lab exam 3 Flashcards
(132 cards)
1
Q
Two divisions of the nervous system
A
Central nervous system (CNS)
Peripheral nervous system(PNS)
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Q
Central Nervous System
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Consists of the brain and the spinal cord; located in the dorsal body cavity surrounded by meninges.
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Q
Peripheral nervous system
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consists
of the all neural structures outside the CNS
including the cranial nerves, spinal nerves,
ganglia and sensory receptors
4
Q
Composition of nervous tissue
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The Nervous System is composed mainly
of Nervous Tissue; connective tissue and
blood vessels are also present.
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Q
The nervous tissue is composed of 2 types of cells:
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-Neurons
-supporting cells
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Q
Neurons
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(nerve cells) are conducting cells because they generate electrical signals
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Q
supporting cells (neuroglia)
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are non-conducting cells because they do not typically generate electrical signals.
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Q
cell body (soma or perikaryon)
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Contains the nucleus and all
other cytoplasmic organelles
EXCEPT CENTRIOLES
hence, neurons are generally
AMITOTIC
Contains well-developed rough
ER called Nissl Body or
Chromatophilic
substance; prominent nucleoli;
they indicate a neuron is a of a
secretory cell –
neurotransmitter from the axon
terminals. Neurotransmitters
are synthesized in the cell
body hence referred to as the
“BIOSYNTHETIC region” a
neuron
9
Q
Axon
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A single process extending from
the cell body – each neuron can
have only one axon; uniform
diameter; unmyelinated or
myelinated
Generates and transmits action
potentials AWAY from the cell body
hence, known as the
“CONDUCTING region” of a
neuron
Branches at the end into telodendria
which end in bulbous ends called
axon terminals (=synaptic
knobs=boutons) – store and release
neurotransmitter hence the axon
terminals are referred to as the
“secretory region” of a neuron
10
Q
dendrites
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Tapering processes that act as the “RECEPTIVE regions” of a neuron
Receive and convey electrical signals toward the cell body.
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Q
A
12
Q
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13
Q
two ways to classify neurons
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structural and functional
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Q
3 structural classifications of neurons
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based on the number of processes extending from the cell body of the neuron
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Q
multipolar neuron
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has at least 3 processes – one axon and at least
2 dendrites; most abundant neuron in the human body
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Q
Bipolar neurons
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has 2 processes – one axon and one dendrite.
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Q
pseudo unipolar neuron
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has one short process extending from the
cell body that bifurcates into a central process and a peripheral
process.
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Q
Sensory or afferent neuron
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transmits impulses from sensory receptors TOWARD the CNS
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Q
association neurons or interneurons
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located in the
CNS between the sensory
neurons and the motor neurons
– Most of the neurons (99%) in the body are association
neurons.
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Q
motor or efferent neuron
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transmits
impulses AWAY from the CNS to effector organs = glands, organs
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nucleus
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a cluster of neuron cell bodies in the
CNS
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Ganglion
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a cluster of neuron cell bodies in the
PNS
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Nerve
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a bundle of axons in the PNS
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tract
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a bundle of axons in the CNS
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axolemma
The plasma membrane of an axon is called an
axolemma.
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ENDONEURIUM
Each axon is wrapped in a delicate connective
tissue membrane called ENDONEURIUM
A bundle of endoneurium-covered axons is
called a fascicle
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Perineurium
Each fascicle is covered by the coarse
connective tissue membrane called the
PERINEURIUM
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epineurium
A bundle of perineurium-covered fascicles form
the nerve or a tract which is covered in a tough
connective tissue membrane called the
EPINEURIUM
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4 supporting cells inside the CNS
– Astrocytes
– Microglia
– Ependymal cells
– Oligodendrocytes
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2 supporting cells are located inside the PNS.
– Schwann cells
– Satellite cells
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microglia
Since the specific immune system does not have access to the
CNS; the microglia are phagocytes to engulf/destroy
pathogens and cell debris.
