to keep controlled conditions within limits that maintain life by regulating body activities by responding rapidly using nerve impulses. Its responsible for our perceptions, behavior, memories and it initates all voluntary movements 

Sensory – sensory receptors detect internal and external stimuli and carry information to brain and spinal cord

Integrative –processing of sensory information and determining response

Motor –responding to information 

Central nervous system (CNS)-brain and spinal cord

Periperal nervous system (PNS)-

• sensory(afferent) neurons
• motor (efferent) neurons 

Stretch receptors, chemoreceptors 

carry signals toward the CNS

(part of PNS)

stimulate movement of food; secretion of gastric juice and hormones from cells in the epithelium that line the GI tract-->regulates the digestive system

Carries signal away from the CNS to effectors 

(part of PNS)

Somatic

Autonomic

Enteric 

part of PNS

Motor neurons transmit signals to skeletal muscles; voluntary control

Effector: skeletal muscle 

Part of PNS

Motor neurons transmit to:

Effectors: smooth muscle, cardiac muscle, glands

Involuntary control

Two divisions:sympathetic and parasympathetic

Part of PNS

Motor neurons transmit signals to:

Effectors: smooth muscle, glands, endocrine cells of the GI tract

Involuntary control

• 5-25 times more prevalent than neurons
• Function: support, nourish and protect neurons
• Produce interstitial fluid
• Repair: can multiply and divide; can fill space that has been occupied by dead neurons as a result of injury or disease
• classified based on size, cytoplamsic processes and intracellular organization
• four types in CNS:astrocytes, oligodendrocytes, microglia, ependymal cells 
• two in CNS: Schwann cells, satellite cells 

Nerve cells

respond to stimulus and convert it into action potential 

• most numerous neuroglia in CNS
• star shaped
• function:physical support of neurons 
• its processes wrap around blood capillaries
• creates a blood-brain barrier
• in embryo, secrete chemicals that regulate growth, migration, and interconnection of neurons in brain
• helps maintain proper chemical environment for nerve impulse generation
• may play role in learning and memory by influencing formation of neural synapses
• absorb glucose from capillaires, partilly metabolize it and pass it on to neuron

Type of astrocyte

short branching processes; found in gray matter

Type of astrocyte

long branched processes; mainly in white matter 

Neuroglia of CNS 

• fewer processes, provide support
• produce myelin sheath-wrapped around axons in brain and cord-each cell extends 15 broad flat processes that spiral around parts of multiple CNS to form a sheath
• no neurolemma is present as cell body and nucleus do not envelop the axon
• have fewer nodes of ranvier
• no regrowth after injury occurs
• amount of myelin increases from birth to maturity which increases speed of nerve impulse and response to stimuli 

• chromic demyelinating disease of the brain and spinal cord (1/1000 people in age of 20-50)
• manifestations: physical, mental and sometimes psychological impairments 

• Neuroglia of CNS
• phagocytes of CNS-during developments prune neurons, rewire the brain
• first and main form of active immune defense in the CNS-consititue 10-15% of the total glidal cells population within the brain 

• neuroglia of CNS
• single layer of epithelial cells with cilia and microvilli
• line ventricles of brain and central canal
• Function: form cerebrospinal fluid(CSF) and assist in circulation 

Neuroglia of PNS

produce myelin sheath around PNS nerve fibers (axons)

sheath is up to 100 layers of cell membrane 

each cell wraps 1mm length of axon 

each cell myelinates a single axon

participates in axon regeneration

• Neuroglia of PNS
• surround neuron cell bodies in the ganglia of PNS
• regulate exchange between neuronal cell bodies and interstitual fluid 
• is neuron cell body 

• is the outermost membrane layer (plasma membrane of neuroglia cell)
• surrounds the cytoplasm and nucleus of schwann cell
• stimulates regrowth of axon when injured 

• soma or perkaryon-cell body
• dendrites-branching process from cell body
• receptors-distal ends of dentries of sensory neurons
• nerve fibers-axons or dentrites
• nissl bodies(chromatophilic)-clusters of RER that synthesize proteins for maintaining and regenerating neurons processes and renewing neurotransmitters
• neurofibrils-fine fibers extending through dendrites, cell bodies, and axons 

