Download Vertebrate Nervous System

Vertebrate Nervous System
Vertebrate Nervous System
Synthesis
Most complex, Rules over everything
Functions are explained in a large part by the nervous system
Set of parts that is responsible for nervous coordination and regulation of the different
metabolic and physiological processes in your body
Central processing or higher processing of the different things or stimuli from the
environment
Accessory functions that we don’t talk about often, we just think of nerve cells
There are other types of cells that have a very impt role in the vertebrate
nervous system like nerve cells of coordination but have other functions
Divisions
Central Nervous System (CNS) brain spinal cord centers for higher processing of
nerve signals particularly the brain for that function
Peripheral Nervous System (PNS) everything else, all nerves spinal nerves
cranial nerves emerging from central nervous system
With exception of the two:
Optic nerves one of the cranial nerves, Part of the Peripheral
Nervous system but considered to be still part of central
nervous system
Still covered in same meninges or layers that cover the
brain
Types of Cells
Neurons
Transmit nerve impulses
Nerve cell body called perikaryon sometimes the soma where you have
the nucleus
Two sets of extensions:
Axon - larger extension, pass on message to succeeding
neurons
Dendrites – much shorter but much more numerous,
emerging directly from the cell body, receives
impulses from preceding nerve cells, dendro means
In some cases neurons may have neurosecretory (endocrine) serve like a
gland, there are some neural cells/neurons that act as endocrine
glands secretes products directly to the blood stream
In the brain particularly the central nervous system you have a lot
of cells that are neurons yet they produce hormones
particularly the seratonin dopamin adrenalin oxytoxin
collectively called neurotransmitters adrenalin epinephrine
seratonin
Aside from neurons
Neuroglial cells (glia)
Do not transmit impulses
Other types of cells without neural function
Astrocytes: look like stars, pass nutrients between blood capillaries and
neurons
Part of blood brain barrier – series of cells tissues that prevent
blood and bacteria from leaking into cerebrospinal fluid,
once you have bacteria that’s sepsis already and lead to
very serious conditions
Also pass nutrients between blood capillaries and neurons
There’s a barrier against glycophilic substances, bacteria
preventing from flowing from blood to csf via tight
junctions of the cells
Certain substances are allowed – Semi-permeability typical
of cell membranes
Nutrients are allowed
Deposit or deliver inflammatory signals in cases where
there is damage to part of the nervous system, to
facilitate the immuno response, inflammation is a
response
Very important
Microglia: engulf foreign material and bacteria, feeding on them,
phagocytic elements of the nervous system
Oligodendroglia/Schwann cells: insulate axons of nerve cells/ neurons,
Axons have to be insulated, long extension of the nerve cell
Axon acts like a wire carries electrical signals
Nerve signals are electrical in nature, except in the part where they
have to cross the synaptic gap in this case they are
chemical in nature but while inside a neuron nerve signals
are electrical in nature, if don’t have insulating agent
electricity will difuse will not be able to travel from one part
to the other, insulation keeps electric signal in place
Myelin sheath – made of either schwann cells or oligodendroglia
found in central nervous system
Nerves cells in central nervous system axons of these nerve
cells are wrapped in oligodendroglial cells
Neurons in the peripheral nervous systems their axons are
wrapped in Schwann cells
Keep electric signal in place, nerves work on electric signals
Same in terms of function
Mechanism or machine that has an interface with nervous system
Ependymal cells: line the central canal of brain and spinal cord
When you dissect brain and spinal cord there’s a central canal or
cavity joining to which the csf flows, lining that central
canal are ependymal cells which are epithelial cells, they
also function in producing the csf
Neuron
Soma or perikaryon, Line extensions of dendrites which receive nerve impulses from
receding neurons and then signal transported via axon, insulated by myelin sheath,
oligodendroglia if in cns or schwann cells if in pns, nerve signal transfer along the
terminal regions of the axon, have to jump a space because the axon terminal buttons of
the preceding neurons and dendrites of the succeeding neurons are not connected to
each other, there’s a space between them, the signals has to pass and cross, cannot cross
signal in the form of electric signal cause brain will be fried by the electricity has to be
converted into a chemical signal first
Neurotransmitters – nerve signals converted into chemicals/hormones, responsible for
Serotonin – calming hormone, feel calm
