chapter 12

What two structures make up the central nervous system?

What two structures make up the central nervous system?

Brain and spinal cord

Define ganglia.

Small masses of nervous tissue consisting of neuron cell bodies located outside the CNS.

What are the 3 divisions of the peripheral nervous system?

Somatic NS, Autonomic NS, Enteric NS.

What does the Somatic Nervous System control?

Controls voluntary actions through sensory and motor neurons.

What does the Autonomic Nervous System control?

involuntary actions.

What are the two parts of the Autonomic Nervous System?

Sympathetic Division and Parasympathetic Division.

What is the function of the Sympathetic Division?

Supports exercise or emergency actions (fight or flight response).

What is the function of the Parasympathetic Division?

Controls 'rest and digest' activities.

What is dual innervation?

Effectors receive nerves from both sympathetic and parasympathetic divisions.

What is an effect of sympathetic neurons on heart rate?

Sympathetic neurons increase heart rate.

What is an effect of parasympathetic neurons on heart rate?

Parasympathetic neurons slow down heart rate.

What is the function of the Enteric Nervous System?

Controls involuntary actions of the gastrointestinal tract.

What are the three functions of the nervous system?

Sensory, integrative, and motor.

What are the parts of a neuron?

Cell body, Nissl bodies, neurofibrils, microtubules, Schwann cell, myelin sheath, neurolemma, axon, dendrites, Nodes of Ranvier, axoplasm, axolemma, synapse.

What is the function of the cell body in a neuron?

Contains the nucleus surrounded by cytoplasm that includes organelles.

What do Nissl bodies contain?

Contain free ribosomes and rER for protein synthesis.

What is the role of neurofibrils?

Provide structure and support to the neuron.

What do microtubules assist with in a neuron?

Assist in moving materials between the cell body and axon.

What is the function of the Schwann cell?

Encircles PNS axons and forms a myelin sheath.

What is the myelin sheath?

A multilayered lipid and protein covering surrounding the axon.

What is the neurolemma?

The outer layer of the Schwann cell.

What is the function of dendrites in a neuron?

Serve as the receiving or input portion of the neuron.

What do Nodes of Ranvier allow?

Allow for saltatory conduction of nerve impulses.

What is axoplasm?

Cytoplasm of the axon.

What is axolemma?

Plasma membrane of the axon.

What is a synapse?

The site of communication between two neurons or a neuron and effector cell.

What are multipolar neurons?

Neurons with several dendrites and one axon.

Where are multipolar neurons primarily found?

In the brain and spinal cord, and as motor neurons.

What are bipolar neurons?

Neurons with one main dendrite and one axon.

Where are bipolar neurons found?

In the retina of the eye, inner ear, and olfactory area of the brain.

What are unipolar neurons?

Neurons with dendrites and one axon that are fused together.

structural classification of neurons

       Classified by number of processes extending from cell body

functional classification of neurons

       Classified according to direction in which nerve impulse (action potential) is conveyed with respect to CNS

What do sensory neurons do?

afferent neurons Convey action potentials into the CNS from receptors.. most unipolar in structure

What do motor neurons do?

efferent neurons. Convey action potentials away from the CNS to effectors.. most are multipolar in structure

What are interneurons?

Neurons located within the CNS that process sensory information.        Process incoming sensory information from sensory neurons

       then elicit motor response by activating motor neurons (integrate)

Most are multipolar in structure (several dendrites and 1 axon)

What are astrocytes?

Star-shaped neuroglial cells that support neurons.

What is the most numerous neuroglial cell in the CNS?

Astrocytes.

What is the function of oligodendrocytes?

Form and maintain the myelin sheath around CNS axons.

What do microglial cells do?

Small cells with slender processes that give off spine-like projections

function as phagocytes that remove cellular debris and microbes.

What are ependymal cells?

Cells that line the ventricles of the brain and produce cerebrospinal fluid.

what are the 2 neuroglia cells of the PNS

Schwann and satellite cells

What are Schwann cells in the PNS?

Cells that myelinate a single axon and participate in axon regeneration.

What are satellite cells?

Cells that regulate exchanges of materials between cell bodies and interstitial fluid in PNS ganglia.

What aids in regeneration of a neuron in the PNS when a neuron is injured?

Neurolemma.

Why is white matter white?

It is composed of fibers with a protective myelin sheath.

Why is gray matter gray?

It is made up of nerve cell bodies.

What are the 4 types of ion channels we discussed in class? 

leak channels, ligand gated channels, mechanically gated channels, and voltage gated channels

What are leak channels?

Channels in plasma membranes that allow more potassium ions to leak out than sodium ions in.

located in plasma membrane

What are ligand-gated channels?

Channels that open and close in response to binding of ligands like neurotransmitters.

Located: dendrites of some sensory neurons (pain receptors) and dendrites and cell bodies of motor neurons

What are mechanically-gated channels?

Channels that open in response to mechanical stimulation like touch or pressure.

Located: dendrites of sensory neurons (touch, pain, and pressure receptors) and in auditory receptors in ears

What are voltage-gated channels?

Channels that open based on changes in membrane potential.

       Location: all neuron types

What is the resting membrane potential of a neuron?

-70 mV.

What are the three factors that maintain a negative resting membrane potential?

Unequal distribution of ions, inability of anions to leave the cell, and Na+ K+ pumps.

What is the threshold potential of a neuron?

-55 mV.

What is a graded potential?

A change in membrane potential that varies in size.

What is the depolarizing phase of an action potential?

Phase where membrane potential becomes less negative and can reach positive.

What occurs during the repolarizing phase of an action potential?

Membrane potential is restored to resting state of -70 mV.

Know the different phases to an action potential. 

depolarizing phase, repolarizing phase, hyper polarizing phase

What is the absolute refractory period?

Time during which a second action potential cannot be initiated.

What is the relative refractory period?

Period when a second action potential can be initiated only by a larger than normal stimulus.

Define presynaptic and postsynaptic neurons.

Presynaptic neuron sends the signal; postsynaptic neuron receives the signal.

What does a synaptic bulb contain?

synaptic vesicles

What is the synaptic cleft?

The space that separates the presynaptic and postsynaptic neurons.

What do synaptic vesicles contain?

Neurotransmitters that transmit signals across the synapse.

What happens during the chemical synapse process?

1.     . Presynaptic neuron – nerve impulse

2.     Depolarization phase. Opens voltage-gated Ca²⁺ channels and Ca²⁺ flows in

3.     Vesicle membranes merge with plasma membrane and neurotransmitters within vesicles are released into synaptic cleft

4.     Neurotransmitters diffuse across cleft and bind to neurotransmitter receptors in postsynaptic neuron’s plasma membrane

5.     Binding of neurotransmitters to receptors on ligand-gated channels:

opens channels and allows ions (Na+) to flow across membrane

6.     As ions (Na+) flow through opened channels:

1.     voltage across membrane changes and is called postsynaptic potential. Depolarization occurs

7.     . When depolarizing postsynaptic potential reaches threshold:

8.     it triggers AP in postsynaptic neuron

How are neurotransmitters removed from the synaptic cleft?

Through diffusion, enzymatic degradation, or uptake by cells.