WEEK 3 BIOSCIENCE - INTRO TO THE NERVOUS SYSTEM Flashcards
1
Q
Functions of the nervous system
A
- sensory function: receptors detect sensory input, which is sent to the control centre
- integrative function: analyses and interprets sensory input, determines an appropriate response, generates motor output that causes the response
- motor function: issues motor function to activate effector
2
Q
general sensory receptors
A
- thermoreceptors: detect changes in temperature
- nociceptors: detect painful stimuli
- mechanoreceptors: tactile receptors (touch, pressure & vibration), baroreceptors (changes in blood pressure), proprioceptors (body position)
3
Q
special sensory receptors
A
- photoreceptors: detect light
- chemoreceptors: detect chemicals in solution
- mechanoreceptors called hair cells: detect hearing and balance stimuli
4
Q
motor output
A
Activates a specific muscle to contract or a gland to secrete to cause a response
5
Q
CNS
A
- consists of the brain and spinal cord
- control centre -> performs the function of integration
- controls our emotions, behaviours and personality
- performs intellectual (cognitive) functions
- stores memories
6
Q
PNS
A
- consists of sensory receptors and the cranial, spinal and peripheral nerves that link all parts of the body to the CNS
- cranial nerves and their branches primarily innervate structures of the head and neck
- spinal nerves branch to form the peripheral nerves that innervate all parts of the body below the head
7
Q
PNS sensory division
A
- afferent
- conveys sensory input from receptors to the CNS
8
Q
PNS motor division
A
- efferent
- conveys motor output from the CNS to a muscle or gland
9
Q
Motor division: somatic nervous system
A
- conveys “somatic” motor output from the CNS to the body’s skeletal muscles
- somatic motor output controls voluntary skeletal muscle movements and involuntary skeletal muscle movements (somatic reflexes)
10
Q
Motor division: autonomic nervous system
A
- conveys “autonomic” motor output from the CNS to the body’s glands, cardiac and smooth muscles
- autonomic motor output controls involuntary activities: heart rate, respiration, blood vessel and pupil diameter, digestion of food, urination and defecation, perspiration and salivation
11
Q
autonomic NS: sympathetic division
A
- controls “fight or flight” activities -> activates body functions that support physical activity and inhibits those that don’t
- increases heart rate, respiratory airflow, blood flow to skeletal muscles and sweat gland activity
- dilates pupils
- inhibits digestive functions
- inhibits urination and defecation
12
Q
autonomic NS: parasympathetic division
A
- controls “rest and digest” activities -> activates body functions that conserve and restore body energy
- stimulates digestive functions, urination and defecation
- constricts pupils
- decreases heart rate
- decreases respiratory airflow
13
Q
neuroglia
A
- support neuron development and function
- six different types of cells which collectively nourish, protect, insulate and structurally support neurons
14
Q
structural components of a neuron
A
- dendrites
- cell body
- axon (fiber)
- axon terminals
15
Q
dendrites
A
- short processes
- are the central receptive (or input) region of a neuron
- act as sensory receptors to detect stimuli
- receive information from other neurons
- convert the information they receive into a graded potential which conveys the information towards the cell body
16
Q
cell body
A
- Contains a nucleus and organelles, e.g., ribosomes, to synthesise chemical neurotransmitters
- Receives information from other neurons & converts this information into a graded potential
- Integrates information (graded potentials) and conveys information towards the initial segment (or first part) of the axon
17
Q
axon
A
- A single process that connects to the cell body at the axon hillock
- Is the conducting region of a neuron
- generates & conducts action potentials to convey information from the initial segment to the axon terminals
- Can be covered with a segmented myelin sheath
18
Q
myelin sheath
A
- produced by Schwann cells and oligodendrocytes
- increases the speed of signal conduction
- gaps separate segments called nodes of Ranvier (internodes)
- the destruction of myelin (oligodendrocytes) in the CNS à multiple sclerosis
19
Q
axon terminals
A
- Form a synapse with another cell i.e. a neuron, muscle or gland
- Are the secretory region of a neuron
- contain synaptic vesicles that store and release
neurotransmitters chemicals that carry the
information from one neuron to another
or to a muscle cell or gland
20
Q
Neuron cell bodies are organised into…
A
- nuclei (nucleus) in the CNS
- ganglia (ganglion) in the PNS
21
Q
Neuron axons are bundled into…
A
- tracts in the CNS
- nerves in the PNS
22
Q
classifications of neurons
A
multipolar
bipolar
unipolar
23
Q
sensory neurons
