Fundamentals of the Nervous System and Ner

Functions of the Nervous System

Sensory Input, Integration, Motor Output (activates effectors)

Central Nervous System

Brain and spinal cord

Peripheral Nervous System

Nerves outside the brain and spinal cord

Sensory (afferent) division

Nerve fibers (axons) that carry information to the CNS

Motor (efferent) division

Nerve fibers (axons) that carry impulses away from the CNS, subdivided into the Somatic Nervous System and Autonomic Nervous System (Sympathetic and Parasympathetic)

CNS neuroglia

much smaller than neurons and outnumber them in the CNS by 10 to 1 (make up half the mass of the brain), astrocytes, microglia, ependymal cells, oligodendrocytes

Astrocytes

most abundant and versatile, star shaped, link neurons to their nutrient source (capillaries), form blood-brian barrier between capillaries and neurons, control chemical environment around neurons, mop up K+ ions and recapture released NTs

Microglia

spider-like phagocytic macrophages, will migrate toward neurons when they sense they are injured, dispose of neuronal debris and invading microorganisms, (immune system cells cannot access the CNS), increased presence indicate brain damage

Ependymal Cells

line cavities of the brain and spinal cord, contain cilia that circulate cerebrospinal fluid (CSF)

oligodendrocytes

forms myelin sheath in the CNS

Satellite cells

surround and protect neuronal cell bodies in PNS

Schwann cells

forms myelin sheath around axons in PNS, also vital to regeneration of damaged peripheral nerve fibers

Nuerons (nerve cells)

irritability, conductivity, extreme longevity, amitotic, high metabolic rate

Ganglion

collection of cell bodies outside the CNS

dorsal root ganglion

contains cell bodies of sensory neurons

White matter

dense collections of myelinated fibers (on the outside in spinal cord)

Grey matter

Collections of unmyelinated fibers and cell bodies

Endoneurium

delicate connective tissue around individual nerve fibers in nerve

Perineurium

coarse connective tissue that bundles fibers into fascicles

Epineurium

surrounds the entire nerve

Cell body (soma)

signal integration, metabolic center of cell and contains organelles

Chromatophilic Substance (Nissl bodies)

clusters of RER and ribosomes which produce membrane and proteins

Golgi Apparatus

forms complete circle around nucleus

Neurofibrils

maintain cell shape and integrity

Nucleolus

Processes

fibers that extend from the cell body

Dendrites

signal input, hundreds of highly branched extensions that increase surface area to accommodate maximum number of synaptic contacts, receive signals and conducts impulses (local depolarization) toward cell body

Axon

signal transmission, conducts impulses away from the cell body, "nerve fiber"

Axon hillock

trigger zone for AP, cone-shaped area of cell body that serves as action potential trigger zone (determines if threshold has been achieved)

axons end at axon terminals

contain synaptic vesicles with NTs, synaptic cleft, synapse

Myelin sheath

high lipid concentration, formed by oligodendrocytes in CNS and Schwann cells in PNS, protects and electrically insulates, increases speed of impulse travel

Neurilemma

only part of PNS myelin sheaths, formed by nucleus and cytoplasm of Schwann cell that gets pushed to outside

Multiple Sclerosis

CNS myelin sheats are gradually destroyed and reduced to non-functional hardened lesions called scleroses, loss of myelin causes such a slow down that impulse conduction eventually ceases, symptoms: visual disturbances, problems controlling muscles etc., cycles of relapse and remission

Nodes of Ranvier

Gaps in the myelin sheath to which voltage-gated sodium channels are confined.

Multipolar neurons

Unipolar neurons (pseudounipolar)

bipolar neuron

sensory (afferent) neurons

bring impulses toward the CNS from receptors, unipolar with cell body in ganglia outside the CNS

motor (efferent) neurons

carry impulses away from the CNS to effector muscles and glands, cell body in the CNS

Interneurons

cells confined to the CNS and make up over 99% of all neurons in body, multipolar and usually have short extensions, lie between motor and sensory neurons in neural pathways and shuttle signals through CNS

Synapse

mediates information transfer from one neuron to the next or to an effector cell

axon/presynaptic terminal

contains synaptic vesicles with neurotransmitters

synaptic cleft

postsynaptic membrane

Excitatory Postsynaptic Potentials (EPSP)

increases membrane permeability to NA+ and depolarizes postsynaptic membrane, is excitatory (increases likelihood of firing an action potential)

Inhibitory Postsynaptic Potentials (IPSP)

increases permeability to K+ and hyper polarizes postsynaptic membrane, is inhibitory, (anesthetics)

Norepinephrine

helps control alertness and arousal, regulated by MAO monoaminoxidase

Too much norepinephrine

over excitation and euphoria, cocaine and amphetamines

Too little norepinephrine

depression, treated with MAOIs (monoaminoxidase inhibitors)

Myelination of a nerve fiber