Upload
rosamund-beasley
View
222
Download
2
Tags:
Embed Size (px)
Citation preview
The Central Nervous SystemChapter 12
Regions and Organization of the CNS
Adult brain regions1. Cerebral hemispheres2. Diencephalon3. Brain stem (midbrain, pons, and medulla)4. Cerebellum
Figure 12.3d
Cerebellum
Diencephalon
Cerebralhemisphere
(d) Birth
Brain stem• Midbrain• Pons• Medullaoblongata
Ventricles of the Brain
• Connected to one another and to the central canal of the spinal cord
• Lined by ependymal cells• Contain cerebrospinal fluid– Two C-shaped lateral ventricles in the cerebral
hemispheres– Third ventricle in the diencephalon– Fourth ventricle in the hindbrain, dorsal to the
pons
Figure 12.5
Anterior horn
Interventricularforamen
Inferiorhorn
Lateralaperture
(b) Left lateral view
Lateral ventricle
Septum pellucidum
Third ventricle
Cerebral aqueduct
(a) Anterior view
Fourth ventricleCentral canal
Inferior horn
Posteriorhorn
MedianapertureLateralaperture
Cerebral Hemispheres
• Surface markings– Ridges (gyri), shallow grooves (sulci), and deep grooves
(fissures)– Five lobes• Frontal• Parietal • Temporal • Occipital• Insula
Cerebral Hemispheres• Surface markings– Central sulcus• Separates the precentral gyrus of the frontal lobe and
the postcentral gyrus of the parietal lobe– Longitudinal fissure• Separates the two hemispheres
– Transverse cerebral fissure• Separates the cerebrum and the cerebellum
Cerebral Cortex
• Thin (2–4 mm) superficial layer of gray matter• 40% of the mass of the brain• Site of conscious mind: awareness, sensory perception,
voluntary motor initiation, communication, memory storage, understanding
• Each hemisphere connects to contralateral side of the body
• There is lateralization of cortical function in the hemispheres
Functional Areas of the Cerebral Cortex
• The three types of functional areas are:– Motor areas—control voluntary movement– Sensory areas—conscious awareness of sensation– Association areas—integrate diverse information
• Conscious behavior involves the entire cortex
Motor Areas
• Primary (somatic) motor cortex• Premotor cortex• Broca’s area• Frontal eye field
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Sensory Areas
• Primary somatosensory cortex• Somatosensory association cortex• Visual areas• Auditory areas
• Olfactory cortex• Gustatory cortex• Visceral sensory area• Vestibular cortex
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Figure 12.8b
Frontal eye field
Prefrontalcortex
Processes emotionsrelated to personaland social interactions
(b) Parasagittal view, right hemisphere
Olfactory bulbOrbitofrontalcortex
Olfactory tractFornix
Temporal lobe
Corpuscallosum
Premotor cortexPrimarymotor cortex
Cingulategyrus Central sulcus
Primary somatosensorycortex
Parietal lobe
Parieto-occipitalsulcus
Somatosensoryassociation cortex
OccipitallobeVisualassociationarea
Calcarine sulcusParahippocampalgyrus
UncusPrimaryolfactory cortex
Primaryvisual cortex
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Multimodal Association Areas
• Receive inputs from multiple sensory areas and sends output to multiple areas
• Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take
• Three parts– Anterior association area (prefrontal cortex)– Posterior association area– Limbic association area
Anterior Association Area (Prefrontal Cortex)
• Most complicated cortical region• Involved with intellect, cognition, recall, and
personality• Contains working memory needed for
judgment, reasoning, persistence, and conscience
• Development depends on feedback from social environment
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Posterior Association Area
• Large region in temporal, parietal, and occipital lobes
• Plays a role in recognizing patterns and faces and localizing us in space
• Involved in understanding written and spoken language (Wernicke’s area)
Limbic Association Area
• Part of the limbic system• Includes: cingulate gyrus, parahippocampal
gyrus, and hippocampus• Provides emotional impact that helps establish
memories
Lateralization of Cortical Function
• Lateralization – Division of labor between hemispheres– Left hemisphere • Controls language, math, and logic
– Right hemisphere• Insight, visual-spatial skills, intuition, and artistic skills
• Cerebral dominance– Designates the hemisphere dominant for language
(left hemisphere in 90% of people)
Cerebral White Matter
• Myelinated fibers and tracts• Communication between cerebral areas, and
between cortex and lower CNS – Association fibers— horizontal; connect different
parts of same hemisphere– Commissural fibers— horizontal; connect gray
matter of two hemispheres – Projection fibers— vertical; connect hemispheres
with lower brain or spinal cord
Basal Nuclei (Ganglia)
• Subcortical nuclei (caudate nucleus, putamen, globus pallidus)
• Functionally associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain)
© 2013 Pearson Education, Inc.
