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Neuroglia of the CNS are divided into four classes by their size, cytoplasmic processes, and intracellular organization
Astrocytes are star-shaped cells with many processes and the largest and most numberous of the neuroglia. What are the two types?
- protoplasmic astrocytes - short branching processes and found in gray matter
- fibrous astrocytes - long unbranched processes; mainly white matter
processes of astrocytes make contact with what?
blood capillaries, neurons, and pia mater (thin layer around the brain and spinal cord
what are the functions of astrocyes?
- 1.contain microfilaments for strength to support neurons
- 2.processes of astrocytes secrete chamicals to maintain selective permeability characteristics of the endothelial cells of capillaries creating blood barrier
- 3. in embryo, secrete chemicals that regulate growth, migration, and interconnection among nerons
- 4. maintain appropriate chemical environment for the generation of nerve impulses
- 5. role in learning and memory by influencing the formation of neural synapses
ogliodendrocytes resemble astrocytes and are smaller and contain fewer processes. These processes are responsible for what?
forming and maintaining the myeline sheath around CNS axons
what is a myelin sheath?
multilayered lipid and protein covering around axons to insulate and increases speed of nerve impulse conduction
Microglia are small cells with slender processes that give off numerous projections. What is there function?
They function like phagocytes removing cellular debris, microbes, and damaged tissue
Ependymal Cells are cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia. Where are they found and what is there function?
- line the ventricles of brain and central canal of the spinal cord.
- ependymal cells produce, and assist in the circulation of cerebrospinal fluid
- form the blood-cerebrospinal fluid barrier
Neuroglia of the PNS completely surround axon and cell bodies. What are the two types?
- Schwann cells which encircle PNA axons to form myelin sheath around axons.
- Satellite cells which are flat cells that surround the cell bodies of neurons of PNS ganglia.
What are the functions of Schwann cells?
myelinates a single axon and can also enclose as many as 20 or more unmyelinated axons; participate in axon regeneration
What are the functions of satellite cells?
provide structural support, regulate exchanges of materials between neuronal cell bodies and interstitial fluid
two main subdivisions of nervous system
- central nervous system - includes the brain and spinal cord
- peripheral nervous system - all the nervous tissue outside the CNS
consists of the brain and spinal cord; source of thoughts, emotions, and memories; most of the nerve impulses that stimulate muscles to contract and glands to secrete
central nervous system
The peripheral nervous system include cranial nerves and their branches, spinal nerves and their branches, ganglia, and sensory receptors. What are the three subdivision?
- somatic nervous system
- autonomic nervous system
- enteric nervous system
consists of sensory neurons that convey information from somatic receptors in the head, body wall, and limbs and from receptors for vision, hearing, taste, and smell; motor neurons that conduct impulses from the CNS to skeletal muscles; voluntary
somatic nervous system (SNS)
sensory neurons that convey informatio from autonomic sensory receptors such as stomach and lungs, to the CNS, and motor neurons that conduct nerve impulses from the CNS to smooth muscle, cardia muscle, and glands; action is involuntary; motor part consists of two branches
autonomic nervous system (ANS)
the motor part of the ANS consists of what two branches?
- sympathetic division involved in fight-or-flight responces
- parasympathetic division involved rest-and-digest activities
the operation is involuntary; "brain of the gut," neurons extend most of the length of the gastrointestinal tract, sensory neurons of the ENS monitor chemical changes within the GI tract as well as as the stretching of its walls
enteric nervous system
an electrical signal that propagates along the surface of the membrane of a neuron in responce to a stimulus; begins and travels due to the movement of ions between interstitial fluid and the inside of a neuron throuhg specific ion channels in its plasma membrane
action potential (nerve impulse)
is any change in the environment that is strong enough to initiate an action potential
ability to respond to a stimulus and convert it into an action potential
A neuron is a nerve cell that possess electrical exitability maening that they have the ability to respond to a stimulus and convert it into an action potential. It consists of what three parts?
