The main components of the nervous system are?
neurons and glial cells
the average adult brain has 100 billion neurons.
All neurons are virtually produced during what period?
detect physical and chemical events, inside and outside of the body and transmit the encoded signals to the central integration centers for analysis
How does learning occur
Learning can occur because the neural circuits continully adapt themselves with experience internal and external environments
Stem cells have been found in the nervous system.
3 major function of nervous system
1. regulates activities of organs, tissues and cells
2. helps maintain homeostasis of the body
3. enable humans to thinkm evaluate and remember. Past, present and future
generate responses. and higher brain functions link these to sensory to create perception, cognition, emotion
brain-4 ventricles and spinal cord with central canal. contained in skull and vertebrae
medulla, pons, cerebullym, midbrain, forebrain
largest and most rostral. includes diencephalon and telencephalon
link betwen brain and various body parts. lower center of intergration of sensory and motor activities
Peripheral nervous system
nerves which connect the CNS. 12 pairs of cranial nerves and 31 pairs of spinal nerves connect to brain and spinal cord to all part of body
consistsof neurons that convey information from sensory receptors in the periphery of the body to the CNS. info is stored in higher brain
neuron that convey info from CNS to muscles and glands. last stop is peripheral effectors.
Somatic nervous system
efferent neurons that conduct impulses from the CNS to skeletal muscles.
regulates movements consciously and voluntary
control skeletal muscles rapidly and precisely
efferent neuron that convey impulses from CNS to smooth muscle, cardiac muscles and glands. involuntary muscles and glands(internal viscera, blood vessels)
two division of autonomic
parasypathetic and sympathetic
Enteric nervous system
network of neurons in the wall of the digestive tract. controlled by autonomic system. helps instestins and bladder
What is aggregated nerve cell bodies in the CNS that have similar connections and fuctions?
What are aggregated nerve cell bodies in the peripheral nervous system?
WHat are aggregated nerve fibers that have similar origin and destination?
3 types of brain imaging
Magnetic Resonance Imaging
Functional Brain Imaging
CT generates images of serial slices of brain.
Xray beam is rotated around head and fed to a computer. can reveal organization of grat and white matter, position of ventricles and specific tissues
Magnetic Resonance Imaging
more detailed than CT. produces brian slices in any plane.
when strong magnetic force is applied to head,brain, then hydrogen atom emit electromagnetic signals which are detected by an array of sensor and fed to comp. detet H nuclei in water.
What can CT and MRI do?
detect structual changes such as brain tumor and brain swelling.
cannot indicate functional status of the brain
What can Functional brain imaging(PET, SPECT, and fMRI do?
reveal physiological ativities and functions of the brain. Neurons that are active require more oxygen and glucose. active brain increase blood flow in specific areas
Positron Emission tomography(PET)
isotopes of oxygen and carbon can be incorpaorted ino water and glucose through blood . in active areas more positrons are emitted by oxygen and carbon isotopes.
positron collide with elections to emit gamma rays which creat brain images. resolution=4mm
Single-photon emission computerized tomography(SPECT)
spet uses radioactive Xe or I to bind to red blood cells. The decray of XE or I emits a high energy phton. low resolution of 8mm
Functional magnetic resonance imagin(fMRI)
currently offer best analysis of brain at work. Blood oxyhemoglobin and deoxyhemoglobin emit different magnetic resonance signals. the active brain uses more oxygen and emits magnetic resonance signals that indicate utilization of more oxygen and glucose
--provides superior spatial localization mm in resolution and good temproal resolution.
no harmful effects
Human nervous system has
simple ectodermal structural orgin
Genetic mutation, disease and drugs/chemicals
may lead to defected neural functions
results from spatial and temporal control of different sets of genes. inducing the molecules modify gene expression to form neural circuits
neuron migration, pathway formation and synaptic connections
develops most extensively. large number of neurons and synapse.