Figure 12.9b Basal nuclei.
Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior hornof lateral ventricle
PutamenGlobus pallidus
Thalamus
Third ventricle
Inferior hornof lateral ventricle
Head of caudate nucleus
Tail of caudate nucleus
Anterior
Posterior
Functions of Basal Nuclei
• Functions thought to be: – Influence muscle movements – Role in cognition and emotion– Regulate intensity of slow or stereotyped
movements– Filter out incorrect/inappropriate responses– Inhibit antagonistic/unnecessary movements
Diencephalon
• Three paired structures– Thalamus– Hypothalamus– Epithalamus
• Encloses the third ventricle
Figure 12.12
Thalamus(encloses third ventricle)
Pineal gland(part of epithalamus)
Hypothalamus
Thalamus• 80% of diencephalon• Gateway to the cerebral cortex• Sorts, edits, and relays information– Afferent impulses from all senses and all parts of the body– Impulses from the hypothalamus for regulation of emotion
and visceral function– Impulses from the cerebellum to help direct the motor
cortical areas• Mediates sensation, motor activities, cortical arousal,
learning, and memory
Hypothalamus
• Autonomic control center for many visceral functions
• Center for emotional response• Regulates body temperature, food intake,
water balance, and thirst• Regulates sleep and the sleep cycle• Controls release of hormones by the anterior
pituitary• Produces posterior pituitary hormones
Epithalamus
• Most dorsal portion of the diencephalon• Pineal gland—extends from the posterior
border and secretes melatonin– Melatonin—helps regulate sleep-wake cycles
Brain Stem
• Controls automatic behaviors necessary for survival
• Associated with 10 of the 12 pairs of cranial nerves
• Three regions– Midbrain– Pons– Medulla oblongata
Figure 12.14
Pons
Medullaoblongata
Spinal cord
Midbrain
Figure 12.15a
Optic chiasmaView (a)
Optic nerve (II)
Mammillary body
Oculomotor nerve (III)
Crus cerebri ofcerebral peduncles (midbrain)
Trigeminal nerve (V)
Abducens nerve (VI)Facial nerve (VII)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Ventral root of firstcervical nerve
Trochlear nerve (IV)
PonsMiddle cerebellarpeduncle
Pyramid
Decussation of pyramids
(a) Ventral view
Spinal cord
Vestibulocochlearnerve (VIII)
Glossopharyngeal nerve (IX)
Diencephalon• Thalamus• Hypothalamus
Diencephalon
Brainstem
Thalamus
Hypothalamus
Midbrain
Pons
Medullaoblongata
Midbrain
• Located between the diencephalon and the pons
• Cerebral aqueduct– Channel between third and fourth ventricles
• Nuclei that control cranial nerves III (oculomotor) and IV (trochlear)
• Releases dopamine from the substantia nigra
Pons
• Fibers of the pons– Connect higher brain centers and the spinal cord– Relay impulses between the motor cortex and the
cerebellum• Origin of cranial nerves V (trigeminal), VI (abducens),
and VII (facial)• Nuclei that help maintain normal rhythm of
breathing
Medulla Oblongata• Joins spinal cord at foramen magnum• Crossover of the corticospinal tracts
(decussation of the pyramids)• Cranial nerves VIII, X, and XII are associated
with the medulla• Autonomic reflex centers• Cardiovascular center– Cardiac center adjusts force and rate of heart
contraction– Vasomotor center adjusts blood vessel diameter
for blood pressure regulation
Medulla Oblongata• Respiratory centers– Generate respiratory rhythm– Control rate and depth of breathing
• Additional centers regulate– Vomiting – Hiccupping – Swallowing – Coughing– Sneezing
Figure 12.17b
(b)
Medullaoblongata
Flocculonodularlobe
Choroidplexus offourth ventricle
Posteriorlobe
Arborvitae
Cerebellar cortex
Anterior lobe
Cerebellarpeduncles• Superior• Middle• Inferior
Cerebellum
The Cerebellum
• 11% of brain mass• Dorsal to the pons and medulla• Subconsciously provides precise timing and
appropriate patterns of skeletal muscle contraction
• Two hemispheres connected by vermis• Folia—transversely oriented gyri• Arbor vitae—distinctive treelike pattern of the
cerebellar white matter
Cognitive Function of the Cerebellum
• Recognizes and predicts sequences of events during complex movements
• Plays a role in nonmotor functions such as word association and puzzle solving
Functional Brain Systems
• Networks of neurons that work together and span wide areas of the brain– Limbic system– Reticular formation
Limbic System
• Structures on the medial aspects of cerebral hemispheres and diencephalon
