Topic 10: CNS structures Flashcards
Rostral
towards the nose
Caudal
toward the tail
Spinal cord functions
- Sensory and motor innervation of body below head
- 2 way conduction pathway for signals between the body and brain
- Center for reflexes
Spinal cord location
Successive vertebral foramina from foramen magnum to L3 in infants and L1/L2 in children and adults
Conus medullaris
Inferior end of spinal cord
Filum terminale
Long filament of connective tissue extending from the conus medullaris down to coccyx inferiorly anchoring the spinal cord in place
Cauda equina
Collection of spinal nerve roots in inferior end of vertebral canal
Cervical and lumbar enlargements
where nerves for upper and lower limbs arise
Spinal nerves
31 pairs of spinal nerves PNS attach to spinal cord through dorsal and ventral nerve roots and lie in intervertebral foramina
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
Spinal cord segments
Indicates the region of spinal cord where nerve fiber emerges. Spinal cord segment T5 emerges above T5 but is located at the level of vertebrae T4; Spinal cord segment S1 is located at the level of vertebrae L1.
Since spinal cord does not extend to the end of the spinal column, the spinal cord segments are located superior to where their corresponding spinal nerves emerge through the intervertebral foramina
Spinal cord deep grooves
Spinal cord is wider laterally than anteroposteriorly
Two deep grooves run the length of the cord and partly divide it into the right and left halves:
DORSAL (posterior) MEDIAN SULCUS
the wider VENTRAL (anterior) MEDIAN FISSURE
White matter of spinal cord
outer region of spinal cord
composed of mainly myelinated axons as well unmyelinated axons (fibers) which allows communication within the spinal cord and brain
White matter funiculi
White matter on each side of the spinal cord is divided into funiculi (long ropes)
Dorsal (posterior) funiculus
Ventral (anterior) funiculus
Lateral funiculus
Fiber classification in white matter:
Ascending fibers
Carry sensory information from sensory neurons up to brain
Fiber classification in white matter:
Descending fibers
Carry motor information from the brain to the spinal cord to stimulate muscle contraction or gland secretion
Fiber classification in white matter:
Commissural fibers
Carry information from one side of the spinal cord to the other
Fiber classification in white matter:
Commissure
Bundle of axons that crosses one side of the CNS to the other
Gray matter of spinal cord:
Gray commissure
Cross bar of the H
composed of unmyelinated axons and contains the narrow central cavity (central canal)
Gray matter of spinal cord:
Dorsal horns
Posterior arms of H
connected to ventral horns
Gray matter of spinal cord:
Ventral horns
Anterior arms of H
connected to dorsal horns
Gray matter of spinal cord:
Lateral horns
Small lateral columns in the thoracic and superior lumbar segments of spinal cord
Dorsal root ganglia
Outside the spinal cord, where sensory neuron cell bodies reside
Dorsal roots
Sensory neuron axons reach the spinal cord via the dorsal roots
Ventral and lateral horns of the gray matter in spinal cord
Contain cell bodies of motor neurons and interneurons
Motor neurons send their axons out of the spinal cord via the VENTRAL ROOTS to supply muscles and glands
Ventral horns are largest in the cervical and lumbar segments of the cord as they innervate the upper and lower limbs
Regions of the gray matter of spinal cord
Dorsal to ventral:
Dorsal sensory half of gray matter
SS somatic sensory
VS visceral sensory
Ventral motor half of gray matter:
VM visceral autonomic motor
SM somatic motor
Paralysis
Damage to the ventral horn or ventral motor roots destroys the motor neurons and causes paralysis of skeletal muscles served
Parathesia
Damage to the dorsal horn or sensory neuron cell bodies in dorsal root ganglia can lead to parathesia, loss of sensory function
Protection of the spinal cord
- Vertebrae
- Meninges
- CSF
Meninges
Three connective tissue membranes that lie just external to the brain and spinal cord
Cover and protect the CNS
Enclose and protect blood vessels that supply CNS
Contains the CNS
Meninges external to internal
Dura mater
Arachnoid mater
Pia mater
Meninges and associated spaces
external to internal
Epidural space: fat-rich cushioning space external to dura mater
Dura mater: strongest layer of meninges, single leathery layer of dense fibrous tissue surrounding CNS
Subdural space: fluid-filled space between dura mater and arachnoid mater
