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Brainstem (II)
李立仁 副教授
解剖學暨細胞生物學科
ljlee@ntu.edu.tw
Brainstem (II)
Long tracts in the brainstem
Corticospinal tract (voluntary movement)
The posterior column‐medial lemniscus system (touch and proprioception)
Anterolateral system (pain and temperature)
Spinocerebellar tract (proprioception)
Brainstem (II)
Long tracts in the brainstem
Corticospinal tract (voluntary movement)
Projecting fibers carrying commands for initiation of voluntary movements originated from motor, premotor, supplementary motor and somatosensory cortices descend through the internal capsule, cerebral peduncle and basal pons in company with corticopontine and corticobulbar fibers.
Brainstem (II)
Long tracts in the brainstem
Corticospinal tract (voluntary movement)
Corticospinal axons continue into the pyramids of the medulla. At the spinomedullary junction, most corticospinal fiber decussate (pyramidal decussation) to form the lateral corticospinal tract. Those do not cross in the pyramidal decussation continue into the smaller anterior corticospinal tract that typically crosses in the spinal cord before terminating. Brainstem (II)
Long tracts in the brainstem
The posterior column‐medial lemniscus system (touch and proprioception)
Large‐diameter afferents with soma in the DRG (1st order), conveying information about position and movement of limb and the details of tactile stimuli, enter the spinal cord and ascend through the ipsilateral posterior funiculus (column) and terminates in the ipsilateral posterior column nuclei (nuclei gracilis and cuneatus).
Axons from these nuclei (2nd order neurons) cross the midline as part of the internal arcuate fibers at the level of midmedulla (sensory decussation) and ascend to the ventral posterolateral nucleus (VPL) of the thalamus.
3rd order neurons in VPL projects to primary somatosensory cortex in postcentral gyrus. Brainstem (III) Cranial nerves and nuclei
Main trigeminal sensory nucleus (V)
Central processes of primary afferents with cell bodies in the trigeminal ganglion (1st order) terminate in the main sensory nucleus of the trigeminal nerve.
Axons of 2nd neurons cross the midline, join the medial lemniscus, and ascend to the ventral posteromedial nucleus (VPM) of the thalamus.
3rd neurons in VPM in turn project to the face area of the postcentral gyrus.
Touch and proprioception of face
Somatic sensory nerves Brainstem (II)
Anterolateral system (pain and temperature)
Small‐diameter afferents with cell body in the dorsal root ganglion (1st order), conveying pain and temperature (and tactile) information, enter the spinal cord in the lateral division of each dorsal root and terminate on the tract cells in the posterior horn.
Axons of 2nd neurons cross and join the spinothalamic tract (somatotopic arranged), then ascend to the ventral posterolateral nucleus (VPL) of the thalamus.
Long tracts in the brainstem
Brainstem (II)
Long tracts in the brainstem
Spinocerebellar tract (proprioception)
Lower limb and trunk: Posterior spinocerebellar tract
Primary afferents (1st order) terminate on the interneurons (2nd order) in the dorsal horn (Clarke's nucleus) on the same side. Projecting axons (2nd order) ascend without crossing and form synapses in cerebella by way of inferior cerebellar peduncle.
Brainstem (II)
Long tracts in the brainstem
Spinocerebellar tract (proprioception)
Upper limb and neck: Spinocuneocerebellar tract
From above T1, primary afferents enter the fasciculus cuneatus
directly and terminate on neurons in the accessory cuneate nucleus (2nd order). Projecting axons (2nd order) enter into the ipsilateral cerebellum via the inferior cerebellar peduncle.
Brainstem (II)
Neurochemistry of the brainstem “Out of billions of neurons in the human brain, relatively few appear to contain biogenic amines – such cells number only in the thousands……many of the cells containing these transmitters are clustered together in a discrete region of the brain, the brainstem.” ‐‐ Nicholls et al., From Neuron To Brain
Glutamate is the most common excitatory transmitter in neurons throughout the brain. Gamma‐aminobutyric acid (GABA) is nearly a ubiquitous inhibitory neurotransmitter. Brainstem (II)
Neurochemistry of the brainstem
Brainstem (II)
Neurochemistry of the brainstem
Norepinephrine (noradrenaline) by neurons only found in pons and medullary tegmental regions.
