Lecture 10: Spinal cord, brain stem, diencephalon, cerebellum Flashcards
Rostral
Toward the nose
Caudal
Toward the tail
Spinal cord functions
Attach spinal nerves; sensory and motor innervation of body below the head; two-way conduction pathway; major center for reflexes
Spinal cord location
Through vertebral canal of vertebral column through successive vertebral foramina; foramen magnum at base of skull to level of L3 in infants and L1 or L2 in children and adults
Conus medullaris
Inferior end of spinal cord tapers into this
Filum terminale
Long filament of connective tissue extending from conus medullaris down to coccyx inferiorly, anchoring spinal cord in place
Cauda equina
Collection of spinal nerve roots in inferior end of the vertebral canal
Cervical and lumbar enlargements
Where nerves for upper and lower limbs arise
Spinal nerves
31 pairs of spinal nerves (PNS); 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
Spinal cord segments
Indicate region of spinal cord where spinal nerve fibers emerge; since spinal cord does not extend to end of spinal column, spinal cord segments are located superior to where corresponding spinal nerves emerge (e.g., spinal cord segment T5 is located at level of vertebra T4 and spinal cord segment S1 is located at level of vertebra L1)
Spinal cord deep grooves
Wider laterally than anteroposteriorly; two deep grooves run length of cord and partly divide it into right and left halves; dorsal (posterior) median sulcus and wider ventral (anterior) median fisure
White matter
Outer region of spinal cord; composed of myelinated axons as well as unmyelinated axons (fibers)
White matter funiculi
White matter on each side of spinal cord is divided into funiculi (“long ropes”); dorsal (posterior) funiculus; ventral (anterior) funiculus; lateral funiculus
Fibers in white matter
Ascending fibers: carry sensory information to brain; descending fibers: carry motor information from brain to spinal cord; commissural fibers: carry information from one side to the other; commisure: bundle of axons that crosses from one side of the CNS to the other
Gray matter
Shaped like “H” or a “butterfly”; gray commisure (cross-bar of the H): unmyelinated axons and contains narrow central cavity; dorsal horns (posterior arms of H); ventral horns (anterior arms of H); lateral horns: small lateral columns in thoracic and superior lumbar segments of spinal cord
Dorsal root ganglia
Sensory neuron cell bodies lie outside in this
Dorsal roots
Sensory neuron axons reach spinal cord via this
Dorsal horn interneurons
Receive information from sensory neurons
Ventral and lateral horns
Contain cell bodies of motor neurons and interneurons; send axons out of spinal cord via ventral roots; largest in cervical and lumbar segments of the cord
Paralysis
damage to ventral horn or ventral motor roots destroys motor neurons
Paresthesia
Damage to dorsal horn or sensory neuron cell bodies in dorsal root ganglia - loss of sensory function
Meninges
Connective tissue membranes that lie just external to brain and spinal cord; cover and protect CNS; enclose and protect blood vessels that supply CNS; contain CSF
Epidural space
Fat-rich cushioning space just external to dura mater
Dura mater
Strongest layer of meninges; two layered; Periosteal layer (periosteum): outer layer which attaches to internal surface of skull bones; Meningeal layer: deeper layer which forms external covering of the brain and is continuous with dura mater that surrounds the spinal cord
Subdural space
Thin fluid-filled space
Arachnoid mater
Deep to the dura mater
Subarachnoid space
Filled with CSF and large blood vessels
Pia mater
Innermost layer; clings tightly to the surface of spinal cord; extends to coccyx covering the filum terminale; contours of gyri, sulci and fissures of brain’s external surface
Denticulate ligaments
Lateral extensions of pia mater anchor spinal cord laterally to dura mater throughout length of cord
CSF
Watery fluid that fills subarachnoid space and hollow cavities of the brain and spinal cord; liquid cushion and buoyancy; nourishes brain and spinal cord; removes wastes produced by neurons
Lumbar puncture/spinal tap
Because adult spinal cord ends at vertebrae L1-L2, lumbar puncture (spinal tap) needs to be inserted between L4-L5 into the subarachnoid space to obtain CSF or inject medicine
Dura sinuses
Two layers of dura maters fused except where they are separated by dural sinuses which collect blood from the brain and conduct it to the large internal jugular veins of the neck; superior sagittal sinus is largest dural sinus and positioned in the superior midline
Falx cerebri
Large sickle shaped vertical sheet in median plane; attaches anteriorly to crista galli of ethmoid bone
Falx cerebelli
Vertical partition runs along vermis of cerebellum in posterior cranial fossa
Tentorium cerebelli
Horizontal sheet lies in transverse fissure between the cerebrum and cerebellum
Arachnoid vili (arachnoid granulations)
Knoblike projections; project through dura mater over superior part of brain; villi act as valves that allow CSF to pass from subarachnoid space into dural blood sinuses
Meningitis
Inflammation of meningeal tissues from infection
Encephalitis
Inflammation of brain or spinal cord from infection
Brain
