biol 105—lab 11---gross anatomy brain 1 central nervous system (cns) cns consists of brain and...

BIOL 105—Lab 11---Gross Anatomy Brain 1

Central Nervous System (CNS)•CNS consists of brain and spinal cord•Surface anatomy includes cerebral hemispheres, cerebellum and brain stem


Embryonic Development•Ectoderm (outermost of the three primary germ layers of an embryo) forms a neural plate which invaginates, forming a groove with neural folds at each side•By week four of embryonic development, the neural groove fuses dorsally and forms the neural tube

•Brain grows faster than membranous skull

– Folds to occupy available space

– Forebrain moved toward brain stem (midbrain, pons, medulla oblongata)

– Cerebral hemispheres double back and envelop diencephalon and midbrain while creasing and folding to increase surface area


• Brain regions1. Cerebral hemispheres

2. Diencephalon

3. Brain stem (midbrain, pons, and medulla)

4. Cerebellum


Regions and Organization of the CNS

•Spinal cord

– Central cavity surrounded by gray matter

• Gray matter will become the processing part of brain

– External white matter composed of myelinated fiber tracts

• White matter is generally protective in nature

•Brain

– Cerebral hemispheres and cerebellum

• Outer gray matter called cortex

• in brain stem we see scattered gray matter nuclei amid white matter


Ventricles of the Brain•Central cavity of neural tube enlarges and forms 4 brain

ventricles •Ventricles filled with cerebrospinal fluid (CSF)•Lined by ependymal cells• Connected to one another and to central canal of spinal

cord and to subarachnoid space– Lateral ventricles--paired, C-shaped

• Separated anteriorly by septum pellucidum– Third ventricle in diencephalon– Fourth ventricle in hindbrain


Cerebral Hemispheres

• 3 basic regions: cortex, white matter and basal nuclei

• Surface markings increase surface area and thus brain activity

– Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures)

– Longitudinal fissure separates two hemispheres


Cerebral Hemispheres•Deep sulci divide the hemispheres into 5 lobes:

– Frontal– Parietal – Temporal – Occipital– Insula--function: associated with visceral

functions, integrates autonomic information


Cerebral HemispheresCerebral cortex--40% mass of brain

– gray matter superficially, white matter internally– Basal nuclei- islands of gray matter deep within white matter

•Site of conscious mind; conscious behavior involves the entire cortex; no functional area acts alone

– Enables awareness, sensory perception, voluntary movements, communication, memory storage, understanding

•Each hemisphere concerned with contralateral (opposite) side of body

– Lateralization or specialization of cortical function in each hemisphere


Functional areas1. Motor areas—control voluntary movement

2. Sensory areas—conscious awareness of sensation

3. Association areas—integrate information

Cerebral Cortex--Motor Areas •Frontal lobe--controls voluntary movement

– Primary (somatic) motor cortex – Premotor cortex anterior– Broca's area-speech musculature &

comprehension


• Parietal lobes: somatosensory lobe and some association areas– Receives sensory information from skin and

proprioceptors of skeletal muscle, joints, and tendons

– spatial discrimination; identification of body region being stimulated

• Occipital lobe: visual lobe, includes association areas


• Temporal lobes: auditory lobes and includes association areas– Interprets information including pitch,

loudness, and location– Stores memories of sounds and permits

perception of sound stimulus• Wernicke’s area--can speak, but speech often

incoherent and makes no sense


Networks of neurons that span wide areas of brain BUT work together •Limbic system: Includes parts of diencephalon and some brain stem structures

• emotional or affective brain; gives emotional responses to odors

• Example: skunks smell bad•Reticular formation- governs brain arousal


Reticular Formation: governs brain arousal •includes RAS•Reticular activating system (RAS)

– Sends impulses to cerebral cortex to keep conscious and alert

– Filters out repetitive, familiar, or weak stimuli• damage in this brain area causes inability to distinguish

between valuable and not valuable information

– Inhibited by hypothalamic sleep centers, alcohol, drugs

– Severe injury results in permanent unconsciousness (coma)


Diencephalon•Consists of 3 structures

– Thalamus– Hypothalamus– Epithalamus (Pineal gland)

•Structures enclose third ventricle


Thalamus-- Function•Gateway to cerebral cortex-is the relay station for brain•Sorts, edits, and relays ascending input

