Download 48.5, .6, .7

48.5
• All vertebrates’ nervous systems show cephalization
along with CNS
and PNS
• Cephalization- an evolutionary trend toward the
concentration of sensory equipment on the
anterior end of the body
• The spinal cord conveys information to and from the
brain that trigger responses to certain stimuli.
• Unlike invertebrates, vertebrates do not contain
segmental ganglia.
• Instead, the segmental ganglia are outside of the
spinal cord, which shows organization
Central Nervous System
48.5
• CNS consists of the brain and spinal cord.
• The Central Nervous System is derived from the dorsal
embryonic nerve cord, which is hollow.
• The feature persists through adulthood with the narrow
central canal of the spinal cord and ventricles of the brain.
• Ventricles are filled with cerebrospinal fluid
– formed in the brain by filtration of blood and assists the
supply of nutrients and hormones to different parts of the
brain while also removing waste.
• Axons carry nerve responses away from cell
body toward target cells.
• Axons in the CNS are found in bundles with a
white appearance due to the myelin sheaths
• Cross sections of the brain and spinal cord
make the white matter distinguishable from
the grey matter.
– Grey matter is mainly dendrites, unmyelinated
axons, and neuron cell bodies.
The Peripheral Nervous System
• Transmits information to and from the CNS
• Regulates vertebrates movements and internal environment
• Consists of cranial and spinal nerves.
– Cranial nerves originate in the brain and terminate mostly in organs of
the head and upper body.
– Spinal nerves tend to parts of the body below the head and originate
in the spinal cord.
•
Mammals have 31 pairs of spinal nerves and 12 pairs of
cranial nerves.
• The PNS can be divided into two functional components
– Somatic Nervous System
– Autonomic Nervous System
Somatic Nervous System
• Carries signals to and from skeletal muscles
– In response to external stimuli
• Voluntary, because it is subject to conscious
control, but a lot of skeletal muscle activity is
controlled by reflexes mediated by the spinal
cord and brain stem.
Autonomic Nervous System
• Regulates internal environment by controlling
smooth and cardiac muscles and the organs of
the digestive, cardiovascular, excretory, and
endocrine systems
• Made up of:
– Sympathetic
– Parasympathetic
– Enteric
Parasympathetic division vs. Sympathetic division
• Parasympathetic division causes opposite
responses that promote calming and return to
self-maintenance functions.
• Rest and digest
• Increased activity in the parasympathetic division
causes
– Increases glycogen production
– Decreases heart rate
– Enhances digestion
• Sympathetic and parasympathetic have
antagonist effects when the neurons innervate
the same organ
Enteric Division
• Consists of networks of neurons in the
digestive tract, pancreas, and gallbladder
• Enteric division can function independently,
but is sometimes
– Regulated by parasympathetic and sympathetic
divisions
• help maintain homeostasis
– Such as shivering to increase hear production
Embryonic Development of the Brain
• Three bilaterally symmetric, anterior bulges of
the neural tube
– Forebrain, midbrain, hindbrain
• As vertebrates develop, the they are divided
structurally and functionally.
Developments
• Midbrain
– Mesencephalon
• Hindbrain
– Metencephalon
– Myelencephalon
• Forebrain
– Telencephalon
– Diencephalon
Forebrain
• Cerebral Cortex- extends over and around
much of the human brain.
– Thalamus
– Hypothalamus
– Epithalamus
Brainstem “Lower Brain”
• Older part of evolutionary vertebrate
• Made up of the medulla, oblongata, the pons,
and the midbrain
• Functions
– Homeostasis
– Coordination of movement
– Conduction of information to higher brain centers
• Medulla Oblongata
– centers that control breathing, heart and blood
vessel activity, swallowing, vomiting, and digestion
• Pons
– regulates breathing centers in the Medulla
• Axons crossing from one side of the CNS to the
other in the Medulla cause the right side of the brain
to control much of the movement to the left and vise
versa
Arousal and Sleep
• Attentiveness and mental alertness vary from movement to
movement
• Counterpart to arousal is sleep
• Controlled by several centers in the brainstem and cerebrum.
• Melatonin promotes sleep and helps the body assimilate to its
environment
• The reticular active system regulates sleep and arousal.
– Serotonin may be the neurotransmitter of the sleepproducing centers
The Diencephalon
• Develops into three adult brain regions.
– Epithalamus: includes pineal gland and choroid plexus and
produces cerebrospinal fluid from blood
– Thalamus: main input center for sensory information going
to the cerebrum and the main output center for motor
information leaing the cerebrum; information from all
senses is sorted in the thalamus
– Hypothalamus: source of posterior pituitary and releasing
hormones that on the anterior pituitary and controls flight
response and mating
Circadian Rhythms
• Biological clock is involved in maintaining circadian
rhythms and a variety of physical phenomena.
– Hormone release, hunger, heightened sensitivity to
external stimuli
• Mammals biological clock is a pair of hypothalamic
structures called Suprachiasmatic nuclei (SCN)
• Usually require external cues to remain synchronized
with environmental cycles.
