Hole's Anatomy and Physiology Chapter 10

Nerve impulses

electrochemical changes that neurons use to transmit information

Dendrites

receive electochemical message while axons send information

Neuroglial cells in CNS

Astrocytes, oligodendrocytes, microglia, ependyma

Central nervous system

brain and the spinal cord

Peripheral nervous system

nerves that connect CNS to other body parts. Cranial (12 pairs) Spinal (31 pairs)

Functions of CNS and PNS

sensory, integrative, and motor

Sensory receptors location

found at ends of peripheral neurons; monitor external and internal environments

Sensory receptors

convert environmental information into nerve impulses; carries info to CNS

Effectors

muscles that contract and glands that secrete based on nerve impulses

Motor functions

tell peripheral nerves to carry impulses from CNS to effectors. decisions are acted upon, impulses carried to effectors. Divided into Somatic and Autonomic.

Somatic nervous system

consciously controlled motor functions (skeletal muscle)

Autonomic nervous system

controls involuntary effectors

Neuroglial cells in PNS

schwann and satellite cells

Microglial cells

throughout CNS and support neruons and phagocytize bacterial cells and cellular debris

Oligodendrocytes

align along nerve fibers and provide myelin sheath around axons within the brain and the spinal cord

Astrocytes

found between neruons and blood vessels. part of blood brain barrier.

1. aid metabolism of certain substances (drugs)

2. induce synapse formation

3. Scar tissue

4. in CNS

Ependymal cells

form epithelia-like membrane covering specialized brain parts (choroid plexuses) and forms inner linings that enclose spaces within brain (ventricles) and spinal cord (central canal) ciliated in CNS

Schwann cells

found in PNS that form a myelin sheath around axons. speed up neurotransmission

Myelin sheaths

cover large axons

Nodes of Ranvier

narrows gaps between Schwann cells

White matter

myelinated axons in CNS. Considered fiber tracts

Gray matter

unmyelinated axons in CNS, cell bodies and dendrites.

Difference between axons in peripheral nerves and axons in CNS

axons in peripheral nerves have neurilemma and can regenerate

Multipolar neurons

many processes from cell bodies; found in brain or spinal cord. most of neurons

Bipolar neruons

two processes from cell bodies at each end; specialized parts of eyes, nose, and ears

Unipolar neurons

single process that has two brances but functions as a single axon; first branch, peripheral process, is associated with dendrites near peripheral body part and other enters the brain or spinal cord. ganglia of PNS

Ganglia

cell bodies of some unipolar neurons aggregate in specialized masses of nervous tissue

Sensory neurons

also afferent neurons; carry nerves impulses from body parts into CNS; most are unipolar and some biopolar; specialized receptor ends in dendrites or dendrites closely associated with receptor cells;

Interneurons

also association or internuncial neurons; found in CNS; multipolar and link others neurons; may direct incoming sensory impulses to approppriate parts. in brain. creates memories

Nuclei

cell bodies of some interneurons aggregate in specialized masses of nervous tissue

Motor neurons

also efferent neurons; multipolar and carry nerve impulses out of the brain or spinal cord to effecors

Synapse

junction between two communicating neurons

Synaptic cleft

gap that separates two neurons at a synapse

Presynaptic neurons

neuron carrying impulse into synapse

Postsynaptic neuron

neuron that receives impulse at the synapse

Synaptic transmission

process of crossing the synaptic cleft; one way process

Neurotransmitters

carry out synaptic transmission. released when impulses reach synaptic knobs

Synaptic ends

found at ends of axons

Synatpic vesicles

found in synaptic knobs; releases neurotransmitters;

Neurotransmitters

diffuses across synatpic cleft and reacts with specific receptors on postsynaptic neuron membrane

Excitatory

turning a process on

Inhibitory

turning a process off

Action of a neurotransmitter on postsynaptic celft

either excitatory or inhibitory

Polarization of cell membranes

occur due to unequal distribution of positive and negative ions between sides of the membrance; allows for conduction of muscle and nerve impulses;

Sodium Ions and Potassium ions (location?)

sodium ions outside and potassium ions inside due to active transport

Potassium ions

contribute to membrane polarization since it passes through cell membrane easily. INTRACELLULAR

Sodium Ions

Extracellular

Distribution of Sodium Potassium pump

Na in; K out. 3:2 ratio = maintaining rest. inside is negatively charged. outside is positive

Outside becomes slightly positive and inside slightly negative

Potassium ions diffuse out faster than sodium ions can come in

Potential difference

difference in electrical charge between two regions

Resting potential

potential difference in resting nerve cell -70 mV inside cell (polarized membrane). (fewer potassium in, lots of Na outside)

Potential changes caused by multiple stimuli

Temperature changes, light, and pressure

Membrane is depolarized when...

resting potential decreases (inside becomes less negative)

Pressure is...

the amount of sodium allowed in. environmental changed open gated ion channel.

channels are

Chemically gated, voltage gated, or mechanically gated

Directly proportional

Relationship between intensity of stimulus and amount of change in resting potential

Threshold potential

reached when membrane is depolarized sufficiently

Action potential

when threshold is reached; basis for nerve impulse; rapid sequence of depolarization and repolarization

Hyperpolarization

membrane potential briefly becomes overly negative

Repolarization

overly negative membrane potential reutrns to resting potential

threshold stimulus

-55; opens electrically charged gate.

