Download Spinal Nerves

Unit 4
Chapters 10-11
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1. Cerebral
hemisphere
2. Diencephalon
4. Cerebellum
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3. Brain stem
• Midbrain
• Pons
• Medulla
oblongata
Figure 12.3d
Lateral ventricle
Anterior horn
Inferior
horn
Posterior
horn
Interventricular
foramen
Third ventricle
Inferior horn
Cerebral aqueduct
Fourth ventricle
Central canal
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Figure 12.5
Cortical Lobes
Frontal
lobe
Parietal lobe
Occipital lobe
Temporal lobe
Fissure
(a deep
sulcus)
Gyrus (ridge)
Cortex (gray matter)
Sulcus (shallow groove)
White matter
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Figure 12.6a
Anterior
Longitudinal
fissure
Frontal lobe
Cerebral veins
and arteries
covered by
arachnoid
mater
Parietal
lobe
Right cerebral
hemisphere
Occipital
lobe
Left cerebral
hemisphere
(c)
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Posterior
Figure 12.6c
1. Cerebral Hemispheres
•
•
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
•
The three types of functional areas are:
Motor areas—control voluntary movement
•
Sensory areas—conscious awareness of sensation
•
Association areas—integrate diverse information
White Matter
•
Myelinated fibers and their tracts
•
Responsible for communication
•
•
•
corpus callosum—connect gray matter of the two hemispheres
Basal Ganglia
•
•
Consists of the corpus striatum
•
Caudate nucleus
•
Lentiform nucleus (putamen + globus pallidus)
Though somewhat elusive, the following are thought to be functions
of basal nuclei
•
Influence muscular control
•
Help regulate attention and cognition
•
Regulate intensity of slow or stereotyped movements
•
Inhibit antagonistic and unnecessary movements
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Anterior
Cerebral cortex
Cerebral white matter
Corpus callosum
Caudate nucleus
Putamen
Globus
pallidus
Basal
Ganglia
Tail of caudate nucleus
Posterior
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Figure 12.11b (1 of 2)
Motor areas
Central sulcus
Primary motor cortex
Premotor cortex
Frontal eye field
Broca’s area
(outlined by dashes)
Prefrontal cortex
Working memory
for spatial tasks
Executive area for
task management
Working memory for
object-recall tasks
Solving complex,
multitask problems
(a) Lateral view, left cerebral hemisphere
Sensory areas and related
association areas
Primary somatosensory
cortex
Somatic
Somatosensory
sensation
association cortex
Gustatory cortex
(in insula)
Taste
Wernicke’s area
(outlined by dashes)
Primary visual
cortex
Visual
association
area
Auditory
association area
Primary
auditory cortex
Vision
Hearing
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
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Figure 12.8a
Lateralization of Cortical Function
• 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)
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• 80% of diencephalon
•
Fx
•
Sorts, edits, and relays information
•
Mediates sensation, motor activities,
cortical arousal, learning, and memory
Thalamus
(encloses third
ventricle)
Pineal gland
(part of epithalamus)
Hypothalamus
•
Infundibulum—stalk that connects to the pituitary gland
•
Fx
•
Autonomic control center for many visceral functions
(e.g., blood pressure, rate and force of heartbeat,
digestive tract motility)
•
Center for emotional response: Involved in perception
of pleasure, fear, and rage and in biological rhythms
and drives
•
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
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• Epithalamus
• Pineal gland—
extends from the
posterior border
and secretes
melatonin
• Melatonin—
helps
regulate
sleep-wake
cycles
Figure 12.12
3. Brain Stem
•
Controls automatic behaviors necessary for survival
•
Associated with 10 of the 12 pairs of cranial nerves
•
Three regions
•
•
Midbrain
•
visual /auditory reflex centers
•
Substantia nigra—functionally linked to basal nuclei
Pons
•
•
Fibers of the pons
•
Connect higher brain centers and the spinal cord
•
Relay impulses between the motor cortex and the cerebellum
•
Some nuclei of the reticular formation
•
Nuclei that help maintain normal rhythm of breathing
Medulla oblongata
•
Decussation of the pyramids—crossover of the corticospinal tracts
•
Autonomic reflex centers
•
Cardiovascular center
•
Respiratory centers
•
Additional centers regulate
•
Vomiting
•
Hiccuping
•
Swallowing
•
Coughing
•
Sneezing
