Download Peripheral Nervous System

Biology 12
Nervous System
Introduction
 Allows us to sense internal and environmental stimuli, react to
stimuli, move, storage of memories, the ability to know we exist,
etc.
 Basic component of nervous system is the _______ or _________
 As cells they contain many organelles and cytoplasm similar to
those found in other cells
Neuronal Anatomy
Basic Parts of a Neuron:
a. Cell Body (soma)
 contains nucleus, cytoplasm and other organelles—e.g.
______________, Golgi body, microtubules,
microfilaments, E.R., lysosomes etc.
 also contains granular material alled _____ _____—many
ribosomes and rough E.R.
b. Axon
 Thin tube-like process arising from cell body

 Typically only one per neuron

 cytoplasm in axon called ______________
 No Nissl bodies or free ribosomes

 longer than dendrites
 contains most of cells cytoplasm
c. Axon Hillock

 Controls generation of action potential (i.e. nerve signal)
d. Dendrites

 Receive excitation from other cells
 branched fibers, spiny in appearance

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 carry signals toward cell body

Note: dendrites and axons are often called ______ or ________
e. Synaptic endings or synaptic bulbs— ends of axons that
release transmitter substances to propagate signal to other
neuron
Neuron Shapes

 Are classified according to how many processes extend from cell
body (soma)
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Neuron Functions:
 3 types of neurons exist based on their function: ______________,
_____________________ and __________________
a. Sensory (afferent) neuron
 Brings nerve impulse from sensory organs to CNS
b. Motor (efferent) neuron

c. Interneuron (association neuron)

 Relays nerve impulses between neurons in CNS
Neuroglial Cells and Meylin Sheath
 Neurons are often associated with other types of cells found only in
N.S.—____________________________________
 Different types of neuroglial cells provide nutrition, support,
communication and protection between neurons
 One type of neuroglial cell is called a __________________ (or
neurolemnmocyte) found in PNS and ____________________ in
CNS
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 Schwann cells and oligodendrocytes encircle axons many times with
their membranes forming ____________________—rich in lipid

 Neurolemma is outermost layer of Schwann cells surrounding
neurons→ does not degenerate after nerve injury but forms template
or tube for nerves to heal in PNS
 Gaps between Schwann cells are called _____________________
 Distance between Nodes of Ranvier are called an _______________
 Because of myelin sheath, electrical current can only flow across
axoplasm at the nodes so speed of propagation of electrical signal is
quick – ______________ _____________
Diagram of Schwann cell encircling axon
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Generaration Of Action Potentials And Nerve
Impulses
A. Resting Potential

Can measure __________________________ (voltage) between
outside and inside of a neuron—using ______________
 Find that the inside of an axon is negative compared to the outside--i.e. (-65 mV)
 Neuron has a negative membrane potential at rest—called its _______
_______________
 Outside ________________ has higher concentration of Na+ ions than
inside _______________ and inside has higher concentration of K+
ions than outside—also, there is a much higher concentration of
negative organic ions (proteins) inside the cell than outside

 This increased permeability to K+ ions contributes to the negative
resting potential shown by neurons
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
 Axomembrane more permeable to K+ ions than Na+ so more K+ tends
to diffuse out than Na+ in which leads to a greater positive charge
outside the cell than inside resulting in a neurons resting membrane
potential

B. Action Potential
 Stimulation of neuron causes axomembrane to increase its
permeability to Na+ ions by opening up gates of Na+ channels→ Na+
move into cell due to concentration gradient and attraction to negative
ions inside axon→ ________________ (charge inside membrane
goes from “–“ to “+” charge

 During above phase, cell is said to be in ____________________—
another action potential cannot occur due to membrane potential
being positive (1-2 ms)
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 Next, Na+ channels close and K+ ion gates in membrane open and K+
start to move outside of axon along concentration gradient and due to
repulsive forces due to excess of positive charge inside axon→
restores negative charge inside membrane relative to outside (-65
mV)→ _________________
 Notice that r.m.p. becomes more negative than normal—called
__________________—due to K+ ions rushing out and making
outside more positive than r.m.p. and inside more negative than r.m.p.
 Na+/K+ pump subsequently return ions to their original positions
 Movement of above cycle of change across axomembrane constitutes
a _________________

Diagram of Action Potential
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Transmission of Nerve Impulse Across Synapses

