Ch. 3 (Nervous System)

What structures make up the nervous system?

What structures make up the nervous system?

the brain, spinal cord, nerves, neural support cells, and certain sensory organs (eye, ear)

What is the functional unit of the nervous system?

neuron

What are the major structures of the neuron?

several dendrites, a single branched axon, and cell body (soma)

What describes the regenerative capabilities of neurons?

they cannot divide

What substances are neurons highly dependent upon for chemical energy?

glucose

neurons use what process to move glucose from the blood into the cell?

facilitated transport

(Note: not uniquely dependent on insulin for this transport)

What describes how neurons store nutrients?

contain low stores of glycogen and oxygen

(Note: depend on blood mostly for these nutrients)

What is the structure where the soma connects to the axon called?

axon hillock

(Note: action potentials are generated here)

What structure receives information and transfers it to the cell body in the neuron?

dendrites

What structure transfers impulses away from the cell body in the neuron?

axon

What distinguishes gray and white matter?

• white: myelinated axons

• gray: neuronal cell bodies (no myelin)

What category of nervous tissue cells are capable of cell division?

glial cells

Which glial cells produce myelin in the central nervous system (CNS)?

oligodendrocytes

Which glial cells produce myelin in the peripheral nervous system (PNS)

Schwann cells

What are the fatty sheaths that act as insulators in the nervous system?

myelin sheaths

Myelin sheaths are separated by what divisions?

nodes of Ranvier

The nodes of Ranvier allow the action potential to do what?

travel continuously down the axon jumping from node to node

(Note: this process is called saltatory conduction, which speeds up the impulse)

What is the only type of animal that has myelinated axons?

vertibrates

What are the phagocytes of the CNS?

microglia

What cells use cilia to circulate cerebrospinal fluid

ependymal cells

What are groups of cell bodies in the PNS that serve as support cells?

satellite cells

What is a kind of satellite cell that provides physical support to neurons of the CNS and maintains the mineral and nutrient balance?

astrocytes

What are the three types of neurons important to the DAT?

1. sensory (afferent) neurons

2. association (interneuron) neurons

3. motor (efferent) neurons

What kind of neuron receives the initial stimulus from the brain (ex: neurons in the skin)?

sensory (afferent) neuron

What kind of neuron is located in the spinal cord and brain, and receives impulses from sensory neurons and sends impulses to motor neurons?

association (interneuron) neuron

Which neurons are integrators as they evaluate impulses for the appropriate response?

association (interneuron) neuron

What percentage of neurons are interneurons?

99%

In which neural pathway are interneurons often found?

reflex arcs

(Note: note required for reflex arc though)

What neurons travel from the brain/spinal cord and stimulate effectors?

motor (efferent) neurons

(Note: May stimulate muscles, sweat glands, or cells in the stomach to secrete gastrin

What are target cells that elicit some response?

effectors

What is an electrical signal that is transmitted along a nerve fiber, allowing us to send signals to perform actions like raising an arm to catch a ball or recoiling a hand when touching a hot stove.

nerve impulse

What is the mechanism behind a nerve impulse?

polarized neurons

(Note: high concentration of Na+ is presented outside the cell and a high concentration of K+ inside)

What channel maintains the resting potential of a neuron?

Na+/K+ ATPase pump

(Note: 3Na+ are pumped out for every 2K+ brought in, resulting in the net removal of one positive charge from the intracellular space)

What are the steps of nerve impulse transmission?

1. resting potential

2. action potential

3. repolarization

4. hyperpolarization

5. refractory period

What is the typical resting potential of a neuron?

-70 mV

What is the first step of an action potential?

a stimulus causes gated ion channels to open and Na+ ions enter the axon, depolarizing the neuron.

What measure needs to be reached in order for an action potential to occur?

the threshold level, which is around -50 mV

(Note: if the threshold level is not reached, no action potential occurs!)

What is the direct result of the threshold level being reached in terms of ion channels?

opening of voltage gated Na+ channels down the entire length of the neuron

(Note: All or nothing event!)

What happens during the repolarization phase in terms of ion channels?

in response to the Na+ flow in, more gated ion channels let K+ out of the cell, restoring polarization

Which ions are in and which ions are out after repolarization?

Na+ are now IN and the K+ are OUT!

What describes hyperpolarization in terms of ions?

too much K+ is released (~ -80 mV)

What term describes the period where the neuron will not respond to a new stimulus until Na+/K+ pumps return the ions to their resting potential locations?

refractory period

What term describes when Na+ channels are inactivated and there is no chance of responding to a new stimulus?

absolute refractory period

(Note: sets an upper limit to action potential frequency)

What period is it called when an abnormally large stimulus can create an action potential after the absolute refractory period?

relative refractory period

What is the function of the refractory period?

prevents an action potential from moving backwards

What metric is related to the frequency of action potential firing, or how many nervous cells contribute to result in the action potential?

strength of a neural signal

What is the name of the ion channel that will close in the presence of ATP, causing K+ to be unable to escape?

K-ATP sensitive channel

(Note: when exposed to ATP, this event causes depolarization, activating voltage dependent calcium channels (VDCC) to open, which results in the exocytosis of insulin)

What is the event called when a signal travels from a pre-synaptic neuron to a post-synaptic neuron?

signal transmission

What are the two types of signal transmission in the nervous system?

electrical and chemical

Which type of signal transmission is a bidirectional action potential

electrical

Which type of signal transmission is a unidirectional action potential that is most typical in animal cells?

chemical

Over what kind of membrane does an electrical transmission occur?

gap junction

In what tissues is electrical signal transmission common?

cardiac and visceral smooth muscle

What are the steps of transmission across a synapse?

