Week 8 - Nervous System

Question 1

What are the 3 basic functions of the nervous system?

Answer 1

three basic functions:
* sensory (input),
* integrative (process),
* and motor (output).

Question 2

What are the two main subdivisions of the nervous system?

Answer 2

1. CNS
   Brain & Spinal Cord
2. PNS
   All nervous tissue outside of the CNS
   Nerves, ganglia, enteric plexuses & secretory receptors

Question 3

What does the CNS do?

Answer 3

1. Processes sensory information
2. Source of thoughts emotions and memories
3. Stimulate muscles to contract, glands to secrete

Question 4

What is 3 systems make up the PNS? of?

Answer 4

Somatic Nervous System
Autonomic Nervous System
Enteric Nervous System

Question 5

What does the Somatic Nervous System do?

Answer 5

• Sensory neurons that conveys info to the SNS from
  somatic receptors in head body and limbs
  receptors for vision, hearing, taste and smell
• Motor neurons that conduct impulses from the CNS to the skeletal muscles only

Question 6

What does the Autonomic Nervous System do?

Answer 6

Sensory neurons that convey information to the CNS from receptors in visceral organs eg stomach and lungs
motor neurons that conduct nerve impulses from CNS to smooth muscles, cardiac mucles and glands

Question 7

Motor part of the ANS has two divisions - sympathetic and parasympathetic, what’s the difference?

Answer 7

Sympathetic - fight or flight
Parasympathetic - rest and digest

Question 8

What is the Enteric Nervous System and what 2 things does it monitor and what 2/3 things does it control?

Answer 8

Brain of the gut
Sensory neurons monitor
chemical and functional changes wihtin GI eg stretching of walls)

Motor neurons control
secretion of GI tract organs (eg stomach acid) & activities of GI endocrine cells (secrete hormones)
contractions of GI tract smooth muscle,

Question 9

What’s the difference between neurons and neuroglia?

Answer 9

Neurons form the complex processing networks within the brain and spinal cord, neurons also connect all regions of the body to the brain and spinal cord.
Neuroglia support, nourish, and protect neurons, and maintain the interstitial fluid that bathes them.

Question 10

What are the three parts of a neuron?

Answer 10

1. Cell body
2. Dendrites
3. Axon

Question 11

What’s the difference between a dendrite and an axon?

Answer 11

Dendrites recive info
Axons send it

Question 12

What is a synapse?

Answer 12

site of communication between two neurons or between a neuron and an effector cell

Question 13

Where are synaptic vesicles that store a chemical called a neurotransmitter located?

Answer 13

tips of some axon terminals swell into synaptic end bulbs ; others exhibit a string of swollen bumps called varicosities

Question 14

How are neurons classified, structurally?

Answer 14

1. Multipolar neurons usually have several dendrites and one axon
2. Bipolar neurons have one main dendrite and one axon
3. Unipolar neurons have dendrites and one axon that are fused together to form a continuous process that emerges from the cell body

Question 15

How are neurons classified, functionally?

Answer 15

1. Sensory (or afferent ) neurons - most are unipolar
2. Motor (or efferent ) neurons convey action potentials away from the CNS to effectors (muscles and glands) in the periphery (PNS) through cranial or spinal nerves - generally multipolar in structure.
3. Interneurons are mainly located within the CNS between sensory and motor neurons (processing the information and then eliciting a response) mainly multipolar

Question 16

What are the four types of CNS neuroglia?

Answer 16

astrocytes
oligodendrocytes
microglia
and ependymal cells

Question 17

What are the two types of PNS neuroglia that surround axons and cell bodies?

Answer 17

Scwann cells
Satellite cells

Question 18

What’s the difference between myelinated and unmyelinated?

Answer 18

1. Axons that are myelinated are covered in a myelin sheath which electrically insulates the axon of a neuron and increases the speed of nerve impulse conduction.
2. Axons without such a covering are said to be unmyelinated

Question 19

What is the difference between a nerve and a tract?

Answer 19

A nerve is a bundle of axons in the PNS
A tract is a bundle of axons located in the CNS

Question 20

What is Resting Membrane Potential?

Answer 20

A voltage difference on either side of the cell membrane, particularly important in muscle and nerve cells.
Caused by the ionic charge of the ions on each side of the membrane.

Question 21

What are the four types of ion channels?

Answer 21

1. Leak Channels
2. Ligand gated channel
3. Mechanically gated channel
4. Voltage gated channel

Question 22

How does a leak channel fn and where are they found?

Answer 22

leak channels randomly alternate between open and closed positions. Typically, plasma membranes have many more potassium ion (K + ) leak channels than sodium ion (Na + ) leak channels, and the potassium ion leak channels are leakier than the sodium ion leak channels.
Leak channels are found in nearly all cells, including the dendrites, cell bodies, and axons of all types of neurons.

