Unit 5 study guide

__ detect (direct) __ and send sensory signals to the spinal cord and brain.

receptors; stimuli

Name the structural organization of the nervous system (2 systems).

central nervous system (CNS) = brain and spinal cord
peripheral nervous system (PNS) = nerves and ganglia

What makes up the CNS? What does CNS stand for?

brain and spinal cord; central nervous system

What makes up the PNS? What does PNS stand for?

nerves and ganglia; peripheral nervous system

The sensory nervous system is also called the _ nervous system.

afferent nervous system

Name and describe the 2 divisions of the sensory nervous system.

somatic sensory system detects stimuli we consciously perceive
visceral sensory system detects stimuli we typically do not perceive
• for example, signals from the heart or kidneys

The motor nervous system is also called the _ nervous system.

efferent nervous system

Name and describe the 2 divisions of the motor nervous system.

somatic motor system sends voluntary signals to skeletal muscles
autonomic motor system (visceral motor) sends involuntary commands to heart, smooth muscle, and glands
• has sympathetic and parasympathetic divisions

What is the difference between the efferent and afferent nervous system?

afferent nervous system: receives sensory information from receptors and transmits it to CNS

efferent nervous system: initiates motor output and transmits it from CNS to effectors

The autonomic nervous system is broken down into what 2 divisions/systems?

sympathetic and parasympathetic

What is a nerve?

a bundle of parallel axons in the PNS

Name the 3 connective tissue wrappings that surround a neuron and know which layer is the innermost, middle and outermost layers.

epineurium: encloses entire nerve
• thick layer of dense irregular connective tissue
perineurium: wraps fascicle (bundle of axons in nerve)
• layer of dense irregular connective tissue
endoneurium: wraps an individual axon
• delicate layer of areolar connective tissue
• separates and electrically insulates each axon

True or False- neurons are vascular.

true

Name the 5 different classifications of nerves. Which one sends signals to the CNS? Which one sends signals from the CNS? Which classification contains both sensory and motor neurons?

sensory nerves contain sensory neurons sending signals to CNS
motor nerves contain motor neurons sending signals from CNS
mixed nerves contain both sensory and motor neurons
• most named nerves are in this category
• individual axons in these nerves transmit only one type of information

What is a ganglion? Define neurofilaments. Define neurofibrils.

ganglion is a cluster of neuron cell bodies in the PNS; neurofibrils: protein filaments that are present in all neurons

What is anterograde transport in relation to axons?

anterograde transport: from cell body
• moves newly synthesized material toward synaptic knobs

What is retrograde transport in relation to axons?

retrograde transport: to cell body
• moves used materials from axon for breakdown and recycling in soma

Define fast and slow axonal transport- what is the difference between these types of transport and why is there a difference in speed?

fast axonal transport
occurs at about 400 mm per day
involves movement along microtubules
powered by motor proteins that split ATP
anterograde or retrograde motion possible
• anterograde transport of vesicles, organelles, glycoproteins
• retrograde transport of used vesicles, potentially harmful agents
slow axonal transport
occurs at about 0.1 to 3 mm per day
results from flow of axoplasm
substances only moved from cell body toward knob
• enzymes, cytoskeletal components, new axoplasm

Name and describe the 3 structural classifications of neurons. Which one is the most common type of neurons?

multipolar neurons: many dendrites, one axon (most common type)
bipolar neurons: one dendrite and one axon (limited number; ex, in retina of the eye)
unipolar neurons (pseudounipolar): one process extends from cell body (splits into two processes)
• peripheral process splits into several receptive dendrites
• central process leads to synaptic knobs in CNS

True or False- there are neurons that do not have axons.

true

What are anaxonic neurons?

anaxonic neurons: have dendrites but no axons
• found in the brain and retina and also found in invertebrates
• considered non-spiking neurons- neurons that do not exhibit the
characteristic “spiking” behavior of action potential-generating
neurons. they work synergistically with other AP-generating
neurons while helping to modulate, or be a part of, the response

Name and describe the 3 functional classifications of neurons and know the differences between them. Which functional classification of neurons consists of mostly unipolar neurons? Which functional classification of neurons consists of mostly multipolar neurons (hint- there are 2)?

