This document summarizes the major motor pathways in the brain and spinal cord. It describes the pyramidal tract, which originates in the motor cortex and is responsible for voluntary muscle control. The pyramidal tract includes the corticospinal and corticobulbar tracts. It also describes the extrapyramidal tracts that originate in the brainstem and are responsible for involuntary muscle control, including balance, posture and locomotion. Each tract is described in terms of its origin, pathway through the central nervous system, functions and clinical significance.

1. BY DR KUSHWAH
PRPFESSOR OF ANATOMY
NSCB MC JABALPUR MP

2.  pathways by which motor signals are sent from the
brain to lower motor neurones. The lower motor
neurones then directly innervate muscles to produce
movement.
 Pyramidal tracts – originate in the cerebral cortex,
carrying motor fibres to the spinal cord and brain
stem. They are responsible for the voluntary control of
the musculature of the body and face.
 Extrapyramidal tracts – originate in the brain stem,
carrying motor fibres to the spinal cord. They are
responsible for the involuntary and automatic control
of all musculature(muscle tone, balance, posture and
locomotion)

3.  There are no synapses within the descending
pathways. At the termination of the descending tracts,
the neurones synapse with a lower motor neurone.
Thus, all the neurones within the descending motor
system are classed as upper motor neurones. Their
cell bodies are found in the cerebral cortex or the brain
stem, with their axons remaining within the CNS.


15.  Pyramidal Tract
 The pyramidal tracts derive their name from
the medullary pyramids of the medulla oblongata,
which they pass through.
 These pathways are responsible for the voluntary
control of the musculature of the body and face.
 Functionally, these tracts can be subdivided into two:
 Corticospinal tracts – supplies the musculature of
the body.
 Corticobulbar /corticonuclear tracts – supplies the
musculature of the head and neck.

16.  Corticospinal Tracts
 The corticospinal tracts begin in the cerebral cortex, from
 Primary motor cortex 4
 Premotor cortex 6
 Supplementary motor area 8
 They also receive nerve fibres from the somatosensory
area, which play a role in regulating the activity of
the ascending tracts.
 After originating from the cortex, the neurones converge
(corona radiata) and descend through the internal
capsule (a white matter pathway, located between the
thalamus and the basal ganglia). This is clinically
important, as the internal capsule is particularly
susceptible to compression from haemorrhagic bleeds,
known as a capsular stroke.

17.  After the internal capsule, the neurones pass through
the crus cerebri of the midbrain, the pons and into
the medulla pyramids.
 In the most inferior (caudal) part of the medulla, the
tract divides into two:
 The fibres within the lateral corticospinal
tract decussate (cross over to the other side of the
CNS). They then descend into the spinal cord,
terminating in the ventral horn (at all segmental
levels). From the ventral horn, the lower motor
neurones go on to supply the muscles of the body.
 The anterior corticospinal tract remains ipsilateral,
descending into the spinal cord. They then decussate
and terminate in the ventral horn of
the cervical and upper thoracic segmental levels

18.  Corticobulbar tracts arise from the lateral aspect of
the primary motor cortex. They receive the same inputs
as the corticospinal tracts. The fibres converge and pass
through the internal capsule to the brainstem.
 The neurones terminate on the motor nuclei of the cranial
nerves. Here, they synapse with lower motor neurones,
which carry the motor signals to the muscles of
the face and neck.
 Clinically, it is important to understand the organisation of
the corticobulbar fibres. Many of these fibres innervate the
motor neurones bilaterally. For example, fibres from the
left primary motor cortex act as upper motor neurones for
the right and left trochlear nerves. There are a few
exceptions to this rule:

19.  Upper motor neurones for the facial nerve (CN VII)
have a contralateral innervation. This only affects the
muscles in the lower quadrant of the face – below the
eyes.
 Upper motor neurons for the hypoglossal (CN XII)
nerve only provide contralateral innervation.

