Module 8 - The Nervous System

Question 1

What do the nervous and endocrine systems do?

Answer 1

They control and integrate all body activities and aid in maintaining homeostasis

Question 2

What 5 functions does the nervous system have?

Answer 2

1. communication between different regions of the body
2. speech
3. memory
4. consciousness (awareness)
5. intelligence (ability to analyze and draw conclusions)

Question 3

What are the anatomical divisions of the nervous system?

Answer 3

The nervous system is divided into 
1. the central nervous system (CNS)
=the brain and spinal cord
2. the peripheral nervous system (PNS)
=cranial and spinal nerves

Question 4

The sensory division of the peripheral nervous system is composed of..

Answer 4

• sensory receptors: that detect changes in the external and internal environment
• sensory (or afferent) neurons: that carry sensory information to the spinal cord and brain

Question 5

The motor division of the peripheral nervous system is composed of..

Answer 5

-motor (or efferent) neurons: that carry motor information from the brain and spinal cord to an effector - muscle or gland

Question 6

There are two divisions of the motor division which are…

Answer 6

1. somatic nervous system (voluntary)
   - controls skeletal muscle (striated)
2. autonomic nervous system (involuntary)
   - controls smooth muscle and glands

Question 7

Two divisions of the autonomic nervous system are..

Answer 7

1. sympathetic division
   -mobilizes body systems during activity “flight and fight”
2. parasympathetic division
   -conserves energy
   -promotes housekeeping functions during rest
   “resting and digesting”

Question 8

Nervous tissue consists of two types of cells:

Answer 8

1. neurons: functional cells of the nervous system, responsible for nerve electrical impulse (action potential) conduction
2. neuroglia(85% of nervous tissue cells):
   - support, nourish and protect neurons
   - found between neurons and blood vessels

Question 9

The neuron is composed of what 3 structures? Describe them

Answer 9

1. cell body
   - contains the nucleus, cytoplasm and organelles
2. axon
   - carries outgoing information to the axon terminals
3. dendrites
   - carries incoming informaiton to the cell body

Question 10

What is myelination? What is myelin?

Answer 10

Myelin is the white phospholipid material that forms around axons
they function to support and electrically insulate axons
insulation increases the speed of electrical impulses (action potentials) along an axon
produced by neuroglia:
1. SCHWANN CELLS in the PNS
2. OLIGODENDROCYTES in the CNS

Question 11

How does the myelinated axon of the PNS work?

Answer 11

1. Schwann cells wrap around the axon up to 100 times - producing a myelin sheath
2. gaps between the smyelin sheath are called nodes of ranvier
3. not all axons are myelinated

Question 12

The brain and spinal cord (CNS) are organized into 2 regions of:

Answer 12

1. white matter
   - contain mainly myelinated axons
   - white due to the colour of myelin
2. gray matter
   - contains mainly cell bodies and axon terminals

Question 13

What are nervous tracts? What are nervous nerves?

Answer 13

1. nervous tissue tracts are bundles of axons within the central nervous system
2. nervous tissue nerves are bundles of axons within the peripheral nervous system

Question 14

When we put an electrode inside a nerve cell at rest we measure a voltage of about?

Answer 14

-70mV (millivolts)
This is called resting membrane potential (RMP)
the RMP is essential in order for a nerve to produce action potentials (electrical impulses)

Question 15

Resting membrane potential is…

Answer 15

the voltage difference across a nerve cell membrane at rest

Question 16

The inside of a cell is ________ relative to the outside

Answer 16

negative

Question 17

RMP is determined mostly by…

Answer 17

the unequal distribution of Na+ and K+ ions on either side of the neuron cell membrane at rest due to the Na/K pump

Question 18

What happens because the membrane is slightly more permeable (leaky) to K+ ions?

Answer 18

the K+ ions diffuse out of the cell down their concentration gradient so that the inside of the cell becomes more negative (because positive ions are moving out)

Question 19

What is the action potential?