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astrocytes
– Most abundant
– Numerous extensions that wrap around neurons
– Involved in forming the BLOOD-BRAIN BARRIER, a selective
barrier that regulate the chemicals environment of the brain
– Regulate brain function
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ependymal cells
Ciliated columnar cells that line the ventricles – cavities in the brain that contain cerebrospinal fluid (CSF)
– Currents created by beating of cilia circulate the CSF
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Oligodendrocytes
Their extensions myelinate axons of neurons in the CNS
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Schwann cells
Schwann cells = neurolemmocytes
– Myelinate axons of neurons in the PNS
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satellite cells
Surround cell bodies of neurons to control their
chemical environment
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function of myelin sheath
Protection- physical
protection against trauma
1. Electrical insulation - to
prevent interference from
neighboring axons in a nerve
(if in the PNS) or tract (if in
the CNS)
2.) Increase in the rate of
impulse transmission – using
saltatory conduction occurring
only at the nodes of Ranvier
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Severed axons in the PNS can regenerate because
When the axon is severed in the PNS, cells of the immune
system clean up the damaged area of cell debris, a process
known as debridement, which sets the stage for regeneration
– The neurilemma of the Schwann cell forms a REGENERATION
TUBE that guides regeneration of the severed axon
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severed axon in the CNS fail to regenerate because
The microglia poorly clean up area of damage – debridement is
not complete
– No neurilemma to form a regeneration tube to guide growth of
severed axon
– Presence of growth-inhibiting proteins in the CNS inhibit
regeneration of a severed axon
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the resting membrane potential (RMP)
-70mV to -90mV
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Neurophysiology
Generation of Action Potential (AP)
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1 phase: depolarization phase
entry of sodium ions (Na+) into
axon referred to as sodium influx makes membrane potential less and
less negative
When the Threshold Potential (-55mV) is reached, an action
potential develops when the threshold potential is
reached. AP is an all-or-none phenomenon
Upshoot or spike due to an explosive entry of Sodium ions = a
positive membrane potential is reached +30mV, the peak
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2 phase: repolarization phase
2 events occur at the peak:
(i) sodium channels close (Na+ influx halts)
(ii) potassium channels open (K+ efflux begins) and potassium ions
(K+) rush out of the axon referred to as potassium efflux; this results in
reversal of the membrane potential toward a negative membrane potential
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3 phase: hyperpolarization
more K+ efflux occurs
past the RMP driving the membrane potential below the RMP
(RMP is restored by the Na+/K+ pump which pumps 3 Na+ out and 2 K+ in
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All or none phenomenon
an action potential will be generated if
depolarization reaches a threshold potential
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SELF PRPAGATING
once generated by the axon, it is propagated
down the axon to the axonal terminals; a propagated or transmitted
action potential is called a nerve IMPULSE
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All action potentials traced have the same shape and the SAME
amplitude (+30mV) irrespective of stimulus strength
All action potentials traced have the same shape and the SAME
amplitude (+30mV) irrespective of stimulus strength. Thus, the
difference between a stronger stimulus that causes the generation of
an action potential and a weaker stimulus that causes the
generation of an action potential is that the stronger stimulus causes
the impulse to be generated at a higher frequency than the weaker
stimulus
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Absolute refectory period (during an action potential)
coincides with the
depolarization phase of the action potential when sodium
channels are opened and therefore another action
potential cannot be generated because all the Na+
channels are already opened, and depolarization is
already occurring
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relative refectory period
coincides with the
repolarization phase of the action potential when the
sodium channels are closed ( potassium channels are
open) thus, an exceptionally strong stimulus can cause
sodium channels to open to allow for sodium ion influx
leading to depolarization and the generation of another
action potential
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factors affecting the rate of impulse transmission= conductive velocity
- diameter of the axon
- degree of myelination
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diameter of the axon
larger axons transmit impulses at a
faster rate than smaller axons because the larger axon have larger
diameter and therefore presents with less resistance impulse
transmission; the resistance in the smaller axons is higher which
impedes impulse transmission
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degree of myelination
myelinated axons transmit impulses
at a faster rate than unmyelinated axons.
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saltatory conduction
Myelinated axons use SALTATORY conduction where action
potentials are generated only at the nodes of Ranvier hence, the
impulse “jumps from node to node down the axon
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Continuous conduction
Unmyelinated axons use CONTINUOUS conduction where
action potentials developed stepwise across the entire axolemma
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classification of nerve fibers
- diameter
- degree of myelination
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group A fibers
have the largest diameter and heavily myelinated:
transmit impulse at the rate of 150 m/s ( 335 miles per hour). Ex. Motor
neurons that innervate skeletal muscles
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Group B fiber
intermediate diameter and lightly myelinated (with
wider gaps of nodes of ranvier); transmit impulses at a rate of 15 m/s (33
miles per hour)
Ex. Preganglionic autonomic fibers
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Group C fibers
smallest diameters and unmyelinated; transmit
impulses at a rate of 1 m/s (2.2 miles per hour)
Ex. Postganglionic autonomic fibers that innervate smooth muscle’
pain fibers
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Multiple sclerosis
Multiple sclerosis (MS) is an autoimmune
disease that results in demyelination of
axons in the CNS. As the disease
progresses, impulse transmission slows
down (fast saltatory conduction slow
continuous conduction- this interferes with
communication/control between the brain
and the rest of the body
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4 protective structures of the brain
- cranium
- meninges
-cerebrospinal fluid
-blood brain barrier
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cranium
bony helmet composed of the 8 cranial bones – frontal,
parietal(paired), temporal(paired), occipital, sphenoid and the ethmoid
bones
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Meninges
3 connective membranes surround the brain
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Dura mater
outermost meninx; double-layered – outer periosteal layer
which lines the internal surface of the cranium and the inner meningeal
layer separated from the underlying arachnoid mater by the SUDURAL
space
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Arachnoid mater
middle meninx separated from the underlying pia mater
by the SUBARACHNOID space. Web-like extensions from the
arachnoid mater to the subarachnoid space gives this meninx its name
( Arachnida = spider family)
The subarachnoid space contains CSF
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pia mater
innermost meninx that clings to the surface of the brain
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Cerebrospinal fluid (CSF)
filtered from blood; located in the ventricles
and also in the subarachnoid space hence, CSF is found inside and outside
of the brain acting as a “liquid” cushion; provides buoyancy to the brain;
provides nutrients; removes metabolic wastes
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Blood-brain barrier
a selective chemical barrier that prevents harmful,
toxic substances in blood from crossing to the neurons in the brain
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Ventricles
Cavities in the brain that contain CSF
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Lateral ventricle
each cerebral hemisphere contains a lateral
ventricle; the 2 lateral ventricles are connected by a median
membrane called the septum pellucidum; 2 lateral ventricles are
connected to the third ventricle below by a channel called the
interventricular foramen.