– Impulses from hypothalamus for regulation of emotion and visceral function

– Impulses from cerebellum and basal nuclei to help direct motor cortex

– Impulses for memory or sensory integration– Impulses from visual and auditory centers

•Essential role in mediating sensation, motor activities, cortical arousal, learning, and memory•When afferent stimuli reach thalamus, we have a recognition of the stimulus as pleasant or unpleasant


Hypothalamus•Located below the thalamus•Primarily involved in hormone productionInfundibulum—stalk that connects it to pituitary gland

Hypothalamic Function•Controls autonomic nervous system •Controls endocrine system•Physical responses to emotions

– Perception of pleasure, fear, and rage, and in biological rhythms and drives

•Regulates body temperature, hunger, thirst•Regulates sleep-wake cycles

– Biological clock


Epithalamus or Pineal gland (body)

•secretes melatonin—helps regulate sleep-wake cycle•Helps regulate body cycles by monitoring length of day via input from optic nerve

Choroid Plexus:•Hang from roof of each ventricle; produce CSF at constant rate; keep in motion


Brain Stem•Consists of 3 regions

– Midbrain

– Pons

– Medulla oblongata

•Controls automatic behaviors necessary for survival

•Provides pathway for nerve tracts connecting higher and lower brain centers

Pons

•Bulging brainstem area between midbrain and medulla oblongata

•helps maintain normal rhythm of breathing


Medulla Oblongata•Most inferior portion of the brain stem; joins spinal cord at foramen magnum

•Cardiovascular center– Cardiac center adjusts force and rate of heart

contraction– Vasomotor center adjusts blood vessel diameter for

blood pressure regulation•Respiratory centers

– Generate respiratory rhythm– Control rate and depth of breathing (with pontine

centers)•Vestibular nuclei (pons and medulla)—mediate responses that maintain equilibrium


Medulla Oblongata

•Additional centers regulate– Vomiting Hiccupping Sneezing– Swallowing Coughing

Cerebellum

•Subconscious input from cortex, brain stem and sensory receptors to allow smooth, coordinated movements of skeletal muscles

•Arbor vitae—treelike pattern of cerebellar white matter•May compare actual with predicted movement sequences and adjust movement accordingly

BIOL 105—Lab 11---Gross Anatomy Brain 2121Nervous System 21

– Meninges--3 protective connective tissue membranes enclose brain and spinal cord• Dura mater is outermost and strongest

layer• Arachnoid mater is middle layer; has

spidery extensions which secure it to innermost layer.

• Pia mater is innermost layer and clings tightly to CNS.


Cerebrospinal Fluid (CSF)•Composition

– Watery solution formed from blood plasma • Contains less protein and different ion

concentrations than plasma– Constant volume

•Functions– Gives buoyancy to CNS structures

• Reduces weight by 97%– Protects CNS from blows and other trauma– Nourishes brain and carries chemical signals


Hydrocephalus•Obstruction blocks CSF circulation or drainage•Fontanelles at skull in newborn allow enlargement of head•Brain damage in adult due to rigid adult skull •Treated by draining with ventricular shunt to abdominal cavity


Blood Brain Barrier•Helps maintain stable environment for brain •Separates neurons from most bloodborne substances•Selective barrier

– Allows nutrients to move by facilitated diffusion– Metabolic wastes, proteins, toxins, most drugs, small

nonessential amino acids, K+ denied– Allows any fat-soluble substances to pass, including

alcohol, nicotine, and anesthetics

•Absent in some areas, e.g., vomiting center and hypothalamus, where necessary to monitor chemical composition of blood


LABWORK (includes next slide)

1. Identify and describe the meninges and structures of the brain stem.

2. Identify and describe the cerebellum and structures of the diencephalon.

3. Identify and describe the structures of the cerebrum.

4.State the function of the cranial nerves.

5. Locate the following on diagrams, human brain models, the sheep brain:

Ventral view: olfactory bulb, pituitary gland, mammillary body, trigeminal nerve, pons, cerebellum, medulla oblongata, oculomotor nerve, optic tract, optic chiasma, optic nerve, cerebrum


Midsagittal view: corpus callosum, thalamus, hypothalamus, optic chiasma, pituitary gland, pons, cerebellum, arbor vitae, corpora quadrigemina (midbrain), pineal body, cerebral hemisphere.

On the human brain models, Locate the lobes of the cerebrum, gyri, sulci, and fissures.

biol 105—lab 11---gross anatomy brain 1 central nervous system (cns) cns consists of brain and...

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