Chapter 12 Nervous System Flashcards
What are the two divisions of the nervous system?
Central nervous system – brain and spinal cord
Peripheral nervous system – all other
What are the two functional divisions of the peripheral nervous system.
Sensory afferent division:
Somatic afferent fibers-(superficial info) convey impulses from skin skeletal muscles and joints.
Visceral afferent fibers-(deep info) convey impulses from visceral organs
Motor efferent division:
Transmits impulses from the CNS to effector organs
What are the two motor divisions of the PNS?
Somatic nervous system (voluntary)
Autonomic involuntary
What are the two divisions of the autonomic nervous system?
Sympathetic – rapid response short-term
Parasympathetic – maintain normal resting position.
What are the two principal cell types? And the names of them?
Neuron Neuroglia: Astrocyte (CNS) microglia (CNS) Ependymal cells (CNS) oligodendrocytes (CNS) satellite cells(PNS) Schwann cells(PNS)
What are microglia cells?
Small, ovoid cells with thorny processes.
Migrate toward injured neurons. Phagocytize microorganisms and neuronal debris.
Explain astrocytes.
Most abundant, versatile, and highly branched Glial cells.
Support and brace neurons.
Guide migration of young neurons. Help determine capillary permeability. Aid the blood brain barrier.
What are ependymal cells?
Cells that line the cerebrospinal fluid filled cavities
Explain oligodendrocytes.
Have processes that form myelin sheaths around CNS nerve fibers.
Explain satellite cells and Schwann cells.
Satellite – surround neuron cell bodies in the PNS.
Schwann – surround peripheral nerve fibers and form myelin sheaths.
Vital to regeneration of damage peripheral nerve fibers.
What cells are absent from the vomit center of the brain and why?
Astrocytes.
Because the blood brain barrier breaks down so the brain can tell the body to remove it by vomiting. Because it doesn’t want more toxins entering the brain.
What are the special characteristics of neurons?
Long lived, amitotic, high metabolic, plasma membrane functions in: electric signaling and cell to cell interactions during development.
Clusters of cell bodies (Gray matter) are called _______ in the CNS, and ________ in the PNS.
Nuclei
ganglia
What are the three functions of the nervous system?
Sensory input (smell touch sight)
Integration (appropriate response)
Motor output (sends message)
What are bundles of processes (white matter) called in the CNS and PNS?
Tracts-CNS
Nerves-PNS
What is the myelin sheath function?
Protect and electrically insulate the axon, increased speed of nerve impulse transmission.
Explain the myelin sheaths of the CNS
Formed by oligodendrocytes not the whole cell.
Nodes of ranvier present.
No neurilemma.
Thinnest fibers unmyelinated.
What is white matter and gray matter?
White – (output) dense collections of myelinated fibers: nerves and tracts (axon).
Gray- (input) cell bodies in dendrites and synapses
What are the three structural classifications of neurons?
Multipolar – (efferent) one axon several dendrites. Most abundant
Motor neurons and interneurons
Bipolar- one axon one dendrite on opp sides of soma. Rare (retinal and olfactory)
Unipolar-single short process with two branches. Mostly sensory neurons (afferent)
What are the three functional classifications of neurons?
1-sensory (afferent): transmit impulses from sensory receptors towards the CNS.
2-Motor (efferent): Carry impulses from the CNS to effectors.
3-Interneurons (processing): shuttle signals through CNS pathways. Connect sensory neurons to motor neurons. Most are entirely within the CNS.
Name three neuron functions.
1: neurons are highly irritable.
2: respond to adequate stimulus by generating an action potential (nerve impulse).
3: impulse is always the same regardless of stimulus.
What are the principles of electricity?
Opposite charges attract each other.
Energy is required to separate opposite charges across a membrane.
Energy is liberated when the charges move towards one another.
If opposite charges are separated, the system has potential energy.
Define the following vocabulary terms: Voltage (V) potential difference current (I) resistance (R) insulator conductor
Vol: Measure of potential energy generated by separated charge
PD: voltage measured between two points
Cur: The flow of electrical charge (ions) between two points
Res: hindrance to charge flow (plasma membrane)
Insul: substance with high electrical resistance
Con: substance with Low electrical resistence (higher current)
What is the equation to solve for current (I) ?
I=v/r
Or
V=i*r
Proteins serve as membrane ion channels. Name the two main types of ion channels and their function.
1: leakage (non-gated) channels – always open
2: gated channels (three types):
a. Chemically gated (ligand-gated) channels-Open with binding of a specific neurotransmitter.
b. Voltage gated channels: Open and close in response to changes in membrane potential.(electrical current)
c. Mechanically gated channels: Open and close in response to physical deformations of receptors. (Shape)
When gated channels are open ions diffuse quickly across the membrane along their electrochemical gradient which is what for chemical and electrical?
Chemical concentration gradients from high concentration to low.
Electrical gradient toward opposite electrical charge.
What are two types of membrane potential signals?