Cerebrum
• Divided to left right cerebral hemispheres
• Outer covering of grey matter
• Inner white matter that contains basal nuclei,
or important centers for planning and learning
movement sequences
• Largest and most complex part of the brain is
the cerebral cortex
– Sensory information is analyzed and motor
commands are issued.
• Neocortex: forms the outermost part of the
mammalian cerebrum, made of of six parallel
layers of neurons arranged tangential to the
brain surface
– Accounts for 80% of total brain mass
• Cerebral Cortex is divided into left and right
halves
• A thick band of axons known as the corpus
callosum enables communication between the
left and right cerebral cortices
• Damage of one are of the cerebrum may cause
redirection of its normal functions to other areas.
• Live can be lived with one hemisphere as seen in
some infants with severe epilepsy that have
entire hemispheres removed
– the other hemisphere will eventually take up most of
the functions of the other hemisphere
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• The cerebral cortex controls voluntary
movement and cognitive functions
– Each side of the cerebral cortex has four lobes;
frontal, temporal, occipital, and parietal lobes
• They are the primary sensory areas, and each
receives a specific type of sensory information
Processing
• Occipital lobe- visual
• Temporal lobe- auditory
• Parietal lobe- somatosensory, taste
– touch, pain, pressure, temperature, and the
position of muscles and limbs
• Frontal lobe- olfactory information
Lateralization of Cortical Function
• During brain development after birth, competing functions
segregate and displace each other in the cortex of the left
and right cerebral hemispheres
• The left hemisphere becomes more adept to language,
math, logical operations, and the serial processing of
sequences of information
• The right hemisphere is stronger at pattern recognition,
face recognition, spatial relations, nonverbal thinking,
emotional processing in general, and the simultaneous
processing of many kinds of information
• Split brain causes each side of the brain to work
independently, occurring when the corpus callosum is cut
Language and Speech
• Can be injured by strokes or tumors.
• Karl Wernicke
– Discovered that damage to a posterior portion of the
temporal temporal lobe, which is now called
Wernicke’s area, destroyed the ability to comprehend
speech, but the speech generator was still in tact.
• Pierre Broca
– Sometimes people can understand language, but not
speak, whom were later examined and it was
discovered that they had defects in a small region of
the left frontal lobe, which is now known as Broca’s
area
Emotions
• Results of complex interplay of many regions
of the brain
– Limbic system: a ring of structures around the
brainstem that includes the cerebral cortex,
amygdala, and the hippocampus.
• Attaches emotional “feelings” to basic survival
• Amygdala- central to recognizing the
emotional content of facial expressions and
laying down emotional memories.
• Hippocampus- explicit recall of events or
emotional memory
• Hypothalamus and Thalamus- interact with
sensory areas of the neocortex and other
higher brain centers, mediating primary
emotions such as laughing and crying
Memory and Learning
• Short-term memory- constantly comparing what
is happening to what just happened
• Long-term memory- names or numbers are
stored in long erm memory along with other data
that has been permanently stored
– Requiring the Hippocampus
• Wernicke’s and Broca’s areas store and retrieve
words and images
• Motor skills are usually learned with repetition
Cellular Mechanisms of Learning
• Long-term potential- increase in strength of synaptic
transmission that occurs when presynaptic neurons
produce a brief, high frequency series of action
potentials.
• LTP can last days or weeks when memories are stored.
• Post synaptic neurons possess two types of glutamate
receptors
– AMPA: part of ligand-gated ion channels; when glutamate
binds to them, Na+ and K+ diffuse through channels
– NMDA: both ligand gated and voltage gated that open only
if glutamate is bound and the membrane is depolarized.
Consciousness
• Was thought to be a subject of
philosophy or religion
• fMRI has allowed the possibility of
comparing activity in the human brain
different states of consciousness
–Offers a detailed picture of how neural
acticty correlates with conscious
experiments
Nerve Cell
• To reach target cells, axons have to elongate
from a few micrometers to a meter or more
• Growth Cone- responsive region at the leading
edge of the growing axon
• Axons respond by growing towards or away
with attraction and repulsion
Neural Stem Cells
• Human brain produces new neurons
• Ericksson: found newly divided neurons in the
hippocampus of all the patients of a cancer
study
• Mature neurons are unable to undergo cell
division
• Progenitor- fact that stem cells are committed
to becoming either neurons or glia
Diseases and Disorders of the Nervous System
• Schizophrenia- severe mental disturbance
characterized by psychotic episodes in which
patients lose the ability to distinguish reality
– Dopamine
• Depression
• Bipolar Disorder- swings of mood from high to low and affects about 1% of
the world’s population
• Major depression- have a low mood most of the time; they constitute roughly
5% of the population
• Alzheimer’s Disease- mental deterioration, or
dementia, characterized by confusion, memory loss,
and a variety of other symptoms. It rises from 10% at
age 65 and 35% at age 85.
• AD is difficult to make while the patient is alive
because it is a form of dementia.
• Parkinson’s Disease- a motor disorder characterized by
difficulty in initiating movements, slowness of
movements. And rigidity.
• Patients of PD often have masked facial expression,
muscle tremors, poor balance, flexed posture, and a
shuffling gait.
• L-Dopa