Brainstem Lecture 1 PDF

Brainstem -- Lecture 1 **Cranial Nerves** Learning Objectives: - Identify the brainstem and its 3 parts. - Identify and describe the major gross morphological features of the brainstem and relate these to the underlying/associated internal structures. - Name and identify the crani...

Brainstem -- Lecture 1 **Cranial Nerves** Learning Objectives: - Identify the brainstem and its 3 parts. - Identify and describe the major gross morphological features of the brainstem and relate these to the underlying/associated internal structures. - Name and identify the cranial nerves, describe their functional components, their nuclei as well as their pathways and target structures/organs. Brainstem consists of **3 parts**: - Midbrain - Pons - Medulla  - Mammillary body -- 2 swellings, part of the hypothalamus - Cerebral peduncle -- ventral part of the midbrain, 2 stalks - Between red boxes -- anterior median fissure, extends along entire length of medulla oblongata - Pyramids -- swellings which lie lateral to anterior median fissure, caused by the pyramidal tract - Olive -- caused by inferior olivary nuclei - Inferior pontine sulcus -- separates pons from medulla, also known as pontomedullary junction - Interpeduncular fossa -- depression found between cerebral peduncle  - CN I -- Olfactory Nerves: Olfaction (sense of smell) - Olfactory nerves terminate in olfactory bulb, known as olfactory tract when it gets smaller - CN II -- Optic Nerve: vision A diagram of the muscles of the eye Description automatically generated - CN III -- Oculomotor Nerve: Nuclei -- Oculomotor/Edinger-Wesphal nuclei which form the nerve (in the midbrain) - Oculomotor nucleus: elevation of eyelid, 4 extraocular muscles EXCEPT 2 muscles (superior oblique & lateral rectus) - Edinger-Wesphal nucleus: pupillary constriction (when light is shone on the retina), accommodation (focus of lens) - Emerges from interpeduncular fossa - **CN IV** -- Trochlear nerve: - Superior oblique -- pulls eyeball down & out - Only nerve to emerge from dorsal surface of brain, specifically midbrain (rest emerge from ventral surface) - **CN V** -- Trigeminal nerve: sensory innervation to the face & motor to muscles of mastication (chew, moves jaw) - Nuclei (extend from midbrain to the medulla) - Mesencephalic nucelus -- proprioception, information from muscles of the face - Main sensory nucleus & spinal nucleus, general movement of face and head - Motor nucleus to muscles of mastication - 3 divisions: - Ophthalmic division (CNV1) -- sensory - Maxillary division (CNV2) -- upper jaw bone + upper lip and teeth, sensory - Mandibular division (CNV3) -- lower jaw and chin, sensory and motor (to muscles of mastication)  - **CN VI** -- Abducent nerve - Lateral rectus -- abduct the eyeball (move it outwards) - **CN VII** -- Facial nerve - Nuclei: - Facial motor nucleus - Motor to muscles of facial expression - Upper part of the nucleus of the tractus solitarius (**NTS**) - Taste from anterior 2/3 of tongue Superior salivatory nucleus & lacrimal nucleus - 2 salivary glands (submandibular & sublingual), lacrimal gland, nasal glands and glands in the palate - **parasympathetic** A diagram of a nervous system Description automatically generated - CN VIII -- Vestibulocochlear nerve - Conducts nerve impulses concerning the position & movements of the head, associated with balance - Cochlear nerve -- hearing - CN IX -- Glossopharyngeal nerve  - CN X -- Vagus nerve - goes down into the abdomen A white background with black text Description automatically generated - CN XI -- Accessory nerve - Cranil root -- nucleus ambiguous - Muscles of the soft palate, pharynx and larynx - Spinal root -- spinal nucleus of the CN XI in upper cervical cord segments - Innervates Sternocleidomastoid and trapezium m. - CN XII - Hypoglossal nerve - Nucleus: hypoglossal nucleus -- muscles of the tongue - Emerge from medulla oblongata, between pyramid and olive  Functions of the brainstem - Serves as a conduit for ascending tracts and descending tracts to reach different parts of CNS - Contains important reflex centres (e.g respiration, cardiovascular system & consciousness) - Contains nuclei of cranial nerves 3-12 Medulla: A close-up of a brain Description automatically generated Nucleus ambiguous -- contributes to formation of 9^th^, 10^th^ and 11^th^ cranial nerves. Innervates muscles of pharynx, larynx and soft palette Pyramidal tract: - Consists of corticospinal tract and corticobulbar tract - Nerve cells which are pyramidal shaped ascend from layer 5 of the cortex down to the medulla - Between medulla & spinal cord, the axon fibres cross at the midline and decussate - These fibres then synapse with interneurons, these then synapse with motor neurons in ventral horn of spinal cord - Remaining fibres cross midline at spinal cord level - Corticobulbar tract -- originates from cortex, terminates in lower motor neurones in cranial nerve nuclei to innervate muscles of facial expression + mastication  Spinothalamic pathway: - 1^st^ order neuron -- dorsal root ganglion, sends central processes into spinal cord, then synapse with 2^nd^ in spinal cord - 2^nd^ order neuron -- spinal cord, sends fibres cross midline which ascend contralaterally, then synapse with 3^rd^ in thalamus - 3^rd^ order neuron -- thalamus, sends projection to cortex Dorsal column pathway: - 1^st^ order neuron -- dorsal root ganglion, sends central processes into spinal cord, ascend ipsilaterally then synapse with 2^nd^ in medulla oblongata - 2^nd^ order neuron -- medulla oblongata, send fibres, cross midline and ascend contralaterally then synapse with 3^rd^ in thalamus - 3^rd^ order neuron -- thalamus, sends projection to cortex Pons: A close-up of a brain Description automatically generated The pathways forms connection linking cortex and cerebellum - Corticopontine fibres -\> pontine nuclei -\> transverse pontine fibres - Fibres cross midline to opposite side, travel to contralateral cerebellum via middle cerebellar peduncle Cerebellar peduncles -- 3 pairs - Contains nerve fibres/tracts which travel to or from cerebellum  Midbrain: A diagram of a brain Description automatically generated Crus cerebri + tegmentum = cerebral peduncle  - Visual reflexes (superior colliculi) & auditory pathway (inferior colliculi) Hydrocephalus: - If cerebral aqueduct is blocked -- caused hydrocephalus - CSF is unable to flow down so ends up filling the ventricles Midbrain: level of superior colliculus A diagram of a bone Description automatically generated - Red nucleus only found at level of superior colliculi Dopaminergic neurons: - Substantia nigra -- contains dopaminergic neurons - Has motor function and also plays important role in motivation & reward Reticular formation: - Resembles a net - Made of nerve cells + nerve fibres scattered throughout centre of brainstem - Direct & indirect connections with all levels of CNS  Major nuclei: - Raphe nuclei - Groups of neurons either in or adjacent to midline (raphe) of brainstem - Synthesise and secrete serotonin (5-HT) - Active in deep sleep - Cholinergic reticular nuclei - Secretes acetylcholine - Active in awake state - Noradrenergic neurons: locus coeruleus - Secretes noradrenaline - Active in awake state - Regulates arousal and attention Function of reticular formation: - Control of skeletal muscles - Control of somatic and visceral sensations - Control of ANS - Control of endocrine nervous system - Sleep, arousal, consciousness - Pain modulation