Unit 4 - Nervous Tissue

Concisely describe the five steps that occur between the arrival of an action potential at the synaptic knob and the beginning of a new action potential in the postsynaptic neuron

1. The action potential reaches the axon terminal and depolarization of the membrane causes the voltage gated calcium channels to open. 2. The high concentrations of intracellular calcium causes synaptic vesicles to fuse with the membrane 3. Neurotransmitters are released by exocytosis 4. Neurotransmitters diffuse through the synaptic cleft, and acts on the post synaptic membrane. 5. Then EPSP is generated. (Or if the released neurotransmitter is inhibitory and causes hyperpolarization of the post synaptic membrane, then IPSP is generated.

What is another name for the visceral motor nervous system? What are its two subdivisions? What are their functions?

Autonomic Nervous System (ANS) Sympathetic Division - mobilizes body systems during activity/action (fight of flight) Parasympathetic Division - conserves energy; promotes house-keeping/maintenance functions during rest

Distinguish between the central and peripheral nervous systems, and between the visceral and somatic divisions of the sensory and motor divisions

Center nervous system (CNS) is brain and spinal cord, and peripheral nerves system (PNS) consists of all the rest; it is composed of nerves and ganglia. Visceral sensory division carries signals mainly from the viscera of the thoracic and abdominal cavities, such as the heart, lungs, stomach, and urinary bladder. Somatic sensory division carries signals from receptors in the skin, muscles, bones, and joints. Somatic motor division carries signals to the skeletal muscles. Visceral motor division( autonomic nervous system or ANS) carries signals to glands, cardiac muscle, and smooth muscle.

Contrast the actions of acetylcholine, GABA, and norepinepherine at their respective synapses

Direct Action - neurotransmitter binds to and opens ion channels; promotes rapid response by altering membrane potential acetylcholine (excitory) binds to the acetylcholine receptor (ion channel); this causes Na+ and K+ channels to open, causing a change in membrane potential; excites some neurons but excites all skeletal muscle Indirect Action - can't get to the messenger so act through intracellular second messengers (longer lasting like in hormones) - biogenic amines, neuropeptides, dissolved gases, catecholomines (influence protein synthesis, enzyme activation, etc.) GABA - takes postsynaptic cell and takes it further from threshold;

What is an EPSP? What is an IPSP?

EPSP - excitatory postsynaptic potential; characterized by its ability to bring postsynaptic neuron closer to threshold IPSP - inhibitory postsynaptic potential; brings you further from threshold (not impossible, but requires more EPSPs to drown it out)

What does it mean to say a local potential is graded, decremental and reversible?

Graded - vary in magnitude with stimulus strength (stimulus does not reach threshold; stimulus causes local change in membrane potential -70 to -60; it dies down over short distance; can be summated; does not obey all or none law) decremental - get weaker the farther they spread from point of stimulation (potential at dendrite won't be strong enough) reversible - as soon as you stop stimulating dendrites and soma, the effect dissipates and the cell is going to return to its normal resting potentials

How is myelin produced? How does myelin production in the CNS differ from that in the PNS

Myelin is present in the central nervous system (CNS) and peripheral nervous system (PNS); however only the central nervous system is affected by MS. It is formed by oligodendrocytes in CNS and by Schwann cells in PNS CNS - each oligodendrocyte reaches out to myelinate several nerve fibers in its immediate vicinity. It must push newest layers of myelin under the older ones, so myelination spirals inward toward the nerve fiber. Nerve fibers of CNS have no neurilemma or endoneurium. PNS - a Schwann cell spirals repeatedly around a single nerve fiber, laying down up to 1-- compact layers of its own membrane with almost no cytoplasm between the membranes. The Schwann cell spirals outward as it wraps the nerve fiber, ending with neurilemma.

What happens to sodium when a neuron is stimulated on its dendrite? Why does the movement of sodium raise the voltage on the plasma membrane?

When an electrical pulse stimulates and destabilizes the membrane, the tiny ion channels open wide and allow positive sodium ions to enter the cell. This, in turn, makes the cell positively charged.

