Lecture 8 & 9: CNS Flashcards
Nervous system function
Receiving and processing impulses from external and internal environments
Initiating appropriate responses
Structural classification of nervous system
Central nervous system
Peripheral nervous system
Functional classification of nervous system
Somatic
Visceral (autonomic)
Enteric
Central nervous system structures
Brain and spinal cord
Brain: cerebral hemispheres, diencephalon, cerebellum, brainstem
Protected by cranial cavity and vertebral canal
Brainstem
Midbrain
Pons
Medulla oblongata
Peripheral nervous system structures
Cranial nerves
Spinal nerves
Associated ganglia
CNS Functions
Process incoming sensory and outgoing motor messages
Higher mental activity: learning, memory, reasoning
CNS Gray matter
Nerve cell bodies
Bundles of unmyelinated nerve fibres
Non-neuronal supportive cells - neuroglia
CNS White matter
Bundles of myelinated nerve fibers - tracts
Spinal cord nervous tissue
Gray matter forms H shaped core, surrounded by white matter
Brain nervous tissue
Thin gray matter cortex surrounds white matter core
Nucleus
Cluster of nerve cell bodies in the CNS
Ganglion
Cluster of nerve cell bodies outside the CNS
Embryonic development of the brain
3 weeks: solid tube
5 weeks: expands and folds
13 weeks: cerebrum grows faster and surrounds diencephalon; folds in 1 direction
Forebrain
AKA Prosencephalon
Telencephalon (cerebrum)
Diencephalon (structures surrounding 3rd ventricle)
Midbrain
Mesencephalon
Hindbrain
AKA rhombencephalon
Metencephalon (pons and cerebellum)
Myelencephalon (medulla oblongata)
Spinal cord
43-45cm in upper 2/3 of vertebral canal
Cylindrical structure
Starts at medulla oblongata at foramen magnum and ends at LI/LII intervertebral disc
Unrelated to height
Enlargement of spinal cord
Cervical enlargement: more neurons to control upper limb muscles
Lumbar enlargement: more neurons to control lower limb muscles
Conus medullaris
Distal end of spinal cord tapers
Cone shaped
Around LI/LII intervertebral disc
Spinal cord grooves
Ventral (anterior) medial fissure [ventral/motor rootlets emerge on either side]
Dorsal (posterior) medium sulcus [dorsal/sensory rootlets emerge on either side]
Spinal nerves
Union of ventral and dorsal roots
Dorsal root ganglion
Each dorsal root has dorsal root ganglion
Cell bodies of sensory neurons
Spinal cord segment
Each spinal cord has spinal nerve 31 segments 8 cervical 12 thoraic 5 lumbar 5 sacral 1 coccygeal
Spinal cord gray matter
H shaped
Anterior/ventral horn (motor)
Posterior/dorsal horn (sensory)
Lateral horn (autonomic) - only present at T1-L2 (sympathetic) and S2-S4 (parasympathetic)
Halves are connected by gray commissure with central canal
Spinal cord white matter
Surrounds gray matter Ventral column Lateral column Dorsal column Has ascending (sensory) tracts and descending (motor) tracts
Sensory Tracts of spinal cord
Relay sensory information from receptors
3 neurons (1st/2nd/3rd order)
1st order: in dorsal root ganglion
2nd order: either dorsal horn of spinal cord, or medulla oblongata
3rd order: thalamus
Then goes to sensory area of parietal lobe
*Some only have 2 neurons; it does not go to thalamus/cerebellum so does not reach conscious level
Dorsal column/medial lemniscus pathway
Fine touch and conscious proprioception
1st ON: dorsal root ganglion and brought up spinal cord in dorsal column
2nd ON: medulla to either nucleus gracilis or nucleus cuneatus, then decussates
3rd ON: thalamus and projects to primary somatosensory cortex
Spinocerebellar pathways
Unconscious proprioception of trunk and lower limbs
1st ON: dorsal root ganglion
2nd ON: in posterior horn at the same level and ascends on the ipsilateral side in lateral column to project to cortex of cerebellum
Lateral spinothalamic pathway
Temperature and pain
1st ON: dorsal root ganglion
2nd ON: posterior horn and immediately decussates and ascends in contralateral side of the spinal cord
