Anat & Physiol, Nervous System

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Functions of the Nervous System

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allows for very fast response to environment
allows for rapid control of internal enviro
rapid coordination

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CNS

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brain and spinal cord.
groups of cells termed nuclei, one cell called neuron

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why do they appear grey

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lack of myelin fat, and groups of Nissl bodies in the neurons that compose the nucleii. nissl bodies are bunch of ribosomes on ER that are needed to make proteins. they're bluish grey.

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processes of nerve cells in CNS

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termed tracts. nerve tracts connect nucleii. they look white b/c of insulating white myelin fat. the myelin fat is there for rapid conduction and so they dont short out by accidentally contacting each other. no neurons. this is termed "white matter".

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PNS

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nervous structures outside of the brain and spinal cord. groups of cells here are not called nucleii, they're ganglia. groups of neuronal processes outside the CNS in the PNS are called nerves.

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Afferent nerve division

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nerves moving toward the CNS, or spinal cord. like the sensory info coming from proprioceptors. visceral afferent comes from heart. if having a heart attack it's generalized, feel pain throughout shoulders. localized like pacinian corpuscles.

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Efferent nerve division

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moving away from a structure. efferent lymph vesses, efferent tubules the kidney. carries info away from CNS.

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somatic efferent nerves

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motor nerves which innervate primarily muscles but also some glands
efferent

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autonomic

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you don't control it with your conscious. innervates glands, smooth and cardiac muscle.
they're still efferent.

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how are cells organized

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they are tightly packed. less than 20% is intercellular space. the synapse is there for 1-way travelling. as many stars in the galaxy. surface of brain highly convoluted = greater surface area = more nerve cells.

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one of two types of cells in NS:
neuroglia

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nerve glue. nuroglia babysit, support, scaffold, guide young cells both during embryonic development and tissue repair, segregate, insulate, provide nutrition, health, and growht. they make up a large portion of the mass of NS. 4 in CNS and 2 in PNS.

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Astrocyte

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neuroglia in the CNS. star cell. most abundant type. large nucleus and numerous cytoplasmic processes. form the physical support network. connect capillaries w neurons, nutrition. stimulate capillary endothilial cells to form blood-brain barrier.

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Astrocytes also:

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repair damaged tissue and form scars. a scar in the brain is also astrocytes. they also guide neuron development.

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blood brain barrier

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impermeable to soluble substances such as metabolic wastes, proteins, some toxins, and most drugs.large esential amino acids, glucose, and some electrolytes move by fac. diff. glycine is special amino acid that serves as neurotransmitter.

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other important exceptions to blood brain barrier

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hypothalamus so that blood hormones can be monitored and releasing factors that control endocrine system can be secreted. hypothalamic osmoreceptors that determine thirst. choroid plexus which produces cerebrospinal fluid. barrier ineffective against fat soluble: drugs, alcohol, nicotine,anesthetics.

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the specific reason for the blood brain barrier is:

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some chemicals in the body, like glycine, act as neurotransmitters in the brain. you want their locations and amounts in brain monitored and controlled, not freely floating around.

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Oligodendrocytes

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name means "few branches". smaller than astrocytes and fewer processes. these are called the schwann cells in the PNS. form myelin fatty insulations around axons in the CNS. organize and improve fn of CNS. they form the white matter of the CNS.

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Axolemmas and neurolemmas

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an axolemma is the membrane of the axon, the neurolemma is the membrane of the oligodendrocyte cell body

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nodes of ranvier

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gaps in the myelin insulation which increase conduction of speed of nerve tracts.

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microglia

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tiny glue cells. macrophage but for the brain. small amoeboid cells w long thorny processes which monitor neuronal health; essentially WBC of CNS. become phagocytic during infect. numbers increase from a normal of 5% during infect.

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ependymal

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"wrapping garmet cells" . layer of ciliated cells which line the spinal canal and ventricles. sensory cells which respond to changes in cerebrospinal fluid and circulate the cerebrospinal fluid by ciliary movement.

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Neuroglia of the PNS

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schwann cells (neurolemma sheath) and satellite cells (neuronal chemical enviro)

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schwann cells

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like the oligodendrocytes in the CNS. but these in peripheral nervous system. produce the neurolemma sheath around the axons of both myelinated and unmyelinated nerves. spiral membrane. aka neurolemmocytes.

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satellite cells

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like astrocytes in CNS, but these in PNS. surround neuronal cell bodies in ganglia. form structure. control the neuronal chemical environment.

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Neurons

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exciteable. cells which function to generate and transmit nerve impulses. amitotic in most cases. long lived. have a large diff in metabolic rate depending on resting (quiescent) or active. cell membrane fns in generating nerve impulses and cell to cell signaling during development.

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perikaryon

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neuronal cell body. it is the biosynthetic center of the cell, chemical products are distributed through the processes by axonic streaming. has neurofilaments, nissl bodies, pigments like melanin and lipfuscin which color them black.

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nissl bodies

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these are unique to neurons in the perikaryon. consist of ribosomes organized on ER (always blue), proteins synthesized here. they color everything grey in the "grey matter" of the CNS.