1. Ca 2+ gates open

2. synaptic vessels release neurotransmitter

3. neurotransmitter binds with post-synaptic receptors

4. post-synaptic membrane is either excited or inhibited

5. Neurotransmitter is degraded/ recycled/diffused away

When the Ca 2+ gates open during synaptic transmission, what event allows Ca2+ to enter the cell via VDCC's (are also found in beta cells!)?

depolarization

Influx of calcium ions during synaptic transmission causes what event?

release of neurotransmitters into the synaptic cleft

By what mechanism do neurotransmitters diffuse across the synapse during synaptic transmission?

brownian motion

In synaptic transmission, what is the result called when Na+ gates open and the membrane is depolarized, allowing an action potential to be generated if threshold potential is succeeded?

excitatory post synaptic potential (EPSP)

In synaptic transmission, what is the result called when K+ gates open and the membrane is hyperpolarized, making it more difficult to generate an action potential?

inhibitory post synaptic potential (IPSP)

What are the mechanisms in which neurotransmitters can be cleared from the synapse?

• broken down by enzymes in the cleft

• reuptaken

• diffused

What are the factors that alter the rate at which impulses travel?

• diameter

• myelination

Which type of diameter will allow an action potential to travel faster?

larger diameter

(Note: less resistance to flow of ions)

Which type of myelination will allow action potential to travel faster?

more myelination

(Note: Na+ ions can't leak out, thereby driving saltatory conduction to occur faster)

What neurotransmitter is secreted at neuromuscular junctions and cause muscle contraction or relaxation?

Acetylcholine (Ach)

In the parasympathetic nervous system, Ach is released from which nerves?

pre and post ganglionic nerves

What enzyme breaks down Ach?

acetylcholinesterase

(Note: terminates the signal)

In what tissues is Ach found?

• nerve tissue

• muscle tissue

(Note: both central and peripheral tissues)

In which nerve fibers is Ach found?

sensory and motor fibers

What neurotransmitter is located at the neuromuscular junction in invertebrates?

Glutamate

(Note: most common CNS neurotransmitter in vertebrates. Is an amino acid)

What neurotransmitter is the inhibitory neurotransmitter among brain neurons

Gamma aminobutyric acid (GABA)

(Note: amino acid)

What neurotransmitter is the inhibitory neurotransmitter among synapses of the CNS outside the brain?

Glycine

(Note: amino acid)

What are the Amino acid-derived neurotransmitters (biogenic amines) that are secreted between neurons of the CNS?

epinephrine, norepinephrine, dopamine, and serotonin (5HT)

In which system do epinephrine/norepinephrine act?

sympathetic nervous system

From what nerves are epinephrine/norepinephrine released?

post ganglionic nerves

What neurotransmitters are short chains of amino acids and are a diverse group including substance P and endorphins?

neuropeptides

What neurotransmitters are not stored in vesicles and are actually synthesized and released into synapse directly?

gases

The autonomic and somatic nervous systems have which branches?

afferent (sensory) and efferent (motor) branches

Which division of the nervous system has sensory components which convey sensations from the eyes, nose, and other sensory organs to the brain + motor components transmitting impulses to the skeletal muscles?

somatic nervous system

Which division of the nervous system conveys sensory impulses form the blood vessels, heart, organs in the chest, abdomen, and pelvis via nerves to the brain. The motor component transmits signals to end organs.?

autonomic nervous system

Which nervous system consists of the interneurons, brain, and spinal cord?

central nervous system

The brain and spinal cord have three layers of protective covering called what?

meninges

(Note: right underneath the bone)

What are the layers of the meninges?

1. dura mater

2. arachnoid mater

3. pia mater

(Note: from outer to innermost layer)

Which meninges layer is the outermost layer; thick, protects brain and spinal cord, has vein-like structures to carry blood from brain back to heart?

dura mater

Which meninges layer is middle layer with a spiderweb-like appearance?

arachnoid mater

Which meninges layer is a delicate innermost membrane covering the brain and spinal cord?

pia mater

Which space in the meninges is filled with cerebrospinal fluid (CSF)?

between arachnoid and pia mater

What substance is produced by tissue called choroid plexus in fluid-filled compartments in the CNS called ventricles

cerebrospinal fluid (CSF)

Where are the choroid plexi located?

ventricles

(Note: fluid-filled compartments in the CNS)

What does CSF act as?

a cushion and shock absorber

What substance circulates chemical substances throughout the brain and into the spinal cord?

CSF

What are the two types of brain matter?

1. gray (outer cell bodies)

2. white (inner axons)

What are the three main regions of the brain?

1. forebrain

2. midbrain

3. hindbrain

What is the largest and most important brain region?

forebrain

(Note: contain cerebrum)

Which part of the forebrain processes sensory input, is important for perception, memory, voluntary movement, and learning?

cerebral cortex

Which part of the forebrain processes the sense of smell?

olfactory bulb

Which part of the forebrain relays sensory information between spinal cord and cerebral cortex?

thalamus

Which part of the forebrain is responsible for visceral function such as water balance, blood pressure regulation, temperature regulation, hunger, thirst, sex, circadian rhythms — circadian rhythms coordinated suprachiasmatic nucleus?

hypothalamus

Which part of the forebrain houses the centers for planning/learning movement sequences?

basal ganglia

Which part of the forebrain is important for memory consolidation and spatial navigation?

hippocampus

Which region of the brain is the relay center for visual and auditory impulses, and motor control?

midbrain