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Ch. 35 The Nervous System
Nervous System
1. Neuron - basic unit of
structure and function
2. Basic unit of neuron
a.) dendrite
b) cell body (soma or cyton)
c) axon
3. The 3 functional kinds of neurons
a) sensory (afferent) - receptor neurons
 carry impulses to brain and spinal cord
(CNS)
b) motor (efferent) - effector neurons 
carry impulses from CNS to effector
(muscle or gland)
c) interneuron (associative) - connector
neurons  found within CNS; transmit
impulses between sensory, motor, and
other interneurons
SENSORY NEURON (AFFERENT)
MOTOR NEURONS (EFFERENT)
INTERNEURONS (IN CNS!)
4. Nerve - an organ composed of:
a) many hundreds, thousands of neurons
b) other tissues - epithelium, connective, blood vessels
5. 3 functional types of nerves
a) sensory nerve - consists of sensory neurons
- auditory
Receptor  CNS(brain, spinal cord)
- optic (ear, eye, skin)
b) motor nerve - consists entirely of motor neurons [ex:CNS  effector
(muscle or gland)]
c) mixed nerve - consists of both sensory and motor neuron bundles neurons separated by connective tissues (spinal cord - all 31 pairs of
spinal nerves)
NERVE
Motor Neuron - Longitudinal View
1. Dendrites - transmit impulses toward cell body
2. Nucleus - essential to cell functions
3. Cell body - synthesizes the neurohumor or neurotransmitter
(adrenaline, acetylcholine)
4. Neurofibrils - protein tubules which carry impulses throughout cell
5. Schwann cell - cell around axon - membrane (neurilemma) essential
to regeneration of neuron
6. Myelin sheath - lipid layer around axon; an insulator and also
increases rate of impulse conduction
7. Axis cylinder - composed of neurofibrils - carry impulses throughout
neuron
8. Nodes of Ranvier - spaces between Schwann cells
9. Motor end plate - (axon terminals) site where neurotransmitters
(neurohumor) are stored and released into synapse or effector
10. Axon - carry impulses away from cell body to synapse or to
effector
Stimulus- Impulse
1.
Stimulus - environmental change which
causes a response; usually a form of energy
a) radiant (heat, light)
d) sound
b) electrical
e) chemical
c) pressure
2.
Impulse - electrochemical change along a
neuron
3.
Threshold level stimulus- minimum strength
stimulus needed to initiate nerve
impulse (varies for different neurons and
individuals)
4.
Nerve Impulse - “All or None” (Property
of neurons)
- Once impulse is initiated by threshold
stimulus the neuron responds 100%
- Impulse travels through the cell at the
same rate and same strength
Figure 35-7 An Impulse
Section 35-2
NERVE IMPULSE
6. Refractory period - lapse of time required for neuron
membrane to restore original charge (at this time the
cell area is insensitive to another stimulus)
7. Human refractory periods (wide range)
a) slowest neurons - longest refractory periods 1/250
sec. --- can transmit 250 impulses per second
b) most rapid neurons - 1/2500 sec. --- can transmit
2500 impulses per second (shortest refractory time)
8. Rate of impulse conduction (dependent
on 2 factors)
a) diameter of neuron - the larger the cell
diameter, the faster the rate
b) myelin - myelin sheath enhances rate
– non-myelinated cells - slowest conduction rate
(sensory neurons)
– myelinated cells (motor) - faster rates
9.
At axon terminal of
neuron - axon stores and
releases neurotransmitter
(NT) into adjacent
tissues:
a) effector - muscle or
gland
b) synapse neurotransmitter either
activates or inhibits
adjacent neuron
10. Activation of cell
- Occurs when NT makes adjacent
neuron membrane more
permeable to Na+
- Impulse initiated
11. Inhibition of cell
- Occurs when NT makes adjacent
neuron (postsynaptic) membrane
less permeable to Na+
- More permeable to Cl- and K+
- Adjacent cell membrane
hyperpolarized
Figure 35-6 Resting Potential
RESTING POTENTIAL (POLARIZED)
Section 35-2
RECAP: NEURONAL CELL MEMBRANE
TRANSPORT
• ACTIVE TRANSPORT:
SODIUM- POTASSIUM
PUMP; NEEDS ATP;
AGAINST CONC.
GRADIENT (LOW HIGH)
• PASSIVE TRANSPORT:
SODIUM & POTASSIUM
CHANNELS (GATES);
FACILITATED
DIFFUSION; NO ATP;
WITH CONC. GRADIENT
(HIGHLOW)
- Bell-Magendie Rule=
IMPULSE AT SYNAPSE
TRAVELS IN ONE
DIRECTION
- From axon of presynaptic
neuron to dendrites/ cell
body of postsynaptic
neuron
- Only axon end of neuron
stores neurotransmitter
12. 4 Major types of Neurotransmitters
a) Acetylcholine (Ach) - motor neurons
b) Adrenalin(epinephrine) - motor, sensory, and
associative
c) Noradrenalin (norepinephrine) - motor,
sensory, associative
d) Seratonin - associative neurons
Section 35-2
SYNAPSE
Direction of Impulse
Dendrite of adjacent
neuron
Axon
Vesicle
Receptor
Axon
terminal
Synaptic cleft
Neurotransmitter
• NEUROTRANSMITTER
ACTIVATES OR
INHIBITS ADJACENT
NEURON
• ANESTHESIA:
1. PREVENTS
OPENING OF SODIUM
GATES
2. BLOCK RECEPTORS
ON POSTSYNAPTIC
NEURON
1. SPINAL CORD- LARGE MIXED NERVE
A. WHITE MATTER- OUTER
PORTION OF MYELINATED
FIBERS RUNNING UP AND DOWN
(TO & FROM BRAIN!)
