ch 13 anatomy of the nervous system
TRANSCRIPT
Ch 13 Anatomy of the
Nervous System
13-1 The Embryologic Perspective
Embryological Development
Determines organization of nervous system
structures
Neural plate Neural groove Neural fold
Neural tube
Origin of CNS (brain, spinal cord) and PNS
The three germ layers are formed at
gastrulation at implantation
Ectoderm: outside, surrounds
other layers later in
development, generates skin
and nervous tissue.
Mesoderm: middle layer,
generates most of the
muscle, blood and
connective tissues of the
body and placenta.
Endoderm: eventually most
interior of embryo, generates
the epithelial lining and
associated glands of the gut,
lung, and urogenital tracts.
Neurulation: folding of the neural plate
Cranial Neural Crest:Contribute to forehead, face, jaw, and pharyngeal arch derivatives
The spinal cord and the vertebral column are the same length up until the 3rd
month.
As each vertebral body grows thicker, the overall length of the vertebral column begins to exceed that of the spinal cord such that , in the adult the spinal cord terminates at L2 or 3 and the dural sac ends at about S2.
The tail end of the dural sac covering the spinal cord and nerve roots remains attached at the coccyx and becomes a long, thin strand called the filum terminale.
“Regression” of the spinal cord
The Embryologic Brain
Origin of brain enlarges into three primary brain vesicles
(3 wks) -prosencephalon – mesencephalon –rhombencephalon
Five Secondary Brain Vesicles – (6 wks) Telencephalon –Diencephalon –
Mesencephalon –Metencephalon-Myelencephalon
Brain Development - Birth
Diencephalon and mesencephalon persist
Telencephalon:
Becomes cerebrum
Metencephalon
Forms cerebellum and pons
Myelencephalon
Becomes medulla oblongata
13-2 The Central Nervous System
Adult Human Brain
Ranges from 750 cc to 2100 cc and contains almost 97% of the body’s
neural tissue
Average weight about 1.4 kg (3 lb)
Six Regions of the Brain
Cerebrum
Cerebellum
Diencephalon
Mesencephalon
Pons
Medulla oblongata
The Brain
Cerebrum
Largest part of brain
Controls higher mental functions & processes
somatic sensory and motor information
Divided into left and right cerebral
hemispheres
Surface layer of gray matter (neural cortex)
Cerebrum
Neural cortex- also called cerebral cortex
Folded surface increases surface area
Elevated ridges (gyri) - shallow depressions (sulci)
Deep grooves (fissures)
Gray matter
In cerebral cortex and basal nuclei
White matter
Deep to basal cortex
Around basal nuclei
Structures of the Cerebrum
Gyri of neural cortex -increase surface area (number of
cortical neurons)
Insula (island) of cortex -lies medial to lateral sulcus
Longitudinal fissure - separates cerebral hemispheres
Lobes -divisions of hemispheres
Sulcus (Sulci)
Central sulcus divides anterior frontal lobe from posterior
parietal lobe
Lateral sulcus divides frontal lobe from temporal lobe
Parieto-occipital sulcus divides parietal lobe from
occipital lobe
Cerebrum
The Cerebrum
Cerebrum
Cerebrum- Basal Nuclei
Basal Nuclei
Also called cerebral nuclei are masses of gray matter
embedded in white matter of cerebrum
Direct subconscious activities
Functions of Basal Nuclei
Involved with
subconscious control of skeletal muscle tone
coordination of learned movement patterns (walking,
lifting)
Basal Nuclei
.
The Basal Nuclei
.
