The Nervous System

Question 1

What does the nervous system do?

Answer 1

• keeps us in contact with the outside world
• responsible for coordination of movement, response to enviornmental stimuli, intelligence, self-awareness, thoughts, emotions
• composed of nerve cells called neurons which are specialized to carry nerve impulses

Question 2

What is CNS?

Answer 2

• central nervous system
• includes spinal core and brain
• unthinkable

Question 3

What is PNS?

Answer 3

• peripheral nervous system
• the rest of the nervous system
• further divided into somatic nervous system & automatic nervous system(connects to smooth (involuntary) muscles)
• automatic nervous system is further divided into the sympathetic nervous system(usually causes affects with emergency situations) & parasympathetic nervous system (promotes activities associated with a normal state)

Question 4

What 3 parts do neurons have?

Answer 4

• dendrites (conducts nerve impulses towards the cell body
• cell body
• axon(conducts nerve impulses away from the cell body)
• dendrites and axons are sometimes called fibers
• most long fibers are covered by a myelin sheath
• the sheath has spaces in it expanding the axon called the nodes of ranver
• the sheath is secreted by Schwann cells each of which has a nucleus

Question 5

What are the 3 types of neurons?

Answer 5

• sensory neuron: takes a message from a sense organ to other neurons
• motor neuron: takes a message to away from CNS to a muscle fiber or gland
• interneuron: completely contained within CNS & conveys messages between parts of the system

Question 6

How is temperature controlled in the body?

Answer 6

-the hypothalamus monitors the body temperature; around 37 degree Celcus; operates on a negative feedback loop
-when overheating: arterioles dilate so blood flow through and the heat of the core is lost through surface of the skin by way of blood flow
^skeletal muscles rest
^sweat is produced and creating a wicking effect when it evaporates
-when chilled: arterioles constrict so less heat is lost
^skeletal muscles make small tiny contractions generating heat
^little to no sweat is produced

Question 7

What is a stimulus?

Answer 7

-a change in the environment,either internal or external, that is detected by a receptor and elicits a response

Question 8

What is a response?

Answer 8

a change in an organism produced by a stimulus

Question 9

What is a reflex?

Answer 9

• a rapid unconscious response to a stimulus
• automatic, involuntary responses to changes occuring inside or outside the body
• can involve the brain(e.g. blinking)or not involve brain (e.g. withdraw hand from hot stove)

Question 10

The reflex arc involve which 5 parts?

Answer 10

• receptors: these can be cells or nerve endings that detect a stimulus
• sensory neurons: these receive messages from receptors and carry them to the brain or spinal cord
• relay neurons(aka interneurons): receive messages from sensory neurons and pass them to motor neurons
• motor neurons: receive messages and carry them to an effector(e.g. muscle)
• effectors: receive messages and respond them through contraction of a muscle or secretion from a gland

Question 11

What is the reflex arc?

Answer 11

• the main functional unit of the nervous system

- allows us to react to internal and external stimuli

Question 12

What are the steps an impulse occurs?

Answer 12

1. receptor (e.g. in skin) generates a nerve impulse
2. sensory neuron takes message to CNS. Impulses move along dendrie, proceed to cell body (in dorsal root ganglia) and then go from cell body to axonin gray matter of cord
3. interneuron(relay neuron) passes message to motor neuron
4. motor neuron takes message away from CNS to axon of spinal nerve
5. effector receives nerve impulses and reacts: glands secrete and muscles contract

Question 13

What is nerve conduction?

Answer 13

• an electrochemical change that moves in one direction along the length of a nerve fiber
• it’s electrochemical because it involves changes in voltage as well as in the concentrations of certain ions
• an oscilloscope is used to measure potential differences

Question 14

How does information flow through neurons?

Answer 14

1. dendrites collect signals
2. cell body integrates incoming signals and generates outgoing signal to axon
3. axon passes electrical signals to dendrites of another cell or to an effector cell

Question 15

What are three phases in the generation of a nerve impulse along an axon?

Answer 15

• resting phase
• action phase
• recovery phase

Question 16

What happens during the resting phase?

Answer 16

• when not conducting impulses, there is a voltage difference across the membrane of the axon of about -60 mV; this is due to the presence of large negative ions in the axoplasm(cytoplam inside an axon)
• Na+ ions are more concentrated on the outside of the membrane than the inside
• K+ ions are more concentrated on the inside of the axon
• the uneven distribution of K and Na ions is maintained by active transport across Na+/K+ pumps which operate whenever the neuron is conducting an impulse

Question 17

What happens during the action phase?

