Nervous System

• 1.) Transmitting impulses: electrical with chemical neurotransmitters
• 2.) Conduction: type of communication to cells of the body, carrying info to regulate body functions

• neurons- they carry impulses, specialized in conduction and responsiveness
• glia

supportive cells of the nervous system

• sensory input
• motor output
• integration

• awareness of changes in the external and internal environment- makes us aware of stimuli
• sensory info is afferent- goes to the brain

• regulates the effectors of the body (structures with all 3 types of muscle and all glands that receive nervous info)
• motor info is efferent- travels from the brain

• not sensory or motor
• happens in 2 ways

• 1. processes sensory info and determines a motor response
• 2. controls a mental function- thinking, analyzing, planning

brain, spinal cord, and nerves attached to the both of them

• the brain and attached spinal cord
• occupies a central location

• all the nerves of the body
• cranial nerves: attached to the brain
• spinal nerves: attached to the spinal cord

• sensory and/or motor neurons
• no integrative neurons

• Somatic nervous system
• autonomic nervous system

nerves to the skeletal muscles and the skin

nerves to the viscera (with smooth and cardiac muscle and glandular tissue) has 2 parts

• sympathetic nervous system: nerves important in stress situations (fight or flight)
• parasympathetic nervous system: nerves important in homeostasis- not stress

• astrocytes
• microglia
• ependymal cells
• oligodendricytes
• satellite cells
• schwan cells

smaller than neurons, some are starlike, but are not dendrites and axon neurons because they dont transmit impulses

• of the glia
• called a glioma

• starlike in shape
• most abundant
• found in the CNS
• found between blood vessels and neurons 
• part of the blood-brain barrier
• help regulate what reaches the neurons from the blood (nutrients rely on these cells)
• has a general physical support function- connection between parts of the nervous system
• regulates the environment of the neuron

• small cells in the CNS
• usually has a similar function to astrocytes, but in an infection/injury they take on a defense role
• can enlarge and carry our phagocytosis of microbes and other material
• immune system function to protect neurons

• in the CNS they line the spaces that contain cerebral spinal fluid (ventricles) 
• filter the cerebral spinal fluid and inluence the environment around the neurons

• have a few processes 
• produce the myelin sheath in the CNS; wrap around the axons
• provides insulation

• found tin the PNS around cell bodies of neurons
• generally located in bumps called ganglia
• protects and supports the neurons

• also called neurolemmacytes
• make the myelin sheath in the PNS
• functions like the oligodendricytes, but also have a role in repair of damaged nerve fibers (axons)

• cell body
• dendrites
• nissa bodies
• nerve fibers
• axon
• myelin sheath (on some)
• axon terminals

• also called perikaryon or soma
• contains nucleus and nucleolus

• often receive info 
• cell body sometimes can receive
• all cells have one or more dendrites and the free end of the dendrite is the receptor which can be stimulated by either a sensory or synapse

• in cell body, type of rough ER
• contain neurofibrils

network of filaments and tubules, important for maintaining the structure of the neuron

• includes the dendrites and the axon
• only one axon but it can branch (called a collateral)

• many neurons have axons covered in this (called myelinated neurons)
• insulates the axon and speeds up impulses

• a fatty material
• protects and insulates
• the tissue looks white- white matter

• areas where the axon is clustered with myelin
• from meylinated axons

• cell bodies grouped and unmyelinated (have fibers)
• areas of grey matter include centers, nuclei (in CNS) 
• in PNS its in the ganglia

using segments, nodes of ranvier and having impulses jump

glial cells wrapping the myelin sheath

spaces between glia

• they jump from node of ranvier to node of ranvier
• unmeylinated must depolarize each space while myelin sheath allows jumping

• exposed part of the schwan cell membrane, only in the PNS
• important in repair to damaged axon

• areas of white matter in the CNS
• All the neurons in a tract complete a similar function
• in the PNS white matter is in nerves

• 1.) by number of processes (axons and dendrites)
• 2.) by function

• multipolar neuron
• bipolar neuron
• unipolar neuron

• 3 or more processes- 1 axon & 2 or more dendrites
• most common type of neuron based on shape
• motor neurons and many interneurons have this shape

• 2 processes, one axon and one dendrite
• rare, only seen in the sensory neurons of the eye and ear

