MOTOR SYSTEMS

Question 1

What parts of the central and peripheral nervous system are involved with motor behaviors?

Answer 1

motor cortex
basal nuclei
cerebellum
brainstem
cranial nerves
spinal cord
spinal and peripheral nerves

Question 2

What is an upper motor neuron?

Answer 2

cell body is in the brain (precentral gyrus of the motor cortex), synapses on a lower motor neuron (in the spinal cord)

initiates movement

Question 3

What is a lower motor neuron?

Answer 3

cell body is in the spinal cord, goes on to innervate muscles and glands

(alpha motor neurons of the ventral horn)

Question 4

What part of the spinal cord is motor? What part is sensory?

Answer 4

Motor:
Lateral and Ventral

Sensory:
Dorsal

Question 5

List all parts of the direct motor pathway in the correct order.
(explained)

Answer 5

Premotor Cortex = Think about moving; Plans and prepares voluntary movements.

Primary Motor Cortex (Precentral Gyrus) = Initiates movement, sends signals to start movement via upper motor neurons.

Subcortical White Matter = Axons travel through subcortical white matter, carry motor signals deeper into the brain.

Internal Capsule = Form the internal capsule.

Crus Cerebri= Motor fibers headed from the precentral gyrus through the posterior limb of the internal capsule to the crus cerebri (in the midbrain).

Basal Pons= Seperate into bundles in the pons.

Pyramids (Medulla) = Defines the border between the spinal cord and medulla oblongata. MOST (not all) decussation occurs here.

Corticospinal Tracts: Lateral and Ventral (Anterior)
- Lateral CST= 90% of axons decussate at pyramids, innervate contralateral muscles, controls limb movement
- Ventral/Anterior CST= 10% of axons decussate in the SC, some do not decussate, controls trunk and posture

Spinal Cord Ventral Horn = Upper motor neurons synapse with lower motor neurons.

Ventral Roots= LMNs/alpha motor neurons project their axons through ventral roots, form spinal nerves. Split into dorsal and ventral primary rami.

Peripheral Nerves= Lower motor neurons send signals to muscles.

Skeletal Muscle = Movement occurs, Muscles contract due to neuromuscular junctions to produce movement.

Question 6

List all parts of the direct motor pathway in the correct order.
(simple)

Answer 6

1. motor cortex
2. subcortical white matter
3. internal capsule
4. crus cerebri
5. basal pons
6. pyramids
7. lateral and ventral/anterior CSTs
8. spinal cord ventral horn
9. ventral roots
10. peripheral nerves
11. skeletal muscles

Question 7

Direct Motor Pathway Summary
Upper Motor Neurons (UMNs):

Answer 7

These originate in the motor cortex of the brain, specifically in the precentral gyrus.

Corona Radiata:

The fibers of the corticospinal tract pass through the corona radiata, the subcortical WM.

Internal Capsule:

For head and neck muscles and precise movement, the fibers pass through the genu of the internal capsule.

For trunk and lower limb muscles, the fibers pass through the posterior limb of the internal capsule.

Crus Cerebri:

After passing through the internal capsule, the fibers enter the crus cerebri (cerebral peduncles) of the midbrain.

Pyramids (Pyramidal Decussation):

In the medulla, the corticospinal fibers form the pyramids, and most of them decussate (cross) to the opposite side, forming the lateral corticospinal tract, which controls voluntary movement of the limbs. The fibers that don’t cross form the anterior corticospinal tract, which controls axial and proximal muscles.

Descent as CSTs:

After decussation, the lateral corticospinal tract continues down the spinal cord, where it synapses with lower motor neurons (LMNs) in the anterior horn of the spinal cord, which then innervate muscles.

Question 8

Where do direct motor fibers decussate?

Answer 8

pyramids in the medulla (pyramidal decussation)

Question 9

What fibers travel in the genu of the internal capsule?

Answer 9

Corticobulbar for head and neck muscles and precise movement

Question 10

What fibers travel in the posterior limb of the internal capsule?

Answer 10

Corticospinal for trunk and lower limb muscles

Question 11

What is different between the lateral and ventral corticospinal tracts?

Answer 11

Lateral:
-ALL fibers have crossed at the pyramidal decussation
-control muscles on opposite side of the body
-precise, voluntary movements of arms and legs

Ventral/Anterior:
-Most fibers cross in the spinal cord
-control muscles on both sides of body
-trunk movements

Question 12

How many motor pathways are there (think direct and indirect)?

Answer 12

Direct (1):
* Corticospinal tract (CST)

Indirect (3):
* Vestibulospinal tracts
* Reticulospinal tracts
* Tectospinal tract

**Rubrospinal may not be that important in human motor function, so we’re not learning about it

Question 13

What are the 3 indirect motor pathways?

