U9- Nervous system

Question 1

list the functions of the nervous system -

Answer 1

1. collecting environmental information - (sensory receptors detect stimuli)
2. integration (processing sensory data into useful information)
3. motor output (activates muscles or glands)

Question 2

Nervous tissue is made of two cells

Answer 2

Neuron - cells that carry nerve impulses

Schwann cells - supporting cells surrounding the axon and or dendrites of a neutron

Question 3

anatomy of a neuron

Answer 3

1. cell body - contains nucleus and other organelles, appears grey
2. dendrites - numerous branched extensions of the cell body, receive nerve impulses from other neurons and carry them to the cell body
3. axon - single, branched extension of the cell body
   carry nerve impulses AWAY from cell body toward another neuron
   - axomembrane - cell membrane lining the length of the axon
   - axoplasm - cytoplasm filling the axon
4. Schwann cells - line the long extensions of neurons, nourishing them away from the cell body
   - membrane has an electrically-insulating glycolipid, forms a layer called the myelin
   sheath
5. nodes of Ranvier - gaps between Schwann cells where there is no myelin sheath
6. synaptic ending - bulbous ends of axons
   - never touch the next cell body or dendrite, there is always a slight gap

Question 4

nervous system organisation

Answer 4

1. central nervous system – processes
   sensory inputs from receptors and
   produces motor responses in effectors
2. peripheral nervous system – carries
   sensory inputs to the CNS and motor
   responses from the CNS

Question 5

Types of neurons

Answer 5

1. sensory neurons - carry sensory impulses
   from receptors to CNS
   - long myelinated dendrites connect the
   receptor to the CNS
   - cell bodies outside CNS in clusters called
   ganglia
   - short axons connect the ganglia to
   interneurons of the CNS
2. interneurons - connect between neurons within the CNS
   - axons and dendrites of mixed length contained completely inside the CNS
3. motorneurons - connect between neurons within the CNS
   - axons and dendrites of mixed length
   - contained completely inside the CNS

Question 6

Central nervous system

Answer 6

• made up of brain and spinal chords

- contains interneurons, axons of sensory neurons, cell bodies and dendrites of motor neurons only

Question 7

peripheral nervous system

Answer 7

• all the nerves outside the CNS
• contains cell bodies and dendrites of sensory neurons, axons of motor neurons
• nerves begin either at the brain (cranial nerves) or at the spinal cord (spinal nerves)

Question 8

Somatic NS division in PNS

Answer 8

• controls voluntary functions (e.g.
  movement)
• external receptors (eyes, skin, etc.)
• skeletal muscle effectors

Question 9

autonomic NS division in PNS

Answer 9

• controls involuntary functions (heart rate,
  breathing, etc.)
• motor neurons work in pairs, meeting at a
  ganglion near the spine or organ
• internal receptors (carotid bodies, alveoli,
  etc.)
• gland and smooth muscle effectors

Question 10

anatomy of CNS

Answer 10

• CNS is protected by bones: skull for the brain, vertebrae for spinal cord
• both are also surrounded by tough membranes called meninges
• circulating within the meninges is fluid, which cushions the CNS

Question 11

Brain anatomy - cerebrum

Answer 11

• wrinkled outer surface of the brain, divided
  into two hemispheres
• responsible for voluntary movement,
  senses, speech, memory, and personality

Question 12

Brain anatomy - corpus callosum

Answer 12

• connection between the right and left cerebral hemispheres

Question 13

Brain anatomy - cerebellum

Answer 13

• receives sensory impulses from joints, muscles about the position of body parts, and passes on motor outputs from the cerebrum
• coordinates these two to maintain balance and smooth muscular movements

Question 14

brain anatomy - thalamus

Answer 14

• receives all sensory inputs, and sends them to the appropriate regions of the cerebrum

Question 15

brain anatomy - hypothalamus

Answer 15

• controls homeostasis through the autonomic
  NS (hunger, thirst, temperature, water
  balance, etc.)
• controls pituitary gland with hormones

Question 16

brain anatomy - pituitary glands

Answer 16

• posterior portion stores hormones from hypothalamus and releases as necessary
• anterior portion creates hormones that tell other glands to release their own hormones

Question 17

brain anatomy - medulla oblongata

Answer 17

• contains reflex arcs that control involuntary functions such as heart rate, breathing, coughing, sneezing, vomiting, swallowing

Question 18

spinal chord anatomy

Answer 18

1. grey matter - central core of the cord, contains the cell
   bodies of motor and interneurons
2. white matter - outer ring of the cord, contains myelinated axons and dendrites of neurons running
   up or down the cord
3. dorsal root - where sensory neurons enter the spinal
   cord cell bodies of sensory neurons are found in a ganglion at the base
4. ventral root - where motor neuron axons leave the
   spinal cord

Question 19

reflex arcs

Answer 19

• reflex arcs are unconscious involuntary
  responses programmed into our CNS at birth
• they protect the body from harm and maintain
  basic homeostatic processes
• many are controlled by the spinal cord, though the cerebrum always receives the same information later and supplies pain, exclamations, etc.
• reflexes are carried to and from the CNS by the PNS
• autonomic reflexes always involve two motor neurons, which meet at a place called a ganglion
• somatic reflexes involve only one motor neuron

Question 20

components of a reflex arc

Answer 20

1. receptor – sensory organ that recognises a
   specific stimulus in our environment (light, sound, touch, heat, etc.)
2. sensory neuron
3. interneuron
4. motor neuron
5. effector – organ that performs a response to environmental changes (muscle, gland, etc.)