• one pole
• 2 process that branches (pseudo unipolar-bc its technically one but has 2 functions)
• most sensory neurons are of this type

• sensory
• motor
• interneuron

• also called afferent neurons
• brings information towards the CNS and up to the brain

• an efferent neuron
• brings info from the CNS down from the brain
• ex: controlling a muscle- brain sends info down the spinal cord towards the motor neurons

• also called association neuron
• neither sensory or motor
• either communicates between sensory and motor neurons or has a mental function
• only in the CNS not nerves

• electrical
• created by the movement of ions in and out of cells

• no impulse yet
• intracellular and extracellular fluids both contain (+) and (-) ions, however even though the total number is about the same the distribution is different

• major cation (+) outside the cell: Na+
• major cation (+) inside the cell: K+
• major anion (-) outside the cell: Cl-
• major anion (-) inside the cell: protein
• overall negative charge inside the cell and positive charge outside

completed by Na+/K+ pumps that keeps the ions concentrated in and out of the cell

• a mircoelectrode
• outside- +30 millivolts
• inside- -70 millivolts

the membrane is polarized

potential differences in charges in and out of the cell

cell is not conducting

differences in Na+ and K+ concentrations and different permeabilities

• vital for impulse
• we cant get impulse if the charge in and out of the cell is equal

• proteins in the membrane form these channels
• 2 types: leakage channel and chemically gated channels

• nongated channels
• always open

• ligangated
• only open if the neuron is stimulated for example by a neurotransmitter
• wont open to let ions flow without a stimulus

pumps are critical for keeping Na+ out and K+ in

• permeability of the membrane changes
• when the gated channels open, ions diffuse down the electrochemical gradient (from area of higher concentration to area of lower concentration)
• Na+ tends to diffuse in while K+ diffuses out
• ions also move towards the opposite charge ex: positive Na will be attracted to - charge of proteins mostly in the cell

• Na+ diffuses in by the chemical gradient 
• it also is attracted to the negative charge in the celll
• some leakage when no stimulation but mostly pumps keep Na out and K in

• ++++++++++++
• ________________
• -----------------------
• ________________

• -----++++++++++++
• ____________________
• +++-----------------------
• ____________________

• the charges begin to reverse at the point of stimulation
• then the impulse must spread down the axon to the termials and you have to restore the resting potential charges so you can get another impulse later

resting potential was the charges in the resting neuron and the action potential is the charges during the impulse (reversed)

• taking away the original polarity
• reversing the charges
• decreasing the membrane potential by stimulation of the axon
• happens when you get an impulse

the minimum stimulus required to cause an impulse (action potential) in a neuron

• either the stimulus is strong enough to cuase an impulse or there will be no impulse at all
• even if you increase the stimulus greater than the threshold, the impulse will always be the same strength
• no such thing as a stronger impulse

• not by impulse strength but by impulse frequency
• rate increases

ion movement causes electrical current in the neuron and propagates down the whole length of the axon

• depolarize the membrane: reverse the charges in and out of the cell to take away original polarity
• at point of stimulation membrane becomes permeable to Na and it enters into the axon hillock
• gated channels open and na will diffuse from high to low concentration (into the cell)
• so much na enters that inside becomes + and leaves outside -
• reversed charges act as a stimulus to the next part of the membrane and that next part becomes permable to na and it starts again-cascade effect
• you create a wave of negative charges outside the axon and it flows to the end of the axon
• repolarization

• positive
• stimulus makes more and more impulses down the neuron

• restoring the resting potential original charges
• starts at the point of stimulation and happens simultaneously while depolarization is still happening further down the cell

• Na channels become inactivated and pumps reset so no more can flow in
• k+ channels open and it diffuses out down the concentration gradient (b/c more k inside) and also towards the outer (-) charge
• sometimes k channles remain open after the sodium pumps have been reset and functioning (na being pumped out) meaning k can diffuse more than the minimum required to restore resting potential
• the K+ pump begins working again and the membrane is now not permeable to k or na

each part of the axon has charge reversed all the way down meaning each part is depolarized bit by bit

• happens if there is a meylin sheath around the axon
• saltitory- "leap"
• the impulse jumps from node to node
• up to 30x faster
• the myelin sheath also prevents any extraneous ion movement by leakage

