Nervous System
Dr. Asif Hasan
Nervous System
• Fundamental Structures and Processes of the cells within brain
• Human Nervous System and its Functions
• Division of Nervous System
• Brain and its Classification
Nervous System
• A network of billions of nerve cells linked
together in a highly organized fashion to form the rapid control center of the body.
• It is the master controlling and communicating system of the body.
• Functions include:
– Integrating center for homeostasis, movement, and almost all other body functions.
– Higher order cognition such as language, thinking etc.
Basic Functions of the Nervous System
• Sensory input
– Monitors changes/events occurring in and outside the body. Such changes are known as stimuli and the cells that monitor them are receptors.
• Integration
– The parallel processing and interpretation of
sensory information to determine the appropriate response
• Motor output .
– The activation of muscles or glands (typically via the release of neurotransmitters (NTs))
Nervous Tissue
• Basic building block of nervous system
• 2 cell types – Neurons
• Functional, signal conducting cells
– Neuroglia
• Supporting cells
Neuroglia
• Outnumber neurons by about
10 to 1 (the guy on the right had an inordinate amount of them). 6 types of supporting cells
• 4 are found in the CNS – Astrocytes
• Star-shaped, abundant, and versatile
• Guide the migration of developing neurons
• Act as K+ and NT buffers
• Involved in the formation of the blood brain barrier
• Function in nutrient transfer
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• Microglia
– Specialized immune cells that act as the macrophages of the CNS
– Why is it important for the CNS to have its own army of immune cells?
• Ependymal Cells
– Low columnar epithelial-esque cells that line the ventricles of the brain and the central canal of the spinal cord
– Some are ciliated which facilitates the movement of cerebrospinal fluid
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• Oligodendrocytes
– Produce the myelin sheath which provides the electrical insulation for certain neurons in the CNS
Neuroglia
• 2 types of glia in the PNS
• Satellite cells
– Surround clusters of neuronal cell bodies in the PNS – Unknown function
• Schwann cell
– Form myelin sheaths around the larger nerve fibers in the PNS.
– Vital to neuronal regeneration
Neuron
• The functional and structural unit of the nervous system
• Specialized to conduct information from one part of the body to another
• There are many, many different types of neurons but most have certain structural and functional characteristics in common
– Cell body – Dendrites – Axon
Neuron
Communication
• Resting Potential
– Nothing is happening. The gates are closed and the positive ions are on the outside with the negative ions on the inside of the cell.
• Action Potential
– a neural impulse; a brief electrical charge that travels down an axon
– generated by the movement of positively charged
atoms in and out of channels in the axon’s membrane
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Cell body end of axon
Direction of neural impulse: toward axon terminals
Stimulation causes the gates to open and the positive ions enter the cell. An electrical spark is produced by the
process call depolarization. The positive ions are then pumped out.
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• Refractory Period
– The time it takes for the positive ions to be pumped out.
• Threshold
– the level of stimulation required to trigger a neural impulse
– Neurons fire or they do not fire a principle called the all or nothing principle
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• Synapse
– junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron – tiny gap at this junction is called the synaptic gap or
cleft
• Neurotransmitters
– chemical messengers that traverse the synaptic gaps between neurons
– when released by the sending neuron, neuro-
transmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby
influencing whether it will generate a neural impulse
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Organization of the Nervous System
• Central Nervous System
– The brain and the spinal cord
• Peripheral Nervous System
– The nervous system outside of the brain and spinal cord
Nervous System .
Central (brain and spinal cord) Nervous
system
Autonomic (controls self-regulated action of internal organs and glands)
Skeletal (controls voluntary movements of
skeletal muscles)
Sympathetic (arousing)
Parasympathetic (calming) Peripheral
Peripheral Nervous System
• Responsible for communication between the CNS and the rest of the body.
