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Brain & Cranial Nerves
The Brain
Ranges from 750 cc to 2100 cc
Contains almost 98% of the body’s neural tissue
Average weight about 1.4 kg (3 lb)
6 Major Regions of the Brain
Cerebrum
Cerebellum
Diencephalon
Mesencephalon
Pons
Medulla oblongata
The Brain
Cerebrum
Largest part of brain
Controls higher mental functions
Divided into left and right cerebral hemispheres
Surface layer of gray matter (neural cortex)
Cerebral Cortex
3 Functional Principles of the Cerebrum
1. Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of body
3 Functional Principles of the Cerebrum
2. The 2 hemispheres have different functions although their structures are alike
3 Functional Principles of the Cerebrum
3. Correspondence between a specific function and a specific region of cerebral cortex is not precise
Motor & Sensory Areas of the Cerebral
Cortex
Where are the motor, sensory, and association
areas of the cerebral cortex, and what are their functions?
Central sulcus separates motor and sensory areas
Motor Areas Precentral gyrus of frontal lobe:
directs voluntary movements
Primary motor cortex: is the surface of precentral gyrus
Pyramidal cells: are neurons of primary motor
cortex
Sensory Area Postcentral gyrus of parietal lobe:
receives somatic sensory information (touch, pressure, pain, vibration, taste, and temperature)
Primary sensory cortex: surface of postcentral gyrus
Special Sensory Cortexes
Visual cortex: information from sight receptors
Auditory cortex: information from sound receptors
Olfactory cortex: information from odor receptors
Gustatory cortex: information from taste receptors
Sensory Association Areas
Somatic sensory association area: interprets input to primary sensory
cortex (e.g., recognizes and responds to touch)
Visual association area: interprets activity in visual cortex
Auditory association area: monitors auditory cortex
Other Integrative Areas
Speech center: is associated with general
interpretive area coordinates all vocalization
functions
Prefrontal cortex of frontal lobe: integrates information from
sensory association areas performs abstract intellectual
activities (e.g., predicting consequences of actions)
Hemispheric Lateralization
Functional differences between left and right hemispheres
Each cerebral hemisphere performs certain functions not performed by the opposite hemisphere
The Left Hemisphere
In most people, left brain (dominant hemisphere) controls: reading, writing, and math decision-making speech and language
The Right Hemisphere
Right cerebral hemisphere relates to: senses (touch, smell, sight,
taste, feel) recognition (faces, voice
inflections)
Cerebellum
Second largest part of brain
Coordinates repetitive body movements
2 hemispheres
Covered with cerebellar cortex
The Cerebellum
An autonomic processing center
Functions of the Cerebellum
1. Adjusts postural muscles
2. Fine-tunes conscious and subconscious movements
Structures of the Cerebellum
Structures of the Cerebellum
Folia: surface of cerebellum highly folded neural cortex
Anterior and posterior lobes: separated by primary fissure
Structures of the Cerebellum
Cerebellar hemispheres: separated at midline by
vermis
Vermis: narrow band of cortex
Flocculonodular lobe: below fourth ventricle
Purkinje Cells
Large, branched cells
Found in cerebellar cortex
Receive input from up to 200,000 synapses
Arbor vitae
Highly branched, internal white matter of cerebellum
Cerebellar nuclei: embedded in arbor vitae relay information to Purkinje
cells
The Peduncles
Tracts link cerebellum with brain stem, cerebrum, and spinal cord: superior cerebellar peduncles middle cerebellar peduncles inferior cerebellar peduncles
Diencephalon Composed of
Epithalmus Hypothalamus thalamus
The Thalamus Final relay point for ascending sensory
information
Coordinates the activities of the cerebral cortex
Hypothalamus Controls somatic motor activities
subconsciously Rage, pleasure, pain, & sexual arousal
Controls autonomic function Regulate heart rate, blood pressure,
respiration, & digestive function
Coordinates activities of the nervous and endocrine systems Inhibits or stimulates endocrine cells in the
pituitary gland
Hypothalmus cont. Secrete 2 hormones
Antidiuretic hormone – restricts water loss at the kidneys
Oxytocin –stimulates smooth muscle contractions Uterus/mammary glands Prostrate gland
Produce emotions & behavioral drives Feeding center, thirst center
Hypothalmus cont. Coordinate voluntary & autonomic functions
Think about a dangerous situation Heart rate increases, respiratory rate
goes up
Regulates body temperature If temp. falls instructions sent to medulla
oblongata to dialate blood vessels
Controls Circadian rhythms 24 hour, day-night cycle
Retina of the eye
Medulla Oblongata
Connects brain and spinal cord
The Pons
Sensory & motor nuclei for 4 cranial nerves
Nuclei that help control respiration
Nuclei & tracts linking the cerebellum with the brain stem, cerebrum, and spinal cord
Ascending, descending & transverse tracts
Cranial Nerves I – olfactory nerves – sensory
Sense of smell
II – optic nerves – sensory Visual information
III – oculomotor – motor Motor eye movements
IV – Trochlear Nerves – motor Superior oblique muscle
Cranial Nerves V - Trigeminal Nerves - mixed, sensory
Motor – jaw, mastication, eyelid, eyebrow, lips, gums. teeth, cheek
Sensory – forehead, palate, nasal cavity
VI - Abducen Nerves - motor Motor eye movement, lateral rectus
VII - Facial – mixed Sensory – anterior 2/3 of tongue Motor – lacrimal gland, nasal mucous gland,
submandibular & sublingual salivary glands
Cranial Nerves VIII – Vestibulocochlear Nerves -
sensory Special sensory – balance &
equilibrium, hearing
IX – Glossopharyngeal – mixed Sensory – posterior 1/3 of tongue, part
of the pharynx & palate, carotid arteries
Motor – pharyngeal muscles, parotid salivary gland
Cranial Nerves X – Vagus – mixed
Sensory – pharynx, diaphragm, Motor – pharyngeal muscles, visceral
organs in thorax & abdominal cavity
XI – Accessory Nerves - motor Muscles of neck & upper back
XII – Hypoglossal Nerves – motor Tongue movement