sensory neurons (afferent neurons)
conduct input from somatic and visceral receptors to CNS
• most are unipolar (a few bipolar)
motor neurons (efferent neurons)
conduct output from CNS to somatic and visceral effectors
• all are multipolar
interneurons (association neurons)
receive, process, and integrate information from many other neurons
communicate between sensory and motor neurons
• located within CNS; make up 99% of our neurons
• generally are multipolar

What is a synapse? What are the 2 types of synapses? Which one is more common?

synapse - place where a neuron connects to another neuron or an effector
two types: chemical and electrical
• chemical synapses are far more common than electrical synapses

What are the 2 types of synapses and know the differences between the two types. Name the two types of chemical synapses. What is the difference between these two types of synapses?

electrical synapse: presynaptic and postsynaptic neurons bound together by gap junctions (fast: no synaptic delay in passing electrical signal)

chemical synapse: presynaptic neuron’s axon terminal produces signal, postsynaptic neuron receives signal (most commonly with one of its dendrites)

What is the synaptic cleft and why it is important?

synaptic cleft: small fluid-filled gap between the two neurons; 

neurotransmitter molecules released from vesicles of synaptic knob into cleft; neurotransmitter diffuses across cleft and binds to postsynaptic receptors; binding of neurotransmitter to receptor initiates postsynaptic potential (a graded potential)

What is a synaptic delay?

synaptic delay: time it takes for all of these events

What are glial cells? What is another name for glial cells? Why do you have glial cells? Name the 4 types of glial cells that are specific to the central nervous system.

glial cells (neuroglia): nonexcitable, support cells found in CNS and PNS
approx. same number of glial cells as there are neurons; glial cells account for about half the volume of nervous system (4: astrocytes, ependymal, microglia, oligodendrocytes)
• capable of mitosis
• protect and nourish neurons
• provide physical scaffolding for nervous tissue
• guide migrating neurons during development
• critical for normal function at neural synapses

What are astrocytes? What is the function of astrocytes?

star-shaped cells (have processes that end in perivascular feet; most abundant glial cell in CNS)
help form blood-brain barrier by wrapping feet around brain capillaries (controls which substances have access to brain)
regulate tissue fluid composition (chemical environment around neurons; ex, can regulate potassium concentration)
form structural support for nearby neurons
assist neuronal development
alter synaptic activity (add, eliminate, influence)
occupy the space of dying neurons

What are ependymal cells? What is the function of ependymal cells?

ependymal cells- line cavities in brain and spinal cord; part of choroid plexus, which produces cerebrospinal fluid

What are microglia? What is the function of the microglia?

microglia- small cells that wander CNS and replicate in infection; phagocytic cells of immune system; engulf infectious agents and remove debris

What are oligodendrocytes? What is the function of ependymal cells?

oligodendrocytes- large cells with slender extensions; extensions wrap around axons of neurons forming myelin sheath

There are two types of cells found in the peripheral nervous system. Name and describe them and know the differences between them.

satellite cells- arranged around neuronal cell bodies in a ganglion—electrically insulate and regulate the exchange of nutrients and wastes
neurolemmocytes (Schwann cells)- elongated, flat cells that ensheath PNS axons with myelin—allows for faster action potential propagation

Neoplasms are __ of the nervous system. Glial cell tumors are also called _.

tumors; gliomas

True or False- All glial cell tumors are malignant.

false

What is myelination? What is myelin and why is it important in neurons?

myelination: process of wrapping an axon with myelin
myelin: several layers of membrane of glial cells
• high lipid content gives it glossy-white appearance and insulates axon
• the glia are neurolemmocytes in PNS; oligodendrocytes in CNS

What are myelin sheaths? Define the neurolemma. What are the nodes of Ranvier? If given a picture of a neuron, could you point out the nodes of Ranvier?

neurolemmocyte encircles neuron axon and wraps it in layers
forming myelin sheath
neurolemmocyte’s cytoplasm and nucleus are pushed to periphery
forming neurilemma
a neurolemmocyte can myelinate only 1 mm of axon, so several
are needed for one axon
gaps between neurolemmocytes are neurofibril nodes (nodes of
Ranvier)

True or False- one oligodendrocyte can myelinate one axon at a time.

false they can myelinate multiple axons at a time.