Arachnoid mater: layer lies deep to the dura mater
Dura and arachnoid extend to level of S2
Subarachnoid space: filled with CNF and large blood vessels that supply the neural tissue; space is spanned by web-like threads that anchor the arachnoid mater to the pia mater
Pia mater: innermost layer of meninges
Meninges pia mater
Innermost later of meninges
Clings tightly to the surface of the spinal cord
Delicate layer of connective tissue, richly vascularized with small blood vessels
Extends to coccyx covering the filum terminale
DENTICULATE LIGAMENTS: lateral extensions of pia mater anchor the spinal cord laterally to the dura mater throughout the length of the cord
Cerebrospinal fluid
Watery fluid that fills the subarachnoid space and hollow cavities of the brain and spinal cord
Provides a liquid cushion and buoyancy for spinal cord and brain
Nourishes brain and spinal cord
Removes wastes produced by neurons
Carries chemical signals between parts of the CNS
Lumbar puncture
Spinal tap
Adult spinal cord ends at L1-L2, spinal tap must be done below this
A needle is inserted between L4-L5 vertebrae into the subarachnoid space to obtain CSF or inject medicine
Brain protection
Skull
Meninges
Cerebrospinal fluid
Blood-brain barrier
Brain protection:
Two-layered dura mater
Strongest part of meninges
Two-layered sheet of fibrous connective tissue
PERIOSTEAL LAYER, outer layer which attached to internal surface of the skull bones
MENINGEAL LAYER, deeper layer which forms external covering of brain and continuous with dura mater that surrounds the spinal cord
Meninges: dura sinuses
Two layers of dura mater are fused except where they separate to enclose the blood-filled sinuses
DURAL SINUSES: collect blood from the brain and conduct it to the large internal jugular veins of neck
SUPERIOR SAGGITAL SINUS, largest dural sinus and is positioned in the superior midline
Falx cerebri
Dura mater extends inward to form flat partitions to subdivide the cranial cavity and stabilize the brain
large sickle shaped vertical sheet in the medal plane in the longitudinal fissure between the cerebral hemispheres; attaches anteriorly to crista galli of ethmoid bone
Falx cerebelli
Dura mater extends inward to form flat partitions to subdivide the cranial cavity and stabilize the brain
Vertical partition extends inferiorly from posterior part of falx cerebri and runs along vermis of cerebellum in the posterior cranial fossa
Tentorium cerebelli
Almost horizontal sheet lies in the transverse fissure between the cerebrum and cerebellum; encloses transverse sinus
Arachnoid villi
Arachnoid granulations
Arachnoid mater forms knoblike projections
Project through dura mater over the superior part of brain into superior sagittal sinus and other dural sinuses
Villi act as valves that allow CSF to pass from subarachnoid space into dural blood sinuses
Pia mater of brain
Delicate vascularized connective tissue
Clings tightly to surface of brain following contours of the gyri, sulci, and fissures of brain’s surface
Meningitis
Inflammation of meningeal tissues from infecion
Encephalitis
Inflammation of brain or spinal cord from infection
Brain general facts
1500 grams
Intelligence, consciousness, memory, sensory-motor integration, cranial nerves innervate head
Maintains autonomic nervous system and endocrine system
Embryonic development of brain: week 4
Arises from rostral part of neural tube in, caudal portion becomes spinal cord
PROSENCEPHALON- forebrain
MESENCEPHALON- midbrain
RHOMBENCEPHALON- hindbrain
Embryonic development of brain: week 4
Primary brain vesicles develop into 5 secondary brain vesicles
Prosencephalon (forebrain) divides into TELENCEPHALON and DIENCEPHALON
Mesencephalon (midbrain) remains undivided
Rhombencephalon (hindbrain) divides into METENCEPHALON and MYELENCEPHALON
Secondary brain vesicles develop into adult brain structures:
Telencephalon
Cerebral hemispheres
Secondary brain vesicles develop into adult brain structures:
Diencephalon
Thalamus, hypothalamus, epithalamus
Secondary brain vesicles develop into adult brain structures:
Mesencephalon
Midbrain
Secondary brain vesicles develop into adult brain structures:
Metencephalon
Pons and cerebellum
Secondary brain vesicles develop into adult brain structures:
Myelencephalon
Medulla oblongata
Brain structure from rostral to caudal
Cerebrum: two cerebral hemispheres
Diencephalon: thalamus, hypothalamus, epithalamus
Cerebellum
Brain stem: midbrain, pons, medulla oblongata
Basic parts and organization of brain
