Download spinal cord

Lauralee Sherwood
Hillar Klandorf
Paul Yancey
Chapter 5
Nervous Systems
Sections 5.5-5.9
Kip McGilliard • Eastern Illinois University
5.5 Spinal Cord
 The spinal cord is a long, slender cylinder of
nerve tissue that retains fundamental segmental
organization.
• The number of spinal cord segments differs between
species.
• Spinal nerves (31 pairs in humans)
•
•
•
•
•
Cervical (8)
Thoracic (12)
Lumbar (5)
Sacral (5)
Coccygeal (1)
• Each region of the body surface, supplied by a
particular spinal nerve, is called a dermatome.
5.5 Spinal Cord
Spinal cord
Dorsal root
ganglion
Spinal
nerve
Meninges
(protective
coverings)
Vertebra
Intervertebral
disk
Sympathetic
ganglion
chain
Figure 5-16 p178
ANIMATION: Organization of the spinal
cord
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5.5 Spinal Cord
 Central gray matter is surrounded by white matter.
• Gray matter
• Cell bodies and their dendrites
• Dorsal horn contains cell bodies of interneurons on which
afferent neurons terminate
• Ventral horn contains cell bodies of efferent motor neurons
• Lateral horn contains cell bodies of autonomic neurons
• White matter
• Bundles of myelinated nerve fibers (tracts)
• Ascending tracts transmit afferent signals to the brain
• Descending tracts relay messages from brain to efferent
neurons
5.5 Spinal Cord
Axon
Myelin
sheath
Connective tissue
around the axon
Connective tissue
around a fascicle
Connective tissue
around the nerve
Blood vessels
Nerve fascicle
(many axons
bundled in
connective
tissue)
Nerve
Figure 5-20 p180
5.5 Spinal Cord
1
Somatosensory
area of cerebral
cortex
2
Thalamus
Primary motor cortex
Cerebral
cortex
3
4
Slide 1
5
Midbrain
Slide 2
Cerebellum
Slide 3
6
Pons
Slide 3
Ventral
spinocerebellar
tract
Medulla
Muscle stretch
receptor
Slide 4
Dorsal
column
tract
Spinal cord
Lateral
corticospinal
tract
Pressure
receptor
in skin
Ventral
corticospinal
tract
Spinal cord
Slide 5
Slide 5
Skeletal
muscle cell
(a) Ascending tracts
Spinal cord
(b) Descending tracts
Slide 6
Figure 5-18 p179
5.5 Spinal Cord
 Spinal nerves contain both afferent and
efferent fibers enclosed in connective
tissue.
• Afferent fibers enter the spinal cord through
the dorsal root
• Cell bodies of afferent neurons are clustered in
dorsal root ganglion
• Efferent fibers leave the spinal cord through
the ventral root
5.5 Spinal Cord
White matter
Gray matter
Cell body of
afferent neuron
Interneuron
Afferent fiber
Cell body of
efferent neuron
Efferent fiber
Dorsal root
Dorsal root
ganglion
From receptors
To effectors
Ventral root
Spinal nerve
Figure 5-17 p178
5.5 Spinal Cord
 Functions of the spinal cord
• Transmits information between the brain and
the body
• Integrates reflex activity between afferent
input and efferent output (spinal reflex)
5.5 Spinal Cord
 Withdrawal reflex
• Withdrawal of a limb from a painful stimulus
• Excited afferent neurons stimulate excitatory
interneurons that stimulate efferent motor
neurons to flexor muscles (polysynaptic reflex)
• Afferent neurons also stimulate inhibitory
interneurons that inhibit efferent neurons
supplying extensor muscles (reciprocal
innervation)
• Other interneurons ascend to carry the signal to a
sensory area of the brain
5.5 Spinal Cord
Stimulus
Thermal pain
receptor in paw
Ascending
pathway to brain
Afferent
pathway
Components of
a reflex arc
Receptor
Afferent pathway
Integrating center
Efferent pathway
Effector organs
Biceps
(flexor) contracts
Efferent pathway
Triceps
(extensor) relaxes
Foot
withdrawn
Integrating center
(spinal cord)
Effector
organs
Response
Figure 5-21 p181
5.5 Spinal Cord
 Stretch reflex
• Skeletal muscle contracts to counteract a stretch
stimulus
• Afferent neuron synapses directly on efferent
neuron (monosynaptic)
 Crossed extensor reflex
• Extension of the opposite limb during the
withdrawal reflex
• Ensures that opposing limb will be in position to
bear weight when the injured limb is withdrawn
5.5 Spinal Cord
Afferent
pathway
Efferent pathway
Efferent
pathway
Flexor
muscle
contracts
Pain
receptor
in heel
Integrating center
(spinal cord)
Extensor
muscle
relaxes
Flexor
