Cranial and Peripheral Nerves Principles of anatomy-ANSC 2202 Fall 2006

Central Nervous System = brain + spinal cord Peripheral Nervous System = cranial + spinal nerves Skin, muscles, tendons, bones Smooth muscles, heart, glands Taste, smell, vision, hearing voluntary involuntary Somatic sensory neurons (afferent) Somatic motor neurons (efferent) Autonomic sensory neurons (afferent) Autonomic motor neurons (efferent) Special sensory fibers Cn I,II,VII, VIII, IX Smooth muscles, heart, glands Parasympathetic NS (rest& digestion): Pelvic nerves+Cranial III, VII,IX,X Skeletal muscles Sympathetic NS (fight or flight): all spinal and most cranial nerves

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 Cerebral cortex: Thought Voluntary movement Language Reasoning Perception Circadian rythm Vision Audition Eye Movement Body Movement Links the 2 hemispheres Movement Balance Posture Brain stem=area of the brain between the thalamus and spinal cord: Breathing . Heart rate, Blood Press

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) 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 III Oculomotor M IV Trochlear V Trigeminal B VI Abducens VII Facial VIII Vestibulocochlear IX Glossopharyngeal X Vagus XI Spinal Accessory XII Hypoglossal

Function of cranial nerves 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: targets Sympathetic 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 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