3. Proprioception
3
Sense the position of body parts in relation to each other
and in space, as well as relative force applied to
movements
Balance
Vestibular system
Muscle length and force
Muscle spindles
Golgi tendon organs
B&L Figure 9-1
4. Muscle Spindles - intro
4
Non-force generating intrafusal muscle
fibers within a fluid filled capsule
(spindle)
Lie in parallel with extrafusal muscle
fibers
Stretch or shorten along with extrafusal
fibers
Innervated by both motor (efferent)
and sensory (afferent) axons
Efferent innervation contracts intrafusal
fiber to match length of extrafusal fiber
Afferent innervation sends info on relative
Kandel Figure 36-3
5. Muscle spindles - structure
5
Three types of intrafusal fibers
Central regions are non-contractile
Mechanoreceptive sensory innervation
Primary Ia afferents
all 3 fibers
Secondary II afferents
static nuclear bag and nuclear chain fibers
Motor innervation
Dynamic γ efferent
Dynamic nuclear bag
Static γ efferent
Combination of chain and static nuclear
bag
Kandel Figure 36-3
6. Muscle spindles – afferent
function6
Each afferent has a tonic, baseline level of firing, and responds to relative stretch
Ia
Static and dynamic firing responses
Firing proportional to amount of and rate of muscle stretch
II
Only static firing response
Firing proportional to amount of stretch
Firing of which afferent is being
assessed during a tendon tap?
B&L Figure 9-2
7. Muscle spindles – efferent
function7
γ motor neurons
maintain sensitivity of
spindle over a range of
muscle lengths
α-γ coactivation
Descending input can
change relative
dynamic vs. static γ
activation to modulate
spindle sensitivity
http://www.ncbi.nlm.nih.gov/books/NBK11119/bin/ch16f10.jpg
Activation of only
dynamic γ motor neurons
increases
responsiveness of _____
afferents
8. Golgi Tendon Organs (GTOs)
8
collagen fibers located within a
capsule near tendon, in series
with extrafusal muscle
innervated by mechanoreceptive
Ib afferent fibers intertwined
between collagen
Activated by muscle
contraction or stretch
Sense changes in tendon
tension/force
Kandel Figure 36-6
9. Reflex organization
9
A reflex is a predictable, involuntary and stereotyped response to an
eliciting stimulus
Can be modulated by stimulus intensity and descending CNS input
Testing reflexes is an important clinical tool in assessing neurological
and spinal function
10. Myotatic or stretch reflex
10
Monosynaptic reflex mediated by muscle
spindles
Contraction in response to lengthening
Reflex arc:
1. Muscle stretches
2. Ia afferent of muscle spindle increase
firing
3. Synapse on α motor neuron and
inhibitory interneuron in spinal cord
4. α motor neuron of homonymous muscle
excited, and of antagonist muscle
inhibited
5. Homonymous muscle contracts to
oppose lengthening, antagonist muscle
relaxes
B&L Figure 9-6
11. Myotatic or stretch reflex
11
Stretch reflex has two phases:
Phasic (Ia) phase
dynamic change in muscle length (ex. tendon tap) triggers a
transient phasic contraction
Physiological importance: reflex contraction prevents
overstretch of extrafusal muscle fiber beyond physiological
limits
Clinical importance: tendon tap used to determine integrity of
spinal cord at different segmental levels
12. Myotatic or stretch reflex
12
Tonic phase
Static stretching of muscles produces a weaker, longer lasting,
tonic contraction
Type II afferents also involved
Physiological importance: maintains muscle tone/posture via negative
feedback
Ex. Soldier standing at attention legs begin to fatigue and flex
quadriceps slowly begin lengthening tonic stretch reflex
maintains tone and prevents collapse (to an extent)
Clinical importance: assessing presence of hypertonia
Ex. Patients with cerebral palsy have very rigid, tight muscles
resistant to stretch overactive tonic stretch reflex due to upper
motor neuron lesion
13. Motor neuron lesions
13
Upper motor neuron lesion of the neural pathway
inside the CNS (not including the ventral horn of the
spinal cord or motor nuclei of the cranial nerves)
stroke, traumatic brain injury or cerebral palsy
Lower motor neuron lesion affects nerve fibers
within the ventral horn of the spinal cord travelling to the
relevant muscle(s)
Nerve trauma, polio
Upper motor neuron
lesion
Lower motor neuron
lesion
Reflexes Increased, may have
pathological reflex
signs (Babinski sign)
Decreased,
Muscle
tone
Increased, contralateral Decreased, ipsilateral
Weakness Yes, contralateral Yes, ipsilateral
14. Inverse myotatic or Ib reflex
14
Disynaptic reflex mediated by GTOs
Relaxation in response to increased
tension
Reflex arc:
1. Muscle contracts
2. Ib afferent of GTO increase firing
3. Synapse on one inhibitory and one
excitatory interneuron
4. α motor neuron of homonymous
muscle inhibited, and of antagonist
muscle excited
5. Homonymous muscle relaxes to
oppose increased force in tendon,
antagonist muscle contracts
B&L Figure 9-7
Ib
15. Inverse myotatic or Ib reflex
15
Physiological importance:
reflex relaxation thought to prevent excessive force from damaging
muscle tissue.
