neural activity by binding to specific, otherwise inert, small molecule drugs -> allowing for precise and reversible control of cell populations and neural circuits

Answer 245

Gi coupled GPCR activated by CNO -> decrease in neuronal firing (les cAMP, less Ca2+, K+ efflux) Silenced WF neurons - prey detection & approach initiation was disrupted but orienting still intact i.e. took long time to notice cricket. Silenced NF neurons - no impact on distant approach, impaired orientation + interception -> increased capture time | WF - wide field, NF- near field, PV - parvalbumin ## Footnote CNO - Clozapine N-oxide, selectie silencing

Answer 246

Fleeing - SC encodes loop stimuli response in layer specific way - Cells in superior layer fire more than dorsal/deep layers which are far more specific in response - Strong habituation in deep layers (reflected in behaviour)

Answer 247

Light can activate iChloC, inhibiting firing Expressd in medial SC -> no fleeing response, glutamatergic dmSC inhibition reduces escape prob Expressed in dPAG -> threat detected but animals freeze, PAG may initiate escape behaviour - prominent output of SC (61% of innervation) | iChloC - specific Cl channel dPAG - dorsal periaqueductal grey

Answer 248

Outputs of the SC: LPTN - lateral posterior thalamic nucleus PBGN - parabigeminal nucelus (projects to PAG) BOTH innervated by PV neurons from SC

Answer 249

PV neurons activated + drive opposite motor responses - LPTN activation stops movement (freezing behaviour) - PBGN activations induced fleeing response So their output pathway interaction determines behvaioural motor responses to same stimuli

Answer 250

Determines which way is up/down & direction of movement 5 organs of vestib labyrinth independently measure linear + angular acceleration of head. Output of organs flows to vestibular nuclei in brainstem -> control of posture & balance

Answer 251

Utricle (horizontal) and saccule (vertical) transduce linear accelerations of head 3 semi-circular canals transduce angular accelerations of the head. - Combination measures angular and linear accelerations along any axis ## Footnote Semi-circular: anterior vertical, horizontal, posterior vertical

Answer 252

Produce endolymph via ion pump action - extracellular fluid that washes over apical surfaces, rich in K+, poor in Ca2+/Na+

Answer 253

5 clusters (1 per organ) -> flask shaped, array of cilia at apical ends & kinocilium at end of array Tip link connects end of stereocilium to side of adjacent, longer stereocilium - physically connected to ion channel at 1 end

Answer 254

Deflecting/moving cilia stretch the tip link -> cation channel opens - Stereocilia deflected towards kinocilium -> ion channels open -> depolarisation -> increased transmitter release. - Stereocilia deflected away from kinocilium -> ion channels close -> hyperpolarisation -> reduced transmitter release.

Answer 255

No, they only release NT to underlying neurons (increasing firing rate) Some APS may be fired in resting state due to leakage

Answer 256

Inputs: brain stem affects sensitivity to perturbations -> hair cells are strain gauges, tip link is a mechanical spring protein Outputs: 8th cranial nerve has ~20,000 myelinated axons, most hair cells fire tonically & phasically - encode info about abrupt & sustained accelerations & translations of the head ## Footnote CN VIII is vestibulocochlear nerve

Answer 257

Utricle & saccule have macula that contains hair cells. Stereocilia at apex of hair cells extend into endolymphatic space + attached to gelatinous sheet (otolithic membrane) -> covers entire macular. Octoconia embedded in + lie on otolithic membrane -> fill endolymphatic cavities of utricle & saccule Detect linear acclerations ## Footnote utricle has ~ 30,000 hair cells vs ~16,000 in saccule

Answer 258

Fine, dense calcium carbonate particles - embedded in + lie on otolithic membrane. - These fill endolymphatic cavities of utricle & saccule

Answer 259

Membranous labyrinth moves (its fixed to skull) SO otolithic membrane free to move within saccule/utricle -> inertia causes it to lag behnd head movement Otolithic membrane shifts relative to underlying epithelium.

Answer 260

Movement deflect hair bundles -> electrical response, NT released. Macula of each utricle oriented to lie in horizontal plane - axes of greatest mechnosensitivity lie in all planes SO acceleration acitvates one group of cells & suppresses oppositely oriented cells (intermediate ones not affected) -> output from each utricle is rich, complex + redundant representation of any acceleration in horizontal plane. ## Footnote Redundancy of otolithic organs (many different orientations)

Answer 261

Vertically, very sensitive to vertical accelerations (gravity changes). Some saccular hair cells attuned to horizontal acceleration in A-P axis (redundancy)

Answer 262

YES - determination of what happened depends on angular acceleration signal by semi-circular canals

Answer 263

When object alters rate of rotation around axis. Detected by 3 semi-cricular canals -> closed tubes filled w/ endolymph, extnd from otolithic organs - also detect acceleration via endolymph motion

Answer 264

Use endolymph mass to generate response. Felatinous diaphragm (capula) spreads across canal in widest region (ampulla) Capula attached to epithelium except at ampulla crista -> where its penetrated by stereocilia of~7,000 hair cells

Answer 265

Acc moves endolymph -> presses against capula, bowing movements Bowing stimulates embedded hair cells, oriented in same direction. Angular acc in one direction excites but opposite direction inhibits

Answer 266

-> 3 canals almost precisely perpendicular to each other SO represent angular accelerations about 3 mutually orthogonal axes Canals act mainly in pairs e.g. head movement left/right detected by left + right horizontal canals. e.g. head turns left, left horizontal canal hairs activated/right are inhibited ## Footnote A-P combination in right & left ears allows complex detection

Answer 267

Fluid rotates at same speed as rotation, so continue pushing hair cells when rotations has stopped

Answer 268

Damage to either labyrinth - conflicitng info from 2 ears worse than 1 set of signals -> disorientation CNS associates specific motor behaviour w/ each vestib pattern so unsual vestib responses causes protective/erroneous reflex

Answer 269

Receptor cells of vestib labyrinth affected - sproadic, relapsing vertigo (associated w/ tinnitus & distorted hearing) Cause unknown. Possible poor endolymph drainage (oedema) -> epithelial damage. - normally drains via endolymphatic duct before reabsorption into spinal fluid ## Footnote Surgical implant shunts bypass drainage port - can work

Answer 270

Vestibulo-ocular - keep images on eyes still when head moves Vestibulospinal - enables skeletomotor system to compensate for head movements Vestib reflexes compensate for head movements & motion perception in space

Answer 271

Main inputs from vestib labyrinth, located in medulla, project to cerebellum, basal ganglia & spinal cord. 4 nuclei: medial, lateral, superior & descending -> send outputs reticular & spinal centres for skeletal movements, vestib regions of cerebellum & oculomotor nuclei

Answer 272

Inputs mainly from semi-circular canals. Outputs to spinal cord & occulomotor centres. Medial nuclei - excitatory neurons Superior nuclei - inhib neurons - Both help generate gaze reflexes

Answer 273

Inputs from semi-circ canals & otolith organs. Outputs mainly to lateral vestibulospinal tract. - Involved in postural reflexes