Two Organ Systems Control All the Other Organ Systems
 Nervous system characteristics
 Rapid response
 Brief duration
 Endocrine system characteristics
 Slower response
 Long duration
Two Anatomical Divisions
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 All the neural tissue outside CNS
 Afferent division (sensory input)
 Efferent division (motor output)
 Somatic nervous system
 Autonomic nervous system
Two Classes of Neural Cells
 Neurons
 For information transfer, processing, and storage
 Neuroglia
 Supporting framework for neurons
 Phagocytes
Three Functional Classes of Neurons
 Sensory neurons
 Deliver information to CNS
 Motor neurons
 Stimulate or inhibit peripheral tissues
 Interneurons (association neurons)
 Located between sensory and motor neurons
 Analyze inputs, coordinate outputs
Neuron Anatomy
 Cell body
 Nucleus
 Mitochondria, RER, other organelles
 Dendrites
 Several branches
 Signal reception (inward)
 Axon
 Signal propagation (outward)
Structural Classes of Neurons
 Unipolar
 Dendrite, axon continuous
 Afferent neurons
 Multipolar
 Many dendrites, one axon
 Most common class of neuron
 Bipolar
 One dendrite, one axon
 Very rare
Types of Neuroglia (glia)
In CNS
 Astrocytes
 Part of blood-brain barrier
 Oligodendrocytes
 Responsible for myelination
 Microglia
 Phagocytic defense cells
 Ependymal cells
 Lining of brain, spinal cord cavities
 Source of cerebrospinal fluid
Two Types of Neuroglia in the PNS
 Satellite cells
 Surround cell bodies
 Schwann cells
 Surround all peripheral axons
 Form myelin sheath on myelinated axons
Key Note
Neurons perform all of the communication, information processing, and control functions of the
nervous system.
Neuroglia outnumber neurons and have functions essential to preserving the physical and
biochemical structure of neural tissue and the survival of neurons.
Anatomic Organization of CNS Neurons
 Center—Collection of neurons with a shared function
 Nucleus—A center with a discrete anatomical boundary
 Neural cortex—Gray matter covering of brain portions
 White matter—Bundles of axons (tracts) that share origins, destinations, and functions
 Ganglia—Groupings of neuron cell bodies
 Nerve—Bundle of axons supported by connective tissue
 Spinal nerves
 To/from spinal cord
 Cranial nerves
 To/from brain
Pathways in the CNS
 Ascending pathways
Carry information from sensory receptors to processing centers in the brain
 Descending pathways
Carry commands from specialized CNS centers to skeletal muscles
Neuron Function: The Membrane Potential
 Resting potential
 Excess negative charge inside the neuron
 Created and maintained by Na-K ion pump
 Negative voltage (potential) inside
 -70 mV (0.07 Volts)
Changes in Membrane Potential
 Result from changes in ion movement
 Ions move in transmembrane channels
 Membrane channels can open or close
 If Na+ channels open  positive charges enter cell  membrane potential moves positive
(depolarization)
 If K+ channels open  positive charges leave cell  membrane potential moves negative
(hyperpolarization)
Key Note
A membrane potential exists across the cell membrane because (1) the cytosol and the
extracellular fluid differ in their ionic composition, and (2) the cell membrane is selectively
permeable to these ions. The membrane potential can quickly change, as the ionic permeability of
the cell membrane changes, in response to chemical or physical stimuli.
Generation of Action Potential
 Depolarization of membrane to threshold
 Rapid opening of voltage-gated Na+ channels
 Na+ entry causes rapid depolarization
 Voltage-gated K+ channels open
 K+ exit causes rapid repolarization
 Refractory period ends as membrane recovers the resting state
Propagation of an Action Potential
 Continuous propagation
 Involves entire membrane surface
 Proceeds in series of small steps (slower)
 Occurs in unmyelinated axons
 Saltatory propagation
 Involves patches of membrane exposed at nodes
 Proceeds in series of large steps (faster)
 Occurs in myelinated axons
Key Note
“Information” travels within the nervous system primarily in the form of propagated electrical
signals known as action potentials.
 The most important information (e.g., vision, balance, movement), is carried by myelinated
axons.
Structure of a Synapse
 Presynaptic components
 Axon terminal
 Synaptic knob
 Synaptic vesicles
 Synaptic cleft
 Postsynaptic components
 Neurotransmitter receptors
Synaptic Function and Neurotransmitters
 Cholinergic synapses
 Release neurotransmitter acetylcholine
 Enzyme in synaptic cleft (acetylcholinesterase) breaks it down
 Adrenergic synapses
 Release neurotransmitter norepinephrine
 Dopaminergic synapses
 Release neurotransmitter dopamine
Neural Communication
 Neuronal pools
Groups of interconnected neurons with specific functions
 Divergence
Spread of information from one neuron to several others
 Convergence
Several neurons send information to one other
Key Note
A synaptic terminal releases a neuro-transmitter that binds to the postsynaptic cell membrane.
The result is a brief, local change in the permeability of the postsynaptic cell.