Early on CNS is continuos tube. Its cranial end expands to form three primary vesicles
The caudal end of the neural tube develops into....
spinal cord. where 31 pairs of nerves arise. each neuron finds the correct pathway to its target cells to form synapses. synapse must have electical and chemical activity to strengthne or they will die out
Neuroblasts(neural precursor cells)
early on migrate to their destination in the brain regions, spinal cord and ganglion then sprout and differentiate furher
help guide migration and axonal growth. and help for synaptic connections at correct site. posess nerve cell adhesion molecules(N-CAM) which attract other neurons to follow their path
The cells in the doral midline of the fertilized eggs becomes
nerve cells and glial cells
The vast majority of neurons are produced during....?
fifth week and fifth month of pregnancy
At the peak of neuron mitosis how many neurons are generated
half a billion
Early stages in neural development
1. neural plate-appears in dorsal midline at 16th day
2. Neural tube-20th day. neural folds fuse to form tube which becomes CNS
3. Formation of sulcus limitans-a groove that divides neural tube into dorsal alar plate and ventral basal plate. separates sensory motor areas of spinal cord and brainstem
4. vesicles-3 vesicles form into prosencephalon, mesencephalon, and rhonbenceophalon
5. Formation of ventricles, central canal and blood-brain barrier- hollow region of tube develops into fro cerebral ventricles and the spinal central canal. BBB is formed by tight junctions.
6. Neural crest-left over neural folds form neurons and glial cells of PNS.
7. Neuron development-mitosis and differentiation occur. dendrites and axon forms.
separates sensory motor areas of the spinal cord and brain stem
CSF is secreted by the
5 steps in the development of neurons
1. Cell birth-neuroblasts pull cell nuclei toward cortical surface. then divide to produce numerous daughter cells
2. cell migration and differentiation- neurons mirate to specific sites by extending grwoth cones. first group of neuron to arive form the VI layers and then 5,4...
3. Cell Differentiation-neurons develop specific structures ie carriers, ionic channels, receptors.
4. Neural maturation of and circuit formation-formation of specific neural circuits. acquisition of myelin sheath occur at this point
5. Cell death-programmed cell death of some neurons during development is normal. due to competitition weaker connections dengenerate
Critical period in brain development
1. growth and dev determined by genetic and environmental factors
2. irreversible differentiation results in special structures pathways ,connections and function(social bahvior, instinctual etc
3. normal interaction with the environment crucial during critical periods for proper structures n functions
4. critical period vary widely
5. axonal growth and connection are influenced by critical periods
6. Position of soma is chemically marked
7. axons grwoth to specifictagret sites with cues
7. Timing of axonal growth is critical to ensure linkages. ie most synaptic connection in the retina are formed during thee crit visual dev period
9. Crit periods determine the behavioral develoment
10. Imprinting occurs shortly after birth. duckling becomes attached by visual stimual folowing hatching. requires normal social interaction with other
11. socially deprived infant exhibit abnormal social behavior for their entire life
12. Sensory deprivation
12. sensory deprivation during the criticla periods affects neural development
A normal visual circuit fro perception develops during first six months after birth.
Deprivation of visual inputs during the critical period for one week results in permanent loss of vision.
Blocking input of one eye impairs the dev of binocular vision. The open eye impulses influence the lateral geniculate
special neurons,pathway circuits requires molecular signals mediated by genes, growth factors and target cell molecular signal mediated by genes growth factor
Grwoth factors are....
peptide molecules which stimular cell division and cell growth. act via tyrosin kinase receptors to enhace growtth, dev and survival
Epidermal growth factors(EGF)
53 peptide stimulates growth early differentiation and cell division of neurons and astrocytes
Nerve growth factor(NGF)
enhances frowth and survive of neurons during developemnt and helps maintain neural connections in adult life.
snake venom, mouse saliva and muscle tumor cells all contain it.
only its beta subunits contain physiological active sites
released by sympathetic target cells to attract innervation and Schwann cells in response to nerve injury.
