Midterm 1 Flashcards
input resistance
small MN (Type I) have high input resistance (leads to a greater response )–>easier to excite
- how difficult it is for the current to get through the MN
what type of fibres are large and small MN
- large MN= fast twitch fibres
- small MN = slow twitch fibres
rheobase
amount of current thats needed to allow the MN to fire AP
- low amount in small MN
conduction velocity
how fast the AP goes from the axon hillock through the neuron
- small MN are slow
After hyperpolarization (AHP)
shorter in large MN
Ohm’s law
AP propagation
(current x resistance = voltage)
MU properties
size principle (what it does and the consequences)
MU recruited from smallest to largest
- simplifies tasks
- ensures smooth increase in force production
- minimizes fatigue
- CANNOT selectively choose which MU to recruit
recruitment threshold
amount of force needed to turn on the MU
- can change within a MU based on the task
- all or none response
- order of MU remains constant
force frequency curve
- sigmoidal relationship
- firing rate matches contractile speed
what controls the muscle movement
the MN
- the MN is the boss
MU force control
- incr number of MU (recruitment)
- incr rate of firing of an indiv MU (rate coding)
what type of firing are MU
MU are partially fused tetanus b/c the units asynchronously with each other
- net force is smooth
electromyography (EMG) and the types
recording the electrical activity from the muscle
- surface EMG (sEMG)
- indwelling EMG
indwelling EMG
- acts as a microphone to tell what MN are activated
- somewhat invasive
- observes a single MU
motor unit (MU)
alpha MN and all skeletal muscle fibres innervated by its axon
- gate keeper of movement
- functional unit of contraction
who identified the MU
charles sherrignton
where does the excitatory post-synaptic potentials summate to generate an AP
axon hillock
MN structures
time vs membrane potential graph
who invented the AP
luigi galvani - frog legs twitched when struck with electricity
what did alessandro volta believe
every cell has a a cell potential (made up of batteries)
what did hodgkin and huxley test on for AP
giant squids
saltatory conduction
- propagation of AP down the axon
- jumps form node to node
myelination
- insulates the axon and prevents movement of ions across the membrane
benefits of saltatory conduction and myleination
- incr conduction velocity without change in axon diameter
- reduces metabolic cost as only small segments of the axon require the Na-K+ pump to restore the resting membrane potential
what happens at the neuromuscular junction (NMJ)
- calcium activates vessicles
- acetylecholine (Ach) is released
- Ach binds to Ach receptors
what is the ratio of MN AP: muscle fibre AP in the NMJ
- 1:1 relationship with a muscle safety factor
- 3-5x Ach released needed for muscle fibre AP
what prevents the binding of Ach to the Ach receptor what occurs and what has it previously been used for
- curare (d-tubocurarine) –> neuromuscular blocker
- muscle fibres cannot generate an AP
- previously used as a medical paralyzing agent (heavy paste on dart heads)
- used as a treatment of tetanus
what prevents the release of Ach and what might occur to a muscle contraction, how long it lasts, what is it used to treat
- botox (botulinum toxin) –> neurotoxin
- inability for excitation along the sarcolemma (prevents muscle contraction)
- lasts 6-8 wks
- treats: overactive muscles, temporary cosmetic improvements
divergence
a single neuron synapses on multiple neurons
convergence
multiple neurons converge on fewer neurons
peripheral structures
- intrafusal: muscle spindles
- extrafusal: skeletal muscle fibers
directions of neural information
- afferent: signals to the brain
- efferent: signals away from the brain (e for exit)
what is the role of afferent/sensory neurons, where does it connect, what type of fibers
- projects centrally to the SC (reflexes) and to more superior structures
- connects to the cell body in the dorsal root ganglion
- afferent fibres
how are afferents spindles labeled and how does conduction velocity depend on diameter
Largest -> smallest
- I (primary)(Ia, Ib), II (secondary), III, IV
- larger diameter = faster conduction
Where are each type of fibres located, what do they detect, what do they receptors do they innervate
- Group Ia:
- muscle spindles
- length and velocity
- connect to bag 1 (dynamic), bag 2 (static), and chain fibres (static) - Group II:
- muscle spindles
- static length
- bag 2, chain fibres - Group Ib:
- golgi tendon
- tension - Group III:
- free nerve endings
- chemical/mechanical - Group IV:
- free nerve endings
- chemical
the relationship between muscle spindles and where they are found
- spindle/fusiform-shaped receptors found in skeletal muscles
- lie in parallel with large force producing skeletal muscles
- different muscles have different numbers of spindles (density)
- hand muscles have higher density of spindles
microneurography
detects single unit AP
- inserts into peripheral nerves
- tells us how they fire and what they innervate
when is Ia and II spindles activated during muscle length