• Includes parts of the diencephalon and some cerebral structures that encircle the brain stem
Limbic System
• Emotional or affective brain– Amygdala—recognizes angry or fearful facial
expressions, assesses danger, and elicits the fear response
– Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict
• Puts emotional responses to odors– Example: skunks smell bad
Limbic System: Emotion and Cognition
• The limbic system interacts with the prefrontal lobes, therefore:– We can react emotionally to things we consciously
understand to be happening– We are consciously aware of emotional richness in
our lives• Hippocampus and amygdala—play a role in
memory
Reticular Formation
• Three broad columns along the length of the brain stem
• Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord
Reticular Formation: RAS and Motor Function
• RAS (reticular activating system) – Sends impulses to the cerebral cortex to keep it
conscious and alert– Filters out repetitive and weak stimuli
• Motor function– Helps control coarse limb movements– Reticular autonomic centers regulate visceral
motor functions
Brain Waves
• Patterns of neuronal electrical activity • Generated by synaptic activity in the cortex• Each person’s brain waves are unique• Can be grouped into four classes based on
frequency measured as Hertz (Hz)
Figure 12.20b
Alpha waves—awake but relaxed
Beta waves—awake, alert
Theta waves—common in children
Delta waves—deep sleep
(b) Brain waves shown in EEGs fall intofour general classes.
1-second interval
Alpha: 8-13 Hz
Beta: 14-30 Hz
Theta: 4-7 Hz
Delta: ≤ 4 Hz
Consciousness
• Conscious perception of sensation & voluntary initiation and control of movement
• Capabilities associated with higher mental processing (memory, logic, judgment, etc.)
• Loss of consciousness (e.g., fainting) is a signal that brain function is impaired
Sleep• State of partial
unconsciousness from which a person can be aroused by stimulation
• Two major types of sleep (defined by EEG patterns)– Nonrapid eye
movement (NREM)– Rapid eye movement
(REM)
Sleep Patterns
• Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm (via Hypothalamus)
• Typical = alternates b/w REM and NREM
Language
• Language implementation system–Broca’s area and Wernicke’s area (in the
association cortex on the left side)–Analyzes incoming word sounds –Produces outgoing word sounds and
grammatical structures• Corresponding areas on the right side are
involved with nonverbal language components
Memory
• Storage and retrieval of information• Two stages of storage– Short-term memory (STM, or working memory)—
temporary holding of information; limited to seven or eight pieces of information
– Long-term memory (LTM) has limitless capacity
Categories of Memory
1. Declarative (fact) memory– Explicit information– Related to conscious thoughts and language ability– Stored in LTM with context in which learned
2. Nondeclarative memory – Less conscious or unconscious– Acquired through experience and repetition– Best remembered by doing; hard to unlearn– Includes procedural (skills) memory, motor
memory, and emotional memory
Figure 12.21a Proposed memory circuits.
Thalamus
Basalforebrain
Prefrontalcortex
Smell
Touch
Hearing
Vision
Hippocampus
Taste
Sensoryinput
Associationcortex
Thalamus
Medial temporal lobe(hippocampus, etc.)
Prefrontalcortex
ACh releasedby basalforebrain
Declarative memory circuits
© 2013 Pearson Education, Inc.
Figure 12.21b Proposed memory circuits.
Sensory andmotor inputs
Associationcortex
Basalnuclei
Thalamus Premotorcortex
Dopamine releasedby substantia nigra
Basalnuclei
Substantianigra
Thalamus
Premotorcortex
Procedural (skills) memory circuits
Protection of the Brain
• Bone (skull)• Meninges• Cerebrospinal fluid• Also…..Blood-brain barrier
Major Protective Structures
Meninges
• Cover and protect the CNS• Protect blood vessels and enclose venous
sinuses• Contain cerebrospinal fluid (CSF)• Form partitions in the skull• Three layers– Dura mater– Arachnoid mater– Pia mater
Dura Mater
• Two layers of fibrous connective tissue– Periosteal and meningeal layers– Layers separate to form dural venous sinuses
• Dural septa limit excessive movement of the brain
Figure 12.24
Skin of scalpPeriosteum
Falx cerebri(in longitudinalfissure only)
Blood vesselArachnoid villusPia materArachnoid mater
Duramater Meningeal
Periosteal
Bone of skull
Superiorsagittal sinus
Subduralspace
Subarachnoidspace
Dural septa!
