The Brain and Cranial Nerves Chapter 14 The Brain and Cranial Nerves

The Brain The Brain is part of Central Nervous System (CNS) It is divided into 6 major parts: The cerebrum The diencephalon The mesencephalon The cerebellum The pons The medulla oblongata

Major divisions of the Brain

The real thing Fig.14.01b

The Human 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)

Protection of the Brain The brain is protected by bone, meninges, and cerebrospinal fluid Harmful substances are shielded from the brain by the blood-brain barrier

Cerebrospinal fluid Protects by absorbing shock (it “floats” the brain. Maintains the electrochemical environment (opitmal pH & osmolality). Circulates nutrients and wastes.

The Ventricles

Formation of CSF

Choroid Plexuses Figure 12.25a

Fig. 14.04c Cirulaation of CSF

Meninges Three connective tissue membranes lie external to the CNS – dura mater, arachnoid mater, and pia mater Functions of the meninges Cover and protect the CNS Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions within the skull

The Meninges of the Brain

Dura Mater Three dural septa extend inward and limit excessive movement of the brain Falx cerebri – fold that dips into the longitudinal fissure Falx cerebelli – runs along the vermis of the cerebellum Tentorium cerebelli – horizontal dural fold extends into the transverse fissure

Dural Folds Falx cerebri, tentorium cerebelli, and falx cerebelli Figure 14–3b

Arachnoid Mater The middle meninx, which forms a loose brain covering It is separated from the dura mater by the subdural space Beneath the arachnoid is a wide subarachnoid space filled with CSF and large blood vessels Arachnoid villi protrude superiorly and permit CSF to be absorbed into venous blood

Blood flow, O2 and the BBB Though only 2% of body mass the brain consumes 20% of the oxygen and glucoseof the resting body. No O2 for a minute = dizziness 4 minutes = brain damage 6 minutes = death The brain is protected by the blood-brain barrier.

Blood-Brain Barrier: Functions Selective barrier that allows nutrients to pass freely Is ineffective against substances that can diffuse through plasma membranes Absent in some areas (vomiting center and the hypothalamus), allowing these areas to monitor the chemical composition of the blood Stress increases the ability of chemicals to pass through the blood-brain barrier

The Blood-brain barrier

The Brain Stem The brain stem is comprised of 3 main subdivisions: The Medulla Oblongata The Pons The Mesencephalon

The diencephalon & brainstem

Medulla Oblongata: 3 Groups of Nuclei Autonomic nuclei: control visceral activities Sensory and motor nuclei: of cranial nerves Relay stations: along sensory and motor pathways

Nuclei of the medulla oblongata

Summary: The Medulla Oblongata Table 14-2

Links cerebellum with mesencephalon, diencephalon, cerebrum, and spinal cord The Pons Figure 14–6c

The Pons: 4 Groups Sensory and motor nuclei of cranial nerves V, VI, VII, VIII Nuclei involved with respiration: apneustic center and pneumotaxic center modify respiratory rhythmicity center activity

The Pons: 4 Groups Nuclei and tracts: process and relay information to and from cerebellum Ascending, descending, and transverse tracts: transverse fibers (axons) link nuclei of pons with opposite cerebellar hemisphere

The Cerebellum An autonomic & motor processing center Figure 14–7a

Functions of the Cerebellum Adjusts postural muscles Fine-tunes conscious and subconscious movements

Structures of the Cerebellum Figure 14–7b

Structures of the Cerebellum (1 of 2) Folia: surface of cerebellum highly folded neural cortex Anterior and posterior lobes: separated by primary fissure

Structures of the Cerebellum (2 of 2) Cerebellar hemispheres: separated at midline by vermis Vermis: narrow band of cortex Flocculonodular lobe: below fourth ventricle

Summary: The Cerebellum Table 14-3

The Mesencephalon Figure 14–8a

Midbrain nuclei Substantia nigra: dopamine release, control of subconscious muscle movents. Red nuclei: synapses between neurons of cerebellum and cerebrum. Also origin of oculomotor nerve (CN III) and trochlear nerve (CN IV).

Some major functions mesencephalon Cerebral peduncles: contain motor axons connecting cerebrum to brain stem and sensory axons that connect medulla to thalamus Tectum: Superior colliculi: visual reflexes, including pupillary reflexes. Inferior colliculi: auditory path from ear to thalamus. Startle reflex

Summary: The Mesencephalon Table 14-4

The Diencephalon The Thalamus - switch board for the cerebrum. Includes the: Geniculate nuclei (part of the ventral group): Medial processes auditory information. Lateral processes visual input. Other ventral nuclei connect motor & sensory areas of cortex to cerebellum & spinal cord Anterior & medial nuclei Anterior connects to limbic system & hypothalamus Medial connects with cortex & limbic system

The Diencephalon

The Thalamus: Filters ascending sensory information for primary sensory cortex. Relays information between basal nuclei and cerebral cortex Figure 14–9

Those pesky thalamic nuclei Fig. 14.09a-d

Oblique section of brain showing the Thalamus and basal nuclei Fig. 14.09e Oblique section of brain showing the Thalamus and basal nuclei

