The Brain (& CNS)

Lecture 12aBIOL241

Final Exam (Exam 4)• Chapters 11 – 15*• 100 points• Multiple choice, T/F, matching, fill in• Short answer, essays (2)*• Labeling (brain [including functions],

cranial nerves, spinal cord)

Outline• Overview of the human brain• Tour through the brain – structures and

functions• Cerebral hemispheres and higher mental

functions• Meninges• Ventricles and CSF• Brain disorders

The Human Brain• Composed of wrinkled, pinkish gray tissue• Surface anatomy includes cerebral

hemispheres, cerebellum, and brain stem• Ranges from 750 cc to 2100 cc• Contains almost 98% of the body’s neural

tissue• Average weight, adult: 1300 – 1400 gm (~3 lb)• 1010 to 1011 neurons• Trillions of connections• men = larger• Women = better connected

Figure 14–1

Major Regions and Landmarks

Table 14-1

Embryology of the Brain

Regions of the Adult Brain• Telencephalon (cerebrum) – cortex, white

matter, and basal nuclei• Diencephalon – thalamus, hypothalamus,

and epithalamus• Mesencephalon –midbrain (brain stem)• Metencephalon – pons (brain stem),

cerebellum• Myelencephalon – medulla oblongata

(brain stem)

Basic Pattern of the Central Nervous System• Spinal Cord

– Central cavity surrounded by a gray matter core

– External to which is white matter composed of myelinated fiber tracts

• Brain– Similar to spinal cord but

with additional areas of gray matter

– Cerebellum has gray matter in nuclei

– Cerebrum has nuclei and additional gray matter in the cortex

Figure 12.4

Some terms• nucleus: collection of neuron cell

bodies in the CNS• tract: collection of axons in the CNS• ganglia: collection of neuron cell

bodies in the PNS• nerve: collection of axons in the PNS

– Cranial nerves– Spinal nerves

Tour of the brain• From caudal/inferior to rostral/superior

The Brain Stem• Processes information between spinal cord and

cerebrum or cerebellum• Controls automatic behaviors necessary for

survival• Associated with 10 of the 12 pairs of cranial

nerves (covered later)• Includes:

– mesencephalon (midbrain)– pons– medulla oblongata– Note: some consider the diencephalon part of the

brain stem as well

Brain Stem

Figure 12.15a

Anatomy:Brain stem

Most cranial nerves are located in the brain stem

Brain Stem

Figure 12.15b

Posterior view

Medulla Oblongata • Most inferior part of brain, connects brain to

spinal cord• Relays information• Pyramids – two longitudinal ridges formed by

corticospinal tracts• Regulates autonomic functions:

– regulates arousal, heart rate, blood pressure, pace for respiration and digestion

• Cranial nerves IX, X, XI, XII come off or enter

Medulla Oblongata

Figure 12.16c

Medulla Oblongata

Medulla Nuclei• Cardiovascular control center – adjusts

force and rate of heart contraction• Respiratory centers – control rate and

depth of breathing• Additional centers – regulate vomiting,

hiccupping, swallowing, coughing, and sneezing

Pons

Pons • Involved in somatic and visceral motor control• Contain the nuclei for cranial nerves V, VI, VII,

VIII• Contains nuclei of the reticular formation• Control of respiration that modifies the info from

the medulla• Nuclei and tracts passing through to the

cerebellum (motor and somatosensory info)• Nuclei and tracts to other portions of the CNS

(just passing through)

Cerebellum

Cerebellum• “little brain”• Second largest part of brain (~10% mass)• Provides precise timing and appropriate patterns of

skeletal muscle contraction to coordinate repetitive body movements and help learning complex motor behaviors

• Adjusts the postural muscles of the body, controls balance and equilibrium

• Has 2 hemispheres, covered with cerebellar cortex• Recognizes and predicts sequences of events• Cerebellar activity occurs subconsciously (as does

all processing that occurs outside the cerebral cortex)

