Download The Nervous System

The Nervous System
The Divisions of the Nervous
System
• The Central Nervous System
– Brain
– Spinal Cord
• The Peripheral Nervous
System
– Mixed Sensory and Motor
Nerves
– Sensory Nerves
– Motor Nerves
– Voluntary Somatic Nerves
– Involuntary Autonomic Nerves
– Sympathetic Nerves
– Parasympathetic Nerves
The Divisions of the Nervous
System
• Somatic v Autonomic
– Somatic: voluntary motor
neurons; cell body in CNS
with axon connecting to
skeletal muscle
– Autonomic: (internal body
organs) Involuntary motor
neuron; two neurons with
one cell body in CNS and
one in PNS
1. Sympathetic - speeds up
heart, constricts vessels
2. Parasympathetic controls body under
normal conditions
The Neuron
The Basics
• The cell body: contains the
nucleus and dendrites
• The Dendrites: carry impulses
to the cell body
• The Axons: carry impulses
away from the cell body
• * The Myelin sheath provides
insulation for the axon and
speeds impulse conduction
from the cell body to the axon
terminals (white fiber)
• * Lose the Myelin sheath and
lose control over skeletal
muscle (multiple sclerosis)
The Neuron
The Basics
• Schwann cell are supporting cells that
wrap themselves tightly around the
axon forming the myelin sheath
• Neurilemma: outer most part of the
Schwann cell
• Nodes of Ranvier: exposed
membrane at regular intervals
• Receptor ending: peripheral nerve
ending specialized for response to
particular types of stimuli
• Synapse: * region of communication
between the axons of one neuron and
the dendrites of another
• Acetylcholine: chemical transmitter
substance released by nerve endings
The Neuron
The Basics
• Nerve fiber: axon or
dendrite of a neuron
• Nerve: bundle of axons
outside of the central
nervous system
• Ganglion: group of
nerve-cell bodies in the
PNS
• Tract: collection of nerve
fibers in the CNS having
the same origin,
termination, and function
Types of Neurons
• Sensory Neurons (Afferent)
Carry impulses to the CNS
• Motor Neurons (Efferent)
Carry impulses from the CNS
to muscles and glands
*instructs muscles to contract
• Inter-Neurons
Carry impulses from one
neuron to another
• Mixed Neurons
Composed of both sensory
and motor fibers (e.g. Cranial
nerve V – Trigeminal: clenches
jaw/chewing, sensation of
forehead, cheeks, and jaw)
Types of Neurons
• Myoneural Junction
Also known as
neuromuscular
junction; Axon
terminal of a motor
neuron, synaptic cleft,
and sarcolemma of a
muscle cell
The Central Nervous System
Protected by:
• *Bones: cranium and spinal
vertebrae, encase the brain
and spinal cord
• *Meninges: cover the brain and
spinal cord, tough membranes
composed of three layers
1. dura mater 2. arachnoid
3. pia mater
• *Ventricles: cavities within the
skull that act as safety valves
to relieve pressure
• *Cerebrospinal Fluid:
surrounds the brain and spinal
cord, transfers impacts over a
greater surface area acting as
a shock absorber
The Central Nervous System
• Encephalon or
Interbrain
• Sits on top of brain
stem
• Includes cerebrum,
cerebellum, medulla
oblongata, pons, and
midbrain
The Central Nervous System
The Brain
• The Cerebrum (largest part)
– Frontal Lobe
– Personality (logic, emotions,
memory, consciousness,
etc.)
– * Motor area
– * Thought processes
•
Parietal Lobe
– Somatic Sensory area
•
Temporal Lobe
– Speech (Broca’s Area)
– Auditory area
•
Occipital Lobe
– Visual area
The Central Nervous System
• The Cortex
– * Outermost layer of
Cerebrum
– * Gray matter of the
brain
– Contains most of the
convolutions (folds)
of the brain
The Central Nervous System
The Brain (cont.)
