1. Divisions of the nervous system
CNS
PNS
EFFERENT
AFFERENT
Somatic
ANS
Somatic
Visceral
Skeletal
muscle
-voluntary
Cardiac &
smooth muscles
Glands
-involuntary
Skeletal
muscle, tendons
joints, skin
Cardiac &
smooth muscles
Glands

2. PNS Terminology Ganglia = neuron cell bodies
Peripheral nerves = neuronal axons
PNS neuroglia
Satellite cells
Enclose neuron cell bodies in ganglia
Schwann cells
Cover peripheral axons

3. Ganglion plural = ganglia collection of neuronal cell bodies
neuron leading into a ganglion = pre-ganglionic neuron
cell bodies are located in the CNS (brain or spinal cord)
axons synapse with the cell bodies of the ganglion
the cell bodies and axons leading from the ganglion = post-ganglionic neuron

4. Efferent Division of the PNS
the somatic nervous system and part of the autonomic nervous system
the somatic = control of skeletal muscle
the ANS = involuntary control over cardiac and smooth muscle + gland secretion

5. -cranial nerves – 12 pairs
I - Olfactory
II - Optic
III - Oculomotor
IV-Trochlear
V - Trigeminal
VI - Abducens
VII - Facial
VIII - Acoustic
IX - Glossopharyngeal
X - Vagus
XI - Accessory
XII - Hypoglossal
-cranial nerves – 12 pairs
-considered part of the peripheral nervous system (PNS)
-olfactory & optic contain only sensory axons = sensory nerves
-remaining are motor or mixed nerves (both motor and sensory axons)

6. SPINAL NERVE Dorsal Root of SN Ventral Root of SN Dorsal Ramus Ventral
Rami
Communicantes
Sensory – IN
Motor – OUT
SKIN of BACK
BACK MUSCLES
Sensory – IN
Motor – OUT
TRUNK
LIMBs
(including skin)
Signals to and from the
ANS
VISCERA – cardiac and
Smooth muscle

7. Spinal Nerve
after passing through intervertebral foramina the spinal nerve branches into 3 rami (singular ramus)
1. Dorsal ramus
Sensory/motor innervation to skin and muscles of back
2. Ventral ramus
Sensory/motor innervation to ventral and lateral body surface, body wall structures, muscles of the upper and lower limbs

8. 3. rami communicantes = a connection between a spinal nerve and the sympathetic trunk of the ANS
two types:
gray ramus communicantes – unmyelinated post-ganglionic axons
white ramus communicantes – myelinated preganglionic axons

9. Somatic Nervous System
somatic/motor axons emerge from the ventral gray horn and travel into the spinal nerve
they then travel through either the:
dorsal ramus to end up at the muscles of the back
OR the ventral ramus to end up at the muscles of the limbs and body wall (chest/abs/pelvis)

10. Somatic Nervous System
considered the voluntary aspect of the PNS
but the muscles of posture and balance are controlled involuntarily by the lower brain centers (brain stem, cerebellum)
cell bodies located in the ventral gray horn of the spinal cord or nuclei of the brain stem
the axons extend continuously to its skeletal muscle target
synaptic terminals release acetylcholine – contraction of skeletal muscle
can only stimulate its target

11. Somatic Nervous System
somatic motor neurons originate in the ventral gray horn or the brain stem
receive incoming information from many presynaptic neurons
both excitatory and inhibitory on the somatic motor neurons

12. Somatic Nervous System
somatic motor neurons also synapse with:
1. reflex interneurons originating in the spinal cord
2. upper level neurons from motor areas of the brain – form the descending white matter tracts
these neurons synapse with the somatic motor neurons and regulate their activity
activation – impulse sent to muscles
inhibition – no impulse, no contraction

13. Somatic Nervous System
no matter what motor pathway you learn – they eventually affect the somatic motor neuron that originates in the ventral gray horn or the brain stem
therefore the somatic motor neuron is considered the final common pathway
considered the only way any other part of the nervous system can influence muscle activity

14. Somatic Motor pathways
all excitatory and inhibitory signals that control skeletal muscle movement converge on the somatic motor neurons
these somatic motor neurons originate in one of two places:
1. Brain Stem nuclei
2. Ventral Gray Horn of Spinal Cord
these somatic motor neurons extend from the brain stem and SC to innervate the skeletal muscles
they are also called lower motor neurons (LMNs)
their axons travel via cranial and spinal nerves to skeletal muscle
only LMNs provide output from the CNS to skeletal muscle fibers
damage to the LMNs produces flaccid paralysis on the same side as the damage – loss of reflex action, motor tone and voluntary contraction