muscle
relaxes
Injured
extremity
(effector
organ)
Extensor
muscle
contracts
Opposite
extremity
(effector
organ)
Response
Response
Stimulus
(a)
(b)
Figure 5-22 p183
ANIMATION: Nerve structure
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5.6 Brainstem and Cerebellum
 Brainstem
• Incoming and outgoing fibers pass through
the brainstem
• Functions
• Sensation input and motor output in the head and
neck via 12 pairs of cranial nerves
• Reflex control of heart, blood vessels, respiration
and digestion
• Modulation of pain sensation
• Regulation of muscle reflexes involved in
equilibrium and posture
• Control of level of cortical alertness via the
reticular activating system
5.6 Brainstem and Cerebellum
Reticular
activating
system
Cerebellum
Visual
impulses
Reticular
formation
Brain
stem
Auditory impulses
Ascending
sensory tracts
Descending motor
tracts
Spinal cord
Figure 5-23 p184
5.6 Brainstem and Cerebellum
 Cerebellum
• Important in balance and coordination
• Three parts
• Vestibulocerebellum -- maintains balance and
controls eye movements
• Cerebrocerebellum -- plans voluntary muscle
activity
• Spinocerebellum -- enhances muscle tone
and coordinates skilled movements
5.6 Brainstem and Cerebellum
Brain stem
Cerebellum
KEY
Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum
(a) Gross structure of cerebellum
Figure 5-24a p185
Regulation of
muscle tone,
coordination of
skilled voluntary
movement
Planning and
initiation of
voluntary activity,
storage of
procedural
memories
KEY
Vestibulocerebellum
Maintenance of
balance, control
of eye movements
Spinocerebellum
Cerebrocerebellum
(b) Unfolded cerebellum, revealing
three functionally distinct parts
Figure 5-24b p185
Median sagittal
section of
cerebellum
and brain stem
KEY
Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum
(c) Internal structure of cerebellum
Figure 5-24c p185
5.7 Basal Nuclei, Thalamus, Hypothalamus, and
Limbic System
 Basal nuclei (basal ganglia)
• Masses of gray matter deep within the
cerebrum
• Functions
• Inhibit muscle tone
• Select and maintain purposeful motor activity,
while suppressing unwanted movements
• Monitor and coordinate slow, sustained
contractions related to posture and support
5.7 Basal Nuclei, Thalamus, Hypothalamus, and
Limbic System
 Thalamus
• Synaptic integrating center for preliminary
processing of all sensory input
• Directs attention to stimuli of interest
5.7 Basal Nuclei, Thalamus, Hypothalamus, and
Limbic System
 Hypothalamus
• Integrating center for homeostatic functions
• Body temperature
• Thirst and urine output
• Food intake
• Controls anterior pituitary hormone secretion
• Produces posterior pituitary hormones
• Stimulate uterine contraction and milk ejection
• Autonomic nervous system coordination
• Emotional and behavioral patterns
• Sleep-wake cycle
5.7 Basal Nuclei, Thalamus, Hypothalamus, and
Limbic System
Corpus callosum
Cerebral cortex
Top
Front
of
brain
Part of the
limbic system
Thalamus
(wall of third
ventricular cavity)
Pineal gland
Bridge
that connects
the two halves
of the thalamus
Cerebellum
Hypothalamus
Brain
stem
Pituitary gland
Spinal cord
Figure 5-26 p187
5.7 Basal Nuclei, Thalamus, Hypothalamus, and
Limbic System
 Limbic system
• Ring of forebrain structures that surround the
brainstem
• Functions
• Emotion
• Amygdala -- gives rise to fear, avoidance of danger,
activates fight or flight responses
• Sociosexual behavior
• Motivation
• Highly motivated activities are eating, drinking, and
sexual behavior
• Learning
• Hippocampus -- memory
5.7 Basal Nuclei, Thalamus, Hypothalamus, and
Limbic System
Cingulate gyrus
Fornix
Thalamus
Hippocampus
Temporal lobe
Hypothalamus
Amygdala
Olfactory bulb
Figure 5-27 p188
5.8 Mammalian Cerebral Cortex
 Cerebrum
• Divided into two cerebral hemispheres
• Cerebral cortex -- outer shell of gray matter
• Six layers organized into functional vertical
columns
• Fiber tracts in white matter transmit signals
from one area to another
• Corpus callosum connects the two cerebral
hemispheres
5.8 Mammalian Cerebral Cortex
 Each hemisphere of the cerebral cortex is
divided into four lobes.
