FUNCTION OF THE NERVOUS SYSTEM
 Directs internal processes
 Link to the external environment

TWO DIVISIONS OF THE NERVOUS SYSTEM
 CENTRAL NERVOUS
SYSTEM (CNS)
 Composed of brain and spinal cord
 Controls entire organism
 Integrates incoming info and responses
 Dependent upon the
PNS
 PERIPHERAL NERVOUS
SYSTEM (PNS)
 Link between CNS, body and environment
 Spinal and cranial nerves
 Composed of sensory and motor divisions
 Sensory:
 Somatic afferents
 Visceral afferents
 Motor:
 somatic nervous system
 autonomic nervous system

TWO DIVISIONS OF THE NERVOUS SYSTEM

DIVISIONS OF THE NERVOUS SYSTEM

DIVISIONS OF THE PNS
 SOMATIC NERVOUS SYSTEM (Voluntary)

Conducts impulses from the CNS to skeletal muscles
 AUTONOMIC NERVOUS SYSTEM
 Innervates smooth muscle (internal organs), glands and cardiac muscle
 Maintains homeostasis

DIVISIONS OF THE AUTONOMIC N.S.
AUTONOMIC NERVOUS
SYSTEM
 Sympathetic N.S.
 “ Flight or fright system”
 Inhibits digestion
 Dilates pupils
 Accelerates heart and respiration rate
 Parasympathetic N.S.
 Brings functions back to normal
 Contracts pupils
 Promotes digestion
 Returns heart and respiration rate to normal

NERVOUS SYSTEM CELL TYPES
 NEURONS
 Excitable
 Conduct nerve impulses
 Amitotic

NERVOUS SYSTEM CELL TYPES

NEUROGLIA (Glial cells)
 Supporting cells
 Surround neurons
 Nonconducting
 6 types
 2 in PNS
 4 in CNS
Astrocyte
Oligodendrocyte
Ependymal Cells Microglia Schwann Cells

SUPPORTING CELLS OF THE CNS
 1) Astrocytes
 In CNS only
 Anchor neurons to capillaries
 Pick up excess K +
 Recapture released neurotransmitters capillary

SUPPORTING CELLS OF THE CNS
 2) Oligodendrocytes
 CNS only
 Wrap extensions around neuron fibers (axons)
 Form myelin sheath axon

SUPPORTING CELLS OF THE CNS
 3) Ependymal Cells
 CNS only
 Line the cavities of the brain and spinal cord
 Ciliated
 Circulate the cerebrospinal fluid
(CSF)

SUPPORTING CELLS OF THE CNS
 4) Microglia
 CNS only
 Migrate toward injured neurons
 Phagocytic cells
 Devour microorganisms or debris from damaged neurons neuron

SUPPORTING CELLS OF THE PNS
 1) Schwann Cells
 PNS only
 Wrap around axons of neurons in the PNS
 Form myelin sheath
 Needed for axon regeneration myelin sheath axon

SUPPORTING CELLS OF THE PNS
 2) Satellite Cells
 PNS only
 Surround neuron cell bodies
 Help control the chemical environment neuron cell body

NEURON STRUCTURE
 Cell Body (soma or perikaryon )
 Contains typical cell organelles (no centrioles)
 Abundant clusters of rER called nissl bodies
 Nerve Processes (Neurites)
 Dendrites
 Short, branched extensions
 Receive input (receptive)
 Axon (nerve fiber)
 Conducting extension

NEURON STRUCTURE
 Axon (Nerve Fiber)
 Abundant organelles
 No nissl bodies
 Axon hillock
 Enlarged part of cell body
 Axoplasm
 Cytoplasm
 Axolemma
 Plasma membrane

NEURON STRUCTURE
 Axon terminal = synaptic knobs or terminal boutons
 Bulb-like ends of the telodendria
 Telodendria (terminal branches)
 Profuse branches at the end of the axon
 Axon collaterals
 Large branches of the axon

NEURON STRUCTURE
 Myelin sheath
 Node of Ranvier
 Neurilemma
 Schwann cell

NEURON STRUCTURE
Presynaptic neuron
Synapse
Postsynaptic neuron

CLASSIFICATION OF NEURONS
 Neurons can be classified by structure:
 Multipolar
 Most common in CNS and
PNS
 Single axon, numerous dendrites (motor neurons and interneurons of CNS)
 Bipolar
 One dendrite, one axon
(sensory neurons found in the retina, olfactory receptors)
 Unipolar
 Single fiber functions as both dendrite and axon (sensory neurons , dorsal root ganglia)

CLASSIFICATION OF NEURONS
 Neurons can be classified by function:
 Afferent (sensory)
 Carry info from receptors towards CNS
 Efferent (motor)
 Carry info from CNS to muscles or glands
 Association or Interneurons
 Link sensory and motor neurons
 Make up 99% of neurons in body

OTHER NERVOUS SYSTEM STRUCTURES
 Ganglion
 Clusters of neuron cell bodies in the PNS
 Nuclei
 Clusters of neuron cell bodies in the CNS (gray matter)
 Tract
 Bundles of nerve fibers together in the CNS
 Nerve
 Bundles of nerve fibers (axons) traveling together in the PNS

NERVE STRUCTURE endoneurium
 Epineurium
 Connective tissue surrounding the entire nerve
 Perineurium perineurium
 C.T. surrounding a bundle of axons
(fascicle)
 Endoneurium epineurium
 C.T. surrounding each individual axon

NEURON FUNCTION: The Synapse
 Synapse
 Junction between one neuron and another
 Most are axodendritic or axosomatic
 Two types:
 Electrical
 Chemical