Describe Multiple Sclerosis. How does it occur?

multiple sclerosis- progressive demyelination of neurons in CNS—autoimmune disorder: oligodendrocytes attacked by immune cells—repeated inflammatory events causing scarring and permanent loss of function

Describe Guillain-Barre Syndrome. How does it occur? Know the difference between these two diseases.

guillain-barré syndrome- loss of myelin from peripheral nerves due to inflammation—muscle weakness begins in distal limbs, advances to proximal muscles—most function recovered with little medical intervention

In neuronal transport, which mechanism of transport is involved in moving materials against the concentration gradient?

pumps

In neuronal transport, which mechanism of transport is involved in moving materials with the concentration gradient?

channels

Name the two types of pumps that are involved in active transport in neurons (require energy).

calcium pumps and sodium-potassium pumps

Name the 3 types of channels that are involved in passive transport in neurons (do not require energy to move substances).

leaky channels, chemically-gated channels and voltage-gated channels

Name the 3 states of voltage-gated sodium (Na+) channels and know what is happening to the sodium ions in each channel. Why is this important? Why do you need to know this? Why are sodium ions necessary?

resting state
• activation gate closed; inactivation gate open
• entry of Na+ prevented
activation state
• activation gate open (due to voltage change); inactivation gate open
• Na+ moves through channel
inactivation state
• activation gate open; inactivation gate closed
• entry of Na+ prevented
• this state lasts a short time—the channel quickly resets to resting state

What type of pumps are necessary to maintain a resting potential?

Na+/K+ pumps

Name and describe the 4 different functional segments of the plasma membrane of a neuron. Which segment is made up the synaptic knobs? Which segment is made up the axon and its branches? Which segment is made up of the axon hillock? Which segment is made up of the dendrites and cell body of the neuron? Which functional segment(s) consists of chemically-gated channels? Which functional segment(s) consists of voltage-gated Na+ channels? Which functional segment(s) consist of voltage-gated calcium (Ca++) channels?

receptive segment (dendrite and cell body)
• chemically gated channels (For example, chemically gated Cl– channels)
initial segment (axon hillock)
• voltage-gated Na+ channels and voltage-gated K+ channels
conductive segment (axon and its branches)
• voltage-gated Na+ channels and voltage-gated K+ channels
transmissive segment (synaptic knobs)
• voltage-gated Ca2+ channels and Ca2+ pumps

What is electrical energy in association with neurons?

electrical energy = movement of charged particles
neuron activity dependent upon electrical current

What is voltage, current and resistance in relation to neurons?

voltage (V)
• amount of difference in electrical charge between two places,
represents potential energy (measured in volts or millivolts)
current (I)
• movement of charged particles across barrier separating them
• can be harnessed to do work
resistance (R)
• opposition to movement of charged particles (that is, the barrier)
• an increase in resistance lowers the current

What is Ohm’s Law and know the formula for it and what it represents in relation to neurons. Can you explain Ohm’s Law?

Ohm’s law
• current = voltage/resistance (I = V/R)
• current increases with larger voltage and smaller resistance
as applied to neurons
• charged particles are ions, and current is generated when
ions diffuse through channels
• voltage exists across the membrane due to unequal
distribution of ions
• the membrane offers resistance to ion flow, and this
resistance changes due to the actions of gated channels
• Resistance decreases when channels open

What are the characteristics of a neuron at rest? What is membrane potential? What is resting membrane potential (RMP) and what is the mV for RMP?

resting neurons- ions are unevenly distributed across the plasma membrane due
to the actions of pumps
• higher concentration of K+ in cytosol verses interstitial fluid (IF)
• higher concentrations of Na+, Cl–, Ca2+ in interstitial fluid (IF) than in cytosol
calcium concentration gradient exists at synaptic knob
gated channels are closed in the functional segments of the cell
membrane potential when there is an electrical charge difference across the membrane
• cytosol is relatively negative compared to IF
resting membrane potential (RMP) is typically –70 mV

What ion is important in setting the RMP?