- Ia: fires when there is a change in length
- II: fires when stretch is constant (static)
Monosynaptic stretch reflex
- tendon tap
- primary (Ia) very sensitive to taps and vibrations and stop firing on release (unloading)
what spindles are apart of the efferent system and where they send information too
- fusimotor/gamma system: muscle spindles
- dynamic: bag 1
- static: bag 2 and chain - Skeletal Motor (Alpha MN): skeletal muscle fibers
why is the gammas system important and specifically what gamma is sensitive to what
prevents the spindle from becoming unloaded during contractions to keep it sensitive to the stretch
- Gamma dynamic: more velocity sensitive
- Gamma static: more length sensitive
alpha gamma coactivation
- coactivation of the gamma and alpha MN maintains a muscles sensitivity to contraction
where are the GTO located
located in a capsule in the tendon junction
- lie in parallel inside the muscle belly
- lie in series with muscle fibres
- bundles within a capsule including nerve endings, and collagen fibres (NE interdigitate among CF)
where does the GTO provide motor feedback
feedback to the SC via Ib afferent
- Ib inhibitory interneuron
- disynaptic connection to motor neuron
whats the role of GTO
sense muscle tension and force (mainly active)
- inhibit the agonist MN (draw it)
- help with modulating force control for low force tasks
- protective mechanism
what technique allows experimenters to record AP from sensory afferents in awake humans
microneurography
what is necessary to excite a GTO on mode of activation
- a level of force
- passive stretch of ~2 newtons
- active contraction ~30-90 milinewtons
- more sensitive actively
what is the force output of a muscle in response to one stimulus
twitch
sensitivity of muscle spindle vs GTO during twitch
- GTO sensitive to muscle contraction, respond to muscle tension during a twitch
- activated at low forces
autogenic inhibition
- reflex
-inhibits agonist MN - decreases force output
where are joint receptors located and where are they not
located in:
- joint capsule, joint ligament, loose articular tissue
not in:
- cartilaginous surfaces or synovial membranes
role of joint receptors
- primarily to the limits of joint movements
- respond to joint pressure
- code ambiguously for joint movement (respond to both flexion and extension)
ambiguous neural code
same AP firing rate for diff movements
reflex activity on alpha MN (joint receptors) and an example
- joint receptors cause weak and infrequent effects on alpha MN
- knee ligaments must heavily be stretched before any measurable EMG activity can be detected (must put a lot of pressure to activate AP –> protective role)
anatomy of the vestibular system (sensory receptors) and what each detect
- semicircular canals: head rotation
- anterior
- posterior
- horizontal - otolith organs: linear motion
- utricle
- saccule
what are the vestibular mechanoreceptors and what they do, and describe them
- hair cells (bundles): transform mechanical energy into neural activity
- kinocilium: apex of the hair cell (tallest)
- stereocilium: linked stair-like structure (shorter hair cells)
describe hyperpolarization,depolarization and at rest of the vestibular mechanoreceptors as well as the firing rate for all, when does excitation, inhibition and resting discharge occur
- hyperpolarization: when stereocilium is pushed away from kinocilium (firing rate of AP is slower–>inhibition)
- depolarization: when stereocilium is pushed towards the kinocilium (firing rate is faster –> excitation)
- rest: hair cells are straight up (firing rate is normal –>resting discharge)
what do the vestibular mechanoreceptors respond to
- respond to acceleration or gravity that is in line with the hair cells
- deflection needs to be in line with direction of pushing or pulling kinocilium to create a response
anatomy of the semicircular canal and what does it detect
- detects angular acceleration
1. canal: filled with fluid (endolymph): moves the hair cells
2. cupula: houses hair cells in the crista
describe the firing rate in the semicircular canal during stationary, acceleration, constant velocity, deceleration,
- stationary: background firing rates
- acceleration: increased firing rate (depolarization)
- constant velocity: hair cells return to normal leakiness (normal firing rate)
- deceleration: decreased firing rate (hyperpolarization)
planes of the SSC
describe an example of turning your head to the left and what occurs in the SSC and what canal it effects
- effects horizontal canal
- head rotation causes opposite endolymph movement
- left side: fluid pushes stereocilium to kinocilium (excitation= depolarization= faster firing rate)
- right side: fluid pushes stereocilium away form kinocilium (inhibition=hyperpolarization=decrease firing rate)
anatomy of the otolith organs and what it detects
- otolithic membrane (gel-like substance)
- detects linear acceleration
1. utricle: horizontal linear acceleration
2. saccule: vertical linear acceleration
3. otoliths/otoconia: small calcium carbonate crystals embedded into gelatinous material
