Chapter 11.1

Question 1

Nervous and endocrine systems work together to maintain what?

Answer 1

homeostasis

Question 2

homeostasis

Answer 2

maintaining internal balance

Question 3

general functions of nervous system

Answer 3

a. reception of stimuli and conduction of impulses (message) to the central nervous system (CNS)
b. interpretation of impulse - followed by decisions
c.sorting of impulses and setting priorities for actions upon them (insignificant info is ignored while urgent info is given priority)
d. transmission- impulses to effectors - carry out appropriate activities

Question 4

nervous system composed to two main types of cells

Answer 4

1) neurons
2) glial cells

Question 5

1) neurons

Answer 5

basic structural, functional unit of nervous system
- specialized to respond to both physical and chemical stimuli
- conduct electrochemical signals (impulses)
-release chemicals that regulate various body processes
individual neurons (nerve fibres) are organized into tissues called nerves

Question 6

2) Glial cells (aka glia)

Answer 6

• non conducting cells
• outnumber neurons by 50:1
• nourish neurons, remove their waste and defend against infection
• also provide supporting framework for the nervous system tissue

Question 7

Sensory neurons

Answer 7

• relay information about the environment to the CNS for processing (e.g) eyes- light, skin-pressure and temp)
• cell body found midway through the axon
• myelinated

Question 8

interneurons

Answer 8

• link neurons within body
• found mainly in brain and spinal cord
• integrate and interpret sensory info & connect to outgoing motor neurons
• unmyelinated and shorter in length

Question 9

motor neurons

Answer 9

• relay info from cns to effectors (muscles, glands)
• myelinated

Question 10

four common features of neurons

Answer 10

dendrites, cell body, axon, axon terminals

Question 11

Dendrites

Answer 11

• numerous and highly branched to increase surface area to receive incoming signals from specialized receptors or other neurons
• conduct nerve impulses toward to the cell body

Question 12

cell body (soma)

Answer 12

• receives impulse from dendrites- then spreads over the cell body and through to the axon (acts as a bridge)
• contains all major cellular organelles (nucleus, ER, ribosomes, etc)

Question 13

Axon

Answer 13

• conducts nerve impulses away from cell body
• range in length from 1mm to 1m depending on neurons location in body
• carries nerve impulses towards other neurons or to effectors

Question 14

myelin sheath

Answer 14

In many vertebrates, axons that convey signals rapidly are enclosed, along most of their length, with a thick insulating material.
- resembles a chain of oblong beads

Question 15

schwann cell

Answer 15

type of glial cell that wraps many times around the axon

Question 16

spaces between schwann cells

Answer 16

nodes of ranvier

Question 17

nerves within the brain contain:

Answer 17

myelinated fibres and neurilemma - called white matter
myelin- white fatty protein
- unmyelinated- grey matter

Question 18

neurilemma

Answer 18

all nerve fibers within the PNS contain a thin membrane, called neurilemma
- surrounds the axon and promotes regeneration of damaged axons

Question 19

Axon terminal

Answer 19

at the end of the axon- branches off to form axon terminals
- axon terminals store neurotransmitters- chemicals that will be released to carry the message across the synapse (space between neurons) to a dendrite of another neuron or an effector

Question 20

Reflex arc

Answer 20

1. receptor
   2.sensory neuron
   3.interneuron in the spinal cord
   4.motor neuron
   5.effector

Question 21

the nerve impulse

Answer 21

neurons establish a voltage difference between the inside and the outside of the cell membrane. This difference is used to generate a neural impulse

Question 22

The electrical nature of nerves

Answer 22

Nerve conduction depends on the movement of ions across the cell membrane of an axon. The charge separation across the membrane is a form of potential energy or membrane potential

Question 23

Non-Voltage Gated Ion Channels

Answer 23

-some are open all the time
-some are stimulated by chemicals to open/close
-ions move via diffusion

Question 24

Voltage gated Ion Channels

Answer 24

• Stimulated by specific charge to open/close.
• ions move via diffusion

Question 25

Na+/K+ pump

Answer 25

- always active - utilizes ATP to actively transport ions across the membrane

Question 26

Resting membrane potential

Answer 26

the potential difference across the membrane in a resting neuron - in most neurons = -70mV - Negative on INSIDE relative to outside

Question 27

Polarization

Answer 27

process of generating a resting membrane potential. The resting membrane is said to be charged or polarized with the potential to do work.

Question 28

How is polarization achieved? Small contributor:

Answer 28

Intercellular fluid exists inside the neuron. The fluid contains large negatively charged protein molecules (cannot escape cell due to size) and small negatively charged ions (Cl-) (cannot escape due to selectively permeable membrane)

Question 29

How is polarization achieved? Most Important contributor:

Answer 29

The sodium-potassium exchange pump in the axon membrane - uses ATP to pump 3 Na+ OUT of the axon and 2K+ ions INTO the axon - An excess of positive charge accumulated outside of the cell.

