Unit 2: Sensory Systems

sensory feedback enables us to not only interact with our environment, but make ____ based on interactions

adjustments

prediction (predict what’s going to happen, usually by sight)

feedforward control

response (response to prediction)

feedback control

theory of feedback control

goals → feedforward controller → controlled system → feedback loop → feedback controller → controlled system

what is the goal in the AC unit example?

keeping a constant temperature

what is the feedforward controller in the AC unit example?

individual

what is the controlled system in the AC unit example?

AC unit

what is the feedback controller in the AC unit example?

thermostat

what is the disturbance in the AC unit example?

window opens

what is the goal in the muscle spindle example?

keep elbow flexed at 90°

what is the feedforward controller for the muscle spindle example?

brain

what is the feedback controller for the muscle spindle example?

muscle spindle

what is the controlled system in the muscle spindle example?

arm (body)

what is the controlled variable in the muscle spindle example?

muscle length

what is the disturbance in the muscle spindle example?

weight is dropped into hand

step 1 of optimal feedback control

brain sends out command

step 2 of optimal feedback control

movement

step 3 of optimal feedback control

detect error (sensory feedback)

step 4 of optimal feedback control

compare to original ‘out’ signal

step 5 of optimal feedback control

make changes (position, velocity, force)

step 6 of optimal feedback control

repeat task, improved performance

where does all sensory information come in?

backside of dorsal horn

short-latency reflex (simple)

* fast
* dumb
* 20 - 50 ms after event
* mutable (somewhat)

SLR pathway

limb (muscle) → spinal cord → limb (muscle)

long latency reflex (complex)

* slower
* smart (\~voluntary, decision based)
* 50 - 100 ms after event
* mutable (persistent)

LLR pathway

limb (muscle) → spinal cord → brain → spinal cord → limb (muscle)

rostral

up

caudal

down

ventral

front

dorsal

back

fine touch and proprioception

travels up the medial lemniscal tract to the decussation, where it travels contralaterally

course touch, pain, and temperature

travels up anterolateral tract to the decussation where it travels contralaterally

gracile nucleus

touch and proprioception for the lower body

cuneate nucleus

touch and proprioception for the upper body

where is sensory information relayed through?

the thalamus to the somatosensory cortex

both group I and II afferents carry information from where?

muscle spindle

static component of muscle spindles

sustained stretch

dynamic component of muscle spindles

transient changes in length

* dynamic nuclear bag fibers
* ONLY Ia afferents carry these

what is the static component of muscle spindles and what afferents do they carry?

static nuclear bag and nuclear chain fibers

* both carry group Ia and II afferents

muscle spindles detect what?

changes in muscle length (stretch reflexes)

* both the amount and rate of change

why is the muscle spindle organization of muscle fibers important?

in-parallel; to detect muscle length changes by lying next to contractile muscle fibers

\
1 muscle spindle to 3-4 contractile fibers

monosynaptic

one synapse

* the sensory neuron synapses directly onto the motor neuron in the spinal cord

what afferents largely make a monosynaptic connection in the spinal cord?

Ia and II afferents

monosynaptic reflex

direct communication between sensory and motor neurons

how do we keep muscle spindles tight?

gamma motor neurons

* keep the muscle spindle tight and ready to respond

tendon tap

used for clinical assessment of stretch reflexes

proprioception

status of the body internally

how can joint positions be manipulated?

* chemicals: lidocaine nerve block
* ischemia: mechanically compressing nerve
* tendon vibration: overexciting muscle spindles
* muscle fatigue

ischemia

mechanically compressing the nerve that we do not get Ia afferent signals back to the spinal cord

* can alter joint position sense

tendon vibration

overexcites causing the muscle spindles to fire at a high rate

muscle fatigue

muscle spindles fatigue causing more error in joint position sense

* as you lose proprioception as you fatigue, more likely an injury can occur

hold relax stretching technique

maximally activate muscle and then relax and stretch

* harder to elicit a stretch reflex for up to 15s following a contraction (momentarily muscle fatigue)
* fatiguing the muscle spindles

agonist contract

by contracting the opposite (antagonist) muscle in which you want to stretch \~ it shuts off the spinal circuit of the muscle you want stretched (agonist) allowing it to relax

plasticity in the stretch reflex (Ia muscle spindle circuits)

with sufficient practice, even a simple stretch reflex can be modified

* example: walking backwards on treadmill
* stretch reflexes are ramped up because protecting you from the expectations of falling
* 2 weeks later: fairly consistent as if you were to walk forward, this is a learning process
* less expectations to fall by the end of 2 weeks and less protective

what is a negative effect of stretch reflexes following a stroke?

hyperreflexia or spasticity

what are the 4 types of touch receptors?