• Relative sizes of these lobes vary between
species
• Occipital lobe -- vision
• Temporal lobe -- hearing
• Parietal lobe -- body sensory (e.g. touch)
• Frontal lobe -- motor activity, speech,
memory, planning
5.8 Mammalian Cerebral Cortex
5.8 Mammalian Cerebral Cortex
5.8 Mammalian Cerebral Cortex
 Somatosensory cortex
• Anterior part of parietal lobe behind the central
sulcus
• Initial processing and perception of somasthetic
(body surface) and proprioceptive (body
position) sensations
• Receives sensory information from the opposite
side of the body
• Different body areas are mapped and unequally
represented on the surface (sensory
homunculus)
5.8 Mammalian Cerebral Cortex
Primary motor cortex
(voluntary movement)
Supplementary motor area
(on inner surface—not visible;
programming of complex movements)
Central
sulcus
Premotor cortex (coordination
of complex movements)
Prefrontal association cortex
(planning for voluntary
activity; decision making;
personality traits)
Somatosensory cortex
(somesthetic sensation
and proprioception)
Posterior parietal cortex
(integration of somatosensory
and visual input;
important for complex
movements)
Wernicke’s area
(speech understanding)
Parietal lobe
Frontal lobe
Broca’s area
(speech formation)
Parietal-temporal-occipital
association cortex
(integration of all
sensory input; important
in language)
Primary auditory cortex
surrounded by higher-order
auditory cortex (hearing)
Occipital lobe
Primary visual cortex
surrounded by higherorder visual cortex (sight)
Limbic association cortex
(mostly on inner and bottom
surface of temporal lobe;
motivation and emotion; memory)
Temporal lobe
Brain stem
Cerebellum
Spinal cord
(a) Regions of the cerebral cortex responsible for various functions
Figure 5-29a p191
5.8 Mammalian Cerebral Cortex
 Primary motor cortex
• Posterior part of frontal lobe in front of the
central sulcus
• Nonreflex control over movement produced by
skeletal muscles
• Controls the opposite side of the body
• Different muscle groups are mapped and
unequally represented on the surface (motor
homunculus)
5.8 Mammalian Cerebral Cortex
Front
Right hemisphere
Left hemisphere
Frontal lobe
Primary motor cortex
of left hemisphere
Somatosensory cortex
of left hemisphere
Central sulcus
Parietal lobe
Back
(a) Top view of brain
Occipital
lobe
Figure 5-30a p193
(a) Top view of brain
Top
Left
hemisphere
Cross-sectional view
Temporal lobe
(b) Sensory homunculus
Figure 5-30b p193
Top
Left
hemisphere
Cross-sectional view
Temporal lobe
(c) Motor homunculus
Figure 5-30c p193
5.8 Mammalian Cerebral Cortex
 Higher motor areas
• Readiness potential occurs about 750 msec
before electrical activity is detectable in motor
cortex
• Motor association areas program and
coordinate complex movements
• Supplementary motor area
• Premotor cortex
• Posterior parietal cortex
• Cerebellum is also involved in anticipatory
planning and timing of some movements
5.8 Mammalian Cerebral Cortex
5.8 Mammalian Cerebral Cortex
 Specialization of cerebral hemispheres
• Left cerebral hemisphere
• Speech
• Fine motor control (in right-handed people)
• Logical, analytical, sequential tasks
• Right cerebral hemisphere
• Nonlanguage skills
• Spatial perception, artistic, musical skills
• Left hemisphere dominant individuals are
“thinkers”, while right hemisphere dominant
individuals are “creators”
5.9 Learning, Memory, and Sleep
 Learning is the acquisition of abilities or
knowledge as a result of experience or
instruction.
 Memory is the storage of acquired
knowledge for later recall.
• Declarative or explicit memory -- learning of
facts, events, places, etc.
• Procedural or implicit memory -- learning of
skilled motor movements
• Imprinting -- programmed behaviors based on
experiences encountered early in life
5.9 Learning, Memory, and Sleep
 Memory
• Memory trace -- neural change responsible
for retention or storage of knowledge
• Short-term memory -- seconds to hours
• Long-term memory -- days to years
• Consolidation is the process of transferring
short-term memory into long-term memory
• Working memory is comparing current
sensory data with relevant stored knowledge
and manipulating that information
5.9 Learning, Memory, and Sleep
5.9 Learning, Memory, and Sleep
 Memory
• Remembering is the process of retrieving
information from memory stores
• Forgetting is the inability to retrieve stored
information
• Anandamide is a neuromodulator that
resets short-term memory neurons to their
unpotentiated state
5.9 Learning, Memory, and Sleep
 Brain regions implicated in memory storage
• Hippocampus
• Part of limbic system in temporal lobe
• Short-term declarative memory
• Consolidation into long-term memory in
prefrontal cortex and medial temporal lobe
• Cerebellum
• Procedural memories involving motor skills
• Gained through repetitive training
5.9 Learning, Memory, and Sleep
 Mechanisms of memory
• Short-term memory involves transient
modifications in the function of preexisting
synapses
• Studies of short-term memory in Aplysia
• Habituation -- decreased responsiveness to
repetitive presentation of an indifferent stimulus
• Sensitization -- increased responsiveness to
mild stimuli following a strong or noxious stimulus
5.9 Learning, Memory, and Sleep
Gill
Anus
Mantle and shell
Figure 5-33 p198
5.9 Learning, Memory, and Sleep
 Mechanisms of memory
• Long-term potentiation (LTP) -- prolonged
increase in the strength of existing synaptic
connections following repetitive stimulation
• Long-term memory involves formation of new
synaptic connections
• Immediate early genes (IEGs) govern synthesis of
the proteins that encode long-term memory
5.9 Learning, Memory, and Sleep
Siphon
Sensory
neuron
Sensory
neuron
Tail
area
Nucleus
Cyclic AMP
response
CREB-2 CREB-1
element
Serotoninreleasing
interneuron
Motor
neuron
Gene
expression
MAP kinase
Gill
Sensory neuron
Stimulus
Serotonin
Repeated
stimulation
Protein
kinase A
Cyclic
AMP
Serotonin
Growth
Protein
kinase A
Receptors
Cyclic
AMP
Motor
neuron
Short-term
A single stimulus increases the amount of
neurotransmitter released, which strengthens
the response.
(a) Short- vs long-term stimulation and CREB
Receptors
Long-term
Repeated stimulation causes kinases to move into
the nucleus, leading to gene expression and
growth of new synapses.
Figure 5-35a p202
5.9 Learning, Memory, and Sleep
 Sleep
• Characteristics
•
•
•
•
Periods of minimal movement
Reduced responsiveness to external stimuli
Rapid reversibility
A characteristic body posture
• Proposed functions
• Restoration and recovery
• Memory processing
• Energy conservation
5.9 Learning, Memory, and Sleep
 Types of sleep
• Slow-wave sleep
• Slow, large electroencephalogram (EEG) waves
• Considerable muscle tone with frequent body shifts
• Paradoxical or REM sleep
• Rapid, small EEG waves
• No muscle tone and little movement
• Rapid eye movements (REM)