Nervous system Flashcards
What is the function of the nervous system ?
- Maintaining homeostasis. Regulate and coordinate physiology
- Receiving sensory input. Monitor internal and external stimuli
- Integrating information. Brain and spinal cord process sensory input and initiate responses
- Controlling muscles and glands
- Establishing and maintaining mental activity. Consciousness, thinking, memory, emotion
What are the components of the nervous system ?
Brain, spinal cord, sensory receptors.
What are the two subdivision of the nervous system.
Central nervous system (CNS) : brain and spinal cord
Peripheral nervous system (PNS) : sensory receptors and nerves.
The periphery nervous system includes …
Sensory receptors , nerve, ganglion and plexus.
Sensory receptors
ending of neurons or separate, specialized cells that detect such things as temperature, pain, touch, pressure, light, sound, odors
Nerve
a bundle of axons and their sheaths that connects CNS to sensory receptors, muscles, and glands
what are the 2 division of the nerve ?
cranial nerves: originate from the brain , 12 pairs
spinal nerves: Originate from spinal cord, 31 pairs
ganglion
collection of neuron cell bodies in PNS.
Plexus
extensive network of axons, and sometimes neuron cell bodies, located in PNS
What are the divisions of the PNS ?
Sensory ( afferent)
Motor (efferent)
Sensory (afferent)
Afferent = towards
Transmit action potentials from sensory receptors to CNS .
ex : If you feel scorching heat on your hands, the message will travel through your afferent pathway to CNS.
Motor (efferent )
efferent = away
transmits action potentials from CNS to effectors ( muscles, glands)
motor division is divided into 2.
somatic nervous system and autonomic nervous system.
Somatic nervous system
from CNS to skeletal muscles
- voluntary (consciously control movement of our skeletal muscles.
- cell body located in CNS and axons extend out via nerves to skeletal muscles.
so, single neuron system
Synapse
junction of a nerve cell with another cell.
what is a neuromuscular junction
is a synapse between a neuron and skeletal muscle cell.
Autonomic division system. (ANS)
- from CNS to smooth muscle, cardiac muscles and certain glands.
- Involuntary control
- Have a 2 neurons system : 1st - from CNS to ganglion, 2nd - from ganglion to effector.
Autonomic nervous system is divided into 2 ;
1) Sympathetic
2) Parasympathetic
3) enteric
Sympathetic
Prepares body for physical activity
Parasympathetic
regulates resting or vegetative functions such as digesting foods or emptying of the urinary bladder.
Enteric
Can control the digestive tract independently of the CNS, but still considered part of ANS because of the parasympathetic and sympathetic neurons that contribute.
What is the organization of the nervous system.
Receptors –> sensory –> Central Nervous system –> MNS –> Effector
glial cells
support and protect neurons
neurons
receive stimuli and transmit action potential
nissi substance
its a chromatophilic substance in the cell cell body.
Has rough ER, primary site of protein synthesis.
Dendrites
short, often highly branched , which have receptors for neurotransmitters - receive information from other nerve cell
dendritic spines
little protuberance where axons synapse with dendrite.
trigger zone of an axon
site where action potentials are generated; axon hillock and part of axon nearest cell body
types of neurons : Structural classification
Multipolar , bipolar and unipolar.
Multipolar
most neurons in CNS, motor neurons
- Have many dendrites and one axon
Bipolar
Sensory in retina of the eye and nose
- one dendrite and one axon.
Unipolar
single process that divides into two branches. Part that extends to the periphery has dendrite-like sensory receptors.
and the other branch extend s to the CNS
Types of neutrons : Functional classification
sensory neurons , motor and interneurons
interneurons
within CNS from one neutron to another
Glial cells of CNS : Astrocytes
Processes form feet that cover the surfaces of neurons and blood vessels and the pia mater.( is a membrane covering the outside of the brain and spinal cord)
• Regulate what substances reach the CNS from the blood (blood-brain barrier). Microfilaments for support.
• Produce chemicals that promote tight junctions to form blood-brain barrier
Blood-brain barrier
protects neurons from toxic substances, allows the exchange of nutrients and waste products between neurons and blood, prevents fluctuations in the composition of the blood from affecting the functions of the brain.
