Ch. 9 check your recall

List the major events of an action potential.

1. Stimulation: environmental changes take place affecting the membrane (light, temperature, pressure) 2. Depolarization: Na+ ions diffuse into membrane causing sodium channels to open, depolarizing the cell 3. Repolarization: K+ channels soon open up causing them to diffuse out of the membrane repolarizing it 4. Hyperpolarization: membrane again becomes negative; action potential occurred; resting potential returned (-70)

Define all-or-none response as it relates to nerve impulse conduction.

If a neuron responds at all, it responds completely, it is either fully or nothing.

Distinguish among the types of neuroglial cells in the central nervous system.

Microglial cells: scattered throughout the CNS, support neurons and phagocytize bacterial cells and cellular debris. Oligodendrocytes: align along nerve fibers, provide insulating layers of myelin aka myelin sheath around axons within the brain and spinal cord. Astrocytes: found between neurons and blood vessels, provide structural support, join parts by their abundant cellular processes, and help regulate the concentrations of nutrients and ions within the tissue, also form scar tissue. Ependymal cells: form an epithelia-like membrane that covers specialized brain parts and forms the inner linings that enclose spaces within the brain and spinal cord.

What is the function of Schwann cells in the peripheral nervous system?

Schwann cells form a myelin sheath around axons.

How does the central nervous system integrate incoming information?

Sensory receptors convert environmental information into nerve impulses, which are then transmitted over peripheral nerves to the CNS. There, the signals are integrated, they are brought together, creating sensations, adding to memory, or helping produce thoughts that translate sensations into perceptions.

Describe the events that occur at a synapse.

The neurons at a synapse are not in direct physical contact, but separated by synaptic cleft. Communication along a nerve pathway must cross these gaps. The neuron carrying the impulse into the synapse is the sender, presynaptic neuron. The neuron that receives this input at the synapse is the receiver, postsynaptic neuron.

What is the relationship between action potentials and nerve impulses?

When an action potential occurs in one region of a nerve cell membrane, it causes a bioelectric current to flow to adjacent portions of the membrane. This local current stimulates the adjacent membrane to its threshold level and triggers another action potential. A wave of action potentials moves down the axon to the end. This constitutes a nerve impulse.

What types of chemicals functions as neurotransmitters?

acetylcholine and biogenic amines

Explain how impulse conduction differs in myelinated and unmyelinated nerve fibers.

an unmyelinated nerve fiber conducts and impulse over its entire surface. myelinated fibers conduct impulses more rapidly. nerves with larger diameters conduct impulses faster than those with small diameter

What are possible fates of neurotransmitters?

are transported back into the synaptic knob that released them into or into nearby neurons or neuroglial cells.

How do sensory receptors collect information?

by detecting changes inside (temperature and oxygen levels) and outside the body (light and sounds)

Describe the components of a neuron.

cell body: the tubular, cytoplasm-filled dendrites dendrites: conduct nerve impulses to the neuron cell body axon: conducts impulses away

What are the two major subdivisions of the nervous system?

central nervous system (CNS) and peripheral nervous system (PNS)

Distinguish between convergence and divergence.

convergence- axons which originate in different parts of the nervous system but lead to the same neuron; divergence- impulses which leave the same neurons, but are received by different axons, amplifying the impulse

Distinguish between a dendrite and an axon.

dendrites conduct impulses to the neuron cell body (soma) and axon conducts impulses away from the neuron cell body.

Distinguish between the actions of excitatory and inhibitory neurotransmitters.

excitatory neurotransmitters increase post synaptic membrane permeability to sodium ions; inhibitory neurotransmitters make it less likely that threshold will be reached.

List the functions of the cells that support neurons.

fills spaces, provide structural frameworks, produce the components of the electrical insulator myelin, and carry on phagocytosis.

Define neuronal pool.

groups of neurons that make hundreds of synaptic connections with each other and work together to perform a common function.

What are the two major types of cells that form nervous tissue?

neurons and neuroglial cells

Name three groups of neurons based on structure and three groups based on function.

neurons are usually classified by multipolar neurons, bipolar neurons, and unipolar neurons. The groups of functions are sensory neurons, interneurons, motor neurons.

Explain why axons of peripheral nerves can regenerate, but axons of central nervous system nerves cannot.

peripheral nerves are damaged, their axons can regenerate, the neurilemma plays an important role in this process. But CNS axons are myelinated by oligodendrocytes, which do not provide a neurilemma so damaged CNS neurons do not regenerate.

Describe how a myelin sheath forms.

produced by Schwann cellsthat wind tightly around axons coating them with many layers of cell membrane that have little or no cytoplasm between them.

What are the two types of motor functions of the nervous system?

somatic nervous system- voluntary skeletal muscle and autonomic nervous system- involuntary heart, smooth muscle in blood vessels.

Summarize how a nerve fiber becomes polarized.

the surface of a cell membrane is usually electrically charged, polarized. This polarization arises from an unequal distribution of positive and negative ions between sides of the membrane and it is important to the conduction of muscle and nerve impulses.