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Nervous system

Central Nervous System

Brain and Spinal Cord


Grouping of neuron cell bodes within CNS


Grouping of Nerve fibers that interconnect regions of CNS

Peripheral Nervous System

Nerves, ganglia, and nerve plexuses

Cranial Nerves

nerves that emerge directly from the brain; twelve pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum; the remaining ten pairs emerge from the brainstem.

Spinal Nerves

emerge from segments of the spinal cord; carries motor, sensory, and autonomic signals between the spinal cord and the body. Humans have 31 left-right pairs of spinal nerves, The spinal nerves are part of the peripheral nervous system (PNS).


cable like collection of many axons, may be mixed with sensory and motor fibers


grouping of neuron cells located outside of CNS

Sensory Neurons

afferent neuron, neurons that transmits impulses from a sensory receptor in the CNS

Motor Neurons

efferent neuron, neuron that transmits impulse from the CNS to effector organ

Effector Organs

a muscle or gland which has an effect when it is turned on by a motor neurone

Somatic Motor

Nerve that stimulates contraction of skeletal muscles

Autonomic Motor

nerve that stimulates or inhibits contraction of smooth and cardiac muscle and stimulates glandular secretions

Smooth Muscles

involuntary non-striated muscle, excited by external stimuli, which causes contraction

Cardiac Muscles

involuntary striated muscle found in the walls and histological foundation of the heart, specifically the myocardium; Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems.

Sympathetic Branch

one of the three parts of the autonomic nervous system, aids in the control of most of the body's internal organs, Stress—as in the flight-or-fight response—is thought to counteract the parasympathetic system

Parasympathetic Branch

responsible for stimulation of "rest-and-digest" activities that occur when the body is at rest, including sexual arousal, salivation, lacrimation (tears), urination, digestion, and defecation.

Guillain - Barre Syndrome

a disorder affecting the peripheral nervous system. Ascending paralysis, weakness beginning in the feet and hands and migrating towards the trunk, is the most typical symptom, and some subtypes cause change in sensation or pain as well as dysfunction of the autonomic nervous system.

Ganglionic Gliocytes

It gives support to the cell bodies in the preipheral nervous system, or PNS.

Multiple Sclerosis

an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms.


CNS; covers capillaries and induce the blood-brain barrier, interact metabolically with neurons and modify the extracellular environment of neurons


CNS, phagocytose pathogens and cellular debris in CNS


form the epithelial lining of brain cavities and central canal of spinal cord, covers tufts of capillaries to form choroid plexuses

Schwann Cells

surrounds axons of peripheral nerve fibers, forming a neurilemmal sheath, also form myelin sheaths; PNS

Satellite Cells

support functions of neurons within sensory and autonomic ganglia; PNS


form myelin sheaths around central axons, producing white matter of CNS; CNS

Mass Activation

a large number of ganglionic neurons activate many effector organs; causes a heightened sense of alertness due to stimulation of reticular activation system

Splanchnic Nerves

aired nerves that contribute to the innervation of the viscera, carrying fibers of the autonomic nervous system (visceral efferent fibers) as well as sensory fibers from the organs (visceral afferent fibers).

Abdominal Ganglia

control movements of abdominal muscles.

Divisions of Automatic Nervous System

Parasympathetic (craniosacral) Division
Adrenergic and cholinergic synaptic transmission
Other autonomic neurotransmittors
Organs with dual innervation

Neurotransmitters in Automatic Nervous System

the chemicals which allow the transmission of signals from one neuron to the next across synapses

Synapses en Passant

Some synaptic junctions appear partway along an axon as it extends

Action Potential

short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory, "nerve impulses" or "spikes"

Refractory Period of Cardiac Muscles

Heart contracts as syncytium & thus can sustain force
Its AP lasts about 250 msec
Has a refractory period almost as long as AP
Cannot be stimulated to contract again until has relaxed

Components of Total Refractory Period

Absolute Refractory Period - due to inactivated Na channels
Relative Refractory Period - due to continued outward K diffusion

Saltatory Conduction

propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials without needing to increase the diameter of an axon.