• myelinated
• axons with a wider diameter (causes less resistance)

• the time after the impulse starts when the neuron will not respond to any stimulus because you have yet restored the resting potential 
• milliseconds long
• 2 types

• absolute refractory period: the impulse has just started flowing and restoration hasnt begun --> absolutely no response to stimulus
• relative refractory period: if you have begun to restore a very strong stimulus could create another impulse

• the junction where a neuron sends info to another cell
• this other cell can be another neuron (for thinking/feeling) or it could be a muscle or gland cell
• includes 2 cells

• presynaptic neuron: the cell that releases the neurotransmitter
• post-synaptic cell: the cell that responds to the neurotransmitter

• usually chemical using neurotransmitters
• there are rare instances in adults where youll have an electrical synapse where the 2 cells are electrically coupled and you dont use a neurotransmitter- this involves synchronizing activity of cells; seen more in an embryo and it is later replaced by the use of a neurotransmitter

released from the synaptic bouton (axon terminal) by exocytosis

• the NT diffuses across the synaptic cleft and binds to a receptor on the post synaptic cell membrane
• then the effects of the neurotransmitter are terminated (ended)- multiple ways to do this

• 1.) degradation of the NT in the synapse by an enzyme that can be in the synaptic cleft or on the post synaptic cell membrane
• 2.) Reuptake- the neurotransmitter is taken back up into the presynaptic neuron and is stored or broken down by an enzyme
• 3.) Diffusion away from the synapse (ex- it could go into a nearby blood vessel or taken up by an astrocyte)

can either be excitatory or inhibitory

• they will stimulate the post synaptic cell 
• will try to get an impulse in the next neuron but may not be strong enough

• will try to prevent the next cell from an impulse (neuron) or being stimulated (another cell)
• they do hyperpolarization: increasing the (+) charges outside the cell

• the post synaptic cell sums up the influence of all the neurotransmitters at the synapse to determine response- do you reach a threshold or not for a response 
• 2 types: temporal summation and spacial summation

• time
• if a neuron has many impulses in a row so that the neurotransmitter accumulates in the synapse before it is removed, there is an additive effect of that neurotransmitter

• you have 2 or more presynaptic neurons releasing neurotransmitters at the same time to the same post synaptic cell causing an additive effect
• it will be the same neurotransmitter

• more than 50
• some release only one type of NT while others release more than one
• found in different parts of the CNS and from different nerves in different pathways

• not having the usual amount of a neurotransmitter
• ex: parkinsons, not enough dopamine

• you can treat it by increasing the synthesis of a neurotransmitter or its release by giving a precursor (ex- for dopamine you can give l-dopa)
• you can give a drug to mimic the neurotransmitter at the receptor
• you can give a drug to prevent the removal of a neurotransmitter at the synapse at a certain time- preventing reuptake or enzyme breakdown (this method used in depression- Seratonin reuptake inhibitors)

you want to decrease synthesis, block the neurotransmitter from the receptor or remove it from the synapse (physically or by breakdown via enzymes)

• a chemical that does not directly cause an action potential at the synapse but in some way it does affect a neurotransmitter at the synapse
• ex: may stimulate release, degradation or reuptake
• may influence the receptor functioning
• may be a paracrine substance
• influences the cell in some way but doesnt function as a direct neurotransmitter

• a regulator that acts locally
• made by one type of cell and released and affects a nearby cell

• GABA- gamma-amino butyric acid
• glutamate
• glycine
• endorphins enkephalins
• substance P
• somatostatin
• cholecystokinin
• nitric oxide
• acetylcholine
• norepinepherine
• dopamine
• serotonin
• histamine

the brain and spinal cord

• early on in prenatal life
• neurons appear early in develoment- you get new ones prenatally and then a few months after birth
• you generally dont get new neurons later in life, but yours will grow
• ability for neuron mitosis only lasts 3-4 years

• forebrain
• midbrain
• hindbrain

• cerebellum
• diencephalon

• medulla 
• pons
• cerebellum

midbrain, pons, medulla

• the largest most superior part of the brain
• has 2 cerebral hemispheres (halves)

5 lobes: frontal, parietal, occipital, temporal and insula (internal)

folds in the cerebrum that increase the surface area

• area of white matter that connects the 2 halves of the cerebrum, a type of commisure (connection)
• there are also association tracts- info going from one part of a hemisphere to another

