Chapter 14: Brain and Cranial Nerves

Brain is divided into?

Three parts

Cerebrum

Cerebellum

Brainstem

Cerebrum?

Makes up a bulk of the brain and is separated into two cerebral → hemispheres

Longitudinal fissure?

Separates the left and right hemispheres

Corpus callosum?

Connects the hemispheres

Cerebellum?

Is posterior and inferior to the cerebrum

Separated by the cerebrum by the transverse cerebral fissure

Brainstem?

Consists of the midbrain, pons, and medulla oblongata

Gray matter?

Contains nerve cell bodies, dendrites, and synapses

Dull color due to → little myelin

Forms surface layer (cortex) over cerebrum and cerebellum

Forms nuclei masses deeper within the brain

White matter?

Bundles of tracts, which are bundles of axons (nerve fibers)

Deep to the gray matter, opposite to the spinal cord

Pearly white color from myelin around nerve fibers

Connect one part of the brain to another, and to the spinal cord

Meninges?

Three connective tissue membranes that surround the brain

Lie between the nervous tissue and bone

Protect the brain and provide structural framework for its arteries and veins

Cranial dura mater has?

Two layers

Outer periosteal

Inner meningeal

Outer periosteal?

Equivalent to periosteum of cranial bones

Dural sinuses form where these layers separate, act to collect blood circulating through brain

Inner meningeal?

Continues into the → vertebral canal

Dural sinuses form where these layers separate, act to collect blood circulating through brain

Dura mater is?

Pressed closely against cranial bones

No epidural space

Dura mater have?

Three extensions that separate the parts of the brain

Falx cerebri

Tentorium cerebelli

Falx cerebelli

Falx cerebri?

Separates the cerebral → hemispheres

Tentorium cerebelli?

Separates the cerebrum from the cerebellum

Falx cerebelli?

Separates the hemispheres of the → cerebellum

Arachnoid mater?

Transparent membrane over the brain → surface

Subarachnoid space separates it from pia mater below

Filled with cerebrospinal fluid and blood vessels

Pia mater?

Very thin membrane that follows contours of brain

Follows arteries as they penetrate into the cerebrum

There are four internal chambers called?

Ventricles in the brain that are filled with CSF

Two Lateral ventricles?

One in each → cerebral hemisphere

Interventricular foremen?

Tiny pores that connect the lateral and third ventricles

Third ventricle?

Narrow cavity along the → midline (thalamus)

Cerebral aqueduct?

Runs through the midbrain and connects third to fourth ventricle

Fourth ventricle?

Between the brainstem and the → cerebellum

Connects to the central canal that runs through the → spinal cord

Choroid plexus?

Produce a majority of CSF, and consist of a network of blood capillaries on the ventricle floors

Substances from blood plasma are modified and secreted by ependymal cells of choroid plexuses to produce CSF

Cerebrospinal fluid (CSF) is continually produced

Cerebrospinal fluid (CSF)?

Clear, colorless liquid that fills the ventricles and canals of CNS

Bathes its external surface

Carries a small amount of O2, glucose, and other necessary chemicals (Na+ and K+)

This fluid is continuously circulating around the brain in ventricles and spinal cord in the subarachnoid space

There are tight junctions between?

Ependymal cells, which keep materials entering the CSF from leaking between cells

Called the blood-cerebrospinal fluid → barrier

Blood-cerebrospinal fluid barrier?

Protects against harmful substances like bacteria, viruses, and fungi that may be in the blood from blood from entering the CSF

CSF continually flows through and around the what?

CNS

Driven by its own pressure, beating of ependymal cilia, and pulsations of the brain produced by each heartbeat

CSF is secreted in?

Lateral ventricles, flows through intervertebral foramina, and into the third ventricle

From the third ventricle CSF moves down the cerebral aqueduct into the fourth ventricle

Third and fourth ventricles add more CSF along the way

Small amount of CSF fills central canal of spinal cord

All CSF escapes through three pores?

Median aperture and two lateral apertures

Leads into subarachnoid space of brain and spinal cord surface

CSF is reabsorbed by?

Arachnoid granulations

Cauliflower-shaped extension of the arachnoid villi (villus)

Protrude through dura mater into superior sagittal sinus

CSF penetrates the walls of the villi and mixes with the blood in the sinus

Goes back into the circulatory system

CSF functions?