3rd ON: thalamus and projects to the primary somatosensory cortex
Anterior spinothalamic pathway
Non discriminative (crude) touch
Motor tracts of spinal cord
Motor instruction from frontal lobe or nuclei in brainstem
2 neurons: upper motor neuron (in cerebrum [voluntary contraction] or brainstem [muscle tone]) and lower motor neuron (in brainstem to cranial nerves or anterior horn of spinal cord)
Pyramidal tracts
Skeletal muscles of limbs and trunks
Ex. Lateral and ventral corticospinal tract
Extrapyramidal tracts
Regulating subconscious/postural body movements
Ex. Rubrospinal, tectospinal, vestibulospinal, reticulospinal
Corticospinal tract
UMN in motor cortex of cerebrum
Lateral corticospinal tract: axons decussate at pyramid in medulla and continue down lateral column to LMN in ventral horn; 80% of pathways; targets limbs
Anterior corticospinal tract: axons descend in anterior column and decussate at level of spinal cord before synapsing with LMN in ventral horn; 20% pathways; targets core muscles
Rubrospinal tract
UMN in red nucleus of midbrain
Axons decussate at midbrain and descend through medulla and lateral column before synapsing with LMN in ventral horn
Brainstem
Medulla oblongata
Pons
Midbrain
Functions of brainstem
Passage for ascending and descending tracts between cerebrum and spinal cord
Contains nuclei for CNIII-XII
Regulates autonomic behaviours
Medulla
Pyramidal Separated from pons by ponto-medullary sulcus Pyramid Olive Inferior olivary nucleus Medial lemniscus pathway Reticular formation CN IX, X, XI, XII emerge Nucleus of CN V, VIII, IX, X, XI, XII 4th cerebral ventricle
Reticular formation
Intranet of CNS
Cluster of nuclei
Keeps you awake/level of alertness
Pons
Anterior is convex with basilar sulcus filled with basilar artery
CN V, VI, VII, VIII emerge; also contains their nuclei
White matter has ascending and descending tracts (Ex. medial lemniscus pathway)
Pontine nuclei
Reticular formation
4th ventricle
Midbrain
Cerebral peduncles Superior colliculus + nucleus Inferior colliculus + nucleus Cerebral aqueduct Nucleus of CN III, IV, V Ascending and descending pathways Reticular formation Red nucleus Substantia Nigra
Pyramid
On either side of the median anterior fissure of medulla
Olive
Lateral to pyramid in medulla
Inferior olivary nucleus
Cooperates with cerebellum to learn new motor skills
Pontine nuclei
Relay center for motor pathways between cerebrum and cerebellum and coordinates voluntary movement
Cerebral peduncles
2 columns anteriorly containing descending pathways
Ex. Corticospinal and corticobulbar = crus cerebra
Superior colliculus
Pair in posterior midbrain
Visual reflexes
Inferior colliculus
Pair in posterior midbrain
Auditory reflexes
Red nucleus
Rubrospinal tract
Coordinates with cerebellum for fine movements
Lesions lead to intention tremor
Substantia Nigra
Regulates movements/coordination of gross movements
Linked to basal ganglia
Lesions lead to Parkinson’s disease = resting tremor
Cerebellum
2 cerebellar hemispheres connected by vermis
Folia: folds in cerebellum, separated by grooves/sulci
Largest sulcus is primary fissure dividing it into the anterior and posterior lobe
Gray matter forms cerebellar cortex and surrounds white matter = arbor vitae; containing 4 pairs of cerebellar nuclei
Cerebellum Function
Coordination of voluntary movements and maintenance of posture and balance
Cerebellar Peduncles
Cerebellum is behind medulla and pons
Superior cerebellar peduncle: to red nucleus of midbrain and thalamus
Middle cerebellar peduncle: to pontine nuclei of pons
Inferior cerebellar peduncle: to medulla
Diencephalon
Between cerebral hemispheres and midbrain Surrounds 3rd ventricle Thalamus Hypothalamus Epithalamus
Thalamus
Cluster of nuclei as a relay centre for senses (except smell) before the cortex
Egg shaped
Hypothalamus
Inferior and medial to thalamus
Center of autonomic nervous system: regulates appetite, blood pressure, body temperature etc.
