neuro unit 2

corticospinal tract - origin

medial and superior aspects of the primary motor cortex M1, supplementary motor cortex, sensory cortex fibers for feedback loop

corticospinal tract - course

medial and superior aspects of M1, corona radiata, internal capsule, cerebral peduncle in midbrain, pons, medullary pyramids

corticospinal tract - termination

spinal cord

corticospinal tract - percentages of decussation

80% cross over, 20% stay ipsilateral

corticobulbar tract - origin

lateral aspects of primary motor cortex, supplementary/premotor cortex, sensory cortex fibers for feedback

corticobulbar tract - course

lateral aspects of M1, corona radiata, internal capsule, cerebral peduncle in midbrain, pons, medulla

corticobulbar tract - termination

ipsilateral and contralateral fibers terminate at nuclei of CN 5, 7, 9, 10, 11, 12

primary motor cortex origins for corticospinal/corticobulbar

corticospinal: medial and superior aspects of M1

corticobulbar: lateral aspects of M1

motor homunculus takaway

face areas for cranial nerves are lateral, limbs and trunk are represented medial/superior

corticostriate fibers - origin

dif areas of cerebral cortex (mostly frontal and parietal) to basal ganglia (caudate nucleus and putamen)

corticostriate fibers - function

part of modulation network, supports vocal imitation

corticothalamic fibers

bi-directional connection between sensory cortices and thalamus

corticopontocerebellar fibers - function

critical part of feedback/feed forward loop for movement tracking and learning

corticoreticular fibers - course

frontal lobe and limbic system to reticular system in the brainstem

corticopontocerebellar fibers - course

info from all lobes to cerebellum via the pons

corticoreticular fibers - function

supports all background function, regulates reflexes in a social and cultural context

tectospinal tract - course

superior colliculi in midbrain to cervical areas of the spinal cord

tectospinal tract - function

supports motor function of the neck muscles, rotation of the head to visual stimuli, works with CN 11 which actually carries muscle contraction signals

rubrospinal tract - course

from red nucleus in the midbrain to all levels of the spinal cord

rubrospinal tract - function

activation and tone of flexor muscles, inhibition of extensor muscles

vestibulospinal tract - course

from vestibular nuclei in pons to spinal cord

vestibulospinal tract - function

balance and position in space, stabilizing head

pontine and medullary reticulospinal tracts - course

from pons/medulla to spinal cord

pontine and medullary reticulospinal tracts - function

excitation of extensor muscles, autonomic info that influences sympathetic functions (pupil dilation, sweating, body temp)

spinal nerves pairs

31 pairs

head, shoulder, arms, neck, diaphragm innervation

C1-C8

diaphragm innervation

C3-C5

intercostal, upper back, abdomen innervation

T1-T12

cerebral peduncle location

midbrain

internal capsule

between thalamus and basal ganglia

corticobulbar tract - site of decussation

begin to decussate at brainstem levels before reaching the nuclei

corticospinal tract - site of decussation

pyramids in medulla

4 ascending tracts

dorsal column via medial lemniscus, spinothalamic, spinocerebellar, cerebellothalamic

significance of corticoreticular fibers act as a vital bridge linking limbic system to brainstem motor networks - mechanism and 2 functions

enabling genuine emotional states to bypass voluntary motor tracts to drive spontaneous facial expressions and defensive posture

progressive maturation of corticoreticular fibers

progressive maturation of these top-down fibers suppresses primitive infant reflexes, a critical neurological step for developing proper emotional regulation and adaptive social behaviors

flexor vs extensor control

activation of flexors = rubrospinal, activation of extensors = pontine and medullary reticulospinal tracts

parotid gland

salivary gland near ears

UMN vs LMN injuries

above CN nuclei is a upper motor neuron injury,

below CN nuclei is a lower motor neuron injury

typical lower motor neuron injury to CN

loss of muscle tone

cranial nerve neuron course

upper motor neuron course (M1 to cranial nerve nucleus in brainstem) to lower motor neuron course (CN nucleus in brainstem to part of body innervated)

sensory only CNs

8 vestibulocochlear

motor only CNs

11 spinal accessory, 12 hypoglossal

taste function

anterior 2/3 of tongue by CN 7 facial

posterior 1/3 of tongue by CN 9 glossopharyngeal

mixed CNs

5 trigeminal

7 facial

9 glossopharyngeal

10 vagus

CN nuclei in the brainstem

3-4 in midbrain

5-8 in pons

9-12 in medulla

CN 5 trigeminal - motor nucleus

mandibular nerve in the pons

somatic senses

pain, touch, pressure sensation

CN 5 trigeminal - sensory nucleus

spinal trigeminal nucleus

tensor veli palatini

elevates soft palate for all non-nasal sounds

spinal trigeminal nucleus

sensory nucleus of CN 5 trigeminal, gray matter extending from midbrain to pons to medulla to C2

CN 5 trigeminal - inputs

corticobulbar tract, receives 30-40% ipsilateral fibers, contralateral fibers

CN 5 trigeminal - exit

at cerebellar pontine angle and out through openings in the sphenoid bone

lower 1/3 of primary motor area (precentral gyrus) - lateral

focused on face and jaw

CN 5 trigeminal - motor function (5)

• muscles of mastication: masseter, temporalis, medial and lateral pterygoid

• tensor tympani (in middle ear)

• tensor veli palatini (in soft palate)

• anterior belly of digastric (under the chin)

• mylohyoid (under the digastric muscles)

CN 5 trigeminal - sensory function (16)

forehead, scalp, iris, cornea, upper and lower eyelid, conjunctiva, nasal mucous membrane, maxilla, upper and lower teeth, upper and lower lip, maxillary sinuses, nasopharynx, external auditory meatus & pinna, anterior 2/3 of tongue

CN 7 facial - motor/secretory nuclei locations

motor facial nerve and nuclei to drive secretions are in the pons

CN 7 facial - sensory nucleus location

spinal trigeminal nucleus stretches between pons, medulla, upper spinal cord

inputs to CN 7 motor and sensory nuclei

CNS: trigeminal, facial, glossopharyngeal, and vagus

CN 7 facial - exit

upper part of the face innervation

upper part of the face has a 50/50 split of ipsilateral and contralateral innervation

lower part of the face innervation