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NB Lecture 18: Muscle Innervation and Spinal Reflexes
Terms in this set (47)
The Muscle spindle participates in the ..... reflexes and provides ...... information to the CNS
-Relation of body parts
The Muscle spindles regulates ........ under the influence of .... motor pathways and .... inputs
Descending (corticospinal and corticobulbar)
Describe what is going in the Knee Jerk Reflex
1- Doctor strike the Patellar tendon which results in stretch of the muscle
2- Muscle spindles within the muscle also become stretched and send signals to Spinal cord via Ia fibers (afferent)
3- Ia fibers synapse in the Ventral horn and becomes the alpha motor neuron
4- the alpha motor neuron travels back to the stretched muscle causing contraction
5- Also to prevent the Hamstrings (lower muscle) from moving inhibitory neurons are sent from the ventral horn thus allowing the kicking/jerking of the leg
-Collateral branch of the Ia afferent fiber activates the inhibitory neuron which is going to suppress the alpha motor neuron, thereby, leading to relaxation of the opposite muscle
Physiological Roles of the Muscle Spindle: Myotatic Reflexes
Muscle spindles and Golgi tendon organs communicate with Spinal ........ and the ..... for regulation of Proprioception
Golgi Tendon Organs are High-threshold receptors that are able to sense ........ of the muscle in relation to .......
Golgi tendon organs are located between ... and .... fibers
*They are in series with muscle fibers
In Golgi tendon organs changes in tension results in the .... fibers to carry that information to the Spinal cord
Explain the Physiological Role of the Golgi Tendon Organ
1- When muscle spindles are stretch they activate 1a afferent fibers
2- 1a afferent fibers excite the alpha motor neurons which then cause contraction of the muscle
3- Contraction/tension of the muscle leads to activation of the Golgi tendon organ
4- Activation of Golgi tendon leads to activation of 1b afferent fibers
•Ib afferents from the organ react to tension in a muscle (related to contraction of extrafusal fibers)
High Contraction/Tension of the Muscles lead to activation of the Golgi tendon organs- they activate .... afferent fibers?- these fibers then activate ..... interneurons that inhibit ...... neurons communicating with the overactive extrafusal muscle fibers?- reduced activity of these neurons relaxes overactive extrafusal fibers thus reducing chances of injury and/or redistributing load to less strained extrafusal fibers ?
- Golgi tendon organs and muscle spindles thus balance each other out
- eg: you are holding a big heavy rock, your muscle spindles tell the muscles to contract and hold the rock but the golgi tendons in order to avoid injury tell the muscles to relax and drop the rock
- this is the inverse myotatic reflex
In conditions of Lower muscular tensions the Golgi tendon organs exerts .... influences that aid in rhythmic muscular contraction?
In the Inverse Myotatic (stretch) reflex the ... fiber activates the ..... interneuron that .... the alpha motor neurons? - •The net effect of this is that the period of contraction of the muscle in response to a stretch is ....?
- and thus is relaxed
When the muscle tension gets high, the .......... reflex limits the contraction of the muscle. This is known as the ....... reflex
What is the afferent limb? the CNS unit? the efferent limb?
Golgi tendon organ reflex
Inverse myotatic reflex
Afferent limb -> Golgi tendon organ and 1b afferents
CNS unit -> Inhibitory interneuron
Efferent limb -> Alpha motor neuron and homonymous muscle
- golgi tendon organ
Noxious/threatening stimuli triggers the ........ responses
Ipsilateral Flexor (withdrawal)
eg: you step on a nail
In the Flexion reflex a painful stimulus leads to the activation of .... fibers which lead to activation of ..... interneurons?- these then activate .... motor neurons and activate the ..... muscles thus move away from the painful stimulus
Signals diverge via the ....... within the cord to ........
Recruit muscles into response
In the Flexion reflex, while the muscle flexors are activated, the ..... muscles are inhibited
-They relax to avoid having extension at the same time as flexion
ie Ipsilateral extensor responses are suppressed
Explain the Flexion Crossed Extension Reflex
Afferent signals of the ........ cross the cord to promote contralateral ....... while suppressing .........
The side that receives the painful stimulus will activate flexion to move away from the painful stimulus. In order for this to happen, extension will be inhibited on that same side
The other side, will have the opposite happening. The flexors will be inhibited while extensors will be activated
eg: this is an example of how walking works --> one leg is forward and one leg is back, both sides of the body are doing the opposite things
eg: if you step on a nail one foot will be flexed and the other will be extended to make sure you do not fall down
Motor Organization: The Big Picture
In The Motor Control System Coordination between contraction and relaxation of muscle groups is controlled via ..... order executive systems as well as by .... mechanisms
eg: Cortex plays a role
Hyporeflexia is a .... reflex while Areflexia is .... reflexes
What are some of the causes that can lead to this?