Answer 13

• Vestibulospinal tracts
• Reticulospinal tracts
• Tectospinal tract

Question 14

Vestibulospinal Tracts

What are their origins?
What are their destinations?
What do they control/regulate/assist?

Answer 14

origin:
vestibular nuclei, pons, and medulla

destination:
cervical segments of spinal cord
lumbar-sacral segments of spinal cord

function:
reflexive regulation of balance and posture

**inner ear contains vestibular apparatus, project through CN VIII to vestibular nuclei, project to SC

Question 15

Reticulospinal Tracts

What are their origins?
What are their destinations?
What do they control/regulate/assist?

Answer 15

origin:
reticular formation in pons and medulla

destination:
all levels of spinal cord

function:
-sets muscle tone (adjusts posture) in anticipation of a movement
-keep LMNs/alpha motor neurons ready to go

Question 16

Tectospinal Tracts

What are their origins?
What are their destinations?
What do they control/regulate/assist?

Answer 16

origin:
superior colliculus (midbrain)

destination:
cervical levels of spinal cord

function:
-mediates reflexive movement of head and neck in response to sensory stimuli (predominantly vision and hearing)
-also coordinate eye movement and sound

Question 17

What are the basal nuclei?
(description)
(aka basal ganglia)

Answer 17

a collection of interconnected subcortical nuclei (deep grey matter) that function as a central link in the part of the motor system that translates the desire to move into action

• The Basal Nuclei are the ‘organ of habit’
• The Basal Nuclei ‘select’ desired behaviors and ‘inhibit’ unwanted behaviors
• Important!! The basal nuclei do not make direct or indirect synaptic connections with the motor neurons in the spinal cord or brainstem
• The basal nuclei consist of parallel, anatomical loops that originate in the cortex, pass through the basal nuclei, project to dorsal thalamus, then back to the cortex

Question 18

Nuclei vs Ganglia

Answer 18

Nuclei= a group of neurons within the CNS with similar connections, neurotransmitters, and functions

Ganglia= a group of neurons outside the CNS with similar connections, neurotransmitters, and functions

Question 19

What are the basal nuclei?
(names and formations)

Answer 19

Striatum - Caudate Nucleus, Putamen

Pallidum - Globus Pallidus (has internal and external segments)

Brain Stem - Substantia Nigra

Diencephalon - Subthalamic Nucleus

Question 20

What is the function of the direct and indirect pathways through the basal nuclei?

Answer 20

Direct pathway= (facilitates appropriate motor programs)

Indirect pathway= (inhibits competing motor programs)

Question 21

Net Effect of The Direct Pathway

Answer 21

increase the activity of the thalamus and the consequent excitation of the cerebral cortex

Question 22

Net Effect of The Indirect Pathway

Answer 22

decrease the activity of the thalamus and the consequent excitation of the cerebral cortex

Question 23

Direct Pathway Summary

Answer 23

cortex sends info to striatum

striatum sends info to globus pallidus

(globus pallidus is an inhibitor, striatum inhibits the globus pallidus, inhibits an inhibitor)

increases activity in thalamus

increases activity in cortex

Question 24

Indirect Pathway Summary

Answer 24

cortex sends info to striatum

striatum sends info to globus pallidus

globus pallidus inhibits the subthalamic nucleus

reactivates the globus pallidus

inhibits the thalamus

inhibits the activation of the cortex

Question 25

What is the significance of dopamine?

Answer 25

substantia nigra sends constant stream of dopamine to striatum, keeps striatum ready to respond to cortex Direct Pathway= without dopamine, striatum wouldn't be able to respond when cortex is ready to go, would be frozen since direct pathway is responsible for initiating movement

Question 26

List 4 functions of the cerebellum.

Answer 26

* The Cerebellum maintains proper posture and balance and is active in learning and performing rapid, coordinated, and highly skilled movements. * The cerebellum monitors intentions for movement by receiving information from the motor cortex via the pontine nuclei (motor cortex to pons, GM in the pons to cerebellum). * The cerebellum monitors actual movement by receiving information from proprioceptors in joints and muscles that reveals what is actually happening (spinocerebellar tract). * The cerebellum compares the command signals with sensory information and if there is a discrepancy between intended and actual movement, the cerebellum sends out corrective feedback to upper motor neurons.

Question 27

Which side of the body does the cerebellum influence?

Answer 27

**IMPORTANT - Each cerebellar hemisphere influences movements on the ipsilateral (same) half of the body. sends info to contralateral side, but is sent back to ipsilateral side (crosses twice)

Question 28

How many peduncles connect the cerebellum with the brain stem? What are they?