Buoyancy

Protection

Chemical stability

Buoyancy?

The brain and CSF have a similar → density

Brain hangs from fibroblasts and has a lower weight when suspended in CSF

Protection?

CSF prevents the brain from hitting the cranium when the head is jolted

But it can’t protect against severe jolting, which can damage the brain

Chemical stability?

CSF removes wastes from nervous tissue and regulates chemical levels

Slight changes in CSF composition can cause nervous system → malfunctions

The internal carotid and vertebral arteries bring blood where?

To the brain

Blood drains into the internal jugular vein and is?

Returned to the heart

Blood-brain barrier (BBB)?

Consists of tight junctions that seal blood capillaries, endothelial cells, and a thick basement membrane that surrounds them

Glucose can cross the BBB by active transport

Proteins and antibiotics → do not

O2, CO2, alcohol, and anesthetic drugs → flow freely

Medulla oblongata?

Continuous with the superior part of the → spinal cord

Contains sensory (ascending) and motor (descending) tracts

Allows for each side of the brain to control voluntary movements on the opposite side of the body

Medulla contains nuclei with the?

Cardiac center

Vasomotor center

Respiratory center

Also controls reflexes for vomiting, swallowing, sneezing, coughing, yawning, and hiccupping

Cardiac center?

Regulates force of our heartbeat

Vasomotor center?

Regulates blood pressure and flow by changing blood vessel → diameter

Respiratory center?

Makes adjustments to the base rhythm of → breathing

Pons?

Superior to the medulla oblongata and is anterior to the cerebellum

Pons is described as a “bridge” connecting parts of the brain with one another with → axons

Some pons axons connect the right and left sides of the cerebellum, while others are part of ascending (sensory) and descending (motor) → tracts

Plays a role in coordination and efficient voluntary skeletal muscle movements from the cerebrum to the cerebellum

Pontine respiratory group?

Helps control breathing along with the medullary respiratory system

Cerebral peduncles?

Thick stalks on posterior pons that connect it (and the midbrain) to the cerebellum

Sensory roles: hearing, equilibrium, taste, facial sensations

Motor roles: eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears

Midbrain?

Extends from the pons to the diencephalon

Cerebral aqueduct passes through this part of the brainstem

Surrounded by central gray matter involved in controlling → pain

Midbrain contains both → nuclei and tracts

Superior colliculi?

Visual attention, tracking moving objects, and some reflexes

Inferior colliculi?

Relays signals from inner ear to thalamus and other parts of the brain

Reticular formation?

Is a loose web of gray matter that runs vertically through all levels of the → brainstem

Integrate visual, auditory, balance and motion stimuli into motor coordination

Gaze centers: allow eyes to track and fixate on objects

Produce rhythmic signals to the muscles of breathing and swallowing

Somatic motor control?

Adjust muscle tension

Relay signals from eyes and ears to cerebellum

Cardiovascular control?

Cardiac and vasomotor centers of the → medulla

Pain modulation?

Some pain signals ascend through the reticular formation

Some descending analgesic (pain relieving) pathways begin in the reticular formation

They end in the spinal cord where they block transmission of pain signals

Sleep and consciousness?

Reticular formation plays a central role in consciousness, alertness, and sleep

Injury here can result in irreversible → coma

Habituation?

Modulates activity in cerebral cortex so that it ignores repetitive, inconsequential stimuli

Cerebellum?

Found in the inferior and posterior parts of the skull

Primary function is to evaluate movements initiated by the motor areas of our cerebrum

If the movements are incorrect the cerebellum detects this and sends out feedback signals to motor areas in the cerebral cortex through the → thalamus

Feedback signal correct the errors by smoothing out the movements and coordinating complex skeletal muscle movements

Diencephalon?

Consists of the thalamus, hypothalamus, and epithalamus

Thalamus?

Located superior to the midbrain, makes up most of the diencephalon

Gateway to the cerebral cortex: nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex

Composed of at least 23 nuclei within five major functional groups

Thalamus does what else?

Plays key role in motor control by relaying signals from cerebellum to cerebrum and providing feedback loops between the cerebral cortex and the basal nuclei

Involved in the memory and emotional functions of the limbic system

Hypothalamus?

Forms part of the walls and floor of the third ventricle

Extends anteriorly to optic chiasm and posteriorly to → mammillary bodies

Each mammillary body contains three or four mammillary nuclei

Relay signals from the limbic system to the thalamus

Infundibulum?

