Download Sensory Areas

13 PART 1
The Central
Nervous System
The Central Nervous System
•
Central nervous system
•
The brain and spinal cord
•
Directional terms unique to the CNS
•
Rostral—toward the nose
•
Caudal—toward the tail
The Brain
•
Brain controls:
•
Heart rate, respiratory rate, blood pressure
•
Autonomic nervous system
•
Endocrine system
•
Is involved in innervation of the head through cranial nerves
The Brain
•
Performs the most complex neural functions
•
Intelligence
•
Consciousness
•
Memory
•
Sensory-motor integration
•
Emotion
•
Behavior
•
Socialization
Embryonic Development of the Brain
•
Brain arises from rostral part of the neural tube
•
Three primary brain vesicles in 4-week-old embryo
•
Prosencephalon—the forebrain
•
Mesencephalon—the midbrain
•
Rhombencephalon—the hindbrain
Embryonic Development of the Brain
•
Secondary brain vesicles
•
Prosencephalon
• Divides into telencephalon and diencephalon
•
Mesencephalon—remains undivided
•
Rhombencephalon
• Divides into metencephalon and myelencephalon
Embryonic Development of the Brain
•
Structures of the adult brain
•
Develop from secondary brain vesicles
•
•
•
•
Telencephalon  the cerebral hemispheres
Diencephalon  thalamus, hypothalamus, and epithalamus
Metencephalon  pons and cerebellum
Myelencephalon  medulla oblongata
Embryonic Development of the Brain
•
Brain stem includes
•
The midbrain, pons, and medulla oblongata
•
Ventricles
•
Central cavity of the neural tube enlarges
Embryonic Development of the Brain
•
Brain grows rapidly
•
Changes occur in the relative position of its parts
•
Cerebral hemispheres envelop the diencephalon and midbrain
•
Wrinkling of the cerebral hemispheres
• More neurons fit within limited space
Basic Parts and Organization of the Brain
•
Classified into four regions
•
Brain stem
• Midbrain, pons, and medulla
•
Cerebellum
•
Diencephalon
•
Cerebral hemispheres
Basic Parts and Organization of the Brain
•
Organization
•
Centrally located gray matter
•
Externally located white matter
•
Additional layer of gray matter external to white matter
• Due to groups of neurons migrating externally
•
Cortex—outer layer of gray matter
• Formed from neuronal cell bodies
• Located in cerebrum and cerebellum
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
Ventricles of the Brain
•
Cerebral aqueduct—connects 3rd and 4th ventricles
•
Fourth ventricle—lies in hindbrain
•
Connects to the central canal of the spinal cord
The Brain Stem
•
Includes the
•
Midbrain
•
Pons
•
Medulla oblongata
The Brain Stem
•
Several general functions
•
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
•
General functions, continued
•
Produces automatic behaviors necessary for survival
•
Integrates auditory and visual reflexes
The Brain Stem—The Medulla Oblongata
•
Most of the caudal level of the brain stem
•
Is continuous with the spinal cord
•
Choroid plexus lies in the roof of the fourth ventricle
The Brain Stem—The Medulla Oblongata
•
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
• Olive (olive of the medulla)
• Contains inferior olivary nucleus
The Brain Stem—The Medulla Oblongata
•
Four pairs of cranial nerves attach to the medulla oblongata
•
VIII—vestibulocochlear nerve
•
IX—glossopharyngeal nerve
•
X—vagus nerve
•
XII—hypoglossal nerve
The Brain Stem—The Medulla Oblongata
•
The core of the medulla contains
•
Much of the reticular formation
• Nuclei influence autonomic functions
•
Visceral centers of the reticular formation include
• Cardiac center
• Vasomotor center
• The medullary respiratory center
• Centers for hiccupping, sneezing, swallowing, and coughing
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
The Brain Stem—The Pons
•
The pons contains
•
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 Midbrain
•
Lies between the diencephalon and the pons
•
Cerebral aqueduct
•
The central cavity of the midbrain
•
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
•
Periaqueductal gray matter surrounds the cerebral aqueduct
•
Involved in two related functions
• Fight-or-flight reaction
• Mediates response to visceral pain
The Brain Stem—The Midbrain
