biol 65. ch 13 - nervous tissue

CNS and PNS

CNS and PNS

2 main divisions of nervous system

CNS

brain and spinal cord

PNS

nerves and ganglia

sensory division and motor division

2 divisions of PNS

sympathetic and parasympathetic division

2 divisions of visceral motor division

nerve cell

neuron

properties of neurons:

excitability, conductivity, secretion

conductivity

can send signals to distant locations quickly

secretion

can release chemical messengers (neurotransmitters)

structure of a neuron

neurosoma (soma/cell body), chromatophilic substance, dendrites, axon, axon terminal

neurosoma (soma/cell body)

control center

chromatophilic substance

compartmentalized rough ER

dendrites

receive signals

axon

sends action potentials

axon terminal

ending of axon branches that communicates with another cell

multipolar

many dendrites, 1 axon

bipolar

1 dendrite, 1 axon

unipolar

no dendrites, 1 axon

sensory (afferent) neurons

detects stimuli

interneurons

receive signals from other neurons and make decisions about the response

motor (efferent) neurons

send signals to muscles to provide a response

types of glial cells in the CNS

• Oligodendrocytes myelinate axons to assist with
  conduction of impulse

• Ependymal cells secrete and circulate cerebrospinal fluid

• Microglia help in defense and disposal

• Astrocytes provide support and nourishment

Oligodendrocytes

myelinate axons to assist with conduction of impulse in CNS

Ependymal cells

secrete and circulate cerebrospinal fluid

Microglia

help in defense and disposal

Astrocytes

provide support and nourishment

PNS glia

schwann cells and satellite cells

schwann cells

myelinate axons to assist with conduction of impulse in PNS

satellite cells

provide support and nourishment

myelin

insulation on a wire, speeds up the signal

oligodendrocytes

make myelin in the CNS

schwann cells

make myelin in the PNS

neurolemma

outermost layer of wrapping around a schwann cell; contains nucleus and cytoplasm

internodal segment

fiber segment covered by myelin

nodes of ranvier

gaps (fuber segment) in myelin sheath

unmyelinated PNS axon

although still surrounded by schwann cells, they do not coil densely around the axon

synapse

meeting point of 2 neurons (or other cell types)

axodendritic synapse

axon to dendtite synapse

axosomatic synapse

axon to neurosoma synapse

axoaxonic synapse

axon to axon

neurotransmitter

chemical messenger molecule

structures at a synapse

• axon terminal of presynaptic cell

• synaptic cleft

synaptic vesicles

packets of neurotransmitters

neural tube defects

• spina bifida (occulta & cystica)

• microcephaly

• anencephaly

spina bifida

vertebrae fail to enclose spinal cord

spina bifida occulta

only 1 to few vertebrae, no functional problems

spina bifida cystica

more severe, sac protrudes from spine

microcephaly

small brain

anencephaly

no brain