Transcript The Nervous System

The
Nervous
System
Chapters 10 and 11
Nervous System
• Master controlling and
communicating system
Basic Functions
1. Sensory input – gather information
2. Integration – process and interpret sensory input
3. Motor output – response by muscles and glands
Organization
A. Central Nervous System (CNS)
▫ Brain & spinal cord
▫ Integrative and control centers
B. Peripheral Nervous System (PNS)
▫ Nerves (spinal nerves, cranial nerves)
▫ Communication lines between CNS and rest of body
▫ Two Divisions:
1. Sensory (afferent) Division: Sensory receptors 
CNS
2. Motor (efferent) Division: CNS  effectors
(muscles & glands)
Motor Division
• Somatic nervous system (voluntary) – control
skeletal muscles
• Autonomic nervous system (ANS) (involuntary)
– regulate smooth muscles, cardiac, glands
▫ Subdivisions: sympathetic & parasympathetic
Hey there, I’m a brain!
Hey there, I’m a sheep brain!
Brain Anatomy…
• Brain: mass of 120 billion neurons and neuroglia weighing
approximately 3 pounds, protected by cranial bones
• Cerebrum: largest mass of brain (83% of brain mass);
responsible for higher mental functions and distribution of
impulses
▫ Cerebral cortex: outer layer of gray matter; short and long term
memory
 Convolutions: elevated ridges/folds that increases gray area of brain
 Sulci: shallower grooves
 Fissures: deep grooves (fetal folds)
 Longitudinal: separates right and left hemispheres; corpus callosum
(large fibers that connect the two hemispheres)
 Transverse: separates cerebrum from cerebellum
 Fissure of Rolando: divides frontal and parietal lobes at coronal
suture
 Fissure of Sylvan/lateral fissure: divides frontal and temporal lobes
Nervous System
Classification of Neurons and Supporting
Cells
Day 2
Brain Anatomy (ctd.)
• Cerebrum (ctd.)
▫ Cerebral medulla: white matter, conduction pathways
▫ Divided into right and left hemispheres (left side governs right side
of body, right side governs left side of body)
▫ Lobes
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Frontal: voluntary motor control, learning, planning, L = motor, speech
Parietal: sensory, distance, size, shape, cognitive/intellectual processes
Occipital: vision, visual memory
Temporal: auditory, olfactory, speech, judgment, reasoning, will power
• Cerebellum: below and posterior to cerebrum
▫ Right and left hemispheres connected by central vermis
▫ Outer gray, inner white forms arbor vitae
▫ Coordinates muscular movement, posture, balance, running,
walking
▫ Damage produces ataxia (lack of coordination due to errors in speed,
force, direction of movement
Brain Anatomy (ctd.)
• Brainstem (damage = coma)
▫ Midbrain: upper part of brainstem
 Controls postural reflexes and walking
 Visual reflexes and auditory control, 3-4 cranial nerves
▫ Pons: a two-way conduction pathway, mixed gray and white
fibers
 Controls inspiration
 Transverse fibers give it a bridge appearance
 Reflex mediation for 5-8 cranial nerves
▫ Medulla oblongata: the bulb (lowest part before the
foramen magnum) made of white and gray fibers called
reticular formation
 75% of fibers cross here
 Controls vital functions: respiration and circulation
 Pyramids: bulges of white tracts on ventral surface
Brain Anatomy (ctd.)
