Brain Spinal cord Central Nervous System:. The Brain Performs the most complex neural functions...
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Transcript of Brain Spinal cord Central Nervous System:. The Brain Performs the most complex neural functions...
• Brain
• Spinal cord
Central Nervous System:
The Brain
• Performs the most complex neural functions
• Intelligence
• Consciousness
• Memory
• Sensory-motor integration
• Involved in innervation of the head
Organization of CNS• Centrally located gray matter – neuron cell bodies, interneurons,
unmyelinated fibers• Externally located white matter – myelinated fibers• Additional layer of gray matter external to white matter is the Cortex
• Formed from neuronal cell bodies migrating externally• Located in cerebrum and cerebellum
Basic Parts and Organization of the Brain
• Divided into four regions
• Cerebral hemispheres - Account for 83% of brain mass
• Diencephalon – includes thalamus and hypothalamus
• Brain stem - includes midbrain, pons, and medulla
• Cerebellum – “little brain”
The Cerebral Hemispheres• Frontal section through forebrain
• Cerebral cortex
• Cerebral white matter
• Deep gray matter of the cerebrum (basal ganglia)
• Corpus Callosum – commissural fibers (white matter) which connects the two hemispheres
The Cerebral Hemispheres• Fissures – deep grooves, which separate major regions of the brain
• Transverse fissure – separates cerebrum and cerebellum• Longitudinal fissure – separates cerebral hemispheres
• Sulci - grooves on the surface of the cerebral hemispheres • Gyri - twisted ridges between sulci • Prominent gyri and sulci are similar in all people
Lobes, sulci, and fissures of the cerebral hemispheres.
Postcentral gyrusCentral sulcus
Precentral gyrus
Frontal lobe Parietal lobeParieto-occipital sulcus (on medial surface of hemisphere)
Lateral sulcus
Transversecerebral fissure
Occipital lobeTemporal lobe
CerebellumPonsMedulla oblongata
Spinal cord
Cortex(gray matter)
Fissure(a deep sulcus)
(a)
Gyrus
Sulcus
White matter
The Cerebral Hemispheres• Central sulcus separates frontal and parietal lobes• Bordered by two gyri
• Precentral gyrus • Postcentral gyrus
• Parieto-occipital sulcus - separates the occipital from the parietal lobe• Lateral sulcus - separates temporal lobe from parietal and frontal lobes• Deeper sulci divide cerebrum into lobes
The Cerebral Hemispheres• Lobes are named for the skull bones overlying them
• Frontal
• Parietal
• Temporal
• Occipital
The Cerebral Cortex• Home of our conscious mind • Composed of gray matter - neuronal cell bodies, dendrites, and short
axons• Folds in cortex – triples its size • Approximately 40% of brain’s mass
The Cerebral Cortex - Functional Areas • Three general kinds of functional areas
• Sensory areas• Association areas• Motor areas
• Each of the major senses has a specific brain region called a primary sensory cortex
• There are also multimodal association areas to process information
Functional Areas Of The Cerebral Cortex
Primary motor area
Motor areas Sensory areas and relatedassociation areas
Prefrontal cortex
Premotor cortex
Frontaleye field
Working memoryfor spatial tasks
Executive areafor taskmanagement
Working memory for object-recalltasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
Central sulcus
Primary somatosensorycortex
Somatosensoryassociation area
Somatic sensation
Gustatory cortex(in insula)
Taste
(a)
Wernicke's area(outlined by dashes)
Primary visualcortex
Visualassociation area
Vision
Auditoryassociation area
Primary auditory cortex
Hearing