• made of white matter which is made up of nerve fibers
• goes between both cerbral hemispheres to communicate between them

• where you communicate info from lowere parts of the nervous system ascending up towards the cerebrum
• --->function is sensory
• you also have projection tracts from the cerebrum descending down to the lower parts of the nervous system
• --->function is motor

• the outside area on the surface of the brain
• grey matter
• has 6 layers of cell bodies

• include basoganglia (nuclei or centers that are deep) and those include the caudate nucleus and putamen
• this part of the brain is affected in Parkionsons disease (stops movement)
• usual function is to prevent unnecessary movement and regulating starting and stopping in movement

dopamine

• left because the pathways  going up and down from the cerebrum cross over 
• ex: stroke on left side of the brain causes right side of body to disfunction

• speech
• written language
• numerical reasoning
• logic
• skilled movements

• musical auditory and artistic awareness
• spacial pattern
• perception
• insight
• imagination

• sensory, motor, visceral and mental
• general sensations
• special sensations 
• fine control of movement
• mental functions

• ie from skin
• primarily regulated by the parietal lobe
• visceral organs regulated by the insula

• vision from the visual cortex of the occipital lobe
• hearing- autidory cortex of temporal lobe
• taste- gustatory cortex of the parietal but also from the frontal and inusla
• smell- olfactory cortex of the temporal lobe
• equiliburim or balance- vestibular cortex of the insula and parietal lobes

• the primary motor area is in the frontal lobe (most important)
• this controls groups of muscles 
• pinpoints exact places where muscle moves

• info travels back and forth by association tracts connecting multiple parts of the brain
• in memory: there are different parts of the cerebral cortex involved
• limbic system
• higher mental functions (ie- planning)- frontal lobe
• personality- prefrontal cortex
• speech- frontal parietal, temporal
• consciousness- cerebral cortex
• influences viscera via autonomic NS

• part of the cerebrum near the corpus collossum (hippocampus)
• also includes the diencephalon (thalmus and hypothalmus)
• important in memory, emotions and motivation
• associates pleasant and unpleasant memories

• controls consciousness- awareness of yourself and others in the environment
• multiple impulses, especially sensory and integrated, alert the cerebrum

the parts of the medulla, pons and midbrain that get info from cranial and spinal nerves+cord that send impulses to the diencephalon then to the cerebrum

• Thalmus
• Hypothalmus 
• Pineal Gland

• important for sensations
• a relay center for most sensory pathways
• contains a synapse and when the info gets there there is a crude understanding of the sensation (once it reaches the cerebrum theres a fine understanding)
• part of the reticular activating system- consciousness
• part of the limbing system- associating emotions with memory
• has some complex cranial reflexes

cerebrum and lower parts of the brain

• makes hormones and influences other hormones
• has pituitary gland attached to it
• a bridge between the 2 communication systems (nervous and endocrine)

• important in reproduction, growth and water balance
• influences viscera via autonomic NS
• part of limbic and reticular activating systems
• important in daily rythems (circadian rythems- around a day), being awake/asleep, eating/not eating, things that change in a day
• influences eating behavior (has feeding and satiety[feeling full] centers)
• contains the thirst center, temperature center (Acts as a thermostat for the body- causes shivering, sweat, etc)

attached to the diencephalon, makes melatonin

• important in sleep and daily rythems
• a biological clock

• Contains nuclei for certain auditory and visual reflexes
• a reflex center for cranial nerves (ocularmotor and trochlear)
• involved in reflexes involving motor coordination and posture

• important in the reticular formation, respiration (has respiratory centers for the rythem of breathing)
• contains nuclei for cranial nerves involved in chewing, taste, eye movement and equilibrium

• trigeminal
• abducens
• facial
• vestibulocochlear

• attaches to the spinal cord
• lowest part of the brainstem
• involved in reticular formation- consciousness

• vestibulocochlear
• glossopharangeal
• vagus
• accessory
• hypoglossal

• respiratory system- regulates the rate and depth of breathing
• circulatory system- regulates the heart and blood vessels (its most important in this system)

• invovled in vommiting, coughing, sneezing and swallowing
• info coming up from the spinal cord has to go through the medulla- it is a place of projection tracts going up to the brain from the spinal cord and going down

