Ch. 12 Nervous Tissue and Neurophysiology

Question 1

What are the structural divisions of the nervous system?

Answer 1

1) Central nervous system CNS
Brain and spinal cord of dorsal body cavity, integration and control center (interpret sensory input and dictates motor output)

2)Peripheral nervous system. PNS
The portion of the nervous system outside the CNS, consist mainly of nerves that extend from the brain and spinal cord. Contains sensory and motor fibers. (spinal nerves two and from spinal cord - cranial nerves to and from brain)
- sensory (afferent) division
- motor (efferent) division

3) PNS - sensory division - the sensory division contains:
- somatic sensory fibers which convey impulses from skin, skeletal muscles and joint to CNS
- visceral sensory fibers which convey impulses from visceral organs to CNS

4) PNS - motor division - transmit impulses from CNS to effector organs, the muscles and glands. It contains two divisions, the somatic nervous system. (voluntary nervous system.) and the autonomic nervous system(involuntary nervous system)

Question 2

What are the functions of the nervous system

Answer 2

Sensory input - information is gathered by millions of sensory receptors about internal and external changes

Integration - the nervous system processes and interprets the sensory input (reflexes)

Motor input - the nervous system activates effector organs (muscles and glands) and produces a response

Question 3

Sensory (afferent) division

Answer 3

Somatic sensory fiber - convey impulses from the skin, skeletal muscle and joints to CNS

Visceral sensory fibers - convey impulses from visceral organs to CNS

Question 4

Motor (efferent) division

Answer 4

Transmit impulses from CNS to effector organs (muscles and glands)

Two divisions
- somatic nervous system
- autonomic nervous system

Question 5

Describe this somatic nervous system

Answer 5

The somatic nervous system is composed of somatic motor nerve fibers
- conduct impulses from CNS to skeletal muscle
- it is often referred to as a voluntary nervous system because it allows us to voluntary contract out muscles

Question 6

Describe the autonomic nervous system

Answer 6

The autonomic nervous system consist of visceral motor fibers that regulate smooth muscle, cardiac muscle and glands

It is often referred to as the involuntary nervous system

Two functional subdivisions
- Sympathetic
- parasympathetic
Opposition to each other (one stimulates, the other inhibits)

Question 7

Levels of organization in the nervous system

Answer 7

Question 8

Identify the types of cells found in the nervous system

Answer 8

CNS
Astrocytes
Microglial cells
Ependymal cells
Oligodendcytes
PNS
Satelite cells
Schwann cells

Question 9

Astrocytes

Answer 9

Most abundant glial cell of the CNS; physically support neurons
- Highly branched their process, clings to neurons, synaptic, endings and capillaries

Exchanges between capillaries and neurons
Guide migration of neurons and the formation of synopsis between neurons
Control chemical environment around neurons
Respond to nerve impulses and releases neurotransmitters
Participate in information processing in brain
Role in neuron-inflammation

Question 10

Microglial cell

Answer 10

Defensive cells of the CNS - have phagocytic activity

Small, ovoid cells with thorny processes that monitor neurons
Sense and migrate toward injured neurons
Can transform to phagocytize microorganisms and neuronal debris

Question 11

Ependymal cells

Answer 11

Line the cavities of the CNS where they form a permeable barrier between CSF and cells of CNS

Ependymal cells formed the epithelial lining of the ventricles of the brain and central canal of the spinal cord
They form a permeable barrier between cerebrospinal fluid (CSF) in the cavities and brain or spinal cord tissue
May be ciliated - help circulate CSF

Question 12

Oligodendrocytes

Answer 12

Oligodendrocytes are moderately branch cells
Their processes wrap CNS nerve fibers, forming insulated Mylin sheets around thicker nerve fibers

Question 13

Satellite cell

Answer 13

Surround and support neurons cell bodies in the PNS
- Function similar to astrocytes of CNS

Question 14

Schwan cells (neurolemmocytes)

Answer 14

Surround all nerve fibers in the PNS and form the myelin sheath in thicker nerve fibers

• Function as Oligodendrocytes (Were they playing important role in nerve impulse transmission speed
• Vital to regeneration of damaged, peripheral nerve fibers

Question 15

Neuron

Answer 15

Large, highly specialized cells that transmit impulses from one part of the body to another (main impulse transmitting cells of the nervous system)

Question 16

Describe and identify the structure and function of neurons

Cell body
Nucleus
Dendrites
Axon
Axon hillock
Myelin sheath

Answer 16

Question 17

Describe the two main functions of the myelin sheath

Answer 17

Function of the mylin sheet is to protect and electrically insulate the axon - increase speed of nerve impulses.