 Each synaptic ending terminates in an axonal ending or ________
_________
 These structures contain vesicles containing __________________
 Synaptic cleft (20 nm) is gap between ___________________ and
_____________________ (i.e. membrane of dendrite of other cell)
Note: sometimes gap junctions do exist between pre and post-synaptic
membranes
 Nerve impulse reaches pre-synaptic membrane → open Ca++ gates
→ Ca++ enters presynaptic bulb → variety of reactions occur
causing→ vesicles to fuse to presynaptic membrane →
neurotransmitter released into synaptic cleft → neurotransmitters
diffuse across synaptic cleft→ neurotransmitter bind to receptors
on post synaptic membrane → change in membrane potential of
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post synaptic cell which can result in excitation or inhibition of
post synaptic membrane (depends on neurotransmitter and receptor
type)
 If excitatory, neurotransmitters cause post-synaptic membrane
potential to decrease (i.e. become less negative)—called _______
or excitatory post synaptic potential

 If inhibitory, neurotransmitter causes post-synaptic membrane
potential to increase (i.e. become more negative)—called _______
or inhibitory post synaptic potential

 If EPSP is great enough to reach the ____________________ (-50
mV) and spread to the axon hillock, it results in an action potential

Summation Across Synapses
 Whether a neuron fires or not depends on ____________

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Figure showing summation:


 In other words, if EPSP is big enough to depolarize the postsynaptic neuron to the ___________________ (about 15-20 mV
less negative than resting potential) and spread to axon hillock a
nerve impulse results
 Once action potentials result they are all the same intensity for a
given neuron—i.e. one action potential is not bigger or smaller
than another— this is known as the ___________________ of
neurons
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Diagram of an Action Potential
Types of Neurotransmitters

 Amino acids, peptides or even some gases such as NO or CO
 Some common transmitters are __________, ___________,
________________, ____________ and ________
 Acetylcholine is a major neurotransmitter of PNS—e.g.
parasympathetic N.S. and motor neurons of PNS, but also found in
CNS.
 Once neurotransmitters released, they are quickly destroyed by
enzymes in synapse or taken up by pre or post-synaptic membrane
and repackaged or destroyed→ prevents overstimulation or overinhibition of post synaptic membrane
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 _________________ is name of enzyme that breaks down AchE
 ________ (monoamine oxidases) break down NE and Serotonin or
Dopamine
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Diagram of Synapse:
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Major divisions of nervous system exist:
a. Central Nervous System (CNS)

f. Peripheral Nervous System (PNS)

 Made up of cranial, spinal nerves and nerves of the
autonomic N.S.
Note: nerves are bundles of neurons with their cell bodies found in
CNS or in ganglia (collection of nerve cell bodies) outside of CNS
 PNS also divided into ________ (responsible for voluntary
control) and _____________ (involuntary control) nervous system
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Peripheral Nervous System—Cranial Nerves

 12 pairs of Cranial nerves serving head, neck and face
 Cranial nerves can be solely motor, sensory or mixed
Peripheral Nervous System—Spinal Nerves

 Spinal nerves can be ________ (under voluntary control) or
______________ (under unconscious control)
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 Are connected to the spinal cord and come out between vertebrae of
spine

 Thus, spinal nerves are ______________________ having both
motor and sensory neurons
 Sensory fibres enter spinal cord via __________ _______
 Motor fibres exit spinal cord via ___________ __________
 Spinal nerves are responsible for reflex responses

 Involve both sensory and motor neurons
 Knee jerk reflex is example of spinal reflex
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Diagram of Spinal Cord Anatomy
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Spinal Reflex or Reflex Arc

 Reflexes are automatic response initiated by some external stimulus
 Also known as a _______ ____—a nerve pathway that carries out a
reflex
 Receptor activated→ sensory neuron→ dorsal root→ dorsal cord→
interneuron→ ventral cord→ motor neuron→ _________ (muscle
or gland)

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Autonomic Nervous System (ANS)

 Autonomic NS under involuntary and unconscious control
 Controls smooth muscle, internal organs and glands of body

 Have motor components only
 Sensory neurons in somatic nerves carry information about state of
organs to CNS

 ANS divided into two parts – ____________ and Parasympathetic
component
 Innervate all internal organs of body
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Diagram of Sympathetic and Parasympathetic Divisions of the Autonomic Nervous
System
 Both parts of ANS made of 2 motor neurons—______________ and
_______________ neurons
Note: Autonomic nervous system only has one pathway—i.e. from CNS
to some organ or tissue
 ___________ neurons in the sympathetic division are myelinated
when exit from CNS→ synapses with _____________ fibers which
are made of un-myelinated neurons innervating target organ (has
cell body in sympathetic ganglion outside of CNS)
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 _____________________ has long and myelinated pre-ganglionic
fibers and short and un-myelinated post-ganglionic fibers.
Sympathetic System
 Associated with “fight or flight” response
 Activates during emergency situations—_____________________
 E.x. dilates bronchi and increases heartbeat, slows down digestion

 Axons exit cord and run to ganglia near the cord where synapse with
post synaptic or second motor neurons whose cell bodies lies within
the ________________________ found in the sympathetic trunk