Many drugs affect the nervous system by stimulating neurotransmitter receptors and thus produce
complex effects on perception, motor control, and emotions.
 Excitatory transmission: creates an action potential by making the membrane permeable to
sodium (ACH, norepinephrine) Caffeine is a stimulant
 Inhibitory transmission: prevents an action potential by making the membrane permeable to
potassium (endorphins, enkephalins, serotonin, epinephrin, GABA-) Alcohol, barbiturate are
depressant
CNS Protection
 Skull/vertebral column
 Cerebrospinal fluid
 Meninges
Meninges
Layers that surround and protect the brain and spinal cord (CNS)
 Dura mater (“tough mother”)
 Tough, fibrous outer layer
 Epidural space above dura of spinal cord
 Arachnoid (“spidery”)
 Subarchnoid space
 Cerebrospinal fluid
 Pia mater (“delicate mother”)
 Thin inner layer
Spinal Cord
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Relays information to/from brain
Processes some information on its own
Divided into 31 segments
Each segment has a pair of:
 Dorsal root ganglia
 Dorsal roots
 Ventral roots
 Gray matter appears as horns
 White matter organized into columns
Foramen magnum: cavity at base of skull for spinal cord
Conus medullaris: end of spinal cord, second lumbar vertebra
Cauda equina: collection of nerves starting at the conus medullaris.
Filum terminale: extension of pia mater
Brain Regions
1- Forebrain
 Cerebrum
 Diencephalon
2- Midbrain
 Midbrain
3- Hindbrain
 Pons
 Medulla oblongata
 Cerebellum
 4- brain stem
 Midbrain
 Pons
 Medulla oblongata
Convolution: result of rapid growth
Gyri: upwards projection of convolution
Sulci: downward shallow groove. A sulcus separates lobes.
Fissure: deep groove
Corpus callosum: brodge connecting both cerebral hemispheres
Four functional regions called lobes: frontal, temporal, parietal, occipital
Ventricles
 Ventricles are cavities in the brain containing CSF. All four ventricles are continuous with the
subarachnoid space.
 Lateral ventricles: one in each cerebral hemisphere
 Foramen of Munroe
 Third ventricle in center of diencephalon
 Cerebral aqueduct
 Fourth ventricle between cerebellum and medulla oblongata
 Central canal
CSF Circulation
 CSF produced by choroid plexus: capillaries in ventricles that filter blood
 CSF is similar to blood plasma but doesn’t contain cells, bacteria or proteins
 CSF circulation:
 Lateral ventricle
 Interventricular foramen
 Third ventricle
 Cerebral aqueduct
 Fourth ventricle
 Central canal
 Subarachnoid space
 Arachnoid villus
 Superior sagittal sinus (vein)
 To blood stream
Function of Cerebrum
 Conscious thought
 Intellectual activity
 Memory
 Origin of complex patterns of movement
Functions of the Cerebral Cortex
 Hemispheres serve opposite body sides
 Primary motor cortex
 Directs voluntary movement
 Primary sensory cortex
 Receives somatic sensation (touch, pain, pressure, temperature)
 Association areas
 Interpret sensation
 Coordinate movement
Hemispheric Lateralization
 Categorical hemisphere (usually left)
 General interpretative and speech centers
 Language-based skills
 Representational Hemisphere (usually right)
 Spatial relationships
 Logical analysis
The Central Nervous System
Brain Waves
(Electroencephalogram)
The Basal Nuclei
 Lie deep within central white matter of the brain
 Responsible for muscle tone
 Coordinate learned movements
 Coordinate rhythmic movements (e.g., walking)
Functions of the Limbic System
 Primitive brain structure on top of the brain stem
 Includes: amygdala, hippocampus, limbic cortex and septal area
 Involved in emotions and motivation related to survival such as fear, anger, and emotions
related to sexual behavior
 Some structures of the limbic system related to memory such as the hippocampus and
amygdala
 Control reflexes associated with eating
 Store and retrieve long-term memories
The Diencephalon
 Switching and relay center
 Integration of conscious and unconscious motor and sensory pathways
 Components include:
 Epithalamus
 Choroid plexus
 Pineal body
 Thalamus
 Hypothalamus
The Diencephalon: Functions of the Thalamus
 Relay and filter all ascending (sensory) information
 Relay a small proportion to cerebral cortex (conscious perception)
 Relay most to basal nuclei and brain stem centers
 Coordinate voluntary and involuntary motor behavior
 Early conscious recognition of very primitive sensations; related to survival
Functions of the Hypothalamus
 Coordinate nervous and endocrine systems
 Secrete hormones
 Coordinate voluntary and autonomic functions: center of autonomic nervous system
 Part of the limbic system
 Regulate body temperature: body thermostat
Anatomy and Function of the Brain Stem
 Midbrain
 Myelinated fibers
 Cerebral peduncles: connection for motor pathway between cerebellum and cerebrum
 Corpora quadrigemina: reflex center for rapid eye mvt, head and trunk movement
 Process visual, auditory information
 Pons
 Links to cerebellum
 Involved in control of movement
 Breathing rhythm, relay of sensory impulsses
 Medulla oblongata
 Relay sensory information
 Regulate autonomic function
 Cardiac center, vasomotor and respiratory center
Anatomy and Function of the Cerebellum
 Oversees postural muscles
 Stores patterns of movement
 Fine tunes most movements
 Links to brain stem, cerebrum, spinal cord
 Communicates over cerebellar peduncles
Key Note
The brain, a large mass of neural tissue, contains internal passageways and chambers filled with
CSF.