Central gray matter contains neuron cell bodies called BRAIN NUCLEI, and interneurons that process info
External white matter is rich in interneurons
Unlike spinal cord, cerebrum CEREBRAL CORTEX and cerebellum CEREBELLAR CORTEX have additional layer of gray matter called CORTEX external to white matter
Ventricles of the brain general information
Expansion of the brain’s central cavity, filled with CSF, lined with ependymal cells, continuous with each other and with the central canal of the spinal cord
Ventricles of the brain
Telencephalon: lateral ventricles
Diencephalon: 3rd ventricle
Midbrain: cerebral aqueduct
Pons, cerebellum, medulla oblongata: 4th ventricle
Paired lateral ventricles
Located in cerebral hemispheres
Horseshoe-shaped from bending of the cerebral hemispheres
Each ventricle has anterior horn, posterior horn, and inferior horn
Anterior horn of each lateral ventricle is separated by a SEPTUM PELLUCIDUM
3rd ventricle and cerebral aqueduct
Third ventricle lies in diencephalon
Anteriorly, 3rd ventricle is connected with lateral ventricles by interventricular foramina
CEREBRAL AQUEDUCT in the midbrain connects 3rd and 4th ventricles
4th ventricle of brain
Lies in hindbrain brainstem dorsal to pons and superior half of medulla oblongata
Caudally, 4th ventricle connects central canal of inferior medulla and spinal cord
Three openings in the walls of the 4th ventricle are the PAIRED LATERAL APERATURES in the side walls and the MEDIAN APERATURE in the roof
Apertures connect ventricles with the subarachnoid space which allows CSF to fill both ventricles and the subarachnoid space
CHOROID PLEXUS lies in roofs of 4th ventricle, 3rd ventricle and lateral ventricles
Choroid plexuses
Capillary rich membranes located in rood of all 4 brain ventricles
Most CSF is formed in choroid plexus
Each choroid plexus consists of a know of porous capillaries surrounded by single layer of ependymal cells joined by tight junctions and have cilia
CSF continually forms from blood plasma by filtration from porous capillaries and passage through the ependymal cells into the ventricles
Waste products move from CSF to capillaries
Components in CSF formed by choroid plexus
Glucose
Oxygen
Vitamins
Ions (Na, Cl, Mg)
CSF movement
- CSF is produced from blood plasma by choroid plexus of each ventricle
- CSF enters ventricles
- Most CSF enters subarachnoid space through the lateral and median apertures in walls of 4th ventricle; some CSF enters the central canal of the spinal cord
- CSF flows through subarachnoid space and bathes outer surface of brain and spinal cord
- CSF passes through arachnoid villi and is absorbed into the blood through the venous dural sinuses
Hydrocephalus
Excessive accumulation of CSF in ventricles and/or subarachnoid space
Blood brain barrier
Tight junctions joins the endothelial cells in the brain capillaries making them the least permeable capillaries in the body
Prevents some blood-borne toxins and some drugs from entering the brain
Vital nutrients such as O2 pass through and fat soluble molecules (alcohol, nicotine, and anesthetics) pass through
Brainstem from rostral to caudal
Midbrain
Pons
Medulla oblongata
Each is about an inch long, making up 2.5% of brain mass together
Brain stem functions
Passage way for all fiber tracts running between the cerebrum and spinal cord
Heavily involved with innervation of face and head
9 of 12 cranial nerves are associated with brain stem
Generates autonomic behaviors necessary for survival
Brain stem
Medulla oblongata
Conical
Continuous with spinal cord at magnum foramen
Most caudal
Part of 4th ventricle lying dorsal to rostral half of medulla
Medulla oblongata
Externally visible landmarks
Inferior cerebellar peduncles
Fiber tracts connecting medulla and cerebellum
Medulla oblongata
Externally visible landmarks
Olive
Contains inferior olivary nucleus
Medulla oblongata
Externally visible landmarks
Pyramids of the medulla
2 longitudinal ridges which lie on ventral surface
Formed by PYRAMIDAL TRACTS, large fiber tracts that extend through the brainstem and spinal cord carrying voluntary motor output from cerebrum to spinal cord
Medulla oblongata
Externally visible landmarks
Dessucation of the pyramids
Crossing over of motor tracts
Caudal part of medulla, pyramidal fibers cross over to opposite side of the brain to enable each cerebral hemisphere to control the voluntary movements of the opposite side of the body
Medulla oblongata
Inferior olivary nucleus