• Diencephalon: area between cerebrum and midbrain
▫ Thalamus: gray matter, relay station for sensory incoming
and motor outgoing impulses; damage - increased
sensitivity to pain, loss of consciousness
▫ Hypothalamus: forms floor of third ventricle
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Regulates autonomic control
Cardiovascular control: dilates/constricts
Temperature control
Controls appetite: hunger and thirst
Water balance
GI control: peristalsis, intestinal secretions
Emotional states: fear, anger, pleasure, pain, sexual reflexes
Nervous Tissue
1. Neurons (nerve cells) - transmit message
Anatomy:
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Cell body – contains nucleus; metabolic center
Dendrite – fiber that conveys messages toward cell body
Axon – conduct nerve impulses away from the cell body
Axon terminals – end of axon; contain neurotransmitters
& release them
Synaptic cleft/synapse – gap between neurons
Nervous Tissue
2. Neuroglial cells - supporting cells
CNS: astrocytes, microglia, ependymal cells, oligodendrocytes
 barrier between capillaries and neurons
 protect neurons
 immune/defense
 line brain and spinal cord cavities
 wrap nerve fibers
 produces myelin sheaths (covering)
PNS: Schwann cells, satellite cells
 surround large neurons
 protect & cushion
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Myelin: whitish, fatty material that covers nerve fibers to
speed up nerve impulses
Schwann cells: surround axons and form myelin sheath
Myelin sheath: tight coil of wrapped membranes
Nodes of Ranvier: gaps between Schwann cells
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Ganglia: collections of cell bodies
Bundles of nerve fibers = tracts (CNS) or nerves (PNS)
White matter: dense collections of myelinated fibers
Gray matter: unmyelinated fibers & cell bodies
Functional Classification: direction nerve impulse is
traveling
Sensory
neurons
Motor neurons
Interneurons
carry impulses from carry impulses from
sensory receptors to CNS to muscles &
CNS
glands
connect sensory &
motor neurons
Vision, hearing,
equilibrium, taste,
smell, pain,
pressure, heat
Structural Classification: # processes extending from cell
body
Multipolar
Bipolar
Unipolar
1 axon, several
dendrites
1 axon, 1 dendrite
1 process
Rare
Short with 2
branches (sensory,
CNS)
Most common
(99%)
Eg. Motor neurons,
Eg. retina, nose, ear
interneurons
Eg. PNS ganglia
Anatomy of the Brain
Day 3
Sheep Brain Dissection Overview
Meninges of the Brain
Brain is protected by the skull and 3 layers of membranes called meninges
Meninges
• DURA MATER (literally means “tough mother”)
▫ Tough outer layer
• ARACHNOID MATER (literally means “spider
mother”)
▫ Beneath and stuck to the dura mater
▫ Stringy, web-like
▫ Space under the arachnoid, the subarachnoid space, is
filled with cerebrospinal fluid and contains blood
vessels.
• PIA MATER (means “tender mother”)
▫ Thin transparent membrane that follows the contour
of the ridges (gyri) and valleys (sulci) of the brain.
Ventricles
• The ventricles of the brain are a communicating
network of cavities filled with cerebrospinal fluid
(CSF)
• The ventricular system is composed of:
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2 lateral ventricles
Third ventricle
Cerebral aqueduct
Fourth ventricle
• The choroid plexuses located in the ventricles
produce CSF, which fills the ventricles and
subarachnoid space, following a cycle of constant
production and reabsorption.
Additional Structures to Discuss…
• Pineal gland: Produces the hormone melatonin
at night
• Mamillary bodies: serve as relay stations for
reflexes related to sense of smell
• Inferior Colliculi: movement of head and trunk
in response to sound stimuli (reflex center)
• Superior Colliculi: movement of eyes, head and
neck in response to visual stimuli (reflex center)
• Infundibulum: connection between the
hypothalamus and the posterior pituitary
And it keeps going…
• Optic chiasma: X-shaped structure on the underside of the
brain formed by a partial crossing over of optic nerves
• Olfactory bulb: Structure located in the forebrain that
receives neural input regarding smell
Arbor Vitae
• White matter of the cerebellum
• Named as much due to its branch-like appearance
• Brings sensory and motor info to and from the
cerebellum
Human vs. Sheep Brain (ctd.)
• The convolutions and sulci comprises of a larger surface area
than sheep brains
▫ Sheep brains have less ridges and contours.
• Human behavior and motor control is typically controlled by
the cerebellum
▫ Sheep brains have a much smaller cerebellum than the human
brain, which, in comparison with humans and their complex
learned behaviors, have less motor control and less learning
abilities.
• The olfactory bulb is larger in the sheep’s brain than that of
the human brain
▫ Animals usually rely more upon their senses and abilities of
smell than humans do.
▫ Humans rely more upon other senses, such as sight and
hearing, rather than smell like sheep and other animals.
Human vs. Sheep Brain
• A sheep’s brain is elongated in shape, whereas a human
brain is rounded.
• The human brain stem is towards the backbone and
downwards, because in the human body the backbone
is vertical;
▫ Sheep’s backbone which is horizontal, and its brain is
directed outwards.
• The human brain is not only larger, but heavier than a
sheep’s brain,
▫ Sheep brain is roughly 140 grams compared to the human
brain, and is only about one third as long.
Human vs. Sheep Brain (ctd.)
• The pineal gland is responsible for controlling
reproduction and circadian rhythms
▫ Larger in the sheep’s brain when compared to the
human brain, that has less basic instinctual
behavior controls.
• Human hind brain positioning
▫ Different from the sheep because of the human’s
erect position.
