Nervous System

Nervous System
  
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nervous system
 
coordinates stimuli betweem the internal and external environment
PROPERTIES
irritability- sensitivity to a stimuli
conductivity- ability to transmit a response to stimulation
structural organization of the nervous system
 
CNS- brain and spinal cord
PNS- cranial nerves and spinal nerves that link the brain and the spinal cord with the receptors and effectors
PNS
afferent system
 
transmits information from sensory receptors to the CNS
PNS
efferent system
 
transmits information from the CNS to muscles and glands

division of the PNS
somatic
 
voluntary division
- requires nerve stimulus. attached to skeletal
concerned with the external environment and the formation of voluntary motor responses in the skeletal muscles

autonomic
 
involuntary division
- controls all internal involuntary responses in the smooth muscle, cardiac muscle and glands by transmitting nerve impulses along two pathways.
visceral
 
internal, central organs
Autonomic Nervous System
 
- involuntary
- consists of visceral efferent fibers
- conducts impulses to smooth muscle, cardiac muscle, and glands.
- automatically controls such activities as heart beat, peristalsis, secretion flow and blood pressure
sympathetic
 
- mobilizes energy during stressful situations
- times of emergency, "fight or flight"
- increase HR
- dialate bronchi, dialate pupils
- does not increase syliva
pre- neurotransmitter: acytlcholine
post- norepinephrine
parasympathetic
 
- responds to everything back to normal
- slow HR
- constrict pupils back to normal
- constrict bronchi
- normal syliva
- increases GI secretion, stimulus for normal urination
Neurotransmitter: acytlcholine
cells of the nervous system
 
- neuron is the functional unit of the nervous system
- has a single nucleus, but no centrioles (doesn't replicate)
- dendrites convey impulses to the cell body
- axons conducts impulses away from the cell body
axon coverings
 
- enveloped by a sheath of schwann, also called a neurilemma, which is produced by schwann cells.
larger axons
 
- have an inner sheath of myelin, which functions as an electrical insulator and speeds conduction of nerve impulses.
- white matter have gaps called, the nodes of Ranvier where the myelin and the sheath of schwann are interrupted.
axons in CNS
 
lack a neurilemma sheath
- unmyelinated fibers withoug a neurilemma occur in the gray substance of the brain and spinal cord
sensory
 
- afferent neuron
conduct impulses from the receptors in the skin
sense organs, or internal organ to the CNS
motor neurons
 
- efferent neuron
neurons relay impulses from the CNS to the effectors
interneurons
 
- associated neurons
are found entirely within the CNS

neuroglia
 
commonly called glia, supporting cells of CNS
astrocytes
 
- star shaped cells
- vascular feet
- requires glucose, ATP. connect
oligodendrocytes
 
similar to schwann cells found in the PNS
- form myelin sheaths that are wrapped around axons in the CNS
microglia
 
cells have a phagocytic role
ependmal cells
 
line the cerebral cavities, form cerebrospinal fluid
Nucleus
 
A collection of neuron cell bodies located inside the CNS
Ganglion
 
Collection of neuron cell bodies located outside the CNS
Nerve
 
Collection of nerve cell processes located outside the CNS
fibers are held together and supported by connective tissue, which carries blood vessels and lymphatics
Endoneurium
 
Surround each individual nerve fiber
Perineurium
 
Surround a group if fibers in a fasicle
Epineurium
 
Surround each group if fascicles
Mixed nerves
 
Most peripheral nerves are mixed
they contain both unmyelinated and myelinated afferent and efferent
Tract
 
Collection of nerve fibers inside the brain or spinal cord that have a common origin and destination
Commissure
 
Band of nerve fibers that joins corresponding opposite sides of the brain or spinal cord
Synapses
 
Synaptic space between the axon of the presynaptic neuron and post synaptic dendrites
- highly susceptible to changes in physiological conditions
- find neurotransmitters in synapse, acytlcholine (main neurotransmitter)
Alkalosis
 
Above pH 7.4
increases neuronal activity
Acidosis
 
Below 7.4
depresses neuronal discharge
Anoxia
 
Depresses neuronal excitability
Drug effects
 
Increase or decrease neuronal excitability
caffeine increase passage of impulse
general anesthesia decrease neuronal activity
Acetylcholine
 
Generally excitatory, inhibitory to some visceral effectors, skeletal muscle
- a chemical
Norepinephrine
 
Excitatory or inhibatiry
found in visceral and cardiac neuromuscular junctions
coccaine and amphetamines exaggerate the effect
Epinephrine
 
Excitatory or inhibitory
found in pathway concerned with behavior and mood
Dopamine
 
Excitatory
foubd in pathway that regulate emotional responses, decreases levels in Parkinson's disease
enhance basal ganglion
Serotonin
 
Inhibitory
inhibits excessive discharge of neurons
Gamma
 
Aminobutyric acid (GABA) inhibitory, inhibits excessive discharge of neurons
Endorphins and enkephalins
 