TYPES OF SYNAPSES
 Electrical Synapses
 Not common
 Protein channels connect pre-synaptic neuron directly to postsynaptic neuron
 Ions flow from one neuron to the next
 Rapid transmission
 In some brain areas, cardiac and smooth muscle
 Chemical Synapses
 Most are this type
 Neurotransmitter released from synaptic knob of pre-synaptic neuron
 Neurotransmitter binds to receptors on membrane of post-synaptic neuron
 Binding of the neurotransmitter to receptor  permeability change in postsynaptic neuron cell membrane

NEUROTRANSMITTERS
Action Potential
Ca 2+ ions axon axon terminal synaptic cleft
 Released at chemical synapses
 Chemicals produced in the cell body or synaptic knob of the neuron
 Stored in synaptic vesicles in the synaptic knob
 Nerve impulse causes release of neurotransmitter into synaptic cleft

NEUROTRANSMITTERS


THE RESTING MEMBRANE POTENTIAL
Na + k +
Na + k +
Na +
Na +
Na +
+
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
–
–
–
Na + k +
Na + k +
Na +
 Inside of cell membrane is more negative than outside
 Due to the presence of more positive ions (Na + ) outside the cell
 Difference between charge inside and outside cell membrane = RESTING
MEMBRANE POTENTIAL
(RMP)
 RMPs vary from -40 to -90mV in different neuron types

EXCITATORY NEUROTRANSMITTERS
 When bound to receptors on the postsynpatic neuron membrane:
 Causes the opening of positive ion channels
 Sodium ions enter rapidly
 RMP becomes more positive
 This positive change in the
RMP is called depolarization
 This brings the neuron closer to firing neurotransmitter sodium receptor ion channel potassium

k +
Na +
Na +
– +
– +
– +
Na +
Na + k +
Na +
Na +
Na +
Na +
Na + k + k +
Na +
DEPOLARIZATION
Na +
Na +
 A positive change in the
RMP
 Caused by influx of positive ions
 Causes the inside of the cell membrane to become less negative
 This sudden positive change in the membrane potential is called
DEPOLARIZATION
 Depolarization spreads to adjacent areas

INHIBITORY NEUROTRANSMITTERS
 When bound to receptors on the postsynaptic membrane:
 Make membrane more permeable to negative ions (usually Cl )
 As negative ions rush into neuron, the
RMP becomes more negative
 The negative change in the RMP is called hyperpolarization
 This brings the neuron farther away from firing

HYPERPOLARIZATION
Na +
Na +
Cl k +
Cl -
Cl k +
Na +
Na +
Cl -
+
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
–
–
–
Cl -
Na +
Cl -
Cl k +
Na + k +
Na +
 A negative change in
RMP
 Usually caused by influx of chloride ions
 Decreases the likelihood of the neuron firing

GRADED POTENTIALS
 Short changes in the RMP in small regions of the membrane
 Can be positive changes or negative changes (they can depolarize or hyperpolarize the membrane)
 Alone, not strong enough to cause a nerve impulse to fire
 Together, can trigger a nerve impulse (action potential) stimulus depolarized region depolarization wave

POSTSYNAPTIC POTENTIALS

 A local graded potential
 Binding of a neurotransmitter on the postsynaptic membrane results in a more positive RMP (depolarization occurs)
 The neuron is brought closer to firing

POSTSYNAPTIC POTENTIALS

 A local graded potential
 Binding of the neurotransmitter on the postsynaptic membrane results in a more negative RMP (hyperpolarization)
 Inhibits the neuron from firing an impulse

TYPES OF NEUROTRANSMITTERS

 Acetylcholine (Ach)
 Released from cholinergic neurons
 Norepinephrine (NE)
 Released by adrenergic neurons
 GABA
 Dopamine
 Serotonin

ACTION POTENTIALS


 Depolarization
 Propagation
 Repolarization

ACTION POTENTIALS
 If depolarization of the membrane reaches threshold (usually a positive change of 15 to 20 mV or more), an action potential is triggered
 The positive RMP change causes electrical gates in the axon hillock to open
 A sudden large influx of sodium ions causes a reversal in the membrane potential (becomes approx. 100mV more positive)
 Begins at the axon hillock and travels down the axon

TYPES OF ION CHANNELS
Chemically Gated
Voltage Gated

PROPAGATION
 Movement of the action potential down the membrane of the axon
 Caused by electrically gated sodium channels opening in response to the positive RMP change
Axon hillock

REPOLARIZATION
 Restoration of the RMP back to it’s negative state
 A repolarization wave follows directly behind the depolarization wave
 3 factors contribute to restoring the negative membrane potential:
 Sodium (Na + ) gates close (it no longer enters)
 Potassium (K + ) gates open, potassium rushes out
 Sodium/potassium pump kicks in

THE SODIUM/POTASSIUM PUMP
 An active process that requires cellular energy
 Actively pumps 3 sodium (Na +) ions out of the cell and 2 potassium
(K +) ions in
 Potassium freely leaks back out of the cell

ABSOLUTE REFRACTORY PERIOD



SUMMATION BY POSTSYNAPTIC NEURON
 A single EPSP cannot induce an action potential
 EPSP’s can add together or SUMMATE to influence a postsynaptic neuron in initiation of an action potential
 Spatial Summation
 Large numbers of axon terminals stimulate the postsynaptic neuron at the same time
 Temporal Summation
 One or more presynaptic neurons transmit impulses in rapid fire succession

ALL-OR-NONE RESPONSE
 An action potential is an “ all or none ” phenomenon
 When threshold is reached, the action potential will happen completely
 If threshold is not reached, the action potential will not occur at all

SALTATORY CONDUCTION
 Occurs only in myelinated axons
 Depolarization wave jumps from one node of
Ranvier to the next
 Results in faster nerve impulse transmission