Cerebellum – side view

Cerebellum• Cerebellum receives impulses of the intent to

initiate voluntary muscle contraction• Monitors all proprioceptive info and visual info

about body position• Cerebellar cortex calculates the best way to

perform a movement• Programs and fine tunes movements by

detecting mismatches in intended and actual movements

-- when learning to ride a bike, throw a curve ball or tie your shoe, cerebellum activity is high. When they become automatic, cerebellum is no longer involved

Mesencephalon

Mesencephalon

• Also called midbrain• Processes sight, sound, and associated

reflexes• Maintains consciousness • Cranial nerve nuclei III and IV• 2 basic divisions

– tectum (roof)– tegmentum

Mesencephalon• Process of visual and auditory sensations

– corpora quadrigemina (in tectum) = superior colliculi (visual reflex) and inferior colliculi (auditory reflex)

• Substantia nigra (in tegmentum)– Neurons inhibit activity of cerebral nuclei by releasing

dopamine– If damaged, results in less dopamine released and muscle

tone increases: muscle rigidity, difficulty initiating movement = Parkinson’s Disease

• Reticular formation: maintain consciousness

Midbrain Nuclei

Figure 12.16a

Mesencephalon

Diencephalon

Figure 12.12

Diencephalon• Located under

cerebrum and cerebellum

• Links cerebrum with brain stem

• Integrates sensory information and motor commands

• Cranial nerve II

Diencephalon• Pineal Gland

– Secretes hormone melatonin• Thalamus:

– relays and processes sensory information• Hypothalamus:

– hormone production– emotion– autonomic function

Diencephalon: Thalamus• Paired, egg-shaped

masses connected at the midline by the intermediate mass

• Nuclei project to and receive fibers from the cerebral cortex

Figure 14–9

Thalamus• Sensory Relay station• All sensory that is projected to the cerebral

cortex stops here first except smell• Filters ascending sensory information for

primary sensory cortex• Relays information between basal nuclei

and cerebral cortex• Mediates sensation, some motor activities,

cortical arousal (thus learning, and memory)

Figure 14–10a

Diencephalon: Hypothalamus• Lies below thalamus

Hypothalamus

• Captain of the Autonomic nervous system, master overseer of homeostasis– Emotions and behavior: mediates perception of

pleasure, fear, and rage– Regulation of body temperature, blood pressure,

digestive tract motility, rate and depth of breathing, and many other visceral activities

– Food intake (drives)– Water balance/thirst– Day/night rhythms– Endocrine functions- ADH and oxytocin

Structures of the Hypothalamus

• Mamillary bodies:– Relay station for olfactory information– control reflex eating movements

Pituitary Gland

• Major endocrine gland, controls all others

• Connected to hypothalamus via infundibulum (stalk)

• Interfaces nervous and endocrine systems because it is controlled by the hypothalamus

Telencephalon• Basal nuclei• Cerebrum

Figure 14–14b, c

The Basal Nuclei (Ganglia)

Basal Nuclei • Also called basal ganglia• Masses of gray matter found deep within the

cortical white matter• The corpus striatum is composed of three

parts– Caudate nucleus– Lentiform nucleus = putamen and the globus

pallidus– Fibers of internal capsule running between and

through caudate and lentiform nuclei• Direct subconscious activities

Functions of Basal Nuclei• Are involved with:

– Subconscious control of skeletal muscle tone– Regulate attention and cognition– Regulate intensity of slow or stereotyped

movements (walking, lifting)– Inhibit antagonistic and unnecessary

movement– Subconscious habit learning – May store simple movement patterns

Basal Nuclei

Figure 12.11b

Cerebrum

• Largest part of brain (make up 83% of its mass)

• Controls higher mental functions including all conscious thoughts and experience including all intellectual functions (more about this later)

• Processes somatic sensory and motor information

• Divided into left and right cerebral hemispheres

• Surface layer of gray matter (cerebral cortex)

(Cerebral) Cortex• Gray matter covering cerebral

hemispheres• Accounts for 40% of the mass of the

brain• Folded surface increases surface area• Elevated ridges = gyri (gyrus)• Shallow depressions = sulci (sulcus)• Deep grooves = fissures

