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