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neurofilaments

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these are fibers in the perikaryon organized into bundles called neurofibrils. they maintain cell shape.

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Neuronal cell processes of multipolar neurons.

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they are cytoplasmic extensions of the perikaryon. it's the dendrites and the axons.

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dendrites

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receptive region. conduct nerve impulses toward the cell body. highly branched with dendritic spines. contain nissl bodies which biosynthesize cell products.

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axons

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conduct nerve impulses away from cell body. can be single or branched. have synaptic knob where neurotransmitters stored and released. may be sythesized within knob or perikaryon. synaptic knob may be the neuromuscular jcn. axons have no nissl bodies.

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cytoplasmic streaming

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axons have no nissl bodies so substances synthesized in the cell body are transported along neurotubules down the axon. it requires atp. slow transport is few mm/day, fast transport is 5-10 mm per hour.

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myelinated neuron axons

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covered with a myelin sheath. its a fatty substance secreted by Schwann cells in PNS, oligodendrites in CNS. insulation. gaps in myelin sheath betw schwann cells called nodes of ranvier, provide for more rapid conduction. depolarizaton only occurs at nodes. an electromagnetic field causes the potential to jump.

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neurolemma

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cell membrane of the schwann cell with the myelin fat.

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Growth of neurons

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dont undergo mitosis after maturation, exceptions include olfactory and hippocampus. migrate from neural crest in embryo to correct location then mature. can grow new cell processes, to recover severed nerves, unique to learning.

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structural classification

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unipolar, bipolar, multipolar

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unipolar neuron

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dendrite is continuous with the axon, found in sensory neurons in PNS. cell body is off to the side.

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bipolar

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neuron possesses one dendrite and one axon; found in sensory neurons in CNS, eye, and ear.

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multipolar.

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neuron possesses one axon but MULTIPLE DENDRITES. most common neuron. dendrites have branches. 99.999%. 2 types are purkinje and pyramidal.

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purkinje

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cerebellum/motor

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pyramidal

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cerebrum/motor

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unmyelinated neurons

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not really a classification. ennervate internal organs. non-jumping conduction, slower. actually still have schwann cells and myelin sheath.

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where is the sensory part of the brain and spinal cord

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the dorsal/back part

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and the motor part?

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the anterior or lateral part

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functional classification of neurons

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sensory/afferent, somatic afferent, visceral afferent, somatic efferent, visceral efferent, interneurons/association

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somatic afferent
efferent

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conducts info from skin, skeletal muscle to CNS
efferent: motor neurons in CNS to skeletal muscles

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visceral afferent
efferent

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from viscera and blood vessels to CNS.
efferent: motor neurons from CNS to smooth and cardiac muscle and glands

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interneurons

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aka association. 99% of neurons. integrative neuron between two other neurons.

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transmission of nerve impulse

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remember, Donnan effect establishes (-) membrane condit (polarized). influx of Na+ causes depol away from -70mv . resting potential restored b/c K+ ions rapidly flow out. all in 2-3 ms. 10^5 action potentials can be generated before Na/K returned to normal.

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threshold pot

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-55mV.

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graded potential

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local. it varies with the strenght of the signal and distance from the stimulus. flow of Na+ creates electrical field in membrane close by.

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AP

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still an all or none thing. fires or it doesn't. the spread of the AP down the neuron is caled nerve conduction. its due to ions, not electrical discharges so therefore doesn't lose strength. goes both ways down the neuron, but once it gets to synapse becomes one-way.

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SPeed of nerve conduction dependent on

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nerve axon diameter, temperature, myelination.

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fast conduction

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myelinated motor and sensory nerves with A fibers w diameter of 1 -20 um.
5-150 m/s

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slow conduction

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unmyelinated C fibers , internal organs , <2 m/s

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saltatory conduction

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jumping

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what does pressure do/

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inhibits conduction along nerve tracts. leg or arm falling asleep.

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refractory period

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neuron cant respond to another stimulus. absolute: opening of Na channels and closing of inactivation gates.
relative: when most Na gates have closed but K gates are open. really strong stim will generate another.

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synapses

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can be either electrical or chemical.

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electrical

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less common than chemical. protein channels connect adjacent neurons whose depol activity is then synchronized. this is important in the hipocampus, for emotion, long term memory, learning, and in communication betw glial cells

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chemical synapses

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most. involves the release of one or more neurotransmitter and/or neuromodulator. 60 or 70, discovering new ones all of the time. there are two types of classifications of chemical synapses: functional and type of neurotransmitter released.

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ionotropic
functional classification of a
chemical synapse

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have direct impact on opening and closing of gated ion channels in the postsynaptic membrane, ex are Ach, glycine and aspartate.

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metabotropic

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another type of functional classification of a chemical synapse. in addition to ion channels, also have an impact on metabolism of post synaptic neuron, ex are glutamate, GABA, NE (norepinephrine), and serotonin.

