Nervous System Part 1 (Cont.) Flashcards
Towards the front
Rostral
Towards the head
Cephalic
Towards the tail
Caudal
Same side
Ipsilateral
Opposite side
Contralateral
Neural Ectoderm: thickened embryonic layer called the germ layer that forms the outside (the skin).
Middle of 3rd week, get a lot of cellular growth around the neural ectoderm. Starts to form a U Shape called the neural folds.
End of 3rd week, the neural groove is closed up like a donut and forms a tube (thick on outside and hollow on inside). Eventually forms the spinal column.
Pre-natal Development (Week 3)
What eventually forms intervertebral discs of the spinal column
Notochord
Crest cells. Cells that migrate, pinch off of the neural ectoderm to form the embryo, come to lie laterally. Eventually become the dorsal root ganglia.
Neural Crests
Neural tube now has thickening sides:
-Very outside of the tube is marginal layer of cells
-Inside is the mantle layer of cells
-Ependymal layer: lines central canal
-Floor plate: thickening at the bottom
-Roof plate: thickening at the top
-Alar Plate: upper half (Dorsal)
-Basal Plate: lower half (Ventral)
-Those two are separated by the sulcus limitans (little line/groove). Divides it into dorsal and ventral part.
Pre-Natal Development (Week 4)
Start to see primary brain vesicles begin to develop.
-Most rostral is Prosencephalon
-Middle is mesencephalon
-Lowest is Rhombencephalon
Dilations in the neural tube occurring cephalically. If everything goes well, these primary brain vesicles will form into the nervous system via differentiation.
Pre-natal Development (Week 5)
Prosencephalon, Mesencephalon, and Rhombencephalon
Primary Brain Vesicles
Telencephalon and Diencephalon
Prosencephalon secondary brain vesicles
Mesencephalon
Mesencephalon secondary brain vesicle
Mesencephalon
Mesencephalon secondary brain vesicle
Metencephalon and Myelencephalon
Rhombencephalon secondary brain vesicle
Has the optic vesicles - the forerunner of the eyes. Eventually becomes the thalamus and hypothalamus.
Diencephalon
Eventually becomes the Cerebrum and Cerebral Cortex
Telencephalon
Eventually becomes the Midbrain
Mesencephalon
Eventually becomes the Cerebellum and the Pons
Metencephalon
Eventually becomes the Medulla
Myelencephalon
Spaces in the brain. The medulla is where you lose CSF into the Subarachnoid space. Have a meningeal container of CSF called a dorsal aperture that allows CSF to flow out from subarachnoid space in the brain to the subarachnoid space in the spinal cord.
Ventricles
A covering that covers the midbrain.
-Contains 4 “bumps” called the Corpora Quadrigeminae.
-Have to remove the Cerebellum to view these.
Midbrain Tectum
Receives visual input to initiate a behavioral response.
-Ex: Following something interesting with your head/eyes
Superior Colliculi
Responsible for Auditory Integration of sound.
-Ex: Hear a sound - withdraw from it (very pronounced in babies)
Inferior Colliculi
Clusters of axons traveling impulses/action potentials back and forth, carrying info to/from brainstem and cerebellum.
-Covered up by the cerebellum hemisphere
-Superior (Brachium Conjunctivum)
-Middle (Brachium Pontis)
-Inferior (Restiform Body)
Cerebellar Peduncles
Contains CSF as it flows through the brain. Have to remove the Cerebellum to view it. Also called the Rhomboid Fossa (Diamond shaped)
Upper 1/2: Overlays the Pons
-Contains the Facial Colliculus (bump caused by the Facial nerve) and the Median Eminence
Lower 1/2: Overlays the Medulla
-Stria Medullaris: transverse stripes that are fibers of CN VIII
-Gracile Tubercle
-Cuneate Tubercle
4th Ventricle
An oblong protrusion of the medulla that carries tactile senses from the lower 1/2 of the body/extremities from the spinal cord up to the brain.
Gracile Tubercle (medial)
An oblong protrusion of the medulla that carries tactile sensations from the upper 1/2 of the body/extremities from the spinal cord up to the brain.
Cuneate Tubercle (lateral)
Where “home plate” of the diamond (4th ventricle) comes together.
Obex
A very small bump between the 4th Ventricle and the Obex. Has chemoreceptors embedded here that measure toxins in the blood to stimulate vomiting.
Area Postrema
Fibers of Vestibulocochlear Nerve (CN VIII) crossing.