• sensory and motor
• when info comes up or down most pathways experience decussion (crossing over to the other side of the body)- happens either in the medulla or spinal cord

• very important in muscle coordination- vital for skilled movements (as opposed to crude reflexes)
• acts with the cerebrum in motor pathways
• important in controlling groups of muscles
• important in memory of movements- ex remembering how to walk
• equilibrium (balance)- receives impulses from the ears
• important in posture- receives info about (ex upsidown) position from ears and from muscles, tendons and joints (ex youre aware if youre holding your arm up)- regulates movements needed to retain posture
• kinesthesia
• equilibrium from eyes- you can see wheere you are

a sense of position and movement of the body (you know if youre upside down spinning etc)

membranes called the meningies, adipose tissue and bone

like an oval cylinder and attaches to the medulla

• paired and attached to the spinal cord
• they come out from different levels of the cord- cervcal, thoracic, lumbar, sacral, and coccygeal

• all are mixed (both sensory and motor)
• spinal nerves contain the dendrites of sensory neurons and axons of motor neurons

branches of the spinal nerve

• in cross section of the spinal cord
• holds cerebral spinal fluid

can be just sensory to motor or go from sensory to interneuron then to motor

• has dorsal root ganglion w/ cell bodies
• sensory only

motor only

a very quick response to a stimulus and the pathway of neurons in a reflex is called a reflex arc

• where you have one synapse 
• sensory neuron to motor neuron
• the fewer number of synapses the faster the reflex

sensory neuron to interneuron to motor neuron

• spinal reflex
• cranial reflex
• ipsilateral reflex
• contralateral reflex

• this involves spinal nerve and spinal cord but not the brain
• ex: knee and kick reflex

• involves cranial nerves and the brain
• ex: pupil constricts when shining light in eye

• the stimulus and response are on the same side of the body
• ex: if you hit your right knee you kick your right knee

• also have a stimulus and response is on the opposite sides of the body
• interneuron: branch of axon that crosses over to the other side-synapse with motor neurons is on the other side
• ex: shining a light in one pupil, both will dialate

• reflexes 
• sensory function
• motor function

• contains ascending pathways to the brain
• there are seperate pathways for the different senses (pain touch, etc)

• contains decending pathways from the brain
• seperate pathways for different movements in distinct areas

• nerve fibers in the CNS go to other places in the CNS
• if a tract has a 2 part name the first part is where the tract starts and the second is where it ends
• ex: spinothalmic tract- spinal cord to thalmus- ascending so sensory

• how the neurons bring info from one place to another, also called circuts
• they do this by divergence or convergence

• if you have one neuron sending info to a number of neurons in different parts of the Nervous system
• ex: you touch a tack and it hurts- info from the sensation of pain and limbic system info to make it a bad memory

• if one neuron receives info from a number of neurons
• ex: multiple parts of the brain send info down the spinal cord by convergence

• ex touch
• starts with the receptor of the sensory neuron (tactile receptors in skin). that neuron is in the spinal nerve and it will have a synapse with another neuron in the spinal cord, info is then sent to thalmus and before it gets there there will be crossover in either the spinal cord or medulla then goes from the talmus to the cerebral cortex (parietal lobe)

start from cerebral cortex (ex- frontal lobe). cerebral cortex sends and impulse down to the medula oblongata. the cerebellum also sends an impulse here. then medulla to the spinal cord to spinal nerve to the effector (usually muscle), again, crossover occurs in the medulla  or spinal cord

• olfactory
• optic
• oculomotor
• trochlear
• trigeminal
• abducens
• facial
• vestibulocochlear
• glossopharangeal
• vagus
• accessory
• hypoglossal

• smell
• only sensory

• vision
• sensory only

• eye movement
• more regulates the pupil size
• adjusts the amount of light
• regulates the lens of the eye, adjusts lens for near and far vision
• motor only

• also moves eye
• motor only

• controls sensation so of the head and chewing
• sensory and motor

• moves eye
• motor

• to ears
• just sensory
• controls hearing and equilibrium (balance)

• involved in taste, swallowing, secretion of saliva
• regulates the blood pressure and breathing
• sensory and motor

