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NERVOUS SYSTEM – BRAIN & CRANIAL NERVESDr. Othman Al-ShboulDepartment of Physiology

الرحمن الله بسمالرحيم

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The Thalamus “Relay station” and synaptic integrating center

for preliminary processing of all sensory input on its way to the cortex

It screens out insignificant signals and routes the important sensory impulses to appropriate areas of the somatosensory cortex (e.g., attention to stimuli of interest)

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The Hypothalamus Important link between the autonomic nervous system and

the endocrine system via the pituitary gland

Contains many nuclei and centers that regulate body temperature, hunger, thirst, fatigue, sleep, and circadian cycles

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The Basal Nuclei Masses of gray matter (neuron cell bodies)

located deep within the cerebral white matter

Functions:

o Fine tuning muscle tone; inhibiting muscle tone throughout the body

Proper muscle tone is normally maintained by a balance of excitatory and inhibitory inputs to the neurons that innervate skeletal muscles)

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The Basal Nuclei Improper function: Parkinson's disease

Deficiency of dopamine, an important neurotransmitter in the basal nuclei

Signs and symptoms: Increased muscle tone, or rigidity Involuntary, useless, & unwanted movements, such as

resting tremors (e.g., hands rhythmically shaking) Slowness in initiating and carrying out different motor

behaviors

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Cerebellum

Does not initiate movement, but contributes to coordination, precision, and accurate timing.

Fine tuning muscle tone;

o Enhancing muscle tone throughout the body

Attached to the back of the upper portion of the brain stem, Lies underneath the occipital lobe of the cortex

Damage to the cerebellum does not cause paralysis, but instead produces disorders in fine movement, equilibrium & posture (intention tremor;

oscillating to-and-fro movements of a limb as it approaches its intended destination)

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Brain Stem The brain stem is a vital link between the spinal cord and

higher brain regions

Main functions:

The majority of the 12 pairs of cranial nerves arise from the brain stem

“Centers,” that control heart and blood vessel function, respiration, and many digestive activities. Important for brain arousal (being awake & alert)

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Cranial Nerve I: Olfactory

Arises from the olfactory epithelium

Carrying afferent impulses for the sense of smell

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Cranial Nerve II: Optic

Arises from the retina of the eye

Carrying afferent impulses for vision

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Cranial Nerve III: Oculomotor

Functions: Eye movement: motor innervation of extrinsic eye muscles

(Superior rectus, Inferior rectus, Medial rectus, Inferior oblique) Raising the eyelid Constricting the iris Controlling lens shape

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Cranial Nerve IV: Trochlear

Function: Eye movement motor innervation of extrinsic eye muscles

(Superior oblique)

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Cranial Nerve V: Trigeminal Composed of three divisions

Ophthalmic (V1) Maxillary (V2) Mandibular (V3) motor innervation for muscles of

mastication

brings sensations from the face

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Cranial Nerve VI: Abducens

Function: Eye movement motor innervation of extrinsic eye muscles

(Lateral rectus)

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Cranial Nerve VII: Facial

Motor innervation of muscles of facial expression

Innervation of lacrimal and salivary glands (submandibular and sublingual glands)

Sensory function is taste from taste buds of anterior two-thirds of the tongue

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Cranial Nerve VIII: Vestibulocochlear

Fibers arise from the hearing and equilibrium apparatus of the inner ear

Two divisions – cochlear (hearing) and vestibular (balance)

Function: sensory – equilibrium and hearing

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Cranial Nerve IX: Glossopharyngeal

Runs to the throat

Motor – innervates part of the tongue and pharynx, (also parotid salivary gland)

Sensory – fibers conduct taste and general sensory impulses from the posterior third of the tongue and pharynx

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Cranial Nerve X: Vagus

The only cranial nerve that extends beyond the head and neck

Motor fibers to the heart, lungs, and visceral organs

Taste sensation

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Cranial Nerve XI: Accessory

Motor innervation for the larynx, pharynx, and soft palate

Innervates the trapezius and sternocleidomastoid, which move the head and neck

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Cranial Nerve XII: Hypoglossal

Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech

If damaged, difficulties in speech and swallowing; inability to protrude the tongue

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Cranial Nerves

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The END