Spinal cord Reflexes-Allard Flashcards
What is a reflex?
automatic responses to sensory stimuli They are : -homeostatic responsee -rapid -unconscious (involuntary) -unlearned -stereotyped
Where are somatic reflexes modified?
higher brain centers
motor cortex
cerebellum and basal ganglia via thalamus
Entire circuit for the somatic reflex lies within the PNS.
What are the 4 different types of somatic reflexes?
- stretch reflex (myotactic reflex) AKA deep tendon reflex
- withdrawal (flexor) reflex
- crossed (extensor) reflex
- plantar (Babinski) response
Which somatic reflex changes with development?
Plantar (Babinski) response
What does it mean to be monosynaptic?
no interneuron between afferent sensory and efferent motor neuron
What are the 5 components of the reflex arc?
- sensory receptor: detects and responds to sensory stimuli
- afferent (sensory neuron): conducts impulses from sensory receptor to CNS
- central integrator (spinal cord synapses) : could monosynaptic or polysynaptic
- Efferent Neuron (motor neuron): transmit impulses from integrator center to effector organ
- Effector organ: muscle or gland
What is reciprocal inhibition?
the main arch may be monosynpatic for contraction of the agonist muscles, however we also have a disynaptic input to inhibit the antagonist muscle
this same sensory neuron has a collateral that will synapse with a neuron in the spinal cord (interneuron) that then makes a synapse with the alpha motor neuron than then goes to the antagonist muscles
the antagonist muscle is inhibited from contracting to allow the agonist muscle to contract
What are myotactic unit?
all of the muscles that cooperate to move a joint is a myotactic unit
- our muscle do not contract by themselves (there are many muscles that can move the knee joint
- when you get contraction of many of the agonist muscles that can extend the joint, you’ll get inhibition of the antagonist muscle
-so you stimulation and inhibition of the muscles of that myotactic unit
What is the function of muscle spindles?
they are a sensory receptor of skeletal muscle
- detect stretch
- encapsulated within collagen fibers
- located within the muscle (within the perimysium so within the fasicles)
- some respond to the speed and some to the amount of stretch
- coupled to Ia and II sensory fibers
- innervated by gamma motor neurons
What is the difference between extrafusal and intrafusal fibers? Which is the majority in our body?
extrafusal: are the skeletal muscle fibers; imbedded within skeletal muscle bundles
intrafusal: compose the muscle spindle
extrafusal is the main cells of contraction for movement of our bodies
Sensitivity of the skeletal muscles (muscle spindle sensory receptors) are regulated by what neuron?
gamma motor neurons
- which innervate skeletal at their distal portions
- sarcomeres are at the distal end of these structures (contractile fibers actin and myosin)
What are the types of the intrafusal fibers?
- nuclear bag: nuclei is bunched up in a region
- nuclear chain: nuclei is lined up in a row
in the distal parts you will see the sarcomeres (contractile unit) which are innervated by gamma motor neuron efferent
contraction of these intrafusal fibers modulates the sensitivity of the spindles
They do not contribute to the overall tension in the muscle. They are all about regulating the sensitivity of these spindles.
What are the types of the intrafusal fibers?
- nuclear bag: nuclei is bunched up in a region
- nuclear chain: nuclei is lined up in a row
in the distal parts you will see the sarcomeres (contractile unit) which are innervated by gamma motor neuron efferent
Intrafusal do not contribute to the overall tension in the muscle. They are all about regulating the sensitivity of these spindles.
What is the difference between the skeletal muscle of a 4 year old and that of an older individuals?
adipocytes surrounding skeletal muscle
The number of spindles corresponce to what?
with muscle dexterity AKA with how fined tuned the muscle is
fingers and toes we have a lot of spindles 16-18 and 16-21 respectively
deltoid has 0.5
gluteus maximus has 0.5-1
What is the difference between the Group Ia and group II sensory fibers for muscle spindles?
Group Ia:
- makes the annulospiral region around the central regions of the intrafusal fibers
- innervated both the nuclear bag and nuclear chain fibers
- this is akin to the alpha A type fibers
- there are two different types of nuclear bag (rate of change- dynamic; amount of the stretch-static)
- detects the amount of stretch and the rate of change of the length of the muscle fiber
Group II:
- make different types of flower spray ending onto the nuclear chain fibers and the STATIC nuclear bag fibers (more similar to nuclear chain fiber)
- really just detects the amount of stretch
Compare the firing pattern of the group Ia and II afferent fibers.