NERVE GROWTH FACTOR
DOES NOT CAUSE MITOSIS OF NEURONS
Actions: 1. enhancing sypathetic development and maintenance
2. enhancing survival of innervation to sensory neurons
3. guiding direction growth of axon during development
guide neural processes through the extracellular matric and over the surface of the other cells. They tell neurons when they have reached an appropriate synaptic target and can stop migration
Last type of neural induction
retinoic acid which modulate gene expression
Fetal alcohol sydrome
impairs dev of growth and dev of CNS before and after results in mental retardation, a smaller head, eyes far apart, messed up cerebrau nuclei and neural ganglia leads to cognitive, movement and behavioral problems
Cocain in uterus
disturbs neuronal proliferation and development. it can cross placenta easily and is retain in fetal circulation for prolonged times
induced by mutation of genes of the X chrome and results in enlarged ventricles and excessive cerebrospinal fluid
movement and postural disorder caused by poor blood and oxygen supply to the developing brain and result in permanent, non progressive damage of the developing brain
Cerebral palsy is aclassified accord to the type of motor disfuctions
Spastic CP caused by damaged neurons around ventricles and results in toe walking and scissor gait
Athetoid cerebral palsy-slow writing movement of the extremities and/or trunk. caused by neural damage in basal ganglia
Ataxic cerebral palsy-incoordination, weakness and shaking during voluntary movement. caused by neural damage in the cerebellum
due to failure the rostral neuropore to close and resulted in missing the forebrain
Mechanism of brain development
specific patterns of connection are extremely complex in the human brain. they are the same in every human brain
1. Chemical signals-gradients of trophic factor encourage the growth of axons in a particular direction and to part set of cells. sperrys experiment of severing optic nerve and eyeball rotation show action of trophic factors
2. fiber guid cell movement-neuron sends out fiber to a target . this is seen in layers of cerebral cortex
3. cell competition and death-final neuronal connection finalized. innervation of skeletal muscle is a good example
sensitive to trophic molecules and the pattern of electrical activites in the deve pathways. most synapses formed before birth but new ones form as demads change
Steps in synpatogenesis
1. contact of the growth cone w/ target
2. inc in neurotransmitter
3. inc in adhesion of synaptic strucutures
4. elim weak synapses by comp
5.cluster receptor at postsynapt membrane
6. synth and insertion of new receptor
7. elim extra receptors
Blood brain barrier formed by tight junction of cerbral capillary cells and glia cells. it prevents harmfuls substances from gettin to neurons
secreted by ependymal glia cells, exchanges substances with the brain interstitial fluid to ensure that the brain has it own stable environment. amount is 140 ml. 500 ml produced daily
hydrocephalus caused when flow is blocked and there is excess csf
orderly genetically programmed cell death to eliminate weak neurons
major role in maintenaince of neuronal forms
1. Neural microtubules-provide rigidity
2. neurofilaments-main component of cytoskeleton,. very strong
3. microfilaments-always broken and reformed. motility and cell shapes
small no axon and no action potential
no directly part in synaptic transmission
divide throughout life, ten times more of glial cells than neurons. totoal volume is close to that of neurons
Glial cells serve to
1. provide mechanical support for neurons
2. establish myelin sheath
3. engulf and destroy cell debris and invaded agents
4. supply nutrients to neurons
5. guide neuronal growth during dev
axons contain no ribosomes to synthesize proteins. all axonal proteins are synthesized in the soma and transported down the axon
dynein-forms legs which walk from axonal terminals in retrograde direction
Two types of fast axon transport
antergrade and retrograde
moves organelles from the soma toward the terminals at 400mm/day.
carried by fast axonal transport. binded by kinesin
transport moves the degraded old membrane from axonal terminals to the soma. 100 mm/day
herpes virus travels from axon terminal to soma
Slow axonal transport
less than 10 mm per day
slow component b transports actin at 5-10 mm per day.
very slow component a goes .5-3mm/day
selectively taken up by axonal terminals and then transported retrogradely to the soma. can be visualized.
provides energy for fact axonal transport
involves in anterograde transport
Fast axonal involves force generating enzyme (FGE)
Slow axonal transport occurs only in anterograde direction necessary for axonal renewal and growth
Common causes of disorder in the nervous system includes
direct injury, hypoxia, hemorrhage, infarction tumor and inflammation
Degeneration is a retrogressive cytoplasmic lesion
may involves axon, myelin or nucleus
Lesion and necrosis induce
mitosis of glia called gliosis
damaged nerves and fill the gap created by injury
axon is transected its distal fiber and axonal myelin disintegrate intro fragments which are then phagocytosed by glia cells
works with Schwann cell.
