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