Anatomy - Nervous system Flashcards
What is the study of the nervous system called
Neuroscience
Neurobiology
What is the function of the nervous system
Homeostasis and coordination. It employs electrical impulses and chemical means to send messages very quickly from cell to cell
How many neurons are there in the body
10^12
nervous system vs endocrine system
The nervous system communicates by means of electrical impulses and neurotransmitters while the endocrine system communicates by means of hormones.
The nervous system releases neurotransmitters at synapses at specific target cells while the endocrine system releases hormones into the bloodstream for general distribution throughout body.
The nervous system usually has relatively local, specific effects while the endocrine system sometimes has very general, widespread effects.
The nervous system reacts quickly to stimuli, usually within 1-10 msec while reacts mores slowly to stimuli, often taking seconds to days.
The nervous system stops quickly when stimulus stops while the endocrine system may continue responding long after stimulus stops.
The nervous system adapts relatively quickly to continual stimulation while the endocrine system adapts relatively slowly; may respond for days to weeks
How are the endocrine system and the nervous system related
They are both involved in homeostasis and coordination but operate in different ways
What are the major subdivisions of the nervous system
Central nervous system (CNS)
Peripheral nervous system (PNS)
What does the Central nervous system include and how is it protected
The brain and spinal cord which are protected by the cranium and the vertebral column
What is the peripheral nervous system
Everything other than the brain and spinal cord so the nerves and their associated ganglia.
What types of nerves are there
The spinal nerves, which emanate from the spinal column.
The cranial brain, which emanate directly from the brain. (There are 12 pares of cranial nerves).
What is a neuron
An electrically excitable cell that we find in the nervous system, they have projections called axons.
What is a nerve
A bundle of nerve fibres, axons, unwrapped in fibrous connective tissue.
What is ganglion
A knot-like swelling in a nerve where the cell bodies of neurons are concentrated (e.g. dorsal root ganglia)
What is the central nervous system divided into
Brain and Spinal cord
What further subdivisions is the peripheral nervous system divided into
Sensory division (afferent) and motor division (efferent)
Sensory or affarent division
carries sensory signals from receptors to the CNS.
The somatic sensory division carries signals from receptors in the skin, muscle bone and joints. And the visceral sensory division carries signals from viscera of the thorax and abdominal cavities (e.g. heart, lungs and stomach)
Motor or efferent division
carries signals from the CNS to the glands and muscle cells (effectors).
The somatic motor division carries signals to the skeletal muscle for voluntary contractions and involuntary somatic reflexes. The visceral (autonomic system) motor division carries signals to the glands, cardiac muscle, smooth muscle for involuntary visceral reflexes.
What are the subdivisions of the Autonomic nervous system
The sympathetic and the parasypathetic division
sympathetic division
tends to arouse the body for action, so its excitatory (increase heart and respiratory rates), but it also inhibits digestion.
parasympathetic division
tends to be inhibitory, so it has a calming effect ( slows down the heart rate), but it stimulates digestion.
What are the three properties of neurons
Excitability (irritability) - all cells are excitable, they respond to stimuli, but neurons have developed this to the highest degree.
Conductivity (electrically conductive) - stimuli produce electrical signals in neurons that are conducted to other cells at distant locations.
Secretion (they are secretory) - electrical signals at the end of nerve fibres cause the release of chemical neurotransmitters at synaptic knobs.
What types of neurons is there
Sensory (afferent)(PNS)
Motor (efferent)(PNS)
Interneurons (association or relay neurons)(CNS)
Sensory neurons
detect signals and carry then towards the central nervous system.
Motor nuerons
carry signals away from the central nervous system to muscle and glands.
Interneurons
connect sensory and motor neurons, they process store and retrieve information and make decisions.
What is the main type of neuron
Interneurons 90 %
soma
neurosoma
perikaryion
It is 5 to 135 micro meters in diameter. It is the cell body.
The cytoskeleton of the neuron
The cytoskeleton includes microtubules and neurofibrils (actin) and it lacks centriols because neurons are non-mitotic (after adolescence)
What are nissl bodies
Nissl bodies are concentrated areas of endoplasmic reticulum and ribosomes, which specialise in protein synthesis.
About dendrites
Dendrites receive signals. At the end of these are post-synaptic membranes; the dendrites converge into the soma.
About axon hillocks
hillocks is the region in which the soma converges to give rise to axons.
The axon nerve fibre
is 1-20 micro metres in diameter and a few millimetres to 1 meter in length. They allow rapid conduction of nerve signals. The axon can have collateral axons and they have terminal arborisations ending in synaptic knobs.
How is the neuron’s cytoplasm called
axoplasm
How is the neuron’s membrane called
axolemma
What are Schwann cells
They are regions of the axons in PNS that are electrically insulated by myelin sheaths. They increase the conductivity of the cell.
What are the nodes of Ranvier
They are the spaces between the Schwann cells, also called internodes.
What are the support cells called and how many are there
Neuroglia
50 x 10^12
What are the four types of neuroglia in the central nervous system
Oligodendrocytes
Ependymal cells
Microglia
Astrocytes
What are the two types of neuroglia in the peripheral nervous system
Schwann cells
Satellites cells
What is the function oligodendrocytes
They form myelin in brain and spinal cord, they are equivalent to Schwann cells in the central nervous system
What is the function of Ependymal cells
They line cavities of brain and spinal cord; they secrete and circulate cerebrospinal fluid-
What is the function of Microglia
Phagocytise and destroy microorganisms, foreign matter, and dead nervous tissue
What is the function of Astrocytes
They cover the brain surface and non-synaptic regions of neurons.
