chapter 9- cns

THE CENTRAL NERVOUS SYSTEM

Chapter 9

Gray Matter vs. White Matter

• Gray Matter – Unmyelinated cell bodies, dendrites, axon

terminals

– Cell bodies form layers or clusters (nuclei)

• White Matter – Myelinated axons, very few cell bodies

– White due to myelin sheath

– Axons in bundles called tracts connect regions of the CNS

CNS: Bone and Connective Tissue

• Brain is encased in bony skull or cranium

• Spinal cord runs through vertebral column

• Meninges lies between bone and tissues

– Dura mater

– Arachnoid membrane

– Pia mater

– Meningeal layers of the brain cushion and protect delicate neural tissue

Cerebrospinal Fluid (CSF)

• Secreted by choroid plexus lining ventricles

• Flows to subarachnoid space

• Absorbed back into the blood by villi on arachnoid membrane

• Replenished 3 times per day

• Protects by – Cushioning and reducing the weight of the brain for

less pressure on blood vessels and nerves

– Regulate extracellular environment for the neurons, differs in ion conc. from blood plasma.

CNS: Cerebrospinal Fluid

Figure 9-5b-d

ANATOMY SUMMARY

CEREBROSPINAL FLUID CIRCULATION

Choroid plexus of third ventricle

Arachnoid villi

Pia mater

(b)

Sinus

Arachnoid membrane

Arachnoid membrane

Dura mater

Subarachnoid space

Central canal

Choroid plexus of fourth ventricle

Spinal cord

Cerebral cortex

Endothelial lining

Blood in venous sinus

Fluid movement

Arachnoid villus Dura mater (inner layer)

Subdural space

Arachnoid membrane

Subarachnoid space

Pia mater

Cerebrospinal fluid

Bone of skull

Dura mater

(d)

Blood Brain Barrier (BBB)

• Between interstitial fluid and blood

• Highly selective permeability of brain capillaries due to tight junctions and astrocytes

• Isolates the CNS from harmful substances

• Drugs

• Some areas of the brain lack the BBB

Special Metabolic Requirements

• Neurons require a constant supply of oxygen and glucose to make ATP for active transport of ions and NTs.

• Brains receives 15% of the blood

• Brain consumes about ½ of body’s glucose

• Diabetes and hypoglycemia

Spinal Cord

• Pathway between the brain and skin, joints, muscles. Locomotion.

• Cervical, thoracic, lumbar, sacral

• Dorsal root and dorsal horn

• Ventral root and ventral horn

• Ascending tracts

• Descending tracts


Brain

Brain Stem

• Transition between spinal cord and midbrain

• Cranial nerves II-XII originate along stem and carry sensory and motor information for the head and neck

• Nuclei involve basic processes like arousal, sleep, muscle tone, stretch reflex, coordination of breathing, bp regulation, pain modulation


Table 9-1

Medulla Oblongata

• White matter includes

– Ascending somatosensory tracts (info to brain)

– Descending corticospinal tracts (info from brain)

• 90% of corticospinal tracts cross midline in the medulla pyramids to control the opposite side of the body

• Gray matter includes

– Nuclei-involuntary functions of bp, breathing, swallowing, vomiting

Pons and Midbrain

• Pons

– Relays info from cerebellum to cerebrum

– Coordinates breathing

• Midbrain

– Mesencephalon

– Controls eye movement, relays auditory and visual reflex signals

Gray matter of the cerebrum

• Cerebral cortex- outer layer where neurons are arranged in vertical columns and horizontal layers

• Basal ganglia (nuclei)-movement

• Limbic system-primitive brain region

– Amygdala

– Cingulate gyrus-emotion and memory

– Hippocampus-learning and memory


Figure 9-11


Cell bodies in the cerebral cortex


Figure 9-13

White matter in the cerebrum

• Interior

• Bundles of fibers transfer information from one hemisphere to another through the corpus callosum (200 million axons


Cerebral cortex is organized into functional areas


Cerebral Dominance

Sensory information

• Primary somatic sensory cortex-parietal lobe

– Process information about touch, temp, pain, itch, body position

– Visual cortex-occipital lobe, vision

– Auditory cortex-temporal lobe, sound

– Olfactory cortex-temporal lobe, smell

– Gustatory cortex- deep near edge of frontal lobe, taste

Motor Output

• Skeletal muscle movement, controlled by the somatic motor division – Reflexes don’t require integration in cerebral cortex but can be

overridden by input form the cognitive system – Voluntary movements initiated by the cognitive system in the primary

motor cortex and motor association area in the frontal lobes.

• Neuroendocrine signals from neurons in hypothalamus and adrenal medulla

• Visceral response

– Brainstem-breathing and blood pressure – Hypothalamus-temp. regulation, eating, osmolality control, etc.


Cerebral cortex is organized into functional areas

Behavioral State System • Neurons found outside cerebral cortex in reticular formation in brain stem, hypothalamus,

limbic system.

• Neurons are called diffuse modulatory system and originates in the reticular formation and project to large areas of the brain.

• Regulates brain function by influencing attention, motivation, wakefulness, memory, motor control, mood, land metabolic homeostasis


Figure 9-19

Reticular Activating System

• Controls levels of consciousness and sleep-wake cycles (keeps the “conscious brain” awake)

• EEG (electroencephalogram)-measures electrical activity created by cortical neurons

– Awake alert (eyes open)= many neurons firing but uncoordinated resulting in rapid, irregular pattern with no dominant waves

-waves decrease frequency as arousal lessens

-waves increase amplitude as cortical neurons fire more synchronously

Four Stages of Sleep

• Stage 1- REM (rapid eye movement) sleep-waves are low amplitude, high frequency waves (like that of an awake person). Brain activity inhibits motor neurons to skeletal muscles except eye and breathing muscles. Homeostatic functions depressed leading to lower body temperature. Dreaming occurs

• Stage 4-slow-wave sleep (deep sleep) delta waves of high-amplitude, low-frequency, long duration (sleepers adjust body position without conscious command from brain)


Figure 9-20

Emotion and Motivation and Moods

• Limbic system (amygdala) is the center of emotion (fear and anxiety) in human brains.

• Motivation-internal signals that shape voluntary behaviors (eating, drinking, curiosity, sex)

• Moods are longer-lasting, relatively stable subjective feelings whose origin is actually a CNS function (abnormal NT release)

Learning and Memory

• Plasticity and long-term potentiation are fundamental to learning and memory

• Associative learning vs. nonassociative learning (habituation and sensitization)

• The hippocampus is involved in both. • Memory

– Short term – Working memory is linked to long-term memory – Long term memory (consolidation) involves new synapses or altered

effectiveness of synaptic transmission (long-term potentiation or depression) • Reflexive (implicit) memory- automatic, amygdala and cerebellum involved

(procedural memory) • Declarative (explicit) memory-requires conscious attention, temporal lobes,

knowledge about ourselves and the world around us


Figure 9-22

Language

• Input sensory info from hearing and vision and motor output for vocalization and writing

• In the left hemisphere of cerebrum • Spoken language integrated in Wernicke’s area (first) in the

temporal lobe and Broca’s area (next) in the frontal lobe • Output from Broca’s area to the motor cortex initiates a spoken or

written action – Receptive aphasia-damage to Wernicke’s area so can’t understand

spoken or visual information and speech is nonsense – Expressive aphasia-damage to Broca’s area understand spoken and

written language but can’t speak or write in normal syntax so that appropriate words are strung together in random order

– Mechanical aphasia-damage to motor cortex, can’t shape sounds that make up words and can’t coordinate muscles of arm and hand to write

chapter 9- cns

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