Summary: Thalamic Nuclei Table 14-5

The Hypothalamus Functions of the hypothalamus ANS control , heart rate, respiration, sweating, digestion, urination, stress response Hormones - ADH, oxytocin, GnRH et al. Basic emotions - rage, sex drive, fear, pain pleasure. Thirst & appetite Temperature & sleep/wake (circadian) cycles

The Hypothalamus Lies below thalamus Figure 14–10a

Summary: The Hypothalamus Table 14-6

The Limbic System Is a functional grouping that: establishes emotional states links conscious functions of cerebral cortex with autonomic functions of brain stem facilitates memory storage and retrieval

The Limbic System Figure 14–11a

The Limbic System Figure 14–11b

Limbic System Structures located on the medial aspects of cerebral hemispheres and diencephalon Includes the rhinencephalon, amygdala, hypothalamus, and anterior nucleus of the thalamus Parts especially important in emotions: Amygdala – deals with anger, danger, and fear responses Cingulate gyrus – plays a role in expressing emotions via gestures, and resolves mental conflict Puts emotional responses to odors – e.g., skunks smell bad

Limbic System: Emotion and Cognition The limbic system interacts with the prefrontal lobes, therefore: One can react emotionally to conscious understandings One is consciously aware of emotion in one’s life Hippocampal structures – convert new information into long-term memories

Summary: The Limbic System Table 14-7

The Cerebrum Major divisions of the Cerebrum Hemispheres - left and right split down the middle by the longitudinal fissure. Lobes: Frontal, parietal, occipital, temporal and insula Delineated by the sulci (singular sulcus): Central Parieto-occipital Lateral

Lobes of the Cerebrum

Landmarks of the cerebrum

White Matter of the Cerebrum Myelinated fibers (axons) Association fibers Commissural fibers Projection fibers Figure 14–13

Cerebral White Matter

The Basal Nuclei Figure 14–14b, c

Functions of Basal Nuclei Are involved with: the subconscious control of skeletal muscle tone the coordination of learned movement patterns (walking, lifting)

Functional map of the cerebrum Fig. 14.15

Motor and Sensory Areas of the Cortex Figure 14–15a

Interpretive Areas of Cortex Figure 14–15b

Hemispheric Lateralization Figure 14–16

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)

The Electroencephalogram Figure 14–17

Types of Brain Waves Alpha waves – 8 - 13 Hz, regular and rhythmic, low-amplitude, slow, synchronous waves indicating an “idling” brain Beta waves – 14 - 30 Hz, rhythmic, more irregular waves occurring during the awake and mentally alert state Theta waves – 4 - 7 Hz, more irregular than alpha waves; common in children but abnormal in adults Delta waves – 1 - 5 Hz, high-amplitude waves seen in deep sleep and when reticular activating system is damped

Brain Waves: State of the Brain Brain waves change with age, sensory stimuli, brain disease, and the chemical state of the body EEGs can be used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions A flat EEG (no electrical activity) is clinical evidence of death

Cranial Nerves Figure 14–18

The 12 cranial nerves On Old Olympus’ Towering Top A Frenchman Viewed Greek Villagers At Home The 12 cranial nerves

The Olfactory Nerve (I) Figure 14–19

The Optic Nerves (II) Figure 14–20

The Oculomotor Nerves (III) Figure 14–21

The Trochlear Nerves (IV) Figure 14–21

The Abducens Nerves (VI) Figure 14–21

The Trigeminal Nerves (V) Figure 14–22

The Facial Nerves (VII) Figure 14–23

The Vestibulocochlear Nerves (VIII) Figure 14–24

The Glossopharyngeal Nerves (IX) Figure 14–25

The Vagus Nerves (X) Figure 14–26

The Accessory Nerves (XI) Figure 14–27

The Hypoglossal Nerves (XII) Figure 14–27

Summary: Cranial Nerves Table 14-9 (1 of 2)

Summary: Cranial Nerves Table 14-9 (2 of 2)

Examples of Cranial Reflexes Table 14-10

Clinical Stuff Epilepsy CVA & TIA Degenerative Diseases Alzheimers Huntington’s Parkinbson’s

Epilepsy A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking, characteristic of epileptic seizure Epilepsy is not associated with, nor does it cause, intellectual impairments Epilepsy occurs in 1% of the population

Epileptic Seizures Absence seizures, or petit mal – mild seizures seen in young children where the expression goes blank Grand mal seizures – victim loses consciousness, bones are often broken due to intense convulsions, loss of bowel and bladder control, and severe biting of the tongue

Control of Epilepsy Epilepsy can usually be controlled with anticonvulsive drugs Valproic acid, a nonsedating drug, enhances GABA and is a drug of choice Vagus nerve stimulators can be implanted under the skin of the chest and can keep electrical activity of the brain from becoming chaotic

Cerebrovascular Accidents (Strokes) Caused when blood circulation to the brain is blocked and brain tissue dies Most commonly caused by blockage of a cerebral artery Other causes include compression of the brain by hemorrhage or edema, and atherosclerosis Transient ischemic attacks (TIAs) – temporary episodes of reversible cerebral ischemia Tissue plasminogen activator (TPA) is the only approved treatment for stroke

Degenerative Brain Disorders Alzheimer’s disease – a progressive degenerative disease of the brain that results in dementia Parkinson’s disease – degeneration of the dopamine-releasing neurons of the substantia nigra Huntington’s disease – a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei