Transcript Document

Axoplasmic transport
Nucleus
Endoplasmic
reticulum
Golgi
complex
Secretory
vesicle
Microtubular “highway”
Axon
Lysosome
Cell body
Debris
Axon
terminal
Neurocytology & Tract-tracing
Widely used techniques for studying neurons and circuits:
Visualization of neurons
Nissl staining, Golgi methods, intracellular dye injections, immunohistochemistry
Degeneration and reactive changes in the neuron after lesion
Wallerian degeneration
Axonal transport methods
Autoradiography, HRP, Lectins, Biocytin, Dextrans, Fluorescent Tracers
Neuronal cell bodies: Nissl method
The Golgi
method
cerebellar
Purkinje cell
Biolistics
(“gene-gun”)
Intracellular injection
of Lucifer Yellow
Immunohistochemistry
L7 protein reveals cerebellar
Purkinje cells
PEP-19 antiserum reveals the
calyx of Held
TractTracing
Anterograde
Degeneration:
Reduced silver
method
and
electron microscopy
Retrograde
degeneration
Anterograde Wallerian
degeneration
Anterograde
Tract-tracing
Autoradiography
Collateral
projections
Labeled
terminals
Anterograde
transport
Radioactively
labeled amino acid
Uptake by
Cell body
Retrograde
Tract-Tracing
HRP, Dextran
Retrograde
transport
Uptake by
terminals
HRP
Tract-tracing:
Fluorescent
tracers
Combining techniques at the
LM and EM level
Protection of the CNS
• The cranium encloses the brain, and the vertebral
column encloses the spinal cord.
• The CNS is wrapped by several meninges: the
outer dura mater, the middle arachnoid mater, and
the innermost pia mater.
• The brain is surrounded by (and suspended in) the
cerebrospinal fluid (CSF).
• The blood-brain barrier limits access of bloodborne substances to the brain.
Cranial cavity: contents
• The cranial cavity (and vertebral canal) are closed,
relatively isolated spaces.
• Basic boundary is the arachnoid mater
• Contents include:
 Brain and spinal cord (intra- and extracellular fluid)
 CSF
 Blood
CSF formation = ~500 ml/day
brain = 1500 ml (1200 ICF; 300 ECF)
CSF = 125 ml (30 in ventricles)
blood = 80 ml
dura
arachnoid
Right lateral
ventricle
Left lateral
ventricle
Third ventricle
Central canal
of spinal cord
Fourth ventricle
The CSF is formed and circulates
in the ventricles.
It is produced by the choroid
plexuses inside the
ventricles, and circulates
through the ventricles.
From the fourth ventricle it
enters the subarachnoid
space, between the
arachnoid mater and pia
mater.
Arachnoid villi in this space
drain the CSF into the blood.
Scalp
Skull bone
Dura mater
Dural sinus
Arachnoid villus
Arachnoid mater
Subarachnoid
space of brain
Pia mater
Venous sinus
Brain (cerebrum)
CSF production
• >80% from choroid plexus
(specialized ependymal cells)
• rate = .3-.4 ml/min
(~500ml total vol./day)
•pressure=<200 mm H2O
CSF composition
•
•
•
•
•
clear and colorless
little/no protein
acellular (0-5 wbc/ml is normal)
low Glucose (30% below plasma)
Ions: = Na+, Cl, K+, Ca++
(comp. to plasma)
• pH =7.33
• *cloudy, colored, cellular CSF implies
pathology
CSF pathology
•too much anywhere = hydrocephalus
•excess production = quite rare
•impeded circulation = “non-communicating” hc
(blockages)
•impeded drainage = “communicating” hc due to
failed reabsorption
•leaking from head = skull fracture
•altered composition = bleeds, infections, tumors
Cerebral circulation
• Brain = 3 - 4% of body weight
 gets 15-18% of cardiac output
 uses 20% of total O2 consumed
• specialized barrier functions (BBB)
• specific areas which lack BBB
Space containing cerebrospinal fluid
Ependymal cell
Neurons
Astrocyte
Capillary
Microglial cell
Oligodendrocyte
Functional blood-brain barrier
• allows: small lipophilic molecules;
substances with mediated transport (amino
acids, glucose)
• blocks: large, charged, hydrophilic
molecules; some therapeutics (antibiotics)
• imaging can detect “leaks” indicating
pathology
Top
Corpus callosum
Cerebral cortex
Front
of
brain
Thalamus
(wall of third
ventricular cavity)
Pineal gland
Hypothalamus
Cerebellum
Pituitary gland
Brain stem
Spinal cord
The CNS consists of the brain
and spinal cord.
