Download Peripheral Nervous System

Nervous System
(Chapters 9 & 10)
Divisions of the Nervous System
Brain
Cranial
nerves
• Central Nervous System (CNS)
• Brain
• Spinal cord
• Peripheral Nervous System (PNS)
• Cranial nerves (12 pairs)
• Spinal nerves (31 pairs)
*Each nerve can be either afferent (sensory),
efferent (motor), or both.
Spinal
cord
Spinal
nerves
Divisions of PNS
• Sensory Division:
• Picks up sensory information & delivers it to CNS
• Motor Division:
• Carries information to muscles & glands
• Divisions of the Motor Division:
• Somatic – voluntary; carries information to skeletal muscle
• Autonomic – involuntary; carries information to smooth muscle, cardiac muscle, glands
• Sympathetic – speeds up reaction
• Parasympathetic – slows
Central Nervous System
(brain and spinal cord)
Brain
Peripheral Nervous System
(cranial and spinal nerves)
Cranial
nerves
Sensory division
Spinal
cord
Sensory receptors
Spinal
nerves
Motor division
Somatic
Nervous
System
Skeletal muscle
Autonomic
Nervous
System
Smooth muscle
Cardiac muscle
Glands
Functions of Nervous System
• Sensory Function (receiving information)
• Info gathered by sensory receptors
• Info carried to the CNS
• Integrative Function (deciding what to do about information)
• Sensory info used to create:
• Sensations, memory, thoughts, decisions
• Motor Function (acting on information)
• Decisions acted upon
• Impulses carried to effectors
Cell Types (Review)
• Neurons
• Neuroglial cells (aka neuroglia, glia, glial cells)
Dendrites
Cell body
Nuclei of
neuroglia
Axon
Structure of a Neuron
Cell Descriptions
Chromatophilic substance
(Nissl bodies)
Dendrites
Cell body
• Neurons vary in shape & size
• All neurons have a cell body,
an axon, and dendrites
• Axon – convey info away from soma
• Dendrites – convey info to soma
• They differ in length and size
of their axons & dendrites
Neurofibrils
Impulse
Axon
Synaptic knob of axon terminal
Nodes of Ranvier
Myelin (cut)
Axon
Portion of a
collateral
Myelination of Axons
Dendrite
Unmyelinated
region of axon
Myelinated region of axon
Node of Ranvier
Axon
• White Matter
• Contains myelinated axons
• Considered fiber tracts
• Gray Matter
Neuron Neuron
cell body nucleus
• Contains unmyelinated structures
• Cell bodies, dendrites
Enveloping
Schwann cell
Schwann
cell nucleus
Longitudinal
groove
Unmyelinated
axon
Classification of Neurons
• Neurons vary in function (can be sensory, motor, integrative neurons)
• They vary in size, shape, number of axons & dendrites
• Classified into three major groups:
• Unipolar neurons
• Bipolar neurons
• Multipolar neurons
Dendrites
Structural Differences
between Neurons:
• Multipolar neurons
• 99% of neurons
• Many processes
• Most neurons of CNS
Peripheral
process
• Bipolar neurons
• Two processes
• Eyes, ears, nose
Axon
Direction
of impulse
Central
process
• Unipolar neurons
• One process
• Ganglia of PNS
• Sensory
Axon
(a) Multipolar
Axon
(b) Bipolar
(c) Unipolar
Functional Differences
between Neurons:
• Sensory Neurons
• Afferent (approach)
• Carry impulse to CNS
• Most are unipolar, some
bipolar
Central nervous system
Cell body
• Motor Neurons
• Efferent (exit)
• Carry impulses away
from CNS to effectors
• Multipolar
Dendrites
Sensory
receptor
Cell body
Axon
(central process)
• Interneurons
• Link neurons in CNS (aka
association neurons)
• Multipolar
Peripheral nervous system
Axon
(peripheral process)
Sensory (afferent) neuron
Interneurons
Motor (efferent) neuron
Axon
Effector
(muscle or gland)
Axon
Axon
terminal
Types of Neuroglial Cells in PNS
• Schwann cells
• Produce myelin found on peripheral myelinated neurons
• Speed up neurotransmission
• Satellite cells
• Support clusters of neuron cell bodies (ganglia)
