a&p chapter 11

nervous system

master controlling and communicating system of body in which cells communicate via rapid, specific electrical and chemical signals, usually causes almost immediate responses

sensory input

information gathered by sensory receptors about internal and external changes (gathers information)

integration

processing and interpretation of sensory input (sends information to brain for interpretation and decision)

motor output

activation of effector organs (muscles and glands) produces a response (muscles and glands carry out nervous system instructions the nervous system is divided into two principle parts)

central nervous system (cns)

brain and spinal cord of dorsal body cavity, acts as control center (interprets sensory input and dictates motor output)

peripheral nervous system (pns)

portion of nervous system outside of cns that consists mainly of nerves that extend from brain and spinal cord

spinal nerves

to and from spinal cord

cranial nerves

to and from brain

sensory (afferent) division of peripheral nervous system

contains somatic sensory fibers and visceral sensory fibers

somatic sensory fibers

convey impulses from skin, skeletal muscles, and joints to cns

visceral sensory fibers

convey impulses from visceral organs to cns

motor (efferent) division of peripheral nervous system

transmits impulses from cns to effector organs (muscles and glands)

somatic nervous system

division of motor division of pns - somatic motor nerve fibers conduct impulses from cns to skeletal muscle

voluntary nervous system

somatic nervous system allows for conscious control of skeletal muscle

autonomic nervous system (automatic)

consists of visceral muscle fibers that regulate smooth muscle, cardiac muscle and glands

involuntary nervous system

autonomic nervous system

sympathetic nervous system

fight or flight division of autonomic nervous system

parasympathetic nervous system

rest and digest division of autonomic nervous system

sympathetic and parasympathetic

work in opposition to each other

neuroglia (glial cells)

small cells that surround and wrap delicate neurons - support cns neurons

neurons (nerve cells)

excitable cells that transmit electrical signals

astrocytes

most abundant, versatile and highly branched of glial cells that cling to neurons, synaptic endings and capillaries

astrocyte functions

support and brace neurons, play a role in exchanges between capillaries and neurons, guide migration of young neurons, control chemical environment around neurons, respond to neurotransmitters and nerve impulses, influence neuronal functioning, participate in brain's information processing

microglial cells

small ovoid cells with thorny processes that touch and monitor neurons and migrate toward injured neurons with the ability to transform to phagocytize microorganisms and neuronal debris

ependymal cells

range in shape from squamous to columnar and may be ciliated (cilia beat to circulate csf)

ependymal cell location

central cavities of the brain and spinal column

oligodendrocytes

branched cells whose processes wrap cns nerve fibers forming insulating myelin sheaths in thicker nerve fibers

satelite cells

surround neuron cell bodies in pns and function similar to astrocytes in cns

schwann cells (neurolemmocytes)

surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers (similar function to oligodendrocytes in cns) - vital to regeneration of damaged peripheral nerve cells

neurons

nerve cells that are structural units of nervous system - large, highly specialized cells that conduct impulses - all have a cell body and one or more processes

special characteristics of neurons

extreme longevity (lasts a persons entire lifetime), amitotic with a few exceptions, high metabolic rate that requires a continuous supply of oxygen and glucose

neuron cell body

biosynthetic center of neuron, contains rough er to make proteins and spherical nucleus with nucleolus

neuron cell body functions

synthesizes proteins, membranes and chemicals

nuclei of neurons

clusters of neuron cell bodies in cns

ganglia

clusters of neuron cell bodies in pns

neuron processes

armlike processes that extend from cell body

neuron processes in cns

contain both neuron cell bodies and their processes

neuron processes in pns

contains chiefly neuron processes

tracts

bundles of neuron processes in cns

nerves

bundles of neuron processes in pns

dendrites

motor neurons can contain 100's of these short tapering branched processes that contain the same organelles as cell body

dendrite function

receptive (input) region of neuron that conveys incoming messages toward cell body as graded potentials

graded potentials

short distance signals

finer dendrites

highly specialized to collect information in many brain areas

dendritic spines

appendages with bulbous or spiky ends (located on dendrites)

axon structure

each neuron has one axon that starts at a cone-shaped area called an axon hillock

axon differences between neurons

in some, they are short or absent in others the axon comprises almost entire length of cell