- a cell body
The cell body (perikaryon or soma) contains a nucleus surrounded by cytoplasm with lysosomes, mitochondria, and golgi complex. Contains nissl bodies, neurofibrils, microtubules, and lipofuscin. What do these do?
are prominent clusters of rough endoplasmic reticulum possesing ribosomes and site of protein synthesis; used to growth or regeneration of damaged axons in PNS
- cytoskeleton includes:
- neurofibrils which are bundles of intermediate filaments that procide the cell shape and support
- microtubules which assist in moving materials between the cell body and axon
wich is a pigment the appears as yellow brownish granules in the cytoplasm
Nerve fiber is a general term for any neuronal process that emerges from the cell body of the neuron. What are the two types of processes?
- Dendrites which are the recieving and input portions of a neuron, tree-shaped, short tapering and highly branched.
- Single Axon is a long, thin, cylindrical projection that joins the cell body at the axon hillock which propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell. Protein synthesis does not occur at axon.
The initial segment is the part of the axon closest to the axon hillock. In most nuerons, nerve impulses arise at the junction of the axon hillock and the initial segment in this area before they travel along the axon to reach their destination.
cytoplasm of an axon
plasma membrane of the axon
side branches found along the length of an axon
many fine processes where the axon and its collaterals end
axon terminals (telodendria)
A synapse is the site of communication between two neurons or between a neuron and an effector cell. Synaptic end bulbs and varicosities are found at the tips of some axon terminal recognized by either bulb-shaped structures or a string of swollen bumps. Both contain tiny membrane-enclosed sacs called synaptic vesicles that store a chemical neurotransmitter. The neurotransmitter molecules are released from these synaptic vesicles to excite or inhibit other neurons, muscle fibers, or gland cells. What are the two types of transport systems that carry materials from the cell body to the axon terminals and back?
- Slow axonal transport conveys axoplsm in one direction-from the cell body to axon terminal. Supplies new axoplasm to developing and regenerating axons.
- Fast axonal transport use proteins to move materials in both directions-away from and toward the cell body. Transports various organelles and materials that orm the membranes of axolemma, synaptic end bulbs, and synaptic vesicles.
Classification of neurons is based upon both structural and functional features. Structural classification is based upon the number of processes that extend from the cell body whereas Functional classification is the based upon the direction in which the nerve impulse is conveyed in relation to CNS. Name the classifications for each.
Structural Classification: Multipolar neurons, Bipolar Neurons, and Unipolar Neurons
Functional Classification: Sensory or afferent neurons, Motor or efferent neurons, and Interneurons or association neurons
Structural Classification includes 3 classifications based off of the number of processes. What are the three types and what does each mean?
- Multipolar neurons have several dendrites, one axon, and are found in brain and spinal cord
- Bipolar neurons have one main dendrite, one axon, and found in the retina , inner ear, and olfactory are of the brain
- Unipolar neurons have dendrites and one axon that fuse together to form a continuous process that emerges from the cell body
Functional Classification of neurons is determined according to the direction in which the nerve impulse is conveyed in respect to the CNS. What are the 3 ways to functionally classify them?
- Sensory/afferent neurons forms an action potential in its axon and the action potential is conveyed into the CNS through cranial or spinal nerves. Mostly unipolar.
- Motor or efferent neurons convey action potentials away from the CNS to effectors in the periphery (PNS) through cranial or spinal nerves. Mostly multipolar.
- Interneurons/association neurons process incoming sensory information from sensory neurons and the elicit a motor response by activating the appropriate motor neurons. Mostly multipolar.
At the synapse between neurons, the neuron sending the signal is called the presynaptic neuron, and the neuron receivein the messsage is called the postsynaptic neuron. Most synapses are either axodendritic (from axon to dendrite), axosomatic (axon to cell body), or axoaxonic (axon to axon). What are the two types of synapses?
Electrical and Chemical
At electrical synapse, action potentials (impulses) conduct directly between adjacent cellls through structures called gap junctions. These gap junctions possess connexons which as a passageways to allow the transportation of ions from one cell's cytosol to the next. Found primarily in visceral smooth muscle, caridac muscle, and the developing embryo. What are the advantages of Electrical synapses?
- Faster Communication because action potential passes directly from the presynaptic cell to the postsynaptic cell.
