U9- Nervous system Flashcards
1
Q
list the functions of the nervous system -
A
- collecting environmental information - (sensory receptors detect stimuli)
- integration (processing sensory data into useful information)
- motor output (activates muscles or glands)
2
Q
Nervous tissue is made of two cells
A
Neuron - cells that carry nerve impulses
Schwann cells - supporting cells surrounding the axon and or dendrites of a neutron
3
Q
anatomy of a neuron
A
- cell body - contains nucleus and other organelles, appears grey
- dendrites - numerous branched extensions of the cell body, receive nerve impulses from other neurons and carry them to the cell body
- 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 - 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 - nodes of Ranvier - gaps between Schwann cells where there is no myelin sheath
- synaptic ending - bulbous ends of axons
- never touch the next cell body or dendrite, there is always a slight gap
4
Q
nervous system organisation
A
- central nervous system – processes
sensory inputs from receptors and
produces motor responses in effectors - peripheral nervous system – carries
sensory inputs to the CNS and motor
responses from the CNS
5
Q
Types of neurons
A
- 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 - interneurons - connect between neurons within the CNS
- axons and dendrites of mixed length contained completely inside the CNS - motorneurons - connect between neurons within the CNS
- axons and dendrites of mixed length
- contained completely inside the CNS
6
Q
Central nervous system
A
- made up of brain and spinal chords
- contains interneurons, axons of sensory neurons, cell bodies and dendrites of motor neurons only
7
Q
peripheral nervous system
A
- 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)
8
Q
Somatic NS division in PNS
A
- controls voluntary functions (e.g.
movement) - external receptors (eyes, skin, etc.)
- skeletal muscle effectors
9
Q
autonomic NS division in PNS
A
- 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
10
Q
anatomy of CNS
A
- 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
11
Q
Brain anatomy - cerebrum
A
- wrinkled outer surface of the brain, divided
into two hemispheres - responsible for voluntary movement,
senses, speech, memory, and personality
12
Q
Brain anatomy - corpus callosum
A
- connection between the right and left cerebral hemispheres
13
Q
Brain anatomy - cerebellum
A
- 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
14
Q
brain anatomy - thalamus
A
- receives all sensory inputs, and sends them to the appropriate regions of the cerebrum
15
Q
brain anatomy - hypothalamus
A
- controls homeostasis through the autonomic
NS (hunger, thirst, temperature, water
balance, etc.) - controls pituitary gland with hormones
16
Q
brain anatomy - pituitary glands
A
- posterior portion stores hormones from hypothalamus and releases as necessary
- anterior portion creates hormones that tell other glands to release their own hormones
17
Q
brain anatomy - medulla oblongata
A
- contains reflex arcs that control involuntary functions such as heart rate, breathing, coughing, sneezing, vomiting, swallowing
18
Q
spinal chord anatomy
A
- grey matter - central core of the cord, contains the cell
bodies of motor and interneurons - white matter - outer ring of the cord, contains myelinated axons and dendrites of neurons running
up or down the cord - dorsal root - where sensory neurons enter the spinal
cord cell bodies of sensory neurons are found in a ganglion at the base - ventral root - where motor neuron axons leave the
spinal cord
19
Q
reflex arcs
A
- 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
20
Q
components of a reflex arc
A
- receptor – sensory organ that recognises a
specific stimulus in our environment (light, sound, touch, heat, etc.) - sensory neuron
- interneuron
- motor neuron
- effector – organ that performs a response to environmental changes (muscle, gland, etc.)
21
Q
sequence of events reflex arc
A
- receptor registers stimulus
- impulse created in dendrite of sensory
neuron, travels along to axon - impulse reaches interneuron of CNS: automatically split and sent to dendrite of motor neuron and upwards to the brain
- impulse travels down motor neuron axon
- impulse reaches effector, response begins
22
Q
autonomic example - breathing
A
- 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
23
Q
somatic example - patellar reflex
A
- 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
24
Q
Neuron polarity - sodium potassium pump
A
- creates polarity across the axoplasm by moving three
Na+ ions out and moving two K+ ions in
25
neuron polarity - sodium and potassium gates
- 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
26
step 1 in nerve impulse - resting potential
- 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
27
step 2 in nerve impulse - depolarization
- 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)
28
step 3 in nerve impulse - repolarization
- 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)
29
step 4 nerve impulse - refractory period
- 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
30
nerve impulse
- 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)
31
anatomy of synapse
- 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
32
transmission across a synapse ( pt 1.)
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
33
transmission across a synapse ( pt. 2)
- 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)
34
autonomic nervous system
- 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
35
sympathetic division
- 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
36
Hypothalamus
- 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)
37
adrenaline
- 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.
