LECTURE 6: NERVOUS SYSTEM Flashcards
➢ Continuously changes
➢ Need to coordinate body functions
➢ Two control systems
Animal Behavior
Animal Behavior: Continuously changes depending on two factors
-Internal Factors
-External Factors
Animal Behavior: two control systems
-Nervous System
-Endocrine System
Three basic functions of Nervous system
o Reception of sensory input from internal and
external environment
o Integration of the input
o Response to the stimuli
➢ An important adaptation in the evolution of body
size and mobility
➢ Coelenterates, cnidarians and echinoderms (radial
symmetry, lacking a head)
Patterns of Organization of Nervous System:
Like the hydra, the jellyfish has a nervous system characterized by a series of interconnected nerve cells (_____________).
nerve net
The __________ conducts
impulses around the entire body of the jellyfish. The strength of a
behavioral response is proportional to the stimulus strength. In other
words, the stronger the stimulus, the larger the response
nerve net
with _______________ come more complex nervous systems
cephalization
The central nervous system has been described as ____________ because of
the nerves connecting the nerve cords.
“ladder-like”
This ladder-like structure or long nerve cords are connected to ________________ located in the head region.
cerebral ganglia
Flatworms have “___________” that
project from the side of the head. These contain chemoreceptors that are used to find food.
auricles
Flatworms also have eyespots called “_________”. That are sensitive to light and are connected to the cerebral ganglia.
Generally, the flatworm avoids light
ocelli
Central Nervous System (CNS) includes?
◦ Brain
◦ Spinal cord
Two system under vertebrate nervous system
➢ Central Nervous System (CNS)
➢ Peripheral Nervous System (PNS)
Peripheral Nervous System (PNS) includes?
Nerves (bundles of neurons)
Parts of the nervous
system that sense
changes in the internal
and external
environment
Receptors
The forms of _______ _________ are converted to a signal and sent to the brain or spinal cord.
sensory input
➢ Input in the brain and spinal cord are integrated to
generate a response (motor output)
➢ Motor output
oIs a signal transmitted to organs that can convert the
signal into some form of action, such as movement,
changes in heart rate, release of hormones, etc.
Integration and Output
Input in the brain and spinal cord are integrated to generate a _____________
response (motor output)
Different forms of Sensory Input
◦ Pressure
◦ Taste
◦ Sound
◦ Light
◦ Blood pH
◦ Hormone levels
Is a signal transmitted to organs that can convert the signal into some form of action, such as movement, changes in heart rate, release of hormones, etc.
Motor Output
PNS: Two types of motor neuron pathways
-Somatic
-Autonomic
PNS: Somatic NS
Skeletal
PNS: Autonomic is categorized into two
-Sympathetic
-Parasympathetic
PNS: Autonomic NS
-Smooth muscle
-cardiac muscle
-glands
➢ Includes all nerves controlling the muscular
system and external sensory receptors
Somatic Nervous System
SNS: ➢ External sense organs (e.g. skin) → ________
➢ Muscle fibers and gland cells → ___________
-receptors
-effectors
Types of Cells in the Nervous System
- Neuroglia
- Neuron or nerve cells
– do not transmit impulses
- support, nourish, insulate and protect the delicate neurons
- bind nervous tissues
Neuroglia
- respond to stimuli and
conduct impulses
Neuron or nerve cells
Types of Neuroglia
a. astrocytes/astroglia
b. microglias
c. oligodendroglia and Schwann cells
d. Ependymal cells
nutrition
astrocytes/astroglia
immune defense cells (similar to macrophages)
microglias
– insulator (myelin sheath)
oligodendroglia and Schwann cells
form myelin in the CNS and hence are responsible for normal propagation of action
potentials. Patchy loss of CNS myelin, as in multiple sclerosis can cause a variety of neurological problems
oligodendroglia
- form the myelin around myelinated
peripheral axons - also envelop unmyelinated axons, but without the dense membrane
Schwann cells
indentations between adjacent neuroglial cells in the myelin sheath
nodes of Ranvier
- circulate the CSF; ciliated; source of CSF in the choroid plexus, line the neurocoel of cord and brian
- oldest neuroglial elements phylogenetically
- sole glial elements in amphioxus and agnathans
