Somatosensory System Flashcards by Mandy Hong

What is the exception of sensory receptors of various sorts

Distributed throughout almost all of the tissues of the body, with nervous tissues as a notable exception

How well did you know this?

Not at all

Perfectly

Somatosensory receptor

Any mechanoreceptors, their … or nocireceptor found embedded in the skin, fatty tissue beneath that skin, muscle tissue of musculoskeletal connective tissue (tendon, ligament or joint capsule tissue)

How well did you know this?

Not at all

Perfectly

Fibre groups 1,2,3,4 and their conduction speed

Large myelinated 80-120m/s
Medium myelinated 35-75m/s
Small myelinated 5-30m/s
Unmyelinated 0.5-2m/s

How well did you know this?

Not at all

Perfectly

Cutaneous mechanoreceptors adaptations

Mechanoreceptors show diff firing patterns to code duration

How well did you know this?

Not at all

Perfectly

2 receptors that are slow adapting fibres

2 - Merkel disk receptors, Ruffini end organ

How well did you know this?

Not at all

Perfectly

3 fast adapting mechanoreceptors

2 - Meissner corpuscle, Pacinian corpuscle, hair follicle receptor

How well did you know this?

Not at all

Perfectly

Slow adapting vs fast adapting mechanoreceptors

Continue to fire as long as stimulus is maintained vs fall silent even when stimulus is maintained

How well did you know this?

Not at all

Perfectly

Where are muscle proprioceptors abundant?

Skeletal muscles

How well did you know this?

Not at all

Perfectly

What do muscle proprioceptors convey info regarding? 1-2

State of muscle

muslce spindles - length of muscle and velocity of stretch
Golgi tendon organs - changes in tension

How well did you know this?

Not at all

Perfectly

GTOs act as?
Innervated by 
Structure -2
Location 
Innervated by 
Intertwined with?

Golgi tendon organs act as force sensors
IB afferents - intertwined within collagen fibres of tendon
Slender encapsuled structures 0.2-1mm
Junction of muscle and tendon: in series
Ib afferent demylinated
IB afferent is intertwined with collagen fibres of tendon

How well did you know this?

Not at all

Perfectly

When do intertwined Ib afferents compress?

In response to muscle force - Ib afferents increases AP firing frequency when muscle force increases

How well did you know this?

Not at all

Perfectly

Compressed of the IB afferents

How well did you know this?

Not at all

Perfectly

Increased muscle force detected by Ib afferent is through 2

Muscle stretch - eccentric contraction/passive stream - when its stretched, most length taken by muslce fibre (more elastic)
Muscle shortening - concentric contraction - force acts directly on tendon when muscle actively contracts - increased tension on collagen fibres compresses sensory receptors of Ib afferent

How well did you know this?

Not at all

Perfectly

In what muscle force generation do you see a higher firing of IB?

Shortening contraction

How well did you know this?

Not at all

Perfectly

2 responses to Ib afferent responses to muscle stretch.

Increased firing frequency upon tension increase

Sustained firing at new tension level

How well did you know this?

Not at all

Perfectly

2 Ib afferent response to muslce shortening

Increased firing frequency upon tension release

Sustained firing at tension level

How well did you know this?

Not at all

Perfectly

muscle spindle structures
location
responds to

encapsulated 2-10mm
parallel to extrafusal muscle fibres
stretch and velocity of muslce stretch

How well did you know this?

Not at all

Perfectly

muslce spindles contain
oriented
connected to
stretch in accordance with

muscle fibres - intrafusal
parallel to extrafusal fibres
connected at each end to extrafusal fibres
extrafusal fibre stretch

How well did you know this?

Not at all

Perfectly

3 main components of muscle spindle

specialized muscle fibres - intrafusal
sensory axons - Ia
motor axons - II - intrafusal fibres have capacity for contraction

How well did you know this?

Not at all

Perfectly

are intrafusal muslce fibres smaller or bigger than extrafusal fibres?

smaller

How well did you know this?

Not at all

Perfectly

two types of intrafusal fibres and how they are differenciated

nuclear bag and nuclear chain - organization of central nuclei - clustered bags vs in series chains

How well did you know this?

Not at all

Perfectly

what are the 2 categories of nuclear bags?

static (BFST)

Dynamic (BFDYN)

How well did you know this?

Not at all

Perfectly

how do the 2 categories of nuclear bags differ ?

motor innervation
sensory innervation
contractile properties

How well did you know this?

Not at all

Perfectly

sensory innervation of muscle spindles - what are they innervated by? where are they?

Ia and II afferents
spiral around or near central region
Ia - all intrafusal fibres at central regions
II - nuclear chain and static bag only - not dynamic bag

How well did you know this?