soma and proximal fiber of transected axon degenerate if the site of lesions is close to the soma
loss of synaptic action leads to degeneration of effector cells. Lower motor neuron lesion result in muscle degen and paralysis
replacement of cells amputated cytoplasmic process.
vertebrate axons can regenerate well unless there is a considerable scarring at the site of injury.
regeneration is 1-3mm per day in mammalian peripheral axons
The success of axonal regneration depends on
1. alignment of proximal stump
2. distance between cut end and target cells
3. trophic factors
CNS axons do not regenerate
because when CNS axons are damaged, their oligodendrocytes release Nogo to inhibit regeneration. CNS is hard to produce new cells because each motor unit has soo many interconnections.
if muscle fails to contract for 3 weeks there will be a loss of msucle mass
developed antibodie to block inhibitors of growth factors to induce spinal neuron regeneration
Adv in spinal cord repair
1. mediciine that enhance repair of myelin
2. treatment of synthetic steroid reduces secondary cascade caused by subsequent inflammation
3. improve treatment of pain
4. improve rehab mathods that reduce bone loss and muscle atrophy
provide structural and metabolic support for the neurons. 90% in cell number and only 50% in volume. no synapses. can regeneration and divide
Neuroglia cells serve to
1. maintain ionic environment of neurons
2. control uptake of neurotransmitters
3. protect and support and repair neurons
brain could not function properly without
star shaped glia cells with long processes. most numerous glia. support neurons metabolically
longer but fewer processes. main supportive cells to provide rigidity. mainly in white matter. play important role in injury responses
shorter but numerous processes. mainly in gray matter.
small round glia few processes. majority of glia cells and form myelin in the CNS. each one forms myelin around several axons
small glia wih delicate spine-like projections. rapid mitosis in response to neural injury and migrate toward the site of injury where they phagocytosize and remove tissue debris
ciliated glia which line the brain ventricles and the spinal cord central canal.
Form CSF that fills the ventricles and canal and facilitate the movement of CSF
Gliocytes of PNS
Schwanna cells(neurolemmocyte) wraparound peripheral axons with layer of membrane to increase the impulse conduction speed in the myelinated fibers. gaps called nodes of Ranvier have no myelination
In the PNS
each Schwann cell wraps only one axon. each axon may have up to 500 Schwann cells to wrap a long axon.
neuropathies often involve demyelination of largest sensory and motor fibers first. caused by matebolic abnormalities, toxins and microbial infection.
actue inflammation and demyelination of peripheral sensory and motor fibers. auto immune attack.
destruction of oligodendrocytes thru brain and spinal cord
disease of CNS with demyelination and inflammation along axonal pathways. cause plaques in the brain.
monocular blindness, double vision, motor weakness or paralysis, dizziness.
Cause of malformation
ossification defect. frequent bone affected is the occipital bone which forms abnormal opening
most serious one arise from failure of neural tube to close
Excessive vitamin A intake
can impede closure of the neural tube and neuronal differentiation
caused by failue of the rostral neuropore to close and result in missing the forebain and the skull. still or or survives only hours
meninges, brainand ventricle penetrate thru large defective bone opening in the head
only meninges protrude out of opening
failure of the caudal neuropore to close properly
most severe form of myeloschisis. vertebral arches are missing bc of non closing caudal neuropore. meninges and spinal cord protrude through
condition which a small amount of spinal cord tissue protrude thru the hole formed by the defected vertebrae
Spina bifida occulta
meninges are intact but arch is missing. may induce pain in back
caused by excessive CSF bc of blocked cerebral aqueduct. the ventricles enlarge. may induce optic atrophy, mnental deficiency and spastic paralysis
3 layers. cover brain and spinal cord
filled with CSF at subarachnoide space, cerebral ventricles and spinal central canal
inner layer folds into the brain to form partitions in the regions
1. falx cerebri-separates 2 cerebral hemisphere
2. falx cerebelli- btw two cerebellar hemisphere
3. tentorium-between cerebrum and cerebullum
has sinuses that drain vein blood. innervated by trigeminal, vagus, sympatheic nerves and contain pain receptors. meningeal arteries run on outiside of dura.