Answer 19

a sequence of rapidly occuring events in which the membrane potential reverses then returns to normal

Question 20

When a neuron is stimulated, it produces an ACTION POTENTIAL, which has two stages:

Answer 20

1. depolarization:
   - occurs when the membrane potential becomes more positive
   - influx of positively charged Na+ ions
2. repolarization:
   - occurs when the membrane potential becomes more negative
   - efflux of positively charged K+ ions

Question 21

What happens during the depolarization phase?

Answer 21

1. at the threshold potential (-55mV), voltage-gated Na+ channels open
2. Na+ enters the cell going down its concentration and electrical gradient
3. the membrane potential becomes more positive and eventually reverses reaching +30mV

Question 22

What happens during the repolarization phase?

Answer 22

1. Na+ channels close
2. voltage-gated K+ channels are opened
3. K+ diffuses out of the cell down its concentration gradient
4. the membrane potential returns to the resting potential

Question 23

What is action potential propagation?

Answer 23

once an action potential is generated, it must be propagated along the axon to the axon terminals
propagation means the movement of a wave of electrical change (like a ripple on water)

Question 24

Two mechanisms of propagation occur in axons:

Answer 24

1. continuous

2. saltatory

Question 25

Continuous conduction occurs in...

Answer 25

continuous conduction occurs in unmyelinated axons (and in muscle fibres)

Question 26

how does continuous conduction work?

Answer 26

- the opening of Na+ channels with the initial action potential, depolarizes adjacent membrane areas to threshold and an action potential is generated - one AP causes a chain reaction along the length of the action

Question 27

how does saltatory conduction work?

Answer 27

saltatory conduction occurs in myelinated axons -ion channels are found mainly at the nodes of ranvier (gaps between myelin) -nerve impulses leap along the axon from node to node (each node depolarizes and repolarizes) Saltatory conduction is much faster!

Question 28

What is neurotransmission (synaptic transmission)?

Answer 28

=the process in which neurons communicate with other neurons or effector cells via chemicals - called chemical transmission - the junction between the neuron and its target is called the synapse - chemicals called neurotransmitters are stored in and released from the axon terminal into the synaptic cleft

Question 29

What are the two different types of neurotransmitters?

Answer 29

Neurotransmitters released may be: 1. excitatory: depolarize the postsynaptic membrane so that new impulses can be generated 2. inhibitory: hyperpolarize the postsynaptic membrane to prevent new impulses from being generated examples include acetylcholine, glutamate, serotonin and GABA

Question 30

What are the 8 steps in neurotransmission?

Answer 30

1. an action potential arrives and depolarizes the synaptic bulb 2. voltage-gated Ca2+ channels open 3. Ca2+ influx stimulates the exocytosis of vesicles containing neurotransmitter (NT) 4. The NT diffuses across the synaptic cleft to bind specific receptors in post-synaptic neuron 5. chemical (ligand) gated Na+ channels open and Na+ rushes into the post-synaptic cell (down its concentration gradient) 6. post synaptic neuron depolarizes (called a graded potential) 7. if depolarization reaches threshold potential a new nerve impulse (action potential) is generated in the post-synaptic nerve 8. neurotransmission is terminated: NT is broken down by enzyme in the presynaptic membrane and reabsorbed, ligand gated channels close

Question 31

What are the 4 regions of the brain divided by?

Answer 31

1. cerebrum 2. diencephalon 3. brain stem 4. cerebellum

Question 32

What is the brain protected by?

Answer 32

1. cranial bones 2. cranial meninges - dura mater - arachnoid mater - pia mater 3. cerebrospinal fluid (CSF)

Question 33

What are meninges?

Answer 33

connective tissue layers that wrap around the: - spinal cord (=spinal meninges) - brain (=cranial meninges)

Question 34

What are the 3 meninges?

Answer 34

1. dura mater - outermost layer: tough for protection 2. arachnoid mater - the middle layer - CSF fills the subarachnoid space between the arachnoid mater and pia mater 3. pia mater - innermost layer - contains numerous blood vessels that supply oxygen and nutrients

Question 35

What is cerebral spinal fluid?