• The outline for brain anatomy is:
 Brain stem
 Cerebellum
 Forebrain
• Diencephalon
 Hypothalamus
 Thalamus
• Cerebrum
 Basal nuclei
 Cerebral cortex
Brain component
Table 5.3 (1)
Page 144
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
Thalamus
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
Brain stem
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
Spinal cord
Major Functions
1. Sensory perception
2. Voluntary control of movement
3. Language
4. Personality traits
5. Sophisticated mental events, such as thinking memory,
decision making, creativity, and self-consciousness
1. Inhibition of muscle tone
2. Coordination of slow, sustained movements
3. Suppression of useless patterns of movements
1. Relay station for all synaptic input
2. Crude awareness of sensation
3. Some degree of consciousness
4. Role in motor control
1. Regulation of many homeostatic functions, such as temperature
control, thirst, urine output, and food intake
2. Important link between nervous and endocrine systems
3. Extensive involvement with emotion and basic behavioral patterns
1. Maintenance of balance
2. Enhancement of muscle tone
3. Coordination and planning of skilled voluntary muscle activity
1. Origin of majority of peripheral cranial nerves
2. Cardiovascular, respiratory, and digestive control centers
3. Regulation of muscle reflexes involved with equilibrium and posture
4. Reception and integration of all synaptic input from spinal cord;
arousal and activation of cerebral cortex
5. Role in sleep-wake cycle
The basal nuclei have an inhibitory role
in motor control:
• inhibiting muscle tone throughout the body
• selecting and maintaining purposeful muscle activity while inhibiting
useless movement
• monitoring and controlling slow, sustained contractions
• Implicated in Parkinson’s Disease (dopamine deficiency)
 Increased muscle tone; resting tremors; slow initiation of movement
The limbic system
Frontal lobe
•
•
•
•
•
functions with the higher cortex.
plays a key role in emotion.
works with the higher cerebral
cortex to control behavioral
patterns.
the limbic system has reward and
punishment centers.
neurotransmitters in the
pathways for emotional behavior
include norepinephrine,
dopamine, and serotonin.
Cingulate gyrus
Fornix
Thalamus
Hippocampus
Temporal lobe
Amygdala
Hypothalamus
Olfactory bulb
Median sagittal section of cerebellum
and brain stem
Regulation of
muscle tone,
coordination of
skilled voluntary
movement
Planning and
initiation of
voluntary activity
Maintenance of
balance, control
of eye movements
Vestibulocerebellum
Spinocerebellum
Cerebrocerebelum
Motor cortex
Spinocerebellum
Informed of
motor command
Makes adjustments
as necessary
Motor command
to muscles
Informed of
actual performance
Activates receptors
in muscles and joints
Movement
Skeletal muscles
The cerebral cortex has four lobes, each
is specialized for different activities.
• The lobes and some of their functions:
 Occipital lobe- initial processing of visual input
 Temporal lobe - integration of multiple sensory inputs, primary
auditory cortex, Wernicke’s area
 Parietal lobe - somatosensory processing. Each region of parietal
cortex receives somesthetic and proprioceptive input from a
specific body area, mostly from the opposite side of the body.
 Frontal lobe - voluntary motor activity, speaking ability (Broca’s
area), and elaboration of thought. Stimulation of different areas of
its primary motor cortex moves different body regions.
Central sulcus
Frontal
lobe
Parietal
lobe
Parietooccipital
notch
Occipital
lobe
Lateral
fissure
Cerebellum
Temporal
lobe
Brain stem
Occipital lobe
Primary visual cortex
Wernicke’s area
Primary auditory cortex
Temporal lobe
Somatosensory cortex
Central
sulcus
Posterior parietal cortex
Parietal lobe
Wernicke’s area
Sensory homunculus
Figure 5.11 (2)
Page 149
Left
hemisphere
Cross-sectional view
Temporal lobe
Primary motor cortex
Central
sulcus
Frontal lobe
Broca’s area
Motor homunculus
Left
hemisphere
Cross-sectional view
Temporal lobe
Other cortices and motor function
• supplementary motor cortex - medial surface of hemisphere
anterior to primary motor cortex.
 Preparatory role in programming complex sequences of movements.
Stimulation results in complex movement patterns. Lesions do not result
in paralysis, but interfere with integration.
• premotor cortex - lateral surface of hemisphere anterior to
primary motor cortex.
 Orienting body and arms toward specific targets. Must be informed of
body’s current position in relation to target. This information is relayed
by the posterior parietal cortex.
• posterior parietal cortex - posterior to the primary
somatosensory cortex.
 Integration of somatosensory and visual input- important for complex
movements.
Supplementary motor area
Premotor cortex
Frontal lobe
Primary motor cortex
Central
sulcus
Posterior parietal cortex
Association areas of the cortex carry out
many higher functions:
• prefrontal association cortex - functions include planning
for voluntary activity, decision-making, creativity, and
developing personality traits.
• parietal-temporal-occipital association cortex integrates somatic, auditory, and visual sensations from
these three lobes.
• limbic association cortex - involved with motivation,
emotion, and memory
Central
sulcus
Prefrontal association cortex
Parietal-temporal-occipital
association cortex
Limbic association cortex
Sensory input
Primary sensory areas
(somatosensory, 1o visual,
1o auditory cortices)
Higher sensory areas
Association areas
Higher motor areas
Primary motor areas
Motor output
Hemispheric specialization
• The left cerebral hemisphere excels in
performing logical, analytical, sequential,
and language/verbal tasks
• The right cerebral hemisphere excels in
spatial perception and artistic and musical
talents.
Different aspects of language are
controlled by different cortical areas.
• Broca’s area is responsible for speaking
ability.
• Wernicke’s area functions for language
comprehension.
• Various language disorders are localized in
different regions of the cerebral cortex.
Damage to these areas can explain the
origin of these disorders.
Facial area of
motor cortex
Angular gyrus of
parietal-temporal-occipital
association cortex
Broca’s
area
Wernicke’s
area
Bundle of
interconnecting fibers
Visual cortex