CNS

parts of the CNS

• brain

  • cerebral hemispheres

  • basal ganglia

  • brainstem

  • cerebellum

  • spinal cord

function of CNS

integrate, correlate, respond to a variety of sensory info

source of thoughts, emotions, and memories

parts of PNS

• cranial nerves

• spinal nerves

• peripheral nerves

• ganglia

functions of PNS

all somatic (sensory and motor) and autonomic processes carried out outside of CNS

what is the nervous system

collection of neurons throughout the brain, spinal cord, peripheral nerves, and sensory organs 

orientation of CNS

above the midbrain: 

• anterior= rostral

• posterior= caudal

• superior= dorsal

• inferior = ventral 

below midbrain 

• anterior= ventral 

• posterior= dorsal 

• superior= rostral

• inferior= caudal 

Week 3 gastrulation produces 3 layers

1. ectoderm

2. mesoderm

3. endoderm 

Ectoderm

• nervous system: CNS+PNS

• epidermis- outer layer of skin

• teeth: enamel of teeth 

• hair, nails, sweat glands 

• lens of eye: cornea and retina

Mesoderm

• musculoskeletal system: bones, muscles, CT

• circulatory system: heart blood vessels, blood cells

• reproductive system: gonads 

• excretory system: kidneys 

• dermis of skin: inner layer of skin

• notochord: temporary rod- like structure that aids in vertebrate development

Endoderm

• digestive system: lining of GI tract

• respiratory system: lungs

• urinary bladder+urethra

• thyroid+parathyroid glands

• thymus 

• lining of respiratory and digestive tracts: mucous membranes

Neurulation

neural tube forms by 4th week

forms 3 bulges to make 3 primary vesicles:

• prosencephalon 

• mesencephalon 

• rhombencephalon 

secondary vesicles

1. telencephalon

2. diencephalon

3. mesencephalon

4. metencephalon

5. myelencephalon

Prosencephalon

• Telencephalon→cerebrum, cerebral hemispheres → lateral ventricle

• diencephalon → diencephalon (thalamus, hypothalamus, epithalamus) + retina→ 3rd ventricle

Mesencephalon

• mesencephalon → brain stem, midbrain → cerebral aqueduct 

Rhombencephalon 

• metencephalon → brain  stem, pons / cerebellum→ 4th ventricle

• myelencephalon → brain stem: medulla oblongata→ 4th ventricle 

Neural tube defects

1. spina bifida (lamina don’t fuse) 

   1. spina bifida occulta 

      1. mildest form, small gap in spine but no protrusion 

   2. meningocele

      1. meninges protrude through gap 

   3. myelomeningocele

      1. spinal cord and meninges protrude through gap → neurological complications 

2. Anencephaly 

   1. cranial end of the neural tube fails to close → parts of brain and skull absent 

   2. infants w this are often stillborn or survive only a short time 

3. encephalocele 

   1. portion of the brain and meninges protrude through opening in skull 

   2. severity depends on extent of protrusion and brain tissue involved 

What vitamin decreases the chances of neural tube defects 

Vitamin B9 (Folate/ Folic Acid) 

• folate is the active form 

Neuron Anatomy

contain all traditional organelles

• nucleus

• mitochondria

• ER (rough and smooth)

• Golgi Apparatus 

• Ribosome 

• lysosomes

• cytoskeleton

  • microtubules

  • microfilaments 

cannot do mitosis 

3 additional regions 

• dendrites

  • receivers of incoming info 

• body(soma)

  • packing+ sorting info

• axon

  • small diameter and variable length projection that conducts nerve impulses away from soma to communicate with neighboring neurons or target tissues 

