This site is 100% ad supported. Please add an exception to adblock for this site.

BRAINSTEM MOTOR MECHANISMS -63

Start Studying!

Terms

undefined, object
copy deck
Describe the role of descending axons from the CNS?

Descending axons from the CNS:
generally terminate on spinal interneurons which mediate spinal reflexes
may gain direct access to the alpha motor neurons
provide a means of influencing and modifying reflex activity

Descending motor tracts to the spinal cord, except for the corticospinal (or pyramidal) tracts originate in the brainstem.
Illustrate the role of different parts of the brain?

Give motor systems, command to move and cortico association area allow for this to happen
Compare TONE and POSTURE and specifically state what they are due to?
A. TONE

1. Is not the intrinsic property of muscle per se.
Section Dorsal/ root = spastic
Section ventral/ root = flaccid

2. It is due to NEURAL ACTIVITY!!!

3. Normal muscle is in partially contracted state (muscle tone)

B. POSTURE:

1. Maintenance of body in upright position with respect to gravity.

2. Provides background upon which voluntary movements are superimposed

3. It is due STRETCH REFLEX!!!!

Also, disruption or relaxation of muscles involved in postural reflexes leads to body collapsing.
1. Describe 4 signs of lower motor neuron lesions?

2. Describe 5 signs of upper motor neuron lesions?
1. Lower motor neuron lesion:

a) flaccid paralysis - (segmental): lack of muscle tone in affected area.
b) muscle atrophy
c) absence of reflex responses
d) fasciculation - muscular twitching involving the simultaneous contraction of contigous groups of muscle fibers.


2. Upper motor neuron lesion:
a) spastic paralysis - more diffuse
b) absence of atrophy
c) hyperactive reflexes
d) Babinski response maybe positive
e) skin reflexes may be lost
Differentiate between:

1. Lesion of Extrapryramidal Motor System (EPMS)

2. Lesion of Pyramidal Motor System (PMS)

3. Lesion of cerebellum
1. Lesion of EPMS: Spastic paralysis

2. Lesion of PMS (cutting the lateral corticospinal tract): weakness
(paresis)

3. Lesion of cerebellum: Incoordination
1. Illustate the 2 tracts in the pyramidal sytem.

2. Demonstrate the study of homonculus?

Some lateral corticospinal do not even cross!
The mouth representation is very big
Trunk gets no action
The fingers has lots of function
This is the motor homonculus, and in sensory homonculus is the same thing too!
Describe what happens in transection of the spinal cord?
Spinal Cord Transection might be a result of gunshot, fracture, etc.
Transection of the spinal cord in man causes
“spinal shock”. Spinal shock is the immediate spinal cord transection response. It is due to: Sudden withdrawal of descending input – (excitatory)!!!

-Due to this spinal shock, these events happen:

1. Skeletal muscle - no tone
2. Abdominal reflex – none
3. Tendon jerk - none
4. ER = Hyperpolarization ( -2 – 6mV) Spinal motoneuron ( i.e. increasing the threshold)
5. No plantar or cremaster reflex
1. What happens during spinal shock recovery?

2. Describe what happens in mass reflex?
1. There is a decrease in the threshold of spinal reflexes and this leads to HYPERREFLEXIA!-so you have spasicity when the reflex comes back.

2. As flexor and autonomic reflexex return, they become hyperactive producing a mass reflex upon stimulation. So, a noxious stimulus such as pinching oneself irradiates to many reflex centers and causes action of events controlled at the spinal level such as bladder emptying, defacation, sweating, palor, withdrawal reflexes.
What 2 areas above the spinal cord are highly facilitatory to extensor motoneurons?
1. The pontine reticular formation.

2. The lateral vestibular nuclei.
Regarding medullary integration, what is decerebrate rigidity?

Transection of the brainstem between the superior and inferior colliculi leading to immediate and sustained contraction of antigravity (extensor) muscles.
---This due to NET in gamma efferent discharge !!!

So, there is enhanced excitation of motor neuron pool below transection. This rigid response is due to gravity.

Moreover, there is removal of tonic inhibition from the highly facilitarory areas in the brainstemleading to excitation of the gamma motor neuron in the dorsal root of the spinal cord so you get extensor rigidity-upright posture.

---Decerebration removes 2 inhibitory areas that drive the Ret. Inhibit. Area
---Net effect on gamma pool is facilitation
---Stretch reflex hyperactive “gamma rigidity”
What are the 3 locations that the inhibitory signals arise from?

1. Basal ganglia
2. Cerebral cortex
3. medulla

NOTE:

The reticular inhibitory area is in the lateral funiculus of the spinal cord?
Describe "alpha rigidity"?
It is attributed to the excitatory influences from the vestibular nuclei which synapses directly on alpha motoneurons via vestibulospinal tracts. Alpha rigidity occurs when there is brainstem transection (decerebration) plus damage to Anterior Lobe of the Cerebellum. The anterior funiculus is involved in this.
What 2 events happen in a mid - pontine transection and what results from this?
1. Removes inhibitory influences from cerebrum and basal ganglia onto pontine excitatory areas of the R.F.

2. Removes excitatory influences from cerebrum and basal ganglia onto the medullary inhibitory areas of the R.F.

This leads to increased facilitation of spinal extensor motoneurons contraction of extensor (antigravity) muscles = “gamma rigidity”
Describe what happens in a mesencephalic transected organism where the lesion is above the midbrain?
There is extensor rigidity only when animal lies quiet on his back (static postural) but during activity, rigidity disappears. (phasic activity).

Also, The capacity to right and walk are recovered after a period of time, if the midbrain is intact (dogs and cats)

Primates are much more incapacitated, are unable to right themselves: (greater encephalization)
What happens in a decorticate transected organism?

Causes few motor deficits in lower vertebrates because Basal Gangl. are centers for coordination of motor activity. Usually seen in patients with lesions (hemorrhage) in Internal Capsule.
Decorticate humans exhibit flexion of the arms at the fingers, elbows, and wrist; legs are extended
-They Can be kept alive more easily than mesencephalic, decerebrate or spinal preparation because of intact hypothalamus. Learning can occur
Start Studying!

Deck Info

15

permalink