Inhibitory, inhibit release of sensory pain neurotransmitters
opiates mimic the effect
CNS- brain
 
human brain comprises of 2% of the total body weight
consumes 25% of its oxygen and receives 15% of cardiac outpu
forebrain
 
telenephalon, cerebral hemispheres, basal ganglia; diencephalon-thalmus and hypothalmus
midbrain
 
cerebral peduncles and corpora quadrigemmina
hindbrain
 
medulla oblongata, pons and cerebullum
central sulcu
 
divide brain into frontal, temporal, parietal, occipital
corpus callosum
 
myelinated fibers
joins the cerebral hemispheres
fissures

sulci
 
deep grooves

shallow grooves
longitudinal fissure
 
divides the cerebrum into left and right hemisphere
occipital lobe
 
primary visual area
auditory area
 
receives nerve impulses concerned with hearing
primary olfactory area
 
temporal lobe is concerned with the sense of smell
primary taste (gustatory)
 
involoved in the preception of taste
frontal lobe
 
higher thinking, artisitc, creativity, intuition, problem solving
can live without
somatic
 
positional relationship of body parts
long and short association tracts
 
interconnect neurons within the same hemisphere
commissure fibers
 
connect one hemisphere to the corresponding area of the other hemisphere
projection fibers
 
ascending and descending pathways coming and going from neurons located in other parts of the brain
descending tracts


ascending tracts
 
motor, cross over at the level of the medulla, down the cord then out

sensory, cross over at the level of the cord, enter opposite side
medulla
 
center of crossing over of motor tracts
cerebral hemisphere
 
main part of the brain
diencephalon
 
"between brain"
lies between the cerebrum and the midbrain and is hidden by the cerebral hemispheres with the exception of the basal view
thalamus
 
2 oval masses
relay station
hypothalamus
 
most important autonomic nervous system control center
part of the forebrain= cerebrum
"primitive activities" maintains water balance and regulates thirst, eating behavior, body temp, and activity of the anterior pituitary gland
brain stem
 
includes the midbrain, pons, medulla oblongata

midbrain
 
contains the corpora quadrigemina, visual and auditory reflex center, the "righting reflex" (keeps the head upright in space)
hindbrain
 
consists of 3 parts, the pons, the medulla oblongata, the cerebellum
pons
 
pneumotaxic aponeustic (control rhythm)
a prominent swelling of the brainstem serves as a bridge between the midbrain and the medulla oblongata
function: conduct impulses, assist in respiratory center (shut breathing off)
medulla oblongata
 
located inferior to the pons and superior to the spinal cord
inferior end: located at the foramen magnum, serves as a conduction pathway and has several functions (vital center, vomitting, coughing, sneezing)
- vital signs minus the temp, increase/decrease HR
cerebellum
 
"little brain"
composed of 2 hemispheres and a central constricted part called the vermis
functions: serves for balance, equilibrium, orientation in space, gives tone to muscles and helps posture, helps in coordination of muscles
spinal cord
 
oval shaped cylinder, 17-18 inches in adult
inner core is composed of gray matter shaped like a three dimensional letter, H

functions of spinal cord
 
serves as a center for the reflex arc
serves as pathway for ascending (sensory) tracts
(sensory tracts enter dorsal area)
serves as pathway for descending tracts (motor)
reflex

receptors (sensory)

efferent (motor)
 
involuntary response to a stimulus

dorsal side

ventral side
reflex arc
 
a place in which incoming sensory impulses become outgoing motor impulses
ascending tracts

descending tracts
 
conduct sensory impulses from afferent neurons upward to the brain

conduct impulses from the brain to the nerves which supply muscles/glands
meninges
 
membranes covering of the brain and spinal cord
connective tissue
cerebral spinal fluid
 
will be found in the sub arachnoid space
dura mater
 
2 layers closely connected except when they separate to form sinuses for venous blood
arachnoid
 
delicate fibrous membrane (cobwebby in appearance)
cob web design allows for blood vessels to continue under arachnoid
pia matter
 
very delicate layer filled with blood vessels
epidural/extradural space
 
between the dura mater and the vertebrae
epidural space only exists in injuries in the cranial cavity.
subdural

subarachnoid
 
between the dura mater and the arachnoid

between the arachnoid and the pia matter. contains cerebrospinal fluid.
cerebrospinal fluid
 
"water helmet"
a clear watery fluid, formed by filtration of blood
found in subarachnoid space
ventricles

spinal cord ends

meninges continue down to sacrum
 
spaces in the brain

between L1-L2

ends at L5, cerebrospinal fluid ends at L5
functions of cerebrospinal fluid
 
acts as a shock absorber
pathway of exchange of nutrient material and waste between the blood and cells of the CNS
spinal puncture
 
performed betwen the 3-4 lumbar vertebrae with no danger to the cord
PNS
 
consists of spinal nerves, cranial nerves, and the autonomic nervous system
spinal nerves
 
31 pair, names for the regions of the vertebral column from which they arise
8 pairs- cervical nerves
12 pairs- thoracic nerve (anterior- sensory, posterior-motor)
5 pairs- lumbar nerves
5 pairs- sacral nerves
1 pair- coccygeal nerves
function: serve as 2 way conduction path between the peripheral nerves and the spinal cord
phrenic
 
nerve which causes movement to diaphram between 3 and 4
cranial nerves
 
12 pair
emerge from the brain

ANS
 
involuntary
branch of PNS
visceral efferent system sends motor impulses
2 neuron relay system
sympathetic
 
times of emergency, "fight or flight"
intervate HR
increase pulse
dialates bronchi/pupils
does not increase syliva
secrete epinephrine
pre neurotransmitter: acetylcholine
post: norepenphrine

parasympathetic
 
responds everything back to normal
neurotransmitter: acetylcholine
slow HR
constrict pupils/bronchi
normal syliva
increase GI secretion
stimulus for normal urination

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