  • myelin sheath 

Synapse

regions at which neurons come nearly together to communicate (neuron or effector organ) 

synaptic cleft

gap between neurons at synapse

synaptic vesicle

packets of neurotransmitters in presynaptic neuron

presynaptic neuron

neuron sending a signal before synapse

postsynaptic neuron

neuron receiving a signal after the synapse

neurotransmitter

substance used to communicate with the next cell

Types of synapses 

By location 

• axodendritic 

  • axon→dendrite

  • most common

• axosomatic

  • axon → soma

  • inhibit neurons, spatial headstart on axon hillock

• axoaxonic

  • axon → axon

  • least common

  • tamps down reaction as a last minute modulation

By physiology

• chemical

  • most synapses are chemical

  • after action potential → release of NT into cleft → bind to next tissue (neuron or target organ)

• electrical

  • less are electrical 

  • use gap junctions 

  • fast transmission without delay

    • not good for all bc we want a bit of back and forth between neurons

  • bidirectional signal transmission 

    • either cell can send or receive signal

  • found in tissues that require synchronized activity 

    • heart, lungs, eye control 

Sensory neurons (afferent)

function

• conduct impulses from receptors→ CNS

structural type 

• pseudounipolar

• bipolar 

role in NS

• transmit info from external env. → CNS

Motor neurons (efferent)

function 

• conduct nerve impulse from CNS → effector organs 

structural type

• multipolar

  • golgi Type 1 

role in NS

• transmit info from CNS → muscle 

interneurons (internuncial)

function

• neurons completely contained within CNS

• no direct contact w peripheral receptors or effectors

structural type

• multipolar 

  • golgi Type 1 

  • Golgi type 2

role in NS

• modification, coordination, integration, facilitation, and inhibition that must occur between sensory input and motor output 

pseudounipolar

2 fused processes that appear as 1

central and peripheral process both function as axon 

Bipolar

2 processes

• 1 axon + 1 dendrite

Multipolar Golgi Type 1

1 axon + 2 more dendrites

axons extend considerable distance to target cell 

multipolar Golgi type 2

1 axon + 2 more dendrites

axons are short and stop close to cell body of origin

basic neuron types 

Neuroglia

non-conducting support cells 

capable of division 

cannot do function of neuron but makes their job easier 

Neuroglia of CNS

1. Ependymal cells

2. oligodendrocytes

3. astrocytes 

4. microglia 

neuroglia of PNS 

1. satellite cells

2. Schwann cells / neurolemocytes

Astrocyte

• part of CNS

• most abundant neuroglial cell of CNS

• structural support to surrounding neurons 

• form the blood brain barrier 

• stores glucose 

• produces scar tissue on damaged neurons → gliosis ( nerve tissue scarring) 

• influences NT release and clean- up

what can cross Blood Brain Barrier 

• oxygen and carbon dioxide 

  • small and lipid soluble 

• water 

  • osmosis 

• glucose 

  • primary energy source of brain 

  • specific transport system needed

• lipid-soluble molecules 

  • alcohol, hormones, certain drugs

• some small molecules

  • amino acids 

  • vitamins 

  • ions

Oligodendrocyte

• myelinating cell of CNS

• 2nd most numerous CNS glial cell 

• myelinate multiple neurons of CNS

Ependymal cells

• found along floor of ventricles and central canal 

• help with CSF creation and appendages flow 

Microglia

• neuronal debris cleaners

• immune response in CNS

• phagocytic function 

  • clear dead and damaged tissue 

  • wall off damaged areas along w astrocytes

Schwann cells

• uses entire cell to form an individual myelin sheath internode in PNS

• similar to oligodendrocyte in CNS

• assist in repair and regeneration of peripheral nervous tissue 

satellite cell

• similar to astrocyte in CNS

• regulates chemical environment for the PNS

Demyelinating disorders

1. multiple sclerosis

   1. attack oligodendrocytes 

   2. CNS

   3. rapid or slow onset 

   4. affect optic nerves, sensation, corticospinal tract, cerebellar pathways, etc

   5. Lhermitte sign 

      1. electric sensation down back / legs with neck flexion

2. Guillain Barre 

   1. attack Schwann cells 

   2. PNS 

   3. rapid onset 

   4. affect muscles+ autonomic instability 

   5. symptoms develop overs days - weeks

   6. resolve over weeks/months 

      1. self-limiting

Regeneration

does not occur in CNS

• no basement membrane/ endoneurial surrounding axons of CNS

• axons in CNS don’t form neurolemomas → don’t survive axonal damage 

• damaged neurons in CNS rapidly turned into scar tissue (proliferation of astrocytes) 

