Human Physiology Central nervous system (CNS)

1. Chapter 8
The Central Nervous System
Human
physiology

2. CNS
• Consists of:
▫ Brain.
▫ Spinal cord.
• Receives input from
sensory neurons.
• Directs activity of motor
neurons.
• Association neurons
maintain homeostasis
in the internal
environment.

3. Embryonic Development
• Groove appears in ectoderm to fuse to form neural tube by
20th
day after conception. Neural tube eventually forms the
CNS.
• During 5th
week, modified:
▫ Forebrain: telencephalon and diencephalon.
▫ Midbrain: unchanged.
▫ Hindbrain: metencephalon and myelencephalon.
• Part of ectoderm where fusion occurs becomes neural crest.
▫ Neural crest forms ganglia of PNS.

4. Embryonic Development (continued)

5. Embryonic Development (continued)
• Telencephalon grows disproportionately
forming 2 the hemispheres of the cerebrum.
• Ventricles and central canal become filled with
cerebral spinal fluid (CSF).
• CNS composed of gray and white matter.
▫ Gray matter consists of neuron cell bodies and
dendrites.
▫ White matter (myelin) consists of axon tracts.

6. Cerebrum
• Only structure of the telencephalon.
• Largest portion of brain (80% mass).
• Responsible for higher mental functions.
• Corpus callosum:
▫ Major tract of axons that functionally interconnects
right and left cerebral hemispheres.

7. Cerebrum (continued)

8. Cerebral Cortex
Characterized by numerous convolutions.
◦ Elevated folds: gyri.
◦ Depressed groves: sulci.
Frontal lobe:
◦ Anterior portion of each cerebral hemisphere.
◦ Precentral gyri:
 Contains upper motor neurons.
 Involved in motor control.
Body regions with the greatest number of motor
innervation are represented by largest areas of
motor cortex.

9. Cerebral Cortex (continued)

10. Cerebral Cortex (continued)
• Parietal lobe:
▫ Primary area responsible for perception of
somatesthetic sensation.
▫ Body regions with highest densities of receptors
are represented by largest areas of sensory
cortex.
• Temporal lobe:
▫ Contain auditory centers that receive sensory
fibers from cochlea.
▫ Interpretation and association of auditory and
visual information.

11. Cerebral Cortex (continued)
• Occipital Lobe:
▫ Primary area responsible for vision and
coordination of eye movements.
• Insula:
▫ Implicated in memory encoding.
▫ Integration of sensory information with visceral
responses.
▫ Coordinated cardiovascular response to stress.

12. Visualizing the Brain
• X-ray computed tomography (CT):
▫ Complex computer manipulations of data obtained from x-ray
absorption by tissues of different densities.
 Soft tissue.
• Positron-emission tomography (PET):
▫ Radioisotopes that emit positrons are injected into blood stream.
 Collision of positron and electron result in emission of gamma rays.
 Pinpoint brain cells that are most active.
▫ Brain metabolism, drug distribution.
• Magnetic resonance imaging (MRI):
▫ Protons (H+
) respond to magnetic field, which align the protons.
 Emit a radio-wave signal when stimulated.
 Brain function.

13. Electroencephalogram (EEG)
• Measures synaptic
potentials produced
at cell bodies and
dendrites.
▫ Create electrical
currents.
• Used clinically do
diagnose epilepsy
and brain death.

14. EEG Patterns
• Alpha:
▫ Recorded from parietal and occipital regions.
 Person is awake, relaxed, with eyes closed.
 10-12 cycles/sec.
• Beta:
▫ Strongest from frontal lobes near precentral gyrus.
 Produced by visual stimuli and mental activity.
 Evoked activity.
 13-25 cycles/sec.
• Theta:
▫ Emitted from temporal and occipital lobes.
 Common in newborn.
 Adult indicates severe emotional stress.
 5-8 cycles/sec.
• Delta:
▫ Emitted in a general pattern.
 Common during sleep and awake infant.
 In awake adult indicate brain damage.
 1-5 cycles/sec.

15. EEG Sleep Patterns
• 2 types of EEG patterns during sleep:
▫ REM (rapid eye movement):
 Dreams occur.
 Low-amplitude, high-frequency oscillations.
 Similar to wakefulness (beta waves).
▫ Non-Rem (resting):
 High-amplitude, low-frequency waves (delta
waves).
 Superimposed on these are sleep spindles:
 Waxing and waning bursts of 7-14 cycles/sec.
 Last for 1-3 sec.