SUMMARY OF EVENTS
 A nerve impulse in the presynaptic neruon causes release of neurotransmitter into synaptic cleft
 Neurotransmitter binding to receptors on postsynaptic neuron dendrite or soma cause certain chemically gated ions to open
 If Na + channels open:
 Rapid influx of Na + ions ( depolarization )
 A small positive graded potential occurs ( EPSP )
 If RMP changes in a positive direction by 20mV ( or reaches the threshold ), voltage gated sodium channels in the axon hillock open
 Sodium rushes in at the axon hillock resulting in an action potential
 As the positive ions get pushed down the axon, more voltage gated sodium channels open and the depolarization continues down the axon ( propagation )
 The process of restoring the negative RMP begins immediately following the depolarization wave
( repolarization )

NERVE FIBER TYPES
 The larger the axon diameter, the faster the impulse travels
 Myelinated axons conduct impulses more rapidly

Fiber Types:
 Type A fibers
 Large diameter axon with thick myelin sheath
 Impulse travels at 15 to 150 m/sec.
 Sensory and motor fibers serving skin, muscles, joints
 Type B fibers
 Intermediate diameter axon, lightly myelinated
 Impulse travels at 3 to 15 m/sec.
 Type C fibers
 Small axon diameter, unmyelinated
 Slow impulse conduction (1 m/sec. or less)

NERVE FIBER TYPES
Type C Fiber
Type B Fiber
Type A Fiber

NEURONAL CIRCUITS

 One incoming fiber triggers responses in increasing numbers of neurons farther down the circuit

NEURONAL CIRCIUTS



REFLEX ARCS
 Neural pathways with 5 components:
 Receptor
 Sensory neuron
 CNS integration center
 Motor neuron
 Effector
 A rapid, automatic response to a stimulus

 Brainstem
 Medulla oblongata (1)
 Pons (2)
 Midbrain (3)
 Diencephalon (4)
 Thalamus
 Hypothalamus
 Epithalamus
 Cerebellum (5)
 Cerebrum (6)
6
4
3
2
1
5

 In anterior and middle cranial fossa
 Six lobes
1
 Frontal (1)
 Parietal (2)
 Occipital (3)
 Temporal (4)
 Limbic (5)
 Insula (6)
5
4
 Many functions in various regions
6
2
3

 Structures that help to protect the brain and spinal cord:
 Skull bones
 Vertebrae
 Cerebrospinal Fluid (CSF)
 Bathes and cushions
 Meninges
 Three connective tissue membranes surrounding the brain and spinal cord

 Flows around and in the brain and spinal cord
 99% water
 Also sugar ( glucose ), chlorides, proteins, ions, vitamin C
 Total volume of 150 ml
( replaced every 3 to 4 hrs .)
 900 to 1200 ml formed daily
 Formed by choroid plexuses in the brain ventricles wastes ependymal cells capillary glucose,
O
2 ions choroid plexus

 Dura Mater
 Most superficial
 Tough, double-layered membrane
 Outer layer is fused to skull
 In some areas the layers separate to enclose dural sinuses
 Extends inward in some areas forming septa to anchor the brain to the skull dura mater dural sinus

 Dural Septa
 Falx cerebri
 Falx cerebelli
 Tentorium cerebelli falx cerebri tentorium cerebelli falx cerebelli

 Subdural space
 Space below dura and above arachnoid layer below
 Epidural space
 Space between bone and the dura
( above the dura )
 Not present in the skull

 Arachnoid (Mater) Layer
 Deep to dura
 Web-like extensions down to pia mater below
 Subarachnoid space
 Space below arachnoid membrane
 Filled with CSF
 Numerous blood vessels
 Arachnoid villi (granulations)
 Drain CSF into dural sinuses arachnoid

 Pia Mater
 Innermost layer
 Adheres to brain and spinal cord
 Follows folds of brain
 Very vascular
 Small extension of pia called the filum terminale fastens the spinal cord down to the coccyx bone pia mater

 Barrier formed by astrocytes and endothelial lining of brain capillaries

Prevents cellular wastes from entering brain tissue capillary astrocyte

 Hydrocephalus
 Build up of CSF due to blockage or obstruction
 Exerts pressure on the brain
 Can cause permanent brain damage
 Meningitis
 Inflammation of the meninges caused by a viral or bacterial infection
 May spread to nervous tissue of CNS
 Encephalitis
 Brain tissue inflammation
 Fatal 50% of the time

 Interconnected chambers within the brain
 Filled with CSF
 Four ventricles:
 1 st and 2 nd (Lateral) Ventricles
 Anterior, inferior and posterior horns
 3 rd Ventricle
 Within diencephalon
 Connected to 4 th ventricle by the cerebral aqueduct
 4 th Ventricle
 Dorsal to pons and medulla
 Opens into central canal of spinal cord and subarachnoid space around brain
1
4
3
2

 Function
 Controls reflex activities
 Transmits info. from peripheral nerves to brain and back
 Structure
 Runs from the foramen magnum to L
1 or L
2
 Cervical and lumbar enlargements
 31 pair of spinal nerves emerge from the cord

 Filum Terminale
 Extension of pia mater attaching the cord to the coccyx
 Conus Medullaris
 Caudal end of spinal cord

Cauda Equina
 Nerves from the lower cord running inferior before exiting the vertebrae conus medullaris filum terminale cauda equina

 Gray Matter
 In the interior of the cord
 Forms an ‘H’ shape
 Ventral Horns
 To anterior projections of gray matter
 Contain cell bodies of large alpha motor neurons gray matter ventral horns

 Dorsal Horns
 Incoming unipolar sensory neurons enter and synapse with association neurons
 Cell bodies of these sensory neurons are in the dorsal root ganglia lateral horn
 Lateral Horns
 Only visible from T
1 to L
2
 Contain autonomic neuron cell bodies dorsal horns

 Gray commissure
 Connects right and left halves of gray matter
 External fissures
 Anterior median fissure
 Posterior median sulcus anterior median fissure posterior median sulcus gray commissure

 White matter
 Divided into columns called columns or funiculi
 Anterior, lateral and dorsal white columns or funiculi lateral funiculus anterior funiculus posterior funiculus