Cerebral Cortex – Motor Areas
Motor and Sensory Areas of the Cortex
Central sulcus separates motor and sensory areas
Motor areas
Precentral gyrus of frontal lobe:
– directs voluntary movements
Primary motor cortex:
– is the surface of precentral gyrus
Pyramidal cells:
– are neurons of primary motor cortex
Cerebral Cortex – Sensory Areas
Sensory areas
Postcentral gyrus of parietal lobe:
– receives somatic sensory information (touch,
pressure, pain, vibration, taste, and
temperature)
Primary sensory cortex:
– surface of postcentral gyrus
Cerebral Cortex- Special Senses
Special Sensory Cortexes
Visual cortex – occipital lobe
Information from sight receptors
Auditory cortex - temporal lobe
Information from sound receptors,long-term
memory
Olfactory cortex -
Information from odor receptors
Gustatory cortex
Information from taste receptors
Cerebrum – Sensory Areas
Sensory Association Areas
Somatic sensory association area
Interprets input to primary sensory cortex (e.g.,
recognizes and responds to touch)
Visual association area
Interprets activity in visual cortex
Auditory association area
Monitors auditory cortex
Cerebral Cortex
Cerebrum- Interpretive Areas
General Interpretive Area also called Wernicke area
Present in only one hemisphere -receives information from all
sensory association areas
Coordinates access to complex visual and auditory memories
Cerebrum- Integrative Areas
Integrative Areas- Frontal Lobe
Speech center
Is associated with general interpretive area
Coordinates all vocalization functions
Prefrontal cortex of frontal lobe
Integrates information from sensory association
areas
Performs abstract intellectual activities (e.g.,
predicting consequences of actions)
The Cerebrum
.
Cerebral Hemispheres
Hemispheric Lateralization
Functional differences between left and right
hemispheres
Each cerebral hemisphere performs certain
functions that are not ordinarily performed by
the opposite hemisphere
Cerebral Hemispheres
Left Hemisphere
In most people, left brain (dominant hemisphere)
controls
Reading, writing, and math
Decision making
Speech and language
Right Hemisphere
Right cerebral hemisphere relates to
Senses (touch, smell, sight, taste, feel)
Recognition (faces, voice inflections)
The Cerebrum
White Matter of Cerebrum
collection of axonal fibers that form
connections within one hemisphere and
connect the hemispheres,
Cerebral White Matter
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Monitoring Brain Activity
Brain activity is assessed by an
electroencephalogram (EEG)
Electrodes are placed on the skull
Patterns of electrical
activity (brain waves)
are printed out
Cerebellum
Second largest part of brain
Coordinates repetitive body movements
Two hemispheres covered with cerebellar cortex
Functions of the Cerebellum
Adjusts postural muscles
Fine-tunes conscious
and subconscious movements
Cerebellum
Cerebellum
Cells and Structures
Purkinje cells
Large, branched cells
Found in cerebellar cortex
Receive input from up to 200,000 synapses
Arbor vitae
Highly branched, internal white matter of
cerebellum
Cerebellar nuclei: embedded in arbor vitae:
– relay information to Purkinje cells
Diencephalon
Located under cerebrum and cerebellum
Links cerebrum with brain stem
Thalamus
Relays and processes sensory information
Hypothalamus
Hormone production
Autonomic function- helps maintains homeostasis
Pituitary gland - Major endocrine gland
Connected to hypothalamus via infundibulum (stalk)
Interfaces nervous and endocrine systems
Diencephalon
Diencephalon
Mamillary bodies
Process olfactory and other sensory information
Control reflex eating movements
Hypothalmus
Eight Functions
Provides subconscious control of skeletal
muscle
Controls autonomic function
Coordinates activities of nervous and
endocrine systems
Secretes hormones
Antidiuretic hormone (ADH)
Oxytocin (OT; OXT)
Hypothalamus
Produces emotions and behavioral drives
The feeding center (hunger)
The thirst center (thirst)
Coordinates voluntary and autonomic
functions
Regulates body temperature
