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60 Cards in this Set

  • Front
  • Back

Where are the cells of the lower motor neuron located?

Localized in the ventral horn of the spinal cord

Axons of lower motor neurons leave via the

ventral root

What are lower motor neurons responsible for?

Muscle contraction

What are signs of lower motor neuron lesion?

-Flaccid Paralysis

-Hyporeflexia (loss of reflexes)

-Hypotonia (loss of tone)

-Fascicultation (spontaneous, uncoordinated muscle fiber contraction)

-Muscle atrophy

Where are upper motor neurons located?

The brain

Where are the axons of upper motor neurons located?

The descending motor tracts

What do upper motor neurons do?

They initiate, terminate, and modify responses and reflexes by facilitation or inhibiting the activity of lower motor neurons.

What are signs of an upper motor neuron lesion?

-Spastic paralysis



-No muscle atrophy

What would happen if there was an upper cervical cord lesion (C1-C5)?

The patient would display UMN signs in both the upper and lower extremities.

What would happen if there was a lower cervical cord lesion (C6-T2)?

Upper limbs: LMN

Lower limbs: UMN

What would happen if there was a thoracic cord lesion (T3-L3)?

Upper limbs: Normal

Lower limbs: UMN

What would happen if there was a lumbar cord lesion (L4-S2)?

Upper limbs: normal

Lower limbs: LMN

What would happen if there was a hemisection cord lesion?

Brown-Séquard Syndrome

-Ipsolateral loss of proprioreception and UMN signs

-Contralateral loss of pain and temperature sensation

The gray matter (the internal "butterfly" in the sliced spinal cord) is composed of what?

cell bodies

The white matter of the spinal cord is composed of what?

Myelinated axons

What are the two types of motor neurons?

Alpha motor neurons and Gamma motor neurons

What does an alpha motor neuron innervate?

Normal (extrafusal) muscle fibers

What is a motor unit?

An alpha motor neuron plus all the muscle fibers that it innervates

What do gamma motor neurons innervate?

Muscle spindle (intrafusal) fibers

Where are interneurons found and what are they?

Interneurons can be found in all areas of the gray matter in the spinal cord.

They integrate information and participate in reflexes.


The awareness of posture and movement. The knowledge of position, weight and resistance of objects in relation to the body.

What sensors are involved in proprioception?

Muscle spindle organs and Golgi tendon organs

When are the primary endings stimulated?

The onset of stretch (phasic)

When are secondary endings stimulated?

Most stimulated in sustained (tonic) fashion

What causes contraction of the intrafusal fibers?

Gamma motor neurons


The muscle spindle sensory neurons synapse directly onto the alpha motor neuron

What reflex is monosynaptic?

Knee-jerk stretch reflex

The knee-jerk stretch reflex is a form of....

negative feedback: stretching the muscle causes the muscle to contract

It keeps the muscle at optimal length to apply force and accommodates unexpected forces

Explain the order of the effects of the knee-jerk stretch reflex.

1. Pt is hit in the patellar ligament with a rubber mallet

2. The muscle spindle organs are stretched

3. Primary endings in the spindle are activated

4. These sensory neurons synapse with alpha motor neurons

5. Motor neurons stimulate the extrafusal fibers causing the contraction of the muscle

What does the knee jerk stretch reflex stimulate

contraction of the muscle

Reciprocal Innervation

In many reflexes the sensory neuron that stimulates the motor neuron of a muscle also inhibits the antagonistic muscle.

Explain DoubleReciprocal Innervation and the Crossed Extensor Reflex via the tack example

Stepping on a tack causes contraction of the flexors (to get away from the pain source!) and relaxation of extensors of the affected foot.

Contraction of the extensors and relaxation of the flexors occurs in the other leg to help you keep balance.

Define Cross Extensor Reflex

A reflex involving opposingbehaviors on either side of the body designed to avoid an unpleasant stimuluswhile maintaining balance.

Where is the Golgi Tendon Organ located?

In the tendons

What does the Golgi Tendon Organ do?

Protects the muscle from damage of too much exertion

(TheGolgi tendon tells the body that a muscle is being contracted too much, letslay off a bit so that we do not damage it.)

What does the spindle do?

-Accommodates unexpected forces

(Thespindle tells the body there is a new force stretching that muscle: contract itto accommodate.)

When is the spindle stimulated?

When the muscle is stretched

When is the Golgi stimulated?

When the muscle is contracted

The cortex is divided into....


What does the frontal lobe of the brain contain?

-premotor cortex

-motor cortex (precentral gyrus)

-areas involved in planning of behavior

What is represented on the cortex of the primary motor cortex?

Homunculus called motor man, is the cortex of this region of the brain drawn topographically.

(note: post-central gyrus, containing the somatosensory cortex contains a Homunculus named sensory man)

Where do a majority of the fibers in the pyramidal tract originate?

Primary motor cortex

What is the pathway of the pyramidal tracts?

From the cortex through the internal capsule to the brainstem where they form the pyramids of the medulla.

The majority of the fibers then cross to the contralateral side (90%) forming the lateral corticospinal tracts, while the others (10%) do not cross forming the anterior corticospinal tracts.

Babinski Reflex

-Test that can be used to detect pyramidal tract damage

-Run hard blunt instrument from heel to toe of person's foot

-Normal = curling of the toes

-Babinski's sign = extending and fanning of the toes, indicating probably pyramidal motor system damage.

How many pairs of deep nuclei are found in the cerebellum?


How many pairs of peduncles are found on the cerebellum? What are there purpose?

3, connects cerebellum to brainstem

Describe the weight of the cerebellum vs. amount of neurons it contains.

Cerebellum makes up for only 10% of the brain weight, but contains over half of the neurons.

What is the function of the cerebellum?

Coordinates the planning of limb movements.

Modifies movements as they are performed.

Corrects errors of overshooting or undershooting.

What can occur if there are lesions in the cerebellum?

Behavior similar to intoxication (alcohol effects cerebellar activity)

Besides the percentral gyrus and postcentral gyrus, where else in the brain are there homunculuses?

The cerebellum

Where does the cerebellum receive input from?

Motor cortex and parietal cortex via the pons

Inferior olive

Spinal cord

Vestibular nucleus

What is the purkinje cell?

The sole output from the cerebellar processing and innervates cells in the deep cerebellar nuclei (which then innervate cells in VL complex, which then go to motor and premotor cortex).

What is important to note regarding the cerebellum?

There are no descending tracts from the cerebellum.

(basically modifies behaviors at upper levels)

What is the function of the basal ganglia?

Appears to play a crucial role in initiating and terminating movements.

Disease states resulting in dysfunction of the basal ganglia can lead to what?

Chorea (uncontrolled movements)

ex. Parkinson's Disease

The basal ganglia receives input from where?

Prefrontal cortex, premotor cortex, parietal cortex, temporal cortex, and substantia nigra.

The basal ganglia sends output to where?


Are Purkinje cells inhibitory or excitatory?


What is the main mechanism of basal ganglion modulation of movements?

Disinhibition of thalamocortical neurons (disinhibit thalamus, which stimulates cortex)

Explain disinhibition

Inhibition of the inhibitory neuron (leads to excitation)

(basal ganglion is an example of this)