THE NERVOUS SYSTEM Flashcards
What is the function of the nervous system
homeostasis and coordination. employs electrical and chemical means to send messages very quickly from cell to cell
What are the two major subdivisions of the nervous system
CNS and PNS
What does the CNS consist of
brain and spinal chord
what does the PNS consist of
ganglia and nerves
what is a neuron
a cell of the nervous system
what is a nerve
bundle of nerve fibres (axons) wrapped in fibrous connective tissue
what is the ganglion
a knotlike swelling in a nerve where the cell of bodies of neuron are concentrated
what are the subdivisions of the PNS
- sensory (afferent) division
i. somatic sensory
ii. visceral sensory - motor (efferent)
i. somatic motor
ii. visceral motor
a. sympathetic
b. parasympathetic
what is the sensory (afferent) division
carries sensory signals from receptors (sense organs and simple sensory nerve endings) to the CNS
what is the somatic sensory division
signal from receptors in the skin, muscle, bones and joints
what is the visceral sensory division
signals from viscera of the thorax and abdominal cavities e.g. heart, lungs and stomach
what is the motor (efferent) division
carries signals from the CNS to the glands and muscle cells (effectors)
what is the somatic motor division
signals to skeletal muscle for voluntary contraction and involuntary somatic reflexes
what is the visceral motor division (autonomic nervous system)
signals to glands, cardiac muscle, smooth muscle; involuntary visceral reflects
what is the sympathetic division
tends to arouse the body for action e.g. increases heart and respiratory rates, but inhibits digestion
emergency response
what is the parasympathetic division
tends to have a calming effect e.g. slowing downtime heart rate, but stimulates digestion
normal everyday conditions
what are the properties of neuron
- excitability(stability)
- conductivity
- secretion
how are cells excitable
all cells are excitable e.g. they respond to stimuli, but neurons have developed this to the highest level
how are cells conductive
stimuli produce electrical signals in neurons that are conducted to other cells at distant locations
secretion of cells
electrical signals at the end of nerve fibres cause the release of chemical neurotransmitters
what are the type of neurons
sensory (afferent)
interneurons (association neurons)
motor (efferent)
what are sensory (afferent) neurons
detection of signals;
neurons conduct signals from receptors to CNS
what are interneurons
they lie in the CNS; process, store, retrieve information and make decision ; 90% of all neurons;
they are confined to CNS
what are motor (efferent) neurons
signals to muscle and glands;
neurons conduct signals from the CNS to effectors such as muscles and glands
what is the structure of a neuron
- soma/neurosoma/cell body
i. cytoskeleton-microtubules
ii. nil bodies- dark staining RER
iii. no mitosis after adolescence
iv. inclusions
v. dendrites
vi. axon hillcock
How big is the soma
5-135μm dia
what is the cytoskeleton made of
neurofibrils (actin)
what is inclusions
glycogen granules, lipid droplets, melanin, lipofuscion (golden brown pigment produced when liposomes digest worn out organelles, wear and tear granules)
what are dendrites
receive stimulus and carries it impulses toward the cell body
what is the axon hillcock
they give rise to the axon
What is the structure of a neuron
- axon/ nerve fibre
i. may be myelinated
ii. may have collaterals
iii. terminal arborisation ending in synaptic knob
iv. substances are produced in the soma and transported along the axon (axonal transport)- movement from the to the axon is called anterograde transport and the reverse is called retrograde transport
how big is the axon
1-20μm dia, few mm to 1m in length
what is the axon
fibre which carries impulses away from cell body
rapid conduction of nerve signals; cyptoplasm= axoplasm; membrane = axolemma
what are glue cells called
support cells neuroglia
What are the neuroglia of CNS
oligodendrocytes
epdnymal cells
microglia
astrocytes
what are the neuroglia of PNS
Schwann cells
satellite cells
what is oligodendrocytes
form myelin in brain and spinal cord
what is myelin
a mixture of proteins and phospholipids forming a whitish insulating sheath around many nerve fibres