Ependymal cells
Parts of a Neuron
a. soma/perikaryon
b. nerve fibers
body of the neuron
Soma/Perikaryon
cytoplasmic extensions from the soma
nerve fibers
Types of Nerve Fibers
-Axon
-Dendrites
carry impulses away from the soma
Axon
transmit incoming electrical impulses toward the soma
dendrite
Functional Units of Nervous System
Neurons
Length of Fibers: Long dendrites
and short axon
Sensory neuron
Different types of Neurons
- sensory or afferent neuron
- motor or efferent neuron
- interneuron
Length of Fibers: Long dendrites
and short axon
Sensory neuron
Length of Fibers: Short dendrites
and short or long axon
Interneuron
Length of Fibers: Short dendrites
and long axons
Motor Neuron
Location of Sensory Neuron: Cell body and
dendrite are _________________; the
cell body is located in a _________________
-outside of the spinal cord
-dorsal root ganglion
Location of Interneuron
Entirely within the spinal cord or CNS
Location of Motor Neuron: Dendrites and
the cell body are located in the ___________; the
axon is ______________________
-spinal cord
-outside of the spinal cord
Conduct impulse to the spinal cord
Sensory neuron
Interconnect the
sensory neuron
with appropriate
motor neuron
Interneuron
Conduct impulse
to an effector
(muscle or
gland)
Motor Neuron
every cell has a ________or ________________
across its plasma membranes
voltage or membrane potential
a membrane potential is a localized ___________________ across membrane
electrical gradient
o ________ are more concentrated within a cell
o _________are more concentrated in the extracellular fluid
-anions
-cations
an unstimulated cell usually has a resting potential of __________
70mV
Cations:
-_____the principal intracellular cation
-_____is the principal extracellular cation
- K+
- Na+
Anions:
- ________, __________, ___________, and __________ are the principal intracellular anions
-______is principal extracellular anion
-proteins, amino acids, sulfate, and phosphate
-Cl-
Formation of Resting Potential: In a mammalian neuron at resting potential, the
concentration of K+ is greater ________the cell,
while the concentration of Na+ is greater __________the cell
-inside
-outside
Formation of Resting Potential: ________________ use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane.
Sodium-potassium pumps
Formation of Resting Potential: These concentration gradients of K+ and Na+ represent ______________
chemical potential energy.
Formation of resting potential: The opening of ion channels in the plasma membrane converts chemical potential to____________
electrical potential
Formation of resting potential: A neuron at resting potential contains many open
____ channels and fewer open ____ channels; K+ diffuses out of the cell
-K+
-Na+
Formation of resting potential: Anions trapped inside the cell contribute to the
______________ within the neuron
negative charge
___________________ allow ions to diffuse across the plasma membrane
Ungated ion channels
Ungated ion channels are always ___________
Open
_____________ have the ability to generate large
changes in their membrane potentials
excitable cells
gated ion channels open or close in response to _________
stimuli
opening or closing of ion channels alters the __________________ to particular ions, which in turn alters the _____________
- membrane‘s permeability
-membrane potential
Types of gated ion channels
➢ chemically-gated ion channels
➢ voltage-gated ion channels
open or close in response to a chemical stimulus
chemically-gated ion channels
open or close in response to a change in membrane potential
voltage-gated ion channels
changes in membrane potential of neuron
give rise to _____________
nerve impulses
◦ action potential travels directly from the
presynaptic to the postsynaptic cells via gap
junctions
Electrical Synapses
o more common than electrical synapses
o postsynaptic chemically-gated channels exist for ions such as Na+, K+, and Cl-
* depending on which gates open the
postsynaptic neuron can depolarize or
hyperpolarize
Chemical Synapses
A ________is a region
where neurons nearly
touch and where nerve
impulse is transferred
synapse
Small gap between
neurons is the _________
synaptic cleft
Transmission across a
synapse is carried out
by ________________
neurotransmitters
How is neurotransmitter released?