how does the hair cells movie in the otolith organs and what direction causes depolarization and hyperpolarization
- shearing of the otolithic membrane from the otoliths cause the cilia to move
- backwards head tilt: depolarization
- forward head tilt: hyperpolarization
describe the spins
- alcohol is a blood thinner (density of blood decreases)
- density between the endolymph and the cupula (hair cells) is disrupted/imbalanced
- less density in the cupula = hair cells move artificially
describe BPPV and what it stands for
- Benign: not life threatening
- Paroxysmal: sudden, breid epochs
- Positional: symptoms triggered by specific head position
- Vertigo: false sense of rotational motion (mild-intense dizziness)
when does BPPV occur, and what are the causes and what occurs
- occurs in older adults (>65)
causes:
1. idiopathic (not one source of cause)
2. hit to the head
What occurs: - otolith dislodged into SSC
- especially when lying down
- canal becomes more sensitive
what is the treatment of BPPV
- epley maneuver: directs the crystals out of canal
Nystagmus
- reflexive movement caused by the vestibular system
- rapid movement of the eyes
Meniere’s disease cause and what occurs
- presented unilaterally
cause: - idiopathic
what occurs: - excess fluid in the labyrinth (canals)
- increase endolymph pressure
- decrease firing in affected side and increase firing on intact side
- sense of spinning
- hearing loss at low frequencies
what with the endolymph and perilymph in meniere’s disease (draw it and describe)
- perilymph is K+ poor
- endolymph is k+ rich
causes:
1. disruption of membrane channels
2. break in endo and peri membrane
what occurs: - mix of fluid (decrease firing rate)
- increase endlymph pressure
types of sensory receptors and what they respond to
- chemoreceptors: chemical concentrations
- thermoreceptors: changes in temp
- nociceptors: pain signals
- mechanoreceptors: mechanical changes (shape, size, pressure)
types of nociceptors
- A-fibres: sharp, localized pain
- C-fibres: dull, burning, delayed pain
types of mechanoreceptors
- cutaneous (tactile) receptors: under the skin (vibration, pressure, temp)
- baroreceptors: linked with vest. system (help distribute blood)
- proprioceptors: muscle spindles, GTO (body position, joint orientation)
how is stimulus intensity/duration signaled with cutaneous receptors
slow vs rapid adapting receptors (cutaneous)
- Tonic receptors: slow adapting to continual stimulation
- phasic receptor: rapid adapting to continual stimulation then reactivated when stimulation ends (only fires when change in stimulation)
receptive field
spatial extent of the receptor surface from which the sensory neuron receives input
hot spot
within the receptive field, most sensitive (faster firing rate)
type 1 vs 2 cutaneous receptors, size of receptive fields, how many hot spots
- superficial receptors (type 1): smaller receptive fields, multiple hot spots
- deep receptors (type II): bigger receptive fields, one hot spot
polysynaptic pathways
- mediate flexion and cross-extension reflexes, more than one synapse onto a neuron
types of cutaneous receptors
- merkel cells
- meissner corpuscle
- ruffini endings
- pacinian corpuscle
merkel cells- % of innervation with hand, afferent type, function, physiology, threshold, superficial or deep, frequency, firing rate
- % of innervation with hand: 25%
- afferent type: slow adapting type 1
- function: curvature, edges of objects
- physiology: small, densely packed receptive fields, multiple hot spots
- threshold: moderately low (30 um)
- superficial or deep: superficial
- frequency: 0-100 Hz (most sensitive to 5Hz)
- firing rate: irregular when stimulated
meissner corpuscle- % of innervation with hand, afferent type, function, physiology, threshold, superficial or deep, frequency, firing rate
- % of innervation with hand: 40%
- afferent type: fast adapting type 1
- function: stroking, velocity, or motion across skin
- physiology: small, densely packed receptive fields, multiple hot spots
- threshold: low threshold (6um)
- superficial or deep: superficial
- frequency: low frequency (most sensitive to 40-50Hz)
- firing rate: only at beginning and end of stimulus
ruffini endings- % of innervation with hand, afferent type, function, physiology, threshold, superficial or deep, frequency, firing rate
- % of innervation with hand: 20%
- afferent type: slow adapting type II
- function: skin stretch
- physiology: large receptive fields, one hot spot
- threshold: high threshold to indentation (300um)
- superficial or deep: deep
- frequency: low frequency (0.5–> Hz)
- firing rate: faster at beginning of stimulus then constant
pacinian corpuscle- % of innervation with hand, afferent type, function, physiology, threshold, superficial or deep, frequency, firing rate
- % of innervation with hand: 15%
- afferent type: fast adapting type II
- function: vibration feeling through objects
- physiology: large receptive fields, one hot spot
- threshold: extremely low (0.08um)
- superficial or deep: deep
- frequency: high frequencies (200-400Hz)
- firing rate: only changes in stimulus
