Neurophysiology (2)
Abbas A. Abbas Shawka
Medical student / 2nd grade

Subjects
•Brain stem
- Medulla oblongata function
- Pons function
- Midbrain function
• Important points about ascending and descending tract
• Lesions of the spinal cord

Medulla oblongata function
• 1- pathway for ascending and descending tracts.
• 2- House of vital centres. The medulla oblongata houses
many important centres, which control the vital functions
of the body:
- Respiratory centres (inspiratory and expiratory) control the
normal rhythmic respiration
- Vasomotor and cardiac centres control the blood pressure
and functions of heart and vascular system
- Deglutition centre controls the pharyngeal and
oesophageal phase of deglutition
- Vomiting centre is responsible for inducing vomiting in
disorders of gastrointestinal tract
- Control the salivary secretion. Superior and inferior salivary
nuclei, located in the medulla, control the salivary
secretion
• 3- contain the cranial nerve nuclei ( IX, X, XI, XII )

Pons function
• 1. Connecting pathway between cerebral cortex and
cerebellum. The pontine nuclei receive corticopontine
fibres and their axons from the middle cerebellar
peduncles, which serve as a connecting pathway between
the cerebral cortex and the cerebellum.
• 2. Pathway for ascending and descending tracts of spinal
• cord and medulla oblongata.
• 3. Houses the nuclei of 5th, 6th, 7th and 8th cranial nerves.
• 4. Joining station for medial lemniscus with fibres of 5th,
7th, 9th and 10th cranial nerves.
• 5. respiratory centers. Contains pneumotaxic and apneustic
centres for regulation of respiration

Midbrain function
• 1- cranial nerves nuclei ( III,IV )
• 2- Control posture through the red nucleus
• 3- Part of the auditory and visual pathway ( superior and
inferior colliculi )
• 4- Pathway for ascending and descending tract
• 5- Contains the substantia nigra which have an important
rule in BG physiology ..

Ascending tracts
SC = Superior colliculus; SO = superior olivary nucleus; Vn =
vestibular nucleus; OL = olivary nucleus; IC = inferior colliculus

PC-ML pathway
• The fibres derived from the
lowest ganglia are situated
most medially; while those
from the highest ganglia are
most lateral. Therefore:
1. Fasciculus gracilis (tract of
Gall), which lies medially, is
composed of fibres from
the coccygeal, sacral,
lumbar and lower thoracic
ganglia and
2. Fasciculus cuneatus (tract
of Burdach), which lies
laterally, consists of fibres
from upper thoracic and
cervical ganglia.

PC-ML pathway function
• 1. Components of sense of touch include:
- Deep touch and pressure
- Fine touch, i.e. epicritic tactile sensations,
- Tactile localization, i.e. ability to localize, exactly the part of
skin touched
- Tactile discrimination, i.e. the ability to recognize as
separate two points on the skin that are touched
simultaneously.
- Stereognosis, i.e. the ability to recognize the shape of
known objects by touch with closed eyes.

DC-ML pathway
• 2. Proprioceptive impulses help in conscious kinaesthetic
sensations, i.e. the sense of position of different parts of
the body under static conditions as well as rate of change
of movement of different parts during body movements.
• 3. Sense of vibrations, i.e. ability to detect rapidly changing
peripheral conditions. This is the ability to perceive the
vibrations conducted to deep tissues through the skin.

Spinothalamic tract
• Traditionally, it has been said
that the anterior
spinothalamic tracts carry
sensations for crude touch and
pressure, while the lateral
tracts carry sensations of pain
and temperature.
• Lissauer's tract ?!
• Fibers of anteriolateral
spinothalamic tract before
decussation may travel up for
1 segment or 2  dorsolateral
spinothalamic tract 
Lissauer's tract

Ascending tracts ending in brain stem
• 1- spinoreticular tract : The fibres of the spinoreticular tract
are the components of ascending reticular activating
system and are concerned with arousing consciousness or
alertness.
• 2- spinotectal tract :- These fibres form alternate route for
conduction of slow pain and are also concerned with
spinovisual reflexes.
• 3- spino-olivary tract :- This tract is concerned with
proprioception.

Spinocerebellar tracts
• The spinocerebellar tracts carry proprioceptive impulses
arising in the lower part of the body to the cerebellum.
• Consist of :-
• 1- Ventral spinocerebellar tract
• 2- Dorsal spinocerebellar tract
• 3- Cuneo-cerebellar tract :- This tract brings the conscious
proprioception impulses from the upper limb. Thus, it may
be regarded as the forelimb equivalent of the dorsal
spinocerebellar tract.
• 4- Rostral spinocerebellar tract :- This pathway is regarded,
functionally, as the forelimb equivalent of the ventral
spinocerebellar tract.

