Nervous System II

Chapter 12

Major Organs • Brain

• Spinal Cord

• Cranial Nerves

• Spinal Nerves

Brain• May appear

somewhat unimpressive at first glance.

• Average adult brain- Male 3.5 lbs the Female 3.2 lbs.

• Quivering pink tissue with the appearance of cold oatmeal.

Brain• Functions- contains

nerve centers associated with sensory functions and is responsible for sensations and perceptions. (motor functions, memory, reasoning, nerve pathways)

Cerebrum

• The cerebrum, which develops from the anterior portion of the brain, is the largest part the mature brain.

• It consists of two large masses or cerebral hemispheres.

• Together they account for about 83% of total brain mass.

Cerebrum

• A deep bridge of nerve fibers called the corpus callosum connects the cerebral hemispheres.

• This is the structure that is located beneath the Cerebrum in the pictures.

Cerebrum• Many ridges called

Gyri or (convolution,) separated by grooves, mark the cerebrum.

• A shallow to somewhat deep groove is called a sulcus.

• A very deep grove is called a fissure.

• The pattern of these elevations and depressions is complex, and it is distinct in all normal brains.

Cerebrum

Cerebrum

Cerebrum• You need to be able to located the

following sulcus and fissures on the brain.• Central Sulcus (Separates the frontal

and parietal lobes)• Lateral Sulcus (Separates the temporal

lobe from the parietal and frontal lobes)• Transverse Fissure (Is anterior to the

cerebellum)• Longitudinal Fissure (Separates the

left and right hemispheres)

Cerebrum• Each Cerebral hemisphere has three

basic regions– Cortex Matter- A superficial layer that looks

gray in fresh brain tissue.– Internal White Matter-internal layer.– Basal Nuclei- islands of gray matter situated

deep within the white matter. They relay motor impulses originating in the cerebral cortex and aid in controlling motor activities.

–

Cerebrum

Cerebrum

• The cerebral cortex is the “executive suite” of the nervous system, where our conscious mind is found.

Cerebrum

• A think layer of gray matter called the cerebral cortex, constitutes the outermost portion of the cerebrum.

• It covers the gyri or convolutions.

Cerebral Cortex

• The cerebral cortex contains nearly 75% of all the neuron cell bodies in the nervous system.

• The cerebral cortex has sensory, motor and association areas.

Functions of The Cerebrum

• The cerebrum provides higher brain functions: interpreting impulses from sense organs, initiating voluntary muscular movements, storing information as memory, and retrieving this information in reasoning.

• The cerebrum is also the seat of intelligence and personality.

Frontal Lobe of the Cerebral

Frontal Lobe of the Cerebral

• Functions: Motor areas control movements of voluntary skeletal muscles

• Association areas carry on higher intellectual processes for concentration, planning complex problem solving, and judging the consequences of behavior.

Parietal Lobe of the Cerebral

Parietal Lobe of the Cerebral

• Functions: Sensory areas provide sensations of temperature, touch, pressure, and pain involving the skin.

• Association areas function in understanding speech and in using words to express thoughts and feelings.

Temporal Lobe of the Cerebral

Temporal Lobe of the Cerebral

• Functions: Sensory areas are responsible for hearing

• Association areas interpret sensory experiences and remember visual scenes, music, and other complex sensory patterns.

Occipital Lobe of the Cerebral

Occipital Lobe of the Cerebral

• Functions: Sensory areas are responsible for vision.

• Association areas combine visual images with other sensory experiences.

Dominant Hemisphere• Both cerebral hemispheres

participate in basic functions, such as receiving and analyzing sensory impulses, controlling skeletal muscles on opposite sides of the body.

• However, 90% of the population is left hemisphere dominant for the language-related activities of speech, writing, and reading.

Diencephalon

• The diencephalon forms the central core of the forebrain and surrounded by the cerebral hemispheres….. contains the thalamus, hypothalamus, and epithalamus.

Thalamus

• The thalamus selects incoming sensory impulses and relays them to the cerebral cortex

Hypothalamus• The Hypothalamus is important in

maintaining the homeostasis. • Helps maintain the following….Autonomic

control center, center for emotional response, body temperature regulation, regulatin of food intake, water intake, and thirst, sleep cycles,etc.

• Pituitary Gland- secrets at least 9 hormones. Size and shape of a pea. Located below the hypothalamus. (add to notes)

Hypothalamus

Epithalamus

• The Epithalamus is the most dorsal portion of the diencephalon forms the roof of the third ventricle.

• It works in close association with the Hypothalamus and pineal gland.

• The Pinal Gland secrets melatonin which plays a role in the sleep/wake cycle. (yes, you have to adjust your notes here)

The Brain Stem

• The brain stem extends from the base of the brain to the spinal cord.

• The brain stem consists of the midbrain, pons, and medulla oblongata.

The Brain Stem

The Brain Stem

• The midbrain contains reflex centers associated with eye and head movement

The Brain Stem• The pons transmits impulses between

the cerebrum and other parts of the nervous system and contains centers that help regulate rate and depth of breathing.

• The medulla oblongata transmits all ascending and descending impulses and contains several vital and non-vital reflex centers. (blood pressure, heart rate, and respiration)

Cerebellum

• The cerebellum consists of two hemispheres connected by the vermis.

Cerebellum• A thin cortex of gray

matter surrounds the white matter of the cerebellum

• The arbor vitae (Latin for "Tree of Life") is the cerebellar white matter, so called for its branched, tree-like appearance.

Cerebellum

Cerebellum

• The cerebellum functions primarily as a reflex center, coordinating skeletal muscle movements and maintaining equilibrium.