Oxytoxin - hugging hormone
Endorphins – feeling of elation
Astrocyte
Have very extensive networks coming from astrocyte cell body these extensions provide
the bridge between capillaries and neurons to exchange nutrients or other important
products like inflammatory signal proteins
Prevent passing on of materials that shouldn’t be passed off like bacteria lipids or larger
substances like proteins
Canal central canal of the spinal cord
Ependymal cells lining
Astrocytes not responsible only for transmitting nutrients but also inflammatory signals
and neurotrophic and protective factor
Important cell for normal functioning of the nervous system
Without astrocytes you would have significant damage to your functions
Microglia – phagocytosis
Resting microglia and fully activated microglia
Signals from damaged neurons are cascading into the interstitial fluid that initiates
series of processes which includes astrocytes releasing inflammatory cells
Information Transmission
Electric signals
Nerve impulses along plasma membranes of neurons
Electrical in nature until they cross the synapse
Action potential driving of nerve signal all or none nature, threshold that must be
reached, when switch is off position light is closed
Chemical signals
Generated at synapses - gap between axon of preceding neuron and dendrites of
the succeeding neuron
Neurotransmitters – come in not all emotional
Electrical signal converted into chemical signal carried by vesicles from one
neuron to another, carrying electrical signal in the form of chemical
Neurotransmitters have particular functions
Regulatory mechanisms with regard to body temperature
breathing, emotions
Peripheral Nervous System
Somatic vs. Visceral
Distinction when talk about reflex arcs
Somatic nerves found in muslce particularly skeletal muscle ones you can control
Visceral nerves are found in the viscera smooth muscle parts of the body that
you can’t actually move like the internal organs
Afferent (sensory - dorsal) vs Efferent (motor - ventral)
Roots of a nerve
A particular nerve coming from the spinal cord would have an Afferent and
Efferent root
Afferent neuron – transmits nerve impulses toward the central nervous system
Efferent – transmits signals from central nervous system to effector organ
Receptor organ– body part that receives signal from particular part of the body
whether muscle bundle of nerves, have both sensory and motor
neurons
Central nervous system bring response back to the organ
Effector organ – organ that responds to the signal, neuron is the motor or
efferent neuron
Muscular system – fishes have a horizontal septum and spinal cord of the fish
have a nerve there and there are two rami dorsal ramus supplying the
hypaxial body mass ventral ramus supply the ventral body mass
General vs Special
Some nerves are very general for example vagus nerve supplies many diff. parts of the
body from head to toe
Has sensory and motor functions
Receiving impulses and motor transmiting the response signal
Autonomic Nervous System (ANS)
Part of the PNS which you can’t regulate
Sympathetic and Parasympathetic nervous system
Independent of control
Fight or flight response
Adrenalin driven responses of the body governed by this
Spinal Nerves
Number sequentialy and named after vertebral section (Cervical vertebrae
nerves C1 C2 C3,Thoracisc, Lumbar,Sacral)
Dorsal afferent root or sensory root, ventral efferent root or motor root coming
from the spinal chord
Associated with ganglia which is diff. from the brain (just collection/masses of
peripheral nerves)
Brain is a true organ, we have several ganglia
Responsible for a lot of diff. nervous processes
Viscera reflex arch or autonomic reflex arch – ganglia sites of connection
between primary motor neuron and secondary motor neuron
before motor responds or motor signal is transferred to effector
organ, sort of meeting place between successive neurons
Cranial Nerves
Emerging from the brain, already part of the peripheral nervous system or optic
nerve but are found in the head region, not coming from the spine
May be visceral/somatic, sensory/motor, general/special
Terminal (0) – sensory (olfactory) zeroth nerve cause it’s the first nerve, not
present in all vertebrates, prominent in fishes appearance is controversial
in mammals, serves as sensory function, particularly for olfactory signals
Olfactory (I) – sensory (olfactory), purely sensory nerve, for receiving signals
from the outside environment
Optic (II) – not a true nerve, controversial as well, for visual signals, still part
of the central nervous system, covered in the same layers that normally
cover the brain
Oculomotor (III) – motor (extrinsic eye muscles), a lot of eye muscles, actual
response of the body, if brain is intact you can see
Trochlear (IV) – motor (extrinsic eye muscles), thin and found at the sides of
the brain
Trigeminal (V) – sensory & motor (skin of head, teeth, jaws), large 5th nerve,