•
Corpora quadrigemina
•
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—The Midbrain
•
Embedded in the white matter of the midbrain
•
Two pigmented nuclei
• Substantia nigra—neuronal cell bodies containing melanin
• Functionally linked to the basal nuclei
• Red nucleus—lies deep to the substantia nigra
• Largest nucleus of the reticular formation
The Cerebellum
•
Located dorsal to the pons and medulla
•
Smoothing and coordinating body movements
•
Helps maintain equilibrium
The Cerebellum
•
Consists of two cerebellar hemispheres
•
Surface folded into ridges called folia
•
Separated by fissures
•
Hemispheres each subdivided into
•
Anterior lobe
•
Posterior lobe
•
Flocculonodular lobe (tiny)
The Cerebellum
•
Composed of three regions
•
Cortex—gray matter
•
Arbor vitae
• Internal white matter
•
Deep cerebellar nuclei—deeply situated gray matter
The Cerebellum
•
To coordinate body movements, the cerebellar cortex receives three types of
information
•
Information on equilibrium
•
Information on current movements of the limbs, neck, and trunk
•
Information from the cerebral cortex
The Cerebellum
•
Coordinating movement
•
The cerebellum receives information on movement from the motor cortex of the
cerebrum
•
The cerebellum compares intended movement with body position
•
The cerebellum sends instructions back to the cerebral cortex to continuously
adjust and
fine-tune motor commands
The Cerebellum
•
Higher cognitive functions of the cerebellum
•
Learning a new motor skill
•
Participates in cognition
• Language, problem solving, task planning
The Cerebellum—Cerebellar Peduncles
•
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
13 PART 2
The Central
Nervous System
The Diencephalon
•
Forms the central core of the forebrain
•
Surrounded by the cerebral hemispheres
•
Composed of three paired structures
•
Thalamus
•
Hypothalamus
•
Epithalamus
•
Border the third ventricle
•
Primarily composed of gray matter
The Diencephalon—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 cerebral cortex relays signals through
thalamic nuclei!
•
Send axons to regions of the cerebral cortex
The Diencephalon—The Thalamus
•
Afferent impulses converge on the thalamus
•
Synapse in at least one of its nuclei
•
Is the “gateway” to the cerebral cortex
•
Nuclei organize and amplify or tone down signals
The Diencephalon—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 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 Cerebral Hemispheres
•
Account for 83% of brain mass
•
Fissures—deep grooves that separate major regions of the brain
• Transverse fissure—separates cerebrum and cerebellum
• Longitudinal fissure—separates cerebral hemispheres
The 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
The Cerebral Hemispheres
•
Deeper sulci divide cerebrum into lobes
•
Lobes are named for the skull bones overlying them
•
Central sulcus separates frontal and parietal lobes
•
Bordered by two gyri
• Precentral gyrus
• Postcentral gyrus
The Cerebral Hemispheres
•
Parieto-occipital sulcus
•
Separates the occipital from the parietal lobe
•
Lateral sulcus
•
Separates temporal lobe from parietal and frontal lobes
•
Insula—deep within the lateral sulcus
Lobes of the Cerebral Cortex
•
Frontal lobe
•
Parietal lobe
•
Occipital lobe
•
Temporal lobe
•
Insula
The Cerebral Cortex
•
Home of our conscious mind
•
Enables us to
•
Be aware of ourselves and our sensations
•
Initiate and control voluntary movements
•
Communicate, remember, and understand
The Cerebral Cortex
•
Composed of gray matter
•
Neuronal cell bodies, dendrites, and short axons
•
Folds in cortex—triples its size
•
Approximately 40% of brain’s mass
•
Brodmann areas
•
47 structurally distinct areas
The Cerebral Cortex
•
Functional regions
•
Traditionally studied brain-injured people and animals
• New discoveries—PET and fMRI
•
Regions of the cerebral cortex
• Perform distinct motor and sensory functions
• Memory and language spread over wide area
13 PART 3
The Central
Nervous System
The Cerebral Cortex
•
Three general kinds of functional areas
•
Sensory areas
•
Association areas
•
Motor areas
