Nervous System Overview Flashcards
3 overlapping functions of the NS
- Sensory receptors monitor changes inside and outside the body (stimulus and sensory input)
- Processes and interprets sensory input (integration)
- Dictates a response by activating effector organs (motor output response)
Stimulus vs Sensory Input
Stimulus: changes detected inside of outside the body
Sensory input: information gathered by receptors
CNS
Composed of brain and spinal cord
Integrating and command center
Nuclei present
Securely packing into cranium/intervertebral canal
Nuclei
Clusters of neuronal cell bodies within the CNS
PNS
Consists of nerves extending from brain and spinal cord (cranial and spinal nerves)
Peripheral neves link all regions of the body to CNS
Has ganglia
Ganglia
Clusters of neuronal cell bodies in peripheral NS
Gray matter
Gray coloured and surrounds hollow central cavities of the CNS
Forms H-shaped region in the spinal cord
Is composed primarily of neuronal cell bodies, dendrites, nonmyelinated axons
Surrounds white matter of CNS in cerebral cortex and cerebellum
Some gray tissue in the white matter (from embryonic development when they migrated there)
White matter
Lies external to the gray matter of the CNS
Composed of myelinated axons
Consists of axons passing between specific regions of the CNS
White colour comes from the myelin sheaths around the axons
Nervous tissue (and 2 major cell types)
Cells are densely packed and intertwined
Neurons: transmit electric signals
Support cells: neuroglia in CNS - nonexcitable, surround and wrap neurons
Neurons
Basic structural unit of the NS
Specialized cells conduct electrical impulses along the PM
Special characteristics of neurons (3)
Longevity: can live and function for a long time
Do not divide: fetal neurons lose their ability to undergo mitosis, neural stem cells are an exception
High metabolic rate: require abundant oxygen and glucose (die after a few minutes without them(
Chromatophilic bodies
Nissl bodies
Clusters of rough ER and free ribosomes
Function to renew membranes of the neuron
Can be easily stained by basic dyes
Extend only into the basal part of dendrites and to the base of the axon hillock
Dendrites
Extensively branching from the cell body
Transmit electrical signals toward the cell body
Function as receptive sites for receiving signals from other neurons
Axons
Neuron usually only has one
Impulse generator and conductor
Transmits impulses away from the cell body
No chromatophilic bodies
No protein synthesis in the axon
Neurofilaments and microtubules provide strength and aid in transport of substances
Branches are infrequent
Axonal transport
Movement of substances to and from the cell body
Axon collaterals
Branches along the axon length
Rare
Terminal arborization
Multiple branches of the axon at the end
End in knobs called terminal boutons
Synapses
Sites where the neurons communicate
Most information passed through chemical messengers
Some info transmitted electrically through gap junctions
Structural classification of neurons
- Multipolar
- Bipolar
- Unipolar
- Possess more than 2 processes (numerous dendrites and one axon)
- Possess 2 processes (rare, found in eyes and olfactory)
- Possess one short, single process (starts as bipolar during development, somatosensory)
Motor (efferent) neurons
Carry impulses away from the CNS to effector organs
Most are multipolar
Cell bodies are in the CNS
Form junctions with effector cells
Interneurons (association neurons)
Most are multipolar
Lie between motor and sensory neurons
Confined to the CNS
Sensory (afferent) neurons
Transmit impulses towards the CNS
Virtually all are unipolar neurons
Cell bodies in ganglia
Short process divides into central process (into CNS) and peripheral process (to receptors)
2 types of glial cells in PNS
Satellite cells
Schwann cells
Astrocytes
Star shaped
Most abundant glial cells of the CNS
Regulate exchange of molecules between the circulatory system and NS contributing to the BBB
Regulate NT levels by uptake
Signal increased blood flow through capillaries in active regions of the brain
Control ionic environment around neurons
Oligodendrocytes
Produce myelin sheaths around axons in the CNS
Fewer branches than astrocytes
Line up in small groups and wrap their cell processes around the thicker axons in the CNS
Gaps between the myelin sheaths are the nodes of Ranvier
Myelin sheath
Segmented structures that are composed of the lipoprotein myelin and surround the thicker axons of the body
They form an insulating layer that prevents the leakage of electrical current from the axon, increase the speed of impulse conduction along the axon, and makes impulse propagation more energy-efficient
Microglia
Defensive cells in the CNS
Phagocytes - the migrate to, and engulf invading microorganisms and injured or dead neurons
Do not originate in nervous tissue, like the other macrophages, they are derived from blood cells called monocytes during embryonic and fetal periods
Ependymal cells
Form simple epithelium that line central cavity of the CNS
Provide a fairly permeable layer between cerebrospinal fluid that fills the cavity and the tissue fluid that bathes the cells in the CNS
Bear cilia that help circulate the cerebrospinal fluid
Choroid plexus
Site of cerebrospinal fluid formation
Continuous with the ependyma projects into ventricles
Schwann cells
Produce myelin sheaths around axons in the PNS
Unlike oligodendrocytes, each Schwann cell actually wraps around and forms the sheath, not just the processes that wrap
Satellite cells
Surround neuron cell bodies in the ganglia
Nerves
Cable like organs in the PNS
Consist of numerous axons wrapped in connective tissue
Most nerves contain myelinated and nonmyelinated sensory and motor axons
Axon is surrounded by Schwann cells
Endoneurium
Layer of delicate connective tissue surrounding the axon
Perineurium
Connective tissue wrapping surrounding a nerve fasicle
Nerve fasicles
Groups of axons bound into bundles
Epineurium
Whole nerve is surrounded by tough fibrous sheath
Location of cell bodies for
- Motor neurons
- Sensory neurons
- In CNS
2. Outside CNS
