Chapter 11.1 Cheat Sheet (DRAFT) by jjovann

•Main electrical signal conducting region of neuron
•Generates and conveys nerve impulses (action potent­ials)
–Transmits them along axolemma (neuronal cell membrane) to axon terminal
•Secretory region
–Neuro­tra­nsm­itters (NTs) are released into extrac­ellular space in response to AP
•NTs either excite or inhibit cells with which axon terminals form synapses (chemical or electrical connec­tions)
•A single neuron may carry on many conver­sations with different neurons at same time through axonal branches
–Splitting of the axon that leads to multiple axon terminals
•Lacks rough ER and Golgi apparatus
–Relies on cell body to renew proteins and membranes
–Efficient transport mechanisms move substances up and down axons
–Axons quickly decay if cut or damaged

Astrocytes are the most abundant CNS neuroglia.

•Nervous and endocrine systems share respon­sib­ility for mainta­ining homeos­tasis
–Objective
•Keep controlled conditions within limits that maintain life
–Nervous system
•Rapid response using action potentials
–Endocrine
•Slow response using hormones

•Sensory
–Transmit impulses from sensory receptors toward CNS
–Almost all are Unipolar
–Cell bodies in ganglia in PNS
•Motor
–Carry impulses from CNS to effectors
–Multi­polar
–Most cell bodies in CNS (except some autonomic neurons)
•Inter­neurons (assoc­iation neurons)
–Are typically found between motor and sensory neurons
–Shuttle signals through CNS pathways
•Most of the brain and spinal cord neurons are intern­eurons because they connect with each other and relay info
–99% of body's neurons
–Most confined to CNS. However, ENS has some as well.

•Helpful Mnemonic
•S-A-M-E
–Sensory
–Afferent
–Motor
–Efferent

•Somatic nervous system (SNS)
–Somatic sensory neurons convey inform­ation from somatic receptors in the head, body wall, and limbs to the CNS
•Also includes receptors for senses such as hearing, vision, taste and smell
–Somatic motor neurons conduct impulses from the CNS to skeletal muscles only
•These motor responses can be consci­ously controlled meaning this part of the PNS is voluntary

•Dendrites (little trees) are the receiving end of the neuron.
–Short, highly branched structures that receive neurot­ran­smitter signals and conduct impulses (voltage changes) toward the cell body.
–They may also contain some organe­lles.

•Neurons do not only secrete at the axon terminals, they can also take substances in.
•Many substances that enter the neuron at the axon terminals can move to the cell body by fast retrograde transport.
•These substances include trophic chemicals (such as nerve growth factor)as well as harmful agents (such as tetanus toxin),and the viruses that cause rabies and polio.
•A deep cut or puncture wound in the head or neck is a more serious matter than a similar injury in the leg because of the shorter transit time for the harmful neurop­ath­ogenic substance to reach the brain (treatment must begin quickly.)

•Synaptic end bulbs and other varico­sities on the axon terminals of presyn­aptic neurons contain many tiny membra­ne-­enc­losed sacs called synaptic vesicles that store packets of neurot­ran­smitter chemicals.
–Many neurons contain two,or even three,­types of neuro-­tra­nsm­itters, each with different effects on the postsy­naptic cell.

•Neurons display great diversity in size and shape –the longest ones are almost as long as a person is tall, extending from the toes to the lowest part of the brain.
–The pattern of dendritic branching is varied and distin­ctive for neurons in different parts of the NS.
–Some neurons have very short axons,or lack axons altoge­ther.
•Both structural and functional features are used to classify the various neurons in the body.

•Axon terminals
–The axon and its collat­erals end by dividing into many fine processes called axon terminals (telod­end­ria). Like the dendrites, telode­ndria may also be highly branched as they interact with the dendritic tree of neuron­s“d­own­str­eam”.
–The tips of some axon terminals swell into bulb-s­haped structures called synaptic end bulbs.

•Elect­rical impuls­es,or action potentials (AP),c­annot propagate across a synaptic cleft of neuronal synapses. Instead, neurot­ran­smi­tters are used to commun­icate at the synapse andre-­est­ablish, or inhibit, an AP in the postsy­naptic cell.
•This is called a chemical synapse
–Chemical synapse
•The use of neurot­ran­smi­tters to modify electrical activity in the post-s­ynaptic cell
–Elect­rical Synapse
•Allowing an electrical impulse to directly modify electrical activity in a post-s­ynaptic cell
•Uses gap junctions to allow the passage of ions between pre and post-s­ynaptic cell

•The cell body (Perik­aryon, or Soma) has the nucleus surrounded by cytoplasm.
–Like all cells, neurons contain organelles such as lysosomes, mitoch­ondria, Golgi complexes, SER, and Rough ER (in neurons, RER is called Nissl bodies)
– it imparts a striped “tiger appear­ance”.
–No mitotic appara­tusis present.