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Superior
corpus
callosum
Lateral
ventricle
Basal nuclei
• Caudate
• Putamen
• Globus
pallidus
Thalamus
Gray matter
Third
ventricle
White matter
Pons
Medulla oblongata
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Decussation
of pyramids
Figure 12.10a
• 11% of brain mass
• Subconsciously provides precise timing and
appropriate patterns of voluntary skeletal
muscle contraction
• Folia—transversely oriented gyri
• Arbor vitae—distinctive treelike pattern of the
cerebellar white matter
• Signals from proprioceptors and visual and
equilibrium pathways continuously “inform” the
cerebellum of the body’s position and
momentum
• Recognizes and predicts sequences of events
during complex movements
• Plays a role in nonmotor functions such as
word association and puzzle solving
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4. The Cerebellum
NetworkingFunctional
Brain Systems:
Limbic
RAS
Visual
impulses
Radiations
to cerebral
cortex
Auditory
impulses
Reticular formation
Ascending general
sensory tracts
(touch, pain, temperature)
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Descending
motor projections
to spinal cord
Figure 12.19
EEG
• Records electrical activity that accompanies
brain function
• Measures electrical potential differences
between various cortical areas
• Change with age, sensory stimuli, brain
disease, and the chemical state of the body
• EEGs used to diagnose and localize brain
lesions, tumors, infarcts, infections,
abscesses, and epileptic lesions
• A flat EEG (no electrical activity) is clinical
evidence of death
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Figure 12.20a
Epilepsy
• A victim of epilepsy may lose consciousness, fall stiffly,
and have uncontrollable jerking
• Epilepsy is not associated with intellectual impairments
• Epilepsy occurs in 1% of the population
• Absence seizures, or petit mal
•
Mild seizures seen in young children where the expression
goes blank
• Tonic-clonic (grand mal) seizures
•
Victim loses consciousness, bones are often broken due to
intense contractions, may experience loss of bowel and
bladder control, and severe biting of the tongue
• Anticonvulsive drugs
• Vagus nerve stimulators implanted under the skin of the
chest can keep electrical activity of the brain from
becoming chaotic
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Higher Brain Functions: 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)
•
First two stages of NREM occur during the first 30–45 minutes of sleep
•
Fourth stage is achieved in about 90 minutes, and then REM sleep begins abruptly
•
Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm
•
RAS activity is inhibited during, but RAS also mediates, dreaming sleep
•
Narcolepsy Lapsing abruptly into sleep from the awake state
•
Insomnia Chronic inability to obtain the amount or quality of sleep needed
•
Sleep apnea Temporary cessation of breathing during sleep
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Higher Brain Functions: Language
• Broca’s area
• motor speech
• Wernicke’s area
• language recognition
• Basal Ganglia
• Experiences/perceptions
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Higher Brain Functions: Memory
• Storage and retrieval of information
• 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
• Factors that affect transfer from STM to LTM
• Emotional state—best if alert, motivated,
surprised, and aroused
• Rehearsal—repetition and practice
• Association—tying new information with old
memories
• Automatic memory—subconscious
information stored in LTM
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Protection of the Brain
Superior
sagittal sinus
Subdural
space
Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Subarachnoid
space
• Membranes (meninges)
•
Dura mater
•
•
•
Strongest meninx
Arachnoid mater
•
Middle layer with weblike extensions
•
Separated from the dura mater by the subdural space
•
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
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Figure 12.24
Superior
sagittal sinus
4
Choroid
plexus
Arachnoid villus
Interventricular
foramen
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
1
Right lateral ventricle
(deep to cut)
Choroid plexus
of fourth ventricle
3
Third ventricle
1 CSF is produced by the
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
(a) CSF circulation
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2
choroid plexus of each
ventricle.
