cell body endoplasmic reticulum nucleus lysosome golgi complex microtubular “highway” axondebris...
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Cell body
EndoplasmicreticulumNucleus
Lysosome
Golgicomplex
Microtubular “highway”
Axon Debris
Secretoryvesicle
Axonterminal
Axoplasmic transport
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
cerebellarPurkinje cell
Intracellular injectionof Lucifer Yellow
Biolistics (“gene-gun”)
Immunohistochemistry
PEP-19 antiserum reveals the calyx of Held
L7 protein reveals cerebellar Purkinje cells
Tract-Tracing
Anterograde Degeneration:Reduced silver
method and
electron microscopy
Anterograde Walleriandegeneration
Retrogradedegeneration
AnterogradeTract-tracing Autoradiography
Anterogradetransport
Uptake by Cell body
Collateralprojections
Labeledterminals
Radioactively labeled amino acid
RetrogradeTract-Tracing HRP, Dextran
Retrogradetransport
HRP
Uptake by terminals
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 blood-borne 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
dura
arachnoid
CSF formation = ~500 ml/day
brain = 1500 ml (1200 ICF; 300 ECF)
CSF = 125 ml (30 in ventricles)
blood = 80 ml
Right lateralventricle
Left lateralventricle
Central canalof spinal cord
Fourth ventricle
Third 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.
Subarachnoid space of brain
Arachnoid villus
Dural sinus
Pia mater
Dura mater
Arachnoid mater
Scalp
Skull bone
Venous sinus
Brain (cerebrum)
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
• >80% from choroid plexus
(specialized ependymal cells)
• rate = .3-.4 ml/min
(~500ml total vol./day)
•pressure=<200 mm H2O
CSF production
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
Oligodendrocyte
Capillary
Microglial cell
Astrocyte
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
Frontofbrain
Corpus callosum
Cerebral cortex
Thalamus(wall of thirdventricular cavity)
Pineal gland
Cerebellum
Hypothalamus
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
Table 5.3 (1)Page 144
Hypothalamus
Brain stem
Cerebral cortex
Thalamus(medial)
Basal nuclei(lateral to thalamus)
Cerebellum
Spinal cord
Midbrain
Pons
Medulla
Brain component
Cerebral cortex
Basal nuclei
Thalamus
Hypothalamus
Cerebellum
Brain stem(midbrain, pons,and medulla)
Major Functions
1. Sensory perception2. Voluntary control of movement3. Language4. Personality traits5. Sophisticated mental events, such as thinking memory, decision making, creativity, and self-consciousness
1. Inhibition of muscle tone2. Coordination of slow, sustained movements3. Suppression of useless patterns of movements
1. Relay station for all synaptic input2. Crude awareness of sensation3. Some degree of consciousness4. Role in motor control
1. Regulation of many homeostatic functions, such as temperature control, thirst, urine output, and food intake2. Important link between nervous and endocrine systems3. Extensive involvement with emotion and basic behavioral patterns
1. Maintenance of balance2. Enhancement of muscle tone3. Coordination and planning of skilled voluntary muscle activity
1. Origin of majority of peripheral cranial nerves2. Cardiovascular, respiratory, and digestive control centers3. Regulation of muscle reflexes involved with equilibrium and posture4. Reception and integration of all synaptic input from spinal cord; arousal and activation of cerebral cortex5. 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
Frontal lobe
Cingulate gyrus
Fornix
Thalamus
Hippocampus
Temporal lobe
Amygdala
Hypothalamus
Olfactory bulb
The limbic system
• 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.
Median sagittal section of cerebellumand brain stem
Vestibulocerebellum
Spinocerebellum
Cerebrocerebelum
Regulation of muscle tone,coordination of skilled voluntary movement
Planning and initiation of voluntary activity
Maintenance of balance, control of eye movements
Motor cortex
SpinocerebellumInformed ofmotor command
Makes adjustmentsas necessary
Motor commandto muscles
Informed ofactual performance
Activates receptorsin 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.
Frontallobe
Central sulcus
Parietallobe
Parietooccipitalnotch
Occipitallobe
Cerebellum
Brain stem
Temporallobe
Lateralfissure
Occipital lobe
Primary visual cortex
Wernicke’s area
Temporal lobe
Primary auditory cortex
Centralsulcus
Somatosensory cortex
Posterior parietal cortex
Wernicke’s area
Parietal lobe
Figure 5.11 (2)Page 149
Lefthemisphere
Cross-sectional view
Temporal lobe
Sensory homunculus
Primary motor cortex
Centralsulcus
Broca’s area
Frontal lobe
Lefthemisphere
Cross-sectional view
Temporal lobe
Motor homunculus
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 Primary motor cortex
Centralsulcus Posterior parietal cortex
Frontal lobe
Premotor 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
Centralsulcus
Parietal-temporal-occipitalassociation cortex
Limbic association cortex
Prefrontal 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 ofmotor cortex
Broca’sarea
Bundle ofinterconnecting fibers
Wernicke’sarea
Visual cortex
Angular gyrus ofparietal-temporal-occipitalassociation cortex