Controls circadian rhythms (day–night cycles)
The Brain
StemProcesses information between spinal cord and cerebrum or
cerebellum Includes:
Mesencephalon
Pons
Medulla oblongata
Mesencephalon -called midbrain
Processes sight, sound, and associated reflexes
Maintains consciousness
Pons -connects cerebellum to brain stem
involved in somatic and visceral motor control
Mesencephalon
Tectum -Two pairs of sensory nuclei (corpora
quadrigemina):
–superior colliculus (visual)
– inferior colliculus (auditory)
Tegmentum
Red nucleus
Substantia nigra
(pigmented gray
matter)
Limbic System
Functional group of structures that establishes emotional states
Links conscious functions of prefrontal cortex with
autonomic functions of brain stem and facilitates memory
storage and retrieval
-Involves part of cerebrum and diencephalon
Cerebrum -Amygdaloid body
Acts as interface between the limbic system, the cerebrum,
and various sensory systems; modulates memory
Cerebrum
Cingulate gyrus, Dentate gyrus, Parahippocampal gyrus,
Hippocampus - “affective brain”
Limbic System
Tracts -Fornix
Tract of white matter
Connects hippocampus with hypothalamus
Diencephalon
Anterior nucleus of the thalamus
Relays information from mamillary body to
cingulate gyrus
Reticular formation
Stimulation or inhibition affects emotions (rage,
fear, pain, sexual arousal, pleasure)
Hypothalamus
Emotional responses
The Limbic System
Pons
Nuclei involved with respiration– modify respiratory rhythmicity center activity
Nuclei and tracts
Process and relay information to and from
cerebellum
Brain Stem
Medulla oblongata
Connects brain to spinal cord
Allows brain and spinal cord to communicate
Coordinates complex autonomic reflexes
Controls visceral functions
Relays information
Regulates autonomic functions:
–heart rate, blood pressure, and digestion
The Brain
Spinal Cord
Gross Anatomy of the Spinal Cord
About 18 inches (45 cm) long and 1/2 inch (14 mm) wide
Ends between vertebrae L1 and L2
Bilateral symmetry
Enlargements of the Spinal Cord
Caused by amount of gray matter in segment
Involvement with sensory and motor nerves of limbs
Cervical enlargement -nerves of shoulders and upper limbs
Lumbar enlargement -nerves of pelvis and lower limbs
Spinal Cord
Gross Anatomy of the Spinal Cord
The Distal End
Conus medullaris:
– thin, conical spinal cord below lumbar enlargement
Filum terminale:
– thin thread of fibrous tissue at end of conus
medullaris
– attaches to coccygeal ligament
Cauda equina:
– nerve roots extending below conus medullaris
Spinal Cord
Spinal Cord
Spinal Cord
Gray Matter and White Matter
White matter
Is superficial
Contains myelinated and unmyelinated axons
Gray matter
Surrounds central canal of spinal cord
Contains neuron cell bodies, neuroglia,
unmyelinated axons
Has projections (gray horns)
Spinal Cord Summary
Gray matter- covered by a thick layer of white matter
White matter
Consists of ascending and descending axons
Organized in columns/ tracts
Containing axon bundles with specific functions
Spinal cord is so highly organized
It is possible to predict results of injuries to specific
areas
Spinal Cord
Gray Matter and White Matter
Gray Matter of Spinal Cord
Organization of Gray Matter
The cell bodies of neurons form functional groups called
nuclei
Sensory nuclei:
– dorsal (posterior)
– connect to peripheral receptors
Motor nuclei:
– ventral (anterior)
– connect to peripheral effectors
Spinal Cord Gray Matter
Gray Horns
Posterior gray horns: contain somatic and visceral
sensory nuclei
Anterior gray horns: contain somatic motor nuclei
Lateral gray horns: are in thoracic and lumbar
segments; contain visceral motor nuclei
13.3 Circulation and the CNS
Blood Supply to the Brain
Supplies nutrients and oxygen to brain
Delivered by internal carotid arteries and vertebral arteries
Removed from dural sinuses by internal jugular veins
Cerebrovascular Disease
Disorders interfere with blood circulation to brain
Stroke or cerebrovascular accident (CVA)
Shuts off blood to portion of brain
Neurons die
Brain Blood Support
.