‐ Locus ceruleus (blue spot) near the floor of the 4th ventricle ‐‐ project mainly to cerebral cortex ‐‐ silent during sleep, active during wakefulness ‐‐ form part of the ascending reticular activating system
‐ Reticular formation in the lateral part of medulla ‐‐ send fibers to spinal cord
‐ Solitary nucleus and dorsal motor nucleus of vagus
Brainstem (II)
Neurochemistry of the brainstem
Norepinephrine (noradrenaline) innervates the entire CNS ‐ ascending fibers to thalamus, hypothalamus, limbic forebrain and cerebral cortex (SI) ‐ descending fibers to brainstem, cerebellum and spinal cord Brainstem (II)
Neurochemistry of the brainstem
Dopamine
used by neurons mostly located in the midbrain ‐ compact part of substantia nigra (SNc)
‐ ventral tegmental area (VTA)
involved in the initiation of movement cf. Parkinson’s disease also involved in motivation and cognition cf. drug addiction and schizophrenia Brainstem (II)
Neurochemistry of the brainstem
Dopamine
projecting fibers are grouped into three bundles
‐ nigrostriatal (mesostriatal) afferents: SNc to caudate nucleus and putamen) ‐ mesolimbic afferents: VTA to limbic structures ex. amygdala and hippocampus ‐ mesocortical afferents: VTA to cerebral cortex (frontal) Brainstem (II)
Neurochemistry of the brainstem
Serotonin (5‐HT)
used by neurons in the raphe nuclei throughout the BS ‐ rostral raphe nuclei project to forebrain (sensory and limbic) ‐ caudal raphe nuclei project to brainstem and spinal cord and may modulate thetransmission of pain
‐ form part of the ascending reticular activating system ‐ target of antidepressants
Brainstem (II)
Neurochemistry of the brainstem
Acetylcholine used as neurotransmitter by some neuron groups in the RF, motor and preganglionic autonomic neurons
involved in sleep‐wakefulness control Brainstem (II)
Reticular formation A diffusely organized area in the central portion of the brainstem)
Caudally, RF is continuous with the intermediate gray matter of the spinal cord. Rostrally, RF continues into the intralaminar nuclei of the thalamus. Brainstem (II)
Four major groups :
Precerebellar
reticular nu. coordination of muscle contraction
Raphe (median) and catacholamine nu.
sleep‐alertness
pain modulation
Brainstem (II)
Central (medial) reticular nu.
eye movement conscious state
Lateral reticular nu.
respiratory and circulatory system feeding
Brainstem (II)
Functions of reticular formation
Control of movement
Spinal motor neurons are influenced (in addition to the corticospinal pathway) by reticulospinal pathways.
Reticulospinal neurons receive collaterals from spinoreticular fibers and spinothalamic fibers and inputs from red nucleus, cerebellum and somatosensory as well as motor cortices.
The reticulospinal tracts carry descending motor commands generated within RF.
Reticular formation Brainstem (II)
Functions of reticular formation
Modulates pain transmission
Neurons in the periaqueductal
gray (PAG) receives collaterals of spinothalamic (pain‐conducting) fibers and projects to the raphe
nuclei (particularly nucleus raphe
magnus) in the RF. Neurons in these areas in turn send afferents to the superficial laminae of the posterior horn, suppressing the transmission of pain information received by spinothalamic neurons.
Reticular formation Brainstem (II)
Reticular formation Functions of reticular formation
Controls the arousal and consciousness
Neurons in RF collect multiple sensory information and send ascending projections to diencephalon and telencephalon. This pathway collaborates with monoamine‐containing reticular projections form the ascending reticular activating system (ARAS) that continuously send signals to sustain cerebral activities and consciousness. Brainstem (II)
Reticular formation Functions of reticular formation
Controls the arousal and consciousness
The ascending reticular activating system also works together with histaminergic and cholinergic projections from hypothalamus and basal forebrain regulate the sleep‐awake cycle.
