Transcript Nervous System

Nervous System
Academic Anatomy
& Physiology
The Function
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To act as the
master controlling
and
communicating
system for the
body
Subdivided into
CNS & PNS
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ervsys.gif
Cells of the Nervous System
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1. Neuroglia
Acts to support neurons
 Makes up ~ 90% of brain and spinal
cord (s.c.)
 There are 5 different types of
neuroglial cells
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Types of Neuroglia
A.
 B.
 C.
 D.
 E.
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Astrocytes
Oligodendrocytes
Microglial cell
Ependymal Cells
Schwann Cells
Assignment
Using page 225 in your text, draw
the different types of neuroglia and
list their location and function within
the nervous system below each
drawing
 DO NOT draw Schwann cells but do
list its location and function
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Cells of the Nervous System
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2. Neurons
The conducting nerve cell
 Senses changes in environment,
integrates information, carries out
motor responses
 Structure: each neuron varies in shape
and size, but all have 3 main parts
(dendrite, axon and cell body)
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Neuron
Neuron Anatomy
A. Dendrite: a process off of the cell
body; receives impulses from
adjacent neurons & conducts
electrical impulses TOWARD the
cell body; ~1000/neuron
Neuron Anatomy
B. Axon: aka nerve fiber; acts to
transmit impulses AWAY from the
cell body; 1 axon/neuron
C. Cell Body: contains the nucleus
and metabolic center of the cell
Neuron Anatomy
D. Myelin sheath: made by schwann cells
in PNS and oligodendrocytes in CNS;
encloses the axon & speeds up the rate
of nervous conduction
i. Gray matter: non-myelinated
nerve fiber
ii. White matter: myelinated nerve
fiber
Neuron Anatomy
E. Nodes of Ranvier: gaps in
myelin sheath @ regular intervals;
aids in increasing speed of nervous
conduction
3 Types of Neurons
1. Afferent (sensory) Neurons:
transmit impulses from PNS to CNS
i.e. pain receptors and
proprioceptors
2. Efferent (motor) Neurons:
transmit impulses from CNS to
muscles or glands
Motor Neuron
3 Types of Neurons
3. Interneurons (association
neurons): located within CNS and
conducts impulses between sensory
and motor neurons
Nerve Conduction:
Distribution of Ions
More Na+ on outside than inside a
neuron
 More K+ on inside than outside +
negatively charged particles
 K+ ions permeate through lipid bi-layer
more easily than Na+ ions do
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Nerve Conduction: Resting
Potential
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Describes a polarized, resting nerve
K+ and Na+ follow laws of diffusion
Na+/K+ pump maintains the unequal
distribution of these ions across
membrane
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Cell uses energy to keep Na+ out and K+ in
despite natural diffusion
Inside of cell is more negative than outside
Nerve Conduction:
Depolarization
An activated nerve cell; has been
stimulated
 Na+ specific channels in the
membrane open and Na+ floods into
the cell
 The charge on the inside of the cell
is now LESS negative (more
positive)
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Nerve Conduction:
Repolarization
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Returning to a resting state
K+ specific channels in the membrane
open and K+ floods the outside of the
cell
This returns the inside of the cell to a
MORE negative (less positive) state
Depolarization + Repolarization of a nerve
cell = An Action Potential
Impulse Conduction
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A wave of bioelectric action potentials
travels the length of a neuron, stimulating
adjacent neurons as it goes
Unmyelinated neurons slower than
myelinated
Impulses on myelinated neurons seem to
jump from one node of Ranvier to the
next
The Synapse
An action potential is electrical
across the neuron and chemical
once it reaches the synaptic cleft
 Presynaptic Neurons
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Have synaptic knobs sensitive to Ca+
 When Ca+ is present allow synaptic
vesicles within them to release
neurotransmitters
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The Synapse
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Neurotransmitters cross the synaptic cleft
and bind to postsynaptic neurons
Excitatory Neurotransmitters:
triggers action potential to continue in
postsynaptic neuron
Inhibitory Neurotransmitters: lessens
the chance of a continuing
neurotransmitter
Impaired Conduction
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The following block nervous
impulses by reducing the membrane
permeability to sodium ions
Alcohol
 Sedatives
 Anesthetics
 Cold and pressure (slows, does not
impair)
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Structural Classifications of
Nervous System
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Central Nervous
System (CNS)
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Includes brain and
spinal cord
Acts as integrating
and command
center
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Peripheral
Nervous System
(PNS)
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Includes nerves
outside of CNS
• Spinal nerves
• Cranial nerves
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Links all parts of
body by carrying
impulses
Subdivisions of PNS
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1.) Somatic system: voluntary
nervous system
Contains sensory and motor nerves
 Makes you aware of the world around
you & allows you conscious control
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Subdivisions of PNS
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2.) Autonomic System:
involuntary nervous system
Consists of motor nerves that carry
impulses to organs, blood vessels and
glands
 The unconscious or “automatic control”
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Subdivisions of Autonomic
System
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A. Sympathetic
division
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Active during stress
heart rate,
respiratory rate
and rate of ATP
breakdown
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B. Parasympathetic Division