15. Somatic Motor pathways
neurons in four distinct circuits control movement by providing input to these LMNs
1. local circuit neurons
2. upper motor neurons (UMNs)
3. basal ganglial neurons
4. cerebellar neurons

16. Local Circuit neurons

17. UMNs: Upper Motor Neurons
provide input to the local circuit and LMNs
essential for planning, initiating and directing sequences of voluntary movements
extend from the brain to the LMNs via two types of somatic motor pathways:
1. Direct Pathways
2. Indirect Pathways

18. UMNs: Upper Motor Neurons
1. direct motor pathways: nerve impulses for voluntary movement
lateral corticospinal, anterior corticospinal and corticobulbar (brain stem)
UMNs originate in the motor cortex and travel down the spinal cord as the corticospinal tracts to synapse with the LMN
OR – UMNs exit the brain stem as corticobulbar tracts
the LMN emerges as spinal nerves or through the brain stem and out as cranial nerves

19. Direct Motor Pathway: The Corticospinal tracts
1. lateral corticospinal
2. anterior corticospinal
major motor tract for voluntary skeletal muscle movement
especially fine motor skills
UMNs originate from motor cortex and travel through brain stem
as they pass through the medulla they form the pyramids
lateral corticospinal – one tract decussates; the other continues
connection between UMN and LMN may involve a local circuit interneuron
e.g. lateral corticospinal to LMN

20. UMNs: Upper Motor Neurons
2. indirect motor pathways: or extrapyramidal pathways
nerve impulses follow complicated circuits that involve the cortex, basal ganglia, thalamus and brain stem
descending axons/tracts pass outside the pyramids of the medulla
1. rubrospinal = facial expression via VII; walking
2. reticulospinal = posture and walking
3. vestibulospinal = posture and balance

21. Basal Ganglia Pathways
Motor Cortex
Basal Ganglia
Thalamus
assist movement by providing input to the UMNs
“okays” the motor pathways that emerge from the motor cortex
also suppresses unwanted movements and initiates and terminates movement
the production of dopamine by the substantia nigra also effects muscle tone by modifying this path
caudate nucleus and putamen receive sensory input from several areas of the brain – to know what muscles are doing

22. Cerebellar Neurons function involves four activities:
1. monitoring intentions for movement
2. monitoring actual movement
3. comparing the command (intention and movement) with sensory information
4. correction – to UMNs
travels via the thalamus to the UMNs in the cerebral cortex
can affect the corticospinal and corticobulbar paths
or can go directly to the UMNs in the midbrain of brain stem
can affect the rubrospinal path
Cerebellum
Thalamus
Midbrain
Motor Cortex

23. Medical application: Lou Gehrig’s Disease
Amyotrophic lateral sclerosis: Lou Gehrig’s disease
-unknown cause
-attacks motor areas of the cortex, axons of motor neurons
in the spinal cord and motor neuron cell bodies
-muscle weakness and atrophy
-begins in regions of the SC that affect hands and arms and
then spreads
specific destruction of the axons of UMNs in the corticospinal (direct UMN)
and rubrospinal (indirect UMN) tracts plus the cell bodies of LMNs
about 15% of cases are inherited = familial ALS
buildup in the synaptic cleft of the NT glutamate – released by motor neurons because the gene controlling the recycling of this NT is mutated
excess glutamate causes motor neuron malfunction and death
drug – riluzole – may help by reducing damage to these neurons
by decreasing glutamate concentration

24. The Neuromuscular Junction
end of the lower motor neuron (synaptic terminal or axon bulb) communicates with a muscle fiber/cell
nerve impulse leads to release of a acetylcholine  muscle contraction
therefore the NMJ is ALWAYS excitatory
the only way inhibition can take place is through the inhibition of the neuron “connecting” with the muscle – i.e. upper motor neurons

25. NMJ Medical Applications
black widow
triggers an explosive release of ACh
also at other sites other than the NMJ (i.e. neurons that release ACh = cholinergic neurons)
prolonged depolarization of target
paralysis of the diaphragm – respiratory failure
botulism
blocks release of ACh from the neuron at the NMJ
from Clostridium botulinum bacteria – toxin
death due to respiratory failure
curare
reversibly binds to the muscle cell
but doesn’t trigger the opening of Na channels – no contraction
ACh antagonist

26. The Autonomic Nervous System: ANS
two divisions that innervate the same organs
efferent branch regulates “visceral” activities (motor commands, involuntary, organs)
also has an afferent branch that receives sensory information from these areas

27. ANS
involuntary motor commands (and associated sensory information) supplies cardiac and smooth muscle, glands (i.e. viscera)
comprised of two neurons:
preganglionic and postganglionic
preganglionic synapses with the cell body of the postganglionic within the ganglion
therefore the collection of their cell bodies forms the ganglion itself!!!

