Transcript Lecture Slides - Austin Community College

Central Nervous
System:
• Brain
• Spinal cord
The Brain
• Performs the most complex neural functions
• Intelligence
• Consciousness
• Memory
• Sensory-motor integration
• Involved in innervation of the head
Organization of CNS
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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
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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
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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.
Precentral gyrus
Central sulcus
Postcentral gyrus
Parietal lobe
Parieto-occipital
sulcus (on medial
surface of
hemisphere)
Frontal lobe
Lateral sulcus
Occipital lobe
Temporal lobe
Transverse
cerebral fissure
Cerebellum
Pons
Medulla
oblongata
Spinal cord
(a)
Gyrus
Cortex
(gray matter)
Sulcus
White matter
Fissure
(a deep sulcus)
The Cerebral Hemispheres
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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
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Lobes are named for the skull bones overlying them
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Frontal
Parietal
Temporal
Occipital
The Cerebral Cortex
• Home of our conscious mind
• Composed of gray matter - neuronal cell bodies, dendrites, and short
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axons
Folds in cortex – triples its size
Approximately 40% of brain’s mass
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The Cerebral Cortex - Functional Areas
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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
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cortex
There are also multimodal association areas to process information
Functional Areas Of The Cerebral Cortex
Motor areas
Central sulcus
Sensory areas and related
association areas
Primary motor area
Premotor cortex
Frontal
eye field
6
Broca’s area
(outlined by dashes)
Primary somatosensory
cortex
3 1
2
4
5
7
8
Somatosensory
association area
Somatic
sensation
Gustatory cortex
(in insula)
Prefrontal cortex
Working memory
for spatial tasks
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Solving complex,
multitask problems
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41 42
Executive area
for task
management
Working memory
for object-recall
tasks
Wernicke's area
(outlined by dashes)
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44
Taste
47
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22
19 18
17
Primary visual
cortex
Visual
association
area
Vision
Auditory
association area
(a)
Primary
auditory cortex
Hearing
Primary Somatosensory Cortex
• Located along the postcentral gyrus
• Involved with conscious awareness of general somatic senses
Motor areas
Central sulcus
Sensory areas and related
association areas
Primary motor area
Premotor cortex
Primary somatosensory
cortex
3 1 2
4
5
7
(a)
Somatosensory
association area
Somatic
sensation
Primary Visual Cortex
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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
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Primary visual
cortex
Visual
association
area
(a)
Vision
Primary Auditory Cortex
• Located at superior edge of the temporal lobe
• Conscious awareness of sound
• Impulses transmitted to primary auditory cortex
Auditory
association area
(a)
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
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Visual association
area
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Olfactory bulb
Olfactory tract
(b)
Fornix
Primary
visual cortex
Temporal lobe
Primary olfactory
cortex
Gustatory Cortex
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Involved in the conscious awareness of taste stimuli
Located on the “roof” of the lateral sulcus
Gustatory cortex
(in insula)
(a)
Taste
Functional Areas Of The Cerebral Cortex
Motor areas
Central sulcus
Sensory areas and related
association areas
Primary motor area
Premotor cortex
Frontal
eye field
6
Broca’s area
(outlined by dashes)
Primary somatosensory
cortex
3 1
2
4
5
7
8
Somatosensory
association area
Somatic
sensation
Gustatory cortex
(in insula)
Prefrontal cortex
Working memory
for spatial tasks
45
Solving complex,
multitask problems
22
41 42
Executive area
for task
management
Working memory
for object-recall
tasks
Wernicke's area
(outlined by dashes)
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44
Taste
47
11
22
19 18
17
Primary visual
cortex
Visual
association
area
Vision
Auditory
association area
(a)
Primary
auditory cortex
Hearing
Motor Areas – Primary Motor Cortex
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Controls motor functions
Located in precentral gyrus
Motor areas
Primary motor area
Premotor cortex
Frontal
eye field
(a)
Central sulcus
6
Primary somatosensory
cortex
3 1 2
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5
The Diencephalon
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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
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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
Fornix
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of
thalamus)
Choroid plexus
Interventricular
foramen
Pineal body/gland
(part of epithalamus)
Corpora
quadrigemina
Hypothalamus
Cerebral
aqueduct
Thalamus
(encloses third
ventricle)
Optic chiasma
Pituitary gland
Midbrain
Arbor vitae
Fourth ventricle
Mammillary body
Pons
Medulla oblongata
Spinal cord
Choroid plexus
Cerebellum
The Thalamus
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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
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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
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Functions include the following
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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
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Forms part of the “roof” (top) of
the third ventricle
Consists of a tiny group of nuclei
Includes the pineal gland (pineal
body)
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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
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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
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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
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pyramidal (corticospinal) tracts
Superior cerebellar peduncles - connect midbrain to the cerebellum
The Brain Stem – The Midbrain
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Corpora quadrigemina (quad-ri-gemina)
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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
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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
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Connect portions of the
cerebral cortex and
cerebellum
Send axons to cerebellum
through the middle
cerebellar peduncles
The Brain Stem – The Medulla Oblongata
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The core of the medulla contains
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Much of the reticular
formation
Nuclei then influence
autonomic functions
• Cardiac center
• Vasomotor center
• The medullary respiratory
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center
Centers for hiccupping,
sneezing, swallowing, and
coughing
Functional Brain Systems – The Reticular Formation
Figure 13.29
The Brain Stem – The Medulla Oblongata
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Most caudal level of the brain stem
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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
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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
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Lateral ventricles – located in cerebral hemispheres
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Horseshoe-shaped from bending of the cerebral hemispheres
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Connected with lateral ventricles by interventricular foramen
• Third ventricle – lies in diencephalon
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Cerebral aqueduct – connects 3rd and 4th ventricles
Fourth ventricle – lies in hindbrain
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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)
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Formed in choroid plexuses in the brain ventricles
Choroid plexus is
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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
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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
Blood Brain Barrier
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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
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Many glucose transporters
• Nutrients such as oxygen pass through
• Allows alcohol, nicotine, and anesthetics through
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
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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
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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
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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
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Fibers classified by type
• Ascending fibers - afferent (sensory)
• Descending fibers – efferent (motor)
• Commisural fibers
Major Fiber Tracts in White Matter of the Spinal Cord
Figure 13.34
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
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Divided according to somatic and visceral regions
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SS – somatic sensory
VS – visceral sensory
VM – visceral motor
SM – somatic motor
Protection of the Spinal Cord
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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
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sensory impulses
Chains of neurons composed
of
• First-, second-, and thirdorder neurons
Four main ascending
pathways
• Dorsal column pathway
• Spinothalamic pathway
• Posterior spinocerebellar
pathway
• Anterior spinocerebellar
pathway
Descending Pathways
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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
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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
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Tectospinal tracts
Vestibulospinal tract
Rubrospinal tract
Reticulospinal tract