• CNS oligodendrocytes have growth- inhibiting proteins to prevent CNS fiber regeneration

does occur in PNS 

• proximal tip of severed neuron → endoneurial tube that has Schwann basement membrane / endoneurium

• to regen neurons must 

  • be myelinated 

  • have intact cell body

  • have functional schwann cell

  • axonal sprout growth rate of 1-4 mm/day

types of ion channels 

1. ligand- gated 

   1. requires NT key to open

   2. chemical

2. mechanically- gated

   1. require physical pressure

3. voltage gated

   1. require change in electrical charge to open

4. leaky/ passive

   1. always open

Resting Membrane potential

sum of the electrical charges of ions and negatively charged proteins

neurons have internal -70 mV charge → makes it polarized 

Na+ and K+ movement

Na+ goes in and inside gets less neg

K+ leaves and inside gets more neg 

Maintaining RMP 

ions follow conc gradient

• Na+ flows in 

• K+ flows out 

to maintain polarity, active pump is used with the use of ATP

Graded Potentials

signal from previous neurons can be excitatory (closer to 0 and positive) or inhibitory (more negative)

at -55mV voltage-gated Na channels open → flood of (+) ions lead to depolarization → cause action potential 

Action potentials

Neurotransmitters

1. glutamate 

   1. most common excitatory NT

2. GABA

   1. most common inhibitory NT

3. Acetylcholine (ACh)

   1. 1st discovered 

   2. autonomic NS

4. adrenaline 

   1. fight /flight 

5. noradrenaline

   1. concentration

6. dopamine

   1. self-pleasure 

7. serotonin

   1. mood 

   2. social hapiness

8. endorphins

   1. euphoria

most neurons make a single NT→ package in vesicle → transport to axon terminal 

as neuron receives AP NT released into synaptic cleft where NT can bind to next neuron → NT binding opens ion channels → affects next neurons RMP → excitatory or inhibitory effect 

Sulci and Gyrus

sulcus= space

gyrus= ridge

• more SA = more processing power 

4 lobes of the brain 

1. frontal 

2. parietal 

3. temporal 

4. occipital 

Frontal lobe

largest lobe w 4 main functional areas 

1. primary motor cortex, all parts of body represented

2. premotor 

3. supplementary motor areas 

4. frontal operculum (Broca’s area) motor mechanisms of speech is formulated 

   1. speech production + mouth movement 

5. mental activity, executive function, decision making 

issues → voluntary motor function 

Parietal lobe

somatosensory (pain, touch, position, localization)

main clearinghouse of somatosensory appraisal

1. postcentral gyrus

   1. primary somatosensory cortex → somatosensory reception, integration, processing sensory info from surface of body + viscera

   2. formulation of perception

2. superior parietal gyrus

   1. body image

   2. spatial orientations

3. inferior parietal gyrus 

   1. cortical association → integrates and processes sensory info from multiple modalities (audio+ visual info)

4. part of Wernicke’s area in inferior parietal lobe

issues = spatial awareness, touch localization, tactile based memory (agraphthesia/ astereognosis)

Homunculus 

somatotopy: primary motor and somatosensory cortices have point for point correspondence of a specific area of body to a specific functional area of cortex 

Temporal lobe

1. upper surface of the superior temporal gyrus → extend into lateral fissue 

   1. this is primary auditory cortex

2. caudal part of superior temporal gyrus → extens up to parietal cortex → forms part of Wernicke’s area

   1. Wernicke’s area - processing the auditory info and comprehension of language 

   2. recall and memory 

3. inferior part (occipitotemporal gyri) involved in visual and cognitive processing 

