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NERVOUS SYSTEM FUNDAMENTALS (Senses (Stimulus Type (Thermoreceptor: cold…
NERVOUS SYSTEM FUNDAMENTALS
Nervous System Organization
CNS
Structure:
Brain & Spinal Cord
Function:
Receive, process and respond to sensory input
PNS
Structure:
Cranial Nerves, Spinal Nerves & Ganglia
Function:
Gather sensory info from receptors and pass onto CNS
SNS
Somatic Motor:
Travels to skeletal muscle, skin, body wall (not body cavity. Involuntary, motor/efferent/output
Somatic Sensory:
Travels from skeletal muscle, skin, joints. Includes - proprioception, hearing, vision, equilibrium. Sensory/afferent/input
ANS
Autonomic/Visceral Motor:
Travels to ventral body cavity, smooth muscle (blood vessels), cardiac muscle, (sweat) glands. Involuntary, motor/efferent/output
Autonomic/Visceral Sensory
: Travels from ventral body cavity, includes- taste and smell. sensory/afferent/input
Anatomy of Nervous System
Nerve Components Description
: Basic unit is the
axon
, some of which are wrapped in insulated coating,
myelin sheath
, this is deep to
endoneurium
(loose C.T.). A bundle of these axons make up a
fascicle
which is wrapped in a layer of
perineurium
(fibrous C.T.). Fascicles are wrapped up together including
blood vessels
under a layer of
epineurium
(tough fibrous C.T.) to make up a
nerve
.
CNS Neuroglials
Astrocytes:
Most abundant, function: support, communication and maintaining chemical balance
Microglia:
smallest and able to replicate, function: phagocyte - eats invading microbes and damaged/ dying nervous tissue
Ependymal Cells
: simple cuboidal looking epithelium with cilia on one end and microvilli on the other, functions to circulate cerebospinal fluid. located in ventricles.
Oligodendrocytes
: Produces myelin sheath, wraps around axons
PNS Neuroglials
Schwann Cells
: produces myelin sheath, can wrap around one axon many times or many axons
Satellite Cells:
found in ganglia, surrounding neuron cell bodies. function as support, regulating what goes in and out of neuron cell bodies
Neurons
Structural types of Neurons
Multipolar:
many process extend off of cell body, one is an axon, the rest are dendrites
Bipolar:
two processes extend off of the cell body, one is an axon and the other is a fused dendrite
Unipolar:
one process extends off of the cell body and splits to form the central and peripheral processes (axon)
Functional types of Neurons
Motor (efferent)
: sends signals away, multipolar in structure
Sensory (afferent):
sends signals to, unipolar in structure. Special senses are bipolar in structure
Interneurons
(between/association): Between neurons, in CNS only, multipolar in structure
Neuron Components:
cell body:
(soma) single nucleus surrounded by cytoplasm
nucleus & nucleolus:
creates ribosomes
chromatophilic substance:
dense region of rough ER and ribosomes (creates proteins and plasma membrane)
dendrites:
large surface area, receptive site, conduct electrical signal toward cell body
axon hillock:
where axon leaves cell body
axon:
impulse generator and conductor transmitting nerve impulses away from cell body
axon collaterals
: branch of axon from main axon
terminal arborization:
branched end of axon
terminal boutons (axon terminals):
secretory region, end knob of axon
Senses
Stimulus Origin
Exteroceptors:
stimulus origin is our environment (skin and special senses
Interoceptors:
Stimulus is our internal organs
Proprioceptors
: stimulus origin is in muscles, tendons, ligaments and joints (sense of where body is)
Stimulus Type
Thermoreceptor:
cold and warm
Photoreceptor:
light
Chemoreceptor:
chemicals (smell, taste and blood)
Nociceptor
: pain
Mechanoreceptor:
touch, vibration, stretch, pressure
Baroreceptor:
sense of pressure (blood) (mechanoreceptor)
Eye
Pathway
: cornea --> lens --> retina --> optic nerve --> cranial nerve II --> optic chiasma --> optic tract --> mid brain --> thalamus --> primary visual cortex
Components
: sclera, cornea, choroid, lens, retina, optic disc, cones and rods, optic nerve, iris, macula lutea, fovea centralis, cililary body,
Olfaction
Pathway
: PCE tissue (w/ olfactory sensory nerves) --> olfactory bulb --> olfactory tract --> limbic region (emotional brain) OR primary olfactory cortex (temporal lobe)
Components
: Smell receptors in nasal cavity roof (olfactory epithelium), olfactory sensory neurons, olfactory stem cells, olfactory cilia in epithelium,
Ear
Pathway
: Tympanic membrane (ear drum) vibrates --> transmits vibrations to middle ear --> auditary ossicles (3) --> transmits vibrations to fluid filled cochlea --> vestibular & cochlear nerve --> medulla oblongata --> pons --> mid brain --> thalamus --> primary auditory cortex
Components
: tympanic membrane, auditory ossicles, cochlea, internal acoustic meatus, vestibular nerve, external acoustic meatus, auditory tube,
Gustation
Pathway
: tastebud receptor cells --> 3 cranial nerves --> medulla oblongata --> thalamus --> primary gustatory cortex
Components
: Tastebuds in tongue, inner cheeks, pharynx, palate, epiglottis, Cranial Nerves VII, IX & X, vagus, papillae, fungiform, vallate & foliate papilla, taste pore, gustatory hairs, gustatory epithelium