Question 21

sequence of events reflex arc

Answer 21

1. receptor registers stimulus
2. impulse created in dendrite of sensory
   neuron, travels along to axon
3. impulse reaches interneuron of CNS: automatically split and sent to dendrite of motor neuron and upwards to the brain
4. impulse travels down motor neuron axon
5. impulse reaches effector, response begins

Question 22

autonomic example - breathing

Answer 22

• receptors in the carotid and aortic bodies
  register low O2 levels in the blood
• sensory neurons carry the impulse to the
  interneurons of the medulla oblongata
• impulses are sent more often down motor
  neurons to the diaphragm and rib cage,
  increasing the rate of breathing and raising
  O2 levels

Question 23

somatic example - patellar reflex

Answer 23

• striking the patellar ligament under the
  kneecap stretches the quadriceps muscle
• stretch receptors create an impulse up a
  sensory neuron to the base of the spinal cord an impulse is created back down a motor neuron to the quadriceps, causing contraction
• this reflex is ordinarily part of maintaining
  balance while walking

Question 24

Neuron polarity - sodium potassium pump

Answer 24

• creates polarity across the axoplasm by moving three

Na+ ions out and moving two K+ ions in

Question 25

neuron polarity - sodium and potassium gates

Answer 25

• in the axomembrane open and close to control the
  ion’s diffusion
• nerve impulses travel along neurons as waves of positive electrical charge called action potentials

Question 26

step 1 in nerve impulse - resting potential

Answer 26

• neuron is at rest
• Na+/K+ pump is on: there are more positive ions outside than inside, creating a net charge of -65 mV (axoplasm is negative)
• Na+ and K+ gates are closed, but some K+ leaks out

Question 27

step 2 in nerve impulse - depolarization

Answer 27

• Na+/K+ pump turns off
• Na+ gates open, and Na+ diffuses into the axoplasm from outside
• K+ gates remain closed
• axoplasm changes from -65 mV to +40 mV as Na+ rushes in (called upswing)

Question 28

step 3 in nerve impulse - repolarization

Answer 28

• Na+/K+ pump is off
• Na+ gates close
• K+ gates open, allowing K+ to diffuse out of
  the axoplasm
• axoplasm changes from +40 mV to –65mV
  (called downswing)

Question 29

step 4 nerve impulse - refractory period

Answer 29

• neuron unable to carry another impulse
  because the ions are in the wrong places
• Na+/K+ pump switches on to restore the ion
  concentrations typical of resting potential
• Na+ and K+ gates close

Question 30

nerve impulse

Answer 30

• to create an impulse, the axomembrane must
  be stimulated by a minimum positive charge called the threshold value
• this is an “all-or-none” response: below the threshold no impulse is created
• action potentials cause the next region of the axon to respond, and the impulse travels as a wave of positive charge down the neuron
• impulses travel faster along myelinated axons because the action potential jumps between nodes of Ranvier (saltatory transmission)

Question 31

anatomy of synapse

Answer 31

• junction between two neurons is a gap called
  a synapse
• end of an axon is a bulbous synaptic ending, this is the presynaptic membrane (PreM)
• cross the synapse is the dendrite or cell body of another neuron, the postsynaptic membrane (PostM)
• between the two is a fluid-filled space called
  the synaptic cleft
• in the synaptic ending are synaptic vesicles
  filled with neurotransmitters
• vesicles are pulled towards the PreM by
  contractile proteins
• neurotransmitters bind to specific receptors
  in the PostM
• facilitated transport of calcium ions (Ca2+) is
  controlled by calcium gates in the PreM

Question 32

transmission across a synapse ( pt 1.)

Answer 32

1. impulse travelling down the axon reaches
   the synaptic ending
2. depolarisation causes calcium gates to open, and Ca2+ diffuses into the ending
3. this causes contractile proteins to pull the synaptic vesicles and they fuse with the PreM
4. neurotransmitters are released into the cleft
   by exocytosis and diffuse across

Question 33

transmission across a synapse ( pt. 2)

Answer 33

• neurotransmitters bind to receptors on the PostM
• some neurotransmitters bind to receptors that open to allow Na+ into the PostM, starting a new impulse: called excitatory (e.g. acetylcholine, norepinephrine)
• other neurotransmitters prevent the neuron from forming a new action potential: called inhibitory (e.g. dopamine)

Question 34

autonomic nervous system

Answer 34

• ANS always uses two motor neurons in sequence, which synapse at a ganglion
• ANS has two divisions which either excite or relax the body according to the situation:
  a. sympathetic – excited “fight or flight” responses, neurotransmitter norepinephrine (= noradrenalin)
  b. parasympathetic – relaxed “rest and digest” responses, neurotransmitter acetylcholine

Question 35

sympathetic division

Answer 35

• effects prepare the body for increased activity:
  1. increases heart rate
  2. increases breathing rate
  3. widens bronchioles
  4. dilates pupils
  5. releases adrenalin from adrenal gland
  6. releases glucose from the liver
  7. decreases rate of digestion

Question 36

Hypothalamus

Answer 36

• hypothalamus controls the ANS and the attached pituitary gland
• pituitary releases hormones which control other glands
• two together are called the neuroendocrine control center: maintaining homeostasis through nervous control (ANS) and hormones (pituitary)

Question 37

adrenaline

Answer 37

• the adrenal glands, small organs just above the kidneys, are innervated by the sympathetic division of the ANS
• the inner part of the adrenal gland, the adrenal medulla, releases adrenaline when stimulated by norepinephrine
• adrenaline produces “fight or flight” effects: increased heart rate, blood pressure, blood glucose, etc.