brain and special senses

8/14/2019 Brain and Special Senses

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The Brain, Cranial Nerves, Autonomic Nervous

System and Special Senses

Functional Anatomy of the Brain

Cerebral hemispheres Diencephalon

Brain stem

Cerebellum

Cerebral Hemispheres Most superior part of the brain

Gyri: elevated ridges

Sulci: shallow grooves Fissures: deeper grooves which separate large

regions of the brain

Longitudinal fissure: single deep fissure thatseparates the cerebral hemispheres

Lobes Parietal

Frontal

Temporal

Occipital

Parietal

Somatic sensory area Posterior to the central sulcus

Body is represented in an upside down manner

Sensory pathways are crossed pathways

Frontal

Primary motor area Anterior to the central sulcus

Major voluntary tract: pyramidal or

corticospinal tract Body is represented in an upside down manner

The pathways are crossed

Areas of higher intellectual reasoning Complex memories (also seen in the temporal

lobe)

Speech area Language comprehension

Brocas area

Specialized area involved in ability to speak Found at the base of the precentral gyrus

Located only in one hemispehere (left)

Damage to this area: inability to say wordsproperly (you know what you want to say, but

you cant vocalize the words)

Occipital Visual area

Temporal Auditory area

Olfactory area

Cerebral Hemispheres

Gray matter: outermost layer of the cerebral

cortex White matter: deeper


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Corpus callosum: connects the cerebral

hemispheres

Diencephalon interbrain

Sits atop the brainstem and enclosed by the

cerebral hemispheres Major structures: thalamus, hypothalamus,

epithalamus

Thalamus: relay station for sensory impulsespassing upward to the sensory cortex

Hypothalamus regulation of body temperature, water

balance and metabolism part of the limbic system

Epithalamus: composed of the pineal body and

choroid plexus

Brain Stem

Composed of the midbrain, pons and medulla

oblongata Contains the nuclei of many spinal nerves

Midbrain Cerebral aqueduct

Cerebral peduncles

Corpora quadrigemina

Pons

Contains many fiber tracts (bridge)

Medulla Oblongata

Contains many fiber tracts

Contains cranial nerve nuclei

Controls heart rate, blood pressure, breathing,swallowing, and vomiting

Reticular Formation Diffuse mass of gray matter

Motor control of visceral organs

Ascending Reticular Activating System

(ARAS) Role in consciousness and the

awake/sleep cycles

Damage: permanent unconsciousness(coma)

Cerebellum

Has two hemispheres and a convolutedsurface

Outer gray matter and inner white matter

Precise timing for skeletal muscle activity Controls balance and equilibrium (motor

coordination)

Damage: ataxia Clumsy and disorganized movements

Protection of the CNS Skull and vertebral column


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Meninges

CSF Blood-brain barrier

Three connective tissue membranes Dura mater

Double-layered membrane (periosteal

layer and meningeal layer)

Arachnoid mater Weblike

Subarachnoid space

Arachnoid villi Pia mater

Clings tightly to the surface of the brain

Cerebrospinal Fluid Similar plasma, but has less protein and more

vitamin C

Formed by the choroid plexus

Watery cushion Lumbar tap: method of obtaining CSF

Lateral ventricles third ventricle cerebral

aqueduct (of Sylvius) fourth ventricle central

canal of spinal cord / subarachnoid space ( blood)

Blood-brain Barrier Least permeable capillaries in the body

Only water, glucose and essential amino acids

can pass through easily Metabolic wastes (urea, toxins, proteins and

most drugs) are prevented from entering

Nonessential amino acids and potassium ions

are actively pumped from the brain to theblood

Fats, respiratory gases and other fat-soluble

molecules easily diffuse through the barrier

The Cranial Nerves

12 pairs Primarily serve the head and neck

Only one pair (vagus nerve) extends to the

thoraco-abdominal cavity Numbered in order

I: Olfactory

II: OpticIII: Oculomotor

IV: Trochlear

V: TrigeminalVI: Abducens

VII: Facial

VIII: Vestibulocochlear (Acoustic)IX: Glossopharyngeal

X: Vagus

XI: [Spinal] AccessoryXII: Hypoglossal


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Most cranial nerves are mixed nerves (both

