bio 252 unit 1

3 different types of neurons

sensory, motor, and interneurons

what type of neuron is a bipolar neuron?

“special” sensory neuron, located in the head and used for olfaction, vision, and hearing

what type of neuron is a pseudo-unipolar neuron?

all other sensory neurons, responds to pain, temperature, and pressure

has its dendrites and axon fused into a single process emerging from the cell body, with most of these neurons having their cell bodies located in the ganglia of spinal and cranial nerves

what type of neuron is a multipolar neuron?

interneurons and motor neurons

multipolar neurons have the largest number of inputs, why is this important?

these neurons can receive many different signals from your brain (motor) or have large networks of neurons interacting with one another (interneurons), so they need to have a wide variety of dendrites

why is it important for sensory neurons to have narrow input?

so that there can be precision/resolution as to where a signal came from

neuroglia

non neuron cells that live in neural tissue (brain, spinal cord, nerves, cranial nerves, spinal nerves)

central nervous system Glia

astrocyte, microglia, ependymal cell, oligodendrocyte

peripheral nervous system Glia

satellite cells, Schwaan cells

postmitotic

a cell has finished dividing by mitotis and is in a state where it no longer divides (neurons are in this state)

astrocytes

anchor neurons and blood vessels, facilitate the formation of the blood-brain barrier, regulate the extracellular environment

microglia

unique type of immune system cell, travel around the tissue of the central nervous system and look for things that shouldn’t be there, considered phagocytic cell

ependymal cells

function as the boundary between cerebrospinal fluid and fluid surrounding our nervous system cells (line cavities in brain and spinal cord), circulate fluid with cilia

oligodendrocytes

oligo - few, small number, -dendro - dendrites/branch

these cells wrap their cell membranes around axons of neurons (“myelinate” axons)

chance for recall - white matter vs. gray matter

schwann cells

found in peripheral nervous system, wrap cell membranes around axon multiple times to create myelin sheath, facilitate regeneration of neurons (neuron can grow back through the tube that is left behind by schwann cells)

myelin

acts as an electrical insulator, allows action potentials to “jump” to the next mode

internodes

myelinated gap of a nerve fiber between two nodes of Ranvier

Nodes of Ranvier

space between internodes, electrical signals jump from node to node

satellite cells

surround nucleus, control environment

A 28-year-old man sustains a crush injury to a peripheral nerve in his arm. Over the following months, sensation gradually returns to the affected hand. Which structural feature most directly enabled this recovery?

neurolemma formed by Schwann cells

Which neuroglial cell type helps form the blood-brain barrier by regulating the permeability of CNS capillary endothelial cells?

astrocytes

White matter in the CNS appears white primarily because it is composed predominantly of:

myelinated axons

A researcher finds that a patient's ependymal cells are nonfunctional. Which of the following findings would most likely result?

Disrupted production and circulation of cerebrospinal fluid

A disease selectively destroys oligodendrocytes throughout the brain and spinal cord, while peripheral nerves remain completely unaffected. Which of the following is the most likely consequence?

Conduction velocity along the affected CNS axons will decrease, and regeneration will be limited because these axons lack a neurolemma.

why do we have a resting membrane potential?

1) Ions (especially K+) have different concentrations across the membrane

2) chemical diffusion occurs through leak channels

3) principles of electrical attraction/repulsion

Na+ is concentrated…

outside the cell (extracellular fluid levels much higher than intracellular levels)

K+ is concentrated…

inside the cell (intracellular fluid levels much higher than extracellular)

why do ions have different concentrations across the membrane?

the Na+/K+ ATPase pump moves sodium ions out of the cell and potassium ions into the cell, ATP is needed to push these molecules against their concentration gradient

tract

bundle of axons located within the CNS that interconnects the brain and spinal cord

If the purpose of local potentials is to communicate a stimulus from another cell and to influence the production of action potentials, what is the role of hyperpolarizing local potential?

To reduce the likelihood that an action potential is generated

A researcher applies a toxin that blocks voltage-gated Ca²⁺ channels in presynaptic axon terminals. Which of the following best describes the expected effect on chemical synaptic transmission?

Neurotransmitter release into the synaptic cleft will be prevented

how does a typical chemical synapse transmit a signal?

1. An action potential arrives at a synaptic end bulb (or at a varicosity) of a presynaptic axon.

2. The depolarizing phase of the action potential opens voltage-gated Ca²⁺ channels, which are present in the membrane of synaptic end bulbs. Because calcium ions are more concentrated in the extracellular fluid, Ca²⁺ flows inward through the opened channels.