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Active during
conditions of
normal organ
functioning
These 2 divisions often work antagonistically
to one another
CNS: The Brain
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4 major portions:
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Cerebrum: largest; sensory & motor
function, higher thought, memory & reasoning
Cerebellum: coordination of skeletal
muscles
Diencephalon: sensory information
Brain stem: connects parts of nervous
system; controls visceral activities
CNS: Cerebrum
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Cerebral
Hemispheres
Cerebral Cortex
Corpus Callosum
Gyri
Sulci
Fissures
CNS: Cerebral Lobes
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Frontal Lobe: anterior portion
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Primary motor area
Concentration, planning, problem solving
Broca’s Area: motor speech
Temporal Lobe: lateral lobe
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Interpretation of sensory impulses, memory,
visual & auditory patterns
Auditory area
Olfactory area
CNS: Cerebral Lobes
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Parietal Lobe: superior, lateral
lobe
Sensory area
 Understanding speech; using words
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Occipital Lobe: posterior lobe
Vision
 Combining visual images; visual
recognition
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CNS: Hemisphere
Dominance
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Equal participation in receiving and
analyzing sensory information, controlling
skeletal muscles and storing memory
Dominant Hemisphere: ability to
understand language
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90% of people dominant left side
Nondominant Hemisphere: nonverbal
functions, orientation in space, musical
patterns, nonverbal visual experiences
CNS: Cerebellum
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Located inferior to
occipital lobes and
posterior to brain
stem
Functions in:
positioning of limbs,
coordinating skeletal
movements,
maintanance of
posture
CNS: Diencephalon
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Located between cerebral hemispheres;
superior to midbrain
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Thalamus: central relay center for sensory
impulses; allows awareness of pain, touch &
temperature
Hypothalamus: regulates visceral activities;
links nervous and endocrine systems
Also holds: optic chiasma, posterior pituitary
gland, pineal gland, infundibulum
CNS: Brainstem
Connects cerebrum to spinal cord
 Midbrain: b/n diencephalon and
pons
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Visual, auditory reflex centers; head
movement for hearing
Pons: rounded bulge b/n midbrain
and medulla
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Relays sensory impulses; helps
regulate breathing
CNS: Brainstem
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Medulla
Oblongata: from
pons to spinal cord
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Cardiac center,
vasomotor center,
respiratory center
CNS: Spinal Cord
A continuation of the brain running
from base of brain to 1st or 2nd
lumbar vertebrae
 Is enclosed within spinal column
 Is ~ size of thumb except at
enlarged cervical and lumbar
plexuses (spinal nerve distribution to
upper and lower limbs)
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CNS: Spinal Cord
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Provides a 2-way pathway to and from
the brain
Serves as a reflex center
Has 31 linear segments giving way to 31
spinal nerves (relay info. from PNS to
CNS and vice versa)
Cauda Equina: collection of spinal
nerves at the inferior end of the vertebral
column
Spinal Cord in Column
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Spinal Cord Cross Section
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Spinal_Cord/sp_cd_jpgs/Spinal_Cord_PC271478md.JPG
Spinal Cord Cross-Section
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Gray Matter: unmyelinated
Located in center of cord forming an
“H”: divided into horns
 Each horn runs a different fiber tract
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• Posterior Horn: sensory neurons
• Anterior Horn: motor neurons
• Lateral Horn: motor neurons in autonomic
system
Spinal Cord Cross-Section
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White Matter: myelinated fibers
Surrounds central gray matter
 Divided into anterior, posterior and
lateral columns
 Each column holds longitudinal nerve
tracts
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• Ascending tracts: carry sensory info to
brain
• Descending tracts: carry motor info.
away from brain
Reflex Center
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Reflex: an extremely rapid response to
an emergency situation
Occurs in spinal cord or lower brain; does
not require thinking
The Reflex Arc:
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Receptor: at end of sensory neuron; can
generate an action potential to CNS
Association neurons: receive info. from
sensory neuron and routes response to motor
neuron
Motor neurons: conduct impulses to effectors
Reflex Arc
Protections of CNS
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Bone: skull and
vertebral column
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Cerebrospinal Fluid
(CSF):
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Made from the blood
Forms a watery cushion
that protects tissue
from trauma
Changes in composition
indicates brain
pathology
Protections of CNS
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Meninges: connective tissue
membranes
A. Dura mater: tough outer covering of
brain and s.c.
B. Arachnoid mater: middle layer
C. Pia mater: inner surface which clings
tightly to surface of brain and s.c.
• Subarachnoid space: separates the
arachnoid and pia maters; filled with CSF
Protections of CNS
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Blood-Brain Barrier
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Composed of least permeable capillaries in
body
Brain depends on a very constant internal
environment
• Allows: water, glucose, and essential amino acids
• Disallows: urea, protein and most drugs
• Cannot block: fats, respiratory gases and fat
soluble molecules (alcohol, nicotine and anesthetics)