Weighs 1500 grams; complex neural functions; autonomic nervous system; endocrine system
Embryonic development: week 4
Brain from rostral part of neural tube; caudal portion becomes spinal cord; three primary brain vesicles (prosencephalon, mesencephalon, rhombencephalon)
Embryonic development: week 5
Prosencephalon (forebrain) divides into telencephalon and diencephalon; Mesencephalon (midbrain) remains undivided; rhombencephalon (hindbrain) divides into metencephalon and myelencephalon
Talencephalon
Cerebral hemispheres
Diencephalon
Thalamus, hypothalamus, epithalamus
Mesencephalon
Midbrain
Metencephalon
Pons, cerebellum
Myelencephalon
Medulla oblongata
Brain structures from rostral to caudal
Cerebrum (two hemispheres), diencephalon (thalamus, hypothalamus, epithalamus), cerebellum, brain stem (midbrain, pons, medulla oblongata)
Ventricles of the brain
Expansion of brain’s central cavity; filled with CSF; lined with ependymal cells; continuous with each other and with the central canal of the spinal cord
The Ventricles
Telencephalon: lateral ventricles; diencephalon: 3rd ventricle; midbrain: cerebral aqueduct; pons, cerebellum, medulla oblongata: 4th ventricle
Paired lateral ventricles
Cerebral hemispheres; horseshoe-shaped; each has anterior horn, posterior horn, and inferior horn; anterior horn is separated by septum pellucidum
Third ventricle
Diencephalon; connected by lateral ventricles by interventricular foramen
Cerebral aqueduct
Midbrain connects third and fourth ventricles
Fourth ventricle
Hindbrain; connects to central canal of inferior medulla and spinal cord; three openings of 4th ventricles are paired lateral apertures in side walls and median aperture in roof; aperture holes connect ventricles with subarachnoid space which allows cerebral spinal fluid to fill both ventricles and space
Choroid plexus
Lies in roofs of 4th ventricle, 3rd ventricle, and later ventricles; where CSF is formed; knot of porous capillaries surrounded by ependymal cells; CSF continually forms from blood plasma by filtration from porous capillaries and passage through ependymal cells into ventricles; waste products move from CSF to capillaries
Components of CSF formed by choroid plexus
Glucose, oxygen, vitamins, ions
CSF movement
Produced from blood plasma by choroid plexus; enters ventricles and subarachnoid space through lateral and median apertures in walls of 4th ventricle; flows through subarachnoid space and baths outer surfaces of brain and spinal cord; passes through arachnoid villi and is absorbed into blood through venous dural sinuses
CSF cycling
Arises from blood and returns to it at a rate of about 500 ml/day
Hydrocephalus
Excessive accumulation of CSF in ventricles and/or sub-arachnoid space
Blood-brain barrier
Capillaries provide nutrients to brain; some blood borne molecules can cross other capillaries but not the brain capillaries; tight junctions make them least permeable capillaries in body; prevents some blood-borne toxins and some drugs; vital nutrients such as oxygen pass through and fat soluble molecules
Brainstem: rostral to caudal
Midbrain, pons, medulla oblongata; each 1 inch long; together make about 2.5% brain mass
Brainstem functions
Passageway for all fiber tracts running between cerebrum and spinal cord; innervation of face and head; 9/12 pairs of cranial nerves are associated with brain stem; generates autonomic behaviors necessary for survival
Medulla oblongata
Conical shaped; continuous with spinal cord at level of foramen magnum; most caudal of brain stem; part of 4th ventricle
Inferior cerebellar peduncles
Fiber tracts connecting medulla and cerebellum
Olive (of the medulla)
Contains inferior olivary nucleus; each olive lies lateral to a pyramid and contains brain nucleus called inferior olivary nucleus which is large wavy fold of gray matter; relay station for sensory information traveling to cerebellum, especially for proprioceptive information ascending from the spinal cord
Pyramids of the medulla
Two longitudinal ridges which lie on ventral surface
Decussation of the pyramids
Pyramidal fibers crossing over of motor tracts; ventral surface; formed by pyramidal tracts carrying voluntary motor output from cerebrum
Reticular formation
Loose cluster of brain nuclei that run through core of brainstem; stimulate cerebral alertness and regulates muscles; form three columns that extend length of brainstem (midline raphe nuclei, medial nuclear group, lateral nuclear group)
Visceral motor nuclei
Cardiac center regulates force and rate of heartbeat; vasomotor center regulates blood pressure; respiratory center regulates breathing; centers for hiccupping, sneezing, swallowing and coughing
Medulla oblongata: gray matter
Cranial nerve nucleii: VIII-XII; nucleus cuneatus and nucleus gracilis; inferior olivary nucleus; reticular formation nuclei
Medulla oblongata: white matter
Pyramidal motor tracts; inferior cerebellar peduncles
Pons
Bulge in brainstem between midbrain and medulla oblongata; form ventral bridge between brainstem and cerebellum; separated from cerebellum by 4th ventricle; ventral to cranial nerve nuclei lies part of reticular formation; ventral to reticular formation lies thick pyramidal motor tracts descending from cerebral cortex
Pontine nuclei