16. Basal Nuclei (basal ganglia)
• Masses of gray matter
composed of neuronal
cell bodies located deep
within white matter.
• Contain:
▫ Corpus striatum:
 Caudate nucleus.
 Lentiform nucleus:
 Putman and globus pallidus.
• Functions in the control
of voluntary movements.

17. Cerebral Lateralization
• Cerebral dominance:
▫ Specialization of one
hemisphere.
• Left hemisphere:
▫ More adept in language
and analytical abilities.
▫ Damage:
 Severe speech problems.
• Right hemisphere:
▫ Most adept at visuospatial
tasks.
▫ Damage:
 Difficulty finding way
around house.

18. Language
• Broca’s area:
▫ Involves articulation of speech.
▫ In damage, comprehension of speech in unimpaired.
• Wernicke’s area:
▫ Involves language comprehension.
▫ In damage, language comprehension is destroyed, but speech
is rapid without any meaning.
• Angular gyrus:
▫ Center of integration of auditory, visual, and somatesthetic
information.
▫ Damage produces aphasias.
• Arcuate fasciculus:
▫ To speak intelligibly, words originating in Wernicke’s area
must be sent to Broca’s area.
 Broca’s area sends fibers to the motor cortex which directly
controls the musculature of speech.

19. Emotion and Motivation
• Important in the neural basis
of emotional states are
hypothalamus and limbic
system.
• Limbic system:
▫ Group of forebrain nuclei and
fiber tracts that form a ring
around the brain stem.
 Center for basic emotional
drives.
• Closed circuit (Papez circuit):
▫ Fornix connects
hippocampus to
hypothalamus, which projects
to the thalamus which sends
fibers back to limbic system.

20. Emotion and Motivation (continued)
▫ Areas or the hypothalamus and limbic system are
involved in feelings and behaviors.
▫ Aggression:
 Amygdala and hypothalamus.
▫ Fear:
 Amygdala and hypothalamus.
▫ Feeding:
 Hypothalamus (feeding and satiety centers).
▫ Sexual drive and behavior:
 Hypothalamus and limbic system.
▫ Goal directed behavior (reward and punishment):
 Hypothalamus and frontal cortex.

21. Memory
• Short-term:
▫ Memory of recent events.
• Medial temporal lobe:
▫ Consolidates short term into long term
memory.
• Hippocampus is critical component of
memory.
• Acquisition of new information, facts and
events requires both the medial temporal lobe
and hippocampus.

22. Long-Term Memory
• Consolidation of short-term memory into long-term
memory.
▫ Requires activation of genes, leading to protein synthesis and
formation of new synaptic connections.
 Altered postsynaptic growth of dendritic spines in area of contact.
• Cerebral cortex stores factual information:
▫ Visual memories lateralized to left hemisphere.
▫ Visuospatial information lateralized to right hemisphere.
• Prefrontal lobes:
▫ Involved in performing exact mathematical calculations.
 Complex, problem-solving and planning activities.

23. Long-Term Potentiation
• Type of synaptic learning.
▫ Synapses that are 1st
stimulated at high frequency will
subsequently exhibit increased excitability.
• In hippocampus, glutamate is NT.
▫ Requires activation of the NMDA receptors for glutamate.
 Glutamate and glycine or D-serine binding and partial
depolarization are required for opening of channels for Ca2+
and
Na+
.
• May also involve presynaptic changes:
▫ Binding of glutamate to NMDA receptors and simultaneous
depolarization, open receptor channels for Ca2+
.
 Ca2+
causes long-term potentiation in postsynaptic neuron, release
of NO from postsynaptic neuron.
 NO acts as a retrograde messenger, causing release of NT.

24. Neuronal Stem Cells in Learning and
Memory
• Neural stem cells:
▫ Cells that both renew themselves through mitosis
and produce differentiated neurons and neuroglia.
• Hippocampus has been shown to contain
stem cells (required for long-term memory).
• Neurogenesis:
▫ Production of new neurons.
• Indirect evidence that links neuogenesis in
hippocampus with learning and memory.