•Astro­cytes (CNS)
•Micro­glial cells (CNS)
•Ependymal cells (CNS)
•Oligo­den­dro­cytes (CNS)
•Satellite cells (PNS)
•Schwann cells (PNS)

•Small, ovoid cells with thorny processes that touch and monitor health of neurons
•Migrate toward injured neurons
•Can transform to phagoc­ytize microo­rga­nisms and neuronal debris in CNS

•Nervous tissue commonly exhibits high cell density with little extrac­ellular space
–Tightly packed
•Two principal cell types
–Neurons (nerve cells)­—ex­citable cells that transmit electrical and chemical signals
–Neuro­glia– small cells that support, surround, and wrap delicate neurons

•The autonomic nervous system (ANS)
–Autonomic sensory receptors and Autonomic sensory neurons convey inform­ation from various body regions to the CNS
•However, located primarily in visceral organs
–Ex. Kidneys, liver, heart, lungs, etc.
–Autonomic motor neurons conduct impulses from the CNS to smooth muscle, cardiac muscle, and glands
•Because these structures are not under conscious control, this division is considered involu­ntary
–Two motor subdiv­isions of the ANS
•Sympa­thetic nervous system
–Fight or flight
•Paras­ymp­athetic nervous system
–Rest and digest

•Central nervous system (CNS)
–Brain and spinal cord•In dorsal body cavity
–Integ­ration and control center
•Inter­prets sensory input and dictates motor output
•Perip­heral nervous system (PNS)
–The portion of the nervous system outside CNS
•Spinal nerves to and from spinal cord
•Cranial nerves to and from brain

•Brain
–Central control center
–~100 billion neurons
•Spinal chord
–Connects the brain to the nerves in the body
–Contains about 100 million neurons
•Nerves
–Bundles of hundreds to thousands of axons
–Each nerve follows a defined path and serves a specific region of the body
•Neuron
–Basic functional unit of the nervous system

•Axons conduct impulses "­awa­y"from the cell body toward another neuron or effector cell.
–The “axon hillock” is where the axon joins the cell body.
–The “initial segment” is the beginning of the axon.
–The “trigger zone” is the junction between the axon hillock and the initial segment.

•The site of commun­ication between two neurons,or between a neuron and another effector cell,is called a synapse.
•The synaptic cleft is the gap between the pre and post-s­ynaptic cells.

•Though there are several different types of neurons, most have;
–A cell body
–An axon
–Dendrites
–Axon terminals

•Many substances that are synthe­sized or recycled in the neuron cell body are needed in the axon, or at the axon terminals. Two types of transport systems carry materials from the cell body to the axon terminals and back.
–Slow axonal transport
•conveys axoplasm, mostly,in one direction only – from the cell body toward the axon terminals.
–Fast axonal transport
•moves materials in both direct­ions.
•Anter­ograde (forward)
–Uses motor proteins to move organelles and synaptic vesicles from the cell body to the axon terminals.
•Retro­grade (backward)
–Uses motor proteins to move membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled.

•The Enteric Nervous system (ENS)
–ENS is also known as the “brain of the gut”
–Enteric Sensory receptors monitor and commun­icate the conditions of, and in, the GI tract to the intern­eurons (integ­ration neurons) of the ENS and to the CNS
–Enteric Motor neurons modify GI propul­sion, acid, glandular, and hormonal secret­ion­s.–­Inv­olu­ntary
–Enteric Intern­eurons may process enteric sensory inform­ation and decide to modify GI muscle contra­ction and secretion through enteric motor neurons, if needed.
–Once considered part of the ANS, the ENS consists of over 100 million neurons in enteric plexuses that extend most of the length of the GI tract.
•Some actions of ENS can be modified by ANS
•Some sources still list GI control under the ANS
–To be covered in more detail in A and P 2

•Struc­tural classi­fic­ation is based on the number of processes (axons or dendrites) extending from the cell body.

•Two main functional divisions
–Sensory (afferent) division
•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
•Transmits impulses from CNS to effector organs
–Muscles and glands
–Three subdiv­isions of peripheral nervous system
•Somatic nervous system
•Autonomic nervous system
•Enteric nervous system

•Most abundant, versatile, and highly branched glial (neuro­glial) cells
–Star shaped
•Cling to neurons, synaptic endings, and capill­aries
•Functions include
–Support and brace neurons
–Play very important role in exchanges between capill­aries and neurons
–Guide migration of young neurons
–Control chemical enviro­nment around neurons
–Respond to nerve impulses and neurot­ran­smi­tters
–Influence neuronal functi­oning
•Parti­cipate in inform­ation processing in brain

•Sensory input
–Sensory receptors detect internal and external changes
–Carried to the brain through the spinal and some cranial nerves
•Integ­ration
–Proce­ssing and interp­ret­ation of sensory input
–Perce­ption is an important integrated function
•Conscious awareness of stimuli
•Occurs in the brain•­Motor output
–Activ­ation of effector organs (muscles and glands) through spinal and some cranial nerves to produce a response
•Causes muscles to contract and glands to secrete