2 CSF flows through the
ventricles and into the
subarachnoid space via the
median and lateral apertures.
Some CSF flows through the
central canal of the spinal cord.
3 CSF flows through the
subarachnoid space via Ependymal cells.
4 CSF is absorbed into the dural venous
sinuses via the arachnoid villi.
Figure 12.26a
Blood
Brain
Barrier
•
•
•
•
•
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Helps maintain a stable environment
for the brain
Separates neurons from some
bloodborne substances
Composition
• Continuous endothelium of
capillary walls
• Basal lamina
• Feet of astrocytes
• Provide signal to
endothelium for the
formation of tight junctions
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
Traumatic brain injuries
• Concussion
• temporary alteration
in function
• Contusion
• permanent damage
• Subdural or
subarachnoid
hemorrhage
• may force brain stem
through the foramen
magnum, resulting in
death
• Cerebral edema
• swelling of the brain
associated with
traumatic head injury
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Cerebrovascular accidents
(CVAs)(strokes)
• Blood circulation is
blocked and brain
tissue dies, e.g.,
blockage of a cerebral
artery by a blood clot
• Transient ischemic
attacks (TIAs)
• temporary episodes
of reversible
cerebral ischemia
• Tissue plasminogen
activator (tPA) is the
only approved
treatment for stroke
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Progressive, Degenerative
brain disorders
•
Alzheimer’s disease (AD):
• Excess accumulation of
protein tangles and plaques
that results in dementia
• Low Ach
•
Parkinson’s disease:
• Substantia nigra
• Low DA, excess Ach
•
Huntington’s disease:
• accumulation of the protein
huntingtin that leads to
degeneration of the basal
nuclei and cerebral cortex
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Spinal Cord
• Location
•
Begins at the foramen magnum
•
Ends as conus medullaris at L1 vertebra
• Functions
•
Provides two-way communication to and from the
brain
•
Contains spinal reflex centers
• Protection
•
Bone, meninges, and CSF
•
Cushion of fat and a network of veins in the epidural
space between the vertebrae and spinal dura mater
•
CSF in subarachnoid space
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Cervical
spinal nerves
• 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
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Dura and
arachnoid
mater
Cauda
equina
Thoracic
spinal nerves
Lumbar
spinal nerves
Sacral
spinal nerves
Figure 12.29a
Epidural space
(contains fat)
Subdural space
Subarachnoid
space
(contains CSF)
Pia mater
Arachnoid
mater
Dura mater
Spinal
meninges
Bone of
vertebra
Dorsal root
ganglion
Body
of vertebra
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Figure 12.31a
Dorsal median sulcus
Dorsal root
ganglion
Spinal nerve
Dorsal root
Central canal
Ventral median
fissure
Ventral root
Pia mater
Arachnoid mater
Spinal dura mater
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Figure 12.31b
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Somatic
motor neuron
Spinal nerve
Ventral root
(motor)
Ventral horn
(motor neurons)
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
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Figure 12.32
Spinal Cord Trauma
• Functional losses
•
Parasthesias
•
•
Sensory loss
Paralysis
•
Loss of motor function
•
Flaccid paralysis—severe damage to the
ventral root or ventral horn cells
•
•
Impulses do not reach muscles;
there is no voluntary or involuntary
control of muscles
•
Muscles atrophy
Spastic paralysis—damage to upper motor
neurons of the primary motor cortex
•
Spinal neurons remain intact;
muscles are stimulated by reflex
activity
•
No voluntary control of muscles
• 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
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Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
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Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 13.1
Classification by Location or Stimulus Type
1.
Exteroceptors
•
•
•
2.