Types of Neuroglial Cells in CNS
1. Microglia
• Phagocytic cells of the CNS
2. Astrocytes
•
•
•
•
Scar tissue
Get rid of excess ions
Induce synapse formation
Connect neurons to blood vessels
3. Oligodendrocytes
• Myelinating cells of the CNS
4. Ependymal cells
•
•
•
•
Ciliated
Line central canal of spinal cord
Line ventricles of brain
Keep CSF moving
Neuroglial Cells
Fluid-filled cavity
of the brain or
spinal cord
Neuron
Ependymal
cell
Oligodendrocyte
Astrocyte
Microglial cell
Axon
Myelin
sheath (cut)
Capillary
https://www.youtube.com/watch?v=qPix_X-9t7E
Node of
Ranvier
Regeneration of a Nerve Axon
Skeletal
muscle fiber
Motor neuron
cell body
Changes
over time
Site of injury
Schwann cells
Axon
(a)
Distal portion of
axon degenerates
(b)
Proximal end of injured axon
regenerates into tube of sheath cells
(c)
Schwann cells
degenerate
(d)
Schwann cells
proliferate
(e)
Former connection
reestablished
The Synapse
• Nerve impulses pass from
neuron to neuron at
synapses
• They move from a presynaptic neuron to a postsynaptic neuron
Synaptic
cleft
Dendrites
Axon of
presynaptic
neuron
Axon of
postsynaptic
neuron
Axon of
presynaptic
neuron
Cell body of
postsynaptic
neuron
Direction of
nerve impulse
Synaptic Transmission
• Neurotransmitters are
released when impulse
reaches synaptic knob
Axon
Ca+2
Synaptic knob
Synaptic
vesicles
Presynaptic neuron
Ca+2
Cell body or dendrite
of postsynaptic neuron
Mitochondrion
Ca+2
Synaptic
vesicle
Vesicle releasing
neurotransmitter
Axon
membrane
Neurotransmitter
Synaptic cleft
Polarized
membrane
https://www.youtube.com/watch?v=90cj4NX87Yk
Depolarized
membrane
Cell Membrane Potential
• Cell membrane is electrically charged or polarized
• Inside of membrane is negative, with respect to positively-charged outside
• Due to unequal distribution of ions inside/outside
• Thanks to…
Distribution of Ions
• K+ ions = major intracellular cation
• Na+ ions = major extracellular cation
• Distribution created by Na+ /K+ pump
• Actively transports Na+ out of cell, K+ into the cell
Resting Potential
• Resting Membrane Potential (RMP)
•
•
•
•
70 mV difference from inside to outside of cell
Polarized membrane
Inside of cell = negative relative to outside of cell
RMP = -70 mV
• Due to distribution of ions inside vs. outside from Na/K pump
• Na/K pump resets/restores this membrane potential
Local Potential Changes
• Changes caused by various stimuli:
• Temperature changes, light, pressure
• Environmental changes affect
membrane potential by opening a
gated ion channel
• Channels can be:
• Chemically gated
• Voltage gated
• Mechanically gated
Gatelike mechanism
(a) Channel closed
(b) Channel open
Local Potential Changes
• Hyperpolarization: membrane potential becomes more negative
• Depolarization: membrane potential becomes less negative
• Graded to intensity of stimulation reaching the threshold potential
• Reaching threshold potential results in a nerve impulse, starting an
action potential
Na+
Na+
–62 mV
Chemically-gated
Neurotransmitter Na+ channel
(a)
Presynaptic
neuron
Voltage-gated
Na+ channel
Trigger zone
Na+
Na+
Na+
Na+
–55 mV
(b)
Na+
Action Potentials
Na+
• At rest, the membrane potential
is polarized (RMP = -70 mV)
• Threshold stimulus reached (-55)
• Na+ channels open and
membrane depolarizes
(toward 0)
• K+ leaves cytoplasm and
membrane repolarizes (+30)
• Brief period of hyperpolarization
(-90)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
Na+
–0
–70
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
(a)
K+
Na+ Na+ Na+
K+
K+
Threshold
stimulus K+
K+
Na+
Na+
K+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
–0
Na+ channels open
K+ channels closed
–70
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Region of depolarization