2 Types of Nerve Fibers

Myelinated Fibers - rapid conduction velocity; Control rapid body movements by skeletal muscles; Transmit sensory signals from receptors to CNS

Unmyelinated fibers - slower conduction velocity
Control subconscious activities via ANS

Function of Myelin Sheath

to increase the speed at which impulses propagate along the myelinated fiber, provides a track along which regrowth can occur

All or None Law in Nerve Fibers

principle that the strength by which a nerve or muscle fiber responds to a stimulus is not dependent on the strength of the stimulus. If the stimulus is any strength above threshold, the nerve or muscle fiber will give a complete response or otherwise no response at all; Henry Pickering Bowditch in 1871

Speed of Conduction Velocities



frequency summation is the method of signal transduction between neurons, which determines whether or not an action potential will be triggered by the summation of postsynaptic potentials.

Neural physiology

the additive effects of graded nerve potentials

Muscle physiology

The additive effects of contractions of different muscle fibers

Types of Summation

Spatial summation and temporal summation

Spatial Summation

recruitment of variable numbers of nerve fibers in a nerve
1. Minimal stimulus or threshold stimulus - voltage at which only one nerve fiber stimulated to fire
2. Maximal stimulus - voltage all the nerve fibers in the nerve fire

Temporal Summation

frequency modulation - variation in number of action potentials sent along a nerve fiber per second: (frequency is limited by the refractory period of the nerve fiber)

Neuronal Junctions

Electrical synapses, synaptic transmission, neuromuscular junction

Electrical Synapses

Cardiac muscle
Some smooth muscles
Some neurons in the brain

Synaptic Transmission

1. Action Potentials reach axon terminals
2. Voltage gated Ca channels open
3. Ca in cytoplasm activates proteins, leading to fusion of vesicles with plasma membrane
4. Pore forms in fused vesicle and exocytosis releases neurotransmitter

Neuromuscular Junction

Motor Unit
Physiological anatomy
Details of transmission
Effect of drugs on the neuromuscular junction
Effect of ions on the neuromuscular junction

Morphology of Gap Junctions

plasma membrane of one cell, plasma membrane of connecting cell, connexin proteins forming gap junctions, surrounding cytoplasm

Skeletal Muscle Neuromuscular Junction

terminal bouton of axon, mitochondria, synaptic vesicles, synaptic cleft, post synaptic cell/skeletal muscle

Excitatory Postsynaptic Potential

a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels.

Inhibitory Postsynaptic Potential

result from the flow of negative ions into the cell or positive ions out of the cell.

Drugs and Effects on Neurol Control of Skeletal Muscles

Botulinium toxin - stops release of acetylcholine (ACH)
Curare - Prevents interaction of ACH with post synaptic receptor protein
Saxitoxin/Tetrodotoxin - blocks voltage gated Na channels
Nerve gas/Neostigmine - stops acetylcholinesterase in postsynaptic membrane
Strychnine - prevents IPSPs in spinal chord

Basic Neuronal Pools

Accumulations of neurons making up the numerous anatomical regions of the CNS

Area of Stimulation

sphere of influence upon neurons with which the neuron synapses

Discharge Zone

Presynaptic neuron causes the postsynaptic neuron to fire

Facilitated Zone

presynaptic neuron fires causes the postsynaptic neurons membrane potential to approach but not reach the threshold potential

Circuits in Neuronal Pools

One oncoming/outgoing, Diverging, Converging, inhibitory

One oncoming - outgoing Circuit


Diverging/ Amplifying Circuit

1 →many neurons
Amplifying - CNS control of skeletal muscles
Diverging circuit → multiple tracts
Sensory information in dorsal columns of spinal cord to:
Cerebellum and Thalamus and cerebral cortex

Converging Circuit

simultaneous control of one neuron by two or more input neurons - sensory branch of the nervous system

Inhibitory Circuit

- shuts off one pathway while opening another

Sensory Receptors

detect intensity gradients of such sensory stimuli as touch, sound, light, smell, taste, cold and warmth; produce generator (= receptor) potentials in proportion to the strength of the environmental stimulus and send pulse encoded information to the CNS for processing

Receptor Potential

produced by sensory transduction., form of graded potential, a depolarizing event resulting from inward current flow. The influx of current will often bring the membrane potential of the sensory receptor towards the threshold for triggering an action potential.