The Cerebral Cortex
•
There is a sensory area for each of the major senses
•
A “primary sensory cortex”
•
Each primary sensory cortex
•
Has an association area that processes sensory information
•
Sensory association areas
The Cerebral Cortex
•
Multimodal association areas
•
Receive and integrate input from multiple regions of the cerebral cortex
The Cerebral Cortex
•
Motor cortex
•
Plans and initiates voluntary motor functions
The Cerebral Cortex—Information Processing
•
Sensory information received by primary sensory cortex
•
Information relayed to sensory association area
•
Multimodal association areas receive input in parallel from sensory areas
•
Motor plan enacted
Sensory Areas
•
Cortical areas involved in conscious awareness of sensation
•
Located in
• Parietal lobes
• Temporal lobes
• Occipital lobes
•
Distinct regions of each lobe interpret each of the major senses
Sensory Areas—Primary Somatosensory Cortex
•
Located along the postcentral gyrus
•
Involved with conscious awareness of general somatic senses
•
Spatial discrimination
•
Precisely locates a stimulus
•
Certain regions are more adept at distinguishing precise stimuli
Sensory Areas—Primary Somatosensory Cortex
•
Projection is contralateral
•
Cerebral hemispheres
• Receive sensory input from the opposite side of the body
•
Sensory homunculus
•
A body map of the sensory cortex
Sensory Areas—Somatosensory Association Cortex
•
Lies posterior to the primary somatosensory cortex
•
Integrates different sensory inputs
•
Touch
•
Pressure
•
Draws upon stored memories of past sensory experiences
•
You are able to recognize keys or coins in your pocket without looking at them
Sensory Areas—Visual Areas
•
Primary visual cortex
•
Location is deep within the calcarine sulcus
• On medial part of the occipital lobe
•
Largest of all sensory areas
• Receives visual information that originates on the retina
• Exhibits contralateral function
•
First of a series of areas processing visual input
Sensory Areas—Visual Areas
•
Visual association area
•
Surrounds the primary visual area
•
Continues the processing of visual information
• Analyzes color, form, and movement
•
Complex visual processing extends into
• Temporal and parietal lobes
Sensory Areas—Auditory Areas
•
Primary auditory cortex
•
Function
• Conscious awareness of sound
• Sound waves excite receptors in the inner ear
• Impulses transmitted to primary auditory cortex
•
Location
• Superior edge of the temporal lobe
Sensory Areas—Auditory Areas
•
Auditory association area
•
Lies posterior to the primary auditory cortex
•
Permits evaluation of different sounds
•
Processes auditory stimuli serially and in parallel
• Posterolateral— “where” pathway
• Anterolateral— “what” pathway
•
Lies in the center of Wernicke’s area
• Involved in recognizing and understanding speech
Sensory Areas—Vestibular Cortex
•
Responsible for
•
Conscious awareness of sense of balance
•
Located in the posterior part of the insula
•
Deep to the lateral sulcus
Sensory Areas—Gustatory Cortex
•
Function
•
Involved in the conscious awareness of taste stimuli
•
Location
•
On the “roof” of the lateral sulcus
Sensory Areas—Olfactory Cortex
•
Lies on the medial aspect of the cerebrum
•
Located in the piriform lobe
•
Olfactory nerves transmit impulses to the olfactory cortex
•
Provides conscious awareness of smells
Sensory Areas—Olfactory Cortex
•
Part of the rhinencephalon—“nose brain”
•
Includes
•
The piriform lobe, olfactory tracts, and olfactory bulbs
•
Connects the brain to the limbic system
•
Explains why smells trigger emotions
•
Involved with consciously identifying and recalling specific smells
Visceral Sensory Areas
•
Location
•
Within the lateral sulcus
•
On the insula lobe
•
Receives general sensory input
•
Pain
•
Pressure
•
Hunger
Motor Areas
•
Cortical areas controlling motor function
•
Premotor cortex
•
Primary motor cortex
•
Frontal eye field
•
Broca’s area
•
All localized in posterior frontal lobe
Motor Areas—Premotor Cortex
•
Located anterior to the precentral gyrus
•
Controls more complex movements
•
Receives processed sensory information
•
