Introduction To Nervous System Flashcards
CNS
- central nervous system
- brain- in skull
- spinal chord- vertebral canal
- connect at foramen magnum
PNS
- peripheral nervous system
- made if nervous tissue, with sensory receptors, ganglia, plexuses, nerves
- external to CNS
- sensory and motor division
Sensory division
Ending of neurons that detect, heat, pain, light
•sensory receptors
•transmits action potential from receptors to CNS
Motor division
Efferent way •response transmits action potential from CNS to effector organs •ex: muscle glands Subdivisions: Somatic and autonomic
Somatic (motor division, PNS)
Conscious control movement
•cell bodies in CNS,axons extend to skeletal muscles
Autonomic (PNS, motor division)
•transmits action potential from CNS to specific sites
•out put, in voluntary
•two sub divisions:
Sympathetic and parasympathetic
Sympathetic (PNS, motor division, autonomic subdivision)
Most active during physical activity
•fight or flight
Parasympathetic (PNS, motor division, autonomic subdivision)
•regulates resting functions
Ex: digesting food, emptying bladder
•rest and relax
Neurons
Receive stimuli
•transmits action potentials to other neurons or effector glands
•3 parts:
Cell body, axon and dendrites
Cell body
- aka soma
* source of info for protein synthesis
Dendrites
Inputs
•different neurons have different amount if dendrites
Multipolar neuron
Has multiple dendrites and an axon
•most common neuron
•most neurons in the CNS and motor neurons
•axon conducts action potential to CNS
Bipolar neuron
Has a dendrite and an axon
•dendrite is specialized to receive stimuli
•axon conducts action potentials to the CNS
•sensory organs: eyes nose ears
Pseudo-unipolar neuron
An axon
No dendrites
•sensory receptor to CNS
•mostly sensory neurons
Axon
Nerve fivers
•most have straight alignment and uniform diameter
Trigger zone
Made of:
Axon hillock
Initial segment
Axon hillock
Where action potential starts
Initial segment
Beginning of axon
Presynaptic terminals
Output
•enlarged ends branching out from axons
•contain neurotransmitters in small vesicles
Sensory neurons conduct towards:
CNS
Motor neurons conduct away from:
CNS and towards muscles or glands
Interneurons
Conduct action potential from one neuron to another
Neuroglia
•supporting cells •help form a permeability barriers between blood and neurons •produce cerebral fluid 3 types Astrocytes, choroid plexus, microglia
Astrocytes
Star shaped neuroglia
•cytoplasmic processes extend from cell body
•cover surfaces: blood vessels, pia matter, neurons
•with foot processes
•blood-brain barrier
•regulate extra extracellular composition of brain fluid
Blood-brain barrier
Astrocytes Creates a water tight junction between endothelial cells
•determines what passes from the blood to nervous tissue of the brain or spinal chord
Ependymal cells
- produce cerebrospinal fluid
- line ventricles of brain and central canal of spinal chord
- bear patches of cilia that help move cerebrospinal fluid
Choroid plexuses (CNS neuroglia)
- specialized ependymal cells and blood vessels
- central regions of ventricles
- secrete spinal fluid
Cerebrospinal fluid (CNS)
- secreted by choroid plexus
- moved through out brain cavities on patches of cilia
- cilia helping with movement
Microglia (CNS)
Neuroglia in CNS
•free swimming
•phagocytic in response to stimulation
•move to areas of stroke, trauma, infection, perform phagocytosis
Oligodendrocytes CNS
Have cytoplasmic extensions that can surround axons
•if wrapped many times, forms a myelin sheath
•can for myelin sheaths around portions of several axons
Peripheral nervous system
- Schwann cells
* satellite cells
Schwann cells PNS
Neuroglia in PNS
•wrap around axons
•wrap many times creates myelin sheath
•only wrap around a portion of one axon
Satellite cells PNS
•surround neuron cell bodies in sensory ganglia
•provide nutrients and support to neuron cell bodies
•protect neurons from heavy metal poisons
- absorbs and reduces access to neuron cell bodies
Myelinated
- Schwann cells or oligodendrocytes wrap repeatedly around axon
- makes action potential faster
- wrapped membranes rich in phospholipids
- cytoplasm sandwich between layers
Unmyelinated
- rest in invaginations of Schwann or oligodendrocytes
- surrounds but does not wrap
- able to surround many cells at once
- nucleus in center of surrounding axons, in cytoplasm
Gray matter
- groups of neurch cell bodies and dendrites
* little myelin
White matter
Myelinated areas
CNS gray matter
- cortex: grey matter on the surface of the brain
* clusters of grey matter located deeply in the brain are called NUCLEI
PNS gray and white matter
Ganglia: gray matter, clusters if neuron cell bodies
Nerves: white matter
Bundles if axons with connective tissue and sheathes
Leak ion channel
Non gated
# of each leak ion channel in membrane determines its permeability characteristics of plasma to different ions
• permeable to k+ and cl-
•less permeable to na+ due to lack of channels
Ligand gated ion channels
- has an extracellular receptor site and membrane spanning part, forms ion channel
- Ligand Neurotransmitter that binds to receptor to open or close
- in nervous and muscle tissues as well as glands
Ganglion
Cluster of cell bodies in PNS
Nerve tracts are formed by what?