- Sudden rise in calcium at
end of one neuron - Stimulates synaptic vesicles
to merge with the
presynaptic membrane - Neurotransmitter molecules
are released into the
synaptic cleft
The same neurotransmitter can produce __________ effects in different types of cells
different
5 major classes of neurotransmitters
-acetylcholine,
-biogenic amines,
-amino acids,
-neuropeptides,
-gases
➢ The circuits in the brain are more complex than
the most powerful computers.
➢ The vertebrate brain is organized into regions with
different functions.
➢ Each single-celled organism can respond to
stimuli in its environment.
➢ Animals are multicellular and most groups
respond to stimuli using systems of neurons
Brain
➢ conveys information from the brain to the PNS
➢ produces reflexes independently of the brain
➢ A reflex is the body’s automatic response to a stimulus
Spinal Cord
A ____________ is the body’s automatic response to a stimulus
reflex
Embryonic Brain Regions of a one month old
- Forebrain
- Midbrain
- Hindbrain
Embryonic Brain Regions of a 5 weeks old
- Forebrain
-Telencephalon
-Diencephalon - Midbrain
-Mesencephalon - Hindbrain
-Metencephalon
-Myelencephalon
Brain structures present in adult
- Forebrain
-Telencephalon
-Cerebrum
-Diencephalon - Midbrain
-Mesencephalon
-Midbrain - Hindbrain
-Metencephalon
-Pons
-Myelencephalon
-Medulla oblongata
-Motor area controls voluntary muscle movements;
-sensory cortex is center of conscious perception of touch, pressure, vibration, pain, temperature, and taste;
-association areas integrate and process sensory data
Telencephalon/Cerebrum
-Part of limbic system
-integrates sensory information arriving at thalamus, projects to cerebral frontal lobes
Diencephalon: Thalamus
-Controls autonomic functions
-sets appetitive drives and reproductive behavior
-participates in emotional responses
-secretes ADH, oxytocin, releasing hormones for anterior pituitary regulation
Diencephalon: Hypothalamus
Integrate visual information with other sensory inputs and relays auditory information
Mesencephalon: Optic Lobes (tectum)
Involuntary control of muscle tone, processing incoming sensations and outgoing motor commands
Mesencephalon: Midbrain Nuclei
Involuntary coordination and control of outgoing movements for equilibrium, muscle tone, posture
Metencephalon: Cerebellum
◦ contains nuclei that control visceral (autonomic homeostatic) functions:
- breathing
- heartbeat and blood pressure
-swallowing
-vomiting
-digestion
Myelencephalon: Medulla oblongata
contains nuclei involved in the regulation of
visceral activities such as breathing
Metencephalon: Pons
➢ functions in homeostasis, coordination of movement,
conduction of impulses to higher brain centers
➢ relays information to and from higher brain centers
Brainstem (midbrain, pons, medulla oblongata)
◦ contains nuclei involved in the integration of
sensory information
- superior colliculi are involved in the -
regulation of visual reflexes
-inferior colliculi are involved in the
regulation of auditory reflexes
Midbrain
includes a choroid plexus and the pineal
gland-secretes melatonin
Epithalamus
where sensory information is integrated and assessed and motor responses are planned
Association areas
Lateralization of Brain Function
-Left Hemisphere
-Right Hemisphere
-specializes in language, math, logic
operations, and the processing of serial
sequences of information, and visual and
auditory details
-specializes in detailed activities required for
motor control
The left hemisphere
specializes in pattern recognition, spatial
relationships, nonverbal ideation, emotional
processing, and the parallel processing of