Answer 17

• occurs when a nerve is stimulaated by electric shock, pH change, mechanical stimulation, then a nerve is generated and a change in potential can be seen on the oscilloscope
• during the upswing(-60mV to +40mV) depolarization occurs(the inside of the axon becomes positive); Na+ ions move from outside to inside the axon
• during the downswing(+40mV to -60mV), repolarization occurs(the inside of the axon becomes negative again); K+ moves from inside to the outside of the axon

Question 18

What happens during the recovery phase?

Answer 18

between transmissions, K+ ions are returned to inside of axon, Na+ to the outside and this is done actively

Question 19

What is the speed of transmission?

Answer 19

• speed of nerve impulses is rapid; this is due to the structure of the nerve, specifically the myelin sheath of most nerve fibers(this sheath is formed by tightly packed spirals of the cell membrane of Shwann cells), and the gaps of the sheath called the nodes of Ranvier; this sheath gives their characteristic white appearance
• the speed of transmission is ~200m/s in myelinated fibers, but only 0.5m/s in non-myelinated fibers
• in myelinated fiber, the nerve impulse “jumps” from node to node
• in non-myelinated fiber, the nerve impulse must depolarize and repolarize each point along the nerve fiber

Question 20

What happens to a nerve impulse once it reaches the end of an axon?

Answer 20

-specialized regions at the end of axons called synapses release neurotransmitters to affect the potential of the next neurons
-a neuron is on the receiving end of many synapses-some may be giving inhibitory and some may give stimulatory impulses
-whether or not the neuron they are attached to fire depends on the summary effect of the exitatory neurotransmitters received
^if amount of exitatory neurtransmitters received is sufficient to overcome the amount of inhbitory neurotransmitters received, the neurons fires; if not, only local exitation occur; the total process allows neurons to fine tune to the enviornment

Question 21

What is a synapse?

Answer 21

the region between end of an axon and the cell body or dendrite to which it is attached

Question 22

What is synaptic ending?

Answer 22

swollen terminal knobs on the ends of axon terminal branches

Question 23

What is presynaptic membrane and postsynaptic membrane?

Answer 23

• presynaptic membrane: the membrane of the xon synaptic ending
• postsynaptic: the membrane of the next neuron just beyond the axon’s synaptic membrane

Question 24

What is synaptic cleft?

Answer 24

the space between the presynaptic and the postsynaptic membranes

Question 25

What are neurotransmitter substances?

Answer 25

• chemicals that transmit the nerve impulses across a synaptic cell
• can be amino acids or derivatives of protein
• proper brain and nervous system function depends on the proper balance of exitatory and inhibitory synaptic transmitters
• excitatory transmitters include acetylcholine, adrenaline, dopamine, serotonin, and noradrenalin
• inhibitory transmitters include gaba(gamma aminobutryic acid-a type of amino acid), glycine, seotonin
• neurotransmitters include endorphins and enkephalins(a 5 amino-acid chain that functions as a natural pain reliever in brain)
• whether or not a neuron “fires” off an action potential at any particular instant depends on its ability to integrate these multiple positive and negative inputs

Question 26

What are synaptic vesicles?

Answer 26

contain the neurotransmitters near surface of synaptic endings

Question 27

What are acetylcholine, noradrenaline, serotonin, and adrenalin?

Answer 27

important transmitters

Question 28

What are the steps of synaptic transmission?

Answer 28

1. nerve impulse travel along axon, reach a synaptic ending
2. arrival of nerve impulse at synaptic ending changes membrane; Ca++ flows into ending
3. Ca++ ions cause contractile proteins to pull synaptic vesicles to inner surface of the presynaptic membrane
4. vesicle fuses with presynaptic membrane, releasing neurotransmitters into synapse
5. neurotransmitters diffuse across synaptic cleft to receptors on postsynaptic membrane
6. the resulting ion flux changes the voltage of the postsynaptic membrane. The neurotransmitters binding to receptors on the dendrite causes the nerve impulse to be transmitted down the dendrite of the second neuron; the nerve impulse has now been transmitted from the first neuron to the second neuron
7. neurotransmitters are quickly deactivited to prevent them from continually acting on postsynaptic membrane by either degrade the neurotransmitter by enzymes or synaptic ending reabsorbs the neurotransmitter

Question 29

What is sympathetic nervous system?