axon length

some can be over a meter long

nerve fibers

the name for long axons

axon collaterals

occasional branches on axons

terminus

axon ends that branch profusely and can have as many as 10,000 terminal branches

axon terminals/terminal buttons

distal ends of axons

axon functional characteristics

conducting region of neuron, generates nerve impulses and transmits them to axon terminal, carries on many conversations with different neurons at the same time

terminal region function

secrete neurotransmitters into extracellular space (can excite or inhibit neurons it contacts)

axon reliance on cell body

to renew proteins and membranes otherwise they decay if cut or damaged

axon internal transport mechanisms

efficient movement of molecules and organelles are moved along axons by motor proteins and cytoskeletal elements

anterograde axon transport

away from cell body

retrograde axon transport

toward cell body

effects of viruses and bacterial toxins

damage neural tissues by using retrograde axon transport but research is underway to investigate using retrograde transport to treat genetic diseases by viruses containing "corrected" genes or microma to suppress defective genes by entering cell through retrograde transport

myelin sheath

composed of myelin

myelin

a whiteish protein lipid substance

function of myelin

protect and electrically insulate axon and increase speed of nerve impulse transmission

myelinated fibers

segmented sheath surrounds most long or large-diameter fibers

non-myelinated fibers

do not contain sheath so they conduct impulses more slowly - thin fibers not wrapped in myelin (surrounded by schwann cells but no coating)

myelination in the pns

formed by schwann cells that wrap around axon in a jelly roll like fashion - one cell forms one segment of myelin sheath

myelin sheath gaps

gaps between adjacent schwann cells - are the sites where axon collaterals may emerge (formerly called nodes of ranvier)

myelination in the cns

formed by processes of oligodendrocytes not whole cells, each cell can wrap up to 60 axons at once - myelin sheath gap is present but the thinnest fibers are unmyelinated but coverage by long extensions of adjacent neuroglia

white matter

regions from the brain and spinal cord with dense myelinated fibers

gray matter

mostly neuron cell bodies and non-myelinated fibers

types of neurons

grouped by direction impulse travels relative to cns

sensory neurons

transmit impulses from sensory receptors toward cns

sensory neuron cell body location

ganglia in pns

motor neurons

carry impulses from cns to effectors

sensory neuron polarity

almost all are unipolar

motor neuron polarity

multipolar

motor neuron cell body location

in cns, except some autonomic neurons

interneurons (association neurons)

shuttle signals through cns pathway (lie between motor and sensory neurons) - 99% of body's neurons

interneuron location

most are entirely within cns

neurons have a resting membrane potential

the ability to do something

membrane potential

neurons can rapidly change membrane potential - neurons are highly exciteable

basic principles of electiricity

opposite charges attract (+ and -)

requirements for charge separation

energy is required to keep opposite charges separated across a membrane

energy liberation

happens when charges move toward one another

potential energy generation

when charges are separated

ion diffusion speed

quickly when gated channels are open

ion diffusion

along concentration gradients from high to low or along electrical gradients toward opposite charge

extracellular fluid ion composition

ecf has higher sodium concentration that icf - it is balanced chiefly by chloride ions (cl-) - more sodium outside of cell causes a positive charge outside the cell

intracellular fluid composition

icf has higher concentration of potassium than ecf - it is balanced by negatively charged proteins - more potassium inside of cell causes a negative charge inside the cell

membrane potential changes when

concentrations of ions across a membrane changes or membrane permeability to ions changes

action potentials

long distance signals of axons

function of changes in membrane potential

used as signals to receive, integrate and send information (constantly changing places with na+ and k+ which fires off electrical signals)

depolarization

decrease in membrane potential - inside of membrane becomes more negative than when resting - probability of producing impulse increases

hyperpolarization

increase in membrane potential - inside of membrane becomes more negative than when resting - probability of producing impulse decreases

short lived localized changes in membrane potential

the stronger the stimulus, the more voltage changes and the further the stimulus flows

trigger of changes in membrane potential

stimulus that opens gated ion channels (change places with na+ and k+)

post gated ion channel opening

depolarization spreads from one area of membrane to the next

principle way neurons send signals (means of long distance neural communication)

brief reversal in membrane potential that occurs only in muscle cells and axons of neurons (called nerve impulses), action potentials do not decay over distance, involves opening of specific voltage gated channels

step one of generating an action potential

resting state: all gated na+ and k+ channels are closed (only leakage channels for na and k are open which maintain resting membrane potential)

na+ channel gate number

2

activation gates

closed at rest, open with depolarization allowing na+ to enter cell