Ch. 12: Nervous Tissue

The PNS is also known as

Somatic nervous; somatic senses & special senses

The CNS is also known as

Autonomic nervous; enteric nervous & somatic nervous

Major structures of the CNS are

Brain & spinal cord

Major structure of the PNS are

Nerves

Neurons contain an

Axon, dendrites, cell body

Difference between neurons are neuroglia

Neurons are electrically excitable & non-mitotic, neuroglia are for support, protection, nourishment & are mitotic

What are all the neuroglia in the CNS?

Astrocytes, oligodendrocytes, microglial, ependymal

Describe astrocytes cells

Star shaped; for structural support, forms blood-brain barrier, regulate ion & neurotransmitters in interstitial fluid, formation of neural synapse

Describe oligodendrocytes cells

Extends & wraps around neurons; forms & maintains myelin sheath

Describe microglial cells

Phagocytic cells

Describe ependymal cells

Lines ventricles of brain & canal of spinal cord; produces cerebrospinal fluid, forms blood-CSF barrier

What are the neuroglia in the PNS?

Schwann & satelite cells

Describe Schwann cells

Encloses axons & forms myelin sheath; can myelinate 1 or enclose 20, helps with axon regeneration

Describe satellite cells

Wraps around bundles of neurons (ganglions), protects & supports neurons, regulates exchange of materials

Why does myelination do?

Electrically insulates axons increasing velocity of nerve impulse propagation

Myelination in the PNS contains

Narcolemma, sheath gaps at intervals

Myelination at CNS contains

No narcolemma, fewer sheath gaps

Differentiate between nucleus & ganglion

Nucleus are neuronal bodies in the CNS while ganglion are in the PNS

Differentiate between tracts & nerves

Tracts are groups of fibers in CNS while nerves are in the PNS

White matter contains

Myelinated axons

Grey matter contains

Nonmyelinated axons, cell bodies, neuroglia, dendrites, axon terminals, Nissl bodies

What are leak channels

Everywhere, randomly opens & closes; more K+ than Na+

What are ligand-gated channels

Responds to chemical stimulus

What are mechanically-gated channels

Responds to vibration & pressure

What are voltage-gated channels

On axons of all neurons; responds to membrane voltage

Resting membrane potential is

-70

How is resting membrane potential maintained

Difference in distribution of leak channels, inability of most anions leaving, activity of sodium-potassium pumps

What is depolarization

Cytosol becomes negative and membrane becomes more positive, Na+ channels open

What is repolarization

Cytosol becomes more positive, K+ & Na+ leave

Absolute refractory period is when

Second action potential won’t go through (Na+ channel open/inactivated)

Relative refractory period is when

Second action potential in response to massive stimuli (Na+ channel resting)

Describe electrical synapses

Contains gap junctions for fast transfers

Describe chemical synapse

Requires Ca+ postsynaptic neurons that may form action potential; slower release of neurotransmitter (exocytosis of synaptic vesicles)

Inhibitory postsynaptic potential is

Hyperpolarization of post-synaptic membrane; farther from threshold

Excitatory postsynaptic potential is

Depolarization of post-synaptic membrane; closer to threshold

What is summation

When a postsynaptic neuron receives both EPSP & IPSP at once, creating a nerve impulse

Describe spatial summation

Different membrane site, several presynaptic neurons, at the same time

Describe temporal summation

Same membrane site, one presynaptic neuron, different times (rapid)

Ionotropic receptors are

Same protein containing NT binding site; ligand & ion channel

Metabotropic receptors are

Protein containing only a NT binding site & requires G protein to open/close; ligand only

How are neurotransmitter removed from synaptic cleft?

Diffusion, enzymatic degradation, re-uptake endocytosis

Acetylcholine (small mlc NT)

PNS/CNS; IPSP or EPSP

Amino acids (small mlc NT)

CNS; EPSP

GABA (small mlc NT)

CNS; IPSP

Glycine (small mlc NT)

CNS; IPSP

Biogenic amines (small mlc NT)

CNS; IPSP or EPSP

ATP (small mlc NT)

PNS/CNS; EPSP

Nitric acid (small mlc NT)

PNS/CNS; EPSP

Carbon monoxide (small mlc NT)

CNS; EPSP

Enkephalins, endorphins, dynorphins (neuropeptides)

CNS/PNS; IPSP or EPSP (pain killers)

Substance P (neuropeptides)

CNS; IPSP or EPSP (pain perception)