Types of Sensory Receptors

Electromagnetic receptors


Mechanical force, deforms cell membranes of sensory dendrites or deforms hair cells that activate sensory nerve endings

Pain Receptors

Tissue damage, damaged tissues release chemicals that excite sensory endings


dissolved chemicals, chemical interactions affects ionic permeability of sensory cells


light, photochemical reactions affect ionic permeability of receptor cells

Cutaneous Receptors

Free Nerve Endings - light touch, hot, cold, pain
Merkel's Disc - sustained touch and pressure
Ruffini's Corpuscles - sustained pressure
Meissner's Corpuscles - change in texture, slow vibrations
Pacinian Corpuscles - deep pressure, fast vibrations

Fibrous Tunic

Outer eyeball, gives shape to eyeball


white of eye, supports and protects eyeball


inside surface of eyeball, transmits and refracts light

Vascular Tunic

uvea, middle layer of eyeball, supplies blood, prevents reflection


middle layer of posterior of eyeball, supplies blood to eyeball

Ciliary Body

anterior portion of vascular tunic, supports lens through suspensory ligaments and decides thickness, secretes aqueous humor


continous to ciliary body, regulates diameter of pupil, and amount of light that enters

Internal Tunic

inner layer of eyeball, provides location and support for robs and cones


principal portion of internal tunic, photoreception, transmits impulses


between posterior and vitreous chamber, refracts light and focuses on fovea centralis


normal vision, rays focus on retina, no correction needed


nearsightedness, rays focus on front of retina, concave lens


farsightedness, rays focus behind retina, convex lens


rays do not focus, uneven lens

Pupil Reflex

reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the eye, thereby assisting in adaptation to various levels of darkness and light, in addition to retinal sensitivity.

Rod Cell

photoreceptor cells in the retina of the eye that can function in less intense light, approximately 125 million rod cells in the human retina, rod cells are almost entirely responsible for night vision.

Cone Cell

photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, six million in the human eye was found

Optic Nerve

known as cranial nerve 2, transmits visual information from the retina to the brain, does not regenerate after transection.

Tympanic Membrane

ear drum, cone-shaped membrane that separates the external ear from the middle ear in humans and other tetrapods; transmit sound from the air to the ossicles inside the middle ear

Ossicular System

Stapes → Oval window

Spiral Organ of Corti

the organ in the inner ear found only in mammals that contains auditory sensory cells, or "hair cells."

Vestibular Apparatus

contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance.

Ear Anatomy

Outer Ear - helix, auricle, external auditory meatus, earlobe
Middle Ear - auditory ossicles, tympanic membrane, semicircular canals
Inner Ear - Semicircular canals, facial nerve, vestibular nerve, cochlear nerve, cochlea, temporal bone, round window, cavity cavitiy, auditory tube

Primary Sensations of Taste

Sour - H channels
Sweet - Na Channels
Sweet and meaty - sugars and glutamate via g-protein receptors
Bitter - quinine vi g protein receptors

Taste Buds

on papillae of tongue, includes tongue surface, taste pore, taste hair, taste bud - gustatory cell, supporting cell, sensory nerve fiber

Olfactory Cells

bipolar nerve cells derived initially from the CNS,

Primary Sensations of Smell


General Sensory Receptors

Primary receptors = free nerve endings (taste, pain, touch)
Secondary receptors - specialized epithelial cells which form synapses with sensory neurons


neurotransmitter responsible for much of the stimulation of muscles, including the muscles of the gastro-intestinal system, has a part in scheduling REM (dream) sleep.


neurotransmitter strongly associated with bringing our nervous systems into "high alert." It is prevalent in the sympathetic nervous system, and it increases our heart rate and our blood pressure. It is also important for forming memories.


It is an inhibitory neurotransmitter, is strongly associated with reward mechanisms in the brain. Drugs like cocaine, opium, heroin, and alcohol increase the levels.


acts like a brake to the excitatory neurotransmitters that lead to anxiety, and associated with epilepsy


most common neurotransmitter in the central nervous system, actually toxic to neurons, and an excess will kill them. Sometimes brain damage or a stroke will lead to an excess and end with many more brain cells dying than from the original trauma. (ALS disease)


inhibitory neurotransmitter that has been found to be intimately involved in emotion and mood. Too little has been shown to lead to depression, tied to migraines, irritable bowel syndrome, and fibromyalgia.


short for "endogenous morphine.", Inhibitory, it is involved in pain reduction and pleasure, drug associated (heroin)

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