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99 Cards in this Set

  • Front
  • Back
Nervous System
The master controlling and communicating system of the body
Functions of the Nervous System
Sensory input
Motor output
Sensory Input
monitoring stimuli- internal (blood sugar) and external (temperature)
interpretation of sensory input and decide what to do with it

ex: hormones or skeletal muscle
Motor Output
response to stimuli; muscle contraction
Central nervous system (CNS)
Brain and spinal cord

Integration and command center
Peripheral nervous system (PNS)
Paired spinal and cranial nerves

Carries messages to and from the spinal cord and brain
Peripheral Nervous System (PNS): Two Functional Divisions
*Sensory (Afferent) division

*Motor (Efferent) division
Sensory (afferent) division
afferent= towards brain

Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain

Visceral afferent fibers – transmit impulses from visceral organs to the brain
Motor (efferent) division
efferent=away from brain

Transmits impulses from the CNS to effector organs
Motor Division: Two Main Parts
Somatic nervous system

Autonomic nervous system (ANS)
Somatic nervous system
Conscious control of skeletal muscles
Autonomic nervous system (ANS)
Regulates smooth muscle, cardiac muscle, and glands

Divisions – sympathetic and parasympathetic
The two principal cell types of the nervous system are:
Neurons – excitable cells that transmit electrical signals

Supporting cells – cells that surround and wrap neurons
Supporting Cells: Neuroglia
-Provide a supportive scaffolding for neurons
-Segregate and insulate neurons
-Guide young neurons to the proper connections
-Promote health and growth
Most abundant, versatile, and highly branched glial cells

They cling to neurons and their synaptic endings, and cover capillaries
Function of Astrocytes
Support and brace neurons

Anchor neurons to their nutrient supplies

Guide migration of young neurons (control capillary permeability)

Control the chemical environment
small, ovoid cells with spiny processes

Phagocytes that monitor the health of neurons
Ependymal cells
range in shape from squamous to columnar

They line the central cavities of the brain and spinal column

have cilia- help circulate cerebral spinal fluid around brain & cord
branched cells that wrap CNS nerve fibers

Produce insulating covering called myelin sheath
Schwann cells (neurolemmocytes)
surround fibers of the PNS

help form myelin sheath in PNS

vital for regeneration of damaged peripheral nerve tissue
Satellite cells
surround neuron cell bodies

part of PNS; serve same function as astrocytes
Neuron Structure
Composed of a body, axon, and dendrites

Long-lived, amitotic, and have a high metabolic rate

amitotic= don't reproduce
Neuron Plasma Membrane Function
Electrical signaling

Cell-to-cell signaling during development
Nerve Cell Body (Perikaryon or Soma)
-Contains the nucleus and a nucleolus
-Is the major biosynthetic center
-Is the focal point for the outgrowth of neuronal processes
-Has well-developed Nissl bodies (rough ER)
-Contains an axon hillock – cone-shaped area from which axons arise
Processes of Neuron
Armlike extensions from the soma

Called tracts in the CNS and nerves in the PNS

There are two types: axons and dendrites
Dendrites of Motor Neurons
-Short, tapering, and diffusely branched processes
-They are the receptive, or input, regions of the neuron
-Electrical signals are conveyed as graded potentials (not action potentials)
Axons: Structure
-Slender processes of uniform diameter arising from the hillock
-Long axons are called nerve fibers
-Usually there is only one unbranched axon per neuron
-Rare branches, if present, are called axon collaterals
-Axonal terminal – branched terminus of an axon
Axons: Function
-Generate and transmit action potentials
-Secrete neurotransmitters from the axonal terminals
-Movement along axons occurs in two ways
-Anterograde — toward axonal terminal
-Retrograde — away from axonal terminal
Myelin Sheath
Whitish, fatty (protein-lipoid), segmented sheath around most long axons
Function of myelin sheath
Protect the axon

Electrically insulate fibers from one another

Increase the speed of nerve impulse transmission
Myelin Sheath and Neurilemma: Formation
Formed by Schwann cells in the PNS
Schwann cell
Envelopes an axon in a trough

Encloses the axon with its plasma membrane

Has concentric layers of membrane that make up the myelin sheath
Nodes of Ranvier (Neurofibral Nodes)
Gaps in the myelin sheath between adjacent Schwann cells