Cerebral Gray and White Matter• Gray matter:

– Cell bodies– Found in cerebral cortex and basal nuclei

• White matter:– Fiber tracts (axons)– Deep to cerebral cortex– Surrounding basal nuclei

Figure 14–13

White Matter of the Cerebrum

• Myelinated fibers (axons)– Association fibers:

• arcuate: local• longitudinal: within one

hemisphere– Commissural: between

hemispheres– Projection: link

cerebral cortex with rest of CNS

Examples• Projection Fibers: Internal capsule

– all ascending and descending projection fibers to and from cerebral cortex, passes though basal nuclei

• Commissural fibers: corpus callosum– Connect the two cerebral hemispheres

Fiber Tracts in White Matter

Figure 12.10b

Limbic System

Figure 12.18

The Limbic System• One of two networks of neurons working

together and spanning wide areas of the brain – the other is the consciousness regulating reticular formation (where?)

• A of the medial functional grouping of the medial cerebral hemispheres and diencephalon that:– establishes emotional states and drives– links conscious functions of cerebral cortex with

autonomic functions of brain stem– Allows us to react emotionally to conscious

understanding and to be aware of emotions– facilitates memory storage and retrieval

Figure 14–11a

The Limbic System

Components of the Limbic System

• Amygdala– deals with anger, danger, and fear responses,

along with emotional smell memories• Limbic lobe of cerebral hemisphere:

– Cingulate gyrus: plays a role in expressing emotions via gestures, and resolves mental conflict (emotion)

– Hippocampus: convert new information into long-term memories (patient H.M.?)

Components of the Limbic System Continued

• Fornix:– tract of white matter that connects

hippocampus with hypothalamus • Diencepalic structures:

– Portions of thalamus, hypothalamus

Reticular Formation

Figure 12.19

Sends impulses to the cerebral cortex to keep it conscious and alert

Higher Level Functions ofCerebral Hemispheres

Figure 14–12b

The Cerebral Cortex4 Lobes:FrontalParietalTemporalOccipital

Cerebral cortex• It enables sensation, communication,

memory, understanding, and voluntary movements

• Temporal lobe: memory, hearing• Frontal lobe: executive function, language• Parietal lobe: sense of self• Occipital lobe: vision

Cerebral Cortex landmarks• Lateral sulcus • Longitudinal fissure• Central sulcus• Precentral gyrus (primary motor)• Postcentral gyrus (primary sensory)• Association areas are for integrating

information

Figure 14–15a

Motor and Sensory Areas of the Cortex

• Central sulcus separates motor and sensory areas

Functional Areas of the Cerebral Cortex

• The three types of functional areas are:– Motor areas – control voluntary movement– Sensory areas – conscious awareness of

sensation– Association areas – integrate diverse

information

Functional Areas of the Cerebral Cortex

Figure 12.8a

Functional Areas of the Cerebral Cortex

Figure 12.8b

Motor Areas• Precentral gyrus of frontal lobe:

– directs voluntary movements• Primary motor cortex:

– is the surface of precentral gyrus

Sensory Areas• Postcentral gyrus of parietal lobe:

– receives somatic sensory information (touch, pressure, pain, vibration, taste, and temperature)

• Primary sensory cortex:– surface of postcentral gyrus

Association Areas• Any brain region that receives input from

more than one sensory modality• aka “integrative areas” or higher level

association areas• Relative abundance determines intellectual

capacity • Include:

– Prefrontal cortex– Language areas– General (common) interpretation area– Visceral association area

Functional Principles of the Cerebral hemispheres

1. Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of body

2. The 2 hemispheres have somewhat different functions although their structures are alike

3. Correspondence between a specific function and a specific region of cerebral cortex is not precise

4. No functional area acts alone; conscious behavior involves the entire cortex

Higher level: Prefrontal Cortex• Most complicated region, coordinates

info from all other association areas• Important in intellect, planning,

reasoning, mood, abstract ideas, judgement, conscience, and accuratley predicting consequences

• Phineas Gage?