4. medially = parahippocampal gyrus involved in learning and memory 

Occipital lobe

visual

1. most caudal part of brain 

   1. lies on tentorium cerebelli and is made of several irregular lateral gyri 

2. medial surface - calcarine fissure and parieto-occipital sulcus 

3. contains primary and higher-order visual cortex

6 common laminae of the isocortex (external to internal)

1. lamina 1 molecular

   1. gray matter

   2. outermost layer closest to the pia mater

   3. filled w synaptic activity between dendrites of pyramidal cells and axons of other cell types

   4. integration center

2. lamina II- external granular lamina II

   1. many small closely packed granular neurons

   2. associative lamina

3. lamina III- external pyramidal lamina III

   1. small pyramidal-shaped neuron cell bodies

   2. associative lamina

      1. axons extend out of the cortex to the white matter → return to the gray matter

      2. projection, association, commissural fibers

4. Lamina IV- internal granular

   1. receive external input

   2. small cell bodies

   3. well developed in sensory areas

   4. most thalamic inputs arrive here

5. Lamina V- internal pyramidal (ganglionic)

   1. large pyramidal-shaped neurons cell bodies

   2. axons project to other brain and cord centers from here

   3. corticospinal + corticobublbar fibers

   4. famous for large pyramidal Betz cells

   5. projection lamina

6. Lamina VI- multiform(fusiform)

   1. a mix of incoming and outgoing projection fibers in this layer

   2. projection lamina

Association fibers

connect different regions within the same hemisphere of the brain

• long association fibers connect different lobes of the hemisphere to each other

• short association fibers connect different gyri within a single lobe

• link perceptual and memory centers of the brain

Commissures

bring 2 halves of brain together

commissural tracts cross from one cerebral hemisphere to the other through commissures

• majority of the commissural tracts pass thru the large corpus callosum ( responsible for task-switching)

• few tracts pass through anterior and posterior commissures commissures

internal capsule

superior to brain stem

tracts form a broad dense sheet = internal capsule

• between thalamus + basal nuclei

fibers → radiate in fan-like array to specific areas of cortex

basal ganglia

a group of nuceli of varied origin in the brains of vertebrates that act as a cohesive functional unit

base of forebrain + strongly connected w cerebral cortex, thalamus, other brain areas

act as braking system on motor control

• direct= promote

• indirect = inhibit

components: caudate +putamen(corpus striatum), Globus pallidus (internal + external) substantia nigra, and subthalamic nucleus

basal ganglia pathways

voluntary motor control, procedural learning relating to routine behaviors/ habits

• bruxism

• eye movement

• cognitive

• emotional functions

has inhibition and de-inhibition

• increase basal ganglia activity = decreased movement (hypokinesis)

• decrease basal ganglia activity = increased movement (hyperkinesis

Basal ganglia related disorders 

1. Huntington’s disease 

   1. neurodegenerative disorder that affects muscle coordination and leads to cognitive decline and psychiatric problems 

   2. hyperkinetics - not enough basal ganglia activity 

   3. Putamen + GABA

2. Parkinson’s disease 

   1. chronic neurological disorder resulting in lack of control over movement, poor balance and coordination 

   2. hypokinesis - overactivation of basal ganglia 

   3. dopamine + substantia nigra

lateralization 

2 hemispheres do different things

Left: 

• sensory stim from R body 

• motor control of R body 

• speech, language and comprehension 

• analysis +calculations

• time and sequencing 

• recognition of words, letters, numbers 

Right 

• sensory stim from left body 

• motor control of left body 

• creativity 

• spatial ability

• contex/ perception 

• recognition of faces, place, and objects 

Broca’s area

• in frontal lobe of dominant hemisphere

• responsible for speech production 

• broca’s apahasia (expressive)

  • can understand

  • words not formed properly 

  • speech = slow and slurred 

Wernicke’s area 

• comprehension / understanding of written and spoken language 

• Wernicke’s aphasia (affluent)

  • loss of ability to understand language 

  • can speak clearly but words make no sense