Ch 37, 38 & 39: Neurons and Nervous System

Question 1

Describe the functions of the nervous system

Answer 1

• Functions:
  
  • Sensation & perception
  • Integration
  • Motor outputs
  • Regulates many aspects of homeostasis along with the endocrine system

Question 2

Describe the organization of the human nervous system

Answer 2

• Central Nervous System: Receives and processes information; Initiates Action
  
  • Brain
  • Spinal Cord
• Peripheral Nervous System: Transmits signals between CNS and body
  
  • Sensory division
    
    • Visceral sensory division: Info from inside the body
    • Somatic sensory division: Info from outside body via senses
  • Motor division
    
    • Visceral motor division: Involuntary/Automatic
      
      • Sympathetic division: Fight or Flight
      • Parasympathetic division: Rest and Digest
    • Somatic motor division: Voluntary

Question 3

Draw, label, and describe the functions of different parts of a neuron

Answer 3

• Dendrites - Short, highly branched extensions of a neuron that receive signals from other neurons
• Soma - The part of the neuron that houses the nucleus and other organelles
• Axon - Typically long extensions of a neuron that carry nerve impulses away from the cell body toward target cells
• Axon Hillock - The cone-shaped base of an axon where signals that travel down the axon are generated.
• Nodes of Ranvier - Gap in the myelin sheath of certain axons where an action potential may be generated.
• Myelin Sheath (Schwann Cells) - Wrapped around the axon of a neuron, an insulating coat of cell membranes from Schwann cells or oligodendrocytes.
• Synapse - The junction where a neuron communicates with another cell across a narrow gap via a neurotransmitter or an electrical coupling
• Neurotransmitters - A molecule that is released from the synaptic terminal at a chemical synapse, diffuses across the synaptic cleft and binds to the postsynaptic cell, triggering a response

Question 4

Contrast the function of sensory, interneurons, and motor

Answer 4

• Sensory neuron - transmit information about external stimuli, such as light, touch, or smell, or internal conditions, such as blood pressure or muscle tension.
• Interneuron - form the local circuits connecting neurons in the brain or ganglia. Interneurons are responsible for the integration (analysis and interpretation) of sensory input.
• Motor neuron - transmit signals to muscle cells, causing them to contract. Additional neurons that extend out of the processing centers trigger gland activity.

Question 5

List the different types of neuroglia in the CNS and PNS and describe the functions of astrocytes, oligodendrocytes and Schwann cells.

Answer 5

CNS

• Astrocyte - workhorses of the central nervous system
  
  • Anchors neurons and blood vessels
• Oligodendrocyte
  
  • Myelinate certain axons in the CNS
• Microglial Cell - most prominent immune cells of the CNS
  
  • Act as phagocytes
  • Promote immune defenses
• Ependymal Cell - **neuroepithelial multiciliated cells lining the spinal cord and cerebral ventricles
  
  • Line cavities
  • Cilia circulate fluid around brain and spinal cord
    
    • Some secrete this flid

PNS

• Myelin Sheath (Schwann Cell) - Myelinate certain axons in the PNS
• Satellite Cell - Surround and support cell bodies

Question 6

What does it mean to say that a neuron is at rest?

Answer 6

A neuron that is not sending a signal; The membrane potential characteristic of a nonconducting excitable cell, with the inside of the cell more negative than the outside

Question 7

What is meant by membrane potential?

Answer 7

The difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions.

Question 8

What ions are important for establishing the resting membrane potential?

Answer 8

Potassium ions (K+) and sodium ions (Na+) play an essential role in the formation of the resting potential. These ions each have a concentration gradient across the plasma membrane of a neuron. For most neurons, the concentration of K+ is higher inside the cell, while the concentration of Na+ is higher outside.

Question 9

What roles do ion channels and ion pumps play in establishing the resting membrane potential?

Answer 9

These Na+ and K+ gradients are maintained by the sodium-potassium pump. The Na+ gradient results in very little net diffusion of Na+ in a resting neuron because very few sodium channels are open. In contrast, the many open potassium channels allow a significant net outflow of K+, which leads to a net negative charge inside the cell.

Question 10

What drives the movement of ions across the membrane?

Answer 10

This pump uses the energy of ATP hydrolysis to actively transport Na+ out of the cell and K+ into the cell.

Question 11

Contrast leak channels, voltage gated channels, ligand (chemically) gated channels, and mechanically gated channel.

Answer 11

Leak channels - these channels are always open

Voltage-gated ion channels - Specialized ion channels that open or close in response to changes in membrane potential

Ligand gated - A group of transmembrane ion channels that open or close in response to the binding of a chemical messenger (ligand) such as a neurotransmitter.

Mechanically gated - open and close in response to mechanical vibration or pressure, such as sound waves or the pressure of touch

Question 12

Where on the neuron are different types of channels located?

Answer 12

¯_(ツ)_/¯ don’t know lol

Question 13

How many ions are moved (and in which direction) by the sodium-potassium pump?

Answer 13

The sodium-potassium pump transports three Na+ out of the cell for every two K+ that it transports in. Although this pumping generates a net export of positive charge, the pump acts slowly. The resulting change in the membrane potential is therefore quite small—only a few millivolts

Question 14

What are equilibrium potentials?

Answer 14

The magnitude of a cell’s membrane voltage at equilibrium

Question 15

What is the value of the neuron resting membrane potential?

Answer 15

-70 Millivolts

Question 16

What is an action potential? (what does it mean?)

Answer 16

An electrical signal that propagates (travels) along the membrane of a neuron or other excitable cell as a nongraded (all-or-none) depolarization.

Question 17

Be able to understand the action potential diagram

Question 18

Explain what “threshold” is.

Answer 18

The potential that an excitable cell membrane must reach for an action potential to be initiated.