They form a supportive framework in the central nervous system.
They induce the formation of blood-brain barrier.
They nourish neurons.
They produce growth factors that stimulate neurons.
They communicate electrically with neurons and may influence synaptic signaling.
They remove potassium and some neurotransmitters from the extracellular fluid of the brain and spinal cord-
They help to regulate the composition of the extracellular fluid.
They scar tissue to replace damaged nervous tissue.
What is the function of Schwann cells
Form neurilemma around all the peripheral nervous fibers and myelin around most of them; and they aid in regeneration of damaged nerve fibers.
What is the function of the Satellites cells
They surround somas of neurons in the ganglia; they provide electrical insulation and regulate the chemical environment of neurons.
What does myelination do
It provides insulation along axons. Increase nerve conduction speed by, approximately, an order of magnitude (a factor of 10).
A 2-4 micrometers in diameter unmyelinated fibre can conduct an electrical signal with a speed of half a meter to two metres per seconds, but a myelinated, 3 to 15 metres per second.
What cells myelinate the PNS cells and how
Schwann cells
spiral outwards
What cells myelinate the CPS cells and how
Oligodendrocytes
spiral inwards
What is the membrane potential
It is the potential difference between the intercellular fluid (ICF) and extracellular fluid (ECF).
What is the resting membrane potential
It is the potential difference at the rest state of a cell. fir electrically active cells it is non-zero and negative.
What is the typical resting membrane potential of neurons
-70mV
How is the resting membrane potential originated
The membrane is most permeable to potassium.
If there was only potassium in the intra-cellular fluid at the start, this would diffuse out down to a concentration gradient.
Non-diffusable anions in intracellular fluid attracts potassium back.
At equilibrium, the potassium is 40 times more concentrated in the intracellular fluid than extracellular fluid; this gives a RMP of -90mV.
Sodium is twelve times more concentrated in ECP than ICF, this diffuses down the concentration gradient into the cell and reduces negative charge in ICF, which gives a resting membrane potential of -67mV.
Therefore, potassium leaks out and sodium leaks in.
A Na-K pump consumes one ATP to pump 3 na out and 2 Na in, which contributes -3mV to the RMP.
this accounts for 70 percent of the energy requirements of the nervous system.
The net effect fives a resting membrane potential of -70 mV.
How is the local membrane potential triggered
Chemical messengers neurotransmitters impinge on the receptors in the dendrites of the neuron which leads to the opening (or closing) of the ion channels. (on the unbound state it is closed and in the bound state it is open.
How does depolarisation happens
The sodium ions flow into the cell causing the membrane potential to become less negative, so an increase in the local transmembrane voltage happens.
This is excitatory.
How does repolarization happens
When potassium ions, which are concentrated inside the cell, flow out of the membrane, it leads to a decrease in the transmembrane voltage.
This is inhibitory.
What has to happen for an action potential to take place
The current that travels to the soma needs to reach a threshold value.
What are the events of the action potential
The sodium ions arrive at the axon hillock and cause a depolarisation.
The membrane potential rises above -55 mV, the threshold value.
The voltage-regulated sodium gates open quickly and sodium flows into the cell to cause a rapid depolarisation, meanwhile potassium gates also open, but slower.
At 0 mV, sodium gates close, and at 35 mV the maximum depolarisation is reached.
Now potassium gates are fully opened and moves out of the cell to cause repolarization.
More potassium leaves than sodium enters so hyperpolarization occurs.
Membrane potential is restored to resting membrane potential.
What is the refractory period
It is a period of resistance to stimulation. During absolute refractory period that section of the neuron cannot have another action potential happening and uring the relative refractory period, the membrane is hyperpolarized so it would take higher excitatory input to trigger another action potential.
How does the signal travels along the axon
The signal travels unidirectionally along the axon by diffusing sodium ions into the next part of the neuron causing it to reach threshold and triggering an action potential. Backwards the neuron will still be in the refractory period so the action potential won’t be triggered again in this direction and the signal will travel forwards.
Myelinated axonal conduction
In the internodes the action potential cannot happen because the Myelin sheath is isolating the axon in Schwann cells. Therefore, the action potential travels only at the nodes of Ranvier in what is called saltatory conduction. By missing out on big chunks of axonal length, the speed of conduction is faster, so myelinated neurons have a higher conduction.
What else affects the conductivity of axons
The thicker the more conductive.
How does synaptic transmission happen
When the electrical signal reaches the terminal arborisations and synaptic knobs, it triggered the influx of calcium by opening voltage-gated calcium channels and the calcium causes the exocytosis of neurotransmitter vesicles.
These then then bind with pre-synaptic the membrane and release the neurotransmitter into the synaptic cleft, to then impinge on the receptors in the post-synaptic membrane.
How many types of neurotransmitters are there in the body
More than 100
First example of how neurotransmitters act
The neurotransmitter binds to sodium channels, sodium flows into the post synaptic cell causing the depolarisation of the cell; if it binds to potassium ligand-gated channels, potassium flows out causing repolarization.
Seconds example of how neurotransmitter act
The neurotransmitter can use noradrenaline, which when bind to its receptor, it dissociates into two parts. the G-protein bit binds to an adenylate cyclase enzyme which converts ATP to cyclic AMP when activated. When the concentration of cyclic AMP goes up inside the cell it causes whatever effect.
