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The Nervous System
Functions of the Nervous System
Sensory input—gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is needed
Functions of the Nervous System
Motor output A response to integrated stimuli The response activates muscles or glands
Structural Classification of the Nervous System
Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerves outside the brain and spinal cord Spinal nerves Cranial nerves
Functional Classification of the Peripheral Nervous System
Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system
Organization of the Nervous System
Functional Classification of the Peripheral Nervous System
Motor (efferent) division (continued) Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary
Nervous Tissue: Support Cells
Support cells in the CNS are grouped together as “neuroglia” Function: to support, insulate, and protect neurons
Nervous Tissue: Support Cells
Astrocytes Abundant, star-shaped cells Brace neurons Form barrier between capillaries and neurons Control the chemical environment of the brain
Nervous Tissue: Support Cells
Microglia Spiderlike phagocytes
Dispose of debris
Nervous Tissue: Support Cells
Ependymal cells Line cavities of the brain and spinal cord Circulate cerebrospinal fluid
Nervous Tissue: Support Cells
Oligodendrocytes Wrap around nerve fibers in the central nervous system Produce myelin sheaths
Nervous Tissue: Support Cells
Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system
Nervous Tissue: Neurons
Neurons = nerve cells Cells specialized to transmit messages Major regions of neurons Cell body—nucleus and metabolic center of the cell Processes—fibers that extend from the cell body
Nervous Tissue: Neurons
Cell body Nissl substance Specialized rough endoplasmic reticulum Neurofibrils Intermediate cytoskeleton Maintains cell shape
Nervous Tissue: Neurons
Cell body Nucleus Large nucleolus Processes outside the cell body Dendrites—conduct impulses toward the cell body Axons—conduct impulses away from the cell body
Nervous Tissue: Neurons
Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap Synaptic cleft—gap between adjacent neurons Synapse—junction between nerves
Nervous Tissue: Neurons
Myelin sheath—whitish, fatty material covering axons Schwann cells—produce myelin sheaths in jelly roll–like fashion Nodes of Ranvier—gaps in myelin sheath along the axon
Neuron Cell Body Location
Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane The sodium-potassium pump, using ATP, restores the original configuration
Nerve Impulses
Transmission of a Signal at Synapses
Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite
The Reflex Arc
Reflex—rapid, predictable, and involuntary response to a stimulus Occurs over pathways called reflex arcs Reflex arc—direct route from a sensory neuron, to an interneuron, to an effector
Simple Reflex Arc
Types of Reflexes and Regulation
Somatic reflexes Activation of skeletal muscles Example : When you move your hand away from a hot stove
Types of Reflexes and Regulation
Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation
Types of Reflexes and Regulation
Patellar, or knee-jerk, reflex is an example of a two-neuron reflex arc
Central Nervous System (CNS)
CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles Four chambers within the brain Filled with cerebrospinal fluid
Central Nervous System (CNS)
Regions of the Brain
Cerebral hemispheres (cerebrum) Diencephalon Brain stem Cerebellum
Regions of the Brain: Cerebrum
Cerebral Hemispheres (Cerebrum) Paired (left and right) superior parts of the brain
Includes more than half of the brain mass The surface is made of ridges (gyri) and grooves (sulci)
Regions of the Brain: Cerebrum
Lobes of the cerebrum Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum Frontal lobe Parietal lobe Occipital lobe Temporal lobe
Regions of the Brain: Cerebrum
Specialized areas of the cerebrum Primary somatic sensory area Receives impulses from the body’s sensory receptors Located in parietal lobe Primary motor area Sends impulses to skeletal muscles Located in frontal lobe Broca’s area Involved in our ability to speak
Regions of the Brain: Cerebrum
Cerebral areas involved in special senses Gustatory area (taste) Visual area Auditory area Olfactory area
Regions of the Brain: Cerebrum
Interpretation areas of the cerebrum Speech/language region Language comprehension region General interpretation area
Regions of the Brain: Cerebrum
Layers of the cerebrum Gray matter—outer layer in the cerebral cortex composed mostly of neuron cell bodies White matter—fiber tracts deep to the gray matter Corpus callosum connects hemispheres Basal nuclei—islands of gray matter buried within the white matter
Regions of the Brain: Cerebrum
Regions of the Brain: Diencephalon
Sits on top of the brain stem Enclosed by the cerebral hemispheres Made of three parts Thalamus Hypothalamus
Merges into the spinal cord Includes important fiber tracts Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting
Regions of the Brain: Brain Stem
Reticular Formation Diffuse mass of gray matter along the brain stem Involved in motor control of visceral organs Reticular activating system (RAS) plays a role in awake/sleep cycles and consciousness