25. Thalamus and Epithalamus
• Thalamus:
▫ Composes 4/5 of the diencephalon.
▫ Forms most of the walls of the 3rd
ventricle.
▫ Acts as relay center through which all sensory information
(except olfactory) passes to the cerebrum.
 Lateral geniculate nuclei:
 Relay visual information.
 Medial geniculate nuclei:
 Relay auditory information.
 Intralaminar nuclei:
 Activated by many sensory modalities.
 Projects to many areas.
▫ Promotes alertness and arousal from sleep.
• Epithalamus contains:
▫ Choroid plexus where CSF is formed.
▫ Pineal gland which secretes melatonin.

26. Hypothalamus
• Contains neural centers for hunger, thirst, and
body temperature.
• Contributes to the regulation of sleep,
wakefulness, emotions, sexual arousal, anger,
fear, pain, and pleasure.
• Stimulates hormonal release from anterior
pituitary.
• Produces ADH and oxytocin.
• Coordinates sympathetic and parasympathetic
reflexes.

27. Pituitary Gland
• Posterior pituitary:
▫ Stores and releases ADH (vasopressin) and oxytocin.
• Hypothalamus produces releasing and
inhibiting hormones that are transported to
anterior pituitary.
▫ Regulate secretions of anterior hormones.
• Anterior pituitary:
▫ Regulates secretion of hormones of other endocrine
glands.

28. Midbrain
• Contains:
▫ Corpora quadrigemina:
 Superior colliculi:
 Involved in visual reflexes.
 Inferior colliculi:
 Relay centers for auditory information.
▫ Cerebral peduncles:
 Composed of ascending and descending fiber tracts.
▫ Substantia nigra:
 Required for motor coordination.
▫ Red nucleus:
 Maintains connections with cerebrum and cerebellum.
 Involved in motor coordination.

29. Hindbrain
• Metencephalon:
▫ Pons:
 Surface fibers connect to cerebellum,
and deeper fibers are part of motor and
sensory tracts.
 Contains several nuclei associated with
cranial nerves V, VI, VII.
 Contains the apneustic and
pneumotaxic respiratory centerss.
▫ Cerebellum:
 Receives input from proprioceptors.
 Participates in coordination of
movement.
 Necessary for motor learning,
coordinating different joints during
movement, and limb movements.

30. Hindbrain (continued)
• Myelencephalon (medulla oblongata):
▫ All descending and ascending fiber tracts between
spinal cord and brain must pass through the
medulla.
 Nuclei contained within the medulla include VIII, IX, X,
XI, XII.
 Pyramids:
 Fiber tracts cross to contralateral side.
▫ Vasomotor center:
 Controls autonomic innervation of blood vessels.
▫ Cardiac control center:
 Regulates autonomic nerve control of heart.
▫ Regulates respiration with the pons.

31. Reticular Formation
• Reticular Formation:
▫ Complex network of nuclei and nerve fibers within
medulla, pons, midbrain, thalamus and
hypothalamus.
▫ Functions as the reticular activating system (RAS).
 Non specific arousal of cerebral cortex to incoming sensory
information.

32. Ascending Spinal Tracts
• Convey sensory
information from
cutaneous
receptors,
proprioceptors and
visceral receptors to
cerebral cortex.
• Sensory fiber tract
decussation may
occur in medulla or
spinal cord.

33. Descending Spinal Tracts
• Pyramidal
(corticospinal) tracts
descend directly
without synaptic
interruption from
cerebral cortex to spinal
cord.
▫ Function in control of fine
movements that require
dexterity.
• Reticulospinal tracts
(extrapyramidal):
▫ Influence movement
indirectly.
 Gross motor movement.

34. Cranial and Spinal Nerves
• Cranial nerves:
▫ 2 pairs arise from neuron cell bodies in forebrain.
▫ 10 pairs arise from the midbrain and hindbrain.
 Roman numerals refer to the order in which the nerves are
positioned from front of the brain to the back.
▫ Most are mixed nerves containing both sensory and motor
fibers.
• Spinal nerves:
▫ 31 pairs grouped into 8 cervical, 12 thoracic, 5 lumbar, 5
sacral, and l coccygeal.
▫ Mixed nerve that separates near the attachment of the nerve
to spinal cord.
 Produces 2 roots to each nerve.
 Dorsal root composed of sensory fibers.
 Ventral root composed of motor fibers.

35. Reflex Arc
• Unconscious motor
response to a sensory
stimulus.
• Stimulation of sensory
receptors evokes APs
that are conducted into
spinal cord.
▫ Synapses with
association neuron,
which synapses with
somatic motor neuron.
• Conducts impulses to
muscle and stimulates a
reflex contraction.
▫ Brain is not directly
involved.