Anatomy Exam 4 chapter 12

what does the endocrine system do?

communicates by chemical messengers (hormones) secreted into the blood

what does the nervous system do?

employs electrical and chemical means to send messages fron cell to cell

the 3 steps the nervous system carries out its task

1. sense organs receive information about changes in the body ans external environment and transmit sensory input to the CNS

2. CNS processes this information, relates it to past experiences, and determines appropriate response (integration)

3. CNS issues motor output commands to muscles and gland cells to carry out a response

where does the CNS go to?

brain and spinal cord

what does the PNS branch to?

sensory and motor division

Sensory: visceral and somatic

motor: visceral and somatic

Visceral motor (ANS): sympathetic and parasympathetic

the sensory (afferent) division does..?

carries signals from receptors to CNS

• somatic sensory: carries signals from receptors in the skin, muscles, bones and joints

• special sensory: carries signals from the special senses (sight, sounds, balance, taste, smell)

• visceral sensory: carries signals from the viscera (heart, lungs, stomach, urinary bladder)

the motor (efferent) division does..?

caries signals from CNS to effectors

• somatic motor: carries signals to skeletal muscles

• visceral motor: carries signals to glands, cardiac, and smooth muscle

the autonomic nervous system

also known as the visceral motor division

has sympathetic and parasympathetic

sympathetic: arouse body for action, speeds up HR and respiration, inhibits digestion and urinary system

parasympathetic: calming effect, slows HR, stimulates digestion and urinary system

the universal properties of neurons are?

• excitability: responds to environmental changes called stimuli

• conductivity: responds to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations

• secretion: when electrical signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter that influences the next cell

what is the neurosoma?

• cell body

• control center of the neuron

• single, centrally located nucleus

• contains all regular organelles of a cell

• has no centrioles, amitotic

what are dendrites?

• branches that come off of the neurosoma

• the primary site for receiving signals from other neurons

• the more dendrites the neuron has, the more information it can receive

• provide precise pathways for the reception an processing of information

what are axons?

• specialized for rapid conduction of signals to distant points

• originates from the axon hillock

• cylindrical, relatively unbranched for most of its length

• may have branches

• some axons have myelin sheaths

• branches extensively on the distal end (axon terminal)

what is the axon terminal?

• contains synaptic vesicles full of neurotransmitters

• forms a junction (synapse) with the next cell

what is a multipolar neuron?

• one axon and multiple dendrites

• most common form, most in the CNS

what is a bipolar neuron?

• one axon and one dendrite

• olfactory cells, retina and inner ear

what are unipolar neurons?

• single process leading away from neurosoma

• sensory cells from skin and organs to spinal cord

what are anxonic neurons?

• many dendrites but no axon

• retina, brain, and adrenal gland

what is anterograde transport?

• movement down the axon away from the neurosoma

• uses kinesin motor proteins

• slow axonal transport(.5-10 mm/day), moves enzymes, components during repair and regeneration of damaged axons

• fast axonal transport (20-400 mm/day), organelles, enzymes, vesicles

what is retrograde transport?

• movement up the axon toward the neurosoma

• uses dynein motor proteins

• fast axonal transport (20-400 mm/day)

• for recycled materials and pathogems

• the delay between infection and symptoms is the time needed for transport up the axon

what arer neuroglia?

• protect neurons and help them function

• 1 trillion neurons

• glia outnumber neurons 10 to 1

• binds neurons together and form framework for nervous tissue

• if mature neuron is not in synaptic contact with another neuron, it is covered by glial cells

what are oligodendrocytes?

• forms myelin sheaths in CNS that speed signal conduction

• type of neuroglis in CNS

what are ependymal cells?

• type of glia cell in CNS

• lines internal cavities of the brain; secrete and circulate cerebrospinal fluid (CSF)

what are microglia?

• types of glia cells in the CNS

• wander through CNS looking for debris and damage

• protective

what are astrocytes?

• type of glia cell in CNS

• most abundunt glial cell in CNS

• covers brain surface abd most nonsynaptic regions of neurons in the gray matter

• serves many diverse functions

what are schwann cells?

• type of glial cell in PNS

• envelope nerve fibers in PNS

• wind repeatedly around a nerve fiber

• produces a myelin sheath similar to oligodendrocytes

• assists in regeneration of damaged cells

what are satellite cells?