sensory and motor functions) Three pairs are purely sensory: Optic, olfactory,

vestibulocochlear Longest intracranial course: Abducens

Longest extracranial course: Vagus

Autonomic Nervous System

Motor subdivision of the PNS that controls body

activities automatically Two divisions:sympathetic and

parasympathetic

Has a chain of two motor neurons: Preganglionic axon

The neuron is in the brain and

spinal cord

Leaves the CNS to synapse withthe second motor neuron in a

ganglion outside the CNS

Postganglionic axon Extends from the ganglion to the

organ it serves

Parasympathetic Division

Cranial nerves III, VII, IX and X

Serve the head and neck organs

Synapse with the second motor neuron

in a terminal ganglion S2 to S4

Form the pelvic nerves (pelvic

splanchnic nerves) Most active when the body is at rest and not

threatened in any way

D division: digestion, defecation and

diuresis Neurotransmitter: acetylcholine (cholinergic)

Sympathetic Division thoracolumbar division

T1 to L2

Sympathetic chain ganglion (sympathetictrunk) lie alongside the vertebral column on

each side

Collateral ganglion: where the splanchnicnerves synapse to supply the abdominal and

pelvic organs

Neurotransmitter: norepinephrine (adrenergic)

The preganglionic axons of both

divisions release acetylcholine fight or flight response

E division: exercise, excitement, emergency

and embarrassment


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The Special Senses

The Eye About 2.5 cm in diameter

Extrinsic eye muscles aim the eye for following

moving objects and for convergence

Lacrimal apparatus: lacrimal gland and series of

ducts that produce tears (for washing andlubricating the eyeball)

Eyelids protect the eyes

Conjunctiva: mucous membrane that covers theanterior eyeball and lines the eyelids

Sclera: outer, tough, protective tunic (anterior

portion is the cornea) Choroid: middle tunic

Provides nutrition to the internal eye

structures

Prevents lights scattering in the eye Retina: innermost (sensory) coat

Contains photoreceptors (rods and

cones) Fovea centralis: contains only cones

Blind spot: optic disk

Lens: major light-bending structure of the eye Pathway of light:

cornea aqueous humor pupil aqueous humor

lens vitreous humor retina

Pathway of nerve impulses in the eye

Optic nerve optic chiasma optic tract

thalamus optic radiation visual cortex in theoccipital lobe of the brain


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The Ear

Three major areas: outer ear, middle ear, inner

ear

Outer Ear

Pinna, external auditory canal, and tympanicmembrane

Involved in sound transmission only

Middle Ear

Ossicles and auditory tube Involved with sound transmission only

Inner Ear Bony labyrinth

Cochlea, vestibule, and semicircular canal

Contains perilymph and membranous sacs filledwith endolymph

Equilibrium receptors within the membranous

sacs of the vestibule and semicircular canal Hearing receptors within the membranes of the

cochlea Organ of Corti:

Contains hair cells Stimulated by sound vibrations

transmitted through air, membranes,

bone and fluids Deafness

Conduction deafness: transmission of

sound vibrations through the externaland middle ears is hindered

Sensorineural deafness: there is

damage to the nervous systemstructures involved in hearing

Semicircular Canals Receptors are for dynamic equilibrium

Respond to angular or rotational body

movements

Vestibule Receptors are for static equilibrium

Respond to pull of gravity and report on headposition

Chemical Senses

Smell and Taste

Chemoreceptors: receptors for taste and

olfaction

Respond to chemicals in solution Olfactory receptors: located in the superior

aspect of each nasal cavity

Olfactory pathways are closely linked to thelimbic system


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Gustatory cells are located in the taste buds Four major taste sensations: sweet, salty, sour

and bitter

Taste and appreciation of foods are influenced

by the sense of smell and the temperature andtexture of foods

brain and special senses

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