Answer 28

3 * Superior cerebellar peduncle: main outflow, fibers project to motor thalamus then to cortex * Middle cerebellar peduncle: fibers enter from the pons * Inferior cerebellar peduncle: fibers enter from the medulla and spinal cord

Question 29

Which of the peduncles is (are) afferent, and which is (are) efferent relative to the cerebellum?

Answer 29

Afferent -middle cerebellar peduncle -inferior cerebellar peduncle Efferent -superior cerebellar peduncle

Question 30

Cerebellum vs Basal Nuclei

Answer 30

* The Basal Nuclei choose the motor behavior * The Cerebellum monitors and corrects the motor behavior ex- basal nuclei tell you to close the door, cerebellum asks "how hard"

Question 31

Information comes through the ___ and ___ ___ and is processed in the ___ ___.

Answer 31

Information comes through the middle and inferior peduncles and is processed in the cerebellar cortex. the cerebellar cortex has 3 main layers, including the purkinje cell layer Purkinje Cells are the primary output neurons of the cerebellar cortex. These axons descend through the cerebellar white matter (the myelinated axons) and synapse/project to the deep cerebellar nuclei, which are located in the gray matter deep within the cerebellum. The deep cerebellar nuclei send information to the spinal cord, brainstem and thalamus via the superior cerebellar peduncle.

Question 32

Define homeostasis.

Answer 32

maintenance of a dynamically stable state within a system by means ofinternal regulatory processes that counteract external disturbances of the equilibrium

Question 33

Describe the differences and/or similarities between the autonomic nervous system and the somatic nervous system with respect to: number of neurons types of synapses target organs

Answer 33

somatic NS: * 1-neuron pathway (alpha motor neuron sends its axons out to a peripheral nerve/lower motor neuron, peripheral nerve/lower motor neuron makes contact with neuromuscular junction) -alpha motor neuron directly to target * innervates skeletal muscle * Neuromuscular junction synapses (AMNs send axons out using ACh and synapse via neuromuscular junctions) autonomic NS: * 2-neuron pathway (autonomic neuron in the intermediolateral column of the SC or brainstem nuclei , sends axons through ventral rootlets, synapses in autonomic ganglion) **ganglionic neuron is the one that contacts the target, rather than neuromuscular junction in somatic NS -autonomic neuron in the intermediolateral column of the SC or brainstem nuclei, to a ganglion, to target * innervates smooth muscle, cardiac muscle, and glands * Boutons en passant synapses (have lumps of neurotransmitters along the axons that are released when the axons are depolarized, rather than discrete firing and contraction, has wave of depolarization and wave of contraction)

Question 34

Compare and contrast the parasympathetic and sympathetic nervous systems with regard to: location of preganglionic neurons location of the ganglia length of pre and post ganglionic fibers neurotransmitters

Answer 34

sympathetic NS: -thoracolumbar (T1-L2), sympathetic preganglionic neurons are found in the intermediolateral cell column of the spinal cord * Short preganglionic fibers, cuz they're close to the vertebral column (ACh) * Long postganglionic fibers, cuz they're farther from their target (NE) * Whole body distribution parasympathetic NS: -craniosacral (CNs III, VII, IX, and X...S2-4), S2-4 are found in the intermediolateral cell column of the spinal cord * Parasympathetic ganglia are near or within their target organs * Long preganglionic fibers, found in brain stem and spinal cord (ACh) * Short postganglionic fibers (ACh) * Restricted distribution

Question 35

Compare and contrast the parasympathetic and sympathetic nervous systems with regard to their effects on: heart rate respiratory rate pupil constriction/dilation blood vessel constriction/dilation gut motility sweating

Answer 35

sympathetic NS: (fight or flight) increased heart rate increased respiratory rate pupil dilation blood vessel constriction (increases blood pressure) gut motility decreases sweating increases parasympathetic NS: (relaxed state) heart rate decreases respiratory rate decreases pupil constriction blood vessel dilation (blood pressure decreases) gut motility increases sweating decreases

Question 36

What 3 parts of the CNS contribute the most to autonomic function?

Answer 36

hypothalamus, brainstem (medulla and pons), and spinal cord

Question 37

Which cranial nerves have a parasympathetic component, and what are their target organs/muscles/glands?

Answer 37

CN III: ciliary muscle, sphincter pupillae CN VII: salivary glands, nasal/oral mucosa, lacrimal glands CN IX: parotid gland CN X: thoracic & abdominal viscera, innervates gut to the splenic flexure