• type of glial cell in PNS

• surrounds the neurosomas in ganglia of the PNS

• provides electrical insulation around the neurosoma

• regulates the chemical environment of the neurons

what is a myelin sheath?

• insulation around a nerve fiber

• formed by oligiodendrocytes in CNS

• formed by schwann cells in PNS

• consists of the plasma membrane of glial cells

• 20% protein and 80% lipid

what is myelination?

• production of the myelin sheath

• begins at week 14 of fetal development

• proceeds rapidly during infancy

• completed in late adolescence

• dietary fat is important to the CNS development

what is the neurilemma?

• thick, outermost coil of myelin sheath

• contains nucleus and most of its cytoplasm

• external neurilemma is the basal lamina and a thin layer of fribrous connective tissue called the endoneurium

myelin in PNS vs CNS

PNS: shwann cells spirals around a single nerve fiber

CNS: oligodendrocyte myelinates several nerve fibers in its immediate vicinity

what are the nodes of ranvier?

the gaps between segments

what are internodes?

myelin-covered segments from one gap to the next

what is the initial segment?

a short section of nerve fiber between the axon hillock and the first glial cell

what is the trigger zone?

the axon hillock and the initial segment

• plays an important role in initiating a nerve signal

what is multiple sclerosis?

• Oligodendrocytes and myelin sheaths in the CNS deteriorate

• myelin replaced by hardened scar tissue

• Nerve conduction is disrupted (double vision, tremors, numbness, speech defects)

• onset between 20-40 years and fatal from 25-30 years after diagnosis

• cause may be autoimmune triggered by a virus

what is Tay-Sachs disease

• Abnormal accumulation of glycolipid called GM2 in the myelin sheath

• hereditary disorder of infants of Eastern European Jewish ancestry

• normally decomposed by lysosomal enzyme, but the enzyme is missing in individuals homozygous for the The Tay-Sachs allele

• accumulation of ganglioside (GM2) disrupts the conduction of nerve signals

• blindness, loss of coordination, and dementia

• fatal before age 4

what about unmyelinated nerve fibers?

PNS: schwann cells hold 1-12 small nerve fibers in surface grooves

membrane folds once around each fiber

what are the conduction speed factors?

diameter of fiber (the larger, the more rapid)

presence of myeline (myelin speeds it up)

slowest to fastest ranking of nerve fibers

1. small, unmyelinated: .5-2 m/s

2. small, myelinated: 3 - 15 m/s

3. large, myelinated fibers: up to 120 m/s

• slow usualy goes to GI tract

• fast goes to skeletal muscles

how to know if nerve regeneration can happen?

• neurosoma is intact

• at least some of the neurilemma remains

when cant a nerve not regenerate?

• if a fiber is distal to the injury

what is electrophysiology?

study of cellular mechanisms for producing electrical potentials and currents

until 19th century scientists thought brain pumped psychic pneuma to make muscles contract

cajal used stains to trace nerual pathways and asked:

• how does a neuron generater an electrical signal?

• how does it transmit a menaningful message to the next cell?

what is an electrical potential?

a difference in concentration of charged particles between one point and another

• Living cells are polarized and have a resting membrane potential

• Cells are more negative on the inside than outside

• Neurons have -70 mV resting membrane potential

what is an electrical current?

• a flow of charged particles from one point to another

• usually uses gated channels to turn electrical currents on and off

What is resting membrane potential?

• exists because of the unequal electrolyte distrivution between ECF and ICF

• results from combined effort of three factors:

1. ions diffuse down their concentration gradient through the membrane

2. plasma membrane is selectively permeable and allows some ions to pass easier than others

3. electrical attraction of cations and anions to each other

what has the greatest influence on RMP

• potassium (K+)

• more permeable than any other ion

• K+ is about 40x as concentrated in ICF than ECF

• not very permeable to sodium (Na) and RMP is only slightly influenced by it

what is the ion basis of the RMP?

3 Na+ out for every 2 K+ it brings in to remain RMP

about 70% of the energy requirement of the nervous sytem

1 ATP per exchange

how to describe changes in membrane potential?

the plasma membrane is polarized at rest (there is a difference in potential across the membrane)

what are the two types of signals of membrane potentials?