(b)
K+
K+
K+
Na+
Na+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
Region of repolarization
(c)
Na+
Na+
Na+
Na+
Na+
–0
–70
Na+
K+ channels open
Na+ channels closed
Action Potentials
Membrane potential (millivolts)
+40
Action potential
+20
0
–20
–40
–60
Resting potential
reestablished
Resting
potential
–80
0
Hyperpolarization
1
2
3
4
5
Milliseconds
6
7
8
Region of
action potential
Action Potentials
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
–
–
–
+
+
+
(a)
+
–
+
+
–
–
+
+
Direction of nerve impulse
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
(b)
https://www.youtube.com/watch?v=OZG8M_ldA1M
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
+
(c)
+
+
+
+
+
+
+
+
All-or-None Response
• If a neuron responds at all, it responds completely
• A nerve impulse is conducted whenever a stimulus of threshold
intensity or above is applied to an axon
• All impulses carried on an axon are the same strength
Refractory Period
• Absolute Refractory Period
• Time when threshold stimulus does not start another action potential
• Relative Refractory Period
• Time when stronger threshold stimulus can start another action potential
Synaptic Transmission
• Where released neurotransmitters cross the synaptic cleft and reacts
with receptors in the postsynaptic neuron membrane
• Effects of neurotransmitters vary
• Some may open ion channels, others may close them, making it more
or less likely for an action potential to occur
https://www.youtube.com/watch?v=VitFvNvRIIY
Synaptic Potential
• EPSP
•
•
•
•
Excitatory postsynaptic potential
Graded
Depolarizes membrane of postsynaptic neuron
Action potential of postsynaptic neuron becomes more likely
• IPSP
•
•
•
•
Inhibitory postsynaptic potential
Graded
Hyperpolarizes membrane of postsynaptic neuron
Action potential of postsynaptic neuron becomes less likely
Summation of EPSPs and IPSPs
• EPSPs and IPSPs are added together in
a process called summation
• More EPSPs lead to greater
probability of an action potential
• More IPSPs lead to lower probability
of an action potential
Neuron
cell body
Nucleus
Presynaptic
knob
Presynaptic
axon
Impulse Processing
• Different ways the nervous system processes nerve impulses and acts
upon them:
• Neuronal pools of interneurons
• Convergence
• Divergence
• Neuronal pools
• Groups of interneurons that make synaptic connections with each other
• Interneurons work together to perform a common function (can be excitatory
or inhibitory)
• Each pool receives input from other neurons
• Each pool generated output to other neurons
Impulse Processing
• Convergence
• Neuron receives input from several
neurons
• Incoming impulses represent
information from different types of
sensory receptors
• Allows nervous system to collect,
process, and respond to information
• Makes it possible for a neuron to sum
impulses from different sources
1
3
2
Impulse Processing
• Divergence
• One neuron sends impulses to
several neurons via its branched axon
• Can amplify an impulse
• Impulse from a single neuron in CNS
may be amplified to activate enough
motor units for muscle contraction or
glandular secretion
4
6
5
Central Nervous System (CNS)
• Consists of brain & spinal cord
• Brainstem connects the brain to the spinal cord
• Communication to the PNS is by way of the spinal cord
Meninges
• Membranes of the CNS; protection
• Three layers:
• Dura mater “tough mother”
• Venous sinuses
• Arachnoid mater “spider mother”
• Space contains cerebrospinal fluid (CSF)
• Pia mater “little mother”
• Encapsulates blood vessels
Skin
Scalp
Subcutaneous tissue
Cranium
Bone of skull
Cerebrum
Dural sinus (superior
sagittal sinus)
Tentorium
cerebelli
Arachnoid
granulation
Dura mater
Cerebellum
Vertebra
Arachnoid