Pyramidal tract function
• The cerebral cortex controls voluntary fine skilled movements of
the body through the corticospinal tracts. Interruption of the
tract anywhere in its course leads to paralysis of the muscles
concerned.
• Note. As the fibres are closely packed in their course through the
internal capsule and brain stem, small lesions here can cause
widespread paralysis.
• The pyramidal tract fibres also send collaterals to other areas of
the motor control systems thus communicating motor command
to the basal ganglia, cerebellum and the brain stem.
• In their course through the brain stem, some of the fibres
(corticonuclear fibres) terminate directly on the motor nuclei of
cranial neurons controlling facial muscles. Since these fibres
perform the same function as pyramidal tracts, they are also
considered part of the pyramidal system.

Extrapyramidal tracts
• 1- Rubrospinal tract :-
- This tract exhibits facilitatory influence on the flexor
muscles and inhibitory influence on the extensor muscles
of the body.
- The red nucleus also receives the corticorubral fibres from
the ipsilateral motor cortex. The corticorubro-spinal tract
thus formed may act as an alternate route of pyramidal
system to exert influence on the lower motor neurons.
- The rubrospinal tract is most important and much better
developed in some animals than in human. In human
beings, the red nucleus is relatively small and the
rubrospinal tract reaches only

Extrapyramidal tracts
• 2- Vestibulospinal tract :-
• Lateral vestibulospinal tract
• Vestibular nucleus receives afferents from the vestibular
apparatus mainly from utricles. This pathway is principally
concerned with adjustment of postural muscles to linear
acceleratory displacements of the body. Lateral
vestibulospinal tract mainly facilitates activity of extensor
muscles and inhibits the activity of flexor muscles in
association with the maintenance of balance.
• Medial vestibulospinal tract
• This part of the vestibular nucleus receives signals from the
vestibular apparatus mainly from the semicircular canals.
Functionally, medial vestibulospinal tract is the donor
connection of medial longitudinal fasciculus. This tract
provides a reflex pathway for movements of head, neck
and eyes in response to the visual and auditory stimuli.

Extrapyramidal tracts
• 3- Reticulospinal tract :-
- The reticular formation of the brain stem receives input
mostly from the motor cortex through the corticoreticular
fibres which accompany the corticospinal tracts.
- Thus the corticoreticulospinal tracts form additional
polysynaptic pathways from the motor cortex to the spinal
cord. These tracts are concerned with control of
movements and maintenance of muscle tone.
- The reticulospinal tracts, probably, also convey autonomic
information from higher centres to the intermediate region
of spinal grey matter and regulate respiration, circulation
and sweating.
- The pontine and medullary reticular nuclei mostly function
antagonistic to each other.

Extrapyramidal tracts
• 4- Tectospinal tract :-
• This tract forms the motor limb of the reflex pathway for
turning the head and moving the arms in response to
visual, hearing or other exteroceptive stimuli.
• 5- Olivospinal tract :-
• Inferior olivary nucleus receives afferent fibres from the
cerebral cortex, corpus striatum, red nucleus and spinal
cord. It influences muscle activity. Probably, it is involved in
the reflex movements arising from the proprioceptors.

Extrapyramidal tracts
• 6- Medial longitudinal fasciculus
- MLF plays an important role in the pathway of ocular
movements.
- Its function can be summarized as:
1. It ensures harmonious movements of the eyes and neck
(head) in response to vestibular stimulation and auditory
stimuli.
2. It facilitates simultaneous movements of the lips and
tongue as in speech.

Descending tracts ending in the brain stem
• Corticonuclear tract
- The nuclei of cranial nerves that supply skeletal muscles
are functionally equivalent to ventral horn cells of the
spinal cord. These are controlled by corticonuclear fibres.
• Cortico-ponto-cerebellar pathway
- This pathway forms the anatomical basis for control of
cerebellar activity of cerebral cortex.

Descending tracts ending in the brain stem
• Other fibres arising from the cerebral cortex end in the
following masses of grey matter of brain stem:
1. Red nucleus (corticorubral fibres),
2. Tectum (corticotectal fibres),
3. Substantia nigra,
4. Inferior olivary nucleus (cortico-olivary fibres) and
5. Reticular formation (corticoreticular fibres).
• The above fibres ultimately form part of extrapyramidal
system.

Complete Transection of the spinal cord
• Common causes of complete transection are: Gunshot
injuries, Dislocation of spine and Occlusion of the blood
vessels.
• Three stages !!
1. Stage of Spinal cord shock
2. Stage of reflex activity
3. Stage of reflex failure

Stage of spinal shock
• Spinal shock refers to the cessation of all the functions and
activity below the level of the section immediately after
injury.
• complete transection in cervical region (above C5) is
usually fatal, because of cutting of connections between
respiratory centre and respiratory muscles leading to
paralysis of respiratory muscles.
• Cause of stage of spinal shock (also called stage of
flaccidity) is not known, but it is related to cessation of
tonic neuronal discharge from upper brain stem or
supraspinal pathway

Stage of spinal shock
• 1. Motor effects include:
- Paralysis of the muscles occurs below the level of
section.transection between cervical and lumbosacral
enlargementsit is called paraplegia and when all the four
limbs are affected (transection below C5) it is called
quadriplegia.
- Loss of tone occurs in the paralysed muscles. So the
muscles become atonic or flaccid. This is called state of
flaccid paralysis.
- Areflexia, i.e. all the superficial and deep reflexes are
markedly decreased or lost.
• 2. Sensory effects. All the sensations are lost below the
level of transections.