more vulnerablec can caused subdural hemorhage
Dura mater is used as
graft for replacing the thoracic wall, diaphragm and cardiac valves
middle layer. extend spider web like to the pia. if a dural vessels breaks it can leak onto the arachnoid causing subdural hematoma.
must drill hole to drain blood out
thinnest layer. intimatlely attached to brain and spinal cord. limits passage of bad things.
together with capillaries forms the choroid plexus in the ventricles to secrete CSF
formed by lumen of neural tube also creates spinal central canal. filled with CSF.
lie in the cerebrum are the largest.
C shaped cavity thalamus as floow and caudate nucleus as lateral wall. consists of anterior hor, body ,inferior horn and posterior horn.
small camber located in midline. fllor formed by hypothalamus and subthalamus. Third connected to 4th through cerebral aqueduct
cavity btwn pons and medulla. continuous with spinal central canal.
rich network of blood vessels in pia mater. projecti intro ventricles to be transporter between blood and csf.
recieved blood from ant and pos choroid arteries .
CP of lateral ventricle are largest and produce most CSF. total of 140ml in adult
CSF passes to veinous blood
thru arachnoid villi
Function of CSF
1. protect brain from impact with skull
2. CSF buoyancy reduces brain weigth 30 folds
3. carries way waste of neurons
4. stable fluid n nutrients for neurons
Blockage of CSF
raises intracranial pressure causes swelling of brain.
1. headache, vomiting, low cardiac, coma, palsises of nerves 3 and 4.
Glucose is main energy for
25% of total body glucose. 20% of oxygen consumption at rest for brain.
sodium potassium pump is the main energy consuming process
caused by death and dysfunction of brain tissue die to vascular lesion followed by occlusion or hemorrahage
Arteries of the brain
branches of internal carotid arteries and vertebral arteries. carotid mainly supply anterior and middle cerebrum and vertebral supply, brain stem, post cerebrum and spinal cord
Internal carotid artery
runs forward along lateral sie of optic chiasma. supplies majority of blood to brain.
1. anterior cerebral artery-runs medially along the longitudinal cerebral fissure to supply blood to the frontal lobe. branches again into ant communication artery to supply basal ganglia and internal capsule
2. middle cerebral artery-along lateral sulcus and supplie lateral aspect of temporal and parietal lobes
branches into lateral strical and post comm artery
3. anterior choroidal artery supplies blood to choroid plexuses
Vertebral artery system
Each vertebral artery branches in 3 major branches
1. Spinal artery supplies blood to spinal cord
2. posterior inferior cerebellar artery-runs between medulla and cerebellum. supplies blood to medulla vermis and cerebellar deep nuclei
3. Basilar artery- large gives offs branches: labryinthine, pontine, post choroidal post cerebral
Circle of Willis
ant and pos cerebral and communication arteries converge at base of brain in the ring called Circle of Willis.
surrounds optic chiasm and pituitary stalk. alternated path for blood if there is a blocked carotid or vertebral artery
imp channel bwteen internal carotid and vertebral basilar system
direct or indirect blood flow between vessuls allow alternate pathway
all veins terminate in dural sinuses/ eventually collected into jugular vein to return to circulation
superior sinus, inferior sinus, straight, occipital, transverse, confluence
Major cerebral veins
external, superior, middle, inferior, basal vein drains blood from insula to striatum
Internal cerebral veins
drain blood from deeper cortical region, the thalamus and striatum
internal anterior, internal posterior
Blood Brain barrier
histamin bacteria and others which incrase capillary permeability do not increase brain capillary permeablility.
formed by tight junctions between endothelial and ependymal cells. astrocytic feet surround outside for protection
exist in brain, spinal cord, optic nerve, and retina.