mater
Pia mater
Spinal cord
Subarachnoid space
Falx cerebri
Meninges
(a)
Meninges
Gray matter
White matter
(b)
Cerebrum
Spinal cord
Ventral root
Dorsal root
Spinal nerve
Dorsal root
ganglion
Subarachnoid
space
Pia mater
Arachnoid mater
Epidural space
Dura mater
Dorsal root
Dorsal branch
(dorsal ramus)
Spinal
nerve
Ventral branch
(ventral ramus)
Dorsal root
ganglion
Spinal cord
Ventral root
Epidural
space
Thoracic
vertebra
(a)
(b)
Body of
vertebra
Ventricles
Lateral ventricle
Interventricular
foramen
Third ventricle
• They are interconnected cavities within
cerebral hemispheres and brain stem
• Continuous with the central canal of the
spinal cord
• Filled with CSF
• Four ventricles:
• 2 lateral ventricles (first and second)
• Third, fourth ventricles
Cerebral
aqueduct
(a)
Fourth ventricle
To central canal
of spinal cord
Interventricular
foramen
Lateral
ventricle
Third ventricle
Cerebral
aqueduct
• Other nearby components: interventricular
foramen & cerebral aqueduct
Fourth
ventricle
(b)
To central canal
of spinal cord
CSF
Arachnoid
granulations
Blood-filled
dural sinus
Choroid plexuses
of third ventricle
• Secreted by choroid plexus
Third ventricle
Cerebral aqueduct
(ependymal cells)
Fourth ventricle
• Circulates in ventricles, central canal of
spinal cord, and subarachnoid space
• Completely surrounds brain & spinal
cord
• Excess or wasted CSF is absorbed by
arachnoid villi
• It is a clear fluid similar to blood plasma
• Provides nutrients, protection, and a
stable concentration of ions in the CNS
Pia mater
Subarachnoid space
Arachnoid mater
Dura mater
Choroid plexus of
fourth ventricle
Central canal of spinal cord
Pia mater
Subarachnoid space
Filum terminale
Arachnoid mater
Dura mater
Spinal Cord
Brainstem
Foramen
magnum
• Slender column of nervous tissue,
continuous with brain and brainstem
• Extends downward through vertebral
canal
• Begins at formamen magnum in skull,
ends at L1/L2 interspace (lumbar
vertebrae)
• Conduit for nerve impulses to/from
brain and brainstem
• Center for spinal reflexes
Cervical
enlargement
Cervical
enlargement
Spinal cord
Vertebral
canal
Lumbar
enlargement
Conus
medullaris
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Filum
terminale
(a)
(b)
Structure of Spinal Cord
Posterior horn
Posterior funiculus
Posterior median
sulcus
White matter
Gray matter
Gray commissure
Lateral funiculus
Dorsal root
of spinal nerve
Central canal
Anterior
funiculus
Dorsal root
ganglion
Ventral root
of spinal nerve
Anterior
horn
Anterior
median
fissure
Portion of
spinal nerve
Tracts of the Spinal Cord
• Ascending tracts (dorsal) conduct sensory impulses to the brain
• Descending tracts (ventral) conduct motor impulses from the brain to
motor neurons reaching muscles & glands
Reflex Arcs
• Automatic, subconscious responses to stimuli
• Simple reflex arc (sensory – motor)
• Most common reflex arc (sensory – association – motor)
Sensory or
afferent neuron
Receptor
Central
Nervous
System
Motor or
efferent neuron
Effector
(muscle or gland)
Interneuron
Spinal cord
Dorsal
1
Receptor
3
2
Sensory neuron
Cell body
of sensory
neuron
White matter
Gray matter
4
Ventral
Motor neuron
5
Effector
(muscle
or gland)
Central
canal
Reflex Behavior
• Example: Knee-jerk reflex; a simple monosynaptic reflex
• Helps maintain an upright posture
Axon of sensory
neuron
Cell body of
sensory neuron
Direction of impulse
Spinal cord
Cell body of
motor neuron
Axon of motor
neuron
Effector (quadriceps femoris
muscle group)
Receptor associated with
dendrites of sensory neuron
Patella
Patellar ligament
Reflex Behavior
• Example: Withdrawal reflex
• Prevents or limits tissue damage
Direction
of impulse
Dendrite of
sensory
neuron
Pain
receptor
in skin
Tack
Cell body of sensory neuron
