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 DevelopmentPrimary vesicle system

Secondary vesicle system

Adult brain structures Ventricle system

Lateral ventricles 3rd ventricle

Cerebral aqueduct

4th ventricle

prosencephalon

mesencephalon

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

http://www.fizyka.umk.pl/~duch/ref/01/01-plastic/motorsomato.gifhttp://www.pc.rhul.ac.uk/staff/J.Zanker/PS1061/L6/homuncul.gif

• 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

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

• 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

http://academic.kellogg.cc.mi.us/herbrandsonc/bio201_McKinley/f15-15_diencephalon_c.jpg

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

• 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

Limbic System

Reticular Formation

http://www.daviddarling.info/images/reticular_formation.jpg

• 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

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