Development& Functions Of Various Parts Of Cns

CNS

Consists of: Brain. Spinal cord.

Receives input from sensory neurons.

Directs activity of motor neurons.

Association neurons maintain homeostasis in the internal environment.

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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.


Embryonic Development (continued)


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.


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.


Cerebrum (continued)


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.


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.



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.


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.


Electroencephalogram (EEG) Measures

synaptic potentials produced at cell bodies and dendrites. Create electrical

currents. Used clinically do

diagnose epilepsy and brain death.


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.


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.www.freelivedoctor.com

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.


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.


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.


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.


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. www.freelivedoctor.com

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.


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.www.freelivedoctor.com

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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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Development& Functions Of Various Parts Of Cns