Transcript Central Nervous System

Central Nervous System
Chapter 12
Embryonic Nervous System
Development
• Ectoderm thickens to form the neural
plate
• Invaginates to form neural groove
• Neural folds fuse to neural tube (3rd
week)
– Anterior end expands out = brain
– Posterior = spinal cord
• Neural crest become PNS ganglia and
glia
– Pigment cells too
Embryonic Brain Development
Primary vesicle
system
Secondary vesicle
system
Adult brain structures
Ventricle
system
Lateral ventricles
prosencephalon
3rd ventricle
Cerebral aqueduct
mesencephalon
4th ventricle
rhombencephalon
ANATOMICAL BRAIN REGIONS
Ventricles
•
•
•
•
Interconnected tubular system
Filled with CSF (ependymal cells)
Apertures in 4th ventricle connect to subarachnoid space
Need to know (CSF pathway):
–
–
–
–
–
–
–
–
Lateral ventricles
Septum pellucidum
Interventricular foramen
3rd ventricle
Cerebral aqueduct
4th ventricle
Central canal
Aperatures
Cerebral Hemispheres
• Gyri - ridges of tissue
– Pre- & postcentral
• Sulci – shallow grooves
– Central, pareito-occipital, &
lateral
• Fissures – deeper grooves
– Longitudinal & transverse
• Lobes
– Frontal, parietal (2), temporal (2),
occipital, & insula*
• Basic regions
– Cotex, white matter, & basal
nuclei
Cerebral Cortex
• Gray matter composed of
interneurons
• 3 Functional areas
– Motor areas
– Sensory areas
• Olfactory cortex
– Association areas
• Demonstrates lateralization
– Left: math, speech, concrete
processing, logic
– Right: creativity, facial and pattern
recognition
• Contralateral control
Homunculus
• Entire body mapped within the brain = somatotopy
– Most neurons to areas w/ most precise control or
sensitivity
• Somatosensory version receives message from sensors
– Spatial discrimination
• Motor version sends message to muscles
• Areas are adjacently mapped
• Contralateral control
http://www.pc.rhul.ac.uk/staff/J.Zanker/P
S1061/L6/homuncul.gif
http://www.fizyka.umk.pl/~duch/ref/01/01-plastic/motorsomato.gif
Cerebral Cortex Damage
• Primary motor cortex
– Paralyzes voluntary muscles; reflexes intact
– Contralateral effects
• Premotor cortex
– Loss of motor skills; strength and ability unaffected
– Practice rewires
• Visual cortex
– Primary: functional blindness
– Association: can see, but not comprehend
• Language areas
– Broca’s: speech production
– Wernike’s: speech comprehension
Cerebral White Matter
• Communication between cerebral
areas and lower CNS
• Directional myelinated fibers
– Commissural fibers
• Connect hemispheres
• E.g. corpus callosum
– Association
• Connect parts of same hemisphere
• Adjacent gyri or different lobes
– Projection
• Enter or leave cerebral cortex
• Connect cortex to rest of NS, receptors, &
effectors
• E.g internal capsule & corona radiata
Basal Nuclei
• Input from all of cerebral cortex
– Project to premotor & prefrontal
areas via the thalamus
• Limit excessive mov’ts;
multitasking
– PD and HD connection
• Corpus striatum
– Caudate nucleus
– Lentiform nucleus
• Putamen
• Globus pallidus
• Associated with subthalamic
nuclei and substantia nigra
Diencephalon
• Thalamus
– Gray matter masses joined by the intermediate mass
– Regionally named specialty nuclei
http://academic.kellogg.cc.mi.us/
herbrandsonc/bio201_McKinley/f
15-15_diencephalon_c.jpg
• All afferents ‘relay’ through  sorts and edits
• Mediates sensation, motor activities, arousal, learning and memory
• Hypothalamus
– Walls form infundibulum which attaches to pituitary gland
– Homeostatic control
• Basic survival needs
• 4 F’s: feeding, fighting, fleeing, and sex
• Epithalamus
– Pineal gland produces melatonin to help regulate sleep-wake cycle
Brain Stem
• Brain stem organized like spinal cord
• Survival responses and cranial nerves (10 of 12)
• Midbrain
– Cerebral peduncles: pyramidal motor tracts (descending)