Because voltage gated ion channels are only found in the gaps, action potential seem to “jump” from gap to gap, rather than having to travel continuously down the axon

Myelinated fibers conduct nerve impulses quickly, whereas nonmyelinated fibers conduct impulses more slowly(dendrites are always nonmyelinated)

Question 18

Describe how the myelin sheath is created and how this differs in the CNS and PNS

Answer 18

PNS - myelin sheath are formed by schwann cells
- wraparound axon in Jelly roll fashion
- One cell forms, one segment of myelin sheath
- The contents of the cytoplasm end up squeezed into a ridge.

CNS - myelin sheaths our formed by multiple flat processes of Oligodendrocytes not whole cells oligodendrocytes not whole cells
- Can wrap up to 60 axons at once
- myelin sheath gap is present
- No outer ridge of cytoplasm

Question 19

Describe an identify the three “structural classifications” of neurons

Answer 19

Question 20

Describe the three “functional classifications” of neurons

Answer 20

Functionally, neurons are grouped by the direction in which nerve impulse travels relative to CNS
SENSORY (afferent) (in) FUCK AROUND
- transmit impulses from sensory receptors towards CNS
- almost are all our unipolar
- Cell bodies are sensory ganglia located in the PNS
MOTOR (efferent) (out) FIND OUT
- Carry impulses from CNS to effectors
- multipolar
- most bodies in CNS
(except some autonomic neurons)
INTERNEURONS (association neurons)
- 99% of bodies neurons
- lay between motor and sensory neurons
- shuttle signals through CNS pathways
- are multipolar
- mostly confined in CNS

Question 21

Explain what resting membrane potential is and how it’s maintained

Answer 21

Resting membrane potential is created by the differential permability of NA+ and K+ in the neurons plasma membrane. The extra cellular fluid (ECF) has a higher concentration NA+ than the intercellular fluid (ICF). The NA concentration is balanced by Cl- ions. The ICF has a higher concentration of K+ than the ECF. The concentration is balanced by negatively charged proteins, equalizing the two fluids inside and outside the cell.

The cell membrane is slightly permeable to NA+ (through leakage channels) and NA+ diffuses into the neuron down its concentration gradient. The cell membrane is 25X more permeable to K+ than NA+ (more leakage channels) and K+ diffuses out of the cell down its concentration gradient. Overall more K+ diffuses out than Na+ diffuses in which leaves a cell more negative inside the membrane than outside. (because of the negatively charged proteins) This is what establishes resting membrane potential.

Potential is maintained by NA+ & K+ pumps, which maintain the concentrate gradients for an NA+ & K+ by continually pumping back out of the cell and back into the cell (this creates the gradient so they can right back out)

Question 22

Describe the two ways that membrane potential can be changed

Answer 22

Membrane potential can be changed by ion concentrations across the membrane and/or changes in membrane permeability to ions.

These can lead to depolarizations - a decrease in membrane potential, or hyperpolarizations - an increase in membrane potential

Question 23

Differentiate between depolarization and hyperpolarization

Answer 23

Depolarization: there is a decrease in membrane potential (towards zero and above). the inside of the membrane becomes less negative than the resting membrane potential depolarization increase the probability of producing a nerve impulse

Hyperpolarization: in a hyperpolarization, there is an increase in membrane potential (away from zero). The inside of the cell becomes more negative than the resting membrane potential hyperpolarizations reduce the probability of producing a nerve impulse.

Question 24

Describe a graded potential - what they are used for what triggers them were they occur and why are they so short-lived?