• Can be divided into:
– Sensory Division
• Afferent division
– Conducts impulses from receptors to the CNS
– Informs the CNS of the state of the body interior and exterior
– Motor Division
• Efferent division
– Conducts impulses from CNS to effectors (muscles/glands) – Motor nerve fibers
Motor Efferent Division
• Can be divided further:
– Somatic nervous system
• VOLUNTARY (generally)
• Somatic nerve fibers that conduct impulses from the CNS to skeletal muscles
– Autonomic nervous system
• INVOLUNTARY (generally)
• Conducts impulses from the CNS to smooth muscle, cardiac muscle, and glands
Autonomic Nervous System
• Can be divided into:
– Sympathetic Nervous System
• “Fight or Flight”
– Parasympathetic Nervous System
• “Rest and Digest”
Central Nervous System
• Brain and Spinal Cord
• Brain
– Left & Right sides are separate
– Corpus Callosum : major pathway between hemispheres
– Some functions are ‘lateralize
• language on left
• math, music on right
Brain
• Hind Brain
• Mid Brain
• Forebrain
Hindbrain
• Most primitive brain structure; responsible for basic survival functions
• Consists of the metencephalon and
myelencephalon
Hindbrain – Myelencephalon
• Hindbrain – Myelencephalon
– Caudal-most region of the brain – Contains the medulla oblongata
• Cardiovascular & respiratory functions, muscle tone, arousal
Hindbrain - Metencephalon
• Cerebellum (dorsal brainstem)
– Attached to the pons by the cerebellar peduncles – Coordinates movement
• Pons (ventral brainstem)
– Projects information from cortex to cerebellum – Role in sleep and arousal
Midbrain (Mesencephalon)
• Structurally and evolutionarily between the diencepalon and the hindbrain
• Only two major structures
– Tectum
– Tegmentum
Forebrain - Telencephalon
• Cerebral cortex – surrounds the cerebral hemispheres
– Gyri (singular: Gyrus) – Sulci (Sulcus)
– Fissures
• Cortex consists of densely packed glia and neurons
• Four lobes of the brain
– Frontal – Parietal – Temporal – Occipita
Telencephalon – Limbic system
• Limbic system
– Located within the telencephalon – Includes:
• Limbic cortex
• Amygdala
• Hippocampus
• Mammillary bodies of the hypothalamus
• Major role in emotion, learning and memory
Telencephalon – Basal ganglia
• Motivation and generation of movement
• Include:
– Caudate nucleus – Putamen
– Globus pallidus
Forebrain - Diencephalon
• Diencephalon
– Located between the telencephalon and the midbrain – Includes:
• Thalamus: relay information to the proper cortical regions
• Hypothalamus
– Controls the autonomic nervous system and the endocrine system
– Two major structures control endocrine function
» Anterior pituitary gland
» Posterior pituitary gland
Lobes
• Each hemisphere is divided into 4 lobes
Frontal
Parietal
Occipital Temporal
Occipital Lobe
• Input from Optic nerve
• Contains primary visual cortex
– most is on surface inside central fissure
• Outputs to parietal and temporal lobes
Temporal Lobe
• Contains primary auditory cortex
• Inputs are auditory, visual patterns
– speech recognition – face recognition – word recognition – memory formation
• Outputs to limbic System, basal Ganglia, and
brainstem
Parietal Lobe
• Inputs from multiple senses
• contains primary somatosensory cortex
• borders visual & auditory cortex
• Outputs to Frontal lobe
– hand-eye coordination – eye movements
– attention
Frontal Lobe
• Contains primary motor cortex
• No direct sensory input
• Important planning and sequencing areas
• Broca’s area for speech
• Prefrontal area for working memory
Lateralization
• Principle is Contralateral Organization
• Sensory data crosses over in pathways leading to the cortex
• Visual Crossover
– left visual field to right hemisphere – right field to left
• Other senses similar
Contralateral Motor Control
• Movements controlled by motor area
• Right hemisphere controls left side of body
• Left hemisphere controls right side
• Motor nerves cross sides in spinal cord
Somatosensory Cortex Motor Cortex
