5.1 Nervous tissue Flashcards
divisions of motor system
Central Nervous System (CNS):
- Brain annd spinal chord of doral body cavity
- integration and control center: interprets sensory input and dictates motor output
Peripheral Nervous System
- portion of the nervous system CNS
- Consists mainly or nerves that extend from brain and spinal chord
- spinal nerves to and rom spinal chord
- Cranial neres to and from brain
Sensory division of PNS
and ex
*afferent pathway
- somate and visceral sensory nerve fibers
- conducts impulses from receptos to CNS
ex: Skin -> Somatic sensory fibers
Ex: stomac -> isceral sensory fibers
Motor divison of CNS
* efferent pathway: motor nerve fibers (conduct impulses from CNS -> effectors
- somatic (voluntary, cns -> skeletal muscles) and autonomic division (visceral motor fibers, involuntary)
- autonomic is further divided into: sympathetic and parasympathetic
What are the two principal types of cells in the NS
1) Neurons: excitable cells that transmit electrical signals
2) Neuroglia (glial cells): supporting cells (6 types)
* Neuroglia out number neurons by a 10:1 ratio -> make up half the mass of the brain
*in CNS extracellular space is less than 20%
What are the types of neuroglia?
CNS: Astrocytes, microglia, ependymal cells, oligodendrocytes
PNS: Satellite and Schwann cells
What are astrocytes
*only in CNS, most abundant cell in brain (20-40% of gial cells)
- guides migration of young neurons an dformation of synpases, suppors anchors and braces neurons
- cover capillaries and help determine capillary permeability
- control chemical env (neurotransmitters and ions, mop up K+)
- have gap junctions to communicate between astrocytes (Ca2+ pulses)
participate in information processing in brain -> modulate synpatic transmission and play role in long term propogation
Role of astrocytes in BBB
- NOT A BIG RILE
- tight junctions and basal lamina of cerebral endothelial cells play biggest role in BBB
What are Microglia?
Small, ovoid cells with thorny processes
- Migrate toward injured neurons
- Phagocytize microorganisms & neuronal debris
WHat are ependymal cells
*CNS
- range in shape from squamous to columnar
- Ciliated cells circulate cerebrospinal fluid (CSF) around CNS
- Line central ventricular cavities of brain & spinal column
- Produce CSF
- Separate the CNS interstitial fluid from CSF
what are oligodentrocutes
*CNS
One cell can produce processes that wrap up to 60 axons (1 μm)
• Forming insulating myelin sheaths
What are satellite glial cells (SGC)
*PNS
Surround neuron cell bodies in ganglia of PNS
- Control microenvironment around neuron cell body
- Similar to astrocytes of the CNS
What are Schwann cells
*PNS
Most form myelin sheaths around axons
• Vital for function, maintenance and regeneration of damaged nerve fibers
How do schwann cells myelinate?
- envelopes an axon
- Schwann cell rotates around axon, wrapping its plasma membrane loosely around it in successive layers.
- Schwann cell cytoplasm is forced from between membranes (tight membrane wrappings surrounding axon form myelin sheath).
what is the Myelin Sheath?
Composed of myelin, a whitish, protein-lipid substance
Function: Protect and electrically insulate axon & Increase speed of nerve impulse transmission
– Myelinated fibers: segmented sheath surrounds most long or large-diameter axons
– Nonmyelinated fibers: do not contain sheath -> Conduct impulses more slowly
Myelin sheaths in the PNS
- Schwann cells wrap many times around axon
- neurilemma: peripheral buldge of Schwann cell cytoplasm
- gaps in myelin sheal between adjacent schwann cells = Nodes of Ranvier
*sites wehre axon collaterals can emerge
Unmyelinated Axons in the PNS
- thin nerve fibers are unmyelinated
- one Schwann cell may incompletely enclose 15+ unmyelinated exaons
Myelin Sheaths in the CNS
Formed by processes of oligodendrocytes
- Nodes of Ranvier
- No neurilemma
- Thinnest fibers (axons) are unmyelinated
- One oligodendrocyte can wrap around up to 60 axons
- Gives rise to white matter
what are Neurons/ their special charcateristics of neurons
- Neurons = structural units of the nervous system
- large highly specialized cells that conduct impulses
Special characteristics: exteme longevity (lasts lifetime), amitotic (non dividing), high metabolic rate: req continuous supply of oxygen and glucose
*al have cell body and one or more processes
What is the other name for the Neuron cell body?
It is the ____ center of the neuron
what structureal features does it contain?
Neuron cell body = Perikaryon or soma
- biosynthetic centre of the neuron
*synthesizes proteins, membranes and chemicals
contains a Rouhg ER (chromatophilic substance or Bissl bodies
*PM is part of the region that receives input along with the dendrites
CLusters of Nuerno cell bodies are called ___ in the CNS and ___ in the PNS
Nuclei in CNS
– Ganglia in PNS
what is the axon hillock
part of neuron cell body (perikaryon)
- cone shaped area from which axon arises (lacks nissle bodies)
What are the two types of neuron processes?
What are the bundles of these processes called?