-Lesion of a spinal cord segment
-Lesion of the efferent limb (lower motor neuron lesion)
-Lesion of the afferent limb (sensory loss)
-Peripheral nerve lesion
-Diseases of the NMJ
-Lesion of the muscle
Lower Motor Neuron Syndrome occurs as a result of damage to cells derived from the .... plate that communicate with ... muscle cells
Symptoms of Lower Motor Neuron Syndrome include ..... , ...... , ...... , ...... , profound ..... and ..... paralysis?
Flaccid (limp muscle)
as well as Paresis (if not that bad) and Paralysis (if bad)
Hypotonia is pathologically reduced level of ......... ie reduced levels of sustained partial .... of ... fibers
Hypotonia can be assessed with ....? It can also be assessed by assessing ..... to passive movement?- if this is absent then it confirms Hypotonia?
Hypotonia may reflect damage to ......... or ........
Alpha motor neurons
- Mild hypotonia can arise from other lesions (e.g., cerebellar), but other accompanying signs would permit differential diagnostics
Acute Transection of the Spinal cord leads to a period of ......
This can lead to ..... of spinal (including autonomic) reflexes mediated caudal to the lesion
How do these patients present? (symptoms wise)
•It can take several weeks until spinal reflexes return. The mechanism underlying spinal shock is poorly understood
the patients present with LMN symptoms. Only ~4-5 weeks later, they show UMN symptoms
A Motor unit is composed of ..... neuron and the ..... fibers that it innervates
-The fibers that it talks to
•Up to 100 motor neurons per muscle
Fine movements (e.g. extraocular muscles) require ...... (small or large) motor units?
(e.g., about 10 extrafusal fibers per alpha motor neurons)
eg: Eye movements
Coarsely controlled muscles utilize .... (small or large) motor units ?
(e.g., about 1000 extrafusal muscle fibers per alpha motor neuron)
What are the 3 Types of Motor Units?
1- Type I
2- Type IIA
3- Type IIB
Type I motor units are known as ........ fibers. They are ....... in tension and they are ........ resistant + they are ........
They are innervated by relatively ..........
Small motor neuron and axon
These fibers are important in repetitive movements such as walking
Type II a fibers are known as ........ They are relatively ....... resistant and have ........ tension. They have some ....... capacity
They are innervated by relatively .........
Large motor neuron and axon
Type IIB are known as ....... and they are ...... susceptible. They have ........ tension and they are ..........
They are innervated by relatively ..........
Large motor neuron and axon
The 2 Crucial factors that control contraction of a muscle are the .......... and ...........
The firing rates of the Motor neurons
Increased AP = NT release = increased muscle contraction
Number of motor Units recruited
more fibers recruited = more contraction
atrophy is associated with lower motor neuron syndrome
The rest of the choices are UMN signs
Clinical Correlations: Case
Clinical Correlations: Case part 2
"very brisk" = +3 Hyperreflexia!!!!
Bilateral extensor plantar response (babinski response)
Clinical Correlations: Case - Part 3 - Neuroimages
Left - image of an inflammatory response and some swelling
Clinical Case- Diagnosis
HTLV-1 Associated Myelopathy aka Topical Spastic Paraparesis (TSP) is a chronic degenerative neurological disease that causes the .... of the ....?
Symptoms of HTLV-1 Associated Myelopathy aka Topical Spastic Paraparesis (TSP) aka as HTLV-1-associated myelopathy (HAM) include .... , ...... , weakness of the .... limbs and .... abnormality?
•Also known as HTLV-1-associated myelopathy (HAM). The virus can be spread through the placenta, and also through blood transfusions, breastfeeding, contaminated needles, and sexual contact
HAM/TSP usually occurs in tropical locales. It is most frequently found in
Caribbean, Japan, the Seychelles Islands, regions of South America, western Africa.
HAM/TSP usually affects adults between the ages of .. and .. and is far more common in ....than in ....? It can be dormant for a long time but when it gets activated it can lead to gradual loss of strength and flexibility in the ....?
•The disease may remain undetected for decades after infection. When the immune system's response to the virus causes diffuse (rather than patchy) demyelination, the legs gradually lose strength and flexibility.
-MRI of the spinal cord.
-Nerve conduction studies, EMG
HTLV-1 Associated Myelopathy aka Topical Spastic Paraparesis (TSP) aka as HTLV-1-associated myelopathy (HAM) is currently incurable but significant improvement has been seen with administration of ....?
• HIV- and MS-related myelopathy. Clinicians should be sensitive to coinfection with HIV.
gamma motor neurons innervate intrafusal muscle fibers
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