1. local (graded) potentials; incoming short-distance signals

2. action potentials; long distance signals of axons

how to excite a neuron by a chemical stimulus?

ligands can bind and cause opening of certain ion channels in membrane

allows ions to travel into the cell, changing the membrane potential.

this change is a local potential

what are the properties of local potentials?

• graded: vary in magnitude with stimulus strength (a stronger stimuli opens more Na+ gates)

• decremental: gets weaker the farther they spread from the point of stimulation (voltage shift dimishes with distance)

• reversible: if stimulation ends, the cell quickly returns to its normal resting potential

• can be excitatory or inhibitory: some neurotransmitters make membrane more negative so it becomes less likely to produce an action potential

what are action potentials?

a dramatic change in membrane polarity produced by voltage gated ion channels

how to reach threshold?

if the stimulus makes the conditionsat the axon hillock reach thershold stimulus of -55mV, an action potential will travel down the whole axon

trigger zone is where action potential is generated

what are the actions of the sodium and potassium channels during an action potential?

1. Na+ and K+ channels are closed (RMP)

2. Na+ channels open, Na+ enters cell, K+ channels beginning to open (depolarization begins)

3. Na+ channels closed, K+ channels fully open, K+ leaves cell (depolarization ends, repolarization begins)

4. Na+ channels closed, K+ channels closing (repolarization complete)

written out steps of an action potential?

1. arrival of current at axon hillock depolarizes membrane

2. depolarization must reach threshold (-55mV) required to open voltage regulated gates

3. when voltage gated Na+ channels open, Na+ enters and depolarizes cell, which opens more channels

4. when membrane potential rises above 0mV, Na+ channels are inactivated and close, peaks at +35 mV

5. K+ channels open and outflow of K+ repolarizes cell

6. K+ remain open so membrane is briefly hyperpolarized (more negative than RMP)

7. RMP is restored as Na+ leaks in and extracellular K+ is removed by astrocytes

characterisitc of action potentials?

1. all or none: if threshold is reached, neruon fires at maximum voltage; if not, it does not fire

2. nondecremental: do not get weaker with distance

3. irreversible: once its started, it goes to completion and cant be stopped

what is a refractory period?

after an action potential where it is difficult to stimulate again

absolute: no stimulus will trigger AP. lasts as long as Na+ gates are open

relative: only very strong stimulus will trigger new AP. K+ gates are still open and any effect if incoming Na+ is opposed by the outgoing K+. lasts until hyperpolarization ends

what is the conduction of an unmyelinated fiber?

• chain reaction contiunues until the nerve signal reaches the end of the axon

• the nerve signal is like falling dominoes

• called continuous conduction

what is the conduction in a myelinated fiber?

• conduct signals with saltatory conduction (jump from node to node)

• nodes of ranvier contain many voltage gated ion channels, while myelin covered contain few

what are synapses?

2 of them

1. first neuron in the signal path is the presynaptic neruon (releases neurotransmitter)

2. second neuron is postsynaptic neuron (responds to neurotransmitter)

what are the steps of synaptic transmission

1. nerve impulse

2. Ca+ goes in

3. trhough vesicle

4. neurotransmitter through channel

5. depolarization

6. nerve impulse

different classifications of neurotransmitters

1. acetylcholine

2. amino acids (GABA)

3. monoamines (epinephrine, dopamine, seratonin, )

4. neuropeptides (endorphins)

what are neuromodulators?

chemicals secreted by neurons that have long term effects on groups of neurons

• may alter the rate of neurotransmitter synthesis, release, reuptake, or breakdown

• nitric oxide is a simple neuromodulator

what is neural coding?

the way the nervous system converts information into a meaningful pattern of action potentials

qualitative: which neurons fire

quantitative: information about the intensity of a stimulus

what are the four types of neural circuits?

1. diverging

2. converging

3. reverberating

4. parallel after-discharge

what is alzheimer disease?

• 100,000 deaths/year. 11% of population

• memory loss, moody, lose ability to walk, talk and eat

• show deficiences of acetylcholine and nerve growth factor

• diagnosis is confirmed at autopsy

• treatment” ways to clear B-amyloid or stop production, some results with NGF or cholinesterase inhibitors

what is parkinson disease?

• progressive loss of motor function beginning in 50s or 60s

• no recovery

• degeneration of dopamine releasing neurons

• dopamine normally prevents excessive sctivity in motor centers

• involuntary muscle contracitons

• treatment: drugs and PT