Areas in hypthalamus
lack BBB because they must sense blood substances
Somatic Nervous system efferent
soma located in spinal ventral horn. axons run through ventral roots.
propagate 100m/s. precise rapid movement
Autonomic nervous system
innvervate cardiac and smooth muscle. travels thru pre and post ganglionic fibers. slow propagation1m/s
numerous rootlets which jointo from one sensory dorsal and one ventral motor root. the dorsal and ventral fuse to from mixed spinal nerve.
Each mixed nerve divides into dorsal ramus(dorsal skin and muscles of the trunk) and ventral ramus(limbs and ventrals part of trunk)
4 spinal chord plexuses
Cervical plexus- formed by ventral rami of c1-c5 whic innervate skin and muscles of head, neck and upper shoulder. phrenic nerve arises from here and innervates diaphragm
Brachial plexus-C5-C8 and T1-2. Innervate upper limbs
Lumbar plexus-L1-4 nerves for ab walls and external genitals. femoral nerve is largest nerves arising from lumbar
Sacral plexus-ventral rami of L4-5 and S1-4. innvervates buttocks perineum and lower extrems
Innervation of voluntary skeletal muscle by ventral spinal roots
C5-6 biceps brachii flexes
C6-8 triceps brachii extends
T1-8 thoracic muscles
T6-T12 ab muscles
L2-4: quad, knee reflex
L5, S1-2 Achilles tendon reflex
Cranial nerve classification
1. General somatic afferent nerves(GSA)-CN 5,7,9,10- innvervate touch,pain and temp receptors
2. Special somatic afferent nerves(SSA): CN 2,8 innervate eyes and ears
3. General visceral afferent nerves(GVA): CN 9,10 which flex internal mechanical and chemical receptor
4. Special visceral afferent nerve(SVA)-CN1,7,9. smell and taste receptors
5. General visceral efferent-CNX cardiac smooth msucles
6. Special vsiceral efferent-CN 5,7,9,11 chewiing pharynx, larynx and facial expression
7. General somatic efferrent-CN 3,4,6,12-eye and tongue muscles
1. Olfactory-smell sensory
2. Optic nerve-vision motor
3. Oculomotor-move eye motor
5. Trigeminal-snesory face and tongue muscle movements
6. Abducens-lateral rectus
7. Facial nerve-taste expressions nasal and salivary glands
8. Vestibulocochlear-hearing and body balance
9. Glossopharygeal-taste pharaynx
10. Vagus-visceral snesation and muscles
11. Spinal accesory nerve-neck and back muscles
12. Hypoglossal nerve-tongue
Classification of Nerve fibers(numerical systems)
1. 1A fibers are largest myelinated fiberswith diameter of 17microns or larger. 100m/s conduction. innervates muscles spindles
2. 1B-myelinates and conduct at 96m/s. golgi tendon organ
3. Type 2-myelinated 30-60m/s
4. Type 3-smallest myelinated fibers. 4-24m/s. fast pain and temperature receptors
5. Type 4-smallest unmyelinated less than 1 meter a second. slow pain, temp and crude touch receptors
Classification(Alpha betic system)
both motor and sensory fibers
1. A-alpha-70-120m/sec. innervate muscle fibers and proprioceptors
2. A-beta-30-70m/sec. innvervate touch and pressure receptor
3. A-gamma-15-36 m/sec intrafusla muscle fibers
4. A-delta-12-30m/s. innervate pain and temp receptor
5. B fiber 5-15m/s. preganglionic autonomic fibers are B fibers
6. C fibers-smallest and unmyelinated.
Class I mononeuropathy
Results from focal compression due to entrapment or pressure on the nerve. recovery is rapid when it decompresses
Carpal tunnel syndrome is a common compression injuryof the median nerve
Class 2 mononeuropathy
arises from crushing the nerve. Reflexes are greatlt reduced or absent Wallerian degeneration occurs distal to the lesion
CLass 3 mononeuropathy
nerves severed by excessive stretch or laceration causing immediate loos of sensation n paralysis. if lesion is far from target it may not restore completely
from ischemia, diabetes, inflammation which involve two or more nerves in different part of body
involves sensory, motor and autonomic nerves. develops from distal to proximal regions.
common causes-diabetes, alcoholism, autoimmune disease