D
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Functional Classification
• Direction in which the nerve impulse travels relative to the CNS
▫ Sensory/Afferent: dendrites are connected to receptors where
stimulus is initiated in skin/organs and carry impulse
toward CNS; axons are connected to other neuron dendrites;
unipolar except for bipolar neurons in special sense organs; cell
bodies in sensory ganglia outside CNS Receptors:
▫ extroceptors (pain, temperature, touch)
▫ interoceptors (organ sensation)
▫ proprioceptors (muscle sense, position, movement)
▫ Motor/Efferent: carry messages from CNS to effectors; dendrites
are stimulated by other neurons and axons are connected to
effectors (muscles and glands); multipolar
▫ Association/Interneurons: carry impulses from one neuron to
another (afferent to efferent); found only in CNS; lie between
sensory and motor neurons; shuttle signals; 99% of neurons in
body
Neuron Function
1. Irritability: ability
to respond to
stimulus & convert
to nerve impulse
2. Conductivity:
transmit impulse to
other neurons,
muscles, or glands
Irritability of a Neuron:
• Cell membrane at rest = polarized
▫ Na+ outside cell, K+ inside cell
▫ Inside is (-) compared to outside
• Stimulus  excited neuron (Na+ rushes in) 
becomes depolarized
• Depolarization activates neuron to transmit an
action potential (nerve impulse)
▫ All-or-none response
▫ Impulse conducts down entire axon
• K+ diffuses out  repolarization of membrane
• Na+/K+ ion concentrations restored by sodiumpotassium pump (uses ATP)
Depolarization
Nerve Conduction
• Action potential reaches
axon terminal  vesicles
release neurotransmitters
(NT) into synaptic cleft
• NT diffuse across synapse
 bind to receptors of
next neuron
• Transmission of a nerve
impulse = electrochemical
event
Gated Ion Channels (Na+ and K+)
Neurotransmitters
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50+ identified
Excitatory: cause depolarization
Inhibitory: reduce ability to cause action potential
Eg. acetylcholine, serotonin, endorphins
Neurotransmitters
• Acetylcholine: most common, it excites skeletal muscle,
but inhibits cardiac muscle; is also involved with memory;
deficiency of ACh could be a cause of Alzheimer’s.
• Amines: synthesized from amino acid molecules
▫ Serotonin: CNS inhibitory; moods, emotions, sleep
▫ Histamine: CNS stimulant; regulation of water balance and
temperature, emotions
▫ Dopamine: inhibitory effect on somatic motor; without
dopamine body has general over stimulation of muscles =
Parkinsonism tremors; cocaine blocks uptake of dopamine
▫ Epinephrine: autonomic nervous response, beta receptors,
dilation
▫ Norepinephrine: autonomic nervous response, alpha
receptors, constriction; antidepressants increase amount of
norepinephrine in brain - relieving depression
Neurotransmitters
• Amino acids
▫ Glutamate: CNS excitatory
▫ Glycine: CNS inhibitory
• Neuropeptides: short strands of amino
acids called polypeptides
▫ Enkephalins/endorphins: inhibitory, act like
opiates to block pain
▫ VIP: vasoactive intestinal peptide
▫ CCK: cholecystokinin
▫ Substance P: excitatory, transmits pain
information
Neurotransmitters
Neurotransmitter
Action
Affected by:
Acetylcholine
muscle contraction
botulism, curare
(paralytic), nicotine
Dopamine
“feeling good”
cocaine,
amphetamines
Serotonin
sleep, appetite, nausea,
mood, migraines
Prozac, LSD,
ecstasy
Endorphins
inhibit pain
morphine, heroin,
methadone
GABA
main inhibitory NT
alcohol, Valium,
barbiturates
Reflexes
• Rapid, predictable, involuntary responses to stimuli
1. Somatic Reflexes: stimulate skeletal muscles
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Ex.) Pulling away hand from hot object
2. Autonomic Reflexes: regulate smooth muscles,
heart, glands
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Ex.) salivation, digestion, blood pressure, sweating
Reflex Arc (neural pathway)
Five elements:
1. Receptor – reacts to stimulus
2. Sensory neuron
3. CNS integration center (interneurons)
4. Motor neuron
5. Effector organ – muscle or gland
Reflex Activities
Patellar (Knee-jerk)
Reflex
Pupillary Reflex
Patellar (Knee-jerk)
Reflex
Pupillary Reflex
• Stretch reflex
• Tapping patellar
ligament causes
quadriceps to contract
 knee extends
• Help maintain muscle
tone, posture, &
balance
• Optic nerve 
brain stem 
muscles constrict
pupil
• Useful for checking
brain stem function
and drug use
Flexor (withdrawal) reflex:
painful stimulus  withdrawal of
threatened body part
▫ Pin prick
Plantar reflex:
draw object down sole of foot 
curling of toes
▫ Babinski’s sign: check to see if
motor cortex or corticospinal tract is
damaged