Group Ia has a baseline firing frequency at the initial length as the muscle gets stretched the frequency goes up and when it stays at the new longer length it goes back to a sort of baseline frequency
-very responsive to when the muscle is actually being stretched most rapidly; gives info about the overall length of the muscle
Group II: has a baseline firing frequency and when the muscle is stretched it does not respond to the rate but rather to the length; it is hard to determine when the muscle is being stretched or released; does no respond to the rapid changes in length
Gamma motor neurons
- are stretch activated afferents
- innervate intrafusal fibers as well as alpha motor neurons
- cell bodies are located in the ventral horn (30% in ventral horn are gamma motor neuron)
- smaller and slower than alpha motor neurons
- a lot of modulating input from higher centers
- responsible for adjusting how sensitive our muscle spindles are
- “increasing the game” = increase the sensitivity of the muscle spindle
- contracts the contractile fibers at the periphery of the muscle spindle
- receive input from higher centers
- less stretch will generate more AP in the intrafusal fibers
- lower degree of stretch in these fibers will generate a bigger explosive response in the alpha motor neurons and thus contraction of the muscle
- loose intrafusal fibers is not sensitive to stretch
- are co-activated with alpha motor neurons
What is the difference between nuclear chain and static and dynamic nuclear bag in terms of functions?
STATIC nuclear bag similar to nuclear chain which is concerned with detecting the amount of stretch
If I suddenly place 2 more block for a patient to carry at the elbow joint without letting the patient know, which sensory and motor fibers is working?
- Ia sensory neuron which senses the RAPID change in stretch
- gamma motor neurons puts increased tension in the muscle tension to make the muscle spindle sensitive
- alpha motor neuron tells you to contracts
If I place 2 more block for a patient to carry at the elbow joint and let the patient know, which sensory fiber is working?
stretch reflex will only occur if you do not know the load is coming; thus you will have enough tension prepared to carry the load, so NO stretch reflex occurs
Golgi Tendon organ
they are sensory receptors of skeletal muscle
- encapsulated
- innervated by Ib fibers
- connected to 10-15 muscle fibers
- senses the amount of TENSION in a muscle
- tension in the tendon emulates the tension in the muscle
- release of tension via disynaptic pathway
The firing rate of type Ib fibers is _________ to the tension.
proportional
Explain the role of golgi tendon organ in myotactic reflex
AKA reverse myotactic reflex: -tension on tendon activates sensory neuron -sensory neuron stimulates interneuron -interneuron inhibits motor neuron -tension on tendon is reduced
- similar to the stretch reflex there will be collaterals that will go to the agonist muscle to release contraction
Flexion withdrawal reflex
elicited by various cutaneous receptors: pain, temperature, pressure, propioeceptors and any sort of unexpected stimulus to the skin
- any somatosensory receptor initiates this reflex really
- afferent neurons may include: touch/pressure fibers (group I or II) or pain fibers (group III and IV)
- multilevel/ multijoint inhibitory and excitatory stimulation
- will have collaterals
- these are POLYSYNAPTIC reflex
excitatory interneurons innervates the alpha motor neuron of the flexor muscles and then you’ll have collaterals that go and inhibit the extensor muscles
What are collaterals?
Sensory info with collateral diverging information to body and CNS to help decide what your next voluntary movement should be
What is primarily coupled to the withdrawal flexor reflex?
withdrawal flexor reflex is COUPLED to crossed extensor reflex
-interneurons crosses over to inhibit muscles on the opposite side
limbs of other parts of the body will be extended to maintain BALANCE and posture
How is the flexor and extensor reflex compared to the other somatic reflexes in terms of the timing?
-they last longer than the other reflexes especially the stretch reflex
reverberating circuits prolong the duration of the withdrawal-crossed reflex
-involves circuits of EXCITATORY interneurons that re-excite each other
What is tone?
- excitability of the stretch reflex
- resistance to passive stretch during the resting state
- maintained by muscle spindles
- provides tonic innervation of muscle required for muscle health
you don’t use it–> you lose it
you always need tone of muscles
What is the purpose of stretch reflexes?
testing the integrity of different levels of the spinal cord
How do you rate stretch reflex?
0–> no reflex
1 plus: some with reinforcement
2 plus: normal reflex
3 plus: hyperreflexic
always want to compare left to right to see if something is normal or pathological
What is hyperreflexia a symptom of?
symptom of upper motor neuron disease with many inhbitory interneurons in the spinal cord alnog with biochemical changes in the spinal cord regarding our reflex pathways
UMN excite lower motor neurons
What are the symptoms of upper motor neuron lesions ?
- hyperreflexia
- hypertonia (rigid or spasticity)
- spastic paralysis
- extensor plantar Babinski response
- little or no muscle atrophy (takes a longer time to manifest)
you will have trouble eliciting voluntary muscle control
What are the symptoms of both upper and lower motor neuron lesions?
paresis
What are the symptoms of lower motor neuron lesions ?
- flaccid paralysis
- hypotonia
- hyporeflexia or areflexia
- fasciculations (twitching eye during stress) or fibrillations (whole motor unit contracting)
- negative or absent plantar reflex
- muscle atrophy (we’re dealing DIRECTLY with the muscle now
The condition below are associated with what motor neuron lesion?