3. An increase in the concentration of Ca²⁺ inside the presynaptic neuron serves as a signal that triggers exocytosis of the synaptic vesicles. As vesicle membranes merge with the plasma membrane, neurotransmitter molecules within the vesicles are released into the synaptic cleft. Each synaptic vesicle contains several thousand molecules of neurotransmitter.

4. The neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors in the postsynaptic neuron's plasma membrane. The receptor shown in Figure 12.23 is part of a ligand-gated channel (see Figure 12.11b); you will soon learn that this type of neurotransmitter receptor is called an ionotropic receptor. Not all neurotransmitters bind to ionotropic receptors; some bind to metabotropic receptors (described shortly).

5. Binding of neurotransmitter molecules to their receptors on ligand-gated channels opens the channels and allows particular ions to flow across the membrane.

6. As ions flow through the opened channels, the voltage across the membrane changes. This change in membrane voltage is a postsynaptic potential. Depending on which ions the channels admit, the postsynaptic potential may be a depolarization (excitation) or a hyperpolarization (inhibition). For example, opening of Na⁺ channels allows inflow of Na⁺, which causes depolarization. However, opening of Cl^- or K⁺ channels causes hyperpolarization. Opening Cl^- channels permits Cl^- to move into the cell, while opening the K⁺ channels allows K⁺ to move out—in either event, the inside of the cell becomes more negative.

7. When a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the axon of the postsynaptic neuron.

2 main advantages of electrical synapses

faster communication - action potentials conduct directly through gap junctions

synchronization - can coordinate activity of group of neurons or muscle fibers

A patient is prescribed an acetylcholinesterase inhibitor for myasthenia gravis. What is the primary mechanism by which this drug improves neuromuscular transmission?

It prolongs acetylcholine availability in the synaptic cleft by slowing degradation

inhibitory postsynaptic potential (IPSP)

hyper polarizing postsynaptic potential - hyper polarization of the postsynaptic membrane, which moves the membrane potential further away from the threshold required to fire an action potential

A single EPSP is generated in a postsynaptic neuron but fails to trigger an action potential. Twenty milliseconds later, another EPSP of identical magnitude is generated at the same synapse. Which of the following best explains why the second EPSP still fails to reach threshold?

Too much time has elapsed between the two EPSPs for temporal summation

temporal summation

summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at different times

spatial summation

summation of postsynaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time

summation

the process by which graded potentials add together

ANS two-neuron pathway

preganglionic → ganglion → postganglionic → effector

innervation of the adrenal medulla

sympathetic preganglionic neurons synapse directly with chromaffin cells in the adrenal medulla, which then release epinephrine and norepinephrine into the bloodstream (functioning as hormones, not neurotransmitters). There is no postganglionic neuron

Which of the following is a defining structural difference between somatic and autonomic motor pathways?

Autonomic pathways use two neurons in series with a ganglion; somatic pathways use a single neuron from CNS to effector

A drug that destroys chromaffin cells in the adrenal medulla would be expected to primarily disrupt which of the following?

Hormonal release of epinephrine and norepinephrine into the bloodstream during a stress response

Which structures receive sympathetic innervation only, without opposing parasympathetic input?

Sweat glands, arrector pili muscles, and most blood vessels

Axons leave the sympathetic trunk in four possible ways:

1. sympathetic nerves

2. splanchnic nerves

3. spinal nerves

4. carotid plexus

What role do vagus nerve axons play in the parasympathetic nervous system?

They carry nearly 80% of the craniosacral outflow to thoracic and abdominal organs.

autonomic (visceral) reflexes

responses that occur when a nerve passes through an autonomic reflex arc

• play key role in controlling blood pressure, digestion, deification & urination

Which of the following accurately describes the role of cholinergic neurons in the autonomic nervous system (ANS)?

They release acetylcholine and have receptors named nicotinic and muscarinic.

components of autonomic reflex arc

1) sensory receptor

2) sensory neuron

3) integrating center

4) motor neurons - Nerve impulses triggered by the integrating center propagate out of the CNS along motor neurons to an effector.

5) effector - effectors are smooth muscle, cardiac muscle, and glands

why are we not aware of muscular contractions of our digestive organs, heartbeat, etc?

the integrating centers for these autonomic responses are in the spinal cord or the lower regions of the brain

• sensory neurons deliver input to these centers

autonomic neurons are classified as ___ or ____ based on the neurotransmitter they produce and release

cholinergic, adrenergic

cholinergic neurons

neuron that releases acetylcholine as its neurotransmitter

• in the ANS, these neurons include all sympathetic and parasympathetic preganglionic neurons, sympathetic postganglionic neurons that innervate most sweat glands, and all parasympathetic postganglionic neurons