21.  Corticonulcear/corticobulbar tract is responsible for
influencing the motor nuclei of a number of cranial nerves
including the:
 oculomotor (III)
 trochlear (IV)
 mandibular component of the trigeminal (V3)
 abducens (VI)
 facial (VII)
 glossopharyngeal (IX)
 vagus (X)
 spinal accessory (XI)
 hypoglossal (XII) nerves
 UMNs descending from the cortex to the CN nuclei are
considered part of the corticobulbar tract; whereas LMNs are
considered as part of the CNs themselves, with their cell bodies
in the CN nuclei and their axons projecting to the muscles of
the face, head, and neck.

31.  Extrapyramidal Tracts
 originate in the brainstem, carrying motor fibres to
the spinal cord. responsible for
the involuntary and automatic control of all
musculature, such as muscle tone, balance, posture
and locomotion.
 There are four tracts in total.
The vestibulospinal and reticulospinal tracts do
not decussate, providing ipsilateral innervation.
The rubrospinal and tectospinal tracts do
decussate, and therefore provide contralateral
innervation

33.  Vestibulospinal Tracts
 There are two vestibulospinal pathways; medial and
lateral. They arise from the vestibular nuclei, which
receive input from the organs of balance. The tracts
convey this balance information to the spinal cord,
where it remains ipsilateral.
 Fibres in this pathway
control balance and posture by innervating the ‘anti-
gravity’ muscles (flexors of the arm, and extensors of
the leg), via lower motor neurones.

35.  Reticulospinal Tracts
 The two recticulospinal tracts have differing functions:
 The medial reticulospinal tract arises from
the pons. It facilitates voluntary movements, and
increases muscle tone.
 The lateral reticulospinal tract arises from
the medulla. It inhibits voluntary movements, and
reduces muscle tone.

37.  Rubrospinal Tracts
 The rubrospinal tract originates from the red
nucleus, a midbrain structure. As the fibres emerge,
they decussate (cross over to the other side of the CNS
frorming ventral tegmental decussation), and descend
into the spinal cord. Thus, they have
a contralateral innervation.
 exact function is unclear, but it is thought to play a
role in the fine control of hand movements
(unconscious control of muscle tone and synergy of
movements)

39.  Tectospinal Tracts
 Pathway begins at the superior colliculus of the
midbrain. The superior colliculus is a structure that
receives input from the optic nerves. The neurones
then quickly decussate(dorsal tegmental decussation),
and enter the spinal cord. They terminate at the
cervical levels of the spinal cord.
 The tectospinal tract coordinates movements of the
head in relation to vision stimuli

41.  From hyothalamus to lateral horn of T 1 to L2 spinal
segments (sympathetic outflow) and lateral horn of
S2,3,4 spinal segment (parasympathetic outflow).
 Tract is seen in lateral white columnTS of spinal cord
on medial side of lateral cortico spinal tract

42.  Damage to the fibres of the corticospinal tracts,
anywhere along their course from the cerebral
cortex to the lower end of the spinal cord, can
cause an upper motor neuron syndrome
 A few days after the injury to the upper motor
neurons, a pattern of motor signs and symptoms
appears, including spasticity,hyperactive reflexes, a
loss of the ability to perform fine movements, and
an extensor plantar response known as
the Babinski sign.
 Symptoms generally occur alongside other sensory
problems.

43.  Causes may include disorders such as strokes,cerebral
palsy, subdural hemorrhage, abscesses and tumours,
neurodegenerative diseases such as multiple system
atrophy , inflammation such
as meningitis and multiple sclerosis , and trauma to
the spinal cord, including from slipped discs
 If the corticobulbar tract is damaged on only one
side, then only the lower face will be affected, however
if there is involvement of both the left and right tracts,
then the result is pseudobulbar palsy. This causes
problems with swallowing, speaking, and emotional
lability.
 Severe disabling involuntary movements such
as hemiballismus or severe chorea might exhaust the
patient and become a life threatening situation.

46.  Babinski sign- extension upward of the toes when the
sole of the foot is stroked firmly on the outer side from
the heel to the front; normal in infants under the age
of two years but a sign of brain or spinal cord injury in
older persons.