Not at all

Perfectly

effect of muscle stretch

intrafusal stretch which leads to spindle loading

Spindle loading ? | majority of length change occurs in?

increased AP firing frequency - elongation of afferent ending depolorizes membranes and generates AP in both sensory afferents (Ia and II) equatorial region so more robust effect (higher firing frequency) in Ia

spindle unloading

concentric contraction - decreased firing frequency - slacking of all activity and eventually stops - dramatically diff afferent (Ia, II) firing pattern compared to stretch The release of stretch or extrafusal shortening causes intrafusal to slacken

diff in response in GTO with spindle loading and unloading

when muslce stretches, the spindle stretches - more response in spindles, when muslce shortens - the spindles are unladed but sensory neurons in GTO increases

AP firing during spindle unloading

decreases in both sensory afferents - Ia stops firing completely for a period of time until muslce returns to its normal length

Ia firing frequency changes with?

muslce length

muslce spindles are sensitive to?

changes in length -

AP firing Ia and II neurons differ during ...

static and dynamic phases of muscle length

AP firing during static phase

when muscle gets stretched or released, both Ia and II afferents reach steady state firing rate that reflexts new muscle length

AP firing during dynamic phase

Ia and II respond differently Ia more robust during dynamic phase than steady state phase II firing frequency increases slightly, but without the same vigor as Ia

who has a greater dynamic sensitivity

Ia because it is more sensitive to transient changes in length

Diff in Ia and II firing patterns is due to

innervation sites of these afferents, because the majority of length change happens at the equatorial region, which means most centrally located afferents (Ia) have greater opportunity for detecting length change

what else are Ia afferents sensitive to?

stretch velocity - velocity sensitivity

As velocity increases

Firing frequency increases - dynamic response

steady state firing firing in Ia

reflects resting length

Transient increase in Ia firing state

more sensitive to small length change (<0.1mm) - magnitude of transient increase in firing frequency reflects stretch velocity

Ia encodes 3

static length, dynamic length, rate of length change | position, movement, and velocity of movement

where do motor neurons innervate on intrafusal fibers?

polar regions - fusimotor system

gamma motor system

regulate sensitivity of muslce spindles for detecting stretch

2 types of gamma MN

increased steady state firing - static gamma MN | increased firing state during dynamic phase of stretch - dynamic gamma MN

spindle efferents innervate diff types of intrafusal fibres

dynamic gamma MN - dynamic nuclear bag | static gamma MN - static nuclear bag and nuclear chain

Diff gamma mn provide opportunity to differentially regulate

dynamic or static sensitivity of muslce spindle

innervation of dynamic nuclear bags

junction of polar and central

Region of Ia afferent

equatorial of all fibres

Region of II afferent

near equatorial, nuclear chain and static bag only

gamma dynamic innervates

dynamic nuclear bag

gamma static innervates

static nuclear bag and nuclear chain

how does CNS ensure that info regarding muscle length/rate of length change will be received during muslce contraction if muslce shortening means spindle unloading? - 3

activation of gamma motor neuron fusimotor system counteracts intrafusal slackening during muslce shortening simultaneous activation of alpha and motor MN prevents spindle from unloading during muslce shortening

mechanistic foundation of gamma activation - what happens?

gamma activation leads to contraction (shortening) of polar regions which stretches the equatorial ends from both ends.

Vallbo, 1981 - 3

spindle (Ia) discharge is maintained during slow concentric contractions if gamma MN were not firing, Ia afferent would cease alpha MN Gamma MN activited in con

Why can gamma MN activity be adjusted independently of alpha MN activity? 2

CNS capable of contracting intrafusal fibres independently of extrafusal fibres alpha gamma coactivation: MN activated synchronously

gamma activation prior to alpha activation

prestretch central regions of intrafusal fibres and alter their sensitivity

Who regulates the sensitivity of spindles to stretch

gamma MN

influence of gamma MN activity known as 3

gamma bias gamma gain fusimotor set

Prochazka, 1988 - regulation of? | How is fusimotor activity set?

spindle sensitivity, fusimotor activity is set according to complexity of behaviour

Prochaska: if activity necessitates slow and predictable changes in muslce length, what MNs are activated?

static gamma

Prochaska: if activity neccesitates rapid and unpredictable changes in muslce length, what MNs are activated?

static gamma and dynamic gamma

Prochaka and Hulliger, 1988

fusimotor set theory

activation of gamma MN increases as requirements for

stretch sensitivity increases | i.e. walking on ice

CNS uses fusimotor system to

prime impending stretch

Gamma bias can be adjusted by 2

upper motor neurons and lower neuron circuits

to maintain constant force -

You can recruit fewer MU and have them fire at a higher frequency, or recruit more MUs and have them fire at a lower frequency

receptive fields can vary in

size and definition

increase of stim intensity

increase AP firing frequency which increases neurotransmitter output - compounded by increasing stim duration

Somatosensory System Flashcards

(68 cards)