Anatomy - Organization of Nervous Tissue

Neurons

(nerve cells) receive stimuli and transmit action potentials to other Hurons or effector

• cell body (soma)

• Dendrites -input

• Axons - output, transmit electrical signal (AP)

Neuroglia

(glial cells) non-neural cell that support and protect neurons

• can’t send AP or electrical signals

• 4 types in in CHS

• 2 types in PNS

• unique structure and function

Dendrites

• input part of neuron, that can interact with axons of other neurons

• short cytoplasmic extensions coming off of soma

Axons

• arises at the cone shaped axon hillock

• start if the axon is called initial segment

• diameter is constant but length can vary mm up to 1m

trigger zone

axon hillock and initial segment

• information from other regions collected and create action potentials

cytoplasm and membrane

axoplasm and axolemma, help to create membrane and action potential

terminal end

presynaptic terminal - synaptic end bulb

create connection between terminals to target tissue

• start of synapse

Axonal transport

way disease can be transmitted to the CNS

vesicles/ neurotransmitters

• in the presynaptic terminal

• can release neurotransmitters to stimulate or inhibit postsynaptic cell

• can move up and down the axon transporting neurotransmitter

Sensory or afferent

action potential towards CNS

Motor or efferent

action potentials away from CNS

Interneurons or association neurons

within CNS from one neuron to another

• sensory to motor

• create decision if action is to be taken

Multipolar

• many dendrites

• single axon

• most neurons in the CNS and motor neurons

Bipolar

• 1 dendrite

• 1 axon

• sensory organs ex. eye (retina), ear (sound), olfactory (smell)

Unipolar

single process extending from cell body

• divides into 2 branches

  • one part extending to periphery that has dendrites that typically function as sensory receptors

Astrocytes

• star shaped, largest

• cytoplasmic extensions branch to form foot processes that cover the surface of blood vessels, neurons, Pia mater

• release chemicals to form tight junctions between endothelial cells of capillaries

  • help regulate the movement of substances

• forms blood brain barrier that protects against toxic substances

• assist in formation of synapses between neurons in CNS

Ependymal

• cuboidal, columnar shaped

• lines the ventricles of the brain and central canal of the spinal cord

• helps form the choroid plexus which produces cerebral spinal fluid (CSF)

  • (cells + capillaries = choroid plexus)

• patches contain cilia which help move cerebral spinal fluid through ventricles

Microglia

• smaller, thinner, fewer processes

• protective mechanism for CNS

• specialized microphages in theCNS

• digest dying tissue, microorganisms, foreign substances that invade the CNS

• phagocytic - inflammation

  • wrap around/engulf/ingest

Oligodendrocytes

• smaller than astrocytes, fewer processes

• cytoplasmic extensions surround axons

• have many processes that form myelin sheaths around portions of several axons

Schwann cells

• wrap around axons multiple times

• pushes cytoplasm to outside of cell

• forms myelin sheath around a portion of only one axon

• myelin sheath speeds up transmission of action potential and provides layer of protection

Satellite Cells

• surround neuron cell bodies in ganglia

• provides nutrients to cell body

• flattened, provides protection and support

Myelinated

• myelin protects and insulates axons from one another

• conducts signals more rapidly

Unmyelinated

• hard to keep proper chemical environment

• action potential much slower

Tract

bundle in myelinated axons in the CNS

Nucleus

collection of neuron cell bodies in the CNS

White matter

Myelinated axons, ner e tracts populate action potentials from one area in the CNS to another

• signals move up and down

Gary matter

Unmyelinated axons, cell bodies, dendrites, neuroglia

• integrative functions

  • decisions being made

Spinal Cord

White outer, myelinated

Gray inner, unmyelinated

Brain

White deeper, myelinated

Gray in outer cortext and inner nuclei