Potassium (K+) diffusion

Potassium diffuses ____ of the cell due to its concentration gradient during RMP.

out

What ion, other than potassium, is important to RMP?

sodium (Na+)

Sodium diffuses ____ of the cell due to its concentration gradient during RMP. Answer:

in

When sodium diffuses into the cell, the RMP is more or less negative?

less negative changes from -90mV to -70mV

What is the role of sodium-potassium (Na+/K+) pumps to establish RMP?

by pushing 3 positive charges out and pushing in only 2, the pump contributes about –3 mV (of the –70 mV total)
more importantly, it maintains the concentration gradients for these ions

What are graded potentials? What are the characteristics of graded potentials? What 2 phenomena can graded potentials cause?

graded potentials are small, short-lived changes in the RMP with the following characteristics:
• they are established in the receptive segment by the opening of chemically gated ion channels
• local current changes are short-lived (a few ms or less)
• they vary in degree of change and direction of change of the RMP
• They can be large or small
can cause a depolarization or hyperpolarization

What are postsynaptic potentials? What is EPSP? What is IPSP? What causes EPSPs?

graded potentials in a postsynaptic neuron = postsynaptic potentials

EPSP (excitatory postsynaptic potential): depolarization-sodium ions entering the neuron—

IPSP(inhibitory postsynaptic potential): potassium (K+) ion entry and chloride (Cl-) ion exit from the neuron

What is summation and when does it occur? What is the threshold membrane potential? What voltage is achieved at threshold?

summation of EPSPs and IPSPs occurs at axon hillock
• voltage changes from the dendrites and soma are added
• the sum may or may not reach threshold membrane potential for initiating an action potential (threshold is the minimum voltage change required; -55mV)

True or False- Multiple IPSPs must be added to reach threshold membrane potential.

false- Multiple EPSPs must be added to reach threshold membrane potential.

What is summation and where does it occur on the neuron? Name and describe the differences between spatial and temporal summation.

If threshold is reached at the axon hillock (initial segment)
• voltage-gated channels open, and an action potential is generated

spatial summation
• multiple locations on cell’s receptive regions receive
neurotransmitter simultaneously and generate postsynaptic
potentials
temporal summation
• a single presynaptic neuron repeatedly releases neurotransmitter
and produces multiple EPSPs within a very short period of time

What is the “all or none law?”

if threshold reached, action potential generated and propagated down axon without any loss in intensity—if threshold not reached, (stimulus is subthreshold), voltage-gated channels stay closed, no action potential—the axon shows same intensity of response to values greater than threshold

ex: similar to what occurs with a gun
• with sufficient pressure on trigger, gun fired
• with insufficient pressure on trigger, not fired
• firing is the same even if trigger squeezed very hard

What happens when the threshold membrane potential is met? What happens when the threshold membrane potential is not met?

if threshold reached, action potential generated and propagated down axon without any loss in intensity—if threshold not reached, (stimulus is subthreshold), voltage-gated channels stay closed, no action potential

True or False- the higher the voltage, the more intense response from a neuron?

false-the axon shows same intensity of response to values greater than threshold

Where is an impulse conducted in a neuron?

the cell membrane of the axon, known as the axolemma

What 2 steps are involved in conducting an action potential?

depolarization and repolarization

Define depolarization and repolarization. What is happening with different ions at both of these steps along the axolemma. Which ions are entering the axon? Which ions are leaving the axon during an action potential to keep the AP (action potential) moving along down the axon?

depolarization is gain of positive charge as Na+ enters through voltage-gated Na+ channels
repolarization is return to negative potential as K+ exits through voltage-gated K+ channels (K+ channels stay open for a longer time, so K+ exit makes cell more negative than RMP (hyperpolarization))

Action potentials are propagated down the axon to the_.

synaptic knob

While an AP is moving down the axolemma, _ channels are opening down the axolemma.

voltage-gated

Propagation is called a _.

nerve signal or nerve impulse

Describe the 5 steps that are occurring during an action potential. Know what channels are opened and closed and what ions are moving in relation to an AP. Which steps are part of the depolarization of an AP? Which steps are part of the repolarization of an AP?

