Anatomy

Controls and integrates all body activities (along with the endocrine system)

What are the three basic function?

Sensing changes with sensory receptors

Interpreting and remembering those changes

Reacting to those changes with effectors
-Muscular contractions
-Glandular secretions

Nervous System Division:
Consists of the brain and spinal cord

Consists of cranial and spinal nerves that contain both sensory and motor fibers
Connects CNS to muscles, glands & all sensory receptors

Subdivisions of the PNS
Sensory neurons from sensory receptors to the CNS
Motor neurons to skeletal muscle tissue

Sensory neurons from visceral organs to CNS
Motor neurons to smooth & cardiac muscle and glands

Autonomic nervous system:
Fight or flight

Autonomic nervous system:
Rest & digest

Histology of Nervous Tissue
Consists of two main cell types:

Half of the volume of the CNS
Smaller cells than neurons
50X more numerous

Cells can divide – rapid mitosis in tumor formation (gliomas)

What are the 4 cell types in CNS?

What are the 2 cell types in PNS?

Star-shaped cells
Form blood-brain barrier by covering blood capillaries

Metabolize neurotransmitters
Regulate K+ balance
Provide structural suppor

Most common glial cell type
Each forms myelin sheath around more than one axon in CNS

Analogous to Schwann cells of PNS

Small cells found near blood vessels
Phagocytic role -- clear away dead cells

Derived from cells that also gave rise to macrophages & monocytes

Form epithelial membrane lining cerebral cavities & central canal
Produce cerebrospinal fluid (CSF)

Flat cells surrounding neuronal cell bodies in peripheral ganglia

Support neurons in the PNS ganglia

Cells encircling PNS axons

Each cell produces part of the myelin sheath surrounding an axon in the PNS

Functional unit of nervous system

Neurons: Have capacity to produce action potentials

Single nucleus with prominent nucleolus
Nissl bodies (chromatophilic substance)
-- rough ER & free ribosomes for protein synthesis
Neurofilaments give cell shape and support
Microtubules move material inside cell

Neuron Cell Processes

Dendrites: Conducts impulses _________ the cell body (receptive zone)

Typically short, highly branched & unmyelinated
Surfaces specialized for contact with other neurons
Contains neurofibrils & Nissl bodies

Axon: Conduct impulses ________ from cell body (conductive zone)

Long, thin cylindrical process of cell
Arises at axon hillock
Impulses arise from initial segment (trigger zone)

Side branches (collaterals) end in fine processe

Swollen tips that contain vesicles filled with neurotransmitters

What are axons surrounded by?

What is the myelin sheath produced by?

Myelinated axons appear what color?

Axon Coverings in PNS:
jelly-roll like wrappings made of lipoprotein

Acts as electrical insulator
Speeds conduction of nerve impulses

Axon Coverings in PNS:
Regular spaces or gaps in myelin sheath

Axon Coverings in PNS:
Slow, small diameter fibers
Surrounded by glia cell processes but no myelin sheath wrapping

Myelination in PNS:
What myelinate (wrap around) axons in the PNS during fetal development?

Forms outermost part with inner portion being the myelin sheath

Guides growing axons that are repairing themselves

Parts of a synapse:
Synaptic end bulb
Synaptic vesicles
Presynaptic membrane

What are the three parts of a synapse?

Parts of a synapse:
Postsynaptic membrane
Neurotransmitter receptor sites

Transmission of Nerve Impulse:
Axon terminals form synapses on dendrites and cell body

Summation takes place at initial segment on axon hillock (concentration of Na ion channels)

At threshold Na channels open and nerve impulse is conducted down the axon
Myelinated axon, Na channels open at nodes of Ranvier, saltatoryconduction
Unmyelinated axon, Na channels open on adjacent patch of membrane, slower

Structural Classification of Neurons is based on:

Several dendrites & one axon
Most common cell type

One main dendrite & one axon
Found in retina, inner ear & olfactory

One process only (develops from a bipolar)
Are always sensory neurons

What are the three functional classifications of neurons?

Transport sensory information from skin, muscles, joints, sense organs & viscera to CNS

Send motor nerve impulses to muscles & glands

Connect neurons to neurons
90% of neurons in the body

single cell stimulates many other

One cell stimulated by many others

Impulses from later cells repeatedly stimulate early cells in the circuit (short-term memory)

Single cell stimulates a group of cells that all stimulate a common postsynaptic cell (math problems)

Sprouting of new dendrites
Synthesis of new proteins
Changes in synaptic contacts with other neurons

PNS can repair damaged dendrites or axons
CNS no repairs are possible

Axons and dendrites may be repaired if... (3 reasons)

24-48 hours after injury, Nissl bodies break up into fine granular masses

Repair within the PNS:
How long...
Wallerian degeneration occurs (breakdown of axon & myelin sheath distal to injury)
Retrograde degeneration occurs back one node

How long for regeneration when:
Neuroglia on each side of injury repairs tube (Schwann cell mitosis)
Axonal buds grow down the tube to reconnect (1.5 mm per day)