Answer 35

=fluid that circulates through the subarachnoid space (surrounding the brain and spinal cord), ventricles, and the central canal of the spinal cord Functions: - carries oxygen, glucose, and other needed chemicals from the blood - removes wastes - cushions and protects (the brain floats in the skull)

Question 36

What are the four ventricles? What are they?

Answer 36

- four cavities filled with CSF (L, R, third and fourth) - contain regions called choroid plexus - the choroid plexus contains specialized neuroglia called ependymal cells - ependymal cells produce CSF by the filtration of capillary blood

Question 37

Where is the spinal cord located?

Answer 37

- located in the dorsal - vertebrae provide boney protection of spinal chord - begins as a continuation of the medulla oblongata - terminates at the level of the 2nd lumbar vertebra (L2) - each spinal segment (31) gives rise to a pair spinal nerves

Question 38

What are the three spinal cord functions?

Answer 38

1. to convey sensory information from the periphery to the brain via sensory nerve tracts = ascending tracts 2. to conduct motor impulses from the brain to the periphery via motor nerve tracts = descending tracts 3. to act as a reflex centre Ascending tracts carry sensory information to the brain Descending tracts carry commands to motor neurons

Question 39

What are spinal cord reflexes?

Answer 39

- they are fast and involuntary response to internal or external changes - shortest route for a nerve impulse to travel from a sensory receptor to an effector (muscle) - the reflex arc contains a sensory neuron, sometimes an interneuron and a motor neuron - can be illustrated by the "knee jerk" response

Question 40

What are the 3 regions of the brain stem?

Answer 40

1. midbrain 2. pons 3. medulla oblongata

Question 41

What is medulla oblongata? What does it control?

Answer 41

- continuous with the spinal cord: looks like a slight thickening - contains groups of nerve cells (nuclei) that regulate vital reflexes, including: 1. cardiovascular centre - controls blood pressure by varying heart rate and/or constricting or dialating blood vessels (=vasoconstriction/vasodilation) 2. respiratory centre - controls O2 and CO2 levels in the blood by varying breathing rate and rhythm

Question 42

What is the diencephalon?

Answer 42

=structures above the midbrain 1. thalamus 2. hypothalamus 3. pineal gland (secretes melatonin)

Question 43

What is the thalamus?

Answer 43

- relays all sensory impulses (except smell) travelling to the cerebral cortex i. e the higher functioning regions of the brain associated with consciousness

Question 44

What is the hypothalamus?

Answer 44

-lies below the thalamus and above the pituitary gland (perhaps the most important endocrine gland) the endocrine system (hormones)

Question 45

What are the functions of the hypothalamus?

Answer 45

- regulation of many activities of the ANS - control of the pituitary gland and hormone production - eating and drinking (contains thirst and satiety centres) - control of body temperature - circadian rhythms (daily pattern of awakening and sleep)

Question 46

What is the cerebrum? What are the 3 things it consists of?

Answer 46

-largest part of the brain consists of: 1. cerebral cortex (outer rim of gray matter) 2. internal region of white matter (nerve tracts) 3. deep nuclei (cell bodies of the CNS)

Question 47

What are the 4 lobes?

Answer 47

Each cerebral hemisphere is subdivided into four lobes 1. parietal lobe 2. occipital lobe 3. frontal lobe 4. temporal lobe

Question 48

What are the key functions of the lobes?

Answer 48

1. frontal lobe: - primarily controls motor functions (control muscular movements) - also regulates behaviour, emotions, intellectual function 2. parietal lobes: primarily control sensory functions (interpret sensory information) 3. occipital lobe: visual centre 4. temporal lobes: roles in hearing and smelling

Question 49

What are the 3 functions of the cerebellum "hind brain"?

Answer 49

1. coordination of muscular movement: makes movements smooth and coordinated; not jerky 2. maintenance of posture 3. maintenance of equilibrium (balance) by using information from the inner ear, the eyes and proprioceptors in skeletal muscles and tendons