- amylotrophic lateral sclerosis (Lou Gehrig disease)
- brain tumor or injury
- meningitis
- multiple sclerosis
- spinal cord tumor or injury
- stroke
Upper motor neuron lesion
What is the difference between rigidity and spasticity?
Rigidity:
- will feel resistance (stiffness) is all over
- lesion in the basal ganglia
- accompanied with tremors
Spasticity:
- resistance is pronounced in one direction
- velocity dependent: the faster you try to move the more it will resist
- force dependent
What is the clasp knife spasticity and what is it a result of?
spastic limb that initially resists movement and then suddenly releases the tension
- due to dysregulation of the golgi tendon organ reflex
- loss of regulatory UMNs
What is clonus a result of?
pathological oscillation of muscle reflex
- muscular spasm involving repeated, often rhythmic, contractions.
- occurs only when the stretch reflex is highly sensitized by facilitatory impulses from the brain
- reverberating (repeating) stretch reflexes
- stretch reflex in the antagonist muscles is hyperactivated)
-spasticity
Can positive Babinski be considered normal?
YES normal up to 2 years of age
-corticospinal pathways are not fully myelinated in newborns and infants
Cerebellar lesion
are often associated with depressed tendon reflexes
hyporeflexia
hypotonia
The condition below are associated with what motor neuron lesion?
- Myasthenia gravis
- amyotrophic lateral sclerosis (ALS) AKA Lou Gehrig disease
- Guillan-Barre syndrome
- muscular dystrophy
- bulbar palsy
lower motor neuron lesions
TIMING IS IMPORTANT IN determining upper and lower motor neuron lesions.
FACTS!!!
UMN will initially present as lower motor neuron lesions
What are the two types of reflexes?
autonomic (visceral) and somatic
What is the difference between autonomic and somatic reflexes?
effector organs and level of consciousness are DIFFERENT
- autonomic: smooth muscle, cardiac muscle, glands; generally not consciously perceived
- somatic: skeletal muscle; consciously perceived
Pupillary light reflex, cough reflex, and withdrawal reflexes are what kinds of reflexes?
Pupillary light reflex: autonomic
withdrawal reflexes: somatic
cough reflex: both
What are other names for the stretch reflex?
- deep tendon reflex
- myotactic reflex
- monosynaptic reflex
What is the difference between static and dynamic gamma motor neuron?
static: innervates nuclear chain and static nuclear bag
dynamic: innervates dynamic nuclear bag
The patellar reflex (knee jerk) tests what spinal nerves?
L2, L3, L4
The achilles reflex (ankle jerk) tests what spinal nerves?
S1
The biceps reflex tests what spinal nerves?
C5, C6
The triceps reflex tests what spinal nerves?
C7, C8
The brachioradialis reflex tests what spinal nerves?
C5, C6
What is the Babinski reflex?
tests the integrity of the cortical spinal tract (CST)
- stimulation of the lateral aspect of the foot normally results in plantar flexion of toes
- initiated by nociceptors (pain) fibers
- positive (abnormal in adults) Babinski response leads to contraction of the toe extensors which are usually inhibited by CST
What is the difference between lead pipe and cogwheel rigidity?
lead pipe rigidity: joints are very stiff and physician is having a hard time moving it in any direction
cogwheel rigidity: same rigidity but with tremors on top of that rigidity
What is fasciculation of the lower motor neuron?
Fasciculation represents a brief spontaneous contraction that affects a small number of muscle fibers, causing a flicker of movement under the skin.
-is associated with LMN diseases
Where are our motor and sensory neurons located?
ventral horn
Sensory cell bodies: dorsal root ganglion
Sensory endings are in the skeletal muscles where we find the sensory organ: muscle spindle
Why do spinal reflexes activate myotatic units?
a group of agonist and antagonist muscles function together as a unit because they SHARE common spinal reflex responses
- The agonist muscle may act in series or in parallel
- Muscles around a joint act in concert
- Divergent connection of spindle afferents establish strong neural linkages between muscles acting around a joint so that muscle do not act independent of each other.
divergent: moving or extending in different directions from a common point
What are the sensory nerve endings of type Ia and II sensory fibers that are coupled to sensory receptor muscle spindle?
- flower sprayed ending with type II sensory fibers
- annulospiral endings with type Ia sensroy fibers
Ia
II
Aa
Agamma
Sensory nerve fibers
-Ia is larger than II and does more than II
Motor neurons
-Type A gamma nerve fibers (5um in diameter compared to 14 um for type A alpha)
Static gamma motor neurons respond to what intrafusal fibers?
nuclear chain and static nuclear bag
Dynamic gamma motor neurons respond to what intrafusal fibers?
dynamic nuclear bag
Sensory Ia and II nerve fibers sense what intrafusal fibers?
Ia: nuclear chain and nuclear bag (detect both amount of stretch and rate of change in the length of muscle)
II: nuclear chain and STATIC nuclear bag( detect amount of stretch)