 Ascending Tracts
 Spinothalamic
 Ascending afferent sensory fiber tract
 Info regarding pain, temperature and crude touch
 Spinocerebellar
 Afferent sensory tract
 Carries info regarding movement and limb position spinocerebellar spinothalamic

 Ascending Tracts
 Fasciculus cuneatus & Fasciculus gracilis
 Afferent sensory tract
 Carries info from skin, joints and muscles concerning discriminative touch, pressure, vibration and body position fasciculus cuneatus fasciculus gracilis

 Descending Tracts
 Corticospinal
 Descending efferent fiber tract
 Carry info for voluntary movement of skeletal muscle corticospinal corticospinal

 An automatic response to a specific stimulus
 Reflex Arcs
 Most don’t involve conscious thought
 Some involve lower brain
 Some are carried out by the spinal cord without any brain involvement


 Chain of only 2 neurons involved
 Example: Patellar reflex (stretch reflex)
– Quadriceps tendon stretched  muscle spindles send impulse (muscle stretching)
 spinal cord
 motor neuron
 quadriceps muscle contracts


 Require 3 or more sets of neurons
 Example: Withdrawal reflex ( crossed extensor reflex )
–
Pain receptors
 spinal cord
 association neuron
 integration
 motor neurons (to muscles for contraction)
 flexors contract
 extensors extend for balance



 Circle of Willis
 Circular network of blood vessels supplying the brain
 2 vertebral, 2 internal carotid arteries contribute
 Many anastamoses help curtail inadequate blood supply to the brain

 Cerebral Cortex
 Gray matter
 Neuron cell bodies
 Outer layer of cerebrum

Gray matter also in basal nuclei gray matter


Also called basal ganglia
 Areas of gray matter deep within the cerebrum
 Putamen, globus pallidus, caudate nucleus caudate nucleus lentiform nucleus
( putamen + globus pallidus )

 Receive input from cerebral cortex caudate nucleus
 Project messages through thalamus to premotor and prefrontal areas
 monitor and regulate movements from motor cortex
 Regulate intensity of movements, inhibit unnecessary movements lentiform nucleus putamen globus pallidus

 Gyri (gyrus)
 Folds or hills in the cerebral tissue longitudinal fissure
 Sulci (sulcus)

 Shallow grooves or valleys
Fissures central sulcus
 Deeper grooves and valleys precentral gyrus

 Gyri
 Precentral gyrus (1)
 Postcentral gyrus (2)
 Superior temporal gyrus (3)
 Cingulate gyrus (4)
3
1
2
4

 Sulci
 Central sulcus (1)
 Lateral (Sylvian) sulcus or fissure (2)
 Parieto-occipital sulcus (3)
 Calcarine sulcus (4)
2
1
3
4

The Cerebrum: Fissures
 Fissures
 Longitudinal fissure (1)
 Transverse fissure (2)
1
2

association fibers  White matter = myelinated axons
 Three types of fibers in cerebral white matter:
 Association fibers
 Travel to other areas in the same hemisphere

The Cerebrum: White Matter commissural fibers
 Commissural fibers
 Connect areas from one hemisphere to the other hemisphere
 Projection fibers
 Descend from cortex towards lower brain or spinal cord projection fibers

corpus callosum
 Commissures
 Regions with commissural fibers
 Corpus callosum
 Anterior commissure fornix anterior commissure

Cerebrum: Functions
 Three Functional Types of Areas Within the
Cerebrum:
À Sensory Areas
 Conscious awareness of sensations
 Motor Areas
 Control voluntary functions
 Association Areas
 Integrate information for a purposeful action

 Frontal Lobe
 Primary Motor Cortex (1)
 Precentral gyrus
 Allows conscious control of skeletal muscle
 Contralateral innervation
2 1
 Premotor Area (2)
 Controls learned, repetitious motor skills
3
 Broca’s Area (3)
 Directs the movement of muscles involved in speech
(lips, tongue, throat)


Parietal Lobe
 Primary Somatosensory
Cortex (4)
 Postcentral gyrus
 Receives input from sensory receptors in skin, muscles
 I.D. body region input is from
 Sensory Association Area (5)
 Integrates and analyzes sensory input
 Evaluates size, texture, relationships etc.
4
5

 Occipital Lobe
 Primary Visual Cortex (6)
 Posterior occipital lobe
( calcarine sulcus )
 Receives input from retina
 Info relayed through lateral geniculate body of thalamus
 Visual Association Area (7)
 Surrounds visual cortex
 Interprets visual inputs, uses past experiences
 Allows for visual recognition
7
6

 Temporal Lobe
 Primary Auditory
Cortex (8)
 Superior temporal gyrus
 Receives info. from receptors in inner ear for sound
8
 Auditory Association
Area (9)
 Uses memories of sounds for sound recognition
9

 Posterior Temporal Lobe
 Wernicke’s Area (11)
 Understanding written and spoken language
 Sounding out unfamiliar words
10


Limbic Lobe
 Cingulate gyrus, parahippocampal gyrus, hypothalamus and part of the thalamus
 “Emotional brain”
 Extensive link to lower and higher brain areas
 Allows emotional and visceral responses to things we are consciously aware of cingulate gyrus hypothalamus parahippocampal gyrus

 Insula
 Deep within the cerebrum in area deep to lateral sulcus
 May be involved with autonomic and somatic activities lateral sulcus insula

 Aphasias
 Inability to speak in grammatical sentences due to lesions in Broca’s area
 Electroencephalograph (EEG)
 Used to trace patterns of brain activity
 Can be used to detect regions where seizures are occurring

 Consists of the
Thalamus, Hypothalamus and Epithalamus
 Thalamus
 Makes up 80% of the diencephalon
 Two large gray masses connected by the intermediate mass
 Contains many nuclei
 Projects fibers to and from the cortex
 Sorts and edits info. headed for the cortex
 Directs info. to proper cortical region thalamus intermediate mass of thalamus