A
- Conduct sensory input from receptors to the CNS
- Unipolar in structure
24
Q
interneurons
A
- Conduct information within the CNS
- Multipolar in structure
25
motor neurons
- Conduct motor output away from the CNS to a muscle or gland
- lower motor neurons conduct somatic motor output
- preganglionic & postganglionic neurons conduct autonomic motor output
- Multipolar in structure
26
chemically gated channels
- Open in response to a chemical stimulus, e.g. neurotransmitters
- Located along the plasma membrane of the dendrites & cell body
27
mechanically gated channels
- Open in response to mechanical stimulation e.g. touch, vibration and pressure
- Located along the plasma membrane of
the dendrites
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voltage-gated channels
- Open and close in response to voltage changes (i.e. changes in membrane potential)
- Located along the plasma membrane of the axon and axon terminals
29
depolarization
= membrane potential becomes less negative
- When a stimulus opens Na+ gated channels:
-> influx of Na+ ions into the ICF
-> ICF gains +ve ions cell interior becomes less negative
-> membrane potential becomes less negative e.g. -70 mV to -60 mV
30
hyperpolarization
= membrane potential becomes more negative
- When a stimulus opens K+ gated channels:
-> efflux of K+ ions out of the ICF
-> ICF loses +ve ions cell interior becomes more negative
-> membrane potential becomes more negative e.g. -70 mV to -80 mV
31
graded potentials
- Are small changes in the membrane potential (i.e., small depolarisation or hyperpolarisation)
- Originate in the dendrites or cell body of a neuron, when
a stimulus opens chemically-gated or mechanically-gated
channels
- Are short-distance signals
- distance travelled is proportional to stimulus strength
- stronger stimulus = bigger change in membrane potential = further signal will travel
32
for an action potential to occur:
- in response to a stimulus, a graded potential can:
-> travel to the initial segment of an axon
-> depolarise the initial segment to -55 mV = threshold
-> stimulate voltage-gated Na+ channels to open
-> generate an AP
33
action potentials
- Are long distance signals
- Originate at the initial segment of an axon
- Involve voltage-gated channels
- Are self-propagating
34
action potential: depolarisation
At threshold (-55 mv):
* voltage-gated Na+ channels open
* Na+ ions enter ICF
* membrane potential becomes LESS negative shifts from -55 mV to +30 mV
35
action potential: repolarisation
At +30 mV:
* voltage-gated Na+ channels close
* voltage-gated K+ channels open
* K+ ions leave ICF
* membrane potential RETURNS to resting state shifts from +30 mV to -70 mV
36
action potential: hyperpolarisation
As the membrane potential approaches -70 mV
* voltage-gated K+ channels close slowly
* excess K+ ions leave ICF
* membrane potential becomes MORE negative shifts from -70 mV to -90 mV
37
continuous conduction
- Occurs in unmyelinated axons
- Action potentials are generated at the voltage-gated channels along the length of the axon
- Conduction occurs at speeds ≤ 2 m/s
38
saltatory conduction
- Occurs in myelinated axons
- Action potentials are generated at the nodes of Ranvier
- Conduction occurs at speeds >100 m/s
39
what can impair an action potential?
- Local anesthetics block voltage-gated Na+ channels
-> no action potential
-> no conduction of pain signal to the brain
-> no sensation of pain
- Cold and pressure reduced pain sensations by impairing signal conduction
40
chemical synapse
- A junction that mediates the transfer of information
- At a chemical synapse between two neurons:
-> the neuron sending the information = presynaptic neuron
-> the neuron receiving the information = postsynaptic neuron
-> a synaptic cleft separates presynaptic and postsynaptic membranes
-> signal transmission involves chemical neurotransmitters
41
information transfer at a synapse
1. Action potential arrives at and depolarises axon terminal.
2. Voltage-gated Ca2+ channels open.
3. Influx of Ca2+ triggers synaptic vesicles to release neurotransmitter into the synaptic cleft.
4. Neurotransmitter binds to chemically-gated channels on the postsynaptic neuron (dendrites or cell body).
5. Chemically-gated ion channels open Na+ ions enter ICF plasma membrane of postsynaptic neuron depolarises graded potential known as an “excitatory postsynaptic potential” (EPSP) is produced
6. EPSP depolarises initial segment of postsynaptic neuron to threshold (-55 mV) action potential generated information successfully transmitted
42
termination of synaptic transmission
1. The neurotransmitter diffuses away from the synaptic cleft
2. The neurotransmitter is degraded by enzymes present in the synaptic cleft
3. The neurotransmitter re-enters the axon terminal and is destroyed by enzymes or reused. This process is known as reuptake.
