Cranial and Peripheral Nerves

Principles of anatomy-ANSC 2202

Fall 2006

Somatic motor neurons (efferent)

Somatic sensory neurons (afferent)

Central Nervous System = brain + spinal cord

Peripheral Nervous System = cranial + spinal nerves

Nervous System

Skeletal

muscles Parasympathetic NS (rest& digestion):Pelvic nerves+Cranial III, VII,IX,X

Sympathetic NS (fight or flight):all spinal and most cranial nerves

Skin, muscles, tendons, bones

Smooth muscles, heart, glands

Autonomic motor neurons (efferent)

Autonomic sensory neurons (afferent)

Smooth muscles, heart, glands

voluntary involuntary

Special sensory fibersCn I,II,VII, VIII, IX

Taste, smell, vision, hearing

Types of neurons in the PNS

Cranial - connects the brain with the periphery Sensory (afferent) - carry information INTO the CNS

from sense organs Motor (efferent) - carry information away from the

CNS (for muscle control).

Spinal - connects the spinal cord with the periphery: Somatic - connects the skin or muscle with the CNS;

afferent and efferent Autonomic - connects the internal organs with the

CNS; afferent and efferent

Central nervous system

The Brain: sagittal section of a sheep’s brain: A review

Links the 2 hemispheres

Cerebral cortex:•Thought •Voluntary movement •Language •Reasoning •Perception

•Movement •Balance •Posture Brain stem=area of the brain

between the thalamus and spinal cord:•Breathing . Heart rate, Blood Press

•Vision •Audition •Eye Movement •Body Movement

Circadian rythm

The spinal cord

Extension of brain stem starting at the foramen magnum and ending at:– L1 in humans (extension of pia matter attaches to

coccyx)– S2 in animals

2 roles:– Transmission of nerve impulses (white matter-

axons; grey matter-nuclei)– Spinal reflexes

The spinal cord

The spinal cord

The spinal cord

Spinal reflexes

Damages to the Central Nervous System

Brain does not regenerate Spinal cord:

– If severed: function below the lesion will not be restored

Babinski (extensor toe) reflex: withdrawal = chronic spinal cord lesion

Patellar (knee-jerk) reflex: no kick = femoral nerve and/or segment of spinal cord L4-6

– Partial damage: may recover but stagnates after a certain period

Peripheral nervous system

PNS: Cranial nerves(12 pairs)

Cranial nerve Nerve type (Sensory, Motor, Both)

I Olfactory S “On Old Oklahoma’s Towering Tops a Fine Vet Gastroenterologist Viewed Some Horses”

“Six Sailors Made Merry But My Brother Said Bad Business My Man”

II Optic S

III Oculomotor M

IV Trochlear M

V Trigeminal B

VI Abducens M

VII Facial B

VIII Vestibulocochlear S

IX Glossopharyngeal B

X Vagus B

XI Spinal Accessory M

XII Hypoglossal M

Function of cranial nerves

I  Olfactory Nerve: sense of smell

II Optic Nerve: vision

III Oculomotor Nerve: eye movements, pupillary constriction and  accommodation, eyelid muscles

IV Trochlear Nerve: eye movements

V Trigeminal Nerve: somatic sensations from face, mouth, cornea; muscles of mastication (chewing)

VI Abducens Nerve: eye movements

VII Facial Nerve: controls the muscles of facial expression, taste from anterior tongue, lacrimal (tears) and salivary glands

VIII Auditory/Vestibular Nerve: hearing, sense of balance

IX Glossopharyngeal Nerve: sensation from pharynx, taste from posterior tongue, carotid baroceptors

X Vagus Nerve: autonomic functions of gut, sensation from pharynx, muscles of vocal cords, swallowing

XI Accessory Nerve: shoulder and neck muscles

XII Hypoglossal Nerve: movements of tongue

Cranial nerves: origin

Damage to the cranial nerves

Pupillary light reflex: oculomotor nerve: flash light in right pupil: right pupil should constrict more

Corneal and palpebral (eyelid) reflexes (state of anesthesia): trigeminal nerve: blink before touching eyelids (ophtalmic branch); retraction of ocular globe when touch cornea (maxillary branch)

Reaction to smell (link with appetite): olfactory nerve (see experiment with Boar Mate)

Torticollis: spinal accessory nerve: neck muscles innervation

Pharynx paralysis: glossopharyngeal and vagus nerves: rabies!!

PNS: Spinal nerves(31 pairs; don’t need to identify them all)

Anatomy:– Emerges from dorsal and ventral roots– Emerges through intervertebral foramen (except 1st

spinal nerve)

Somatic and autonomic systems

Somatic nervous system (skeletal muscles)

Autonomic nervous system: organization

Autonomic nervous system: organization

Differences between sympathetic and parasympathetic (autonomic nervous system)

Autonomic nervous system: targets

Autonomic nervous system: targetsSympathetic Parasympathetic

Eye Dilates pupil Constricts pupil

Salivary glands Dry mouth (thick saliva)

Lots of dilute saliva

Heart rate Increases Decreases

Lungs (bronchi) Dilates Constricts

GI activity Decreases Increases

Liver Increases blood sugar

None

Adrenal medulla Stim.secretion none

Penis Ejaculation Erection

Some important spinal nerves (pig)

Some important spinal nerves (human)

Damages to peripheral nerves

Sciatic nerve pinched: lower back pain Foot nerves: 90% of all lameness in horses.

Heel, pastern/foot and fetlock blocks should identify damage; if not, work way up he limb.

Knee-jerk reflex

Conclusion

CNS: brain + spinal cord PNS: cranial+ peripheral nerves:

– Somatic nervous system: skeletal muscle control– Autonomic nervous system: smooth and cardiac muscle.

Sympathetic/parasympathetic and fight/flight reactions

Neurological exams: non invasive, symptoms often specific to one type of lesion

To suspect if pain does not originate in muscles, tendons,…

The end

Stations - Knee-jerk reflex- Pupillary light reflex- Palpebral reflex- Spinal cord model- Fetal pig, dissect:

- Vagus and sciatic nerves- Brain

Handout - Table of cranial nerves

(with function and type-sensory or motor or both)

- Answer the vignettes- Sympathetic/

parasympathetic actions