Answer 24

Graded potentials are short-lived, localized changes and membrane potential which can either be excitatory, (causing a depolarization) or inhibitory (causing a hyper polarization). They are short lived because the change in membrane potential is localized and decays overtime this is why graded potentials are signals only over short distances. This is because the ion channels involved in graded potentials are ligand-gated not voltage-gated (thus you don’t see the positive feedback mechanism or change in membrane). Potentials opens the next set of gates, etc.). They occur at dendrites or on the cell body. Graded potentials are triggered by some external stimulus that opens a ligand-gated or mechanically-gated ion channels usually a neurotransmitter. Typically graded to potentials occur before action potentials (if they are strong enough to trigger one).

Question 25

Describe action potential

Answer 25

Action potentials are the principal means of long-distance neural communication. They only occur in muscle cells and the axons of neurons and action potential a brief reversal of membrane potential with a change in voltage of 100mV. Unlike graded potential action potential did not decay over distance. Action potentials are triggered by membrane depolarization that reach threshold. Great potentials are responsible for the initial depolarization.

Question 26

Describe the four steps of an action potential

Answer 26

1. Resting potential. - all gated NA and K channels are closed only ligand-gated channels for NA+ K+ are open which maintains the resting membrane and potential. 2. Depolarization - as local currents (graded potentials) depolarize the axon membrane voltage gated NA channels open and NA+ rushes into the cell. The influx causes depolarization more channels open , and the ICF becomes less negative. At threshold (-55 to -50mV) positive feedback causes opening of all NH channels and results in reversal of membrane polarity to +30mV. 3. Repolarization - the slow inactivation gates of the of the NA channels began to close and membrane permeability to NA declines to resting levels. At the same time low-voltage gated K channels open and K exit the cell following its electrochemical gradient, and the interior of the cell becomes negative once again 4. Hyperpolarization-after the repolarization of the membrane channels remain open, allowing excessive K to leave the cell. This results in the inside of the membrane more negative than the resting state. This causes a hyperpolarization of the membrane a (slight debt below resting voltage). At the same time NA channels begin to reset to the original position by changing shape to reopen their inactivation gates and close their activation gates.

Question 27

Describe how an action potential is propagated down the axon why does it only go in one direction?

Answer 27

When any channels are open during a depolarization NA+ ions rush in once; inside the cause nearby regions of the neuron to become depolarized by moving laterally through the axon. This in turn causes the opening of more voltage-gated NA+ channels in those regions. Thus the NA+ channel activation moves in a wave like fashion - A.P. is propogated down the length of the axon to the synaptic terminals. The NA+ channels have a mechanism that avoids “back propagation” of the AP potential which could result in a confused signal. After opening the NA+ channels become inactivated as a potential becomes more positive and they cannot open again until they are “reset” by hyperpolarization at the end of an AP. This brief period of NA+ channel inactivation is called a refractory period, prevent bidirectional propagation of the AP constraining it to only go in one direction.

Question 28

What are three functions of the nervous system

Answer 28

Sensory input- information is gathered by millions of sensory receptors about internal and external changes Integration - The CNS processes and interprets the sensory input. Motor output - The nervous system activates effector organs ( muscles and gland) and produces a response

Question 29

Neuroglia

Answer 29

Cells which support neurons both functionally and structurally

Question 30

Most common type of neuron

Answer 30

Multipolar

Question 31

Rare type of neuron

Answer 31

Bipolar

Question 32

Neuron found mainly in the PNS

Answer 32

Unipolar

Question 33

Neuron which would connect to a muscle

Answer 33

Multipolar

Question 34

Neuron which would be found in the retina of the eye

Answer 34

Bipolar

Question 35

Neurons that connect impulses along afferent pathways to CNS

Answer 35

Unipolar

Question 36

Describe the function of a synapse

Answer 36

Synopsis are junctions at mediate the information transfer Synopsis connect one neuron, another neuron or neuron an effector cell (muscle or gland)

Question 37

Identify the structure and function of a synapse

Answer 37

Question 38

Describe the difference between pre-synaptic and postsynaptic neurons

Answer 38

Pre-synaptic neuron The pre-synaptic neuron is the neuron conducting impulses toward the synapse SENDS THE INFORMATION Synaptic neuron (in PNS may be a neuron, muscle cell, or gland cell) The post-synaptic neuron is the neuron transmitting electrical signals away from the synapse RECEIVES THE INFORMATION