Visual, auditory, and general somatic sensory
•
Controls voluntary actions dependent on sensory feedback
•
Involved in planning movements
Motor Areas—Primary Motor Cortex
•
Controls motor functions
•
Primary motor cortex (somatic motor area)
•
Located in precentral gyrus
•
Pyramidal cells
•
Large neurons of primary motor cortex
Motor Areas—Primary Motor Cortex
•
Corticospinal tracts descend through brain stem and spinal cord
•
Axons signal motor neurons to control skilled movements
•
Contralateral
• Pyramidal axons cross over to opposite side of the brain
Motor Areas
•
Specific pyramidal cells control specific areas of the body
•
Face and hand muscles are controlled by many pyramidal cells
•
Somatotopy
•
Body is represented spatially in the primary motor cortex
Motor Areas—Frontal Eye Field
•
Lies anterior to the premotor cortex
•
Controls voluntary movement of the eyes
•
Especially when moving eyes to follow a moving target
Motor Areas—Broca’s Area
•
Located in left cerebral hemisphere
•
Manages speech production
•
Connected to language comprehension areas in posterior association area
•
A corresponding region in the right cerebral hemisphere controls emotional overtones
to spoken words
Multimodal Association Areas
•
Large areas of the cerebral cortex
•
Receive sensory input from
• Multiple sensory modalities
• Sensory association areas
•
Make associations between kinds of sensory information
Multimodal Association Areas
•
Three multimodal association areas
•
Posterior association area
•
Anterior association area
•
Limbic association area
Posterior Association Area
•
Located at interface of visual, auditory, and somatosensory association areas
•
Integrates sensory information into unified perception
•
Allows awareness of spatial location of body
• “Body sense”
•
Related to language comprehension and speech
Posterior Association Area
•
Dorsal stream
•
Extends to the postcentral gyrus
•
Perceives information about spatial relationships
•
“Where” pathway—location of objects
•
Ventral stream
•
Passes information into inferior part of the temporal lobe
•
Responsible for recognizing objects, words, and faces
•
“What” pathway—identifies objects
Auditory Pathways
•
Auditory stimuli processed in two streams
•
From auditory association area through multimodal association areas
• Parietal lobe and lateral part of frontal
lobe—evaluate location of sound stimulus
• “Where” pathway
• Anterior region of temporal lobe and inferior region of frontal lobe—process
sound identification
• “What” pathway
Posterior Association Area
•
Multiple language areas in left cerebral cortex
•
Wernicke’s area functions in
• Speech comprehension
• Coordination of auditory and visual aspects of language
• Initiation of word articulation
• Recognition of sound sequences
Posterior Association Area
•
Areas in right cerebral hemisphere act in
•
Creative interpretation of words
•
Emotional overtones of speech
Anterior Association Area
•
A large region of the frontal lobe
•
The prefrontal cortex
•
Receives information from posterior association area
•
Integrates information with past experience
•
Initiates and plans motor movements
•
Has links to the limbic system
Anterior Association Areas
•
More complex functions include all aspects of
•
Thinking, perceiving, intentionally remembering
•
Processing abstract ideas, reasoning, judgment
•
Impulse control, mental flexibility, social skills
•
Humor, empathy, conscience
Anterior Association Area
•
Functional neuroimaging techniques
•
Reveal functions of specific parts of the prefrontal cortex
•
Anterior pole of frontal cortex
•
Active in solving the most complex problems
•
More complex problems, emotions, cognition at anterior part of frontal lobe
Anterior Association Area
•
Additional functions
•
Stores information for less than 30 seconds
•
Three working memory areas
• Visual working memory
• Auditory working memory
• Executive area
Limbic Association Areas
•
Located on medial side of frontal lobe
•
Involved with memory and emotions
•
Integrates sensory and motor behaviors
•
Aids in the formation of memory
•
Processes emotions