 Hypothalamus
 Initiates physical expression of emotions (linked to the limbic system)
 Regulates thirst, food intake, body temp., sexual behavior, pleasant and painful feelings, pleasure, fear, rage
 Regulates autonomic centers in the brain stem controlling B.P., digestive rate, respiration rate hypothalamus

 Hypothalamus
 Infundibulum
 Stalk connecting the hypothalamus to the pituitary gland
 Mammillary bodies
 Relay station for olfactory pathways infundibulum mammillary body

 Hypothalamus
 Supraoptic Nucleus
 Contains neurons that produce ADH (antidiuretic hormone)
 Paraventricular Nucleus
 Contains neurons that produce oxytocin
– Stimulates uterine contractions in labor and milk ejection for nursing paraventricular nucleus
Supra-optic nucleus

 Other structures in the region
 Optic chiasma
 Pituitary gland (hypophysis)
 Diaphragma sella optic chiasma hypophysis

 Epithalamus
 Pineal gland
 Secretes melatonin
 Helps regulate sleep/wake cycles
 May be influenced by light (intensity and day length) pineal gland

 Cerebral Aqueduct
 Runs through midbrain from 3 rd to 4 th ventricle
 Cerebral Peduncles
 Stalks
 Contain motor fibers coming from the motor cortex (corticospinal tract) cerebral aqueduct
Posterolateral View cerebral peduncle

 Cranial Nerves III and IV
 Corpora Quadrigemina
 Four dome-shaped nuclei on the dorsal midbrain
 Superior colliculi
 Visual reflex centers
 Coordinate head and eye movements
 Inferior colliculi
 Act in reflexive responses to sound
Posterior View
Trochlear (IV)
Nerve

 Mostly contains tracts
 Cranial nerves V, VI, and VII
Trigeminal (V)
Nerve
Abducens
(VI) Nerve middle cerebellar peduncles
Facial (VII) Nerve
View

 Pyramids
 Anterior bulges containing white matter
 Carry corticospinal tracts running from motor cortex
(voluntary muscle movement)
 These fibers decussate
(cross over) in the lower medulla = decussation of pyramids medulla oblongata
Anterior View pyramid

decussation of pyramid

 Plays a role as an autonomic relay center
 Contains several visceral motor nuclei:
 Cardiovascular Center

Cardiac center- force and rate of heart contraction
 Vasomotor center regulates B.P.
-changes diameter of blood vessel walls
 Respiratory Centers
 Control rate and depth of breathing (works with pons )
 Other Centers
 Regulate activities such as hiccuping, vomiting, swallowing, coughing, sneezing


 Nucleus cuneatus
 Relay nuclei for ascending sensory information
 Nucleus gracilis
 Relay sensory info. from the spinal cord up to the somatosensory cortex

 Neuron cell bodies that relay info. regarding stretch of muscles and joints to the cerebellum

 C.N. VIII, IX, X, XI and XII
 Reticular Formation
 Clusters of neuron cell bodies scattered throughout the white matter of the midbrain, pons and medulla
 Project to the hypothalamus, thalamus, cerebellum and spinal cord
 Govern arousal of the brain by sending continuous impulses to the cerebral cortex to keep it alert (RAS)
 Filters out repetitive or weak signals to dampen unnecessary input

 Two hemispheres
 Separated by the falx cerebelli
 Vermis
 Worm-like structure between the 2 hemishperes
 Folia and fissures
 Similar to gyri and sulci
 Arbor vitae
 White matter with a tree- like appearance arbor vitae folia vermis

 Function
 Processes info. from the cerebral motor cortex, brainstem nuclei and sensory receptors
 Sends output regarding timing and coordination of skeletal muscle contraction
 Makes movements smooth and coordinated cerebellum

 3 Cerebellar Peduncles
 Connect the cerebellum to the brainstem
 Superior Cerebellar Peduncle (1)
 Carries axons between midbrain and cerebellum
 Middle Cerebellar Peduncle (2)
 Carries axons between the pons and cerebellum
2
3
1
 Inferior Cerebellar Peduncle (3)
 Carries axons between the medulla and cerebellum cerebellum


 Staggering gait, slurred speech, overshooting of target when touching things
 May result from damage to cerebellum

 Caused by lack of blood to the brain
 Possible blockage of a cerebral artery or rupture of an aneurysm

 Transient Ischemic Attacks (TIA’s)
 Temporary blood deprivation lasting from 5 to
50 min.
 Temporary numbness, paralysis, or impaired speech
 Usually warning of an impending, more serious stroke
 Alzheimer’s Disease
 Progressive degeneration of brain function
 Deficit of Ach
 Memory loss, shortened attention span, disorientation, possible language loss

 Parkinson’s Disease
 Degeneration of dopamine releasing neurons
 Basal ganglia become deprived of dopamine
 Persistent tremors, forward bent posture when walking and shuffling gait

 Huntington’s Disease
 Hereditary
 Massive degeneration of the basal ganglia and eventually the cerebral cortex
 Causes spastic, abrupt, jerky movements
 Mental deterioration and death result

The Peripheral Nervous System
CNS
PNS
Sensory Division Motor Division
Sympathetic
Division
Parasympathetic
Division
Autonomic
Nervous
System
Somatic
Nervous
System
Links the external environment and the body to the CNS

Peripheral N.S.: Components
 Sensory Division
 Sensory fibers carry impulses from receptors in the skin, muscles and joints ( somatic afferents )
 Sensory fibers carry impulses from the visceral organs ( visceral afferents )
 Motor Division
 Efferent motor fibers carry impulses from the
CNS to effectors (muscles, glands and viscera)
 31Pair of spinal nerves
 12 Pair of cranial nerves

PNS: The Motor Division
Consists of Two Subdivisions
 Somatic Nervous System
 Somatic motor fibers
 Conduct impulses to skeletal muscles
 Allows conscious control of skeletal muscles
 Autonomic Nervous System
 Visceral motor fibers
 Regulate smooth muscles, cardiac muscle and glands
 Regulates involuntary activities
 Divided into two subdivisions:
 Sympathetic N.S.
 Parasympathetic N.S.