Regulates endocrine system through pituitary gland
Epithalamus
Posterior and superior to thalamus
Contains pineal gland: regulates circadian rhythm and melanin in skin
Cerebrum
Outer cerebral cortex and inner white matter with nuclei
Anterior and middle cranial fossa
L and R cerebral hemispheres separated by longitudinal fissure
Folds: gyrus
Grooves: sulcus
Lobes of cerebrum
Frontal: initiate motor impulses, higher order thinking/reasoning, judging
Parietal: general sensory cortex (touch, temperature, pain)
Temporal: auditory, taste
Occipital: visual
Sulci separating the lobes of the brain
Central sulcus: separates frontal and parietal lobe
Lateral sulcus: separates parietal and temporal and frontal
Pareto-occipital sulcus: separates parietal and occipital
Basal ganglia/nuclei
Cluster of nuclei in the white matter
Caudate nucleus (tail)
Leniform (head) - contains putamen and globes pallidus
Coordination of motor function
Classification of white matter in CNS
Commissural fibers: connecting similar regions of the L and R hemisphere (crosses midline) Ex. corpus callous
Projection fibers: ascending and descending fibers connecting cortex to lower centers of CNS Ex. internal capsule
Association fibers: connecting different areas of the same hemisphere
Cerebral ventricles
Cerebral ventricles have choroid plexus which secretes cerebrospinal fluid
2 lateral ventricles in cerebral hemisphere; has anterior, posterior and inferior horn; connects to 3rd ventricle via interventricular foramen of Monro
3rd ventricle: in between diencephalon; connects to 4th ventricle via cerebral aqueduct
4th ventricle: in brainstem and connects to central canal of spinal cord and subarachnoid space
Function of cerebrospinal fluid
Fluid extracted from blood plasma to surround CNS
Cushion against trauma
Protects brain from acceleration/deceleration
Carries waste away from the brain
Meninges
3 membranes of connective tissue
Dura mater
Arachnoid mater
Pia mater
Dura mater
Attaches to inner surface of neurocranium
Ends at level of vertebra SII
In the skull, composed of outer periosteal layer (attached to inner cranial cavities) and inner meningeal layer separates from periosteal layer)
Dural reflections
Partitions to divide cranial cavity
Falx cerebra: Dura mater occupying longitudinal fissure partially separating cerebral hemispheres
Tentorium cerebella: horizontal sheet between cerebellum and occipital lobe, notched anteriorly for the mibrain
Falx cerebelli: vertical reflection of dura mater in sagittal plane along the vermis separating the cerebellar hemispheres
Dura sinus
Drain venous blood of the brain to the circulatory system
Arachnoid mater
Loose connective tissue attached to inner dura mater
Involved in the circulation of CSF (does not produce it)
Epidural space
Dura mater separated from vertebral canal
Filled with fat
Only in spinal cord, does not exist in skull
Subarachnoid space
Separates arachnoid and pia mater
Filled with CSF
Surrounds spinal cord and continues inferiorly until level of SII vertebrae
In skull and spinal cord
Lumbar cistern
Space between end of spinal cord at LI/LII and vertebrae SII
Contains roots of spinal nerves and CSF
Arachnoid granulations (villi)
Finger like projects of arachnoid mater in the superior part of the brain to drain CSF information dural sinuses
Pia mater
Delicate thin layer of connective tissue attached to the brain and spinal cord
Carries blood vessels for nutrients/oxygen to the CNS
Denticulate ligaments
Lateral triangular extensions of Pia mater that anchor spinal cord to arachnoid and dura mater
Filum terminale
Extension of pia mater from conus medullaris extending inferiorly and fuses with arachnoid and dura mater to anchor spinal cord to coccyx