• Regulate extracellular brain fluid composition
- Hence, det. what substances can pass from the blood into the nervous tissue of the brain and spinal cord.
Glial cell: Ependymal cells
line ventricles of brain and central canal of spinal cord and cilia help to circulate cerebral spinal fluid.
- Specialized versions of ependymal form choroid plexuses which help to form CSF.
Choroid plexus
within certain regions of ventricles. Secrete cerebrospinal fluid. Cilia help move fluid thru the cavities of the brain. Have long processes on basal surface that extend within the brain tissue, may have astrocyte-like functions.
Microglia
specialized macrophages. Respond to inflammation, phagocytize necrotic tissue (dead tissue), microorganisms, and foreign substances that invade the CNS.
Oligodendrocytes
form myelin sheaths if surrounding axon. Single oligodendrocytes can form myelin sheaths around portions of several axons.
Schwann Cells
wrap around portion of only one axon to form myelin sheath. Wrap around many times. During development, as cells grow around axon, cytoplasm is squeezed out and multiple layers of cell membrane wrap the axon.
Satellite cells
surround neuron cell bodies in sensory ganglia, provide support and nutrients
Myelinated axons
-Myelin protects and insulates axons from one another, speeds transmission, functions in repair of axons.
– Not continuous
Nodes de Ranvier
– Completion of development of myelin sheaths at 1 yr. but NOT all parts of the brain are fully myelinated until adulthood (when does it complete?)
– Degeneration of myelin sheaths occurs in multiple sclerosis and some cases of diabetes mellitus.
Unmyelinated axons
rest in invaginations of Schwann cells or oligodendrocytes. Not wrapped around the axon; gray matter.
Grey matter
unmyelinated axons, cell bodies, dendrites, glia. Integrative functions
White matter
myelinated axons. Nerve tracts propagate action potentials from one area in the CNS to another
( Axons)
Where is the gray and white matter located in the brain ?
gray is outer cortex as well as inner nuclei (this represents groups of neuron cell bodies); white is deeper.
Where is the grey and white matter located in the spinal cord ?
white is outer, gray is deeper.
ganglia
PNS gray matter is groups of cell bodies
Action potential
Its an electrical signal that is produce by the cell
• Transfer of information from one part of body to another
• Electrical properties result from ionic concentration differences across plasma membrane and permeability of membrane
What causes the ion concentration difference across the membrane ?
• These ion concentrations are a result of two processes: the Na+/K+ pump and membrane permeability. Note high concentration of Na and Cl- ions outside and high concentration of K+ and proteins on inside. Note steep concentration gradient of Na+ and K+, but in opposite directions.
Ligand gated channel
requires that a molecule (drug or neurotransmitter) binds to a receptor to cause it to open; receptors are usually protein or glycoprotein
- ex : acetylcholine binds to acetylcholine receptor on a Na+ channel. Channel opens, Na+ enters the cell.
gated ion channels
open and close because of some sort of stimulus. When they open, they change the permeability of the cell membrane.
Proteins and Cl-
Permeability
Proteins: synthesized inside cell: Large, don’t dissolve in phospholipids of membrane. Proteins are negatively charged.
• Cl- are repelled by proteins and they exit thru always-open nongated Cl- channels (leak channels).
Leak ion channels
Many more of these for K+ and Cl- than for Na+. So, at rest, more K+ and Cl- are moving than Na+.
• How are they moving? Protein repels Cl-, they move out. K+ are in higher concentration on inside than out, they move out.
– Always open and responsible for permeability when membrane is at rest. – Usually specific for one type of ion although not absolute.
Voltage gated channel
open or close in response to small voltage changes across the cell membrane.
At rest, is it more negative in the inside or outside ?
• At rest, membrane is negative on the inside relative to the outside.
What happens when cells are stimulated ?
When cell is stimulated, that relative charge changes and voltage-gated ion channels either open or close. Most common voltage gated are Na+ and K+. In cardiac and smooth muscle, Ca2+ are important.
Speed of conduction
Faster in myelinated than in non-myelinated
• In myelinated axons, lipids act as insulation forcing ionic currents to jump from node to node
• In myelinated, speed is affected by thickness of myelin sheath
• Diameter of axons: large-diameter conduct more rapidly than small-diameter. Large have greater surface area and more voltage-gated Na+ channels