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Primary Somatosensory Cortex• Located along the postcentral gyrus
• Involved with conscious awareness of general somatic senses
Primary motor area
Motor areas Sensory areas and relatedassociation areas
Premotor cortex
Central sulcus
Primary somatosensorycortex
Somatosensoryassociation area
Somatic sensation
(a)
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7
3 1 25
Primary Visual Cortex• On medial part of the occipital lobe
• Largest of all sensory areas
• Receives visual information that originates on the retina
• First of a series of areas processing visual input
(a)
Primary visualcortex
Visualassociation area
Vision
19 1817
Primary Auditory Cortex• Located at superior edge of the temporal lobe
• Conscious awareness of sound
• Impulses transmitted to primary auditory cortex
(a)
Auditoryassociation area
Primary auditory cortex
Hearing
Olfactory Cortex• Olfactory nerves transmit impulses to the olfactory cortex
• Provides conscious awareness of smells
• Lies on the medial aspect of the temporal lobe
(b)
Olfactory bulb
Olfactory tract
Fornix
Temporal lobe
Visual associationarea
Primary olfactorycortex
Primaryvisual cortex
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Gustatory Cortex• Involved in the conscious awareness of taste stimuli
• Located on the “roof” of the lateral sulcus
Gustatory cortex(in insula)
Taste
(a)
Functional Areas Of The Cerebral Cortex
Primary motor area
Motor areas Sensory areas and relatedassociation areas
Prefrontal cortex
Premotor cortex
Frontaleye field
Working memoryfor spatial tasks
Executive areafor taskmanagement
Working memory for object-recalltasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
Central sulcus
Primary somatosensorycortex
Somatosensoryassociation area
Somatic sensation
Gustatory cortex(in insula)
Taste
(a)
Wernicke's area(outlined by dashes)
Primary visualcortex
Visualassociation area
Vision
Auditoryassociation area
Primary auditory cortex
Hearing
8
6 4
4445
41 4222
2247
11
19 18
7
3 1 25
43
17
Motor Areas – Primary Motor Cortex• Controls motor functions
• Located in precentral gyrus
Primary motor area
Motor areas
Premotor cortex
Frontaleye field
Central sulcus
Primary somatosensorycortex
(a)
6 4
3 1 25
The Diencephalon• Forms the center core of the forebrain, primarily composed of gray matter
• Surrounded by the cerebral hemispheres
• Composed of three paired structures: thalamus, hypothalamus, epithalamus
• Border the third ventricle
The Diencephalon• Forms the center core of the forebrain, primarily composed of gray matter• Surrounded by the cerebral hemispheres• Composed of three paired structures: thalamus, hypothalamus, epithalamus• Border the third ventricle
Corpus callosum
Choroid plexus
Thalamus(encloses third ventricle)
Pineal body/gland(part of epithalamus)
Corporaquadrigemina
Cerebralaqueduct
Arbor vitae
Fourth ventricle
Choroid plexus
Cerebellum
Septum pellucidum
Interthalamicadhesion(intermediatemass of thalamus)
Interventricularforamen
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Spinal cord
Midbrain
Fornix
The Thalamus• Makes up 80% of the diencephalon
• Contains approximately a dozen major nuclei
• Act as relay stations for incoming sensory message
• Every part of brain communicating with cerbral cortex relays signals through thalamic nuclei!
• Is the “gateway” to the cerebral cortex
The Hypothalamus• Lies between the optic chiasm and the mammillary bodies
• Pituitary gland projects inferiorly
• Contains approximately a dozen nuclei
• Main visceral control center of the body
• The master gland’s master!!