White matter of the CNS
•propagate APs from one area of the CNS to another
Voltage gated ion channels
- open and close in response to small voltage across plasma membrane
- measured in millivolts
- Na+ K+: electrically excited tissue
- Ca+ : smooth muscle and cardiac muscle fibers
Plasma membrane of voltage gated channels
- millivolts measured by charge difference, due to neg charge inside plasma membrane relative to outside
- stimulated cell changes permeability of membrane due to open gates
- movement if ions into or out of cell changes charge difference across the plasma membrane
Resting membrane potential
- in stimulated, is potential difference
- intercellular fluid neutral (cations and anions)
- extracellular fluid also neutral
Polarized
Due to changes across membrane
•inside negative outside positive
Potential difference
Electrical charge difference across membrane
Depolarization
- decrease in the membrane potential
- caused by decrease in charge difference (polarity) across plasma membrane
- inside becomes more positive
Hyperpolarization
- increase in membrane potential
- caused by increase of charge difference across plasma membrane
- inside becomes more negative
Grades potential
- chance in membrane potential that is localized to one area of the plasma membrane
- potential change can vary from small to large
Nerve fiber types are classified by what
Size and myelination
•structure reflects function
Nerve fiber types
1- large and myelinated, 15-20 mls
• motor neurons supporting skeletal muscles, most sensory neurons
2-lightly myelinated medium sized 3-15 mls
3- small and unmyelinated
Type 2 and 3 nerve fiber types are mostly:
- part of the ANS, stimulates internal organs ( stomach heart intestines)
- responses necessary to maintain internal homeostasis
- don’t need to be as rapid as responses to external environment
Synapsis
Junction between two cells
•where communication takes place
Presynaptic cell (terminal)
•transmits a signal towards the synapse
Postsynaptic cell (membrane)
•cell that receives the signal from presynaptic terminal
Postsynaptic membrane
Membrane of post synaptic cell
•usually neurons, muscle cells or glands
Neurotransmitter
- in chemical synapse
- action potentials do not pass directly from the presynaptic terminal to postsynaptic membrane
- instead, AP causes the release of neurotransmitters from terminals
Synaptic vesicles
- contains neurotransmitters
* are membrane bound
How action potential travels
- AP arrives at presynaptic terminal
- initiate a series of specific events
- = the release of neurotransmitters
- voltage gate Ca2+ channels open
- Ca2+ diffuse into presynaptic terminals
- ions cause synaptic vesicles to fuse with presynaptic membrane
- release neurotransmitter by exocytosis into synaptic cleft
Presynaptic terminals job:
•produce and release neurotransmitters
Exocytosis
Elimination of material from a cell through the formation of vacuoles
Post synaptic potentials
When Hyperpolarization occurs in post synaptic membrane
Excitatory postsynaptic potential
- when depolarization occurs
- the response is stimulatory
- graded potential is called “EPSP”
Excitatory postsynaptic potential “EPSP”
- important because depolarization might reach threshold and fire off action potential
- excitatory neurons: release neurons that cause EPSP
Inhibitory postsynaptic potential
- when neurotransmitter and receptor result in Hyperpolarization
- “IPSP”
Inhibitory postsynaptic potential “IPSP”
- important because they reduce the likelihood of producing action potential
- movement and potential farther from threshold
Inhibitory neurons
- release neurotransmitter substances that cause IPSP
* results from increase if permeability of the plasma membrane to Cl- or K+
Axoaxon synapse (CNS)
•the axon of one neuron synapses with the presynaptic terminal if another
Presynaptic inhibition
The amount of neurotransmitter release from the presynaptic terminal decreases
•ex: endorphins can reduce or eliminate pain by inhibiting the release of neurotransmitter from presynaptic terminals
Presynaptic facilitation
The amount if neurotransmitter release from presynaptic terminal increases
Ex: serotonin, release in certain axoaxonic synapses, function as neuromodulator that increase release of neurotransmitters from the presynaptic terminal, opening voltage gated Ca2+ channels
Spatial summation
- occurs when multiple action potentials arrive at two presynaptic terminals
- that synapse with same post synaptic neuron
Temporal summation
Two or more action potentials arrive in very close succession @ single presynaptic terminal
•combine where IPSP and EPSP summate to reach threshold