Respond to stimuli arising
outside the body
Receptors in the skin for touch,
pressure, pain, and
temperature
•
Respond to stimuli arising in
internal viscera and blood
vessels
•
Sensitive to chemical changes,
tissue stretch, and temperature
changes
Mechanoreceptors
•
2.
3.
•
Respond to stretch in skeletal
muscles, tendons, joints,
ligaments, and connective
tissue coverings of bones and
muscles
•
Inform the brain of one’s
movements
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5.
respond to light energy
(e.g., retina)
Chemoreceptors
Proprioceptors
•
sensitive to changes in
temperature
Photoreceptors
•
4.
respond to touch, pressure,
vibration, stretch, and itch
Thermoreceptors
•
Most special sense organs
Interoceptors (visceroceptors)
3.
1.
respond to chemicals (e.g.,
smell, taste, changes in
blood chemistry)
Nociceptors
•
sensitive to pain-causing
stimuli (e.g. extreme heat or
cold, excessive pressure,
inflammatory chemicals)
Perceptual level (processing in
cortical sensory centers)
3
• Sensation
Motor
cortex
• the awareness of
changes in the
internal and
external
environment
• Perception
• the conscious
interpretation of
those stimuli
•
Levels of neural
integration in
sensory systems:
Somatosensory
cortex
Thalamus
Reticular
formation
Pons
2 Circuit level
(processing in
Spinal
ascending pathways) cord
Free nerve
endings (pain,
cold, warmth)
Muscle
spindle
Cerebellum
Medulla
1.
Receptor level—the
sensor receptors
2.
Circuit level—
ascending
pathways
3.
Perceptual level—
neuronal circuits in
the cerebral cortex
Receptor level
(sensory reception Joint
and transmission
kinesthetic
to CNS)
receptor
1
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Figure 13.2
Adaptation of Sensory Receptors
• Adaptation is a change in
sensitivity in the presence of a
constant stimulus
• Receptor membranes
become less responsive
• Receptor potentials decline
in frequency or stop
• Phasic (fast-adapting)
receptors signal the beginning
or end of a stimulus
• Examples: receptors for
pressure, touch, and smell
• Tonic receptors adapt slowly
or not at all
• Examples: nociceptors and
most proprioceptors
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Nerves
• Most nerves are mixtures
of afferent and efferent
fibers and somatic and
autonomic (visceral) fibers
Endoneurium
Axon
Myelin sheath
• Pure sensory (afferent) or
motor (efferent) nerves
Perineurium
are rare
• Types of fibers in mixed
nerves:
• Somatic afferent and
somatic efferent
• Visceral afferent and
visceral efferent
• Peripheral nerves
classified as cranial or
spinal nerves
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Epineurium
Fascicle
Blood
vessels
Ganglia
• Contain neuron cell
bodies associated
with nerves outside
of brain
• Dorsal root ganglia
(sensory, somatic)
(Chapter 12)
• Autonomic ganglia
(motor, visceral)
(Chapter 14)
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Cranial Nerves
• Twelve pairs of nerves associated with the
brain
• Most are mixed in function; two pairs are
purely sensory
• Each nerve is identified by a number
(I through XII) and a name
“On occasion, our trusty truck acts funny—very
good vehicle anyhow”
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Cranial nerves
I – VI
I
II
III
IV
V
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
VI Abducens
Cranial nerves
VII – XII
VII Facial
VIII Vestibulocochlear
IX
X
XI
XII
(b)
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Glossopharyngeal
Vagus
Accessory
Hypoglossal
Sensory
function
Motor
function
PS*
fibers
Yes (smell)
Yes (vision)
No
No
Yes (general