Answer 29

-under autonomic nervous system
-associated with “fight or flight” reactions(emergency situations)
-in an emergency:
^energy away from digestion
^pupils dilate
^heart rate increases
^perspiration increases
^salivation decreases
^breathing rate increases
-noradrenalin is released by the axon(closely related to adrenalin; a known heart stimulant; when released the heart rate increases)

Question 30

What is parasympathetic nervous system?

Answer 30

• promotes all the internal responses associated with a relaxed state
• causes pupils to contract
• energy diverted for digestion of food
• heart rate slows
• important neurotransmitter is acetylcholine

Question 31

Describe the CNS

Answer 31

• consists of the brain and spinal cord
• lies in the mid-line of the body and is the place where sensory information is received and motor control is initiated
• protected by bone (skull, vertebrae)
• wrapped up in three protective membranes called meninges; spaces between meninges filled with cerebrospinal fluid for cushioning and protection and this is also found within central canal of the spinal cord and ventricle of brain

Question 32

Describe the spinal cord

Answer 32

-central cana filled with cerebrospinal fluid
-contains gray matter(inner layer) which contains cell bodies of neurons and short fibers and looks kind of like a butterfly with open wings
^dorsal cell bodies function primarily in receiving sensory information, and ventral cell bodies send along primarily motor information
-contains white matter(outer layer) which contains long fibers of interneurons that run together in bundles called tracts that connect the cord to the brain; within white matter, ascending tracts take information to the brain, descending tracts in the ventral part carry information down from the brain

Question 33

Describe the structure of the brain

Answer 33

• contains parts which function in the coordination of movement, sensing & consciousness and areas that are below the level of conscious control
• when one is born they had the max number of neurons; thousands are lost daily, never to be replaced

Question 34

What is the medulla oblongata?

Answer 34

It controls heart rate, breathing, blood pressure, reflex reactions like coughing, sneezing, vomiting, hicoughing, swallowing

Question 35

What is the thalamus?

Answer 35

• receives all sensory info (except for smell) from all parts of the body and sends them to appropriate regions of the cortex for interpretation
• the last portion of the brain for sensory input before the cerebrum
• serves as a relay station for sensory impulses coming spinal cord and other parts of the brain to the cerebrum
• has connections to various parts of the brain and is part of the RAS

Question 36

What is RAS?

Answer 36

• reticular activating system
• sorts out incoming stimuli, passing on to the cerebrum only those that require immediate attention
• extends from the medulla oblongata to the thalamus

Question 37

What is the cerebellum?

Answer 37

• controls balance and complex muscular movement
• second largest portion of the brain
• butterfly shaped
• functions in muscle coordination and makes sure skeletal muscles work together smoothly
• responsible for maintaining normal muscle tone, posture, balance
• receives sensory information from the inner ear which senses balance

Question 38

What is the hypothalamus?

Answer 38

• one of the most important sites for the regulation of homeostasis
• maintains internal environment, contains centres for hunger, sleep, thirst, body temperature, water balance, blood pressure
• controls the pituitary gland and thus serves as a link between the nervous system and the endocrine systems
• plays a role in sexual response, mating behaviours, and “fight or flight” response

Question 39

What is the pituitary gland?

Answer 39

• has 2 lobes that release hormones:
• anterior pituitary: makes and releases ADH
• posterior pituitary: stores and releases hormones made in the hypothalamus

Question 40

What is the corpus callosum?

Answer 40

• the horizontal connecting piece between the 2 hemispheres of the brain
• transmits information between the 2 central hemispheres
• the right hemisphere of the brain controls the left side of the body(except for smell) and vice versa
• left hemisphere is the “logical side” and right hemisphere is the “intuitive(creative) side”

Question 41

What is the cerebrum?

Answer 41

• largest, most prominent, most highly developed portion of the brain
• consciousness resides only in this part of the brain
• intellect, learning, memory, sensations are formed here
• outer layer is the corex(gray); it is the largest and most complex part of the brain and the part that has changed the most during the vertebrae evolution

Question 42

What are the 4 lobes of the cerebrum?

Answer 42

• frontal: higher intellectual processes(e.g. problem solving, concentration, lanning, etc); left side only
• parietal: sensations e.g. touch, temperature, pressure, pain, understanding, using words
• temporal: hearing, smelling, interpretation of experiences, memories, music, complex sensory patterns
• occipital: vision, combining visual experiences with other sensory experiences