What is the functional difference between an axon and a dendrite?

dendrites - project off the thick branches of the soma; multiple branches that go out into the environment and sense/pick up information; one dendrite can produce multiple branches axon (nerve fiber) - single projection that originates from one side of the soma called the axon hillock; information travels along the axon to the target axon hillick (trigger zone) - where you need to open enough sodium channels to generate a large enough action potential to move down the entire axon

Describe three mechanisms that stop a synaptic transmission

diffusion - neurotransmitter escapes the synapse into the nearby ECF; astrocytes in CNS absorb it and return it to neurons reuptake - synaptic knob reabsorbs amino acids and monoamines by endocytosis; break neurotransmitters down with monoamine oxidase (MAO) enzyme; some antidepressant drugs work by inhibiting MAO degradation in the synaptic cleft - enzyme acetylcholinesterase (AchE) in synaptic cleft degrades ACh into acetate and choline; choline reabsorbed by synaptic knob

List four ways in which an action potential is different from a local potential

local potential - occur at dendrites and the soma; still involve opening of Na+ and K+ channels; goal is to stimulate an action potential in the trigger zone to fire along the axon; each local potential will change the voltage but not enough to stimulate trigger zone to fire so you need MULTIPLE local potentials (allows for better decision making) action potential - stimulus reaches threshold level therefore causes AP; stimulus causes depolarization to threshold level; it is propogated; can not be summated; obeys all or none law

Name the six types of glial cells and their functions

microglia - clean up debris via phagocytosis Peripheral satellite cells - support/cover cell body of the neuron; protect from electrical signals in tissue fluid by maintaining integrity in signaling pathway schwann cells - provide myelin sheath in the peripheral that insulates the axon (neurotrophic factors); wrap entire cell body around the axon; prevents charge leaking from one axon to another; myelated axons send the signal quicker CNS oligodendrocytes - form the myelin sheath in the CNS; look like octopi; legs reach out and surround the axon microglia (modified immune cells) - scavenge and consume any dust, debris, pathogens in the CNS; phagocytic (eating) cells; astrocytes - important in maintaining an environment that is optimal for neuron function; maintain electrolyte balance, make sure neurons have nutrients they need, get rid of metabolic waste in the tissue that is not needed ependymal - secrete cerebral spinal fluid that circulates around and through the brain and spinal cord; line the ventricles and central canal found within the spinal cord

Explain why myelinated fibers conduct signals much faster than unmyelinated fibers

saltatory conduction in myelinated fibers - AP skips along nodes of ranvier (skipping is faster than walking); nodes of ranvier have large amount of Na+ channels, and this allows for when threshold is reached, all channels open and a huge amount of Na+ gets in, and there is enough that it can diffuse to the next node, causing all of those channels to open (signal skips axon and moves form node to node to node) unmyelinated fibers must walk across entire length of the axon neurosomas can have 10,000 unique axons synapsing with one neurosoma dendrites can have thousands of synapses

Explain the difference between a sensory neuron, a motor neuron, and an interneuron

sensory (afferent) - conduct signals from receptors to the CNS (from peripheral to CNS) motor (efferent) - from CNS out to peripheral interneurons (association) - lie 100% in the CNS and integrate information and relate new info to past experiences and issue command to efferent neurons

Contrast the two types of summation at a synapse

temporal summation (loud) - loud and sure of itself spatial summation - multiple EPSPs come together and bring you to threshold neural integration - the ability of your neurons to process information, store and recall it, and make decisions postsynaptic potential - summative;

What makes an action potential rise to +35mV? What makes it drop again after this peak?

the threshold for an action potential is typically -55mV) when a neuron fires the voltage-gated Na+ channels open quickly and K+ open more slowly, this depolarizes the membrane which stimulates still more voltage gated Na+ creating a positive feedback look that makes the membrane voltage rise rapidly. Once the rising potential passes 0mV, Na+ channels are inactivated and begin closing. by the time they all close the Na+ flow ceases, the voltage peaks around +35mV It then starts to drop because the Na+ gate has closed and the K+ channels are fully open. The K+ exit the cell and their outflow repolarizes the membrane and shifts the voltage back to negative numbers.

How does the plasma membrane at the trigger zone differ from that on the soma? How does it resemble the membrane at the nodes of ranvier?

there are less voltage-gated channels (50-70 per square micrometer) and cannot generate action potentials and there are 350-500 channels per square micrometer at the trigger zone