They are the sites where axon collaterals can emerge
White matter
dense collections of myelinated fibers
Gray matter
mostly soma and unmyelinated fibers
3 structural classifications of a neuron
*Multipolar- 3 or more processes (99% of neurons)

*Bipolar- 2 processes (axon & dendrite)

*Unipolar- single, short process
3 functional classifications of a neuron
Sensory (afferent) — transmit impulses toward the CNS

Motor (efferent) — carry impulses away from the CNS

Interneurons (association neurons) — shuttle signals through CNS pathways
Neurons are highly irritable/excitable-
Action potentials, or nerve impulses, are:
Electrical impulses carried along the length of axons

Always the same regardless of stimulus

The underlying functional feature of the nervous system
Conduction Velocities of Axons
Conduction velocities vary widely among neurons
Rate of impulse propagation is determined by:
Axon diameter – the larger the diameter, the faster the impulse

Presence of a myelin sheath – myelination dramatically increases impulse speed
Saltatory Conduction
Current passes through a myelinated axon only at the nodes of Ranvier

Action potentials are triggered only at the nodes and jump from one node to the next

Much faster than conduction along unmyelinated axons
*A junction that mediates information transfer from one neuron:

-To another neuron
-To an effector cell
Presynaptic neuron
conducts impulses toward the synapse
Postsynaptic neuron
transmits impulses away from the synapse
synapses between the axon of one neuron and the dendrite of another
synapses between the axon of one neuron and the soma of another
Other types of synapses include:
-Axoaxonic (axon to axon)
-Dendrodendritic (dendrite to dendrite)
-Dendrosomatic (dendrites to soma)
Electrical synapses:
Are less common than chemical synapses

Correspond to gap junctions found in other cell types
Why are electrical synapses important to CNS?
-Arousal from sleep
-Mental attention
-Emotions and memory
-Ion and water homeostasis
Chemical Synapses
Specialized for the release and reception of neurotransmitters
Chemical Synapses Typically composed of two parts:
Axonal terminal of the presynaptic neuron, which contains synaptic vesicles

Receptor region on the dendrite(s) or soma of the postsynaptic neuron
Synaptic Cleft
Fluid-filled space separating the presynaptic and postsynaptic neurons

Prevents nerve impulses from directly passing from one neuron to the next
Transmission across the synaptic cleft:
Is a chemical event (as opposed to an electrical one)

Ensures unidirectional communication between neurons
Step 1 of Synaptic Cleft: Information Transfer
Nerve impulses reach the axonal terminal of the presynaptic neuron and open Ca2+ channels
Step 2 of Synaptic Cleft: Information Transfer
Neurotransmitter is released into the synaptic cleft via exocytosis in response to synaptotagmin
Step 3 of Synaptic Cleft: Information Transfer
Neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic neuron
Step 4 of Synaptic Cleft: Information Transfer
Postsynaptic membrane permeability changes, causing an excitatory or inhibitory effect
Termination of Neurotransmitter Effects
Neurotransmitter bound to a postsynaptic neuron:
-Produces a continuous postsynaptic effect
-Blocks reception of additional “messages”
-Must be removed from its receptor
Removal of neurotransmitters occurs when they:
Are degraded by enzymes

Are reabsorbed by astrocytes or the presynaptic terminals

Diffuse from the synaptic cleft
Synaptic Delay
*Neurotransmitter must be released, diffuse across the synapse, and bind to receptors
*Synaptic delay – time needed to do this (0.3-5.0 ms)
*Synaptic delay is the rate-limiting step of neural transmission
Postsynaptic Potentials
Neurotransmitter receptors mediate changes in membrane potential according to:
-The amount of neurotransmitter released
-The amount of time the neurotransmitter is bound to receptors
The two types of postsynaptic potentials are:
EPSP – excitatory postsynaptic potentials

IPSP – inhibitory postsynaptic potentials
EPSPs are graded potentials that can initiate an action potential in an axon
Use only chemically gated channels

Na+ and K+ flow in opposite directions at the same time

Postsynaptic membranes do not generate action potentials
Neurotransmitter binding to a receptor at inhibitory synapses:
Causes the membrane to become more permeable to potassium and chloride ions

Leaves the charge on the inner surface negative

Reduces the postsynaptic neuron’s ability to produce an action potential
A single EPSP cannot induce an action potential