• Synapse-junction of two neurons or a neuron and effector muscle(muscle or gland)
• Neurotropins-proteins that regulate normal growth and development of neurons which include nerve growth factor, brain derived neurotropic factor, and neurotropins 3,4, and 5 

Synapse between a neuron and a muscle 

• Single process but may have collateral branches
• originates from cell body at axon hillock
• impulses arise at junction of axon hillock and initial segment called trigger zone
• axon terminals (telodendria)-fine filaments branching from axon 
• terminate in synaptic end bulbs 

bundles of myelinated fibers located outside brain and spinal cord 

• several dendrites, one axon 
• all motor neurons, most neurons in CNS 

• one dendrite and one axon
• found in retnia, inner ear, and olfactory areas of the brain 

• most sensory neurons 
• dendrites and axon are fused to continuous process
• dendrites function as receptors for touch, pressure, pain or heat

• potentials that triggers impulse conduction 

• always open 
• allows materials to move across membrane by diffusion 

• open and close in response to mechanical vibration or pressure such as sound waves or pressure of touch
• not specific (doesnt care what caused vibration) 

• opens in response to direct change in membrane potential 
• gives nerves and muscle plasma membrane property of excitibility 
• doesnt care what caused change 

• opens/ closes in response to specific chemical stimulus such as neurotransmitters (NT) or via second messenger (horomones and ions) 
• highly specific 

• -70 mV 
• potential across the nonconducting membrane
• 3 Na in/2K out
• # of Na leakage channels are less than K+leakage channels
• large amount of anions are trapped in the cell and minute excess of positive ions outside it producing resting potential 

• role of graded potential is to excite or inhibit action potential 
• occurs in dendrites and cell body membrane where mechanical and ligand gated channels are located
• signals are graded (vary in size depending on strength of stimulus)
• signals can be added to create larger membrane values
• localized-flow of current produced by opening of channels spreads to adjacent regions along the membrane 

Action Potential 

• also known as nerve impulse 
• follows all or none principle
• requires thershold stimulus located at trigger zone
• Na comes into axon induces opening of neighboring Na gated channels triggering new action potential in the next segment of the axon

• action potential initated: rapid inward diffusion of Na causes membranes inner surface to become + (-55)
• at threshold activation gates open followed shortly by closing inactivation gates

• purpose to return to the resting potential 
• threshold opens K+ channels but at slower rate than Na channels
• plasma membrane becomes impermeable to Na
• K+ move through membrane than move in (3Na in 2K out)

• because region of a membrane that has just undergone and action potential and in temperarily in refractory period 
• large diameter axon (.4 msec)
• smaller diameter axon (4 msec) 

• new action potential cant be initated 

• stronger stimulus required to reach a suprathreshold level and initiation of action potential 

• occurs only in myelated fibers; action potential leaps from one node of Ranvier to the next 
• because most of the gation ion channels are localized at the nodes of Ranvier
• myelin insulation prohibits loss of charge across the membrane 

• A fibers (5-20 microns) myelinated 27-290 mph;sensory neurons touch, pressure, joint position, temperature; motor neurons to skeletal muscles 
• B fibers (2-3) myelinated; impulses from visceral to CNS and visceral(motor) neurons
• C fibers (.5-1.5) unmyelinated; pain from viscera and motor autonomic ganglia 

• ion current spreads directly from one cell to another through gap junction 
• each jap junction contains proteins called connexons that form tunnels to connect cytosol of 2 cells
• found in visceral smooth muscle, cardiac muscle and developing embryo
• allows for 2 way transmission of impulses
• synchronize activity of group of neurons 

• neurons do not touch and neurontransmiter crosses cleft and acts on receptors in postsynaptic neurons
• when action potential reaches axon terminals voltage gated Ca+2 channels are opened 
• Ca causes neurontransmitter molecules to be released from synaptic bulb vesicles
• binding of neurotransmitter to receptors opens channels to flow across membrane causing depolarizaion or hyperpolarization 