Question 30

Excitation of the neuron definition:

Answer 30

The action potentials (nerve impulses) occur in the axons of neurons and in the dendrites of certain sensory cells. A nerve impulse is established once the resting potential voltage is altered or depolarized, creating an electrical current that travels across the neural membrane

Question 31

Excitation of a neuron steps

Answer 31

1. The graph starts at the membrane's resting potential (-70mV) - the inside of the axon is negatively charged compared to the outside - both voltage gated sodium and potassium gates remain closed 2. The stimulus is applied - It triggers the opening of a few non voltage gated sodium gates - If it is strong enough, the voltage rises to what is called the threshold (-55mV) - the difference between the threshold and the resting potential is the minimum change in the membrane's voltage that must occur to generate the action potential 3. Once the threshold is reached, the action potential is triggered - voltage gated sodium channels open, allowing even more sodium to diffuse into the cell - the membrane polarity is reversed abruptly ( = depolarized) - as more Na+ moves into the axon, the voltage reaches it's peak ( approx. +35mV) 4. The peak voltage triggers closing and inactivation of the voltage gated sodium channels - meanwhile the voltage gated potassium channels open, allowing potassium to diffuse out rapidly -these changes produce the downswing int he graph = membrane rapidly repolarizes as the voltage drops back down - na+/k+ pump will also assist in the repolarization process by actively pumping 3 sodium out and 2 potassium into the axon 5. a very brief undershoot of the resting potential (= hyperpolarization) results because the K+ channels close slowly ( @-80mV) 6. The membrane then returns to its resting potential

Question 32

refractory period

Answer 32

repolarization takes approx 0.001s or 1ms. this time frame is known as the refractory period. (impulse cannot be activated during this time

Question 33

Impulse propagation

Answer 33

1. an action potential continues to travel down the neuron in a wavelike motion 2. The depolarization associated with an action potential in one region stimulated an action potential in the adjacent region that is at rest. Therefore, action potentials are propagated in only one direction along the axon.

Question 34

saltadory conduction

Answer 34

Action potentials are generated by the movement of ions into and out of the axon. Therefore they can only occur where the axon membrane is exposed

Question 35

continuous conduction

Answer 35

Unmyelinated neurons: Action potentials occur at every location along the membrane. as a result, the impulse transmission along an unmyelinated axon is much slower (5m/s) than the saltadory conduction along a myelinated neuron (150m/s)

Question 36

Saltadory conduction in what type of neurons?

Answer 36

Myelinated neurons: Action potentials "JUMP" from one node of Ranvier to the next (action potentials only occur where axon membrane is exposed)

Question 37

Threshold levels

Answer 37

In experiments with nerve and muscle- electrical stimulus has to be at a certain value before a neuron will fire and the muscle will contract - if below value- no response, if at or above value - response. (known as threshold level) - each neuron has a different threshold level ( MOST are close to -55mV) - once the threshold level is reached - nerve impulse is total

Question 38

Stimulus can be:

Answer 38

changes in pH, pressure, or specific chemicals

Question 39

All or none response

Answer 39

Increasing intensity of stimuli above threshold value will not produce an increased response - nerve impulse and speed of transmission remain the same

Question 40

How can we detect intensity? (ie. warm vs hot)

Answer 40

1. Increase stimulus- more neurons are stimulated (due to their different threshold levels) the brain interprets a high number of neurons firing as an increased intensity 2. Increase stimulus - increased frequency of action potentials

Question 41

The synapse

Answer 41

known as synaptic cleft - small spaces between neurons or between neurons and effectors. Neuromuscular junction is the specific synapse between a motor neuron and muscle

Question 42

neurotransmitter process

Answer 42

1. nerve impulse (action potential) moves along the axon to the end plate (axon terminal/presynaptic knob) which has small vesicles containing chemicals called neurotransmitters. 2. The neurotransmitters (example- acetylcholine) are released from the presynaptic neuron and travel to the post- synaptic neurons via diffusion 3. neurotransmitters binds to receptors on the post synaptic dendrite 4. An excitatory neurotransmitter, OPENS chemically gated sodium chennels- causing depolarization 5. Action potential 6. The neurotransmitter is eventually deactivated by an enzyme (example : cholinesterase), resulting in the closure of chemically gated sodium channels 7. post synaptic neuron begins repolarization. components of neurotransmitter get reabsorbed by presynaptic knob and repackaged in vesicles

Question 43

Excitatory neurotransmitters

Answer 43

neurotransmitters that stimulate an action potential on post synaptic neuron

Question 44

Inhibitory neurotransmitters

Answer 44

neurotransmitters that prevent an action potential on post synaptic neuron

Question 45

Summation

Answer 45

A single neuron may be influenced by many different neurons. Summation is the final outcome of the simultaneous released of excitatory and inhibitory neurotransmitters in a synapse