EPSPs must summate temporally or spatially to induce an action potential
Temporal summation
presynaptic neurons transmit impulses in rapid-fire order
Spatial summation
postsynaptic neuron is stimulated by a large number of terminals at the same time
What happens when IPSPs summate with EPSPs
They cancel each other out
*Chemicals used for neuronal communication with the body and the brain
*50 different neurotransmitters have been identified
*Classified chemically and functionally
Chemical Neurotransmitters
Acetylcholine (ACh)
Biogenic amines
Amino acids
Novel messengers: ATP and dissolved gases NO and CO
Neurotransmitters: Acetylcholine
-First neurotransmitter identified, and best understood
-Released at the neuromuscular junction
-Synthesized and enclosed in synaptic vesicles
-Degraded by the enzyme acetylcholinesterase (AChE)
Acetylcholine is released by:
All neurons that stimulate skeletal muscle

Some neurons in the autonomic nervous system
Neurotransmitters: Biogenic Amines
Broadly distributed in the brain

Play roles in emotional behaviors and our biological clock
Biogenic Amines include:
Catecholamines – dopamine, norepinephrine (NE), and epinephrine

Indolamines – serotonin and histamine
Neurotransmitters: Amino Acids
-GABA – Gamma (γ)-aminobutyric acid

*Found only in the CNS
Neurotransmitters: Peptides
Act as natural opiates; reduce pain perception

Bind to the same receptors as opiates and morphine

Gut-brain peptides – somatostatin, and cholecystokinin
Neurotransmitters: Peptides include:
Substance P – mediator of pain signals

Beta endorphin, dynorphin, and enkephalins
ATP (novel messenger of neurotransmitters)
-Is found in both the CNS and PNS
-Produces excitatory or inhibitory responses depending on receptor type
-Induces Ca2+ wave propagation in astrocytes
-Provokes pain sensation
Nitric oxide (NO) (novel messenger of neurotransmitters)
Is involved in learning and memory
Two functional classes of Neurotransmitters
excitatory and inhibitory
Excitatory neurotransmitters
cause depolarizations 
(e.g., glutamate)

more positive
Inhibitory neurotransmitters
cause hyperpolarizations (e.g., GABA and glycine)

more negative
Some neurotransmitters have both excitatory and inhibitory effects
*Determined by the receptor type of the postsynaptic neuron

*Example: acetylcholine
-Excitatory at neuromuscular junctions with skeletal muscle
-Inhibitory in cardiac muscle
Neurotransmitter Receptor Mechanisms- DIRECT
*neurotransmitters that open ion channels

Promote rapid responses
Examples: ACh and amino acids
Neurotransmitter Receptor Mechanisms- INDIRECT
*neurotransmitters that act through second messengers

-Promote long-lasting effects
-Examples: biogenic amines, peptides, and dissolved gases
Channel-Linked Receptors
-Composed of integral membrane protein
-Mediate direct neurotransmitter action
-Action is immediate, brief, simple, and highly localized
-Ligand binds the receptor, and ions enter the cells
-Excitatory receptors depolarize membranes
-Inhibitory receptors hyperpolarize membranes
G Protein-Linked Receptors
Responses are indirect, slow, complex, prolonged, and often diffuse

These receptors are transmembrane protein complexes

Examples: muscarinic ACh receptors, neuropeptides, and those that bind biogenic amin
Neural Integration: Neuronal Pools
*Functional groups of neurons that:

-Integrate incoming information

-Forward the processed information to its appropriate destination
Input fiber (simple neuronal pool)
presynaptic fiber
Discharge zone (simple neuronal pool)
neurons most closely associated with the incoming fiber
Facilitated zone (simple neuronal pool)
neurons farther away from incoming fiber
Divergent (circuit in neuronal pools)
one incoming fiber stimulates ever increasing number of fibers, often amplifying circuits
Convergent (circuit in neuronal pools)
opposite of divergent circuits, resulting in either strong stimulation or inhibition
Reverberating (circuit in neuronal pools)
chain of neurons containing collateral synapses with previous neurons in the chain
Parallel after-discharge (circuit in neuronal pools)
incoming neurons stimulate several neurons in parallel arrays
Serial Processing (Patterns of Neural Processing)
Input travels along one pathway to a specific destination

Works in an all-or-none manner

Example: spinal reflexes
Parallel Processing (Patterns of Neural Processing)
Input travels along several pathways

Pathways are integrated in different CNS systems

One stimulus promotes numerous responses

Example: a smell may remind one of the odor and associated experiences