Functions of the nervous system
- Sensory input (PNS)
- Integration (CNS)
- Motor output (PNS)
Peripheral Nervous System (PNS)
Not including the CNS (brain and spinal cord)
Consists or spinal and cranial nreves
PNS functional subunits
Afferent
Efferent
Afferent Division
Sensory “carrying towards”
- Somatic sensory fibers: convey impulses from skin, muscles and joints
- Visceral sensory fibers: transmit from visceral organs (in ventral body cavity)
Efferent Division
Motor “carrying away”
- Somatic NS: voluntary, controls skeletal muscles
- Autonomic NS: involuntary, controls heart pumping digestion ect.
Neuroglia (or glial cells)
6 cells that make us neurons:
Neuroglia of the CNS
Astrocytes
Microglial
Ependymal
Oligodendrocytes
Neuroglia of the PNS
Satellite cells
Schwann Cells
Astrocytes
Most abundant & versatile
Making exchanges between capillaries and neurons
Mopping up leaked K+
Recycling released neurotransmitters
Microglial Cells
Type of macrophage
Phagocytize microorganisms and neural debres
Janitor
Ependymal Cells
Line CNS cavities
Cilia helps circulate CSF
Oligodendrocytes
Form myelin sheaths around CNS fibers
Satellite cells
unknown function may be similar to astrocytes
Schwann Cells
Vital for regeneration of peripheral nerve fibers.
Form myelin sheath
Similar to oligodendrocytes
Dentrites
Receptive, input region
Each neuron has many dentrites
Motor neurons, off the cell body
Short, tapering, diffusley branching extentions
Axons
Each neuron has one axon
spender process
long axon = nerve fiber
Conducting region
Axon Hillock
cone shaped initial region of the axon
Axon Collaterals
Extend from axon at right angles
Axon terminals
Secretory region
knoblike distal ends of axon terminal branches
Myelin Sheath
White, fatty fibers (protein-lipiod)
Protects, electronically insulates and increases speed on nerve impulse
Only on axons not dendrites.
White matter
Myelinated regions of the CNS, primary fiber tracts.
Grey matter
Unmyrlinated fibers and contains mostly nerve cell bodies.
Nodes of Ranvier
Gaps in myelin sheath
Neuron structural classifications
Multipolar
Bipolar
Unipolar
Multipolar neurons
3 or more processes (1 axon the rest dendrites)
Most common
Major type in CNS
Bipolar neurons
2 processes
(1 axon 1 dendrite)
retina and olfactory mucosa
Unipolar neurons
Single short process
emerges from cell body
divides T-like into proximal and distal branches
Found in PNS ganglia
Interneurons
Multipolar
lie between sensory and motor
In CNS
Action Potential
Nerve impulse, conduction impulse that travels down the axon.
Voltage
Potential energy generated by separated charge.
Current
Flow of electrical charge from one point to another
Resistance
The hindrance to charge flow provided by substance it passes through
Ohm’s Law
Current= voltage/resistance
2 membrane ion channels
- Chemically gated
2. Voltage gated
Chemically gate ion channels
Open when neurotransmitter binds
Voltage gated ion channels
Open and close in response to changes in membrane potential.
Resting membrane potemtial
The potential difference in a resting neuron
Generating resting membrane potential depends on:
- Differences in K+ and Na+ concentrations in and out of the cell.
- Differences in permeability of plasma membrane to those ions.
Change in membrane potential can produce:
- Graded potentials:Incoming signals over short distances
2. Action potentials: long dostance signals of axons
Depolarization
Decrease in membrane potential
Hyperpolarization
Increase in membrane potential