28. ANS post-ganglionic neurons are non-myelinated
the pre-gang and post-gang neurotransmitters can differ
glands are innervated by preganglionic neurons – e.g adrenal gland which then releases epinephrine or norepinephrine in response
the gland itself acts as the post-ganglionic neuron!!
cardiac and smooth muscle innervated by postganglionic neurons

29. Somatic
ANS

31. Parasympathetic Division
cell bodies of the preG neurons are located in the brain stem
axons form the four cranial nerves III, VII, IX and X
also found in the lateral gray horns of sacral spinal nerves
emerge as part of the sacral spinal nerves S2 through S4

32. Parasympathetic Division
parasympathetic ganglia are located near or in the target
called terminal ganglia
the preG fibers are very long because they must extend from the CNS to an organ
synapse with postG within the terminal ganglia
four major terminal ganglia are located close to the organ they innervate
1. otic (parotid gland)
2. submandibular (submandibular and sublingual glands)
3. pterygopalatine (lacrimal gland)
4. ciliary (pupils)

33. Sympathetic Division for visceral motor commands
cell bodies of the preG neurons are located in the lateral gray horns of T1 to L2
axons exit the lateral gray horn through the ventral root of the spinal cord
axons form part of the spinal nerves T1 to L2
form part of the spinal nerve along with somatic motor nerve axons and parasympathetic preG axons
BUT the axons then enter the rami communicantes and pass to the nearest sympathetic trunk ganglion – synapse with the postG neuron
*** whether it is sympathetic or parasympathetic – the preG neurons release AcH

34. Sympathetic Division
cell bodies of postG neurons form the sympathetic ganglia
site of the synapse between the preG and postG neurons
short preG lead into these ganglia
long postG axons lead out to target

35. Sympathetic Division two groups of sympathetic ganglia:
1. sympathetic trunk ganglia
forms a vertical row lateral to the vertebral column
3 cervical, 11 or 12 thoracic, 4 or 5 lumbar and 4 or 5 sacral
the three cervical are known as superior, middle and inferior cerebral ganglia
2. prevertebral ganglia:
three major prevertebral ganglia: celiac, superior mesenteric and inferior mesenteric
located near the large abdominal arteries
these postG neurons innervate the abdominal organs

36. ANS Neurotransmitters
specific neurons release specific NTs – have distinct names
cholinergic neurons –release of ACh
all preG neurons from sympathetic and parasympathetic neurons
all parasympathetic postG neurons
two types of receptors
1. nicotinic
2. muscarinic
adrenergic neurons – release of NE
most sympathetic postG are adrenergic
1. alpha – a1 and a2
2. beta – b1 and b2 and b3

37. ANS receptors
the NTs released by the ANS can either stimulate or inhibit its target – depends on the receptors located in the target
1. Cholinergic receptors – respond to AcH
a. Nicotinic – named because they also bind and respond to nicotine
b. Muscarinic – named because they also bind and respond to muscarene from the mushroom Amanita muscaria

38. ANS receptors: Cholinergic receptors
1. Cholinergic receptors – respond to Acetylcholine
a. nicotinic:
found in the ganglia of the symp. and parasymp. division – i.e. all ANS ganglia
respond to ACh release from symp and parasymp preG fibers
called ionotropic receptors – non-selective ligand gated ion channels that open to allow entry and exit of more than one type of ion – Na+ and K+
activation of postganglionic neurons
e.g. if more Na enters the target neurons within the ganglion – depolarization and initiation of an AP by the postG neurons
nicotinic R
muscarinic R
adrenergic R

39. b. muscarinic receptors
known as metabotropic receptors – ion specific channel proteins
coupled to G protein signaling mechanisms
expressed on tissues “downstream” of post-ganglionic neurons – at the target tissue
also found in the post-ganglionic neuron – responds to Ach released by the pre-ganglionic neuron along with the nicotinic receptor
nicotinic R
muscarinic R
adrenergic R

40. ANS receptors: Adrenergic receptors
alpha and beta classes – a1, a2, b1, b2, b3
distributed in a specific tissue pattern and respond to either NE or Epi or both
expressed on tissues that are targeted by the sympathetic division of the PNS
respond to signal by activating G proteins -> second messengers are produced (cAMP or calcium)
the 2nd messengers eventually open ion channels for depolarization

41. Reflex Arc Neural “wiring” of the reflex
Requires 5 functional components:
1. sensory receptor, 2. sensory neuron, 3. integrating center (SC or BS), 4. motor neuron & 5. effector