The six major regions of the brain have specific functions.
As you ascend from the medulla oblongata to the cerebrum, those functions become more
complex and variable.
Conscious thought and intelligence are provided by the cerebral cortex.
PERIPHERAL NERVOUS SYTEM
PNS Basics
 Links the CNS with the body
 Carries all sensory information and motor commands
 Axons bundled in nerves
 Cell bodies grouped into ganglia
 Includes cranial and spinal nerves
CRANIAL NERVES
 12 Pairs
 Connect to brain not the cord
 Olfactory (CN I)
 Sense of smell
 Optic (CN II)
 Sense of vision
 Oculomotor (CN III)
 Eye movement
 Trochlear (CN IV)
 Eye movement
 Trigeminal (CN V)
 Eye, jaws sensation/movement
 Abducens (CN VI)
 Eye movement
 Facial (CN VII)
 Face, scalp, tongue sensation/movement
 Vestibulocochlear (CN VIII)
 Hearing, balance
 Glossopharyngeal (CN IX)
 Taste, swallowing
 Vagus (CN X)
 Autonomic control of viscera
 Accessory (CN XI)
 Swallowing, pectoral girdle movement
 Hypoglossal (CN XII)
 Tongue movement
Key Note
The 12 pairs of cranial nerves are responsible for the special senses of smell, sight, and
hearing/balance, and control movement of the eye, jaw, face, tongue, and muscles of the neck,
back, and shoulders.
They also provide sensation from the face, neck, and upper chest and autonomic innervation to
thoracic and abdominopelvic organs.
The Spinal Nerves
 31 Pairs
 8 Cervical
 12 Thoracic
 5 Lumbar
 5 Sacral
 1 coccygeal
 Dermatome—Region of the body surface monitored by a pair of spinal nerves
Nerve Plexus
A complex network of nerves
 Four Large Plexuses
 Cervical plexus
 Brachial plexus
 Lumbar plexus
 Sacral plexus
Reflex
An automatic involuntary motor response to a specific stimulus
 The 5 steps in a reflex arc
 Arrival of stimulus and activation of receptor
 Activation of sensory neuron
 CNS processing of information
 Activation of motor neuron
 Response by effector (muscle or gland)
Examples of Reflexes
 Monosynaptic reflex—Simplest reflex arc; sensory neuron synapses directly on motor
neuron
 Stretch reflex—Monosynaptic reflex to regulate muscle length and tension (example:
patellar reflex)
 Muscle spindle—Sensory receptor in a muscle that stimulates the stretch reflex
Polysynaptic reflex
A reflex arc with at least one interneuron between the sensory afferent and motor efferent
 Has a longer delay than a monosynaptic reflex (more synapses)
 Can produce more complex response
 Example: flexor reflex, a withdrawal reflex
 Brain can modify spinal reflexesA
Key Note
Reflexes are rapid, automatic responses to stimuli that “buy time” for the planning and execution
of more complex responses that are often consciously directed.
PNS FUNCTIONAL DIVISIONS
I- SOMATIC SYSTEM
 Conscious effort
 Divided into sensory and motor pathway
 sensory pathway: One sensory neuron between receptor and CNS
 Motor pathway: only one motor neuron
 One type of neurotransmitter: Ach, excitatory transmission
II- autonomic system
 No conscious effort
 Sensory pathway: simple, impulses go directly to hypothalamus, brain stem, or spinal cord, one
sensory neuron
 Motor pathway: more complex; two different antagonistic routes: sympathetic and
parasympathetic
 1- preganglionic neuron from CNS, myelinated
 Leaves with cranial or spinal nerve
 Parasympathetic: originates from either brain or sacral area
 Sympathetic : originates from T1 to L2 area
 Separates from above and goes to
 2- ganglion
 A- parasympathetic, ganglion is near/on visceral organ
 B- sympathetic, ganglia form a chain parallel to spinal cord
 3- postganglionic neuron: unmyelinated
 4- visceral organ
The Autonomic Nervous System
The two divisions of the ANS operate largely without our awareness.
Fight or flight
The sympathetic division increases alertness, metabolic rate, and muscular abilities,
neurotransmitter ACh preg, noradrenaline post ganglionic.
The parasympathetic division reduces metabolic rate and promotes visceral activities such as
digestion, neurotransmitter ACH for both pre and post ganglionic.
Relationship between the Two Divisions
 Many organs receive dual innervation
 In general, the two divisions produce opposite effects on the their target organs
Aging and the Nervous System
Age-Related Changes
 Reduction in brain size and weight
 Loss of neurons
 Decreased brain blood flow
 Changes in synaptic organization of the brain
 Intracellular and extracellular changes in CNS neurons