Autonomic Nervous System
 Nerves and receptors involved with homeostasis
 Sympathetic System
 Fight or flight
 Parasympathetic System
 Return to resting state

Sensory Receptors of the PNS
 Classified by location or type of stimuli detected
 Location
 Exteroceptors
 Interoceptors
 Proprioceptors
 Stimuli Detected
 Mechanoreceptors
 Chemoreceptors
 Photoreceptors
 Thermoreceptors
 Nociceptors

Exteroreceptors




Exteroreceptors
 Examples:
 Free Nerve Endings
 In all body tissues (esp. epithelium) - pain, temp., and pressure
 Merkel’s Discs
 Free nerve with disc shaped endings
 Found in deep epidermis
 Light touch

Exteroreceptors
 Examples:
 Meissner’s Corpuscles
 In dermal papillae of hairless skin (lips, nipples, fingertips)
 Light pressure and discriminative touch
 Krause’s End Bulbs
 In mucosa
(mouth,conjunctiva, hairless skin near body openings)
 Detect the same stimuli as
Meissner’s

Exteroreceptors
 Examples
 Pacinian Corpuscles
 In hypodermis of skin, periostea, ligaments, joint capsules, fingers, soles of feet, external genitalia and nipples
 Deep pressure and stretching
 Respond only when pressure first applied
 Ruffini’s Corpuscles
 Found in deep dermis, hypodermis and joint capsules
 Detect the same as
Pacinian’s

Interoreceptors (Visceroreceptors)
 Detect stimuli originating from within the body
 Pain, discomfort, stretching tissue, temperature
 Examples:
 Free nerve endings
 Pacinian corpuscles

Propioceptors
 Respond to internal stimuli
 In muscles, tendons, ligaments and joints
 Monitor degree of stretch
 Examples: muscle spindle
 Free nerve endings
 Pacinian’s corpuscles
 Ruffini’s corpuscles
 Golgi tendon organs
 Muscle spindles
Golgi tendon organ

Mechanoreceptors
 Send impulses when tissues deformed by mechanical forces
 Touch, pressure, vibrations, itching
 Examples:
 Merkel’s discs
 Meissner’s corpuscles
 Pacinian corpuscles
 Muscle spindles and Golgi tendon organs

Chemoreceptors & Photoreceptors
 Chemoreceptors
 Detect dissolved chemicals
 Examples:
 Olfactory receptors
 Taste receptors
 Photoreceptors
 Detect changes in light energy
 Examples:
 Retina of the eye

Thermoreceptors & Nociceptors
 Thermoreceptors
 Detect changes in temperature
 Examples:
 Free nerve endings
 Nociceptors
 Detect pain or potentially damaging stimuli
 Examples:

Free nerve endings
 All receptor types may function in this respect at one time or another

Pain
 Pain Receptors
 Pain receptors (free nerve endings) are stimulated by noxious stimuli
 Damaged body tissues release chemicals bind to pain receptors
 ATP released from injured cells may stimulate some pain receptors

Pain Receptor
 Classification
 Somatic Pain
 From skin, muscles or joints
 Visceral Pain
 From receptors in organs in the body cavities
 Results from stretching tissue, muscle spasms, or chemicals
 Because visceral pain and somatic pain follow the same neural pathway, visceral pain may be perceived as somatic pain ( referred pain )

gallbladder liver liver gallbladder appendix kidneys urinary bladder
Referred Pain Areas heart lungs & diaphragm heart stomach pancreas small intestine ovaries colon ureters

optic chiasma
Trochlear nerve (IV)
Trigeminal nerve (V)
Facial nerve (VII)
Vagus nerve (X)
Hypoglossal nerve (XII)
Cranial Nerves
Olfactory nerve (I)
Optic nerve (II)
Occulomotor nerve (III)
Abducens nerve (VI)
Vestibulocochlear nerve (VIII)
Glossopharyngeal nerve (IX)
Accessory nerve (XI)

Cranial Nerves
 12 pair numbered by their location (from rostral to caudal)
 C.N. (I) and (II) originate from the cerebrum
 C.N. (III) through (XII) originate from the brainstem
 Almost all of the cranial nerves serve the head and neck
 C.N. (X), Vagus, extends down into the abdominal cavity
 Cranial nerves can have sensory, motor or parasympathetic neuron fibers (or all of these)
 C.N. (III), (VII), (IX), and (X) contain parasympathetic fibers
 Old Opie Occasionally Tries Trigonometry And Feels
Very Gloomy, Vague, And Hypoactive

C.N. I: Olfactory Nerves
 Sensory only
 Carry sensations of smell from nasal cavity
 Originate in the mucosa of the nasal cavity
 Pass through the cribiform plate of the ethmoid bone to the olfactory bulb
 Olfactory nerves  olfactory bulb  olfactory tract  inferior frontal and medial temporal lobes

C.N. II: Optic Nerves
 Sensory only
 Originate from the retina
 Optic nerves  optic chiasma  optic tracts  lateral geniculate bodies of thalamus  optic radiations  visual cortex in occipital lobe

C.N. III: Occulomotor Nerves
 Motor, sensory and parasympathetic fibers
 Motor to 4 of the 6 extrinsic eye muscles ( inferior oblique, superior rectus, inferior rectus, medial rectus )
 Parasympathetic fibers to the constrictor pupillary muscles and the ciliary muscles (constrict the pupils and thicken the lens)
 Proprioceptive afferents from 4 eye muscles it innervates