Axon of sensory neuron
Interneuron
Axon of
Effector (flexor
motor neuron
muscle contracts
and withdraws part
being stimulated)
Spinal cord
Cell body of
motor neuron
Reflex Arc
• Example: crossed extensor reflex
• Crossing of sensory impulses +– == Stimulation
Inhibition
within the reflex center to
produce an opposite effect
Sensory neuron
Interneuron
–
+
–
Extensor
relaxes
+
Extensor
contracts
Flexor
relaxes
Motor
neurons
Flexor contracts
Motor
neurons
The Brain
• Interprets sensations
• Determines perception
• Stores memory
• Reasoning
• Makes decisions
• Coordinates muscular movements
• Regulates visceral activities
• Determines personality
• Major parts:
• Cerebrum
•
•
•
•
•
Frontal lobes
Parietal lobes
Occipital lobes
Temporal lobes
Insula
• Diencephalon
• Cerebellum
• Brainstem
• Midbrain
• Pons
• Medulla oblongata
Gyrus
Skull
Meninges
Cerebrum
Diencephalon
Midbrain
Sulcus
Corpus
callosum
Fornix
Brainstem Pons
Medulla
oblongata
Cerebellum
Spinal cord
(a)
Fornix
Cerebrum
Corpus
callosum
Diencephalon
Midbrain
Pons
Transverse fissure
Cerebellum
Medulla oblongata
Spinal cord
Structure of the Cerebrum
Central sulcus
Parietal lobe
Gyrus
• Corpus callosum
• Connects cerebral hemispheres
• Gyri
• Bumps or convolutions
Sulcus
Frontal lobe
Lateral sulcus
Occipital lobe
Temporal lobe
Transverse fissure
(a)
Cerebellar
hemisphere
Central sulcus
Parietal lobe
• Sulci
• Grooves in gray matter
• Fissures
Central sulcus
Longitudinal
fissure
Parietal lobe
Occipital lobe
• Longitudinal: separates the cerebral (b)
hemispheres
• Transverse: separates cerebrum from
cerebellum
Occipital lobe
Frontal lobe
Insula
Retracted
temporal lobe
(c)
Split Brain Research
• Video 1 – corpus callosum severed
http://www.youtube.com/watch?v=lfGwsAdS9Dc&feature=related
• Video 2 – corpus callosum missing
http://www.youtube.com/watch?v=VHgClWAPbBY&feature=related
Lobes of the Cerebrum
• Five lobes bilaterally:
• Frontal, parietal, temporal, occipital, and insula
• Insular cortex functions in awareness & judging intensity of pain, among other things
Central sulcus
Parietal lobe
Occipital lobe
Frontal lobe
Insula
Retracted
temporal lobe
Cerebrum Functions
• Interprets impulses
• Initiates voluntary movements
• Stores information as memory
• Retrieves stored information
• Reasoning
• Seat of intelligence and personality
Cerebral Cortex
• Thin layer of gray
Concentration, planning,
matter that
problem solving
constitutes the
Frontal eye field
outermost portion of Auditory area
Front lobe
the cerebrum
Motor speech area
• Contains 75% of all (Broca’s area)
Lateral sulcus
neurons in the
Interpretation of auditory patterns
nervous system
Motor areas involved with the control
of voluntary muscles
Temporal lobe
Central sulcus
Sensory areas involved with
cutaneous and other senses
Parietal lobe
Sensory speech area
( Wernicke’s area)
Occipital lobe
Combining
visual images,
visual recognition
of objects
Visual area
Cerebellum
Brainstem
Sensory Areas (post-central sulcus)
• Cutaneous sensory area
• Parietal lobe; interprets sensations on skin
• Visual area
• Occipital lobe; interprets vision
• Auditory area
• Temporal lobe; interprets hearing
• Sensory area for taste
• Near base of central sulcus
• Sensory area for smell
• Arises from centers deep within the cerebrum
Motor &
Sensory
Areas
Arm
Forearm
Trunk Pelvis
Trunk
Pelvis
Neck
Forearm Arm
Thigh
Thigh
Thumb,
fingers,
and hand
Leg
Foot and
toes
Facial
expression
Hand, fingers,
and thumb
Upper
face
Leg
Foot and
toes
Genitals
Lips
Salivation
Vocalization
Mastication
Teeth and
gums
Swallowing
Tongue and
pharynx
Longitudinal
fissure
(a) Motor area
Longitudinal
fissure
(b) Sensory area
Frontal lobe
Motor area
Sensory area
Central sulcus
Parietal lobe