Excitatory Postsynaptic Potentials (EPSP)

• depolarized postsynaptic membrane
• brings the membrane closer if not to threshold
• induces gated potential
• opens Na channels 

• causes hyperpolarization 
• increases negativity above resting potential
• results fom opening Cl (in) or K+ (out)

• Nt activity terminated at synapse by diffusion out of synaptic cleft
• deactivation by enzymes
• recycling 

• adding together of effects of excitatory and inhibitory NT released from various knobs that synapse with the same postsynaptic neuron (more than one presynaptic)

• buildup of neurotransmitter released by a single presynaptic end bulb firing 2 or more times in rapid succession 

• sub threshold EPSP-decrease in negativity of postsynaptic neurons potential to level above its resting potential but below threshold of stimulation 

Glutamic and aspartic amino acids 

• most common excitory transmitters at brain synapses 

• is most common NT in brain (also present in spinal cord
• opens Cl channels 
• Valium (antianxiety drug) enhances action of GABA 

• is inhibitory NT in spinal cord
• opens Cl channels 

• inhibitory NT involve in emotional responses, addicitive behaviors and pleasureable experiance; caused subconscious movements of skeletal muscles
• parkinsons muscular stiffness due to degeneration of neurons releasing dopamine

• sensory nerves, spinal cord pathways, brain
• pain

• supresses substance p 

• excitatory in brain
• inducing sleep, sensory perception, temperature regulation, control of mood and appetite 

• excitatory NT in PNS
• sympathetic nervous system
• within brain may be related to arousal, dreaming and regualtion of mood 

• condution pathway for sensory and motor impulses
• site for the integration of EPSP and IPSP
• processes reflexes 

• between dura mater and vertebral canal 

• white fibrous tissue outer layer

• potential space between dura mater and arachnoid created by mild trama, contains serous fluid 

• cobwebby, delicate middle mater

• between arachmoid and pia mater contains cerebrospinal fluid 

• transparent, fibrous membrane
• adheres to outer surface of cord and brain 
• contains blood vessels (nutrtious layer)

• thickening of pia mater in spinal cord; project laterally and serve with dura mater between ventral and dorsal nerve roots of spinal nerves 

• cervical and lumbar 

• spinal cord tapers to conical portion between 1st and 2nd lumbar 

• arises from conus medullaris
• extension of pia mater 

• tail like collection of roots of spinal nerves at inferior end of spinal cord 

• shaped like 3D H
• consists of cell bodies of neurons, neuroglia, unmyelinated axons
• gray commissure-cross bar of H, contains central canal

• consists of myelinated axons of motor and sensory neurons arranged in columns
• sensory tracts conduct nerve impulses upward toward brain 
• motor tracts conduct nerve impulses down the spinal cord

• carry impulse for pain, temperature, crude touch, deep pressure
• sensory tract 

• carry impulse for discrimination touch, light pressure, vibration, conscious proprioception (awareness of postion and movements of muscles)

• rubropspinal, tectospinal, vestibulospinal 
• carry impulses for automatic movements, tone and posture, equlibrium, coordinate body movements with visual stimuli 

• white matter of spinal cord and ascend to brain 
• may enter posterior gray horn and synapse with an interneuron whose axon ascends to the brain 
• may enter posterior gray horn and synapse with an interneuron which synapses with a somatic neuron in spinal reflex pathway 

• synapse with somatic motor neurons either direclty 
• indirectly by first synapsing with interneurons that in turn synapse with somatic neuron whos axon pass through anteriot gray horn

• fast response to changes (stimulus) in internal or external enviornment allowing the body to maintain homeostasis 
• inborn: pulling hand away from hot stove
• learned: slamming in contraction of skeletal muscle

• cause contraction of smooth or cardiac muscle, glands 

• carried out by spinal cord alone
• integration takes place in spinal cord gray matter
• knee jerk

• involve brian and cranial nerves 
• integration in brain stem
• tracking movements of eyes as you read 