B. GRAY MATTER- CELL BODIES OF
ASSOCIATIVE & MOTOR
NEURONS
1. 31 PAIRS OF SPINAL NERVES
(MIXED) – SENSORY FIBERS
ENTER DORSAL ROOT, MOTOR
LEAVE VENTRAL ROOT
• DESTRUCTION OF DORSAL ROOT – LOSS OF
SENSATION IN PARTS THAT SUPPLYSENSORY
NEURONS
• DESCRUCTION OF VENTRAL ROOT – MUSCULAR
PARALYSIS OF BODY PART SUPPLIED BY MOTOR
NEURON
• 2 MAIN FXN OF THE SPINAL CORD:
1. COORDINATING CENTER – REFLEXES (MOST,
LIKE KNEE JERK)
2. CONNECTS PNS TO BRAIN
Cross Section of the Spinal Cord
Section 35-3
Gray matter
Spinal nerve
Central canal
White matter
Meninges
Figure 35-9 The Brain
2. BRAIN (MENINGES, CSF)
- 4 VENTRICLES (FLUID CIRCULATES W/IN CAVITIES)
- 12 PRS. CRANIAL NERVES
- 2 LARGE HEMISPHERES (LONGITUTINAL HALVES)
- 3 REGIONS (FORE-, MID-, & HINDBRAIN)
Cerebrum
Thalamus
Pineal
gland
Hypothalamus
Cerebellum
Pituitary gland
Pons
Medulla oblongata
Spinal cord
STRUCTURAL DIVISIONS OF HUMAN BRAIN
1. HINDBRAIN
A. MEDULLA OBLONGATA (BRAINSTEM)
• ESSENTIAL TO LIFE
(VITAL CENTER)
• BREATHING RATE
(VAGUS & PHRENIC
NERVES)
• HEART RATE
• BLOOD PRESSURE
• SWALLOWING, VOMITING,
COUGHING CENTER
B. CEREBELLUM
• “LITTLE BRAIN”- LARGEST
SEGMENT OF HINDBRAIN
• CENTER FOR BALANCE &
COORDINATION
• COORDINATES MUSCLE
ACTIVITY
• COORDINATES IMPULSES
FROM EYES &
SEMICIRCULAR CANALS
TO MAINTAIN BALANCE
(EQUILIBRIUM)
C. PONS (“BRIDGE”)
• CARRIES IMPULSES
FROM ONE SIDE OF
CEREBELLUM TO
THE OTHER
• COORDINATES
LEFT SIDE OF
BRAIN WITH RIGHT
2. MIDBRAIN
• BETWEEN
CEREBELLUM AND
PONS – SLIGHTLY
ABOVE
• CONTROLS
SENSORY
PROCRESSES
3. FOREBRAIN
a.HYPOTHALAMUS
(HOMEOSTATIC CENTER)
REGULATES:
• BODY TEMP
• WATER BALANCE
• FOOD INTAKE
• GASTRIC SECRETION
• ANTERIOR PITUITARY
GLAND WITH RELEASING
HORMONES
b. PITUITARY
(HYPOPHESIS)
• ENDOCRINE GLAND
THAT SECRETES
HORMONES THAT
MAINTAIN
HOMEOSTASIS
• HAS ANTERIOR &
POSTERIOR LOBES
)
C. THALAMUS
• RELAY CENTER B/W
BRAINSTEM &
CEREBRUM (B/T
SENSE ORGANS &
CEREBRUM
• REGULATES STATES
OF SLEEP AND
WAKEFULNESS
D. CEREBRUM
• SETS MAN APART FROM OTHER
VERTEBRATES!
• LEARNING, REASONING,
MEMORY, JUDGEMENT
• SPEECH:
1. BROCA’S AREA – MOTOR
2. WERNICKE’S AREA –
COMPREHENSION OF SPOKEN
OR WRITTEN LANGUAGE
• LEFT BRAIN: SPEECH, LOGIC,
WRITING, MATH
• RIGHT BRAIN: DISCRIMINATION
OF SHAPE & FORM
E. CORPUS CALLOSUM
CONNECTS RIGHT & LEFT
CEREBRAL HEMISPHERES
Concept Map
Section 35-3
The Nervous
System
is divided into
Central nervous
system
Peripheral
nervous system
Motor
nerves
which consists of
that make up
Somatic nervous
system
Autonomic
nervous system
which is divided into
Sympathetic
nervous system
Parasympathetic
nervous system
Sensory
nerves
AUTONOMIC NERVOUS SYSTEM
• CHECK & BALANCE SYSTEM THAT MAINTAINS
HOMEOSTASIS (ANTAGONISTIC TO ONE ANOTHER)
• 2 DIVISIONS:
1. SYMPATHETIC
2. PARASYMPATHETIC
• FIGHT-FLIGHT RXN:
NERVOUS CONTROL EVOKES THESE RXN’S
RAPIDLY IN TIMES OF DANGER/STRESS.
HORMONES PROVIDE A BACKUP THAT CAN
MAINTAIN A RESPONSE FOR A LONGER PERIOD.
AUTONOMIC NERVOUS
SYSTEM
REFLEX ARC
REFLEX ARC