Question 39

Describe how an action potential moves from a pre-synaptic neuron to a post-synaptic neuron

Answer 39

AP arrives at axon terminal vaulted-gauges CA channels open allowing CA to enter the axon terminal CA causes vesicles to fuse with terminal endings and release their products (neurotransmitters) via exocytosis Neurotransmitters diffuse across the synaptic cleft Neurotransmitters bind to ligand-gated channels, allowing ions to flow in/or out of the cell resulting in grated potential Neurotransmitters are rapidly degraded or flushed away from the receptors

Question 40

Differentiate between EPSP and IPSP ( i.e. graded potentials)

Answer 40

ESPS’s are a temporary depolarization of the postsynaptic membrane caused by the flow of positively charged ions into postsynaptic cell as revolved of a opening of a ligand-gated ion channels (by binding excitatory neurotransmitters for example) A postsynaptic potential is defined as EXCITATORY if it makes the neuron more likely to fire an action potential. ISPS’s reduce the postsynaptic neurons ability to produce an action potential. They are caused by the binding of inhibitory neurotransmitters at inhibitory synapses - these hypopolarize the postsynaptic cell membrane by making it more permeable to K or CL ( ultimately making it more negative)

Question 41

Summation

Answer 41

To influence the activity of a post-and optic neuron

Question 42

Temporal summation

Answer 42

One or more presynaptic neurons transmit impulses in rapid-fire order

Question 43

Spatial summation

Answer 43

Postsynaptic neuron stimulated simultaneously by large number of terminals at same time

Question 44

Describe the summation in EPSP’s including temporal and spatial summation. Are ISPS’s also sensitive to summation

Answer 44

A single EPSP cannot induce an action potential. If many excitatory axon terminals fire upon the same postsynaptic, neuron (spatial summation) or if a small number of axon terminals fire rapidly (temporal summation) the probability of reaching threshold increases. In this way, EPSP’s can summate or add together to influence the activity of a postsynaptic neuron. IPSP’s are also sensitive to summation.

Question 45

List the neurotransmitters found in the nervous system

Answer 45

Acetylcholine Biogenic amines (which include dopamine, norepinephrine, serotonin,histamine) GABA Glutamate Endorphins Nitric oxide

Question 46

Acetylcholine

Answer 46

Acetylcholine is an EXCITATORY neurotransmitter at neuromuscular junctions in skeletal muscle. In cardiac tissue acetylcholine has INHIBITORY effect which lowers heart rate. In the CNS it acts as a neural modulator alters the way the brain processes information.

Question 47

Biogenic amines (which include dopamine, norepinephrine, serotonin, histamine)

Answer 47

The biogenic amines play major rules in learning emotions and mood most can be both excitatory and inhibitory, depending on receptor types

Question 48

GABA

Answer 48

GABA is a principle inhibitory neurotransmitter in the brain. It is involved with cortical function, such as motor commission control, and vision. It may also play an anti-anxiety role. Alcohol mimics, GABA and binds to receptors = an agonist.

Question 49

Glutamate

Answer 49

Glutamate is the main EXCIATORY neurotransmitter in the brain, it is important in cognition, memory, and learning

Question 50

Endorphins

Answer 50

Endorphins are generally inhibitory they have many functions. They act as natural opiates to reduce pain perception.

Question 51

Nitric Oxide

Answer 51

Can be excitatory or inhibitory Important in vasodialation

Question 52

Differentiate between neurotransmitters that act directly versus those act indirectly

Answer 52

Direct acting neurotransmitters - are those that find two and open ion channels are direct acting. they promote rapid responses by altering membrane potential (I.e. lead to the deep polarizations of hyperpolarizations) Indirect acting neurotransmitters - are those that act through second messengers they do not bind to receptor to produce a direct response may influence the strength of synaptic transmission influence re-uptake of neurotransmitters module other neurotransmitter activity or membrane sensitivity to a neurotransmitter they generally have longer lasting affect, similar to hormones