ch 3a- sensory contribution Flashcards
sensory systems important for control of movement
visual, vestibular, somatosensory
describe how sensory feedback works (loop)
loop:
Integration (brain/CNS= decision making)—-> signal to effectors (e.g muscles) to produce an action –> movement is sensed by sensory receptors (e.g. eyes or muscle spindles) –> feedback is sent back to brain/CNS for integration and decision making again
Visual sensory feedback
- self and object motion
-position of limbs relative to body
-position of limbs/body in relation to environment
Vestibular sensory feedback
-self motion
-head position
Somatosensory feedback (proprioception)
-muscle length (muscle spindles)
-muscle force (golgi tendon organs)
-joint angles (joint receptors)
-pressure under feet and contact with the environment
Mediating factors that may affect visual feedback
-ambient light
-contrast
-peripheral vs. central visual field
Most neurons have 4 functional components that generate signals to transmit information
- Local input (receptive) component
- Trigger (summing) component
- Long range conducting (signalling) component
- Output (sensory) component
affarent neurons
carry info towards CNS and brain. associated w sensory neurons
efferent neurons
carry info away from the CNS and brain. associated with motor neurons
interneurons
connect other neurons. abundant in the brain
two factors related to the signal transmitted by a neuron
- number of action potentials
- time intervals between action potentials
what determines intensity of sensation or speed of movement?
frequency of individual action potentials (firing rate)
What information does the nervous system extract from its receptors?
-modality
-intensity
-duration
-location
MODALITY
what is the stimulus?
(sight, touch, taste, or smell)
–> each of theses modalities has sub modalities
Somatosensory system receptors that detect different sub-modalities
-cutaneous mechanoreceptors (touch e.g. Pacinian corpuscle= vibration and pressuren)
-thermal receptors (temperature)
-nocireceptors (pain)
-muscle mechanoreceptors (e.g. muscle length sensed by muscle spindles)
INTENSITY
how much we feel stimulus depends on the strength of the stimulus
intensity is encoded by
- frequency of actions: frequency coding
- number of sensory receptors activated: called population coding
strong stimulus results in
activation of more receptor endings OR activation of more sensory neurons
threshold
intensity at which stimulus can be perceived
sensory threshold
stimulus intensity is detected on 50% of trials
DURATION
how long you perceive a stimulus depends on how long the stimulus is present and intensity of the stimulus
as a stimulus persists, you
adapt/become desensitized
LOCATION
where is the stimulus? (depends on the receptive field of the sensory neuron)
receptive field of sensory neuron
the spatial area in the sense organ where stimuli excite or inhibit the neuron
sensory receptive fields provide info about
spatial location of a stimulus and spatial resolution of the sensory system
greater spatial resolution means…
where is an example of an area on your body w/ a lower threshold (greater spacial resolution)
you can discriminate smaller stimuli
ex. hands
How to test for touch sensations
the two-point discrimination test
the two point disrcimination test determines
the location at which two closely spaces stimuli can be perceived as separate
“labelled line” concept
sensory afferents carry info about a single type of receptor from a specific part of the body. nervous system “knows” what info is being carried by what neurons.
What is proprioception?
the sensation of limb, trunk, and head position
sources of proprioceptive info
-muscle spindles (length)
-golgi tendon organs (force)
-joint receptors (angle)
-vestibular system
-cutaneous receptors (mechanoreceptors)
-visual info/optic flow
muscle spindles are:
spindle shaped receptors in the muscle belly of skeletal muscles
What are muscle spindles composed of?
