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 Adjusts postural muscles 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 XI – Accessory Nerves - motor 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