Lecture 18 and 19: Functional Neuroanatomy

neurolocalization yields a

differential list

functional divisions of the brain

• cerebrum

• diencephalon (thalamus, hypothalamus)

• brainstem (midbrain, pons, medulla)

• cerebellum

• vestibular system

UMN (upper motor neuron)

• located entirely within CNS

• descend from brain to every segment of spinal cord

• imitate voluntary movement

• both excitatory and inhibitory influence on LMN to maintain muscle tone and reflex arcs

LMN (lower motor neuron)

• located in CNS and PNS

• involved with reflex arc (sensory and motor)

• carry out motor function

the upper motor neuron system originates in

• pyramidal system (motor cortex) → corticospinal tracts

• extrapyramidal system (basal nuclei) → rubrospinal tracts

the pyramidal system and extrapyramidal system stimulate or inhibit the neurons that

directly innervate the muscles

responsibilities of UMN system

• initiate/influence voluntary movement

• regulation of posture → maintain muscle tone to oppose gravity, keep reflex arcs in check

gait in UMN system

• mainly from basal nuclei and brainstem

• red nucleus of the midbrain is thought to play the biggest role in gait

what are 22a, 24, 25, and 26 representing?

basal nuclei

what are the 2 red circles representing?

red nucleus of midbrain

what is the top arrow pointing at?

motor cortex

what is the bottom arrow pointing at?

basal nuclei and red nucleus

frontal lobe of cerebrum

motor areas

piriform lobe/cortex of cerebrum

smell → olfactory bulbs

parietal lobe of cerebrum

somatosensory

temporal lobe of cerebrum

hearing and vestibular input

occipital lobe of cerebrum

vision

somatosensory cortex

• important for both brain and spinal diseases

• conscious perception of touch, pain, pressure, temperature

• conscious perception of proprioception

forebrain signs of lesions in the cerebrum

• alterations in behavior or mental status

• walking in circles/pacing

• seizures (most common)

• central blindness (contralateral) → intact PLR

• decrease in facial sensation (contralateral)

• postural reaction deficits (contralateral)

• no gait deficits

• circling, head pressing, compulsive pacing

decrease in facial sensation and postural reaction deficits are involved with

somatosensory cortex in parietal lobe

gait deficits for cerebrum lesions

• usually none!

• fine control/discrimination lost (steps of ladder)

• ± mild ataxia (usually not noticed)

circling signs with lesions in the cerebrum

• usually towards side of lesion

• can also be seen with brainstem/vestibular disease

diencephalon

• chief sensory integrating center of nervous system

• plethora of relay nuclei

• 5 major divisions

what are the 5 major divisions of the diencephalon?

• thalamus

• metathalamus → geniculate nuclei, LGN involved with vision, MGN involved with hearing and balance

• epithalamus

• hypothalamus

• subthalamus

what is the most rostral position of the diencephalon?

ARAS

the reticular formation runs through

the entire brainstem into thalamus

ascending reticular activating system (ARAS)

• carries afferents going to thalamic nuclei

• awakens and prepares the cerebral cortex

• switchboard → accepts what is needed for consciousness and rejects what is irrelevant

• influenced by sleep centers in pons and medulla

hypothalamus (in diencephalon)

• functions as higher center for regulation of visceral motor activity → home office of ANS, functions with voluntary control

• influenced by olfaction and limbic systems

• many important nuclei → superoptic and paraventricular

what hormone is highly associated with superoptic nuclei?

ADH

what hormone is highly associated with paraventricular nuclei?

oxytocin

clinical signs of diencephalon issues

• signs of dysfunction often similar to cerebral

• they may circle to either side

• visual impairment

• possibly endocrine dysfunction

• behavioral problems

• temperature regulation

• non-specific pain

midbrain

• ARAS → maintains consciousness, alerts the cerebral cortex

• red nucleus → axons cross immediately and descend as rubrospinal tract

what is the major motor component of the midbrain?

red nucleus

nerves associated with midbrain

• oculomotor (III) nuclei → motor (GSE) to extraocular muscles, parasympathetic (GVE) to constrict pupil

• trochlear (IV) nuclei

• tectotegmentospinal tract → sympathetic innervation to the eye (dilate), possibly hypothalamus

clinical signs of midbrain lesions

• typically cause severe gait abnormalities → UMN paresis and ataxia

• abnormal mentation → disruption of ARAS, stupor or coma

• decerebrate rigidity → massive release of UMN inhibition

structures of the pons

• more of the ARAS

• motor nucleus of trigeminal (CN V) nerve

• sensory nuclei of trigeminal (CN V)

• pontine micturition center (PMC)

clinical signs of pons lesions

• marked mentation change

• gait disturbance

• dysfunction of CN V

• possibly dysuria

medulla contains

nuclei of CN VI through XII → vestibular nuclei

reticular formation of medulla

• ARAS

• respiratory centers

• autonomic control of HR and BP

• sleep centers

• medullary reticulospinal tract (UMN tract)