Question 23

How does a ligand channel fn, and where are they found?

Answer 23

A ligand-gated channel opens and closes in response to the binding of a ligand (chemical) stimulus incl neurotransmitter acetylcholine, for example, opens cation channels that allow Na + and Ca 2+ to diffuse inward and K + to diffuse outward
Ligandgated channels are located in the dendrites of some sensory neurons, such as pain receptors, and in dendrites and cell bodies of interneurons and motor neurons.

Question 24

How does a mechanically gated channel fn and where are they found?

Answer 24

A mechanically gated channel opens or closes in response to mechanical stimulation in the form of vibration (such as sound waves), touch, pressure, or tissue stretching
and examplesare those found in auditory receptors in the ears, in receptors that monitor stretching of internal organs, and in touch receptors and pressure receptors in the skin.

Question 25

How do voltaged gated channels fn, and where are they found?

Answer 25

A voltage-gated channel opens in response to a change in membrane potential Voltage-gated channels participate in the generation and conduction of action potentials in the axons of all types of neurons.

Question 26

Describe the electrochemical basis of the resting membrane potential

Answer 26

1. Depolarisation: a decrease in the membrane potential – the inside of the membrane becomes less negative 1. Repolarisation: a return to resting membrane potential from a depolarised state – the inside of the membrane becomes more negative 1. Hyperpolarisation: an increase in the membrane potential – the inside of the membrane becomes more negative than resting membrane potential

Question 27

What's the difference between Graded & Action Potentials?

Answer 27

* Graded Potentials: Usually incoming signals operating over short distances that have variable strength. Triggered by a stimulus in the neurons environment that opens gated ion channels. * Action Potentials: long-distance signals of axons that always have the same strength.

Question 28

Name the two different graded potentials?

Answer 28

Given different names depending on where they occur and the function they perform * Receptor/Generator Potential: produced when a sensory receptor is excited by its stimulus (light, pressure, chemicals) * Postsynaptic potential: produced when the stimulus is a neurotransmitter released by another neuron

Question 29

What is summation?

Answer 29

Summation is the porcess by which graded potentials add together

Question 30

What are action potentials?

Answer 30

It is an all or nothing reaction. If depolarisation doesn’t meet a certain threshold the action potential does not occur If it reaches that threshold the action potential will occur. Unlike graded potentials they: do not decay with distance and are generated only in the axons. Also known as a nerve impulse

Question 31

What role do sodium-potassium pumps play in maintaining sodium and potassium concentration gradients and therefore the resting membrane potential?

Answer 31

Membrane permeability to Na + is very low because there are only a few sodium leak channels. Nevertheless, sodium ions do slowly diffuse inward, down their concentration gradient. Left unchecked, such inward leakage of Na + would eventually destroy the resting membrane potential. The small inward Na + leak and outward K + leak are offset by the Na + –K + ATPases (sodium– potassium pumps) . These pumps help maintain the resting membrane potential by pumping out Na + as fast as it leaks in. At the same time, the Na + –K + ATPases bring in K + . However, the potassium ions eventually leak back out of the cell as they move down their concentration gradient. Recall that the Na + –K + ATPases expel three Na + for each two K + imported

Question 32

Conduction speed - what is continuous conduction?

Answer 32

continuous conduction , involves step-by-step depolarisation and repolarisation of each adjacent segment of the plasma membrane In continuous conduction, ions flow through their voltage-gated channels in each adjacent segment of the membrane. Continuous conduction occurs in unmyelinated axons and in muscle fibres.

Question 33

Conduction speed - what is saltatory conduction?

Answer 33

Saltatory conduction is the special mode of action potential propagation that occurs along myelinated axons It occurs because of the uneven distribution of voltage-gated channels. Few voltage-gated channels are present in regions where a myelin sheath covers the axolemma. By contrast, at the nodes of Ranvier (where there is no myelin sheath), the axolemma has many voltage-gated channels. Hence, current carried by Na + and K+ flows across the membrane mainly at nodes

Question 34

Conduction speed - what factors effect conduction speed?

Answer 34

1. Amount of myelination. As you have just learned, action potentials propagate more rapidly along myelinated axons than along unmyelinated axons. 2. Axon diameter. Larger diameter axons propagate action potentials faster than smaller ones due to their larger surface areas. 3. Temperature. Axons propagate action potentials at lower speeds when cooled.

Question 34

What is a synapse?

Answer 34

A synapse is a region where communication occurs between two neurons or between a neuron and an effector cell (muscle cell or glandular cell).

Question 35

What is a presynaptic neuron?

Answer 35

a nerve cell that carries a nerve impulse towards a synapse. It is the cell that sends a signal.

Question 36

What is a postsynaptic neuron?