Stage of spinal shock
• 3. Vasomotor effects. The sympathetic vasoconstrictor fibres
leave the spinal cord between T1 and L2.
• Below L2 : No or minimal drop in BP
• At T1 level : sharp dropping in BP due to loss of sympathy.
Discharge.
• 4- Visceral effects produced are:
- Urinary bladder is paralysed, however, the sphincter vesicae
regains tone early leading to retention of urine.
- Rectum is also paralysed. Since the bowels become hypotonic
there occurs constipation.
- Penis becomes flaccid and erection becomes impossible.
- When lesion is at T6 level, all impulses coming in from the
abdominal viscera are cut off from the brain; therefore, gripping
sensations or distension of viscera are not appreciated.

Stage of reflex activity
• If the patient survives the stage of spinal shock, gradually
he/she gains few functions. That is why this is also called
stage of recovery.
1. Smooth muscles regain functional activity first of all.
2. Sympathetic tone of the blood vessels is regained.
3. Skeletal muscle tone then recovers slowly after 3–4 weeks.
4. Reflex activity begins to return after few weeks of recovery of
muscle tone.

Stage of reflex failure
• The failure of reflex activity may occur when general
condition of the patient starts deteriorating due to
malnutrition, Infections or toxaemia

Incomplete Transection of the spinal cord
• Stage of spinal shock = the same as in complete
transection
• Stage of reflex activity
• 1. Tone appears in extensor muscles first
• 2. Extensor reflexes (stretch reflexes) return first
• 3. Mass reflex is not elicited
• Stage of reflex failure = the same as in complete
transection

(BROWN-SEQUARD SYNDROME)
• Hemisection of the spinal cord
1. there is paralysis and loss of
touch and kinaesthetic sense
below the level of the lesion
on the same side (lateral
corticospinal tract and
posterior column
interruption).
2. loss of pain and temperature
sensation on the opposite side
(because of interruption of
the crossed anterolateral
tract).
hemisection
at T11

LMNL
• LMNL refers to the involvement of neurons (α and γ) of anterior
horn of spinal cord and neurons of cranial nerve nuclei.
• LMN paralysis is typically observed in poliomyelitis, when the
polio virus selectively affects the lower motor neurons of spinal
cord and brain stem.
• Usually a single or individual muscle is affected.
• Flaccid paralysis of the involved muscle as muscle tone is lost
due to involvement of stretch reflex arc.
• Muscle power is lost and ultimately muscles degenerate and
undergo wasting due to disuse (disuse atrophy).
• Areflexia, i.e. all the superficial as well as deep reflexes are lost.
• Babinski’s sign is negative, i.e. on stroking the outer edge of sole
of the foot with firm tactile stimulus there occurs plantar flexion
(downward movement). It is called flexor response (withdrawal
reflex) and is considered a normal response.
• Clonus is absent.
• Clasp knife reflex is absent.

UMNL
• UMNL refers to the involvement of motor neurons that
influence the activity of LMN of spinal cord or cranial nerve
nuclei located in brain stem. Thus in UMNL the pyramidal
and extrapyramidal descending tracts are involved.
• UMN paralysis occurs commonly in vascular accidents or
space occupying lesions.
• Usually a group of muscles are affected.
• Spastic paralysis of the involved muscles as the inhibitory
higher control is lost and stretch reflex arc is intact.
• No degeneration and wasting of muscles as they are
constantly involved in reflex activity (though the voluntary
movements are lost).
• Superficial reflexes {abdominal, cremasteric, anal are lost
but deep reflexes are exaggerated (because of increased
gamma-motor discharge)}.

UMNL
• Babinski’s sign is positive, i.e. on stroking the outer edge of the
sole of the foot with firm stimulus, there occurs dorsiflexion of
the great toe and fanning out (abduction) of small toes. It is also
called extensor response. Positive Babinski’s sign indicates
involvement of corticospinal tract. In normal infants, this sign is
positive prior to myelination of the corticospinal tract (i.e. below
1 year of age).
• Clonus is present. It refers to a sustained series of rhythmic
muscle jerks when a quick stretch is applied to a tendon. Ankle
clonus is usually observed in UMNL by a sudden dorsiflexion of
the foot.
• Clasp knife reflex is present, i.e. muscular resistance to passive
movement is exaggerated, this resistance is strong at the
beginning of movement, but yields suddenly in a clasp knife
fashion as more force against resistance is applied. The initial
resistance is offered because of the stretch reflex developed in
extensor muscles, e.g. triceps of the elbow. The sudden relax of
resistance is due to the activation of inverse stretch reflex.

Thank You