Regions of the Brain: Reticular Formation of the Brain Stem
Regions of the Brain: Cerebellum
Two hemispheres with convoluted surfaces Provides involuntary coordination of body movements
Protection of the Central Nervous System
Scalp and skin Skull and vertebral column Meninges Cerebrospinal fluid (CSF) Blood-brain barrier
Protection of the Central Nervous System
Meninges
Dura mater Double-layered external covering Periosteum—attached to inner surface of the skull Meningeal layer—outer covering of the brain Folds inward in several areas
Meninges
Arachnoid layer Middle layer Web-like Pia mater Internal layer Clings to the surface of the brain
Cerebrospinal Fluid (CSF)
Similar to blood plasma composition Formed by the choroid plexus Forms a watery cushion to protect the brain Circulated in arachnoid space, ventricles, and central canal of the spinal cord
Ventricles and Location of the Cerebrospinal Fluid
Hydrocephalus in a Newborn
Hydrocephalus CSF accumulates and exerts pressure on the brain if not allowed to drain
Blood-Brain Barrier
Includes the least permeable capillaries of the body Excludes many potentially harmful substances Useless as a barrier against some substances Fats and fat soluble molecules Respiratory gases Alcohol Nicotine Anesthesia
Traumatic Brain Injuries
Concussion Slight brain injury No permanent brain damage Contusion Nervous tissue destruction occurs Nervous tissue does not regenerate Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue
Cerebrovascular Accident (CVA)
Commonly called a stroke The result of a ruptured blood vessel supplying a region of the brain Brain tissue supplied with oxygen from that blood source dies Loss of some functions or death may result
Alzheimer’s Disease
Progressive degenerative brain disease Mostly seen in the elderly, but may begin in middle age Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons Victims experience memory loss, irritability, confusion, and ultimately, hallucinations and death
Spinal Cord
Extends from the foramen magnum of the skull to the first or second lumbar vertebra 31 pairs of spinal nerves arise from the spinal cord Cauda equina is a collection of spinal nerves at the inferior end
Spinal Cord Anatomy
Internal gray matter is mostly cell bodies Dorsal (posterior) horns Anterior (ventral) horns Gray matter surrounds the central canal
X Vagus nerves—sensory and motor fibers for pharynx, larynx, and viscera XI Accessory nerve—motor fibers to neck and upper back XII Hypoglossal nerve—motor fibers to tongue
PNS: Distribution of Cranial Nerves
PNS: Spinal Nerves
There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs Formed by the combination of the ventral and dorsal roots of the spinal cord Named for the region from which they arise
PNS: Spinal Nerves
PNS: Anatomy of Spinal Nerves
Spinal nerves divide soon after leaving the spinal cord Dorsal rami—serve the skin and muscles of the posterior trunk Ventral rami—form a complex of networks (plexus) for the anterior
PNS: The Spinal Nerves
PNS: Spinal Nerve Plexuses
PNS: Distribution of Major Peripheral Nerves of the Upper
and Lower Limbs
PNS: Autonomic Nervous System
Motor subdivision of the PNS Consists only of motor nerves Also known as the involuntary nervous system Regulates activities of cardiac and smooth muscles and glands Two subdivisions Sympathetic division Parasympathetic division
PNS: Differences Between Somatic and Autonomic Nervous
Systems
Nerves Somatic: one motor neuron Autonomic: preganglionic and postganglionic nerves Effector organs Somatic: skeletal muscle Autonomic: smooth muscle, cardiac muscle, and glands
PNS: Differences Between Somatic and Autonomic Nervous
Systems
Neurotransmitters Somatic: always use acetylcholine Autonomic: use acetylcholine, epinephrine, or norepinephrine
PNS: Comparison of Somatic and Autonomic Nervous
Systems
PNS: Anatomy of the Sympathetic Division
Originates from T 1 through L 2 Ganglia are at the sympathetic trunk (near the spinal cord) Short pre-ganglionic neuron and long post-ganglionic neuron transmit impulse from CNS to the effector Norepinephrine and epinephrine are neurotransmitters to the effector organs
PNS: Anatomy of the Autonomic Nervous System
PNS: Sympathetic Pathways
PNS: Anatomy of the Parasympathetic Division
Originates from the brain stem and S 1 through S 4 Terminal ganglia are at the effector organs Always uses acetylcholine as a neurotransmitter
PNS: Autonomic Functioning
Sympathetic—“fight or flight” Response to unusual stimulus Takes over to increase activities Remember as the “E” division Exercise, excitement, emergency, and embarrassment
PNS: Autonomic Functioning
Parasympathetic—“housekeeping” activites Conserves energy Maintains daily necessary body functions Remember as the “D” division digestion, defecation, and diuresis
Effects of the Sympathetic and Parasympathetic Divisions of
the ANS
Development Aspects of the Nervous System
The nervous system is formed during the first month of embryonic development Any maternal infection can have extremely harmful effects The hypothalamus is one of the last areas of the brain to develop
Development Aspects of the Nervous System
No more neurons are formed after birth, but growth and maturation continues for several years The brain reaches maximum weight as a young adult
