Brain Stem & Cerebellum.docx

7 Pages
Unlock Document

Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

Brain Stem & Cerebellum Brain Stem • Most caudal of the four major structure • From caudal  rostral: medulla oblongata, pons & midbrain • Make up 2.5% of total brain mass • Four major functions o Passageway for all the fibre tracts running between cerebrum & spinal cord o Heavily involved with the innervation of the face & head – 10/12 of cranial nerves attach o Produces the rigidly programmed, autonomic behaviours necessary for survival o Integrates auditory reflexes & visual reflexes • Outer white matter surrounding inner region of gray matter • Brain nuclei of gray matter are also located in the white matter of the brain stem • Relay nuclei – process & edit information before sending it along o Somatosensory nuclei (cuneate & gracile): relay station for sensory information o Olivary nucleus: to cerebellum from spinal cord – proprioception o Vestibular nuclei: equilibrium o Cochlear nuclei: hearing o Solitary nuclei: visceral o Motor nuclei: initiate motor responses  Pontine nuclei: coordinates voluntary movements b/w cerebral cortex & cerebellum   Reticular formation: coordinates reflexes & involuntary movements (heart beat, blood pr., breathing, hiccupping, swallowing, coughing, sneezing)   Superior colliculus: visual reflexes  Inferior colliculus: auditory system  Substantia nigra: link to basal ganglia of cerebrum  Red nucleus: flexion movements of limbs  Cranial nerves nuclei  Nucleus ambiguus: vagal motor  Medulla Oblongata • Most caudal part of the brain stem & continuous with spinal cord • Part of the 4 ventricle lies dorsal to the superior half of medulla • White matter fibre tracts connecting more rostral regions of brain with spinal cord must pass through medulla – run vertically and some are continuations of fibres from cerebral penuncle • Two longitudinal ridges: pyramids flank ventral midline of medulla • Ridges are formed by pyramidal tracts – large fibre tracts that originate from pyramid-shaped neurons in cerebrum & descend through brain stem o Carry voluntary motor output to the spinal cord • In caudal part of medulla – 70-90% of pyramidal fibres cross over the opposite side of the brain through: decussation of the pyramids o Each hemisphere controls the voluntary movements of the opposite side • Lateral to each pyramid is bulge olive o Enlargement contains inferior olivary nucleus o Large wavy fold of gray matter o Relay station for sensory information travelling to cerebellum – especially for proprioceptive information ascending from spinal cord • Inferior cerebellar peduncles – fibre tracts that connect medulla to cerebellum dorsally • Nucleus fasiculatus & Nucleus cuneatus o Internally – two nuclei located in caudal medulla o Ascending fibres carrying input from senses (touch, pressure, limb/joint position) from skin & proprioceptors - synapse in these nuclei along pathway to cerebrum • Visceral sensory nuclei of the solitary tract – activated when you increase blood pressure (vagus nerve) • Dorsal nucleus of the vagus – output of vagus nerve information • Cranial Nerves – attach to medulla o Four pairs of cranial nerves o Nuclei associated with nerves may be sensory (receive input) or motor nuclei (initiate response) o Nuclei associated with these cranial nerves lie near 4 ventricle o Vestibulocochlear nerve (cranial nerve VIII)  Attaches at junction of medulla & pons  Sensory nerve of hearing and equilibrium  Vestibular & cochlear nuclei (sensory)  Located on the dorsolateral portion of medulla o Glossopharyngeal nerve (cranial nerve IX)  Innervates part of the tongue & pharynx  Nucleus ambiguus (motor) and solitary nucleus (sensory) o Vagus Nerve (cranial nerve X)  Innervates many visceral organs in thorax & abdomen  Dorsal motor nucleus of vagus, solitary nucleus & nucleus ambiguus o Hypoglossal nerve (cranial nerve XII)  Innervates tongue muscles  Hypoglossal nucleus (motor) – located dorsomedially – just deep to 4 ventricle • Running through core of brain stem is loose cluster of nuclei: reticular formation o Form three columns on each side that extend the length of brain stem  Midline raphe nuclei – flanked laterally by:  Medial nuclear group  Lateral nuclear group o Clustered around motor nuclei of cranial nerves o Function to coordinate reflexes & autonomic behaviours involving cranial nerves o Most important nuclei involved:  Cardiac centre – adjusts force & rate of heartbeat  Vasomotor centre – regulates blood pressure by stimulating/inhibiting contraction of smooth muscle of blood vessels (dilating or constricting)  Medullary respiratory centre – controls basic rhythm and rate of breathing The Pons • Bulge wedged between midbrain & medulla • Dorsally – separated from cerebellum by 4 ventricle • Forms ventral bridge between brain stem & cerebellum • Thick pyramidal motor tracts descending from cerebral cortex pass through ventrally – vertical • Interspersed amount fibre tracts are numerous pontine nuclei – relay brain nuclei – ipsilateral termination of some fibre tracts from cerebral peduncle originating from internal capsule & motor cortex – corticopontine tract  next nuclei in line will cross midline and terminate in cerebellu • Pathway involved with coordination of voluntary movements • Send axons to cerebellum in the thick middle cerebellar peduncles • Cranial nerves o Trigeminal (cranial nerve V) innervates the skin of the face & chewing muscles o Abducens (cranial nerve VI) innervates an eye-moving muscles o Facial (cranial nerve VII) supplies muscles of facial expression & other functions • Reticular formation nuclei o Lie ventral to cranial nerve nuclei o Function in control of autonomic behaviours Midbrain • Most rostral part of the three regions of brain stem • Lies between diencephalon & pons • Central cavity of midbrain is; cerebral aqueduct – divides midbrain into tectum (dorsally) & paired cerebral peduncles (ventrally) • Cerebral peduncles o Ventral surface of the midbrain o Form vertical pillars that appear to hold up cerebrum o Contain pyramidal motor tracts descending from cerebrum toward the spinal cord o Ventral part of each peduncle contains this tract is: crus cerebri o Fibres run vertical • Superior cerebellar peduncle o Located dorsally o Contain fibre tracts that connect midbrain to cerebellum • Substantia Nigra o Embedded in white matter of midbrain o Pigmented & band-like o Neuronal cell bodies contain dark melanin pigment o Deep to pyramidal tracts in cerebral peduncle o Functionally linked to deep gray matter of cerebrum: basal nuclei o Involved in controlling voluntary movement o Degeneration: Parkinson’s disease • Red nucleus o
More Less

Related notes for Anatomy and Cell Biology 3319

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.