• Cerebellum
– * Balance
– * Equilibrium
– * Coordination
The Central Nervous System
The Brain (cont.)
• Hypothalamus
– * Regulates body temp
– * Regulates water
homeostasis
– * Regulates
metabolism
The Central Nervous System
• Hemispheres
– Connected by cerebral
nerves to opposite sides of
the cerebrum
• Right Side
– Controls left side of body
– Controls speech,
calculation, and writing
– Main language center
• Left Side
– Controls right side of body
– Controls spatial abilities,
simple language,
comprehension, nonverbal
ideation
The Central Nervous System
The Brain (cont.)
• Thalamus
– Relay station for
sensory impulses
passing up to the
sensory cortex
– Encloses 3rd ventricle
of the brain
The Central Nervous System
The Brain-stem (joins
spinal cord to brain)
• Medulla oblongata:
*controls vital body
functions
–
–
–
–
–
Heart rate
Blood pressure
Breathing
Swallowing
Vomiting
The Central Nervous System
The Brain-stem
• Pons
– “Bridge” area, mostly
fiber tracts
– Does have important
nuclei involved in
controlling breathing
The Central Nervous System
The Brain-stem
• Midbrain
– Anteriorly composed
of two bulging fiber
tracts which convey
ascending and
descending impulses
– Posteriorly, composed
of four bulging nuclei
which are reflex
centers involved with
vision and hearing
The Central Nervous System
• Meninges
– *Dura mater: double
layered membrane,
outermost covering, very
strong, fused to inner
surface of skull (periosteal
layer) and covers brain
(meningeal layer)
– *Arachnoid mater: middle
layer, web like
• Subarachnoid space:
area where cerebrospinal
fluid
– *Pia mater: innermost
layer, very delicate, clings
to brain and spinal cord
following every fold
The Central Nervous System
• Brain matter:
– Gray: composed of
neuron cell bodies;
concentrated in
cerebral cortex
– White: composed of
fiber tracts (bundles of
nerve fibers); connects
various parts of the
brain with each other
and the spinal cord
The Central Nervous System
•
Spinal Cord Matter
– Gray matter:
• located in center of cord in an Hshape
consists of cell bodies and
dendrites
• Anterior or ventral horns contain
motor neurons of the somatic
(voluntary) NS
• Posterior or dorsal horns contain
association neurons, interneurons,
and sensory neurons
• Sensory nerves that enter the
cord via the dorsal root have their
cell bodies in the dorsal root
ganglion
• Motor nerves exit the cord via the
ventral root
• The dorsal and ventral roots make
up the spinal nerve
The Central Nervous System
• Spinal Cord Matter
– White matter:
• surrounds gray matter
• Consists of myelinated
fiber tracts (axons) that
transmit impulses to or
from the brain or from one
side of the cord to the
other
• Afferent tracts: Fiber
tracts that carry sensory
impulses to the brain are
sensory tracts
• Efferent tracts: Fiber
tracts that carry impulses
from the brain to skeletal
muscle are motor tracts
The Central Nervous System
• Spinal Cord
– *Is the pathway for
messages to get from
the body to the brain
and vice versa via
– *It is the reflex center
and allows reflex
impulses to bypass the
brain and go directly to
the motor neurons to
protect the body
Peripheral Nervous System
• Link between CNS and
the rest of the body
Consists of all nerves
outside of the CNS
– Cranial Nerves
– Spinal Nerves
– Autonomic Nervous
System
• Sympathetic Nerves
• Parasympathetic Nerves
• Cranial Nerves
Cranial Nerves
• On I - Olfactory
Old II - Optic
Olympus III - Oculomotor
Towering IV - Trochlear
Tops V - Trigeminal
A VI - Abducens
Finn VII - Facial
And VIII - Acoustic
German IX - Glossalpharyngeal
Viewed X - Vagus (abdominal
viscera, longest nerve)
Some XI – Spinal Accessory
Hops XII - Hypoglossal