supplies and innervates the skin of the head, teeth and jaws
Abducens (VI) – motor (extrinsic eye muscles), small thin tendency to
remove them accidentaly, infront of the medulla oblungata
Facial (VII) – sensory (taste buds) & motor (2nd hyoid arch)
Auditory (VIII) – aka vestibulocochlear; sensory (inner ear) hearing
Glossopharyngeal (IX) – sensory (taste buds, gill pouches) & motor (3rd hyoid
arch)
Vagus (X) – sensory & motor (mouth, pharynx, viscera)
Spinal Accessory (XI) – motor (mastoids, trapezius)
Hypoglossal (XII) – motor (hyoid and tongue muscles) below tongue
Telencephalon and Diencephalon both part of the forebrain/procencephalon
Mesencephalon – middle
Metencephalon – hindbrain
Myelencephalon
Cerebral peduncle – where you have oculomotor nerve
Pons – you can see abducens here in the actual ventral surfaces
Trochlear thin nerves emerging at the side
Trigeminal Nerve
Facial
Auditory
Glossopharyngeal spinal accessory and hypoglossal - succeeding nerves which are the
smallest
Spinal Reflexes (knee jerk response tendon of patella, hitting a bundle of nerves in
quadriceps)
When have nerve signals transmitted but the brain is not involved
In normal responses brain is involved, reflex arc is faster
When touch a hot object
Still goes to the Central Nervous System but only till spinal chord, signal still go
to brain but after effector muscle relax, late notice by the brain
Somatic relfex arcs
Usually involve three neurons (sensory, interneuron,motor) for skeletal
muscles, jerking hand away from hot
Visceral reflex arcs
Usually involve four neurons (sensory, interneuron between bridging the
two, two motor neurons: preganglionic and postganglionic)
Peristaltic motion
Ganglia meeting of 1 primary motor neuron and secondary motor neuron
Primary and secondary meet at a ganglion
Primary pre ganglionic going into the ganglion
Second motor neuron is the postganglionic coming from ganglion going to
the effector, not as fast, no control, can’t be regulated by the body
Ganglion – meeting or cluster, between motor and motor
Stimulus is received by the receptor organ which is the muscles of the hand palm
muscle, sensory neuron or afferent dorsal neuron is activated by the signal go to
the dorsal root then go into the spinal cord, sensation is eventually relayed to the
brain after the effector muscles did the act
Butterfly shape in spinal cord dorsal wings are for sensory the ventral wings are for
motor
Sensory signal being processed very quickly by the spinal cord
Motor response is transferred by the ventral or efferent root into the effector organ, in
this case the effector is the biceps
Viscera
Basic difference addition of motor neuron have a second one, postganglionic and
preganglionic axon
Reflexes that body goes through that you can see are somatic, don’t see the viscera
Knee jerk response reaction
When you tap the tendon of the patella you strike a bundle of nerves in the
quadriceps thus the receptor organ then signal will travel via the afferent then to
the interneuron then to the efferent into the hamstrings and quadriceps but a
separate set of interneurons affect the hamstrings, not a direct effect but makes
or blocks signals going into the hamstrings so that it will stay relaxed, when
hamstrings are contracted your leg is flexed
A knee jerk stretches its leg against your will same time that the motor or
efferent root
At the same time that the motor or efferent root is stimulating the quadriceps to
extend the length set of interneurons is blocking nerve signals toward the
hamstrings so that they relax thus causing the leg to move forward not
just as simple as 1 muscle is just being affected, other muscles are also
being affected
Autonomic Nervous System
Sympathetic nervous system
Adrenaline rush – during certain circumstances something will drive you to
exert more effort
Such processes are generally stimulatory for instance burst of strength
Thoracolumbar as you can see the sympathetic nervous system branches are
found in the thorax and lumbar area
Adrenergic the primary hormone or neurotransmitter responsible for a lot of the
functions is Adrenalin or epinephrine
Stimilatory functions like speeding of the heart rate
Fight or flight response when facing the threat to yourself, pumped up with
adrenaline, flight is for survival
Relaxation of the digestive muscles
Parasymphathetic nervous system
Generally inhibitory/resting
Craniosacral cervical and sacral
Cholinergic primary neurotransmitter is acetyl cholin
Certain functions that are stimulatory
What one does the other one does the opposite of
Central Nervous System
Spinal Cord
Brain
Origins
Meninges – mostly ectodermal (dura mater)
Layer that covers the central nervous system for protection
Mostly ectodermal have the Dura mater Pia mater and Arachnoid mater
Mater means mother
Pia is gentleman
Arachnoid means spiderlike
Dura mater
Pia
Arachnoid
Only the dura mater is not from dermal because it comes from the mesoderm
