L11 - Motor Neurons, Corticospinal tract and Corticobrainstem tract

upper motor neuron (UMN)

location in spnial cord and brainstem

function

signs of inj

location

• primary motor cortex or brainstem

• pathways that originate from …

  • cortex = corticospinal tract, corticobrainstem tract

  • brainstem = vestibulospinal, reticulospinal, rubrospinal ,tectospinak

travel on cortico spinal tract

corticospinal tract

• descending

1) internal capsule

2) mid-brain (cerebral peduncle)

3) pons (cerebral peduncle)

4) upper and lower medulla pyramids (cerebral peduncle)

5a) 95% cross in pyramidal decessation before spinal cord enterance (enter on opp side of body from where they originated) (lateral corticospinal tract)

5b) 10% continue into spinal cord on same side of body (anterior corticospinal tract)

5b.2) anterior corticospinal tract synapse on LMN on level of spinal cord and enter

function:

• voluntary control of precise mvm of distal muscles of limbs (lateral CST)

• control of less precise mvm of proximal muscles of limbs and trunk (medial CST)

corticobrainstem

descending

1) primary motor cortex

2) internal capsule

3) terminate at location of cranial nerve

function:

serves as UMN to all motor cranical nerves

lower motor neuron (LMN)

location in spnial cord and brainstem

function

signs of inj

location

• CNS

• anterior horn of spinal cord (then go out through peripheral nerves)

• brainstem (cranial nerves w/ motor output) (axons then go through cranial nerves)

function

• convey signals to skeletal muscles

types

alpha

• large cell bodies

• large myelinated axons

• project to extrafusal muscle fibres (muscles that do mvm)

gamma

• medium sized

• project to intrafusal muscle fibres in muscle spindles (regulate stretch)

Identify the function of the neurotransmitter ACH at the neuromuscular junction.

• motor unit = 1 alpha LMN and all the muscle fibres it innervates

  • when one neuron fibres of all connected muscle cells contract due to release of Ach

Describe the structure and function of the motor unit and the relationship between cortical tissue with (i) the intricacy of movements of that part of the body and (ii) the size of motor units.

motor unit:

• motor unit = 1 alpha LMN and all the muscle fibres it innervates

  • when one neuron fibres of all connected muscle cells contract due to release of Ach

• strength of muscle contract

  • large motor unit = larger fibres for gross control

  • small motor unit = smaller fibres for precise control

• inverse rel. with motor homunculus (aka less representation in cortex = greater value of feature)

  • larger cortical tissues (more UMN cell bodies) = smaller motor unit

  • smaller cortical tissue (less UMN cell bodies

Describe the systems involved in the execution of voluntary movement including speech production.

The corticobulbar tracts, originating from the motor cortex, descend via the internal capsule to brainstem motor nuclei, controlling facial, head, and neck muscles.

Describe the structure and function of the tracts controlling fractionated movements, gross and postural and movements of the face

tectospinal tract

• reflexive head mvm

• respond to visual or auditory input

vestibulospinal tract

• arises from vestiublar nucleus to help control neck and upper back muscles

• aid balance

rubrospinal tract

• arise from red nucleus in midbrain

• minimal cont. to upper limb extensor muscles

Apply an understanding of the function of the functioning of the primary motor and motor planning areas of the cortex to predict likely impairments, changes to activity and participation following a lesion in this area in conditions such as stroke, tumour and MS.

UMN dysfunction

decerebrate rigidity

• sevre midbrain lesions

• extension of limbs, trunk, internation rotatio of upper limbs and plantar flexion

decorticate rigidity

• sevre lesions above midbrain

• rigid flexed UL, extended neck and lower limbs and plantar flexion

Describe reflexes and identify pathologies that would result in change to this reflex

reflex = involuntary motor response to an external stimulus

• facilitated by descending pathways from cortex and brainstem

abnormal reflexes

babinki sign

• extension of big toe