Brain Stem Exterior Lecture 2 PDF

ILOs: ❑Describe parts of the white matter of the spinal cord. ❑Enumerate ascending and descending tracts of the spinal cord. ❑List the components of brain stem. ❑Describe the site of brain stem. ❑Describe the relations between components of brain stem & their relations to cerebellum. ❑Describe t...

ILOs: ❑Describe parts of the white matter of the spinal cord. ❑Enumerate ascending and descending tracts of the spinal cord. ❑List the components of brain stem. ❑Describe the site of brain stem. ❑Describe the relations between components of brain stem & their relations to cerebellum. ❑Describe the external features of both ventral & dorsal surfaces of brain stem. ❑List cranial nerves emerging from brain stem. ❑Describe the site of emergence of each cranial nerve. ❑ Surrounds the central grey matter contains s hort tracts and long tracts. ❑ divided into two halves. ❑ Each half is further subdivided by the dorso-lateral and ventro-lateral sulci into three columns; dorsal, lateral and ventral columns. ❑ The dorsal column is divided by the intermediate septum into gracile fasciculus medially and cuneate fasciculus laterally. ❑ The white color is due to high proportion of myelinated nerve fibers. ❑ Tract is a group of nerve fibers that share a common origin, termination and function. ❑ Tracts are often named according to their points of origin and destination e.g, spinothalamic, corticospinal. ❑ Carry sensory information from sensory receptors through peripheral nerves to the spinal cord. ❑ They either: 1. Connect spinal cord to higher centers (long tracts). 2. Connect different segments of spinal (short tracts). ❑ Three neuron pathways: 1. 1st order neuron: Dorsal root ganglia. 2. 2nd order neuron: in the spinal cord or brainstem 3. 3rd order neuron: thalamus then pass through posterior limb of internal capsule to the primary motor cortex. ❑ Consists of two motor neurons: 1. Upper motor neurons (UMNs): originates in: cerebral cortex, cerebellum and brainstem. 2. Lower motor neurons (LMNs): originates in: spinal cord and cranial nerve nuclei in the brainstem.  Lumbar puncture ❑ Definition: introducing a needle into the subarachnoid space for injection of drugs into the CSF or obtaining sample of CSF. ❑ Site: the needle is introduced between L3-L4. ❑Connects the cerebrum with the spinal cord. clivus ❑It lies on the basilar part of occipital bone (clivus). ❑Formed from three parts from above downwards: Mid brain, pons& medulla oblongata. ❑Each part of brain stem is connected to cerebellum by cerebellar peduncles (superior, middle & inferior).  FUNCTIONS OF BRAIN STEM 1. Pathway of tracts between cerebral cortex & spinal cord. 2. Site of origin and emergence of cranial nerve nuclei and cranial nerves (from 3rdto 12th). 3. Contains groups of nuclei & related fibers known as reticular formation responsible for: control of level of consciousness, perception of pain, regulation of cardiovascular& respiratory systems. ❑ Ventral median fissure: ❖ Continuation of ventral median fissure of spinal cord ❖ Divides the medulla into 2 halves ❖ Its lower part is marked by decussation of most of pyramidal fibers. ❑Pyramid: ❖ An elevation, lies on either side of ventral median fissure ❖ Produced by corticospinal tract. ❑Olive: ❖ An elevation, lies lateral to the pyramid. ❖ Produced by inferior olivary nucleus. ❑Nerves emerging from Medulla (4 nerves): ❖ Hypoglossal (12th): from sulcus(anterolateral sulcus) between pyramid & olive ❖ Glossopharyngeal(9th), vagus (10th) & cranial part of accessory (11th): from (posterolateral sulcus)sulcus dorsolateral to olive (from above downwards). ❑ Basilar sulcus: ❖ Divides the pons into 2 halves, occupied by basilar artery. ❑Transverse pontine (pontocerebellar) fibers: ❖ Originate from pontine nuclei, cross the midline &pass through the contralateral middle cerebellar peduncle to enter the opposite cerebellar hemisphere. ❑Nerves emerging from Pons (4 nerves): Trigeminal (5th): from the middle of ventrolateral aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root. Abducent (6th): from sulcus between pons & pyramid. Facial (7th) & vestibulocochlear(8th): at cerebellopontine angle (junction between medulla, pons& cerebellum). Both nerves emerge as 2 roots: from medial to lateral: motor root of 7th, sensory root of 7th, vestibular part of 8th& cochlear part of 8th. ❑ large column of descending fibers (crus cerebri or basis pedunculi), on either side, separated by a depression called the interpeduncular fossa ❑Nerve emerging from Midbrain (two): ❖ Occulomotor (3rd): from medial aspect of crus cerebri. ❖ Trochlear: on the lateral aspect of crus cerebri. ❑ The features differ in the caudal part (closed medulla) and the cranial part(open medulla). ❑ Cavity: central canal. ❑Composed of: Dorsal median sulcus: divides the closed medulla into 2 halves. Fasciculus gracilis: on either side of dorsal median sulcus. Gracile tubercle: an elevation produced at the upper part of fasciculus gracilis, marks the site of gracile nucleus. Fasciculus cuneatus: on either side of fasciculus gracilis. Cuneate tubercle: an elevation produced at the upper part of fasciculus cuneatus, marks the site of cuneate nucleus. ❑Cavity:4thventricle ❑On either side, an inverted V-shaped sulcus divides the area into 3 parts (from medial to lateral): 1.Hypoglossal triangle: overlies hypoglossal nucleus. 2.Vagal triangle: overlies dorsal vagal nucleus. 3.Vestibular area: overlies vestibular nuclei. ❑ Separated from open medulla by an imaginary line passing between the margins of middle cerebellar peduncle ( stria medullaris). ❑ On either side of median sulcus, it divides into 2 parts (from medial to lateral): ▪Medial eminence & facial colliculus: overlies abducent nucleus. ▪Vestibular area : overlies vestibular nuclei. Marked by 4 elevations: 1.Two superior colliculi: concerned with visual reflexes. 2.Two inferior colliculi: forms part of auditory pathway. ❑Nerve emerging from the back of Midbrain (one): Trochlear(4th): just caudal to inferior colliculus (The only cranial nerve emerging from dorsal surface of brain stem). White matter of spinal cord contains…. A. Nerve axons B. Cell bodies C. Clusters of neurons and cell bodies D. Motor neurons In the spinal cord: A. There is no gray matter B. There is no white matter C. White matter and gray matter are mixed together into a homogenous mixture D. White mater sits internal to the gray matter E. Gray matter sits internal to the white matter space superficial to the meninges in the spinal cord area in which an anesthetic is injected to block pain impulses from the pelvic area A. Dural sinus B. Epidural space C. Subarachnoid space D. Subdural space The white matter in each half of the spinal cord is organized into three columns. Which of the following is NOT one of the columns? A) ventral column B) lateral column C) inferior column D) dorsal column What does the brain stem connect the brain to? A. spinal cord B. lower back C. neck D. Cerebellum Which Cranial nerve(s) come from the midbrain? A. CN IV B. CN V C. CN III D. CN X