Association Areas
•
•
•
•
•
•
•
Regions that are not primary motor or primary sensory areas
Widespread throughout cerebral cortex
Analyze & interpret sensory experiences
Provide memory, reasoning, verbalization, judgment, emotions
Frontal – concentration/planning/complex problem solving
Parietal – understanding speech/choosing words to express thought
Temporal – interpret complex sensory experiences/store memories of
visual scenes, music, and complex patterns
• Occipital – analyze and combine visual images with other sensory
experiences
Hemisphere Dominance
• Left dominant in most individuals
• Dominant hemisphere controls:
• Speech, writing, reading
• Verbal skills, analytical skills, computational skills
• Non-dominant hemisphere controls:
• Nonverbal tasks, motor tasks
• Understanding and interpreting musical and visual patterns
• Provides emotional and intuitive thought processes
Memory
• Short term
• Working memory; closed neuronal circuit
• Circuit is stimulated over and over
• When impulse flow ceases, memory does also unless it enters long-term
memory via memory consolidation
• Limited information storage
• Long term
• Changes structure or function of neurons
• Enhances synaptic transmission
Diencephalon
• Between cerebral hemispheres and above the brainstem
• Surrounds the third ventricle
• Contains:
Superior
Corpora quadrigemina colliculus
Optic nerve
•
•
•
•
•
•
•
•
•
Thalamus
Epithalamus
Hypothalamus
Optic tracts
Optic chiasm
Infundibulum
Posterior pituitary
Mammillary bodies
Pineal gland
Optic chiasma
Inferior
colliculus
Pituitary gland
Mammillary body
Thalamus
Optic tract
Third
ventricle
Pons
Cerebral
peduncles
Pineal gland
Fourth
ventricle
Pyramidal tract
Olive
Cerebellar
peduncles
Medulla
oblongata
Spinal cord
(a)
(b)
Diencephalon
• Thalamus
• Gateway for sensory impulses heading to cerebral cortex
• Receives all sensory impulses except smell
• Channels impulses to appropriate part of cerebral cortex for interpretation
• Epithalamus
• Functions to connect the limbic system to other parts of the brain
• Hypothalamus
• Maintains homeostasis by regulating visceral activities
• Links nervous and endocrine systems
• Limbic System
• Consists of parts of the frontal & temporal lobes, hypothalamus, thalamus, basal
nuclei, other deep nuclei
• Functions to control emotions, produce feelings, and interpret sensory impulses
Hypothalamus
Diencephalon
Brainstem
Thalamus
Corpus
callosum
• Midbrain
• Pons
• Medulla oblongata
Corpora
quadrigemina
Midbrain
Pons
Cerebral
aqueduct
Reticular
formation
Medulla
oblongata
Spinal cord
Pons & Medulla Oblongata
• Pons
• Rounded bulge on underside of brainstem
• Helps regulate breathing
• Relays nerve impulses to/from medulla oblongata and cerebellum
• Medulla oblongata
• Continuation of spinal cord
• Cardiac, vasomotor, respiratory control centers
• Non-vital reflexes (coughing, sneezing, swallowing, vomiting)
Longitudinal
fissure
Cerebellum
Thalamus
• Inferior to occipital lobes
Superior peduncle
• Posterior to pons & medulla
Pons
Middle peduncle
Inferior peduncle
• Two hemispheres
Medulla oblongata
(like cerebrum)
• Integrates sensory information concerning position of body parts
• Coordinates skeletal muscle activity
• Maintains posture
Corpus callosum
Cerebellum
Lifespan Changes
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Brain cells begin to die before birth
Over average lifetime, brain shrinks 10%
Most cell death occurs in temporal lobes
By age 90, frontal cortex has lost half its neurons
Number of dendritic branches decreases
Decreased levels of neurotransmitters
Fading memory
Slowed responses and reflexes
Increased risk of falling
Changes in sleep patterns that result in fewer sleeping hours