Each olive lies just lateral to a pyramid and contains a brain nucleus called the inferior olivary nucleus which is a large wavy fold of gray matter
it acts as a relay station for sensory information traveling to cerebellum especially for PROPRIOCEPTIVE INFORMATION ascending from the spinal cord (sense of relative position of neighboring parts)
Reticular formation
Loose cluster of brain nuclei that run through the core of the brain stem
Stimulate cerebral alertness and regulates muscles
Mostly present in medulla
3 columns that extend the length of the brainstem:
- midline raphe nuclei
- medial nuclear group
- lateral nuclear group
Visceral motor nuclei in medulla
Cardiac center regulates force and rate of heart beat
Vasomotor center regulates blood pressure
Respiratory center regulates breathing
Centers for hiccups, sneezing, swallowing, coughing
PART OF RETICULAR FORMATION
Medulla oblongata
Gray matter vs. white matter
Gray: Cranial nerve nuclei: VIII-XII nucleus cuneatus & nucleus gracilis Inferior olivary nucleus Reticular formation nuclei
White:
Pyramidal motor tracts
Inferior cerebellar peduncles
Pons of brainstem
A bulge in the brainstem between midbrain and medulla oblongata forming a ventral bridge between the two
Dorsally, it is separated from the cerebellum by the 4th ventricle
Ventral to cranial nerve nuclei lies part of the reticular formation
Ventral to the reticular formation lies the thick pyramidal motor tracts descending from the cerebral cortex
Interspersed among the fibers of these motor tracts are numerous PONTINE NUCLEI
Pontine nuclei
Are relay brain nuclei in a path that connects a portion of the cerebral cortex with the cerebellum which contributes to coordination of voluntary movements
Pontine nuclei send axons to the cerebellum in thick MIDDLE CEREBELLAR PEDUNCLES
Pons
Gray matter vs. white matter
Gray matter
Cranial nerve nuclei V, VI, VII
Pontine nuclei
Reticular formation nuclei
White matter
Pyramidal motor tracts
Middle cerebellar peduncles
Midbrain of brainstem
Most rostra region of brainstem
Between pons and diencephalon
Central cavity of midbrain: CEREBRAL AQUEDUCT
Ventral surface: CEREBRAL PEDUNCLES contain PYRAMIDAL (CORTICOSPINAL) TRACTS descending from the cerebrum to spinal cord; ventral part od each peduncle is called the CRUS CEREBRI
Dorsally a PAIR OF SUPERIOR CEREBELLAR PEDUNCLES connect midbrain to cerebellum
Midbrain
Periaqueductal gray matter
Surrounds cerebral aqueduct
Involved in sympathetic (fight/flight) reaction; midbrain link between part of brain that perceives fear and autonomic pathway that triggers the sympathetic reaction
Mediates response to visceral pain
Brain nuclei in midbrain:
Corpora quadrigemina
Brain nuclei make up gray matter that is embedded in midbrain white matter
Corpora quadrigemina is largest of these brain nuclei which make up the tectum (roof) of dorsal midbrain and form four bumps on dorsal surface of midbrain
Divided into:
2 superior colliculi: nuclei that act in visual reflexes
2 inferior colliculi: nuclei that act in auditory reflexes
Brain nuclei in midbrain:
Substantia nigra
Gray matter is embedded in midbrain white matter
Contain neuronal cell bodies with melanin in band-like distributions
Positioned deep to pyramidal tracts of cerebral peduncle
Functionally linked to the basal nuclei and deep gray matter od cerebrum
Degeneration of neurons in substantia nigra contribute to Parkinson’s disease
Brain nuclei in midbrain:
Red nucleus
Gray matter embedded in midbrain white matter
Lies deep to substantia nigra
Reddish hue due to rich blood supply presence of iron pigment in neuron cell bodies
Associated with cerbellum
Cerebellum general facts
Dorsal to pons, separated by 4th ventricle
11% of brain mass
Smoothes and coordinates body movements directed by other brain regions
Helps maintain posture and equilibrium
Consists of two cerebellar hemispheres connected medially by the VERMIS
Surface folded into ridges called FOLIA separated by grooves called FISSURES
Each hemisphere subdivided into:
Anterior lobe
Posterior lobe
Flocculondular lobe (tiny)
Regions of cerebellar hemispheres
Cortex
Outer gray matter
Neuron rich calculator that smooths out body movements
Regions of cerebellar hemispheres
Arbor vitae
Internal white matter
Rich in axons which carry information to and from cortex
Regions of cerebellar hemispheres
Deep cerebellar nuclei
Deeply situated gray matter
Gives rise to axons that relay instructions from cerebellar cortex to other parts of the brain
How does the body coordinate movements?