Action potential

rapid sequence of depolarization and repolarization

Events leading to conduction of a nerve impulse

1. neuron membrane maintains resting potential

2. threshold stimulus is received (-55)

3. sodium channels in the trigger zone of the neuron open

4. sodium ions diffuse inward, depolarizing the membrane (toward zero)

5. potassium channels in the membrane open

6. potassium ions diffuse outward, repolarizing the membrane (+30)

7. the resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane

8. a wave of action potentials travels the length of the axon as a nerve impulse

Myelinated v Myelinated

found between Schwan cells and interrupt the sheath where action potential ocurs at exposed sodium and potassium channel. those with myelin accelerated for potential to jump door to door. without myelin has to open every single door.

propagation

movement

Greater diameter of axon

faster the impulse

All-or-none response

Define nerve impulse; when a stimulus of threshold intensity or above is applied to an axon, all impulses carried on that axon are of the same strength

Greater intensity of nerve impulse

increase number of impulses per second

Refractory period

short time following nerve impulse in which another impulse will not be triggered

1. limits impulse frequency

2. ensures impulse goes in one direction - down the axon

2 kinds of refractory period

Absolute and relative refractory period

Absolute refractory period

time when threshold stimulus foes not start an action potential

Relative refractory period

time when stronger threshold stimulus can start another action potential

Impulse conduction

how we get a nerve to send a signal; myklinated Jacobs transmit impulses through saltatory conduction, faster than on unmyelinated axons, (beta (pain) is slow. Gamma (soothing) is faster)

Neurotransmitters released by presynaptic knobs

affects whether the threshold is reached thus whether the action is inhibitory or excitatory

Synaptic potentials are created by..

chemically gated ion channels respond to neurotransmitters

EPSP

excitatory postsynaptic potential; graded, depolarizes membrane of post-synaptic neuron. Action potential of postsynaptic neuron becomes more likely

IPSP

inhibitory postsynaptic potential; graded, hyper polarizes membrane od postsynapic neuron. action potential of post synaptic neuron becomes less likely

Summation of ESPS and ISPS

when they are added together; more EPSP lead to greater probability of an action potential. Occurs at trigger zone

Neuropeptides

synthesized by brain or spinal cord. act as neurotransmitters. some are neuromodulators

Neuromodulators

substances that alter a neurons response to a neurotransmitter or block the release of a neurotransmitter

examples of neuropeptides

Enkephalins, beta endorphins, substance P

enkephalins

reduce pain

beta endorphins

reduce pain

substance P

pain perception

Acetylcholine

neurotransmitter that stimulates skeletal muscle contractions

Neurotransmitters (storage?)

made in synaptic knobs' cytoplasms and stored in synaptic vesicles

Decomposition of neurotransmitters by enzymes

prevents continous stiumulation of postsynaptic nuerons; others return to synaptic knob or to nearby neurons

Integrative Function

sensory info used to create sensations, memories, thoughts and decisions. (remember color of shoes without seeing)

cell body

contains nucleus

Axon

transmits impulses and releases neurotransmitters to another neuron of effector

Satellite cells

in PNS support clusters of neuron cell bodies (ganglia)

Neuroglia and axonal regeneration

neurons cannot divide. If body is injured, neuron dies. If peripheral axon is injured, it can regenerate due to schwann cells.

Neuronal pools

impulses and actions depend on neuron and axon organization in CNS. interneurons work together to perform a common function. pool receives input from other neurons and generates output to other neurons. Facilitation may occur

Neuronal Pool facilitation

don't reach threshold; but if NT are released at the right time, it makes action happen anyways.

Convergence

neuron receives input from several neurons; represents information from different types of sensory receptors, allows system to collect, process and respond to info. 2 times as likely to depolarize. mom and dad make you do something

Divergence

one neuron sends impulses to several neurons, can amplify impulse, impulse from single neuron can be amplified to activate enough motor units needed for muscle contraction. 2 times electrical charge, 1 brain make whole leg move. mom tells you and dad to do something