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Cholinergenic synapse

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chemical synapse whose classification based on type of neurotransmitter released. AP arrives at presynaptic membrane, Na and Ca rush into cytoplasm of synaptic knob. synaptic knob depolarized. ca ions trigger exocytosis of synaptic vesicles filled with acetylcholine. removal of ca ions stops exocytosis of vesicles w/ achl.

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what happens after vesicles of achl cross the snaptic cleft

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Ach binds with chemically regulated Ach receptors on post-synaptic membrane. this results in incr. Na ion permeability and an excitory post-synaptic potential (EPSP). Ach in synaptic cleft destroyed by acetylcholinesterase. choline recycled to pre-syn neuron.

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fatigue in cholinergenic synapse

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when Ach cant be replenished fast enough to be released from presynaptic neuron.

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delay on cholinergenic synapse
how long does it last

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this is the neuromuscular jncn, has to be fast. 0.2 to 0.5 ms. the effect of Ach release can be felt for 20 minutes.

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What does Ach typically do

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excites muscle, but inhibitory on cardiac f'n.

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Adrenergic synapse

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neurotransmitter is norepinephrine. action pot arrives at presynaptic membrane. Both Na and Ca flow into the knob. knob depol. the Ca ions trigger the release of NE.

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after NE binds to postsynaptic membrane:

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causes the conversion of ATP into cyclic AMP by adenyl cyclase in the post synaptic neuron. NE is the first messenger, cAMP is 2nd. cAPM activates enzymes that which open chemically gated Na channels and Na ions flood in.this causes depol, and metabolic effects.

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what happens to the 1st and 2nd messenger?

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cAMP is destroyed by posphodiesterase and NE is destroyed by monoamine oxidase and other enzymes?

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how long do effects last

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NE release will last for 5 -30 ms and the impact will last for several minutes

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Amines

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these are "biogenic" amines. tend to have inhibitory effects on CNS or brain. These include serotonin, dopamine, and histamine.

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amino acids

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only in CNS. Gama amino butyric acid (GABA) : found in the brain and stabilizes membrane potentials by hyperpolarizing the membrane. Glycine has inhib effects on CNS. Both glutamate and aspartate excite the CNS.

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Neuropeptides

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substance "P" involved in pain generation. opium and morphine bind to same receptors and block pain generation. natural opiates do to, like endorphin, to keep you going and block pain

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neuromodulators

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synapses may release other chemical substances during neurotransmitter release. neuromodulators change the postsynaptic neuron's response to neurotransmitter. Neuropeptides are protein chains. opioids bind to same reactors as opium and morphine and inhibit the CNS, espec substance P. endorphins,

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curare

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prevents Ach from binding

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Strychnine and malathione (a pesticide)

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inactivate acetylcholinesterase

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bromides

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like asprin, opiates including morphine, they inhibit post-synaptic neuron

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cocaine

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inhibits the removal of dopamine in specific areas of the brain, rise in dopamine changes inhib/excit balance

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antidepressents

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such as Prozac, Paxil, Zoloft, . inhibit reabsorption of serotonin, rise in serotonin relieves depression, and impacts wake/sleep cycles.

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what is the oldest part of the brian

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the brain stem. next is the limbic system, which deals w emotion. next is cerebrum, next is pre-frontal lobes, which inhibit impulses coming from the limbic system. social graces and estimations

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Beta blockers

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act on pacemaker heart cells which lower blood pressure.

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what is the limiting factor in the speed of a nerve impulse

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the synaptic delay. Cholinergenic synapses only 0.3 to 0.5ms, adrenergic synapses take longer. fewer synapses make for a faster impulse.

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excitory response

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this happens when neurotransmitters cause a decrease of resting potential (depol) towards the threshold pot in postsynaptic neuron. EPSP. these are Ach, NE, epinephrine. gorillas and chimps have a very exciteable brain

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Inhibitory response

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make membrane more permeable to K+ or Cl- depending on the synapse, causing hyperpolarization or increase in resting potential towards more negative potential. Inhibitory Postsynaptic Potentials IPSPs. depresses neuronal activity in brain.

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IPSP neurotransmitters

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GABA, glycine, dopamine, serotonin.If these aren't working, you get a violent and antisocial individual. these are just as important as excitation.

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integration of info, neural integration at synapses

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this occurs b/c 1 post synaptic neuron may have numerous synapses w/ neighboring ones that have both EPSPs and IPSPs. THe balance of firing betw presynaptic neurons determines whether the post syn neur will generate an AP

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summation

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effect of EPSPs on post synaptic neuron, each produces a graded pot that lowers toward threshhold

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temporal summation

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one neuron fires repeatedly

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spatial summation

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when a lot of presynaptic neurons fire simultaneously

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facilitation

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the process of partially depolarizing a neuron so it more readily generates an AP

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fatigue

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good ex. is hearing/nagging. a decrease in signal strength even though stimulus is constant. caused by exhaustion of neurotransmitter.

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potentiation

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contin firing of synapse makes post syn neur more sensitive to presyn neuron. learning.

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neuronal pools

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aka circuits. thousands of excitatory and inhib.
converging: input from several sourcesand funnels to next pool
diverging: input from one or few other pools and generates to many pool, amplifying signal.
reverbating: rhythmic activity