information
The right hemisphere
- mediates basic emotions (fear, anger), involved in emotional
bonding, establishes emotional memory
– e.g., the amygdala is involved in recognizing the emotional
content of facial expression
Limbic System
___________ is continuous with ventricles
central canal
Central canal contains __________________
cerebrospinal fluid (CSF)
__________ is composed of bundles of myelinated axon
white matter
___________ consists of unmyelinated axons, nuclei, and dendrites
gray matter
➢ Instantaneous and involuntary
➢ Dependent on both sensory and motor nerves
➢ It is an autonomic response
Reflex
The reflex action is mediated by a neural
pathway called the
reflex arc
Reflex Arc
A Simple Nerve Circuit
-Mediates reflex action
-Most sensory neurons do not directly pass the
brain, but synapses with spinal cord
Reflex Arc
Pathway of Reflex Arc
Stimulus (Internal/External)—>Receptor (Cell or Organ)—>Sensory Neuron—> Coordinator (Brain or Spinal cord-Interneurons)—>Motor Neuron—> Effector (muscle or glands)—>Response (Movement, secretion, behavior)
A reflex arc is
composed of:
➢sensory receptor
➢sensory neuron
➢motor neuron
➢effector
activates a nerve impulse in a sensory
neuron in response to changes in the body’s internal or external environment.
Receptor
conducts the impulse from the
receptor to its axonal end in the CNS
Sensory neuron
usually located in the central nervous system, is a receiving area in which the incoming sensory impulse connects with an outgoing motor impulse (this impulse may be repressed, transmitted, or rerouted in the center area)
Center
transmits the impulse to the proper body
organ
Motor neuron
is the organ that responds to the impulse from a motor neuron, may be a muscle or a gland
Effector
Reflex Arc Can be classified based on the organs that they affect
-Autonomic
-Somatic
-internal organs
-2 motor neurons
-Don’t reach level of consciousness
Reflex Arc: Autonomic
-Muscles
-1 motor neuron
-Reaches level of consciousness
Reflex Arc: Somatic
Two types of Reflex Arc based on organs they affect
➢ Visceral /Autonomic reflex arc
➢ Somatic reflex arc
involves effectors located in the
visceral organs; e.g. glands or smooth
muscles
Visceral /Autonomic reflex arc
involves effector organs
located in body structures that are acted upon by skeletal muscles
Somatic reflex arc
Two types of Reflex Arc based on Composition
➢ Monosynaptic reflex
➢ Polysynaptic reflex
A simple reflex arc
consisting of only one sensory neuron and one
motor neuron
Monosynaptic reflex
a sensory neuron
influences several motor neurons through
intermediate (association) neurons of the spinal
cord which forms a complex reflex arc
Polysynaptic reflex
Monosynaptic Reflex Arcs
consists of only 2 neurons (e.g. : patellar reflex)
Additional components of monosynaptic
reflex arc:
➢As the sensory axon enters the spinal cord, it
sends out a collateral axon which synapses into an inhibitory interneuron.
➢When inactivated, this inhibitory neuron releases chemical that inhibits the activity of the antagonist muscles.
➢This reinforces the activity of the antagonist
muscles by removing tonic activity.
Polysynaptic Reflex Arcs
one or more interneurons connect the sensory and motor neurons
Other examples of Reflex Arc
➢ Balance
➢ Blinking reflex
➢ Stretch reflex
➢ Patellar reflex
an involuntary and
instantaneous response to a certain stimuli
Reflex Action
time between onset of stimulus
and actual response
Reflex Time
➢ Withdrawal reflex
➢ When the reflex occurs…
- Flexors in the withdrawing limb contract
- Extensors relax, while in the other limb,
the opposite occurs.