1. As Na+ enters from adjacent region, voltage-gated Na+ channels open
2. Na+ enters the axon causing the membrane to have a positive potential Inactivation state: Na+ channels close becoming inactive (unable to open) temporarily
(steps 1-2 repeat in adjacent regions and the impulse moves toward synaptic knob)
3. Depolarization slowly opens K+ channels, and K+ diffuses out, causing negative membrane potential
4. K+ channels stay open for a longer time, so K+ exit makes cell more negative than RMP (hyperpolarization) K+ channels
5. K+ channels eventually close and RMP is reestablished (steps 3-5 repeat in adjacent regions as the impulse moves toward synaptic knob)

What is a refractory period? What is the difference between an absolute refractory period and a relative refractory period?

refractory period- period of time after start of action potential when it is impossible or difficult to fire another action potential
absolute refractory period (about 1 ms)- no stimulus can initiate another action potential—na+ channels are open, then inactivated—ensures propagation goes toward synaptic knob; doesn’t reverse direction
relative refractory period (just after absolute)- another action potential is possible (Na+ channels have reset) but the minimum stimulus strength is now greater—some K+ channels are still open; cell is slightly hyperpolarized and
further from threshold

What is continuous conduction and saltatory conduction? What is the difference between these two phenomena?

continuous conduction occurs on unmyelinated axons— charge opens voltage-gated channels, which allows charge to enter, which spreads to adjacent region and opens more channels, sequentially— action potential occurs along entire length of axon

saltatory conduction occurs on myelinated axons— action potential occurs only at neurofibril nodes, which is where the axon’s voltage-gated channels are concentrated— after Na+ enters at a node it starts a rapid positive current down the inside of the axon’s myelinated region— the current becomes weaker with distance, but still strong enough to open voltage-gated channels at the next node— action potential occurs at the node, and the process repeats at the next node; impulse appears to jump from node to node— saltatory conduction is much faster than continuous conduction and myelinated cells use less ATP to maintain resting membrane
potential

True or False- An action potential occurs along the entire length of an axon.

true

Activity at the synaptic knob describes which segment of an AP?

transmissive

What channels are opened up at the synaptic knob during an AP? Why is the opening of these channels necessary in the process of propagating an AP? What is released as a result of these channels opening up at the synaptic knob?

voltage gated Ca++; Ca2+ binds to proteins associated with synaptic vesicles and
triggers exocytosis; vesicles fuse with membrane, neurotransmitter released; neurotransmitter binds to ligand receptors

What is the difference between graded and action potentials?

graded potentials
• occur in neuron’s receptive region due to ion flow through chemically gated channels
• can be positive or negative changes in charge
• are graded: have larger potential change to stronger stimulus
• are local (travel only a short distance)
action potentials
• occur on neuron’s conductive region (axon) due to ion flow through voltage-gated channels
• involve depolarization (Na+ in) then repolarization (K+ out)
• are all or none once threshold is reached
• propagate down entire axon to synaptic knob

Conduction speed of an AP depends on what 2 factors on a neuron? Explain how these 2 characteristics determine the speed of an diameter and myelination. Explain how these 2 characteristics determine the speed of an AP. For example- does an impulse travel faster with or without a myelinated axon? Does an impulse travel faster with a larger axon diameter or with a smaller axon diameter?

axon diameter and myelination; thicker fibers conduct faster than thin ones
• thick axons offer less resistance to current flow down the axon
myelinated fibers conduct much faster than unmyelinated ones
• current flow under myelin (between nodes) is very fast

What makes up an axon fiber? There are 2 types of nerve fibers- name and describe them. Which one is faster?

nerve fiber: an axon and its myelin sheath
group A: conduction velocity as fast as 150 m/sec
• large diameter, myelinated fibers
• ex, most somatic sensory neurons; all somatic motor neurons
group B: conducts at 15 m/sec; Group C: at 1 m/sec
• small diameter and/or unmyelinated
• ex, some visceral neurons; some somatic sensory
neurons from skin

Change in voltage is known as _.

amplitude

True or False- during an AP, the change in voltage is always consistent, but the firing frequency varies with the strength of the actual stimulus.

true

What causes an AP to generate more tension?

fire at faster frequency (motor nerves fire)

What are neurotransmitters and what are their functions?