sensation)
No
No
Yes
Yes
Yes
No
No
Yes
No
No
No
Yes
No
Sensory
function
Motor
function
PS*
fibers
Yes (taste)
Yes (hearing
and balance)
Yes
Some
Yes
No
Yes (taste)
Yes (taste)
No
No
Yes
Yes
Yes
Yes
Yes
Yes
No
No
*PS = parasympathetic
Figure 13.5 (b)
Spinal Nerves
Cervical plexus
Brachial plexus
Cervical
enlargement
Intercostal
nerves
Cervical
nerves
C1 – C8
Thoracic
nerves
T1 – T12
• 31 pairs of mixed
nerves named
according to their
point of issue from
the spinal cord
• 8 cervical (C1–C8)
Lumbar
enlargement
Lumbar plexus
Sacral plexus
Cauda equina
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• 12 thoracic (T1–T12)
Lumbar
nerves
L1 – L5
Sacral nerves
S1 – S5
• 5 Lumbar (L1–L5)
• 5 Sacral (S1–S5)
• 1 Coccygeal (C0)
Coccygeal nerve Co1
Figure 13.6
Spinal Nerves: Roots and Rami
• Each spinal nerve connects to the
spinal cord via two roots
•
• Ventral roots
•
•
Contain motor (efferent) fibers from
the ventral horn motor neurons
Fibers innervate skeletal muscles)
• Dorsal roots
•
•
Contain sensory (afferent) fibers from
sensory neurons in the dorsal root
ganglia
Conduct impulses from peripheral
receptors
Each spinal nerve branches into mixed rami
•
Dorsal ramus
•
Larger ventral ramus
•
Meningeal branch
•
Rami communicantes (autonomic pathways)
join to the ventral rami in the thoracic region
•
All ventral rami except T2–T12 form interlacing
nerve networks called plexuses (cervical,
brachial, lumbar, and sacral)
•
The back is innervated by dorsal rami via
several branches
•
Ventral rami of T2–T12 as intercostal nerves
supply muscles of the ribs, anterolateral thorax,
and abdominal wall
Dorsal ramus
Ventral ramus
Spinal nerve
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Dorsal root
ganglion
Dorsal root
Ventral root
Dermatome
• the area of skin
innervated by the
cutaneous branches of
a single spinal nerve
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
C2
C3
C4
C5
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T2
C5
C6
C6
C7
L1
C8
L2
T12
S2
S3
T2
C5
C6
L1
C8
L2
S1
L4
S2
S3
S4
S5
C6
C7
C6
C7
S2
• Most dermatomes
overlap, so destruction
of a single spinal nerve
will not cause complete
numbness
S1
L1
L3
L2
• All spinal nerves except
C1 participate in
dermatomes
C8
C8
L2
L5
L4
T11
T12
L1
L3
L5
C7
C6
S1 S2
L3
C5
L5
L4
L3
L5
L5
L4
S1
S1
L4
L5
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L4
L5
S1
Figure 13.12
Reflexes
Stimulus
Skin
• Inborn (intrinsic) reflex: a rapid,
involuntary, predictable motor
response to a stimulus
• Learned (acquired) reflexes result
from practice or repetition,
• Example: driving skills
1 Receptor
Interneuron
2 Sensory neuron
3 Integration center
4 Motor neuron
5 Effector
Spinal cord
(in cross section)
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Figure 13.14
The patellar (knee-jerk) reflex—a specific example of a stretch reflex
2
Quadriceps
(extensors)
1
3a
3b
3b
Patella
Muscle
spindle
Spinal cord
(L2–L4)
Hamstrings
(flexors)
Patellar
ligament
1 Tapping the patellar ligament excites
muscle spindles in the quadriceps.
2 Afferent impulses (blue) travel to the
spinal cord, where synapses occur with
motor neurons and interneurons.
3a The motor neurons (red) send
+
–
Excitatory synapse
Inhibitory synapse
activating impulses to the quadriceps
causing it to contract, extending the
knee.
3b The interneurons (green) make
inhibitory synapses with ventral horn
neurons (purple) that prevent the
antagonist muscles (hamstrings) from
resisting the contraction of the
quadriceps.
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Figure 13.17 (2 of 2)