42. Classification of Reflexes
By development
Innate, acquired
Where information is processed
Spinal, cranial
Motor response
Somatic, visceral
Complexity of neural circuit
Monosynaptic

43. Spinal Reflexes: Monosynaptic
Monosynaptic reflex: only one synapse in the CNS - between and single sensory and motor neuron
ipsilateral reflexes - input and output on same side
e.g. Stretch reflex: causes contraction in response to muscle stretch
regulates skeletal muscle length and tone
sensory receptors are found in muscle spindles – activated when stretched

44. Spinal Reflexes: Monosynaptic
e.g. Patellar stretch reflex – patellar tendon is hit with a mallet
stretches the muscle spindles within the quadriceps
results in contraction of the quadriceps (inhibition of hamstring contraction)
reflex results

45. Spinal Reflexes: Polysynaptic
Polysynaptic reflex: more than one synapse involved
sensory receptor synapses with interneurons (associate neurons)
interneuron synapses with a motor neuron
e.g. Tendon reflex - controls muscle tension by causing muscle relaxation before muscle contraction rips tendons

46. Spinal Reflexes: Polysynaptic
Tendon reflex:
a sensory receptor detects the stretch of a tendon (tendon organs)
synapse with two interneurons:
1. an inhibitory interneuron - synapses with motor neurons and causes inhibition and relaxation of one set of muscles
2. a stimulatory interneuron synapses with motor neurons and causes contraction of the antagonistic muscle
reflex results

47. Polysynaptic reflex: Postural Reflexes
crossed extensor reflex
withdrawl
(flexor reflex)

48. Other reflexes
scratch reflex - transmitted by very sensitive nerve endings near the surface of the skin
frequently inherited by mammals - to help an organism protect and rid its body of parasites and other irritants
nerve signal includes positioning to pinpoint the location of the itch
effect of the reflex is an involuntary action to make a scratching movement that usually relieves the itch
scratching can cause pain - pain signals are believed to suppress the itch signals due to a lateral inhibition effect

49. Other reflexes oculocardiac reflex (Aschner reflex)
a decrease in pulse rate associated with traction applied to extraocular muscles and/or compression of the eyeball
mediated by nerve connections between the trigeminal nerve (ophthalmic division) and the visceral motor nucleus of the vagus nerve
motor commands are sent cardiovascular center via the vagus nerve to decrease the output of the sinoatrial node.
especially sensitive in neonates and children, and must be monitored

50. Other reflexes sneeze reflex
a sneeze is a very complicated thing, involving many areas of the brain
a sneeze is triggered by sensory stimulation of the membranes in the nose, resulting in a coordinated and forceful expulsion of air through the mouth and nose.
polysynaptic reflex
why do some people sneeze when they look at the sun?

51. Other reflexes
Photic sneeze reflex - medical condition by which people sneeze with sudden exposure to bright light
also referred to as sun sneezing
Autosomal dominant Compelling Helio-Ophthalmic Outburst syndrome
passed along genetically as an autosomal dominant trait – 25% of population
probable cause is a congenital malfunction in nerve signals involving the trigeminal nerve
there is an association between this nerve and the optic nerve
pupillary light reflex may also trigger the trigeminal nerve and the sneeze
the wires are “crossed a little bit” in some people - so shining a light in the eye "accidentally" activates two different outgoing pathways.

52. Other reflexes Moro reflex: also known as the startle reflex
normally lost by the 6th month of life postpartum
a response to unexpected loud noise or when the infant feels like it is falling
it is believed to be the only unlearned fear in human newborn
origin of this reflex can be found in that fact that primate infants of our ancestors clung to their mother's fur soon after birth
if human babies are falling backward - innate reflex will be to stretch out the arms to grab and cling to their mother
1. Startle
2. abduction of arms – spreading out of arms
3. unspreading the fingers
4. Crying (usually)
this reflex is tested in evaluating integration of the central nervous system (CNS), since the reflex involves these 4 distinct components

53. Reflexes – Laboratory Exercise
patellar tendon
also called knee jerk reflex
stretch reflex

54. Reflexes – Laboratory Exercise
achilles tendon
also called the ankle-jerk reflex
stretch reflex in the Achilles tendon is tapped while the foot is dorsi-flexed – results in plantar flexion (pointing of toes)

55. Reflexes – Laboratory Exercise
triceps
stretch reflex
elicits involuntary contraction of the triceps brachii muscle

56. Reflexes – Laboratory Exercise
biceps:
stretch reflex: inside the biceps brachii muscle

57. Reflexes – Laboratory Exercise
Babinski
Joseph Babinski
identifies disease of the spinal cord and brain
also exists as a primitive reflex in infants
Babinski's sign refers to its pathological form