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third ventricle
located in the diencephalon; connected to the
fourth ventricle below via the cerebral aqueduct
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fourth ventricle
located in the brain stem (continued by the
central canal in the core of the spinal cord)
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How much CSF is drained each day?
600 ml of CSF/day is
filtered into the ventricles
and circulated when the
cilia of ependymal cells
beat to create
unidirectional currents.
Thus 600 ml of CSF
drains each day
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hydrocephaly: buildup of CSF in the ventral
600 ml of CSF is produced and
drained/day
Hydrocephaly is caused by increased
rate CSF production or blockage in
draining CSF.
Hydrocephaly can increase pressure
and damage the neurons in the adult
brain because the sutures are
synarthrotic joints and resist pressure; in
infants, the sutures are amphiarthrotic
joints which “give” and allow expansion
of the brain without exerting inward
pressure to damage neurons in the
brain
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how much does the brain weigh?
3.5 lb, 1600g
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surface of cerebrum is marked by gyri:
elevated ridges
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Cerebrum
Superior region of the brain – accounts for 83% of total brain mass
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4 major regions in the adult brain
- cerebellum
- brainstem
- diencephalon
- cerebellum
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surface of cerebrum is marked by sulci:
shallow groves
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fissures
deeper grooves
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longitudinal fissure
A median fissure called the LONGITUDINAL FISSURE divides the
cerebrum into right and left cerebral hemispheres
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corpus callosum
2 cerebral hemispheres are held together medially by the CORPUS
CALLOSUM
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each cerebral hemisphere is divided into 5 lobes.
- Frontal lobe
– Temporal lobe named for overlying cranial bones
– Parietal lobe
– Occipital lobe
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insula
The frontal, temporal, parietal and occipital lobes can be viewed externally
and are named for the overlying cranial bones
****The insula can not be viewed on the external surface of the cerebrum and
located deep to the lateral sulcus, covered by the frontal, temporal and
parietal lobes
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the sulci int he cerebral hemispheres
separate each cerebral hemisphere into lobes
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central sulcus
separates the frontal lobe from the parietal
lobe. The gyrus in the frontal lobe located immediately in front of the
central sulcus is called the PRECENTRAL GYRUS which contains
the motor control area; the gyrus in the parietal lobe immediately
behind the central sulcus is called the POSTCENTRAL GYRUS
which contains the somatosensory area
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lateral sulcus
separates the temporal lobe from the parietal
lobe and frontal lobe
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parieto-occipital sulcus
separates the parietal lobe from
the occipital lobe
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three regions in each cerebral hemisphere
- cerebral cortex
- cerebral white matter
- basal nuclei
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cerebral cortex
highly convoluted and 2-4 mm
thick; accounts for 40% of total brain mass; composed of
gray matter = cell bodies, dendrites; location of our
conscious mind.