C.N. IV: Trochlear Nerves
 Motor and sensory
 Motor to the superior oblique muscle
 Proprioceptive afferents from the superior oblique

C.N. V: Trigeminal Nerves
 Motor, sensory
 Three branches:
 Ophthalmic Branch V
1
 Sensory from upper eyelid, eye surface, tear glands, nose, scalp and forehead

C.N. V: Trigeminal Nerves
 Maxillary Branch V
2
 Sensory from upper teeth, gum and lip, palate and skin of cheek and lower eyelid

C.N. V: Trigeminal Nerves
 Mandibular Branch V
3
 Motor to muscles of mastication
 Sensory from lower teeth, gum, lip, skin of jaw and part of scalp

C.N. VI: Abducens Nerves
 Motor and sensory
 Motor to lateral rectus muscles
 Proprioceptive afferents from the lateral rectus

C.N. VII: Facial Nerves
 Motor, sensory and parasympathetic fibers
 Motor to muscles of facial expression
 Taste from anterior 2 /
3 of tongue
 Parasympathetic innervation of salivary glands
(submandibular and sublingual)

C.N. VIII: Vestibulocochlear Nerves
 Sensory only
 Two branches
 Cochlear Branch
 Afferent fibers from cochlea in inner ear carrying auditory messages
 Vestibular Branch
 Afferents from vestibule and semicircular canals carrying info. on equilibrium

C.N. IX: Glossopharyngeal Nerves
 Motor, sensory and parasympathetic fibers
 Motor to muscles of the pharynx for swallowing
 Taste from posterior 1 /
3 of tongue
 Sensory from tongue, tonsils, eustachian tubes
 Sensory from carotid arteries regarding blood pressure and chemistry
 Parasympathetic innervation of the Parotid salivary glands

C.N. X: Vagus Nerve
 Motor, sensory and parasympathetic fibers
 Motor to muscles of pharynx and larynx
 Sensory from posterior tongue and pharynx, thoracic and abdominal viscera
 Parasympathetic innervation of heart, lungs, smooth muscles of pharynx, larynx, thoracic and abdominal viscera

C.N. XI: Spinal Accessory Nerves
 Motor and sensory
 Motor to the muscles of the shoulder, neck
(sternocleidomastoid, trapezius) pharynx, larynx
 Proprioceptive afferents from the same muscles

C.N. XII: Hypoglossal nerves
 Mostly motor, some sensory
 Motor to intrinsic and extrinsic tongue muscles
(move the tongue)
 Proprioceptive afferents back from the same muscles

Spinal Nerves
 31 pair of mixed nerves arising from the spinal cord
 Transmit sensory info. to the cord ( afferents )
 Transmit motor info. from the
CNS to the body ( efferents )
 Numbered according to where they leave the spinal cord
 C
1 exits between the occipital bone and the atlas
 C
2 through C
7 exit through intervertebral foramina above which they are named (C
8 above T
1
) is
 All of the rest exit below the vertebrae they are named after
 There is only one small pair of coccygeal nerves (Co)

Spinal Nerve Composition
 Dorsal Root
 Dorsal root ganglion
 Ventral Root dorsal root dorsal root ganglion ventral root

Spinal Nerve Divisions
 Dorsal Ramus
 Ventral Ramus
 Meningeal Branches
 Rami Communicantes dorsal ramus rami communicantes ventral ramus

The Cervical Plexus

The Brachial Plexus

Branches of the Brachial Plexus

Brachial Plexus Nerves
 Musculocutaneous
 From lateral cord
 Median
 From lateral and medial cords
 Ulnar
 From medial cord
 Radial
 From posterior cord
 Axillary
 From posterior cord
LATERAL
CORD

The Lumbar Plexus

The Sacral Plexus

Lumbosacral Nerves
 Femoral
 Obturator
 Sciatic
 Tibial
 Common peroneal
 Superficial branch
 Deep branch

Nerve Damage

 Pain radiating down the posterior and lower leg along the branches of the sciatic nerve
 Usually the result of compression of the nerve root from a herniated disc

Brachial Plexus Injuries
 Brachial Plexus Injuries
 Cause weakness or paralysis to the upper limb
 Median nerve damage
 Loss of pincer grasp and flexion of wrist and fingers (lateral 3 1 /
2
)
 Ulnar nerve damage
 Results in clawhand (medial two fingers become hyperextended)
 Radial nerve damage
 Results in wrist drop (inability to extend the hand at the wrist and extend fingers)

THE AUTONOMIC NERVOUS SYSTEM




THE AUTONOMIC NERVOUS SYSTEM
 Regulation
 By brainstem, spinal cord, hypothalamus and parts of the cerebrum

AUTONOMIC GANGLIA AND CIRCUITS

The motor units of the ANS consist of two neurons:
 Preganglionic Neuron
 Cell body is in the CNS
 Synapses with another neuron before reaching the effector
 The synapse occurs in an autonomic ganglion outside the CNS
 (The somatic motor unit consists of one neuron with its cell body in the CNS and its axon extending to the effector)
 Postganglionic Neuron
 Extends from the autonomic ganglion in the PNS to the effector

AUTONOMIC GANGLIA AND CIRCIUTS
CNS PNS Effector

THE AUTONOMIC NERVOUS SYSTEM

DIVISIONS OF THE ANS:
The Sympathetic System (see table 14.4)
 Fight or flight system activated in emergency situations
 Effects:
 Increases heart rate
 Dilates bronchial tubes and pupils
 Constricts blood vessels
 Stimulates secretion of epinephrine and norepinephrine from the adrenal gland
 Stimulates sweat glands
 Inhibits digestion
 Aids in ejaculation in males

THE SYMPATHETIC SYSTEM
 Neurons
 Emerge through the ventral roots of spinal nerves T
1 through L
(thoracolumabar outflow)
2

