Spinal Cord, Motor Cortex, Cerebellum Week 4 Flashcards
What is the spinal cord a-motor neuron?
it is the final common pathway of motor control
receives input form local circuit neurons withing the spinal cord and directly from the brainstem and motor cortex.
what do the cerebellum and basal ganglia do
basal nuclei - assists initiation and termination of movement
cerebellum - assists posture and movement coordination by detecting error signals.
What does the thalamus do
the gateway for cerebellar and basal nuclei input to the cerebral cortex
the spinal cord
- a neural highway, info is sent to and from the brain and body vis the spinal cord.
There are 31 pairs of spinal nerves
- 8 cervical
-12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
each spinal nerve constits of a ventral (motor) and DORSAL (SENSORY) root
What are grey and white matter?
grey matter - where the cell bodies are located
White matter - myelinated, where the tracts are.
What are the descending fibre systems to the spinal cord?
- corticospinal
- rubrospinal
- reticuospinal
-vestibulospinal
what systems are lateral descending tracts
corticospinal and rubrospinal
what systems are medial descending tracks?
reticulospinal and vestibulospinal
what is somatotopy?
the point for point reference of part of the body in the central nervous system
flexors - medial
extensors - lateral
corticospinal track
- largest descending tract.
- also known as the pyramidal tract
- responsible for voluntary control of movement
contains direct and indirect connections to motor neurons
Direct pathways constrain lateral and anterior/ventral aspects
- 90% of corticospinal pathways are lateral (crossed)
- pyramidal decussation is why the brain controls the contralateral side of the body.
Indirect connections are known as corticobullar tracts.
lateral corticospinal tract
- projects from the motor cortex (precentral gyrus) to the spinal cord
- upper motor neuron descends through the cerebral peduncles in the midbrain
- decussates at the base of the medullary pyramids
- descends through the lateral corticospinal tract.
- a-motor neuron (or lower motor neuron|) innervates skeletal muscle in distal parts of the limbs such as muscles of the hand or lower leg/.
anterior/ventral corticospinal tract
- projects from the motor cortex to spinal cord
-upper motor neuron descends through the cerebral peduncles in the midbrain - does not decussate in medulla
- a - motor neuron (lower motor neuron) innervattes skeletal muscles in trunk and spine such as upper arm or upper leg.
corticospinal tract - differences between species and dexterity
in higher animals, there are more direct connections to spinal motor neurons
- corticospinal tract is an evolutionary
- correlates with manual dexterity.
What is the Babinski sign?
it is a diagnostic of a lesion to the corticospinal tract
- characterised by abnormal plantar response
how do you stimulate the corticospinal tract
by using magnetic or electrical stimulation.
- magnetic stimulation has many applications . assesses integrity of corticospinal tract. fist demonstrated by Anthony barker.
corticobullar tract
- Corticobulbar tract forms connections from the motor cortex
to brainstem
o The corticobulbar tract is a relay to the brainstem
o Terminates mainly on interneurons
o Importance in volitional control of breathing - Upper motor neuron projects from cerebral cortex to
brainstem (pons and medulla) via cerebral peduncles and
innervates interneurons or cranial nerves - Cranial nerves are lower motor neurons and include:
o CN VII from pons (facial, facial expression)
o CN XII from medulla (hypoglossal, tongue) - Interneurons innervate the reticular formation
o Project to various sites involved in somatic, autonomic,
sensory/neuromodulatory functions
rubrospinal tract
- The rubrospinal tract originates in the red nucleus
- The red nucleus is a spherical collection of cell bodies in
the midbrain (rostral to pons)
o Highly vascularised
o Large input from cerebellum and primary motor cortex - Primarily involved in activation of flexor motor neurons
rebrospinal tract part 2
- Axons originating from the red nucleus cross the midline
of the ventral midbrain (ventral tegmental
decussation) - Fibres terminate on interneurons that project to the
ventral horn - Primary function is voluntary control of muscle
o Stimulation of red nucleus produces contralateral flexion
and inhibition of extension
o Also involved in compensation.