Stalk attaching pituitary to hypothalamus

Hypothalamus is a major what?

Major control center of autonomic nervous system and endocrine system

Plays essential role in homeostatic regulation of all body systems

Hormone secretion(Hypothalamus)?

Controls anterior pituitary: regulating growth, metabolism, reproduction, and stress responses

Produces posterior pituitary hormones for labor contractions, lactation, and water conservation

Autonomic effects(Hypothalamus)?

Major integrating center for autonomic nervous system

Influences heart rate, blood pressure, gastrointestinal secretions, motility, etc.

Thermoregulation(Hypothalamus)?

Hypothalamic thermostat monitors body temperature

Food and water intake(Hypothalamus)?

Regulates hunger and satiety responds to hormones influencing hunger, energy expenditure, and long-term control of body mass

Thirst center monitors osmolarity of blood and can stimulate production of antidiuretic hormone (ADH)

What else does the Hypothalamus have?

Sleep and circadian rhythms

Memory(Hypothalamus)?

Mammillary nuclei receive signals from the → hippocampus

Emotional behavior and sexual response(Hypothalamus)?

Anger, aggression, fear, pleasure, contentment, sexual drive

Epithalamus?

Very small mass of tissue composed of Pineal gland and Habenula

Pineal gland?

Endocrine gland that produces → melatonin

Habenula?

Relay from the limbic system to the midbrain

Cerebrum?

Largest, most visible part of the human brain

Responsible for sensory perception, memory, thought, judgment, and voluntary motor actions

Cerebrum is separated into left and right what?

Hemispheres

Left hemisphere of cerebrum?

Controls the right side of the body and helps with math, analytical, and speech skills

Right hemisphere of cerebrum?

Controls the left side of the body and helps with music, art and abstract ideas

Frontal lobe?

Voluntary motor functions, motivation, foresight, planning, memory, mood, emotion, social judgment, and aggression

Parietal lobe?

Integrates general senses, taste, and some visual information

Occipital lobe?

Primary visual center of brain

Temporal lobe?

Functions in hearing, smell, learning, memory, and some aspects of vision and emotion

Insula (hidden by other regions)?

Helps in understanding spoken language, taste, and integrating information from visceral receptors

Most of the volume of cerebrum is?

White matter

Glia and myelinated nerve fibers that → transmit signals

Tracts are?

Are bundles of nerve fibers in the central nervous system

Three types of tracts: projection tracts, commissural tracts, and association tracts

Neural integration is carried out in the what?

Gray matter of the cerebrum

Cerebral gray matter found in what three places and has two principle neurons?

Cerebral cortex Stellate cells

Basal nuclei Pyramidal cells

Limbic system

Cerebral cortex?

Covers the surface of the hemispheres

90% of human cerebral cortex is neocortex – six-layered tissue that has relatively recent evolutionary origin

Stellate cells?

Receive sensory input and process information on a local level

Pyramidal cells?

Include the output neurons of the cerebrum

Only neurons that leave the cortex and connect with other parts of the → CNS

Limbic System?

Important center of → emotion and learning

Hippocampus?

Memory functions

Amygdala?

Emotion functions

Limbic system structures have centers for both what?

Gratification and Aversion

Gratification?

Sensations of → pleasure or reward

Aversion?

Sensations of → fear or sorrow

Basal nuclei?

Masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus

Receive input from the midbrain and the motor areas of the cortex

Send signals back to both of these locations

Involved in motor control

Olfactory (I) nerve?

Sensory nerve, contains axons that conduct nerve impulses for the sense of → smell (olfaction)

Found in the nasal cavity and are made up of bipolar neuron

In the nose these nerves are paired with olfactory bulbs – two gray matter extension in the brain

Signals go to the temporal lobe, which is the primary olfactory area

Optic (II) Nerve?

Sensory nerve, axons conduct nerve impulses for → vision

Bipolar neurons receive signals from the → retina, rods, and cones

Optic nerves merge and form the → optic chiasm

Optic tracts are formed in this area

Send signals to the primary visual areas of the occipital lobe of the cerebrum

Vestibulocochlear (VIII) nerve?

Sensory nerve with two branches

Vestibular nerve – carries impulses for → equilibrium

Extends from the semicircular canals, the saccule, and the utricle of the inner ear

Send signals to the → cerebellum