• Cranial Nerve Testing Video
Cranial Nerve Assessment Neurological Examination of the Nervous
System
• Cranial Nerve I
– Olfactory: Test sense of
smell
with spirits of ammonia
• Cranial Nerve II
– Optic: Test for visual acuity
•
•
•
•
read printed material
count fingers at distance
distinguish light from dark
read eye chart
Cranial Nerve Assessment
• Cranial Nerve II and III
– Optic and Oculomotor
• Inspect size and shape of pupils
– pupils equal & round
• Test pupillary response to light
– pupils constrict when a light
is shined into eye
– opposite eye should reflexively
constrict (consensual reaction)
– record normal response
as “PERL” - pupils equal and
reactive to light
Cranial Nerve Assessment
• Cranial Nerve III, IV, VI
– Oculomotor, Trochlear, Abducens
• Test extraocular movements (EOM) by asking
patient to look to the extreme left and then up and
down; to the extreme right then up and down with
no head movement
– movements referred to as the six cardinal
directions of gaze
- Oculomotor: pupillary reaction, Trochlear: eye
movement, Abducens: lateral eye movement
Cranial Nerve Assessment
• Cranial Nerve V
– Trigeminal
• Test motor movement by asking
patient to clench teeth while
palpating temporal muscle
(in front of ear) and masseter muscles
(muscles used to raise/lower jaw and
assists in mastication or chewing)
• Test sensation by touching forehead,
cheeks, jaw on each side
Cranial Nerve Assessment
• Cranial Nerve VII
– Facial
• Inspect the face at rest and during conversation,
noting symmetry, tics, or abnormal movements
• Ask patient to raise the eyebrows, frown, show both
upper and lower teeth, smile, and puff out both
cheeks
• Assess strength of facial muscles by asking patient
to close eyes tightly so they cannot be opened, and
gently attempt to raise the eyelids
• Observe for weakness or asymmetry
Cranial Nerve Assessment
• Cranial Nerve VIII
– Acoustic: Assess hearing acuity
cover one ear at a time and ask patient to
repeat short test words spoken softly
and
then louder by examiner
Cranial Nerve Assessment
• Cranial Nerve IX and X
– Glossopharyngeal and Vagus
• Assess patient’s ability to swallow with ease; to
produce saliva; and produce normal voice sounds
• Instruct patient to hold breath, and assess
for normal slowing of the heart rate
• Testing for the gag reflex also will test
the cranial nerves
• Innervates abdominal viscera
• Vagus is the longest cranial nerve
Cranial Nerve Assessment
• Cranial Nerve XI
– Spinal Accessory
• Ask patient to raise and lower shoulders
and to turn head
• Cranial Nerve XII
– Hypoglossal
• Ask patient to stick out tongue and to
move it in several directions
Peripheral Nervous System
•
Spinal Nerves – 31 pairs
– Innervate muscles and organs
Both sensory and motor nerves
•
Autonomic Nervous System
– Governs internal organs
•
Peripheral Nervous System
– Sensory Nerves
• Dermatomes: areas of sensation
on the skin that innervated by
different spinal nerve levels
•
Peripheral Nervous System
– Motor Nerves
• Myotomes: motor nerves that
innervate muscles allowing certain
muscle actions
Peripheral Nervous System
– Sensory Nerves
• Dermatomes: areas of
sensation on the skin
that innervated by
different spinal nerve
levels
– Motor Nerves
• Myotomes: motor
nerves that innervate
muscles allowing
certain muscle actions
Peripheral Nervous System
• The ANS is the self governing
division of the nervous system
– Comprised of the
Parasympathetic and
Sympathetic Nervous Systems
which are antagonistic to each
other but balance each other
out
• Parasympathetic NS
– Carries out normal functions
• Sympathetic NS
– Takes over in times of stress;
works with adrenaline