CNS Protection and Support
Bones of the cranium and vertebrae
Meninges stabilize brain in cranial cavity
Cerebrospinal fluid (CSF)protects against
sudden movement
CSF provides nutrients and removes wastes
Blood–brain barrier and blood (BBB)–CSF
barrier
Selectively isolate brain from chemicals in blood that
might disrupt neural function
The Meninges
Specialized membranes isolate CNS from surroundings
Functions of the spinal meninges include
Protect spinal cord and carry blood supply
Spinal meninges continuous with cranial meninges
Meningitis: Viral or bacterial infection of meninges
3 Layers
Dura mater -Outer layer
Arachnoid membrane (mater) -Middle meningeal layer
Pia mater - Innermost meningeal layer
Spinal Cord
Dura Mater
Tough and fibrous
Cranially -fuses with periosteum of occipital bone
Protect the brain from cranial trauma
Caudally –Spinal Cord
Tapers to dense cord of collagen fibers
Joins filum terminale to coccygeal ligament
Epidural Space in Spinal Cord
Between spinal dura mater and walls of vertebral
canal
Contains loose connective and adipose tissue
Anesthetic injection site
The Cranial Dural Meninges
Cranial Dural Folds
Folded inner layer of dura mater extends into cranial cavity
Stabilize and support brain
Contain collecting veins (dural sinuses)
Falx cerebri,
tentorium cerebelli, and
falx cerebelli
Dural Folds
Falx cerebri
Projects between the cerebral hemispheres
Contains superior sagittal sinus and inferior sagittal
sinus
Tentorium cerebelli
Separates cerebellum and cerebrum
Contains transverse sinus
Falx cerebelli
Divides cerebellar hemispheres below the tentorium cerebelli
Arachnoid Membrane/Mater
Middle meningeal layer
Arachnoid membrane -Simple squamous epithelia
Covers arachnoid mater
Spaces of Arachnoid Mater
Subdural space -between arachnoid mater and dura mater
Subarachnoid space-between arachnoid mater and pia mater
Contains collagen/elastin fiber network (arachnoid trabeculae)
Filled with cerebrospinal fluid (CSF)
Cerebrospinal Fluid (CSF) carries dissolved gases, nutrients,
and wastes
Spinal tap: withdraws CSF
Pia Mater
Is the innermost meningeal layer
Is a mesh of collagen and elastic fibers
Is bound to underlying neural tissue
The Brain- Ventricles
Four Ventricles of the Brain- internal passageways and
chambers filled with cerebrospinal fluid
2 lateral (1-2), 3rd, and 4th ventricles
Lateral ventricles
Each cerebral hemisphere contains one large lateral ventricle
Separated by a thin medial partition (septum
pellucidum)
Third ventricle -ventricle of the diencephalon
Lateral ventricles communicate with third ventricle:
– via interventricular foramen (foramen of Monro)
Ventricles
Fourth ventricle - Extends into medulla oblongata and
ecomes continuous with central canal of the spinal cord
and connects with third ventricle:
Cerebrospinal Fluid (CSF)
Surrounds all exposed surfaces of CNS
Interchanges with interstitial fluid of brain
Functions of CSF
Cushions delicate neural structures
Supports brain
Transports nutrients, chemical messengers, and
waste products
Choroid Plexus and CSF
Choroid plexus-specialized ependymal cells and
capillaries:
– secrete CSF into ventricles
– remove waste products from CSF
– adjust composition of CSF
Produces about 500 mL of CSF/day
CSF circulates-from choroid plexus through ventricles to central
canal of spinal cord
Into subarachnoid space around the brain, spinal cord, and cauda
equina
Brain Protection and Support
The Blood-Brain Barrier (BBB)
Isolates CNS neural tissue from general circulation
Formed by network of tight junctions
Between endothelial cells of CNS capillaries
Lipid-soluble compounds (O2, CO2), steroids, and
prostaglandins diffuse into interstitial fluid of brain and
spinal cord
Astrocytes control blood–brain barrier by releasing
chemicals that control permeability of endothelium
Breaks in the BBB
Four Breaks in the BBB
Portions of hypothalamus
Secrete hypothalamic hormones
Posterior lobe of pituitary gland
Secretes hormones ADH and oxytocin
Pineal glands
Pineal secretions
Choroid plexus
Where special ependymal cells maintain blood–
CSF barrier
13-4 The Peripheral Nervous System
Anatomy
Ganglia –groups of neuronal cell bodies that are either
sensory of autonomic
Most Common:
Cranial nerve ganglia
contain cell bodies of sensory neurons associated
with spinal nerves
Dorsal root ganglia
contain cell bodies of sensory neurons near spinal
cord.