Acts synonymously with the myotatic stretch reflex to maintain posture
and balance
Clinical importance: Clasp knife reflex: seen in patients with upper
motor neuron lesions muscle has increased tone and resistance to
stretch if sufficient force is applied, limb resistance suddenly
decreases thought to be mediated by high threshold firing of GTO
afferents (but other receptors may be involved as well)
16. Flexion withdrawal
reflex16
Polysynaptic reflex mediated by FRAs
(flexion reflex afferents: nociceptors,
mechanoreceptors etc.)
flexion in response to painful stimuli
FRAs synapse on inhibitory and
excitatory interneurons which excite
ipsilateral flexor motorneurons & inhibit
extensor motorneurons
Physiological importance:
Rapid flexion away from painful
stimuli
Clinical importance: upper motor
neuron lesion impairs flexion reflex
pathalogical Babinski sign
B&L Figure 9-8
17. Upper motor neuron lesion:
Babinski sign17
(Type of flexion reflex) (pathological reflex)
18. Crossed extension reflex
18
occurs in lower limbs as part of
reflex arc for flexion reflex
FRAs synapse on interneurons
which elicit contralateral limb
extension to help maintain
balance
Similar neuronal circuits involved
in central pattern generators
governing locomotion (next
lecture)
B&L Figure 9-8
19. Summary of reflexes
19
REFLEX
STIMULU
S
(CLINICA
L TEST)
RESPONS
E
SENSORY
RECEPTO
R
SYNAPSE
S
EFFECT
ON
MUSCLE
OTHER
EFFECTS
FUNCTIO
N
Stretch
(Myotatic)
Reflex
Rapid
Stretch of
muscle
(test: tap on
muscle
tendon)
Stretched
muscle
contracts
rapidly (ex.
knee jerk)
Muscle
Spindle
Primary (Ia)
and
Secondary
(II) sensory
neurons
(tonic
phase)
Ia: Mono-
synaptic
II: (tonic
phase)
monosynapt
ic and
polysnaptic
Excite
Homonymo
us (same
muscle)
Also Excite
synergist
muscles;
Inhibit
antagonist
muscles
(Reciprocal
Inhibition)
Aid in
maintaining
posture,
counter
sudden
stretch
Inverse
Myotatic
Reflex
Large force
on tendon
(pull on
muscle
when
resisted)
Muscle
tension
decreases
Golgi
Tendon
Organ (Ib)
Disynaptic
(via
interneuron)
Inhibit
Homonymo
us (same
muscle)
Also Inhibit
synergist
muscles;
Excite
antagonist
muscles
Protective,
prevent
damage to
tendon
Flexor
Reflex
Sharp,
painful
stimulus (as
in stepping
on nail)
Limb is
rapidly
withdrawn
from
stimulus
Cutaneous
(skin) and
pain
receptors
Poly-
synaptic
(via
interneuron)
Excite
Flexor
muscle
Also Inhibit
extensor
muscle of
same limb;
Excite
extensor
muscles
and Inhibit
flexors of
opposite
limb
(Crossed
Extensor
Reflex)
Protective,
withdraw
from painful
stimulus;
Cross
extension
aids in
maintaining
posture
when leg is
lifted
http://musom.marshall.edu/anatomy/grosshom/spinalreflexes.html
20. Objectives
After this lecture you should be able to:
Compare and contrast the structure and function of
muscle spindles with golgi tendon organs
Describe the importance of αγ coactivation
Describe the reflex pathway for the myotatic, inverse
myotatic, and flexion reflexes
Give an example of a physiological and clinical importance for
each reflex
Distinguish between upper and lower motor neuron lesions
20
21. 21
1. Type __________ spindle afferents are responsive to
the rate of change of muscle length.
2. A Babisnki sign is often associated with _____________
motor neuron lesions.
3. Relaxation of the quadriceps muscle
increases/decreases firing of Ia afferents and
increases/decreases firing of Ib afferents.
Test your knowledge
Hinweis der Redaktion
Readings
Berne and Levy: Chapter 9, pages 157 – 179
Chapter 6, pages 82 – 91 (Focus on Neuromuscular Junction and End Plate Potential)
Chapter 12, pages 233-246
Cutaneous mechanoreceptors because we already talked about mechanically gated receptors: Hair cells in vestibular and auditory system
size of spindle: 4-10 mm long
Intrafusal fibers are specialized for sensory function and do not contribute significantly to force produced by extrafusal muscle fibers. (Extrafusal muscle fibers are normal skeletal muscle fiber that produce force).
Spindles lie in parallel with extrafusal muscle fibers since the ends of the muscle spindle attach to connective tissue in muscle.
Tap – tendon tap, the firing of which afferent is being assessed during a tendon tap?