THE SYMPATHETIC SYSTEM
 Preganglionic
Sympathetic Neurons
 Preganglionic bodies are in the lateral horns of the spinal cord at the T
1 through L
2 levels
 Preganglionic sympathetic axons are short
 Preganglionic fibers pass through the ventral root into the white rami communicantes

THE SYMPATHETIC SYSTEM
 Preganglionic
Sympathetic Neurons
 Preganglionic sympathetic neurons synapse with a postganglionic neuron in the paravertebral chain ganglia
 Paravertebral chain ganglia run lateral to the spinal cord on both sides
 There are 22 to 23 pair of paravertebral ganglia on both sides of the vertebral column

THE SYMPATHETIC SYSTEM
 Preganglionic
Sympathetic Neurons
 Preganglionic fibers may ascend or descend within the chain to synapse within a ganglion at a different level
 Some sympathetic preganglionic fibers pass through the chain ganglion without synapsing
 These are called sympathetic splanchnic nerves

THE SYMPATHETIC SYSTEM
 Preganglionic
Sympathetic Neurons
 Sympathetic splanchnic nerves synapse in ganglia anterior to the vertebral column (near the aorta)
 These ganglia are called prevertebral or collateral ganglia
 Sympathetic splanchnics innervate smooth muscles of the abdominal and pelvic viscera and their blood vessels

THE SYMPATHETIC SYSTEM
 Postganglionic
Sympathetic Neurons
 Post ganglionic sympathetic axons are long
 Post ganglionic sympathetic neurons exit the paravertebral ganglia via the gray rami communicantes
(unmyelinated) and reenter the spinal nerve
 From here they continue on to the effector (viscera, blood vessels, sweat glands)

THE SYMPATHETIC SYSTEM
 All sympathetic preganglionic neurons release acetylcholine as a neurotransmitter ( cholinergic )
 Sympathetic postganglionic neurons release norepinephrine ( adrenergic ) with the exception of neurons to blood vessels and sweat glands
( cholinergic )

THE SYMPATHETIC SYSTEM
 Adrenal Medulla
 Preganglionic sympathetic neurons innervate the adrenal medulla
 Cause release of epinephrine and norepinephrine into the bloodstream
 Has the same effect as the sympathetic system only lasts 5 to 10 times longer

THE SYMPATHETIC SYSTEM
 Norepinephrine & Epinephrine
 Norepinephrine and epinephrine both have similar effects on the body
 Epinephrine has a greater effect on cardiac stimulation, raising B.P. and increasing metabolic rate
 Both are secreted by the adrenal medulla in response to sympathetic stimulation
 Same effect as stimulating organs via sympathetic nerves only lasts 5 to 10 times longer

THE PARASYMPATHETIC SYSTEM
 Effects:
 Constricts the pupils and bronchi
 Restores gland and digestive system activity
 Slows heartrate

THE PARASYMPATHETIC SYSTEM
 Neurons:
 Emerge with the cranial nerves (III, VII,
IX and X)
 Some emerge with the sacral spinal nerves
 Craniosacral outflow
 Neuron cell bodies for the fibers traveling with cranial nerves are in the brainstem
 Cell bodies for the fibers traveling with the sacral spinal nerves are in the lateral gray horns of spinal levels S
2
-S
4
C.N. III
C.N. VII
C.N. IX
C.N. X

THE PARASYMPATHETIC SYSTEM
 Preganglionic
Parasympathetic Neurons
 Preganglionic neurons are long
 Preganglionic neurons travel from the CNS almost all the way to the effector before synapsing with a postganglionic neuron

THE PARASYMPATHETIC SYSTEM
 Postganglionic
Parasympathetic Neurons
 Postganglionic parasympathetic neurons are short
 Postganglionic neurons synapse with preganglionics on or near the effector organ in terminal ganglia
(collectively called intramural ganglia )
 Postganglionic neurons travel from the terminal ganglia to the effector cells

THE PARASYMPATHETIC SYSTEM
 Cranial Outflow
 With C.N. III, VII, IX and X
 Preganglionic fibers travel with each cranial nerve
 Postganglionic fibers for
C.N. III, VII and IX travel with C.N. X for distribution to the face
 Vagus nerve accounts for 90% of all preganglionic parasympathetic fibers in the body
 Parasympathetic fibers from the Vagus nerve supply almost every thoracic and abdominal organ
C.N. III
C.N. VII
C.N. IX
C.N. X

THE PARASYMPATHETIC SYSTEM
 Sacral Outflow
 Axons run from the spinal cord with the ventral rami of
S
2
-S
4
 Fibers branch into pelvic splanchnic nerves
 Most fibers go on to synapse in intramural ganglia near the effector organ
 Pelvic splanchnics innervate the distal large intestine, urinary bladder, ureters and reproductive organs

ANS RECEPTORS
 Cholinergic Receptors
 Activated by acetylcholine (Ach)
 Two types:
 Muscarinic
– Found on all effector cells stimulated by postganglionic cholinergic fibers (all parasympathetic target organs and some sympathetic)
 Nicotinic
– Found on motor end plates of skeletal muscle
– Found on all postganglionic neurons (sympathetic and parasympathetic)
– Found on the hormone producing cells of the adrenal medulla

ANS RECEPTORS

ANS RECEPTORS
 Adrenergic Receptors
 Activated by epinephrine and norepinephrine
 Two types:
 Alpha (

)
– Epinephrine has a greater effect on these than norepinephrine
– Found on all sympathetic target organs except the heart
– Usually stimulatory when NE or Epinephrine binds to them
 Beta (

)
– Found in the heart, adipose tissue and most sympathetic organs
– Usually inhibitory when either hormone binds to them
(except in the heart)
– Cause dilation of blood vessels

ANS RECEPTORS

VISCERAL REFLEXES
 Visceral Reflex Arcs