• nucleus ambiguus → larynx, pharynx, and esophagus

medial longitudinal fasciculus (MLF)

connects CN III, IV, and VI + vestibular nuclei to coordinate conjugate eye movements and head/eye position

clinical signs of medulla lesions

• alterations in consciousness

• autonomic dysfunction → abnormal HR, BP

• respiratory problems (the UMN for respirations) → cheyne-stokes respirations

• UMN paresis

cerebellum is anatomically made up of

• cerebellar cortex (arbor vitae)

• medulla

• nuclei

the cerebellum is functionally made up of

• cerebrocerebellum → cerebellar hemispheres and dentate nucleus

• spinocerebellum → vermis, fastigial, and interposital nuclei

• vestibulocerebellum → flocculonodular lobe and fastigial nucleus

cerebellum does not initiate

movement

cerebellum regulates

rate, range, and force of movements

clinical signs of cerebellum lesions

• intention tremor

• truncal sway

• cerebellar ataxia and hypermetria

• disequilibrium

• ipsilateral menace deficits

cerebellum lesions subject to congenital diseases

• hypoplasia

• abiotrophy

spinal cord motor section

UMN tracts descend in white matter to synapse on the LMN in the gray matter

UMN that facilitate to flexors =

walking → corticospinal, rubrospinal, medullary reticulospinal

UMN that facilitate to extensors =

standing → vestibulospinal, pontine reticulospinal

spinal cord sensory section

ascending fibers for proprioception and pain are located mainly dorsally and laterally

lesions on the sensory spinal cord are usually affecting

both the ascending GP and the descending UMN for a combination of proprioceptive ataxia and paresis

interference with the UMN influence over the LMN results in

release of muscle inhibition

what is this showing?

ascending tracts

what is this showing?

descending tracts

what are the clinically important spinal cord LMNs?

• limbs, bladder, sphincters

• C6-T2 and L4-S3 segments

damage to the spinal cord LMN will cause

• paresis or plegia

• depressed or absent spinal reflexes

• decreased muscle tone

pertinent anatomy of C1-C5

• descending UMN tracts to all 4 limbs

• ascending GP and nociception from all 4 limbs

• origins of the phrenic nerve (C5-C7)

• descending sympathetic fibers to the eye

lesions at C1-C5

• gait affected in all 4 limbs

• UMN signs to all 4 limbs → increased extensor tone, normal to hyperactive spinal reflexes

• delayed postural reactions in all 4

• UMN bladder

• rarely respiratory difficulty

• rarely Horner’s syndrome

pertinent anatomy of C6-T2 (brachial plexus)

• descending UMN tracts to all 4 limbs

• ascending GP and nociception from all 4 limbs

• LMNs to the front limb

• pre-ganglionic sympathetic fibers

• LMN of phrenic nerve

• lateral thoracic nerve

lesions at C6-T2

• gait affected in all 4 limbs

• delayed postural reactions in all 4

• LMN signs to forelimbs → decreased muscle tone and reflexes in forelimbs

• UMN to hindlimbs → normal to hyperactive reflexes in rear

• UMN bladder

pertinent anatomy of T3-L3

• descending UMN to rear limbs only

• ascending GP and nociception from rear limbs

• hypogastric nerve = L1-L4

• border cells

border cells

• located in dorsolateral border of the ventral gray column in lumbar segments

• provide tonic inhibitory influence on muscle of the forelimbs → schiff-sherrington phenomenon (posture)

what is this showing?

schiff-sherrington phenomenon

lesions at T3-L3

• gait affected in hind limbs only

• normal postural reactions and reflexes in forelimbs

• UMN to hindlimbs → normal to hyperactive reflexes in hindlimbs, possible crossed extensor reflex

• delayed postural reactions in hindlimbs

• UMN bladder/sphincter

• possible schiff-sherrington

pertinent anatomy of L4-S3 (lumbosacral plexus)

• UMN to the rear limbs only

• GP and nociception from rear limbs only

• LMN to the rear limb

• L4-L6 = femoral nerve

• L6-S1 = sciatic nerve

• S1-S3 = pudendal nerve

• S1-S3 = pelvic nerve

lesions at L4-S3

• gait affected in hindlimbs only

• normal postural reactions and reflexes in forelimbs

• LMN signs to hindlimbs → decreased spinal reflexes in hindlimbs, decreased muscle tone in hindlimbs, tail, and anal sphincter

• delayed postural reactions in hindlimbs

• LMN bladder/sphincter

S1-S3 (pelvic plexus, pudendal nerve)

• forelimbs normal

• gait may be normal

• posture could be normal or only slightly plantigrade in hindlimbs

• LMN anal sphincter

• LMN bladder

caudal nerves (Cd1-5)

• LMN tail

• bladder should be normal

• anal tone should be normal