Cerebellar cortex receives three types of information:
Information on equilibrium: relayed from receptors in inner ear through VESTIBULAR NUCLEI in medulla to FLOCCULONODULAR LOBE
Information on current movements of the limbs and trunk: travels from PROPRIOCEPTORS up the spinal cord through OLIVARY NUCLEI in the medulla to the medial portions of anterior and posterior lobes
Information from the cerebral cortex: from cerebral cortex through pontine nuclei in the pons to the LATERAL PORTIONS OF ANTERIOR AND POSTERIOR LOBES
Cerebellar peduncles
Superior cerebellar peduncles
Three thick tracts of nerve fibers connect the cerebellum to the brain stem
Connect midbrain and carry instructions away rom cerebellum to the cerebral cortex
Fibers to and from the cerebellum are ipsilateral
Cerebellar peduncles
Middle cerebellar peduncles
Three thick tracts of nerve fibers connect the cerebellum to the brain stem
Connect to pons and carry information into the cerebellum from cerebral cortex through pontine nuclei
Fibers to and from the cerebellum are ipsilateral
Cerebellar peduncles
Inferiror cerebellar peduncles
Three thick tracts of nerve fibers connect the cerebellum to the brain stem
Arise from medulla and carry fibers from VESTIBULAR NUCLEI (equilibrium) and from spinal cord (proprioception) through olivary neclei in the medulla into the cerebellum
Fibers to and from the cerebellum are ipsilateral
Coordinating movement by cerebellum
- Cerebellum receives info on movement from motor cortex of cerebrum
- Cerebellum compares intended movement with body position
- Cerebellum sends instructions back to cerebral cortex to continuously coordinate, adjust fine-tune motor commands and sending it to the spinal cord
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 cerbellum
Damage to anterior/posterior lobes:
disorders in coordination
Damage to flocculondular lobe:
disorders in equilibrium
Diencephalon
Center core of forebrain Surrounded by cerebral hemispheres Composed of 3 paired structures: -Thalamus -Hypothalamus -Epithalamus Border third ventricle Mostly gray matter
Thalamus of diencephalon
Form superolateral walls of third ventricle
Contains ~12 major brain nuclei each of which send axons to regions of cerebral cortex
Thalamic nuclei act as relay stations for incoming sensory images
Regions of the body communicating with cerebral cortex relay signals through thalamic nuclei
Gateway to cerebral cortex
Nuclei organize and amplify or scale down signals
Nuclei in thalamus
Afferent impulses from all conscious sense except olfaction converge on thalamus and synapse in at least one of its nuclei
Ventral posteriolateral nuclei: relay station for sensory information ascending to the primary sensory areas of the cerebral cortex
Medial geniculate body receives auditory input
Lateral geniculate body receives visual input
Hypothalamus of diencephalon general facts
Inferior to thalamus
Forms inferolateral walls of third ventricle
LIES BETWEEN OPTIC CHASM AND POSTEIRO BORDER OF MAMMILLARY BODIES
Pituitary gland projects inferiorly from hypothalamus
Contains ~12 brain nuclei
Main visceral control center of body
Sleep-wake cycles
Regulated by hypothalamus
SUPRACHIASMATIC NUCLEUS in hypothalamus is body’s biological clock regulating the circadian rhythm in response to daylight-dark cycles sensed via the optic nerve
PREOPTIC NUCLEUS in hypothalamus responds to signals from suprachiasmatic nucleus to induce sleep
Mammillary bodies
Mediate arousal from sleep
Located on undersurface of brain as part of diencephalon
Closely associated with hypothalamus
Part of limbic system
Act as a relay of impulses coming from the amygdala and the hippocampus
Functions of hypothalamus
Control endocrine system, autonomic nervous system,
Body temperature, hunger, thirst,
Feeding-initiating centers are in lateral part of hypothalamus
Feeding-inhibition centers are in ventromedial part of hypothalamus
Control of emotional responses: pleasure, sex drive, rage
Control motivational behavior
Formation of memory: brain nucleus in the mammillary body receives abundant inputs from hippocampal formation
Sleep
Epithalamus of diencephalon
Most dorsal part, forming roof of third ventricle
One tiny group of brain nuclei
Contain PINEAL GLAND
- influenced by hypothalamus
- secretes melatonin contributing to circadian rhythm
Functions of hypothalamus
Control endocrine system, autonomic nervous system,
Body temperature, hunger, thirst,
Feeding-initiating centers are in lateral part of hypothalamus
Feeding-inhibition centers are in ventromedial part of hypothalamus
Control of emotional responses: pleasure, sex drive, rage
Control motivational behavior
Formation of memory: brain nucleus in the mammillary body receives abundant inputs from hippocampal formation
Sleep
Epithalamus of diencephalon
Most dorsal part, forming roof of third ventricle
One tiny group of brain nuclei
Contain PINEAL GLAND
- influenced by hypothalamus
- secretes melatonin contributing to circadian rhythm