➢ Contralateral
- Reflex occurs on the opposite side from
the stimulus
Cross-Extensor Reflex Arc
➢ allows an organism to maintain erect
posture and balance
➢ integrated at different sites of the CNS
Postural Reflex
Postural Reflex is integrated in
-spinal
-medullary
-midbrain
-cortical
➢ muscles contract in response to a
stretching force applied
➢ knee-jerk reflex or patellar reflex
➢ sensory receptors within these muscles
are also stretched
➢ descending neurons within the spinal
cord synapse with the neurons of stretch
reflex
➢ maintenance of posture and muscle
activity coordination
➢ Absence or exaggeration of stretch reflex
→ neurons within the brain or spinal cord
is damaged
Stretch Reflex
Tissue damage stimulates __________
abrupt temperature change stimulates
thermoreceptors on sensory neurons
nociceptors
nociceptors
pain sensory receptors
Interneurons synapse with different neurons
(e.g. hamstring flexon):
1) Motor neurons on the same segment
of spinal cord
2) Motor neurons on higher and lower
segments (e.g. hamstring is innervated
by several motor neurons)
3) Neurons in the brain so individual
becomes aware
-transmits information to and from the
CNS and regulates movement and the internal
environment
The Peripheral Nervous System (PNS)
In the PNS, ________________ transmit information to the CNS and _______________ transmit information away from the CNS
-afferent neurons
-efferent neurons
Two functional components of PNS
-motor system
-autonomic nervous system
carries signals to skeletal
muscles and is voluntary
motor system
regulates the
internal environment in an involuntary manner
autonomic nervous system
The autonomic nervous system has 3 divisions:
-sympathetic,
-parasympathetic
-enteric
The sympathetic and parasympathetic divisions have ___________ effects on target organs
antagonistic
correlates with the
“fight-or-flight” response
sympathetic division
promotes a return
to “rest and digest”
parasympathetic division
controls activity of the
digestive tract, pancreas, and gallbladder
enteric division
Constricts pupil
of eye
Parasympathetic division
Stimulates salivary
gland secretion
Parasympathetic division
Constricts
bronchi in lungs
Parasympathetic division
Slows heart
Parasympathetic division
Stimulates activity
of stomach and
intestines
Parasympathetic division
Stimulates activity
of pancreas
Parasympathetic division
Stimulates
gallbladder
Parasympathetic division
Dilates pupil
of eye
Sympathetic division
Inhibits salivary
gland secretion
Sympathetic division
Promotes emptying
of bladder
Parasympathetic division
Promotes erection
of genitals
Parasympathetic division
Relaxes bronchi
in lungs
Sympathetic division
Accelerates heart
Sympathetic division
Inhibits activity
of stomach and
intestines
Sympathetic division
Inhibits activity
of pancreas
Sympathetic division
Stimulates
adrenal medulla
Sympathetic division
Inhibits emptying
of bladder
Sympathetic division
Stimulates glucose
release from liver;
inhibits gallbladder
Sympathetic division
Promotes ejaculation and
vaginal contractions
Sympathetic division
Parasympathetic Division: Preganglionic Neurons Location
Brainstem, Sacral of Spinal Cord
Parasympathetic Division: Neurotransmitter Released (preganglionic Neurons)
Acetylcholine
sympathetic Division: Preganglionic Neurons Location
Thoracic and lumbar segments of spinal cord
sympathetic Division: Neurotransmitter released (Preganglionic Neurons)
Acetylcholine
Parasympathetic Division: Postganglionic Neurons Location
Ganglia close to or within target organs
Parasympathetic Division: Neurotransmitter Released (postganglionic Neurons)
Acetylcholine
sympathetic Division: Postganglionic Neurons Location
Ganglia close to target organs or chain of ganglia near spinal cord
sympathetic Division: Neurotransmitter Released (postganglionic Neurons)
Norepinephrine
originate in the brain and mostly terminate
in organs of the head and upper body
Cranial nerves
originate in the spinal cord and extend to
parts of the body below the head
Spinal nerves