Relay brain nuclei in path that connects a portion of cerebral cortex with the cerebellum which contributes to coordination of voluntary movements; sends axons to cerebellum in thick middle cerebellar peduncles
Pons: gray matter
Cranial nerve nuclei: V, VI, VII; pontine nuclei; reticular formation nuclei
Pons: white matter
Pyramidal motor tracts, middle cerebellar peduncles
Midbrain
Most rostral; between pons and diencephalon; central cavity: cerebral aqueduct; ventral surface: cerebral peduncles containing pyramidal tracts
Periaqueductal gray matter
Surrounds cerebral aqueduct; involved in sympathetic (fight-and-flight) reaction; perceives fear and autonomic pathway that triggers sympathetic reaction; mediates response to visceral pain
Corpora quadrigemina
Brain nuclei made of gray matter embedded in white matter; largest of brain nuclei; divided into two superior and two inferior colliculi
Superior colliculi
Visual reflexes
Inferior colliculi
Reflexive response to sound
Substantia nigra
Gray matter embedded in midbrain white matter; neuronal cell bodies; deep to pyramidal tracts
Parkinson’s Disease
Degeneration of neurons in substantia nigra
Red nucleus
Gray matter embedded in midbrain white matter; lies deep in substantia nigra; reddish hue due to rich blood supply and presence of iron pigment in neuron cell bodies; associated with cerebellum
Cerebellum
Dorsal to pons and medulla from which it is separated by 4th ventricle; 11% of brain mass; smoothes and coordinates body movements; helps maintain posture and equilibrium; two cerebellar hemispheres; each hemisphere divided into anterior lobe, posterior lobe, and flocculonodular lobe (tiny)
Folia
Ridges from folds on surface separated by grooves called fissures
Cortex
Outer gray matter which is neuron rich; smooths out body movements
Arbor vitae
Internal white matter rich in axons which carry information to and from cortex
Deep cerebellar nuclei
Deeply situated gray matter gives rise to axons that relay instructions from cerebellar cortex to other parts of the brain
Information on equilibrium
Relayed from receptors in inner ear through vestibular nuclei in the medulla to flocculonodular lobe
Information on current movements of limbs and trunk
Travels from proprioceptors up spinal cord through olivary nuclei in medulla to medial portions of anterior and posterior lobes
Information from cerebral cortex
Through pontine nuclei in pons to lateral portions of anterior and posterior lobes
Superior cerebellar peduncle
Connect to midbrain and carry instructions away from cerebellum to cerebral cortex
Middle cerebellar peduncle
Connect to pons and carry information into cerebellum from cerebral cortex through pontine nuclei
Inferior cerebellar peduncle
Arise from medulla and carry fibers from vestibular nuclei (equilibrium) and from spinal cord (proprioception) through olivary nuclei in medulla into the cerebellum
Ipsilatera
Fibers to and from cerebellum
Coordinating movement
Receives information from motor cortex of cerebrum; compares intended movement with body position; sends instructions back to cerebral cortex to continuously coordinate, adjust and fine tune motor commands
Higher cognitive functions of cerebellum
Refines movements when learning a new motor skill and establish a motor memory; participates in cognition of language, problem-solving, task planning
Injury to cerebellum
Damage to anterior and/or posterior lobes: disorders in coordination; damage to flocculonodular lobe: disorders in equilibrium
Diencephalon
Center of forebrain; surrounded by cerebral hemispheres; border third ventricle; primarily composed of gray matter
Thalamus
Deep brain region; “inner room,” paired structure that makes up 80% of diencephalon; a dozen major brain nuclei each of which axons to regions of cerebral cortex; relay stations for incoming sensory messages; regions of body communicating with cerebral cortex relay signals through thalamic nuclei; “gateway” to cerebral cortex; afferent impulses from all conscious senses except olfaction; organizes, amplifies, or scales down signals
Ventral posteriolateral nuclei
Relay station for sensory information ascending to primary sensory areas of cerebral cortex
Medial geniculate body
Receives auditory input
Lateral geniculate body
Receives visual input
Hypothalalmus
Between optic chiasm and posterior border of mammillary bodies; main visceral control center of body; regulates sleep-wake cycles
Suprachiasmatic nucleus
Body’s biological clock; regulates timing of circadian rhythms in response to daylight-dark cycles via optic nerve
Preoptic nucleus
Responds to signals from suprachiasmatic nucleus to induce sleep
Mammillary body
Mediates arousal from sleep; located on undersurface of brain; part of limbic system; relay of impulses coming from amygdala and hippocampus
Functions of hypothalamus
Endocrine system, autonomic nervous system, body temperature, hunger and thirst, feeding-initiating, feeding-inhibiting, emotional responses, motivational behavior, formation of memory (mammillary body), regulation of sleep-wake cycle
Epithalamus
Most dorsal; one tiny group of brain nuclei; contains pineal gland (pineal body): influenced by hypothalamus, secretes melatonin hormone, contributes to control of circadian rhythms