Two types of processes: Dendrites & axons
Bundles of processe sare called: Tracts in CNS and Nerves in PNS
What are Dendrites
- motor neurons contains 100s of dendries (short tapering diffusely bracnhes processes)
*contain same organelles as in cell body
- Receptive (input) region of neuron
– Convey incoming messages toward cell body as graded potentials (short distance signals)
– Finer dendrites are highly specialized to collect information
What are structures on finer dendries
contain dendritic spines, appendages with bulbous or spiky ends
Describe the axon/ its structure
- one per neuron, starts at axon hillock
- some axons can be over 1m long
- branches are called axon collaterals
Axons branch profusely at their end (terminus)
• Can number as many as 10,000 terminal branches (telodendria)
– Distal endings are called axon terminals or terminal boutons
What is the function of the axon?
- generates & transmits nerve impulses (action potentials) away from cell body
- Trafficking along axons by motor molecules in two directions:
- Anterograde: away from cell body (twds axon term)
- can move: mitochondria, cytoskeletal elements, membrane components, enzymes
- Retrograde: toward cell body
- organelles to be degraded, signal molecules, viruses, and bacterial toxins
- Anterograde: away from cell body (twds axon term)
what are the 3 structural classifications of neurons
multipolar, bipolar and unipolar
what are multipolar neurons?
three or more processes with one axon and rest dendrites,
most abundant (>99% CNS neurons are multipolar) includes motor neurons and interneurons
What are bipolar neurons
two processes with one axon + one dendrite
(Rare) found in retina and olfactory mucosa
*found in sensory organs (olfactory, mucosa, eye and ear)
what are unipolar neurons
(pseudounipolar): single, short process that has 2 branches.
Cell bodies typically are found in ganglia in the PNS where they function as sensory neurons
* Peripheral process: more distal branch, often associated with a sensory receptor
* Central process: branch entering CNS
*common only in dorsal root ganglia of spinal chord and sensory ganglia of cranial nerves
What are the functoinal classifications of neurons
- Sensory(afferent):Transmitimpulsesfromsensoryreceptors toward CNS
- Interneurons (association neurons): Shuttle signals through CNS pathways; most within CNS
- Motor(efferent):CarryimpulsesfromCNStoeffectors
What is white matter and gray matter?
White matter: Dense collections of myelinated fibers
Gray matter: Mostly neuronal cell bodies & unmyelinated fibers
Basic principles of electricity for potentials
what is voltage, current and resistance?
- Voltage (V) = measure of potential energygenerated by separated electrical charges
- measured between two points -> potential difference
- Flow of electrical charges (electrons and ions) from one point to another = current (I)
• Resistance (R) = hindrance to charge flow
* Insulator: substance with high electrical resistance
*Conductor: substance with low electrical resistance
What is Ohms law
Current (I) = voltage (V)/resistance (R)
Current directly proportional to voltage
• Greater the voltage (potential difference) = greater current
*No net current flow between points with same potential
– Current = inversely proportional to resistance
* The greater the resistance, the smaller the current
What are the two main types of ion channels when dealing w/ electricity in cell
- Leakage (nongated) channels * always open
- Gated channels, in which part of the protein changes shape to open/close the channel
- Three main gated channels: chemically gated, voltage- gated, or mechanically gated
compare the 3 types of electical gated channels
chemically gates; open with bidnign of specific neurotransmitter *assist w/ graded potential
Voltage: open and close in response to changes in membrane potential * assist with active
Mechanically gated: open and close in response to physical deformation of receptors (assist w/ graded pot
What is resting membrane potential and what is it influenced by?
RMP of neuron ~70 mV
- cytoplasmic side of neutron is neg charged rel to outside
RMP influenced by:
- Impermeable to negatively charged proteins
– Slightly permeable to Na+ (Na+ leakage channels)
– 25-100 times more permeable to K+ (K+ leakage channels)
– Freely permeable to Cl–
– Differences in ionic composition of ICF and ECF
– Differences in plasma membrane permeability
Sodium and potassium conc on either side of memrbane at rest
Na conc higher outside cell
K conc hgiher inside cell
*Na+-K+ ATPases (pumps) maintain concentration gradients of Na+ & K+ across membrane.
How is resting membrane potential generated?
*ranges from -20 to -200 mV
- Requirements:
Na+ /K+ pump: pumps more cations out
The concentration gradient of K+
Higher permeability to K+
Membrane impermeable anionic proteins
What signals cause changes in membrane potential?
- Membrane potential changes when: Concentrations of ions across membrane change & Membrane permeability to ions changes
Graded potentials; incoming signals operating over short distances
Action potentials; long distance signals of axons
* Changes in membrane potential are used as signals to receive, integrate, and send information
Depolarization vs hyperpolarization
Depolarization
- reduction in membrane potential
- Inside of membrane becomes less negative than resting potential
- ↑ probability of producing a nerve impulse
Hyperpolarization
- increase in membrane potential
- Inside of membrane becomes more negative than resting potential
- ↓ probability of producing a nerve impulse
What are graded potentials?
What are the two types?
Short-lived, localized changes in membrane potential
– stronger the stimulus = more voltage changes -> farther current flows
- Triggered by stimulus that opens gated ion channels -> depolarization or hyperpolarization
Named according to location and function
– Receptor potential (generator potential): graded potentials in receptors of sensory neurons excited by some form of energy (e.g. heat, light or other)
– Postsynaptic potential: neuron graded potential
How do graded potentials travel? what happens w/ distance
Depoalrization causes small patch of membrane to depolarize
- spreads -> opposite charges attract each other creating local currents that depoalrize adjactent areas
- membrane potential decays w/ distance bc current is last thru leaky plasma membrane
*graded potentials are short distance signals
