Pryamidal Tracts

• Direct connection between brain and muscles
• 2-neuron pathway
• Upper motor Neuron -> Lower Motor Neuron
• 1 synapse between brain and muscle

Upper Motor Neurons

• Cell bodies in motor cortex
• axons project to brain stem
• part of Central Nervous System

Lower Motor Neurons

• cell bodies in brain stem or spinal cord
• axons project to muscles
• "final common pathway"
• part of Peripheral Nervous System

Types of Pyramidal Tracts

• Corticobulbar tracts
• 70%
• UMNs end in brain stem
• LMNs = cranial nerves
• Corticospinal tracts
• 30%
• UMNs end in spinal cord
• LMNs = spinal nerves

Corticobulbar tracts:

UMN

• Cell bodies in motor strip (pre-central gyrus)
• Axons travel through
• corona radiata
• internal capsule
• Cross over in small groups and synapse onto LMN in brain stem
• LMN = cranial nerves
• UMNs for each cranial nerve cross over separately

Lower Motor Neuron

Motor Unit

• Motor cell body (LMN cell body)
• Efferent axons (LMN axon)
• Motor end plate (LMN axon terminal)
• Muscle fibers (contain post-synaptic receptors)
• PNS: Neuromuscular Junction

List of Cranial Nerves

and CN function

1. Olfactory - Sensory
2. Optic - sensory
3. Occulomotor - motor
4. Trochlear - motor
5. Trigeminal - both
6. Abducens - motor
7. Facial - both
8. Auditory/Vestibular - both
9. Glossopharyngeal - Both
10. Vagus - both
11. Spinal accessory - motor
12. Hypoglossal - motor

Cranial Nerves:

Corticobulbar tract

• UMN cell bodies in motor strip
• cross over to respective cranial nerve nucleus
• synapse on LMN cell bodies in brain stem
• LMN axons = cranial nerves

Cranial Nerve I

• Olfactory
• Sensory only
• Enters brain directly from olfactory bulb
• Sensory cells in epithelium in roof of nasal cavity
• Cribiform plate of ethmoid bone
• receptor neurons replaced every 30-60 days
• Only mammalian neurons to be consistently replaced
• Terminate/synapse on cells in olfactory bulb
• Integrate with opposite side via anterior commissure

Cranial Nerve I:

Projections

• Anterior commissure
• Subcallosal area (limbic system
• smell and emotion
• Medial temporal lobe (amygdala, hippocampus
• Smell and memory
• Connections to orbitofrontal cortex, insula
• Odor discrimination
• Connections to hypothalamus
• Feeding behaviors

Cranial Nerve I:

Aging

• Aging -> reduce acuity in smell
• reported as reduction in taste

Anosmia

• Loss of sense of smell
• damage to olfactory cells
• Traumatic Brain Injury (TBI)

Cranial Nerve II

• Optic Nerve
• Sensory only
• Fibers from Retina
• Converge at optic chiasm
• Optic tract fibers -> thalamus (LGB)
• Geniculocalcarine fibers (optic radiation)
• Through temporal lobe to occipital lobe
• Occipital lobe - midsagittal region
• Superior/inferior opercula of calcarin fissure
• Broadman's area 17

Cranial Nerve III

• Oculomotor nerve
• Exits from midbrain
• Edinger-Westphal nucleus: parasympathetic
• Constrictor muscles of iris
• Pupillary light reflex

Cranial Nerve III:

Nerve Damage

• Lateral strabismus
• Deviation of ipsilateral eye to lateral position
• ->diplopia (double vision)
• Ptosis
• Drooping eyelid
• Mydriasis
• Permanent dilation of pupil

Cranial Nerve IV

• Trochlear
• Motor only
• innervates 1 of the 6 eye muscles
• superior oblique muscle
• Exits midbrain on DORSAL surface
• integrates with vestibular system and neck movements
• Damage
• Difficuly looking down/outward
• Diplopia when 1 eye moves down

Cranial Nerve V

• Trigeminal
• Mixed motor and sensory
• Enter/exits brainstem at pons
• Motor:
• muscles of mastication, tensor veli palatini
• Sensory:
• face, teeth, dura, mucous membranes of mouth/nose

Cranial Nerve V:

Motor Component

• Muscles of mastication
• Masseter, pterygoids, temporalis
• Digrastric, tensor veli palatini, tensor tympani

Cranial Nerve V:

Sensory Branches

• Opthalmic
• forehead, anterior scalp, eyeball, upper eyelid, cornea, lateral nose, sinuses, tentorium cerebelli
• Maxillary:
• temples posterior nose, upper cheeks/lips, upper gums/teeth, palates, medial dura mater
• Mandibular:
• side of scalp, lower lips/gums, mouth, anter/middle meninges, external auditory meatus, anterior 2/3 tongue (touch/pain/temp)

Cranial Nerve V:

Damage

• Trigeminal neuralgia (tic douloureux)
• Opthalmic/mandibular branches
• excruciating chronic pain
• Unilateral LMN damage -> flaccid paresis
• slight deviation of jaw; minimal weakness
• Bilateral UMN damage -> masticator palsy
• Paralysis of masticator muscles; mandible hangs open

Cranial Nerve VI

• Abducens
• Motor only
• Innervates 1 of the 6 eye muscles
• Lateral rectus
• Integrates with vestibular system and neck movements
• exits from midbrain
• Damage
• Medial strabismus
• Eye deviated medially
• Diplopia