• sensations of the throat
• regulates the blood pressure and breathing
• swallowing, coughing, speaking 
• regulates the heart and the other viscera

area of the cerebrum associated with speaking language

area of the cerebrum associated with understanding language

• important in swalliowing 
• head and shoulder movement
• motor

• swallowing and speech
• motor

• nerves to internal organs
• sensory, motor and reflex pathways

• culomotor
• facial
• glossopharangeal
• vagus

• smooth or cardiac
• or they are glandular cells

• 2- dual innervation
• have sympathetic and parasympathetic nerves- they have opposite functions
• but some organs only have sympathetic nerves

• somatic: one motor neuron connected to accessory, releases acetyl choline to skeletal muscle
• autonomic: 2 motor neurons, motor neuron 1 always releases acetylcholine while #2 releases norepinepherine (sympathetic) or acetylcholine too (parasympathetic)

autonomic ganglion

• motor neuron number 1
• releases acetyl choline

• motor neuron #2
• releases acetylcholine or norepinepherine

• called the thoracolumbar division
• spinal nerves that are comming out from lumbar and thoracic regions of the spinal cord

spinal only

• sympathetic ganglia are near the spinal cord in a chain
• sympathetic chain ganglia impulses can go up and down the chain in addition to directly to the organ (so something going down one neuron can affect another because they are connected)
• preganglionic neurons are short-cholonergic neuron- release acetylcholine
• postganglionic neurons are long- release norepinepherine, called adrenergic neurons if they release norepinepherine

• medulla, inner portion of adrenal gland
• in sympathetic ns
• makes hormones- epinepherine+ norepinepherine (also a NT)
• develops alongside the sympathetic ganglia
• a motor neuron releases acetylcholine causing adrenal medulla to release epinepherine/norep into the blood

• fight or flight hormone
• released into the blood

craniosacral division

• oculomotor
• facial
• vagus
• glossopharangeal
• also involves spinal nerves from the saccral region

• pregangionic motor neuron is long
• parasympathetic ganglion is near the organ or effector
• postganglionic motor neuron is short

• the one nerve is always sympathetic
• adrenal medula: regulates secretion of hormones epinepherine and norepinepherine
• sweat glands:when stressed, these increase sweat production and release 
• most blood vessels only get a sympathetic nerve: causes the constriction (narrowing) of the smooth muscle on an artery
• spleen: influences blood flow
• arrector pilli: hair movement
• kidneys: decrease urination in the sympathetic NS

• if there are 2 nerves its not just on or off situation, there is a balance between the 2
• --- sympathetic will dominate in stress situations
• --- parasympathetic will dominate in non stress situations for homeostasis

• in stress- heart pumps faster is stimulated and digestion is inhibited or slowed down
• balance regulated by the hypothalmus

• the sympathetic ns gets the most out of the body (ie you can run faster, do more)
• this is very fast
• adrenal medulla helps to prolong the stress response and the sympathetic ns is stimulated while the parasympathetic is inhibited

• in stress- epinepherine and nor epinepherine
• in homeostasis- hormoens such as hydrocortizone help return to homeostasis

• physical
• emotional
• medical

• beats faster
• is stronger
• pumps blood to the skeletal muscles to bring o2 and nutrients to get the most out of the muscle

sympathetic ns and norepinepherine dialate the passageways to get as much o2 in the body as possible

symp ns cuases dialation of pupils to get the maximum amount of light into the eyes

makes epinepherine to prolong effects of symp ns

• digestive organs
• kidneys
• these are inhibited
• you return to homeostasis after stress and parasympathetic does reverse effects

• decreses rate and force of heart contraction
• decreases diameter of respiratory passageways
• decreses pupil size
• stimulates digestion, urine formation
• sends impulses to inhibit during stress but symp still sending many impulses so you only see the inhibitory effect of the parasympathetic ns after the stress is over

• certain regions are key to controlling viscera (ex medulla controlling heart and blood vessels)
• hypothalmus integrates the parasym and symp to determine the balance and gets info from the cerebrum
• hypothalmus also stimulates the brainstem
• cerebrum- cerebral cortex and limbic system
• brainstem-bottom line for survival

• mental functions and emotions can influence the autonomic nerves and therefore the viscera
• a mental function (thinking aobut some stress) is a function of cerebral cortex while a direct emotion is limbic system
• both influence viscera