Nervous System Unit 1

Nervous system

Master controlling and communicating system of body

Sensory input

Information gathered by sensory receptors about internal and external changes

Integration

Processing and interpretation of sensory input

Motor output

Activation of effector organs (muscles and glands) produces a response

Central nervous system (CNS)

Brain + spinal cord
Integration and control center

Peripheral nervous system (PNS)

Nervous system outside CNS
Consists mainly of nerves that extend from brain to spinal cord

Spinal nerves

to and from spinal cord

Cranial nerves

to and from brain

Somatic sensory fibers

Convey impulses from skin skeletal muscles, and joints to CNS

Visceral sensory fibers

Convey impulses from visceral organs to CNS

Sensory (afferent) division

Collects sensory information and sends it towards the CNS

Motor (efferent) division

Transmits impulses from CNS to effector organs (muscles and glands)

Neuroglia (glial cells)

Small cells that surround and wrap delicate neurons

Neurons (nerve cells)

Excitable cells that transmit electrical signals

Astrocytes

Most abundant, versatile, and highly ranched of gial cells

Cling to neurons, synaptic endings, and capillaries

• Support and brace neurons

• Play role in exchanges between capillaries and neurons

• Guide migration of young neurons

• Control chemical environment

Microglial cells

specialized resident immune cells (macrophages) of the central nervous system (CNS)

• Small, ovoid cells with thorny processes that touch and monitor neurons

• Migrate toward injured neurons

• Can transform to phagocytize microorganisms and neuronal debris

Ependymal cells

• May be ciliated

• Lines the central cavities of the brain and spinal cord

Oligodendrocytes

• Branched cells

• Processes wrap CNS nerve fibers, forming insulating myelin sheaths in thicker nerve fibers

Satellite cells

• Surround neuron cell bodies in PNS

• Function similar to astrocytes of CNS

Schwann cells

Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers

• Similar function as oligodendrocytes

Vital to regeneration of damaged peripheral nerve fibers

Cell body (soma)

Every neuron has __.

Nuclei

Clusters of neuron cell bodies in CNS

Ganglia

Clusters of neuron cell bodies in PNS

Tracts

Bundles of neuron processes in CNS

Nerves

Bundles of neuron processes in PNS

Dendrites and Axon

Two types of neuron processes

Dendrites

Motor neurons can contain 100s of these short, tapering, diffusely branched processes

Receptive (input) region of neuron

Dendritic spines

Appendages with bulbous or spiky ends

Axon

Can number as many as 10000 terminal branches

Can be over 1 meter long

Can excite or inhibit neurons it contacts

• Carries on many convos with different neurons at the same time

• Rely on cell bodies to renew proteins and membranes

• Quickly decay if cut or damaged

Axon hillock

Most neurons have one axon that starts at cone-shaped area called __.

Nerve fibers

Long axons are called __.

Axon terminals

Distal endings are called __.

Axolemma

Neuron cell membrane

Generates nerve impulses and transmits them along __ to axon terminal

Axon terminal

Region that secretes neurotransmitters

Neurotransmitters

Released into extracellular space

Anterograde

Away from cell body

Ex: Mitochondria, cytoskeletal elements, membrane components, enzymes

Retrograde

Toward cell body
Ex: Organelles to be egraded, signal molecules, viruses, and bacterial toxins

Myelin sheath

Composed of myelin, a whitish, protein-lipid substance

Protects and electrically insulate axon

Increase speed of nerve impulse transmission

Myelinated fibers

Segmented sheath surrounds most long or large-diameter axons

Nonmyelinated fibers

Do not contain a myelin sheath

Conduct impulses more slowly

Myelination in the PNS

Formed by Schwann cells

Wraps around axon in jelly roll fashion

One cell forms one segment of myelin sheath

Myelin sheath gaps

Gaps between adjacent Schwann cells

Also called nodes of Ranvier

Nonmyelinated fibers

Thin fibers not wrapped in myelin; surrounded by Schwann cells but no coiling; one cell may surround 15 diff fibers

White matter

Regions of brain and spinal cord with dense collections of myelinated fibers

Gray matter

Mostly neuron cell bodies and nonmyelinated fibers

Myelin sheaths in the CNS

Formed by processes of oligodendrocytes, not whole cells

Each cell can wrap up to 60 axons at once

Myelin sheath gap is present

No outer collar of perinuclear cytoplasm

Thinnest fibers are unmyelinated, but covered by long extensions of adjacent neuroglia

White matter

Regions of brain and spinal cord with dense collections of myelinated fibers

Gray matter

Mostly neuron cell bodies and nomyelinated fibers