Stria Medullares
Composed of the Cerebral Peduncles, with the fossa in between them called the Interpeduncular Fossa (contains CN III).
Midbrain
Composed of Fibers that are numerous in number, and right near the surface. Long motor system that starts in brain (Cerebral cortex) and come on down through the brainstem and spinal cord to produce a big swelling that you see.
Cerebral Peduncles
Fibers continue down and cause a large bulge. Consisting of large, heavily myelinated fibers (Called the Cortico-Spinal System) that start in the cerebral cortex and end in the Spinal Cord.
-Huge in number and close to the surface = create the bulge.
Fibers that have descended over on right side and cross over to the left side at the Pons (Decussating fibers). Cross and form the command center up in the brain to tell it what to do.
-CN are influences by fibers that cross in this area
Basis Pontis (Pons)
Part of the Medulla that serves as a landmark and works with the cerebellum in a synergistic fashion.
Olivary Eminence
Part of the Medulla that is a continuation of the Cortico-spinal fibers that descended from the Cerebral Peduncles and the Basis Pontis.
Pyramids
85% of the very large Cortico-spinal tract fibers cross over to the contralateral side here. Injury above this causes damage on the contralateral side of the body.
-Fibers that crossed (85%) are now called the Lateral Cortico-spinal tract
-Fibers that did not cross (15%) are called Anterior Cortico-spinal Tract and cross in the Cervical portion of the spinal cord.
Decussation of the Pyramids
Primary Motor Cortex (Precentral Gyrus) -> Internal Capsule (contains lots of myelinated axons) -> Cerebral Peduncles -> Basis Pontis -> Medulla -> Pyramids -> Decussation of the Pyramids -> Spinal cord
Cortico-spinal Motor Pathway
Start at the Median Longitudinal Fissure:
-Lower limbs (toes, ankles, knees)
Come around the bend:
-Hip, trunk, etc.
Middle of the way:
-HAND (lots of neurons)
Keep moving down:
-Lips, Larynx, tongue, swallowing, etc.
A motor representation of the Cerebral Cortex. These neurons come out of these areas and come to a cluster called the Internal Capsule.
Motor Homunculus
2 Hemispheres: Anterior and Posterior that are separated by a Primary Fissure.
Posterior lobe is larger than the Anterior lobe due to receiving more information from the Cerebral Cortex.
Cerebellum
Elongated elevation that is associated with Balance and Equilibrium.
-Vestibular Nuclei (found in the brainstem) fibers project into the Vermis (also called the Vestibulocerebellum)
Vermis
Two triangular nodes of the Posterior Lobe that can be pushed through the Foramen Magnum with injury/swelling
Cerebellar Tonsils
Spinal Cord -> Anterior Lobe (Spinocerebellum)
Vestibular Nuclei of the Brainstem -> Vermis (Vestibulocerebellum)
Cerebral Cortex -> Posterior Lobe (Corticocerebellum)
Cerebellum Input
Fibers from Receptor (knee/elbow/etc) -> Spinal cord via dorsal root -> new fibers originate and CROSS OVER over Dorsal Root -> Medulla -> Pons -> CROSS OVER AGAIN -> Inferior Cerebellar Peduncle -> Spinal Cerebellum (Ant. Lobe).
-Has double decussation
-Lesion and side of injury will be IPSILATERAL
Spinocerebellar Pathway (Double Decussation)
Ensures that motor actions are coordinated and you move in a balanced fashion.
-Modifies motor signals, doesn’t originate motor signals. Make corrections that are needed to make actions smooth and deliberate.
Vestibulocerebellar Pathway
Vestibular Apparatus (Semicircular canals; vestibule) -> CN VIII -> Brainstem -> Vestibular Nucleus -> Vermis -> Deep Cerebellar Nucleus -> Medulla -> Vestibular Nucleus -> Spinal Cord -> Ventral Root -> Peripheral Nerves/Muscles
Vestibulocerebellar Pathway
Motor Portion of Cerebral Cortex (Corticopontine Tract) (Precentral Gyrus)-> Fibers gather together to form Internal Capsule -> Midbrain -> Basis Pontis -> fibers encounter Pontine Nuclei -> Corticopontine Tract ends and fibers exit Pontine Nuclei -> CROSS OVER -> enter Middle Cerebellar Peduncle on the contralateral side -> Corticocerebellum (Post. Lobe)
Corticocerebellar Pathway
Fibers arrive to Cerebellum -> Deep Cerebellar Nuclei (Dentate Nucleus) -> initiates new fibers that ascend to Superior Cerebellar Peduncle -> CROSSING OCCURS -> Thalamus -> initiates new fibers that go back into the Motor Region of the Cerebellar Cortex
Cerebellocortical Pathway
Where does the Spinocerebellar Pathway Cross?
