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Brain and spinal cord enclosed in bony coverings


nerve = bundle of axons in connective tissue

Sensory (afferent) divisions

Going to CNS

Motor (efferent) divisions

CNS to effectors that divides into the ANS and Somatic motor division

Sensory (afferent) neurons

Detect changes in body and external environment
Info transmitted into brain or spinal cord


Most abundant, bring info between afferent and motor, connect afferent and efferent

Motor (efferent) neuron

Sends signals out to muscles and gland cells

Excitability (irritability)

Ability to respond to changes in the body and external environment called stimuli
Respond electrically

Cell body

Perikaryon = soma
Single, central nucleus with large nucleolus, cytoskeleton of microtubules and neurofibrils


Projections for receiving signals


Arising from axon hillock for rapid conduction


Form myelin sheaths ONLY in CNS

Ependymal cells

produce CSF (cerebral spinal fluid)


(macrophages) formed from monocytes

Neuroglial Cells

support cells for neurons

Neuroglial tumor

Brain cancer


Most abundant glial cells
- contribute to Blood Brain Barrier (BBB) and regulate composition of brain tissue fluid


Cells make myelin in the PNS

Node of Ranvier

Gaps between myelin segments

Trigger Zone

Initial segment (area before 1st schwann cell) and axon hillock

Speed of Nerve Signals

Large, myelinated fibers > small, myelinated fibers > small, unmyelinated fibers

Regeneration of Peripheral Nerves

Occurs if soma and neurilemmal tube is intact

Types of Nerve Injury

1. Laceration
2. Evulsion - worst prognosis
3. Compression - Best prognosis

Resting Membrane Potentials

~-70mV inside the cell comparing to outside the cell
- electrolytes such as Na+ and K+ pump in/out to maintain the equilibrium

Local Potentials

1. Occurs on a part of the neuron when that part has been stimulated
2. They are graded and decremental (it gets weaker as spread out more)
3. Reversible, work like a dimer

Action Potentials

Electrical information found on axon, only be found within an axon and it will only occur if that trigger zone said it should occur

Characteristics of AP

1. All-or-nothing
2. Always be the same, if it occurs, it occurs all the way
like a light switch
3. Irreversible

Absolute Refractory period

Axon cannot have another action potential

Relative Refractory period

Action potential/axon can make another action potential, but the stimulus for that to occur has to be greater than normal

Purpose of Refractory Period

Preventing back-fire of the conduction, so the electrical msg only go down one direction

Saltatory Conduction

Myelinated fibers insulate the fibers, make the skips down, only the nodes of Ranvier conduct down

Neuron use other chemicals as neurotransmitters

Amino acid neurotransmitters

Excitatory postsynaptic potentials neurotransmitters

Glutamate and Asparate
Increase the mV

Inhibitory postsynaptic potentials

GABA and Glycine
Decrease the mV

Temporal Summation

Single synapse receives many ESPS's in short time

Spatial Summation

Single synapse receives many EPSP's from many cells

Converging circuit

Taking msg from a whole lot different nerve cells and stimulate the axon hillock

Diverging circuit

Same nerve cells spreads out to many different nerves

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