- Synchronization. With the ability to work as a group, large numbers of neurons and muscle fibers can produce action potentials in unison if connected by gap junctions.
Chemical synapses possess a seperation between presynaptic and postsynaptic neurons called the synaptic cleft (space filled with interstitial fluid). In responce to a nerve impulse, the presynaptic neuron releases a nuerotransmitter that diffuses toward receptors in the plasma membrane of postsynaptic neuron resulting in a postsynaptic potential (electrical signal/graded potentail). Electrical-Chemical-Electrical progression requires a certain amount of time called the synaptic delay. What are the 7 steps involved in a chemical synapse?
- 1.nurve impulse arrives at synaptic end bulb/varicosity
- 2. depolarization phase opens voltage gated Ca++ channels (membrane of synaptic end bulbs) to flow in
- 3. Ca++ inside the presynaptic neuron triggers exocytosis and release of ndurotransmitter
- 4. diffuse across to bind to neurotransmitter receptors associtated with ligand-gated channel
- 5. opening of channel and allow particular ions to flow acrross the membrane
- 6. voltage change creating a postsynaptic potential (deploarization/hyperpolarization)
- 7. when depolarizing postsynaptic potentil reaches threshold it triggers an action potential in axon of postsynaptic neuron
Neurostransmitters bind to receptors act to open/shut ion channels or work by second-messenger systems to influence chemical reactions inside cells. Serves to inhibit or excite postsynaptic neuron. Some neurotransmitters are released as hormones by neurosecretory cells. Neurotransmitters are divided into two classes based on size: small-molecule neurotransmitters and neuropeptides. Name each type of neurotransmitter found in each class.
- Small-molecule neurotransmitters include:
- Amino Acids - glutamate, aspartate, gamma aminobutyric acid, glycine
- Biogenic Amines - norephinephrine, epinephrine, dopamine, catecholamines, serotonin
- Purines - adenosine
- Nitric Oxide
- Neuropeptides include:
Acetylcholine are released by many PNS neurons and by some CNS neurons. They are excitatory when bound to ionotropic receptors and inhibitory when metabotropic receptors coupled to G proteins that open K+ channels. What enzyme inactivateds ACh?
Amino Acids are neurotransmitters in the CNS. These include glutamate and aspartate which have excitatory effects. Glutamate is invovled in half of the synapses in the brain. Binding of glutatmete to ionotropic receptors opens cation channels. Inactivation via glutamate reuptake. Gamma aminobuttyric acid and glycine are also important inhibitory neurotransmitters. GABA and glycine bound to ionotropic receptros opens Cl- channels. Includes half of the inhibitory synapses in the spinal cord use the amino acid glycine and rest use GABA.
Biogenic amines are modified and decarboxylated amino acids. What are the most prevalent ones found in the human body.
norepinephrine, epinephrine, dopamine, and serotonin
Norepinephrine playes roles in arousal, dreaming, and regulating mood. Epinephrine and norepinephrine serve as hormones in this way. Associated with adrenal medulla. Also neurons containing the neurotransmitter dopamine are active during emotional responses, addictive behaviors, and pleasurable experiences. These three are classified as what group due to the fact that they include an amino group and catechol ring with six carbons and two adjacent hydroxyl groups (from tyrosine). Inactivation by uptake.
Serotonin (5-hydroxytryptamine) is involved in sensory perception, temperature regulation, control of mood, appetite, and the induction of sleep.
ATP and other purines have the characteristic ring structure called the purine ring. ATP, ADP, and AMP are all excitatory neurotransmitters in both CNS and PNS. Usually associated with the release of other neurotransmitters at the same synapse.
The neurotransmitter nitric oxide is formed on demand acts immediately because it disipates quickly as a free radical. It is lipid-soluble and diffuses from cell to cell activating an enzyme for second messnger called cyclic GMP. Plays role in memory and learning. What enzyme is responsible for the formation of nitric acid?
nitric oxide synthase
Neuropeptides are neurotransmitters consisting of 3 - 40 amino acids linked by peptide bonds called neuropeptides and are found in both the CNS and the PNS. Neuropeptides are formed in the neuron cell body, packaged into vesicles, and transported to axon terminals. Neuropeptides includes enkephalins