Arachnoid Mater
• Middle layer with weblike extensions• Subarachnoid space contains CSF and blood
vessels• Arachnoid villi protrude into the superior
sagittal sinus and permit CSF reabsorption
Pia Mater
• Layer of delicate vascularized connective tissue that clings tightly to the brain
Cerebrospinal Fluid (CSF)
• Composition– Watery solution – Less protein and different ion concentrations than
plasma• Functions– Gives buoyancy to the CNS organs– Protects the CNS from blows and other trauma– Nourishes the brain and carries chemical signals
Choroid Plexuses
• Produce CSF at a constant rate • Hang from the roof of each ventricle
Figure 12.26a
Superiorsagittal sinus
Arachnoid villus
Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater
Right lateral ventricle(deep to cut)Choroid plexusof fourth ventricle
Central canalof spinal cord
Choroidplexus
Interventricularforamen
Third ventricle
Cerebral aqueductLateral apertureFourth ventricleMedian aperture
(a) CSF circulation
CSF is produced by thechoroid plexus of eachventricle.
1
CSF flows through theventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord.
2
CSF flows through thesubarachnoid space. 3
CSF is absorbed into the dural venoussinuses via the arachnoid villi. 4
1
2
3
4
Blood-Brain Barrier
• Helps maintain a stable environment for the brain
• Separates neurons from some bloodborne substances
Blood-Brain Barrier
• Composition– Continuous endothelium of
capillary walls– Basal lamina– “Feet of astrocytes”
Blood-Brain Barrier: Functions
• Selective barrier– Allows nutrients to move by facilitated diffusion– Allows any fat-soluble substances to pass,
including alcohol, nicotine, and anesthetics • Absent in some areas, e.g., vomiting center
and the hypothalamus, where it is necessary to monitor the chemical composition of the blood
Spinal Cord
• Location– Begins at the foramen magnum, ends (conus
medullaris) at L1
• Functions• Two-way communication to/from the brain, spinal
reflex centers• Protection– Bone, meninges, and CSF
Figure 12.29a
Cervicalenlargement
Dura andarachnoidmater
LumbarenlargementConusmedullarisCaudaequina
Filumterminale
Cervicalspinal nerves
Lumbarspinal nerves
Sacralspinal nerves
Thoracicspinal nerves
(a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.
Spinal Cord
• Spinal nerves– 31 pairs
• Cervical and lumbar enlargements– The nerves serving the upper and lower limbs
emerge here• Cauda equina– The collection of nerve roots at the inferior end of
the vertebral canal
Cross-Sectional Anatomy
• Two lengthwise grooves divide cord into right and left halves – Ventral (anterior) median fissure – Dorsal (posterior) median sulcus
• Gray commissure—connects masses of gray matter; encloses central canal
Figure 12.31b
(b) The spinal cord and its meningeal coverings
Dorsal funiculus
Dorsal median sulcus
Central canal
Ventral medianfissure
Pia mater
Arachnoid mater
Spinal dura mater
Graycommissure Dorsal horn Gray
matterLateral hornVentral horn
Ventral funiculusLateral funiculus
Whitecolumns
Dorsal rootganglion
Dorsal root(fans out into dorsal rootlets)
Ventral root(derived from severalventral rootlets)
Spinal nerve
Figure 12.32
Somaticsensoryneuron
Dorsal root (sensory)
Dorsal root ganglion
Visceralsensory neuron
Somaticmotor neuron
Spinal nerve
Ventral root(motor)
Ventral horn(motor neurons)
Dorsal horn (interneurons)
Visceralmotorneuron
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Pathway Generalizations
• Pathways decussate (cross over)• Most consist of two or three neurons (a relay)• Most exhibit somatotopy (precise spatial
relationships)• Pathways are paired symmetrically (one on
each side of the spinal cord or brain)
See figures 12.30 and 12.31, Table 12.2
Spinal Cord Trauma
• Functional losses– Parasthesias (abnormal sensation)– Paralysis (loss of motor function)
• Transection– Cross sectioning of the spinal cord at any level– Results in total motor and sensory loss in regions
inferior to the cut– Paraplegia—transection between T1 and L1
– Quadriplegia—transection in the cervical region