Question 19

Describe/ define each phase of the action potential

Answer 19

Resting Potential → Depolarization → Rising phase of the action potential (Threshold) → Repolarization → Hyperpolarization -> Na/K pump restores Resting Potential → Ready for another AP

Question 20

Identify the phases of depolarization, repolarization, and after hyperpolarization on a diagram of the action potential

Answer 20

• Depolarization - A change in a cell’s membrane potential such that the inside of the membrane is made less negative relative to the outside (if resting potential of -70 mV goes towards 0 mV)
• Hyperpolarization - A change in a cell’s membrane potential such that the inside of the membrane becomes more negative relative to the outside. Hyperpolarization reduces the chance that a neuron will transmit a nerve impulse.

Question 21

For each phase of the action potential, indicate the status of the K+ and Na+ channels, and whether K+ and Na+ ions are entering or leaving the neuron

Answer 21

Depolarization → Na+ channels open and Na+ ions enter the neuron

Repolarization → Na+ channels close, K+ channels open and K+ ions exit the neuron

Question 22

Explain what is meant by an action potential being “all or none”

Answer 22

Because action potentials either occur fully or do not occur at all, they represent an all-or-none response to stimuli.

Question 23

How is the signal propagated between neurons?

Answer 23

The majority of synapses are chemical synapses, which rely on the release of a chemical neurotransmitter by the presynaptic neuron to transfer information to the target cell.

Question 24

Define synaptic transmission

Answer 24

Synaptic transmission is the process by which one neuron communicates with another; transmission of the Action Potential from one neuron to the next – chemical signal

Question 25

Explain what a synapse is

Answer 25

Synapse - The junction where a neuron communicates with another cell across a narrow gap via a neurotransmitter or an electrical coupling

Question 26

What are neurotransmitters?

Answer 26

Neurotransmitters - A molecule that is released from the synaptic terminal at a chemical synapse, diffuses across the synaptic cleft and binds to the postsynaptic cell, triggering a response

Question 27

Describe the series of events leading to the release of neurotransmitter molecules at a chemical synapse

Answer 27

When an action potential arrives at the synapse, it depolarizes the plasma membrane at the synaptic terminal, opening voltage-gated channels that allow Ca2+ to diffuse in. The Ca2+concentration in the terminal rises, causing synaptic vesicles to fuse with the terminal membrane and release the neurotransmitter.

Question 28

Contrast an excitatory synapse versus an inhibitory synapse

Answer 28

Excitatory synapse - The binding of an excitatory neurotransmitter makes it more likely for a postsynaptic neuron to generate an action potential

Inhibitory synapse - The binding of an inhibitory neurotransmitter makes it more difficult for a postsynaptic neuron to generate an action potential

Question 29

Define the terms: reception, sensation, perception, transduction, response

Answer 29

• Perception: The interpretation of sensory system input by the brain.
• Reception: The detection of a stimulus by sensory cells.
• Response: In cellular communication, the change in a specific cellular activity brought about by a transduced signal from outside the cell.
• Transduction: Converting/translating stimuli into action potentials
• Sensation: Reception + Transduction

Question 30

Contrast afferent versus efferent pathways

Answer 30

• Afferent Pathway: Information flow from periphery to central
• Efferent Pathway: Information flow from central to periphery

Question 31

What types of stimuli are transduced by chemoreceptors, mechanoreceptors, and photoreceptors?

Answer 31

• Chemoreceptors - Achemoreceptor, also known aschemosensor, is a specializedsensory receptorwhichtransducesachemical substance(endogenousor induced) to generate a biological signal.
• Thermoreceptors - Thermoreceptors arefound in the dermis and basically register hot or cold.
• Mechanoreceptors - Amechanoreceptor, also calledmechanoceptor, is asensory receptorthat responds to mechanicalpressureor distortion.
• Photoreceptors - Photoreceptors arethe cells in the retina that respond to light.

Question 32

What does it mean that stimuli are “transduced”?

Answer 32

External stimuli are converted into action potentials that produce responses

Question 33

What type of sensory receptor cells are responsible for hearing?

Answer 33

Hair cells → type of mechanoreceptor

Question 34

Where are the auditory receptors located?

Answer 34

cochlea of the inner ear

Question 35

Where are photoreceptors located?

Answer 35

Retina of the eye

Question 36

Contrast the role of the rods & cones

Answer 36

Rods - Vision in dim light and peripheral vision

Cones - Sharply focus color vision in bright light

Question 37

Are photoreceptors depolarized or hyperpolarized in the light? In the dark?

Answer 37

Photoreceptors are hyperpolarized in the light and depolarized in the dark.

Question 38

What is rhodopsin? and what does it do? and when does it work?

Answer 38

Rhodopsin does transduction

Rhodopsinis the light receptor in rod photoreceptor cells of the retina that plays a central role in phototransduction and rod photoreceptor cell health

Question 39

What is the cerebral cortex and why is it important? What is the cerebral cortex made of?

Answer 39

The major function of the cerebrum isto control the voluntary muscular movements of the body. The cerebral cortex is mainly involved in the consciousness.

Cerebral cortex (Cerebrum) divided into 4 lobes:

Frontal Lobe

Parietal Lobe

Occipital Lobe

Temporal Lobe

Question 40

What is the significance of a particular region of the body having a larger area of representation in the primary somatosensory cortex? How about in the primary motor cortex?

Answer 40

Areas with greater representation in the somatosensory cortex are those parts of the body that are more sensitive

Areas with greater representation in the motor cortex are those parts of the body capable of finer movements

Question 41

What are homunculi (plural of homunculus)?

Answer 41

the cortical homunculus represents either the motor or the sensory distribution along the cerebral cortex of the brain.