Answer 36

a postsynaptic neuron carries a nerve impulse away from a synapse or an effector cell (that responds to the impulse at the synapse).

Question 37

Synapses can be electrical or chemical - True or False?

Answer 37

True

Question 38

Describe how electrical synapses fn

Answer 38

Much less common than chemical synapses At an electrical synapse, action potentials (impulses) conduct directly between the plasma membranes of adjacent neurons through structures called gap junctions . Each gap junction contains a hundred or so tubular connexons, which act like tunnels to connect the cytosol of the two cells directly As ions flow from one cell to the next through the connexons, the action potential spreads from cell to cell. Gap junctions are common in visceral smooth muscle, cardiac muscle, and the developing embryo. They also occur in the brain.

Question 39

What are the two main advanatges of electrical synapses over chemical?

Answer 39

1. Faster communication. Because action potentials conduct directly through gap junctions, electrical synapses are faster than chemical synapses. 2. Synchronisation. Electrical synapses can synchronise (coordinate) the activity of a group of neurons or muscle fibres. The value of synchronised action potentials in the heart or in visceral smooth muscle is coordinated contraction of these fibres to produce a heartbeat or move food through the gastrointestinal tract.

Question 40

Describe how chemical synapses work

Answer 40

Although plasma membranes of presynaptic and postsynaptic neurons in a chemical synapse are close, they do not touch. They are separated by the synaptic cleft Nerve impulses cannot conduct across the synaptic cleft, so an alternative, indirect form of communication occurs. In response to a nerve impulse, the presynaptic neuron releases a neurotransmitter that diffuses through the fluid in the synaptic cleft and binds to receptors in the plasma membrane of the postsynaptic neuron. The postsynaptic neuron receives the chemical signal and in turn produces a postsynaptic potential, a type of graded potential.

Question 41

What's the difference b/w Excitatory & Inhibitory Postsynaptic Potentials (PSPs)?

Answer 41

A neurotransmitter that causes depolarisation of the postsynaptic membrane is excitatory because it brings the membrane closer to threshold - an excitatory postsynaptic potential (EPSP) . Although a single EPSP normally does not initiate a nerve impulse, the postsynaptic cell does become more excitable. Because it is partially depolarised, it is more likely to reach threshold when the next EPSP occurs. A neurotransmitter that causes hyperpolarisation of the postsynaptic membrane is inhibitory. During hyperpolarisation, generation of an action potential is more difficult than usual because the membrane potential becomes inside more negative and thus even farther from threshold than in its resting state.

Question 42

What are the two neurotransmitter receptor types?

Answer 42

Ionotropic Metabotropic

Question 43

How does an ionotropic receptor work?

Answer 43

When the correct neurotransmitter binds to the ionotropic receptor, the ion channel opens, and an EPSP or IPSP occurs in the postsynaptic cell. It is a type of ligand-gated channel

Question 44

How does an metabotropic receptor work?

Answer 44

Metabotropi receptors contains a neurotransmitter binding site but lacks an ion channel as part of its structure. However, a metabotropic receptor is coupled to a separate ion channel by a type of membrane protein called a G protein . When a neurotransmitter binds to a metabotropic receptor, the G protein either directly opens (or closes) the ion channel or it may act indirectly by activating another molecule, a ‘second messenger’, in the cytosol, which in turn opens (or closes) the ion channel Thus, a metabotropic receptor differs from an ionotropic receptor having components of different proteins.

Question 45

neurotransmitter can be excitatory at some synapses and inhibitory at other synapses, - true or false

Answer 45

true

Question 46

Removal of the neurotransmitter from the synaptic cleft is essential for normal synaptic function. How is the neurotransmitter removed (3 ways)?

Answer 46

Uptake by cells Diffusion Enzymatic Degradation

Question 47

What is the difference between spatial and temporal summation (postsynaptic potentials)?

Answer 47

A typical neuron in the CNS receives input from 1000 to 10 000 synapses. Integration of these inputs involves summation of the postsynaptic potentials that form in the postsynaptic neuron Many people voting ‘yes’ or ‘no’ on an issue at the same time can be compared to **spatial summation**. One person voting repeatedly and rapidly is like **temporal summation**. Most of the time, spatial and temporal summations are acting together to influence the chance that a neuron fires an action potential.

Question 48

PSPs can lead to three different outcomes. What are they?

Answer 48

1. EPSP. If the total excitatory effects are greater than the total inhibitory effects but less than the threshold level of stimulation, the result is an EPSP that does not reach threshold. 2. Nerve impulse(s). If the total excitatory effects are greater than the total inhibitory effects and threshold is reached, one or more nerve impulses (action potentials) will be triggered. 3. IPSP. If the total inhibitory effects are greater than the excitatory effects, the membrane hyperpolarises (IPSP). The result is inhibition of the postsynaptic neuron and an inability to generate a nerve impulse.