and its outermost
Pia and arachnoid are ectodermal (neural plate)
Spinal cord and brain – ectodermal (neural plate)
How parts of the nervous system are formed
Invagination above the notochord forms first from mesodermal conglomeration
Invagination to create the neural plate that is ectoderm
Eventually, there will be a paging off to create a tube made of ectoderm which
becomes the spinal cord
Meninges and Cerebrospinal Fluid
For protection of spinal cord and brain
In fishes, only one primary meninx
In tetrapods, with secondary meninx (arachnoid and pia mater, primary meninx
is dura mater)
Cerebrospinal Fluid (CSF)
Common medium that doctor gets for diagnosis
Detect various pathogens for example when you have meningitis
When CSF swelling under the arachnoid
Protection of the spinal cord
Produt of choroid plexus (blood vessels) associated with ependymal cells
This tells me that they are like lymph, excess tissue fluid, produced by
hydrostatic pressure from blood vessels
Has a high rate of producing
For cushioning of spinal cord and brain watery medium
In fishes, there is just 1 primary menyx
The fish is surrounded in water so it has a habitat that is naturally
protective
In tetrapods, there is secondary menyx
Outside water, brain has to be surrounded with fluid environment
Made of arachnoid and pia mater
Dua mater – outermost
Pia mater and arachnoid mater – responsible for keeping in place the csf, it flows
sin these two, if there is a damage you will have severe implications
150mL in humans
Spinal Cord
Butterfly shape in the middle
Gray matter nerves are there but the ones in the middle
where you find the nerve cell bodies perikaryon and soma
White matter where you have the axons, surrounded by the myelin sheath
Dorsal efferent root
Ventral efferent root
Central canal where csf will flow
Ganglion part where two motor neurons will meet
Brain
Made of three distinct regions
Responsible for a particular set of functions
Forebrain – procencephalon divided into two:
Telencephalon are the cerebral vesicles embryologically but they eventually
become the cerebral cortex main part of the brain higher processing units
of the brain for various types of signals you receive
Speech centers of the brain:
Broca’s anterior part of the brain if damaged, Actual physical speech is affaced by
Broca’s
Wernicke’s posterior - Ablity to understand, able to speak normally but not able
to analyze deeper meaning very well
Aphasia – speech defects may be related to damage of broca’s or wernicke’s
Diencephalon still part of the forebrain part where you have the thalamus and
hypothalamus
Cerebrum part of the telencephalum
Cerebrum part of the Telencephalon
Hypothalamus found below the thalamus connected to a very impt gland called
pituitary gland which produces 9 different hormones
Thalamus is a relay center responsible for bridging between diff. areas of the brain for
processing of nerve signals, also responsible for various autonomic functions
Hypothalamus impt in interacting w/ the pituitary gland, impt functions in regulating
body temperature also hunger thirst
Still part of the forebrain, ventral part of the midbrain is the tegmentum and tegtum
superior and inferior folliculi
Tegmentum responsible for various autonomic functions
Tectum primary responsible for auditory and visual signals
Both part of the diencephalon
Still part of the procencephalon or forebrain
Another part is the limbic system not just a part but consists of many diff. parts
including the hypo and hippocampus responsible for memory
Amygdla for feelings of fear, if you want to not feel fear remove this
Limbic memory fear and hunger, sexual drive
Midbrain mesencephalon
Hindbrain collective term is rhombencephalon
Divided into two distinct sections
Metencephalon is the cerebellum smaller lobe behind the cerebrum, for
coordinated muscular movement and depth perception
Myelencephalon fons reading center for nervous signals and medulla oblongata
or brainstem is for houskeeping functions like heart breathing and
respiration, when deprived of oxygen high levels of carbon dioxide will
tell your medulla oblongata to signal body to breathe
Marine mammals don’t have very carbon dioxide sensitive medulla
oblongata tells body when to take breaths, when damaged fatal
To kill a zombie – shoot it in medulla oblongata
See some variations in birds and mamalls large cerebral cortex or telencephalon needed
for higher processing
Bony fishes have very prominent mid brain or mesencephalon or tectum in particular
for visual signals, visual cortex large, large for bony fishes tectum
Sharks have small brains, tectum tegmentum and visual cortex, use ampullae of
lorenzini for electrical signals, sense of smell chemoreception
Not so much on visual signals, bigger olfactory
Brains of vertebrates differ in terms of enlargement depending on what they
require
Mammals – cerebellum for more coordinated movement
Aquatic animals not very well developed