Double Decussation:
-Dorsal Root of Spinal Cord
-Pons
Where does the Corticocerebellar Pathway Cross?
Double Decussation:
-Pontine Nuclei
-Superior Cerebellar Peduncle
Signals originate in Motor Cortex (precentral Gyrus) - internal capsule - pons -pontine nuclei - fibers cross - enter cerebellum via Middle cerebellar peduncle - Initiate new fibers - ascend via superior cerebellar peduncle - cross again - ascend to thalamus - new fibers originate to Motor Cortex (precentral gyrus). Allows for a functioning unit between structures to carry out voluntary tasks and to do it in a smooth, coordinated fashion.
Corticocerebellar & Cerebellocortical Pathways
Allows the Cerebral Cortex to have Contralateral control and the Cerebellum to have Ipsilateral Control
Double Decussation
Muscle coordination and coordinated body movement (disorder = tremors, unsteadiness)
-Can affect equilibrium and balance if vermis is effected
-Maintains muscle tone (resistance to passive stretch).
-Problems will show ipsilateral to where the lesion occurs
Cerebellum Functions
A general term; cerebellar lesions/disorders.
-Truncal Instability: trunk is unable to be still
-Broad based stance to keep from falling
-Unsteady gait
-High Fall Risk
Ataxia
Intention Tremor: only get the tremor when you intend to do an action.
Dysynergia
Difficulty in performing rapidly alternating movements (can’t supinate/pronate hands back/forth)
Dysdiadochokinesia
Past pointing
-Can’t touch finger to nose
-Have tremors and shaking, will miss the object they’re supposed to touch
Dysmetria
A bilateral network of multisynaptic neurons in the brainstem. Functions to regulate level of consciousness, breathing cycle, and muscle tone.
-Found in the Medulla, Pons, and Midbrain up to Thalamus
Reticular Formation
Has ascending and descending portions. Located within the Medulla, dorsal to the Inferior Olivary Nucleus (what forms the Olive). Above is the 4th ventricle and below is the pyramids.
Reticular Formation (Medulla)
Located in the Pons just below the roof of the 4th ventricle, and above the decussating fibers
Reticular Formation (Pons)
Located in the Midbrain, found right underneath the Putamen (roof of midbrain) and dorsal to the Red Nucleus
Reticular Formation (Midbrain)
Important for regulating level of consciousness, also called the Reticular Activating System (RAS)
Ascending Portion of the Reticular Formation
A collection of axons that project up through the brainstem to thalamus (relay nuclei) to cerebral cortex.
Relay Nuclei of the Thalamus: have incoming fibers that are then relayed up to certain portions of the Cerebral Cortex. When activity of the system is high, it increases arousal (wakes you up)
Regulates your awareness level via increases/decreases in activity.
Ascending Portion of the Reticular Formation
During trough activity:
-Decreased activity of the RAS (wanes)
-Cortical activity decreases also.
-Leads to decreased level of consciousness and arousal (sleep)
Quiessence
Receives input from all over the body (Skin, joints, muscles, Visual System, Auditory System, Visceral System, etc.) and funnels it through the Ascending Portion of the RF into the thalamus and Cerebral Cortex. RAS will wax/wane depending on activity.
Influenced by medications such as Propofol, Versed, and Benzos
Ascending Portion of the Reticular Formation
During Peak Activity:
-Increased activity of the RAS (waxes)
-Cerebral Cortex activity increases
-Level of consciousness and arousal increases
-Can be influenced by caffeine
Arousal
Occurs when the RAS fails to screen out “noise” from the environment
ADHD
Schizophrenia, PTSD, Parkinson’s Disease, REM Behavior Disorder, Narcolepsy, Progressive Supranuclear Palsy (PSP), Depression, Autism, Alzheimer’s Disease, ADD/ADHD
Pathologies associated with RAS Dysfunction
Axons coming off of the Reticular Formation are projected down.
Regulates muscle tone:
-Highly active = hypertonia
-Slow/Depressed = Hypotonia
Affected by Level of Consciousness
Descending Portion of the Reticular Formation
Location of the Respiratory Centers.
-Medulla: Controls muscles of breathing
-Pons: Controls rate of breathing
Injury or lesion to the RF causes breathing issues.
Reticular Formation