Descending tracts can affect whether static or dynamic gamma motor neurons preferrentially fire, affecting the nature of reflex activity in the spinal cord. Static gamma stimulated: static and dynamic response of Ia and II enhanced. Dynamic gamma stimulated: only dynamic response of Ia enhanced
http://www.ncbi.nlm.nih.gov/books/NBK11119/bin/ch16f10.jpg
Stretch of collagen fibers occurs when force is applied to tendon either by:
stretching muscle or by
contraction of extrafusal muscle fibers that are connected directly (in series) with tendon organ
Provides complementary information about the mechanical state of the muscle
Input from the GTO’s relays info about the tension in the muscle. This input can be useful in a variety of motor acts such as maintaining a steady grip on an object or compensating for the effects of fatigue.
aka the monosynaptic stretch reflex or myotatic reflex
elicited by: e.g., tendon tap or rapid movement of joint
monosynaptic stretch reflex response can be used as diagnostic tool to determine integrity of spinal cord at different segmental levels
Tonic phase is not apparent in intact animals (only in the decerebrate preparation) because the steady state discharge of muscle spindles is not strong enough to raise the resting potential of motor neurons above threshold for firing.
aka the monosynaptic stretch reflex or myotatic reflex
elicited by: e.g., tendon tap or rapid movement of joint
monosynaptic stretch reflex response can be used as diagnostic tool to determine integrity of spinal cord at different segmental levels
Tonic phase is not apparent in intact animals (only in the decerebrate preparation) because the steady state discharge of muscle spindles is not strong enough to raise the resting potential of motor neurons above threshold for firing.
aka the monosynaptic stretch reflex or myotatic reflex
elicited by: e.g., tendon tap or rapid movement of joint
monosynaptic stretch reflex response can be used as diagnostic tool to determine integrity of spinal cord at different segmental levels
An upper motor neuron lesion is a lesion of the neural pathway above the anterior horn cell (grey matter in front of spinal cord containing cell bodies of alpha motor neurons) of the spinal cord or motor nuclei of the cranial nerves. This is in contrast to a lower motor neuron lesion, which affects nerve fibers traveling from the anterior horn of the spinal cord to the relevant muscle(s).[1]
Upper motor neuron lesions occur in conditions affecting motor neurons in the brain or spinal cord such as stroke, traumatic brain injury and cerebral palsy.
Cerebral palsy (CP) is an umbrella term encompassing a group of non-progressive,[1][2] non-contagious motor conditions that cause physical disability in human development, chiefly in the various areas of body movement.[3]
Cerebral refers to the cerebrum, which is the affected area of the brain (although the disorder most likely involves connections between the cortex and other parts of the brain such as the cerebellum), and palsy refers to disorder of movement.
Upper motor neuron lesions cause spastic paralysis of muscles on the opposite side of the body. Muscle tone is increased, reflexes exaggerated, and babinski sign (pathalogical reflexes) Spasticity is probably caused by the removal of inhibitory influences exerted by the cortex on the postural centers of the vestibular nuclei and reticular formation
Lower motor neuron lesions: flaccid paralysis of muscles on the same side of the body. NO voluntary or reflex action of the innervated muscle fibers, muscle tone is decreased or lost, and the muscle remains limp or flaccid.
Prevents tearing of muscle fibers in response to force overload
Vis versa: reflex contraction in response to lowered tension: explain how this is actually acting synonymously with the myotatic stretch reflex: soldier at attention, quads fatigue, force in patellar tendon decreases, inhibition of homonymous muscle prevented, homonymous muscle can contract, the lengthening of quads also stimulates muscle spindles to activate same muscle to contract
Prevents tearing of muscle fibers in response to force overload
Vis versa: reflex contraction in response to lowered tension: explain how this is actually acting synonymously with the myotatic stretch reflex: soldier at attention, quads fatigue, force in patellar tendon decreases, inhibition of homonymous muscle prevented, homonymous muscle can contract, the lengthening of quads also stimulates muscle spindles to activate same muscle to contract
The flexion reflex afferents include group II and group III afferents from the skin, joints, and muscles, and the group II afferents from the secondary endings of muscle spindles.
opposite response pattern = flexor inhibition; extensor excitation
produces coordinated response of multiple joints, e.g., ankle, knee and hip
mediated by polysynaptic pathway (multiple interneurons)
stimulus strong enough to activate nociceptors elicits flexion withdrawal, which causes stimulated limb to be quickly withdrawn from stimulus
flexion withdrawal can inhibit activation of extensor muscles of injured limb (limping)
The flexion reflex afferents include group II and group III afferents from the skin, joints, and muscles, and the group II afferents from the secondary endings of muscle spindles.
opposite response pattern = flexor inhibition; extensor excitation
produces coordinated response of multiple joints, e.g., ankle, knee and hip
mediated by polysynaptic pathway (multiple interneurons)
stimulus strong enough to activate nociceptors elicits flexion withdrawal, which causes stimulated limb to be quickly withdrawn from stimulus
flexion withdrawal can inhibit activation of extensor muscles of injured limb (limping)
Type 1a
Upper motor neuron lesions
Increases Ia, decreases Ib