• two or more neurons conduct impulses from periphery to spinal cord or brain stem and back to periphery
• impulse begins in receptors and ends in effectors

• 2 neuron 
• simplest arc
• can be ipsilateral reflex: sensory impulses enter and motor impulses leave on same side 

• ipsilateral
• important for maintaining muscle tone and coordination during excercise 
• sensory axon synapses with motor neuron inducing contraction; monosynaptic
• purpose:control muscle length by inducing contraction 

• ipsilateral
• muscle relaxation
• protective measure to prevent tearing of tendons
• can override the stretch reflex when tension is great
• sensory receptor:golgi tendon organs 

• contraction of antagonist muscle
• a collateral branch synaoses with an inhibitory interneuron that sensds a hyperpolarizing signal to the motor neuron inducing relaxation of antagonist muscle

• polysynaptic, ipsilateral
• requires contraction of more than 1 muscle group
• removal of a foot when step on tack

• polysynaptic 
• involves contralateral reflex arc (crossing)
• often induced with flexor reflex

• 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal 
• mixed
• cell bodies are located in posterior (dorsal) root ganglion

Endoneurium

Perineurium

Epineurium

• connective tissue covering individual fibers
• covering of fascicles
• outermost covering fuses with meninges 

• serves deep back muscles and skin of dorsal surface of trunk 

• serves muscles/structure of upper, lower extremities, and lateral, ventral trunk 

• reenters spinal canal and supplies vertebrae, vertebral ligaments, blood vessels of cord and meninges

• autonomic nervous system 

• C1-C4
• supply skin and muscles of head, neck, upper shoulders, diaphram

• C5-C8 and T1
• nerve supply for upper extremites and shoulder region 

• L1-L4 
• abs, externial genitalia, lower extremity 

• L4-L5 and S1-S4
• buttocks, perineum, lower extremities 
• contains sciatic(largest nerve in body)

• S4-S5
• small area of skin 

• area of skin that provides a sensory imput to the CNS via posterior roots
• knowlegde of dermatoves help doctors determine which segment of the spinal cord is malfunctioning

• forms a roof over the cerebellum seperates cerebrum from cerebellum 

• extend downward from tentorium separates cerebellum into two hemispheres

• large cavities in each cerebral hemisphere 
• connected to third ventricle by foramen of monro

• verticle slit in cerebrum beneath corpus collsum and longitudinal fissure 

• diamond shaped space between cerebellum and medulla and pons
• expansion of central canal of cord
• connected to 3rd ventricle by cerebral aquadect 
• 3 openings (median aperture of Magendie and 2 lateral aperture of luschka) 

• blood plasma, capillary wall, ependymal cells, ventricle 
• choriod plexus 

• glucose, proteins, lactic acid, urea, cation and anion,white blood cells

• enlargement of cord as enters through foramen magnum
• control of heartbeat, blood pressure, respiration
• centers for reflexes of swallowing, vomiting, coughing, sneezing, hiccuping
• equlibrium
• craninal nerves 8-12 

• above medulla
• pneumotaxic and apenustic areas respiration
• arousal from sleep and consciousness 
• cranial nerves 5-8

• above pons, below diencephalon and cerebrum
• motor coordination, reward(substantia nigra)
• conveys motor impluses from cerebrum to cerebellum and spinal cord
• conveys sensory impusles from spinal cord to thalamus 

• netlike arrangement of small areas of gray matter among white matter of the brainstem that extend througout the brain stem
• regulate muscle tone
• maintaining consciousness 

• attached to brain stem by cerebellar peduncles 
• arbor vitae
• coordination of skeletal muscle contractions

• thalmus, hypothalmus, epithalmus 

• large mass of gray matter in each hemisphere
• major relay station for sensory imput 
• relays motor information form cerebellum and basal nuclei to motor area of cerebral cortex
• pain,temp, awareness of light touch and pressure

• optic chiasma, pituitary stalk (infudibulum), mammilary bodies
• automonic regluation
• syntheizes hormones
• rage, aggression, thirst, appetite, temperature
• mind over body 

• day and night cycles
• olfactory response