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cerebral white matter
deep to the cerebral
cortex; composed of tracts with myelinated axons which
have a “whitish” appearance
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basal nuclei
islands of nuclei(clusters of neuron
cell bodies) within the cerebral White Matter
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motors areas
control voluntary movements.
consist of the primary motor cortex, Premotor cortex, Broca’s area,
frontal eye field. All located in the frontal lobes
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3 functional areas in the cerebral cortex
-motor areas
- sensory areas
- association areas
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sensory areas
for the conscious awareness of
sensation; consist of the Primary somatosensory cortex, Primary
visual cortex, Primary auditory cortex, Primary olfactory cortex,
Primary gustatory cortex
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association areas
integrate and interpret sensory
inputs from the sensory areas hence, each primary sensory area
has its own associated area (will be covered with the sensory areas)
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4 motor area in..
the left cerebral hemisphere
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3 motor areas in
the right cerebral hemisphere
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primary motor cortex
control voluntary movement of skeletal muscles
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premotor cortex
controls learned motor skills that are patterned or repetitive in nature such as typing, driving, playing an instrument.
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Broca's area
controls skeletal muscles involved in speech production, motor speech area.
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Frontal eye field
controls voluntary movements of the skeletal muscles that position
the eyes called the extrinsic eye muscles
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cerebral white matter
Second region in the cerebrum deep to the cerebral cortex; consists
of myelinated tracts.
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commissural tracts
Commissures – connect corresponding
areas in the two cerebral hemispheres. Corpus callosum is a
commissure that connects the right and left cerebral hemispheres.
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projection tracts
connect the cerebrum to lower brain areas and
the spinal cord. 2 types: Descending projection tracts send
information from the cerebral cortex (such as the Pyramidal tracts)
and Ascending projection tracts that send sensory information up to
the cerebral cortex (such as the spinothalamic tract)
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Association tracts
connect areas within the same cerebral
hemisphere. Arcuate fasciculus is an association tract that connects
the Broca’s area and the Wernicke’s area both located in the same
cerebral hemisphere, usually in the left cerebral hemisphere.
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basal nuclei
Islands of gray matter in the cerebral white matter
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3 major basal nuclei
- caudate nucleus
- putamen
globus pallidus
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diencephalon
contains the third ventricle.
3 paired structures
- thalamus
-hypothalamus
- epithalamus
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Thalamus
he relay station for sensory inputs to the cerebral cortex
hence, the thalamus is referred to as the “Gateway to the cerebral cortex”.
Visual relay center in the thalamus is the lateral geniculate nucleus (LGN);
auditory relay center is the medial geniculate nucleus (MGN). Thalamus
contains the third ventricle
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Hypothalamus
located below the thalamus; controls
– Activities of the Autonomic Nervous System
– Emotional response
– Core body temperature as it contains the body’s thermostat
– Food intake as it contains the satiety center
– Water intake as it contains the thirst center
– Sleep-wake cycles
– Endocrine function - produces 9 hormones
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Epithalamus
forms the roof of the third ventricle; contains the pineal
gland, an endocrine gland that secretes the hormone, melatonin, the sleep-
inducing hormone.
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brain stem
Cell bodies of 10 of the 12 cranial nerves are inside the brain stem:
* CNII – CNXII which control autonomic functions required for survival hence, damage to the
brain stem can result in death
* The brain stem consists of an outer white matter and an inner gray matter
* Brain stem consists of 3 areas
- midbrain
-pons
-medulla oblongata
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pons
located between the midbrain and the medulla oblongata. connect the motor cortex
and the cerebellum . Th pons contains respiratory centers (apneustic and pneumatoxic centers
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medulla oblongata
most inferior region that blends in with the spinal cord at the level of
the foramen magnum. Decussation of the pyramids occurs on its ventral surface.
Medulla oblongata contains autonomic reflex centers: Cardiovascular control center, respiratory
centers (dorsal respiratory group and the ventral respiratory group), emetic center, swallowing
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midbrain
contains the cerebral aqueduct which connects the 3rd ventricle to the 4th
ventricle in the brain stem
* Midbrain contains four nuclei called the corpora quadrigemina:
* - 2 superior nuclei are called the superior colliculi which act as the visual reflex centers
* - 2 inferior nuclei are called the inferior colliculi which act as auditory reflex centers
Midbrain contains 2 pigmented nuclei: red nuclei and the substantia nigra (slide #39)
i) Red nuclei regulate limb flexion
ii) Substantia nigra contains dopamine-releasing neurons (=dopaminergic neurons)
which project and modulate activities of the basal nuclei – degeneration of the dopaminergic
neurons from the substantia nigra to the basal nuclei causes Parkinson’s disease
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cerebellum
11% of the total brain mass
* Transverse fissure separates the cerebellum and the cerebrum
* Cerebellum is separated into 2 cerebellar hemispheres which are
held together medially by the VERMIS
Function of the cerebellum: processes information from cerebral motor
areas, visual and equilibrium inputs; smooth and coordinated skilled
voluntary skeletal muscle movements. For equilibrium/maintenance
of balance.
Function of the cerebellum is affected by alcohol intoxication
Can be viewed on the external surface of the
cerebellar hemisphere
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3 protective structures of the spinal cord
- vertebral column
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