Brainstem (II)
Blood supply of the brainstem
Vertebral‐basilar system
Medulla oblongata
Anterior spinal a. Posterior spinal a. Posterior inferior cerebellar a. Brs. Vertebral a. Pons
Brs. Basilar a.
Midbrain
Brs. Basilar a.
Superior cerebellar aa. Posterior cerebral aa.
F
E
D
C
B
A
Brainstem (II)
General arrangement of
cranial nerve nuclei
(SA)
(VA)
Alar
plate
Basal
plate
(VE)
(SE)
Brainstem (II)
General Arrangement
Brainstem (II) Cranial nerve nuclei
General Arrangement
General
General somatic afferents (GSA) : from skin, skeletal muscles, joints and ligaments General visceral afferents (GVA) : from visceral organ and blood vessels
General somatic efferents (GSE) : to skeletal muscles derived from myotomes
General visceral efferents (GVE) : to smooth and cardiac muscles and glands Special Special somatic afferents (SSA) : from visual and auditory organs
Special visceral afferents (SVA) : from visceral sense (taste and smell) organs
Branchial
Branchial efferents (BE) : to striated muscles derived from branchial arches
Brainstem (II) Cranial nerve nuclei
GSE (3, 4, 6, 12)
Oculomotor (III) Trochlear (IV) Abducens (VI)
Hypoglossal (XII) GVE (3, 7, 9, 10)
Edinger‐Westphal n. (III)
Sup. Salivatory nu. (VII)
Inf. Salivatory nu. (IX) Dorsal nu. Vagus (X)
BE (5, 7, 9, 10, 11)
Trigeminal motor nu. (V)
Facial motor nu. (VII)
Nu. Ambiguus (IX, X)
Accessory nu. (XI)
General Arrangement
Brainstem (II) Cranial nerve nuclei
SSA (8)
Cochlear and vestibular nuclei (VIII) GSA (5, 7, 9, 10)
Main trigeminal sensory nucleus (V) Mesencephalic
trigeminal nucleus (V) Spinal trigeminal nucleus (V, VII, IX, X) GVA/SVA (VA) (7, 9, 10)
Nu. Solitary tract (VII, IX, X) General Arrangement
Brainstem (II) Cranial nerve nuclei
Brainstem (III)
Cranial nerves and nuclei
Somatic motor nerves (3, 4, 6, 12) ‐‐‐ GSE
Oculomotor nerve (III) innervates four extra‐ocular muscles
Trochlear nerve (IV) innervates superior oblique
Abducens nerve (IV) innervates lateral rectus Hypoglossal nerve (XII) innervates tongue muscles
Brainstem (III) Cranial nerves and nuclei
Oculomotor
nerve (III) Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Somatic motor nerves
Oculomotor nerve (III) Supplies : Levator palpebrae
superioris
Superior rectus
Medial rectus, inferior oblique, inferior rectus
Brainstem (III) Cranial nerves and nuclei
Oculomotor nerve (III) Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Trochlear nerve (IV) Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Somatic motor nerves
Trochlear nerve (IV) Supplies : Superior oblique (SO4)
Brainstem (III) Cranial nerves and nuclei
Trochlear nerve (IV) A unique cranial nerve that :
exit from the dorsal surface of the brain
all the lower motor neuron fibers decussate
longest intracranial course
smallest number of axons
Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Abducens nerve (VI) Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Abducens nerve (VI) Supplies : Lateral rectus
Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Abducens nerve (VI) Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Inter‐nuclear connection ‐‐ between abducens nucleus and oculomotor nucleus
Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Hypoglossal nerve (XII) Somatic motor nerves
Brainstem (III) Cranial nerves and nuclei
Somatic motor nerves
Hypoglossal nerve (XII) Hypoglossal trigone
Brainstem (III) Cranial nerves and nuclei
Somatic motor nerves
Hypoglossal nerve (XII) Supplies : intrinsic and most extrinsic tongue muscles of same side
If damaged :
Tongue is deviated
toward the side of lesion. Bilateral lesions of hypoglossal nerve
cause difficulties in eating & speaking