The Diencephalon – The Hypothalamus
• Functions include the following• Control of the ANS• Control of emotional responses• Regulation of body temperature• Regulation of hunger and thirst
sensations• Control of behavior• Regulation of sleep-wake cycles• Control of the endocrine system• Formation of memory
The Diencephalon – The Epithalamus
• Forms part of the “roof” (top) of the third ventricle
• Consists of a tiny group of nuclei
• Includes the pineal gland (pineal body)• Secretes the hormone melatonin
• Under influence of the hypothalamus
• Aids in control of circadian rhythm
The Brain Stem
• Several general functions
• Produces automatic behaviors necessary for survival
• Passageway for all fiber tracts running between the cerebrum and spinal cord
• Heavily involved with the innervation of the face and head
• 10 of the 12 pairs of cranial nerves attach to it
The Brain Stem• Includes the midbrain, pons, and medulla oblongata
The Brain Stem – The Midbrain• The midbrain processes
visual and auditory information and generates involuntary somatic motor responses
• Has reticular activing system-arousal of the whole brain
• Has nuclei for cranial nerves II and IV
• Has ascending and descending tracts
The Brain Stem – The Midbrain• Lies between the diencephalon and the pons
• Cerebral peduncles located on the ventral surface of the brain, contain pyramidal (corticospinal) tracts
• Superior cerebellar peduncles - connect midbrain to the cerebellum
The Brain Stem – The Midbrain• Corpora quadrigemina (quad-ri-gemina)
• The largest nuclei• Divided into the superior and inferior colliculi
• Superior colliculi – nuclei that act in visual reflexes
• Inferior colliculi – nuclei that act in reflexive response to sound
The Brain Stem – Dorsal View
Figure 13.13c
The Brain Stem – The Pons• A “bridge” between the
midbrain and medulla oblongata
• Pons contains the nuclei of cranial nerves • V – Trigeminal nerve• VI – Abducens nerve• VII – Facial nerve• Motor tracts coming from
the cerebral cortex• Pontine nuclei
• Connect portions of the cerebral cortex and cerebellum
• Send axons to cerebellum through the middle cerebellar peduncles
The Brain Stem – The Medulla Oblongata
• The core of the medulla contains• Much of the reticular formation
• Nuclei then influence autonomic functions
• Cardiac center
• Vasomotor center
• The medullary respiratory center
• Centers for hiccupping, sneezing, swallowing, and coughing
Functional Brain Systems – The Reticular Formation
Figure 13.29
The Brain Stem – The Medulla Oblongata• Most caudal level of the brain stem
• Is continuous with the spinal cord• Choroid plexus lies in the roof of the fourth ventricle
• Cranial nerves VIII–XII attach to the medulla• External landmarks of medulla
• Pyramids of the medulla lie on its ventral surface • Decussation of the pyramids - crossing over of motor tracts• Inferior cerebellar peduncles - fiber tracts connecting medulla and cerebellum
The Cerebellum• Located dorsal to the pons and medulla
• Smoothes and coordinates body movements • Helps maintain equilibrium
• Consists of two cerebellar hemispheres• Cortex – gray matter• Arbor vitae - internal white matter
• Thick tracts connecting the cerebellum to the brain stem are superior, middle, inferior cerebellar peduncles
The Cerebellum• Composed of
• Cortex – gray matter• Arbor vitae - internal white matter
• Thick tracts connecting the cerebellum to the brain stem are• Superior cerebellar peduncles• Middle cerebellar peduncles• Inferior cerebellar peduncles
• Fibers to and from the cerebellum are ipsilateral -run to and from the same side of the body
The Cerebellum
• Cerebellum receives information from the cerebral cortex
• On equilibrium
• On current movements of
• Limbs, neck, and trunk
Ventricles of the Brain• Expansions of the brain’s central cavity
• Filled with cerebrospinal fluid
• Lined with ependymal cells
• Continuous with each other
• Continuous with the central canal of the spinal cord
Ventricles of the Brain• Lateral ventricles – located in cerebral hemispheres
• Horseshoe-shaped from bending of the cerebral hemispheres
• Third ventricle – lies in diencephalon • Connected with lateral ventricles by interventricular foramen
• Cerebral aqueduct – connects 3rd and 4th ventricles• Fourth ventricle – lies in hindbrain
• Connects to the central canal of the spinal cord
Protection of the Brain
