The Central Nervous System

Ch. 5

Objectives• Understand how the nervous system is organized

• Know the various cell types that are found in nervous tissue and their function

• Identify and understand the function of the various parts of the central nervous system

• Define and know what memory is

• Understand how a reflex arc works

Organization and Cells

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Neurons and Glial Cells• Three functional classes of

neurons– Afferent

• sensory

– Interneurons

– Efferent• motor

• Four types of glial cells– Astrocytes

• Spatial orientation and support• Synapse formation

– Thrombospondin• Repair and barrier formation• Nourish• Degradation of neurotransmitters• K+ regulation

– Oligodendrocytes• myelination

– Microglia• Immune protection• Nerve growth factor

– Ependymal cells• Internal lining of CNS• Production of CSF• Neural stem cells

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Protection and Nourishment• Skull

• Meninges– Dura mater– Arachnoid mater– Pia mater

• Cerebral Spinal fluid– Secreted by choroid plexus– Rich in Na+

• Blood-brain barrier– Anatomical and physiological

barrier

•Oxygen– neuroglobin

•Glucose

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Overview of CNS• Brain and spinal cord

• Brain organization– Forebrain

• Cerebrum– Cerebral cortex– Basal nuclei

• Diencephalon– Thalamus – Hypothalamus

– Cerebellum– Brain stem

• Midebrain• Pons • medulla

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Cerebrum• Composed of two hemispheres divided into four lobes

– Frontal• Voluntary motor skills, speaking, though

– Parietal• Somatosensory processing

– Temporal• Auditory processing

– Occipital• Visual processing

– Hemispherical specialization• Left – logical and analytic• Right – creative and artisitic

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Motor and Sensory Humunculi

• Use-dependent competition– Modifications

based on use

• Plasticity– Ability to be

functionally remodeled

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Electroencephalogram (EEG)

• Record of postsynaptic activity in cortical neurons– EPSPs or IPSPs

• Uses– Brain dysfunction– Brain death– Sleep stages

Basal Nuclei and Diencephalon• Basal Nuclei

– Regulatory inhibition of motor control

– Divided into four regions of grey matter• Caudate nucleus• Putamen• Globus pallidus• Claustrum

– Associated with Parkinson’s disease

• Diencephalon– Thalamus

• Relay station for sensory input

• Also involved in motor control

– Hypothalamus• Integrates and regulates

important homeostatic functions– Body temp– Thirst – Adenohypophysis control

The Limbic System

• Associated with learning and emotions

• Controls basic behavioral patterns– Reward and punishment centers– Motivation – ability to direct behavior to toward

specific goals

• Norepinephrine, dopamine, and seratonine

Learning and Memory

• The acquisition of knowledge or skills as a consequence of experience or instruction

• The storage of acuired knowledge for later recall

• Memory traces– Neural changes

responsible for storage of knowledge

Short-term Memory• Involve temporary modifications in the function of

preexisting synapses

• Two types– Habituation

• Decreased responsiveness to a repetitive indifferent stimulus• Ca2+ channels do not readily open

– Sensitization• Increased responsiveness to mild stimuli following a strong stimulus • Ca2+ channel open and stay open longer

– K+ influx prevented

• Long term Potentiation– Modifications due to increased use, connection gets stronger the more it is

used– Transition to long term memory

Long-Term Memory

• Involves formation of new, permanent synaptic connections

• Immediate early genes– Play a role in memory consolidation– Genes may encode for proteins that are necessary

for synapse formation, production of neurotransmitters, answer not clear yet

Memory Traces in the Brain• Hippocampus– Declarative memory

• The “what’ memories of specific people, places, objects, facts (semantic) and events (episodic)

• Cerebellum– Procedural memories

• “how to” memories involving repetitive motor skills

• Prefrontal cortex– Working memory

• Memory necessary to integrate information that is relevant now

Cerebellum

• Balance and coordination

• Three regions– Vestibulocerebellum

• Balance and controls eye movements– Spinocerebellum

• Enhances muscle tone and coordinates voluntary movements

– Cerebrocerebellum• Plans and initiates voluntary activity by providing input to

cortical motor areas– Procedural memory

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Brain Stem• Link between spinal cord and high brain

– Medulla, pons, midbrain

• 12 cranial nerves arise from brain stem

• Cardiac, respiratory, and digestive control centers

• Reticular formation (RAS)

• Regulates muscle reflexes involved with euilibrium and posture

• House the sleep center

Spinal Cord

• Slender tube that extends from the brain stem and goes through vertebral column

• Gives rise to 31 pairs of spinal nerves– Cervical, thoracic, lumbar, sacral, coccygeal

• Grey matter core, white matter on the periphery– White matter organized into tracts

• Begin and end in specific brain regions and transmit specific information

Spinal Tracts• Ascending tracts

– Carry sensory information up

• Descending tracts– Carry motor input down

• Horns of spinal cord– Dorsal

• Synapse with sensory neurons

– Ventral• Cell bodies of motor

neurons– Lateral

• Fibers supplying cardiac and smooth muscle, glands

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Reflexes• Response that occurs automatically without conscious

effort– Basic reflexes – Acquired reflexes

• Reflex arc– Sensory receptor– Afferent pathway– Integrating center– Efferent pathway– Effector

• Please know reflexes described