Lateralization of Cortical Functioning
•
The two hemispheres control opposite sides of the body
•
Contralateral  opposite side
•
Hemispheres are specialized for different cognitive functions
Lateralization of Cortical Functioning
•
Left cerebral hemisphere—control over
•
Language abilities, math, and logic
•
Right cerebral hemisphere—involved with
•
Visual-spatial skills
•
Reading facial expressions
•
Intuition, emotion, artistic and musical skills
13 PART 4
The Central
Nervous System
Cerebral White Matter
•
Different areas of the cerebral cortex
•
Communicate with each other
•
Communicate with the brain stem and spinal cord
•
Fibers communicating are
•
Usually myelinated and bundled into tracts
Cerebral White Matter
•
Types of tracts
•
Commissures—composed of commissural fibers
• Allows communication between cerebral hemispheres
• Corpus callosum—the largest commissure
•
Association fibers
• Connect different parts of the same hemisphere
• Parts of Wernike’s and Broca’s areas are connected by association fibers
Cerebral White Matter
•
Types of tracts (continued)
•
Projection fibers—run vertically
• Descend from the cerebral cortex
• Ascend to the cortex from lower regions
• Corticospinal tracts begin with pyramidal cells
Projection Tracts
•
Internal capsule—projection fibers form a compact bundle
•
Passes between the thalamus and basal nuclei
•
Corona radiata—superior to the internal capsule
•
Fibers run to and from the cerebral cortex
13 PART 5
The Central
Nervous System
Deep Gray Matter of the Cerebrum
•
Consists of
•
Basal nuclei (basal ganglia)
• Involved in motor control
•
Basal forebrain nuclei
• Associated with memory
•
Claustrum
• A nucleus of unknown function
•
Amygdaloid body
•
Located in cerebrum but is considered part of the of the limbic system
Basal Nuclei
•
A group of nuclei deep within the cerebral white matter
•
Formed from
•
Caudate nucleus—arches over thalamus
•
Putamen
•
Globus pallidus
Basal Ganglia
•
•
•
Complex neural calculators
•
Cooperate with the cerebral cortex in controlling movement
Receive input from many cortical areas
Substantia nigra also influences basal ganglia
Basal Nuclei
•
Evidence shows that they
•
Start, stop, and regulate intensity of voluntary movements
•
Select appropriate muscles for a task and inhibit others
•
In some way estimate the passage of time
Basal Forebrain Nuclei
•
Structures composing basal forebrain nuclei
•
Septum
•
Diagonal band of Broca
•
Horizontal band of Broca
•
Basal nucleus of Meynert
Basal Forebrain Nuclei
•
Part of cholinergic system
•
That is, they synthesize and release acetylcholine
•
Location
•
Anterior and dorsal to hypothalamus
•
Functions related to
•
Arousal
•
Learning
•
Memory
•
Motor control
•
Degeneration of basal forebrain nuclei
•
Associated with Alzheimer’s disease
13 PART 6
The Central
Nervous System
Functional Brain Systems
•
Networks of neurons functioning together
•
Limbic system
• Spread widely in the forebrain
•
The reticular formation
• Spans the brain stem
Functional Brain Systems—The Limbic System
•
Location
•
Medial aspect of cerebral hemispheres
•
Also within the diencephalon
•
•
Composed of
•
Septal nuclei, cingulate gyrus, and hippocampal formation
•
Part of the amygdaloid body
The fornix and other tracts link the limbic system together
Functional Brain Systems—The Limbic System
•
The “emotional brain”
•
Cingulate gyrus
• Allows us to shift between thoughts
• Interprets pain as unpleasant
•
Hippocampal formation
•
Hippocampus and the parahippocampal gyrus
Functional Brain Systems—The Reticular Formation
•
Runs through the central core of the medulla, pons, and midbrain
•
Forms three columns
•
Midline raphe nuclei
•
Medial nuclear group
•
Lateral nuclear group
Functional Brain Systems—The Reticular Formation
•
Widespread connections
•
Ideal for arousal of the brain as a whole
•
Reticular activating system (RAS)
•
Maintains consciousness and alertness
•
Functions in sleep and arousal from sleep
•
Malfunctions in people with narcolepsy
Protection of the Brain
•
The brain is protected from injury by
•
The skull
•
Meninges
•
Cerebrospinal fluid
•