* meissner’s corpuscles
* merkel’s disks
* pacinian corpuscles
* ruffini endings

meissner’s corpucle

specific receptive fields

* fast adapting
* stroking
* fluttering

merkels disk

specific

* slow adapting
* pressure
* texture
* corse touch

ruffini endings

diffuse

* slow adapting
* skin stretch

pacinian corpuscle

diffuse

* fast adapting
* vibration

group III and IV afferents

sensitive to hot, cold, pain, chemical irritation, mechanical pain, etc

what are the receptor types?

* mechanoreceptor
* chemoreceptor
* thermoreceptor

III and IV endings that initiate the sensation of pain are called

nociceptors

photoreceptor

take in light and turn it into an electrical signal

Aδ

* group III
* small
* myelinated
* first pain

C fibers

* group IV
* small
* unmyelinated
* second pain

what type of cutaneous nerves correspond to groups III and IV afferents?

group III is Aδ and group IV is c-fibers

what do GTO detect?

changes in muscle tension

* if muscle creates too much force, they will tear off bone (muscle strain), but GTO turns “off” the muscle when it is too much

group Ib carry information from what?

GTOs

why is the GTOs lying in-series with extrafusal muscle fibers important?

they detect WHOLE muscle tension, therefore need to be positioned at the end of it so they can accurately measure that force

anytime we have inhibition in the spinal cord…

you have to have an interneuron

monosynaptic is always what?

excitatory

polysynaptic is always what?

inhibitory

first pain

a short, intense, sharp pain

* a-delta

second pain

a dull, aching, longer lasting pain

* c fibers

crossed extension reflex

a signal will flex the harmed limb to remove it from the painful stimulus \~ at the same time \~ the SAME signal travels to the opposite limb extending it to maintain balance

\
* step on something with R foot → R hamstring will be flexed → L quad will extend to maintain balance

a weight is dropped into your hand stretching the bicep

* this activates what specific muscle spindle?
* afferents?
* what kind of synaptic connection is it?

* dynamic nuclear fiber bag
* Ia afferents (primary spindle endings)
* monosynaptic

you’re bench pressing and build up too much force on the pec major muscle

* what receptor detects this?
* what will happen?

* GTO
* inhibition of the pec major (keeping activity in a safe range)

what type of inhibition doesn’t come from a specific peripheral receptor

* what interneuron does it use?

recurrent inhibition

* renshaw cells

these protective reflexes modulate their activity based on where you step on a tack on your foot

* what afferents?
* what’s the receptor?

* III/IV afferents
* cutaneous receptors

\*\*\* can be excitation or inhibition

activating agonist while stretching antagonist is what PNF stretch?

* this is what spinal circuit?
* how would you do this if you wanted to stretch the tibialis anterior?

agonist contract

* reciprocal inhibition
* contract gastrocnemius while stretching TA at the same time

\*\*\*inhibition will always be the muscle that is being stretched

you step on a sharp object on your R foot

* what reflex circuit will this evoke?
* what will happen?

* crossed extension reflex
* flex R hamstring, extend L quadricep

central pattern generators

a network of neurons capable of generating rhythmic patterns of motor activity in the absence of rhythmic sensory or central input

* snake moving back and forth to move

what are the 5 receptors of the vestibular system?

* utricle
* saccule
* 3 semicircular canals

what do utricle and saccule detect?

linear acceleration

what do the 3 semicircular canals detect?

angular motion

vestibular-ocular reflex

keeps the eyes stable when the head moves

how can the vestibular system be artificially stimulated?

through galvanic stimulation

what region was stimulated in the study about cats discussed in the lecture recording?

mesencephalic locomotor region (MLR)

nystagmus

voluntary/involuntary eye movement

* spinning/saccades

vertigo

inadvertently experiencing/perceiving motion

* colds, flu, drinking, MS

cornea

covers eye

iris

controls the amount of light let in

rods

color insensitive and work in dim light

* 120 million

cones

detect color vision and work in bright light

* 6 million

visual system pathway

light enters the eye through the cornea and iris → photoreceptors (bright light: cones) (dim light: rods) → bipolar and horizontal cells → ganglion cells → lateral geniculate nucleus via optic nerve → visual cortex (through monocular or binocular layer) → simple cells → complex cells → see image

monocular deprivation

covering one eye of a newborn kitten removes virtually all connections to the visual cortex for that eye

strabismus

cutting a lateral muscle in the eye of baby kittens (wall-eyed) removes the bilateral function of the eyes

hemispatial neglect

awareness of sensory information (visual, auditory, kinesthetic) on the left side of the body is diminished and can lead to difficulties in balance and performing daily activities of living

* 45% of patients with TBI to the R hemisphere

what is the sensory pathway of reaching out & touching an object that is hot/cold with your hand or upper body limb?

touch receptor → enters the dorsal horn of the spinal cord ipsilaterally (same side the signal occurred) → cuneate nucleus tract within the anterolateral tract → travels rostrally to the medulla → decussates at the sensory decussation → continues contralaterally (opposite side the signal occurred) to the thalamus → area 3b