rubrospinal tract : compensation
- The rubrospinal tract can compensate for damage to the
corticospinal tract - Lawrence & Kuypers (1968) surgically severed corticospinal
tract in monkeys
o Image A (left) shows normal grasping function
o Movements were significantly altered immediately after lesion
o Improvements were rapid and reached near identical function
after a few weeks (image B)
o Only remaining deficit was the inability to use individual fingers
o Note the ability to pick up food between finger and thumb on
left but not on the right
o Corticospinal and rubrospinal tracts form the lateral
descending system and are primarily involved in voluntary
control of human movement
reticulospinal tract
Originates in the brainstem reticular formation
* Reticular formation is a complex network of
brainstem nuclei and poorly anatomically defined
* Reticular formation coordinates many body
functions necessary for survival
* Reticulospinal tracts include:
o Lateral tracts (medullary)
o Medial tracts (pontine)
* Projects to somatic (e.g., respiratory muscle) and
autonomic (e.g., heart and kidneys) neurons
reticulospinal tract : mediall versus lateral
Medial (or pontine) reticulospinal tract arises
from the pons
o Projects ipsilaterally to entire spinal cord
o Facilitate extensor spinal reflexes
* Lateral (or medullary) reticulospinal tract
arises from the medulla
o Projects bilaterally to entire spinal cord
o Suppresses extensor activity
* Unlike other descending tracts, there is no
somatotopic arrangement
vestibulospinal tract
Originates in the vestibular nuclei in the pons-medulla
junction
o Vestibular nuclei receives input from CN VIII
(vestibulocochlear nerve)
o CN VIII arises from the inner ear (otolith organs)
* Lateral and medial tracts
* Vestibulospinal information contracts and relaxes muscles
to maintain balance, posture and muscle tone when the
head moves
o Descending tracts innervate neck muscles
o Ascending tracts innervate oculomotor nuclei to control eye
movements
vestibulospinal tract : medial versus lateral
Medial vestibulospinal tract
o Arises from ipsilateral and contralateral medial vestibular
nuclei at the pons-medulla junction
o Descends in the ventral funiculus of the cervical spinal cord
and terminates in the ipsilateral ventral horn
* Lateral vestibulospinal tract
o Arises from neurons of the lateral vestibular nucleus at the
pons-medulla junction
o Descends the entire length of the spinal cord
o Receives inhibitory inputs from the cerebellum
* Both tracts produce excitation of extensors and
inhibition of flexors
* Main functions are to control the muscles that maintain
upright posture and balance
what is the primary motor cortex also known as?
M1 or Broadmann’s area 4.
- origin of the corticospina tract (30% of fibres)
What is somatotopy?
it is the point for point correspondence of an area of the body to a specific region of the central nervous system.
what is the Jacksonian march?
observed the pattern of focal epileptic seziures that spread to different parts of the body in a fixed temporal pattern varying from patient to patient.
Jackson speculated that the progression, or march, was due to propagation of activity along the central sulcus.
- starts in hand , spreads to arm and nexk.
who developed mapping of the cortex?
sir David ferrier
developments un anaesthesia allowed for stimulation of animal brains during surgery. Electrical stimulation of sections of the cortex evoked movements of contralateral body parts. identified 15 distinct sections of the cortex that precisely control movement. Removal of the cortical sections resulted in no movement.
What is the Montreal procedure?
Penfield
- treated patients with severe epilepsy by destroying nerve cells in the brain where the seizures originated.
- before operating, penfeild stimulated in the brain with electrical probes while the patient was conscious and observed the response , enabling more accurate surgery.
- also allowed penfield to map the sensory and motor cortices.
what are the methods used to record the motor cortex
1) EEG - indirect
2) ECOG - electrodes onto surface of the brain
3) microelectrodes - implanted directly onto the brain tissue
what is EEG
electroencephalography uses electrodes plaed on the skull to record brain activity under the recording site
- indirect method