neurotransmitters:
1. are synthesized by neurons and stored within vesicles in synaptic knobs
2. are released from the vesicles when action potential triggers calcium entry into synaptic knob
3. bind to a receptor in a target cell
4. trigger a physiologic response in the target cell

True or False- there are only 5 different types of neurotransmitters currently known to science.

false- there are approximately 100 different neurotransmitters known to science

Name the chemical neurotransmitter involved in muscle contraction (which you learned in the last unit) and Aps. This neurotransmitter is utilized in the _ system to stimulate skeletal muscle. In the ____ system, this transmitter is utilized to increase arousal.

acetylcholine; peripheral nervous system; central nervous system

What type of enzyme breaks down this chemical neurotransmitter?

acetylcholinesterase

How can the neurotransmitters be removed from the synaptic cleft? Why is this necessary in an AP? How are neurotransmitters involved for treating depression?

enzymes might degrade neurotransmitter
presynaptic transporters might import neurotransmitter (“reuptake”)
some neurotransmitter diffuses away from synapse, reabsorbed by glia
some drugs have their effect by influencing transmitter removal
• ex, selective serotonin reuptake inhibitors treat depression

Name and describe the 4 major brain regions.

cerebrum (two hemispheres; five lobes per hemisphere), diencephalon, brainstem, cerebellum

What are gyri? What are sulci? What are fissures? Can you tell the difference between these three surface features on the brain?

gyri- ridges; sulci- depressions between ridges; fissures- deep sulci

What is the difference between the terms rostral and caudal when referring to the brain?

anterior = rostral; posterior = caudal

What does TBI stand for and what causes it?

traumatic brain injury (TBI)- acute brain damage occurring as a result of trauma

Describe a concussion and now the difference between a concussion and a contusion.

concussion- most common type of TBI
• temporary loss of consciousness, headache, drowsiness, confusion, and amnesia possible
• may have cumulative effect on intellect, personality, mood
contusion
• Bruising of brain due to trauma
second impact syndrome (2nd injury before 1st resolves)
• develop severe brain swelling
progesterone is possibly therapeutic for TBI

Embryologically, the brain and spinal cord begin as a _.

neural tube

Name the 3 primary brain vesicles. Which one is commonly called the hindbrain? Which one is commonly called the midbrain? Which one is commonly called the forebrain?

forebrain= prosencephalon

midbrain= mesencephalon

hindbrain= rhombencephalon

What are the 5 secondary brain vesicles? Which secondary vesicle develops into the medulla oblongata? Which secondary vesicle develops into the pons and cerebellum? Which secondary vesicle develops into the midbrain? Which secondary vesicle develops into the thalamus, hypothalamus and epithalamus? Which secondary brain vesicle becomes the cerebrum?

telencephalon becomes cerebrum
diencephalon becomes thalamus, hypothalamus, epithalamus
mesencephalon becomes midbrain
metencephalon becomes pons and cerebellum
myelencephalon becomes medulla oblongata

Name the 3 things that make up gray matter. What is the superficial layer of gray matter called? Clusters of cell bodies are known as ____, which are regions of grey matter on the surface or deep within the brain.

gray matter made of neuron cell bodies, dendrites, and unmyelinated axons; cortex superficial layer; nucleus

What is white matter consisted of? Organized bundles of white matter are called .

white matter consist of myelinated axons; tracts

Name the 4 things that actively protect the brain? What does CSF stand for?

bone of the skull, meninges, cerebrospinal fluid (csf) (liquid cushion), blood brain barrier (controls what passes from blood to brain, glial cells (support cells) provide the separation of blood from brain components.)

Name the 3 cranial meninges from deep to superficial. Name the 3 cranial meninges from superficial to deep. What are the 3 functions of your meninges?

superficial to deep: dura mater, arachnoid mater, pia mater;

pia mater- innermost of the meninges; adheres to brain surface

arachnoid mater- lies external to pia mater (arachnoid trabeculae (superficial) extend to pia mater through subarachnoid space; subarachnoid space (deep) contains cerebrospinal fluid) made of a web of collagen and elastic fibers; lies deep to dura mater; subdural space is a potential space that can fill with blood if a vein is ruptured

Which meninges adheres directly to the brain’s surface?

pia mater