Blood brain barrier
Protection of the Brain—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
The Dura Mater
•
Strongest of the meninges
•
Composed of two layers
•
Periosteal layer
•
Meningeal layer
• Two layers are fused except to enclose the dural sinuses
The Dura Mater
•
Largest sinus—the superior sagittal sinus
•
Dura mater extends inward to subdivide the cranial cavity
The Arachnoid Mater
•
Located beneath the dura mater
•
Arachnoid villi
•
Project through the dura mater
•
Allow CSF to pass into the dural blood sinuses
The Pia Mater
•
Delicate connective tissue
•
Clings tightly to the surface of the brain
•
Follows all convolutions of the cortex
13 PART 7
The Central
Nervous System
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 produced per day
•
Only 100–160 ml present at any one time
Blood-Brain Barrier
•
Prevents most blood borne toxins from entering the brain
•
Impermeable capillaries
•
Not an absolute barrier
•
Nutrients such as oxygen pass through
•
Allows passage of alcohol, nicotine, and anesthetics
The Spinal Cord
•
Functions of
•
Spinal nerves attach to it
•
Provides two-way conduction pathway
•
Major center for reflexes
•
Location
•
Runs through the vertebral canal
•
Extends from the foramen magnum to the level of the vertebra L1 or L2
The Spinal Cord
•
Conus medullaris
•
The inferior end of the spinal cord
•
Filum terminale
•
Long filament of connective tissue
•
Attaches to the coccyx inferiorly
•
Cervical and lumbar enlargements
•
Where nerves for upper and lower limbs arise
•
Cauda equina
•
Collection of spinal nerve roots
The Spinal Cord
•
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
•
Outer region of the spinal cord
•
Composed of myelinated and nonmyelinated axons
•
Allow communication between spinal cord and brain
•
Fibers classified by type
•
Ascending fibers
•
Descending fibers
•
Commissural fibers
Gray Matter of the Spinal Cord and Spinal Roots
•
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
Gray Matter of the Spinal Cord
•
Gray matter is primarily neuronal cell bodies and some nonmyelinated axons
•
Regions of gray matter
•
Gray commissure
•
Dorsal horns
•
Ventral horns
•
Lateral horns
Gray Matter of the Spinal Cord
•
Gray matter
•
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
• Extends to the coccyx
• Denticulate ligaments—lateral extensions of pia mater
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
Sensory and Motor Pathways in the CNS
•
Multineuron pathways connect brain and body periphery
•
Pathways are composed of tracts
•
Ascending pathways—carry information to more rostral areas of the CNS
•
Descending pathways—carry information to more caudal regions of the CNS
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
Exhibit somatotopy
• Tracts arranged according to the body region they supply
All pathways are paired
•
One of each on each side of the body
Descending Pathways
•
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
Disorders of the Central Nervous System
•
Spinal cord damage
•
Paralysis—loss of motor function
•
Parasthesia—loss of sensation
•
Paraplegia—injury to the spinal cord is between T1 and L2
• Paralysis of the lower limbs
•
Quadriplegia—injury to the spinal cord in the cervical region
• Paralysis of all four limbs
Disorders of the Central Nervous System
•
Brain dysfunction
•
Degenerative brain diseases
• Cerebrovascular accident (stroke)
• Blockage or interruption of blood flow to a brain region
• Alzheimer’s disease
• Progressive degenerative disease leading to dementias
Disorders of the Central Nervous System
•
Congenital malformations
•
Hydrocephalus
•
Neural tube defects
• Anencephaly—cerebrum and cerebellum are absent
• Spina bifida—absence of vertebral lamina
•
Cerebral palsy—voluntary muscles are poorly controlled
• Results from damage to the motor cortex
Postnatal Changes in the Brain
•
Brain structures complete development at different times
•
Critical periods in learning
• Language
•
•
Some development occurs into early 20s
Decline with age attributed to changes
• In neural circuitry
• Amount of neurotransmitters being released