PNS Start
Peripheral Nerves
Nerves – bundles of axons in the PNS
Three Connective Tissue Layers of Nerves
Epineurium
Outer layer
Dense network of collagen fibers
Perineurium
Middle layer
Divides nerve into fascicles (axon bundles)
Endoneurium
Inner layer
Surrounds individual axons
Peripheral Nerves
Spinal Nerves
Each side of spine -Dorsal and ventral roots join
To form a spinal nerve
Mixed Nerves
Carry both afferent (sensory) and efferent
(motor) fibers
Roots -two branches of spinal nerves
Ventral root: contains axons of motor neurons
Dorsal root: contains axons of sensory neurons
Motor Spinal Nerves
Sensory Spinal Nerves
Nerve Plexuses
Nerve Plexuses Complex, interwoven networks of nerve
fibers formed from blended fibers of ventral rami of adjacent
spinal nerves
Control skeletal muscles of the neck and limbs
Four Major Plexuses
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Spinal Nerves and Plexuses
Peripheral Nerves and Nerve Plexuses.
Spinal Nerves and Plexuses
Peripheral Nerves and Nerve Plexuses.
Brachial Plexuses
Brachial Plexus
Major nerves of brachial plexus
Musculocutaneous
Median nerve
Ulnar nerve
Axillary nerve
Radial nerve
Lumbar and Sacral Plexus
spinal nerves T12–L4 & L4–S4
Major nerves
Sciatic
Femoral
Saphenous
Branches of sciatic nerve
Fibular nerve
Tibial nerve
Lumbar and Sacral Plexuses
Cranial Nerves
12 pairs connected to brain -classified by primary
functions but may also have important secondary
functions
Distributing autonomic fibers to peripheral ganglia
Four Classifications of Cranial Nerves
Sensory nerves: carry somatic sensory information,
including touch, pressure, vibration, temperature, and pain
Special sensory nerves: carry sensations such as smell,
sight, hearing, balance
Motor nerves: axons of somatic motor neurons
Mixed nerves: mixture of motor and sensory fibers
Cranial Nerves
Olfactory Nerves (I)
Primary function
Special sensory (smell)
Origin
Receptors of olfactory epithelium
Pathway
Olfactory foramina in cribriform plate of ethmoid
Destination
Olfactory bulbs- on either side of crista galli
Olfactory tracts-Axons of postsynaptic neurons
leading to cerebrum
Optic Nerves (II)
Primary function
Special sensory (vision)
Origin
Retina of eye
Pathway
Optic canals of sphenoid
Destination
Diencephalon via optic chiasm-Where sensory fibers
converge and cross to opposite side of brain
Oculomotor Nerves (III)
Primary function - Motor (eye movements)
Trochlear Nerves (IV)
Primary function -Motor (eye movements)
Abducens Nerves (VI)
Primary function -Motor (eye movements)
Trigeminal Nerves (V)
Primary function –
Mixed (sensory and motor)
Maxillary branch (sensory)
– -lower eyelid
– upper lip, gums, and teeth
– cheek and nose
– palate and part of pharynx
Mandibular branch (sensory):
– lower gums, teeth, and lips
– palate and part of tongue
Mandibular branch (motor):
– motor nuclei of pons
Facial Nerves (VII)
Primary function
Mixed (sensory and motor) to face
Vestibulocochlear Nerves (VIII) Primary function: special sensory
Vestibular branch:
– balance and equilibrium
Cochlear branch:
– hearing
Glossopharyngeal Nerves (IX)
Primary function
Mixed (sensory and motor) to head and neck
Vagus Nerves (X)
Primary function Mixed (sensory and motor)
– Widely distributed in thorax and abdomen
– muscles of the palate and pharynx
– muscles of the
digestive, respiratory,
and cardiovascular
systems in thoracic
and abdominal cavities
Accessory Nerves (XI)
Primary function -Motor to muscles of neck and
upper back
Hypoglossal Nerves (XII)
Primary function -motor (tongue movements)