Optic Chiasma

• A point near the thalamus and hypothalamus at which portions of each optic nerve cross over.

• We will try to find this in a sheep brain!

Optic Chiasma..in the human brain!

Olfactory Bulb

• One of two enlargements at the terminus of the olfactory nerve at the base of the brain just above the nasal cavities

Olfactory Bulb

• Again this is something that we will really observe in the sheep brain. Larger in sheep than humans!

Cerebrospinal Fluid• The entire surface of central

nervous system is bathed by a clear, colorless fluid called cerebrospinal fluid (CSF).

• The CSF is contained within a system of fluid-filled cavities called ventricles.

Cerebrospinal Fluid• Found in and around the brain and spinal

cord• Reduces brain weight by 97% and

prevents the brain from crushing under its own weight.

• Protection: the CSF protects the brain from damage by "buffering" the brain. In other words, the CSF acts to cushion a blow to the head and lessen the impact.

• Buoyancy: because the brain is immersed in fluid, the net weight of the brain is reduced from about 1,400 gm to about 50 gm. Therefore, pressure at the base of the brain is reduced.

Cerebrospinal Fluid• Excretion of waste products: the

one-way flow from the CSF to the blood takes potentially harmful metabolites, drugs and other substances away from the brain.

• Endocrine medium for the brain: the CSF serves to transport hormones to other areas of the brain. Hormones released into the CSF can be carried to remote sites of the brain where they may act.

Cerebrospinal Fluid• The CSF is formed by the

choroid plexuses that hang from the roof of each ventricle…primarily the first and second ventricles. (lateral)

• CSF is replaced in an average human once about every 8 hours.

Cerebrospinal Fluid• CSF flows from the lateral

ventricle to the third ventricle through the interventricular foramen (also called the foramen of Monro).

• The third ventricle and fourth ventricle are connected to each other by the cerebral aqueduct

Cerebrospinal Fluid

Cerebrospinal Fluid

Spinal Cord• The spinal cord is a

nerve column that extends from the brain into the vertebral canal.

• Consists of 31 segments, each of which gives rise to a pair of spinal nerves.

• Divided into right and left halves.

Functions of the Spinal Cord

• The spinal cord is the center for spinal reflexes (1) Reflexes are automatic, subconscious responses to changes. (2) They help maintain homeostasis. (3) The knee-jerk reflex employs only two neurons. (4) Withdrawal reflexes are protective actions

• The cord provides a two-way communication system between the brain and structures outside the nervous system.

Spinal Nerves• Consists of thirty-

one pairs of spinal nerves

• Functions- they provide two way communication between the spinal cord and parts of the upper and lower limbs, neck and trunk

Cranial Nerves• There are twelve

pairs of cranial nerves

• Functions- consists of sensory fibers (smell and vision) and motor fibers (controls muscles and glands)

Protection of the Brain

• Nervous tissue is soft and delicate and neurons are injured by even slight pressure.

• However the brain is protected in 4 keys ways.

Protection of the Brain

• 1.) Skull- we will go into more detailed in the Skeletal System

• 2.) Membranes (Meniges)• 3.) Watery Cushions (Cerebrospinal

Fluid)• 4.) Blood-brain Barrier.

Protection of the Brain

• Membranes (Meniges)- are three connective tissue membranes that lie just external to the CNS

• Functions– Cover and protect the CNS– Protect blood vessels and enclose venous

sinuses– Contain CSF fluid– Form partitions in the skull

Protection of the Brain

• The leathery Dura Mater, meaning “tough mother” is the strongest meninx

• Surrounds the brain• Two-layered sheet of fibrous

connective tissue. • The two other meninges are the

Arachnoid and Pia Mater.

Protection of the Brain

• Meningitis? Inflammation of the meninges…serious threat to the brain because a bacterial or viral meningitis may spread to the CNS..

• Meningitis is diagnosed by obtaining a sample of CSF via a lumbar tap.

Protection of the Brain

• Blood-Brain Barrier (BBB) is semi-permeable; that is, it allows some materials to cross, but prevents others from crossing.

Protection of the Brain

• The BBB functions are…• Protects the brain from "foreign

substances" in the blood that may injure the brain.

• Protects the brain from hormones and neurotransmitters in the rest of the body.

• Maintains a constant environment for the brain.

Degenerative Brain DisordersAlzheimer's Disease

• Alzheimer is a progressive degenerative disease of the brain that ultimately results in dementia.

• Alzheimer’s patients represent about ½ of the people living in a nursing home.

• Extreme memory loss, shortened attention span, disorientation, and eventually memory loss.

Degenerative Brain Disorders Alzheimer's Disease

• Examination of brain tissue reveal senile plaques littering the brain like shrapnel between neurons. The presence of neurofibrillary tangles inside neurons have also been identified. Both of these seem to be a malfunction of key proteins.

Degenerative Brain Disorders Parkinson’s Disease

• Typically striking people in their 50’s and 60’s

• Afflicted individuals have a persistent tremor at rest, forward-bent walking posture and shuffling gait, and stiff facial expression.

Degenerative Brain Disorders Parkinson’s Disease

• PD results from a degeneration of the dopamine-releasing neurons of the sustantia nigra.

• As those neurons deteriorate the dopamine-deprived basal nuclei they target become overactive.

Degenerative Brain Disorders Huntington’s Disease

• Huntington’s Disease is a fatal hereditary disorder that strikes during middle age.

• HD is caused by a mutant Huntington protein that accumulates in brain cells and the tissue dies.

• Symptoms include wild jerky movements, mental deterioration and is usually fatal within 15 years of onset. .