what is the epdnymal cells
line cavities of brain and spinal cord; secrete and circulate cerebrospinal fluid
what is microglia
phagocytise and destroy microorganisms; foreign matter, and dead nervous tissue
what are astrocytes
they cover brain surface and non synaptic regions of neurons; form supportive framework in CNS; induce formation of blood brain barrier; nourish neurons; produce growth factors that stimulate neurons; communicate electrically with neurons and may influence synaptic signalling; remove K+ and some neurotransmitters from ECF of brain and spinal cord; help to regulate composition of ECF; form scar tissue to replace damaged nervous tissue
what are the neuroglia of PNS
Schwann cells and satellite cells
What are the Schwann cells
they are cells which produce myelin or fat layer in PNS
form neurilemma around all PNS nerve fibres and myelin around most of them; aid in regeneration of damaged nerve fibres
what are the satellite cells
surround somas of neurons in the ganglia; provide electrical insulation and regulate chemical environment of neurons
what is myelination
it provides insulation along axons
it increases nerve conduction speed by approx an order of magnitude
•2-4μm dia fibre- 0.5 to 2m/s unmyelinated and 3 to 15m/s myelinated
•20μm fibre myelinated 120 spiral outwards
Schwann cells in PNS- spiral outwards
Oligodendrocytes in CNS- spiral outwards
what is the resting membrane potential
- membrane potential = the pd between the ICF and ECF, about -70mV at rest= resting membrane potential
- origin of RMP
i. membrane is most permeable to K+
Imagine k+ only in ICF at start- this would diffuse out down concentration gradient
Non diffusible anions in ICF attract K+ back
At equilibrium K+ is 40 x more concentrated in ICF and ECF- this would give RMP at -90mV
Na+ is 12 x more concentrated in ECF than ICF- this diffuses down concentrated gradient into cell and reduces negative charge in ICF
Therefore K+ leaks out and Na+ leaks in
Na+ K+ pump- this consumes 1 ATP to pump 3Na+ out and 2K+ in- contributes -3mV to RMP; accounts for 70% energy requirement of nervous system
Net effect is RMP of -70mV
what is local potential
typically beings at dendrite- stimulus causes the opening of Na+ channels; membrane potential becomes less negative- depolarisation; current traceless to the neuron’s trigger zone; can be inhibitory- hyperpolarisation
what is action potential
it typically beings at trigger zone- produced by voltage regulated ion gates; high density go theses at trigger zone; strong local potentials can trigger that action potential
how does the action potential work
- Na+ ions arrive at the axon hillock and cause a depolarisation
- the membrane potential rises above -55mV - the threshold potential
- voltage regulated Na+ gates open quickly and Na+ flows into cell to cause rapid depolarisation; slower K+ gates also open
- At 0mV, Na+ gates colse- maximum depolrisation is reached at +35mV
- Slow k+ gates are fully open and K+ moves out of cell to cause repolarisation
- More k+ leaves than na+ enters so hyper polarisation occurs
- membrane potential is restored to RMP
what is the difference between depolarisation and repolarisation
The main difference between depolarization and repolarization is that the depolarization is the loss of resting membrane potential due to the alteration of the polarization of cell membrane whereas repolarization is the restoration of the resting membrane potential after each depolarization event.
what is refractory period
period of restumulation
myelinated axonal conduction
- APs ont at nodes of Ranvier
- AP appears to jump from node to node across the internodes- saltatory conduction
- Faster than unmyelinated conduction
what is the myelin sheath
dense lipid layer which insulates the axon- makes the axon look gray
what is the node of ranvier
gaps or nodes in the myelin sheath
what is neurilemma
thin sheath around a nerve axon (including myelin where this is present)
what is the somatic nervous system made up of
spinal nerves and peripheral nerves
astrocytes
found in blood brain barrier; have a role in transferring nutrients from capillaries to deeper regions of brain
what is depolarisation
when it becomes less negative