Phineas Gage

Phineas Gage• In 1848 in Vermont, had a 3.5-foot-long,

13 lb. metal rod blown into his skull, through his brain, and out of the top of his head. Gage survived. In fact, he never even lost consciousness.

• Friends reported a complete change in his personality after the incident. He lost all impulse control.

“Right Brain – Left Brain”

Hemispheric Lateralization• Functional differences between left and

right hemispheres• In most people, left hemisphere

(dominant hemisphere) controls:– reading, writing, and math, decision-making,

logic, speech and language (usually)• Right cerebral hemisphere relates to:

– recognition (faces, voice inflections), affect, visual/spatial reasoning, emotion, artistic skills

Brain Waves• Alpha waves – regular and rhythmic, low-

amplitude, slow, synchronous waves indicating an “idling” brain (drifting off)

• Beta waves – rhythmic, more irregular waves occurring during the awake and mentally alert state

• Theta waves – more irregular than alpha waves; common in children but abnormal in adults

• Delta waves – high-amplitude waves seen in deep sleep and when reticular activating system is damped

Types of Brain Waves

Figure 12.20b

Ventricles of the brain

Ventricles• Lined by ependymal cells which help to

form the choroid plexus• There are two lateral ventricles in the

cerebral hemispheres• Third ventricle is located in the

diencephalon• Fourth ventricle is located between the

pons and the cerebellum

Cranial meninges

Cranial meninges • Dura mater consists of an outer

(endosteal layer) and an inner (meningeal layer)– In between the layers find the dural sinus

• Arachnoid membrane covers the surface of the brain, have a subarachnoid space

• Pia mater is anchored to the brain by astrocytes, wraps brain tightly like saran wrap

Inter-Layer Spaces – just like in the brain

• Subdural space:– between arachnoid mater and dura mater

• Subarachnoid space:– between arachnoid mater and pia mater – contains collagen/elastin fiber network that’s

“spiderweb-like” (arachnoid trabeculae)– filled with cerebrospinal fluid (CSF)

Subdural, subarachanoid spaces are frequent sites of intracranial bleeding

Cerebrospinal Fluid (CSF)• Surrounds all exposed surfaces of CNS• Cushions, supports, and transports• Interchanges with interstitial fluid of brain• Like plasma or interstitial fluid elsewhere

except much more pure• Arachnoid villi protrude superiorly into

dural sinus and permit CSF to be absorbed into venous blood

Choroid Plexuses• Clusters of

capillaries lined by ependymal cells that form tissue fluid filters, which hang from the roof of each ventricle

• Have ion pumps that allow them to alter ion concentrations of the CSF

• Help cleanse CSF by removing wastes

CSF flow: through ventricles, to arachnoid space, to dural sinuses (back to circulation)

Blood Supply to the Brain• Supplies nutrients and oxygen to brain• Delivered by internal carotid arteries

and vertebral arteries• Removed from dural sinuses by

internal jugular veins

Blood–Brain Barrier• Isolates CNS neural tissue from general

circulation• Formed by network of tight junctions

between endothelial cells of CNS capillaries and by feet of astrocyte processes

• Astrocytes control blood–brain barrier by releasing chemicals that control permeability of endothelium

Blood–Brain Barrier

• Lipid–soluble compounds (O2, CO2), steroids, and prostaglandins diffuse into interstitial fluid of brain and spinal cord

• Other things have to be transported in

Cerebrovascular Disease• Disorders interfere with blood circulation to

brain• Stroke or cerebrovascular accident (CVA):

– shuts off blood to portion of brain– neurons die

• Tissue plasminogen activator (TPA) is the only approved treatment for stroke (except aspirin)

• Transient Ischemic Attach (TIA)

Degenerative Brain Disorders• Alzheimer’s disease – a progressive

degenerative disease of the brain that results in dementia (usually frontotemporal)

• 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