–>Intrafusal muscle fibers: nuclear bag (dynamic bag1 and static bag2) and chain fibres
–>Sensory neuron endings: group 1a and group 2 affarents
–>Motor neuron endings: static and dynamic gamma motor neurons
sensory neuron endings
wrap around central regions of intrafusal fibres. carry sensory info from spindle to spinal cord
motor neuron endings
activate polar contractile regionals of intrafusal fibres. unique because they have efferent parts
detect muscle length
muscle spindles
static muscle POSITION
sensed by mostly group 2 afferents
detect CHANGES in muscle lenth
dynamic= limb/muscle MOVEMENT
sensed by 1a afferents
gamma motor neurons elastic band analogy
gamma motor neurons tighten the muscle spindle to make it more sensitive to change in length
Alpha-gamma coactivation
both extrafusal and intrafusal muscle fibers contract
How is muscle stretch detected?
in an unstretched muscle, action potentials are generated at a constant rate.
in a stretched muscle, muscle spindle is activated and rate of action potentials is increased
If only alpha motor neurons were activated?
Only extrafusal muscle fibers contract.
Muscle spindle becomes slack and no action potentials are fired.
Unable to signal further changes in length.
For voluntary contractions, spindles and muscle fibers….
are activated the same amount and only gamma motor neurons connected to the activated muscle(s) are used
Eccentric contractions generate very strong..
1a afferent activity because lengthening is paired with gamma drive
(lengthening AND gamma drive increase 1a afferent activity individually so together the firing is even stronger)
Feedback from muscle spindles is used to
-regulate muscle activity through the alpha motor neuron
-elicit the stretch reflex
-signal higher centres about muscle length (and limb position)
3 types of potentials
- receptor potential
- synaptic potential
- action potential
receptor potential
-sensory receptors detect specific form of energy, disturbs resting membrane potential due to influx of ionic current (sensory transduction) –> drives membrane potential to receptor potential
-graded signal; spreads passively and decreases w distance
synaptic potential
-neurotransmitter release via synapse alters membrane potential of post synaptic neuron
-graded signal; spreads passively
action potential
-neurons propagate signals via action potentials that spread along their axons
all on none!!! (stronger signals cause more frequent action potentials, but each is the same size)
greater spacial resolution: small or large receptive field?
smaller receptive field: more sensitive= greater spacial resolution
group 2 afferents sense?
static muscle position
1a afferents sense?
dynamic (changes in muscle/limb movement)
dynamic gamma motor neurons increase sensitivity to…
detect muscle length changes (which are signalled by 1a afferents)
static gamma motor neurons increase sensitivity to…
detect static muscle length (which is signalled by group 2 afferents)
main driver of 1a firing?
dynamic changes in muscle length
1a afferents also wrap around…
static bag 2 and chain fibers so they ALSO sense static muscle length but main driver of firing is dynamic CHANGES in muscle length
highest spindle density muscles?
extraocular
whenever the muscle is actively contracted, the muscle spindle is as well; in other words…
brain sends a command via alpha and gamma motor neurons at the same time
describe monosynaptic stretch reflex
muscle is stretched, muscle spindles detect this change in length. The muscle contracts in response to the stretch. Monosynaptic pathway causes the stretch (1a afferent connects to alpha motor neuron controlling antoagonist muscle). A disynaptic pathway is used to inhibit antagonist muscle (1a afferent connects to an inhibitory interneuron in the spinal cord which connects to an alpha motor neuron)
real life example of a monosynaptic stretch reflex
step on uneven terrain; ankle joint rotates unexpectedly which stretches the muscles around it. Spindle feedback results in greater muscle activity of the muscle stretched and increased joint stability
GTOs
-tiny receptors located at muscle-tendon junction
-sensory info relayed via group 1b afferents
-senses muscle load/force
-no efferent connections
how do GTOs create an action potential?
under force/load, collagen fibrils pinch the axon of a 1b afferent => graded receptor potentials= action potential
FA 1
Meissener’s endings (shallow)
SA 1
Merkel’s disks (shallow)
FA 2
Pacini ending (deep)
SA 2
Ruffini endings (deep)
ascending sensory tracts
- dorsal column
- spinocerebral tracts
dorsal column
transmits touch, vibration, and CONSCIOUS proprioceptive info to supraspinal centres
spinocerebellar tracts
UNCONSCIOUS proprioceptive info to the cerebellum.
transmits muscle spindle and GTO input
gamma motor neurons are responsible for muscle —–
stretch
alpha motor neurons are responsible for muscle —-
contraction