1: graded potential – incoming short distance signals (dendrites/soma. Variable size signal)
2: action potentials – long-distance signals (axons. Same size of signal)
After repolarization, hyperpolarization can occur. How?
Some potassium channels remain open, allowing excessive potassium reflux.
What restores the resting electrical conditions of a neuron? What restores the resting ionic conditions?
Repolarization
Sodium potassium pump
What are the three threshold stimuluses?
Sub threshold stimulus – weak local depolarization that does not reach threshold.
Threshold stimulus – strong enough to push the membrane potential toward and beyond the threshold.
Action potential – all or none phenomenon.
All action potentials are alike and are independent of stimulus intensity?
True
How does the CNS tell the difference between a weak and strong stimulus?
Strong stimuli can generate action potentials more often than weaker. They’re all the same size just increased volume for a strong signal.
What ensures that action potential is all or none event in refractory period?
Time from the opening of the sodium channels until the resetting of channels is an absolute refractory period. Enforces one way transmission of nerve impulses
What follows an absolute refractory period?
Relative refractory period.
Most sodium channels @ resting state.
Some potassium channels open.
Repolarization is occurring.
What are two ways conduction velocity varies.
1: effect of axon diameter: less resistance to local current flow and faster impulse conduction.
2: effect of myelination: continuous conduction in myelinated axon is slower than saltatory conduction in myelinated axons.(myelin sheath insulate and prevent leakage of charge, salted Tory conduction is 30 times faster.)
Explain multiple sclerosis.
An autoimmune disease that mainly affects young adults.
Symptoms are: visual disturbances, weakness, loss of muscular control, speech disturbances and urinary incontinence.
Myelin sheaths in the CNS become nonfunctional scleroses.
Shunting and short-circuiting of nerve impulses occurs.
Impulse conduction slows and eventually ceases.
What are three ways a neurotransmitter is terminated?
Degradation by enzymes.
Reuptake by astrocytes or axon terminal.
Diffusion away from the synaptic cleft.
What is the rate limiting step of neurotransmission?
Synaptic delay
What are the two postsynaptic potentials?
1: EPSP – excitatory postsynaptic potential
2: IPSP – inhibitory postsynaptic potentials
What does EPSP help trigger?
AP at the axon Hillock if of threshold strength and opens voltage gated channels. Depolarization
What does IPSP do?
hyperpolarization.
What are two types of summations?
Temporal summation: one or more presynaptic neuron transmit impulses in rapid fire order.
Spatial summation: postsynaptic neuron is stimulated by a large number of terminals at the same time.
In neurotransmitter chemical classes, Biogenic amines include?
Catecholamines: dopamine, norepinephrine, epinephrine
Indolamines: serotonin and histamine
Neurotransmitter chemical class amino acids include?
GABA
Glycine
aspartate
glutamate
Neurotransmitter chemical class peptides include?
Substance P: mediator of pain signals
Endorphins: natural opiates, reduce pain perception
Neurotransmitter chemical class gases include?
Nitric oxide
Carbon monoxide
Neurotransmitter chemical class lipid includes?
Endocannabinoids:
Lipid soluble, synthesized on demand from membrane lipid.
Binds with G protein – coupled receptors in the brain.
Involved in learning and memory.
A neurotransmitter direct action receptor example?
Ach
(neurotransmitter binds to channel linked receptor and opens ion channels)
Rapid response
What is indirect neurotransmitter action?
Neurotransmitter binds to a G protein linked receptor and acts through an intracellular second messenger.
Long lasting effects
What are two types of neurotransmitter receptors?
Channel linked receptors
G protein linked receptors
What is a simple neuronal pool? And the two zones?
Single presynaptic fiber branches in synapses with several neurons in the pool.
Discharge down – neurons most closely associated with incoming fiber.
Facilitated zone – neurons farther away from incoming fiber.
What are the three types of circuits in neuronal pools?
Diverging circuit
converging circuit
Reverberating circuit
Explain diverging circuit.
One incoming fiber stimulates an ever increasing number of fibers, often amplifying circuits.
Explain converging circuit.
Many input to common output.
Explain reverberating circuit.
Chain of neurons containing collateral synapses with previous neurons in the chain.
What is the (five) pattern of neural processing
1-receptor 2 sensory neuron 3-integration center 4-Motor neuron 5-effector
What is parallel processing?
Diverging circuit. Input travels along several pathways, one stimulus promotes numerous responses.
The nervous system originates from the neural tube and neural crest formed from ________.
Ectoderm
The neural tube becomes the _______.
CNS ( brain to spine)
What are the three phase processes of differentiation of neurons?
Proliferation: appropriate number of cells created.
Migration: cells become amitotic and migrate.
Differentiation: neuroblast become proper motor, sensory, or Interneurons.
About two thirds of neurons die before birth. Name three reasons why.
Death results in cells that failed to make functional synaptic contacts.
Many cells also died due to a pop ptosis during development.
Those that remain constitute the majority of the neurons for life.