• The brain is protected from injury by
• The skull
• Meninges
• Cerebrospinal fluid
• Blood-brain barrier
Cerebrospinal Fluid (CSF)• Formed in choroid plexuses in the brain ventricles
• Choroid plexus is• Located in all four ventricles
• Composed of ependymal cells and capillaries
• Arises from blood - 500 ml/day
Cerebrospinal Fluid
• Fills the hollow cavities of the brain and spinal cord
• Provides a liquid cushion for the spinal cord and brain
• Other functions
• Nourishes brain and spinal cord
• Removes wastes
• Carries chemical signals between parts of the CNS
Cerebrospinal Fluid (CSF)
Figure 13.32b
• Extensive impermeable capillaries & sinuses• Perivascular feet of astrocytes cover and wrap around capillaries
and promote tight junction formation• Protects brain from hormones & circulating chemicals• Prevents most blood-borne toxins from entering the brain• Not an absolute barrier
• Nutrients such as oxygen pass through• Allows alcohol, nicotine, and anesthetics through
• Many glucose transporters
Blood Brain Barrier
Figure 9-6: The blood-brain barrier
Meninges• Functions of meninges
• Cover and protect the CNS
• Enclose and protect the vessels that supply the CNS
• Contain the cerebrospinal fluid between pia and arachnoid maters
Meninges• Dura Mater
• Strongest of the meninges • Composed of two layers: periosteal layer & meningeal layer
• Arachnoid Mater • Located beneath the dura mater• Arachnoid villi - Project through the dura mater, allow CSF to pass
into the dural blood sinuses
• Pia Mater • Delicate connective tissue, clings tightly to the surface of the brain• Follows all convolutions of the cortex
The Spinal Cord
• Functions of the spinal cord
• Spinal nerves attach to it
• Provides two-way conduction pathway
• Major center for reflexes
• Location of the spinal cord
• Runs through the vertebral canal
• Extends from the foramen magnum to the level of the vertebra L1 or L2
The Spinal Cord
• Cervical and lumbar enlargements - where nerves for upper and lower limbs arise
• Conus medullaris - the inferior end of the spinal cord
• Cauda equina - collection of spinal nerve roots
• Filum terminale - long filament of connective tissue, attaches to the coccyx inferiorly
Spinal Cord Segments
• Indicate the region of the spinal cord from which spinal nerves emerge
• Designated by the spinal nerve that issues from it
• T1 is the region where the first thoracic nerve emerges
The Spinal Cord
• Two deep grooves run the length of the cord• Posterior median sulcus
• Anterior median fissure
White Matter of the Spinal Cord• White columns
• Dorsal (posterior) funiculus
• Ventral (anterior) funiculus
• Lateral funiculus
• Composed of myelinated axons
• Allow communication between spinal cord and brain
White Matter of the Spinal Cord• Fibers classified by type
• Ascending fibers - afferent (sensory)
• Descending fibers – efferent (motor)
• Commisural fibers
Figure 13.34
Major Fiber Tracts in White Matter of the Spinal Cord
Gray Matter of the Spinal Cord• Shaped like the letter “H”
• Gray commissure – contains the central canal
• Dorsal horns consist of interneurons
• Ventral and lateral horns contain cell bodies of motor neurons
Organization of the Gray Matter of the Spinal Cord
• Divided according to somatic and visceral regions• SS – somatic sensory
• VS – visceral sensory
• VM – visceral motor
• SM – somatic motor
Protection of the Spinal Cord• Protected by vertebrae, meninges, and CSF
• Meninges
• Dura mater – a single layer surrounding spinal cord
• Arachnoid mater – lies deep to the dura mater
• Pia mater – innermost layer, delicate layer of connective tissue
Ascending Pathways
• Conduct general somatic sensory impulses
• Chains of neurons composed of
• First-, second-, and third-order neurons
• Four main ascending pathways
• Dorsal column pathway
• Spinothalamic pathway
• Posterior spinocerebellar pathway
• Anterior spinocerebellar pathway
Descending Pathways• Most motor pathways
• Decussate at some point along their course
• Consist of a chain of two or three neurons• Tracts arranged according to the body region
they supply
• All pathways are paired - one of each on each side of the body
• Deliver motor instructions from the brain to the spinal cord
• Divided into two groups
• Pyramidal (corticospinal) tracts
• Other motor pathways• Tectospinal tracts
• Vestibulospinal tract
• Rubrospinal tract
• Reticulospinal tract