 Neurotransmitter released by postganglionic neuron is usually ____
Parasympathetic System
 Promotes internal body responses associated with relaxation

 Neurotransmitter on postganglionic neuron is usually ______
 Cell bodies of pre-synaptic neurons of parasympathetic system exit
from medulla and from sacral regions of spinal cord
 synapse with post-synaptic neurons occur near or inside target
organs

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Note: most but not all organs innervated by both systems—e.g. adrenal
medulla and sweat glands for example are only innervated by the
sympathetic division of the ANS.
Central Nervous System

 spinal cord allows communication between brain and spinal nerves
as well as being centre for reflex actions


 both are also protected by 3 coverings called the ____________
 different layers of meninges sandwiched together and contain
cerebrospinal fluid between them—functions as a cushion against
trauma
 csf also found in _____________ of spinal cord and __________ of
brain (brain has four ventricles—2 lateral, a 3d and a 4th) as well as
the sub-arachnoid space.
 ____ functions in variety of ways such as: protection of CNS from
injury when jarred by acting as shock absorber and cleansing the
CNS of metabolic wastes and then reabsorbed back in bloodstream
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
 _______________ = infection of meninges→ can be serious
Meninges
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Parts of Brain
 brain made of many different structures: ___________ (medulla,
pons and midbrain), __________, _________, _____________,
__________ cortex (also called ____________)
1. Brain Stem
 Made of medulla, pons and midbrain

 Primitive brain
Diagram of Brain
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Medulla
 regulates heartbeat (through A.N.S.), breathing (through
chemoreceptors as discussed in respiratory system) and
vasoconstriction (through pressure receptors)

 contains connections to spinal cord and higher brain centres
Pons
 important connection between cerebellum and spinal cord as
well as higher brain centres such as cerebral cortex

 helps regulate breathing rate along with medulla
Midbrain

 also a reflex centre for visual, auditory and tactile responses
2. Diencephalon

 Regulates body functions and emotions
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a) Hypothalamus


 Regulates hunger, sex drive, sleep, thirst, body
temperature, water balance, and blood pressure
 Controls pituitary gland (part of endocrine system)—thus
it is a link between nervous and endocrine system
 Makes ____ (vasopressin) and _________ by
______________________ which are passed onto and
stored in posterior pituitary gland
Connection between hypothalamus and posterior pituitary
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 Notice how neurosecretory cells in hypothalamus terminate in
posterior part of pituitary gland and secrete hormones into blood
stream
b) Thalamus

 Regulates states of sleep and arousal or wakefulness
(damage to it causes coma)
3. Pituitary gland
 Referred to as the “master gland” because it controls many
of the functions of other glands of body
 Made of ________ and _________ pituitary
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 Axon endings of hypothalamus in posterior pituitary store
____ (antidiuretic hormone) or ___________ (ADH) made
by hypothalamus

 Also stores _________ (also made in hypothalamus)—
causes contraction of uterus and release of milk from
mammary glands
Diagram of Pituitary Gland
4. Cerebellum

 processes info from inner ear and send impulses to muscles
to maintain balance

 has outer layer of gray matter and inner layer of white matter
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Diagram of Cerebellum
5. Cerebrum

 Higher brain centre
 Responsible for consciousness
 Outer layer called _________ _____ and contains grey
matter (cell bodies and short unmyelinated fibres)

 Made of 2 halves—_____ and ____ cerebral hemispheres
 Joined together by densely packed nerve bundle called
_____________ _____________
 Cerebrum divided into frontal, temporal, parietal and
occipital lobes
Parts of Cerebrum
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
 folded cortex has increased surface area
 has ______ areas that initiate and control voluntary movement
 ______ areas are areas that receive and process sensory
information
 _____________ areas are places in cerebrum where integration of
information occurs. They deal with higher consciousness, learning,
memory, intellect and artistic ability; they relay information on
actions for your body to take
Diagram of Association Areas of Cortex
 Basal nuclei _________________________________________
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Adrenal Glands & Fight or Flight Response

 Made of inner ________ and outer ________
 Stimulated directly by ANS and indirectly by hypothalamus
 Hormones produced by adrenal cortex are released during times of
stress-- _____________ , ___________ and some sex hormones–
regulate amount of minerals and glucose in blood

 Adrenal medulla controlled by ANS
 Adrenal medulla produces ____________ (adrenaline) and
_______________ (noradrenaline)
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Effects of Epinephrine and Norepinephrine:
a. ↑ metabolic rate
b. ↑ blood glucose levels
c. Bronchioles dilate
d. Rate of breathing ↑
e. Blood vessels of skin and digestive tract constrict while
those in skeletal muscles dilate
f. Heart rate ↑ and cardiac muscle contracts with more force
 Above help get one ready for emergency
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