– Corpora quadrigemina: superior (eyes) and inferior (ears)
– Substantia nigra: melanin (DA); voluntary initiation of mov’t
(PD)
– Red nucleus: hemoglobin; coordinates limb motor mov’ts
• Pons
– Bridges cerebrum and cerebellum
– Respiratory centers assist breathing
• Medulla oblongata
– Decussation of pyramids
– Olives: sensory info about muscle and joint stretch to
cerebellum
– Cardiovascular and respiratory centers; emesis, hiccupping,
sneezing, and coughing
Cerebellum
• Anterior & posterior lobes
– Vermis connects 2 hemispheres of posterior
• Instructions for coordination, balance, &
proprioception
– Ipsilateral input/output
• Cerebellar processing
– Interprets intent of mov’t from cortex & proprioception
from sensors
– Plans best means of mov’t execution
– Sends plans to motor cortex to coordinate
• Constant monitoring to adjust as needed
• Damage results in clumsy, misguided mov’ts
FUNCTIONAL BRAIN REGIONS
Limbic System
• Emotional center
• Interactions with prefrontal lobes
– Coordinates sensory input with emotions
• Hippocampus
– Learning and memory
• Amygdala
– Emotional center of self (laughter, fear, aggression, etc.)
– Assess situation and elicit response to emotional stimuli
– Perception of emotion in others
• Cingulate gyrus
– Associating memories to smells and pain
– Expression of emotions through gestures
– Focusing attention on emotionally significant events
Reticular Formation
• Arousal and alertness due to
constant stimulation
– Studying w/ background noise
– Filters repetitive, familiar, and
weak stimuli
– 99% sensory stimuli ignored
– LSD interrupts = overload stimuli
• Inhibited by sleep centers
• Depressed by alcohol &
tranquilizers
• Coarse skeletal mov’t
http://www.daviddarling.info/images/reticular_formation.jpg
PROTECTING OUR BRAIN
Meninges
• Covers and protects CNS
• 3 layers (superficial to deep)
– Dura mater
• Periosteal layer attaches to skull (periosteum)
• Meningeal layer invaginates into fissures to form septa which anchor brain in
place
– Falx cerebri: longitudinal fissure
– Falx cerebelli: vermis
– Tentorium cerebelli: transverse fissure
• Sinuses (superior sagittal and transverse) where layers separate to collect
blood
– Arachnoid mater
• Doesn’t follow convolutions
• Serous fluid in subdural space above
• CSF in subarachnoid space below (arachnoid villi) into superior sagittal sinus
– Pia mater
• Connected to brain, follows all convolutions
Cerebrospinal Fluid
• Surrounds the brain & spinal cord
– Buoyancy
– Supply for nutrients & chemical
signals
• Secreted by choroid plexus
– In all ventricles
– Lined with ependymal cells
– Selective barrier to ions and removes
wastes
• CSF pathway
– Basic ventricle pathway (earlier)
Blood Brain Barrier
• Maintains stable environment for brain
• Allows selective permeability
– Nutrients in
– Wastes and toxins/dugs out
– Ineffective against fats, O2, and CO2
• Absent at 3rd and 4th ventricle
– Alcohol and other poisonings
– Metabolic activity monitoring
SPINAL CORD
Vertebral Protection
• Within the vertebral foramen
– End L1/L2
– Lumbar puncture L3/L4 or L4/L5
• Epidural space
– Padding of veins and fat
• Dura mater
– Meningeal layer only
• Subdural space – histology only
• Arachnoid
• Subarachnoid space
– Extends beyond spinal cord (S2)
• Pia mater
– Denticulate ligaments connect to dura
External Anatomy
• Cervical and lumbar enlargements
– Increased gray matter
• Conus medularis, cauda equina, &
filum terminale
• 31 spinal nerve pairs
– Dorsal roots: sensory w/ganglia
– Ventral roots: motor
• Shingles attacks dorsal root
ganglia and cranial nerves
Internal Anatomy
• Anterior median fissure
• Posterior median sulcus
• Gray commissure
– Central canal
• Gray and white matter
– Anterior, posterior, and lateral
horns
• Ascending (sensory) and
descending (motor) tracts